Citation
Water quality management plan, 2004

Material Information

Title:
Water quality management plan, 2004
Creator:
Wright Water Engineers, Inc.
Wenk Associates, Inc.
Muller Engineering
Matrix Design Group
Smith Environmental
Place of Publication:
Denver, CO
Publisher:
City and County of Denver
Publication Date:
Language:
English

Subjects

Subjects / Keywords:
Water quality management
Water utilities -- Management
City planning

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Source Institution:
Auraria Library
Holding Location:
Auraria Library
Rights Management:
Copyright [name of copyright holder or Creator or Publisher as appropriate]. Permission granted to University of Colorado Denver to digitize and display this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.

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WRIGHT WATER ENGINEERS, INC. WENK ASSOCIATES, INC,
MULLER ENGINEERING MATRIX DESIGN GROUP SMITH ENVIRONMENTAL


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TABLE OF CONTENTS___________________________________________________________________________
Acknowledgments..........................................................................A-l
Executive Summary.......................................................................ES-1
Overview.............................................................................ES-1
Approach.............................................................................ES-1
Stormwater Quality BMP Implementation Guidelines.....................................ES-3
Recommendations And Conclusions......................................................ES-4
Chapter 1 Introduction.................................................................. 1-1
Purpose And Goals....................................................................1 -2
Goal 1 : Develop A Framework And Shared Vision For Meeting Denver's
Stormwater Quality Requirements And Goals.......................................1 -2
Goal 2: Develop BMP Strategies That Work In Various Denver Settings...............1 -3
Goal 3: Develop A Common Foundation For Interdepartmental Understanding
Of Stormwater Quality Requirements And Their Role In The Planning Process.......1 -4
Goal 4: Develop Framework And Priorities For Future Work Needed To Meet Goals.....1 -4
Approach.............................................................................1 -4
Principles And Policies..............................................................1 -7
Opportunities And Challenges.........................................................1 -9
Address Water Quality Issues..................................................... 1 -9
Improve Interdepartmental Cooperation With Regard To Water Quality................1 -9
Coordinate Compatible Uses Between Parks And Water Quality Facilities.............1-10
Enhance Compatibility Between Urban Design Goals And Water Quality Facilities.....1-10
Implement Effective, Sustainable, Attractive, Multi-Purpose, Safe, And Well-Designed Bmps 1-11
Ensure Long-Term BMP Operation And Maintenance....................................1 -1 1
Develop Financing And Institutional Strategies For Regional Bmps..................1 -1 1
Scope Limitations....................................................................1 -1 2
Plan Overview........................................................................1 -1 3
Chapter 2 Overview Of Major Denver Drainage Basins And Potential
Urban Stormwater Impacts..........................................................2-1
Overview Of Denver Drainage Basins....................................................2-1
South Platte River.................................................................2-7
First Creek........................................................................2-7
Second Creek.......................................................................2-8
Third Creek........................................................................2-8
Box Elder Creek....................................................................2-9
Irondale Gulch.....................................................................2-9
Clear Creek........................................................................2-9
Sand Creek........................................................................2-1 0
Westerly Creek....................................................................2-1 0
Cherry Creek......................................................................2-1 1
Goldsmith Gulch...................................................................2-1 1
Sloan's Lake......................................................................2-12
Lakewood Gulch....................................................................2-1 2
Dry Gulch.........................................................................2-1 2
Weir Gulch........................................................................2-1 2
Sanderson Gulch...................................................................2-1 3
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West Harvard Gulch..................................................................2-1 3
Harvard Gulch.......................................................................2-1 4
Bear Creek...........................................................................2-14
Marston Lake North (Tributary Of Bear Creek)........................................2-15
Overview Of Lakes......................................................................2-1 5
Characterization Of Denver Lake And Stream Conditions..................................2-1 8
Overview Of The Effects Of Urbanization On Receiving Waters............................2-20
Adverse Physical Impacts Of Urban Runoff.............................................2-22
Chemical Characteristics Of Urban Runoff.............................................2-24
Summary................................................................................2-30
Chapter 3 Regulatory Drivers................................................................3-1
Phase I Stormwater CDPS Permit...........................................................3-1
Denver International Airport (DIA) CDPS Permit...........................................3-5
EPA's April 2004 Audit Of Denver's Stormwater Management Program.......................3-6
Denver's Stormwater Quality Related Policies.............................................3-6
Other Denver Ordinances, Rules And Regulations.........................................3-1 0
Colorado Water Quality Control Act And Regulations.....................................3-1 1
Total Maximum Daily Loads (Tmdls) ......................................................3-14
Regional Efforts And Agreements........................................................3-1 7
Denver Regional Council Of Governments/Clean Water Plan ............................3-1 7
Joint Stormwater Task Force.........................................................3-1 7
South Platte Cooperative For Urban River Evaluation (CURE)..........................3-18
Cherry Creek Stewardship Partners....................................................3-21
Barr Lake/Milton Reservoir Watershed Association.....................................3-21
Selenium Stakeholders Group..........................................................3-22
Other Federal And State Regulations.....................................................3-22
Current And Future Compliance Implications Of Evolving Regulations.....................3-24
Section 309 Report And Potential Aquatic Life Classification Changes................3-25
Possible Stream Standard Changes Under Consideration For July 2005..................3-26
Source Water Protection..............................................................3-27
Nutrient Criteria....................................................................3-27
Sediment Deposition..................................................................3-29
Pollutant Trading....................................................................3-29
Summary.................................................................................3-29
Chapter 4 Related Documents.................................................................4-1
Urban Storm Drainage Criteria Manual, Volumes 1 -3.......................................4-1
Denver Storm Drainage Design And Technical Criteria Manual...............................4-2
Denver Storm Drainage Master Plan And Other Drainage Master Plans......................4-3
Standards, Details And Technical Criteria Documents......................................4-4
Metro Vision 2020 And The Clean Water Plan...............................................4-4
Water Quality Improvement In The South Platte River, Report To The Mayor...............4-5
Denver Comprehensive Plan 2000...........................................................4-6
Blueprint Denver.........................................................................4-9
Denver Parks And Recreation Game Plan..................................................4-1 1
Natural Areas Program Field Guide.......................................................4-12
Design Guidelines For Stapleton Water Quality...........................................4-12
Long Range Management Framework South Platte River Corridor............................4-1 3
Cherry Creek Greenway Corridor Master Plan..............................................4-14
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Denver Water Quality Management Plan
Cherry Creek Watershed Smart Growth For Clean Water Report..............................4-14
Lake Management And Protection Plan.....................................................4-15
Summary................................................................................4-1 6
Chapter 5 National Case Studies.............................................................5-1
City Of Austin, Texas: Watershed Protection Master Plan..................................5-1
City Of Portland, Oregon: Clean River Plan...............................................5-5
Snohomish County, Washington.............................................................5-9
San Diego, California...................................................................5-12
Prince George's County, Maryland And Low Impact Development.............................5-13
Summary................................................................................5-1 6
Chapter 6 Stormwater Quality BMP Implementation Guidelines..................................6-1
Part 1 Introduction.....................................................................6-1
Design And Stormwater Quality Principles..............................................6-2
Stormwater Quality Design Process.....................................................6-7
How To Use The Guidelines...........................................................6-1 0
Part 2Development Types Guidelines....................................................6-1 1
Ultra Urban.........................................................................6-1 4
High Density Mixed Use..............................................................6-1 6
Campus..............................................................................6-1 8
Industrial...........................................................................6-20
Low Density Mixed Use................................................................6-22
Residential..........................................................................6-24
Parks And Natural Areas Open Space...................................................6-26
Part 3Implementation Details...........................................................6-29
Roofs................................................................................6-29
Parking Medians And Islands..........................................................6-33
Stormwater Distribution..............................................................6-36
Sediment Removal Traps And Forebays..................................................6-37
Soils................................................................................6-38
Planting.............................................................................6-39
Part 4BMP Fact Sheets..................................................................6-43
Grass Buffers........................................................................6-43
Grass Swales.........................................................................6-45
Detention Basins.....................................................................6-53
Treatment Wetlands...................................................................6-56
Subsurface Treatment Devices.........................................................6-56
Other Alternative Technologies.......................................................6-58
Industrial Source Controls...........................................................6-58
Drainageway Stabilization............................................................6-58
Part 5Maintenance Policies And Guidelines..............................................6-61
Defining Maintenance Responsibility For Public And Private Facilities................6-61
Developing A Maintenance Plan........................................................6-63
Maintenance Requirements.............................................................6-64
Grass Buffers And Grass Swales....................................................6-66
Porous Pavement And Porous Pavement Detention.....................................6-68
Porous Landscape Detention........................................................6-70
Extended Detention And Retention Basins...........................................6-72
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Sand Filter Extended Detention Basin...............................................6-74
Constructed Wetland Basins And Channels............................................6-75
Green Roofs/Treatment Roofs........................................................6-76
Low Impact Development Designs.....................................................6-78
Subsurface Treatment Devices.......................................................6-78
Conclusions And Recommendations For Maintenance.......................................6-79
Chapter 7 Pollution Source Controls (Non-Structural Bmps)....................................7-1
Overview Of Pollution Source Controls (Non-Structural Approaches).........................7-1
Industrial And Commercial "Hot Spots"..................................................7-9
Household Waste (Litter, Pet Waste, Yard Waste, Used Oil And Automotive
Fluids, And Other Hazardous Waste).................................................7-12
Pesticide, Herbicide, And Fertilizer Management (Including Integrated
Pest Management)...................................................................7-14
Efficient Irrigation..................................................................7-16
Materials Storage Practices...........................................................7-16
Good Housekeeping.....................................................................7-18
Spill Prevention And Response.........................................................7-18
Preventative Maintenance..............................................................7-21
Summary And Conclusions..................................................................7-25
Chapter 8 Potential Regional Facilities......................................................8-1
South Platte River........................................................................8-7
Prairie Gateway (Basin 0058)...........................................................8-7
1-70 & Colorado Boulevard (Basin 0060-01)..............................................8-8
1-70 & York (Basin 0060-02)............................................................8-9
Lower Platte Valley (Basin 0062-01 /4500-02).........................................8-1 0
Central Platte Valley (Basin 0063-01)................................................8-1 1
1 st & Federal (Basin 0064-01) .......................................................8-12
Valverde (Basin 0064-02)...............................................................8-1 3
Ruby Hill (Basin 0065-01)..............................................................8-1 4
Dartmouth (Basin 0065-02)..............................................................8-1 5
College View (Basin 0067-01)...........................................................8-1 6
West Belleview Avenue (Basin 0067-02)..................................................8-1 7
Sloan's Lake (Basin 4700-01)..........................................................8-18
1-25 (Basin 5000-01)..................................................................8-19
West Harvard Gulch (Basin 5300-01)....................................................8-20
First Creek..............................................................................8-21
First Creek (Basin 3700)..............................................................8-21
Irondale Gulch...........................................................................8-22
Irondale Gulch (Basins 3900 & 3901)...................................................8-22
Clear Creek..............................................................................8-23
Clear Creek (Basins 4300-03 & 4309-01)................................................8-23
Sand Creek...............................................................................8-24
North Stapleton (Basin 4400-01).......................................................8-24
Quebec Corridor (Basin 4400-02).......................................................8-25
South Stapleton (Basin 4400-03).......................................................8-27
East Stapleton (Basin 4400-04)........................................................8-28
Westerly Creek........................................................................8-29
South Stapleton (Basin 4401 -01)......................................................8-29
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Denver Water Quality Management Plan
1 1 th Avenue To Montview (Basin 4401 -02)....................................8-30
Lowry (Basin 4401 -03)........................................................8-31
Upper Westerly Creek (Basin 4401 -04).........................................8-32
Cherry Creek.....................................................................8-33
Central Business District (Basin 4600-01).....................................8-33
Cherry Creek Mall (Basin 4600-02).............................................8-34
Upper Cherry Creek (Basin 4600-03)............................................8-35
Upper Cherry Creek (Basin 4600-04)............................................8-36
Goldsmith Gulch..................................................................8-37
Goldsmith Gulch (Basin 4601 -01)..............................................8-37
Dry Gulch And Lakewood Gulch.....................................................8-38
Lakewood & Dry Gulches (Basins 4800-01 & 4801 -01)............................8-38
Weir Gulch.......................................................................8-39
Weir Gulch (Basin 4900-01)....................................................8-39
Sanderson Gulch..................................................................8-40
Sanderson Gulch (Basin 51 00-01)..............................................8-40
Greenwood Gulch..................................................................8-41
Greenwood Gulch (Basin 5401 -01)..............................................8-41
Bear Creek.......................................................................8-42
Fort Logan (Basin 5500-01)....................................................8-42
Upper Bear Creek (Basin 5500-02)..............................................8-43
Marston Lake North (Basin 5500-04)............................................8-45
Pinehurst Tributary (Basin 5500-05)...........................................8-46
Henry's Lake (Basin 5501 -01).................................................8-47
Dutch Creek......................................................................8-48
Coon Creek (Basin 5901 -01)...................................................8-48
Summary..........................................................................8-48
Chapter 9 Recommendations And Implementation Plan
Recommendations...................................................................9-1
Implementation Plan...............................................................9-5
References...........................................................................R-l
Glossary.............................................................................G-l
Appendices
Appendix AColorado Water Quality Control Commission Stream Classifications
And Water Quality Standards Relevant To Denver
Appendix BDenver's Response To April 2004 EPA Audit Of Stormwater Program
Appendix CWater Quality Improvement In The South Platte River, Report To The Mayor
Appendix DRepresentative Stormwater BMP Maintenance Agreements
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ACKNOWLEDGEMENTS
This Plan was developed through the collaboration and dedication of many Denver staff, an
outside review committee and a diverse project team under the direction of Denver Wastewater
Management Division Project Manager Terry Baus, P.E. Significant time was invested in
determining the priorities of various Denver staff and departments through a detailed series of
interviews. The project team would like to thank all of these individuals for providing their
insights and expertise with regard to stormwater quality planning priorities and issues for
Denver.
DENVER ADVISORY COMMITTEE
Terry Baus, P.E., Public Works, Wastewater Management Division (Project Manager)
Susan Baird, Parks and Recreation
Janet Burgessor, Environmental Health
Leslie Lipstein, Community Planning and Development
Darren Mollendor, P.E., Public Works, Wastewater Management Division
Ruth Murayama, Parks and Recreation
Alan Sorrel, P.E., Public Works, Department of Engineering Services
Ben Urbonas, P.E., Urban Drainage and Flood Control District
Gayle Weinstein, Parks and Recreation
PROJECT CONSULTANT TEAM
Jonathan Jones, P.E., Wright Water Engineers, Inc. (Project Manager)
Jane Clary, Wright Water Engineers, Inc. (Project Coordinator)
Bill Wenk, Wenk Associates
Paul Thomas, Wenk Associates
Ilene Marcus Flax, Wenk Associates
Jim Wulliman, P.E., Muller Engineering Company
John Blanchard, P.E., Matrix Engineering
Robert Krehbiel, P.E., Matrix Engineering
Peter Smith, Smith Environmental
Dr. James C.Y. Guo, P.E., University of Colorado at Denver
Dr. James P. Heaney, P.E., University of Florida (formerly at University of Colorado-Boulder)
EXTERNAL REVIEW COMMITTEE
John Carroll, P.E., Carroll and Lange, Inc.
John Doerfer, P.E., Urban Drainage and Flood Control District
Bill Ruzzo, P.E., Cherry Creek Basin Water Quality Authority
Dr. F. Robert McGregor, P.E., AMEC Earth and Environmental, Inc.
Susan Powers, Urban Ventures, L.L.C.
Michael Weiss, McStain Enterprises, Inc.


Acknowledgements
DEPARTMENTAL INTERVIEWS1
Beth Conover, Environmental Policy Aid to Mayor Hickenlooper, Mayors Office
Tyler Gibbs, Director of Planning and Urban Design Services, Community Planning and
Development
Steve Gordan, Community Planning and Development
Reza Kazemian, P.E., Public Works, Director of OperationsWastewater Management Division
Nicholas Skifalides, P.E., Deputy Manager of Public WorksWastewater Management Division
Lesley Thomas, P.E., City Engineer, Department of Engineering Services, Public Works
Val Webster, Parks and Recreation
Jim Wiseman, P.E., Director of Engineering, Public Works
OTHER ACKNOWLEDGEMENTS
The Urban Drainage and Flood Control Districts Storm Drainage Criteria Manual, Volumes 1-
3, was the foundation for much of this document. Portions of this Manual were paraphrased in
several chapters of this Plan, particularly Chapters 6 and 7, which include both paraphrases and
direct quotations.
The Greenway Foundation provided attractive photographs of the South Platte River for
inclusion in this Plan.
1 All members of the Advisory Committee participated in interviews with their respective departments, but their
names have not been repeated in this interview list.
s


EXECUTIVE SUMMARY
OVERVIEW
The purpose of this Denver Water Quality
Management Plan (Plan) is to advance a
framework for better integrating stormwater
management and water quality protection into
planning, engineering, and infrastructure
management for the City and County of Denver
(Denver). This Plan will serve as a common
authoritative reference identifying Denvers
commitments, priorities, and strategies for
protecting its rivers, streams, lakes, and wetlands
from the adverse impacts of urban stormwater
runoff. In addition, the Plan provides a practical
initial strategy for managing stormwater runoff
quality in the near term, while laying the
groundwork for a long-term vision. This Plan is
relevant to Denver staff, land developers
undertaking new or redevelopment projects, other
parties conducting activities that impact urban
runoff, and citizens who want to support water
quality protection in the Denver area. The primary
goals of this Plan are identified in Exhibit ES. 1.
The remainder of this Executive Summary
describes the project approach, stormwater quality
Best Management Practice (BMP)1 implementation
guidelines, and recommendations resulting from the Plan.
APPROACH
This Plan has been developed using a multi-faceted approach to ensure that a practical and
innovative strategy for addressing water quality is developed for Denver. Multiple interviews
and meetings were conducted with key Denver staff to develop a Plan that will be beneficial to
many Denver departments. Key aspects of the project approach include:
Extensive collaboration among multiple city departments. Acceptance and use of this
Plan across city departments is critical to its success. This document has been developed
through close collaboration and frank discussion among multiple departments within
EXHIBIT ES.l
PLAN GOALS
DEVELOP A FRAMEWORK AND SHARED
VISION FOR MEETING DENVERS
STORMWATER QUALITY REQUIREMENTS
AND GOALS
DEVELOP BMP STRATEGIES THAT WORK
IN VARIOUS DENVER SETTINGS
DEVELOP A COMMON FOUNDATION
FOR INTERDEPARTMENTAL
UNDERSTANDING OF STORMWATER
QUALITY REQUIREMENTS AND THEIR
ROLE IN THE PLANNING PROCESS
DEVELOP A FRAMEWORK AND
PRIORITIES FOR FUTURE WORK NEEDED
TO MEET GOALS
1 Best Management Practices (BMPs) include a variety of both structural and non-structural techniques implemented
to help minimize pollution of streams, rivers, lakes, and wetlands. BMPs are the foundation of stormwater quality
management and regulation and are a key topic throughout this Plan. Representative examples of BMPs include
source controls such as proper fertilizer use and structural BMPs such as water quality detention basins and porous
landscape detention. See Chapter 6 of this Plan for more information.
Executive Summary
Page ES1


Executive Summary
Denver including Public Works, Parks and
Recreation, Community Planning and
Development, Environmental Health, and the
City Attorneys Office. By diligently
working together to prepare this document, a
more unified position and vision for
stormwater quality management has
emerged. Some of the opportunities and
challenges identified during interviews and
Advisory Committee meetings are
summarized in Exhibit ES.2.
Identification and review of regulations
and existing Denver planning documents
affecting or interfacing with stormwater
quality management strategies in Denver.
Many existing and proposed federal, state
and local water quality regulations directly
influence stormwater quality management in
Denver. Key regulations were inventoried
and described in order to provide a common
basis for understanding stormwater quality
management requirements. Similarly,
Denver has many excellent planning
documents and programs that help guide
planning and watershed management
decisions. In order to avoid reinventing the
wheel, a review and summary of these key
documents was completed.
Review of similar efforts in other
communities with advanced stormwater
programs. Communities throughout the
country are reassessing their approach to
stormwater and watershed management.
Early in development of this Plan, five
communities with advanced stormwater programs were identified to explore their
approaches, successes, and difficulties in addressing urban runoff. Interviews and review
of key documents were conducted for these communities: Portland, Oregon; San Diego,
California; Austin, Texas; Prince Georges County, Maryland; and Snohomish County,
Washington. Findings from this research have been taken into account in development of
this Plan with regard to general approach, as well as for recommendations for specific
BMPs.
EXHIBIT ES.2
STORMWATER QUALITY
MANAGEMENT
OPPORTUNTIES AND CHALLENGES
ADDRESS WATER QUALITY ISSUES (E.G.,
SOS(D) LISTED SEGMENTS, STREAM
STANDARDS)
IMPROVE INTERDEPARTMENTAL
COOPERATION WITH REGARD TO
INTEGRATING WATER QUALITY INTO
SITE DEVELOPMENT
COORDINATE COMPATIBLE USES
BETWEEN PARKS AND WATER QUALITY
FACILITIES
ENHANCE COMPATIBILITY BETWEEN
URBAN DESIGN GOALS AND WATER
QUALITY FACILITIES
IMPLEMENT EFFECTIVE, SUSTAINABLE,
ATTRACTIVE, MULTI-PURPOSE, SAFE
AND WELL-DESIGNED BMPS
ENSURE LONG-TERM BMP OPERATION
AND MAINTENANCE
DEVELOP FINANCING AND
INSTITUTIONAL STRATEGIES FOR
REGIONAL BMPS
Executive Summary
Page ES-2


Denver Water Quality Management Plan
Identification of stormwater BMPs that have been both successful and unsuccessful
in the Denver area. The Project Team spent several days in the field visiting BMP sites
in Denver. The strengths and weaknesses observed at these sites have been incorporated
into the recommendations and strategies identified in this Plan. Photographs of many of
these BMP sites are interspersed throughout this document.
Review of new stormwater BMP technology and approaches for potential
applicability to Denver. Policy statements on new BMP technology such as
underground proprietary treatment devices have been developed and provided in Chapter
6. Approaches that manage runoff close to the source and promote infiltration through
landscape-based strategies are explored for more extensive application in the Denver
area. Terms commonly used for these approaches include Minimizing Directly
Connected Impervious Area, Smart Growth for Clean Water, and Low Impact
Development. Circumstances under which new approaches may be considered are also
identified.
Development of practical stormwater quality BMP implementation guidelines. As a
result of the initial project tasks described above, the most significant need identified was
practical guidance for implementing and managing stormwater quality in Denver.
Chapters 6 and 7 provide this guidance, with the Stormwater Quality BMP
Implementation Guidelines further summarized below.
Accommodation of periodic updates and revisions. Denver recognizes and intends
that this Plan will be a living document that will need to be updated periodically to
reflect changes in the Denver area, BMP technology, and various regulations and policy
shifts. These updates will be posted on Denvers web site, www.denvergov.org. The
principles of adaptive management apply to this plan, as is the case for many related
Denver planning documents.
STORMWATER QUALITY BMP IMPLEMENTATION GUIDELINES
A top priority identified through departmental interviews and Project Advisory Committee input
was the need to provide clear guidance on how stormwater quality management could be
effectively accomplished in a variety of development settings. To accomplish this task, the
Project Team worked closely with the Project Advisory Committee to develop stormwater
quality management strategies for seven common development types, including Ultra Urban,
High Density Mixed Use, Campus, Industrial, Low Density Mixed Use, Residential, and Parks
and Open Space Natural Areas. The Plan provides design recommendations for these
development types addressing several factors:
Executive Summary
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Executive Summary
1. Runoff reduction techniques to decrease runoff volume and reduce the Water Quality
Capture Volume2 requiring treatment.
2. BMPs to treat the Water Quality Capture Volume appropriate for the development
type.
3. Flood detention methods to attenuate peak runoff from larger storm events on site.
4. More in depth guidance on specific aspects of BMP implementation.
Sketches and photographs showing how design recommendations can be implemented on typical
development sites help to communicate effective stormwater management strategies for the
various development types. The Plans recommended strategies build upon the BMPs in the
Urban Drainage and Flood Control Districts (UDFCDs) Urban Storm Drainage Criteria
Manual, Volume 3.
Stormwater quality BMP implementation guidelines for the various development types are
further supplemented by implementation details for topics such as roof runoff treatment,
stormwater management in parking lots, stormwater runoff distribution approaches, sediment
removal traps and forebays, planting/vegetation considerations, and soils. BMP fact sheets
describing grass buffers, grass swales, porous pavement, porous pavement detention, porous
landscape detention, detention basins, and other approaches are also provided. Although detailed
design guidance in the Urban Storm Drainage Criteria Manual, Volume 3 (UDFCD 1999) is not
reproduced in this Plan, the fact sheets provide practical supplemental information for the BMPs
on topics such as typical applications, operation and maintenance considerations, landscape
considerations, retaining walls, vehicular access, outlets, etc. The final portion of Chapter 6
provides suggestions for better integrating BMP maintenance into stormwater quality planning
and provides specific recommendations for maintenance of various BMPs.
RECOMMENDATIONS AND CONCLUSIONS
As is the case with cities throughout the country, Denver is faced with complex regulatory
requirements with regard to water quality. Denvers Phase I Colorado Discharge Permit System
(CDPS) permit specifies stringent requirements with which Denver must comply or face
significant penalties. Fortunately, Denver already has many sound water quality requirements in
place in the form of policies and regulations. Specific action items requiring additional work that
are not currently included in existing Denver departmental programs are highlighted in Exhibit
ES.3. An overall summary of recommendations for on-going and future water quality protection
efforts by Denver follows.
2 The Water Quality Capture Volume is the quantity of stormwater runoff that must be treated in stormwater quality
BMPs in Denver. This volume is equivalent to the runoff from an 80th percentile storm, meaning that 80 percent of
the most frequently occurring storms are fully captured and treated and larger events are partially treated. In simple
terms, this quantity is about half of the runoff from a 2-year storm.
Executive Summary
Page ES-4


Denver Water Quality Management Plan
1. All new and redevelopment projects must
address water quality in their development
plans, complying with the stormwater
policies and design criteria specified in the
Urban Storm Drainage Criteria Manual,
Volumes 1-3 (UDFCD 1999, 2001) and in
Denvers CDPS permit. Particularly critical
is the four-step BMP planning process that
requires:
Implementing stormwater runoff
reduction practices.
Providing treatment of the Water
Quality Capture Volume.
Implementing streambank and
channel stabilization techniques for
any drainageways within or adjacent
to a project site.
Providing additional treatment for
pollution hot spots.
2. Under Denvers CDPS permit, adverse
impacts to receiving waters posed by urban
stormwater discharges must be minimized to
the maximum extent practicable.3
Examples of these adverse impacts can
include increased pollutant loading,
increased runoff rates and volumes, channel
instability, modification of aquatic habitat
and increased sediment loading, both during
and after construction. It is essential to
recognize that, despite the best efforts to
control stormwater runoff, there will be some
change in receiving water characteristics due
to development; therefore, a zero impact
policy is not realistic or attainable. As a
result, Denver advocates management of
stormwater through the implementation of
BMPs designed in accordance with the
guidelines established by UDFCD (UDFCD 1999, 2001), as summarized in #1, above.
EXHIBIT ES.3
NEW ACTION ITEMS
UPDATE DENVERS STORM DRAINAGE
CRITERIA MANUAL AND STORMWATER
QUALITY CONTROL PLAN GUIDANCE
TO REFLECT THE POLICIES, STRATEGIES
AND RECOMMENDATIONS OF THIS
PLAN
UPDATE DENVERS STORM SEWER
EASEMENT AND INDEMNITY
AGREEMENT TO IDENTIFY SPECIFIC BMP
MAINTENANCE REQUIREMENTS
EXPAND INTERDEPARTMENTAL AND
CITYWIDE PUBLIC EDUCATION ON
STORMWATER QUALITY MANAGEMENT
CONDUCT A FEASIBILITY STUDY OF
POTENTIAL REGIONAL STORMWATER
QUALITY FACILITY LOCATIONS
COMPLETE REGIONAL BMP FINANCING
ALTERNATIVES ANALYSIS
CONDUCT WATERSHED-BY-
WATERSHED WATER QUALITY
ASSESSMENTS
DEVELOP EASY-TO-UNDERSTAND BMP
MAINTENANCE GUIDANCE
DOCUMENT(S)
SPONSOR PILOT-TESTING OF
INNOVATIVE BMPS IN DENVER
3 See the Glossary for the regulatory definition of maximum extent practicable.
Executive Summary
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Executive Summary
3. Denver will continue to advocate the use of multiple BMPs, including non-structural
measures, source controls, and structural BMPs, to reduce stormwater pollution.
Whenever practicable, combining BMPs in series can be very effective in reducing
stormwater pollution.
4. The stormwater quality BMP implementation guidelines provided in Chapter 6 of this
Plan will be shared with developers and city staff alike to promote better integration of
water quality into site designs, including more substantial use of runoff reduction
techniques.
5. Denver will work to ensure that water quality is addressed in the very beginning of the
site development process so that stormwater quality BMPs are better and more cost
effectively integrated into site designs. Various Denver departments (e.g., Public Works,
Planning, Parks, Environmental Health) must work together with a shared vision of
stormwater quality management to accomplish this goal.
6. Urban stormwater management must be an integral part of site design and take into
consideration multiple objectives. As stated in the Urban Storm Drainage Criteria
Manual, Volume 1 (UDFCD 2001), the many competing demands placed on space and
resources require that stormwater management strategies take into account water quality
enhancement, groundwater recharge, recreation, wildlife habitat, wetland protection,
protection of landmarks/amenities, control of erosion and sediment deposition, and
creation of open space. In addition, the appearance of BMPs is particularly important;
Denver will expect to receive site development plans that feature attractive BMPs that
will be viewed as assets by the community. Denver will encourage multi-purpose usage
of BMPs; however, compatibility among uses must be demonstrated (e.g., compatibility
between recreational areas and detention areas).
7. Planning for water quality must proceed hand-in-hand with drainage planning for
quantity (rate and volume). In urban areas, these two planning efforts are inseparable.
When these issues are addressed together and early in the site planning process, more
efficient, economical and attractive land uses generally result.
8. Denver will continue to review BMP designs for pubic safety and maintenance
accessibility, maintainability, documentation of maintenance requirements and schedule,
and assured long-term funding for maintenance. Proper maintenance is fundamental to
public safety and long-term effectiveness of stormwater BMPs; therefore, Denver will
take these steps to promote better long-term maintenance of BMPs:
Require inclusion of a simple BMP maintenance plan as part of Denvers
Stormwater Quality Control Plan submittal requirements.
Require a legally binding description of BMP maintenance requirements and
arrangements as part of development plan approval.
Clearly identify BMP maintenance requirements in forthcoming updates to
Denvers Storm Drainage Criteria Manual.
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Denver Water Quality Management Plan
Prepare easy-to-understand maintenance guidance documents and brochures for
both pubic and private facility owners. These documents will be based on
maintenance recommendations of UDFCD and the guidelines provided in Chapter
6 of this Plan.
9. The same stormwater quality management expectations and practices that apply to
projects in the private sector also apply to projects that are the responsibility of Denver,
such as buildings, parks, streets, utilities, etc. When Denver is preparing plans for any
such projects or managing, maintaining and/or upgrading existing facilities, potential
adverse stormwater quality effects must be evaluated and suitably mitigated.
10. Denver will continue to actively participate in regional water quality management efforts
such as those being conducted by South Platte Cooperative for Urban River Evaluation
(CURE), the Cherry Creek Basin Stewardship Partners, and the Barr Lake-Milton
Reservoir Watershed Group. These on-going efforts emphasize the importance of
Denver partnering with neighboring communities to tackle difficult water quality issues.
Denver must also stay abreast of forthcoming regulatory changes that affect management
of the many lakes and streams within its boundaries.
11. Denvers stormwater management strategies must be consistent with the principles,
criteria, and priorities in its multiple planning and technical criteria documents, as
described in Chapter 4.
12. Denver will work to remove obstacles to innovative stormwater management approaches
by reviewing regulations and codes and, where practical, modifying requirements that
conflict with the principles of this Plan. For example, such conflicts may arise with
regard to parking lot and curb and gutter design requirements relative to some Low
Impact Development approaches.
13. Denver will continue to promote managing and treating stormwater quality using
aboveground facilities, rather than in subsurface, vault-type treatment devices.
Nevertheless, Denver recognizes that there are some cases where the use of such facilities
is necessary due to extreme space constraints in smaller redevelopment sites, such as
those located in the downtown area.
14. Denver will evaluate the feasibility of collaborating with UDFCD, a university, other
local governments, and other organizations to pilot-test innovative BMPs. Denver will
continue to actively partner with UDFCD to develop design guidance for new BMPs
for the Denver area.
15. Denver will continue to educate the public on stormwater quality issues. Additional
opportunities for Denvers existing public education program include:
Provide additional educational brochures and water pollution prevention resources
on the Denver website. For example, as discussed in Chapter 5, many of the
national case studies provide extensive web resources.
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Executive Summary
Develop pollution prevention programs for specific industries that require further
attention and/or partner with entities providing existing programs. For example,
the City of Boulders Partners for a Clean Environment (PACE) program targets
and provides educational information to specific industry segments including auto
repair, auto body, green building, dental offices, dry cleaning, landscaping,
manufacturing, printing, restaurant, and retail sectors. The City of Portland has a
similar program. As an alternative to independently developing such programs,
Denver can partner with professional organizations and industry groups to support
their efforts in this type of training.
Educate developers and Denver staff on the benefits of land management
strategies such as open space/natural areas preservation and/or restoration,
riparian buffer zone protection, Smart Growth, Green Development, and Low
Impact Development strategies.
Continue educational campaigns on specific measures to minimize pollution at its
source. These efforts will include a multi-faceted approach directed to the public,
Denver staff and elected officials, and neighboring communities.
16. Based on an initial reconnaissance level evaluation (as described in Chapter 8), there are
promising opportunities for regional water quality BMPs, including large retention basins
and wetlands, that could reduce impacts to downstream receiving waters. Methods to
finance the development and maintenance of these facilities are urgently needed. In
addition, Denver will proceed with more detailed citywide planning to identify and
prioritize regional BMP alternatives. As a part of any regional facility evaluation, it will
be important to clearly define under what circumstances a developer can have their
requirement for onsite water quality treatment waived (e.g., paying a fee-in-lieu-of
treatment) due to regional treatment facilities.
17. Closely related to regional water quality facilities is the need to conduct a watershed-by-
watershed evaluation of current stream and lake conditions, including steps that are
necessary to improve the status quo. The purpose of such an evaluation is to identify
watershed-specific goals, priorities, data gaps and practicable mitigation measures that
could be developed to strategically improve conditions. It is logical to focus initially on
303(d)-listed streams (i.e., those that are considered to be impaired for one or more
pollutants) and to work closely with existing efforts such as those of South Platte CURE,
the Barr-Milton Watershed Group, and Denver Public Works and Environmental Health.
18. Denver will continue to monitor approaches used throughout the country related to
stormwater and watershed management. Lessons learned from case studies evaluated in
this Plan will be kept in mind during decision-making and planning for Denver.
Examples of common themes from communities with advanced stormwater programs
include:
Comprehensive approaches are being used to address drainage, flooding, erosion,
aquatic life, native habitat, and water quality in an integrated manner.
Executive Summary
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Denver Water Quality Management Plan
Watershed-based approaches are being used for planning and problem solving.
Geographic Information System (GIS) tools are being used effectively to
prioritize stormwater improvements and to more effectively communicate to
citizens, staff, and developers.
Storm runoff volume reduction practices are being used in many of these
communities. These practices include a variety of runoff reduction techniques
such as grass buffers and swales, green roofs, and other landscape-based
approaches.
The importance of sound long-term maintenance of BMPs is widely recognized,
as is the need to provide pubic safety at drainage facilities.
Strong public education and outreach campaigns in combination with extensive
web sites are substantive components of these programs. Education is being
aggressively used as a key strategy to improve runoff quality.
Significant financial investments, often measured in millions of dollars, have been
required for many communities to conduct their stormwater quality planning
efforts. These communities recognize that comparable future expenditures will be
required to implement their plans, and are implementing suitable methods of
financing.
19. Because the water quality challenges facing Denver will require significant funding, new
and potentially innovative financing strategies that capitalize on public/private
partnerships will be investigated.
20. Although this Plan provides a solid framework and foundation for effective stormwater
quality management in Denver, follow-up implementation measures are needed to ensure
that the principles and practices set forth in this Plan are implemented throughout Denver.
An initial implementation plan specifying target timeframe, activities, responsible
departments, and approximate costs has been developed in Chapter 9 of this Plan.
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Chapter 1
INTRODUCTION
Protecting and enhancing water quality has long been an important objective in the City and
County of Denver (Denver). Additionally, Denver is obligated under penalty of law to comply
with the requirements of its Colorado Discharge Permit System (CDPS) municipal stormwater
discharge permit. A stronger push towards clean water in Denver has been prompted by recent
changes such as:
Current and anticipated federal and state regulatory and CDPS permit requirements.
The water quality improvement goals of Mayor Hickenlooper and his Administration.
Increased recognition of the economic, ecological and social importance of water features
for Denver residents, businesses and visitors.
The need to protect natural resources, including preservation of open space, due to
population growth.
Recognition of the public health, safety and welfare implications of stormwater
management programs and facilities.
Proliferation of new approaches for protecting and improving water quality.
When looking at Denver as a whole, a
key influence on stream and lake water
quality is urban stormwater runoff from
rainfall and snowmeltthe water that
runs off streets, parking lots, buildings,
ball fields, industrial/commercial sites,
residential neighborhoods, etc. Without
control measures, or Best Management
Practices (BMPs), urban runoff typically
adversely affects the physical, chemical
and biological characteristics of streams,
lakes and wetlands. For example,
without mitigation, increased runoff
volumes and peak discharges commonly
associated with urbanization often cause
stream channels to degrade through
widening, deepening, accumulation of
unsightly sediment deposits, significant
modification to aquatic habitat, and other
impacts. Elevated concentrations of
substances such as gasoline and diesel
fuel, oil, grease, fertilizer, heavy metals,
EXHIBIT 1.1
THE SOUTH PLATTE RIVER: AN URBAN AMENITY
Source: The Greenway Foundation.
Chapter 1
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Introduction
pesticides, and pet waste can be harmful to aquatic
life, native plants and wildlife and/or impair the
ability of waterways to support recreation, industrial
and municipal water supply, and other beneficial
uses.
This chapter defines the purpose, approach, guiding
principles, opportunities and challenges, overview,
and scope limitations of this Plan, which has been
developed to create a framework to enable Denver to
address current and future challenges posed by urban
runoff.
PURPOSE AND GOALS
The purpose of this Denver Water Quality
Management Plan (Plan) is to advance a framework
for better integrating stormwater management and
water quality protection into planning, engineering,
and infrastructure management for Denver. This
Plan will serve as a common authoritative reference
identifying Denvers commitments, priorities, and
strategies for protecting its rivers, streams, lakes, and
wetlands from the adverse impacts of urban
stormwater runoff. In addition, the Plan provides a practical initial strategy for managing
stormwater runoff quality in the near term, while laying the groundwork for a long-term vision.
This Plan is relevant to Denver staff, land developers undertaking new or redevelopment
projects, other parties conducting activities that impact urban runoff, and citizens who want to
support water quality protection in the Denver area. The primary goals of this Plan follow.
Goal 1: Develop a Framework and Shared Vision for Meeting Denvers
Stormwater Quality Requirements and Goals
As is the case in many cities, decision-making in Denver is shared across multiple departments
and guided by many rules and regulations with inherently different goals and priorities. Water
quality-related issues have historically been addressed primarily through departments such as
Public Works and Environmental Health; however, due to the advent of the Phase I stormwater
regulation1, water quality-related issues are increasingly relevant to Parks and Recreation,
Community Planning and Development, Asset Management, and other Denver departments.
EXHIBIT 1.2
PLAN GOALS
DEVELOP A FRAMEWORK AND SHARED
VISION FOR MEETING DENVERS
STORMWATER QUALITY REQUIREMENTS
AND GOALS
DEVELOP BMP STRATEGIES THAT WORK
IN VARIOUS DENVER SETTINGS
DEVELOP A COMMON FOUNDATION
FOR INTERDEPARTMENTAL
UNDERSTANDING OF STORMWATER
QUALITY REQUIREMENTS AND THEIR
ROLE IN THE PLANNING PROCESS
DEVELOP A FRAMEWORK AND
PRIORITIES FOR FUTURE WORK NEEDED
TO MEET GOALS
1 The U.S. Environmental Protection Agency (EPA) issued the Phase I stormwater regulations requiring National
Pollutant Discharge Elimination System (NPDES) point source permit coverage for stormwater discharges from: (1)
medium and large Municipal Separate Storm Sewer Systems (MS4s) generally serving populations of 100,000
or greater; (2) construction activity disturbing 5 or more acres of land; and (3) 10 categories of industrial activity.
Chapter 1
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Denver Water Quality Management Plan
A primary goal of this document is to develop a shared vision for achieving Denvers water
quality protection requirements under its CDPS stormwater permit. This permit identifies
specific requirements intended to decrease the adverse impacts of stormwater discharged from
Denvers municipal separate storm sewer system (MS4). This permit clearly identifies binding
provisions and serious penalty clauses if violated and essentially states that Denver must
aggressively address the problems caused by urban stormwater discharges. State stream
standards help to assess whether receiving waters in Denver meet their designated uses such as
recreation, aquatic life, and water supply. In the event that streams receiving stormwater
discharges from Denver do not meet state-designated stream standards, Denver will likely be
required to enter into a more comprehensive regulatory process with additional requirements
under the Total Maximum Daily Load (TMDL) process (as discussed in Chapter 3).
In addition to purely regulatory-driven requirements, water quality protection and improvement
has been identified as an important goal in the Denver Comprehensive Plan 2000 (Denver 2000),
Cherry Creek Greenway Corridor Master Plan (BRW 2000), Natural Areas Program Field
Guide (Denver Parks and Recreation 2004), Design Guidelines for Stapleton Water Quality
(Denver 2001), and others. For these reasons, water quality protection and improvement are not
only legal requirements, but also high priorities for a city known for its natural beauty.
Developing a shared citywide vision and framework will help Denver to achieve its water quality
protection goals.
Goal 2: Develop BMP Strategies that Work in Various Denver Settings
Denvers Phase I stormwater permit requirements are based on both structural and non-structural
BMPs to minimize the impacts of urban runoff. Design criteria for stormwater management
practices appropriate for Denver have been clearly defined in the Urban Storm Drainage
Criteria Manual, Volumes 1 through 2 (UDFCD 1999, 2001) and adopted into Denvers Storm
Drainage Design and Technical Criteria Manual (Denver 1992). While these documents
provide sound engineering guidance on designing these BMPs, less information has been
provided on how to best integrate these
types of BMPs into specific settings EXHIBIT 1.3
likely to be found in Denver. The KENNEDY SOCCER COMPLEX DETENTION BASIN
Design Guidelines for Stapleton Water
Quality were successful in helping
achieve an integrated water quality plan
for the Stapleton Redevelopment area;
therefore, this Plan has used a similar
approach to provide BMP
implementation guidelines for the
entire city. To achieve the goal of
developing BMP strategies that work in
various settings, this Plan assesses a
The final Phase II storm water regulations were published in December 1999 and require NPDES permit coverage
for construction activities that disturb 1 to 5 acres and for regulated small MS4s.
Chapter 1
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Introduction
variety of existing and new BMPs and identifies implementation strategies appropriate for
development types in Denver. These BMP strategies build on the Urban Storm Drainage
Criteria Manual, Volumes 1-3 (UDFCD 1999, 2001), providing additional information on how
BMPs can best be integrated into and be more effective for various development types. To the
extent possible, the development types in this Plan are consistent with those found in the citys
planning document, Blueprint Denver (Denver 2000).
Goal 3: Develop a Common Foundation for Interdepartmental Understanding of
Stormwater Quality Requirements and Their Role in the Planning Process
In order for any water quality protection strategy to be effective, it needs to be clearly
documented, understood, accepted, and implemented across city departments. The strategies in
this Plan have been developed based on input from multiple city departments to identify
concerns and priorities related to water quality. Early integration of water quality requirements
into site designs has been identified as critical for development and redevelopment projects.
This Plan is intended to provide a common base of understanding across city departments to
facilitate more effective integration of water quality requirements. This Plan also contains a
glossary of key terminology to facilitate a common understanding of key concepts by users with
varied backgrounds. Concurrent with development of this Plan, the development review process
was undergoing review and revision; therefore, additional work will likely be needed to ensure
that the priorities of this Plan are integrated into the development review process.
Goal 4: Develop Framework and Priorities for Future Work Needed to Meet
Goals
The Wastewater Management Divisions initial vision for this Plan identified many potential
topics to be addressed. It was not possible to cover all of these topics in detail; therefore, a key
goal of this Plan has been to identify topics and issues that will be important to the future of
Denvers water quality management strategy, but that were beyond the scope of this document.
Recommendations and an initial implementation plan for future work on these topics have been
included in the Chapter 9 of this Plan. Representative topics include a watershed-by-watershed
assessment of water quality conditions, identification of specific locations for potential future
regional water quality treatment facilities, and exploration of funding alternatives for providing
regional water quality facilities.
APPROACH
This Plan has been developed using a multi-faceted approach to ensure that a practical and
innovative strategy for addressing water quality is developed for Denver. Multiple interviews
and meetings were conducted with key Denver staff to develop a Plan that will be beneficial to
many Denver departments. Key aspects of the project approach include:
Extensive collaboration among multiple city departments. Acceptance and use of this
Plan across city departments is critical to the success of this Plan. This document has
been developed through close collaboration and frank discussion among multiple
Chapter 1
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Denver Water Quality Management Plan
departments within Denver including Public Works, Parks and Recreation, Community
Planning and Development, Environmental Health, and the City Attorneys Office. By
working together to prepare this Plan, a more unified position and vision for stormwater
quality management has emerged.
Identification and review of regulations and existing Denver planning documents
affecting or interfacing with stormwater quality management strategies in Denver.
Many existing and proposed federal, state and local water quality regulations directly
influence stormwater quality management in Denver. Key regulations were inventoried
and described in order to provide a common basis for understanding stormwater quality
management requirements. Similarly, Denver has many excellent planning documents
and programs that help guide planning and watershed management decisions. In order to
avoid reinventing the wheel, a review of these key documents was completed.
Review of similar efforts in communities with advanced stormwater programs.
Communities throughout the country are reassessing their approach to stormwater and
watershed management. Early in the development of this Plan, five communities were
identified to explore their approaches, successes and difficulties in addressing urban
runoff. Interviews and review of key documents were conducted for these communities:
Portland, Oregon; San Diego, California; Austin, Texas; Prince Georges County,
Maryland; and Snohomish County, Washington. Findings from this research have been
taken into account in development of this Plan with regard to general approach, as well as
for recommendations for specific BMPs.
Identification of stormwater BMPs that have been both successful and unsuccessful
in the Denver area. The Project Team spent several days in the field visiting BMP sites
in Denver. The strengths and weaknesses observed at these sites have been taken into
account in the recommendations and strategies identified in this Plan. Photographs of
many of these BMP sites (both good and bad) are interspersed throughout this Plan.
Review of new stormwater BMP
technology and approaches for
potential applicability to Denver.
Policy statements on new BMP
technology such as underground
proprietary treatment devices have
been developed and provided in
Chapter 6. Approaches that
manage runoff close to the source
and promote infiltration through
landscape-based strategies are
explored for more extensive
application in the Denver area.
Terms commonly used for these
approaches include Minimizing
Directly Connected Impervious
EXHIBIT 1.4
STORMWATER BMPS SHOULD BE DESIGNED AND
MAINTAINED TO PROTECT PUBLIC HEALTH AND
AVOID NUISANCE CONDITIONS
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Introduction
Area, Smart Growth for Clean Water, and Low Impact Development. Circumstances
under which new approaches may be considered are also identified.
Development of practical stormwater quality BMP implementation guidelines. As a
result of the initial project tasks described above, the most significant need identified was
practical guidance for implementing and managing stormwater quality in Denver.
Chapters 6 and 7 provide this guidance. Representative questions considered as part of
development of this guidance are summarized in Exhibit 1.5
Accommodation of periodic updates and revisions. Denver recognizes and intends
that this Plan will be a living document that will need to be updated periodically to
reflect changes in the Denver area, BMP technology, and various regulations and policy
shifts. These updates will be posted on Denvers web site, www.denvergov.org. The
principles of adaptive management apply to this plan, as is the case for many related
Denver planning documents.
EXHIBIT 1.5 QUESTIONS CONSIDERED DURING PLAN DEVELOPMENT
What stormwater quality requirements apply to development and redevelopment sites?
What are the key regulatory requirements that are prompting mandatory implementation of
BMPs on new development and redevelopment sites? Are these requirements anticipated to
change in the future and, if so, in what ways?
What factors influence BMP selection for a given site?
What selection process should be utilized to determine the most appropriate BMP plan for a
particular site?
What performance criteria or standards apply, if any?
How do stormwater quality requirements interface with more traditional drainage and flood
control requirements?
To what extent can Denver parks and natural area open spaces be utilized for stormwater
quality management? What precautions need to be taken to assure that stormwater
management does not impair intended park or natural area open space uses?
How can BMPs be planned, designed and maintained to be viewed as community assets
rather than liabilities?
How should the BMP selection and design process account for issues such as public safety,
maintenance, environmental permitting, and others?
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Denver Water Quality Management Plan
PRINCIPLES AND POLICIES
Early in development of this Plan, the Project Advisory Committee and the Project Team agreed
on several foundational principles and policies, including:
All new and redevelopment projects must address water quality in their development
plans, complying with the stormwater policies and design criteria specified in the Urban
Storm Drainage Criteria Manual, Volumes 1-3 (UDFCD 1999, 2001) and in Denvers
CDPS permit. Particularly critical is the four-step BMP planning process that requires:
1. Implementing stormwater runoff reduction practices.
2. Providing treatment of the Water Quality Capture Volume.
3. Implementing streambank and channel stabilization techniques for any drainageways
within or adjacent to a project site.
4. Providing additional treatment for pollution hot spots.
Under Denvers CDPS permit, adverse impacts to receiving waters posed by urban
stormwater discharges must be minimized to the maximum extent practicable.
Examples of these adverse impacts can include increased pollutant loading, increased
runoff rates and volumes, channel instability, modification of aquatic habitat and
increased sediment loading, both during and after construction. It is essential to
recognize that, despite the best efforts to control stormwater runoff, there will be some
change in receiving water characteristics due to development; therefore, a zero impact
policy is not realistic or attainable. As a result, Denver advocates management of
stormwater through the implementation of BMPs designed in accordance with the
guidelines established by UDFCD (UDFCD 1999, 2001), as summarized above.
Denver will continue to advocate the use of multiple BMPs, including non-structural
measures, source controls, and structural BMPs, to reduce stormwater pollution.
Whenever practicable, combining BMPs in series can be very effective in reducing
stormwater pollution.
Urban stormwater management must be an integral part of site design and take into
consideration multiple objectives. As stated in the Urban Storm Drainage Criteria
Manual, Volume 1 (UDFCD 2001), the many competing demands placed on space and
resources require that stormwater management strategies take into account water quality
enhancement, groundwater recharge, recreation, wildlife habitat, wetland protection,
protection of landmarks/amenities, control of erosion and sediment deposition, and
creation of open space. In addition, the appearance of BMPs is particularly important;
Denver will expect to receive site development plans that feature attractive BMPs that
will be viewed as assets by the community. Denver will encourage multi-purpose usage
of BMPs; however, compatibility among uses must be demonstrated (e.g., compatibility
between recreational areas and detention areas).
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Introduction


Planning for water quality must
proceed hand-in-hand with drainage
planning for quantity (rate and
volume). In urban areas, these two
EXHIBIT 1.6
ATTRACTIVE GRADE CONTROL STRUCTURE ON
THE SOUTH PLATTE RIVER HELPS TO REDUCE
THE IMPACTS OF URBANIZATION
planning efforts are inseparable
(UDFCD 2001). When these issues
are addressed together and early in
the site planning process, more
efficient, economical and attractive
land uses generally result.
Water quality must be addressed in
the very beginning of the site
development process to ensure that
water quality BMPs are incorporated
into the site design. Benefits of this
practice include better site designs and more cost-effective BMPs
Denver will continue to review BMP designs for pubic safety and maintenance
accessibility, maintainability, documentation of maintenance requirements and schedule,
and assured long-term funding for maintenance. Proper maintenance is fundamental to
public safety and long-term effectiveness of stormwater BMPs.
Denver Strongly prefers managing Source: The Greenway Foundation,
and treating stormwater quality on the
ground surface, rather than in subsurface, vault-type treatment devices. Nevertheless,
Denver recognizes that there are some cases where the use of such facilities is necessary.
For example, this approach may be acceptable in cases of extreme space constraints that
occur on smaller redevelopment sites, which are essentially completely impervious in
their current condition, such as some locations in the downtown area. Chapter 6 provides
specific guidance on the conditions under which these types of treatment devices may be
considered.
The same stormwater quality management expectations and practices that apply to
projects in the private sector also apply to projects that are the responsibility of Denver,
such as buildings, parks, streets, utilities, etc. When Denver is preparing plans for any
such projects or managing, maintaining and/or upgrading existing facilities, potential
adverse stormwater quality effects must be evaluated and suitably mitigated.
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Denver Water Quality Management Plan
OPPORTUNITIES AND CHALLENGES
A primary goal of this Plan is to develop a framework for managing runoff water quality in a
manner that is not only effective, but that also takes into consideration the goals of the many city
departments and citizens. For these reasons, the Project Team worked closely with an
interdepartmental advisory committee and conducted multiple interviews to identify key
concerns and priorities of various city departments. As a result, several key opportunities and
challenges emerged for this Plan that are summarized in Exhibit 1.7 and discussed in more detail
below. This Plan provides a framework for
addressing these challenges.
Address Water Quality Issues
Portions of the South Platte River, Sand Creek,
Berkley Lake, and other Denver waterbodies do not
currently meet state stream standards for one or
more constituents, resulting in listing of
waterbodies on the states 303(d) list. (See Chapter 3
for more information.) In addition, continued
growth will apply increasing pressure on water
quality. Working towards attainment of water
quality standards and complying with Denvers
stormwater CDPS permit are high priorities for
Denver and have been strongly emphasized by the
Public Works Department and the Mayors office.
Chapters 6 and 7 of this Plan provide structural and
non-structural BMP strategies that can be used to
help Denver improve the quality of urban runoff. In
addition, stormwater quality BMP implementation
guidelines for a variety of land use types are
provided to aid developers and planners in selecting
strategies that work in various settings.
Recommendations regarding future watershed-by-
watershed assessments of water quality are also
identified in Chapter 9 as an important step to
developing and/or advancing basin-specific
approaches to water quality issues facing Denver.
Improve Interdepartmental Cooperation
With Regard to Water Quality
Stormwater quality treatment requirements are best
integrated into the early stages of site design. In
many cases, stormwater treatment requirements have
EXHIBIT 1.7
STORMWATER QUALITY
MANAGEMENT OPPORTUNTIES AND
CHALLENGES
ADDRESS WATER QUALITY ISSUES (E.G.,
303(D) LISTED SEGMENTS, STREAM
STANDARDS)
IMPROVE INTERDEPARTMENTAL
COOPERATION WITH REGARD TO
INTEGRATING WATER QUALITY INTO
SITE DEVELOPMENT
COORDINATE COMPATIBLE USES
BETWEEN PARKS AND WATER QUALITY
FACILITIES
ENHANCE COMPATIBILITY BETWEEN
URBAN DESIGN GOALS AND WATER
QUALITY FACILITIES
IMPLEMENT EFFECTIVE, SUSTAINABLE,
ATTRACTIVE, MULTI-PURPOSE, SAFE
AND WELL-DESIGNED BMPS
ENSURE LONG-TERM BMP OPERATION
AND MAINTENANCE
DEVELOP FINANCING AND
INSTITUTIONAL STRATEGIES FOR
REGIONAL BMPS
Chapter 1
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Introduction
not been considered early in the site design, resulting in few effective options for treatment, or
installation of unattractive, unsafe, and unmaintainable facilities that become public nuisances,
rather than amenities. Community Planning and Development, Parks and Recreation, and Public
Works all recognize the importance of early discussion regarding water quality treatment
requirements and plans. The stormwater quality BMP implementation guidelines provided in
Chapter 6 will help provide developers and planners with reasonable approaches to stormwater
treatment that take into consideration multi-departmental goals.
Interdepartmental communication and understanding regarding the legal obligations that Denver
has under its CDPS stormwater permit are vitally important to encouraging departments to work
cooperatively toward meeting these requirements. Chapter 3 of this Plan provides a common
foundation regarding Denvers obligations under its stormwater permit, along with implications
of anticipated future regulatory changes.
Coordinate Compatible Uses Between Parks and Water Quality Facilities
Parks, golf courses and natural areas open space are often viewed as opportunities for stormwater
detention; however, it is critical that the uses of these areas be taken into account to ensure that
usage conflicts are minimized. For example, areas used as soccer fields or golf courses need to
drain within a reasonable timeframe to prevent soggy fields that are incompatible with
recreational use. Other park and BMP conflicts may relate to safety in areas used for child play,
West Nile virus concerns, and/or protection and enhancement of wildlife. This Plan recognizes
that conflicts between parks and stormwater BMPs exist in some locations in Denver and care
must be taken in the future when selecting, designing, and maintaining BMPs in parks. Public
input and acceptance of stormwater BMPs in parks is particularly important, as is public
education on the purposes of BMPs. The BMP fact sheets provided in Chapter 6 identify
considerations to be taken into account when choosing various BMPs and can provide a starting
point to reduce conflicts between park and BMP functions.
Enhance Compatibility Between Urban Design Goals and Water Quality Facilities
Blueprint Denver (Denver 2000) provides a clear vision for Denvers development goals. The
Community Planning and Development Department, with the assistance of other Denver
departments, has the responsibility of moving Denver towards meeting these goals. In some
cases, stormwater BMPs can be difficult to fit into site designs that conform with these design
goals. For this reason, interdepartmental agreement regarding BMP design and integration into
various settings is important. Chapter 6 provides templates of possible site layouts with BMPs
integrated into the designs of various development types. In some cases, on-site stormwater
facilities are challenging due to space constraints; in these cases, opportunities for regional
stormwater facilities should be explored. Chapter 8 provides conceptual-level locations where
regional facilities warrant further exploration.
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Denver Water Quality Management Plan
Implement Effective, Sustainable, Attractive, Multi-purpose, Safe, and Well-
Designed BMPs
Denvers CDPS stormwater permit, Denvers Storm Drainage Design and Technical Criteria
Manual (Denver 1992) and other documents specify water quality treatment requirements for
new development and redevelopment projects. In addition to meeting the technical requirements
for these BMPs, the Project Advisory Committee and city department staff interviewees agreed
that these BMPs also must be sustainable, attractive, multi-purpose, safe, and well-designed
(Exhibit 1.8). Ensuring that these requirements and goals are met and that BMPs are maintained
on a long-term basis is critical for Denver to
successfully minimize the impacts of urban
runoff.
Many examples of BMPs that do and do not
meet these criteria were identified and visited
during the development of this Plan. Early
consideration of water quality requirements in
the site design can help prevent water quality
BMPs from being an afterthought, which may
result in poor BMP design and implementation.
Chapter 6 identifies specific considerations when
selecting BMPs that provide a foundation for
more sustainable, attractive, multi-purpose, safe
and well-designed BMPs.
EXHIBIT 1.8
SAFE, ATTRACTIVE, MAINTAINABLE
INFILTRATION BASIN
Ensure Long-term BMP Operation and Maintenance
Even when BMPs are thoughtfully designed and properly installed, they can become eyesores,
breed mosquitoes, and cease to function if not properly maintained. BMPs can be more
effectively maintained when they are designed to allow easy access for inspection and
maintenance and take into consideration factors such as property ownership, easements, visibility
from easily accessible points, slope, vehicle access, and other factors. Clear, legally-binding
written agreements assigning maintenance responsibilities and committing adequate funds for
maintenance are also critical. Chapter 3 describes Denvers requirements for BMP maintenance,
and Chapter 6 provides BMP maintenance recommendations. In addition, Chapter 5 describes
how other communities such as Portland, Oregon have invested in easy-to-understand guidance
documents for BMP maintenance that are useful for both private and public owners of BMPs.
Develop Financing and Institutional Strategies for Regional BMPs
The concept of regional stormwater facilities is supported across Denver departments,
particularly in redevelopment areas where land is unavailable or at a premium cost. The
challenges to implementing regional BMPs lie in three key areas: 1) institutional constraints, 2)
land availability, and 3) financing. Chapter 8 provides a conceptual-level assessment of Denver
drainages where regional facilities may be realistic. In order to take advantage of these
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Introduction
opportunities, a sound financing strategy must be developed. This can be challenging,
particularly in areas where development is phased over a number of years. Chapter 9
recommends future work to help develop financing strategies for regional BMPs, including a
discussion of institutional opportunities and constraints.
SCOPE LIMITATIONS
In order to develop a meaningful document, the width of this Plans scope has been limited to
enable increased depth on key subject areas. Related water quality and watershed management
topics that are not covered or are only briefly covered in this document include:
Construction site stormwater management. Construction site stormwater management
is a critical component of protecting receiving waters and a key requirement of Denvers
stormwater CDPS permit. Strong existing guidance on construction site stormwater
management is provided by UDFCD, Denver, the Colorado Department of Public Health
and Environment (CDPHE), and numerous other entities and is not repeated herein;
instead, the focus of this Plan is on permanent, post-development stormwater
management strategies.
Sanitary wastewater discharges and sanitary sewer overflows. Although sanitary
wastewaster discharges and sanitary sewer overflows (SSOs) are critical aspects of
addressing water quality issues in receiving waters, these discharges are believed to be
effectively addressed through CDPS permits. For specific water quality problems caused
by a combination of wastewater, stormwater, and nonpoint source discharges, an
interface with sanitary wastewater discharges will be required under pollutant load
allocations under the TMDL process. (See Chapter 3 for more information.)
Detailed design criteria for stormwater BMPs. This document is not intended to be a
design manual. To the contrary, excellent BMP design guidance exists in Volume 3 of
the Urban Storm Drainage Criteria Manual (UDFCD 1999), along with other references
(e.g., WEF and ASCE 1992 and 1998; CASQA 2003; City of Portland 2002).
Stream channel morphology, sediment transport and channel stabilization and
restoration practices. Topics excluded from discussion include use of turf
reinforcement mats, geotextiles, and other comparable materials in drainage channels,
other channel stabilization measures including bioengineering techniques, hydraulic
structures such as energy dissipaters downstream of bridge and culverts, grade control
structures, drop structures, etc. Many of these practices either directly or indirectly
contribute to stream channel stability and favorable water quality; however, they were
deemed to be beyond the scope of this document.
Detailed regional water quality facility master planning. Although an initial glimpse
of potential regional water quality BMPs that could be used in Denvers primary drainage
areas is provided in Chapter 8, it was beyond the scope of this Plan to address facility
master planning in detail. Follow-up work needed for such an effort is defined in
Chapter 9.
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Denver Water Quality Management Plan
Receiving Water Impact Assessment. Detailed guidance on this topic is beyond the
scope of this Plan. This Plan assumes that in most cases involving typical urban
stormwater discharges from development and redevelopment sites, site-specific impact
assessments will not be necessary, provided that practices specified in the Urban Storm
Drainage Criteria Manual (UDFCD 1999, 2001) are implemented.
Development of Financing Strategies for Regional BMPs. Realistic and well-thought-
out financing strategies for regional BMPs are necessary for the success of any regional
BMP. Exploration of these financing strategies was beyond the scope of this document,
but has been recommended as a future task in Chapter 9 of this Plan.
Life Cycle Cost Analysis. Detailed BMP cost data were not included in this Plan. The
concept of life cycle costs for BMPs is relevant to BMP selection because it takes into
consideration the design, construction, maintenance and rehabilitation costs of the BMP
over its expected lifetime. The reader is referred to references for more information on
BMP costs in Chapter 6 of this Plan.
PLAN OVERVIEW
Given the purpose, goals, approach, foundational policies, and scope limitations that evolved
during the course of this project, the Project Team and Advisory Committee determined that this
Plan should address these topics:
Overview of key drainage basins in the Denver area.
Discussion of basic tenets of urban runoff impacts.
Discussion of key current and future regulatory drivers affecting stormwater and
receiving waters.
Identification of key documents (e.g., Urban Storm Drainage Criteria Manual Volumes
1-3, Blueprint Denver) that this Plan must interface with in order to be effective.
Identification of strategies that are successfully being used in other communities to
address urban runoff.
Development of stormwater BMP implementation guidelines identifying how these
BMPs can be integrated into various development types in Denver.
Development of BMP fact sheets, implementation details, and maintenance guidelines
that identify how BMPs can be better implemented and maintained in Denver.
A broad-level assessment of potential regional water quality facility locations in Denver.
Identification of future tasks that need to be completed in order for Denver to achieve its
water quality objectives.
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Chapter 2
OVERVIEW OF MAJOR DENVER DRAINAGE BASINS
AND POTENTIAL URBAN STORMWATER IMPACTS
A common understanding of Denver drainage basins, lakes, and the potential adverse impacts of
stormwater from urbanization is necessary for understanding and applying this Plan. This
chapter provides an overview of these topics.
OVERVIEW OF DENVER DRAINAGE BASINS
The City of County of Denver includes approximately 155 square miles of land area (nearly
100,000 acres). Denver receives about 15 inches of rainfall and 55 inches of snowfall each year.
Denvers drainageway s receive runoff from approximately 190 square miles of land area, some
of which is located outside of Denvers jurisdictional boundaries. The South Platte River is the
major river basin receiving runoff from Denver, with Sand Creek and Cherry Creek being
significant tributaries to the South Platte River (Exhibit 2.1). Relatively small reaches of Clear
Creek and Bear Creek, which are also significant tributaries to the South Platte, traverse the
northwest and southwest portions of Denver, respectively. While a watershed-by-watershed
assessment of water quality issues is beyond the scope of this Plan, readily available basic
information on these watersheds is available from the Denver Storm Drainage Master Plan
(Matrix 2003) and other plans, as summarized in Exhibits 2.2 and 2.3. Specific opportunities for
potential regional water quality facilities and more detailed hydrologic characterization of these
drainage basins are discussed in Chapter 8.
EXHIBIT 2.1
CHERRY CREEK NEAR THE CONFLUENCE WITH THE
SOUTH PLATTE RIVER
Source: The Greenway Foundation.
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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts
Exhibit 2.2 Major Denver Drainage Basins
ID OUTFALL NAME/LOCATION AREA (mi2) COMPOSITE IMPERVIOUSNESS
0058-01 South Platte River Prairie Gateway 1.59 25.0%
0059-01 South Platte River Globeville 3.72 51.4%
0060-01 South Platte River 1-70 & Colorado Boulevard 2.73 68.7%
0060-02 South Platte River 1-70 & York 1.47 71.8%
0061-01 South Platte River 27th & Federal 5.1 7 66.8%
0062-01 South Platte River Lower Platte Valley 2.73 77.5%
0063-01 South Platte River Central Platte Valley 2.10 83.2%
0064-01 South Platte River 1 st & Federal 0.50 74.4%
0064-02 South Platte River Valverde 2.66 69.2%
0065-01 South Platte River Ruby Hill 1.25 70.1%
0065-02 South Platte River Dartmouth 0.76 86.8%
0067-01 South Platte River Colleqe View 1.29 21.7%
0067-02 South Platte River West Belleview 4.24 12.5%
0067-03 No Outfall Marston Lake 1.03 100.0%
3300 Third Creek Third Creek 16.36 40.1%
3500 Second Creek Second Creek 8.02 30.4%
3501-01 Second Creek West Fork Second Creek 3.37 36.8%
3700-01 First Creek 56th to 64th Avenue 5.36 33.4%
3700-02 First Creek 38th to 56th Avenue 2.92 60.6%
3702-01 First Creek Picadillv & 56th Avenue 1.34 78.0%
3900-01 Irondale Gulch North Stapleton 0.48 20.4%
3900-02 Irondale Gulch West of Chambers Road 1.85 40.0%
3900-03 Irondale Gulch Tower to Chambers Road 2.91 54.7%
3900-04 Irondale Gulch 1-70 to 42nd Avenue 1.83 68.7%
3901-01 Irondale Gulch Peoria 4.44 43.4%
3901-02 Irondale Gulch 40th & Chambers Road 0.97 64.9%
4000-01 Rocky Mountain Arsenal Stapleton North 0.78 29.1%
4300-03 Clear Creek North of 1-70 1.79 58.2%
4309-01 Clear Creek Berkeley Lake 1.83 55.1%
4400-01 Sand Creek North Stapleton 5.07 42.5%
4400-02 Sand Creek Quebec Corridor 5.01 65.0%
4400-03 Sand Creek South Stapleton 1.49 70.8%
4400-04 Sand Creek East Stapleton 2.77 74.1%
4401-01 Westerly Creek Stapleton 3.03 50.6%
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Denver Water Quality Management Plan
Exhibit 2.2 Major Denver Drainage Basins
ID OUTFALL NAME/LOCATION AREA (mi2) COMPOSITE IMPERVIOUSNESS
4401-02 Westerly Creek 11th Avenue to Montview 2.83 62.6%
4401-03 Westerly Creek Lowry 3.51 40.6%
4401-04 Westerly Creek South of Alameda 2.85 55.6%
4500-01 Montclair City Park 4.30 54.4%
4500-02 South Platte 36th & Downing 1.74 65.2%
4500-03 Montclair Park Hill 1.51 59.7%
4500-04 Montclair Park Hill 3.69 54.4%
4600-01 Cherry Creek Central Business District 2.1 7 83.2%
4600-02 Cherry Creek Cherry Creek Mall 4.61 57.7%
4600-03 Cherry Creek Upper Cherry Creek 5.62 68.9%
4600-04 Cherry Creek Upper Cherry Creek 5.77 51.3%
4601-01 Goldsmith Gulch Cherry Creek Outfall 3.92 54.1%
4601-02 Goldsmith Gulch Middle Goldsmith Gulch 1.34 59.0%
4700-01 Sloans Lake West Colfax Avenue 1.59 65.0%
4800-01 Lakewood Gulch 1 2th & Federal 1.17 59.6%
4801-01 Dry Gulch 1 2th & Sheridan 0.39 62.0%
4900-01 Weir Gulch West 6th Avenue 2.30 58.3%
5000-01 1-25 & South Platte West Washington Park 1.25 71.9%
5000-02 1-25 University & Mexico 5.02 60%*
5100-01 Sanderson Gulch West Florida Avenue 5.57 54.6%
5200-01 Harvard Gulch West Fork Second Creek 0.83 63.8%
5200-02 Harvard Gulch 56th to 64th Avenue 6.62 50.4%
5300-01 West Harvard Gulch West Yale Avenue 1.44 57.1%
5401-01 Greenwood Gulch South Monaco Parkway 0.16 50%*
5500-01 Bear Creek Fort Logan 3.12 52.8%
5500-02 Bear Creek Upper Bear Creek 1.84 45.5%
5500-03 Bear Creek Academy Park Tributary 0.60 62.7%
5500-04 Bear Creek Marston Lake North 2.24 46.0%
5500-05 Bear Creek Pinehurst Tributary 0.72 42.2%
5501-01 Bear Creek Henry's Lake 1.35 35.0%
5901-01 Dutch Creek Coon Creek 3.10 53.2%
8056 Barr Lake Barr Lake 3.86 7.9%
81 50 Box Elder Creek Box Elder Creek 3.10 53.2%
* Approximate further evaluation pending.
TOTAL 189.89
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Insert Exhibit 2.3 Location Map Here
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Denver Water Quality Management Plan
South Platte River
The South Platte River is the largest
receiving waterway in the Denver
metropolitan area and flows from south
to north along the 1-25 corridor through
Denver. Within the city limits of
Denver, the South Platte River meanders
along a path some 10.5 miles in length
from West Dartmouth Avenue to
Franklin Street. The drainage basin
covers approximately 4,850 square
miles extending from the Continental
Divide in the Rocky Mountain Front
Range to the high plains and foothills of
eastern Colorado. The mountainous
portion of this basin is generally
unsuited for dense development, while
the foothills and high plains areas are
actively being developed. The intense
urbanization in the metropolitan area
consists primarily of residential and
commercial areas and some industrial regions along the river valley.
EXHIBIT 2.4
THE SOUTH PLATTE RIVER BASIN IS THE LARGEST
DENVER DRAINAGE BASIN AND IS HIGHLY
URBANIZED (IN DENVER)
Source: The Greenway Foundation.
The South Platte River flood potential is mitigated by Chatfield Reservoir located on the South
Platte River, along with Cherry Creek Reservoir and Bear Creek Reservoir located on major
tributaries. Peak 100-year flows of the South Platte vary from 5,000 cubic feet per second (cfs)
near Chatfield to 38,000 cfs at the confluence with Sand Creek. Normal discharges in the South
Platte River are generally about 100 cfs, but approach about 1,000 cfs during the spring runoff
period. Average daily flows are highly affected by treated effluent discharges from Metro
Wastewater.
First Creek
The First Creek basin drains an area of 47.2 square miles. The headwaters of First Creek are
located in Arapahoe County, south of 1-70 and east of E-470. Runoff from the basin flows in a
northwesterly direction. First Creek crosses Pena Boulevard just north of 56th Avenue and then
flows through the northeastern portion of the Rocky Mountain Arsenal. First Creek is a right-
bank tributary to the South Platte River, and outfalls at approximately 128th Avenue. The basin
shape is long and narrow, approximately 26 miles long and 2 to 4 miles wide. The average
stream slope above Rocky Mountain Arsenal is about 31 feet per mile, and flattens to about 23
feet per mile below Rocky Mountain Arsenal
The upper reaches of First Creek are primarily undeveloped irrigated cropland with wide swales
and channels for drainageways. Toward the center of the basin, First Creek bisects Green Valley
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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts
Ranch, which consists of medium density, single-family residences. First Creek then enters
Rocky Mountain Arsenal with a more incised, low flow channel and wider floodplain areas.
The lower First Creek basin is located downstream from 56th Avenue and Pena Boulevard and
continues to the South Platte River. The lower First Creek basin consists of irrigated farmland
with pockets of light industrial and residential properties. Conveyance within the lower First
Creek drainage consists of broad undefined channels with little or no defined thalweg. Between
US-85 and Brighton Boulevard, the channel is incised with a well-defined thalweg. The OBrian
Canal and the Burlington Ditch, which intercept runoff from First Creek, cross First Creek below
Rocky Mountain Arsenal.
Second Creek
Second Creek drains about 27 square miles of area to the South Platte River. The basin is about
15 miles long and 3.4 miles wide at its widest point. The drainage basin ranges in elevation from
4,990 feet at the South Platte River to 5,650 feet at the basin divide. Second Creek has a natural
irregular channel section in the upper reaches above the OBrian Canal.
The southern land area within the Second Creek drainage basin in Denver city limits drains via a
tributary known as the West Fork of Second Creek. This tributary drains 3.03 square miles of
area to Second Creek. The Highline Canal terminates at the West Fork. The sustained unused
flow in the Highline Canal is wasted to the West Fork downstream of 64th Avenue, and the flows
have eroded the channel on the West Fork. At Tower Road, the West Fork channel is about 15
feet deep with vertical and very steep, unstable banks. The confluence of Second Creek and the
West Fork of Second Creek is a wide, relatively flat area supporting a stand of cottonwood trees.
Some wetland areas are present in the upper reaches of the West Fork, but, as the channel has
eroded, the channel banks have become incised and support only a narrow band of wetland or
riparian vegetation. The floodplain is contained within the channel except at road crossings,
where overtopping will occur. The banks are unstable and some lateral channel migration may
occur during large flows.
Third Creek
Third Creek is an east bank tributary of the South Platte River and is located northeast of
Downtown Denver. Third Creek flows through Denver International Airport (DIA) and is
experiencing development in the drainage basin. Third Creek drains approximately 31 square
miles of area to the South Platte River. The basin is about 14 miles long and 3.2 miles wide at its
widest point and ranges in elevation from 4,960 feet at the South Platte River to 5,485 at the
basin divide. Third Creek has a natural irregular channel section above the OBrian Canal, and a
small, poorly defined channel section between the OBrian Canal and the South Platte River.
Third Creek is crossed by Highway 85,1-76, the Union Pacific and Burlington Northern
Railroads, and the OBrian Canal, Fulton Ditch, McCann Ditch, and the Burlington Ditch.
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Denver Water Quality Management Plan
Box Elder Creek
Box Elder Creek is located east of the Denver metropolitan area, with a portion of the watershed
draining the easternmost portion of Denver. Major tributaries include Bear Gulch and
Hayesmount Creek. The watershed is long and narrow, extending from El Paso County in the
south a distance of approximately 100 miles to its confluence with the South Platte River in
Weld County downstream of the City of Greeley. The watershed encompasses about 370 square
miles located in Weld, Adams, Arapahoe and Elbert Counties. Box Elder Creek is generally dry
except for short periods of runoff after intense rainfall events, although portions of the creek
have a small amount of flow for longer periods. The Box Elder Creek watershed is currently
mostly undeveloped grassland and agricultural areas. The portion of the watershed that lies
within DIA, however, has some areas that are heavily developed. Developed areas within the
DIA property include runways and taxiways, concourses, and support facilities. Additionally,
there are scattered relatively low-density housing developments along the central portion of the
creek.
Irondale Gulch
The Irondale Gulch basin, which contains approximately 26.7 square miles, lies immediately
southwest of First Creek and drains the area from the intersection of 1-70 and Arapahoe Road
and the Adams County line, through the Montbello area, the Arsenal and Commerce City with an
eventual outfall to the South Platte River at approximately East 96th Avenue. The southwest
boundary of the basin is primarily the north side of 1-70 until it reaches the former Stapleton
International Airport, where the basin boundary lies just west of Havana Street. This basin is
long and narrow, with a total length of 28 miles to the South Platte River and a width of IV2 to 2
miles. The average slope of the basin is about 26 feet per mile, which remains fairly constant
throughout the drainageway. The drainageways through the Arsenal contain several lakes and
detention areas. The drainage below the Arsenal is primarily storm sewer or roadside ditches,
with capacity for only minor floods.
Clear Creek
Clear Creek is a left bank tributary to the South Platte River, and has its source in the Rocky
Mountains west of Denver. Flowing in a generally easterly direction from the Continental
Divide, Clear Creek enters the high plains in Golden. Within this lower reach, Clear Creek
passes through unincorporated areas of Adams and Jefferson Counties, and the cities of Denver,
Arvada, Wheat Ridge and Golden. Clear Creek crosses the northwest corner of Denver for a
distance of 0.2 miles in the vicinity of 52nd Avenue and Gray Street.
The drainage area at the mouth is 575 square miles, of which 400 square miles is in the mountain
region above Golden. There are 11 major reservoirs in the lower Clear Creek basin, three of
which are on-stream and provide some residual flood control effects downstream from each site.
Ralston Reservoir was built in 1938 by Denver and receives water from Ralston and South
Boulder Creeks. Although Ralston Reservoir is not operated for flood control purposes, there is
approximately 2,400 acre-feet of storage available. Maple Grove Reservoir is located on Lena
Gulch at West 27th Avenue and has approximately 452 acre-feet of available storage. Leyden
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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts
Lake is an irrigation water storage reservoir on Leyden Creek upstream from Indiana Street, and
has approximately 550 acre-feet of uncontrolled storage.
Sand Creek
Sand Creek is an east bank plains tributary of the South Platte River and lies to the east and
northeast of Denvers Central Business District. The Sand Creek basin encompasses an area of
189 square miles. The basin is long and narrow, with a length of 32 miles and an average width
of 6 miles. Portions of Elbert, Douglas, Arapahoe, Denver, and Adams Counties are included in
the drainage area. Sand Creek originates at the confluence of Coal Creek and Murphy Creek.
Sand Creek joins the South Platte River in the vicinity of 1-270 in Commerce City, north of
Denver city limits. The reach of Sand Creek within Denver is located along 1-70 near the
Stapleton Redevelopment area. Principle tributaries of Sand Creek are Toll Gate Creek and
Westerly Creek.
Westerly Creek
The Westerly Creek tributary area
consists of approximately 18 square
miles of highly developed area from
the low rolling divide between
Cherry Creek and West Toll Gate
Creek to the confluence with
Sand Creek. The basin is about
8.5 miles long and 3 miles wide at
its widest point. The crescent-
shaped area drains in a northwest-
to-north direction with an average
slope of 0.9 percent.
The Westerly Creek drainage
basin is at a state of full
development consisting of townhouses, condominiums, apartments, single family homes, motels,
large shopping complexes, streets, parking areas, and highways. This development and the 0.9
percent slope contribute to a rapid response time for storm runoff and increased stormwater
flows.
The upper reaches of Westerly Creek begin in the City of Aurora. Runoff of peak events is
captured in Westerly Creek Dam, built in 1989 on the former Lowry Air Force Base at Alameda
and Havana. As Westerly Creek outlets from the dam, it flows in a 48-inch underground pipe.
Flows from the Lowry Redevelopment area enter Westerly Creek and then are detained in Kelly
Road Dam at 11th Avenue. The channel and culverts from Kelly Road Dam to Montview at the
Stapleton Redevelopment area have been improved to handle the 10-year design storm. The
Westerly Creek channel through the Stapleton site has been improved to 100-year capacity. All
storm outfalls to Westerly Creek within the Stapleton site have regional water quality treatment
at the end of pipe.
RECENTLY CONSTRUCTED DETENTION BASIN
(VEGETATION NOT YET ESTABLISHED) ON WESTERLY
CREEK IN THE STAPLETON REDEVELOPMENT AREA
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Denver Water Quality Management Plan
EXHIBIT 2.6
CHERRY CREEK IN DENVER, COLORADO
Cherry Creek
The Cherry Creek tributary area consists
of 410 square miles, 385 square miles
of which drain into Cherry Creek
Reservoir. The dam is designed to
release a maximum of 5,000 cfs to the
lower Cherry Creek channel, which has
a current capacity of between 4,000 and
11,000 cfs.
The lower Cherry Creek basin (Exhibit
2.6) covers 25.2 square miles, with
Goldsmith Gulch contributing 7.7
square miles of the total area. The
lower channel of Cherry Creek flows
11.5 miles from the reservoir to the
South Platte River confluence in the vicinity of Speer Boulevard.
The lower channel has been improved to contain the 100-year storm from 1st Avenue to the
confluence. These improvements generally consist of cleaning, shaping, and landscaping the
channel bottom.
EXHIBIT 2.7
GOLDSMITH GULCH IN DENVER, COLORADO
Goldsmith Gulch
The Goldsmith Gulch basin
encompasses an area of 7.8 square
miles from Arapahoe Road northwest
to the confluence with Cherry Creek.
Through Denver, the tributary area is
primarily urbanized or in the process
of development with a mix of
commercial and residential
construction.
Many channel improvements have
been completed along Goldsmith
Gulch to reduce the potential of flood
damage. The channel has been
stabilized (Exhibit 2.7) and regional
parks have been constructed in the floodplain. Detention facilities have also been constructed
along the channel at Bible Park, Wallace Park, Rosamond Park, and at Iliff and Monaco.
Channel slopes are generally mild with several newer drop structures along the reach.
The Highline Canal bisects Goldsmith Gulch at East Cornell Avenue. Goldsmith Gulch passes
underneath the Highline Canal and East Cornell Avenue through a concrete box culvert. The
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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts
upper portion of Goldsmith Gulch includes the T-REX construction site. New storm sewer and
detention facilities drain the 1-225 and 1-25 interchange to Goldsmith Gulch.
Sloans Lake
The Sloans Lake drainage basin flows eastward from a high point near 26th Avenue and
Garrison Street in Lakewood and outfalls into the South Platte River near Colfax Avenue and
Invesco Field. The drainage basin lies within Denvers jurisdiction east of Sheridan Boulevard
and is bounded by West 32nd Avenue on the north, Colfax Avenue on the south, Garrison Street
on the west, and the South Platte River on the east. The basin totals almost 5.5 square miles
within Denver, Lakewood, Edgewater, and Wheatridge. Since the basin is frilly developed and
heavily urbanized, the major drainageways are not clearly identifiable. Most of the historic
drainage channels have either been filled in or built over to the point of obliteration.
The most prominent geographic feature within the basin is Sloans Lake. The lake, which
occupies 176.5 acres of a 290-acre Denver park, has been and continues to be a valuable
recreational resource for the metropolitan area. In addition to its scenic and recreational
significance, the lake provides the important function of regulating and controlling downstream
flows that otherwise would be allowed to run uninhibited through West Denver. The lake
reduces peak flow rates from about 2,904 cfs to 166 cfs during the 100-year event.
Lakewood Gulch
Lakewood Gulch is a major drainageway that originates in Lakewood and flows easterly toward
the South Platte River between 6th Avenue and Colfax Avenue. The Lakewood Gulch basin
consists of approximately 16 square miles beginning in the foothills and extending easterly 10
miles to the South Platte River in the vicinity of Colfax Avenue. The tributary area is essentially
fully developed in Denver and in the eastern portion of Lakewood. The basin is also developed
in the western portion of Lakewood and Jefferson County.
Dry Gulch
The Dry Gulch basin consists of approximately 3.7 square miles lying predominantly in
Lakewood. Dry Gulch is tributary to Lakewood Gulch in the vicinity of 10th Avenue and Perry
Street in Denver, and extends westward a length of 5.7 miles along the general alignment of
Colfax Avenue to Simms Street. The basin is essentially fully developed, with commercial
establishments along Colfax Avenue and residential development comprising the remainder of
the basin.
Weir Gulch
Weir Gulch meanders eastward from Green Mountain Village for approximately 8.3 miles to the
confluence with the South Platte River in the vicinity of West 9th Avenue. The basin, which
comprises some 7.2 square miles, is fully urbanized in Denver and mostly developed west of
Sheridan Boulevard in Lakewood.
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Denver Water Quality Management Plan
There are two drainageways tributary to Weir Gulch within Denver. The 1st Avenue tributary to
Weir Gulch is located just north of 1st Avenue and flows in an easterly direction. The drainage
basin is bounded by 6th Avenue on the north, West Alameda Avenue on the south, Raleigh Street
on the east, and Wadsworth Boulevard on the west. This tributary of the Weir Gulch system is
approximately 2 miles long and about 0.8 mile wide, with an average slope of 1.5 percent.
The Dakota Avenue Tributary to Weir Gulch lies within Denvers jurisdiction east of Sheridan
Boulevard and is located just south of Dakota Avenue flowing in an easterly direction. It is
bounded by West Alameda Avenue on the north, West Alaska Avenue on the south, Sheridan
Boulevard on the west, and Xavier Street on the east. This tributary is about A-mile wide and
has an average slope of 1A percent.
Strip parks have been developed by the Denver Parks and Recreation Department from 1st
Avenue to Alameda Avenue along the gulch. This development consists mainly of grassed
channels and the installation of asphalt bike paths. Barnum Park is located on each side of 6th
Avenue on the west side of Federal Boulevard. Barnum Lake, located south of 6th Avenue, has
been improved to contain the 100-year storm within the Weir Gulch channel. The open park
area north of 6th Avenue, known as the Federal Boulevard Detention Reservoir, is designed to
reduce the 25-year flow to a 10-year flow or less. The lower Weir Gulch channel from Federal
to the South Platte River outfall has capacity for the 10-year storm.
Sanderson Gulch
Sanderson Gulch flows 8.63 miles in an easterly direction from South Union Boulevard above
Smith Reservoir to the South Platte River in the vicinity of West Florida Avenue. This drainage
basin, which encompasses approximately 9 square miles, is fully developed in Denver and is
being rapidly urbanized west of Sheridan Boulevard. The entire basins drainage area extends
west to the top of Green Mountain, and channel slopes are generally mild.
Green belts and parks have been located along the Sanderson Gulch floodplain. Drainageway
improvements have been constructed to contain the 100-year event within open channels;
however, culverts were designed for the 10-year frequency discharge.
West Harvard Gulch
West Harvard Gulch flows east 2.8 miles through Denver to its confluence with the South Platte
River in the vicinity of Yale Avenue. The total area of the drainage basin is approximately 1.4
square miles. The average width of the basin is 0.66 mile, and the channel slopes range from 1.3
to 2.4 percent. The basin elevations range from approximately 5,525 feet to 5,250 feet.
The West Harvard Gulch basin is primarily in residential development. Commercial areas are
situated along Federal Boulevard, and a light industrial park is located in the basins lower
reaches. Loretto Heights College sits on the ridge that forms the southern boundary of the basin.
In the West Harvard Gulch Basin, the main drainageway was piped in an underground conduit
that extended from just above the Colorado and Southern Railroad to Zuni Street. This reach has
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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts
been restored and an improved grass lined and concrete trickle channel carries the flood events.
Channel slopes within this reach are stabilized with grouted sloping boulder drops.
During the 100-year flood event, most of the flood flow will be contained in the channel. At the
confluence of the South Platte River, the main channel flows through an 84-inch-diameter
concrete pipe. This pipe has inadequate capacity to carry the 100-year flow, resulting in shallow
flooding around the Arapahoe Power Plant. Some ponding and overtopping will occur at Zuni,
Clay and Decatur Street crossings during the 100-year flood event.
Harvard Gulch
Harvard Gulch flows west through the southern part of Denver for a length of 5.6 miles to reach
its confluence with the South Platte River at Wesley Avenue. The total drainage basin area is
approximately 7.7 square miles. The Highline Canal meanders through the southeast portion of
the basin and intercepts storm flow. Single-family residences primarily urbanize the basin.
Commercial development is generally located along Colorado Boulevard, Broadway, and Santa
Fe Drive. The residential portion of the basin is very dense with small lots having an estimated
52 percent average imperviousness.
The Harvard Gulch Flood Control project, completed in 1966, was designed for the 10-year
flood and included an underground box culvert from Logan Street to the South Platte River. A
grass-lined open channel was designed though Logan Park, which also serves as an inlet to a
detention pond in the park.
Highway 1-25 and the T-REX construction project bisect the upper portion of Harvard Gulch.
Drainage improvements for T-REX through the Holly Hills area include several detention/water
quality basins as well as a new storm sewer system. The T-REX storm sewer is connected to
Denvers existing storm sewer system at two locations along the west side of 1-25: 1) the T-REX
storm sewer system to the south outfalls to the Highline Canal; and 2) the storm sewer system to
the north outfalls to the existing 36-inch storm sewer within Yale Avenue.
Bear Creek
Bear Creek generally flows eastward from its headwaters at Mount Evans through the towns of
Evergreen and Morrison until it reaches the metropolitan area of Denver where it is tributary to
the South Platte. The drainage basin is approximately 36 miles long and has an average width of
about 9 miles. This encompasses approximately 261 square miles of drainage area. Elevations
in the basin range from approximately 14,260 feet at Mount Evans to 5,260 feet at the mouth.
Turkey Creek, a major tributary, drains about 52 square miles and enters into Bear Creek
approximately 2 miles downstream of Morrison. The majority of the basin is in the mountains,
with the remainder draining the foothills and high plains region. The drainage basin area inside
the Denvers city limits is about 12 miles in size.
The completion of Bear Creek dam just downstream of Morrison has had a great effect on the
peak discharges of the 8.2-mile Bear Creek reach below the dam. The dam acts as a flood
control reservoir that intercepts flows from areas in the upper and middle parts of the basin. At
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Denver Water Quality Management Plan
the Bear Creek dam, peak flows from the 100-year event have been reduced from 30,000 cfs to
approximately 1,000 cfs through storage in the reservoir.
Marston Lake North (Tributary of Bear Creek)
The Marston Lake drainage basin consists of approximately 2.1 square miles of limited
developed area in the southwest comer of Denver. Various areas within the basin are subject to
flooding, which could increase in severity and frequency with continued urbanization of the
basin without drainageway improvements. The basin originates approximately U mile west of
Kipling Street between Belleview and Quincy Avenues, and extends approximately 4.4 miles in
a northeasterly direction to its confluence with Bear Creek. Continued development in these
areas, planned for mostly residential with some light commercial business, is expected to
increase runoff rates.
Marston Lake is owned and operated by the Denver Water Board and serves as a major link in
the water supply system for Denver and much of the metropolitan area. The lake acts as a sump
and is isolated from receiving or discharging stormwater.
The drainage basin traverses various jurisdictions and ownerships including Jefferson County,
Denver, Denver Water Board, Marston Water Treatment Plant grounds, Pinehurst Country Club
Golf Course, and United Sates Government properties to the south of Fort Logan National
Cemetery.
Improvements to the drainageway have been accomplished by Denver Water and UDFCD. The
north side of the Marston Lake Dam, which was reconstructed to allow room for an open channel
and improved by UDFCD, provides an improved 100-year capacity channel from Old
Wadsworth Boulevard to West Quincy Avenue.
OVERVIEW OF LAKES
Denver has many lakes within its boundaries that are managed by Denver Parks and Recreation.
Exhibit 2.8 provides an overview of these lakes based on the recently completed Lake
Management and Protection Plan (Dudley 2004). The Colorado Water Quality Control
Commission (CWQCC) has assigned water quality standards to most of these lakes. For lakes
without assigned standards, the principles of water quality protection discussed in this Plan
remain relevant for supporting healthy, aesthetically pleasing conditions in the lakes.
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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts
EXHIBIT 2.8 DENVER LAKE LOCATIONS AND CHARACTERISTICS (DUDLEY 2004)
Manage- ment Type Lake Name Location Characteristics
Southwest District Barnum Lake in Barnum Park West of Federal Blvd. between 6th Ave. and 3rd Ave. 9 acres; 5 feet maximum depth; perimeter: 0.7 mile.
Southwest District Bear Creek Ponds in Bear Creek Park Bear Creek Park is located at S. Raleigh Street and W. Hampden Avenue. Located along Kenyon Avenue off of Sheridan Boulevard. There is a series of four ponds along a soft trail across from the Fort Logan Cemetery. 70 acres of natural areas can be accessed from the south boundary of the park.
Northwest District Berkeley Lake in Berkeley Park South of 1-70 between Sheridan Blvd. And Tennyson St. 40 acres; 1 2 feet maximum depth; perimeter: 0.9 miles.
East Montclair District City Park Lakes North of 1 7th Ave. and west of Colorado Blvd. Parking area on the northwest side of the lake between the park and the Denver Zoo. Ferril Lake 25 acres; 8 feet maximum depth; perimeter 0.8 miles. There is a sediment basin at 1 7th Street at the point where the storm sewer/city ditch daylights that is 2 acres in size. The sediment basin discharges to Ferril Lake. Duck Lake 6.3 acres; perimeter: 0.4 mile.
Southwest District Garfield Lake in Garfield Park South of W. Mississippi Ave. between S. Federal Blvd. and S. Sheridan Blvd. 1 0 acres; 4 feet maximum depth; perimeter: 0.5 mile.
Southwest District Harvey Lake in Harvey Park Between S. Sheridan Blvd. and S. Federal Blvd., just south ofW. Evans Ave. and east of S. Tennyson St. 8.5 acres; 1 4 feet maximum depth; perimeter: 0.4 mile.
Southwest District Huston Lake in Huston Lake Park East of S. Federal Blvd. about 4 blocks, between W. Ohio Ave. and W. Kentucky Ave. Southeast of the intersection of Ohio and S. Clay St. 13 acres; 6 feet maximum depth; perimeter: 0.6 mile.
Southwest District Lake of Lakes (A.K.A. Little Lake Henry) Carr St. and Quincy Ave. 3.5 acres, perimeter: 0.4 mile.
Southeast District Lollipop Lake in Garland Park Between S. Holly St. and S. Kearney St. north of Cherry Creek Dr. N. 4 acres; 8 feet maximum depth; perimeter: 0.4 mile.
Southwest District Overland Pond in Overland Pond Park North ofW. Florida Ave. between S. Santa Fe Dr. and the South Platte River trail. 1.5 acre; 7 feet maximum depth; perimeter: 0.2 mile.
Northeast District Parkfield Lake in Developing Park Area DIA Cateway/Chambers north of 1- 70. 14 acres; 6 feet mean depth; perimeter: approximately 1 mile.
Northwest District Rocky Mountain Lake in Rocky Mountain Lake Park W. 46th Ave. between Federal Blvd. and Lowell Blvd. Parking areas north of 46th Ave. 29 acres; 40 feet maximum depth; perimeter: 0.9 mile.
Northwest District Sloans Lake (including Cooper Lake) in Sloans Lake Park East of Sheridan Blvd. between W. 25th Ave. and W. 1 7th Ave. 1 74 acres; 5 feet deep in the main body of the lake west of the island but upwards of 8 feet deep east of the island; perimeter: 2.6 miles.
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Denver Water Quality Management Plan
EXHIBIT 2.8 DENVER LAKE LOCATIONS AND CHARACTERISTICS (DUDLEY 2004)
Manage- ment Type Lake Name Location Characteristics
Southwest District Vanderbilt Pond in Vanderbilt Park North of W. Tennessee Ave. between S. Santa Fe Dr. and S. Huron St. Access from W. Mississippi Ave. 6 acres; 1 5 feet maximum depth.
South Denver Park District Washington Park Lakes Northeast of the intersection of S. Downing St. and E. Louisiana Ave. Smith Lake 9 acres; 1 2 feet maximum depth; perimeter: 0.6 mile. Grasmere Lake 1 9 acres; 1 0 feet maximum depth; perimeter: 0.8 mile. Lily Pond 1 acre; 8 feet maximum depth; perimeter: 0.18 mile.
Natural Area Bluff Lake in Bluff Lake Park Havana at 32nd Ave. 9 acres
Natural Area Heron Pond in Northside Park 51st Ave. and Downing St. 3 acres
Denver City Golf Course Kennedy Lake in J.F. Kennedy Golf Course 1 0500 E. Hampden Ave. 5 acres; perimeter: 0.4 mile.
Denver City Golf Course Skeel Reservoir in Wellshire Golf Course 3333 S. Colorado Blvd. 1 3.4 acres, perimeter: 0.6 mile.
Golf Conces- sion Overland Lake in Overland Lake Open Space North ofW. Florida Ave. between S. Santa Fe Dr. and the South Platte River trail. Parking area is north of Florida. 11 acres; perimeter 0.7 mile.
EXIBIT 2.9
WELL VEGETATED, NATURAL SHORELINE ALONG
BERKELEY LAKE
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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts
CHARACTERIZATION OF DENVER LAKE AND STREAM
CONDITIONS
In order to protect and enhance the condition of Denver lakes and streams, it is necessary to have
a sound scientific understanding of their baseline chemical, physical, and biological conditions
and identify key sources of impacts to these water bodies. Because this process is cumbersome,
time-consuming, and costly, the Project Team and Advisory Committee determined that the
highest priority for this Plan was to identify strategies and tools to minimize stormwater impacts
to these water bodies in the near termthis is the focus of Chapter 6, Stormwater Quality BMP
Implementation Guidelines. As a result, a watershed-by-watershed assessment of stream
conditions was deferred to a future project.
Nonetheless, several key building blocks for watershed-by-watershed assessments have been
completed in this Plan in Chapter 3-Regulatory Drivers, Chapter 4-Related Documents, Chapter
5-National Case Studies, and in Chapter 8-Potential Regional Facilities. In Chapter 3, known
water-quality limited stream segments in Denver are discussed. In Chapter 4, several on-going
regional efforts to assess and address water body conditions are described. In Chapter 5,
watershed assessment approaches used by other communities with advanced stormwater
programs are described, along with the associated costs of such efforts. In Chapter 8, locations
that should be further evaluated for use as regional stormwater quality treatment facilities have
been identified. Additionally, Appendix D provides a variety of specific recommendations
regarding water quality improvement that were submitted in a report to the Mayor in June
(Bergstedt 2004). All of this information will be important in developing targeted approaches to
improving conditions in various Denver water bodies and ensuring that the wheel is not
reinvented with regard to specific watershed efforts.
Another key component when characterizing lakes and streams is having a reasonable
understanding of what data sources already exist. A brief list of these sources that, at a
minimum, should be included in more detailed watershed analyses includes the following:
Denver Environmental Health, Environmental Protection Division (DEH-EPD) data set:
This data set includes over 25 years of dry-weather monitoring data for the South Platte
River system, including surface water, biotic, and sediment samples from both streams
and lakes. Additionally, DEH-EPD is compiling a GIS database of stormwater outfalls to
model watershed drainage areas (Bergstedt 2004).
Denver Public Works, Wastewater Management Division dry weather monitoring data:
As part of Denvers CDPS stormwater permit, dry weather discharges have been
monitored. GIS-based mapping is also being completed to identify discharge points,
post-construction BMPs, and other features.
Barr Lake/Milton Reservoir water quality database: this extensive water quality
database, compiled by Hydrosphere in 2004, contains most of the readily available water
quality data for the South Platte and its tributaries in the Denver area from Chatfield dam
to the Barr/Milton diversion points on the South Platte. One of the reasons that this data
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Denver Water Quality Management Plan
set is important is that it includes water quality data from neighboring municipalities that
influence conditions in the South Platte.
South Platte Cooperative for Urban River Evaluation (South Platte CURE) Database:
This database focuses on the South Platte River and selected tributaries over the last eight
years. Most of this data was also submitted to the Barr Lake/Milton Reservoir effort.
South Platte CURE also continues to serve as a data clearinghouse for ongoing
monitoring efforts along the South Platte River. This data set has been standardized into
a STORET-compatible format and is uploaded to STORET on a periodic basis. South
Platte CURE and DEH-EPD coordinate sampling programs and share data to help with
stream characterization, but South Platte CURES primary focus is on point source
(sanitary wastewater) discharges.
Joint Task Force Stormwater Monitoring Data: this dataset includes both the initial
Phase I stormwater permit wet weather monitoring data and the ongoing trend analysis
data conducted by the U.S. Geological Survey on behalf of Denver, Aurora, Lakewood
and UDFCD. This dataset is important because it focuses on stormwater discharges,
whereas other monitoring programs have focused on dry weather conditions.
U.S. Geological Survey (USGS) National Water Database (NWISWeb at
http://waterdata.usgs.gov/nwis/): This database can also be queried for water quality and
flow data for the Denver area.
STORET: This is EPAs water quality database that can be queried for historical data
available for the Denver area.
Instream Issues Task Force/Mayors South Platte River Commission: The Instream
Issues Report, South Platte River Corridor, as contained in the Appendix to the Long
Range Management Framework South Platte River Corridor (Mayors South Platte River
Commission 2000) contains segment-by-segment characterizations of the South Platte
River.
The following section provides a general
overview of the impacts of urbanization
on receiving waters that should also be
included as a building block to shape
future analyses of watershed-specific
conditions in Denver. This section
emphasizes the importance of a holistic
approach to improving receiving water
conditions that addresses not only water
quality, but also habitat, water quantity
(flow regime), aquatic life, and stream
channel conditions.
EXHIBIT 2.10
CONFLUENCE OF THE SOUTH PLATTE RIVER AND
CHERRY CREEK
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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts
OVERVIEW OF THE EFFECTS OF URBANIZATION ON
RECEIVING WATERS
A sound understanding of the widely documented (e.g., WEF and ASCE 1992, 1998; Debo and
Reese 2002; Horner, et al. 1994; and Schueler and Holland 2000) effects of urban runoff on the
physical, chemical, and biological characteristics of receiving waters is important for those
involved with mitigating the impacts of urban runoff. The following discussion provides a
general overview of the effects of urbanization on receiving waters followed by a more detailed
discussion of the physical impacts and chemical characteristics of urban runoff documented both
nationally and for the Denver area.
Traditional stormwater management focused on moving water away from people, structures, and
transportation systems as quickly and efficiently as feasible. This was accomplished by creating
conveyance networks of impervious storm sewers, roof drains, and lined channels, which
concentrated runoff flows for discharge to receiving waters. There were many consequences of
this traditional approach to drainage such as:
Increased runoff frequency.
Increased runoff volume.
Larger peak discharges.
Higher flow velocities.
Change in base flow (dry weather) regime.
Increased flooding risk.
Introduction of new pollutant sources and types.
Increased runoff temperature.
Loss of riparian zones and wetlands, with associated negative effects.
Habitat damage and ecosystem disruption associated with stream bed and bank erosion
leading to sediment and pollutant transport, channel widening and instability, and
destruction of both aquatic and terrestrial physical habitats.
Increased contaminant transport, leading to increased water quality degradation.
Production and long-term accumulation of potentially toxic concentrations of
contaminants in receiving waters.
It is particularly important to recognize that urban runoff impacts are complex, including
chemical, physical, and biological responses. Various experts have developed helpful schemes
for categorizing and interrelating adverse receiving water impacts. Two particularly valuable
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Denver Water Quality Management Plan
representations are provided in Exhibits 2.11 and 2.12. With increasing frequency, these adverse
impacts are being addressed by communities around the U.S. Recognition of these impacts has
been a driving force behind federal, state and local government regulations concerning
stormwater quality (see Chapter 3). The remainder of this section describes the potential
physical and chemical impacts of uncontrolled urban runoff on receiving waters.
EXHIBIT 2.1 1
ECOLOGICAL IMPACT OF HUMAN-INDUCED ALTERATIONS
Ecological impact
of human-induced
alterations
Energy Source
type, amount, and particle size of organic
material entering a stream from the riparian
zone versus primary production in the stream
seasonal pattern of available energy
Water Quality
temperature
turbidity
dissolved oxygen
nutrients (primarily nitrogen and phosphorus)
organic and inorganic chemicals, natural and
synthetic
heavy metals and toxic substances
pH
Habitat Quality
substrate type
water depth and current velocity
spawning, nursery, and hiding places
diversity (pools, riffles, woody debris)
Flow Regime
water volume
temporal distribution of floods and low flows
Biotic Interactions
competition
predation
disease
parasitism
=3
decreased coarse particulate organic
matter
increased fine particulate organic matter
increased algal reproduction
{expanded temperature extremes
increased turbidity
{altered diurnal cycle of dissolved oxygen
increased nutrients
increased suspended solids
w
=>
decreased stability of substrate & banks
due to erosion & sedimentation
more uniform water depth
reduced habitat heterogeneity
decreased channel sinuosity
reduced habitat area due to shortened
channel
decreased in-stream cover and riparian
vegetation
altered flow extremes
y increased maximum flow velocity
decreased minimum flow velocity
reduced diversity of microhabitat velocities
fewer protected sites

Source: National Research Council. 1992.
Restoration of Aquatic Ecosystems:
Science, Technology, and Public Policy .
increased frequency of diseased fish
altered primary and secondary production
altered trophic structure
altered decomposition rates and timing
disruption of seasonal rhythms
shifts in species composition and relative
abundances
shifts in invertebrate functional groups
shifts in trophic guilds
increased frequency of fish hybridization
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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts
EXHIBIT 2.1 2
IMPACTS OF URBANIZATION ON PHYSICAL HABITAT AND BIOTA
Urbanization
Characteristics
Imperviousness
Total
Effective
BMPs
Drainage Infrastructure
Conveyance/capacity
Connectivity
detention/retention
Time of concentration
Phased sediment delivery
Watershed
Characteristics
Drainage Network
pattern
density
Geology
Slope
Infiltration/Soils
Vegetation
Climate
Flow Regime
Magnitude
Frequency
Duration
Timing
Rate of change
Wet
Weather
Flows
Stream Power
Channel
geometry
Gradient
Roughness/En
ergy
Dissipation
Geomorphic
Characteristics
Stream Type
Confinement
Bed Material
Riparian/Bank
Condition
o Sedimentary
o Vegetation
o Stability
Geologic
Control
Physical Habitat
Channel substrate
sizes, types and
mobility
Diversity and
complexity of instream
substrates, refugia and
hydraulic conditions
Channel morphology
and stability
Disturbance regime
Riparian condition and
connectivity including
bank structural
features/ stability
Channel-riparian
interactions

Biotic
Response
Source: Roesner, L. A. and B. P. Bledsoe. 2003. Physical Effects of Wet Weather Flows on Aquatic
Habitats. Water Environment Research Foundation: Alexandria, VA. Co-published by IA Publishing:
United Kingdom.
Adverse Physical Impacts of Urban Runoff
In the absence of properly designed, constructed, and maintained best management practices
(BMPs), urbanization can adversely impact stream channels due to increased peak discharges,
increased magnitude and duration of flows, increased sediment loads during construction, and
increased erosive forces that are effective at transporting larger-sized particles. This is why
volume control for small, frequently occurring storm events is strongly emphasized by UDFCD
in Volume 3 of the Urban Storm Drainage Criteria Manual (UDFCD 1999).
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Denver Water Quality Management Plan
The widely cited Lanes Balance is helpful in understanding the physical impacts of
unmitigated urbanization as shown in Exhibit 2.13. This schematic demonstrates that if more
runoff is created as a consequence of urbanization, the right side of the scale will drop, and the
left side of the scale will rise, thus leading to channel degradation, in the absence of suitable
mitigation. By contrast, if excessive sediment is added to the stream during construction, the left
side of the scale drops and the right side of the scale rises, leading to aggradation (deposition of
sediment in the channel).
EXHIBIT 2.1 3
SCHEMATIC OF LANES BALANCE DESCRIBING PHYSICAL STREAM PROCESSES
Qs D50 ot Qw S
Source: Rosgen, D. 1 996. Applied River Morphology. Pagosa Springs, Colorado: Wildland Hydrology.
Another potential negative consequence of urbanization is increased stream power (with power
meaning the ability of flowing water to alter channel geomorphology), as depicted in Exhibit
2.14. In Exhibit 2.14, comparison of the before and after curves shows that after
urbanization, the stream has a much greater ability to alter the channel and remove sediment
from its banks. The problems depicted by Exhibits 2.13 and 2.14 are mitigated through such
measures as detention/retention facilities with sophisticated outlet structures that control a wide
range of return frequency floods (including small, frequently occurring events that significantly
influence channel stability). Other measures include channel stabilization techniques such as
grade control structures, toe protection, special stabilization on outer banks at channel bends, etc.
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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts
EXHIBIT 2.1 4
IMPACT OF URBANIZATION ON STREAM CEOMORPHOLOCY
Source: National Research Council, 1992. Restoration of Aquatic Ecosystems: Science, Technology, and
Public Policy. Washington, DC: National Academy Press.
Chemical Characteristics of Urban Runoff
Urban settings typically contain multiple pollutant sources, as shown in Exhibit 2.15, which lists
representative sources of solids, nutrients, pathogens, dissolved oxygen demands, metals, and
oils. In addition to these pollutants, Urbonas and Doerfer (2003) have reported that atmospheric
dust fallout is a significant contributor to urban runoff pollution in Denver. Some of their key
findings include:
1. Atmospheric dust fallout in the Denver area is a significant source of total suspended
solids and potentially of other pollutants found in stormwater runoff.
2. Streets, parking lots, sidewalks and roofs all accumulate this type of fallout.
3. Breaking up directly connected impervious areas with landscaping and lawns can help to
capture this fallout and minimize its chances of reaching stormwater conveyance systems. 4
4. The BMPs recommended in UDFCDs Storm Drainage Criteria Manual, Volume 3 are
well-suited to removing these types of pollutants.
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Denver Water Quality Management Plan
Another potential pollutant source in Denver involves snow and ice management activities.
Storage and disposal of snow that can be contaminated by hydrocarbons and pet waste, as well as
the types of chemicals and materials used to melt snow and ice, are both important
considerations for runoff quality management. Commonly used de-icers in Denver are highly
soluble and have low toxicity to plants and animals; however, in some cases, they may contribute
to biochemical oxygen demand (BOD) as they decompose, resulting in lower dissolved oxygen
(DO) levels in streams. Denvers snow and ice management practices are addressed under its
CDPS stormwater permit requirements.
EXHIBIT 2.1 5 URBAN RUNOFF POLLUTANT SOURCES
Pollutant Category Sou rce Solids Nutrients Pathogens DO Demands Metals Oils Synthetic Organics
Soil erosion X X X X
Cleared vegetation X X X
Fertilizers X
Human waste X X X X
Animal waste X X X X
Vehicle fuels and fluids X X X X X
Fuel combustion X
Vehicle wear X X X
Industrial and household chemicals X X X X X X
Industrial processes X X X X X X
Paints and preservatives X X
Pesticides X X X
Stormwater facilities X X
Source: Horner, R.R., J.J. Skupien, E.H. Livingston and H.E. Shaver. 1994. Fundamentals of Urban Runoff
Management: Technical and Intuitional Issues. Washington, DC: Terrene Institute, in cooperation with the
Environmental Protection Agency.
Representative concentrations of pollutants in urban runoff have been documented in multiple
studies over the last several decades. Several key studies relevant to Denver include:
1) The National Urban Runoff Program (NURP), which was conducted between 1978 and
1983 by the EPA and USGS and included stormwater quality monitoring of 81 outfalls in
28 communities around the U.S. for a total of 2,300 storm events.
2) The National Stormwater Quality Database, Version 1.1, as compiled by Pitt, Maestre
and Morquecho (2004) and as available through the website
www.unix.eng.ua.edu/~rpitt/Research/ms4/mainms4.shtml. This database contains Phase
I stormwater permit monitoring data for over 100 constituents in 65 communities across
the U.S. for atotal of 3,700 storm events at 350 locations collected over roughly the last
10 years. This database does not include the historical NURP data.
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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts
3) The Denver Regional Urban Runoff Program (DRURP) conducted by the Denver
Regional Council of Governments (DRCOG) in 1983, providing data for nine basins with
various land uses for 15 constituents of concern and for the EPAs Priority Pollutants.
These data have been supplemented with monitoring by UDFCD and were submitted as
part of the Stormwater NPDES Part 2 Permit Application Joint Appendix (Aurora et al.
1992). Since that time, monitoring in the Denver area has also been completed under the
Phase I stormwater permit program.
Data from each of these three sources are tabulated in Exhibits 2.16, 2.17, and 2.18.
EXHIBIT 2.1 6 NURP SUMMARY DATA MEDIAN EVENT MEAN CONCENTRATIONS FOR URBAN LAND USES FOR VARIOUS CONSTITUENTS BASED ON DATA FROM 28 AMERICAN CITIES
Pollutant Units Residential Mixed Commercial Open/ Non-Urban
Median COV2 Median cov Median COV Median COV
Bio- chemical Oxygen Demand (BOD) mg/L 10 0.41 7.8 0.52 9.3 0.31
Chemical Oxygen Demand (COD) mg/L 73 0.55 65 0.58 57 0.39 40 0.78
Total Suspended Solids (TSS) mg/L 101 0.96 67 1.14 69 0.85 70 2.92
Total Lead Ufl/L 144 0.75 114 1.35 104 0.68 30 1.52
Total Copper Mg/L 33 0.99 27 1.32 29 0.81 - -
Total Zinc mq/l 1 35 0.84 1 54 0.78 226 1.07 195 0.66
Total Kjeldahl Nitrogen M9/L 1,900 0.73 1,288 0.50 1,1 79 0.43 965 1.00
Nitrate + Nitrite M9/L 736 0.83 558 0.67 572 0.48 543 0.91
Total Phosphorus M9/L 383 0.69 263 0.75 201 0.67 121 1.66
Soluble Phosphorus M9/L 143 0.46 56 0.75 80 0.71 26 2.1 1
1 Source: EPA, 1 999. Preliminary Data Summary of Urban Stormwater Best Management Practices.
EPA-821-R-99-012.
2 COV= Coefficient of variation.
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Denver Water Quality Management Plan
Exhibit 2.17 National Stormwater Quality Database Summary (Version 1.1)
OVERALL RESIDENTIAL MIXED RESIDENTIAL COM- MERCIAL MIXED COM- MERCIAL INDUSTRIAL MIXED INDUSTRIAL INSTITU- TIONAL FRffiWAYS MIXED FREEWAYS OPEN SPACE MIXED OPEN SPACE
MEDIAN COV MEDIAN COV MEDIAN COV MEDIAN COV MEDIAN COV MEDIAN COV MEDIAN COV MEDIAN COV MEDIAN COV MEDIAN COV MEDIAN COV MEDIAN COV
Land Use
Drainage Area 56.00 3.64 57.30 4.73 150.80 2.07 38.80 1.22 75.00 2.05 39.00 1.58 127.70 1.96 36.00 0.00 1.61 1.43 63.13 0.29 73.50 1.76 115.36 0.88
% Imperviousness 54.30 0.43 37.00 0.42 44.90 0.28 83.00 0.12 60.00 0.30 75.00 0.30 44.00 0.26 45.00 0.00 80.00 0.13 38.00 0.00 2.00 1.26 34.00 0.14
Precipitation Depth (in) 0.47 0.96 0.46 1.01 0.55 0.79 0.39 1.04 0.47 0.95 0.49 0.96 0.45 0.84 0.18 0.91 0.54 1.05 0.68 0.61 0.48 1.13 0.43 0.88
Runoff (in) 0.18 1.97 0.11 1.96 0.18 1.42 0.23 1.21 0.35 1.10 0.14 2.67 0.29 1.16 0.00 2.09 0.41 1.70 0.28 0.89 0.17 1.31 0.12 1.20
Conductivity (pS/cm @25C) 120.00 1.76 96.00 1.51 112.00 1.15 118.50 0.98 103.00 0.59 135.50 1.31 110.50 0.81 99.00 1.01 418.00 0.56 155.00 0.67 214.70 1.83
Hardness (mg/L CaC03) 38.00 1.44 32.00 1.04 39.70 1.17 38.90 1.05 35.00 1.83 39.00 1.52 33.00 0.54 34.00 1.85 83.00 0.28 116.50 0.63 55.00 1.47
Oil and Grease Total (mg/L) 4.00 10.07 3.14 8.04 4.00 2.54 4.70 3.16 4.00 2.93 4.00 12.44 3.30 2.21 8.00 0.62 4.00 1.63 11.00 1.39 2.00 2.47
PH 7.50 0.10 7.30 0.10 7.50 0.09 7.30 0.10 7.60 0.08 7.50 0.11 7.69 0.11 7.10 0.11 7.80 0.06 7.70 0.08 7.97 0.07
Tern perature (C) 16.45 0.36 16.40 0.36 16.00 0.33 16.00 0.39 15.00 0.35 17.85 0.33 18.00 0.35 14.00 0.35 16.00 0.30 15.50 0.24 16.00 0.33
TDS (m g/L) 80.00 2.52 70.75 2.05 86.00 2.24 77.00 1.84 69.00 1.94 92.00 3.48 80.00 2.41 52.50 0.67 77.50 0.80 174.00 0.40 113.00 0.70 106.00 2.33
TSS (m g/L) 58.00 1.78 48.00 1.78 67.82 1.58 43.00 1.98 53.50 1.36 76.36 1.54 82.00 1.39 17.00 0.83 99.00 2.53 81.00 1.18 51.00 1.87 78.00 1.40
BOD5 (m g/L) 8.60 1.57 9.00 1.48 7.67 1.30 11.90 1.11 9.00 1.70 9.00 1.71 7.20 1.71 8.50 0.70 8.00 1.26 7.40 0.67 4.20 0.70 6.59 2.40
COD (mg/L) 53.00 1.19 55.00 1.13 42.00 1.42 63.00 1.00 60.00 0.98 60.00 1.19 40.00 1.12 50.00 0.91 100.00 1.06 48.00 0.47 21.00 1.82 39.00 1.54
Fecal Coliform (#/100 m L) 5,081 4.6 7,750 5.1 10,950 3.3 4,550 2.8 4,990 3.2 2,500 5.6 3,033 2.5 1,700 1.9 730 2.0 3,100 2.9 3,250 2.1
Fecal Streptococcus (#/100 m L) 17,000 3.8 24,000 1.8 26,000 2.2 10,800 2.7 11,000 2.8 13,000 6.9 10,000 2.6 17,000 1.2 19,000 1.1 24,000 2.6 21,000 2.3
Total Coliform (#/100mL) 11,000 2.4 5,467 1.4 9,000 12,500 2.4 50,000 1.5 62,000
Am m onia (m g/L) 0.44 3.57 0.31 1.09 0.40 4.35 0.50 1.20 0.60 0.99 0.50 4.04 0.43 0.72 0.31 0.53 1.07 1.30 0.92 0.53 0.30 1.13 0.51 1.17
N02+NO3 (mg/L) 0.60 1.06 0.59 1.25 0.56 0.99 0.61 1.06 0.56 0.67 0.73 0.95 0.56 0.74 0.60 0.64 0.28 1.23 0.65 0.67 0.59 0.86 0.70 0.94
Nitrogen Kjeldahl Total (mg/L) 1.40 1.35 1.42 1.26 1.33 1.93 1.60 0.94 1.38 0.92 1.40 1.15 1.00 1.54 1.35 0.50 2.00 1.37 1.62 0.93 0.61 1.04 1.20 1.32
Phosphorous Dissolved (mg/L) 0.12 1.58 0.17 0.95 0.12 1.09 0.11 1.25 0.11 2.12 0.11 1.16 0.08 2.25 0.13 0.49 0.20 2.13 0.04 0.84 0.08 1.22 0.09 1.08
Phosphorous Total (m g/L) 0.27 1.51 0.30 1.14 0.27 1.71 0.22 1.15 0.25 1.48 0.26 1.37 0.20 1.52 0.18 0.99 0.25 1.76 0.26 0.79 0.25 3.62 0.27 1.02
Antimony Total (pg/L) 3.20 2.61 28.00 1.48 1.00 2.11 69.00 0.79 15.00 0.99 4.00 3.01 1.00 3.00 0.25 340.00 1.00 0.00
Arsenic Total (pg/L) 3.00 2.42 3.00 2.10 3.10 3.86 2.30 3.15 2.20 1.04 4.00 1.38 3.00 0.96 2.40 0.70 3.00 0.71 5.00 1.18 4.00 0.78
Arsenic Dissolved (pg/L) 1.50 1.00 1.48 0.50 2.00 0.84 1.50 0.47 1.75 0.20 1.00 0.43 2.00 0.41 1.43 1.15
Beryllium Total (pg/L) 0.40 2.47 0.50 2.52 0.30 2.70 0.50 1.99 0.35 1.60 0.39 2.50 0.30 0.47 27.00
Cadmium Total (pg/L) 1.00 28.17 0.50 1.67 0.80 3.85 0.84 1.57 0.86 1.11 2.00 2.34 1.00 10.87 0.50 0.69 1.00 0.90 0.50 0.68 0.50 1.69 1.00 1.85
Cadmium Dissolved (pg/L) 0.50 1.14 0.70 0.55 0.30 0.64 0.30 1.34 0.40 0.87 0.60 1.10 0.60 0.58 0.68 1.03
Chromium Total (pg/L) 7.00 1.48 4.50 1.40 7.00 1.55 6.00 1.35 4.50 1.16 14.50 1.15 8.00 1.69 8.30 0.71 6.00 0.99 5.00 2.08 5.00 1.49
Chromium Dissolved (pg/L) 2.08 0.73 1.28 0.44 2.00 0.80 2.00 0.59 2.00 0.72 3.00 0.73 2.00 0.69 2.30 0.70
Copper Total (pg/L) 16.00 2.21 12.00 1.83 17.39 1.33 17.00 1.48 17.00 2.96 22.00 1.99 17.40 0.89 17.00 0.59 34.70 0.95 8.50 1.05 5.30 2.24 11.00 1.47
Copper Dissolved (pg/L) 8.00 1.63 7.00 1.96 5.50 0.86 7.57 0.83 9.50 0.61 8.00 0.67 6.00 0.58 10.90 1.50 1.00
Lead Total (pg/L) 16.00 1.85 12.00 1.89 18.00 1.37 18.00 1.59 17.00 1.47 25.00 1.81 18.50 1.50 5.75 0.79 25.00 1.45 10.00 0.90 5.00 2.02 10.00 2.28
Lead Dissolved (pg/L) 3.00 2.02 3.00 1.87 3.00 0.68 5.00 1.59 6.00 0.61 5.00 1.58 5.00 0.97 1.80 1.65 2.00 0.00
Mercury Total (pg/L) 0.20 2.68 0.20 1.17 0.20 1.00 0.20 0.84 0.10 1.12 0.20 2.66 0.25 0.58 0.19 0.80 0.10 1.05
Nickel Total (pg/L) 8.00 2.13 5.40 1.21 7.93 0.83 7.00 3.78 5.00 1.33 16.00 1.24 9.00 0.92 9.00 0.91 27.00 0.87 7.00 1.16
Nickel Dissolved (pg/L) 4.00 1.47 2.00 0.51 5.50 0.87 3.00 0.84 3.00 0.57 5.00 1.43 5.00 0.57 4.00 1.38
Zinc Total (pg/L) 116.51 3.35 73.00 1.30 99.50 1.04 150.00 1.22 132.00 1.70 210.00 2.25 160.00 3.32 305.00 0.81 200.00 1.01 90.00 0.86 39.00 1.32 100.00 1.02
Zinc Dissolved (pg/L) 52.00 3.89 31.50 0.84 48.00 0.88 59.00 1.37 94.00 0.74 111.50 3.62 2100.00 1.18 51.00 1.86 160.00 14.00 0.61
Chapter 2
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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts
EXHIBIT 2.1 8
EVENT MEAN CONCENTRATIONS (MG/L) OF CONSTITUENTS IN DENVER METROPOLITAN AREA
RUNOFF, PER DRURPAND PHASE 1 STORMWATER CDPS PERMIT APPLICATION FOR DENVER,
LAKEWOOD, AND AURORA1___________________________
Constituent Natural Grassland Commercial Residential Industrial
Total Phosphorus 0.4 0.42 0.65 0.43
Dissolved or Ortho-Phosphorus 0.1 0.1 5 0.22 0.2
Total Nitrogen 3.4 3.3 3.4 2.7
Total Kjeldahl Nitrogen 2.9 2.3 2.7 1.8
Ammonia Nitrogen 0.1 1.5 0.7 1.2
Nitrate + Nitrite Nitrogen 0.5 0.96 0.65 0.91
Lead (Total Recoverable) 0.1 0.059 0.053 0.1 3
Zinc (Total Recoverable) 0.1 0.24 0.18 0.52
Copper (Total Recoverable) 0.04 0.043 0.029 0.084
Cadmium (Total Recoverable) Not Detected 0.001 Not Detected 0.003
COD 72 1 73 95 232
Total Organic Carbon 26 40 72 22-26
Total Suspended Solids 400 225 240 399
Total Dissolved Solids 678 129 119 58
BOD 4 33 1 7 29
1 Source: Aurora et al. 1992. Stormwater NPDES Part 2 Permit Application Joint Appendix. Based on data reported by
DRCOC, 1 983. Urban Runoff Quality in the Denver Region, as updated with more recent data from UDFCD 1 992.
The results in the Denver region parallel, in many respects, the findings of NURP. To the extent
that there are discrepancies or inconsistencies between Exhibits 2.16, 2.17 and 2.18, Exhibit 2.18
should govern for projects in Denver. (Note: While these results are representative of general
conditions within the Denver region, site-specific data from watershed studies should be used
when available.) In general, DRURP identified constituents such as lead, zinc, cadmium, fecal
coliform bacteria, and total suspended solids as significant pollutants in urban runoff. Other
selected statements from the DRURP summary report (DRCOG 1983) relevant to this Plan
include:
Very few EPA Priority Pollutants were detected in runoff samples. Organic pollutants
found were particularly sparse, and the most commonly occurring one detected was a
pesticide. The most significant non-priority pollutant found was 2, 4-D which is an
herbicide.
Pollutant loading per runoff amount was not found to be well related to basin
imperviousness or land use. Vague relationships between event mean concentrations and
imperviousness were noted, but proved statistically insignificant. Concentrations of
pollutants did not vary in a predictable or anticipated pattern.
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Denver Water Quality Management Plan
A receiving water assessment was included in the program to denote the effects of urban
runoff for the South Platte River, which is the ultimate receiving water for both
wastewater effluent and urban runoff generated within the Denver metropolitan area.
Significant amounts of sediment, bacteria, nutrients, organic matter, and heavy metals
were found to enter the river during storm events compared with discharges from
wastewater treatment plants over the same time period.
The investigation of the effects of urban runoff on receiving waters involved three
considerations: 1) comparison of pollutant concentrations monitored in the South Platte
River during storm events with those occurring during ambient streamflow; 2)comparison
of the relative amounts of pollutant loads entering the river from storm runoff with those
from municipal wastewater sources; and 3) comparison of pollutant concentrations during
periods of storm runoff and ambient streamflow with water quality standards in effect for
the study segment of the South Platte River.
Several water quality constituents had mean concentrations that were greater during
storm runoff than during ambient streamflow. Suspended sediment and fecal coliform
bacteria exhibited much greater concentrations during storm events, as did oxygen-
demanding substances and heavy metals. Total metals concentrations for lead, zinc,
copper, cadmium, iron, and manganese during storm-runoff periods were greater than
mean ambient concentrations and exceeded established stream standards 100 percent of
the time. Effective control of urban runoff to reduce the concentrations of these
constituents was identified as being important to improve the quality of water of the
South Platte River.
A comparison of the relative loading from point sources, base flow and urban runoff was
necessary to denote the effects of urban runoff on the South Platte River. Results
indicated that municipal wastewater discharges contributed the greatest amount of
nitrogen, phosphorus, and organic carbon to the river on an annual basis. Total
suspended solids and lead loading were shown to be predominantly influenced by
contributions from urban runoff.
The study showed that urban runoff is a significant source of some water pollutants. The
most obvious pollutant is total suspended solids. This was true regardless of the
existence of major land disturbances causing erosion. Urban runoff was also a significant
source of fecal coliform bacteria, oxygen demanding substances, and metals during
storms. In addition, nutrients from urban runoff are and will be a problem for lakes and
reservoirs.
Non-storm urban runoff (e.g., dry weather discharges such as irrigation runoff) was also
identified as a source of pollutants. This was not expected and was determined indirectly
in the study analysis.
Since DRURP, DRCOG has been involved in six watershed studies that were designed to assess
the nature, severity and impact of stormwater and/or nonpoint sources on water quality. These
efforts characterized urban runoff in relation to development patterns. The results have been
developed into predictive planning tools to estimate stormwater and nonpoint source quality,
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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts
quantity and effects on receiving waters. BMPs have been recommended, updated, and
incorporated as an integral component of watershed management plans. Watershed controls
include structural systems, nonstructural practices and institutional policies (DRCOG 1998).
SUMMARY
Denver faces a significant challenge in addressing urban runoff water quality issues over a large
land area with varied drainage basins. The impacts of urbanization are multi-faceted and require
integrated approaches in order to be most effective. The remainder of this Plan provides a
framework for an integrated strategy to address these challenges. Additional work in the form of
watershed-by-watershed assessments (See Chapter 9) will be needed to achieve Denvers goals
in these basins.
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Chapter 3
REGULATORY DRIVERS
Denver is committed to protecting and improving water quality conditions in waterbodies
receiving stormwater runoff from areas within its boundaries. This commitment is driven not
only by local, state, and federal regulations, but also by Denvers staff and citizens who view the
lakes, stream, and rivers within Denver as an amenity and a significant part of its natural
resources.
The key federal regulation that pushes communities throughout the U.S. toward the goal of
fishable, swimmable waters is the federal Clean Water Act. This Act establishes a variety of
requirements intended to protect and improve conditions in streams, lakes, and wetlands.
Aspects of the Clean Water Act particularly relevant to this Plan focus on regulation of
stormwater discharges, water quality standards for waterbodies receiving runoff from stormwater
discharges, and implications for water quality standards not being attained. The discussion which
follows briefly identifies some of the key regulatory drivers relevant to this project that have
evolved in large part from the Clean Water Act, including:
Denvers Phase I Stormwater Colorado Discharge Permit System (CDPS) Permit
Denver International Airport (DIA) CDPS Permit
U.S. Environmental Protection Agencys (EPAs) April 2004 Audit of Denvers
Stormwater Management Program
Denvers stormwater-related requirements and regulations
Other Denver ordinances, rules and regulations
Colorado Water Quality Control Act and Regulations, including state stream standards
Total Maximum Daily Loads (TMDLs)
Regional water quality efforts
Potential future changes to state and federal water quality permits and regulations
PHASE I STORMWATER CDPS PERMIT
Denver was required to obtain a stormwater discharge permit due to the National Pollutant
Discharge Elimination System Permit Application Regulation for Inclusion of a Stormwater
Discharge Regulation, which was issued on November 16, 1990 (Federal Register, Volume 55,
No. 222). There are three major objectives of the stormwater discharge permitting program:
Reduce pollutant loadings in municipal storm sewer discharges to the maximum extent
practicable (MEP).
Eliminate illicit wastewater connections, illegal discharges and non-exempt non-
stormwater discharges to municipal storm sewer systems.
Implement management programs that apply best available technology (BAT), best
conventional pollutant control technology (BCT) and, where necessary, water-quality
based controls directed at controlling industrial stormwater pollution.
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Regulatory Drivers
Denver is permitted to discharge municipal stormwater runoff to state waters in the South Platte
River watershed under CDPS Permit No. COS-OOOOOl, which was renewed on March 20, 2003
and remains effective until April 30, 2008 (CWQCD 2003). This permit covers all areas within
the corporate boundary of Denver served by, or otherwise contributing to discharges to state
waters, from municipal separate storm sewers (MS4s) owned or operated by Denver. This
includes the storm sewer system at DIA, excluding DIAs industrial system, which is covered
under DIAs industrial stormwater permit (COS-000008).
Denvers permit was originally issued in 1996 under the Phase I stormwater regulation. The
subsequent Phase II stormwater regulation, which is best known for the requirements it places
on smaller communities, also affected Denvers permit. Examples of key changes to Denvers
permit due to the Phase II stormwater regulation included: 1) regulation of one acre or more of
disturbance at construction sites, whereas a five-acre trigger was in place under the initial permit;
and 2) increased emphasis on public education/outreach.
Denvers current permit specifies stringent requirements with which Denver must comply
through a combination of a Stormwater Management Program, regular program review and
modification, wet weather monitoring, conformity with a compliance schedule, annual reporting,
signatory certification, and other measures. The Stormwater Management Program must address
these five major categories: commercial/residential management, illicit discharge management,
construction sites, municipal facility runoff controls and industrial facilities runoff. To frame the
seriousness and extent of the requirements under this permit, the terms shall and will are
used over 200 times in the permit. Consequences for violations include significant fines and
possible imprisonment for knowing violations of the permit. In addition to measures it must
implement, Denver is also required to ensure, insure, or assure the following:
With regard to new development planning procedures for commercial/residential areas,
the permit specifies: City ordinances and rules shall be revised as necessary to include
provisions to ensure that stormwater quality controls installed for significant development
or redevelopment are adequately operated and maintained. (Part 1, B. 2.c.).
With regard to inspection and enforcement procedures as part of project review and
approval procedures for new commercial/residential development, the permit specifies:
Developments shall be inspected for compliance to insure that all specified BMPs are
constructed in accordance with the approved plan. (Part 1, B. 2.e. iii.).
With regard to assessing the impacts of flood management projects under the
commercial/development management program, the permit specifies: The permittee
shall continue to implement procedures to assure that the impact on water quality is
assessed for proposed flood management projects. (Part 1, B. 4.).
With regard to procedures for site inspection and enforcement at construction sites, the
permit specifies: procedures to insure that BMPs are being installed and maintained
according to the approved plan and that sediment sources, materials, equipment
maintenance areas (including fueling) and other significant sources of pollution have
been addressed and enforcement provisions to insure compliance with requirements as
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Denver Water Quality Management Plan
defined in Denver ordinances and rules, and
approved plans and to insure effective operation
and maintenance of BMPs. (Part 1, B. 2.d.3.a.i. &
iii)
A brief overview of the specific types of requirements in
the permit includes the following:
Residential/Commercial Management Program
1. Maintenance of Structural Controlsimplement a
program of routine maintenance activities for
municipally owned structural controls to reduce
pollutants.
2. New Development Planning Procedurescontinue
to implement comprehensive planning procedures
and enforce controls to reduce the discharge of
pollutants after construction is complete from
areas of new development and significant
redevelopment.
3. Public Street Maintenancecontinue to operate
and maintain public streets, roads and municipal
parking lots in a manner so as to reduce the discharge of pollutants (including those
related to road repair, street sweeping, snow removal, sanding activities and herbicide
application).
4. Assess Impacts of Flood Management Projectscontinue to implement procedures to
assure that the impact on water quality is assessed for proposed flood management
projects.
5. Pesticide, Herbicide, and Fertilizer Applicationcontinue to implement controls to
reduce the discharge of pollutants related to application of pesticides, herbicides, and
fertilizers.
Illicit Discharges Management Program
1. Prevention of Illicit Discharges and Improper Disposalcontinue to implement an
ongoing program to detect and remove (or require the discharger to the MS4 to obtain a
separate CDPS permit for) illicit discharges and improperly disposed materials into the
MS4 in accordance with this program area.
2. Ongoing Field Screeningcontinue to implement an ongoing program to screen the MS4
for illicit discharges, illegal dumping and illicit connections.
EXHIBIT 3.1
OVERVIEW OF DENVERS
STORMWATER PERMIT
REQUIREMENTS
RESIDENTIAL/COMMERCIAL
MANAGEMENT PROGRAM
ILLICIT DISCHARGE
MANAGEMENT PROGRAM
INDUSTRIAL FACILITIES PROGRAM
CONSTRUCTION SITES PROGRAM
MUNICIPAL FACILITY RUNOFF
CONTROL PROGRAM
WET WEATHER MONITORING
PROGRAM
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Regulatory Drivers
3. Investigation of Suspected Illicit Dischargescontinue to implement a program to locate
and eliminate suspected sources of illicit connections and improper disposal.
4. Procedures to Prevent, Contain, and Respond to Spillscontinue to implement a
program to prevent, contain, and respond to spills that may discharge into the MS4.
5. Educational Activities to Promote Public Reporting of Illicit Discharges and Improper
Disposalcontinue to implement a plan to promote and facilitate public reporting of the
presence of illicit discharges or improper disposal of materials into the MS4.
6. Public Educational Activities to Promote Proper Management and Disposal of Potential
Pollutantscontinue to implement a plan to promote the proper management and
disposal of used motor vehicle fluids and household chemical wastes, and to reduce or
eliminate the discharge of other pollutants to the MS4.
7. Household Chemical Waste Collection Programscontinue to sponsor a door-to-door
household hazardous waste collection program, or substitute an equivalent program that
has the same result of making reasonably available to Denver residents the means to
recycle/properly dispose of the more common household chemical wastes.
8. Control of Sanitary Sewer Seepage into the MS4continue the existing program to
detect and eliminate sources of sanitary sewer seepage into the MS4.
Industrial Facilities ProgramDevelop and implement a program to promote proper
management of industrial sites regarding stormwater quality and industrial BMPs. The program
shall provide education and outreach on pollutants in stormwater discharges to municipal
systems from industrial facilities that the permittee determines are contributing or have the
potential to contribute a substantial pollutant loading to the MS4.
Construction Sites Program
1. Procedures for Site Planningcontinue to implement procedures for site planning that
incorporate consideration of potential water quality impacts from construction sites
within Denver.
2. Structural and Non-Structural BMPscontinue to implement requirements for the
selection, implementation, installation, and maintenance of appropriate BMPs at
construction sites.
3. Procedures for Site Inspection and Enforcementcontinue to implement procedures for
inspection and enforcement of control measures at construction sites. 4
4. Training and Education for Construction Site Operatorscontinue to develop, support
and encourage attendance at an education and training program for construction site
operators.
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Denver Water Quality Management Plan
Municipal Facility Runoff Control Programcontinue to implement runoff control plans for
specified Denver-owned and/or operated facilities that do not have independent CDPS
stormwater permits. New plans shall be developed for any new facilities. Currently covered
facilities include:
Vehicle maintenance facilities (maintenance includes equipment rehabilitation,
mechanical repairs, painting, fueling and lubrication).
Asphalt and concrete batch plants which are not already individually permitted.
Solid-waste transfer stations.
Exposed stockpiles of materials, including stockpiles of road deicing salt, salt and sand,
sand, rotomill material.
Sites used for snow dumps, and/or for temporary storage of sweeper tailings or other
waste piles.
Wet Weather Monitoring Programcontinue to implement a wet weather monitoring program to
assess wet weather conditions, particularly urban stormwater effects on state waters. Denver,
Aurora, Lakewood, and Urban Drainage and Flood Control District (UDFCD) work together (as
the Joint Stormwater Task Force) on this program, with actual monitoring conducted by the U.S.
Geological Survey (USGS). Samples are collected from receiving waters at five locations: an
upstream site, a downstream site, an intermediate site, one major tributary, and a tributary to a
major tributary. The monitoring program was designed based on land use considerations, and
sampling is conducted based on the rising limb of the hydrograph associated with a precipitation
event. The monitoring program was initiated in 1997, with active monitoring beginning in 1998
and continuing through the present. The four-year baseline monitoring period associated with
Denvers first permit term is complete, with a second four-year period in progress for purposes
of trend analysis (SAIC 2004).
DENVER INTERNATIONAL AIRPORT (DIA) CDPS PERMIT
When the Colorado Water Quality Control Division (CWQCD) renewed Denvers municipal
stormwater permit in May of 2003, the permit additions included coverage of the MS4 system at
DIA. Similar to other U.S. airports, prior to 2002, DIA was already covered under an industrial
stormwater permit (COS-000008) which includes industrial activities such as aircraft deicing.
Denvers renewed MS4 permit provides an implementation schedule to bring the airport into
MS4 permit compliance with the rest of Denver. As a result, the areas of the airport that are not
impacted by industrial activity will follow the same policies, rules and regulations regarding
stormwater discharges as the rest of Denver. Extensive coordination between the Department of
Public Works and the Department of Aviation is ongoing. Development parcels at the airport
will be handled in the same manner as development parcels elsewhere in Denver.
DIA is also covered under a CDPS stormwater construction permit and a Minimum Industrial
Discharge (MINDI) permit. The Roadmap to Development Review, Permitting, and
Construction Sites Program Process, Wastewater Management Division Rules and Regulations
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Regulatory Drivers
andMS4 Permit Requirements was developed in December 2003 (Denver 2003) and can be
referenced for more information on DIAs construction-related stormwater management
requirements.
EPAS APRIL 2004 AUDIT OF DENVERS STORMWATER
MANAGEMENT PROGRAM
During April 2004, EPA Region 8 conducted an audit of Denvers permitted stormwater
management program. Appendix B contains a summary of the action items from this audit,
combined with Denvers responses to EPAs comments. The goal of the audit was to determine
the overall success and effectiveness of Denvers compliance with the conditions and
requirements of its CDPS permit. The audit included interviews, file review and field
inspections. As a result of the final report prepared by SAIC, Denver was required to provide
written responses within 60 days on the action items identified by EPA. Overall, the audit
indicated that Denver was well along with the implementation of its MS4 program and has
achieved many positives in its program; however, some concerns have been identified. EPAs
general program findings included:
Denver has an effective public education and outreach program.
Denver inspectors thoroughly understand their responsibilities, the MS4 permit
requirements, and how to implement these requirements.
Denver has areas of its program where additional coordination between Denver
departments and between Denver and the CWQCD would be beneficial.
Denver has not adequately implemented all standardized procedures throughout the MS4
program. (Better documentation is needed.)
Denver has not designated a staff person to be responsible for the stormwater runoff
control program at its municipal facilities.
Overall, the comments on the program were positive, with required changes to the program
generally characterized as administrative loose ends that are relatively easily addressed, as
described in Denvers responses to the audit in Appendix B.
DENVERS STORMWATER QUALITY RELATED POLICIES
The Wastewater Management Division of the Department of Public Works is organized to
operate the sewerage system of Denver and to implement and enforce the Rules and
Regulations Governing Sewerage Charges and Fees and Management of Wastewater and
Chapter 56, Articles 91 through 107 of the Revised Municipal Code. A variety of drainage and
stormwater-quality-related requirements are identified, the most explicit of which are in Chapter
10, Section 10.17 of the rules and regulations. Because the requirements of this section provide a
critical foundation for this Plan, the requirements of Section 10.17 are reproduced in full as
follows:
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Denver Water Quality Management Plan
Pursuant to the terms, conditions and
requirements of CDPS Permit No. COS-OOOOOl,
issued to the City and County of Denver by the
State of Colorado; the City is required to
implement specific programs to control discharges
to and from the Municipal Separate Storm Sewer
System (MS4) owned or operated by the City and
County of Denver. Elements of these mandatory
programs require that the City take steps to
minimize the discharge of sediment, debris, and
other pollutants from construction sites; and
provide for enhancing the water quality of storm
runoff from fully developed sites.
a. Technical Criteria. The minimum technical
requirements for all proposed required BMPs
relating to water quality are to be based on
those specified in the UDFCD Criteria
Manual, Volume 3, Best Management
Practices, September 1992 and as may be
amended.
b. Water Quality Requirements.
1. All development and re-development projects that are located within the
Corporate Boundaries of the City and County of Denver shall include in
their design, specific measures to enhance the water quality of storm-
generated runofffrom the fully developed project site. All Best
Management Practices (BMPs) identified in the UDFCD Volume 3
Manual are applicable to development and re-development projects within
the City and County of Denver.
2. All facilities designed to provide detention of storm-generated runofffor
drainage andflood control purposes shall be required to provide water
quality enhancement through the use of a timed-release water quality
outlet structure or an approved alternative.
3. Timed release water quality outlet structures shall be designed to allow
either a 40-hour or 12-hour drain time of a portion of the runoff identified
as the Water Quality Capture Volume. The drain time is dependent on the
type ofproposed detention facility. At a minimum, the determination of
the Water Quality Capture Volume and design requirements for timed-
release outlet structures shall conform to the methods and procedures
outlined in the Urban Storm Drainage Criteria Manual, Volume 3.
EXHIBIT 3.2
SELECTED REQUIREMENTS FOR
DEVELOPMENT AND
REDEVELOPMENT PROJECTS IN
DENVER
PROVIDE BMPS TO ENHANCE
STORMWATER RUNOFF
PROVIDE TIMED RELEASE OF THE
WATER QUALITY CAPTURE
VOLUME FOR SITES REQUIRED TO
DETAIN RUNOFF FOR DRAINAGE
PURPOSES
SUBMIT A STORMWATER QUALITY
CONTROL PLAN TO ADDRESS
WATER QUALITY ISSUES AND
IDENTIFY BMPS FOR THE SITE
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4. All sites that are not required to provide detention of storm runofffor
drainage andflood control purposes may still be required to detain for
water quality purposes.
c. Waivers. Upon application, review, and approval of said application, waivers
from the requirement to detain solely for water quality purposes may be
granted.
d. Stormwater Quality Control Plans. All development, re-development, or other
construction projects, regardless of size, are required to submit a Stormwater
Quality Control Plan that addresses water quality issues and describes all
permanent water quality "Best Management Practices" to be used on the fully
developed site. The type and scope of this plan varies with the size of the site.
Review and approval of this plan by the Manager or his/her duly authorized
agents is required before any Wastewater Management Division Permits are
issued that relate to the project.
e. Plan submittals. Plans and drawings relating to water quality issues that are
submittedfor review and approval shall conform to the requirements set forth
in the Wastewater Management Divisions 1995 guidebook entitled
Stormwater Quality Control Plans: An Information Guide and as may be
amendedfrom time to time.
f. Fees. At the time of issuance of an applicable Sewer Use and Drainage
Permit, a non-refundable review fee shall be paid to the City and County of
Denver. The amount of such fee shall be charged as established by the
Manager.
g. Compliance with Chapter Requiredfor Site Development Plan(s) Approval.
No Site Development Plan(s) shall be approved unless saidplan(s) include
water quality enhancing measures consistent with the requirements of this
Chapter and related land development regulations.
Other key aspects of the Wastewater Management Division regulations that outline requirements
related to stormwater quality and quantity and/or elucidate the permitting process related to
stormwater and new developments include the following:
Sewer Use & Drainage Permit (Section 2.17): A sewer use and drainage permit must be
obtained for any new structure or addition to an existing structure. A permit may also be
required for any situation which may affect storm drainage, the sanitary sewer system or
the storm sewer system. A permit may also be required for any situation which requires
review by the Wastewater Management Division. No repair or replacement of any
building sewer is allowed prior to the issuance of a Sewer Inspection Permit.
Prohibited Discharges to the Storm Sewer System (Section 7,01): Discharges of polluted
water, waste or materials into Denvers storm sewers or into water courses that traverse
Denver are prohibited. Discharges of industrial or commercial wastewater or any
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Denver Water Quality Management Plan
polluted or contaminated water upon any sidewalk, street, alley, or any gutter are also
prohibited. Other prohibitions are also identified.
Subdivision/Planned Unit Development/Planned Building Group/Planned Development
(Chapter 9): Specific requirements for storm drainage studies, development site plans,
construction drawings, grading plans, and protective covenants are outlined. Drainage
plans must provide for detention of the 100-year storm event in compliance with the
UDFCDs Storm Drainage Criteria Manual and current Wastewater Management
Division criteria. The owner/maintenance organization is required to be responsible for
and pay for all installation and maintenance costs related to on-site storm sewers and
storm drainage control facilities. A pre-application conference with the Wastewater
Management Division is offered, but not required, to ensure that the developer is properly
informed regarding requirements, criteria, and problems related to drainage.
Section 9.04 identifies the Wastewater Management Division-related requirements that
must be fulfilled on the Building Department Inspection Record form in order to receive
a Certificate of Occupancy:
a. A Sewer Use and Drainage Permit has been issued.
b. Construction of all required storm and sanitary drainage facilities has been
completed and accepted by the City.
c. The Certificate of Inspection for all storm drainage and sanitary sewer
facilities has been submitted.
d. The building sewer connection has been inspected by the Division and a
Sewer Inspection Permit has been issued.
e. All fees required by the City and County of Denver have been received by
the City.
f. All other requirements of the Sewer Use and Drainage Permit have been
completed.
Water Quality, Grading, and Erosion Control (Chapter 10): Requirements related to earth
disturbance are specified to ensure that soil erosion and sedimentation (and changed
water flow characteristics) are controlled to the extent necessary to avoid damage to
personal and real property, and to prevent pollution of the MS4 and receiving waters.
Post-construction requirements are specified in Section 10.17, as previously discussed.
Storm Drainage Planning and Design (Chapter 11): This chapter requires that all
developers plan, design and install storm drainage facilities in compliance with the
Denver Storm Drainage Master Plan to insure coordinated development of a system
which is self-sufficient in each storm drainage basin. Drainage facilities are also required
to comply with the Denver Comprehensive Plan in cases where future land uses are a
consideration in the development of storm drainage facilities. Drainage facilities are also
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required to comply with the Denver Storm Drainage Design and Technical Criteria
Manual and UDFCDs Urban Storm Drainage Criteria Manual. Specific storm drainage
design criteria are provided for various development types. For example, the initial storm
drainage system for commercial/industrial areas must be planned based on the 5-year
storm and major drainage systems must be based on the 100-year storm. On-site
stormwater runoff detention facilities are required to attenuate the peak flow conditions
for both the 100-year and 10-year storm events under fully developed conditions. Other
requirements apply for residential development, Planned Urban Developments (PUDs),
etc.
The requirements of Chapter 11 are relevant to this Plan for a variety of reasons. One key
issue is understanding the difference between requirements for detaining stormwater from
a water quantity management perspective and the requirement for detaining stormwater
from a water quality perspective. Chapter 11 identifies the water quantity management
requirements important for stormwater conveyance systems, whereas Chapter 10 identifies
the requirements for the water quality capture volume necessary for water quality
protection. The water quality capture volume is calculated in accordance with the Urban
Storm Drainage Criteria Manual, Volume 3 (UDFCD 1999) based on smaller, frequently
occurring storms (e.g., typically less than the 1-year storm), whereas the water quantity
management requirements are based on the 2-, 5-, 10- and/or 100-year storms, depending
on the type of development. Opportunities for integration of these requirements are
explored further in Chapter 6 of this Plan.
Floodplain Management (Chapter 12): This chapter focuses on requirements and
prohibitions on development or alteration of property within the Regulatory Floodplain of
Denver, except pursuant to the terms of a Sewer Use and Drainage Permit issued by
Denver which authorizes such development or alterations.
In summary, Denver has specific rules and regulations in place for managing stormwater quality
and quantity. This Plan plays a supporting role relative to these rules, providing approaches and
strategies to facilitate better implementation of these rules and regulations.
OTHER DENVER ORDINANCES, RULES AND REGULATIONS
In addition to Denvers rules and regulations that directly relate to water quality, other rules and
regulations can restrict the types of stormwater quality management strategies that are
implemented at a site. For example, many rules and guidelines exist as part of zoning codes and
urban design guidelines specific to various development areas. A review of these rules and
guidelines was beyond the scope of this Plan, but would be a valuable step in ensuring that there
are not unnecessary hurdles and restrictions that prevent innovative stormwater quality
management. As an example, there may be requirements for curbs and gutters or minimum
street widths that, under some conditions, would prohibit implementation of certain Low Impact
Development techniques.
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Denver Water Quality Management Plan
COLORADO WATER QUALITY CONTROL ACT AND
REGULATIONS
The Colorado Water Quality Control Act (CRS 25-8-101 through 25-8-702) provides the policy
direction to conserve, protect, maintain, and improve, where necessary and reasonable, the
quality of state waters. The act also authorizes water pollution prevention, abatement and
control programs. In Colorado, the Colorado Water Quality Control Commission (CWQCC)
regulates water quality and is responsible for establishing classifications and standards to protect
beneficial uses of streams, lakes and groundwater in the state (CRS 25-8-201 through 25-8-406).
Discharge permits to waterbodies are issued in a manner intended to protect these beneficial
uses. For this reason, the underlying classifications and standards are relevant to Denver in terms
of its stormwater discharge permit, even though the permit itself contains no numeric standards.
A variety of standards for physical and chemical constituents have been developed for Colorado
streams based on their assigned classifications. A brief overview of the subset of use
classifications relevant to streams and/or lakes in the Denver area from the Basic Standards and
Methodologies for Surface Water (5 CCR 1002-31) includes the following:
Recreation Class 1Primary Contact: These surface waters are suitable or intended to
become suitable for recreational activities in or on the water when the ingestion of small
quantities of water is likely to occur.. .Waters shall be presumed to be suitable for Class 1
uses and shall be assigned a class la or class lb classification unless a use attainability
analysis demonstrates that there is not a reasonable potential for primary contact uses to
occur in the water segment(s) in question within the next 20 years.
Agriculture: These surface waters are suitable or intended to become suitable for
irrigation of crops usually grown in Colorado and which are not hazardous as drinking
water for livestock.
Aquatic Life Class 1 Warm Water: These are waters that (1) currently are capable of
sustaining a wide variety of warm water biota, including sensitive species, or (2) could
sustain such biota except for correctable water quality conditions.
Aquatic Life Class 2 Warm Water: These are waters that are not capable of sustaining a
wide variety of cold or warm water biota, including sensitive species, due to physical
habitat, water flows or levels, or uncorrectable water quality conditions that result in
substantial impairment of the abundance and diversity of species.
Domestic Water Supply: These surface waters are suitable or intended to become
suitable for potable water supplies. After receiving standard treatment (defined as
coagulation, flocculation, sedimentation, filtration, and disinfection with chlorine or its
equivalent), these waters will meet Colorado drinking water regulations and any
revisions, amendments, or supplements thereto.
In addition to these classifications, the majority of the streams and lakes in the Denver area are
also classified as Use Protected which means that that the CWQCC has determined that the
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waters do not warrant the special protection provided by the outstanding waters designation or
the antidegradation review process. (Use-protected waters are allowed to degrade to the level
of water quality standards and are not considered reviewable waters under the antidegradation
regulation [CWQCD 2001].) A variety of criteria can be applied to result in a segment being
use-protected, one example of which is an Aquatic Life Warm Water Class 2 designation.
Under its CDPS stormwater permit, Denver is permitted to discharge to multiple locations in the
South Platte River basin with stream standards assigned by the CWQCC as summarized in
Exhibit 3.3. (See Chapter 2, Exhibit 2.3 for stream locations.) The specific numeric standards
associated with these classifications are provided in Colorado Department of Public Health and
Environment Water Quality Control Commission Regulation 38 Classification and Numeric
Standards South Platte River Basin, Laramie River Basin, Republican River Basin, Smoky Hill
River Basin, as summarized in Appendix A of this Plan.
One recent change to the classifications that is noteworthy with regard to water quality issues
affecting DIA arose from the difficulty of several streams in the DIA drainage basin meeting
stream standards for dissolved oxygen (DO). In the July 2004 Triennial Review hearing for the
South Platte, Denver proposed adoption of ambient-based DO standards for Second Creek, Third
Creek, and Box Elder Creek based on the demonstration that natural conditions or a
combination of natural and irreversible anthropogenic conditions preclude the attainment of the
existing DO standards for those streams. DIA is located in the Third Creek headwaters. In its
proposal, Denver (2004) stated:
Stormwater runoff from the airport has enhanced instream flows; however, this
runoff may carry aircraft deicing fluid, which has the potential to exert an oxygen
demand when the aircraft deicing fluid biodegrades. To minimize human-induced
conditions, DIA has satisfied regulatory requirements for implementation of all
best practical, available, and economically achievable technology for the control
of aircraft deicing fluid. Denver considers the establishment of DIA in this
watershed as an irreversible condition because the airport is a permanent part of
the landscape and is an important part of the state economy. Deicing will
continue to be a requirement for ensuring the safety of air travel.
Denver also conducted a Receiving Water Study to evaluate the aquatic communities of Second
Creek, Third Creek, and Box Elder Creek. The study demonstrated that ambient-quality-based
DO standards will protect instream classified uses (Denver 2004).
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Denver Water Quality Management Plan
Exhibit 3.3 Denver Receiving Water Descriptions and Classifications (CWQCD 2003)
Receiving Water Basin & Segment Designated Use1 Classification
Box Elder Creek Middle South Platte River, Segment 5 UP Aquatic Life Warm 2, Rec. 1 a, Agriculture
Bear Creek Bear Creek, Segment 2 UP Aquatic Life Warm 1, Rec. 1 a, Water Supply, Aqriculture
Grasmere Lake Upper South Platte River, Segment 1 7a UP Aquatic Life Warm 1, Rec. 1 a, Agriculture
Lakewood Gulch Upper South Platte River, Segment 1 6 UP Aquatic Life Warm 2, Rec. 1 a, Agriculture
Sloans Lake Upper South Platte River, Segment 1 7b n/a Aquatic Life Warm 1, Rec. 1 a, Agriculture
Cherry Creek Cherry Creek, Segment 3 UP Aquatic Life Warm 2, Rec. 1 a, Water Supply, Agriculture
City Park Lake Upper South Platte River, Segment 1 7a UP Aquatic Life Warm 1, Rec. 1 a, Agriculture
Sand Creek Upper South Platte River, Segment 1 6a n/a Aquatic Life Warm 2, Rec. 1 a, Agriculture
Rocky Mtn. Lake Upper South Platte River, Segment 1 7a UP Aquatic Life Warm 1, Rec. 1 a, Agriculture
Berkeley Lake Upper South Platte River, Segment 1 7a UP Aquatic Life Warm 1, Rec. 1 a, Agriculture
Clear Creek Clear Creek, Segment 1 5 UP Aquatic Life Warm 1, Rec. 1 a, Water Supply, Agriculture
First Creek Upper South Platte River, Segment 1 6c UP Aquatic Life Warm 2, Rec. 1 a, Agriculture
Second Creek Upper South Platte River, Segment 1 6d UP Aquatic Life Warm 2, Rec. 1 a, Agriculture
Third Creek Upper South Platte River, Segment 1 6e UP Aquatic Life Warm 2, Rec. 1 a, Agriculture
Bowles Lake Upper South Platte River, Segment 1 7c n/a Aquatic Life Warm 1, Rec. 1 a, Agriculture
Smith Lake Upper South Platte River, Segment 1 7a n/a Aquatic Life Warm 1, Rec. 1 a, Agriculture
South Platte River Upper South Platte River, Segment 14 n/a Aquatic Life Warm 1, Rec. 1 a, Water Supply, Agriculture
South Platte River2 Upper South Platte River, Segment 1 5 UP Aquatic Life Warm 2, Rec. 1 a, Water Supply, Agriculture
Exhibit Notes: 1 UP = use protected, n/a = not applicable; 2 Segment 1 5 of the South Platte River is immediately
downstream of Denvers boundary, but is relevant to Denver from a regional water quality planning perspective.
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TOTAL MAXIMUM DAILY LOADS (TMDLs)
Although numeric discharge limits are not generally required under stormwater discharge
permits, stormwater and nonpoint source discharges can be affected by numeric stream standards
when streams do not attain their designated uses. Specifically, the federal Clean Water Act
provides for the total maximum daily load (TMDL) process to allocate pollutant loads or
potential pollutant loads among all identified discharge sources so that the combined discharges
do not cause the water quality standards for a given waterbody to be exceeded under existing and
future conditions (DRCOG 1998). A simplified formula for the components of a TMDL is
represented as follows:
TMDL = WLA + LA + NBG + MOS
where:
WLA = wasteload allocation representing the portion of loading capacity attributed to
point sources and piped stormwater (permitted wet weather stormwater runoff and dry
weather flows)
LA = load allocation representing the portion of loading capacity attributed to nonpoint
sources
NBG = natural background representing the portion of loading capacity attributed to
natural background conditions (generally a component of the LA)
MOS = margin of safety portion of loading capacity attributed to uncertainty
It is important to note that the Clean Water Plan (DRCOG 1998) differentiates between wet
weather and dry weather conditions as follows:
TMDL (dry weather) =
WLA (piped dry weather runoff & point sources) + NBG (low flow) + Margin of Safety (MOS)
TMDL (wet weather)
WLA (unit area stormwater & point sources) + LA (unit area) + NBG (high flow) + MOS
Given that TMDLs are driven by the 303(d) list, it is critical that water quality planning in
Denver take into consideration known stream segments that do not attain stream standards. The
CWQCDs draft 303(d) list for 2004, which was released in November 2003, identified several
stream segments receiving stormwater discharges from Denver that do not attain stream
standards, as summarized in Exhibit 3.4. The segment listings in this table are generally
consistent with similar information contained in Denvers current stormwater permit.
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Denver Water Quality Management Plan
Exhibit 3.4 CWQCD Preliminary 303(d) List for 2004
ID Segment Description Portion Parameters
COSPCL1 5 Clear Creek, Youngfield St. to S. Platte River All fecal coliform
COS PUS 14 S. Platte River, Bowles Ave. to Burlington Ditch All Nitrate, fecal coliform, E. coli
COS PUS 1 51 S. Platte River, Burlington Ditch to Big Dry Creek Cadmium upstream of MWRD, E. coli from Clear Creek to Fulton Canal diversion and Burlington canal headgate to MWRD Cadmium2, E. coli
COSPUS1 6a Tributaries to S. Platte River, Chatfield Reservoir to Big Dry Creek Lower portion of Sand Creek Selenium, fecal coliform, E. coli
COSPUS1 6c Tributaries to S. Platte River, Chatfield Reservoir to Big Dry Creek except specific listings East Tollgate Creek, West Tollgate Creek, Tollgate Creek3 Selenium
COSPUS1 7a Washington Park Lakes, City Park Lake, Rocky Mountain Lake, Berkeley Lake Berkeley Lake Arsenic
Exhibit Notes:
1 Segment 1 5 of the South Platte River is immediately downstream of Denvers boundary, but is relevant to Denver from
a regional water quality planning perspective. Segment 1 5 also receives treated municipal wastewater discharges from
the Metro Wastewater Reclamation District (MWRD), which serves much of Denver.
2The cadmium listing is associated with the ASARCO plant.
3 None of the specific stream segment portions listed for COSPUS1 6c receive runoff from Denver.
During wet weather periods, stormwater and nonpoint source discharges are expected to be the
leading contributors of elevated bacteria (i.e., fecal coliform, e. coli) in these stream segments,
which are all required to meet the stringent Recreation Class la standards. Leading sources of
bacteria are expected to include pet waste, waterfowl, and wildlife. Most of these sources are
difficult, if not impossible, to control and will be a challenge for Denver to address. Denvers
efforts to develop a better understanding of the bacteria sources include an outfall investigation
study in the Upper Central Platte Valley of the South Platte River. The Wastewater Management
Division accelerated its broken tap and illicit connection program to upgrade sewer conditions in
this area. Additionally, the Wastewater Management Division supported a study based on an
antibiotic resistance analysis for fecal coliform to try to better define the sources of the bacteria
(e.g., animal or human sources) (Baus 2004). Unfortunately, the results of this study were
relatively inconclusive; however, additional opportunities exist to support ongoing bacterial
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Regulatory Drivers
source tracking studies being conducted by the Colorado School of Mines (Munakata-Marr
2004).
Metals listed in Exhibit 3.4 may be associated with wastewater treatment plant discharges,
stormwater, and/or naturally elevated conditions. Nitrate concentrations in Exhibit 3.4 are
primarily associated with municipal wastewater treatment plant discharges. The draft TMDL for
nitrate on Segment 14 of the South Platte River states, Stormwater runoff from nonpoint
sources does not contribute significantly to the nitrate impairment (South Platte CURE 2003).
In Denvers stormwater permit, the CWQCD (2003) states that a TMDL for the parameters listed
in Exhibit 3.4 will be developed at some point in the future and that this could have an impact on
future permit requirements. The CWQCD (2003) further notes in the permit that for the
parameters potentially related to stormwater discharges, development of the TMDLs is expected
to include the effects of precipitation-related events. The TMDL development may indicate that
discharges from Denvers MS4 have a reasonable potential to cause exceedances of the
applicable stream standards and provide a loading allocation that includes stormwater discharges.
If this is the case, the CWQCD states that the permit could be amended to include additional
requirements for the discharges to the TMDL segments. Such requirements would likely be
based on BMPs as opposed to numeric limits (CWQCD 2003). Looking to the future, however,
it is important to consider the possibility that federal and state agencies could regulate urban
stormwater discharges on the basis of numeric standards, rather than the current BMP-based
approach.
With regard to addressing stream segments requiring TMDLs, it is important to recognize
Denvers participation in the South Platte Cooperative for Urban River Evaluation (South Platte
CURE) (as discussed later in this chapter). The members of South Platte CURE cooperatively
share in-stream monitoring data, conduct modeling, and work toward cooperative development
of TMDLs on stream segments requiring them, as is the case of Segment 14 of the South Platte
for nitrate.
Although Barr Lake (COSPMS03) and Milton Reservoir (COSPMS03) are not listed as
receiving streams in Denvers permit, it is important to note that these two lakes are listed on the
303(d) list for non-attainment of the pH standard. During 2003, the CWQCD provided a 319
grant to assemble data on conditions in these reservoirs, which could eventually lead to a TMDL
on these waterbodies. In the 319 grant application, Denver was identified as contributing over
75 percent of the drainage to these reservoirs; therefore, water quality issues in these waterbodies
may also be relevant to Denver from a planning perspective. Denver is listed as a stakeholder in
the Barr Lake/Milton Reservoir group.
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Denver Water Quality Management Plan
REGIONAL EFFORTS AND AGREEMENTS
Denver participates in several regional efforts related to water quality planning and improvement
efforts. Key efforts discussed in this section that are vital to future water quality planning in
Denver include:
Denver Regional Council of Governments (YPRCOG)! Clean Water Plan
Joint Stormwater Task Force (Denver, Aurora, Lakewood and UDFCD)
South Platte Cooperative for Urban River Evaluation (South Platte CURE)
Cherry Creek Stewardship Partners
Barr Lake/Milton Reservoir Watershed Association
Selenium Stakeholders Group
Denver Regional Council of Governments/Clean Water Plan
Denver participates in the Denver Regional Council of Governments (DRCOG), which is
responsible under state and federal statutes for regional water quality planning in the Denver
area. In this capacity, DRCOG prepares and updates the Clean Water Plan, which is the
management plan for achieving water quality standards pursuant to Sections 208, 303(e), and
305(b) of the federal Clean Water Act. In keeping with this Act, the regions goal is to "restore
and maintain the chemical and physical integrity, in order to assure a balanced ecological
community, in waters associated with the region." The objectives, policies and guidelines used
in water quality planning and wastewater management, as described in the Clean Water Plan, are
intended to steer the regional water quality planning process. The Clean Water Plan describes
wastewater management strategies, watershed water quality programs, wasteload allocations,
stream standards, priority regional projects, nonpoint source
control strategies and stormwater management programs. The Exhibit 3.5
plan provides a regional context for protecting and maintaining Clear Choices for
water quality through integrated watershed management Clean Water
processes. The objectives, policies and guidelines used in water
quality planning and wastewater management are described in the plan.
Denver is part of the South Platte Urban Watershed, which is
recognized in the Clean Water Plan.
Joint Stormwater Task Force
Denver, Aurora, Lakewood and UDFCD work together as the Joint
Stormwater Task Force to implement a variety of stormwater-permit-
related requirements such as public education and stormwater
monitoring. The original purpose of this group was to submit a joint
Phase I stormwater permit application in 1992; however, the group has
continued to work together to implement requirements of the Phase I
permit through collaboration on a variety of projects. For example, the
group prepared the Clear Choices for Clean Water brochures to
educate the public on stormwater pollution prevention and continues to
coordinate the wet weather monitoring program under the Phase I
Hil
Managing
Your
Household
Wastes
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1 UUIHiyilUlUlltlUlUIHlIi


Regulatory Drivers
permits. Most recently, the group has developed an educational booklet targeting industrial
stormwater BMP maintenance and management (Doerfer 2004).
South Platte Cooperative for Urban River Evaluation (CURE)
The South Platte Cooperative for Urban River Evaluation (CURE) was formed in 1999 for a
variety of purposes related to water quality on the South Platte River and its tributaries in the
metro Denver area. South Platte CURE is a non-profit Colorado corporation primarily made up
of municipal entities (i.e., municipal wastewater treatment providers, municipal stormwater
agencies, local health departments, and municipal drinking water providers). Specific stream
segments addressed by South Platte CURE include Segments 6, 14 and 15 of the South Platte
River; Cherry Creek below Cherry Creek Reservoir; Bear Creek below Bear Creek Reservoir;
Clear Creek below the ditch diversions near Golden; and Sand Creek. Denver is a financially
supporting member of South Platte CURE. A few representative purposes of South Platte CURE
include:
Coordinate water quality monitoring and data sharing at permanent trend monitoring
locations and for special studies. Exhibit 3.6 identifies these monitoring locations.
Maintain, improve and operate low-flow point source and nonpoint source water quality
models for use in water quality decisions related to discharge permits.
Cooperatively develop recommendations for TMDLs and wasteload allocations.
Some specific South Platte CURE activities of particular relevance to Denver include:
A proposed 309 pilot project study that would recalculate the use-specific Table Value
Standards (i.e., stream standards) based on the proposed changes to aquatic life use
classifications.
Cooperative modeling and development of a nitrate TMDL for Segment 14 of the South
Platte River. (Segment 14 includes the portion of the South Platte River from Bowles
Avenue in Littleton to the Burlington Ditch.)
A copper study to evaluate the potential of a site-specific standard for copper on Segment
15 of the South Platte River, which is on the Monitoring and Evaluation portion of the
303(d) list. (Segment 15 includes the portion of the South Platte River from Burlington
Ditch to below the confluence with Big Dry Creek.) The study is using a variety of
techniques to assess the toxicity of copper in the stream to determine the potential
appropriateness of a site-specific stream standard for copper for Segment 15 of the South
Platte River. Stormwater has been discussed as the major source of copper affecting
attainment of stream standards. In the July 2004 Triennial Review for the South Platte
River, South Platte CURE formally proposed site-specific standards for copper as a result
of this study (South Platte CURE 2004).
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Denver Water Quality Management Plan
Ongoing studies and modeling related to sulfate and dissolved oxygen (DO) on the South
Platte River.
Standardizing and uploading instream data for relevant stream segments into STORET
(EPAs water quality database) for public retrieval.
Cooperative monitoring of South Platte River Segments 6, 14, and 15 as part of TMDL
development. Monitoring includes nutrients, microbiology, and selected metals.
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EXHIBIT 3.6 SOUTH PLATTE CURE MONITORING LOCATIONS
(Map Source: South Platte CURE 2004)
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Denver Water Quality Management Plan
Cherry Creek Stewardship Partners
Denver is a signatory to the Cherry Creek Watershed Water Quality and Resource Stewardship
Regional Memorandum of Understanding (MOU), along with Arapahoe County, Douglas
County, the City of Glendale, the City of Greenwood Village, the Town of Parker, and the City
of Centennial. This MOU evolved from the Smart Growth for Clean WaterCherry Creek
Watershed Partnership project. The purpose of the Smart Growth project was to promote the
establishment of a continuous natural greenway and innovative watershed enhancements to
protect the water quality and the public enjoyment of Cherry Creek, its tributaries, and the Lake.
The overall goals of the Partnership are to promote the long-term improvement of water quality
in the Cherry Creek Basin through land conservation and innovative streamside and watershed
enhancements; to promote regional cooperation on these issues; to enhance coordination among
land use and water quality leaders; and to pursue funding strategies for these activities.
Several specific goals in the MOU that are particularly relevant to this Plan include the
following:
Support smart growth practices to mitigate development-induced water quality impacts.
Provide buffers to development.
Provide recommendations on urban design to protect Cherry Creek as a natural amenity.
Support regional approaches to water quality improvement in the Cherry Creek basin,
throughout Douglas and Arapahoe Counties, and in Denver.
Barr Lake/Milton Reservoir Watershed Association
Denver is an active participant in the Barr Lake/Milton Reservoir Watershed Association, which
includes stakeholders assembled to evaluate water quality in Barr Lake and Milton Reservoir,
including upstream impacts from the Denver metropolitan area. The stakeholders group includes
representatives from permitted wastewater dischargers, recreation and aquatic interests,
agriculture, industry, water utilities, and local governments. The watershed study area includes a
system of canals and streams draining to Barr Lake and Milton Reservoir, located northeast of
Denver. Barr Lake is about 15 miles northeast of Denver, and Milton Reservoir is about 20
miles further to the northeast.
Since Denver discharges both stormwater and wastewater into the basin, Denver is providing
support in establishing a watershed association and participating in the 319 project to develop a
better understanding of water quality issues in the basin. Part of this project includes
development of a comprehensive water quality database.
Selenium Stakeholders Group
The Selenium Stakeholders Group consists of the City of Aurora, Conoco, Inc. (now Suncor
Energy), Ultramar Diamond Shamrock (now Valero Energy), and Metro Wastewater
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Reclamation District. This group is studying the elevated selenium concentrations on Sand
Creek (Segment 16a) and the South Platte River (Segment 15). As a result of a stipulation for a
temporary modification to the selenium standard on these segments, the Stakeholder Group has
developed and is implementing a study plan to develop site-specific criteria for selenium based
on data collection and exploration of other options (Lord-Reeves 2003). After three years of data
collection, the data collected have not given a clear indication of the sources of selenium within
the City of Aurora; therefore, the City of Aurora has undertaken additional studies such as
geologic evaluations to explore the potential existence of selenium-bearing rock units within the
Tollgate Creek basin (Piatt-Kemper 2003). Both the CWQCD and the parties involved in the
Selenium Stakeholders Group recognize that selenium is a statewide issue and agencies within
the state are looking at a more statewide solution to the selenium standard issue. The efforts of
this group should continue to be monitored for those stream segments receiving runoff from
Denver, particularly those that do not currently meet the selenium stream standards. The
selenium issue on Sand Creek also highlights the importance of working with neighbors such as
Aurora to address these multi-jurisdictional problems.
At the July 2004 Triennial Review, the CWQCD proposed a temporary modification for the
chronic dissolved selenium standard on Sand Creek of 19.3 pg/L. This temporary modification
was also proposed for East and West Tollgate Creeks and Tollgate Creek through February 2010
(CWQCD 2004).
OTHER FEDERAL AND STATE REGULATIONS
In addition to the specific regulations, permits and efforts already discussed, a wide variety of
federal and state environmental regulations have the potential to affect water quality
management in the Denver area. An exhaustive review of these regulations is beyond the scope
of this Plan; however, a brief bullet list of some laws, regulations, and issues that may be
potentially relevant includes:
National Environmental Protection Act (e.g., for federally funded transportation projects)
Groundwater Management Regulations (e.g., dewatering, discharges to groundwater)
Resource Conservation and Recovery Act
Individual Sewage Disposal Systems (ISDS) Regulations
Safe Drinking Water Act/Source Water Protection
Threatened and Endangered Species Act
Wetlands (i.e., sections 401 and 404 of the 1987 Clean Water Act amendments)
401 Certification
Colorado water law (e.g., affects length of time stormwater may be detained)
Additionally, those managing stormwater planning should be particularly aware of the following
common environmental issues and/or permit requirements:
Hazardous Materials and Phase 1 Site Assessments: Many old industrial areas occur in
Denver; some of those areas have had releases of hazardous materials or contain
hazardous substances. Several Superfund sites exist (such as the ASARCO Globeville
Smelter and Koppers facility) in and around the Denver area. In these areas, a Phase I
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Environmental Site Assessment should be conducted in accordance with ASTM Standard
E 1527-00 and new federal standards expected to be circulated by the EPA in late 2004 or
early 2005 to identify potential environmental risks and liabilities to the project and
construction worker health and safety. This site assessment should consist of a site
inspection, records review, and report.
Spill Reporting at Construction Sites: Contain and clean up spills such as, but not limited
to, wash water, paint, automotive fluids, fuel or other petroleum based products, solvents,
oils, or soaps, as soon as possible. Do not bury or wash spills into the storm drain or
stream. Report all releases of materials into the environment to the Colorado Department
of Public Health and Environment (CDPHE) 24-hour Environmental Emergency Spill
Reporting Line (877-518-5608).
Section 404 Permit: Section 404 of the Clean Water Act is administered by the U.S.
Army Corps of Engineers (USACE) and regulates filling Waters of the U.S. Section 404
permits from the USACE are required for the placement of dredged or fill materials into
waters of the U.S., including wetlands. Dredged or fill material includes any solid
material commonly used in construction such as, but not limited to, soil, concrete, metal
structures, rock, and pipe. There are various types of Section 404 Permits, including
Nationwide Permits, which are issued for activities with relatively minor impacts. An
Individual Permit is issued for more major impacts such the relocating of a stream or
creek segment, or filling over 0.5 acre of a jurisdictional wetlands. For information about
what type of 404 permit may be required, contact the USACE Denver Regulatory office
(303-979-4120).
Threatened and Endangered Species: In the Denver area, wetlands are potential habitat to
three federally listed threatened and endangered species, which are protected under the
Endangered Species Act. Before the USACE issues a Section 404 Permit, it requires the
proposed project have clearance for: 1) Ute Ladies tresses orchid (Spiranthes diluvialis),
2) Colorado butterfly plant (Gaura neomexicana ssp. coloradensis), and 3) Prebles
meadow jumping mouse (Zapus hudsonius preblei). A habitat suitability assessment is
sufficient to determine if habitat for these species occurs in the proposed project area. If
habitat for any of these species, or any other federally listed species (there are over 30 in
Colorado), is suspected of occurring in a project area, a trapping or flowering period
survey should be conducted to confirm absence or presence.
Section 401 Permit: If an Individual Permit is needed from the USACE, a Section 401
Water Quality Certification, issued by the CDPHE Water Quality Control Division
(CWQCD), is required for a proposed project to fulfill regulatory requirements of Section
401 of the Clean Water Act. Specific requirements of this permit application and permit
may be obtained from the CWQCD (303-692-3500 or
http://www.cdphe.state.co.us/wq/PermitsUnit/wqcdpmt.htmD.
Construction Stormwater Permit: Discharges of stormwater runoff from construction
sites disturbing one acre or more of land and certain types of industrial facilities require a
Colorado Discharge Permit System Stormwater Permit. The Stormwater Permit
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application needs to include a Stormwater Management Plan (SWMP), which details
erosion and runoff control measures, such as, but not limited to, a revegetation plan and
silt fencing, to prevent surface stormwater quality degradation. Current BMPs are to be
presented in the SWMP. Specific requirements of the permit application and permit may
be obtained from the CWQCD (same contact information as above).
Construction Dewatering (Discharge or Infiltration) Permit: Discharges of water
encountered during excavation or work in wet areas may require a discharge permit. If
the water is discharged to waters of the state, a Construction Dewatering Discharge
Permit is required. If the water is discharged to land and allowed to infiltrate, approval
from the CWQCD is required. Specific requirements of this permit application and
permit may be obtained from the CWQCD (same contact information as above).
Minimal Industrial Discharge Permit: Discharges of small quantities of wastewater or
wastewater requiring minimal treatment, such as that resulting from hydrostatic testing or
certain wash waters, may require a Minimal Industrial Discharge Permit (MINDI).
Specific requirements of this permit application and permit may be obtained from the
CWQCD (same contact information as above).
CURRENT AND FUTURE COMPLIANCE IMPLICATIONS OF
EVOLVING REGULATIONS
Water quality regulations continue to evolve at both the state and federal levels. Changes to
these regulations have the potential to impact water quality management in Denver for both point
and nonpoint source discharges. Although stormwater and nonpoint source discharges continue
to be based on BMPs instead of numeric criteria, these discharges can be drawn into the
regulatory process through TMDLs when stream standards are not attained; therefore, regulatory
changes that impact stream standards and classifications have significant relevance for
stormwater discharges. Several key regulatory changes that are in progress can be reviewed
through the Section 309 Report (CWQCD 2003) and through the activities of the Colorado Water
Quality Forum (CWQF) work groups that explore topics such as impacted water supplies,
nutrient criteria, sediment guidance, TMDL/303(d) issues, and water quality trading concepts.
The CWQF work group activities are often driven by changes at the EPA under its Clean Water
Act programs. (See http://www.is.ch2m.com/cwqf/ for a list of current CWQF work groups and
topics.) Highlights of several emerging regulations are provided below based on the efforts of
the CWQF work groups.
Section 309 Report and Potential Aquatic Life Classification Changes
In December 2003, the CWQCD released the Section 309 Report, which focused on review of
the state standards-setting and classification process. This document provides a basic road
map of water-quality-related regulatory issues that the state may consider over the next few
years. The purpose of the Section 309 Report is to assess whether regulatory or policy changes
are warranted based on the unique attributes of Colorado waterbodies. Some of the key
considerations in the report were affected by the Arid West Water Quality Research Project
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(Pima County Wastewater Management Department 2003). Some of the specific topics
addressed in the Section 309 Report (CWQCD 2003) included:
The physical, chemical, flow, and habitat characteristics associated with waterbodies,
including the ephemeral or effluent-dependent nature of many waterbodies.
The potential need for refined designated uses and additional site-specific standards.
The benefit of maintaining the functions of constructed water conveyance and storage
facilities.
The nature of the current use-attainability analysis process and any necessary
adjustments.
The benefits associated with maintaining downstream ecosystems that are dependent, at
least in part, upon the continuation of effluent discharges.
The study process identified a wide variety of distinguishing features of Colorado waterbodies,
with particular focus upon natural and human-induced variations in the flow regimes,
variabilities in habitat and biological diversity, and the impact of effluent returns on otherwise
water-short stream systems.
One key area of discussion with potential relevance to Denver is the identification of potential
refined designated uses under the state use classification system, primarily with regard to
aquatic life classifications. Based on a strawman proposal presented by the state, the idea of
adopting additional aquatic life use classifications to more accurately describe the actual use of
stream systems and establish appropriate accompanying water quality standards is one key
potential area of change. These types of revisions would be most significant for effluent
dependent or effluent dominated waterbodies or those that have experienced significant
hydrologic modifications. The key implication of such a revised classification system is the
removal of needless impairment listings under the TMDL program.
Triennial reviews of Colorados major river basins will serve as an opportunity to field-test a
variety of aquatic life classification modifications and bring them before the Commission at the
Basic Standards Rulemaking Hearing in July of 2010 (CWQCD 2003). Currently, the aquatic
life classification system includes three categories: Aquatic Life Warm 1 and 2 and Aquatic Life
Cold. The new proposed system includes nine principal use classifications that are developed
from combining cold water aquatic life, transition zone aquatic life or warm water aquatic life
with the categories of aquatic life for lakes/reservoirs, streams with fish, or streams with no fish.
In addition to the principal use classifications, several sub-classifications could also be assigned
to account for influences from treated effluent or hydrologic/habitat modifications, including
considerations such as:
Effluent dependent: Waters that would otherwise have an Aquatic Life-StreamsNo
Fish classification, but which have flows adequate to support fish due to treated effluent.
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Effluent dominated: Waters that would have an Aquatic Life-Streams-Fish
classification without the presence of treated effluent, but for which the flow for the
majority of the year consists of treated effluent.
Hydrologic/Habitat Modifications: Waters that are affected by irreversible human
impacts (e.g., water rights diversions, stormwater flows, and agricultural return flows)
such that the resulting expected condition differs from that for the associated principal
use classification. (The Hydrologic/Habitat Modification sub-classification would only
apply when supporting data demonstrates that the modifications are significant enough to
change the expected condition.)
The new proposed system embodies the concept of defining an expected condition for each of
the nine principal use classifications. Expected conditions would not be based on the pristine or
totally un-impacted reference condition, but rather on the characteristics of the aquatic
community that .. .generally would be anticipated without the influence of major human
modifications.
Other concepts explored under the Section 309 Report include the net environmental benefit
concept, which is basically a potential relaxation of standards/effluent limitations on point
sources discharging to water-short stream systems in order to encourage the continued
beneficial discharge of the ecosystem-sustaining flows (CWQCD 2003).
Although the Section 309 Report itself did not result in any recommended changes to state
statutes, the concepts and issues raised could impact future policies, potentially as early as the
Basic Standards Rulemaking Hearing in July of 2005. The CWQCD will continue its work with
stakeholders to develop a state policy on the potential use of the net environmental benefit
concept by October of 2004, which could also be brought before the CWQCC in July of 2005.
The CWQCD will also initiate a pilot program to explore refined designated aquatic life use
categories.
Possible Stream Standard Changes Under Consideration for July 2005
A variety of issues will be considered at the July 2005 Rulemaking Hearing, in addition to the
aquatic life issues discussed above. Some of these issues have implications for stormwater. A
brief overview includes changes to organic chemical standards (will be addressed in 2004 in
combination with Regulation 41, Basic Standards for Groundwater); revised table value criteria
for ammonia, cadmium, copper, antimony, arsenic and uranium; selenium criteria (when
developed by EPA); options for decoupling the aquatic life class 2 and use-protected
designations; and other issues (CWQF 2003).
Source Water Protection
Source water (i.e., drinking water supply source) protection activities have a link to stormwater
issues in that raw water quality for drinking water may be affected by pollutants in stormwater
discharges. Sediment, nutrients, pesticides, pathogens, and other pollutants in source waters can
decrease treatability, increase treatment costs, and ultimately increase risks to public health.
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Denver Water Quality Management Plan
Water utilities typically respond to deteriorating raw water quality by increasing chemical
dosages or adding additional processes. As an alternative or supplement to treatment changes,
managers may consider promoting BMPs to protect raw water quality.
A study funded by the American Water Works Association Research Foundation and the Water
Environment Research Foundation (AWWARF and WERF 2003) to address these issues found
that moderate deteriorations in raw water quality such as a 25 percent increase in solids and total
organic carbon (TOC) levels can increase routine operating costs by roughly 10 percent. Many
BMPs can prevent water quality deterioration when targeted to major pollutant source areas.
AWWARF and WERF note that funding a fraction of BMP implementation costs can be a cost-
effective means of reducing routine operating costs for some utilities. AWWARF and WERF
recommend that utilities in developing watersheds should promote low impact development
practices to reduce long-term water quality degradation. The study recommended that utilities
can help protect source quality and reduce treatment costs at minimal expense by forming
partnerships with watershed stakeholders. Utility participation in protection efforts helps
leverage funds and prioritizes the watershed as a drinking water catchment.
Due to the high cost of treatment plant capital improvements relative to watershed BMPs,
AWWARF and WERF recommend that utilities should consider long-term investment in source
protection measures in order to reduce the need for major process changes. Utilities should also
consider non-economic benefits of source protection, including the public health benefit of
reduced exposure to pesticides, pathogens, and emerging contaminants (AWWARF and WERF
2003).
Nutrient Criteria
In September 2002, the CWQCD presented its Nutrient Criteria Development Plan to EPA in
response to EPAs January 9, 2001 Federal Register notice that was intended to address nutrient
over-enrichment in the nations surface waters. According to EPA (1996), nitrogen and
phosphorus are among the leading causes of water quality impairment in the U.S., with 40
percent of rivers and 51 percent of lakes having designated uses impairments from excess
nutrients.
EPA has called for states to develop region-specific nutrient criteria for different types of
waterbodies to account for the wide natural variation in nutrient loading. For rivers and streams,
the CWQCD anticipates developing a statewide approach with regionalization for establishing
nutrient criteria. Key elements of the conceptual approach include:
Assessments conducted at the basin or sub-basin level (it is anticipated that in some cases
site-specific standards may need to be implemented where basin or sub-basin level
assessments are not refined enough to account for local conditions).
Criteria based on comparisons to expected conditions.
Criteria based on biological endpoints of the algal community that are linked to the
designated uses.
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Colorado is working on the nutrient criteria using a phased approach, which will first focus on
developing nutrient standards for selected targeted waterbodies that have significant nutrient
issues and that are high on the priority list. Nutrient criteria for Colorado lakes and rivers will be
based on the causal parameters nitrogen and phosphorus, as well as the response parameters
Chlorophyll-a, algal communities and transparency (Secchi depth or turbidity). Other
possibilities for causal parameters that will be considered include orthophosphate, total Kjeldahl
nitrogen, ammonia, nitrate, and dissolved organic carbon (DOC). Additional response
parameters such as dissolved oxygen, pH, plankton or macrophyte biomass, percent cover, and
species composition may also be considered. Considerations in the form of the criteria may
include spatial scale, temporal cycles such as diel or seasonal cycles, and determination of
attainment. Colorado anticipates developing numeric criteria (CWQCD 2002).
Of particular relevance to Denver is that the CWQCD is starting with High Priority Sites first,
one of which is Barr Lake. Barr Lake is located outside of Denvers boundaries, but it
eventually receives runoff from much of the metro Denver area and was named as a receiving
water in Denvers initial CDPS permit. Although Barr Lake is not a direct receiving water for
Denver stormwater, EPA has provided the states with the following regulations in CFR Part
131.10(b):
... in designating uses of a waterbody and the appropriate criteria for those
uses, the State shall take into consideration the water quality standards of
downstream waters and shall ensure that its water quality standards provide for
the attainment and maintenance of the water quality standards of downstream
waters.
EPA (Grubbs 2001) provides additional guidance stating:
...even if a state identifies waters that are not threatened or impairedfrom
nutrient overenrichment, they should also consider whether the nutrient levels in
this waterbody could contribute to an impairment downstream before determining
that nutrient criteria are not needed. If it is likely that a downstream impairment
is occurring, yet quantified criteria in downstream waters have not been
established, then a state/tribe should consider employing nutrient load reduction
strategies for the upstream waters. EPA recommends that these nutrient load
reduction strategies are effective ways of reducing the effects on downstream
uses, prior to adopting any specific nutrient criteria values.
Colorados timeline with regard to nutrient criteria includes developing interim measures by
December 2004 that will provide nutrient triggers and screening-level measures such as add-on
narratives to the Basic Standards and site-specific standards through the 303(d) listing process.
Current timelines identify the 2010 Basic Standards Rulemaking Hearing as the target date for
adopting nutrient criteria into the state standards (CWQCD 2002).
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Denver Water Quality Management Plan
Sediment Deposition
In May 2002, the CWQCD, CWCC, and the Colorado Sediment Task Force released the
Provisional Implementation Guidance for Determining Sediment Deposition Impacts to Aquatic
Life in Streams and Rivers, building upon draft guidance originally issued in 1998. This
guidance provides an interpretation of the CWQCCs "narrative standards" as they apply to
sediments which may form deposits detrimental to the attainment of aquatic life uses, as
described in the Basic Standards and Methodologies for Surface Water, Regulation 31 (5CCR
1002-31). The guidance is intended as a first step toward providing a consistent approach to
implementation of the statewide narrative basic standard that addresses sediment deposition,
which is an important cause of impacts to aquatic life. The guidance applies to substances,
primarily sediment caused by human induced erosion, which create a stress to aquatic life
through the deposition of materials. The guidance provides a means for the CWQCD and the
CWQCC to consider the impacts of bottom deposits on the attainment of the aquatic life uses,
particularly with regard to assessing the status of water quality as required in §305(b) of the
federal Clean Water Act, and establishing a listing of waterbodies requiring TMDLs under
§303(d) of the Act (CWQCC et al. 2002). Because stormwater can be a leading contributor of
sediments to streams, Denver should actively participate in activities that involve development of
guidance and regulations related to the sediment narrative standard.
Pollutant Trading
Pollutant trading is a concept being explored by the CWQF and the CWQCD. The concept is
also defined by EPA (2003) in its Water Quality Trading Policy. Various pollutant-trading
programs in Colorado have focused primarily on lakes and reservoirs such as phosphorus trading
programs in Lake Dillon and Cherry Creek Reservoir and a relatively young selenium-trading
program in the Grand Valley. The CWQCD is in the process of developing the state Water
Quality Trading Guidance document that includes topics such as pre- and post-TMDL trading.
Progress on this document has potential relevance to Denvers stormwater discharges for streams
with TMDLs.
SUMMARY
As is the case with cities throughout the U.S., Denver is faced with complex regulatory
requirements with regard to water quality. The Phase I CDPS permit specifies stringent
requirements with which Denver must comply or face significant penalties. Fortunately, Denver
already has many sound water quality requirements in place in the form of policies and
regulations. It will be imperative for Denver to continue to actively interface with regional water
quality efforts and to stay abreast of forthcoming regulatory changes.
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Chapter 4
RELATIONSHIP TO OTHER DOCUMENTS
Denver has completed multiple documents that provide important interfaces with water quality
planning. Some of the key documents, which were completed either by Denver or related
entities, are briefly summarized in this chapter, including:
Urban Storm Drainage Criteria Manual, Volumes 1-3
Denver Storm Drainage Design and Technical Criteria Manual
Denver Storm Drainage Master Plan and other drainage master plans
Standards, details and technical criteria documents
Metro Vision 2020 and the Clean Water Plan
Water Quality Improvement in the South Platte River, Report to the Mayor
Denver Comprehensive Plan 2000
Blueprint Denver
Denver Parks and Recreation Game Plan
Natural Areas Program Field Guide
Design Guidelines for Stapleton Water Quality
Long Range Management Framework South Platte River Corridor
Cherry Creek Greenway Corridor Master Plan
Cherry Creek Watershed Smart Growth for Clean Water Report
Lake Management and Protection Plan
Basic familiarity with these documents is important to this Plan for several reasons. The first
four documents listed identify already-established, accepted criteria and strategies for managing
stormwater in the Denver area. This Plan does not reinvent the wheel with regard to these
documents, rather it builds upon them. Documents such as the Denver Comprehensive Plan
2000, Blueprint Denver, and the Denver Parks and Recreation Game Plan summarize some of
the existing goals of various city departments with which this Plan must interface in order to be
most effective. Documents such as Metro Vision 2020, the Clean Water Plan, the Long Range
Management Framework South Platte River Corridor, the Cherry Creek Greenway Corridor
Master Plan, Cherry Creek Watershed Smart Growth for Clean Water, and Natural Areas
Program Field Guide are an important interface with regard to regional water quality goals and
goals for specific river corridors. The Lake Management and Protection Plan is important
because it provides the framework for maintenance and protection of Denver lakes. Design
Guidelines for Stapleton Water Quality is included because this Plan builds upon many of the
strategies developed and accepted in the Stapleton guidelines. Highlights of each of these
documents follow.
URBAN STORM DRAINAGE CRITERIA MANUAL, VOLUMES 1-3
The Urban Drainage and Flood Control District (UDFCD) was established by the Colorado
legislature for the purpose of assisting local governments in the Denver metropolitan area with
multi-jurisdictional drainage and flood control problems. Since 1969, UDFCD has maintained
and distributed the Urban Storm Drainage Criteria Manual, which consists of three volumes.
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Relationship to Other Documents
Volumes 1 and 2 (UDFCD 2001) provide guidance for planning and design of drainageway
channels, storage facilities, culverts, hydraulic structures, and other structures. Volume 3
(UDFCD 1999) provides guidance for the selection and design of stormwater quality BMPs. The
policies and design criteria set forth in these documents are the foundation of the stormwater
BMP information provided in this Plan.
Since the primary focus of this Plan is stormwater quality management, the topics covered in
Volume 3 are particularly salient and include:
General principles of stormwater quality management
Guidance for BMP planning for new development and redevelopment
Structural BMP design criteria, details and forms to facilitate design
BMP maintenance recommendations
Recommended BMPs for industrial and commercial sites
Nonstructural BMPs
Construction-phase BMPs, including erosion and sediment control
The basic philosophy of stormwater quality management presented in Volume 3 is based on this
four-step process:
1. Employ runoff reduction practices such as reducing paved area, providing grassed buffers
and swales, and minimizing directly connected impervious area (MDCIA).
2. Provide treatment for the water quality capture volume (WQCV) through
implementation of various BMPs that detain or infiltrate runoff.
3. Stabilize downstream drainageways.
4. Provide BMPs for specific industrial and commercial uses.
More detail on these practices and their applications in Denver is provided in Chapter 6 of this
Plan.
DENVER STORM DRAINAGE DESIGN AND TECHNICAL CRITERIA
MANUAL
In 1999, Denver updated the City and County of Denver Storm Drainage Design and Technical
Criteria Manual. (Note: This Manual is being updated again in 2005.) This manual provides
the minimum design and technical criteria for the analysis and design of storm drainage
facilities. The criteria require that all subdivisions, re-subdivisions, planned unit developments,
or any other regulated proposed development provide adequate storm drainage system analysis
and appropriate drainage system design in accordance with the manual requirements, which are
consistent with UDFCDs Storm Drainage Criteria Manual. Denvers manual provides drainage
plan submittal requirements along with drainage policies and floodplain regulations of the city.
The manual then provides engineering criteria for topics such as rainfall/design storms, runoff,
open channel design, storm sewers, storm sewer inlets, streets, culverts, hydraulic structures,
erosion control, detention and standard forms for use in design. The manual provides specific
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Denver Stormwater Quality Management Plan
design standards for flood detention in open space, parking lots and underground facilities. The
manual refers the user to the Urban Storm Drainage Criteria Manual, Volume 3 (UDFCD 1999)
for addressing water quality requirements.
DENVER STORM DRAINAGE MASTER PLAN AND OTHER
DRAINAGE MASTER PLANS
In December 2003, Denver completed the first phase of a three-phase Storm Drainage Master
Plan (Matrix 2003), which identifies capital improvements related to flood hazard reduction and
improving drainage conveyance for 15 major drainage basins within Denver. The document will
help Denver comply with its stormwater permit because it provides an inventory of stormwater
systems and recommends regional capital improvements. The Storm Drainage Master Plan also
integrates several different documents and programs into a comprehensive Public Works
management program. Although the Storm Drainage Master Plan does not address stormwater
quality issues, its comprehensive GIS mapping, database, hydrology and report provide a strong
base of information useful to this Plan. In particular, a description of the drainage basins in the
Storm Drainage Master Plan is provided in Chapter 2 along with opportunities for integration of
regional stormwater quality facilities in Chapter 8.
Working with UDFCD, Denver has also completed multiple drainage master plans for specific
drainage basins. These plans are important to water quality planning and should be referenced
with regard to stormwater-related improvements in various drainage basins. As examples, three
particularly relevant plans include:
Preliminary Design Report for the Upper Central Platte Valley South Platte River
Restoration (McLaughlin Water Engineers 1998). The plan covers a one-mile reach of
the South Platte River directly west of downtown between 8th Avenue and 1-25. The
goals of this plan include: flood damage reduction, elimination of Zuni Power Plant dam,
fish habitat improvements, recreation improvements, wildlife habitat and wetland
improvements, and improved access.
Stormwater Outfall Systems Plan Stapleton Area (McLaughlin Water Engineers 1995).
This plan provides a comprehensive plan for development of a drainage outfall system to
serve the Stapleton redevelopment area. Primary streams addressed include Sand Creek
and Westerly Creek.
Major Drainageway Planning South Platte River, Chatfield Dam to Baseline Road,
Phases A andB (Wright Water Engineers 1984). This three-volume series covers a 40-
mile reach of the South Platte River from the Chatfield Dam to the City of Brighton. The
purpose of Phase A of the report was to develop alternatives to solve flooding problems,
while maintaining a balance of different uses of the river such as water supply, recreation
and open space, to name a few. Phase B of the report provided preliminary designs for
engineering and flood-related aspects of the river and a master plan for recreation,
landscaping, and wildlife along the corridor.
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Relationship to Other Documents
STANDARDS, DETAILS AND TECHNICAL CRITERIA DOCUMENTS
Denver has several existing documents that specify standards, details and other technical criteria
that may be applicable to stormwater BMP and site designs and should be adhered to as
appropriate. These documents include:
Storm Drainage and Sanitary Construction Detail and Technical Specifications (City and
County of Denver Department of Public Works Engineering Division 2003)
Standards and Details for City Engineering, Section I, Minor Projects (City and County
of Denver Department of Public Works Engineering Division 2002)
Standard Details (City and County of Denver Department of Public Works Wastewater
Management Division 1995)
METRO VISION 2020 AND THE CLEAN WATER PLAN
Metro Vision 2020 (DRCOG 1998) is the long-range growth strategy for the Denver region.
(Note: Metro Vision 2030 was being completed concurrently to development of this Plan and
should be referenced for possible changes.) It examines both the current and preferred pattern of
development to the year 2020. One of the six core values included in Metro Vision 2020 is
environmental quality. The plan acknowledges that the location and type of growth and land
development have significant effects on air and water and that these issues are truly regional in
nature. The Clean Water Plan was identified as the mechanism by which regional water quality
issues should be addressed (DRCOG 1998).
The Denver Regional Council of Governments (DRCOG) is responsible under state and federal
statutes for regional water quality planning in the Denver area. In this capacity, DRCOG
prepares and updates the Clean Water Plan, which is the management plan for achieving water
quality standards pursuant to Section 208 of the federal Clean Water Act. The most recent update
to the Clean Water Plan is titled Metro Vision 2020 Clean Water Plan Policies, Assessments and
Management Programs (DRCOG 1998). The document describes wastewater management
strategies, watershed water quality programs, nonpoint source control strategies, stormwater
management programs, wasteload allocations, stream standards and priority regional projects.
The plan covers a 25-year planning process with additional wastewater treatment facility
planning data for up to a 50-year horizon. The Clean Water Plan also provides a regional
context for protecting and maintaining water quality through integrated watershed management
processes (DRCOG 1998). The BMPs and other water quality measures proposed in this Plan
should be consistent with the measures identified in the Clean Water Plan.
The Clean Water Plan states that the goal for the region is to restore and maintain the chemical
and physical integrity [of waterbodies] in order to assure a balanced ecological community in
waters associated with the region. Five key objectives were adopted as part of Metro Vision
2020 to support a proactive bottom-up planning process with regional coordination, including: 1
1. A locally defined balanced ecological community will be achieved through
implementation of water quality protection and appropriate water resource management
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Denver Stormwater Quality Management Plan
initiatives, provided that a balance will be maintained between the natural environment
and those designated uses of the resource.
2. The chemical and physical integrity of the region's aquatic environments will be restored
and maintained through a coordinated watershed management process.
3. Effective wastewater treatment will be identified through a regional process, with local
implementation of wastewater management strategies.
4. Effective and balanced stormwater and nonpoint source management will best be
achieved through local implementation processes.
5. Effective and cost-efficient water quality management and supply will require an
integrated resource management program.
One of the key strategies identified in the Clean Water Plan for water quality protection is
watershed planning. The document recognizes eleven designated watersheds, three of which
receive runoff from Denver, primarily the South Platte Urban and Cherry Creek watersheds, and,
to a lesser extent, Box Elder Creek. The document provides a summary of water quality and
regulatory information relevant to each of these watersheds that should be considered for future
water quality planning in these areas.
WATER QUALITY IMPROVEMENT IN THE SOUTH PLATTE
RIVER, REPORT TO THE MAYOR
Concurrent to the development this Plan, the Mayors Office commissioned an evaluation of
information regarding water quality in the South Platte River through Denver, which culminated
in the report Water Quality Improvement in the South Platte River, Report to the Mayor
(Bergstedt 2004). The findings of that report parallel and support the recommendations
contained in this Plan. Bergstedts report is provided in Appendix C of this Plan, with key
recommendations paraphrased as follows:
1. Increased communication and streamlining of procedures between various departments
with responsibilities affecting the South Platte River is needed.
2. Long-range regional initiatives and near-term program support with regard to stormwater
inputs to the river are necessary to adequately protect water quality in the river.
3. Recommendations related to regional stormwater initiatives include:
a. Promote a Denver-inspired regional watershed initiative, building on existing
efforts (including this Plan).
b. Enforce existing stormwater ordinances with regard to installation and
maintenance of BMPs.
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Relationship to Other Documents
c. Fund and empower the Natural Areas Program to help reduce contamination
before it reaches the river.
4. To address sewerage infrastructure and contamination issues:
a. Pursue additional storage in Chatfield Reservoir for additional base flow storage
and timely water releases to promote dilution of sewer discharges, particularly
during drought conditions.
b. Continue to support water quality improvement efforts of wastewater treatment
plants discharging to the river.
c. Continue diligent monitoring, improvement and coordination efforts related to the
sanitary sewer system, especially in northwest Denver.
DENVER COMPREHENSIVE PLAN 2000
Exhibit 4.1
The Denver Comprehensive Plan 2000: A Vision for Denver
and Its People provides a comprehensive framework for
addressing long-term issues such as environmental
sustainability, land use, mobility, Denvers legacies, housing,
economic activity, neighborhoods, education, human services,
arts/culture, and metropolitan cooperation. The Denver
Comprehensive Plan 2000 then outlines a long-term
implementation strategy to achieve the goals identified for
each of these issues. One of the primary goals with regard to
Denvers long-term physical environment is environmental
sustainability, specifically preserving and enhancing the
natural environment. The Denver Comprehensive Plan 2000
states:
Denvers relationship with the environment is above
all a matter of balance. Clean water, clean air, clean
parks and streets, efficient use and reuse of resources,
and protection of the mountain parks and open spaces
must be abiding goals.
Most basic to sustainable quality of life in Denver and the region are the land we
live on, the air we breathe, the water we drink and the natural beauty we enjoy.
The greatest challenge to the environment in the early 21st century is managing
growthslowing the loss of land, the consumption of resources, the congestion,
and the human stress created by urban sprawl. At the same time, the public-
policy challenge to develop and implement balanced and sustainable growth
strategies addressing equity, stewardship and cooperation becomes more critical.
As part of its Vision of Success for environmental sustainability, the following selected
statements pertaining to water quality are provided:
Comprehensive Plan 2000
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Table of Contents Page TOC-1 TABLE OF CONTENTS Acknowledgments...................................................................................................A-1 Executive Summary................................................................................................ES-1 Overview............................................................................................................................ES-1 Approach...........................................................................................................................ES-1 Stormwater Quality BMP Implementation Guidelines.............................................................ES-3 Recommendations And Conclusions.....................................................................................ES-4 Chapter 1 Introduction............................................................................................1-1 Purpose And Goals..............................................................................................................1-2 Goal 1: Develop A Framework And Shared Vision For Meeting Denver s Stormwater Quality Requirements And Goals................................................................1-2 Goal 2: Develop BMP Strategies That Work In Various Denver Settings..............................1-3 Goal 3: Develop A Common Foundation For Interdepartmental Understanding Of Stormwater Quality Requirements And Their Role In The Planning Process.................1-4 Goal 4: Develop Framework And Priorities For Future Work Needed To Meet Goals..........1-4 Approach............................................................................................................................1-4 Principles And Policies..........................................................................................................1-7 Opportunities And Challenges..............................................................................................1-9 Address Water Quality Issues............................................................................................1-9 Improve Interdepartmental Cooperation With Regard To Water Quality..............................1-9 Coordinate Compatible Uses Between Parks And Water Quality Facilities.........................1-10 Enhance Compatibility Between Urban Design Goals And Water Quality Facilities.............1-10 Implement Effective, Sustainable, Attractive, Multi-Purpose, Safe, And Well-Designed Bmps1-11 Ensure Long-Term BMP Operation And Maintenance.......................................................1-11 Develop Financing And Institutional Strategies For Regional Bmps....................................1-11 Scope Limitations...............................................................................................................1-12 Plan Overview....................................................................................................................1-13 Chapter 2 Overview Of Major Denver Drainage Basins And Potential Urban Stormwater Impacts.............................................................................2-1 Overview Of Denver Drainage Basins....................................................................................2-1 South Platte River.............................................................................................................2-7 First Creek.......................................................................................................................2-7 Second Creek..................................................................................................................2-8 Third Creek.....................................................................................................................2-8 Box Elder Creek...............................................................................................................2-9 Irondale Gulch................................................................................................................2-9 Clear Creek....................................................................................................................2-9 Sand Creek...................................................................................................................2-10 Westerly Creek..............................................................................................................2-10 Cherry Creek.................................................................................................................2-11 Goldsmith Gulch...........................................................................................................2-11 Sloan s Lake..................................................................................................................2-12 Lakewood Gulch...........................................................................................................2-12 Dry Gulch.....................................................................................................................2-12 Weir Gulch...................................................................................................................2-12 Sanderson Gulch...........................................................................................................2-13

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Table of Contents Table of Contents Page TOC-2 West Harvard Gulch......................................................................................................2-13 Harvard Gulch..............................................................................................................2-14 Bear Creek....................................................................................................................2-14 Marston Lake North (Tributary Of Bear Creek).................................................................2-15 Overview Of Lakes.............................................................................................................2-15 Characterization Of Denver Lake And Stream Conditions......................................................2-18 Overview Of The Effects Of Urbanization On Receiving Waters.............................................2-20 Adverse Physical Impacts Of Urban Runoff......................................................................2-22 Chemical Characteristics Of Urban Runoff......................................................................2-24 Summary...........................................................................................................................2-30 Chapter 3 Regulatory Drivers...................................................................................3-1 Phase I Stormwater CDPS Permit...........................................................................................3-1 Denver International Airport (DIA) CDPS Permit......................................................................3-5 EPA s April 2004 Audit Of Denver s Stormwater Management Program...................................3-6 Denver s Stormwater Quality Related Policies.........................................................................3-6 Other Denver Ordinances, Rules And Regulations................................................................3-10 Colorado Water Quality Control Act And Regulations...........................................................3-11 Total Maximum Daily Loads (Tmdls)....................................................................................3-14 Regional Efforts And Agreements.........................................................................................3-17 Denver Regional Council Of Governments/Clean Water Plan..........................................3-17 Joint Stormwater Task Force...........................................................................................3-17 South Platte Cooperative For Urban River Evaluation (CURE)............................................3-18 Cherry Creek Stewardship Partners.................................................................................3-21 Barr Lake/Milton Reservoir Watershed Association...........................................................3-21 Selenium Stakeholders Group........................................................................................3-22 Other Federal And State Regulations...................................................................................3-22 Current And Future Compliance Implications Of Evolving Regulations...................................3-24 Section 309 Report And Potential Aquatic Life Classification Changes...............................3-25 Possible Stream Standard Changes Under Consideration For July 2005............................3-26 Source Water Protection.................................................................................................3-27 Nutrient Criteria.............................................................................................................3-27 Sediment Deposition......................................................................................................3-29 Pollutant Trading...........................................................................................................3-29 Summary...........................................................................................................................3-29 Chapter 4 Related Documents..................................................................................4-1 Urban Storm Drainage Criteria Manual, Volumes 1-3............................................................4-1 Denver Storm Drainage Design And Technical Criteria Manual...............................................4-2 Denver Storm Drainage Master Plan And Other Drainage Master Plans...................................4-3 Standards, Details And Technical Criteria Documents.............................................................4-4 Metro Vision 2020 And The Clean Water Plan.......................................................................4-4 Water Quality Improvement In The South Platte River, Report To The Mayor.............................4-5 Denver Comprehensive Plan 2000........................................................................................4-6 Blueprint Denver...................................................................................................................4-9 Denver Parks And Recreation Game Plan.............................................................................4-11 Natural Areas Program Field Guide.....................................................................................4-12 Design Guidelines For Stapleton Water Quality....................................................................4-12 Long Range Management Framework South Platte River Corridor..........................................4-13 Cherry Creek Greenway Corridor Master Plan......................................................................4-14

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Denver Water Quality Management Plan Table of Contents Page TOC-3 Cherry Creek Watershed Smart Growth For Clean Water Report...........................................4-14 Lake Management And Protection Plan................................................................................4-15 Summary...........................................................................................................................4-16 Chapter 5 National Case Studies..............................................................................5-1 City Of Austin, Texas: Watershed Protection Master Plan........................................................5-1 City Of Portland, Oregon: Clean River Plan...........................................................................5-5 Snohomish County, Washington............................................................................................5-9 San Diego, California.........................................................................................................5-12 Prince George s County, Maryland And Low Impact Development.........................................5-13 Summary...........................................................................................................................5-16 Chapter 6 Stormwater Quality BMP Implementation Guidelines....................................6-1 Part 1 Introduction.............................................................................................................6-1 Design And Stormwater Quality Principles.........................................................................6-2 Stormwater Quality Design Process...................................................................................6-7 How To Use The Guidelines...........................................................................................6-10 Part 2 Development Types Guidelines...............................................................................6-11 Ultra Urban...................................................................................................................6-14 High Density Mixed Use.................................................................................................6-16 Campus........................................................................................................................6-18 Industrial.......................................................................................................................6-20 Low Density Mixed Use...................................................................................................6-22 Residential.....................................................................................................................6-24 Parks And Natural Areas Open Space.............................................................................6-26 Part 3 Implementation Details...........................................................................................6-29 Roofs............................................................................................................................6-29 Parking Medians And Islands..........................................................................................6-33 Stormwater Distribution..................................................................................................6-36 Sediment Removal Traps And Forebays...........................................................................6-37 Soils..............................................................................................................................6-38 Planting........................................................................................................................6-39 Part 4 BMP Fact Sheets....................................................................................................6-43 Grass Buffers.................................................................................................................6-43 Grass Swales.................................................................................................................6-45 Detention Basins............................................................................................................6-53 Treatment Wetlands.......................................................................................................6-56 Subsurface Treatment Devices........................................................................................6-56 Other Alternative Technologies.......................................................................................6-58 Industrial Source Controls..............................................................................................6-58 Drainageway Stabilization..............................................................................................6-58 Part 5 Maintenance Policies And Guidelines......................................................................6-61 Defining Maintenance Responsibility For Public And Private Facilities.................................6-61 Developing A Maintenance Plan.....................................................................................6-63 Maintenance Requirements.............................................................................................6-64 Grass Buffers And Grass Swales.................................................................................6-66 Porous Pavement And Porous Pavement Detention......................................................6-68 Porous Landscape Detention......................................................................................6-70 Extended Detention And Retention Basins....................................................................6-72

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Table of Contents Table of Contents Page TOC-4 Sand Filter Extended Detention Basin..........................................................................6-74 Constructed Wetland Basins And Channels.................................................................6-75 Green Roofs/Treatment Roofs....................................................................................6-76 Low Impact Development Designs..............................................................................6-78 Subsurface Treatment Devices....................................................................................6-78 Conclusions And Recommendations For Maintenance......................................................6-79 Chapter 7 Pollution Source Controls (Non-Structural Bmps).........................................7-1 Overview Of Pollution Source Controls (Non-Structural Approaches).......................................7-1 Industrial And Commercial Hot Spots .............................................................................7-9 Household Waste (Litter, Pet Waste, Yard Waste, Used Oil And Automotive Fluids, And Other Hazardous Waste)..........................................................................7-12 Pesticide, Herbicide, And Fertilizer Management (Including Integrated Pest Management)....................................................................................................7-14 Efficient Irrigation...........................................................................................................7-16 Materials Storage Practices.............................................................................................7-16 Good Housekeeping......................................................................................................7-18 Spill Prevention And Response........................................................................................7-18 Preventative Maintenance...............................................................................................7-21 Summary And Conclusions.................................................................................................7-25 Chapter 8 Potential Regional Facilities......................................................................8-1 South Platte River..................................................................................................................8-7 Prairie Gateway (Basin 0058)...........................................................................................8-7 I-70 & Colorado Boulevard (Basin 0060-01).....................................................................8-8 I-70 & York (Basin 0060-02)............................................................................................8-9 Lower Platte Valley (Basin 0062-01/4500-02).................................................................8-10 Central Platte Valley (Basin 0063-01)..............................................................................8-11 1st & Federal (Basin 0064-01).......................................................................................8-12 Valverde (Basin 0064-02)..............................................................................................8-13 Ruby Hill (Basin 0065-01)..............................................................................................8-14 Dartmouth (Basin 0065-02)...........................................................................................8-15 College View (Basin 0067-01)........................................................................................8-16 West Belleview Avenue (Basin 0067-02)..........................................................................8-17 Sloan s Lake (Basin 4700-01).........................................................................................8-18 I-25 (Basin 5000-01).....................................................................................................8-19 West Harvard Gulch (Basin 5300-01).............................................................................8-20 First Creek.........................................................................................................................8-21 First Creek (Basin 3700).................................................................................................8-21 Irondale Gulch...................................................................................................................8-22 Irondale Gulch (Basins 3900 & 3901)............................................................................8-22 Clear Creek.......................................................................................................................8-23 Clear Creek (Basins 4300-03 & 4309-01)......................................................................8-23 Sand Creek........................................................................................................................8-24 North Stapleton (Basin 4400-01)....................................................................................8-24 Quebec Corridor (Basin 4400-02)..................................................................................8-25 South Stapleton (Basin 4400-03)....................................................................................8-27 East Stapleton (Basin 4400-04)......................................................................................8-28 Westerly Creek..............................................................................................................8-29 South Stapleton (Basin 4401-01)....................................................................................8-29

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Denver Water Quality Management Plan Table of Contents Page TOC-5 11th Avenue To Montview (Basin 4401-02).....................................................................8-30 Lowry (Basin 4401-03)...................................................................................................8-31 Upper Westerly Creek (Basin 4401-04)...........................................................................8-32 Cherry Creek.....................................................................................................................8-33 Central Business District (Basin 4600-01)........................................................................8-33 Cherry Creek Mall (Basin 4600-02)................................................................................8-34 Upper Cherry Creek (Basin 4600-03).............................................................................8-35 Upper Cherry Creek (Basin 4600-04).............................................................................8-36 Goldsmith Gulch................................................................................................................8-37 Goldsmith Gulch (Basin 4601-01)..................................................................................8-37 Dry Gulch And Lakewood Gulch.........................................................................................8-38 Lakewood & Dry Gulches (Basins 4800-01 & 4801-01)...................................................8-38 Weir Gulch........................................................................................................................8-39 Weir Gulch (Basin 4900-01)..........................................................................................8-39 Sanderson Gulch...............................................................................................................8-40 Sanderson Gulch (Basin 5100-01)..................................................................................8-40 Greenwood Gulch.............................................................................................................8-41 Greenwood Gulch (Basin 5401-01)................................................................................8-41 Bear Creek........................................................................................................................8-42 Fort Logan (Basin 5500-01)...........................................................................................8-42 Upper Bear Creek (Basin 5500-02)................................................................................8-43 Marston Lake North (Basin 5500-04)..............................................................................8-45 Pinehurst Tributary (Basin 5500-05)................................................................................8-46 Henry s Lake (Basin 5501-01)........................................................................................8-47 Dutch Creek......................................................................................................................8-48 Coon Creek (Basin 5901-01).........................................................................................8-48 Summary...........................................................................................................................8-48 Chapter 9 Recommendations And Implementation Plan Recommendations................................................................................................................9-1 Implementation Plan.............................................................................................................9-5 References..............................................................................................................R-1 Glossary...............................................................................................................G-1 Appendices Appendix A Colorado Water Quality Control Commission Stream Classifications And Water Quality Standards Relevant To Denver Appendix B Denver s Response To April 2004 EPA Audit Of Stormwater Program Appendix C Water Quality Improvement In The South Platte River, Report To The Mayor Appendix D Representative Stormwater BMP Maintenance Agreements

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Acknowledgements Page A-1 ACKNOWLEDGEMENTS This Plan was developed through the collaboration and dedication of many Denver staff, an outside review committee and a diverse project team under the direction of Denver Wastewater Management Division Project Manager Terry Baus, P.E. Significant time was invested in determining the priorities of various Denver staff and departments through a detailed series of interviews. The project team would like to thank all of these individuals for providing their insights and expertise with regard to stormwater quality planning priorities and issues for Denver. DENVER ADVISORY COMMITTEE Terry Baus, P.E., Public Works, Wastewater Management Division (Project Manager) Susan Baird, Parks and Recreation Janet Burgessor, Environmental Health Leslie Lipstein, Community Planning and Development Darren Mollendor, P.E., Public Works, Wastewater Management Division Ruth Murayama, Parks and Recreation Alan Sorrel, P.E., Public Works, Department of Engineering Services Ben Urbonas, P.E., Urban Drainage and Flood Control District Gayle Weinstein, Parks and Recreation PROJECT CONSULTANT TEAM Jonathan Jones, P.E., Wright Water Engineers, Inc. (Project Manager) Jane Clary, Wright Water Engineers, Inc. (Project Coordinator) Bill Wenk, Wenk Associates Paul Thomas, Wenk Associates Ilene Marcus Flax, Wenk Associates Jim Wulliman, P.E., Muller Engineering Company John Blanchard, P.E., Matrix Engineering Robert Krehbiel, P.E., Matrix Engineering Peter Smith, Smith Environmental Dr. James C.Y. Guo, P.E., University of Colorado at Denver Dr. James P. Heaney, P.E., University of Florida (formerly at University of Colorado-Boulder) EXTERNAL REVIEW COMMITTEE John Carroll, P.E., Carroll and Lange, Inc. John Doerfer, P.E., Urban Drainage and Flood Control District Bill Ruzzo, P.E., Cherry Creek Basin Water Quality Authority Dr. F. Robert McGregor, P.E., AMEC Earth and Environmental, Inc. Susan Powers, Urban Ventures, L.L.C. Michael Weiss, McStain Enterprises, Inc.

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Acknowledgements Acknowledgements Page A-2 DEPARTMENTAL INTERVIEWS 1 Beth Conover, Environmental Policy Aid to Mayor Hickenlooper, Mayor s Office Tyler Gibbs, Director of Planning and Urban Design Services, Community Planning and Development Steve Gordan, Community Planning and Development Reza Kazemian, P.E., Public Works, Director of Operations Wastewater Management Division Nicholas Skifalides, P.E., Deputy Manager of Public Works Wastewater Management Division Lesley Thomas, P.E., City Engineer, Department of Engineering Services, Public Works Val Webster, Parks and Recreation Jim Wiseman, P.E., Director of Engineering, Public Works OTHER ACKNOWLEDGEMENTS The Urban Drainage and Flood Control District s Storm Drainage Criteria Manual, Volumes 13, was the foundation for much of this document. Portions of this Manual were paraphrased in several chapters of this Plan, particularly Chapters 6 and 7, which include both paraphrases and direct quotations. The Greenway Foundation provided attractive photographs of the South Platte River for inclusion in this Plan. 1 All members of the Advisory Committee participated in interviews with their respective departments, but their names have not been repeated in this interview list.

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Executive Summary Page ES-1 EXECUTIVE SUMMARY OVERVIEW The purpose of this Denver Water Quality Management Plan (Plan) is to advance a framework for better integrating stormwater management and water quality protection into planning, engineering, and infrastructure management for the City and County of Denver (Denver). This Plan will serve as a common authoritative reference identifying Denver s commitments, priorities, and strategies for protecting its rivers, streams, lakes, and wetlands from the adverse impacts of urban stormwater runoff. In addition, the Plan provides a practical initial strategy for managing stormwater runoff quality in the near term, while laying the groundwork for a long-term vision. This Plan is relevant to Denver staff, land developers undertaking new or redevelopment projects, other parties conducting activities that impact urban runoff, and citizens who want to support water quality protection in the Denver area. The primary goals of this Plan are identified in Exhibit ES.1. The remainder of this Executive Summary describes the project approach, stormwater quality Best Management Practice (BMP) 1 implementation guidelines, and recommendations resulting from the Plan. APPROACH This Plan has been developed using a multi-faceted approach to ensure that a practical and innovative strategy for addressing water quality is developed for Denver. Multiple interviews and meetings were conducted with key Denver staff to develop a Plan that will be beneficial to many Denver departments. Key aspects of the project approach include: 4 Extensive collaboration among multiple city departments. Acceptance and use of this Plan across city departments is critical to its success. This document has been developed through close collaboration and frank discussion among multiple departments within 1 Best Management Practices (BMPs) include a variety of both structural and non-structural techniques implemented to help minimize pollution of streams, rivers, lakes, and wetlands. BMPs are the foundation of stormwater quality management and regulation and are a key topic throughout this Plan. Representative examples of BMPs include source controls such as proper fertilizer use and structural BMPs such as water quality detention basins and porous landscape detention. See Chapter 6 of this Plan for more information. EXHIBIT ES.1 PLAN GOALS DEVELOP A FRAMEWORK AND SHARED VISION FOR MEETING DENVER S STORMWATER QUALITY R EQUIREMENTS AND GOALS DEVELOP BMP STRATEGI ES THAT WORK IN VARIOUS DENVER SETTINGS DEVELOP A COMMON FOUNDATION FOR INTERDEPARTMENTAL UNDERSTANDING OF STORMWATER QUALITY REQUIREMENTS AND THEIR ROLE IN THE PLANNING PROCESS DEVELOP A FRAMEWORK AND PRIORITIES FOR FUTUR E WORK NEEDED TO MEET GOALS

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Executive Summary Executive Summary Page ES-2 Denver including Public Works, Parks and Recreation, Community Planning and Development, Environmental Health, and the City Attorney s Office. By diligently working together to prepare this document, a more unified position and vision for stormwater quality management has emerged. Some of the opportunities and challenges identified during interviews and Advisory Committee meetings are summarized in Exhibit ES.2. 4 Identification and review of regulations and existing Denver planning documents affecting or interfacing with stormwater quality management strategies in Denver. Many existing and proposed federal, state and local water quality regulations directly influence stormwater quality management in Denver. Key regulations were inventoried and described in order to provide a common basis for understanding stormwater quality management requirements. Similarly, Denver has many excellent planning documents and programs that help guide planning and watershed management decisions. In order to avoid reinventing the wheel, a review and summary of these key documents was completed. 4 Review of similar efforts in other communities with advanced stormwater programs. Communities throughout the country are reassessing their approach to stormwater and watershed management. Early in development of this Plan, five communities with advanced stormwater programs were identified to explore their approaches, successes, and difficulties in addressing urban runoff. Interviews and review of key documents were conducted for these communities: Portland, Oregon; San Diego, California; Austin, Texas; Prince George s County, Maryland; and Snohomish County, Washington. Findings from this research have been taken into account in development of this Plan with regard to general approach, as well as for recommendations for specific BMPs. EXHIBIT ES.2 STORMWATER QUALITY MANAGEMENT OPPORTUNTIES AND CHALLENGES ADDRESS WATER QUALIT Y ISSUES (E.G., 303(D) LISTED SEGMENTS, STREAM STANDARDS) IMPROVE INTERDEPARTMENTAL COOPERATION WITH REGARD TO INTEGRATING WATER QUALITY INTO SITE DEVELOPMENT COORDINATE COMPATIBLE USES BETWEEN PARKS AND WATER QUALITY FACILITIES ENHANCE COMPATIBILITY BETWEEN URBAN DESIGN GOALS AND WATER QUALITY FACILITIES IMPLEMENT EFFECTIVE, SUSTAINABLE, ATTRACTIVE, MULTI-PURPOSE, SAFE AND WELL-DESIGNED BMPS ENSURE LONG-TERM BMP OPERATION AND MAINTENANCE DEVELOP FINANCING AND INSTITUTIONAL STRATEGIES FOR REGIONAL BMPS

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Denver Water Quality Management Plan Executive Summary Page ES-3 4 Identification of stormwater BMPs that have been both successful and unsuccessful in the Denver area. The Project Team spent several days in the field visiting BMP sites in Denver. The strengths and weaknesses observed at these sites have been incorporated into the recommendations and strategies identified in this Plan. Photographs of many of these BMP sites are interspersed throughout this document. 4 Review of new stormwater BMP technology and approaches for potential applicability to Denver. Policy statements on new BMP technology such as underground proprietary treatment devices have been developed and provided in Chapter 6. Approaches that manage runoff close to the source and promote infiltration through landscape-based strategies are explored for more extensive application in the Denver area. Terms commonly used for these approaches include Minimizing Directly Connected Impervious Area, Smart Growth for Clean Water, and Low Impact Development. Circumstances under which new approaches may be considered are also identified. 4 Development of practical stormwater quality BMP implementation guidelines. As a result of the initial project tasks described above, the most significant need identified was practical guidance for implementing and managing stormwater quality in Denver. Chapters 6 and 7 provide this guidance, with the Stormwater Quality BMP Implementation Guidelines further summarized below. 4 Accommodation of periodic updates and revisions. Denver recognizes and intends that this Plan will be a living document that will need to be updated periodically to reflect changes in the Denver area, BMP technology, and various regulations and policy shifts. These updates will be posted on Denver s web site, www.denvergov.org The principles of adaptive management apply to this plan, as is the case for many related Denver planning documents. STORMWATER QUALITY BMP IMPLEMENTATION GUIDELINES A top priority identified through departmental interviews and Project Advisory Committee input was the need to provide clear guidance on how stormwater quality management could be effectively accomplished in a variety of development settings. To accomplish this task, the Project Team worked closely with the Project Advisory Committee to develop stormwater quality management strategies for seven common development types, including Ultra Urban, High Density Mixed Use, Campus, Industrial, Low Density Mixed Use, Residential, and Parks and Open Space Natural Areas. The Plan provides design recommendations for these development types addressing several factors:

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Executive Summary Executive Summary Page ES-4 1. Runoff reduction techniques to decrease runoff volume and reduce the Water Quality Capture Volume 2 requiring treatment. 2. BMPs to treat the Water Quality Capture Volume appropriate for the development type. 3. Flood detention methods to attenuate peak runoff from larger storm events on site. 4. More in depth guidance on specific aspects of BMP implementation. Sketches and photographs showing how design recommendations can be implemented on typical development sites help to communicate effective stormwater management strategies for the various development types. The Plan s recommended strategies build upon the BMPs in the Urban Drainage and Flood Control District s (UDFCD s) Urban Storm Drainage Criteria Manual, Volume 3 Stormwater quality BMP implementation guidelines for the various development types are further supplemented by implementation details for topics such as roof runoff treatment, stormwater management in parking lots, stormwater runoff distribution approaches, sediment removal traps and forebays, planting/vegetation considerations, and soils. BMP fact sheets describing grass buffers, grass swales, porous pavement, porous pavement detention, porous landscape detention, detention basins, and other approaches are also provided. Although detailed design guidance in the Urban Storm Drainage Criteria Manual, Volume 3 (UDFCD 1999) is not reproduced in this Plan, the fact sheets provide practical supplemental information for the BMPs on topics such as typical applications, operation and maintenance considerations, landscape considerations, retaining walls, vehicular access, outlets, etc. The final portion of Chapter 6 provides suggestions for better integrating BMP maintenance into stormwater quality planning and provides specific recommendations for maintenance of various BMPs. RECOMMENDATIONS AND CONCLUSIONS As is the case with cities throughout the country, Denver is faced with complex regulatory requirements with regard to water quality. Denver s Phase I Colorado Discharge Permit System (CDPS) permit specifies stringent requirements with which Denver must comply or face significant penalties. Fortunately, Denver already has many sound water quality requirements in place in the form of policies and regulations. Specific action items requiring additional work that are not currently included in existing Denver departmental programs are highlighted in Exhibit ES.3. An overall summary of recommendations for on-going and future water quality protection efforts by Denver follows. 2 The Water Quality Capture Volume is the quantity of stormwater runoff that must be treated in stormwater quality BMPs in Denver. This volume is equivalent to the runoff from an 80th percentile storm, meaning that 80 percent of the most frequently occurring storms are fully captured and treated and larger events are partially treated. In simple terms, this quantity is about half of the runoff from a 2-year storm.

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Denver Water Quality Management Plan Executive Summary Page ES-5 EXHIBIT ES.3 NEW ACTION ITEMS UPDATE DENVER SSTORM DRAINAGECRITERIA MANUAL AND STORMWATER QUALITY CONTROL PLAN GUIDANCE TO REFLECT THE POLIC IES, STRATEGIES AND RECOMMENDATIONS OF THIS PLAN UPDATE DENVER S STORM SEWER EASEMENT AND INDEMNITY AGREEMENT TO IDENTIFY SPECIFIC BMP MAINTENANCE REQUIREMENTS EXPAND INTERDEPARTMENTAL AND CITYWIDE PUBLIC EDUCATION ON STORMWATER QUALITY MANAGEMENT CONDUCT A FEASIBILITY STUDY OF POTENTIAL REGIONAL STORMWATER QUALITY FACILITY LOCATIONS COMPLETE REGIONAL BMP FINANCING ALTERNATIVES ANALYSIS CONDUCT WATERSHED-BYWATERSHED WATER QUALITY ASSESSMENTS DEVELOP EASY-TO-UNDERSTAND BMP MAINTENANCE GUIDANCE DOCUMENT(S) SPONSOR PILOT-TESTING OF INNOVATIVE BMPS IN DENVER 1. All new and redevelopment projects must address water quality in their development plans, complying with the stormwater policies and design criteria specified in the Urban Storm Drainage Criteria Manual, Volumes 1-3 (UDFCD 1999, 2001) and in Denver s CDPS permit. Particularly critical is the four-step BMP planning process that requires: 4 Implementing stormwater runoff reduction practices. 4 Providing treatment of the Water Quality Capture Volume. 4 Implementing streambank and channel stabilization techniques for any drainageways within or adjacent to a project site. 4 Providing additional treatment for pollution hot spots. 2. Under Denver s CDPS permit, adverse impacts to receiving waters posed by urban stormwater discharges must be minimized to the maximum extent practicable. 3 Examples of these adverse impacts can include increased pollutant loading, increased runoff rates and volumes, channel instability, modification of aquatic habitat and increased sediment loading, both during and after construction. It is essential to recognize that, despite the best efforts to control stormwater runoff, there will be some change in receiving water characteristics due to development; therefore, a zero impact policy is not realistic or attainable. As a result, Denver advocates management of stormwater through the implementation of BMPs designed in accordance with the guidelines established by UDFCD (UDFCD 1999, 2001), as summarized in #1, above. 3 See the Glossary for the regulatory definition of maximum extent practicable.

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Executive Summary Executive Summary Page ES-6 3. Denver will continue to advocate the use of multiple BMPs, including non-structural measures, source controls, and structural BMPs, to reduce stormwater pollution. Whenever practicable, combining BMPs in series can be very effective in reducing stormwater pollution. 4. The stormwater quality BMP implementation guidelines provided in Chapter 6 of this Plan will be shared with developers and city staff alike to promote better integration of water quality into site designs, including more substantial use of runoff reduction techniques. 5. Denver will work to ensure that water quality is addressed in the very beginning of the site development process so that stormwater quality BMPs are better and more cost effectively integrated into site designs. Various Denver departments (e.g., Public Works, Planning, Parks, Environmental Health) must work together with a shared vision of stormwater quality management to accomplish this goal. 6. Urban stormwater management must be an integral part of site design and take into consideration multiple objectives. As stated in the Urban Storm Drainage Criteria Manual, Volume 1 (UDFCD 2001), the many competing demands placed on space and resources require that stormwater management strategies take into account water quality enhancement, groundwater recharge, recreation, wildlife habitat, wetland protection, protection of landmarks/amenities, control of erosion and sediment deposition, and creation of open space. In addition, the appearance of BMPs is particularly important; Denver will expect to receive site development plans that feature attractive BMPs that will be viewed as assets by the community. Denver will encourage multi-purpose usage of BMPs; however, compatibility among uses must be demonstrated (e.g., compatibility between recreational areas and detention areas). 7. Planning for water quality must proceed hand-in-hand with drainage planning for quantity (rate and volume). In urban areas, these two planning efforts are inseparable. When these issues are addressed together and early in the site planning process, more efficient, economical and attractive land uses generally result. 8. Denver will continue to review BMP designs for pubic safety and maintenance accessibility, maintainability, documentation of maintenance requirements and schedule, and assured long-term funding for maintenance. Proper maintenance is fundamental to public safety and long-term effectiveness of stormwater BMPs; therefore, Denver will take these steps to promote better long-term maintenance of BMPs: 4 Require inclusion of a simple BMP maintenance plan as part of Denver s Stormwater Quality Control Plan submittal requirements. 4 Require a legally binding description of BMP maintenance requirements and arrangements as part of development plan approval. 4 Clearly identify BMP maintenance requirements in forthcoming updates to Denver s Storm Drainage Criteria Manual

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Denver Water Quality Management Plan Executive Summary Page ES-7 4 Prepare easy-to-understand maintenance guidance documents and brochures for both pubic and private facility owners. These documents will be based on maintenance recommendations of UDFCD and the guidelines provided in Chapter 6 of this Plan. 9. The same stormwater quality management expectations and practices that apply to projects in the private sector also apply to projects that are the responsibility of Denver, such as buildings, parks, streets, utilities, etc. When Denver is preparing plans for any such projects or managing, maintaining and/or upgrading existing facilities, potential adverse stormwater quality effects must be evaluated and suitably mitigated. 10. Denver will continue to actively participate in regional water quality management efforts such as those being conducted by South Platte Cooperative for Urban River Evaluation (CURE), the Cherry Creek Basin Stewardship Partners, and the Barr Lake-Milton Reservoir Watershed Group. These on-going efforts emphasize the importance of Denver partnering with neighboring communities to tackle difficult water quality issues. Denver must also stay abreast of forthcoming regulatory changes that affect management of the many lakes and streams within its boundaries. 11. Denver s stormwater management strategies must be consistent with the principles, criteria, and priorities in its multiple planning and technical criteria documents, as described in Chapter 4. 12. Denver will work to remove obstacles to innovative stormwater management approaches by reviewing regulations and codes and, where practical, modifying requirements that conflict with the principles of this Plan. For example, such conflicts may arise with regard to parking lot and curb and gutter design requirements relative to some Low Impact Development approaches. 13. Denver will continue to promote managing and treating stormwater quality using aboveground facilities, rather than in subsurface, vault-type treatment devices. Nevertheless, Denver recognizes that there are some cases where the use of such facilities is necessary due to extreme space constraints in smaller redevelopment sites, such as those located in the downtown area. 14. Denver will evaluate the feasibility of collaborating with UDFCD, a university, other local governments, and other organizations to pilot-test innovative BMPs. Denver will continue to actively partner with UDFCD to develop design guidance for new BMPs for the Denver area. 15. Denver will continue to educate the public on stormwater quality issues. Additional opportunities for Denver s existing public education program include: 4 Provide additional educational brochures and water pollution prevention resources on the Denver website. For example, as discussed in Chapter 5, many of the national case studies provide extensive web resources.

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Executive Summary Executive Summary Page ES-8 4 Develop pollution prevention programs for specific industries that require further attention and/or partner with entities providing existing programs. For example, the City of Boulder s Partners for a Clean Environment (PACE) program targets and provides educational information to specific industry segments including auto repair, auto body, green building, dental offices, dry cleaning, landscaping, manufacturing, printing, restaurant, and retail sectors. The City of Portland has a similar program. As an alternative to independently developing such programs, Denver can partner with professional organizations and industry groups to support their efforts in this type of training. 4 Educate developers and Denver staff on the benefits of land management strategies such as open space/natural areas preservation and/or restoration, riparian buffer zone protection, Smart Growth, Green Development, and Low Impact Development strategies. 4 Continue educational campaigns on specific measures to minimize pollution at its source. These efforts will include a multi-faceted approach directed to the public, Denver staff and elected officials, and neighboring communities. 16. Based on an initial reconnaissance level evaluation (as described in Chapter 8), there are promising opportunities for regional water quality BMPs, including large retention basins and wetlands, that could reduce impacts to downstream receiving waters. Methods to finance the development and maintenance of these facilities are urgently needed. In addition, Denver will proceed with more detailed citywide planning to identify and prioritize regional BMP alternatives. As a part of any regional facility evaluation, it will be important to clearly define under what circumstances a developer can have their requirement for onsite water quality treatment waived (e.g., paying a fee-in-lieu-of treatment) due to regional treatment facilities. 17. Closely related to regional water quality facilities is the need to conduct a watershed-bywatershed evaluation of current stream and lake conditions, including steps that are necessary to improve the status quo. The purpose of such an evaluation is to identify watershed-specific goals, priorities, data gaps and practicable mitigation measures that could be developed to strategically improve conditions. It is logical to focus initially on 303(d)-listed streams (i.e., those that are considered to be impaired for one or more pollutants) and to work closely with existing efforts such as those of South Platte CURE, the Barr-Milton Watershed Group, and Denver Public Works and Environmental Health. 18. Denver will continue to monitor approaches used throughout the country related to stormwater and watershed management. Lessons learned from case studies evaluated in this Plan will be kept in mind during decision-making and planning for Denver. Examples of common themes from communities with advanced stormwater programs include: 4 Comprehensive approaches are being used to address drainage, flooding, erosion, aquatic life, native habitat, and water quality in an integrated manner.

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Denver Water Quality Management Plan Executive Summary Page ES-9 4 Watershed-based approaches are being used for planning and problem solving. 4 Geographic Information System (GIS) tools are being used effectively to prioritize stormwater improvements and to more effectively communicate to citizens, staff, and developers. 4 Storm runoff volume reduction practices are being used in many of these communities. These practices include a variety of runoff reduction techniques such as grass buffers and swales, green roofs, and other landscape-based approaches. 4 The importance of sound long-term maintenance of BMPs is widely recognized, as is the need to provide pubic safety at drainage facilities. 4 Strong public education and outreach campaigns in combination with extensive web sites are substantive components of these programs. Education is being aggressively used as a key strategy to improve runoff quality. 4 Significant financial investments, often measured in millions of dollars, have been required for many communities to conduct their stormwater quality planning efforts. These communities recognize that comparable future expenditures will be required to implement their plans, and are implementing suitable methods of financing. 19. Because the water quality challenges facing Denver will require significant funding, new and potentially innovative financing strategies that capitalize on public/private partnerships will be investigated. 20. Although this Plan provides a solid framework and foundation for effective stormwater quality management in Denver, follow-up implementation measures are needed to ensure that the principles and practices set forth in this Plan are implemented throughout Denver. An initial implementation plan specifying target timeframe, activities, responsible departments, and approximate costs has been developed in Chapter 9 of this Plan.

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Chapter 1 Page 1-1 EXHIBIT 1.1 THE SOUTH PLATTE RIVER: AN URBAN AMENITY Source: The Greenway Foundation Chapter 1 INTRODUCTION Protecting and enhancing water quality has long been an important objective in the City and County of Denver (Denver). Additionally, Denver is obligated under penalty of law to comply with the requirements of its Colorado Discharge Permit System (CDPS) municipal stormwater discharge permit. A stronger push towards clean water in Denver has been prompted by recent changes such as: 4 Current and anticipated federal and state regulatory and CDPS permit requirements. 4 The water quality improvement goals of Mayor Hickenlooper and his Administration. 4 Increased recognition of the economic, ecological and social importance of water features for Denver residents, businesses and visitors. 4 The need to protect natural resources, including preservation of open space, due to population growth. 4 Recognition of the public health, safety and welfare implications of stormwater management programs and facilities. 4 Proliferation of new approaches for protecting and improving water quality. When looking at Denver as a whole, a key influence on stream and lake water quality is urban stormwater runoff from rainfall and snowmelt the water that runs off streets, parking lots, buildings, ball fields, industrial/commercial sites, residential neighborhoods, etc. Without control measures, or Best Management Practices (BMPs), urban runoff typically adversely affects the physical, chemical and biological characteristics of streams, lakes and wetlands. For example, without mitigation, increased runoff volumes and peak discharges commonly associated with urbanization often cause stream channels to degrade through widening, deepening, accumulation of unsightly sediment deposits, significant modification to aquatic habitat, and other impacts. Elevated concentrations of substances such as gasoline and diesel fuel, oil, grease, fertilizer, heavy metals,

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Introduction Chapter 1 Page 1-2 pesticides, and pet waste can be harmful to aquatic life, native plants and wildlife and/or impair the ability of waterways to support recreation, industrial and municipal water supply, and other beneficial uses. This chapter defines the purpose, approach, guiding principles, opportunities and challenges, overview, and scope limitations of this Plan, which has been developed to create a framework to enable Denver to address current and future challenges posed by urban runoff. PURPOSE AND GOALS The purpose of this Denver Water Quality Management Plan (Plan) is to advance a framework for better integrating stormwater management and water quality protection into planning, engineering, and infrastructure management for Denver. This Plan will serve as a common authoritative reference identifying Denver s commitments, priorities, and strategies for protecting its rivers, streams, lakes, and wetlands from the adverse impacts of urban stormwater runoff. In addition, the Plan provides a practical initial strategy for managing stormwater runoff quality in the near term, while laying the groundwork for a long-term vision. This Plan is relevant to Denver staff, land developers undertaking new or redevelopment projects, other parties conducting activities that impact urban runoff, and citizens who want to support water quality protection in the Denver area. The primary goals of this Plan follow. Goal 1: Develop a Framework and Shared Vision for Meeting Denver s Stormwater Quality Requirements and Goals As is the case in many cities, decision-making in Denver is shared across multiple departments and guided by many rules and regulations with inherently different goals and priorities. Water quality-related issues have historically been addressed primarily through departments such as Public Works and Environmental Health; however, due to the advent of the Phase I stormwater regulation 1 water quality-related issues are increasingly relevant to Parks and Recreation, Community Planning and Development, Asset Management, and other Denver departments. 1 The U.S. Environmental Protection Agency (EPA) issued the Phase I stormwater regulations requiring National Pollutant Discharge Elimination System (NPDES) point source permit coverage for stormwater discharges from: (1) medium and large Municipal Separate Storm Sewer Systems (MS4s) generally serving populations of 100,000 or greater; (2) construction activity disturbing 5 or more acres of land; and (3) 10 categories of industrial activity. EXHIBIT 1.2 PLAN GOALS DEVELOP A FRAMEWORK AND SHARED VISION FOR MEETING DENVER S STORMWATER QUALITY R EQUIREMENTS AND GOALS DEVELOP BMP STRATEGI ES THAT WORK IN VARIOUS DENVER SETTINGS DEVELOP A COMMON FOUNDATION FOR INTERDEPARTMENTAL UNDERSTANDING OF STORMWATER QUALITY REQUIREMENTS AND THEIR ROLE IN THE PLANNING PROCESS DEVELOP A FRAMEWORK AND PRIORITIES FOR FUTUR E WORK NEEDED TO MEET GOALS

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Denver Water Quality Management Plan Chapter 1 Page 1-3 EXHIBIT 1.3 KENNEDY SOCCER COMPLEX DETE NTION BASIN A primary goal of this document is to develop a shared vision for achieving Denver s water quality protection requirements under its CDPS stormwater permit. This permit identifies specific requirements intended to decrease the adverse impacts of stormwater discharged from Denver s municipal separate storm sewer system (MS4). This permit clearly identifies binding provisions and serious penalty clauses if violated and essentially states that Denver must aggressively address the problems caused by urban stormwater discharges. State stream standards help to assess whether receiving waters in Denver meet their designated uses such as recreation, aquatic life, and water supply. In the event that streams receiving stormwater discharges from Denver do not meet state-designated stream standards, Denver will likely be required to enter into a more comprehensive regulatory process with additional requirements under the Total Maximum Daily Load (TMDL) process (as discussed in Chapter 3). In addition to purely regulatory-driven requirements, water quality protection and improvement has been identified as an important goal in the Denver Comprehensive Plan 2000 (Denver 2000), Cherry Creek Greenway Corridor Master Plan (BRW 2000), Natural Areas Program Field Guide (Denver Parks and Recreation 2004), Design Guidelines for Stapleton Water Quality (Denver 2001), and others. For these reasons, water quality protection and improvement are not only legal requirements, but also high priorities for a city known for its natural beauty. Developing a shared citywide vision and framework will help Denver to achieve its water quality protection goals. Goal 2: Develop BMP Strategies that Work in Various Denver Settings Denver s Phase I stormwater permit requirements are based on both structural and non-structural BMPs to minimize the impacts of urban runoff. Design criteria for stormwater management practices appropriate for Denver have been clearly defined in the Urban Storm Drainage Criteria Manual, Volumes 1 through 3 (UDFCD 1999, 2001) and adopted into Denver s Storm Drainage Design and Technical Criteria Manual (Denver 1992). While these documents provide sound engineering guidance on designing these BMPs, less information has been provided on how to best integrate these types of BMPs into specific settings likely to be found in Denver. The Design Guidelines for Stapleton Water Quality were successful in helping achieve an integrated water quality plan for the Stapleton Redevelopment area; therefore, this Plan has used a similar approach to provide BMP implementation guidelines for the entire city. To achieve the goal of developing BMP strategies that work in various settings, this Plan assesses a The final Phase II storm water regulations were published in December 1999 and require NPDES permit coverage for construction activities that disturb 1 to 5 acres and for regulated small MS4s.

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Introduction Chapter 1 Page 1-4 variety of existing and new BMPs and identifies implementation strategies appropriate for development types in Denver. These BMP strategies build on the Urban Storm Drainage Criteria Manual, Volumes 1-3 (UDFCD 1999, 2001), providing additional information on how BMPs can best be integrated into and be more effective for various development types. To the extent possible, the development types in this Plan are consistent with those found in the city s planning document, Blueprint Denver (Denver 2000). Goal 3: Develop a Common Foundation for Interdepartmental Understanding of Stormwater Quality Requirements and Their Role in the Planning Process In order for any water quality protection strategy to be effective, it needs to be clearly documented, understood, accepted, and implemented across city departments. The strategies in this Plan have been developed based on input from multiple city departments to identify concerns and priorities related to water quality. Early integration of water quality requirements into site designs has been identified as critical for development and redevelopment projects. This Plan is intended to provide a common base of understanding across city departments to facilitate more effective integration of water quality requirements. This Plan also contains a glossary of key terminology to facilitate a common understanding of key concepts by users with varied backgrounds. Concurrent with development of this Plan, the development review process was undergoing review and revision; therefore, additional work will likely be needed to ensure that the priorities of this Plan are integrated into the development review process. Goal 4: Develop Framework and Priorities for Future Work Needed to Meet Goals The Wastewater Management Division s initial vision for this Plan identified many potential topics to be addressed. It was not possible to cover all of these topics in detail; therefore, a key goal of this Plan has been to identify topics and issues that will be important to the future of Denver s water quality management strategy, but that were beyond the scope of this document. Recommendations and an initial implementation plan for future work on these topics have been included in the Chapter 9 of this Plan. Representative topics include a watershed-by-watershed assessment of water quality conditions, identification of specific locations for potential future regional water quality treatment facilities, and exploration of funding alternatives for providing regional water quality facilities. APPROACH This Plan has been developed using a multi-faceted approach to ensure that a practical and innovative strategy for addressing water quality is developed for Denver. Multiple interviews and meetings were conducted with key Denver staff to develop a Plan that will be beneficial to many Denver departments. Key aspects of the project approach include: 4 Extensive collaboration among multiple city departments. Acceptance and use of this Plan across city departments is critical to the success of this Plan. This document has been developed through close collaboration and frank discussion among multiple

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Denver Water Quality Management Plan Chapter 1 Page 1-5 EXHIBIT 1.4 STORMWATER BMPS SHOULD BE DESIGNED AND MAINTAINED TO PROTECT PUBLIC HEALTH AND AVOID NUISANCE CONDITIONS departments within Denver including Public Works, Parks and Recreation, Community Planning and Development, Environmental Health, and the City Attorney s Office. By working together to prepare this Plan, a more unified position and vision for stormwater quality management has emerged. 4 Identification and review of regulations and existing Denver planning documents affecting or interfacing with stormwater quality management strategies in Denver. Many existing and proposed federal, state and local water quality regulations directly influence stormwater quality management in Denver. Key regulations were inventoried and described in order to provide a common basis for understanding stormwater quality management requirements. Similarly, Denver has many excellent planning documents and programs that help guide planning and watershed management decisions. In order to avoid reinventing the wheel, a review of these key documents was completed. 4 Review of similar efforts in communities with advanced stormwater programs. Communities throughout the country are reassessing their approach to stormwater and watershed management. Early in the development of this Plan, five communities were identified to explore their approaches, successes and difficulties in addressing urban runoff. Interviews and review of key documents were conducted for these communities: Portland, Oregon; San Diego, California; Austin, Texas; Prince George s County, Maryland; and Snohomish County, Washington. Findings from this research have been taken into account in development of this Plan with regard to general approach, as well as for recommendations for specific BMPs. 4 Identification of stormwater BMPs that have been both successful and unsuccessful in the Denver area. The Project Team spent several days in the field visiting BMP sites in Denver. The strengths and weaknesses observed at these sites have been taken into account in the recommendations and strategies identified in this Plan. Photographs of many of these BMP sites (both good and bad) are interspersed throughout this Plan. 4 Review of new stormwater BMP technology and approaches for potential applicability to Denver. Policy statements on new BMP technology such as underground proprietary treatment devices have been developed and provided in Chapter 6. Approaches that manage runoff close to the source and promote infiltration through landscape-based strategies are explored for more extensive application in the Denver area. Terms commonly used for these approaches include Minimizing Directly Connected Impervious

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Introduction Chapter 1 Page 1-6 EXHIBIT 1.5 QUESTIONS CONSIDERED DURING PLAN DEVELOPMENT 4 What stormwater quality requirements apply to development and redevelopment sites? 4 What are the key regulatory requirements that are prompting mandatory implementation of BMPs on new development and redevelopment sites? Are these requirements anticipated to change in the future and, if so, in what ways? 4 What factors influence BMP selection for a given site? 4 What selection process should be utilized to determine the most appropriate BMP plan for a particular site? 4 What performance criteria or standards apply, if any? 4 How do stormwater quality requirements interface with more traditional drainage and flood control requirements? 4 To what extent can Denver parks and natural area open spaces be utilized for stormwater quality management? What precautions need to be taken to assure that stormwater management does not impair intended park or natural area open space uses? 4 How can BMPs be planned, designed and maintained to be viewed as community assets rather than liabilities? 4 How should the BMP selection and design process account for issues such as public safety, maintenance, environmental permitting, and others? Area, Smart Growth for Clean Water, and Low Impact Development. Circumstances under which new approaches may be considered are also identified. 4 Development of practical stormwater quality BMP implementation guidelines. As a result of the initial project tasks described above, the most significant need identified was practical guidance for implementing and managing stormwater quality in Denver. Chapters 6 and 7 provide this guidance. Representative questions considered as part of development of this guidance are summarized in Exhibit 1.5 4 Accommodation of periodic updates and revisions. Denver recognizes and intends that this Plan will be a living document that will need to be updated periodically to reflect changes in the Denver area, BMP technology, and various regulations and policy shifts. These updates will be posted on Denver s web site, www.denvergov.org The principles of adaptive management apply to this plan, as is the case for many related Denver planning documents.

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Denver Water Quality Management Plan Chapter 1 Page 1-7 PRINCIPLES AND POLICIES Early in development of this Plan, the Project Advisory Committee and the Project Team agreed on several foundational principles and policies, including: 4 All new and redevelopment projects must address water quality in their development plans, complying with the stormwater policies and design criteria specified in the Urban Storm Drainage Criteria Manual, Volumes 1-3 (UDFCD 1999, 2001) and in Denver s CDPS permit. Particularly critical is the four-step BMP planning process that requires: 1. Implementing stormwater runoff reduction practices. 2. Providing treatment of the Water Quality Capture Volume. 3. Implementing streambank and channel stabilization techniques for any drainageways within or adjacent to a project site. 4. Providing additional treatment for pollution hot spots. 4 Under Denver s CDPS permit, adverse impacts to receiving waters posed by urban stormwater discharges must be minimized to the maximum extent practicable. Examples of these adverse impacts can include increased pollutant loading, increased runoff rates and volumes, channel instability, modification of aquatic habitat and increased sediment loading, both during and after construction. It is essential to recognize that, despite the best efforts to control stormwater runoff, there will be some change in receiving water characteristics due to development; therefore, a zero impact policy is not realistic or attainable. As a result, Denver advocates management of stormwater through the implementation of BMPs designed in accordance with the guidelines established by UDFCD (UDFCD 1999, 2001), as summarized above. 4 Denver will continue to advocate the use of multiple BMPs, including non-structural measures, source controls, and structural BMPs, to reduce stormwater pollution. Whenever practicable, combining BMPs in series can be very effective in reducing stormwater pollution. 4 Urban stormwater management must be an integral part of site design and take into consideration multiple objectives. As stated in the Urban Storm Drainage Criteria Manual, Volume 1 (UDFCD 2001), the many competing demands placed on space and resources require that stormwater management strategies take into account water quality enhancement, groundwater recharge, recreation, wildlife habitat, wetland protection, protection of landmarks/amenities, control of erosion and sediment deposition, and creation of open space. In addition, the appearance of BMPs is particularly important; Denver will expect to receive site development plans that feature attractive BMPs that will be viewed as assets by the community. Denver will encourage multi-purpose usage of BMPs; however, compatibility among uses must be demonstrated (e.g., compatibility between recreational areas and detention areas).

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Introduction Chapter 1 Page 1-8 Source: The Greenway Foundation. EXHIBIT 1.6 ATTRACTIVE GRADE CONTROL STRUCTURE ON THE SOUTH PLATTE RIVER HELPS TO REDUCE THE IMPACTS OF URBANIZATION 4 Planning for water quality must proceed hand-in-hand with drainage planning for quantity (rate and volume). In urban areas, these two planning efforts are inseparable (UDFCD 2001). When these issues are addressed together and early in the site planning process, more efficient, economical and attractive land uses generally result. 4 Water quality must be addressed in the very beginning of the site development process to ensure that water quality BMPs are incorporated into the site design. Benefits of this practice include better site designs and more cost-effective BMPs. 4 Denver will continue to review BMP designs for pubic safety and maintenance accessibility, maintainability, documentation of maintenance requirements and schedule, and assured long-term funding for maintenance. Proper maintenance is fundamental to public safety and long-term effectiveness of stormwater BMPs. 4 Denver strongly prefers managing and treating stormwater quality on the ground surface, rather than in subsurface, vault-type treatment devices. Nevertheless, Denver recognizes that there are some cases where the use of such facilities is necessary. For example, this approach may be acceptable in cases of extreme space constraints that occur on smaller redevelopment sites, which are essentially completely impervious in their current condition, such as some locations in the downtown area. Chapter 6 provides specific guidance on the conditions under which these types of treatment devices may be considered. 4 The same stormwater quality management expectations and practices that apply to projects in the private sector also apply to projects that are the responsibility of Denver, such as buildings, parks, streets, utilities, etc. When Denver is preparing plans for any such projects or managing, maintaining and/or upgrading existing facilities, potential adverse stormwater quality effects must be evaluated and suitably mitigated.

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Denver Water Quality Management Plan Chapter 1 Page 1-9 EXHIBIT 1.7 STORMWATER QUALITY MANAGEMENT OPPORTUNT IES AND CHALLENGES ADDRESS WATER QUALIT Y ISSUES (E.G., 303(D) LISTED SEGMENTS, STREAM STANDARDS) IMPROVE INTERDEPARTMENTAL COOPERATION WITH REGARD TO INTEGRATING WATER QUALITY INTO SITE DEVELOPMENT COORDINATE COMPATIBLE USES BETWEEN PARKS AND WATER QUALITY FACILITIES ENHANCE COMPATIBILITY BETWEEN URBAN DESIGN GOALS AND WATER QUALITY FACILITIES IMPLEMENT EFFECTIVE, SUSTAINABLE, ATTRACTIVE, MULTI-PURPOSE, SAFE AND WELL-DESIGNED BMPS ENSURE LONG-TERM BMP OPERATION AND MAINTENANCE DEVELOP FINANCING AND INSTITUTIONAL STRATEGIES FOR REGIONAL BMPS OPPORTUNITIES AND CHALLENGES A primary goal of this Plan is to develop a framework for managing runoff water quality in a manner that is not only effective, but that also takes into consideration the goals of the many city departments and citizens. For these reasons, the Project Team worked closely with an interdepartmental advisory committee and conducted multiple interviews to identify key concerns and priorities of various city departments. As a result, several key opportunities and challenges emerged for this Plan that are summarized in Exhibit 1.7 and discussed in more detail below. This Plan provides a framework for addressing these challenges. Address Water Quality Issues Portions of the South Platte River, Sand Creek, Berkley Lake, and other Denver waterbodies do not currently meet state stream standards for one or more constituents, resulting in listing of waterbodies on the state s 303(d) list. (See Chapter 3 for more information.) In addition, continued growth will apply increasing pressure on water quality. Working towards attainment of water quality standards and complying with Denver s stormwater CDPS permit are high priorities for Denver and have been strongly emphasized by the Public Works Department and the Mayor s office. Chapters 6 and 7 of this Plan provide structural and non-structural BMP strategies that can be used to help Denver improve the quality of urban runoff. In addition, stormwater quality BMP implementation guidelines for a variety of land use types are provided to aid developers and planners in selecting strategies that work in various settings. Recommendations regarding future watershed-bywatershed assessments of water quality are also identified in Chapter 9 as an important step to developing and/or advancing basin-specific approaches to water quality issues facing Denver. Improve Interdepartmental Cooperation With Regard to Water Quality Stormwater quality treatment requirements are best integrated into the early stages of site design. In many cases, stormwater treatment requirements have

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Introduction Chapter 1 Page 1-10 not been considered early in the site design, resulting in few effective options for treatment, or installation of unattractive, unsafe, and unmaintainable facilities that become public nuisances, rather than amenities. Community Planning and Development, Parks and Recreation, and Public Works all recognize the importance of early discussion regarding water quality treatment requirements and plans. The stormwater quality BMP implementation guidelines provided in Chapter 6 will help provide developers and planners with reasonable approaches to stormwater treatment that take into consideration multi-departmental goals. Interdepartmental communication and understanding regarding the legal obligations that Denver has under its CDPS stormwater permit are vitally important to encouraging departments to work cooperatively toward meeting these requirements. Chapter 3 of this Plan provides a common foundation regarding Denver s obligations under its stormwater permit, along with implications of anticipated future regulatory changes. Coordinate Compatible Uses Between Parks and Water Quality Facilities Parks, golf courses and natural areas open space are often viewed as opportunities for stormwater detention; however, it is critical that the uses of these areas be taken into account to ensure that usage conflicts are minimized. For example, areas used as soccer fields or golf courses need to drain within a reasonable timeframe to prevent soggy fields that are incompatible with recreational use. Other park and BMP conflicts may relate to safety in areas used for child play, West Nile virus concerns, and/or protection and enhancement of wildlife. This Plan recognizes that conflicts between parks and stormwater BMPs exist in some locations in Denver and care must be taken in the future when selecting, designing, and maintaining BMPs in parks. Public input and acceptance of stormwater BMPs in parks is particularly important, as is public education on the purposes of BMPs. The BMP fact sheets provided in Chapter 6 identify considerations to be taken into account when choosing various BMPs and can provide a starting point to reduce conflicts between park and BMP functions. Enhance Compatibility Between Urban Design Goals and Water Quality Facilities Blueprint Denver (Denver 2000) provides a clear vision for Denver s development goals. The Community Planning and Development Department, with the assistance of other Denver departments, has the responsibility of moving Denver towards meeting these goals. In some cases, stormwater BMPs can be difficult to fit into site designs that conform with these design goals. For this reason, interdepartmental agreement regarding BMP design and integration into various settings is important. Chapter 6 provides templates of possible site layouts with BMPs integrated into the designs of various development types. In some cases, on-site stormwater facilities are challenging due to space constraints; in these cases, opportunities for regional stormwater facilities should be explored. Chapter 8 provides conceptual-level locations where regional facilities warrant further exploration.

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Denver Water Quality Management Plan Chapter 1 Page 1-11 EXHIBIT 1.8 SAFE, ATTRACTIVE, MAINTAINABLE INFILTRATION BASIN Implement Effective, Sustainable, Attractive, Multi-purpose, Safe, and WellDesigned BMPs Denver s CDPS stormwater permit, Denver s Storm Drainage Design and Technical Criteria Manual (Denver 1992) and other documents specify water quality treatment requirements for new development and redevelopment projects. In addition to meeting the technical requirements for these BMPs, the Project Advisory Committee and city department staff interviewees agreed that these BMPs also must be sustainable, attractive, multi-purpose, safe, and well-designed (Exhibit 1.8). Ensuring that these requirements and goals are met and that BMPs are maintained on a long-term basis is critical for Denver to successfully minimize the impacts of urban runoff. Many examples of BMPs that do and do not meet these criteria were identified and visited during the development of this Plan. Early consideration of water quality requirements in the site design can help prevent water quality BMPs from being an afterthought, which may result in poor BMP design and implementation. Chapter 6 identifies specific considerations when selecting BMPs that provide a foundation for more sustainable, attractive, multi-purpose, safe and well-designed BMPs. Ensure Long-term BMP Operation and Maintenance Even when BMPs are thoughtfully designed and properly installed, they can become eyesores, breed mosquitoes, and cease to function if not properly maintained. BMPs can be more effectively maintained when they are designed to allow easy access for inspection and maintenance and take into consideration factors such as property ownership, easements, visibility from easily accessible points, slope, vehicle access, and other factors. Clear, legally-binding written agreements assigning maintenance responsibilities and committing adequate funds for maintenance are also critical. Chapter 3 describes Denver s requirements for BMP maintenance, and Chapter 6 provides BMP maintenance recommendations. In addition, Chapter 5 describes how other communities such as Portland, Oregon have invested in easy-to-understand guidance documents for BMP maintenance that are useful for both private and public owners of BMPs. Develop Financing and Institutional Strategies for Regional BMPs The concept of regional stormwater facilities is supported across Denver departments, particularly in redevelopment areas where land is unavailable or at a premium cost. The challenges to implementing regional BMPs lie in three key areas: 1) institutional constraints, 2) land availability, and 3) financing. Chapter 8 provides a conceptual-level assessment of Denver drainages where regional facilities may be realistic. In order to take advantage of these

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Introduction Chapter 1 Page 1-12 opportunities, a sound financing strategy must be developed. This can be challenging, particularly in areas where development is phased over a number of years. Chapter 9 recommends future work to help develop financing strategies for regional BMPs, including a discussion of institutional opportunities and constraints. SCOPE LIMITATIONS In order to develop a meaningful document, the width of this Plan s scope has been limited to enable increased depth on key subject areas. Related water quality and watershed management topics that are not covered or are only briefly covered in this document include: 4 Construction site stormwater management. Construction site stormwater management is a critical component of protecting receiving waters and a key requirement of Denver s stormwater CDPS permit. Strong existing guidance on construction site stormwater management is provided by UDFCD, Denver, the Colorado Department of Public Health and Environment (CDPHE), and numerous other entities and is not repeated herein; instead, the focus of this Plan is on permanent, post-development stormwater management strategies. 4 Sanitary wastewater discharges and sanitary sewer overflows. Although sanitary wastewaster discharges and sanitary sewer overflows (SSOs) are critical aspects of addressing water quality issues in receiving waters, these discharges are believed to be effectively addressed through CDPS permits. For specific water quality problems caused by a combination of wastewater, stormwater, and nonpoint source discharges, an interface with sanitary wastewater discharges will be required under pollutant load allocations under the TMDL process. (See Chapter 3 for more information.) 4 Detailed design criteria for stormwater BMPs. This document is not intended to be a design manual. To the contrary, excellent BMP design guidance exists in Volume 3 of the Urban Storm Drainage Criteria Manual (UDFCD 1999), along with other references (e.g., WEF and ASCE 1992 and 1998; CASQA 2003; City of Portland 2002). 4 Stream channel morphology, sediment transport and channel stabilization and restoration practices. Topics excluded from discussion include use of turf reinforcement mats, geotextiles, and other comparable materials in drainage channels, other channel stabilization measures including bioengineering techniques, hydraulic structures such as energy dissipaters downstream of bridge and culverts, grade control structures, drop structures, etc. Many of these practices either directly or indirectly contribute to stream channel stability and favorable water quality; however, they were deemed to be beyond the scope of this document. 4 Detailed regional water quality facility master planning. Although an initial glimpse of potential regional water quality BMPs that could be used in Denver s primary drainage areas is provided in Chapter 8, it was beyond the scope of this Plan to address facility master planning in detail. Follow-up work needed for such an effort is defined in Chapter 9.

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Denver Water Quality Management Plan Chapter 1 Page 1-13 4 Receiving Water Impact Assessment. Detailed guidance on this topic is beyond the scope of this Plan. This Plan assumes that in most cases involving typical urban stormwater discharges from development and redevelopment sites, site-specific impact assessments will not be necessary, provided that practices specified in the Urban Storm Drainage Criteria Manual (UDFCD 1999, 2001) are implemented. 4 Development of Financing Strategies for Regional BMPs. Realistic and well-thoughtout financing strategies for regional BMPs are necessary for the success of any regional BMP. Exploration of these financing strategies was beyond the scope of this document, but has been recommended as a future task in Chapter 9 of this Plan. 4 Life Cycle Cost Analysis. Detailed BMP cost data were not included in this Plan. The concept of life cycle costs for BMPs is relevant to BMP selection because it takes into consideration the design, construction, maintenance and rehabilitation costs of the BMP over its expected lifetime. The reader is referred to references for more information on BMP costs in Chapter 6 of this Plan. PLAN OVERVIEW Given the purpose, goals, approach, foundational policies, and scope limitations that evolved during the course of this project, the Project Team and Advisory Committee determined that this Plan should address these topics: 4 Overview of key drainage basins in the Denver area. 4 Discussion of basic tenets of urban runoff impacts. 4 Discussion of key current and future regulatory drivers affecting stormwater and receiving waters. 4 Identification of key documents (e.g., Urban Storm Drainage Criteria Manual Volumes 1-3 Blueprint Denver ) that this Plan must interface with in order to be effective. 4 Identification of strategies that are successfully being used in other communities to address urban runoff. 4 Development of stormwater BMP implementation guidelines identifying how these BMPs can be integrated into various development types in Denver. 4 Development of BMP fact sheets, implementation details, and maintenance guidelines that identify how BMPs can be better implemented and maintained in Denver. 4 A broad-level assessment of potential regional water quality facility locations in Denver. 4 Identification of future tasks that need to be completed in order for Denver to achieve its water quality objectives.

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Chapter 2 Page 2-1 EXHIBIT 2.1 CHERRY CREEK NEAR THE CONFLUENCE WITH THE SOUTH PLATTE RIVER Source: The Greenway Foundation. Chapter 2 OVERVIEW OF MAJOR DENVER DRAINAGE BASINS AND POTENTIAL URBAN STORMWATER IMPACTS A common understanding of Denver drainage basins, lakes, and the potential adverse impacts of stormwater from urbanization is necessary for understanding and applying this Plan. This chapter provides an overview of these topics. OVERVIEW OF DENVER DRAINAGE BASINS The City of County of Denver includes approximately 155 square miles of land area (nearly 100,000 acres). Denver receives about 15 inches of rainfall and 55 inches of snowfall each year. Denver s drainageways receive runoff from approximately 190 square miles of land area, some of which is located outside of Denver s jurisdictional boundaries. The South Platte River is the major river basin receiving runoff from Denver, with Sand Creek and Cherry Creek being significant tributaries to the South Platte River (Exhibit 2.1). Relatively small reaches of Clear Creek and Bear Creek, which are also significant tributaries to the South Platte, traverse the northwest and southwest portions of Denver, respectively. While a watershed-by-watershed assessment of water quality issues is beyond the scope of this Plan, readily available basic information on these watersheds is available from the Denver Storm Drainage Master Plan (Matrix 2003) and other plans, as summarized in Exhibits 2.2 and 2.3. Specific opportunities for potential regional water quality facilities and more detailed hydrologic characterization of these drainage basins are discussed in Chapter 8.

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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts Chapter 2 Page 2-2 Exhibit 2.2 Major Denver Drainage Basins ID OUTFALL NAME/LOCATION AREA (mi 2 ) COMPOSITE IMPERVIOUSNESS 0058-01 South Platte River Prairie Gateway 1.59 25.0% 0059-01 South Platte River Globeville 3.72 51.4% 0060-01 South Platte River I-70 & Colorado Boulevard 2.73 68.7% 0060-02 South Platte River I-70 & York 1.47 71.8% 0061-01 South Platte River 27th & Federal 5.17 66.8% 0062-01 South Platte River Lower Platte Valley 2.73 77.5% 0063-01 South Platte River Central Platte Valley 2.10 83.2% 0064-01 South Platte River 1st & Federal 0.50 74.4% 0064-02 South Platte River Valverde 2.66 69.2% 0065-01 South Platte River Ruby Hill 1.25 70.1% 0065-02 South Platte River Dartmouth 0.76 86.8% 0067-01 South Platte River College View 1.29 21.7% 0067-02 South Platte River West Belleview 4.24 12.5% 0067-03 No Outfall Marston Lake 1.03 100.0% 3300 Third Creek Third Creek 16.36 40.1% 3500 Second Creek Second Creek 8.02 30.4% 3501-01 Second Creek West Fork Second Creek 3.37 36.8% 3700-01 First Creek 56th to 64th Avenue 5.36 33.4% 3700-02 First Creek 38th to 56th Avenue 2.92 60.6% 3702-01 First Creek Picadilly & 56th Avenue 1.34 78.0% 3900-01 Irondale Gulch North Stapleton 0.48 20.4% 3900-02 Irondale Gulch West of Chambers Road 1.85 40.0% 3900-03 Irondale Gulch Tower to Chambers Road 2.91 54.7% 3900-04 Irondale Gulch I-70 to 42nd Avenue 1.83 68.7% 3901-01 Irondale Gulch Peoria 4.44 43.4% 3901-02 Irondale Gulch 40th & Chambers Road 0.97 64.9% 4000-01 Rocky Mountain Arsenal Stapleton North 0.78 29.1% 4300-03 Clear Creek North of I-70 1.79 58.2% 4309-01 Clear Creek Berkeley Lake 1.83 55.1% 4400-01 Sand Creek North Stapleton 5.07 42.5% 4400-02 Sand Creek Quebec Corridor 5.01 65.0% 4400-03 Sand Creek South Stapleton 1.49 70.8% 4400-04 Sand Creek East Stapleton 2.77 74.1% 4401-01 Westerly Creek Stapleton 3.03 50.6%

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Denver Water Quality Management Plan Chapter 2 Page 2-3 Exhibit 2.2 Major Denver Drainage Basins ID OUTFALL NAME/LOCATION AREA (mi 2 ) COMPOSITE IMPERVIOUSNESS 4401-02 Westerly Creek 11th Avenue to Montview 2.83 62.6% 4401-03 Westerly Creek Lowry 3.51 40.6% 4401-04 Westerly Creek South of Alameda 2.85 55.6% 4500-01 Montclair City Park 4.30 54.4% 4500-02 South Platte 36th & Downing 1.74 65.2% 4500-03 Montclair Park Hill 1.51 59.7% 4500-04 Montclair Park Hill 3.69 54.4% 4600-01 Cherry Creek Central Business District 2.17 83.2% 4600-02 Cherry Creek Cherry Creek Mall 4.61 57.7% 4600-03 Cherry Creek Upper Cherry Creek 5.62 68.9% 4600-04 Cherry Creek Upper Cherry Creek 5.77 51.3% 4601-01 Goldsmith Gulch Cherry Creek Outfall 3.92 54.1% 4601-02 Goldsmith Gulch Middle Goldsmith Gulch 1.34 59.0% 4700-01 Sloan s Lake West Colfax Avenue 1.59 65.0% 4800-01 Lakewood Gulch 12th & Federal 1.17 59.6% 4801-01 Dry Gulch 12th & Sheridan 0.39 62.0% 4900-01 Weir Gulch West 6th Avenue 2.30 58.3% 5000-01 I-25 & South Platte West Washington Park 1.25 71.9% 5000-02 I-25 University & Mexico 5.02 60%* 5100-01 Sanderson Gulch West Florida Avenue 5.57 54.6% 5200-01 Harvard Gulch West Fork Second Creek 0.83 63.8% 5200-02 Harvard Gulch 56th to 64th Avenue 6.62 50.4% 5300-01 West Harvard Gulch West Yale Avenue 1.44 57.1% 5401-01 Greenwood Gulch South Monaco Parkway 0.16 50%* 5500-01 Bear Creek Fort Logan 3.12 52.8% 5500-02 Bear Creek Upper Bear Creek 1.84 45.5% 5500-03 Bear Creek Academy Park Tributary 0.60 62.7% 5500-04 Bear Creek Marston Lake North 2.24 46.0% 5500-05 Bear Creek Pinehurst Tributary 0.72 42.2% 5501-01 Bear Creek Henry's Lake 1.35 35.0% 5901-01 Dutch Creek Coon Creek 3.10 53.2% 8056 Barr Lake Barr Lake 3.86 7.9% 8150 Box Elder Creek Box Elder Creek 3.10 53.2% Approximate further evaluation pending. TOTAL 189.89

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Denver Water Quality Management Plan Chapter 2 Page 2-5 Insert Exhibit 2.3 Location Map Here

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Denver Water Quality Management Plan Chapter 2 Page 2-7 EXHIBIT 2.4 THE SOUTH PLATTE RIVER BASIN IS THE LARGEST DENVER DRAINAGE BASIN AND IS HIGHLY URBANIZED (IN DENVER) Source: The Greenway Foundation South Platte River The South Platte River is the largest receiving waterway in the Denver metropolitan area and flows from south to north along the I-25 corridor through Denver. Within the city limits of Denver, the South Platte River meanders along a path some 10.5 miles in length from West Dartmouth Avenue to Franklin Street. The drainage basin covers approximately 4,850 square miles extending from the Continental Divide in the Rocky Mountain Front Range to the high plains and foothills of eastern Colorado. The mountainous portion of this basin is generally unsuited for dense development, while the foothills and high plains areas are actively being developed. The intense urbanization in the metropolitan area consists primarily of residential and commercial areas and some industrial regions along the river valley. The South Platte River flood potential is mitigated by Chatfield Reservoir located on the South Platte River, along with Cherry Creek Reservoir and Bear Creek Reservoir located on major tributaries. Peak 100-year flows of the South Platte vary from 5,000 cubic feet per second (cfs) near Chatfield to 38,000 cfs at the confluence with Sand Creek. Normal discharges in the South Platte River are generally about 100 cfs, but approach about 1,000 cfs during the spring runoff period. Average daily flows are highly affected by treated effluent discharges from Metro Wastewater. First Creek The First Creek basin drains an area of 47.2 square miles. The headwaters of First Creek are located in Arapahoe County, south of I-70 and east of E-470. Runoff from the basin flows in a northwesterly direction. First Creek crosses Pena Boulevard just north of 56 th Avenue and then flows through the northeastern portion of the Rocky Mountain Arsenal. First Creek is a rightbank tributary to the South Platte River, and outfalls at approximately 128 th Avenue. The basin shape is long and narrow, approximately 26 miles long and 2 to 4 miles wide. The average stream slope above Rocky Mountain Arsenal is about 31 feet per mile, and flattens to about 23 feet per mile below Rocky Mountain Arsenal The upper reaches of First Creek are primarily undeveloped irrigated cropland with wide swales and channels for drainageways. Toward the center of the basin, First Creek bisects Green Valley

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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts Chapter 2 Page 2-8 Ranch, which consists of medium density, single-family residences. First Creek then enters Rocky Mountain Arsenal with a more incised, low flow channel and wider floodplain areas. The lower First Creek basin is located downstream from 56 th Avenue and Pena Boulevard and continues to the South Platte River. The lower First Creek basin consists of irrigated farmland with pockets of light industrial and residential properties. Conveyance within the lower First Creek drainage consists of broad undefined channels with little or no defined thalweg. Between US-85 and Brighton Boulevard, the channel is incised with a well-defined thalweg. The O Brian Canal and the Burlington Ditch, which intercept runoff from First Creek, cross First Creek below Rocky Mountain Arsenal. Second Creek Second Creek drains about 27 square miles of area to the South Platte River. The basin is about 15 miles long and 3.4 miles wide at its widest point. The drainage basin ranges in elevation from 4,990 feet at the South Platte River to 5,650 feet at the basin divide. Second Creek has a natural irregular channel section in the upper reaches above the O Brian Canal. The southern land area within the Second Creek drainage basin in Denver city limits drains via a tributary known as the West Fork of Second Creek. This tributary drains 3.03 square miles of area to Second Creek. The Highline Canal terminates at the West Fork. The sustained unused flow in the Highline Canal is wasted to the West Fork downstream of 64 th Avenue, and the flows have eroded the channel on the West Fork. At Tower Road, the West Fork channel is about 15 feet deep with vertical and very steep, unstable banks. The confluence of Second Creek and the West Fork of Second Creek is a wide, relatively flat area supporting a stand of cottonwood trees. Some wetland areas are present in the upper reaches of the West Fork, but, as the channel has eroded, the channel banks have become incised and support only a narrow band of wetland or riparian vegetation. The floodplain is contained within the channel except at road crossings, where overtopping will occur. The banks are unstable and some lateral channel migration may occur during large flows. Third Creek Third Creek is an east bank tributary of the South Platte River and is located northeast of Downtown Denver. Third Creek flows through Denver International Airport (DIA) and is experiencing development in the drainage basin. Third Creek drains approximately 31 square miles of area to the South Platte River. The basin is about 14 miles long and 3.2 miles wide at its widest point and ranges in elevation from 4,960 feet at the South Platte River to 5,485 at the basin divide. Third Creek has a natural irregular channel section above the O Brian Canal, and a small, poorly defined channel section between the O Brian Canal and the South Platte River. Third Creek is crossed by Highway 85, I-76, the Union Pacific and Burlington Northern Railroads, and the O Brian Canal, Fulton Ditch, McCann Ditch, and the Burlington Ditch.

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Denver Water Quality Management Plan Chapter 2 Page 2-9 Box Elder Creek Box Elder Creek is located east of the Denver metropolitan area, with a portion of the watershed draining the easternmost portion of Denver. Major tributaries include Bear Gulch and Hayesmount Creek. The watershed is long and narrow, extending from El Paso County in the south a distance of approximately 100 miles to its confluence with the South Platte River in Weld County downstream of the City of Greeley. The watershed encompasses about 370 square miles located in Weld, Adams, Arapahoe and Elbert Counties. Box Elder Creek is generally dry except for short periods of runoff after intense rainfall events, although portions of the creek have a small amount of flow for longer periods. The Box Elder Creek watershed is currently mostly undeveloped grassland and agricultural areas. The portion of the watershed that lies within DIA, however, has some areas that are heavily developed. Developed areas within the DIA property include runways and taxiways, concourses, and support facilities. Additionally, there are scattered relatively low-density housing developments along the central portion of the creek. Irondale Gulch The Irondale Gulch basin, which contains approximately 26.7 square miles, lies immediately southwest of First Creek and drains the area from the intersection of I-70 and Arapahoe Road and the Adams County line, through the Montbello area, the Arsenal and Commerce City with an eventual outfall to the South Platte River at approximately East 96 th Avenue. The southwest boundary of the basin is primarily the north side of I-70 until it reaches the former Stapleton International Airport, where the basin boundary lies just west of Havana Street. This basin is long and narrow, with a total length of 28 miles to the South Platte River and a width of 1 to 2 miles. The average slope of the basin is about 26 feet per mile, which remains fairly constant throughout the drainageway. The drainageways through the Arsenal contain several lakes and detention areas. The drainage below the Arsenal is primarily storm sewer or roadside ditches, with capacity for only minor floods. Clear Creek Clear Creek is a left bank tributary to the South Platte River, and has its source in the Rocky Mountains west of Denver. Flowing in a generally easterly direction from the Continental Divide, Clear Creek enters the high plains in Golden. Within this lower reach, Clear Creek passes through unincorporated areas of Adams and Jefferson Counties, and the cities of Denver, Arvada, Wheat Ridge and Golden. Clear Creek crosses the northwest corner of Denver for a distance of 0.2 miles in the vicinity of 52 nd Avenue and Gray Street. The drainage area at the mouth is 575 square miles, of which 400 square miles is in the mountain region above Golden. There are 11 major reservoirs in the lower Clear Creek basin, three of which are on-stream and provide some residual flood control effects downstream from each site. Ralston Reservoir was built in 1938 by Denver and receives water from Ralston and South Boulder Creeks. Although Ralston Reservoir is not operated for flood control purposes, there is approximately 2,400 acre-feet of storage available. Maple Grove Reservoir is located on Lena Gulch at West 27th Avenue and has approximately 452 acre-feet of available storage. Leyden

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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts Chapter 2 Page 2-10 EXHIBIT 2.5 RECENTLY CONSTRUCTED DETENTION BASIN (VEGETATION NOT YET ESTABLISHED) ON WESTERLY CREEK IN THE STAPLET ON REDEVELOPMENT ARE A Lake is an irrigation water storage reservoir on Leyden Creek upstream from Indiana Street, and has approximately 550 acre-feet of uncontrolled storage. Sand Creek Sand Creek is an east bank plains tributary of the South Platte River and lies to the east and northeast of Denver s Central Business District. The Sand Creek basin encompasses an area of 189 square miles. The basin is long and narrow, with a length of 32 miles and an average width of 6 miles. Portions of Elbert, Douglas, Arapahoe, Denver, and Adams Counties are included in the drainage area. Sand Creek originates at the confluence of Coal Creek and Murphy Creek. Sand Creek joins the South Platte River in the vicinity of I-270 in Commerce City, north of Denver city limits. The reach of Sand Creek within Denver is located along I-70 near the Stapleton Redevelopment area. Principle tributaries of Sand Creek are Toll Gate Creek and Westerly Creek. Westerly Creek The Westerly Creek tributary area consists of approximately 18 square miles of highly developed area from the low rolling divide between Cherry Creek and West Toll Gate Creek to the confluence with Sand Creek. The basin is about 8.5 miles long and 3 miles wide at its widest point. The crescentshaped area drains in a northwestto-north direction with an average slope of 0.9 percent. The Westerly Creek drainage basin is at a state of full development consisting of townhouses, condominiums, apartments, single family homes, motels, large shopping complexes, streets, parking areas, and highways. This development and the 0.9 percent slope contribute to a rapid response time for storm runoff and increased stormwater flows. The upper reaches of Westerly Creek begin in the City of Aurora. Runoff of peak events is captured in Westerly Creek Dam, built in 1989 on the former Lowry Air Force Base at Alameda and Havana. As Westerly Creek outlets from the dam, it flows in a 48-inch underground pipe. Flows from the Lowry Redevelopment area enter Westerly Creek and then are detained in Kelly Road Dam at 11 th Avenue. The channel and culverts from Kelly Road Dam to Montview at the Stapleton Redevelopment area have been improved to handle the 10-year design storm. The Westerly Creek channel through the Stapleton site has been improved to 100-year capacity. All storm outfalls to Westerly Creek within the Stapleton site have regional water quality treatment at the end of pipe.

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Denver Water Quality Management Plan Chapter 2 Page 2-11 EXHIBIT 2.7 GOLDSMITH GULCH IN DENVER, COLORADO EXHIBIT 2.6 CHERRY CREEK IN DENVER, COLORADO Cherry Creek The Cherry Creek tributary area consists of 410 square miles, 385 square miles of which drain into Cherry Creek Reservoir. The dam is designed to release a maximum of 5,000 cfs to the lower Cherry Creek channel, which has a current capacity of between 4,000 and 11,000 cfs. The lower Cherry Creek basin (Exhibit 2.6) covers 25.2 square miles, with Goldsmith Gulch contributing 7.7 square miles of the total area. The lower channel of Cherry Creek flows 11.5 miles from the reservoir to the South Platte River confluence in the vicinity of Speer Boulevard. The lower channel has been improved to contain the 100-year storm from 1 st Avenue to the confluence. These improvements generally consist of cleaning, shaping, and landscaping the channel bottom. Goldsmith Gulch The Goldsmith Gulch basin encompasses an area of 7.8 square miles from Arapahoe Road northwest to the confluence with Cherry Creek. Through Denver, the tributary area is primarily urbanized or in the process of development with a mix of commercial and residential construction. Many channel improvements have been completed along Goldsmith Gulch to reduce the potential of flood damage. The channel has been stabilized (Exhibit 2.7) and regional parks have been constructed in the floodplain. Detention facilities have also been constructed along the channel at Bible Park, Wallace Park, Rosamond Park, and at Iliff and Monaco. Channel slopes are generally mild with several newer drop structures along the reach. The Highline Canal bisects Goldsmith Gulch at East Cornell Avenue. Goldsmith Gulch passes underneath the Highline Canal and East Cornell Avenue through a concrete box culvert. The

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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts Chapter 2 Page 2-12 upper portion of Goldsmith Gulch includes the T-REX construction site. New storm sewer and detention facilities drain the I-225 and I-25 interchange to Goldsmith Gulch. Sloan s Lake The Sloan s Lake drainage basin flows eastward from a high point near 26 th Avenue and Garrison Street in Lakewood and outfalls into the South Platte River near Colfax Avenue and Invesco Field. The drainage basin lies within Denver s jurisdiction east of Sheridan Boulevard and is bounded by West 32 nd Avenue on the north, Colfax Avenue on the south, Garrison Street on the west, and the South Platte River on the east. The basin totals almost 5.5 square miles within Denver, Lakewood, Edgewater, and Wheatridge. Since the basin is fully developed and heavily urbanized, the major drainageways are not clearly identifiable. Most of the historic drainage channels have either been filled in or built over to the point of obliteration. The most prominent geographic feature within the basin is Sloan s Lake. The lake, which occupies 176.5 acres of a 290-acre Denver park, has been and continues to be a valuable recreational resource for the metropolitan area. In addition to its scenic and recreational significance, the lake provides the important function of regulating and controlling downstream flows that otherwise would be allowed to run uninhibited through West Denver. The lake reduces peak flow rates from about 2,904 cfs to 166 cfs during the 100-year event. Lakewood Gulch Lakewood Gulch is a major drainageway that originates in Lakewood and flows easterly toward the South Platte River between 6 th Avenue and Colfax Avenue. The Lakewood Gulch basin consists of approximately 16 square miles beginning in the foothills and extending easterly 10 miles to the South Platte River in the vicinity of Colfax Avenue. The tributary area is essentially fully developed in Denver and in the eastern portion of Lakewood. The basin is also developed in the western portion of Lakewood and Jefferson County. Dry Gulch The Dry Gulch basin consists of approximately 3.7 square miles lying predominantly in Lakewood. Dry Gulch is tributary to Lakewood Gulch in the vicinity of 10th Avenue and Perry Street in Denver, and extends westward a length of 5.7 miles along the general alignment of Colfax Avenue to Simms Street. The basin is essentially fully developed, with commercial establishments along Colfax Avenue and residential development comprising the remainder of the basin. Weir Gulch Weir Gulch meanders eastward from Green Mountain Village for approximately 8.3 miles to the confluence with the South Platte River in the vicinity of West 9th Avenue. The basin, which comprises some 7.2 square miles, is fully urbanized in Denver and mostly developed west of Sheridan Boulevard in Lakewood.

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Denver Water Quality Management Plan Chapter 2 Page 2-13 There are two drainageways tributary to Weir Gulch within Denver. The 1 st Avenue tributary to Weir Gulch is located just north of 1 st Avenue and flows in an easterly direction. The drainage basin is bounded by 6 th Avenue on the north, West Alameda Avenue on the south, Raleigh Street on the east, and Wadsworth Boulevard on the west. This tributary of the Weir Gulch system is approximately 2 miles long and about 0.8 mile wide, with an average slope of 1.5 percent. The Dakota Avenue Tributary to Weir Gulch lies within Denver s jurisdiction east of Sheridan Boulevard and is located just south of Dakota Avenue flowing in an easterly direction. It is bounded by West Alameda Avenue on the north, West Alaska Avenue on the south, Sheridan Boulevard on the west, and Xavier Street on the east. This tributary is about -mile wide and has an average slope of 1 percent. Strip parks have been developed by the Denver Parks and Recreation Department from 1 st Avenue to Alameda Avenue along the gulch. This development consists mainly of grassed channels and the installation of asphalt bike paths. Barnum Park is located on each side of 6 th Avenue on the west side of Federal Boulevard. Barnum Lake, located south of 6 th Avenue, has been improved to contain the 100-year storm within the Weir Gulch channel. The open park area north of 6 th Avenue, known as the Federal Boulevard Detention Reservoir, is designed to reduce the 25-year flow to a 10-year flow or less. The lower Weir Gulch channel from Federal to the South Platte River outfall has capacity for the 10-year storm. Sanderson Gulch Sanderson Gulch flows 8.63 miles in an easterly direction from South Union Boulevard above Smith Reservoir to the South Platte River in the vicinity of West Florida Avenue. This drainage basin, which encompasses approximately 9 square miles, is fully developed in Denver and is being rapidly urbanized west of Sheridan Boulevard. The entire basin s drainage area extends west to the top of Green Mountain, and channel slopes are generally mild. Green belts and parks have been located along the Sanderson Gulch floodplain. Drainageway improvements have been constructed to contain the 100-year event within open channels; however, culverts were designed for the 10-year frequency discharge. West Harvard Gulch West Harvard Gulch flows east 2.8 miles through Denver to its confluence with the South Platte River in the vicinity of Yale Avenue. The total area of the drainage basin is approximately 1.4 square miles. The average width of the basin is 0.66 mile, and the channel slopes range from 1.3 to 2.4 percent. The basin elevations range from approximately 5,525 feet to 5,250 feet. The West Harvard Gulch basin is primarily in residential development. Commercial areas are situated along Federal Boulevard, and a light industrial park is located in the basin s lower reaches. Loretto Heights College sits on the ridge that forms the southern boundary of the basin. In the West Harvard Gulch Basin, the main drainageway was piped in an underground conduit that extended from just above the Colorado and Southern Railroad to Zuni Street. This reach has

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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts Chapter 2 Page 2-14 been restored and an improved grass lined and concrete trickle channel carries the flood events. Channel slopes within this reach are stabilized with grouted sloping boulder drops. During the 100-year flood event, most of the flood flow will be contained in the channel. At the confluence of the South Platte River, the main channel flows through an 84-inch-diameter concrete pipe. This pipe has inadequate capacity to carry the 100-year flow, resulting in shallow flooding around the Arapahoe Power Plant. Some ponding and overtopping will occur at Zuni, Clay and Decatur Street crossings during the 100-year flood event. Harvard Gulch Harvard Gulch flows west through the southern part of Denver for a length of 5.6 miles to reach its confluence with the South Platte River at Wesley Avenue. The total drainage basin area is approximately 7.7 square miles. The Highline Canal meanders through the southeast portion of the basin and intercepts storm flow. Single-family residences primarily urbanize the basin. Commercial development is generally located along Colorado Boulevard, Broadway, and Santa Fe Drive. The residential portion of the basin is very dense with small lots having an estimated 52 percent average imperviousness. The Harvard Gulch Flood Control project, completed in 1966, was designed for the 10-year flood and included an underground box culvert from Logan Street to the South Platte River. A grass-lined open channel was designed though Logan Park, which also serves as an inlet to a detention pond in the park. Highway I-25 and the T-REX construction project bisect the upper portion of Harvard Gulch. Drainage improvements for T-REX through the Holly Hills area include several detention/water quality basins as well as a new storm sewer system. The T-REX storm sewer is connected to Denver s existing storm sewer system at two locations along the west side of I-25: 1) the T-REX storm sewer system to the south outfalls to the Highline Canal; and 2) the storm sewer system to the north outfalls to the existing 36-inch storm sewer within Yale Avenue. Bear Creek Bear Creek generally flows eastward from its headwaters at Mount Evans through the towns of Evergreen and Morrison until it reaches the metropolitan area of Denver where it is tributary to the South Platte. The drainage basin is approximately 36 miles long and has an average width of about 9 miles. This encompasses approximately 261 square miles of drainage area. Elevations in the basin range from approximately 14,260 feet at Mount Evans to 5,260 feet at the mouth. Turkey Creek, a major tributary, drains about 52 square miles and enters into Bear Creek approximately 2 miles downstream of Morrison. The majority of the basin is in the mountains, with the remainder draining the foothills and high plains region. The drainage basin area inside the Denver s city limits is about 12 miles in size. The completion of Bear Creek dam just downstream of Morrison has had a great effect on the peak discharges of the 8.2-mile Bear Creek reach below the dam. The dam acts as a flood control reservoir that intercepts flows from areas in the upper and middle parts of the basin. At

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Denver Water Quality Management Plan Chapter 2 Page 2-15 the Bear Creek dam, peak flows from the 100-year event have been reduced from 30,000 cfs to approximately 1,000 cfs through storage in the reservoir. Marston Lake North (Tributary of Bear Creek) The Marston Lake drainage basin consists of approximately 2.1 square miles of limited developed area in the southwest corner of Denver. Various areas within the basin are subject to flooding, which could increase in severity and frequency with continued urbanization of the basin without drainageway improvements. The basin originates approximately mile west of Kipling Street between Belleview and Quincy Avenues, and extends approximately 4.4 miles in a northeasterly direction to its confluence with Bear Creek. Continued development in these areas, planned for mostly residential with some light commercial business, is expected to increase runoff rates. Marston Lake is owned and operated by the Denver Water Board and serves as a major link in the water supply system for Denver and much of the metropolitan area. The lake acts as a sump and is isolated from receiving or discharging stormwater. The drainage basin traverses various jurisdictions and ownerships including Jefferson County, Denver, Denver Water Board, Marston Water Treatment Plant grounds, Pinehurst Country Club Golf Course, and United Sates Government properties to the south of Fort Logan National Cemetery. Improvements to the drainageway have been accomplished by Denver Water and UDFCD. The north side of the Marston Lake Dam, which was reconstructed to allow room for an open channel and improved by UDFCD, provides an improved 100-year capacity channel from Old Wadsworth Boulevard to West Quincy Avenue. OVERVIEW OF LAKES Denver has many lakes within its boundaries that are managed by Denver Parks and Recreation. Exhibit 2.8 provides an overview of these lakes based on the recently completed Lake Management and Protection Plan (Dudley 2004). The Colorado Water Quality Control Commission (CWQCC) has assigned water quality standards to most of these lakes. For lakes without assigned standards, the principles of water quality protection discussed in this Plan remain relevant for supporting healthy, aesthetically pleasing conditions in the lakes.

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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts Chapter 2 Page 2-16 EXHIBIT 2.8 DENVER LAKE LOCATIONS AND CHARACTERISTICS (DUDLEY 2004) Management Type Lake Name Location Characteristics Southwest District Barnum Lake in Barnum Park West of Federal Blvd. between 6 th Ave. and 3 rd Ave. 9 acres; 5 feet maximum depth; perimeter: 0.7 mile. Southwest District Bear Creek Ponds in Bear Creek Park Bear Creek Park is located at S. Raleigh Street and W. Hampden Avenue. Located along Kenyon Avenue off of Sheridan Boulevard. There is a series of four ponds along a soft trail across from the Fort Logan Cemetery. 70 acres of natural areas can be accessed from the south boundary of the park. Northwest District Berkeley Lake in Berkeley Park South of I-70 between Sheridan Blvd. And Tennyson St. 40 acres; 12 feet maximum depth; perimeter: 0.9 miles. East Montclair District City Park Lakes North of 17th Ave. and west of Colorado Blvd. Parking area on the northwest side of the lake between the park and the Denver Zoo. Ferril Lake 25 acres; 8 feet maximum depth; perimeter 0.8 miles. There is a sediment basin at 17th Street at the point where the storm sewer/city ditch daylights that is 2 acres in size. The sediment basin discharges to Ferril Lake. Duck Lake 6.3 acres; perimeter: 0.4 mile. Southwest District Garfield Lake in Garfield Park South of W. Mississippi Ave. between S. Federal Blvd. and S. Sheridan Blvd. 10 acres; 4 feet maximum depth; perimeter: 0.5 mile. Southwest District Harvey Lake in Harvey Park Between S. Sheridan Blvd. and S. Federal Blvd., just south of W. Evans Ave. and east of S. Tennyson St. 8.5 acres; 14 feet maximum depth; perimeter: 0.4 mile. Southwest District Huston Lake in Huston Lake Park East of S. Federal Blvd. about 4 blocks, between W. Ohio Ave. and W. Kentucky Ave. Southeast of the intersection of Ohio and S. Clay St. 13 acres; 6 feet maximum depth; perimeter: 0.6 mile. Southwest District Lake of Lakes (A.K.A. Little Lake Henry) Carr St. and Quincy Ave. 3.5 acres, perimeter: 0.4 mile. Southeast District Lollipop Lake in Garland Park Between S. Holly St. and S. Kearney St. north of Cherry Creek Dr. N. 4 acres; 8 feet maximum depth; perimeter: 0.4 mile. Southwest District Overland Pond in Overland Pond Park North of W. Florida Ave. between S. Santa Fe Dr. and the South Platte River trail. 1.5 acre; 7 feet maximum depth; perimeter: 0.2 mile. Northeast District Parkfield Lake in Developing Park Area DIA Gateway/Chambers north of I70. 14 acres; 6 feet mean depth; perimeter: approximately 1 mile. Northwest District Rocky Mountain Lake in Rocky Mountain Lake Park W. 46 th Ave. between Federal Blvd. and Lowell Blvd. Parking areas north of 46 th Ave. 29 acres; 40 feet maximum depth; perimeter: 0.9 mile. Northwest District Sloan s Lake (including Cooper Lake) in Sloan s Lake Park East of Sheridan Blvd. between W. 25th Ave. and W. 17th Ave. 174 acres; 5 feet deep in the main body of the lake west of the island but upwards of 8 feet deep east of the island; perimeter: 2.6 miles.

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Denver Water Quality Management Plan Chapter 2 Page 2-17 EXIBIT 2.9 WELL VEGETATED, NATURAL SHORELINE ALONG BERKELEY LAKE EXHIBIT 2.8 DENVER LAKE LOCATIONS AND CHARACTERISTICS (DUDLEY 2004) Management Type Lake Name Location Characteristics Southwest District Vanderbilt Pond in Vanderbilt Park North of W. Tennessee Ave. between S. Santa Fe Dr. and S. Huron St. Access from W. Mississippi Ave. 6 acres; 15 feet maximum depth. South Denver Park District Washington Park Lakes Northeast of the intersection of S. Downing St. and E. Louisiana Ave. Smith Lake 9 acres; 12 feet maximum depth; perimeter: 0.6 mile. Grasmere Lake 19 acres; 10 feet maximum depth; perimeter: 0.8 mile. Lily Pond 1 acre; 8 feet maximum depth; perimeter: 0.18 mile. Natural Area Bluff Lake in Bluff Lake Park Havana at 32nd Ave. 9 acres Natural Area Heron Pond in Northside Park 51 st Ave. and Downing St. 3 acres Denver City Golf Course Kennedy Lake in J.F. Kennedy Golf Course 10500 E. Hampden Ave. 5 acres; perimeter: 0.4 mile. Denver City Golf Course Skeel Reservoir in Wellshire Golf Course 3333 S. Colorado Blvd. 13.4 acres, perimeter: 0.6 mile. Golf Concession Overland Lake in Overland Lake Open Space North of W. Florida Ave. between S. Santa Fe Dr. and the South Platte River trail. Parking area is north of Florida. 11 acres; perimeter 0.7 mile.

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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts Chapter 2 Page 2-18 CHARACTERIZATION OF DENVER LAKE AND STREAM CONDITIONS In order to protect and enhance the condition of Denver lakes and streams, it is necessary to have a sound scientific understanding of their baseline chemical, physical, and biological conditions and identify key sources of impacts to these water bodies. Because this process is cumbersome, time-consuming, and costly, the Project Team and Advisory Committee determined that the highest priority for this Plan was to identify strategies and tools to minimize stormwater impacts to these water bodies in the near term this is the focus of Chapter 6, Stormwater Quality BMP Implementation Guidelines. As a result, a watershed-by-watershed assessment of stream conditions was deferred to a future project. Nonetheless, several key building blocks for watershed-by-watershed assessments have been completed in this Plan in Chapter 3-Regulatory Drivers, Chapter 4-Related Documents, Chapter 5-National Case Studies, and in Chapter 8-Potential Regional Facilities. In Chapter 3, known water-quality limited stream segments in Denver are discussed. In Chapter 4, several on-going regional efforts to assess and address water body conditions are described. In Chapter 5, watershed assessment approaches used by other communities with advanced stormwater programs are described, along with the associated costs of such efforts. In Chapter 8, locations that should be further evaluated for use as regional stormwater quality treatment facilities have been identified. Additionally, Appendix D provides a variety of specific recommendations regarding water quality improvement that were submitted in a report to the Mayor in June (Bergstedt 2004). All of this information will be important in developing targeted approaches to improving conditions in various Denver water bodies and ensuring that the wheel is not reinvented with regard to specific watershed efforts. Another key component when characterizing lakes and streams is having a reasonable understanding of what data sources already exist. A brief list of these sources that, at a minimum, should be included in more detailed watershed analyses includes the following: 4 Denver Environmental Health, Environmental Protection Division (DEH-EPD) data set: This data set includes over 25 years of dry-weather monitoring data for the South Platte River system, including surface water, biotic, and sediment samples from both streams and lakes. Additionally, DEH-EPD is compiling a GIS database of stormwater outfalls to model watershed drainage areas (Bergstedt 2004). 4 Denver Public Works, Wastewater Management Division dry weather monitoring data: As part of Denver s CDPS stormwater permit, dry weather discharges have been monitored. GIS-based mapping is also being completed to identify discharge points, post-construction BMPs, and other features. 4 Barr Lake/Milton Reservoir water quality database: this extensive water quality database, compiled by Hydrosphere in 2004, contains most of the readily available water quality data for the South Platte and its tributaries in the Denver area from Chatfield dam to the Barr/Milton diversion points on the South Platte. One of the reasons that this data

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Denver Water Quality Management Plan Chapter 2 Page 2-19 EXHIBIT 2.10 CONFLUENCE OF THE SOUTH PLATTE RIVER AND CHERRY CREEK set is important is that it includes water quality data from neighboring municipalities that influence conditions in the South Platte. 4 South Platte Cooperative for Urban River Evaluation (South Platte CURE) Database: This database focuses on the South Platte River and selected tributaries over the last eight years. Most of this data was also submitted to the Barr Lake/Milton Reservoir effort. South Platte CURE also continues to serve as a data clearinghouse for ongoing monitoring efforts along the South Platte River. This data set has been standardized into a STORET-compatible format and is uploaded to STORET on a periodic basis. South Platte CURE and DEH-EPD coordinate sampling programs and share data to help with stream characterization, but South Platte CURE s primary focus is on point source (sanitary wastewater) discharges. 4 Joint Task Force Stormwater Monitoring Data: this dataset includes both the initial Phase I stormwater permit wet weather monitoring data and the ongoing trend analysis data conducted by the U.S. Geological Survey on behalf of Denver, Aurora, Lakewood and UDFCD. This dataset is important because it focuses on stormwater discharges, whereas other monitoring programs have focused on dry weather conditions. 4 U.S. Geological Survey (USGS) National Water Database (NWISWeb at http://waterdata.usgs.gov/nwis/ ): This database can also be queried for water quality and flow data for the Denver area. 4 STORET: This is EPA s water quality database that can be queried for historical data available for the Denver area. 4 Instream Issues Task Force/Mayor s South Platte River Commission: The Instream Issues Report, South Platte River Corridor, as contained in the Appendix to the Long Range Management Framework South Platte River Corridor (Mayor s South Platte River Commission 2000) contains segment-by-segment characterizations of the South Platte River. The following section provides a general overview of the impacts of urbanization on receiving waters that should also be included as a building block to shape future analyses of watershed-specific conditions in Denver. This section emphasizes the importance of a holistic approach to improving receiving water conditions that addresses not only water quality, but also habitat, water quantity (flow regime), aquatic life, and stream channel conditions.

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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts Chapter 2 Page 2-20 OVERVIEW OF THE EFFECTS OF URBANIZATION ON RECEIVING WATERS A sound understanding of the widely documented (e.g., WEF and ASCE 1992, 1998; Debo and Reese 2002; Horner, et al. 1994; and Schueler and Holland 2000) effects of urban runoff on the physical, chemical, and biological characteristics of receiving waters is important for those involved with mitigating the impacts of urban runoff. The following discussion provides a general overview of the effects of urbanization on receiving waters followed by a more detailed discussion of the physical impacts and chemical characteristics of urban runoff documented both nationally and for the Denver area. Traditional stormwater management focused on moving water away from people, structures, and transportation systems as quickly and efficiently as feasible. This was accomplished by creating conveyance networks of impervious storm sewers, roof drains, and lined channels, which concentrated runoff flows for discharge to receiving waters. There were many consequences of this traditional approach to drainage such as: 4 Increased runoff frequency. 4 Increased runoff volume. 4 Larger peak discharges. 4 Higher flow velocities. 4 Change in base flow (dry weather) regime. 4 Increased flooding risk. 4 Introduction of new pollutant sources and types. 4 Increased runoff temperature. 4 Loss of riparian zones and wetlands, with associated negative effects. 4 Habitat damage and ecosystem disruption associated with stream bed and bank erosion leading to sediment and pollutant transport, channel widening and instability, and destruction of both aquatic and terrestrial physical habitats. 4 Increased contaminant transport, leading to increased water quality degradation. 4 Production and long-term accumulation of potentially toxic concentrations of contaminants in receiving waters. It is particularly important to recognize that urban runoff impacts are complex, including chemical, physical, and biological responses. Various experts have developed helpful schemes for categorizing and interrelating adverse receiving water impacts. Two particularly valuable

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Denver Water Quality Management Plan Chapter 2 Page 2-21 representations are provided in Exhibits 2.11 and 2.12. With increasing frequency, these adverse impacts are being addressed by communities around the U.S. Recognition of these impacts has been a driving force behind federal, state and local government regulations concerning stormwater quality (see Chapter 3). The remainder of this section describes the potential physical and chemical impacts of uncontrolled urban runoff on receiving waters. EXHIBIT 2.11 ECOLOGICAL IMPACT OF HUMAN-INDUCED ALTERATIONS

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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts Chapter 2 Page 2-22 EXHIBIT 2.12 IMPACTS OF URBANIZATION ON PHYSICAL HABITAT AND BIOTA Adverse Physical Impacts of Urban Runoff In the absence of properly designed, constructed, and maintained best management practices (BMPs), urbanization can adversely impact stream channels due to increased peak discharges, increased magnitude and duration of flows, increased sediment loads during construction, and increased erosive forces that are effective at transporting larger-sized particles. This is why volume control for small, frequently occurring storm events is strongly emphasized by UDFCD in Volume 3 of the Urban Storm Drainage Criteria Manual (UDFCD 1999). Source: Roesner, L. A. and B. P. Bledsoe. 2003. Physical Effects of Wet Weather Flows on AquaticHabitats. Water Environment Research Foundation: Alexandria, VA. Co-published by IA Publishing: United Kingdom.

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Denver Water Quality Management Plan Chapter 2 Page 2-23 The widely cited Lane s Balance is helpful in understanding the physical impacts of unmitigated urbanization as shown in Exhibit 2.13. This schematic demonstrates that if more runoff is created as a consequence of urbanization, the right side of the scale will drop, and the left side of the scale will rise, thus leading to channel degradation, in the absence of suitable mitigation. By contrast, if excessive sediment is added to the stream during construction, the left side of the scale drops and the right side of the scale rises, leading to aggradation (deposition of sediment in the channel). EXHIBIT 2.13 SCHEMATIC OF LANE S BALANCE DESCRIBING PHYSICAL STREAM PROCESSES Source: Rosgen, D. 1996.Applied River Morphology. Pagosa Springs, Colorado: Wildland Hydrology. Another potential negative consequence of urbanization is increased stream power (with power meaning the ability of flowing water to alter channel geomorphology), as depicted in Exhibit 2.14. In Exhibit 2.14, comparison of the before and after curves shows that after urbanization, the stream has a much greater ability to alter the channel and remove sediment from its banks. The problems depicted by Exhibits 2.13 and 2.14 are mitigated through such measures as detention/retention facilities with sophisticated outlet structures that control a wide range of return frequency floods (including small, frequently occurring events that significantly influence channel stability). Other measures include channel stabilization techniques such as grade control structures, toe protection, special stabilization on outer banks at channel bends, etc.

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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts Chapter 2 Page 2-24 EXHIBIT 2.14 IMPACT OF URBANIZATION ON STREAM GEOMORPHOLOGY Source: National Research Council, 1992.Restoration of Aquatic Ecosystems: Science, Technology, andPublic Policy. Washington, DC: National Academy Press. Chemical Characteristics of Urban Runoff Urban settings typically contain multiple pollutant sources, as shown in Exhibit 2.15, which lists representative sources of solids, nutrients, pathogens, dissolved oxygen demands, metals, and oils. In addition to these pollutants, Urbonas and Doerfer (2003) have reported that atmospheric dust fallout is a significant contributor to urban runoff pollution in Denver. Some of their key findings include: 1. Atmospheric dust fallout in the Denver area is a significant source of total suspended solids and potentially of other pollutants found in stormwater runoff. 2. Streets, parking lots, sidewalks and roofs all accumulate this type of fallout. 3. Breaking up directly connected impervious areas with landscaping and lawns can help to capture this fallout and minimize its chances of reaching stormwater conveyance systems. 4. The BMPs recommended in UDFCD s Storm Drainage Criteria Manual Volume 3 are well-suited to removing these types of pollutants.

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Denver Water Quality Management Plan Chapter 2 Page 2-25 Another potential pollutant source in Denver involves snow and ice management activities. Storage and disposal of snow that can be contaminated by hydrocarbons and pet waste, as well as the types of chemicals and materials used to melt snow and ice, are both important considerations for runoff quality management. Commonly used de-icers in Denver are highly soluble and have low toxicity to plants and animals; however, in some cases, they may contribute to biochemical oxygen demand (BOD) as they decompose, resulting in lower dissolved oxygen (DO) levels in streams. Denver s snow and ice management practices are addressed under its CDPS stormwater permit requirements. EXHIBIT 2.15 URBAN RUNOFF POLLUTANT SOURCES Pollutant Category Source Solids Nutrients Pathogens DO Demands Metals Oils Synthetic Organics Soil erosion X X X X Cleared vegetation X X X Fertilizers X Human waste X X X X Animal waste X X X X Vehicle fuels and fluids X X X X X Fuel combustion X Vehicle wear X X X Industrial and household chemicals X X X X X X Industrial processes X X X X X X Paints and preservatives X X Pesticides X X X Stormwater facilities X X Source: Horner, R.R., J.J. Skupien, E.H. Livingston and H.E. Shaver. 1994.Fundamentals of Urban RunoffManagement: Technical and Intuitional Issues. Washington, DC: Terrene Institute, in cooperation with the Environmental Protection Agency. Representative concentrations of pollutants in urban runoff have been documented in multiple studies over the last several decades. Several key studies relevant to Denver include: 1) The National Urban Runoff Program (NURP), which was conducted between 1978 and 1983 by the EPA and USGS and included stormwater quality monitoring of 81 outfalls in 28 communities around the U.S. for a total of 2,300 storm events. 2) The National Stormwater Quality Database, Version 1.1, as compiled by Pitt, Maestre and Morquecho (2004) and as available through the website www.unix.eng.ua.edu/~rpitt/Research/ms4/mainms4.shtml This database contains Phase I stormwater permit monitoring data for over 100 constituents in 65 communities across the U.S. for a total of 3,700 storm events at 350 locations collected over roughly the last 10 years. This database does not include the historical NURP data.

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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts Chapter 2 Page 2-26 3) The Denver Regional Urban Runoff Program (DRURP) conducted by the Denver Regional Council of Governments (DRCOG) in 1983, providing data for nine basins with various land uses for 15 constituents of concern and for the EPA s Priority Pollutants. These data have been supplemented with monitoring by UDFCD and were submitted as part of the Stormwater NPDES Part 2 Permit Application Joint Appendix (Aurora et al. 1992). Since that time, monitoring in the Denver area has also been completed under the Phase I stormwater permit program. Data from each of these three sources are tabulated in Exhibits 2.16, 2.17, and 2.18. EXHIBIT 2.16 NURP SUMMARY DATA MEDIAN EVENT MEAN CONCENTRATIONS FOR URBAN LAND USES FOR VARIOUS CONSTITUENTS BASED ON DATA FROM 28 AMERICAN CITIES 1 Pollutant Units Residential Mixed Commercial Open/ Non-Urban Median COV 2 Median COV Median COV Median COV Biochemical Oxygen Demand (BOD) mg/L 10 0.41 7.8 0.52 9.3 0.31 Chemical Oxygen Demand (COD) mg/L 73 0.55 65 0.58 57 0.39 40 0.78 Total Suspended Solids (TSS) mg/L 101 0.96 67 1.14 69 0.85 70 2.92 Total Lead g/L 144 0.75 114 1.35 104 0.68 30 1.52 Total Copper g/L 33 0.99 27 1.32 29 0.81 Total Zinc g/L 135 0.84 154 0.78 226 1.07 195 0.66 Total Kjeldahl Nitrogen g/L 1,900 0.73 1,288 0.50 1,179 0.43 965 1.00 Nitrate + Nitrite g/L 736 0.83 558 0.67 572 0.48 543 0.91 Total Phosphorus g/L 383 0.69 263 0.75 201 0.67 121 1.66 Soluble Phosphorus g/L 143 0.46 56 0.75 80 0.71 26 2.11 1 Source: EPA, 1999.Preliminary Data Summary of Urban Stormwater Best Management Practices. EPA-821-R-99-012. 2 COV= Coefficient of variation.

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Denver Water Quality Management Plan Chapter 2 Page 2-27 MEDIANCOVMEDIANCOVMEDIANCOVMEDIANCOVMEDIANCOVMEDIANCOVMEDIANCOVMEDIANCOVMEDIANCOVMEDIANCOVMEDIANCOVMEDIANCOV Land Use Drainage Area 56.003.64 57.304.73150.802.07 38.801.22 75.002.05 39.001.58127.701.96 36.000.00 1.611.43 63.130.29 73.501.76115.360.88 % Imperviousness 54.300.43 37.000.42 44.900.28 83.000.12 60.000.30 75.000.30 44.000.26 45.000.00 80.000.13 38.000.00 2.001.26 34.000.14 Precipitation Depth (in) 0.470.96 0.461.01 0.550.79 0.391.04 0.470.95 0.490.96 0.450.84 0.180.91 0.541.05 0.680.61 0.481.13 0.430.88 Runoff (in) 0.181.97 0.111.96 0.181.42 0.231.21 0.351.10 0.142.67 0.291.16 0.002.09 0.411.70 0.280.89 0.171.31 0.121.20 Conductivity (S/cm @25C) 120.001.76 96.001.51112.001.15118.500.98103.000.59135.501.31110.500.81 99.001.01418.000.56155.000.67214.701.83 Hardness (mg/L CaCO3) 38.001.44 32.001.04 39.701.17 38.901.05 35.001.83 39.001.52 33.000.54 34.001.85 83.000.28116.500.63 55.001.47 Oil and Grease Total (mg/L) 4.0010.07 3.148.04 4.002.54 4.703.16 4.002.93 4.0012.44 3.302.21 8.000.62 4.001.63 11.001.39 2.002.47 pH 7.500.10 7.300.10 7.500.09 7.300.10 7.600.08 7.500.11 7.690.11 7.100.11 7.800.06 7.700.08 7.970.07 Temperature (C) 16.450.36 16.400.36 16.000.33 16.000.39 15.000.35 17.850.33 18.000.35 14.000.35 16.000.30 15.500.24 16.000.33 TDS (mg/L) 80.002.52 70.752.05 86.002.24 77.001.84 69.001.94 92.003.48 80.002.41 52.500.67 77.500.80174.000.40113.000.70106.002.33 TSS (mg/L) 58.001.78 48.001.78 67.821.58 43.001.98 53.501.36 76.361.54 82.001.39 17.000.83 99.002.53 81.001.18 51.001.87 78.001.40 BOD5 (mg/L) 8.601.57 9.001.48 7.671.30 11.901.11 9.001.70 9.001.71 7.201.71 8.500.70 8.001.26 7.400.67 4.200.70 6.592.40 COD (mg/L) 53.001.19 55.001.13 42.001.42 63.001.00 60.000.98 60.001.19 40.001.12 50.000.91100.001.06 48.000.47 21.001.82 39.001.54 Fecal Coliform (#/100 mL) 5,081 4.6 7,750 5.1 10,950 3.3 4,550 2.8 4,990 3.2 2,500 5.6 3,033 2.5 1,700 1.9 730 2.0 3,100 2.9 3,250 2.1 Fecal Streptococcus (#/100 mL) 17,000 3.8 24,000 1.8 26,000 2.2 10,800 2.7 11,000 2.8 13,000 6.9 10,000 2.6 17,000 1.2 19,000 1.1 24,000 2.6 21,000 2.3 Total Coliform (#/100 mL) 11,000 2.4 5,467 1.4 9,000 12,500 2.4 50,000 1.5 62,000 Ammonia (mg/L) 0.443.57 0.311.09 0.404.35 0.501.20 0.600.99 0.504.04 0.430.72 0.310.53 1.071.30 0.920.53 0.301.13 0.511.17 N02+NO3 (mg/L) 0.601.06 0.591.25 0.560.99 0.611.06 0.560.67 0.730.95 0.560.74 0.600.64 0.281.23 0.650.67 0.590.86 0.700.94 Nitrogen Kjeldahl Total (mg/L) 1.401.35 1.421.26 1.331.93 1.600.94 1.380.92 1.401.15 1.001.54 1.350.50 2.001.37 1.620.93 0.611.04 1.201.32 Phosphorous Dissolved (mg/L) 0.121.58 0.170.95 0.121.09 0.111.25 0.112.12 0.111.16 0.082.25 0.130.49 0.202.13 0.040.84 0.081.22 0.091.08 Phosphorous Total (mg/L) 0.271.51 0.301.14 0.271.71 0.221.15 0.251.48 0.261.37 0.201.52 0.180.99 0.251.76 0.260.79 0.253.62 0.271.02 Antimony Total (g/L) 3.202.61 28.001.48 1.002.11 69.000.79 15.000.99 4.003.01 1.00 3.000.25 340.00 1.000.00 Arsenic Total (g/L) 3.002.42 3.002.10 3.103.86 2.303.15 2.201.04 4.001.38 3.000.96 2.400.70 3.000.71 5.001.18 4.000.78 Arsenic Dissolved (g/L) 1.501.00 1.480.50 2.000.84 1.500.47 1.750.20 1.000.43 2.000.41 1.431.15 Beryllium Total (g/L) 0.402.47 0.502.52 0.302.70 0.501.99 0.351.60 0.392.50 0.300.47 27.00 Cadmium Total (g/L) 1.0028.17 0.501.67 0.803.85 0.841.57 0.861.11 2.002.34 1.0010.87 0.500.69 1.000.90 0.500.68 0.501.69 1.001.85 Cadmium Dissolved (g/L) 0.501.14 0.700.55 0.300.64 0.301.34 0.400.87 0.601.10 0.600.58 0.681.03 Chromium Total (g/L) 7.001.48 4.501.40 7.001.55 6.001.35 4.501.16 14.501.15 8.001.69 8.300.71 6.000.99 5.002.08 5.001.49 Chromium Dissolved (g/L) 2.080.73 1.280.44 2.000.80 2.000.59 2.000.72 3.000.73 2.000.69 2.300.70 Copper Total (g/L) 16.002.21 12.001.83 17.391.33 17.001.48 17.002.96 22.001.99 17.400.89 17.000.59 34.700.95 8.501.05 5.302.24 11.001.47 Copper Dissolved (g/L) 8.001.63 7.001.96 5.500.86 7.570.83 9.500.61 8.000.67 6.000.58 10.901.50 1.00 Lead Total (g/L) 16.001.85 12.001.89 18.001.37 18.001.59 17.001.47 25.001.81 18.501.50 5.750.79 25.001.45 10.000.90 5.002.02 10.002.28 Lead Dissolved (g/L) 3.002.02 3.001.87 3.000.68 5.001.59 6.000.61 5.001.58 5.000.97 1.801.65 2.000.00 Mercury Total (g/L) 0.202.68 0.201.17 0.201.00 0.200.84 0.101.12 0.202.66 0.250.58 0.190.80 0.101.05 Nickel Total (g/L) 8.002.13 5.401.21 7.930.83 7.003.78 5.001.33 16.001.24 9.000.92 9.000.91 27.000.87 7.001.16 Nickel Dissolved (g/L) 4.001.47 2.000.51 5.500.87 3.000.84 3.000.57 5.001.43 5.000.57 4.001.38 Zinc Total (g/L) 116.513.35 73.001.30 99.501.04150.001.22132.001.70210.002.25160.003.32305.000.81200.001.01 90.000.86 39.001.32100.001.02 Zinc Dissolved (g/L) 52.003.89 31.500.84 48.000.88 59.001.37 94.000.74111.503.622100.001.18 51.001.86 160.00 14.000.61 Exhibit 2.17 National Stormwater Quality Database Summary (Version 1.1) FREEWAYS MIXED FREEWAYS OPEN SPACE MIXED OPEN SPACE MIXED COMMERCIAL INDUSTRIAL MIXED INDUSTRIAL INSTITUTIONAL OVERALL RESIDENTIAL MIXED RESIDENTIAL COMMERCIAL

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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts Chapter 2 Page 2-28 EXHIBIT 2.18 EVENT MEAN CONCENTRATIONS (MG/L) OF CONSTITUENTS IN DENVER METROPOLITAN AREA RUNOFF, PER DRURP AND PHASE 1 STORMWATER CDPS PERMIT APPLICATION FOR DENVER, LAKEWOOD, AND AURORA 1 Constituent Natural Grassland Commercial Residential Industrial Total Phosphorus 0.4 0.42 0.65 0.43 Dissolved or Ortho-Phosphorus 0.1 0.15 0.22 0.2 Total Nitrogen 3.4 3.3 3.4 2.7 Total Kjeldahl Nitrogen 2.9 2.3 2.7 1.8 Ammonia Nitrogen 0.1 1.5 0.7 1.2 Nitrate + Nitrite Nitrogen 0.5 0.96 0.65 0.91 Lead (Total Recoverable) 0.1 0.059 0.053 0.13 Zinc (Total Recoverable) 0.1 0.24 0.18 0.52 Copper (Total Recoverable) 0.04 0.043 0.029 0.084 Cadmium (Total Recoverable) Not Detected 0.001 Not Detected 0.003 COD 72 173 95 232 Total Organic Carbon 26 40 72 22-26 Total Suspended Solids 400 225 240 399 Total Dissolved Solids 678 129 119 58 BOD 4 33 17 29 1 Source: Aurora et al. 1992.Stormwater NPDES Part 2 Permit Application Joint Appendix. Based on data reported by DRCOG, 1983.Urban Runoff Quality in the Denver Region,as updated with more recent data from UDFCD 1992. The results in the Denver region parallel, in many respects, the findings of NURP. To the extent that there are discrepancies or inconsistencies between Exhibits 2.16, 2.17 and 2.18, Exhibit 2.18 should govern for projects in Denver. (Note: While these results are representative of general conditions within the Denver region, site-specific data from watershed studies should be used when available.) In general, DRURP identified constituents such as lead, zinc, cadmium, fecal coliform bacteria, and total suspended solids as significant pollutants in urban runoff. Other selected statements from the DRURP summary report (DRCOG 1983) relevant to this Plan include: Very few EPA Priority Pollutants were detected in runoff samples. Organic pollutants found were particularly sparse, and the most commonly occurring one detected was a pesticide. The most significant non-priority pollutant found was 2, 4-D which is an herbicide. Pollutant loading per runoff amount was not found to be well related to basin imperviousness or land use. Vague relationships between event mean concentrations and imperviousness were noted, but proved statistically insignificant. Concentrations of pollutants did not vary in a predictable or anticipated pattern.

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Denver Water Quality Management Plan Chapter 2 Page 2-29 A receiving water assessment was included in the program to denote the effects of urban runoff for the South Platte River, which is the ultimate receiving water for both wastewater effluent and urban runoff generated within the Denver metropolitan area. Significant amounts of sediment, bacteria, nutrients, organic matter, and heavy metals were found to enter the river during storm events compared with discharges from wastewater treatment plants over the same time period. The investigation of the effects of urban runoff on receiving waters involved three considerations: 1) comparison of pollutant concentrations monitored in the South Platte River during storm events with those occurring during ambient streamflow; 2)comparison of the relative amounts of pollutant loads entering the river from storm runoff with those from municipal wastewater sources; and 3) comparison of pollutant concentrations during periods of storm runoff and ambient streamflow with water quality standards in effect for the study segment of the South Platte River. Several water quality constituents had mean concentrations that were greater during storm runoff than during ambient streamflow. Suspended sediment and fecal coliform bacteria exhibited much greater concentrations during storm events, as did oxygendemanding substances and heavy metals. Total metals concentrations for lead, zinc, copper, cadmium, iron, and manganese during storm-runoff periods were greater than mean ambient concentrations and exceeded established stream standards 100 percent of the time. Effective control of urban runoff to reduce the concentrations of these constituents was identified as being important to improve the quality of water of the South Platte River. A comparison of the relative loading from point sources, base flow and urban runoff was necessary to denote the effects of urban runoff on the South Platte River. Results indicated that municipal wastewater discharges contributed the greatest amount of nitrogen, phosphorus, and organic carbon to the river on an annual basis. Total suspended solids and lead loading were shown to be predominantly influenced by contributions from urban runoff. The study showed that urban runoff is a significant source of some water pollutants. The most obvious pollutant is total suspended solids. This was true regardless of the existence of major land disturbances causing erosion. Urban runoff was also a significant source of fecal coliform bacteria, oxygen demanding substances, and metals during storms. In addition, nutrients from urban runoff are and will be a problem for lakes and reservoirs. Non-storm urban runoff (e.g., dry weather discharges such as irrigation runoff) was also identified as a source of pollutants. This was not expected and was determined indirectly in the study analysis. Since DRURP, DRCOG has been involved in six watershed studies that were designed to assess the nature, severity and impact of stormwater and/or nonpoint sources on water quality. These efforts characterized urban runoff in relation to development patterns. The results have been developed into predictive planning tools to estimate stormwater and nonpoint source quality,

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Overview of Denver Drainage Basins and Potential Adverse Stormwater Impacts Chapter 2 Page 2-30 quantity and effects on receiving waters. BMPs have been recommended, updated, and incorporated as an integral component of watershed management plans. Watershed controls include structural systems, nonstructural practices and institutional policies (DRCOG 1998). SUMMARY Denver faces a significant challenge in addressing urban runoff water quality issues over a large land area with varied drainage basins. The impacts of urbanization are multi-faceted and require integrated approaches in order to be most effective. The remainder of this Plan provides a framework for an integrated strategy to address these challenges. Additional work in the form of watershed-by-watershed assessments (See Chapter 9) will be needed to achieve Denver s goals in these basins.

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Chapter 3 Page 3-1 Chapter 3 REGULATORY DRIVERS Denver is committed to protecting and improving water quality conditions in waterbodies receiving stormwater runoff from areas within its boundaries. This commitment is driven not only by local, state, and federal regulations, but also by Denver s staff and citizens who view the lakes, stream, and rivers within Denver as an amenity and a significant part of its natural resources. The key federal regulation that pushes communities throughout the U.S. toward the goal of fishable, swimmable waters is the federal Clean Water Act. This Act establishes a variety of requirements intended to protect and improve conditions in streams, lakes, and wetlands. Aspects of the Clean Water Act particularly relevant to this Plan focus on regulation of stormwater discharges, water quality standards for waterbodies receiving runoff from stormwater discharges, and implications for water quality standards not being attained. The discussion which follows briefly identifies some of the key regulatory drivers relevant to this project that have evolved in large part from the Clean Water Act, including: 4 Denver s Phase I Stormwater Colorado Discharge Permit System (CDPS) Permit 4 Denver International Airport (DIA) CDPS Permit 4 U.S. Environmental Protection Agency s (EPA s) April 2004 Audit of Denver s Stormwater Management Program 4 Denver s stormwater-related requirements and regulations 4 Other Denver ordinances, rules and regulations 4 Colorado Water Quality Control Act and Regulations, including state stream standards 4 Total Maximum Daily Loads (TMDLs) 4 Regional water quality efforts 4 Potential future changes to state and federal water quality permits and regulations PHASE I STORMWATER CDPS PERMIT Denver was required to obtain a stormwater discharge permit due to the National Pollutant Discharge Elimination System Permit Application Regulation for Inclusion of a Stormwater Discharge Regulation, which was issued on November 16, 1990 (Federal Register, Volume 55, No. 222). There are three major objectives of the stormwater discharge permitting program: 4 Reduce pollutant loadings in municipal storm sewer discharges to the maximum extent practicable (MEP). 4 Eliminate illicit wastewater connections, illegal discharges and non-exempt nonstormwater discharges to municipal storm sewer systems. 4 Implement management programs that apply best available technology (BAT), best conventional pollutant control technology (BCT) and, where necessary, water-quality based controls directed at controlling industrial stormwater pollution.

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Regulatory Drivers Chapter 3 Page 3-2 Denver is permitted to discharge municipal stormwater runoff to state waters in the South Platte River watershed under CDPS Permit No. COS-000001, which was renewed on March 20, 2003 and remains effective until April 30, 2008 (CWQCD 2003). This permit covers all areas within the corporate boundary of Denver served by, or otherwise contributing to discharges to state waters, from municipal separate storm sewers (MS4s) owned or operated by Denver. This includes the storm sewer system at DIA, excluding DIA s industrial system, which is covered under DIA s industrial stormwater permit (COS-000008). Denver s permit was originally issued in 1996 under the Phase I stormwater regulation. The subsequent Phase II stormwater regulation, which is best known for the requirements it places on smaller communities, also affected Denver s permit. Examples of key changes to Denver s permit due to the Phase II stormwater regulation included: 1) regulation of one acre or more of disturbance at construction sites, whereas a five-acre trigger was in place under the initial permit; and 2) increased emphasis on public education/outreach. Denver s current permit specifies stringent requirements with which Denver must comply through a combination of a Stormwater Management Program, regular program review and modification, wet weather monitoring, conformity with a compliance schedule, annual reporting, signatory certification, and other measures. The Stormwater Management Program must address these five major categories: commercial/residential management, illicit discharge management, construction sites, municipal facility runoff controls and industrial facilities runoff. To frame the seriousness and extent of the requirements under this permit, the terms shall and will are used over 200 times in the permit. Consequences for violations include significant fines and possible imprisonment for knowing violations of the permit. In addition to measures it must implement, Denver is also required to ensure, insure, or assure the following: 4 With regard to new development planning procedures for commercial/residential areas, the permit specifies: City ordinances and rules shall be revised as necessary to include provisions to ensure that stormwater quality controls installed for significant development or redevelopment are adequately operated and maintained. (Part 1, B. 2.c.). 4 With regard to inspection and enforcement procedures as part of project review and approval procedures for new commercial/residential development, the permit specifies: Developments shall be inspected for compliance to insure that all specified BMPs are constructed in accordance with the approved plan. (Part 1, B. 2.e. iii.). 4 With regard to assessing the impacts of flood management projects under the commercial/development management program, the permit specifies: The permittee shall continue to implement procedures to assure that the impact on water quality is assessed for proposed flood management projects. (Part 1, B. 4.). 4 With regard to procedures for site inspection and enforcement at construction sites, the permit specifies: procedures to insure that BMPs are being installed and maintained according to the approved plan and that sediment sources, materials, equipment maintenance areas (including fueling) and other significant sources of pollution have been addressed and enforcement provisions to insure compliance with requirements as

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Denver Water Quality Management Plan Chapter 3 Page 3-3 EXHIBIT 3.1 OVERVIEW OF DENVER S STORMWATER PERMIT REQUIREMENTS RESIDENTIAL/COMMERCIAL MANAGEMENT PROGRAM ILLICIT DISCHARGE MANAGEMENT PROGRAM INDUSTRIAL FACILITIES PROGRAM CONSTRUCTION SITES PROGRAM MUNICIPAL FACILITY RUNOFF CONTROL PROGRAM WET WEATHER MONITORING PROGRAM defined in Denver ordinances and rules, and approved plans and to insure effective operation and maintenance of BMPs. (Part 1, B. 2.d.3.a.i. & iii.). A brief overview of the specific types of requirements in the permit includes the following: Residential/Commercial Management Program 1. Maintenance of Structural Controls implement a program of routine maintenance activities for municipally owned structural controls to reduce pollutants. 2. New Development Planning Procedures continue to implement comprehensive planning procedures and enforce controls to reduce the discharge of pollutants after construction is complete from areas of new development and significant redevelopment. 3. Public Street Maintenance continue to operate and maintain public streets, roads and municipal parking lots in a manner so as to reduce the discharge of pollutants (including those related to road repair, street sweeping, snow removal, sanding activities and herbicide application). 4. Assess Impacts of Flood Management Projects continue to implement procedures to assure that the impact on water quality is assessed for proposed flood management projects. 5. Pesticide, Herbicide, and Fertilizer Application continue to implement controls to reduce the discharge of pollutants related to application of pesticides, herbicides, and fertilizers. Illicit Discharges Management Program 1. Prevention of Illicit Discharges and Improper Disposal continue to implement an ongoing program to detect and remove (or require the discharger to the MS4 to obtain a separate CDPS permit for) illicit discharges and improperly disposed materials into the MS4 in accordance with this program area. 2. Ongoing Field Screening continue to implement an ongoing program to screen the MS4 for illicit discharges, illegal dumping and illicit connections.

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Regulatory Drivers Chapter 3 Page 3-4 3. Investigation of Suspected Illicit Discharges continue to implement a program to locate and eliminate suspected sources of illicit connections and improper disposal. 4. Procedures to Prevent, Contain, and Respond to Spills continue to implement a program to prevent, contain, and respond to spills that may discharge into the MS4. 5. Educational Activities to Promote Public Reporting of Illicit Discharges and Improper Disposal continue to implement a plan to promote and facilitate public reporting of the presence of illicit discharges or improper disposal of materials into the MS4. 6. Public Educational Activities to Promote Proper Management and Disposal of Potential Pollutants continue to implement a plan to promote the proper management and disposal of used motor vehicle fluids and household chemical wastes, and to reduce or eliminate the discharge of other pollutants to the MS4. 7. Household Chemical Waste Collection Programs continue to sponsor a door-to-door household hazardous waste collection program, or substitute an equivalent program that has the same result of making reasonably available to Denver residents the means to recycle/properly dispose of the more common household chemical wastes. 8. Control of Sanitary Sewer Seepage into the MS4 continue the existing program to detect and eliminate sources of sanitary sewer seepage into the MS4. Industrial Facilities Program Develop and implement a program to promote proper management of industrial sites regarding stormwater quality and industrial BMPs. The program shall provide education and outreach on pollutants in stormwater discharges to municipal systems from industrial facilities that the permittee determines are contributing or have the potential to contribute a substantial pollutant loading to the MS4. Construction Sites Program 1. Procedures for Site Planning continue to implement procedures for site planning that incorporate consideration of potential water quality impacts from construction sites within Denver. 2. Structural and Non-Structural BMPs continue to implement requirements for the selection, implementation, installation, and maintenance of appropriate BMPs at construction sites. 3. Procedures for Site Inspection and Enforcement continue to implement procedures for inspection and enforcement of control measures at construction sites. 4. Training and Education for Construction Site Operators continue to develop, support and encourage attendance at an education and training program for construction site operators.

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Denver Water Quality Management Plan Chapter 3 Page 3-5 Municipal Facility Runoff Control Program continue to implement runoff control plans for specified Denver-owned and/or operated facilities that do not have independent CDPS stormwater permits. New plans shall be developed for any new facilities. Currently covered facilities include: 4 Vehicle maintenance facilities (maintenance includes equipment rehabilitation, mechanical repairs, painting, fueling and lubrication). 4 Asphalt and concrete batch plants which are not already individually permitted. 4 Solid-waste transfer stations. 4 Exposed stockpiles of materials, including stockpiles of road deicing salt, salt and sand, sand, rotomill material. 4 Sites used for snow dumps, and/or for temporary storage of sweeper tailings or other waste piles. Wet Weather Monitoring Program continue to implement a wet weather monitoring program to assess wet weather conditions, particularly urban stormwater effects on state waters. Denver, Aurora, Lakewood, and Urban Drainage and Flood Control District (UDFCD) work together (as the Joint Stormwater Task Force) on this program, with actual monitoring conducted by the U.S. Geological Survey (USGS). Samples are collected from receiving waters at five locations: an upstream site, a downstream site, an intermediate site, one major tributary, and a tributary to a major tributary. The monitoring program was designed based on land use considerations, and sampling is conducted based on the rising limb of the hydrograph associated with a precipitation event. The monitoring program was initiated in 1997, with active monitoring beginning in 1998 and continuing through the present. The four-year baseline monitoring period associated with Denver s first permit term is complete, with a second four-year period in progress for purposes of trend analysis (SAIC 2004). DENVER INTERNATIONAL AIRPORT (DIA) CDPS PERMIT When the Colorado Water Quality Control Division (CWQCD) renewed Denver s municipal stormwater permit in May of 2003, the permit additions included coverage of the MS4 system at DIA. Similar to other U.S. airports, prior to 2002, DIA was already covered under an industrial stormwater permit (COS-000008) which includes industrial activities such as aircraft deicing. Denver s renewed MS4 permit provides an implementation schedule to bring the airport into MS4 permit compliance with the rest of Denver. As a result, the areas of the airport that are not impacted by industrial activity will follow the same policies, rules and regulations regarding stormwater discharges as the rest of Denver. Extensive coordination between the Department of Public Works and the Department of Aviation is ongoing. Development parcels at the airport will be handled in the same manner as development parcels elsewhere in Denver. DIA is also covered under a CDPS stormwater construction permit and a Minimum Industrial Discharge (MINDI) permit. The Roadmap to Development Review, Permitting, and Construction Sites Program Process, Wastewater Management Division Rules and Regulations

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Regulatory Drivers Chapter 3 Page 3-6 and MS4 Permit Requirements was developed in December 2003 (Denver 2003) and can be referenced for more information on DIA s construction-related stormwater management requirements. EPA S APRIL 2004 AUDIT OF DENVER S STORMWATER MANAGEMENT PROGRAM During April 2004, EPA Region 8 conducted an audit of Denver s permitted stormwater management program. Appendix B contains a summary of the action items from this audit, combined with Denver s responses to EPA s comments. The goal of the audit was to determine the overall success and effectiveness of Denver s compliance with the conditions and requirements of its CDPS permit. The audit included interviews, file review and field inspections. As a result of the final report prepared by SAIC, Denver was required to provide written responses within 60 days on the action items identified by EPA. Overall, the audit indicated that Denver was well along with the implementation of its MS4 program and has achieved many positives in its program; however, some concerns have been identified. EPA s general program findings included: 4 Denver has an effective public education and outreach program. 4 Denver inspectors thoroughly understand their responsibilities, the MS4 permit requirements, and how to implement these requirements. 4 Denver has areas of its program where additional coordination between Denver departments and between Denver and the CWQCD would be beneficial. 4 Denver has not adequately implemented all standardized procedures throughout the MS4 program. (Better documentation is needed.) 4 Denver has not designated a staff person to be responsible for the stormwater runoff control program at its municipal facilities. Overall, the comments on the program were positive, with required changes to the program generally characterized as administrative loose ends that are relatively easily addressed, as described in Denver s responses to the audit in Appendix B. DENVER S STORMWATER QUALITY RELATED POLICIES The Wastewater Management Division of the Department of Public Works is organized to operate the sewerage system of Denver and to implement and enforce the Rules and Regulations Governing Sewerage Charges and Fees and Management of Wastewater and Chapter 56, Articles 91 through 107 of the Revised Municipal Code. A variety of drainage and stormwater-quality-related requirements are identified, the most explicit of which are in Chapter 10, Section 10.17 of the rules and regulations. Because the requirements of this section provide a critical foundation for this Plan, the requirements of Section 10.17 are reproduced in full as follows:

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Denver Water Quality Management Plan Chapter 3 Page 3-7 EXHIBIT 3.2 SELECTED REQUIREMENT S FOR DEVELOPMENT AND REDEVELOPMENT PROJEC TS IN DENVER PROVIDE BMPS TO ENHANCE STORMWATER RUNOFF PROVIDE TIMED RELEASE OF THE WATER QUALITY CAPTURE VOLUME FOR SITES REQUIRED TO DETAIN RUNOFF FOR DRAINAGE PURPOSES SUBMIT A STORMWATER QUALITY CONTROL PLAN TO ADDRESS WATER QUALITY ISSUES AND IDENTIFY BMPS FOR THE SITE Pursuant to the terms, conditions and requirements of CDPS Permit No. COS-000001, issued to the City and County of Denver by the State of Colorado; the City is required to implement specific programs to control discharges to and from the Municipal Separate Storm Sewer System (MS4) owned or operated by the City and County of Denver. Elements of these mandatory programs require that the City take steps to minimize the discharge of sediment, debris, and other pollutants from construction sites; and provide for enhancing the water quality of storm runoff from fully developed sites. a. Technical Criteria. The minimum technical requirements for all proposed required BMPs relating to water quality are to be based on those specified in the UDFCD Criteria Manual, Volume 3, Best Management Practices, September 1992 and as may be amended. b. Water Quality Requirements. 1. All development and re-development projects that are located within the Corporate Boundaries of the City and County of Denver shall include in their design, specific measures to enhance the water quality of stormgenerated runoff from the fully developed project site. All Best Management Practices (BMPs) identified in the UDFCD Volume 3 Manual are applicable to development and re-development projects within the City and County of Denver. 2. All facilities designed to provide detention of storm-generated runoff for drainage and flood control purposes shall be required to provide water quality enhancement through the use of a timed-release water quality outlet structure or an approved alternative. 3. Timed release water quality outlet structures shall be designed to allow either a 40-hour or 12-hour drain time of a portion of the runoff identified as the Water Quality Capture Volume. The drain time is dependent on the type of proposed detention facility. At a minimum, the determination of the Water Quality Capture Volume and design requirements for timedrelease outlet structures shall conform to the methods and procedures outlined in the Urban Storm Drainage Criteria Manual, Volume 3.

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Regulatory Drivers Chapter 3 Page 3-8 4. All sites that are not required to provide detention of storm runoff for drainage and flood control purposes may still be required to detain for water quality purposes. c. Waivers. Upon application, review, and approval of said application, waivers from the requirement to detain solely for water quality purposes may be granted. d. Stormwater Quality Control Plans. All development, re-development, or other construction projects, regardless of size, are required to submit a Stormwater Quality Control Plan that addresses water quality issues and describes all permanent water quality "Best Management Practices" to be used on the fully developed site. The type and scope of this plan varies with the size of the site. Review and approval of this plan by the Manager or his/her duly authorized agents is required before any Wastewater Management Division Permits are issued that relate to the project. e. Plan submittals. Plans and drawings relating to water quality issues that are submitted for review and approval shall conform to the requirements set forth in the Wastewater Management Division s 1995 guidebook entitled Stormwater Quality Control Plans: An Information Guide and as may be amended from time to time. f. Fees. At the time of issuance of an applicable Sewer Use and Drainage Permit, a non-refundable review fee shall be paid to the City and County of Denver. The amount of such fee shall be charged as established by the Manager. g. Compliance with Chapter Required for Site Development Plan(s) Approval. No Site Development Plan(s) shall be approved unless said plan(s) include water quality enhancing measures consistent with the requirements of this Chapter and related land development regulations. Other key aspects of the Wastewater Management Division regulations that outline requirements related to stormwater quality and quantity and/or elucidate the permitting process related to stormwater and new developments include the following: 4 Sewer Use & Drainage Permit (Section 2.17) : A sewer use and drainage permit must be obtained for any new structure or addition to an existing structure. A permit may also be required for any situation which may affect storm drainage, the sanitary sewer system or the storm sewer system. A permit may also be required for any situation which requires review by the Wastewater Management Division. No repair or replacement of any building sewer is allowed prior to the issuance of a Sewer Inspection Permit. 4 Prohibited Discharges to the Storm Sewer System (Section 7.01) : Discharges of polluted water, waste or materials into Denver s storm sewers or into water courses that traverse Denver are prohibited. Discharges of industrial or commercial wastewater or any

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Denver Water Quality Management Plan Chapter 3 Page 3-9 polluted or contaminated water upon any sidewalk, street, alley, or any gutter are also prohibited. Other prohibitions are also identified. 4 Subdivision/Planned Unit Development/Planned Building Group/Planned Development (Chapter 9) : Specific requirements for storm drainage studies, development site plans, construction drawings, grading plans, and protective covenants are outlined. Drainage plans must provide for detention of the 100-year storm event in compliance with the UDFCD s Storm Drainage Criteria Manual and current Wastewater Management Division criteria. The owner/maintenance organization is required to be responsible for and pay for all installation and maintenance costs related to on-site storm sewers and storm drainage control facilities. A pre-application conference with the Wastewater Management Division is offered, but not required, to ensure that the developer is properly informed regarding requirements, criteria, and problems related to drainage. Section 9.04 identifies the Wastewater Management Division-related requirements that must be fulfilled on the Building Department Inspection Record form in order to receive a Certificate of Occupancy: a. A Sewer Use and Drainage Permit has been issued. b. Construction of all required storm and sanitary drainage facilities has been completed and accepted by the City. c. The Certificate of Inspection for all storm drainage and sanitary sewer facilities has been submitted. d. The building sewer connection has been inspected by the Division and a Sewer Inspection Permit has been issued. e. All fees required by the City and County of Denver have been received by the City. f. All other requirements of the Sewer Use and Drainage Permit have been completed. 4 Water Quality, Grading, and Erosion Control (Chapter 10): Requirements related to earth disturbance are specified to ensure that soil erosion and sedimentation (and changed water flow characteristics) are controlled to the extent necessary to avoid damage to personal and real property, and to prevent pollution of the MS4 and receiving waters. Post-construction requirements are specified in Section 10.17, as previously discussed. 4 Storm Drainage Planning and Design (Chapter 11): This chapter requires that all developers plan, design and install storm drainage facilities in compliance with the Denver Storm Drainage Master Plan to insure coordinated development of a system which is self-sufficient in each storm drainage basin. Drainage facilities are also required to comply with the Denver Comprehensive Plan in cases where future land uses are a consideration in the development of storm drainage facilities. Drainage facilities are also

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Regulatory Drivers Chapter 3 Page 3-10 required to comply with the Denver Storm Drainage Design and Technical Criteria Manual and UDFCD s Urban Storm Drainage Criteria Manual Specific storm drainage design criteria are provided for various development types. For example, the initial storm drainage system for commercial/industrial areas must be planned based on the 5-year storm and major drainage systems must be based on the 100-year storm. On-site stormwater runoff detention facilities are required to attenuate the peak flow conditions for both the 100-year and 10-year storm events under fully developed conditions. Other requirements apply for residential development, Planned Urban Developments (PUDs), etc. The requirements of Chapter 11 are relevant to this Plan for a variety of reasons. One key issue is understanding the difference between requirements for detaining stormwater from a water quantity management perspective and the requirement for detaining stormwater from a water quality perspective. Chapter 11 identifies the water quantity management requirements important for stormwater conveyance systems, whereas Chapter 10 identifies the requirements for the water quality capture volume necessary for water quality protection. The water quality capture volume is calculated in accordance with the Urban Storm Drainage Criteria Manual, Volume 3 (UDFCD 1999) based on smaller, frequently occurring storms (e.g., typically less than the 1-year storm), whereas the water quantity management requirements are based on the 2-, 5-, 10and/or 100-year storms, depending on the type of development. Opportunities for integration of these requirements are explored further in Chapter 6 of this Plan. 4 Floodplain Management (Chapter 12): This chapter focuses on requirements and prohibitions on development or alteration of property within the Regulatory Floodplain of Denver, except pursuant to the terms of a Sewer Use and Drainage Permit issued by Denver which authorizes such development or alterations. In summary, Denver has specific rules and regulations in place for managing stormwater quality and quantity. This Plan plays a supporting role relative to these rules, providing approaches and strategies to facilitate better implementation of these rules and regulations. OTHER DENVER ORDINANCES, RULES AND REGULATIONS In addition to Denver s rules and regulations that directly relate to water quality, other rules and regulations can restrict the types of stormwater quality management strategies that are implemented at a site. For example, many rules and guidelines exist as part of zoning codes and urban design guidelines specific to various development areas. A review of these rules and guidelines was beyond the scope of this Plan, but would be a valuable step in ensuring that there are not unnecessary hurdles and restrictions that prevent innovative stormwater quality management. As an example, there may be requirements for curbs and gutters or minimum street widths that, under some conditions, would prohibit implementation of certain Low Impact Development techniques.

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Denver Water Quality Management Plan Chapter 3 Page 3-11 COLORADO WATER QUALITY CONTROL ACT AND REGULATIONS The Colorado Water Quality Control Act (CRS 25-8-101 through 25-8-702) provides the policy direction to conserve, protect, maintain, and improve, where necessary and reasonable, the quality of state waters. The act also authorizes water pollution prevention, abatement and control programs. In Colorado, the Colorado Water Quality Control Commission (CWQCC) regulates water quality and is responsible for establishing classifications and standards to protect beneficial uses of streams, lakes and groundwater in the state (CRS 25-8-201 through 25-8-406). Discharge permits to waterbodies are issued in a manner intended to protect these beneficial uses. For this reason, the underlying classifications and standards are relevant to Denver in terms of its stormwater discharge permit, even though the permit itself contains no numeric standards. A variety of standards for physical and chemical constituents have been developed for Colorado streams based on their assigned classifications. A brief overview of the subset of use classifications relevant to streams and/or lakes in the Denver area from the Basic Standards and Methodologies for Surface Water (5 CCR 1002-31) includes the following: 4 Recreation Class 1 Primary Contact: These surface waters are suitable or intended to become suitable for recreational activities in or on the water when the ingestion of small quantities of water is likely to occur Waters shall be presumed to be suitable for Class 1 uses and shall be assigned a class 1a or class 1b classification unless a use attainability analysis demonstrates that there is not a reasonable potential for primary contact uses to occur in the water segment(s) in question within the next 20 years. 4 Agriculture: These surface waters are suitable or intended to become suitable for irrigation of crops usually grown in Colorado and which are not hazardous as drinking water for livestock. 4 Aquatic Life Class 1 Warm Water: These are waters that (1) currently are capable of sustaining a wide variety of warm water biota, including sensitive species, or (2) could sustain such biota except for correctable water quality conditions. 4 Aquatic Life Class 2 Warm Water: These are waters that are not capable of sustaining a wide variety of cold or warm water biota, including sensitive species, due to physical habitat, water flows or levels, or uncorrectable water quality conditions that result in substantial impairment of the abundance and diversity of species. 4 Domestic Water Supply: These surface waters are suitable or intended to become suitable for potable water supplies. After receiving standard treatment (defined as coagulation, flocculation, sedimentation, filtration, and disinfection with chlorine or its equivalent), these waters will meet Colorado drinking water regulations and any revisions, amendments, or supplements thereto. In addition to these classifications, the majority of the streams and lakes in the Denver area are also classified as Use Protected which means that that the CWQCC has determined that the

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Regulatory Drivers Chapter 3 Page 3-12 waters do not warrant the special protection provided by the outstanding waters designation or the antidegradation review process. (Use-protected waters are allowed to degrade to the level of water quality standards and are not considered reviewable waters under the antidegradation regulation [CWQCD 2001].) A variety of criteria can be applied to result in a segment being use-protected, one example of which is an Aquatic Life Warm Water Class 2 designation. Under its CDPS stormwater permit, Denver is permitted to discharge to multiple locations in the South Platte River basin with stream standards assigned by the CWQCC as summarized in Exhibit 3.3. (See Chapter 2, Exhibit 2.3 for stream locations.) The specific numeric standards associated with these classifications are provided in Colorado Department of Public Health and Environment Water Quality Control Commission Regulation 38 Classification and Numeric Standards South Platte River Basin, Laramie River Basin, Republican River Basin, Smoky Hill River Basin as summarized in Appendix A of this Plan. One recent change to the classifications that is noteworthy with regard to water quality issues affecting DIA arose from the difficulty of several streams in the DIA drainage basin meeting stream standards for dissolved oxygen (DO). In the July 2004 Triennial Review hearing for the South Platte, Denver proposed adoption of ambient-based DO standards for Second Creek, Third Creek, and Box Elder Creek based on the demonstration that natural conditions or a combination of natural and irreversible anthropogenic conditions preclude the attainment of the existing DO standards for those streams. DIA is located in the Third Creek headwaters. In its proposal, Denver (2004) stated: Stormwater runoff from the airport has enhanced instream flows; however, this runoff may carry aircraft deicing fluid, which has the potential to exert an oxygen demand when the aircraft deicing fluid biodegrades. To minimize human-induced conditions, DIA has satisfied regulatory requirements for implementation of all best practical, available, and economically achievable technology for the control of aircraft deicing fluid. Denver considers the establishment of DIA in this watershed as an irreversible condition because the airport is a permanent part of the landscape and is an important part of the state economy. Deicing will continue to be a requirement for ensuring the safety of air travel. Denver also conducted a Receiving Water Study to evaluate the aquatic communities of Second Creek, Third Creek, and Box Elder Creek. The study demonstrated that ambient-quality-based DO standards will protect instream classified uses (Denver 2004).

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Denver Water Quality Management Plan Chapter 3 Page 3-13 Exhibit 3.3 Denver Receiving Water Descriptions and Classifications (CWQCD 2003) Receiving Water Basin & Segment Designated Use 1 Classification Box Elder Creek Middle South Platte River, Segment 5 UP Aquatic Life Warm 2, Rec. 1a, Agriculture Bear Creek Bear Creek, Segment 2 UP Aquatic Life Warm 1, Rec. 1a, Water Supply, Agriculture Grasmere Lake Upper South Platte River, Segment 17a UP Aquatic Life Warm 1, Rec. 1a, Agriculture Lakewood Gulch Upper South Platte River, Segment 16 UP Aquatic Life Warm 2, Rec. 1a, Agriculture Sloan s Lake Upper South Platte River, Segment 17b n/a Aquatic Life Warm 1, Rec. 1a, Agriculture Cherry Creek Cherry Creek, Segment 3 UP Aquatic Life Warm 2, Rec. 1a, Water Supply, Agriculture City Park Lake Upper South Platte River, Segment 17a UP Aquatic Life Warm 1, Rec. 1a, Agriculture Sand Creek Upper South Platte River, Segment 16a n/a Aquatic Life Warm 2, Rec. 1a, Agriculture Rocky Mtn. Lake Upper South Platte River, Segment 17a UP Aquatic Life Warm 1, Rec. 1a, Agriculture Berkeley Lake Upper South Platte River, Segment 17a UP Aquatic Life Warm 1, Rec. 1a, Agriculture Clear Creek Clear Creek, Segment 15 UP Aquatic Life Warm 1, Rec. 1a, Water Supply, Agriculture First Creek Upper South Platte River, Segment 16c UP Aquatic Life Warm 2, Rec. 1a, Agriculture Second Creek Upper South Platte River, Segment 16d UP Aquatic Life Warm 2, Rec. 1a, Agriculture Third Creek Upper South Platte River, Segment 16e UP Aquatic Life Warm 2, Rec. 1a, Agriculture Bowles Lake Upper South Platte River, Segment 17c n/a Aquatic Life Warm 1, Rec. 1a, Agriculture Smith Lake Upper South Platte River, Segment 17a n/a Aquatic Life Warm 1, Rec. 1a, Agriculture South Platte River Upper South Platte River, Segment 14 n/a Aquatic Life Warm 1, Rec. 1a, Water Supply, Agriculture South Platte River 2 Upper South Platte River, Segment 15 UP Aquatic Life Warm 2, Rec. 1a, Water Supply, Agriculture Exhibit Notes: 1 UP = use protected, n/a = not applicable; 2 Segment 15 of the South Platte River is immediately downstream of Denver s boundary, but is relevant to Denver from a regional water quality planning perspective.

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Regulatory Drivers Chapter 3 Page 3-14 TOTAL MAXIMUM DAILY LOADS (TMDLs) Although numeric discharge limits are not generally required under stormwater discharge permits, stormwater and nonpoint source discharges can be affected by numeric stream standards when streams do not attain their designated uses. Specifically, the federal Clean Water Act provides for the total maximum daily load (TMDL) process to allocate pollutant loads or potential pollutant loads among all identified discharge sources so that the combined discharges do not cause the water quality standards for a given waterbody to be exceeded under existing and future conditions (DRCOG 1998). A simplified formula for the components of a TMDL is represented as follows: TMDL = WLA + LA + NBG + MOS where: 4 WLA = wasteload allocation representing the portion of loading capacity attributed to point sources and piped stormwater (permitted wet weather stormwater runoff and dry weather flows) 4 LA = load allocation representing the portion of loading capacity attributed to nonpoint sources 4 NBG = natural background representing the portion of loading capacity attributed to natural background conditions (generally a component of the LA) 4 MOS = margin of safety portion of loading capacity attributed to uncertainty It is important to note that the Clean Water Plan (DRCOG 1998) differentiates between wet weather and dry weather conditions as follows: TMDL (dry weather) = WLA (piped dry weather runoff & point sources) + NBG (low flow) + Margin of Safety (MOS) TMDL (wet weather) = WLA (unit area stormwater & point sources) + LA (unit area) + NBG (high flow) + MOS Given that TMDLs are driven by the 303(d) list, it is critical that water quality planning in Denver take into consideration known stream segments that do not attain stream standards. The CWQCD s draft 303(d) list for 2004, which was released in November 2003, identified several stream segments receiving stormwater discharges from Denver that do not attain stream standards, as summarized in Exhibit 3.4. The segment listings in this table are generally consistent with similar information contained in Denver s current stormwater permit.

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Denver Water Quality Management Plan Chapter 3 Page 3-15 Exhibit 3.4 CWQCD Preliminary 303(d) List for 2004 ID Segment Description Portion Parameters COSPCL15 Clear Creek, Youngfield St. to S. Platte River All fecal coliform COSPUS14 S. Platte River, Bowles Ave. to Burlington Ditch All Nitrate, fecal coliform, E. coli COSPUS15 1 S. Platte River, Burlington Ditch to Big Dry Creek Cadmium upstream of MWRD, E. coli from Clear Creek to Fulton Canal diversion and Burlington canal headgate to MWRD Cadmium 2 E. coli COSPUS16a Tributaries to S. Platte River, Chatfield Reservoir to Big Dry Creek Lower portion of Sand Creek Selenium, fecal coliform, E. coli COSPUS16c Tributaries to S. Platte River, Chatfield Reservoir to Big Dry Creek except specific listings East Tollgate Creek, West Tollgate Creek, Tollgate Creek 3 Selenium COSPUS17a Washington Park Lakes, City Park Lake, Rocky Mountain Lake, Berkeley Lake Berkeley Lake Arsenic Exhibit Notes: 1 Segment 15 of the South Platte River is immediately downstream of Denver s boundary, but is relevant to Denver from a regional water quality planning perspective. Segment 15 also receives treated municipal wastewater discharges from the Metro Wastewater Reclamation District (MWRD), which serves much of Denver. 2 The cadmium listing is associated with the ASARCO plant. 3 None of the specific stream segment portions listed for COSPUS16c receive runoff from Denver. During wet weather periods, stormwater and nonpoint source discharges are expected to be the leading contributors of elevated bacteria (i.e., fecal coliform, e. coli ) in these stream segments, which are all required to meet the stringent Recreation Class 1a standards. Leading sources of bacteria are expected to include pet waste, waterfowl, and wildlife. Most of these sources are difficult, if not impossible, to control and will be a challenge for Denver to address. Denver s efforts to develop a better understanding of the bacteria sources include an outfall investigation study in the Upper Central Platte Valley of the South Platte River. The Wastewater Management Division accelerated its broken tap and illicit connection program to upgrade sewer conditions in this area. Additionally, the Wastewater Management Division supported a study based on an antibiotic resistance analysis for fecal coliform to try to better define the sources of the bacteria (e.g., animal or human sources) (Baus 2004). Unfortunately, the results of this study were relatively inconclusive; however, additional opportunities exist to support ongoing bacterial

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Regulatory Drivers Chapter 3 Page 3-16 source tracking studies being conducted by the Colorado School of Mines (Munakata-Marr 2004). Metals listed in Exhibit 3.4 may be associated with wastewater treatment plant discharges, stormwater, and/or naturally elevated conditions. Nitrate concentrations in Exhibit 3.4 are primarily associated with municipal wastewater treatment plant discharges. The draft TMDL for nitrate on Segment 14 of the South Platte River states, Stormwater runoff from nonpoint sources does not contribute significantly to the nitrate impairment (South Platte CURE 2003). In Denver s stormwater permit, the CWQCD (2003) states that a TMDL for the parameters listed in Exhibit 3.4 will be developed at some point in the future and that this could have an impact on future permit requirements. The CWQCD (2003) further notes in the permit that for the parameters potentially related to stormwater discharges, development of the TMDLs is expected to include the effects of precipitation-related events. The TMDL development may indicate that discharges from Denver s MS4 have a reasonable potential to cause exceedances of the applicable stream standards and provide a loading allocation that includes stormwater discharges. If this is the case, the CWQCD states that the permit could be amended to include additional requirements for the discharges to the TMDL segments. Such requirements would likely be based on BMPs as opposed to numeric limits (CWQCD 2003). Looking to the future, however, it is important to consider the possibility that federal and state agencies could regulate urban stormwater discharges on the basis of numeric standards, rather than the current BMP-based approach. With regard to addressing stream segments requiring TMDLs, it is important to recognize Denver s participation in the South Platte Cooperative for Urban River Evaluation (South Platte CURE) (as discussed later in this chapter). The members of South Platte CURE cooperatively share in-stream monitoring data, conduct modeling, and work toward cooperative development of TMDLs on stream segments requiring them, as is the case of Segment 14 of the South Platte for nitrate. Although Barr Lake (COSPMS03) and Milton Reservoir (COSPMS03) are not listed as receiving streams in Denver s permit, it is important to note that these two lakes are listed on the 303(d) list for non-attainment of the pH standard. During 2003, the CWQCD provided a 319 grant to assemble data on conditions in these reservoirs, which could eventually lead to a TMDL on these waterbodies. In the 319 grant application, Denver was identified as contributing over 75 percent of the drainage to these reservoirs; therefore, water quality issues in these waterbodies may also be relevant to Denver from a planning perspective. Denver is listed as a stakeholder in the Barr Lake/Milton Reservoir group.

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Denver Water Quality Management Plan Chapter 3 Page 3-17 Exhibit 3.5 Clear Choices for Clean Water Brochure REGIONAL EFFORTS AND AGREEMENTS Denver participates in several regional efforts related to water quality planning and improvement efforts. Key efforts discussed in this section that are vital to future water quality planning in Denver include: 4 Denver Regional Council of Governments (DRCOG)/ Clean Water Plan 4 Joint Stormwater Task Force (Denver, Aurora, Lakewood and UDFCD) 4 South Platte Cooperative for Urban River Evaluation (South Platte CURE) 4 Cherry Creek Stewardship Partners 4 Barr Lake/Milton Reservoir Watershed Association 4 Selenium Stakeholders Group Denver Regional Council of Governments/Clean Water Plan Denver participates in the Denver Regional Council of Governments (DRCOG), which is responsible under state and federal statutes for regional water quality planning in the Denver area. In this capacity, DRCOG prepares and updates the Clean Water Plan which is the management plan for achieving water quality standards pursuant to Sections 208, 303(e), and 305(b) of the federal Clean Water Act. In keeping with this Act, the region s goal is to "restore and maintain the chemical and physical integrity, in order to assure a balanced ecological community, in waters associated with the region." The objectives, policies and guidelines used in water quality planning and wastewater management, as described in the Clean Water Plan are intended to steer the regional water quality planning process. The Clean Water Plan describes wastewater management strategies, watershed water quality programs, wasteload allocations, stream standards, priority regional projects, nonpoint source control strategies and stormwater management programs. The plan provides a regional context for protecting and maintaining water quality through integrated watershed management processes. The objectives, policies and guidelines used in water quality planning and wastewater management are described in the plan. Denver is part of the South Platte Urban Watershed, which is recognized in the Clean Water Plan Joint Stormwater Task Force Denver, Aurora, Lakewood and UDFCD work together as the Joint Stormwater Task Force to implement a variety of stormwater-permitrelated requirements such as public education and stormwater monitoring. The original purpose of this group was to submit a joint Phase I stormwater permit application in 1992; however, the group has continued to work together to implement requirements of the Phase I permit through collaboration on a variety of projects. For example, the group prepared the Clear Choices for Clean Water brochures to educate the public on stormwater pollution prevention and continues to coordinate the wet weather monitoring program under the Phase I

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Regulatory Drivers Chapter 3 Page 3-18 permits. Most recently, the group has developed an educational booklet targeting industrial stormwater BMP maintenance and management (Doerfer 2004). South Platte Cooperative for Urban River Evaluation (CURE) The South Platte Cooperative for Urban River Evaluation (CURE) was formed in 1999 for a variety of purposes related to water quality on the South Platte River and its tributaries in the metro Denver area. South Platte CURE is a non-profit Colorado corporation primarily made up of municipal entities (i.e., municipal wastewater treatment providers, municipal stormwater agencies, local health departments, and municipal drinking water providers). Specific stream segments addressed by South Platte CURE include Segments 6, 14 and 15 of the South Platte River; Cherry Creek below Cherry Creek Reservoir; Bear Creek below Bear Creek Reservoir; Clear Creek below the ditch diversions near Golden; and Sand Creek. Denver is a financially supporting member of South Platte CURE. A few representative purposes of South Platte CURE include: 4 Coordinate water quality monitoring and data sharing at permanent trend monitoring locations and for special studies. Exhibit 3.6 identifies these monitoring locations. 4 Maintain, improve and operate low-flow point source and nonpoint source water quality models for use in water quality decisions related to discharge permits. 4 Cooperatively develop recommendations for TMDLs and wasteload allocations. Some specific South Platte CURE activities of particular relevance to Denver include: 4 A proposed 309 pilot project study that would recalculate the use-specific Table Value Standards (i.e., stream standards) based on the proposed changes to aquatic life use classifications. 4 Cooperative modeling and development of a nitrate TMDL for Segment 14 of the South Platte River. (Segment 14 includes the portion of the South Platte River from Bowles Avenue in Littleton to the Burlington Ditch.) 4 A copper study to evaluate the potential of a site-specific standard for copper on Segment 15 of the South Platte River, which is on the Monitoring and Evaluation portion of the 303(d) list. (Segment 15 includes the portion of the South Platte River from Burlington Ditch to below the confluence with Big Dry Creek.) The study is using a variety of techniques to assess the toxicity of copper in the stream to determine the potential appropriateness of a site-specific stream standard for copper for Segment 15 of the South Platte River. Stormwater has been discussed as the major source of copper affecting attainment of stream standards. In the July 2004 Triennial Review for the South Platte River, South Platte CURE formally proposed site-specific standards for copper as a result of this study (South Platte CURE 2004).

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Denver Water Quality Management Plan Chapter 3 Page 3-19 4 Ongoing studies and modeling related to sulfate and dissolved oxygen (DO) on the South Platte River. 4 Standardizing and uploading instream data for relevant stream segments into STORET (EPA s water quality database) for public retrieval. 4 Cooperative monitoring of South Platte River Segments 6, 14, and 15 as part of TMDL development. Monitoring includes nutrients, microbiology, and selected metals.

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Regulatory Drivers Chapter 3 Page 3-20 EXHIBIT 3.6 SOUTH PLATTE CURE MONITORING LOCATIONS (Map Source: South Platte CURE 2004)

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Denver Water Quality Management Plan Chapter 3 Page 3-21 Cherry Creek Stewardship Partners Denver is a signatory to the Cherry Creek Watershed Water Quality and Resource Stewardship Regional Memorandum of Understanding (MOU), along with Arapahoe County, Douglas County, the City of Glendale, the City of Greenwood Village, the Town of Parker, and the City of Centennial. This MOU evolved from the Smart Growth for Clean Water Cherry Creek Watershed Partnership project. The purpose of the Smart Growth project was to promote the establishment of a continuous natural greenway and innovative watershed enhancements to protect the water quality and the public enjoyment of Cherry Creek, its tributaries, and the Lake. The overall goals of the Partnership are to promote the long-term improvement of water quality in the Cherry Creek Basin through land conservation and innovative streamside and watershed enhancements; to promote regional cooperation on these issues; to enhance coordination among land use and water quality leaders; and to pursue funding strategies for these activities. Several specific goals in the MOU that are particularly relevant to this Plan include the following: 4 Support smart growth practices to mitigate development-induced water quality impacts. 4 Provide buffers to development. 4 Provide recommendations on urban design to protect Cherry Creek as a natural amenity. 4 Support regional approaches to water quality improvement in the Cherry Creek basin, throughout Douglas and Arapahoe Counties, and in Denver. Barr Lake/Milton Reservoir Watershed Association Denver is an active participant in the Barr Lake/Milton Reservoir Watershed Association, which includes stakeholders assembled to evaluate water quality in Barr Lake and Milton Reservoir, including upstream impacts from the Denver metropolitan area. The stakeholders group includes representatives from permitted wastewater dischargers, recreation and aquatic interests, agriculture, industry, water utilities, and local governments. The watershed study area includes a system of canals and streams draining to Barr Lake and Milton Reservoir, located northeast of Denver. Barr Lake is about 15 miles northeast of Denver, and Milton Reservoir is about 20 miles further to the northeast. Since Denver discharges both stormwater and wastewater into the basin, Denver is providing support in establishing a watershed association and participating in the 319 project to develop a better understanding of water quality issues in the basin. Part of this project includes development of a comprehensive water quality database. Selenium Stakeholders Group The Selenium Stakeholders Group consists of the City of Aurora, Conoco, Inc. (now Suncor Energy), Ultramar Diamond Shamrock (now Valero Energy), and Metro Wastewater

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Regulatory Drivers Chapter 3 Page 3-22 Reclamation District. This group is studying the elevated selenium concentrations on Sand Creek (Segment 16a) and the South Platte River (Segment 15). As a result of a stipulation for a temporary modification to the selenium standard on these segments, the Stakeholder Group has developed and is implementing a study plan to develop site-specific criteria for selenium based on data collection and exploration of other options (Lord-Reeves 2003). After three years of data collection, the data collected have not given a clear indication of the sources of selenium within the City of Aurora; therefore, the City of Aurora has undertaken additional studies such as geologic evaluations to explore the potential existence of selenium-bearing rock units within the Tollgate Creek basin (Piatt-Kemper 2003). Both the CWQCD and the parties involved in the Selenium Stakeholders Group recognize that selenium is a statewide issue and agencies within the state are looking at a more statewide solution to the selenium standard issue. The efforts of this group should continue to be monitored for those stream segments receiving runoff from Denver, particularly those that do not currently meet the selenium stream standards. The selenium issue on Sand Creek also highlights the importance of working with neighbors such as Aurora to address these multi-jurisdictional problems. At the July 2004 Triennial Review, the CWQCD proposed a temporary modification for the chronic dissolved selenium standard on Sand Creek of 19.3 g/L. This temporary modification was also proposed for East and West Tollgate Creeks and Tollgate Creek through February 2010 (CWQCD 2004). OTHER FEDERAL AND STATE REGULATIONS In addition to the specific regulations, permits and efforts already discussed, a wide variety of federal and state environmental regulations have the potential to affect water quality management in the Denver area. An exhaustive review of these regulations is beyond the scope of this Plan; however, a brief bullet list of some laws, regulations, and issues that may be potentially relevant includes: 4 National Environmental Protection Act (e.g., for federally funded transportation projects) 4 Groundwater Management Regulations (e.g., dewatering, discharges to groundwater) 4 Resource Conservation and Recovery Act 4 Individual Sewage Disposal Systems (ISDS) Regulations 4 Safe Drinking Water Act/Source Water Protection 4 Threatened and Endangered Species Act 4 Wetlands (i.e., sections 401 and 404 of the 1987 Clean Water Act amendments) 4 401 Certification 4 Colorado water law (e.g., affects length of time stormwater may be detained) Additionally, those managing stormwater planning should be particularly aware of the following common environmental issues and/or permit requirements: 4 Hazardous Materials and Phase 1 Site Assessments: Many old industrial areas occur in Denver; some of those areas have had releases of hazardous materials or contain hazardous substances. Several Superfund sites exist (such as the ASARCO Globeville Smelter and Koppers facility) in and around the Denver area. In these areas, a Phase I

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Denver Water Quality Management Plan Chapter 3 Page 3-23 Environmental Site Assessment should be conducted in accordance with ASTM Standard E 1527-00 and new federal standards expected to be circulated by the EPA in late 2004 or early 2005 to identify potential environmental risks and liabilities to the project and construction worker health and safety. This site assessment should consist of a site inspection, records review, and report. 4 Spill Reporting at Construction Sites : Contain and clean up spills such as, but not limited to, wash water, paint, automotive fluids, fuel or other petroleum based products, solvents, oils, or soaps, as soon as possible. Do not bury or wash spills into the storm drain or stream. Report all releases of materials into the environment to the Colorado Department of Public Health and Environment (CDPHE) 24-hour Environmental Emergency Spill Reporting Line (877-518-5608). 4 Section 404 Permit: Section 404 of the Clean Water Act is administered by the U.S. Army Corps of Engineers (USACE) and regulates filling Waters of the U.S. Section 404 permits from the USACE are required for the placement of dredged or fill materials into waters of the U.S., including wetlands. Dredged or fill material includes any solid material commonly used in construction such as, but not limited to, soil, concrete, metal structures, rock, and pipe. There are various types of Section 404 Permits, including Nationwide Permits, which are issued for activities with relatively minor impacts. An Individual Permit is issued for more major impacts such the relocating of a stream or creek segment, or filling over 0.5 acre of a jurisdictional wetlands. For information about what type of 404 permit may be required, contact the USACE Denver Regulatory office (303-979-4120). 4 Threatened and Endangered Species: In the Denver area, wetlands are potential habitat to three federally listed threatened and endangered species, which are protected under the Endangered Species Act. Before the USACE issues a Section 404 Permit, it requires the proposed project have clearance for: 1) Ute Ladies tresses orchid (Spiranthes diluvialis), 2) Colorado butterfly plant (Gaura neomexicana ssp. coloradensis), and 3) Preble s meadow jumping mouse (Zapus hudsonius preblei). A habitat suitability assessment is sufficient to determine if habitat for these species occurs in the proposed project area. If habitat for any of these species, or any other federally listed species (there are over 30 in Colorado), is suspected of occurring in a project area, a trapping or flowering period survey should be conducted to confirm absence or presence. 4 Section 401 Permit: If an Individual Permit is needed from the USACE, a Section 401 Water Quality Certification, issued by the CDPHE Water Quality Control Division (CWQCD), is required for a proposed project to fulfill regulatory requirements of Section 401 of the Clean Water Act. Specific requirements of this permit application and permit may be obtained from the CWQCD (303-692-3500 or http://www.cdphe.state.co.us/wq/PermitsUnit/wqcdpmt.html ). 4 Construction Stormwater Permit: Discharges of stormwater runoff from construction sites disturbing one acre or more of land and certain types of industrial facilities require a Colorado Discharge Permit System Stormwater Permit. The Stormwater Permit

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Regulatory Drivers Chapter 3 Page 3-24 application needs to include a Stormwater Management Plan (SWMP), which details erosion and runoff control measures, such as, but not limited to, a revegetation plan and silt fencing, to prevent surface stormwater quality degradation. Current BMPs are to be presented in the SWMP. Specific requirements of the permit application and permit may be obtained from the CWQCD (same contact information as above). 4 Construction Dewatering (Discharge or Infiltration) Permit: Discharges of water encountered during excavation or work in wet areas may require a discharge permit. If the water is discharged to waters of the state, a Construction Dewatering Discharge Permit is required. If the water is discharged to land and allowed to infiltrate, approval from the CWQCD is required. Specific requirements of this permit application and permit may be obtained from the CWQCD (same contact information as above). 4 Minimal Industrial Discharge Permit: Discharges of small quantities of wastewater or wastewater requiring minimal treatment, such as that resulting from hydrostatic testing or certain wash waters, may require a Minimal Industrial Discharge Permit (MINDI). Specific requirements of this permit application and permit may be obtained from the CWQCD (same contact information as above). CURRENT AND FUTURE COMPLIANCE IMPLICATIONS OF EVOLVING REGULATIONS Water quality regulations continue to evolve at both the state and federal levels. Changes to these regulations have the potential to impact water quality management in Denver for both point and nonpoint source discharges. Although stormwater and nonpoint source discharges continue to be based on BMPs instead of numeric criteria, these discharges can be drawn into the regulatory process through TMDLs when stream standards are not attained; therefore, regulatory changes that impact stream standards and classifications have significant relevance for stormwater discharges. Several key regulatory changes that are in progress can be reviewed through the Section 309 Report (CWQCD 2003) and through the activities of the Colorado Water Quality Forum (CWQF) work groups that explore topics such as impacted water supplies, nutrient criteria, sediment guidance, TMDL/303(d) issues, and water quality trading concepts. The CWQF work group activities are often driven by changes at the EPA under its Clean Water Act programs. (See http://www.is.ch2m.com/cwqf/ for a list of current CWQF work groups and topics.) Highlights of several emerging regulations are provided below based on the efforts of the CWQF work groups. Section 309 Report and Potential Aquatic Life Classification Changes In December 2003, the CWQCD released the Section 309 Report which focused on review of the state standards-setting and classification process. This document provides a basic road map of water-quality-related regulatory issues that the state may consider over the next few years. The purpose of the Section 309 Report is to assess whether regulatory or policy changes are warranted based on the unique attributes of Colorado waterbodies. Some of the key considerations in the report were affected by the Arid West Water Quality Research Project

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Denver Water Quality Management Plan Chapter 3 Page 3-25 (Pima County Wastewater Management Department 2003). Some of the specific topics addressed in the Section 309 Report (CWQCD 2003) included: 4 The physical, chemical, flow, and habitat characteristics associated with waterbodies, including the ephemeral or effluent-dependent nature of many waterbodies. 4 The potential need for refined designated uses and additional site-specific standards. 4 The benefit of maintaining the functions of constructed water conveyance and storage facilities. 4 The nature of the current use-attainability analysis process and any necessary adjustments. 4 The benefits associated with maintaining downstream ecosystems that are dependent, at least in part, upon the continuation of effluent discharges. The study process identified a wide variety of distinguishing features of Colorado waterbodies, with particular focus upon natural and human-induced variations in the flow regimes, variabilities in habitat and biological diversity, and the impact of effluent returns on otherwise water-short stream systems. One key area of discussion with potential relevance to Denver is the identification of potential refined designated uses under the state use classification system, primarily with regard to aquatic life classifications. Based on a strawman proposal presented by the state, the idea of adopting additional aquatic life use classifications to more accurately describe the actual use of stream systems and establish appropriate accompanying water quality standards is one key potential area of change. These types of revisions would be most significant for effluent dependent or effluent dominated waterbodies or those that have experienced significant hydrologic modifications. The key implication of such a revised classification system is the removal of needless impairment listings under the TMDL program. Triennial reviews of Colorado s major river basins will serve as an opportunity to field-test a variety of aquatic life classification modifications and bring them before the Commission at the Basic Standards Rulemaking Hearing in July of 2010 (CWQCD 2003). Currently, the aquatic life classification system includes three categories: Aquatic Life Warm 1 and 2 and Aquatic Life Cold. The new proposed system includes nine principal use classifications that are developed from combining cold water aquatic life, transition zone aquatic life or warm water aquatic life with the categories of aquatic life for lakes/reservoirs, streams with fish, or streams with no fish. In addition to the principal use classifications, several sub-classifications could also be assigned to account for influences from treated effluent or hydrologic/habitat modifications, including considerations such as: 4 Effluent dependent: Waters that would otherwise have an Aquatic Life-Streams No Fish classification, but which have flows adequate to support fish due to treated effluent.

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Regulatory Drivers Chapter 3 Page 3-26 4 Effluent dominated: Waters that would have an Aquatic Life-Streams-Fish classification without the presence of treated effluent, but for which the flow for the majority of the year consists of treated effluent. 4 Hydrologic/Habitat Modifications: Waters that are affected by irreversible human impacts (e.g., water rights diversions, stormwater flows, and agricultural return flows) such that the resulting expected condition differs from that for the associated principal use classification. (The Hydrologic/Habitat Modification sub-classification would only apply when supporting data demonstrates that the modifications are significant enough to change the expected condition.) The new proposed system embodies the concept of defining an expected condition for each of the nine principal use classifications. Expected conditions would not be based on the pristine or totally un-impacted reference condition, but rather on the characteristics of the aquatic community that generally would be anticipated without the influence of major human modifications. Other concepts explored under the Section 309 Report include the net environmental benefit concept, which is basically a potential relaxation of standards/effluent limitations on point sources discharging to water-short stream systems in order to encourage the continued beneficial discharge of the ecosystem-sustaining flows (CWQCD 2003). Although the Section 309 Report itself did not result in any recommended changes to state statutes, the concepts and issues raised could impact future policies, potentially as early as the Basic Standards Rulemaking Hearing in July of 2005. The CWQCD will continue its work with stakeholders to develop a state policy on the potential use of the net environmental benefit concept by October of 2004, which could also be brought before the CWQCC in July of 2005. The CWQCD will also initiate a pilot program to explore refined designated aquatic life use categories. Possible Stream Standard Changes Under Consideration for July 2005 A variety of issues will be considered at the July 2005 Rulemaking Hearing, in addition to the aquatic life issues discussed above. Some of these issues have implications for stormwater. A brief overview includes changes to organic chemical standards (will be addressed in 2004 in combination with Regulation 41, Basic Standards for Groundwater); revised table value criteria for ammonia, cadmium, copper, antimony, arsenic and uranium; selenium criteria (when developed by EPA); options for decoupling the aquatic life class 2 and use-protected designations; and other issues (CWQF 2003). Source Water Protection Source water (i.e., drinking water supply source) protection activities have a link to stormwater issues in that raw water quality for drinking water may be affected by pollutants in stormwater discharges. Sediment, nutrients, pesticides, pathogens, and other pollutants in source waters can decrease treatability, increase treatment costs, and ultimately increase risks to public health.

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Denver Water Quality Management Plan Chapter 3 Page 3-27 Water utilities typically respond to deteriorating raw water quality by increasing chemical dosages or adding additional processes. As an alternative or supplement to treatment changes, managers may consider promoting BMPs to protect raw water quality. A study funded by the American Water Works Association Research Foundation and the Water Environment Research Foundation (AWWARF and WERF 2003) to address these issues found that moderate deteriorations in raw water quality such as a 25 percent increase in solids and total organic carbon (TOC) levels can increase routine operating costs by roughly 10 percent. Many BMPs can prevent water quality deterioration when targeted to major pollutant source areas. AWWARF and WERF note that funding a fraction of BMP implementation costs can be a costeffective means of reducing routine operating costs for some utilities. AWWARF and WERF recommend that utilities in developing watersheds should promote low impact development practices to reduce long-term water quality degradation. The study recommended that utilities can help protect source quality and reduce treatment costs at minimal expense by forming partnerships with watershed stakeholders. Utility participation in protection efforts helps leverage funds and prioritizes the watershed as a drinking water catchment. Due to the high cost of treatment plant capital improvements relative to watershed BMPs, AWWARF and WERF recommend that utilities should consider long-term investment in source protection measures in order to reduce the need for major process changes. Utilities should also consider non-economic benefits of source protection, including the public health benefit of reduced exposure to pesticides, pathogens, and emerging contaminants (AWWARF and WERF 2003). Nutrient Criteria In September 2002, the CWQCD presented its Nutrient Criteria Development Plan to EPA in response to EPA s January 9, 2001 Federal Register notice that was intended to address nutrient over-enrichment in the nation s surface waters. According to EPA (1996), nitrogen and phosphorus are among the leading causes of water quality impairment in the U.S., with 40 percent of rivers and 51 percent of lakes having designated uses impairments from excess nutrients. EPA has called for states to develop region-specific nutrient criteria for different types of waterbodies to account for the wide natural variation in nutrient loading. For rivers and streams, the CWQCD anticipates developing a statewide approach with regionalization for establishing nutrient criteria. Key elements of the conceptual approach include: 4 Assessments conducted at the basin or sub-basin level (it is anticipated that in some cases site-specific standards may need to be implemented where basin or sub-basin level assessments are not refined enough to account for local conditions). 4 Criteria based on comparisons to expected conditions. 4 Criteria based on biological endpoints of the algal community that are linked to the designated uses.

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Regulatory Drivers Chapter 3 Page 3-28 Colorado is working on the nutrient criteria using a phased approach, which will first focus on developing nutrient standards for selected targeted waterbodies that have significant nutrient issues and that are high on the priority list. Nutrient criteria for Colorado lakes and rivers will be based on the causal parameters nitrogen and phosphorus, as well as the response parameters Chlorophyll-a, algal communities and transparency (Secchi depth or turbidity). Other possibilities for causal parameters that will be considered include orthophosphate, total Kjeldahl nitrogen, ammonia, nitrate, and dissolved organic carbon (DOC). Additional response parameters such as dissolved oxygen, pH, plankton or macrophyte biomass, percent cover, and species composition may also be considered. Considerations in the form of the criteria may include spatial scale, temporal cycles such as diel or seasonal cycles, and determination of attainment. Colorado anticipates developing numeric criteria (CWQCD 2002). Of particular relevance to Denver is that the CWQCD is starting with High Priority Sites first, one of which is Barr Lake. Barr Lake is located outside of Denver s boundaries, but it eventually receives runoff from much of the metro Denver area and was named as a receiving water in Denver s initial CDPS permit. Although Barr Lake is not a direct receiving water for Denver stormwater, EPA has provided the states with the following regulations in CFR Part 131.10(b): in designating uses of a waterbody and the appropriate criteria for those uses, the State shall take into consideration the water quality standards of downstream waters and shall ensure that its water quality standards provide for the attainment and maintenance of the water quality standards of downstream waters. EPA (Grubbs 2001) provides additional guidance stating: even if a state identifies waters that are not threatened or impaired from nutrient overenrichment, they should also consider whether the nutrient levels in this waterbody could contribute to an impairment downstream before determining that nutrient criteria are not needed. If it is likely that a downstream impairment is occurring, yet quantified criteria in downstream waters have not been established, then a state/tribe should consider employing nutrient load reduction strategies for the upstream waters. EPA recommends that these nutrient load reduction strategies are effective ways of reducing the effects on downstream uses, prior to adopting any specific nutrient criteria values. Colorado s timeline with regard to nutrient criteria includes developing interim measures by December 2004 that will provide nutrient triggers and screening-level measures such as add-on narratives to the Basic Standards and site-specific standards through the 303(d) listing process. Current timelines identify the 2010 Basic Standards Rulemaking Hearing as the target date for adopting nutrient criteria into the state standards (CWQCD 2002).

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Denver Water Quality Management Plan Chapter 3 Page 3-29 Sediment Deposition In May 2002, the CWQCD, CWCC, and the Colorado Sediment Task Force released the Provisional Implementation Guidance for Determining Sediment Deposition Impacts to Aquatic Life in Streams and Rivers, building upon draft guidance originally issued in 1998. This guidance provides an interpretation of the CWQCC s "narrative standards" as they apply to sediments which may form deposits detrimental to the attainment of aquatic life uses, as described in the Basic Standards and Methodologies for Surface Water, Regulation 31 (5CCR 1002-31). The guidance is intended as a first step toward providing a consistent approach to implementation of the statewide narrative basic standard that addresses sediment deposition, which is an important cause of impacts to aquatic life. The guidance applies to substances, primarily sediment caused by human induced erosion, which create a stress to aquatic life through the deposition of materials. The guidance provides a means for the CWQCD and the CWQCC to consider the impacts of bottom deposits on the attainment of the aquatic life uses, particularly with regard to assessing the status of water quality as required in §305(b) of the federal Clean Water Act, and establishing a listing of waterbodies requiring TMDLs under §303(d) of the Act (CWQCC et al. 2002). Because stormwater can be a leading contributor of sediments to streams, Denver should actively participate in activities that involve development of guidance and regulations related to the sediment narrative standard. Pollutant Trading Pollutant trading is a concept being explored by the CWQF and the CWQCD. The concept is also defined by EPA (2003) in its Water Quality Trading Policy. Various pollutant-trading programs in Colorado have focused primarily on lakes and reservoirs such as phosphorus trading programs in Lake Dillon and Cherry Creek Reservoir and a relatively young selenium-trading program in the Grand Valley. The CWQCD is in the process of developing the state Water Quality Trading Guidance document that includes topics such as preand post-TMDL trading. Progress on this document has potential relevance to Denver s stormwater discharges for streams with TMDLs. SUMMARY As is the case with cities throughout the U.S., Denver is faced with complex regulatory requirements with regard to water quality. The Phase I CDPS permit specifies stringent requirements with which Denver must comply or face significant penalties. Fortunately, Denver already has many sound water quality requirements in place in the form of policies and regulations. It will be imperative for Denver to continue to actively interface with regional water quality efforts and to stay abreast of forthcoming regulatory changes.

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Chapter 4 Page 4-1 Chapter 4 RELATIONSHIP TO OTHER DOCUMENTS Denver has completed multiple documents that provide important interfaces with water quality planning. Some of the key documents, which were completed either by Denver or related entities, are briefly summarized in this chapter, including: 4 Urban Storm Drainage Criteria Manual, Volumes 1-3 4 Denver Storm Drainage Design and Technical Criteria Manual 4 Denver Storm Drainage Master Plan and other drainage master plans 4 Standards, details and technical criteria documents 4 Metro Vision 2020 and the Clean Water Plan 4 Water Quality Improvement in the South Platte River, Report to the Mayor 4 Denver Comprehensive Plan 2000 4 Blueprint Denver 4 Denver Parks and Recreation Game Plan 4 Natural Areas Program Field Guide 4 Design Guidelines for Stapleton Water Quality 4 Long Range Management Framework South Platte River Corridor 4 Cherry Creek Greenway Corridor Master Plan 4 Cherry Creek Watershed Smart Growth for Clean Water Report 4 Lake Management and Protection Plan Basic familiarity with these documents is important to this Plan for several reasons. The first four documents listed identify already-established, accepted criteria and strategies for managing stormwater in the Denver area. This Plan does not reinvent the wheel with regard to these documents, rather it builds upon them. Documents such as the Denver Comprehensive Plan 2000 Blueprint Denver, and the Denver Parks and Recreation Game Plan summarize some of the existing goals of various city departments with which this Plan must interface in order to be most effective. Documents such as Metro Vision 2020 the Clean Water Plan the Long Range Management Framework South Platte River Corridor the Cherry Creek Greenway Corridor Master Plan, Cherry Creek Watershed Smart Growth for Clean Water, and Natural Areas Program Field Guide are an important interface with regard to regional water quality goals and goals for specific river corridors. The Lake Management and Protection Plan is important because it provides the framework for maintenance and protection of Denver lakes. Design Guidelines for Stapleton Water Quality is included because this Plan builds upon many of the strategies developed and accepted in the Stapleton guidelines. Highlights of each of these documents follow. URBAN STORM DRAINAGE CRITERIA MANUAL, VOLUMES 1-3 The Urban Drainage and Flood Control District (UDFCD) was established by the Colorado legislature for the purpose of assisting local governments in the Denver metropolitan area with multi-jurisdictional drainage and flood control problems. Since 1969, UDFCD has maintained and distributed the Urban Storm Drainage Criteria Manual which consists of three volumes.

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Relationship to Other Documents Chapter 4 Page 4-2 Volumes 1 and 2 (UDFCD 2001) provide guidance for planning and design of drainageway channels, storage facilities, culverts, hydraulic structures, and other structures. Volume 3 (UDFCD 1999) provides guidance for the selection and design of stormwater quality BMPs. The policies and design criteria set forth in these documents are the foundation of the stormwater BMP information provided in this Plan. Since the primary focus of this Plan is stormwater quality management, the topics covered in Volume 3 are particularly salient and include: 4 General principles of stormwater quality management 4 Guidance for BMP planning for new development and redevelopment 4 Structural BMP design criteria, details and forms to facilitate design 4 BMP maintenance recommendations 4 Recommended BMPs for industrial and commercial sites 4 Nonstructural BMPs 4 Construction-phase BMPs, including erosion and sediment control The basic philosophy of stormwater quality management presented in Volume 3 is based on this four-step process: 1. Employ runoff reduction practices such as reducing paved area, providing grassed buffers and swales, and minimizing directly connected impervious area (MDCIA). 2. Provide treatment for the water quality capture volume (WQCV) through implementation of various BMPs that detain or infiltrate runoff. 3. Stabilize downstream drainageways. 4. Provide BMPs for specific industrial and commercial uses. More detail on these practices and their applications in Denver is provided in Chapter 6 of this Plan. DENVER STORM DRAINAGE DESIGN AND TECHNICAL CRITERIA MANUAL In 1999, Denver updated the City and County of Denver Storm Drainage Design and Technical Criteria Manual (Note: This Manual is being updated again in 2005.) This manual provides the minimum design and technical criteria for the analysis and design of storm drainage facilities. The criteria require that all subdivisions, re-subdivisions, planned unit developments, or any other regulated proposed development provide adequate storm drainage system analysis and appropriate drainage system design in accordance with the manual requirements, which are consistent with UDFCD s Storm Drainage Criteria Manual Denver s manual provides drainage plan submittal requirements along with drainage policies and floodplain regulations of the city. The manual then provides engineering criteria for topics such as rainfall/design storms, runoff, open channel design, storm sewers, storm sewer inlets, streets, culverts, hydraulic structures, erosion control, detention and standard forms for use in design. The manual provides specific

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Denver Stormwater Quality Management Plan Chapter 4 Page 4-3 design standards for flood detention in open space, parking lots and underground facilities. The manual refers the user to the Urban Storm Drainage Criteria Manual, Volume 3 (UDFCD 1999) for addressing water quality requirements. DENVER STORM DRAINAGE MASTER PLAN AND OTHER DRAINAGE MASTER PLANS In December 2003, Denver completed the first phase of a three-phase Storm Drainage Master Plan (Matrix 2003), which identifies capital improvements related to flood hazard reduction and improving drainage conveyance for 15 major drainage basins within Denver. The document will help Denver comply with its stormwater permit because it provides an inventory of stormwater systems and recommends regional capital improvements. The Storm Drainage Master Plan also integrates several different documents and programs into a comprehensive Public Works management program. Although the Storm Drainage Master Plan does not address stormwater quality issues, its comprehensive GIS mapping, database, hydrology and report provide a strong base of information useful to this Plan. In particular, a description of the drainage basins in the Storm Drainage Master Plan is provided in Chapter 2 along with opportunities for integration of regional stormwater quality facilities in Chapter 8. Working with UDFCD, Denver has also completed multiple drainage master plans for specific drainage basins. These plans are important to water quality planning and should be referenced with regard to stormwater-related improvements in various drainage basins. As examples, three particularly relevant plans include: 4 Preliminary Design Report for the Upper Central Platte Valley South Platte River Restoration (McLaughlin Water Engineers 1998). The plan covers a one-mile reach of the South Platte River directly west of downtown between 8 th Avenue and I-25. The goals of this plan include: flood damage reduction, elimination of Zuni Power Plant dam, fish habitat improvements, recreation improvements, wildlife habitat and wetland improvements, and improved access. 4 Stormwater Outfall Systems Plan Stapleton Area (McLaughlin Water Engineers 1995). This plan provides a comprehensive plan for development of a drainage outfall system to serve the Stapleton redevelopment area. Primary streams addressed include Sand Creek and Westerly Creek. 4 Major Drainageway Planning South Platte River, Chatfield Dam to Baseline Road, Phases A and B (Wright Water Engineers 1984). This three-volume series covers a 40mile reach of the South Platte River from the Chatfield Dam to the City of Brighton. The purpose of Phase A of the report was to develop alternatives to solve flooding problems, while maintaining a balance of different uses of the river such as water supply, recreation and open space, to name a few. Phase B of the report provided preliminary designs for engineering and flood-related aspects of the river and a master plan for recreation, landscaping, and wildlife along the corridor.

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Relationship to Other Documents Chapter 4 Page 4-4 STANDARDS, DETAILS AND TECHNICAL CRITERIA DOCUMENTS Denver has several existing documents that specify standards, details and other technical criteria that may be applicable to stormwater BMP and site designs and should be adhered to as appropriate. These documents include: 4 Storm Drainage and Sanitary Construction Detail and Technical Specifications (City and County of Denver Department of Public Works Engineering Division 2003) 4 Standards and Details for City Engineering, Section I, Minor Projects (City and County of Denver Department of Public Works Engineering Division 2002) 4 Standard Details (City and County of Denver Department of Public Works Wastewater Management Division 1995) METRO VISION 2020 AND THE CLEAN WATER PLAN Metro Vision 2020 (DRCOG 1998) is the long-range growth strategy for the Denver region. (Note: Metro Vision 2030 was being completed concurrently to development of this Plan and should be referenced for possible changes.) It examines both the current and preferred pattern of development to the year 2020. One of the six core values included in Metro Vision 2020 is environmental quality. The plan acknowledges that the location and type of growth and land development have significant effects on air and water and that these issues are truly regional in nature. The Clean Water Plan was identified as the mechanism by which regional water quality issues should be addressed (DRCOG 1998). The Denver Regional Council of Governments (DRCOG) is responsible under state and federal statutes for regional water quality planning in the Denver area. In this capacity, DRCOG prepares and updates the Clean Water Plan which is the management plan for achieving water quality standards pursuant to Section 208 of the federal Clean Water Act. The most recent update to the Clean Water Plan is titled Metro Vision 2020 Clean Water Plan Policies, Assessments and Management Programs (DRCOG 1998). The document describes wastewater management strategies, watershed water quality programs, nonpoint source control strategies, stormwater management programs, wasteload allocations, stream standards and priority regional projects. The plan covers a 25-year planning process with additional wastewater treatment facility planning data for up to a 50-year horizon. The Clean Water Plan also provides a regional context for protecting and maintaining water quality through integrated watershed management processes (DRCOG 1998). The BMPs and other water quality measures proposed in this Plan should be consistent with the measures identified in the Clean Water Plan The Clean Water Plan states that the goal for the region is to restore and maintain the chemical and physical integrity [of waterbodies] in order to assure a balanced ecological community in waters associated with the region. Five key objectives were adopted as part of Metro Vision 2020 to support a proactive bottom-up planning process with regional coordination, including: 1. A locally defined balanced ecological community will be achieved through implementation of water quality protection and appropriate water resource management

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Denver Stormwater Quality Management Plan Chapter 4 Page 4-5 initiatives, provided that a balance will be maintained between the natural environment and those designated uses of the resource. 2. The chemical and physical integrity of the region's aquatic environments will be restored and maintained through a coordinated watershed management process. 3. Effective wastewater treatment will be identified through a regional process, with local implementation of wastewater management strategies. 4. Effective and balanced stormwater and nonpoint source management will best be achieved through local implementation processes. 5. Effective and cost-efficient water quality management and supply will require an integrated resource management program. One of the key strategies identified in the Clean Water Plan for water quality protection is watershed planning. The document recognizes eleven designated watersheds, three of which receive runoff from Denver, primarily the South Platte Urban and Cherry Creek watersheds, and, to a lesser extent, Box Elder Creek. The document provides a summary of water quality and regulatory information relevant to each of these watersheds that should be considered for future water quality planning in these areas. WATER QUALITY IMPROVEMENT IN THE SOUTH PLATTE RIVER, REPORT TO THE MAYOR Concurrent to the development this Plan, the Mayor s Office commissioned an evaluation of information regarding water quality in the South Platte River through Denver, which culminated in the report Water Quality Improvement in the South Platte River, Report to the Mayor (Bergstedt 2004). The findings of that report parallel and support the recommendations contained in this Plan. Bergstedt s report is provided in Appendix C of this Plan, with key recommendations paraphrased as follows: 1. Increased communication and streamlining of procedures between various departments with responsibilities affecting the South Platte River is needed. 2. Long-range regional initiatives and near-term program support with regard to stormwater inputs to the river are necessary to adequately protect water quality in the river. 3. Recommendations related to regional stormwater initiatives include: a. Promote a Denver-inspired regional watershed initiative, building on existing efforts (including this Plan). b. Enforce existing stormwater ordinances with regard to installation and maintenance of BMPs.

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Relationship to Other Documents Chapter 4 Page 4-6 Exhibit 4.1 Comprehensive Plan 2000 c. Fund and empower the Natural Areas Program to help reduce contamination before it reaches the river. 4. To address sewerage infrastructure and contamination issues: a. Pursue additional storage in Chatfield Reservoir for additional base flow storage and timely water releases to promote dilution of sewer discharges, particularly during drought conditions. b. Continue to support water quality improvement efforts of wastewater treatment plants discharging to the river. c. Continue diligent monitoring, improvement and coordination efforts related to the sanitary sewer system, especially in northwest Denver. DENVER COMPREHENSIVE PLAN 2000 The Denver Comprehensive Plan 2000: A Vision for Denver and Its People provides a comprehensive framework for addressing long-term issues such as environmental sustainability, land use, mobility, Denver s legacies, housing, economic activity, neighborhoods, education, human services, arts/culture, and metropolitan cooperation. The Denver Comprehensive Plan 2000 then outlines a long-term implementation strategy to achieve the goals identified for each of these issues. One of the primary goals with regard to Denver s long-term physical environment is environmental sustainability, specifically preserving and enhancing the natural environment. The Denver Comprehensive Plan 2000 states: Denver s relationship with the environment is above all a matter of balance. Clean water, clean air, clean parks and streets, efficient use and reuse of resources, and protection of the mountain parks and open spaces must be abiding goals. Most basic to sustainable quality of life in Denver and the region are the land we live on, the air we breathe, the water we drink and the natural beauty we enjoy. The greatest challenge to the environment in the early 21 st century is managing growth slowing the loss of land, the consumption of resources, the congestion, and the human stress created by urban sprawl. At the same time, the publicpolicy challenge to develop and implement balanced and sustainable growth strategies addressing equity, stewardship and cooperation becomes more critical. As part of its Vision of Success for environmental sustainability, the following selected statements pertaining to water quality are provided:

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Denver Stormwater Quality Management Plan Chapter 4 Page 4-7 4 Water Quality: Water quality will improve, and waterways and groundwater will be cleaned up and greened up. 4 Pollution Prevention: More residents and businesses will be directly involved in voluntary pollution prevention programs, reducing the need for government intervention. 4 Natural and Wildlife Habitat: Denver s natural stream corridors and wetlands will be preserved and maintained for wildlife habitat. Five specific objectives with supporting strategies are identified to achieve the goal of environmental sustainability. These objectives are listed below, along with some selected implementation strategies specifically relevant to water quality planning. Objective 1: Burdens and Benefits Distribute environmental burdens and benefits. 4 Encourage redevelopment of vacant, underutilized and environmentally compromised land known as brownfields. 4 Promote public-private sector involvement and cooperation with citizens to formulate plans and actions that achieve shared responsibilities and benefits. 4 Continue to implement the environmental review function as a tool to address pollution prevention and improve environmental quality. Objective 2: Stewardship of Resources Ensure environmental stewardship of natural resources, taking into account the entire ecosystem, not just human needs. Preventing pollution will be the action of first choice in accomplishing this objective. 4 Promote environmental sustainability within neighborhoods by educating and encouraging residents to adopt environmentally friendly ways of living, such as recycling, water conservation, use of renewable resources, and low-impact methods of transportation. 4 Conserve water and improve water quality by identifying opportunities for City agencies to use native flora in landscape designs. 4 Conserve land by: o Promoting infill development within Denver at sites where services and infrastructure are already in place. o Designing mixed-use communities and reducing sprawl, so that residents can live, work and play within their own neighborhoods. o Adopting construction practices in new developments that minimize disturbance of the land.

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Relationship to Other Documents Chapter 4 Page 4-8 o Protecting natural corridors, wetlands and floodplains from the encroachment of development. o Encouraging the redevelopment of brownfields. 4 Preserve and restore, wherever possible, natural habitat for wildlife and plants native to the region, such as those at the Rocky Mountain Arsenal National Wildlife Area, Bear Creek Park, Bear Valley Park, and the Cherry Creek corridor. Objective 3: Environmental Policy Develop environmental protection policies that take advantage of market forces and provide for regulatory flexibility while meeting the City s environmental objectives. Encourage policies and actions that consider environmental quality, economic prosperity, and social equity as complementary, not conflicting, goals. 4 Establish specific measurable goals for the environment, formulate strategies to accomplish them, and create timelines for implementation. 4 Encourage decision-making throughout Denver government that recognizes long-term impacts on the environment, such as making lifecycle cost analysis the basis for economic decisions. 4 Adopt procedures and regulations that are appropriate to the nature and scale of problems and that reduce waste. 4 Provide market-based incentives and tax incentives to encourage sustainable development. 4 Encourage effective voluntary environmental management programs and activities that require less government intervention. The private sector has found pollution prevention to be profitable, and many businesses are voluntarily embracing opportunities to create a more sustainable environment. Objective 4: The Environment and the Community Achieve environmental sustainability in all aspects of planning, community and building design, and transportation. Encourage implementation of recommended strategies within neighborhoods, citywide, and throughout the metropolitan region. 4 Respect, conserve and expand wildlife habitat, watersheds, open space and other natural resources when planning, designing and building new projects. 4 Use neighborhood development, such as Stapleton, as projects that incorporate principles of sustainable development at the community level. Use these neighborhoods as models to encourage sustainable development throughout the city over time. 4 Introduce natural ecosystem strategies into the maintenance of our public and private lands.

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Denver Stormwater Quality Management Plan Chapter 4 Page 4-9 Objective 5: The Environment and the Region Encourage the broad participation and cooperation of the entire metropolitan community on environmental sustainability issues, including transit, air and water quality, protection of floodways and wildlife habitat, and recreational areas and bike paths. 4 Support and use DRCOG s Metro Vision 2020 Plan, which has been incorporated into Denver Comprehensive Plan 2000 4 Continue Denver s leadership in metropolitan forums on smart growth, air quality, water, energy, natural resources and wildlife, recycling, climate, and other key environmental issues. 4 Partner with other metropolitan jurisdictions to distribute environmental burdens and benefits. 4 Cooperate with neighboring jurisdictions to develop shared open space and outdoor recreation amenities. 4 Maintain existing connections and develop new connections among open space areas within Denver and with those of our neighbors. BLUEPRINT DENVER Blueprint Denver, An Integrated Land Use and Transportation Plan (Denver 2000) presents a planning and development strategy for improving Denver by shaping the places where we live, travel, work, shop and play. Blueprint Denver serves as the first step in implementing and making concrete the vision outlined in Denver Comprehensive Plan 2000 Blueprint Denver adheres to and promotes five elements in Metro Vision 2020 as paraphrased below: 4 Adhere to an established urban growth boundary. 4 Provide substantial open space. 4 Provide a balanced, multi-modal transportation system. 4 Provide urban centers, such as Downtown and Cherry Creek. 4 Support sustainable development to protect regional air and water quality. A central concept of Blueprint Denver that is directly relevant to this Plan is the goal of directing growth to Areas of Change and managing and limiting growth in Areas of Stability. Areas of Stability include the vast majority of Denver and are primarily the fairly stable residential neighborhoods where minimal change is expected during the next 20 years. The goal is to maintain the character of these areas, yet accommodate some new development and redevelopment to prevent stagnation. Meanwhile, the vast majority of new development will be funneled to areas that will benefit from and thrive on an infusion of population, economic activity and investment; these places are Areas of Change (Denver 2000). These Areas of

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Relationship to Other Documents Chapter 4 Page 4-10 EXHIBIT 4.2 BLUEPRINT DENVER AREAS OF CHANGE DISTRICTS DOWNTOWN CHERRY CREEK LOWRY STAPLETON GATEWAY NEIGHBORHOODS BRIGHTON BOULEVARD NORTHEAST DOWNTOWN JEFFERSON PARK-HIGHLAND TRANSIT-ORIENTED DEVELOPMENT WEST COLFAX LIGHT RA IL STATION AREA GATES LIGHT RAIL STATION AREA (I-25/BROADWAY) SOUTHEAST LIGHT RAIL CORRIDOR WEST EVANS LIGHT RAIL CORRIDOR TOWN CENTERS ALAMEDA TOWNCENTER CORRIDORS WEST 38TH PEDESTRIAN SHOPPING CORRIDOR MORRISON ROAD PEDESTRIAN SHOPPING CORRIDOR EAST COLFAX (LINCOLN TO COLORADO) PEDESTRIAN SHOPPING CORRIDOR THE CENTRAL INDUSTRIAL AREA RIVER CORRIDOR SOUTH FEDERAL BOULEVARD COMMERCIAL CORRIDOR HAMPDEN COMMERCIAL CORRIDOR EAST COLFAX (EAST OF COLORADO BLVD) COMMERCIAL CORRIDOR SOUTH BROADWAY COMMERCIAL CORRIDOR Change will provide the most opportunities for implementing new and/ or improved stormwaterrelated infrastructure and BMPs. Although 26 specific Areas of Change are identified in Blueprint Denver (see Exhibit 4.2), these can be lumped into three general categories: 4 Downtown 4 Large development areas such as Lowry, Stapleton and Gateway 4 Areas where land use and transportation are closely linked Another key aspect of Blueprint Denver is its definitions of land-use building blocks. Adoption of these building blocks into this Plan will help to promote better interfacing among multiple departments as part of the planning and development review process. The land-use building blocks defined in Blueprint Denver include: 4 Districts (types: downtown, employment, industrial, campus, entertainment/cultural/civic and parks and open space) 4 Residential areas (types: mixed-use, urban residential, single-family/duplex residential, and single-family residential) 4 Centers (types: regional center, town center, neighborhood center, and transitoriented development) 4 Corridors (types: pedestrian, shopping, commercial) Finally, Blueprint Denver recognizes the critical role that land-use regulations play in shaping development and ensuring that development fits into the public infrastructure. Blueprint Denver also identifies various development standards that impact site designs including factors such as setbacks, parking locations, off-street parking

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Denver Stormwater Quality Management Plan Chapter 4 Page 4-11 requirements, and landscaping, among others. These requirements have the potential to impact locations and space allocated to water quality treatment facilities. As part of Blueprint Denver significant revisions to zoning and development standards are recommended. Ideally, water quality treatment requirements could be integrated into future changes to these regulations, standards, and design review process. DENVER PARKS AND RECREATION GAME PLAN In 2003, Denver completed the Denver Parks and Recreation Game Plan: Creating A Strategy for Our Future, which provides a master plan for Denver s parks and recreation future. The Denver Parks and Recreation Game Plan was created through a two-year public process and provides a 50-year vision and strategic framework plan for transforming Denver into a City in a Park. The proposed physical plan to create a City in a Park is organized into three sections, according to a scale that moves from home and neighborhood to Denver s park and open space role in the region. Design ideas, planning and process principles, supporting analyses, measurable indicators, standards or benchmarks, and cost estimates are provided. As a master plan, the Denver Parks and Recreation Game Plan makes few specific recommendations for individual parks. Rather, it provides an overall assessment of the park system and a framework for making decisions. The Denver Parks and Recreation Game Plan reflects city residents desire for diverse recreational experiences along Denver s waterways such as canoeing, kayaking, green connections to the water s edge, and new parkway connections next to the water, especially along the Platte at South Platte River Drive. Residents are also interested in more opportunities to learn about water quality, native landscapes, and wildlife. Both natural areas and active parks supporting recreation are desired. Several specific goals identified in the Denver Parks and Recreation Game Plan that are beneficial in terms of stormwater quality management include: 4 Provide a tree-canopy cover of 15 to 18 percent in urban residential areas and 10 percent in the central business district by 2025. 4 Provide at least one-half acre of public open space within one-half mile of every resident s home that can be reached without crossing a major barrier. 4 Provide 8-10 acres of parkland for every 1,000 residents. 4 Provide significant natural area acreage in each quadrant of the city. Exhibit 4.3 Denver Parks and Recreation Game Plan

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Relationship to Other Documents Chapter 4 Page 4-12 4 Encourage more natural open space in the design of new parks and the retrofitting of established parks. 4 Restore and protect existing natural open spaces. 4 Install a detached sidewalk with tree lawn where feasible; tree lawns should be at least 8 feet wide. 4 Ensure safe access to urban waterways from major residential areas. 4 Expand natural open space along the Platte, Cherry Creek, and the gulches, improving habitat for urban wildlife. 4 Increase the number and range of parks along the waterways, including some larger parks that support active recreation. 4 Identify priority corridors and areas needing protection or preservation, including: the Cherry Creek Corridor; First, Second and Third Creeks; Westerly Creek; and eastern drainageways connecting Aurora Reservoir with Rocky Mountain Arsenal. Many of the long-term goals presented in the Denver Parks and Recreation Game Plan are beneficial to stormwater quality management. This Plan should reinforce these goals and seek opportunities for mutually beneficial projects. NATURAL AREAS PROGRAM FIELD GUIDE The Natural Areas Program Field Guide (Denver Parks and Recreation 2004) is currently being developed to educate Denver staff and citizens about the purpose and activities of the Denver Natural Areas Program. The guide helps citizens and Denver staff understand how their activities affect natural areas and wildlife. The guide is divided into the following eight sections: rivers; creeks and other waterways; wetlands; prairies and grasslands; woodlands and forests; wildlife and wildlife habitats; community participation; and good land stewardship. DESIGN GUIDELINES FOR STAPLETON WATER QUALITY In 2001, the Denver Planning Board adopted the Design Guidelines for Stapleton Water Quality: Patterns for Integrating Water Quality Treatment into the Community, An Addendum to the Stapleton Rules and Regulations This document provided specific guidelines for developing water quality controls adapted to the highly urbanized setting of the Stapleton Redevelopment area. Parcel-specific BMPs were developed along with a set of details that identified specific opportunities for water quality treatment. Both structural and non-structural BMPs were identified. The document also emphasized opportunities of integrating regional water quality and quantity stormwater controls. In many ways, the Design Guidelines for Stapleton Water Quality laid the foundation for this Plan. A few selected guiding principles of Design Guidelines for Stapleton Water Quality that are instructional for this Plan include:

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Denver Stormwater Quality Management Plan Chapter 4 Page 4-13 4 Supporting the precepts of the related Stapleton drainage and development plans and Denver s stormwater permit. 4 Providing development parcel BMPs that respect the design requirements and challenges of urban development. 4 Providing an appropriate combination of structural and nonstructural BMPs that work at the site. 4 Creating designs that promote a healthy aquatic ecology, provide for sustainability, and minimize maintenance and human intervention. LONG RANGE MANAGEMENT FRAMEWORK SOUTH PLATTE RIVER CORRIDOR In 2000, the Mayor s South Platte River Commission completed the Long Range Management Framework South Platte River Corridor for the purposes of providing a framework for future decision-making and management of the 10.5-mile South Platte River Corridor within Denver s boundaries. The corridor includes 330 acres of land and water within the 100-year floodplain of the South Platte River. The document is intended to provide guidance for continued multiobjective management and project coordination in the corridor. Conclusions and recommendations were developed in four key areas, as summarized in the document s Executive Summary: 1. Development of a Vision and Management Philosophy : An update of the original vision statement developed by the Mayor s South Platte River Commission in 1995 was defined as: We want the South Platte River Corridor to be known and cherished by the citizens of the City and County of Denver. If we care for our River, protect its natural resources and help restore its beauty and quality, the South Platte will provide present and future generations unmatched opportunities for recreation, education and enjoyment. In addition to the vision statement, the Commission also recommended that the City designate and manage the entire Corridor (as defined in the Greenway Ordinance) as a City Active Use Natural Area, with Conservation and Preservation Natural Area designations to be applied to areas needing special protection. It was further recommended that an Adaptive Management approach be applied to overall corridor management, whereby management of land and water resources toward identified goals is continually monitored, evaluated and adapted to integrate best management practices and to respond to changing conditions over time. 2. Identification of a Management Structure : Create a South Platte River Corridor Council made up of all major city agencies working on the River, as well as a number of other stakeholder groups. This advisory group should be empowered by ordinance,

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Relationship to Other Documents Chapter 4 Page 4-14 Exhibit 4.4 Cherry Creek Stewardship Partners Plays an Important Role for Cherry Creek and initially staffed administratively out of Denver Parks and Recreation. It should be co-chaired and convened by the Manager of Parks and Recreation and a community leader appointed by the Mayor. It will meet quarterly to review and make recommendations on all activities taking place on the River Corridor. It will also engage subcommittees to address a variety of topics needing more detailed attention (e.g., water quality, regional cooperation). 3. Achievement of an Integrated and Balanced Management Approach : Use the carefully developed and agreed-upon Guiding Principles and Goals and Objectives laid out in the document as a framework for management decisions. The goals and objectives address multiple issues such as wildlife, recreation, water quality and flood control issues, public safety, regional cooperation and partnership, and public involvement. 4. Develop Resources Necessary to Meet the Challenges : Through the creation of the South Platte River Corridor Council and the initiatives of its members, work collaboratively to identify and attract funding for multi-objective projects. Wherever possible, utilize partnerships with existing non-profits and others to support and build upon programs that meet common goals and objectives. CHERRY CREEK GREENWAY CORRIDOR MASTER PLAN Cherry Creek, from the Cherry Creek Reservoir to its confluence with the South Platte River in downtown Denver, meanders through twelve miles of diverse vegetation and wildlife habitats, rural, suburban, and urban developments, three governmental jurisdictions, seven neighborhoods, and public as well as privately-controlled lands (BRW 2000). As one of the last remaining natural environments within an otherwise urbanized setting, the Cherry Creek corridor provides a unique opportunity to become one of the metropolitan area s major open space resources. The Cherry Creek Greenway Corridor Master Plan (BRW 2000), also referred to as the Cherry Creek South Corridor Master Plan Report, provides an overall master plan for the eight-mile portion of Cherry Creek between University Boulevard and the Cherry Creek Dam. Two of the primary purposes of the plan are to firmly establish the long-term protection and enhancement of its environmental resources and expand opportunities for open space. This plan should be taken into account with regard to stormwater quality planning in the Cherry Creek corridor area. CHERRY CREEK WATERSHED SMART GROWTH FOR CLEAN WATER REPORT Denver continues to be very involved in the planning and implementation of regional watershed and water quality-based land-use initiatives in the Cherry Creek Basin. Historically, the Cherry

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Denver Stormwater Quality Management Plan Chapter 4 Page 4-15 Exhibit 4.5 Wetland Portion of Lake in Garland Park Creek Stewardship Partners had operated successfully as an informal coalition of interests from throughout the watershed. The work of the partners culminated in 2002 with the completion of the Cherry Creek Watershed Smart Growth for Clean Water Report (Cherry Creek Stewardship Partners 2003) and the Cherry Creek Basin Open Space, Conservation and Stewardship Plan (The Trust for Public Land 2002). These plans engaged a broad cross-section of interests within the watershed and specified goals and objectives for realizing land protection and water quality goals. Some of the key findings of the Smart Growth for Clean Water project included: 4 The practice of engaging the development community, local land use agencies and interested citizens in the watershed planning process is a key component of making smart growth for clean water techniques viable in a watershed. 4 There are excellent data sources available on conditions in the Cherry Creek watershed. 4 The watershed can go beyond the level of water quality enhancement mandated by existing regulations. 4 There are available solutions that can be implemented to minimize or remove barriers that block implementation of smart growth practices within the development community and local government planning agencies. 4 Funding and marketing options exist that can provide economic incentives for innovative planning and design and help fund water quality projects. LAKE MANAGEMENT AND PROTECTION PLAN Denver has many agencies that are concerned with maintaining the functions of the lakes within the city. The agencies tackle the issues based upon their specific mission. The purpose of the Lake Management and Protection Plan which was written concurrently with this Plan, is to provide these agencies with a document that summarizes the conditions of the lakes, discusses potential overlap or conflict between various issues/uses for the lakes and identifies future strategies that the agencies can implement (Dudley 2004). More specifically, the plan documents the history and current status of the lakes in Denver parks. This includes basic location, size, and depth information, and as much information on uses and overall health of the lakes as could be documented. Historical records concerning improvement projects, as well as planned improvement projects, are also included. The primary challenges for

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Relationship to Other Documents Chapter 4 Page 4-16 managing and protecting the lakes are discussed (e.g., habitat, water quality, geese) and similarities or conflicts among these challenges are evaluated. The plan provides potential nearand long-term strategies for enhancing and protecting the lakes, emphasizing sustainable strategies (Dudley 2004). The Lake Management and Protection Plan has direct relevance to this Plan in terms of maintenance of ponds with stormwater functions (Chapter 6), as well as with regard to potential future watershed-by-watershed assessments described in Chapter 9. SUMMARY Denver has completed multiple planning and technical criteria documents that are directly relevant to stormwater quality planning. It is important that this Plan be consistent with the principles, criteria, and priorities included in these documents and recognize that strong coordination among Denver departments is essential for long-term success.

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Chapter 5 Page 5-1 EXHIBIT 5.1 AUSTIN WATERSHED MASTER PLAN STORMWATER QUALITY P LANNING Chapter 5 NATIONAL CASE STUDIES As part of Denver s commitment to not reinvent the wheel with regard to stormwater quality management, five communities with reputations for advanced stormwater management programs were selected for review. These communities and the aspect of their program of primary focus for purposes of this Plan include: 4 City of Austin, Texas: Watershed Protection Master Plan 4 City of Portland, Oregon: Clean Rivers Plan 4 Snohomish County, Washington: Drainage Needs Report 4 City of San Diego, California: Think Blue San Diego! 4 Prince George s County, Maryland: Low Impact Development Although the climates in most of these communities differ from Denver, the planning process that each has undertaken is relevant nonetheless. The level of detail and topics addressed in the case studies vary depending on the specific reason that the community was selected. For example, fairly detailed discussions of the planning processes implemented in Austin, Portland and Snohomish County are provided, while more topic-specific information is provided for San Diego with regard to public education and for Prince George s County with regard to Low Impact Development. Interviews with key managers, literature reviews and website reviews were completed to obtain information on each of the communities programs. The highlights of each are provided in the remainder of this chapter, along with a summary of key themes relevant to Denver s stormwater planning process. CITY OF AUSTIN, TEXAS: WATERSHED PROTECTION MASTER PLAN In 2001, the City of Austin, Texas completed a multi-year, $2.1 million watershed protection report titled the Watershed Protection Master Plan Phase I Watersheds Report (Exhibit 5.1). This plan is cutting-edge in many ways, two of which include: 1) its integrated approach to flooding, erosion and water quality issues; and 2) its extensive use of Geographic Information Systems (GIS) as a tool for watershed planning. Some of the highlights of this plan follow. As background, Austin formed its Watershed Protection Department in 1996 from several existing departments to reduce the impact of flooding, erosion and water pollution on the community in order to protect lives, property and the environment. To accomplish this mission, the Watershed Protection Department completed Phase I of a Watershed Protection Master Plan to better prioritize service needs and refine program direction.

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National Case Studies Chapter 5 Page 5-2 The master plan included an extensive public input process that resulted in multiple goals and objectives. The first part of the plan details the development of a system to identify and assess the severity of problem areas, including methods to assign numeric scores to the problem areas, which could in turn be used in GIS mapping. Once this system was developed, each stream segment was assessed regarding creek and local flooding, erosion, and water quality degradation. The water quality assessment, referred to as the environmental integrity index, included not only chemical constituents, but also sediment quality, physical integrity, recreation/aesthetics, aquatic life support, and channel stability. Following the assessments, the stream segments were scored and mapped with GIS. Integrated problem area watershed maps were developed by overlaying the results of individual assessments to identify areas of concurrent flooding, erosion, and water quality problems. The next step in the process was to inventory potential solutions to the identified problems. From this inventory, a set of preferred solutions was developed for various situations. Exhibit 5.2 summarizes the preferred solutions by watershed type developed as a result of the Master Plan. EXHIBIT 5.2 CITY OF AUSTIN PREFERRED ALTERNATIVES BY WATERSHED TYPE Reinforced Earth [erosion side slope projects] Gabions/Concrete Riprap [erosion side slope proj.] Geomorphically-Referenced River Engineering (GRRE) Erosion Detention [Little Wal. & Shoal headwaters] Wet Ponds/Wetlands Wet Ponds + Baseflow Extended Detention Reinforced Earth [erosion side slope projects] Gabions/Concrete Riprap [erosion side slope proj.] Geomorphically-Referenced River Engineering (GRRE) Erosion Detention Erosion Detention + Wet Ponds Erosion Detention + Wet Ponds + Baseflow Extended Detention Retention-Irrigation Ponds Geomorphically-Referenced River Engineering (GRRE) Wet Pond/Wetlands Retention-Irrigation Ponds Solution Options for Erosion and Water Quality Solution Options for Erosion and Water Quality Solution Options for Erosion and Water Quality Property Acquisition (Buyouts) for Flood Control Flood Detention Channelization Flow Diversion: Channels and Tunnels Replacement of Structural Constrictions Levees and Floodwalls Property Acquisition (Buyouts) for Flood Control Flood Detention Channelization Flow Diversion: Channels and Tunnels Replacement of Structural Constrictions Levees and Floodwalls No flooding problems in Barton Creek Solution Options for Flood Control Solution Options for Flood Control Solution Options for Flood Control Existing Impervious Cover >50% Net Future Impervious Cover Increase <5% Existing Impervious Cover >15% Net Future Impervious Cover Increase >5% Future Impervious Cover <15% Urbanized Watershed Characteristics Developing Watershed Characteristics Rural Watershed Characteristics URBANIZED WATERSHEDS DEVELOPING WATERSHEDS RURAL WATERSHEDS Reinforced Earth [erosion side slope projects] Gabions/Concrete Riprap [erosion side slope proj.] Geomorphically-Referenced River Engineering (GRRE) Erosion Detention [Little Wal. & Shoal headwaters] Wet Ponds/Wetlands Wet Ponds + Baseflow Extended Detention Reinforced Earth [erosion side slope projects] Gabions/Concrete Riprap [erosion side slope proj.] Geomorphically-Referenced River Engineering (GRRE) Erosion Detention Erosion Detention + Wet Ponds Erosion Detention + Wet Ponds + Baseflow Extended Detention Retention-Irrigation Ponds Geomorphically-Referenced River Engineering (GRRE) Wet Pond/Wetlands Retention-Irrigation Ponds Solution Options for Erosion and Water Quality Solution Options for Erosion and Water Quality Solution Options for Erosion and Water Quality Property Acquisition (Buyouts) for Flood Control Flood Detention Channelization Flow Diversion: Channels and Tunnels Replacement of Structural Constrictions Levees and Floodwalls Property Acquisition (Buyouts) for Flood Control Flood Detention Channelization Flow Diversion: Channels and Tunnels Replacement of Structural Constrictions Levees and Floodwalls No flooding problems in Barton Creek Solution Options for Flood Control Solution Options for Flood Control Solution Options for Flood Control Existing Impervious Cover >50% Net Future Impervious Cover Increase <5% Existing Impervious Cover >15% Net Future Impervious Cover Increase >5% Future Impervious Cover <15% Urbanized Watershed Characteristics Developing Watershed Characteristics Rural Watershed Characteristics URBANIZED WATERSHEDS DEVELOPING WATERSHEDS RURAL WATERSHEDS

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Denver Water Quality Management Plan Chapter 5 Page 5-3 To address the problems characterized by the watershed studies, the Master Plan identified the need to implement a combination of watershed solutions including: 4 Capital Infrastructure Projects: Over $800 million in capital funds to construct integrated watershed protection facilities including detention ponds, channel stabilization projects, and other flood, erosion, and water quality controls. 4 Operating Program Enhancements: Additional funding of $2 to 5 million per year for infrastructure maintenance, development review and inspection, public education, and design support. 4 Regulatory Modifications: Changes to various codes and criteria to improve customer service, provide developer incentives, reduce long-term maintenance needs, and prevent the creation of new watershed problems in the future. If the additional resources and funding are made available, the city anticipates that it can meet its erosion and flood goals; however, the city does not expect to be able to attain all of its water quality goals based on its Phase I Master Plan solutions. Some of the reasons identified in the report and in a follow-up interview with Jean Drew, the city s Watershed Master Plan Coordinator, include: 4 Limited regional retrofit opportunities in urban watersheds and inadequate regulatory controls in areas outside the city's jurisdiction. 4 Setting potentially unrealistically high water quality goals. (For example, restoration of base flows is a significant problem that is not easily addressed.) 4 Inability of the Master Plan scoring system to credit non-structural BMP methods in reducing pollution. (For example, improved lawn care practices were not considered as a quantifiable factor in nutrient reductions in streams.) Follow-up interviews with Jean Drew, City of Austin, and Michael Barrett, University of Texas, identified some of the challenges encountered during the Austin Watershed Master Plan process that have applicability to Denver s on-going and future work, including: 4 Striking a balance between extensive public involvement and keeping the project moving forward in a timely manner. 4 Striking a balance between multiple priorities within city departments. 4 Agreeing on level of detail/refinement in assessing the problem (e.g., assigning numeric scores to problems has its benefits and limitations). 4 Agreeing on appropriate level of refinement/precision for modeling results. 4 Providing an adequate level of cost projections for future work, while still working within the framework of a planning-level document.

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National Case Studies Chapter 5 Page 5-4 EXHIBIT 5.3 ATTRACTIVE WETLAND/P OND IN AUSTIN 4 Securing future funding to implement the projects identified in the plan. Several specific aspects of the City of Austin s watershed program that are relevant to Denver s efforts include: 4 Capital projects are financed by bond monies, transfers from the Watershed Protection Department s normal operating funds, Urban Water Quality Ordinance fees and Regional Stormwater Management Participation Fees. 4 All water quality controls within the City of Austin s jurisdiction must achieve a minimum runoff capture volume of at least the first one-half inch of runoff from the contributing area once a site reaches 20 percent impervious cover, and the volume increases based on percent impervious cover. Under the Save Our Spring (SOS) regulations in the Barton Springs Zone, higher capture volumes are required for meeting the pollution reduction standard of no increase in the average annual pollutant load, and there is no minimum impervious cover trigger. It is possible that capture volumes could be increased as a potential modification of the requirements under the Phase I Report. 4 Runoff treatment standards are based on providing treatment equivalent to a sedimentation/filtration system designed in accordance with the City of Austin s Environmental Criteria Manual. 4 Austin encourages redevelopment as a means of promoting infill development. The Master Plan notes that waiving existing development standards is one mechanism to promote redevelopment; however, a consequence of waiving development standards is worsening of inner city flooding, erosion and water quality problems. 4 In the urbanized/developed watersheds in Austin, impervious cover is already high and stream channel enlargement processes are already advanced. Since Austin s preferred solutions for runoff treatment are detention/retention pond solutions or wetlands that require land availability (Exhibit 5.3), Austin worked to inventory as many potential pond locations as practical. 4 Austin has pursued projects under its Regional Stormwater Management Program for potential retrofits to provide water quality functions. These projects have also taken into consideration Low Impact Development techniques. As part of the Watershed Protection

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Denver Water Quality Management Plan Chapter 5 Page 5-5 EXHIBIT 5.4 PORTLAND S CLEAN RIV ER PLAN Department s analysis, Austin determined that runoff from at least 25 percent of existing development needs to be treated to have a significant impact on water quality. For highpriority receiving waters, runoff from preferably up to 50 percent of existing development should be treated. More detailed site-specific investigations were identified as necessary to determine the best combinations of large-scale regional water quality ponds and existing pond retrofits. CITY OF PORTLAND, OREGON: CLEAN RIVER PLAN The Bureau of Environmental Services in Portland, Oregon, is responsible for treating wastewater, providing stormwater drainage services, reducing stormwater pollution, restoring native vegetation and improving water quality in rivers and streams. The Bureau serves over 500,000 people in an 85,000-acre area comprised of four major watersheds. There are two key components of their program: the Stormwater Management Manual updated in 2002, and Portland s Clean River Plan which was released in 2000 and revolves around ten actions for success and which identified $877 million worth of needed projects. The Clean River Plan is the primary focus of this discussion. Because much of Portland s effort was driven by significant problems relating to combined sewer overflows (CSOs), Portland s Clean River Plan provides a cutting-edge perspective on reducing storm flow volumes in concert with improving water quality through a variety of innovative approaches. The plan, itself, provides a concise big-picture vision, along with specific goals, in the form of a relatively brief, full-color document that can be widely distributed and understood by citizens and officials with widely varying backgrounds. Some of the highlights of Portland s Clean River Plan follow. One of the main thrusts of Portland s Clean River Plan is to address the city s water quality problems using solutions that address more than one problem at a time in order to minimize costly single-purpose infrastructure such as large pipes, expanded treatment plants and pump stations. The planning strategy involved reviewing each of the four watersheds using consistent assessment strategies and solution option evaluations. As was the case for the City of Austin, numeric scoring criteria were developed and assigned as part of the process. As a result of this process, Ten Actions to improve the rivers, along with cost estimates for the program over a 20-year planning horizon, were developed. A brief overview of these actions follows. Actions that are particularly innovative and/or potentially applicable to Denver are discussed in more detail.

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National Case Studies Chapter 5 Page 5-6 4 Plant trees, native vegetation and create buffers and shade along streams (Cost: $54 million). Tree planting is particularly important to Portland due to stream temperature standard violations and threatened and endangered fish species issues. The presence of woody debris in streams is also important for fish habitat. The city has a program for partnerships with streamside landowners to preserve natural riparian vegetation, plant trees and native vegetation, and remove invasive, non-native plants. There is also a goal to increase urban canopy. The adoption and enforcement of existing and new development standards to protect existing stream buffers and create new stream buffers is also high priority. 4 Reduce stormwater flow and pollutants reaching streams (Cost: $53 million). The primary focus is Low Impact Development techniques including disconnecting downspouts, expanding the roof garden program, and a series of pilot projects to reduce stormwater flows. Examples of pilot projects include stream diversions, downspout disconnection, parking lot detention, eco-roof and landscape infiltration projects. Another priority is to enforce the requirements of the city s Stormwater Management Manual, which strongly encourages Low Impact Development techniques as the first priority, followed by swales, ponds, constructed wetlands, vaults, and other stormwater treatment systems. They also are developing incentive programs for existing developments to provide treatment. 4 Enhance Erosion Control from Construction and Development (Cost: $7 million). Key actions include providing inspection personnel and equipment, an Erosion Control Certification Program and a Citizen Reporting System for erosion problems. 4 Increase pollution prevention and source control efforts (Cost: $7 million). This program focuses on removing illicit discharges, increasing outreach to businesses, developing a comprehensive recognition program modeled on the Eco-Logical Business Program, expanding outreach to medium and small businesses that have non-permitted industries to assist them with techniques to prevent pollution, and enhancing and maintaining the Soil-Trader website. Some specific examples of these efforts include partnering with specific industry groups each year to develop a set of BMPs for that industry and developing a technical assistance guide. The Soil Trader website is a way to exchange information to recycle clean excavated soil, rather than dispose of it. Another example includes a five-year pilot project working with dentists to recycle X-ray fixer due to its silver content and lead foil and amalgam from pump traps due to mercury content. 4 Education and Stewardship (Cost: $9 million). This includes K-12 and adult information programs, stewardship grants to local groups that organize and carry out environmental enhancement work, and development of other educational information. Public education is a key component of the city s overall strategy. Free education programs are offered to schools and communities, in addition to providing community service projects, stewardship grants and curriculum resources for check out. A website has Clean River Games and kid s pages.

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Denver Water Quality Management Plan Chapter 5 Page 5-7 EXHIBIT 5.5 PORTLAND S BUREAU CO ORDINATION NEEDS 4 Floodplain Restoration (Cost: $4.5 million). This involves acquiring flood-prone properties through willing-seller programs and restoring floodplain functions in specific watersheds. 4 Monitoring and Watershed Assessments (Cost: $7.5 million). The key purpose of these assessments is to provide information to evaluate how the watersheds change over time. Monitoring is the foundation of the adaptive management approach. The monitoring program includes establishing baseline conditions, monitoring water quality for a consistent set of constituents, assessing flooding, fish habitat, riparian vegetation, flow/geomorphology, and stewardship. Additional tracking of program effectiveness is also included. 4 Coordination and Partnership. (Cost: included in baseline city budgets). The matrix in Exhibit 5.5 helps to consolidate which city departments are involved in each of the Clean River Plan goals. Additional coordination with state and federal agencies is also important, particularly with regard to the Threatened and Endangered Species issues. With regard to Portland s Stormwater Management Manual which is the foundation of stormwater management strategy described above, the key strategy being emphasized is on-site stormwater management practices. The city now requires all new development and redevelopment projects to include onsite stormwater facilities. The manual emphasizes the simplified approach to stormwater management, which focuses on rooftop systems, porous pavement, planter boxes, vegetated swales, filter strips and basins, sand filters and soakage trenches, and trees. Alternative methods include the more traditional stormwater practices of grassy swales, ponds, constructed wetlands, detention facilities, drywells, manufactured systems, oil/water separators, and stormwater reuse. The manual also provides specific guidance for activity-based pollution controls for fuel-dispensing facilities, aboveground storage of liquid materials, solid waste storage areas, exterior storage of bulk materials, material transfer areas/loading docks, equipment/vehicle washing areas, stormwater disposal for development on recycled land, covered vehicle parking areas, and other requirements. The manual specifically outlines facility landscaping requirements for all BMPs involving vegetation.

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National Case Studies Chapter 5 Page 5-8 EXHIBIT 5.6 PORTLAND S BMP MAINT ENANCE GUID ANCE This includes recommended plant lists, mulch, irrigation, facility screening, and other measures. Specific operations and maintenance requirements are provided for each BMP. Property owners are legally responsible for inspecting and maintaining the facilities, and the city has developed illustrated handbooks (Exhibit 5.6) for homeowners and property owners that clearly describe stormwater facility operation and maintenance guidelines, including inspection record forms. Other highlights of the Portland program with regard to financing and stormwater treatment criteria include: 4 Financing is through sewer fees. Sewer rates are expected to increase from $33/month to $97/month by 2020. 4 All new development and redevelopment with over 500 sq. ft. of impervious development footprint area is required to comply with Portland s stormwater manual requirements. The requirement is removal of 70 percent of total suspended solids (TSS) from runoff generated by a design storm up to and including 0.83 inches of rainfall over a 24-hour period. In addition to this standard, projects discharging to waterbodies with established TMDLs also have to comply with pollutant removal requirements for that waterbody. On-site infiltration is required to the maximum extent possible due to the CSO problem. 4 A new department called the Sustainable Stormwater Management Group has been formed to focus solely on stormwater management opportunities in new development and redevelopment and other acute problem areas (Liptan 2003).

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Denver Water Quality Management Plan Chapter 5 Page 5-9 EXHIBIT 5.7 SNOHOMISH COUNTY DRA INAGE NEEDS REPORT SNOHOMISH COUNTY, WASHINGTON Snohomish County, WA, recently completed a two-year, $12 million study called the Drainage Needs Report (Exhibit 5.7). The goals of this report were to develop a better understanding of drainage systems, streams and wetlands and to plan for existing and future infrastructure needs in a way that: 4 Reduces road and property flooding 4 Protects and enhances aquatic habitat 4 Reduces stormwater pollution and erosion from stormwater runoff Snohomish County s Surface Water Management Division selected this integrated approach because they have found that flooding problems (and their solutions) are usually intertwined with other surface water issues, such as aquatic habitat, water quality and erosion. This is also particularly true in their area due to threatened and endangered species issues. The plan relied heavily on Global Positioning System (GPS) and GIS mapping of drainage systems that covered 73 square miles. As part of the study, 11 individual drainage systems were evaluated in detail regarding the following issues: 4 Drainage problem area 4 Water quality 4 Aquatic habitat 4 Size and location of culverts/pipes for drainage and fish passage 4 Other drainage-specific information Studies in the larger basins included significant hydrologic and hydraulic computer modeling. Recommendations for improvements to all of the basins were provided. The study resulted in 378 recommended projects totaling approximately $123 million. The majority ($84 million) of the projects involved flooding issues typically combined with other issues, while $4.1 million addressed water quality only, $6.9 million addressed erosion only and $27 million addressed habitat only. Specific components of the Drainage Needs Report include: a drainage inventory, information on how to use the report, project implementation strategies, guiding principles and methodology for evaluating the drainage basins, overall program recommendations, and study results for each of the 11 basins. The

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National Case Studies Chapter 5 Page 5-10 EXHIBIT 5.8 SNOHOMISH ANNUAL ACH IEVEMENT REPORT HIGH IGHTS DETENTION FACI LITY RETROFITS individual basin reports, which formed the basis for the overall report, addressed these topics: 4 Basin characteristics 4 Hydrologic and hydraulic modeling to address flooding 4 Habitat assessment 4 Water quality analysis 4 Channel erosion assessment 4 Capital Improvement Project (CIP) guidelines 4 Existing and future problems 4 CIP development, alternatives analysis, and recommend solutions 4 Recommended plan GIS and scoring-type approaches were used to prioritize project recommendations. Implementation considerations such as land acquisition, public or private ownership, and whether the project required early action were also noted. Project sequencing, funding, permitting, maintenance, and additional study requirements were also identified. Several general recommendations of the report included retrofitting detention ponds (Exhibit 5.8) and open ditches to provide water quality benefits and working with landowners to implement BMPs such as preserving streamside vegetation, properly managing livestock, maintaining septic systems, etc.

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Denver Water Quality Management Plan Chapter 5 Page 5-11 In addition to the Drainage Needs Report there are other key components to the Surface Water Management Division s program. Extensive information is available on their website, including a detailed description and photograph catalogue of water quality problems and a reporting hotline number. Key programs covered by their department include community partnerships, water quality, aquatic habitat, urban drainage, and river flooding. The community partnership program is well developed with specific programs to address native plants, salmon, watershed education, watershed stewardship, and volunteer opportunities. Some of the activity areas highlighted in a recent annual achievement report (2001) include: 4 Stormwater detention facility retrofits to incorporate stormwater quality benefits and smaller storm detention into older facilities. 4 Detention facility maintenance program. This program has a database inventory of over 800 residential and Public Works drainage facilities, owned and maintained by either the County or homeowners. Over 200 facilities are inspected yearly and County crews maintained approximately 60 facilities in 2001, including some large rehabilitation projects to improve facility performance. The program has a strong public education program, making hundreds of citizen contacts annually. The cost of this program was about $440,000 for the year. 4 Large woody debris program. The program involved providing large woody debris to streams for aquatic habitat and streambank stabilization. The cost of the program was $154,000 for the year. Other aspects of Snohomish County s program, including stormwater treatment criteria, include: 4 Annual service charges are billed in conjunction with property taxes based on land use classification and/or amount of impervious surface coverage as identified in their Index of Land Use Classifications and Rate Categories. In areas designated as Clean Water Districts, representative annual service charges are $33.01/single family parcel up to $99.02/quarter acre of very heavy development. 4 Snohomish County s stormwater criteria are based on the Washington Department of Ecology s criteria. On-site stormwater management is required for new development if 2,000 square feet or more of impervious area is added or replaced and land-disturbing activity includes 7,000 square feet or greater. Additional measures including runoff treatment, flow control and other measures are required if the new development creates or adds 5,000 square feet of impervious surface, converts or more acres of native vegetation to lawn or landscaped areas or converts 2.5 or more acres to pasture. The requirements for redevelopment are similar but provide some flexibility to not discourage redevelopment. 4 On-site stormwater management (referenced above) requires BMPs that infiltrate, disperse and retain stormwater runoff onsite to the maximum extent feasible without causing flooding or erosion impacts. Roof downspout control BMPs and dispersion and soil quality BMPs (or their functional equivalents) are required to reduce the hydrologic

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National Case Studies Chapter 5 Page 5-12 EXHIBIT 5.9 THINK BLUE SAN DIEGO disruption of developed sites. The intent is to use inexpensive practices on individual properties to reduce the amount of disruption to the natural hydrologic characteristics of the site. 4 Runoff treatment (referenced above) requires construction of stormwater treatment facilities based on pollution generating impervious surfaces (PGIS) and pollution generating pervious surfaces (PGPS). 4 Snohomish County has a well organized website with detailed information available at www.surfacewater.info 4 The Surface Water Management Division has about 75 people, who Director Joan Lee, P.E., credits for a high level of competence and cooperation, enabling the success of the program (Lee 2003). SAN DIEGO, CALIFORNIA The goals of San Diego s Stormwater Pollution Division and their stormwater program include: 4 Investigation: This includes testing for pollutants at over 300 locations and recognizing that everyday activities are a key pollutant source. 4 Pollution abatement: Key successes have included adjusting sprinklers/watering schedules and working to reduce pollution from construction sites and restaurants. 4 Education: Think Blue San Diego ( www.thinkbluesd.org ) (Exhibit 5.9). 4 Enforcement: This includes a Stormwater Code Enforcement Team ( stormwater cops ), citations and fines of $100-10,000/day, and a pollution reporting hotline. 4 Additional Funding: The city recognizes its need for more funding for cleaning and maintenance of the storm drain system and has identified obtaining additional funding as a priority. The City of San Diego has won multiple national awards over the last several years for their public education work related to stormwater. Award-winning aspects include the Think Blue campaign and the Stormwater and You employee education video. The Think Blue education and outreach campaign was chosen as part of EPA s urban city model program in its non-point source pollution toolbox for municipal agencies. With its strong emphasis on public education, Karen Henry, Deputy Director of Public Works, notes that the greatest benefits will be seen in long-term behavioral changes. A user-friendly website is part of their on-going public

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Denver Water Quality Management Plan Chapter 5 Page 5-13 EXHIBIT 5.10 SA N DIEGO S USER FRIEN DLY WEBSITE education program (Exhibit 5.10). The city is conducting annual surveys to try to measure how behavior is changing with regard to water protection practices (Henry 2003). In addition to the education campaigns, the city also has a formal Urban Runoff Management Plan that has identified about $30 million in needed projects. The city recently updated its Stormwater Standards (City of San Diego 2003), which identify requirements for stormwater quality treatment. One innovative aspect of this document is that it provides a GIS map of water-quality sensitive areas so that developers and planners are aware of areas requiring special protection. The plan also includes a BMP selection matrix that recommends selection of different BMP types based on the expected pollutants of concern. The document also provides a standard development project and priority project stormwater BMP requirements matrix. PRINCE GEORGE S COUNTY, MARYLAND AND LOW IMPACT DEVELOPMENT Prince George s County, Maryland, and Associate Director of the Department of Environmental Resources, Larry Coffman, are nationally known for their leadership in implementation of Low Impact Development (LID) strategies beginning in the early 1980s. LID techniques are the focus of this discussion. When discussing LID, it is important to note that many LID techniques have the effect of minimizing directly connected impervious area, which is a foundational concept of stormwater management in Denver (UDFCD 1999). LID practices help to control pollutants, reduce runoff volume, manage runoff timing, and address other ecological concerns. The goal of LID is to mimic a site's predevelopment hydrology by using design techniques that infiltrate, filter, store, evaporate, and detain runoff close to its source. Instead of conveying and treating stormwater in facilities located at the bottom of drainage areas, LID addresses stormwater through small, landscape features at the lot level (Exhibits 5.11-5.13). These landscape features, or Integrated Management Practices (IMPs), are the building blocks of LID (Coffman 2001). Examples of LID techniques include bioretention, permeable pavers, tree box planters, rain gardens, and disconnected downspouts.

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National Case Studies Chapter 5 Page 5-14 EXHIBITS 5.11-5.13 LOW IMPACT DEVELOPME NT FEATURES Source: lowimpactdevelopment.o rg From top to bottom: landscaped parking lot infiltration, residential landscaped infiltration and porous pavement. Larry Coffman (2001) provides the following statement regarding the foundations of LID: The LID principles and practices are based on what we have learned over the years about stormwater management and the transfer of technology from other fields of engineering and science, such as sanitary engineering, agriculture, forestry, soil science, phytoremediation, bioremediation and ecology. As an example, take a look at the data on the 50-year history of successful land application and treatment of wastewater effluent (slow rate irrigation, overland flow, and high rate infiltration). Add to this the existing and growing body of data on the performance of bioswales, bioretention, filter strips and turf from universities (Maryland, Virginia, and Washington State), Federal Highway Administration, USEPA, and others. When you look at the entire body of related scientific and engineering/environmental technologies, you begin to see the advantages and benefits of LID s multiple systems (treatment train) approach. An advantage of LID is that it is a comprehensive multi-systems approach that has built-in redundancy, which greatly reduces the possibility of failure. Basic subdivision and infrastructure design features include: reducing the use of pipes, ponds, curbs and gutters; maintaining recharge areas, buffer zones, and drainage courses; using

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Denver Water Quality Management Plan Chapter 5 Page 5-15 infiltration swales, grading strategies, and open drainage systems; reducing impervious surfaces and disconnecting those that must be used; and conserving open space. The key factor in the success of LID is to ensure that the landscape practices (such as rain gardens) are attractive and perceived by the property owner as adding value to the property. If these LID practices are viewed as assets, the primary motivation for their long-term maintenance is that of property owners protecting their vested economic interests (Coffman 2001; http://www.lidstormwater.net/ ). Another advantage of the LID approach is with regard to preserving stream integrity. As previously discussed, it is important that a stormwater system specifically addresses the frequent storms that occur on a regular basis (weekly or monthly). By using decentralized site-based source controls, LID uses the stormwater from these more frequent events as a resource and is an effective ecosystem approach. LID techniques can also be combined into hybrid programs that address major flood control events, if needed (Coffman 2001; http://www.lid-stormwater.net/ ). The Department of Environmental Resources in Prince George s County, Maryland recently presented results of side-by-side monitoring of two small residential watersheds in the Somerset Heights subdivision (Cheng, et al. 2003). One watershed was developed using conventional curb-and-gutter systems, whereas the other was developed using preliminary LID practices, including only grassed swales, bioretention areas, and disconnected impervious areas. It is important to note that the subdivision was designed and constructed prior to development of design criteria for LID practices. Regardless, over a two-year period, statistically significant differences were measured between the two watersheds in the number of runoff events, the total runoff volumes, and in peak event flow rates. Monitoring revealed that the LID watershed had 20 percent fewer runoff events, and the average peak flow rate was only 56 percent of conventional watersheds. Including groundwater/interflow, the total flow volume at the LID site was approximately 80 percent of the conventional site surface runoff. In the LID watershed, peak flow rates were reduced by approximately 44 percent per acre. Since monitoring occurred prior to site stabilization and without full-scale implementation of LID approaches, water quality comparisons between the sites were not considered to be representative of long-term performance according to current LID design practices. Not all developments in Prince George s County have been planned using LID techniques. Older developments are usually based on more traditional drainage practices and some areas are conducive to hybrid approaches that combine traditional drainage practices with LID (Coffman 2003). With regard to long-term maintenance concerns, Coffman notes that several factors can help promote more effective long-term maintenance, including: 4 Comprehensive site planning, including conserving natural soils, amending soils with organic materials, providing gentle slopes, and conserving drainage patterns. 4 Providing site grading and design that are aesthetically-pleasing amenities and that complement rather than interfere with desirable site uses. 4 Providing a fudge factor in site designs that allows a certain degree of failure in the system.

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National Case Studies Chapter 5 Page 5-16 4 Establishing covenants and outreach programs to train people on how to maintain rain gardens and other features to preserve their function and aesthetics. SUMMARY Several big-picture, planning-level lessons from innovative communities relevant to Denver s current stormwater quality planning process include: 4 Comprehensive approaches are being used to address drainage, flooding, erosion, aquatic life, habitat, and water quality in an integrated manner. 4 Stormwater management approaches that are multi-layered, combining a variety of structural and non-structural practices, are advocated and implemented. 4 Watershed-based approaches are being used for planning and problem solving. 4 GIS tools are being used effectively to prioritize stormwater improvements and to more effectively communicate to citizens, staff and developers. 4 Storm runoff volume reduction practices are being used in the majority of these communities. These practices included a variety of LID techniques such as eco-roofs and rain gardens, tree planting, and irrigation controls. 4 Long-term maintenance of BMPs is recognized as being critical to the success of BMPs. 4 Strong public education campaigns in combination with extensive web sites are substantive components of these programs with significant budget allocations. Education is not an afterthought it is being aggressively used in several of these communities as a key strategy to improve runoff quality. 4 Significant financial investments, spanning from several hundred thousand to several million dollars, have been required for these communities to complete their planning processes. Most of the communities also recognize that significant future expenditures from tens to hundreds of million dollars will be required to meet their future goals and are planning accordingly.

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Chapter 6 Page 6-1 Chapter 6 STORMWATER QUALITY BMP IMPLEMENTATION GUIDELINES A VISION FOR STORMWATER QUALITY TREATMENT IN DENVER Implementing stormwater treatment is not just an engineering issue it involves and affects city planners, park planners, developers, landscape architects, environmental health professionals, and maintenance personnel as well as the citizenry itself. Each of these participants has a unique perspective regarding how stormwater quality facilities should appear, function, and be maintained. To have meaningful guidelines that are used and promoted by each of these diverse groups, a shared vision for stormwater treatment must be bought into by each of the participants. This chapter presents a shared vision for stormwater quality treatment in Denver, which has emerged from a multi-disciplinary process. The vision is to implement stormwater quality Best Management Practices (BMPs) that are: 4 Functional Stormwater quality facilities must accomplish their primary function of effective stormwater quality treatment. 4 Maintainable. Stormwater BMPs must be sustainable and maintainable for the long term. 4 Attractive. Stormwater facilities must be compatible with the site s land use and complementary to the site s character. These goals are at the heart of these stormwater quality BMP implementation guidelines. The techniques in the guidelines are, for the most part, established and approved technologies, having been promoted in the Urban Storm Drainage Criteria Manual, Volume 3 Best Management Practices ( Volume 3 ) (UDFCD 1999) for a number of years. BMPs are structural or nonstructural techniques employed to reduce pollutant levels in stormwater runoff to the maximum extent practicable. Structural practices are discussed in this chapter and non-structural practices in Chapter 7. The intent of this guide is not to replace Volume 3 or other technical manuals, but rather to provide specific guidance on how to better integrate BMPs into a variety of development site types. Because some of the language used to describe these methods may be unfamiliar, a glossary has been included at the end of the document to provide additional information. A NEW STRATEGY FOR STORMWATER QUALITY This chapter describes a new strategy for managing stormwater quality on individual development sites. The strategy is to create facilities that are integrated with the landscape and hard surface elements of a site, compatible with the land use and with community goals, effective for enhancing stormwater quality, and sustainable over the long term.

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-2 This is a departure from past practices that dispose of stormwater quickly through a series of inlets and underground pipes that concentrate flows (thereby increasing runoff peak rates, volumes, and pollutant loads in the process), and then attempt to cure the problems by using detention basins at the edge of the site. Often, these corner-of-site facilities are large, deep basins that detract from the aesthetics of the site, are difficult to maintain, and may be only marginally effective in reducing the impacts of urban runoff. This new strategy seeks to reduce the size of perimeter detention basins by reducing runoff volumes and distributing stormwater quality treatment throughout the site. This will reduce runoff rates, volumes, and pollutant loads by using landscape areas and porous pavements to infiltrate rainfall into the ground to better reproduce conditions that existed before the site was developed. Elements of the strategy are catching on locally and nationally, being promoted under the terms low impact development (LID) (Prince George s County 2000), smart growth for clean water (Cherry Creek Stewardship Partners 2003) and minimizing directly connected impervious areas (MDCIA) (UDFCD 1999). Regardless of the term, the approaches all manage runoff close to its source and promote infiltration. This chapter provides guidance for integrating stormwater quality features into a site to form an effective treatment train first reducing, then cleansing runoff while improving site aesthetics through functional landscaping features, porous pavements, and reduced reliance on large, forced-fit detention basins. Design and Stormwater Quality Principles The following design and stormwater quality principles provide a foundation for developing a stormwater quality strategy, and are the basis for the recommendations presented in these guidelines. Principle 1: Consider stormwater quality needs early in the design process. Left to the end of site development, stormwater quality facilities will often be shoe-horned into the site, resulting in forced, constrained approaches. When included in the initial planning for a project, opportunities to integrate stormwater quality facilities into a site can be fully realized. Stormwater quality and flood control requirements are just as fundamental to good site design as other elements such as building layout, grading, parking, and streets. Dealing with stormwater quality after major site plan decisions have been made is too late. This schematic plan designates specific types of stormwater quality treatment facilities along with buildings, roads, and parks. EXHIBIT 6.1 STORMWATER QUALITY PLANNING IN MINNEAPOLIS, MN

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Denver Water Quality Management Plan Chapter 6 Page 6-3 EXHIBIT 6.3 PLANTER BOX IN BOULDER, CO These planter boxes fill with water, infiltrating significant amounts of stormwater before overflowing into treatment areas, while appearing beautiful throughout the year. Principle 2: Take advantage of the entire site when planning for stormwater quality treatment. Often, stormwater quality and flood detention are dealt with only at the low corner of the site, and ignored on the remainder of the project. The focus is on draining runoff quickly through inlets and storm sewers to the detention facility. In this end-of-pipe approach, all the runoff volume is concentrated at one point and designers often find it difficult to fit the required detention into the space provided. This can lead to drainage plans showing proprietary underground treatment devices as discussed later in this chapter, or deep, walled-in basins that detract from a site and are difficult to maintain. Spreading runoff over a larger portion of the site reduces the need for these undesirable alternatives. Principle 3: Reduce runoff rates and volumes to more closely match natural conditions. Before development, most of the rain that falls on the ground soaks into the soil or is captured by vegetation; very little rainfall runs off and flows downstream. However, after development, rain that falls on roofs and pavement mostly runs off (this is a runoff event ). Whereas one runoff event per year may be typical prior to development, about 30 runoff events per year may occur after urbanization (Urbonas et al. 1989). Peak flows and volumes of runoff are much greater after urbanization than before development. This increased runoff can be environmentally harmful, causing erosion in stream systems and generating greater pollutant loading downstream. One of the most effective stormwater quality BMPs potentially more effective than constructing a detention basin to treat the runoff is reducing urban runoff volumes to the maximum extent practicable to more closely match natural conditions. The following techniques can be used to achieve this goal: 4 Place stormwater in contact with the landscape and soil. Instead of routing storm runoff from pavement to inlets to storm sewers to offsite pipes or concrete channels, an approach is recommended that places runoff in contact with landscape areas to slow down the stormwater and promote infiltration. This linear treatment area between two bays of parking takes advantage of the landscape strip to infiltrate stormwater. EXHIBIT 6.2 INTEGRATED TREATMENT FACILITIES IN BOULDER

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-4 Porous pavement areas also serve to reduce runoff and encourage infiltration. 4 Apply the principle of minimizing directly connected impervious area (MDCIA). Volume 3 promotes MDCIA, breaking up areas of imperviousness and directing runoff from roofs and paved areas to grass buffers, swales, and other landscape areas prior to being conveyed off the site. Volume 3 provides a credit against the actual imperviousness of a site for replacing inlets and storm sewers with grass buffers and swales that break up large expanses of paving. Thi s reduces the effective imperviousness of a site, decreasing the required water quality capture volume (WQCV) by as much as 50 percent, depending on the type of site. Fragmenting impervious areas with even small pervious areas can have a significant impact on reducing runoff and the required water quality capture volume. (Water quality capture volume is the quantity of stormwater runoff that must be treated in stormwater quality BMPs in Denver. See glossary for additional information). 4 Reduce the total amount of impervious area on a site. The less impervious area exists on a site, the less runoff from a site will occur, resulting in a smaller required water quality capture volume. Smaller street sections or porous pavement in fire access lanes, parking lanes, and driveways (using soil reinforcement or modular paving blocks instead) will reduce the total site imperviousness. 4 Select treatment areas that promote greater infiltration. Porous landscape detention, porous pavement detention, and sand-filter detention promote greater volume reduction than extended detention basins, since runoff tends to be absorbed into the filter media or infiltrate into underlying soils. As such, they are more efficient for reducing runoff volume, and can be sized for 20 percent less treatment volume than extended detention. By employing these techniques, projects can reduce the increase in runoff and related stream degradation and pollutant loading that comes with conventional development. In addition, some of these techniques will reduce the required water quality capture volume and may help to create a more attractive site. Denver strongly encourages implementation of these runoff reduction techniques on all new projects to the maximum extent practicable. Between the parking lot and the street, this swale creates a landscape buffer between two paved areas EXHIBIT 6.4 GRASS SWALE IN DENVER, CO

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Denver Water Quality Management Plan Chapter 6 Page 6-5 Principle 4: Integrate stormwater quality management and flood control. On average, it rains or snows over 70 times per year in the Denver area (Urbonas et al. 1989). More than half of these events produce less than 0.1 inch of precipitation and almost 80 percent of the remainder of the storms amount to less than 0.6 inches. These frequently occurring storms are the events that stormwater quality BMPs are designed to treat. Occasional flooding of streets and low-lying areas can occur during less frequent, larger storms, requiring flood control detention. Both stormwater quality treatment and flood control detention goals can be accomplished on a site through a coordinated design approach. In cases where an extended detention basin, retention pond, wetland basin, or sand filter basin is used to address stormwater quality, any of these basins can be modified to include flood control detention in addition to the water quality capture volume. This will generally increase the overall size of the basin. In these situations, all the runoff from a site, from small and large storms alike, is routed to the combined detention basin. Site BMPs, like porous landscape detention and porous pavement detention, are intended to promote a stormwater quality function, and are not normally designed to provide flood control detention as well. In these cases, all runoff is directed to the water quality capture volume facility and larger events spill out over the surface or through an inlet and storm sewer to a separate flood control detention basin. (Alternatively, treatment can be provided within depressed parking lot islands, and flood control detention can take place within the parking lot itself, as long as the depth of water being detained is not too deep and drains quickly (at the historic rate) through an inlet. In parking lots, it is not acceptable to rely on slower draining BMPs such as porous landscape detention and porous pavement detention to infiltrate all of the flood detention volumes. More information on combining stormwater quality and flood control detention is discussed in the parking section of the Implementation Details in this chapter. Principle 5: Develop stormwater quality facilities that enhance the site, the community, and the environment. Stormwater quality areas can add interest and diversity to a site. Gardens, plazas, rooftops, and even parking lots can become amenities and provide visual interest while performing stormwater quality functions and reinforcing urban design goals for the neighborhood and community. Avoiding the placement of stormwater quality facilities along critical street frontage may be necessary to discourage detrimental gaps in the continuity of important urban spaces. The integration of BMPs and associated landforms, walls, landscape, and materials can reflect the standards and patterns of a neighborhood and help to create lively, safe, and pedestrian-oriented districts. Although this is an attractive and well-constructed detention basin, it creates a gap in the commercial urban fabric of Colfax Avenue. EXHIBIT 6.5 DETENTION BASIN IN DENVER

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-6 The quality and appearance of stormwater quality facilities should reflect the surrounding land use type, the immediate context, and the proximity of the site to important civic spaces. Aesthetics will be a more critical factor in highly visible urban commercial and office areas than at a heavy industrial site. The standard of design and construction should maintain and enhance property values without compromising function. In some cases, this means locating a facility to preserve or enhance natural resources. Principle 6: Design sustainable facilities that can be safely maintained. Stormwater quality facilities must be properly and consistently maintained to function effectively and ensure long-term viability. Regular maintenance is also key to public acceptance of these facilities. Typical maintenance operations to consider in designing facilities include: 4 Mowing, trimming, and weed control 4 Pruning of shrub and tree limbs 4 Trash and debris cleanup, especially at grates and flow control structures 4 Sediment removal 4 Removal, replacement, and revegetation of porous landscape detention media 4 Vacuuming/replacement of porous pavement and porous pavement detention media 4 Structural repair Keeping in mind these and other potential maintenance practices, it is also necessary to fully consider how and with what equipment BMPs will be maintained into the future. Facility design should provide for these operations ensuring adequate access with a minimum of disturbance, disruption, and cost. Maintenance should be planned for so that trash, debris, and sediment can be removed on a regular basis. The last part of this chapter describes ways that Denver can enhance its approach to ensuring that stormwater BMPs are properly maintained. It describes required maintenance operations for a variety of BMPs, frequency of maintenance operations, and identifies parties responsible for maintenance. It recommends that the site developer/designer prepare a simple operations and maintenance plan for the site s stormwater quality and flood control facilities in accordance with UDFCD guidelines, so that maintenance may be carried on in perpetuity. Principle 7: Design and maintain facilities with public safety in mind. One of the highest priorities of engineers and public officials is to protect public health, safety, and welfare. Stormwater quality facilities must be designed and maintained in a manner that does not pose health or safety hazards to the public. For the purpose of this discussion, public safety issues are categorized according to public access issues and mosquito/West Nile virus concerns.

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Denver Water Quality Management Plan Chapter 6 Page 6-7 Public Access and Safety 4 Pond Edges: § Create safe pond edges with gradually sloping banks within 10 to 20 feet of shoreline § Reduce perimeter wall heights as much as practicable § Include railings on vertical drops of 30 inches or more (check with City building code) § Locate facilities with steep sides away from major pedestrian routes § Provide an emergency egress route 4 Visibility : Avoid walled-in or steeply sloped, remote ponds that provide hiding places for illicit activity. Consider the need for site lighting. 4 Outlet : Utilize trash/safety rack in accordance with UDFCD design guidance. Mosquitoes and West Nile Virus The West Nile virus first appeared in the U.S. in 1999. Dozens of cases of West Nile virus were documented in Colorado during the summer of 2003. Because the virus is spread by mosquitoes that breed in shallow standing water, it is important that stormwater BMPs that detain or retain water are managed properly to avoid serving as breeding grounds for mosquitoes, which pose both health and nuisance issues. BMP designs that reduce the likelihood and extent of shallow standing water should be implemented. If shallow standing water is unavoidable in publicly owned facilities, Denver Department of Environmental Health, Division of Animal Control officials should be notified so that the area can be routinely treated. Owners of privately owned facilities are responsible for treating their facilities, unless extreme circumstances exist. An important note with regard to BMP selection and mosquitoes is that according to the EPA, healthy wetlands and wetland BMPs are not considered uncontrolled mosquito breeding grounds due to the fact that wetland ecosystems contain numerous fish, insects, amphibians, and birds that feed on mosquitoes (EPA 2003). Moreover, the mosquito species primarily responsible for West Nile virus transmission do not prefer to reproduce in healthy wetlands; instead, they tend to breed in a variety of locations such as abandoned tires, birdbaths, roof gutters, and other artificial containers that lack wetland predators. They are also found in highly polluted environments, contaminated water, and degraded wetlands; therefore, stormwater BMPs and properly designed wetlands can reduce habitat that is suitable to mosquitoes that carry the West Nile virus (EPA 2003). Denver s Lake Management and Protection Plan (Dudley 2004) is consistent with EPA s perspective on the West Nile virus and further notes that properly designed wetlands can be an essential part of a healthy, well-balanced lake ecosystem. Stormwater Quality Design Process The four-step design process in Volume 3 has become the cornerstone of the Urban Drainage and Flood Control District s (UDFCD s) approach to selecting and implementing BMPs. 1. Reduce runoff volume to the maximum extent practicable.

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-8 2. Control the remaining (residual) runoff through BMPs that have the necessary water quality capture volume, with appropriate reduction credits for steps taken to reduce runoff volume. 3. Utilize stream channel stabilization techniques for drainageways on, or adjacent to, the site. 4. If a site includes potential pollutant sources, provide additional treatment, including covering of storage/handling areas, spill containment and control, and other best available technologies. These guidelines deal primarily with the first two steps. Information on stream channel stabilization resources may be found in the BMP Fact Sheets of this chapter and in Volumes 1 and 3 of the Urban Storm Drainage Criteria Manual (UDFCD 1999, 2001). The following process expands on the four steps to create a workable method for addressing stormwater quality and flood control requirements on a site. 1. Create attractive facilities that add value to the site While most designers focus on providing a functional stormwater management system for a site, they should also configure and detail the stormwater system to create an aesthetically pleasing facility. Effective integration of landscape elements and the stormwater system can enhance a project and the community. 2. Develop an initial site design 4 Identify a rough layout of lots, buildings, streets, parking, and landscape areas with a general idea of proposed site grades. 4 Estimate approximate areas associated with roofs, streets, walks, parking lots, and landscaping or open space. 3. Consider the full range of BMP alternatives The stormwater facilities shown in the Development Type Guidelines provide examples of appropriate BMPs for a variety of land uses. 4 Determine which of the seven Development Types in Exhibit 6.6 most closely match the site. 4 Consider the full range of alternative approaches for addressing drainage and stormwater quality for the site, including techniques to reduce runoff and distribute BMPs throughout the site. 4 Test the influence of several alternatives on the overall character and layout of the site, weigh pros and cons of each, and progress towards an optimum approach. 4 Consider long-term or life-cycle costs in the selection of alternative BMPs. These can be assessed by consulting references that discuss life-cycle costs of BMPs

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Denver Water Quality Management Plan Chapter 6 Page 6-9 (EPA 1999; Heaney et al. 2002; Watershed Management Institute 1997; Stormtech 2003), or by developing opinions of probable cost for the construction and maintenance of specific BMP alternatives for the site. 4 When selecting and designing BMPs that provide for infiltration (i.e., grass buffers and swales, porous pavement detention, porous landscape detention, and sand-filter detention), the designer needs to carefully consider geotechnical and foundation issues and the ability of the property owner to understand and properly maintain these facilities. 4. Pursue a functional distribution of landscape areas Keep detention basins shallow and provide some space for tree and shrub plantings. 4 Provide an area about 10 to 15 percent of the size of the impervious area for stormwater quality treatment. This area may be reduced in later stages of design (e.g., porous pavement detention can usually comprise 25 to 35 percent of the impervious area.) 4 Minimize the number of extended detention basins. When included, locate them near a low-lying area of the site away from pedestrian corridors and gathering places. 4 Porous landscape and porous pavement detention areas should be more numerous, and distributed throughout the site. The Implementation Details section of this chapter shows several examples of how porous landscape detention facilities can be configured adjacent to buildings, in parking lots, and in other landscape areas. In general, it is prudent to locate porous landscape detention in close proximity to the impervious area being served. 5. Consider surface conveyance as an alternative to pipes 4 Consider how runoff will be conveyed to stormwater quality facilities. Conveying flows on the surface is the best method for getting runoff to porous landscape and porous pavement detention because it allows the facilities to be shallow in depth. If flow can be conveyed on the surface in grass swales or in strips of porous pavement, additional stormwater quality benefits will accrue and the required water quality capture volume will be reduced. 4 If runoff must be conveyed under the surface in a pipe, area inlets within a landscaped area are preferred over street or curb inlets, since this gives runoff a chance to sheet flow through vegetation and infiltrate prior to entering the storm sewer. The basin or channel receiving these flows must be deep enough to allow the opposite end of the pipe to empty. 6. Integrate flood control detention Multiple approaches exist for addressing flood control detention that dovetail with stormwater quality management.

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-10 4 Locate flood control detention in landscape areas and in parking lots. 4 Retaining walls that fully enclose a landscape detention area are unacceptable as they create a deep basin without adequate access. 7. Tailor approach to the specific pollutants of concern If downstream receiving waters are threatened by any specific stormwater constituents, such as lakes threatened by excessive phosphorus loading leading to eutrophication, provide BMPs that are particularly effective at addressing that pollutant. 4 The Denver Lake Management and Protection Pla n (Dudley 2004) is a good source of information on lakes in the Denver area. 4 Table SQ-6 of Volume 3 provides information on the estimated performance of various BMPs with regard to specific pollutants. 4 The International Stormwater BMP Database ( www.bmpdatabase.org ) provides good information on the performance of BMPs in various settings and provides data on the effluent quality that may be achieved by various BMPs. How to Use the Guidelines These Stormwater Quality BMP Implementation Guidelines are organized in four sections: 1. Development Type Guidelines. Guidelines for implementing stormwater quality treatment systems for seven representative land use types are presented. The BMPs shown are tailored to the nature of the particular development type. Use these as a general guide to developing an overall stormwater quality plan. It may be appropriate to combine concepts from two or more development types to address the specific goals or characteristics of a project. 2. Implementation Details. Detailed guidance on how to integrate BMPs into a site. Implementation Details relevant to individual Development Types are referenced in the Development Type Guidelines. 3. BMP Fact Sheets. Essential planning information for each stormwater quality BMP is summarized on Fact Sheets, including a description of the BMP, a representative illustration, guidance for specific site conditions and requirements, and example images of constructed BMPs. 4. Maintenance. Maintenance methods designed to ensure its continued occurrence, as well as required practices for maintenance of each BMP are discussed at the end of this chapter.

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Denver Water Quality Management Plan Chapter 6 Page 6-11 DEVELOPMENT TYPE GUIDELINES Seven development types have been identified to communicate different strategies for stormwater quality treatment. (See Exhibit 6.6, next page). They are: 4 Ultra Urban 4 High Density Mixed Use 4 Campus 4 Industrial 4 Low Density Mixed Use 4 Residential 4 Parks and Natural Areas Open Space The development types evolve from the city building blocks defined in Blueprint Denver, which is an integrated land use and transportation plan for Denver. As an example, the Ultra Urban development type represents development characteristics of the Downtown, Employment, and Urban Residential building blocks. Because dense developments have been a challenging arena for water quality, they are a main focus of these guidelines. These Development Type Guidelines describe typical characteristics for each development type, as well as potential sites for stormwater quality treatment. Design recommendations have been developed for each that cover these four topics: 1. Runoff Reduction: Techniques that decrease runoff volume and reduce the Water Quality Capture Volume (WQCV) requiring treatment. 2. WQCV Treatment: BMPs that treat the required volume of storm runoff. The BMPs most appropriate for the various sites are summarized in Exhibit 6.7 3. Flood Detention: Methods for attenuating peak runoff from larger storm events on site. 4. Implementation Details : Additional details for specific portions of a site. Within each topic, the user is directed to additional information on Implementation Details or BMP Fact Sheets in sections following the Development Type Guidelines. Availability of this additional information is indicated by the use of bold text (e.g., green roof ). A sketch diagram shows how some of the design recommendations may be implemented on a representative site, and additional details and photographs further describe treatment options. These guidelines are recommendations only; the designer may choose to mix and match approaches from different development types to best meet the needs of a particular project.

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-12 EXHIBIT 6.6 DEVELOPMENT TYPES SUMMARY Development Type Percentage Landscape Percentage Parking/Paving Building Footprint Parking Blueprint Denver Building Block Examples Downtown LODO Employment Portions of Stapleton and Lowry Ultra Urban 0-5%* 0-5% 90-100% structure Urban Residential Capitol Hill Pedestrian Shopping Corridor East Colfax Grant-York Mixed Use Residential Golden Triangle Transportation Oriented Development (TOD) Colorado Station (at I-25) High Density Mixed Use 0-10%* 0-15% 80-90% structure/ surface Neighborhood Centers Old South Gaylord Campus 15-30% 10-25% 45-75% surface/ structure Campus/Institutional Auraria, Tech Center Industrial 10-15% 40-60% 25-50% surface Industrial I-70 Corridor Town Centers 14th and Krameria Commercial Corridor South Colorado Blvd., Colfax Regional Centers University Hills Shopping Center Low Density Mixed Use 10-25% 30-50% 25-60% surface Entertainment/Cultural/ Exhibition Natl. Western, Pepsi Center Single Family/Duplex Residential City Park West Neighborhood Residential 40-70% 5-20% 10-45% surface Single Family Residential Sloan s Lake Neighborhood, Regis Neighborhood Parks and Natural Areas Open Space 80-95% 5-15% 0-10% surface Parks and Natural Areas Open Space City Park The low percentage of landscape does not preclude the use of porous pavement detention or planter box porous landscape detention to provide treatment for the water quality capture volume on Ultra Urban or High Density Mixed Use sites.

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Denver Water Quality Management Plan Chapter 6 Page 6-13 EXHIBIT 6.7 BMP APPLICABILITY MATRIX Runoff Reduction Stormwater Quality Detention Possible Flood Control Detention 5 Development Type Porous Pavement 1 Grass Buffers and Swales Porous Landscape Detention 2 Porous Pavement Detention 1 Dry Ponds: Extended Detention and Sand Filter Basins 3 Wet Ponds: Constructed Wetland Basin and Retention Ponds 4 Landscape Areas Parking Lots Ultra Urban High Density Mixed Use Campus Industrial Low Density Mixed Use Residential Parks and Natural Areas Open Space KEY Highly applicable Somewhat applicable Not recommended Notes: 1. Porous pavement and porous pavement detention may be used in parking areas and other low-use areas where there is no likelihood of groundwater contamination. 2. Porous landscape detention may be applied in the vicinity of buildings, in parking lot islands, and in other landscape areas where there is no likelihood of groundwater contamination or geotechnical concerns. Wherever porous landscape detention is used, geotechnical issues related to building foundation drainage and expansive soils must be addressed. 3. To avoid constrained configurations of forebays, low-flow channels, and outlet structures, extended detention basins are generally recommended only for drainage areas exceeding 1.0 acre, although sand-filter detention basins may be used for areas less than 1.0 acre. Sand-filter detention basins may be considered for use in Ultra Urban and High Density Mixed Use land uses. 4. Constructed wetland basins and retention ponds may only be used for drainage areas exceeding 1.0 acre that have sufficient base flow to support wetlands and permanent pools; water rights considerations need to be addressed. 5. The use of underground vaults for water quality detention is discouraged; however, Denver will consider the use of underground vaults for flood control. Denver s policy on the use of subsurface devices for stormwater quality is discussed in the section entitled Subsurface Treatment Devices in this chapter.

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-14 Ultra Urban Characteristics: Ultra Urban sites are characterized by structured or underground parking, high to mid-rise buildings, and little to no landscape area at grade most landscape is over structure. Buildings occupy up to 100% of the site. These sites will typically have 5-10% open area as paving or landscape area. Potential Stormwater Quality Treatment Sites: Area for treatment is limited to roofs, plazas, and courtyards. Treatment generally occurs over or adjacent to buildings in contained systems or planters that drain to the storm sewer. Design Recommendations: 1. Runoff Reduction 4 Develop green roofs on buildings and parking structures. (See Implementation Details) 4 Develop porous pavement in plazas and courtyards. (See BMP Fact Sheet) 2. WQCV Treatment 4 Develop treatment roofs on buildings and parking structures. (See Implementation Details) 4 Drain roofs to porous landscape detention in planters adjacent to buildings. (See note 1 opposite page, and BMP Fact Sheet) 4 Drain roofs to porous pavement detention or porous landscape detention in plazas and courtyards.(See notes 2, 4 opposite page, and BMP Fact Sheets) 3. Flood Detention 4 Direct roof runoff to porous landscape detention. Convey flows in excess of WQCV to below-grade vaults or directly to storm sewers. (See note 3 opposite page) 4. Implementation Details 4 Roofs. Route drainage from tall buildings through the building. Include on-roof runoff reduction and treatment that can be cost effective on these sites. (See Implementation Detail) 4 Planting. Provide additional support for plants in urban settings where they are subject to the additional stresses of heat and restricted growing area. (See Implementation Detail) 4 Sediment removal. Provide for the removal of sediment loads that come from roof runoff, construction, and street maintenance. (See Implementation Detail)

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Denver Water Quality Management Plan Chapter 6 Page 6-15 EXHIBIT 6.8 ULTRA URBAN DEVELOPMENT TYPE SKETCH AND ENLARGEMENT EXHIBIT 6.9 TYPICAL ULTRA URBAN SITE IN DOWNTOWN DENVER Porous landscape detention can be integrated into parking garages and other structures such as green roofs. Green roofs can also reduce the storage volume needed. Porous landscape detention in a sunken courtyard garden receives roof runoff from the adjacent courtyard and from pipes or chases penetrating below the first floor. KEY 1 Porous landscape detention in planter boxes adjacent to the building. This formal urban detailing can create an attractive landscape edge. 2 Porous landscape detention in courtyard. (see enlargement below) 3 Flood storage for 100-year storm in a below-grade vault with adequate maintenance access. (see enlargement below) 4 Porous landscape detention cross section showing planted growing medium with gravel below, contained within a concrete structure and underdrain to address geotechnical concerns around structural foundations. (see enlargement below)

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-16 High Density Mixed Use Characteristics: High Density Mixed Use sites are characterized by multi-story development with both structured and surface parking. Buildings typically have setbacks from property lines, but rarely more than 5-10 feet on any side. Open space typically consists of paving with some landscape, and accounts for 0-15 percent of the site. Potential Stormwater Quality Treatment Sites: Treatment may be provided on roofs; plazas; courtyards; islands, buffers, and medians at surface parking; and gardens. Landscape areas may be used to infiltrate stormwater into the ground with sufficient distance from the buildings (consult a geotechnical engineer). Design Recommendations: 1. Runoff Reduction 4 Develop green roofs on buildings and parking structures. (See Implementation Detail) 4 Develop porous pavement in plazas and courtyards. (See BMP Fact Sheet) 4 Drain roofs to grass buffers or grass swales in gardens or planters. 4 Drain surface parking to grass buffers or grass swales at islands and perimeters within parking area. (See BMP Fact Sheets) 4 For public projects or privately owned and maintained streets, provide a depressed, continuous planted strip between the sidewalk and the street. 2. WQCV Treatment 4 Develop treatment roofs on buildings and parking structures. (See note 1 opposite page) 4 Develop porous pavement detention in plazas and courtyards. (See note 2 opposite page, and BMP Fact Sheet) 4 Drain roofs to porous landscape detention in gardens or planters. (See note 3 opposite page, and BMP Fact Sheet) 4 Drain surface parking to porous landscape detention at parking islands, medians, and buffers. (See BMP Fact Sheets) 3. Flood Detention 4 Flood water storage may be combined with stormwater quality treatment areas, provided in paved areas or roadways, or in below-grade vaults. (See note 4 opposite page) 4. Implementation Details 4 Roofs. Route roof runoff through the building or through external downspouts. (See Implementation Detail) 4 Parking. Include parking on the surface, in a structure, or in some combination of both. (See Implementation Detail) 4 Planting. Provide plants with regular water and nutrients in urban settings where they are subject to the additional stresses of heat and restricted growing area. (See Implementation Detail) 4 Sediment removal. Provide for removal of sediment loads, which are primarily from roofs, except where plaza areas and surface parking contribute pollutant loads and debris.

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Denver Water Quality Management Plan Chapter 6 Page 6-17 EXHIBIT 6.11 GREEN ROOF PARKING STRUCTURE IN DENVER The green roof water treatment and plantings on this at-grade and underground parking structure can be accessed easily for maintenance. EXHIBIT 6.10 HIGH DENSITY MIXED USE DEVELOPMENT TYPE SKETCH KEY 1 This green roof above the underground parking structure treats runoff from the structure itself as well as roof runoff from the adjacent high-rise building. At-grade vehicle access is provided to facilitate maintenance. 2 Porous pavement detention is provided on a sandstone patio in the courtyard that treats some of the WQCV from the roof. 3 Porous landscape detention treats roof runoff, and wraps around three sides of the building. 4 Flood storage for the 100-year storm is provided above the porous landscape detention areas in the landscape surrounding the building, and within the adjacent roadway.

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-18 Campus Characteristics: A campus site consists of multiple buildings with a related purpose or function, organized around pedestrian-oriented spaces. Emphasis on automobile circulation and parking can vary considerably. Potential Stormwater Quality Treatment Sites: Runoff reduction techniques, infiltration techniques, and WQCV detention options can be integrated into the landscape to create site amenities where space permits. Strategies shown in the High Density Mixed Use Development Type Guidelines are also appropriate for confined spaces on campuses, including treatment in gardens, plazas, islands and buffers at surface parking, and roofs. Design Recommendations: 1. Runoff Reduction 4 Drain roofs, walks, drives and surface parking to grass buffers and grass swales throughout the landscape. Locate grass swales along paths and drives. (See note 1 opposite page, and BMP Fact Sheets) 4 Develop porous pavement in areas with minimal traffic such as outer areas of parking and emergency access drives. (See note 2 opposite page, and BMP Fact Sheet) 4 Develop green roofs on buildings and parking structures. (See Implementation Detail) 2. WQCV Treatment 4 Drain surface parking to porous landscape detention at parking islands, medians, and buffers. (See BMP Fact Sheet) 4 Develop porous pavement detention in pedestrian areas or areas with minimal traffic such as outer areas of parking and emergency access drives. (See BMP Fact Sheet) 4 Develop detention basin BMPs that serve as site amenities including extended detention basins, sand filter basins, constructed wetlands, and retention ponds. (See note 3 opposite page, and BMP Fact Sheets) 4 Develop treatment roofs on buildings and parking structures. (See Implementation Detail) 3. Flood Detention 4 Combine stormwater quality treatment with flood control in detention basins. (See note 4 opposite page) 4. Implementation Details 4 Roofs. Include treatment and runoff reduction on campus roofs where density and land values make them viable. (See Implementation Detail) 4 Parking. Design large parking areas with porous pavement and porous landscape detention in islands or medians where adjacent land cannot be employed for treatment. (See Implementation Detail) 4 Planting. Consider foot traffic patterns when locating and selecting plantings for runoff reduction and WQCV treatment areas. (See Implementation Detail)

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Denver Water Quality Management Plan Chapter 6 Page 6-19 EXHIBIT 6.12 CAMPUS DEVELOPMENT TYPE SKETCH 4 Sediment removal. Provide for periodic removal of sediment that accumulates in detention basins. Include a concrete forebay or rock bench to provide equipment access. (See Implementation Detail) 4 Stormwater Distribution. Include slots or interruptions in curbs that control traffic in parking areas to disperse runoff as it flows to adjacent grass swales and buffers. (See note 5 opposite page, and Implementation Detail) KEY 1 Grass buffers and swales receive runoff from parking and paving throughout campus, and direct it to detention pond. 2 Porous pavement detention in an overflow parking area treats runoff on the paved area. 3 This wet pond ser ves as a campus amenity, supporting a diverse ecology and treating runoff. 4 The wet pond also serves as flood storage for the100-year storm. 5 Slotted curbs disperse runoff flowing from parking areas. EXHIBIT 6.14 FORMAL WET POND AS A SITE AMENITY This detention pond at a park in Aurora has a concrete edge and steps to allow visitors to access the water. The pond also serves as a water source for site irrigation. The detention area adjacent to Goldsmith Gulch in southeast Denver is spanned by a boardwalk. EXHIBIT 6.13 NATURALISTIC WET POND AS A SITE AMENITY

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-20 Industrial Characteristics: Industrial sites consist of one or more large structures surrounded by surface parking and truck access areas. Open area is predominantly paved and accounts for up to 90 percent of the site. Sites include manufacturing, gas stations, car dealerships, and warehouses. Point source pollution can be an issue on industrial sites. Potential Stormwater Quality Treatment Sites : Treatment occurs in islands and perimeters at surface parking. Large buildings with flat roofs are potential sites for green roofs or treatment areas. Corner-of-the-site treatment options may include limited use of retaining walls that minimize the basin s footprint, but still provide for maintenance access. These sites require care to reduce the likelihood of commingling industrial chemicals with stormwater stormwater contaminated by industrial chemicals manufactured or stored on site must be treated separately and cannot be infiltrated. Design Recommendations: 1. Runoff Reduction 4 Drain roofs to grass buffers at parking islands, medians, and buffers. (See BMP Fact Sheet) 4 Sheet-drain parking to grass buffers and grass swales. (See note 1 opposite page, and BMP Fact Sheets) 4 Develop porous pavement in low-traffic areas and places where trailers or equipment are stored. (See BMP Fact Sheet) 4 Where structures do not create an edge at or near the property lines, develop continuous grass buffers (See BMP Fact Sheet) 2. WQCV Treatment 4 Drain runoff to porous landscape detention at parking islands, medians, and buffers. (Seen note 2 opposite page, and BMP Fact Sheet) 4 Develop porous pavement detention in areas with minimal traffic such as outer areas of parking and emergency access drives. (See BMP Fact Sheet) 4 Develop detention basin BMPs including extended detention, sand filter basins, constructed wetlands, and retention ponds (See note 4 opposite page, and BMP Fact Sheets) 4 Incorporate covering of storage, manufacturing and loading areas, spill containment, and prevention of groundwater contamination. 3. Flood Detention 4 Provide flood detention within parking areas without creating a hazard at loading areas. (See notes 3 and 4 opposite page) 4. Implementation Details 4 Parking. Break up extensive parking areas with porous pavement detention or porous landscape detention without creating a hazard at loading docks. (See Implementation Detail)

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Denver Water Quality Management Plan Chapter 6 Page 6-21 EXHIBIT 6.15 INDUSTRIAL DEVELOPMENT TYPE SKETCH EXHIBIT 6.16 LINEAR DETENTION POND AT AN INDUSTRIAL SITE The linear form of this detention pond at an industrial park in Denver follows the street edge, creating a significant landscape buffer. 4 Planting. Where the site is contiguous with open space buffers, develop plantings that create a smooth transition between these spaces. (See Implementation Detail) 4 Stormwater Distribution. Sheet-drain large areas of paving to landscape, or spread flows with slotted curbs or level spreaders. (See Implementation Detail) KEY 1 Grass swales receive roof runoff from downspouts and direct it towards the detention basin at the back of the site, reducing runoff and removing large sediment. 2 Porous landscape detention receives and treats runoff from portions of the roof in the front and back of the building, and creates a landscape amenity. 3 Roof runoff in excess of the WQCV flows through roof downspouts directly to storm sewers and along to the detention basin. 4 A linear detention basin at the back of the site treats the WQCV and detains flood water. 5 Cover storage areas to prevent contaminated runoff. (not shown)

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-22 Low Density Mixed Use Characteristics: Low Density Mixed Use sites consist of commercial, office, event-oriented, or residential structures organized by automobile circulation and parking with some pedestrianoriented spaces and walkways. This typical big-box pattern includes extensive parking areas that account for more than half the site. Potential Stormwater Quality Treatment Sites: Treatment occurs in islands, buffers, and medians at surface parking lots, lawns, plazas, courtyards, and gardens. Parking areas can be designed to both treat the WQCV and store flood volumes for the runoff they generate. Cornerof-the-site treatment options can serve as an amenity along major roads, or be included in unobtrusive portions of the site. Greater area is available for runoff reduction and treatment landscapes when parking requirements are combined for multiple buildings. Design Recommendations: 1. Runoff Reduction 4 Drain roofs to grass buffers in gardens, planters, or parking islands, medians, and buffers. (See BMP Fact Sheet) 4 Develop porous pavement in low traffic areas, including driveways and portions of parking lots. (See BMP Fact Sheet) 4 Sheet drain parking to grass buffers and grass swales (See BMP Fact Sheets) 4 Where structures do not create an edge at or near the property lines, develop continuous grass buffers (See BMP Fact Sheet) 2. WQCV Treatment 4 Develop porous pavement detention in areas with minimal traffic, such as outer areas of parking and emergency access drives. (See note 1 opposite page, and BMP Fact Sheet) 4 Drain surface parking to porous landscape detention at parking islands, medians, and buffers. (See notes 2, 3, 4 opposite page, and BMP Fact Sheet) 4 Where space permits, develop detention basin BMPs at site low points to facilitate gravity flow to them. These include extended detention basins, sand filter basins, constructed wetlands, and retention ponds (See note 5 opposite page, and BMP Fact Sheet) 3. Flood Detention 4 Design parking areas and landscapes to accommodate their own treatment and flood detention requirements. Include shallow paving depressions of less than nine inches in parking lots to detain flood volumes. (See note 6 opposite page) 4. Implementation Details 4 Roofs. Consider treatment roofs on the large roofs of big-box retail. (See Implementation Detail) 4 Parking. Include treatment areas for the runoff parking areas generate. (See Implementation Detail) 4 Planting. Separate trees from porous landscape detention areas so the planting medium may be periodically replaced without impacting tree roots. (See Implementation Detail)

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Denver Water Quality Management Plan Chapter 6 Page 6-23 EXHIBIT 6.17 LOW DENSITY MIXED USE DEVELOPMENT TYPE SKETCH EXHIBIT 6.18 PARKING MEDIAN IN DE NVER, CO A flush curb along this parking median allows stormwater to flow into this swale and move to an extended detention area. 4 Planters. Provide raised or sunken contained planting spaces adjacent to buildings. (See Implementation Detail) 4 Stormwater Distribution. Use slotted curbs or flush curbs and wheel stops to separate vehicles from landscape areas while allowing runoff to flow without concentrating. (See Implementation Detail) 4 Sediment Removal. Provide for periodic removal of the sediment deposited by vehicles. (See Implementation Detail) 1 Porous pavement detention provides treatment in a seldom-used area of parking. 2 Porous landscape detention in parking islands treats runoff from surrounding parking. 3 Porous landscape detention in parking medians treats runoff from surrounding parking. 4 Porous landscape detention adjacent to paved areas receives and treats runoff. 5 An extended detention basin at the low end of the site provides treatment for runoff from roofs and other paved surfaces. 6 Grading adjacent to and within parking and paved areas allows100-year storm to be stored within those areas.

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-24 Residential Characteristics: The Residential development type is characterized by residential structures lining a roadway. Typical development patterns include open areas in the front and back of each structure, as well as communal open space. Potential Stormwater Quality Treatment Sites : The focus in this development type is on reducing runoff from homes. Yards and gardens surrounding each structure or group of structures receive runoff from roofs as well as paved walks and drives. Design Recommendations: 1. Runoff Reduction 4 Drain roofs to grass buffers and grass swales in gardens and yards. (See note 1 opposite page, and BMP Fact Sheets) 4 Drain driveways, walks and patios to adjacent grass buffers either directly or through slot drains or porous pavement. Provide sufficient slope and/or a ledge between the pavement and the landscape to accommodate future thatch buildup on lawns. (See note 2 opposite page, and BMP Fact Sheet) 4 Construct driveways and parking aprons using porous pavement (See note 3 opposite page, and BMP Fact Sheet) 4 Public Space: In appropriate neighborhoods with rural character, develop roadside grass swales with or without curbs. Allow swales to drain frequently to open space areas or storm sewers to maintain shallow swales. (See BMP Fact Sheet) 2. WQCV Treatment 4 In parks, greenways, or open space, develop porous landscape detention to treat runoff from adjacent areas. (See BMP Fact Sheet) 4 In parks, greenways, or open space within residential areas, develop detention basin BMPs, including extended detention sand filter basins constructed wetlands and retention ponds to serve larger tributary areas. (See BMP Fact Sheet) 3. Flood Detention 4 Locate residences at an elevation to accommodate the 100-year storm event within the adjacent roadway. (See note 4 opposite page) 4. Implementation Details 4 Roofs. Drain roofs to adjacent landscape to reduce runoff. Avoid storing water on foundation soils at the building perimeter. (See Implementation Detail) 4 Planting. Design gardens and planting beds to accommodate and thrive on runoff from roofs and paving. (See Implementation Detail) 4 Stormwater Distribution. Direct runoff to roadside swales with curbless streets. (See Implementation Detail)

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Denver Water Quality Management Plan Chapter 6 Page 6-25 EXHIBIT 6.21 SKETCH OF ROOF DRAIN PLANTINGS EXHIBIT 6.19 RESIDENTIAL DEVELOPMENT TYPE SKETCH KEY 1 Roof drains are directed to landscape buffers with plants that thrive on periodic inundation. 2 Positive drainage from the sidewalk to the street allows the tree lawn to act as a grass buffer and reduce runoff. 3 Porous pavement at the lower quarter of each driveway allows runoff to infiltrate. 4 Flood storage for the100-year storm is provided in downstream landscape areas. (not shown) EXHIBIT 6.20 RESIDENTIAL AREA OF MINNEAPOLIS, MN Roads and drives drain to an adjacent rain garden planted with species that thrive on the additional moisture while reducing runoff from the neighborhood. The garden at the outlet from a house roof drain includes plants that thrive on the additional moisture flowing from the roof. Turfgrass is also a good recipient of roof runoff. Source: City of Portland 2002 Stormwater Management Manual.

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-26 Parks and Natural Areas Open Space Characteristics: Due to the minimal amount of impervious area in parks, supplemental efforts to reduce runoff are rarely required. In fact, Denver Parks and Natural Areas Open Space may efficiently serve to treat runoff from surrounding areas if approved by the Parks Department; however, this practice must preserve the quality of park features and programmed uses. In particular, park lakes are of concern because they serve as both park amenities and receiving waters (see Chapter 4). Parks with high intensity use, like sports facilities, may have significant areas of surface parking runoff requiring treatment. Potential Stormwater Quality Treatment Sites: The public nature of park spaces creates a tremendous opportunity for reducing and treating runoff at a regional level. Stormwater quality facilities are best included in parks larger than 10 acres, where they do not take up more than a third of the total park area, and can be combined with other park uses. Facilities should only be included in smaller parks when they are considered early in the public design process. Treatment facilities cannot be combined with active recreation areas like sports fields. Potential regional stormwater quality facilities within parks are identified in Chapter 8. There are more opportunities for integrating stormwater quality treatment in new parks whereas existing parks may not be able to accommodate these features. Criteria for the Use of Parks as Stormwater Treatment Sites: Consider the following in determining a park s feasibility as a stormwater treatment site: 4 Compatibility with design, historic designation or other protective constraints including wildlife habitat and protection. (e.g., Washington Park is a federal historic landmark. Because of this, significant changes to the shape or size of its two major lakes would not be permitted as that would impact the park s character.) 4 Compatibility with recreational uses. The level of organized and informal activity in a park must be considered. 4 Technical constraints and opportunities including soil characteristics, turf management, or terrain. 4 Potential for new natural areas and wildlife corridors. 4 Size and configuration of the park. A small neighborhood park under five acres would probably not be appropriate for a water quality facility. 4 Maintenance and operations, funding resources, successful techniques for dealing with silt, debris, etc. 4 The configuration and easements for underground utilities and their impact on the existing park land. 4 Potential for total rehabilitation of existing sites to accommodate multi-purpose uses. 4 Impacts on all aspects of the open space system: Highline Canal and trails, South Platte River Greenway, natural areas including potential areas such as along gulches, traditional parks, and other publicly owned lands.

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Denver Water Quality Management Plan Chapter 6 Page 6-27 EXHIBIT 6.22 WET POND IN NEIGHBORHOOD PARK IN MINNEAPOLIS, MN Design Recommendations: 1. Runoff Reduction 4 Sheet-drain parking and paving to grass buffers and grass swales .(See note 1 opposite page, and BMP Fact Sheets) 4 Drain roofs to grass buffers grass swales, and porous pavement (See BMP Fact Sheets) 4 Develop multi-purpose trails, maintenance routes, and parking areas to minimize directly connected impervious areas. Avoid concentrating runoff from roadways and parking lots by allowing runoff from those areas to sheet drain over landscape areas. 4 Use porous pavement to the maximum extent practicable for parking areas, patios, trails, etc. (See BMP Fact Sheet) 2. WQCV Treatment 4 Treat runoff from parking lots and roadways using porous landscape detention and porous pavement detention where practicable (See BMP Fact Sheets) 4 Develop regional stormwater quality treatment in detention basin BMPs, including extended detention basins, sand filter basins, constructed wetlands, and retention ponds Construct all facilities as site amenities, with minimal variation in water levels during storm events, the ability to support diverse ecology, and the ability to be drawn down for clean out and maintenance. (See note 3 opposite page, and BMP Fact Sheet) 4 Do not combine WQCV facilities with active recreation. 4 Implement source control BMPs. Proper pesticide, herbicide, fertilizer and other chemical use is important. Use integrated pest management (IPM) and follow the Mayor s Executive Order 121 for pesticide use. Also see the Denver Lake Management and Protection Plan (Dudley 2004) for park lakes. (See note 2 opposite page) 3. Flood Detention 4 Develop berms around existing ponds, lakes, and extended detention facilities to increase water storage capacities within the park. (See note 4 opposite page) 4. Implementation Details 4 Parking. Direct runoff from parking to adjacent landscape areas. (See Implementation Detail) 4 Planting. Parks present a tremendous opportunity to include diverse plantings in larger treatment areas in Natural Areas Open Space. (See Implementation Detail) Shown here under construction, this park pond treats runoff from the surrounding neighborhoods, while creating an amenity for the community.

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-28 EXHIBIT 6.23 PARKS DEVELOPMENT TYPE SKETCH EXHIBIT 6.25 LAKE BUFFER IN DENVER EXHIBIT 6.24 POROUS LANDSCAPE DETENTION AT HUSTON LAKE PARK IN SOUTHEAST DENVER KEY 1 Swales and buffers that intercept runoff before entering the lake allow a diverse ecology to be maintained in park lakes. 2 On-site pollutant sources, including maintenance areas and dog parks, are isolated and runoff from those areas is treated. If possible, divert these flows from entering park ponds and lakes. 3 Detention basins may provide treatment of runoff from surrounding areas as long as this does not compromise park functions. 4 Denver Parks and Natural Areas Open Space may provide storage for the 100-year storm flood waters from surrounding areas in park lakes if the proposed flood storage improvements, especially for frequent storm events, do not significantly impact the integrity of the park s design and function. Planted with diverse wetland vegetation, this treatment area collects and treats runoff from the adjacent neighborhood before it enters the park. Native vegetation forms a buffer along this park lake shoreline. By separating open water from open turf, fertilizers are less likely to directly enter lake water, and geese habitat is minimized. Source: Dudley 2004.

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Denver Water Quality Management Plan Chapter 6 Page 6-29 IMPLEMENTATION DETAILS Roofs Runoff from roof surfaces contains urban pollutants primarily from atmospheric fallout (Urbonas and Doerfer 2004). This water requires treatment before being conveyed offsite. Although roof drains have often been tied directly to storm sewers, this practice is no longer acceptable. Several approaches to treating roof runoff are discussed below. For all of these treatment options, it is essential that the building foundation be protected from moisture. When properly designed, these features can remove pollutants and provide aesthetic appeal. EXHIBIT 6.26 GARDEN SUPPORTED BY ROOF RUNOFF IN DENVER Runoff drains through a spout from the roof to a splash basin and rain garden below, highlighting the flow of stormwater to garden visitors. Due to splashing, this type of detail should not be placed near major pathways. EXHIBIT 6.27 PLANTER GARDEN SUPPORTED BY ROOF RUNOFF IN BOULDER Runoff drains to a planter adjacent to, but separated from, the building. The planter contains a variety of plants that thrive with the additional moisture.

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-30 EXHIBIT 6.29 ROOF DRAINAGE SKETCHES Primary approaches for treating roof runoff at ground level include: 1. Downspouts and scuppers at the building perimeter may be drained to a contained porous landscape detention facility or a porous pavement detention facility located adjacent to the structure. These closed systems drain away from building foundations. 2. Internal roof drain piping may be routed to an exterior wall and daylighted above grade to a contained porous landscape detention or porous pavement detention facility located adjacent to the structure. 3. Internal roof drain piping may be routed under the first floor and directed to a contained below-grade porous landscape detention or other BMP adjacent to the structure. Although not as desirable as daylighting above grade, this is a viable technique in constrained sites. In this case, BMPs must be located down-slope from the building or in a sunken planter. 4. Internal drains may also be conveyed below grade in a pipe to a porous landscape detention area, extended detention basin, or other treatment BMP at the low end of site. a) Runoff drains outside the building through a downspout. b) Runoff drains through and out the side of the building c) Runoff drains through the building, down through the slab, and out below the foundation. Rooftop runoff from an industrial facility splashes into rain gardens set in buried concrete pipe adjacent to the building, and then flows on a concrete pan out of the basin. EXHIBIT 6.28 DOWNSPOUTS IN BOULDER

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Denver Water Quality Management Plan Chapter 6 Page 6-31 EXHIBIT 6.30 INDUSTRIAL FACILITY LIVING ROOF IN DEARBORN, MI EXHIBIT 6.31 CHICAGO, IL CITY HALL GREEN ROOF Green Roofs/Treatment Roofs: A green roof a building roof or parking structure covered with soil and vegetation reduces the impervious area of a site and provides filtering and stormwater quality treatment of rain falling on the roof. This concept requires careful planning, design, construction, and maintenance. Many proprietary green roof systems are available on the market. These roofs have the potential to provide significant runoff reduction and stormwater quality enhancement for a site, particularly when the roof area is large. Access for maintenance must be considered. This technique works particularly well when the structure is underground and at least a portion of the roof is at-grade. Elements of green and treatment roofs include: 4 Roof structure that supports soils, vegetation, and live loads associated with rainfall, snow, people, and equipment. 4 Waterproof membrane. 4 Root barrier. 4 Drainage layer. 4 Soil/growth medium. For treatment roofs, this includes a porous landscape detention or porous pavement detention type soil. 4 Irrigation and plant materials. Native/naturalized, drought-tolerant grasses, perennials, and shrubs are preferred for roof plantings. However, even this low-water vegetation will require some supplemental irrigation in Denver. Treatment roofs include all the elements of a green roof, as well as the detention component of porous landscape detention or porous pavement detention on the roof structure. Green roofs are not currently approved as a standard design for treatment; however, they will be considered on a case-by-case basis. See Exhibit 6.11 for a green roof in Denver. Roof garden plantings reduce the amount of runoff from this urban building with soils that absorb water and plantings that increase evapotranspiration. Source: http://www.roofmeadow.com/ This 10-acre Ford Motor Company facility has a green roof planted with sedum ground cover. Source: http://www.ford.com

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-32 EXHIBIT 6.32 PLANTER POROUS LANDSCAPE DETENTION Infiltration Planters Porous landscape detention can be implemented within planter boxes adjacent to buildings to treat roof runoff. Incorporating the standard porous landscape detention design into a planter box allows treatment to occur in constrained spaces while providing a landscape amenity. It is critical to consider soil types and ensure that building foundations are protected from subsurface water. The planter should be designed to dissipate energy from the downspout or water source, and will usually require irrigation for plant establishment. Any basin adjacent to a building must be completely separated from the building to address geotechnical concerns. Create a stable system that accounts for foundation differential movement by following the recommendations of a structural engineer and including adequate foundation drainage.

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Denver Water Quality Management Plan Chapter 6 Page 6-33 EXHIBIT 6.33 PARKING MEDIAN POROUS LANDSCAPE DETENTION Parking Medians and Islands Parking lots contribute significant pollutant loading to urban runoff. Typical drainage approaches include inlets and storm sewers that capture runoff and convey it to perimeter detention basins. Although this facilitates efficient drainage, runoff volumes are not reduced, and the resulting detention basins are often forced into constrained holes in the ground that are difficult to maintain and add little value to a site. The following techniques for parking medians, parking islands, and shallow parking lot detention incorporate both stormwater quality treatment and flood detention into parking areas to reduce or eliminate detention volumes required elsewhere on the site. Parking Medians Landscape medians between rows of cars can break up large expanses of pavement and provide a location for trees, plantings and turfgrass. Instead of raised medians with curbs, medians can be constructed as shallow depressions and protected with wheel stops or slotted curbs. A standard porous landscape detention design can be incorporated into the median. Exhibit 6.33 illustrates this concept in plan and section. These medians are designed to have a flat longitudinal grade so that the WQCV can have a level water surface (an average depth of 6 inches is recommended). Adjacent pavement should have a cross slope to drain runoff to the porous landscape detention. The flat longitudinal grade allows flood detention to be provided above the WQCV and the adjacent pavement at shallow depths (no more than nine inches above the pavement at the deepest point during the 100-year storm). An overflow inlet is provided in the porous landscape detention to control larger flood events and any porous landscape detention underdrains also tie into this inlet. Medians can be included in every parking bay or in every other bay. If medians are oriented parallel with the flow of pedestrian traffic, access across the median does not present a significant design issue. When pedestrian access crosses the median, include intermittent walkways clearly designated by railings, tall shrubs, or mini-bridges. When trees are planted in

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-34 the median, include a minimum 6-square-foot square planting area without underdrains that is not included in porous landscape detention volume calculations. Parking Islands Parking Islands are individual areas of porous landscape detention within a parking lot. The islands form less of a barrier to pedestrian traffic flow or snow removal than medians. They are best located at approximately 100-foot intervals. Exhibit 6.35 illustrates this concept. Shallow Parking Lot Detention Shallow Parking Lot Detention consists of a relatively flat section of parking lot with slight depressions draining to grated inlets. Flood control detention is provided at shallow depths above the pavement (no more than 9inches deep during the 100-year storm) and stormwater quality detention is provided by porous landscape detention or, for large drainage areas, an extended detention basin located in the perimeter landscaping. Porous pavement can be used in parking lots to reduce runoff and promote infiltration. If configured as porous pavement detention, WQCV treatment can be provided in a oneor twoinch layer above the pavement. (Size pavement with 10 to 15 percent open area with a WQCV design depth of one inch. Size pavement with a 40 percent open area with a two-inch depth.) Shallow flood control detention may also be provided with an overflow inlet to control larger storms. EXHIBIT 6.34 PARKING MEDIAN POROU S LANDSCAPE DETENTION IN BOULDER A narrow median strip receives runoff from two bays of parking. The runoff infiltrates and supports the native grasses, shrubs, and trees planted there. A stone crossing allows pedestrians to cross the median without trampling plantings. An imp ermeable liner extending three feet below each curb protects the pavement from water damage.

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Denver Water Quality Management Plan Chapter 6 Page 6-35 EXHIBIT 6.35 PARKING ISLAND POROUS LANDSCAPE DETENTION

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-36 EXHIBIT 6.36 SLOTTED CURB IN CANYONLANDS NATIONAL PARK, UT EXHIBIT 6.37 LEVEL SPREADER IN AURORA Stormwater Distribution Many of the BMPs described in this chapter require un-concentrated flows to function efficiently. Ideally, flows can sheet-drain to the BMP. A flush curb allows sheet flows to drain to the BMP landscape. However, both the pavement edge and the BMP landscape require protection from cars, which can be achieved by wheelstops, shrubs, or railings. When sheetdraining runoff is not possible, slotted curbs can minimize the amount of concentration, and level spreaders can allow concentrated flows to become re-dispersed. Variations on slotted curbs may be developed using closely spaced standard Colorado Department of Transportation (CDOT) curb inlets to drain paved areas into adjacent open space. This technique does concentrate flows somewhat, so care must be taken to provide adequate drainage in active areas and irrigated turfgrass. The slotted curb at this planted area has depressions between each parking space to allow runoff to flow to the interior landscape area without concentrating. A horizontal slotted pipe level spreader below the curb evenly distributes storm flows to avoid standing water and disperse concentrated flows.

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Denver Water Quality Management Plan Chapter 6 Page 6-37 EXHIBIT 6.39 ROADSIDE SEDIMENT TRAP IN BOULDER Sediment Removal Traps and Forebays Planning for sediment capture and periodic removal during maintenance operations is essential to ensure the long-term sustainability of stormwater BMPs. Particular attention to sediment control is necessary at inlets to all types of detention basins where waterborne sediments in stormwater reach slower velocities and tend to settle out and adjacent to parking lots and roadways where winter use of gravel creates heavy sediment loads. Sediment removal areas are an early step in the treatment train for stormwater, removing large sediments and trash from the runoff. A wide range of sizes and configurations for these areas is possible, from small rock mulch beds to large pre-sedimentation forebays in detention basins. Sediment traps at pipe outlets need to be designed to dissipate the energy of storm flows sufficiently to allow sediment to drop out and not become re-suspended. All types of sediment traps and forebays need to include access for maintenance equipment. Additional information on the design of pre-sedimentation forebays is provided in Volume 3. One-footwide rock mulch along this curbless road at an industrial facility traps sediment from runoff before it enters the swale below and can be replaced easily when clogged. An edger between the mulch and adjacent landscape would help contain the mulch and create a cleaner edge. EXHIBIT 6.38 FOREBAY AT STAPLETON IN DENVER This forebay to a detention basin allows the energy in runoff to dissipate and drop out suspended particles and solids. Designed to the standards described in Volume 3, vehicles can access this area for periodic cleanout.

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-38 Soils Soil characteristics are important to BMP performance because of their ability to 1) trap pollutants and 2) support vegetation that traps pollutants. Runoff that flows across and through the upper part of the soil profile comes in contact with the physical, chemical, and biological components of the soil. The organic material in the soil binds and removes phosphorous, metals, and salts. Most of the BMPs described employ vegetation as an integral component in treating stormwater runoff. The medium in which the vegetation grows is critical to the growth and long-term health of that vegetation. Grass buffers, grass swales, and basin BMPs use native soils, and the characteristics of these soils, including texture, impermeable soil layers, salinity, and the quantity of organic matter, are key considerations in making plant selections. Soils tests should be completed to determine soil characteristics and the type of soil amendments needed to support the desired plant types. For example, three to five cubic yards of organic matter incorporated into the top layers of soil is typically required for turfgrass planted in swales. Porous landscape detention requires an engineered soil either a mix of 75 percent sand and 25 percent peat (Exhibit 6.40), or a sandy loam, (Exhibit 6.41). The soil must allow stormwater to infiltrate while still holding enough fine material and organics with nutrients and moisture to support vegetation and provide some adsorption capacity. The following tables describe these two types of soil. EXHIBIT 6.40 SAND-PEAT MIX 75% sand as defined below, and 25% sphagnum peat Textural class/USDA Designation Size in mm Percent of total weight Gravel >2 mm Less than 5% Sand 0.05-2 mm 95-100% Silt 0.002-0.05 mm Less than 5% Clay <0.002 mm Less than 5% EXHIBIT 6.41 SANDY LOAM 100% sandy loam as defined below Textural class/USDA Designation Size in mm Percent of total weight Gravel >2 mm Less than 5% Sand 0.05-2 mm 70-80% Silt 0.002-0.05 mm 15-20% Clay <0.002 mm Less than 5%

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Denver Water Quality Management Plan Chapter 6 Page 6-39 Planting When selecting plants for use in stormwater quality BMPs, select plants that can survive under the site conditions, perform the desired water quality function, are appropriate to the site context, and can be supported with a realistic maintenance schedule. Key aspects of each of these factors are described below. 1. Plants that can survive. While typical plant choice considerations including site soils, slope, aspect, and exposure apply equally to BMPs, the most significant environmental consideration is water. Plants in BMPs are subject to inundation, prolonged localized saturation, and drought, so they must be selected to thrive in these widely varying conditions. These plants should also be supported with irrigation for establishment and during periods of drought. Consider the typical amount of saturation in a BMP, site-specific conditions as described in Exhibit 6.42, and typical periods of inundation described in Exhibit 6.43 in choosing appropriate plantings. EXHIBIT 6.42 BMP SITE-SPECIFIC CONDITIONS Wet Variable Dry Detention pond basin bottoms Porous landscape detention bottoms Grass Buffers Swale bottoms Pond and basin margins Upper slopes of ponds Wherever irrigation flows concentrate Side slopes of swales and porous landscape detention EXHIBIT 6.43 TYPICAL BMP INUNDATION PERIODS BMP Inundation Period Porous landscape detention 6 hours Sand filter extended detention basins 40 hours Extended detention basins 40 hours Retention ponds Permanent: 12 hours in zone above pool Constructed wetland basins Permanent: 24 hours in zone above pool Soil considerations include texture, compaction, nutrients, permeability of subgrade, salinity, and the quantity of organic matter. For porous landscape detention, employ engineered soils to achieve required permeability.

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-40 EXHIBIT 6.45 RUSHES IN A STORMWATER GARDEN IN DENVER EXHIBIT 6.47 DETENTION BASIN WETLAND MICROPOOL IN AURORA EXHIBIT 6.44 BASIN PLANTINGS IN DENVER Plant trees and shrubs on the side slopes of basins rather than in the wet bottom area. Rushes can withstand up to six months of drought and two months of inundation after establishment. EXHIBIT 6.46 SWALE GRASSES SLOW RUNOFF IN AURORA Both the bluegrass turf in the upper portions and the native grasses in the lower portions of this broad swale serve to slow down or attenuate the velocity of stormwater runoff. Wetland grasses planted in the bottom of this detention basin remove nutrients and pollutants from stormwater runoff.

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Denver Water Quality Management Plan Chapter 6 Page 6-41 2. Plants that perform the desired stormwater quality function. Plants are an integral aspect of most of the BMPs, performing a wide range of functions that improve the quality of stormwater runoff. Runoff typically enters a BMP with some velocity, and one function of the plants is to slow down that water to reduce erosion both within the BMP and downstream of it. The aboveground portions of a plant can reduce the velocity of runoff. For example, grasses and shrubs or groundcovers with stiff stems can filter sheet flows. Root systems serve to stabilize the soil, with fibrous roots systems providing greater stability. These issues are more critical on the sloping portions of BMPs than in flat or gently sloping bottoms. Because some of the most common pollutants in urban runoff are actually excess nutrients, many plants can thrive in BMPs while removing the very nutrients that can cause problems downstream. Many plants also remove other pollutants from runoff, particularly wetland species that are included in basin micropools and wetlands. Slower and more evenly spread-out flow (sheet flow) will greatly improve the treatment effects of vegetation. 3. Plants that are appropriate to the context. Many of the BMPs can perform multiple functions. In addition to providing stormwater quality functions, plants in BMPs can also provide shade and screening for parking lots, color and texture at building entrances, or grassy fields in unprogrammed park areas. The aesthetics of how and which plants are included in a BMP can make all the difference in creating a successful landscape. 4. Plants that can be supported with a realistic maintenance schedule. All plants require some amount of ongoing maintenance. Ensure that the plantings can be cared for within a project budget and schedule, as well as in perpetuity. Weed control in BMPs must be considered both with regard to the overall structure of the BMP, as well as with regard to access to areas for removal of both weeds and trash. Because these areas are intended to improve the quality of stormwater runoff, they are particularly poor choices for the use of herbicides, which pollute the very water being treated. Mulch can provide an effective barrier against weeds. Rock mulch has greater stability than organic mulches, which float and can wash out of the system. Sedimentation on top of mulch, and subsequent plant growth in the sediments, should be considered. In choosing a mulch, consider that it may be necessary to mow these areas after several years of operation. The planting strategy can have a tremendous impact on the requirements of weed control. Masses of dense shrubs or groundcover can often out-compete weeds without appearing overgrown, while more intricate planting patterns with many different plant species require larger spaces between plants that often become subject to weedy invasions. Consider also the ultimate size, growth rate, and other characteristics of all plantings included. Also, consider if the plants can easily be trimmed or mowed, especially on pond bottoms.

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-42 EXHIBIT 6.49 SPLASH OF COLOR AT BUILDING ENTRANCE IN DENVER EXHIBIT 6.50 GRASS FIELD IN DENVER EXHIBIT 6.48 TREES IN GRASS BUFFER IN DENVER Trees in this grass buffer serve to both screen and shade the adjacent parking. The colorful plantings in this stormwater garden provide an attractive feature at the building entrance. The grass over this sand filter can serve as an informal play area during most of the year.

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Denver Water Quality Management Plan Chapter 6 Page 6-43 1: Inlet: Slotted curbs or level spreaders p romote uniform storm flows. Depress grade three inches below pavement to provide positive drainage even with moderate sediment accumulation. 2: Sediment Trap: In areas with high sediment loads, include a rock mulch strip contained by a landscape edger. 3: Vegetation: Irrigated dense turf or native grasses may include other dense groundcovers. 4: Outlet/Overflow : Drain to a grass swale or a depression with inlet and storm sewer. 5: Infiltration Matrix: Native soils. EXHIBIT 6.51 GRASS BUFFER SKETCH BMP FACT SHEETS Grass Buffers Function: Runoff Reduction A grass buffer is a gently sloped turf area designed to disperse runoff over a broad area, promote infiltration, remove large sediment, and reduce the volume of runoff entering treatment facilities. 4 Typical Applications: Landscape edges and transitions to paved areas, roads, and parking lots, and residential lawns. 4 Operation and Maintenance Considerations: Turf should be approximately three inches lower than adjacent paving to provide positive drainage even when a moderate amount of sediment and thatch has accumulated. When used adjacent to parking lots, consider slotted curb, other vehicular controls, or reinforced turf at the edge of the pavement to reduce wheel rutting of the buffer. Avoid heavy use of fertilizers that will undermine stormwater quality goals. Provide sheet flows (unconcentrated flows) to grass buffers to reduce erosion. See Maintenance Guidelines at end of chapter. 4 Landscape Considerations : Select turf or native grasses appropriate to the surrounding landscape. Supplemental irrigation is necessary to establish and maintain turf and should be applied based on water requirements of the selected plant species. When groundwater is close to the surface, use wetland grasses that can tolerate inundation. Dense groundcovers with fibrous root systems may also be considered. 4 Relative Cost : Low 4 Governing Documents: See Volume 3, page S-2

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-44 EXHIBIT 6.52 GRASS BUFFER AT STAPLETON IN DENVER EXHIBIT 6.54 GRASS BUFFER IN DENVER EXHIBIT 6.53 LAWN IN DENVER Stormwater flows directly from the road across the grass buffer planted with turf and trees into a sand filter treatment in a residential parkway. The native grasses of the buffer in this park reduce runoff from the alley, neighborhood, and irrigated turf above, reducing pollutants and protecting the adjacent drainageway. This urban lawn could easily be adapted to create a grass buffer for roof runoff in this area of dense development.

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Denver Water Quality Management Plan Chapter 6 Page 6-45 1: Inlet: Slotted curbs or curbless streets provide uniform flows. Control for sediment and erosion at inlets and wherever flows concentrate. Depress ground three inches below pavement to provide for positive drainage even with moderate sediment accumulation. 2: Sediment Removal: Grass may grow up through accumulated sediment, requiring periodic removal of vegetation. 3: Slopes : Provide slopes and check structures in accordance with Volume 3. 4: Vegetation: Dense turf or native grasses. 5: Underdrain/Liner: In accordance with Volume 3, sandy soils (Type A&B) do not require underdrains, while clay soils (Type C&D) do. 6: Outlet/Overflow: Flows are typically delivered to a BMP that treats the WQCV, or convey runoff from a WQCV facility. (not shown on sketch) 7: Infiltration Matrix: Consists of native soils. EXHIBIT 6.55 GRASS SWALE SKETCH Grass Swales Function: Runoff Reduction A grass swale is a gently depressed turf-lined channel that conveys stormwater slowly, promoting infiltration. 4 Typical Applications: As a flow conveyance facility in lieu of a storm sewer. Use along curbless streets or to capture flow from grass buffers. 4 Operation and Maintenance Considerations: In locations where routine mowing is planned, provide an underdrain, turf reinforcement, or rock mulch and avoid mowing following extended periods of precipitation. Maintain mowable side slopes in accordance with Volume 3. See Maintenance Guidelines at end of chapter. 4 Landscape Considerations : Irrigated turfgrass provides a stable surface for storm flows, but requires regular mowing, which may be difficult when wet. Consider using native grasses that require less frequent mowing. Woody plant material should be avoided as it may trap trash and debris and become difficult to maintain. 4 Relative Cost : Low 4 Governing Documents: See Volume 3, page S-8

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-46 EXHIBIT 6.56 GRASS SWALE IN DENVER EXHIBIT 6.58 GRASS SWALE IN DENVER EXHIBIT 6.57 GRASS SWALE IN BOULDER EXHIBIT 6.59 GRASS SWALE IN BOULDER This roadside grass swale is planted with bluegrass turf along a curbless neighborhood street. A pipe culvert allows water to flow from one side of the driveway to the other. This swale in a depressed parking median removes coarse sediment while conveying flows to an extended detention basin. Note the flush curb that provides a clean edge to the asphalt and allows sheet flows into the swale. This swale planted with native grasses conveys water from planter boxes close to the building around the site. A swale between this industrial building and the entry drive collects runoff from downspouts and pavement then conveys it below the road to an adjacent stormwater quality treatment area.

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Denver Water Quality Management Plan Chapter 6 Page 6-47 Porous Pavement and Porous Pavement Detention Function: Runoff Reduction (porous pavement) and Site WQCV (porous pavement detention) Both porous pavement and porous pavement detention consist of paver blocks or other reinforcement with sufficient void space to allow stormwater to percolate. Porous pavement detention is flat and includes a shallow storage area above the surface for the water quality capture volume (WQCV). Volume 3 describes five types of porous pavement. 1. Modular Block Porous Pavement 2. Cobblestone Block Porous Pavement 3. Reinforced Grass Pavement 4. Poured Porous Concrete Pavement 5. Porous Gravel Pavement Of these types, Modular Block Porous Pavement and Porous Gravel Pavement may be used in porous pavement detention installations. 4 Typical Applications: Use Reinforced Grass Pavement or planted Modular Block Porous Pavement in landscape areas used for maintenance access, in infrequently used overflow parking lots, and adjacent to curbless streets where wheel rutting is a concern. In higher traffic and parking areas, use Cobblestone Block Porous Pavement or Poured Porous Concrete Pavement. Porous Gravel Pavement may be considered for industrial land uses where there is little likelihood of groundwater contamination. 4 Operation and Maintenance Considerations: Void spaces can become clogged over time and require periodic maintenance to re-establish infiltration capacity. Blocks planted with turf cannot easily be plowed. See Maintenance Guidelines at end of chapter. 4 Landscape Considerations : Turf grown in pavers is particularly susceptible to drought, and must be irrigated. Consider irrigation head locations when establishing vehicle routes. Vehicles tend to compact soils, making vegetation growth difficult. Consider Cobblestone Block Porous Pavement or Poured Porous Concrete Pavement for paved pedestrian areas and walkways to reduce tripping hazards. 4 Relative Cost : Moderate to high 4 Governing Documents: See Volume 3, pages S-13, S-22, and www.udfcd.org for updated information

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-48 1: Vegetation: If turfgrass is desir ed, use Reinforced Grass Pavement or Modular Block Porous Pavement with supplemental irrigation. 2: Slopes: Flat with a shallow surcharge zone for porous pavement detention. Gradual slopes for porous pavement. 3: Underdrain/Liner: Underdrain is required when underlying soils have insufficient infiltration capacity. Underdrain and liner are recommended where geotechnical concerns exist. Porous pavement shall not be used if a likelihood of groundwater contamination exists due to the handling of chemicals or petroleum products. 4: Inlet : For porous pavement detention, inlet provided for runoff greater than the recommended WQCV, as specified in Volume 3. 5: Pavers: Install per manufacturer s directions when using proprietary products. 6: Infiltration Matrix: In accordance with design requirements shown in Volume 3. EXHIBIT 6.60 POROUS PAVEMENT SKETCH (COBBLESTONE BLOCK POROUS PAVEMENT SHOWN)

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Denver Water Quality Management Plan Chapter 6 Page 6-49 EXHIBIT 6.61 POROUS PAVEMENT TURF BLOCK IN DENVER EXHIBIT 6.64 REINFORCED GRASS PAVEMENT EXHIBIT 6.62 POROUS PAVEMENT TURF RINGS IN HOUSTON, TX Porous pavement in this small parking lot allows water to infiltrate from the adjacent building, as well as the parking lot itself. Monitoring tubes in the foreground allow visual access to the storage layers below grade. EXHIBIT 6.63 COBBLESTONE BLOCK POROUS PAVEMENT IN DENVER Modular Block Porous Pavement is planted with bluegrass turf to create a driving surface for emergency access only. This installation receives very little traffic. (Blocks are located in area between garage door and street.) Reinforced Grass Pavement stabilized by plastic rings is used for an occasional driving and parking surface outside this stadium. (Rings are located throughout turf area.) Source: www.invisiblestructures.com Proprietary products on the market, installed in accordance with recommendations in Volume 3, stabilize turf enough to allow emergency and occasional vehicle use. Source: www.invisiblestructures.com

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-50 Porous Landscape Detention Function: Site WQCV Porous landscape detention is a depressed landscape area with sandy soil that promotes filtration and infiltration of runoff. 4 Typical Applications: Parking islands, medians, and buffers, courtyards, planters, and green roofs. Excellent on sites with minimal space for detention where landscape and stormwater quality can be combined. Geotechnical and foundation issues must be carefully considered when selecting and locating porous landscape detention facilities and designing underdrains and linings. 4 Operation and Maintenance Considerations: Growing medium will have to be removed and replaced periodically to maintain performance when clogging reduces infiltration capacity to unacceptable levels. Access to facility must be provided to enable maintenance operations. See Maintenance Guidelines at end of chapter. 4 Landscape Considerations : A wide variety of plant types is possible, ranging from irrigated bluegrass turf to native grasses, groundcovers, flowers, and shrubs. Trees should not be included in porous landscape detention areas because the infiltration matrix needs to be replaced periodically; however, trees may be included in oversized porous landscape detention, or outside of porous landscape detention. Dense shrub plantings may become difficult to maintain and must be removed for major maintenance requiring removal of growing medium. If planted with trees, a three-foot radius around each tree should not include underdrains or be counted as porous landscape detention volume. Consider stonework or pedestrian-oriented pavers within the installation. Consider the use of a non-floatable mulch as a water-retaining element of the BMP. 4 Relative Cost : Moderate to high 4 Governing Documents: See Volume 3, page S-27, and www.udfcd.org for updated information

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Denver Water Quality Management Plan Chapter 6 Page 6-51 EXHIBIT 6.65 POROUS LANDSCAPE DETENTION SKETCH 1: Inlet: Level spreader or slotted curbs supply uniform flows to porous landscape detention. 2: Erosion Protection: Include a rock rundown to reduce the likelihood of erosion from inlet flows. (Not shown in sketch) 3: Slopes: Relatively flat bottom with a 6-12 inch deep WQCV zone (six inches recommended). Sides may include up to a 3:1 slope. 4: Vegetation: Turf, native grasses, shrubs, and gardens. See Implementation Details. 5: Underdrain/Liner: Underdrain is required when underlying soils have insufficient infiltration capacity. Underdrain and liner are recommended where geotechnical concerns exist. 6: Outlet/Overflow: Provide overflow above WQCV for larger storm events. 7: Infiltration Matrix: Provide in accordance with design requirements shown in Volume 3.

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-52 EXHIBIT 6.68 POROUS LANDSCAPE DETENTION IN DENVER EXHIBIT 6.67 POROUS LANDSCAPE DETENTION IN DENVER Porous landscape detention adjacent to the roadway is planted with a variety of water-loving plants in a sandy loam soil matrix that filters runoff from the adjacent roadway. EXHIBIT 6.66 POROUS LANDSCAPE DETENTION IN PORTLAND, OR Porous landscape detention can be employed in the small spaces between buildings like the central planters in this residential courtyard. Source: Murase Associates This porous landscape detention area takes the form of a public garden in a townhouse development. The overflow inlet (not visible) prevents flooding of the courtyard. Rock mulch might require less maintenance than the wood chips seen here.

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Denver Water Quality Management Plan Chapter 6 Page 6-53 Detention Basins Function: Site WQCV and Flood Control Detention basins for stormwater quality include the following four types, each capturing the WQCV and slowly releasing it to provide long-term settling. 1. Extended detention basin 2. Sand filter extended detention basin 3. Constructed wetland basin 4. Retention pond These basins are generally intended to serve watershed areas greater than one acre, with areas less than one acre served by WQCV facilities such as porous landscape detention and porous pavement detention. Constructed wetland basins and retention ponds are only suitable if the local hydrology will support viable wetlands or a permanent pool, and if water rights issues are considered and addressed. Flood control detention may be designed in a surcharge zone above any of the water quality detention basins identified above. 4 Typical Applications: Watershed areas typically greater than one acre, generally located in landscape areas. 4 Operation and Maintenance Considerations: Access to the basin by sediment cleanout equipment is required. Provide an all-weather driving surface designed in accordance with Volume 3 to the bottom of the basin near the pre-sedimentation forebay and outlet works. See Maintenance Guidelines at end of chapter. 4 Landscape Considerations : Locate basins along major roads when consistent with zoning and urban design requirements, and when basin can be designed as a site amenity; otherwise, locate in an unobtrusive part of the site. Exclude recreation facilities, bluegrass, and cobble from the bottom of the facility subject to frequent prolonged inundation. The shaping of the detention basin should focus on creating a subtle, attractive facility. Constructed wetland detention basins can create habitat and wildlife amenities while providing additional stormwater quality benefits. 4 Retaining Walls: Attempt to design without the use of retaining walls, but if walls are unavoidable, plan at least one side of the basin perimeter without retaining walls to allow access. Walls over 30 inches in height require handrails designed in accordance with the Uniform Building Code. Locate walls away from main view points to and from the site. 4 Outlets Outlets must control the design release rates and be provided with micro-pools, oversized trash racks, and emergency spillways in accordance with Volume 3. Outlets that are flush with the vegetated side slope are less visually obtrusive. 4 Governing Documents: See Volume 3, pages S-35, S-47, S-53, and S-64.

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-54 EXHIBIT 6.70 PLANTING CONCEPT FOR AN EXTENDED DETENTION BASIN One planting concept for an extended detention basin includes wetlands adjacent to the micropool, trees and shrubs planted on the side slopes, the outlet structure flush with the slope on the more public side of the basin, and masses of shrubs screening the basin. 1: Inlet: Dissipate energy at inlets to prevent erosion and sediment re-suspension. 2: Sediment Trap: Provide forebay in accordance with Volume 3. 3: Slopes: Sideslopes are generally 4:1 or flatter for safety and maintenance. (Not shown on sketch) 4: Vegetation: Should consist of turfgrass supplemented by selected shrubs and trees. When high groundwater is present, include riparian vegetation. 5: Outlet/Overflow: Construct an outlet into the bank closest to most public areas to minimize visibility. Provide micro-pool, trash rack, and emergency spillway in accordance with Volume 3. 6: Infiltration Matrix: Native soils in all but sand filter basins, which are to be designed with a sand layer and underdrain system in accordance with Volume 3. EXHIBIT 6.69 EXTENDED DETENTION BASIN SKETCH

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Denver Water Quality Management Plan Chapter 6 Page 6-55 EXHIBIT 6.71 EXTENDED DETENTION BASIN AT STAPLETON REDEVELOPMENT IN DENVER While attractive, the density of shrubs in the bottom of this basin may complicate maintenance. Native grasses that can easily be mowed would be a better choice. Gravel in the frequently flooded portions of this new grass detention basin is difficult to maintain once vegetation moves in with deposited sediment. Use of riparian or wetland grasses would be a better longterm solution. Trees on the banks of the basin might help it to blend with the surroun ding neighborhood landscape. The outlet structure would be less conspicuous if placed into the slope on the far end of the basin. EXHIBIT 6.74 EXTENDED DETENTION BASIN IN DENVER This is an e xcellent example of including a wide range of plant materials that screen and enhance the basin. EXHIBIT 6.72 EXTENDED DETENTION BASIN IN LOWER DOWNTOWN DENVER EXHIBIT 6.73 EXTENDED DETETION BA SIN AT SPORTS ARENA IN DENVER The fence along this basin prevents pedestrians from shortcutting across it, which is an important detail on high-use sites. Shrubs could provide a similar function, and a flush curb and rock mulch strip could create a cleaner edge.

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-56 Treatment Wetlands For sites with sufficient water to support wetlands, detention facilities can be developed as a constructed wetland basin, as described in Volume 3. The treatment wetland in the bottom of the basin utilizes physical, chemical, and biological processes in the water, soil, root zones, and vegetation to provide additional treatment of stormwater. Design guidance for treatment wetlands, which have been shown to reduce suspended solids, nutrients, and metals in stormwater runoff, is provided in Volume 3 for constructed wetland basins and in a variety of other references for other applications of treatment wetlands (Kadlek and Knight 1996; Hammer 1989). Subsurface Treatment Devices Over the last decade, many proprietary stormwater BMPs have been developed, many of these are subsurface, vault-type treatment devices. Examples of these devices include Stormcepter Vortechnics Bay Saver and Storm Filter As a class of treatment technologies, these devices have proven to be controversial for the following reasons: 4 Unsubstantiated performance claims in some cases. 4 In cases where the manufacturer does provide performance data, such data were often not obtained using independent third parties and lacked appropriate quality assurance/quality control procedures. 4 Because such facilities are normally located below the ground surface, they tend to be out-of-sight, out-of-mind Therefore, they do not receive regular maintenance, nor is their performance periodically monitored. 4 Maintenance access is often poor, which can be a real deterrent to maintenance. 4 To the extent that such devices work, their effectiveness is typically limited to the removal of larger-sized settleable pollutants. Dissolved pollutant removal and the removal of very small solids is typically very low, if at all. 4 Few of these devices provide volume control, consequently, they fail to address perhaps the leading cause of receiving stream degradation from urban stormwater discharges increased frequency, magnitude, and duration of runoff. EXHIBIT 6.75 TREATMENT WETLANDS AT COTTONWOOD CREEK Created wetlands adjacent to the creek provide areas for filtration of stormwater as well as habitat.

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Denver Water Quality Management Plan Chapter 6 Page 6-57 4 Anaerobic (absence of dissolved oxygen) conditions in bottom sediments are more likely to develop in underground devices. This condition can release pollutants that were bound to the sediment and cause bad odors. For all of these reasons, Denver strongly supports managing stormwater quality on the ground surface using the many kinds of BMPs described in this document and in Volume 3 of the Urban Storm Drainage Criteria Manual (UDFCD 2001). Under most circumstances, it should be feasible to manage the modest water quality capture volume (WQCV) on the surface, without having to utilize subsurface, proprietary devices. Nevertheless, Denver recognizes that there are some cases where the use of such facilities is necessary due to extreme space constraints in smaller redevelopment sites, such as ones located in the downtown area. Denver will consider the use of subsurface treatment techniques under certain circumstances; however, the applicant must comply with the following restrictions prior to receiving authorization for the use of such devices: 4 Clear evidence must be provided on why the WQCV cannot be managed on the ground surface through capture, extended detention, filtration and/or infiltration and why the use of a subsurface proprietary device is the best choice for the site, considering factors such as initial installation, maintenance, and ability to assure long-term function. 4 The proprietary device must provide volume control and be sized for the WQCV based on a drain time of no less than six hours. 4 Independent, unbiased test data for the device must be provided to Denver for review. These data must demonstrate that the device is effective. Performance data should be gathered in general accordance with the recommendations of the International Stormwater BMP Database ( www.bmpdatabase.org ). 4 A binding, long-term maintenance plan, including demonstration of adequate funding for such maintenance, must be provided. 4 Because the performance of such devices has been shown to deteriorate over time without proper maintenance, the applicant must either annually submit proof of maintenance or must gather monitoring data to demonstrate that pollutant removals are not declining over an extended period of time (i.e., no less than five years). It is the responsibility of the applicant to submit a monitoring plan to Denver for review and approval. Again, Denver recommends that applicants utilize monitoring recommendations of the International Stormwater BMP Database ( www.bmpdatabase.org ). Given that this field is rapidly changing, those considering alternative stormwater treatment technologies should periodically refer to Denver s website ( http://www.denvergov.org/PublicWorks/ ) for updates and revisions to this policy.

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-58 Other Alternative Technologies In keeping with the above policy statement on subsurface stormwater treatment, new alternative technology can be proposed for consideration with the following information submitted for reference: 4 Description of technology including size, capital costs, design life, installation process and costs, and operating and maintenance requirements and costs. 4 Data on effectiveness including lab testing and prior testing, pollutant removal rates, operational details on any existing installations, and monitoring information. 4 Additional information including articles from peer-review, scientific or engineering journals, approvals or permits from other authorities, and references from other installations. 4 General acceptance by UDFCD and DRCOG municipalities. See Denver s website ( http://www.denvergov.org/PublicWorks/ ) for updates and revisions to this policy and information on acceptable new technologies for implementation in Denver. Industrial Source Controls An important component of any stormwater management strategy involves BMPs to prevent pollution prevention by controlling it at its source. Examples include covering of storage/handling facilities and spill containment and control for sites that handle potential industrial or commercial contaminants, as described in Volume 3. These topics are discussed in more detail in Chapter 7. Drainageway Stabilization Sites that encompass or are adjacent to major drainageways will need to preserve and enhance natural stream functions, provide adequate flood capacity, and protect the channel from degradation. The Urban Storm Drainage Criteria Manual, Volume 1 (UDFCD 2001) provides design criteria for major drainage improvements, and Volume 3 describes constructed wetland channels. Soft stream restoration techniques utilizing channel shaping and riparian vegetation, as well as natural-appearing grade control structures, are favored over more structural approaches to help enhance water quality and aesthetics. Healthy streams and drainageways, if managed well, provide a number of important functions and values, including the following: 4 Conveyance of baseflow and storm runoff 4 Moderation of flood velocities and associated erosion 4 Attenuation of peak flows though channel storage 4 Support of riparian and wetland vegetation

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Denver Water Quality Management Plan Chapter 6 Page 6-59 4 Creation of habitat for wildlife and aquatic species 4 Promotion of infiltration and groundwater recharge 4 Enhancement of water quality 4 Reduction of ongoing maintenance requirements 4 Provision of corridors for trails and open space 4 Provision of favorable aesthetics 4 Enhancement of property values and quality of life Degradation of drainageways from increased urban runoff creates adverse water quality impacts by mobilizing significant quantities of sediment and associated pollutants and conveying them to downstream receiving waters. Stream degradation must be protected against, or, if significant erosion has already taken place, mitigated and repaired through appropriate stabilization improvements. These improvements, besides providing for adequate flood conveyance and a stable channel, should endeavor to provide all of the benefits listed above that are associated with healthy stream systems. EXHIBIT 6.76 DRAINAGEWAY STABILIZATION AT WILLOW CREEK IN ARAPAHOE COUNTY New channel section was stabilized using a combination of bioengineering and rip-rap reinforcement. Low-flow channel edges employed coir fiber rolls. The toe of an unstable slope (distant right on left photo) was stabilized using wrapped soil lifts. The photo on right shows revegetation after two years.

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-60 Urbanization had caused severe erosion on Grange Hall Creek in Northglenn. The stabilization plan called for creating a more stable channel through grade control and a raised channel invert. The new channel utilized a wider, more active flood plain, which allowed frequent flood flows to spread out over channel overbanks, creating a wider, more stable riparian zone and lower flow velocities. Drop structures were designed to fit the prairie context and be accessible and inviting places for public use. EXHIBIT 6.77 DRAINAGEWAY STABILIZATION AT GRANGE HALL CREEK IN NORTHGLENN

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Denver Water Quality Management Plan Chapter 6 Page 6-61 MAINTENANCE POLICIES AND GUIDELINES In order for stormwater BMPs to be effective, proper maintenance is essential. Maintenance includes both routinely scheduled activities, as well as non-routine repairs that may be required after heavy storm events or as a result of other unforeseen problems. Arrangements for BMP maintenance are the responsibility of the entity owning the BMP. More specifically, if Denver owns the BMP, then Denver maintains the BMP. If a private party owns the BMP, then the private party is responsible for arranging for maintenance of the BMP. BMPs should be designed with maintenance as one of the key design considerations, as discussed in the BMP Fact Sheets section of this chapter. This section provides recommendations for Denver to ensure proper maintenance of BMPs, as well as specific guidelines for BMP maintenance. For BMPs currently widely used in the Denver Area, the maintenance guidelines build directly upon Volume 3 of the Urban Storm Drainage Criteria Manual. For BMPs that have been used less frequently in the Denver area, such as green roofs, recommendations for maintenance are provided based on experiences in other parts of the United States. Defining Maintenance Responsibility for Public and Private Facilities Defining who is responsible for maintenance of BMPs and ensuring that adequate budget is allocated for maintenance is critical to the long-term success of BMPs. In Denver, maintenance responsibility may be assigned in four different ways: 1. Municipally owned BMPs are maintained by Denver, typically through the Wastewater Management Division, but occasionally by Parks and Recreation. Denver personnel responsible for maintenance are trained by Denver s Department of Environmental Health. 2. Regional drainage facilities located outside of Denver parks are maintained by UDFCD when specific criteria are met. 3. Privately owned BMPs are maintained by the property owner, Homeowner s Association or property manager. 4. Privately owned BMPs are maintained by Denver under a written agreement with the owner, with appropriate fees assessed for maintenance services. EXHIBIT 6.78 BMP MAINTENANCE POLICIES PROPER LONG-TERM MAINTENANCE OF BMPS IS ESSENTIAL TO BMP EFFECTIVENESS BMPS MUST BE DESIGNED WITH MAINTENANCE IN MIND PRIVATELY-OWNED BMPS MUST BE PROPERLY MAINTAINED BY THEIR OWNER DENVER-OWNED BMPS MUST BE PROPERLY MAINTAINED BY DENVER BMP MAINTENANCE WILL BE ENFORCED UNDER DENVER S CDPS STORMWATER PERMIT

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-62 EXHIBIT 6.79 SEDIMENT REMOVAL FROM A FOREBAY AT THE REGIONAL SHOP CREEK BMP SYSTEM Source: Urban Drainage and Flood Control District. Enforcement of BMP maintenance is required under Denver s Colorado Discharge Permit System (CDPS) stormwater permit and is accomplished through several full-time staff that conduct inspections of permanent BMPs. Additional legal enforcement may be accomplished by a variety of other mechanisms including: 1) agreements establishing legally binding BMP maintenance requirements and responsibilities; 2) permit obligations specifying BMP requirements; or 3) municipal legislative action or rulemaking authority. Examples of maintenance agreements from several communities throughout the country are provided in Appendix D. Examples of some of the specific requirements suggested for legal agreements by the Watershed Management Institute (1997) include: 4 General Assurances: Identify requirements for proper operation and maintenance, conditions for modification of facilities, dedicated easements, binding covenants, operation and maintenance plans, and inspection requirements. 4 Warranty Period: Require the original developer to be responsible for maintenance and operation during a defined short-term period, and identify the entity responsible for longterm operation. The party responsible for long-term maintenance must have appropriate legal authority to own, operate, maintain, and raise funds to complete needed maintenance. 4 Proof of Legal Authority: Require that the entity meet certain conditions verifying its legal authority to ensure maintenance. 4 Conditions for Phased Projects: Clearly specify how maintenance responsibilities are allocated over the long-term for a project that is phased in over time. 4 Remedies: Clearly define remedies in the event that inspections determine that the facility is not being properly maintained. For public facilities, one of the key issues for Denver is ensuring that adequate staff and budget are provided to the department responsible for maintenance. Ponds, lakes or wetland BMPs constructed in Denver Parks must be built with assurances that additional maintenance staff and resources are identified in advance. This is a particularly significant issue for multi-purpose pond or wetland BMPs located in Denver parks. These features require more trash, debris and sediment removal and surface maintenance to control erosion than is typically allocated in Parks and Recreation budgets (Murayama 2004).

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Denver Water Quality Management Plan Chapter 6 Page 6-63 EXHIBIT 6.80 DIFFICULT BMP MAINTENANCE ACCESS For private facilities, such as those owned and maintained by homeowner s associations, there is often a lack of understanding of maintenance required for BMPs. Both Denver s internal staff and outside reviewers of this Plan identified maintenance of private facilities as a top priority. One proposed solution was to require a maintenance plan to be submitted as part of the development review/approval process. Recommendations for such maintenance plans are provided below. In addition to maintenance plans, another important step is educating the general public on the purpose and function of stormwater BMPs. This is critical in cases where Low Impact Development (LID) or landscape-based BMPs are implemented on multiple parcels in developments. In addition to legally binding maintenance agreements, it would also be helpful to have easy-to-understand informational brochures that describe the functions and maintenance requirements for these facilities. Developing a Maintenance Plan At the time that this Plan was completed, the Denver Public Works Rules and Regulations and Stormwater Quality Control Plans, An Information Guide (Denver 2000) did not contain explicit requirements for maintenance of stormwater BMPs. Based on the input of Denver staff and the importance of maintenance to the long-term success of BMPs, it is recommended that a simple maintenance plan be required as part of Stormwater Quality Control Plans. Such a plan (which need not exceed five pages) should include the following key components: 1. A simple sketch of the site showing the locations of all stormwater quality BMPs at the development site and key components such as forebays, inlets, outlets, low-flow channels or other components that require inspection or maintenance. The sketches should be in a form appropriate for easy use by inspectors (e.g., 8.5 x 11 or 11 x 17 paper if possible) and should be kept on site at the property or the property management office. Any changes to the facility over time should be noted on the sketch. 2. A brief description of the maintenance requirements and expected frequency of actions (which can be obtained from the Maintenance Requirements discussion below). It is important to not only identify maintenance requirements related directly to the water quality functions of the BMP, but also to identify public safety aspects of the BMP design and ensure that they are functioning as intended and in good repair (e.g., fences and guard rails, signage, lighting, safety racks, and submerged perimeter benches for BMPs with a permanent pool.). 3. An inspection form or checklist appropriate for the facilities in place at the site. An example inspection form used by the City of Portland, Oregon is provided in Exhibit

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-64 EXHIBIT 6.81 PROPER MAINTENANCE IS ESSENTIAL TO PREVENT NUISANCE CONDITIONS 6.82. A log of inspection forms should be kept on-site or at the property management office to demonstrate that routine inspections and maintenance are occurring. 4. Identification of and contact information for the entity responsible for maintenance of the facility. For example, this could be a Homeowner s Association, Denver Public Works, Denver Parks and Recreation, UDFCD, or another entity. 5. Copies of legally binding agreements associated with the facility which show that the facility owner is aware of and will abide by its maintenance responsibilities. Denver s Storm Sewer Easement and Indemnity Agreement, as contained in Appendix D, is a good starting point. Alternative agreements used in other parts of the country are also provided in Appendix D. Maintenance Requirements Specific maintenance guidelines for the BMPs included in this document are provided below building directly upon the Urban Storm Drainage Criteria Manual, Volume 3 (UDFCD 1999) for BMPs commonly used in Denver. Additional guidelines for new BMPs included in this Plan, such as green roofs, are also provided based on experiences elsewhere. Although subsurface treatment devices are not preferred by Denver for reasons mentioned earlier in this chapter, basic maintenance guidelines for these facilities are also provided, in the event that they are approved on a limited basis under site-specific circumstances. BMP maintenance requirements should be posted on the Denver Public Works website for ready access by the public and be incorporated into updates to Denver s Storm Drainage Design and Technical Criteria Manual Since some of the BMPs included in this Plan are relatively new to Denver, practical experience will likely provide more insight into maintenance needs. As a result, the Denver ( www.denvergov.org ) and UDFCD ( www.udfcd.org ) websites should be periodically checked for updates to maintenance recommendations. It is also important to note that the guidelines included in this Plan should always be combined with common sense and good judgment based on field observations and practical experiences of staff.

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Denver Water Quality Management Plan Chapter 6 Page 6-65 EXHIBIT 6.82 EXAMPLE BMP MAINTENANCE INSPECTION FORM FROMMAINTAINING YOUR STORMWATERMANAGEMENT FACILITY: A HANDBOOK FOR PRIVATE PROPERTY OWNERS. (CITY OF PORTLAND, OR 2002)

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-66 In addition to the guidelines included in this Plan, other excellent supplemental references providing information on stormwater BMP maintenance include: 4 Urban Drainage and Flood Control District. 1999. Urban Storm Drainage Criteria Manual, Volume 3, Stormwater Best Management Practices Denver, CO: Urban Drainage and Flood Control District. Also see the UDFCD website for updates to Volume 3 BMP maintenance recommendations ( www.udfcd.org ). 4 Watershed Management Institute. 1997. Operation, Maintenance and Management of Stormwater Management Systems. Ingleside, MD: Watershed Management Institute. 4 Low Impact Development Center. 2003. Low Impact Development Urban Design Tools. http://www.lid-stormwater.net/ 4 City of Portland, Oregon. 2002. Maintaining Your Stormwater Management Facility: A Handbook for Private Property Owners. Portland, OR: Bureau of Environmental Services. On a general note with regard to BMPs that have a vegetation component or involve weed and pest control, the Mayor s Executive Order 121 establishes specific requirements for pesticide use in Denver (Denver 1997). UDFCD and Chapter 7 of this Plan strongly advocate use of Integrated Pest Management (IPM) practices that help to reduce the level of pesticide and herbicide use through a variety of practices. Although water quality monitoring is not typically required as part of maintenance agreements, it is highly encouraged as an effective tool for determining if the BMP is functioning effectively. Stormwater quality monitoring guidelines can be downloaded from the International Stormwater BMP Database website ( www.bmpdatabase.org ). Grass Buffers and Grass Swales Grass buffers and swales require general maintenance of the turf grass cover and repair of any rill or gully development. Healthy vegetation can generally be maintained without using fertilizers because runoff from lawns and other areas contains the needed nutrients. Occasionally inspecting the vegetation over the first few years will help to determine if any problems are developing and to plan for long-term restorative maintenance needs. Exhibit 6.83 presents a summary of specific maintenance requirements and a suggested frequency of action.

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Denver Water Quality Management Plan Chapter 6 Page 6-67 EXHIBIT 6.83. GRASS BUFFER STRIP AND SWALE MAINTENANCE CONSIDERATIONS (ADAPTED FROM UDFCD 1999) Required Action Maintenance Objective Frequency of Action Mowing Maintain irrigated turfgrass at a recommended height of 2 to 4 inches tall. Non-irrigated native grass should be maintained at 6 to 8 inches tall. Routine As needed to maintain grass height or based on inspection. Will vary from as frequently as weekly during the summer, to no mowing during the winter. Fertilizer, Herbicide and Pesticide Application Use the minimum amount of biodegradable, nontoxic fertilizers and herbicides needed to maintain dense vegetation cover that is reasonably free of weeds. Hand pulling of weeds is preferred in areas with limited weed problems. Comply with Executive Order 121 (Denver 1997) regarding pesticide use and use integrated pest management (IPM) strategies. Routine On an as-needed basis only. Irrigation Adjust irrigation throughout the growing season to provide the proper irrigation application rate to maintain healthy vegetation. Less irrigation is typically needed in early summer and fall, with more irrigation needed during July and August. Check for broken sprinkler heads and repair them, as needed. Do not overwater. Signs of overwatering and/or broken sprinkler heads may include soggy areas and unevenly distributed areas of lush growth. Routine Adjust and maintain throughout growing season. Reseeding/ Vegetation Replacement Reseed and/or patch damaged areas in buffer, sideslopes and/or channel to maintain healthy vegetative cover. Routine As needed by inspection. Expect turf replacement for buffer strips once every 5 to 15 years. Litter and Debris Removal Remove litter and debris to prevent gully development, enhance aesthetics, and prevent floatables from being washed offsite. Routine As needed by inspection, but no less than two times per year. Sediment Removal For Grass Swales: Remove accumulated sediment near culverts and in channels to maintain flow capacity. Replace the grass areas damaged in the process. Routine As needed by inspection. Remove sediment from roughly 3 to 10 percent of the total length of the swale per year, as determined by annual inspection. Inspections Inspect vegetation for uniform cover and heavy traffic impacts, check for sediment accumulation and gully development. Annually and after each major storm (more than 0.75 inches in precipitation). Repair as needed.

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-68 Porous Pavement and Porous Pavement Detention The key maintenance objective for porous pavement and porous pavement detention is to know when runoff is no longer rapidly infiltrating into the surface, which is typically due to void spaces becoming clogged and requiring sediment removal. Exhibit 6.84 identifies key maintenance considerations for various types of porous pavement BMPs. EXHIBIT 6.84. POROUS PAVEMENT MAINTENANCE CONSIDERATIONS (ADAPTED FROM UDFCD 1999, AS AMENDED BY UDFCD S DRAFT POROUS PAVEMENT GUIDANCE, OCTOBER 2004) Required Action Maintenance Objective Frequency of Action Debris and Litter Removal For All Types: Accumulated material should be removed as a source control measure. Routine As needed. Sod Maintenance For Modular Block Pavement: If sandy loam turf is used, provide lawn care, the irrigation system, and inlay depth maintenance as needed. Routine As dictated by inspection. Vacuuming Pavement For Porous Concrete Pavement: Vacuum the porous concrete pavement using high energy purging street vacuuming equipment to remove accumulating sediment from pavement pores. Routine Every year, but may be extended to every two or more years if routine inspections show the infiltration rates continue to be high. Very important to maintain infiltration flow through the full section of the concrete to extend it life during freeze-thaw cycles in colder climates. Inspection For All Types: Inspect representative surface areas for accumulation of sediment or poor infiltration. For Reinforced Grass Pavement: Inspect representative areas of surface for healthy grass growth, surface erosion, accumulation of sediment and poor infiltration. Routine and during a storm event to ensure that water is not frequently bypassing these surfaces by not infiltrating into the pavement. Replace Surface Filter Layer For Modular Block Pavement: Remove, dispose, and replace surface filter media by pulling out turf plugs and by vacuuming out sand media from within the annular spaces of the blocks. Replace with fresh ASTM C-33 sand and, if appropriate, sandy loam turf plugs. For Cobblestone Block Pavement: Remove, dispose, and replace surface filter media by vacuuming out sand media from within the annular spaces of the blocks using scarifying high energy vacuum equipment. Replace with fresh ASTM C33 sand. Non-routine when it becomes evident that runoff does not rapidly infiltrate into the surface. May be as often as every year or as little as every 5 to 10 years for modular block pavement or 2 to 5 years for Cobblestone Block Pavement. Repair and Replacement of Sod Layer For Reinforced Grass Pavement: Repair damaged sod. Remove and replace, as needed, the sod cover to maintain a healthy vegetative cover or when sod layer accumulates significant amount of silt (i.e., >1.5 inches) from atmospheric fallout and Non-routine when it becomes evident that runoff does not rapidly infiltrate into the surface. Repairs may be as often as every

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Denver Water Quality Management Plan Chapter 6 Page 6-69 EXHIBIT 6.84. POROUS PAVEMENT MAINTENANCE CONSIDERATIONS (ADAPTED FROM UDFCD 1999, AS AMENDED BY UDFCD S DRAFT POROUS PAVEMENT GUIDANCE, OCTOBER 2004) stormwater runoff. year. Replacement of sod may be as little as every 10 to 25 years. Replace Pavement For Modular Block Pavement: Remove and replace the modular pavement blocks, the sand leveling course under the blocks, and the infill media when the pavement surface shows significant deterioration. For Cobblestone Block Pavement: Remove and replace the cobble pavement blocks, the sand leveling course under the blocks, and the infill media when the pavement s surface shows significant deterioration. For Porous Concrete Pavement: Remove, dispose, and replace porous concrete when it shows excessive surface deterioration and when it no longer infiltrates stormwater quickly. Inspect the full section of the pavement when the concrete layer is removed for accumulation of sediment in the base course and on top of the sand filter layer or sub-base. Remove and dispose accumulated sediment and replace base course, sand filter layer, and geotextile fabrics. For Porous Gravel Pavement: Remove, dispose, and replace surface gravel layer when it shows excessive surface deterioration and when it no longer infiltrates stormwater quickly. Inspect the full section of the pavement when replacing the surface gravel layer for accumulation of sediment in the base course and on top of the sand filter layer or sub-base. Remove and dispose accumulated sediment and replace base course, sand filter layer and geotextile fabrics. Non-routine when it becomes evident that the modular blocks have deteriorated significantly. Expect replacement every 10 to 25 years, dependent on use and traffic. Repair of Structural Damage For All Types: Structural damage due to improper construction, faulty materials or accidents should be repaired as needed. Non-routine Upon awareness that structural damage such as pavement unraveling has occurred.

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-70 Porous Landscape Detention The primary maintenance objective for porous landscape detention is to keep vegetation healthy, remove sediment and trash, and ensure that the facility is draining properly. The growing medium for these BMPs will need to be replaced periodically to maintain performance. Exhibit 6.85 summarizes key maintenance considerations for porous landscape detention. Porous landscape detention is comparable to bioretention cell and rain garden practices used as part of Low Impact Development strategies. EXHIBIT 6.85. POROUS LANDSCAPE DETENTION MAINTENANCE CONSIDERATIONS (Adapted from UDFCD 1999 and supplemented by Prince George s County Bioretention Manual and the City of Portland Environmental Services Homeowner Handbook) Required Action Maintenance Objectives Frequency Lawn mowing and turf care Occasional mowing of grasses and weed removal to limit unwanted vegetation. Maintain irrigated turf grass at 2 to 4 inches tall and un-irrigated native grasses at 4 to 6 inches. Routine Depending on aesthetic requirements. Debris and litter removal Remove debris and litter from detention area to minimize clogging of the sand media; remove debris and litter from any overflow inlets. Routine depending on aesthetic requirements. Sediment Removal Remove sediment to maintain infiltration. Routine particularly in the inlet area. Soil Prevent erosion and provide healthy growing medium for plants. Routine Visually inspect and repair erosion following major storm events. Use small stones to stabilize erosion along drainage paths. Check the pH once or twice a year. Apply an alkaline product, such as limestone, if needed. Soil replacement may be required every 5 to 10 years, depending on pollutant loads. Mulch Conserve soil moisture and promote plant health. Routine Re-mulch any void areas by hand as needed. Every 6 months, in the spring and fall, add a fresh mulch layer. Once every 2 to 3 years, in the spring, remove old mulch layer before applying new one. Plant Care Maintain attractive, healthy vegetation. Routine Once a month (more frequently in the summer), visually inspect vegetation for disease or pest problems. If treatment is warranted, use Integrated Pest Management (IPM) approaches. In the early spring and late fall, remove and replace all dead and diseased vegetation. Provide adequate irrigation to promote healthy plant growth. During times of extended drought,

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Denver Water Quality Management Plan Chapter 6 Page 6-71 EXHIBIT 6.85. POROUS LANDSCAPE DETENTION MAINTENANCE CONSIDERATIONS (Adapted from UDFCD 1999 and supplemented by Prince George s County Bioretention Manual and the City of Portland Environmental Services Homeowner Handbook) look for physical features of stress (unrevived wilting, yellow, spotted or brown leaves, loss of leaves, etc.). Weed on an as-needed basis. Prune excess growth annually or more often, if desired. Trimmed materials may be recycled back in with replenished mulch or land filled if there is a concern of heavy metals accumulation. Drainage Prevent extended ponding and mosquito reproduction. Non-routine After rainstorms, inspect the area and make sure that drainage paths are clear and that ponding water dissipates over 4-6 hours. (Water may pond for longer times during the winter and early spring.) It is important to note that these features are not ponds and should drain in a manner that does not promote mosquito breeding. Chemical Spill Response Remove soil and plants and replace with new material. Non-routine in the event of a chemical spill, the soils and plant material should be replaced. Inspections Inspect detention area to determine if the sandy loam media is allowing acceptable infiltration. Routine biannual inspection of hydraulic performance.

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-72 Source: Urban Drainage and Flood Control District. EXHIBIT 6.86 MUCKING OUT A MICROPOOL AT AN EXTENDED DETENTION BASIN Extended Detention and Retention Basins Extended detention basins and retention ponds have low to moderate maintenance requirements on a routine basis, but require significant maintenance about once every 10 to 20 years for sediment removal. Sediment removal frequency depends on the amount of construction activity within a basin, the erosion control measures implemented, the size of the basin and the design of the facility. When aggressive erosion control is practiced in the tributary watershed, it is estimated that accumulated sediment will need to be removed at 5to 20-year intervals. Routine and non-routine maintenance is necessary to assure performance, enhance aesthetics, and protect structural integrity. Extended detention (dry) basins can result in nuisance complaints if not properly designed or maintained. If a shallow wetland or marshy area develops, mosquito breeding and nuisance odors could occur if the water becomes stagnant. Biodegradable pesticides may be required to limit insect problems. Frequent debris removal and mowing can reduce aesthetic complaints. Access to critical elements of both dry and wet ponds (inlet, outlet, spillway, and sediment collection areas) must be provided. The basic elements of the maintenance requirements are presented in Exhibit 6.87. EXHIBIT 6.87. EXTENDED DETENTION AND RETENTION BASIN MAINTENANCE CONSIDERATIONS (ADAPTED FROM UDFCD 1999) Required Action Maintenance Objective Frequency of Action Lawn Mowing and Lawn Care Occasional mowing to limit unwanted vegetation. Maintain irrigated turf grass at 2 to 4 inches tall and un-irrigated native turf grasses at 4 to 6 inches. Routine Depending on aesthetic requirements. Debris and Litter Removal Remove debris and litter from the entire pond to minimize outlet clogging and improve aesthetics. Routine Including just before annual storm seasons (that is, April and May) and following significant rainfall events. Erosion and Sediment Control Repair and revegetate eroded areas in the basin and channels. Non-routine Periodic repair as necessary based on inspection. Structural Repair pond inlets, outlets, forebays, lowflow channel liners, and energy dissipaters whenever damage is discovered. Also stabilize banks and berms. Non-routine Repair as needed based on regular inspections.

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Denver Water Quality Management Plan Chapter 6 Page 6-73 EXHIBIT 6.87. EXTENDED DETENTION AND RETENTION BASIN MAINTENANCE CONSIDERATIONS (ADAPTED FROM UDFCD 1999) Inspections Inspect basins to insure that the basin continues to function as initially intended. Examine the outlet for clogging, erosion, slumping, excessive sedimentation levels, overgrowth, embankment and spillway integrity, and damage to any structural element. Routine Annual inspection of hydraulic and structural facilities. Also check for obvious problems during routine maintenance visits, especially for plugging of outlets. Biannual performance and maintenance inspections. Nuisance Control Address odor, insects, and overgrowth issues. For dry ponds, check for stagnant or standing water in the bottom zone that may cause these problems. Non-routine Handle as necessary per inspection or local complaints. Sediment Removal (for Dry Ponds) Remove accumulated sediment from the forebay, micro-pool, and the bottom of the basin. Non-routine Performed when sediment accumulation occupies 20 percent of the WQCV. This may vary considerably, but expect to do this every 10 to 20 years, as necessary per inspection if no construction activities take place in the tributary watershed, but more often if construction is occurring. The forebay and the micropool will require more frequent cleanout than other areas of the basin, roughly every 1 or 2 years. Sediment Removal (for Wet Ponds) Empty the pond, divert the base flow, and dry out bottom sediment in fall and winter months to allow access with backhoe. Remove accumulated sediment along with overlying aquatic growth. Re-establish original design grades and volumes and replant aquatic vegetation. Non-routine As indicated per inspections and sediment accumulation. Expect to do this every 10 to 20 years if no construction activities take place in the tributary watershed. More often if they do. Expect to clean out the forebay every 1 to 5 years. Aquatic Growth Harvesting (Primarily for Wet Ponds) Remove aquatic plants such as cattails or reeds, thereby also permanently removes nutrients. Use an aquatic harvester and dispose of the material offsite. Non-routine Perform every 5 to 15 years or as needed to control accumulation. Forebays Ensure that measures described above (e.g., debris and sediment removal and aquatic harvesting) are also conducted for forebays to the ponds. Routine and Non-routine on an as needed basis, consistent with the practices described above. Trash Racks Regularly remove debris and ensure that trash rack is in good condition. This is important for proper function of the BMP, aesthetics and public safety. Routine Should be checked when mowing is conducted and after major storms.

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-74 Sand Filter Extended Detention Basin Key maintenance considerations for sand filter extended detention basins involve ensuring that infiltration into the sand filter occurs as designed. Key maintenance practices are described in Exhibit 6.88. Exhibit 6.88. Sand Filter Detention Basin Maintenance Considerations (Adapted from UDFCD 1999) Required Action Maintenance Objectives Frequency Debris and Litter Removal Remove debris and litter from detention area to minimize clogging of the sand media. Routine depending on aesthetic requirements. Landscaping Removal and Replacement If the sand filter is covered with rock mulch, bluegrass, or other landscaping covers, the cover must be removed to allow access to the sand media. Replace landscaping cover after maintenance of sand media is complete. Every 2 to 5 years. Scarify Filter Surface Scarify top 3 to 5 inches by raking the filter s surface. Once per year or when needed to promote drainage. Sand Filter Removal Remove the top 3 inches of sand from the sand filter. After a third removal, backfill with 9 inches of new sand to return the sand depth to 18 inches. Minimum sand depth is 12 inches. If no construction activities take place in the tributary watershed, every 2 to 5 years depending on observed drain times (e.g., when it takes more than 24 hours to empty 3-foot-deep pool). Expect to clean out forebay every 1 to 5 years. Flush-out Perforated Pipe Gallery If a clean-out has been provided for the perforated pipe gallery, it can be used to flush out the pipes. Routine Once per year or when needed to promote drainage. Inspections Inspect detention area to determine if the sand media is allowing acceptable infiltration. Routine biannual inspection of hydraulic performance, with one after a significant rainfall.

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Denver Water Quality Management Plan Chapter 6 Page 6-75 Constructed Wetland Basins and Channels To achieve and maintain a healthy wetland for water quality enhancement, the proper depth and spatial distribution of growth zones must be maintained. Exhibit 6.89 summarizes suggested activities and their frequencies to maintain an operational wetland. EXHIBIT 6.89. CONSTRUCTED WETLAND CHANNEL AND BASIN MAINTENANCE CONSIDERATIONS (ADAPTED FROM UDFCD 1999) Required Action Maintenance Objective Frequency of Action Lawn Mowing and Lawn Care Mow occasionally to limit unwanted vegetation. Maintain irrigated turf grass at 2 to 4 inches tall and non-irrigated native turf grasses at 4 to 6 inches. Routine Depending on aesthetic requirements. Debris and Litter Removal Remove debris and litter from entire pond and/or channel to minimize outlet clogging and aesthetics. Include removal of floatable material from the pond's surface. Routine Including just before annual storm seasons (that is, in April and May) and following significant rainfall events. Sediment Removal Remove accumulated sediment and muck along with much of the wetland growth. Re-establish growth zone depths and spatial distribution. Revegetate with original wetland species. Non-routine Every 10 to 20 years as needed by inspection if no construction activities take place in the tributary watershed. More often if they do. Expect to clean out forebay every 1 to 5 years. Aquatic Plant Harvesting Cut and remove plants growing in wetland (such as cattails and reeds) to permanently remove nutrients with manual work or specialized machinery. Non-routine until further evidence indicates such action would provide significant nutrient removal. In the meantime, perform this task once every 5 years or less frequently as needed to clean the wetland zone out. Inspections Observe inlet and outlet works for operability. Verify the structural integrity of all structural elements, slopes, and embankments. Routine At least once a year, preferably once during one rainfall event resulting in runoff.

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-76 Green Roofs/Treatment Roofs As discussed in the BMP Fact Sheets portion of this chapter, green roofs/treatment roofs have not been used extensively in the Denver area, but have been successfully used in other parts of the country and in Europe. If these roofs are selected for use in Denver, proper maintenance is critical for their success, as is the case with all BMPs. The Low Impact Development Center provides guidance on the maintenance requirements for green roofs ( http://www.lidstormwater.net/greenroofs/greenroofs_maintain.htm ) and is reproduced below. The Low Impact Development Center states that once a properly installed green roof is well established, its maintenance requirements are usually minimal, with the extent of maintenance dependent on the type of green roof. Green roofing systems can vary in thickness from two to seven inches (5 to 18 centimeters). The term extensive is used to describe the lighter roofing systems, while the term intensive is used to describe the heavier roofing systems. While a roof s effectiveness in managing runoff generally increases with the thickness and weight of the roofing system, so do the maintenance requirements ( www.lid-stormwater.net ). Critical maintenance requirements include inspection of the roof membrane (the most crucial element of a green roof), routine inspection and maintenance of the drainage layer flow paths, and maintenance of the vegetation on the roof ( www.lid-stormwater.net ). Maintenance requirements for green roofs are reported to be the greatest during the first two years when plants are becoming established (Stormtech et al. 2003). Key maintenance activities are summarized in Exhibit 6.90 below and described in more detail in the remainder of this section. EXHIBIT 6.90. GREEN ROOFS/TREATMENT ROOFS (ADAPTED FROM THE LOW IMPACT DEVELOPMENT CENTER 2004) Required Action Maintenance Objectives Frequency Irrigation and Fertilizing Maintain healthy plant growth. Use of native plants with a drip irrigation system will reduce maintenance efforts in arid environments. The irrigation system should be checked to ensure it is functioning properly. Irrigation and fertilizer requirements are dependent on the plant species selected and the type of irrigation system installed. Drip irrigation system should be inspected monthly. Trimming and Weeding Maintain healthy plant growth. If properly designed and established, a typical green roof does not need to be mowed. A thin soil layer does not support tall vertical growth; therefore, the vegetation mat will tend to spread horizontally (Scholz-Barth 2001). Occasional weeding of the rooftop, especially in the establishment phase, will remain necessary. As needed through growing season. Inspection for Drainage Ensure roof drainage is not blocked to prevent roof leakage and perpetually saturated soils. Because of the severe consequences of drainage backups, inspection of the drainage flow paths (or channels) is crucial, especially on extensive roofs. If drainage routes become blocked, green roofs can cause some flat roofs to leak due to continuous contact with water or wet soil. With insufficient drainage, the plants will also be susceptible to the impact of wide Following major storm events.

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Denver Water Quality Management Plan Chapter 6 Page 6-77 EXHIBIT 6.90. GREEN ROOFS/TREATMENT ROOFS (ADAPTED FROM THE LOW IMPACT DEVELOPMENT CENTER 2004) degrees of variability in the moisture content of the soil. If too much water is present, the soil will be adversely affected and the plants will drown or rot (Peck and Callaghan 1999; ( www.lidstormwater.net ). Inspection for Leaks Ensure roof is not leaking. Roofs can leak from drainage backups or root puncture, or if the correct waterproofing membrane system, root barrier, and/or drainage layer are not selected. Areas where occasional inspection for leaks is advisable include possible problem areas such as abutting vertical walls, roof vent pipes, outlets, air conditioning units, perimeter areas, etc. ( www.greenroofs.com ). Most roofing companies, including those that install green roofs, will provide a warranty for the waterproofing integrity of the roof membrane(s) they have installed, including green roof membranes ( www.lid-stormwater.net ). Following major storm events. Roof Replacement Continue function of green roof. Green roofs are generally more effective than conventional roofing systems in protecting the roof membrane. This reduces regular maintenance costs and extends the life of the membrane itself. According to a study in Germany, a vegetated roof on average can be expected to prolong the service life of a conventional roof by at least 20 years (ZVG 1996; www.lidstormwater.net ). In some cases, green roof maintenance may involve re-waterproofing of the roof membrane. However, if designed and installed properly, the waterproof characteristic of a green roof will be maintained for at least as long as a conventional roof. Variable, typically 20+ years.

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Stormwater Quality BMP Implementation Guidelines Chapter 6 Page 6-78 Low Impact Development Designs Low Impact Development (LID) and other BMPs based on minimizing directly connected impervious area present unique technical and administrative challenges in tracking the status and upkeep of these BMPs over time. The greatest challenge to the success of these practices is proper education on how these BMPs function and ensuring that they are properly maintained over the long-term. It is also critically important that these BMPs are understood by property owners as being permanent, legally required stormwater treatment facilities for the site and are not removed or regraded due to an owner s aesthetic preferences or site remodeling. Due to the localized, integrated nature of these BMPs, there is less likelihood of maintenance by a maintenance contractor or other professional entity. For this reason, very clear guidelines must be provided to homeowners, homeowners associations, and others implementing LID techniques. The Low Impact Development Center website ( www.lid-stormwater.net ) provides maintenance guidelines for a variety of LID techniques. The key component of most LID designs is the bioretention cell, or rain garden. This technique is similar to porous landscape detention, as described in Volume 3 of the Urban Storm Drainage Criteria Manual. For this reason, the guidelines developed by UDFCD for porous landscape detention, as summarized in Exhibit 6.85, are recommended to be followed for landscape-based treatment approaches that have been termed bioretention cells or rain gardens in other parts of the country. Similarly, LID techniques that emphasize runoff reduction by disconnecting impervious area and grassy swales instead of pipes correspond to UDFCD s grass buffers and swales. Maintenance requirements for grass buffers and swales are summarized in Exhibit 6.83. Subsurface Treatment Devices Because subsurface treatment devices are normally located below the ground surface, they tend to be out-of-site, out-of-mind. Therefore, they often do not receive regular maintenance, nor is their performance periodically monitored. This is one of the reasons that Denver strongly prefers above-ground treatment approaches. In the event that subsurface treatment is approved for a site, Exhibit 6.91 outlines maintenance requirements. EXHIBIT 6.91. SUBSURFACE TREATMENT DEVICES Required Action Maintenance Objectives Frequency Accumulated Sediment and Debris Removal Remove the accumulated sediment as recommended by the manufacturer, or when it has reached a depth of roughly half a foot, if not specified. Frequency will vary based on device size and geometry. The approximate required removal frequencies should be calculated based on tributary watershed area, average annual precipitation, representative total suspended solids event mean concentration in runoff and the vault/device surface area. Manufacturer should be able to provide this information. Inspections Inspect device to determine whether it appears to be functioning as designed based on manufacturer s guidelines. At least twice per year following major storm events. Water quality monitoring can help to determine if the device is functioning as intended.

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Denver Water Quality Management Plan Chapter 6 Page 6-79 Conclusions and Recommendations for Maintenance 1. A BMP maintenance plan requirement should become a part of Denver s Stormwater Quality Control Plans, as referenced in Denver s Rules and Regulations. The contents of these maintenance plans should be clearly outlined in Stormwater Quality Control Plans, An Information Guide. 2. A legally binding agreement describing BMP maintenance requirements and arrangements should be necessary for final approval of a development. Denver s existing Sanitary and Storm Sewer Easement and Indemnity Agreement is a good starting point for such an agreement. Examples of agreements used in other parts of the country, as contained in Appendix D, can be used to further develop this agreement with regard to BMP maintenance requirements. 3. Clearly defined maintenance requirements for BMPs should be included in updates to Denver s Storm Drainage Criteria Manual 4. Clearly defined maintenance requirements for BMPs that represent new technologies or practices are essential. This is particularly relevant for low impact development or landscape-based practices that may be spread throughout multiple parcels in developments and that could be confused with ordinary landscaping. Though these techniques have many natural features, they still require intentional maintenance like any stormwater BMP. 5. A simple BMP maintenance brochure or handbook (that can stand-alone from this Plan) that explains the importance of BMP maintenance for stormwater quality management and directs relevant parties to the Denver website for detailed guidance should be developed. This could be jointly developed with the Joint Task Force (with Aurora, Lakewood and UDFCD) as a fourth brochure in the Clear Choices for Clean Water series that is currently posted on Denver s website.

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Chapter 7 Page 7-1 Chapter 7 POLLUTION SOURCE CONTROLS (NON-STRUCTURAL BMPS) OVERVIEW OF POLLUTION SOURCE CONTROLS (NONSTRUCTURAL APPROACHES) Pollution source controls, also commonly referred to as non-structural best management practices (BMPs), are a key component of any effective stormwater management strategy and should be integrated into plans for all development types. This set of BMPs can generally be described as a variety of practices intended to prevent or limit the entry of pollutants into stormwater runoff. In contrast to structural BMPs, which involve the construction of facilities such as ponds, wetlands, infiltration basins, etc., source controls or non-structural BMPs do not normally involve construction, but instead focus on measures to minimize pollution at its source, thereby reducing the amount of pollutants to be removed in downstream structural BMPs. Most source controls are dependent on behavioral change, which is in turn dependent on good education. Denver staff have a real opportunity to set the example for the public with regard to source controls. Non-structural approaches are particularly important in areas that have already been developed and are a key strategy in reducing pollution when new structural controls are not an option due to cost or space constraints. Many non-structural and structural practices are interrelated, but for purposes of this discussion, non-structural/source control BMPs have been grouped into the following general categories: 4 Public Outreach and Education Examples include educating citizens and business owners about topics such as automotive product disposal; good housekeeping practices at commercial, restaurant and retail sites; construction site training; industrial good housekeeping practices; inlet stenciling activities; proper pesticide/herbicide use; and educational programs at schools. 4 Illicit Discharge and Detection Programs This involves identification, detection and prevention of illicit discharges to storm sewers. This BMP relies on other non-structural BMPs such as public education and proper waste disposal programs. Examples of illicit discharges include illegal dumping, accidental chemical spills and illicit connections of sanitary sewers to storm sewers. 4 Source Controls Examples include minimizing exposure of pollutants to stormwater at facilities such as automobile maintenance sites, salvage facilities and service stations; commercial, restaurant and retail sites; construction sites; farming and agricultural sites; and industrial sites. Activities at such sites requiring particular attention include outside materials storage, above ground storage tanks, loading and unloading areas, vehicle washing, fueling, outside manufacturing, etc. It is also important to note that as stormwater management strategies evolve, the line between structural and non-structural controls is increasingly blurred. For example, soft, decentralized natural stormwater systems can also serve as source controls.

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Pollution Source Controls (Non-Structural BMPs) Chapter 7 Page 7-2 4 Recycling/Waste Disposal Programs Examples include household toxics collection and recycling programs and leaf and landscaping waste collection. 4 Good Housekeeping Practices/Spill Prevention and Response Examples include developing spill prevention measures, identifying spill areas, implementing material handling procedures, and spill plan development. 4 Municipal Maintenance Practices Examples include catch basin cleaning; maintenance of structural BMPs; parking lot and street sweeping; road and street pavement repair, sealing, overlay, etc.; road salting and sanding; roadside ditch cleaning and restoring. 4 Land Use Planning and Management (Programmatic) Strategies Examples include new development planning procedures; procedures for site planning at construction sites; protective covenants; riparian buffer zone setbacks; Low Impact Development, green development, and Smart Growth development strategies. For more information on non-structural BMPs, including advantages/disadvantages, costs, and experiences, the following documents are particularly helpful and should be referenced for more detail: 4 Urban Storm Drainage Criteria Manual, Volume 3 (UDFCD 1999) 4 Urban Runoff Quality Management, Water Environment Federation Manual of Practice No. 23 and American Society of Civil Engineers Manual and Report on Engineering Practice No. 87 (WEF and ASCE 1998) 4 Low Impact Development web site ( http://www.lid-stormwater.net/ ) 4 California Stormwater Quality Association Stormwater Best Management Practice Handbook (CASQA 2003) 4 EPA Stormwater Web site ( http://www.epa/gov/npdes/stormwater ) 4 Green Industry Best Management Practices for the Conservation and Protection of Water Resources in Colorado (GreenCO and Wright Water Engineers, Inc. 2004) Denver s Stormwater Management Program, required under its Colorado Discharge Permit System (CDPS) permit, includes five major program components with specific structural and non-structural BMP requirements, as described in Chapter 3 and summarized in Exhibit 7.1. The vast majority of these practices are non-structural, and many of them are education-based. Denver completes an annual report itemizing how each of these BMPs has been implemented. Structural BMPs and site-planning type issues have already been discussed throughout this Plan. Construction-related BMPs are not included in this Plan since this Plan s scope focuses on postconstruction, permanent development. Thus, the remainder of this section describes some of Denver s recent and on-going efforts to implement various non-structural BMPs according to the general categories of public education, illicit discharge and detection, source controls,

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Denver Water Quality Management Plan Chapter 7 Page 7-3 recycling/waste disposal, and maintenance/good housekeeping and highlights some opportunities for better non-structural BMP implementation. For a detailed description of Denver s practices, see the annual reports completed by Denver and submitted to the Colorado Water Quality Control Division (CWQCD). (These reports can be obtained from Denver s Wastewater Management Division or the CWQCD.) EXHIBIT 7.1 PRACTICES REQUIRED IN DENVER S CDPS STORMWATER PERMIT Category Required Practice/Program Commercial/ Residential Management Program 4 Maintenance of Structural Controls 4 New Development Planning Procedures 4 Public Street Maintenance 4 Assessment of Impacts of Flood Management Projects 4 Pesticide, Herbicide, and Fertilizer Application Illicit Discharge Detection Program 4 Prevention of Illicit Discharges and Improper Disposal 4 Ongoing Field Screening 4 Investigation of Suspected Illicit Discharges 4 Procedures to Prevent, Contain, and Respond to Spills 4 Educational Activities to Promote Public Reporting of Illicit Discharges and Improper Disposal 4 Public Educational Activities to Promote Proper Management and Disposal of Potential Pollutants 4 Used Motor Vehicle Fluid and Household Chemical Waste Collection Programs 4 Control of Sanitary Sewer Seepage into the Municipal Storm Sewer System Industrial Facilities Program 4 Education and Outreach on Industrial Pollutant Source Control Construction Sites Program 4 Procedures for Site Planning 4 Structural and Non-Structural BMPs 4 Procedures for Site Inspection and Enforcement 4 Training and Education for Construction Site Operators Municipal Facility Runoff Control Program Facilities addressed: 4 Vehicle maintenance facilities 4 Asphalt and concrete batch plants which are not already individually permitted 4 Solid-waste transfer stations 4 Exposed stockpiles of materials, including stockpiles of road deicing salt, salt and sand, sand, rotomill material 4 Sites used for snow dumps, and/or for temporary storage of sweeper tailings or other waste piles

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Pollution Source Controls (Non-Structural BMPs) Chapter 7 Page 7-4 Applicability of Non-structural Approaches to Development Types In keeping with the discussion of structural approaches to water quality, Exhibit 7.2 summarizes the applicability of various non-structural approaches to the development types discussed in Chapter 6 of this Plan. As a general principle, non-structural strategies should be broadly applied whenever possible to control sources of pollutants. Non-structural BMPs focus on routine day-to-day activities; therefore, public education and employee training regarding the importance of these activities must be on-going in order for many of these practices to be effective. Although it is much more difficult to quantify the effectiveness of non-structural BMPs relative to structural BMPs, common sense suggests that controlling pollution at its source is a sound approach to minimizing pollution and the costs of mitigating its impacts. EXHIBIT 7.2 APPLICABILITY OF NON-STRUCTURAL APPROACHES TO DEVELOPMENT TYPES Development Type Non-Structural BMP UltraUrban High Density Mixed Industrial Low Density Mixed Campus Residential Park Public Outreach/ Education X X X X X X X Source Controls X X X X X X X Industrial/ Commercial Hotspots X X X X X Household Waste X X X X X Pesticide/ Herbicide/ Fertilizer Management X X X X X X Efficient Irrigation X X X X X X Materials Storage Practices X X X X X X Recycling/ Waste Disposal Programs X X X X X X Good Housekeeping X X X X X X Spill Prevention/ Response X X X X X X X Municipal Maintenance Practices X X X X X X X Land Use Planning/Mgmt. X X X X X X X

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Denver Water Quality Management Plan Chapter 7 Page 7-5 EXHIBIT 7.3 DENVER PROACTIVELY WORKS TO ELIMINATE ILLEGAL DUMPING AND ILLICIT DISCHARGES Source: Colorado Nonpoint Source Council 2001. Public Outreach and Education and Illicit Discharge Controls Public education addresses a multitude of pollutant sources by raising the general level of understanding of how individual actions can contaminate surface runoff and downstream waterbodies. Public education includes both educating the general public and Denver employees. Topics often addressed in public education programs include proper disposal of household and toxic waste; proper use of pesticides, herbicides, and fertilizers; and responsible disposal of spent materials. Representative mechanisms for public education may include brochures, posters, signs, and educational videos; utility bill inserts, flyers and handbills; newspaper articles and/or advertisements; public workshops, including field demonstrations; or developing school curricula. Another approach used in many municipalities is storm drain stenciling or signs on storm drains alerting the public that the drain leads to a downstream river or creek and that dumping to the drain is prohibited. Portland, Oregon (see Chapter 5) and Boulder, Colorado are examples of cities that have undertaken in-depth public education and training programs that target specific industry segments. For example, the City of Boulder has developed the Partners for a Clean Environment (PACE) program (see http://www.ci.boulder.co.us/environmentalaffairs/PACE/index.htm ), which targets and provides educational information to specific industry segments including auto repair, auto body, green building, dental offices, dry cleaning, landscaping, manufacturing, printing, restaurant, and retail sectors. Exhibit 7.4 summarizes the activities that Denver has implemented to promote public education regarding stormwater pollution. Public education is critical to all of Denver s stormwater program components (e.g., commercial/residential management program, illicit discharge detection program, etc.). Denver has recognized the importance of providing education and outreach at multiple levels: 1) public and elected officials, 2) schools, and 3) industrial and commercial facilities. In addition to the many educational activities involving schools listed in Exhibit 7.4, one of the important activities Denver has focused on is hands-on experience for public and elected officials. For example, Denver s municipal separate storm sewer system (MS4) compliance group and the Cherry Creek Stewardship Partners conducted two water quality bus tours to promote awareness and understanding of regional impacts to the Cherry Creek watershed.

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Pollution Source Controls (Non-Structural BMPs) Chapter 7 Page 7-6 EXHIBIT 7.4 REPRESENTATIVE PUBLIC EDUCATION ACTIVITIES COMPLETED BY DENVER Activity/Program Element Completion Date Establishment of a water quality web page ( www.denvergov.org ) featuring the stormwater hotline phone number and three educational brochures. February 1999 Operation of a central phone number for the public reporting of illicit discharges. On-going Response to reports of illicit discharges from the public and other public agencies. On-going Placement of Stormwater Hotline phone number in the Metro Denver White Pages. 2000/2001 Updated Stormwater Hotline in the Metro Denver White Pages. 2003 Development of Pollution Prevention pamphlet. May 1998 Posting of household waste and lawn and garden brochures on Denver s web pages ( www.denvergov.org ) under both the Wastewater Management and Denver Recycles sections. February 1999 Distribution of brochures via Wastewater Management Division storm drainage fee billing to approximately 140,000 customers. Began in May 1999, completed in April 2001 Placement of brochures at City Recreation Centers, Public Libraries, and City Permit Centers. Began in February 1999, continued throughout 2003 Provided assistance to Denver Recycles on development of brochure promoting alternatives to household chemical use. Fall 1999 Co-managed the program and provided funding for the collection operations of Denver s Household Hazardous Waste (HHW) Collection Program. Supplemented public education/marketing funding provided by Denver Recycles. Began in November 1999, continued throughout 2003 Inclusion of flyer developed by Denver Recycles promoting the HHW collection program via Wastewater Management storm drainage fee billing to approximately 140,000 households. Began in November 2000, completed in November 2001 Provided assistance to Denver s Department of Environmental Health in the development of a pet waste brochure and garden brochure for Denver residents. Pet brochure completed in December 2000, distributed in 2001; landscape brochure issues to be discussed in next report Assisted River Watch program for high school students. Provided Hach testing equipment, laboratory analysis, and program review. March-April 2001 Purchased Enviroscape NonPoint Source model for elementary and middle school education program. December 2001

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Denver Water Quality Management Plan Chapter 7 Page 7-7 EXHIBIT 7.4 REPRESENTATIVE PUBLIC EDUCATION ACTIVITIES COMPLETED BY DENVER Activity/Program Element Completion Date Implemented Enviroscape NonPoint Source outreach presentations as part of elementary and middle school education program. 2002, 2003 Assisted UDFCD in conducting a series of educational training modules to assist Phase II municipalities in preparation of CDPS applications. July through December 2003, on a monthly meeting schedule Presented nonpoint source model to Denver Public Schools 5 th graders during Water Festival at Fishback Park, Denver. September 2003 Provided personnel and fiscal support to the Cherry Creek Stewardship Partners to conduct a Project WET Teach the Teacher workshop. The workshop will continue to be supported by Denver in 2004. October 2003 Provided personnel and fiscal support to the Cherry Creek Stewardship Partners to conduct the 5 th Annual Partners Conference. The Conference will continue to be supported by Denver in 2004. November 2003 Provided support to Front Range Earthforce middle school environmental steward groups for stenciling projects in the Cole, Highlands, and Park Hill Neighborhoods. 53 middle school age children participated in the three events. Sept. 09 and 12, 2003 Stenciling support for 7th and 8th grade Cole Middle School teachers. Approximately 104 children participated in four separate activities. Sept. 17, 2003 Nonpoint source presentations for 7th and 8th grade Cole Middle School teachers. Approximately 102 children participated in four separate activities. Sept. 17, 2003 Development of a plan to support and encourage attendance at an education and training program for construction site operators. January 1, 1999 July 1999 (full implementation), ongoing program In addition to educating the general public, Denver also works to educate and train Denver staff through a variety of mechanisms, with relevant examples summarized in Exhibit 7.5.

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Pollution Source Controls (Non-Structural BMPs) Chapter 7 Page 7-8 EXHIBIT 7.5 REPRESENTATIVE DENVER STAFF EDUCATION ACTIVITIES Course/Training Date Description Attendance Audience Colorado Contractors Association Workshop Titled "Construction Site Erosion Control" February-03 NPDES compliance including construction activities and erosion control 2 Inspectors and program managers System Maintenance and Response for Structural Controls Throughout 2003 Spill response procedures, to minimize overall environmental impact during emergency conditions 170 Denver facility managers and personnel Pollution Prevention Throughout 2003 Pollution prevention practices and their relationship to protecting human health and the environment 209 Denver facility managers and personnel Hazardous Material Management Throughout 2003 Handling and managing hazardous materials, comprehension of Material Safety Data Sheets, and managing hazardous waste 443 Denver facility managers and personnel GIS Workshop "GIS and Water Quality" November03 Incorporating of GIS technology and water quality data management 1 Engineer, program manager Watershed Water Quality Tour June-03 Awareness of the connection of water quality, planning, engineering, and non-point source pollution 10 Elected officials, regional planners, and Denver engineers and scientists Open Space Water Quality Tour October-03 Awareness of the connection of open space, water quality, planning, engineering, and non-point source pollution 8 Elected officials, regional planners, and Denver engineers and scientists Colorado Water Congress "Water Quality Workshop" October-03 Intensive one-day program on all aspects of water quality subjects 2 Engineer, program manager Cherry Creek Stewardship Partners 5th Annual Conference November03 Awareness of the connection of open space, water quality, planning, engineering, and non-point source pollution in a single watershed 6 Elected officials, regional planners, and Denver engineers and scientists Number of Training Efforts 9 Denver Employees Trained 851

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Denver Water Quality Management Plan Chapter 7 Page 7-9 Source Controls Source controls help prevent the disposal of or limit the application of constituents that may be potential pollutants in the urban landscape. Source controls also help to minimize the migration of constituents offsite from the point where they are being used, stored, or otherwise being exposed to stormwater. General categories of source controls discussed in more detail in this Plan include: 4 Industrial and Commercial Hot Spots (Fueling Areas, Vehicle Washing, etc.) 4 Household Waste (Litter, Pet Waste, Yard Waste, Used Oil and Automotive Fluids, etc.) 4 Pesticide, Herbicide and Fertilizer Management (Including Integrated Pest Management) 4 Efficient Irrigation 4 Materials Storage PracticesIndustrial and Commercial Hot Spots The Urban Storm Drainage Criteria Manual, Volume 3 (UDFCD 1999) provides a succinct description of industrial and commercial pollutant hot spots that should be considered and addressed throughout Denver in terms of both structural and non-structural BMPs. Design considerations for these hot spots include practices such as: providing overhead covering or roof; providing smooth impervious surfaces such as concrete beneath the activity; grading and contouring the site to prevent run-on of stormwater and run-off of pollutants; directing drainage to a structural BMP; strategically locating storm drains away from hot spot activities; and spill response procedures (CSQA 2003). Other practices may include zoning to keep these hot spots out of particularly sensitive areas. The Urban Storm Drainage Criteria Manual, Volume 3 (UDFCD 1999) provides descriptions of these key hot spots: 4 Fueling Areas When stormwater mixes with fuel spilled or leaked onto the ground, it becomes polluted by petroleum-based materials that are harmful to humans, fish, and wildlife. Fuel overflows during storage tank filling can be a major source of contamination. This could occur at large industrial sites or at small commercial sites such as gas stations, convenience stores, strip malls, or garages. Sources of contaminants typically include: spills and leaks during fueling or oil delivery; spills caused by topping off fuel tanks; allowing rainfall to run onto the fuel area; hosing or washing down of the fuel area; or mobile fueling operations. 4 Vehicle and Equipment Maintenance and Storage Vehicle and equipment maintenance operations use materials and create wastes that can be harmful to humans and the environment if not property handled. Stormwater runoff from these areas can become polluted with a variety of contaminants including solvents and degreasing products, waste automotive fluids, oils and greases, acids, and caustic wastes. Sources of contaminants typically include: parts cleaning; shop cleanup; spilled fuel, oil, or other materials such as battery acid; replacement of fluids, such as oil, oil filters, hydraulic fluids, transmission fluid, and radiator fluids; dripping fluids from vehicles and equipment; and disposal of greasy rags, oil filters, air filters, batteries, battery fluids, spent coolant, degreasers, oils, etc.

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Pollution Source Controls (Non-Structural BMPs) Chapter 7 Page 7-10 4 Painting Many painting operations use materials or create wastes that are harmful to humans and the environment. Paint solvents used to remove or thin paint and dusts from sanding and grinding operations contain toxic metals like cadmium and mercury. These can pollute stormwater and create significant water quality impacts. Sources of contamination typically include: painting and chemical paint removal; sanding or paint stripping; spills of paint or paint thinner; sand blasting residue; or equipment painting. 4 Vehicle/Equipment Washing Washing vehicles and equipment outdoors or in areas where wash water flows onto the ground can pollute stormwater. Vehicle wash water is considered process water, not stormwater. Operators must have a CDPS permit to discharge vehicle wash water. Wash waters can contain high concentrations of oil and grease, solvents, phosphates, and high suspended solids loads. Sources of washing contamination typically include: outside equipment or vehicle cleaning (washing, degreasing, or steam cleaning); wash water discharges to the ground or directly to storm drain; mobile fleet washing, or pressure washing of buildings. Other types of washing include spraying down concrete and asphalt surfaces such as those outside of commercial sites where sales of products may have occurred, areas where dirt and mud have accumulated, loading dock areas, or parking and sidewalk areas that have accumulated wastes. These activities must have a CDPS permit. In some cases, these types of discharges are incorporated into the municipal stormwater permit. These areas also need to be taken into consideration with the possibility of potentially polluting stormwater. 4 Loading and Unloading Loading and unloading operations usually take place outside on docks, trucks, terminals, or outside storage or staging areas at both industrial and commercial sites. Materials spilled, leaked, or lost during loading and unloading may collect in the soil or other surfaces and be carried away by runoff, or when the area is cleaned. Rainfall may wash pollutants off machinery used to unload and load materials. Typically sources of contamination include: pumping of liquids or gases to or from a truck or rail car into a storage facility; pneumatic transfer of dry chemicals to or from the vehicles; transfer by mechanical conveyor systems; or transfer of bags, boxes, drums, or other containers by forklift, trucks, or other material handling equipment. 4 Above Ground Tanks Liquid Storage Accidental releases of chemicals from above ground liquid storage tanks can contaminate stormwater with many different pollutants. Materials spilled, leaked, or lost from storage tanks may accumulate in soils or on other surfaces and be carried away by runoff. Typical causes of contamination from accidental releases include: external corrosion and structural failure; installation problems; spills and overfills due to operator error; failure of piping systems, including pipes, pumps, flanges, couplings, hoses, and valves; or leaks or spills during pumping of liquids or gases from trucks or rail cars to a storage facility or vice versa. 4 Outside Manufacturing Outside manufacturing activities can also contaminate stormwater runoff. Activities such as parts assembly, rock grinding or crushing, metals painting or coating, grinding or sanding, degreasing, parts cleaning or operations that use hazardous materials are of concern. Metal and wood shavings, excess lubricants, and other residuals resulting from outside manufacturing that are left on the ground can also

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Denver Water Quality Management Plan Chapter 7 Page 7-11 be washed into the drainage system. Typical contaminant sources include: processes or equipment that generate dust, vapors or other emissions; outside storage of hazardous materials and raw materials; dripping or leaking fluids from equipment or processes; liquid wastes discharged directly onto the ground or into the storm sewer, or concrete manufacturing (pipes, inlets, etc.). 4 Industrial Site Waste Management Areas where industrial or chemical waste is stored, treated or disposed of can cause stormwater pollution. Wastes spilled, leached, or lost from management areas or outside manufacturing activities may build up in soils or on other surfaces and be carried away by rainfall runoff. There is also the potential for liquid wastes from lagoons or surface impoundments to overflow to surface waters or soak the soil where they can be picked up by runoff. Possible stormwater contaminants include toxic compounds, oil and grease, oxygen-demanding organics, paints and solvents, heavy metals, and high levels of suspended solids. 4 Commercial Site Waste Management Improper disposal of liquid wastes in a solid waste dumpster can result in the liquids draining out of the container and into the stormwater system. Lack of coverage of waste receptacles can result in rainwater seeping through the material and collecting contaminants or the material being blown around the site and into the stormwater collection system. Typical contaminant sources include: landfills; waste piles; wastewater and solid waste treatment and disposal sites; land application sites; dumpsters; or unlabeled 55-gallon drums. 4 Outside Storage of Materials Raw materials, by-products, finished products, containers, and materials storage areas exposed to rain and/or runoff can pollute stormwater. Stormwater can become contaminated by a wide range of contaminants (e.g. metals, oils and grease, sediment) when solid materials wash off or dissolve into water, or by spills or leaks. Typical contaminant sources include: fuels, raw materials, byproducts, intermediates, final products, process residuals, or wind-blown debris. 4 Salt Storage Salt left exposed to rain or snow may migrate to the storm sewer or contaminate soils. Salt spilled or blown onto the ground during loading or unloading will dissolve in stormwater runoff. Stormwater contaminated with salt in high concentrations can be harmful to vegetation and aquatic life. Salty stormwater runoff soaking into the ground may contaminate groundwater, thus making the groundwater unsuitable as a drinking water supply. Typical contaminant sources include: salt stored outside in piles or bags that are exposed to rain or snow; salt loading and unloading areas located outside or in areas where spilled salt can contaminate stormwater; or salt/sand storage piles used for deicing operations. 4 Parking. Customer parking areas can also be a source of contamination. Typical sources of contamination can include improper disposal of trash and leaky vehicles that can result in oils and other contaminants being deposited in the parking lot and then washed to the stream during a storm event.

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Pollution Source Controls (Non-Structural BMPs) Chapter 7 Page 7-12 4 Bare Soil Bare soil may be located on unpaved areas or areas under development at commercial and industrial sites. Trash and other contaminants such as vehicle leaks onto the soil can be washed away in stormwater runoff. 4 Landscaping Practices Chemicals used to maintain landscaping areas can have a significant impact on the water quality of stormwater runoff. Herbicides, pesticides, and fertilizers can create impacts if they are not applied correctly. Contaminant sources include: improper storage of chemicals, improper storage of cleaning equipment used to apply these chemicals, or improper application. These hot spots can be addressed through a combination of non-structural practices that include public and employee education, materials storage practices, and thoughtful site designs (e.g., overhead cover and impervious underlying surfaces, etc.). In most cases, structural BMPs are also needed to treat runoff from these hot spots. See the Spill Prevention and Response discussion for additional supplemental information. As shown in Exhibit 7.1, Denver s vehicle maintenance facilities, asphalt and concrete batch plants, solid-waste transfer stations, exposed stockpile areas and snow dump sites, and other facilities require specific attention under Denver s CDPS permit.Household Waste (Litter, Pet Waste, Yard Waste, Used Oil and AutomotiveFluids, and Other Hazardous Waste)Improperly disposed household waste materials can include household chemicals, pet waste, yard waste, litter, automotive maintenance waste, and others. These materials can enter storm runoff and pollute downstream water bodies when these wastes are placed on impervious surfaces such as streets, alleys, parking lots and sidewalks, and pervious structures such as ditches, drainageways, gulches, or discharged directly into the storm drainage system. The development of education programs and dissemination of information that promotes proper disposal of these materials is important. The passage of laws, rules, or ordinances prohibiting improper disposal of these materials, and their enforcement, is another step in this management practice. The Urban Storm Drainage Criteria Manual, Volume 3 (UDFCD 1999) provides this description of household waste that should be managed to minimize stormwater pollution: 4 Litter Most litter is biodegradable and can create an oxygen demand in water as it decomposes. Examples of litter are paper products, used diapers, etc. Reduction of litter through proper disposal can reduce its accumulation on the urban landscape and its eventual entry into the stormwater system. 4 Pet Waste Pet waste deposited on impervious surfaces can be transported by the stormwater drainage system to receiving waters. Fecal matter potentially contains pathogenic viruses and bacteria and also creates an oxygen demand in water. The majority of improperly disposed pet waste occurs in public areas, such as streets and parks. Pet waste ordinances are common in municipalities; however, these are difficult to enforce, especially with limited municipal resources. Public education can help bring this

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Denver Water Quality Management Plan Chapter 7 Page 7-13 EXHIBIT 7.6 DISPOSAL OF USED AUTOMOTIVE PRODUCTS DOWN STORM DRAINS IS PROHIBITED UNDER DENVER S CDPS PERMIT Source: Colorado Nonpoint Source Council 2001. problem to the public's attention and can thereby reduce deposition of pet waste on urban surfaces. 4 Yard Waste Yard waste is also a category of household waste. Examples of yard waste include leaves and grass clippings. It is distinguished from other categories of household waste in that it can be disposed of by composting. Fallen tree leaves, grass clippings, and garden debris can become water pollutants when they are disposed of in alleys, driveways, parking lots, streets, street gutters, irrigation ditches, and drainage channels. Public education efforts on the benefits of composting and on proper disposal of yard waste can help to reduce the volume of yard waste entering the stormwater system and receiving waters. 4 Used Oil and Automotive Fluids Used oil and automotive fluids including antifreeze, brake fluid, transmission fluid, grease, other lubricants, and petroleum-based cleaning solvents are wastes generated during automobile maintenance by residential households and commercial businesses. These can enter the storm drainage system if poured directly into storm inlets or from residue on concrete or asphalt exposed to precipitation. Improper disposal of used oil and automotive fluids causes receiving waters to become contaminated with hydrocarbons and residual metals that can be toxic to stream organisms. Used oil and other petroleum products can be recycled. A number of different recycling centers presently exist in the metropolitan area. Public education on the location of these centers, the benefits of recycling, prevention of fluid leaks, and the importance of proper disposal for improving stormwater quality can reduce the amounts of oil and used automotive fluids reaching receiving waters. 4 Toxic Wastes Toxic wastes are generated by residential households and commercial businesses. These primarily consist of certain types of used and unused consumer products. Included among these are paint, solvents, putties, cleaners, waxes, polishes, oil products, aerosols, acids, caustics, pesticides, herbicides, and certain medicines or cosmetics. These products and their containers should always be disposed of properly. Some of these unused toxic materials can also be recycled. Improper disposal of toxic substances causes stormwater to become contaminated by these wastes. This occurs

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Pollution Source Controls (Non-Structural BMPs) Chapter 7 Page 7-14 when toxic substances are dumped into street gutters or storm inlets. This also happens when stormwater comes in contact with toxic substances where they have been improperly disposed on land surfaces. There is no need for improper disposal of toxic substances because small amounts of toxic materials can legally be disposed of in landfills. Educational efforts to heighten public awareness of the environmental damage due to improper disposal and to encourage proper disposal and recycling, can reduce the amounts of these pollutants entering stormwater, provided the public as a whole actively participates.Pesticide, Herbicide, and Fertilizer Management (Including Integrated PestManagement)Pesticides, herbicides, and fertilizers are used by commercial applicators, Denver staff and the general public to maintain landscaping in residential, commercial and industrial areas. As stated in the Urban Storm Drainage Criteria Manual, Volume 3 (UDFCD 1999), these substances are usually toxic and can contaminate surface runoff if not properly used. While pesticides and herbicides are toxic to aquatic life at low concentrations, fertilizers are usually only toxic at high concentrations. Fertilizers, however, are more commonly a problem because of their nutrientenrichment effect on receiving waterbodies. An oversupply of phosphorus and nitrogen will promote unsightly algal growth that can lead to a depletion of dissolved oxygen needed for fish and other aquatic organisms. These chemicals are applied on urban landscape areas and, when improperly applied or used, can be transported to receiving waters in surface runoff. The rate and timing of application of pesticides, herbicides, and fertilizer are important to minimize transport by surface runoff, as well as to optimize their intended purpose in landscape maintenance. Over-application and over-spraying of pesticides, herbicides, and fertilizers onto impervious areas, such as streets and sidewalks, needs to be avoided, as well as excessive use of these chemicals. Use of these chemicals in accordance with manufacturer's recommendations can prevent most of the surface water contamination being attributed to their use. In 1997, Mayor Webb issued Executive Order 121 on the topic of pesticide usage, identifying specific requirements for pesticide application, spill reporting, disposal practices, public notification, and other related issues. The Order emphasizes following label directions and using pesticides in a manner that does cause injury to humans, non-pest animals and non-pest vegetation, and in a manner that does not contaminate groundwater. Disposal of pesticides and tank rinse in sanitary sewers, storm sewers, ditches, streams, lakes, or in other illegal manners is prohibited (Denver 1997).

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Denver Water Quality Management Plan Chapter 7 Page 7-15 EXHIBIT 7.7 PROPER USE OF FERTILZER IS AN IMPORTANT S OURCE CONTROL Source: Colorado Nonpoint Source Council 2001. Public and landscaping industry education are particularly important to promoting proper landscaping chemical usage. Denver has already undertaken and continues to undertake public education efforts regarding usage of these chemicals, as described in Exhibit 7.4 under the public education discussion. In addition to these efforts, opportunities exist for Denver to target pollutants associated with the landscaping industry. As previously noted, the City of Boulder has developed the Partners for a Clean Environment (PACE) program (see http://www.ci.boulder.co.us/environmentalaffairs/PACE/index.htm ) to provide training and recognition to landscaping professionals who undergo the city s landscaping program. Those completing the program are listed on the city s web site. Another existing opportunity with regard to landscaping BMPs is the recently developed Green Industries of Colorado (GreenCO) Water Conservation and Water Quality Protection Best Management Practices (BMP) training and certificate program, which has been completed under 319 grant funding to improve industry practices. Rather than develop a city-based training program, Denver could partner with GreenCO to support its on-going industry training efforts. (See www.greenco.org for more information.) In addition to proper handling of pesticides, it is important to recognize a body of practices termed Integrated Pest Management (IPM). It uses biological, chemical, and genetic information to determine the best type of control, the timing and extent of chemical applications, and whether non-chemical means can attain an acceptable level of pest control. IPM is a preventive measure aimed at knowing the exact pest(s) being targeted for control, the locations and times when pests will pose problems, the level of pest-induced damage that can be tolerated without taking action, the most vulnerable life stage, and control actions that are least damaging to the environment. The major components of IPM are as follows: monitoring and inventory of pest populations, determination of pest-induced injury and action levels, identification of priority pest problems, selection and timing of least toxic management tools, site-specific treatment with minimized chemical use, and evaluation and adjustment of pesticide applications. Monitoring of pest populations is key to successful IPM implementation. Pest problems are universally easier to control if the problem can be discovered early. With IPM, pesticides are used only as a last resort; maximization of natural controls, including biological controls and removal of pests by hand, is a guiding rule. IPM encourages the use of less toxic or substitute methods of pest and weed control that, if followed, further reduce the amount of pesticides and herbicides in contact with surface runoff.

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Pollution Source Controls (Non-Structural BMPs) Chapter 7 Page 7-16 However, it is difficult to reach and influence all commercial and residential users of these chemicals and to present technical information in simplified form to all users.Efficient IrrigationIn addition to providing water-conservation benefits, designing, installing and maintaining efficient irrigation systems helps to minimize excess irrigation water being conveyed into stormwater drainage systems (CSQA 2003). This helps to minimize pollutant loading associated with commonly used lawn chemicals and to keep dry weather flows out of the storm sewer. Detailed guidance and public education materials on efficient irrigation systems are available from GreenCO ( www.greenco.org ), Denver Water ( www.denverwater.org ), the Irrigation Association ( www.irrigationassociation.org ), EPA ( www.epa.gov ) and others. Efficient irrigation is an important topic for both public education and landscaping industry education. Given recent drought conditions in Colorado, opportunities exist to partner with water supply providers to encourage efficient irrigation.Materials Storage PracticesImproper material storage on site can lead to the release of materials and chemicals that can cause stormwater runoff pollution. Having good materials storage and inventory practices is necessary for all commercial and industrial facilities. Materials storage areas, including bulk solid materials, should be covered and should have adequate aisle space to facilitate material transfer and ease of access for inspection. Containers, drums, and bags should be stored away from direct traffic routes to prevent accidental spills. Manufacturer s instructions should be followed when stacking containers, and containers should be stored on pallets over a paved surface or similar surfaces to prevent corrosion of containers that results from containers coming in contact with moisture on the ground. Container labels should include the name and type of substance, stock number, expiration date, health hazards, handling suggestions, and first aid information. All storage areas should be designed to contain any spills, and procedures should be adopted to reduce the chance of spills or leaks during filling or transfer of materials. An up-to-date inventory for all materials (both hazardous and non-hazardous) will help keep material costs down by reducing overstocking, track how materials are stored and handled onsite, and identify which materials and activities pose the most risk to the environment. Inventory of the site should include a site walk-through, review of purchase orders, listing of all chemical substances used, and obtaining Material Safety Data Sheets (MSDS) for all chemicals. Hazardous materials must be stored according to federal, state, and local HazMat requirements. The responsibility of hazardous material inventory should be assigned to a limited number of people who are trained to handle such materials. Decisions on the amounts of hazardous materials that are stored on site should include an evaluation of any emergency control systems that are in place. Toxic or hazardous liquids should be stored within curbed areas or secondary containers, and the hazardous materials inventory should identify special handling, storage, use, and disposal considerations.

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Denver Water Quality Management Plan Chapter 7 Page 7-17 Recycling/Waste Disposal Programs The purpose of recycling programs in the context of stormwater management is to keep toxic pollutants out of the storm sewer. As part of the public education efforts listed in Exhibit 7.4, several aspects of Denver s recycling program were noted, particularly with regard to Denver s used motor vehicle fluid and household chemical waste collection programs. Denver Recycles has developed numerous educational brochures to promote the proper management of household chemical waste. These brochures promote reduced use of toxic household products, substitution of acceptable alternatives, and proper storage, recycling or disposal of such chemicals. Denver Recycles also maintains a listing of privately operated drop-off facilities for items such as used motor oil, automotive batteries, antifreeze, and other household chemicals and materials. The list is updated regularly and made available to Denver residents to help them recycle or properly dispose of household hazardous waste (HHW) locally, whenever possible. In certain instances, Denver Recycles refers citizens to Denver s Department of Environmental Health and/or the Fire Department. These agencies are equipped to assist residents with items that cannot be disposed of in Denver s HHW program. These items include flammable materials, medical waste, ammunition, radioactive sensors in smoke detectors, and other unusual wastes. Furthermore, Denver s Solid Waste Management Division works with these Denver agencies to manage abandoned or illegally dumped waste on residential and Denver property. Since 1999, Denver Recycles and the Wastewater Management Division have managed and implemented a door-to-door HHW collection program for Denver residents. To operate the program, Denver contracted a private company, with services being provided by Curbside, Inc. The initial 13-month HHW pilot program was completed in December 2000. Denver is now into the fourth year of providing direct residential collection of HHW from Denver residents. This turn-key HHW program approach was chosen after careful evaluation of HHW collection options and the diverse service needs of the nearly 160,000 eligible Denver households. Basic service (items collected at no charge) for this collection program includes residential pickup of lubricants, oil-based paint, latex paint (up to 10 gallons), cleaners and polishes, wood finishes, gasoline and other fuels, oil filters, solvents, thinners and removers, pesticides, insecticides, herbicides, swimming pool chemicals, hobby supplies, photography chemicals, household batteries, thermometers and thermostats, florescent tubes, and aerosol cans containing fluids. For a nominal fee, the contractor will also pick up additional quantities of latex paint over 10 gallons. The Wastewater Management Division provides the funding for this collection program. In 2003, the Wastewater Management Division and Denver Recycles initiated a new contract for this service. The Wastewater Management Division will continue funding for this program as long as funds are available. However, the implementation of co-pays may also be evaluated. It is believed that the HHW collection program has had a positive impact on Denver s stormwater quality as a source-control measure. Many residents have participated and have provided positive responses in written consumer surveys.

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Pollution Source Controls (Non-Structural BMPs) Chapter 7 Page 7-18 Good Housekeeping/Spill Prevention and Response/Preventative Maintenance Good housekeeping, spill prevention and response, and preventative maintenance practices go hand-in-hand. Each of these groups of practices is described below based directly on the guidance provided in the Urban Storm Drainage Criteria Manual, Volume 3 (UDFCD 1999).Good HousekeepingGood housekeeping practices are designed to maintain a clean and orderly work environment and can be applied to homeowners as well as commercial and industrial facilities. The most effective first steps towards preventing pollution in stormwater from work sites simply involves using good common sense to improve the facility s basic housekeeping methods. Poor housekeeping practices result in more waste being generated than necessary and an increased potential for stormwater contamination. A clean and orderly work site reduces the possibility of accidental spills caused by mishandling of chemicals and equipment and should reduce safety hazards to personnel. A well-maintained material and chemical storage area will reduce the possibility of stormwater mixing with pollutants. Many aspects of good housekeeping are part of a strong pollution prevention plan, such as preventative maintenance of equipment, proper materials storage and inventory, and a spill prevention and response plan. Some additional simple procedures to promote good housekeeping are routine and regular clean-up schedules, maintaining well organized work areas, signage, and educational programs for employees and the general public about good housekeeping practices. Examples of other practices include: maintaining dry and clean floors and ground surfaces by using brooms, shovels, vacuum cleaners or cleaning machines rather than wet clean-up methods; regular pickup and disposal of garbage and waste material; routine equipment maintenance and inspections; ensuring employees understand all spill cleanup procedures and that they receive appropriate training; designation of separate areas of the site for auto parking, vehicle refueling and routine maintenance; cleaning up leaks, drips and other spills immediately; and covering and maintaining dumpsters and waste receptacles.Spill Prevention and ResponseSpills and leaks are a large source of stormwater pollutants, and in most cases are avoidable. The storage, transport, and disposal of hazardous and toxic substances are regulated activities under state and federal laws, and many local police, fire, or other departments are equipped to respond to such spills. Nevertheless, most spills have the potential to contaminate receiving waters via transport by the storm sewer system. A good spill prevention and response plan will incorporate good housekeeping and preventative maintenance BMPs. Exhibit 7.8 provides examples of various BMPs to be considered in such a plan. A spill prevention and response plan identifies areas where spills can occur onsite, specifies materials handling procedures, storage requirements, and identifies spill cleanup procedures. Stormwater contamination assessment, flow diversion, record keeping, internal reporting, employee training, preventative maintenance,

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Denver Water Quality Management Plan Chapter 7 Page 7-19 covering pollutants, and providing adequate security are associated BMPs that should be incorporated into a comprehensive plan. Preparation of a spill prevention and response plan may include mapping of storm sewers. Such maps can then be used by the emergency response crews to help identify which inlets, areas, or sewers to protect or block off in the event of a spill. Training, updating of procedures, field exercises, proper equipment, and documentation are all part of a spill response program. Once a spill occurs, it should be monitored to determine when the area of the spill has been adequately cleaned up. Proper clean up procedures include: 4 Wipe up small spills with a shop rag, store shop rags in covered rag containers, and dispose of properly (or take to professional cleaning service and inform them of the materials on the rag). 4 Contain medium-sized spills with absorbents (kitty litter, sawdust, etc.) and use inflatable berms or absorbent snakes as temporary booms for the spill. Store and dispose of absorbents properly. Wet/dry vacuums may also be used, but not for volatile fluids. 4 For large spills, first contain the spill and plug storm drain inlets where the liquid may migrate off-site, then clean up the spill. A summary of the plan should be written and posted at appropriate points in the building (i.e., lunch rooms, cafeteria, and areas with a high spill potential), identifying the spill cleanup coordinators, location of cleanup kits, and phone numbers of regulatory agencies to be contacted in the event of a spill. Emergency spill containment and cleanup kits should also be located at the facility site. The contents of the kit should be appropriate to the type and quantities of chemicals or goods stored at the facility. Key personnel should receive formal training in plan execution for emergency spill cleanup and the appropriate agencies should be notified.

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Pollution Source Controls (Non-Structural BMPs) Chapter 7 Page 7-20 EXHIBIT 7.8 ADVANTAGES AND DISADVANTAGES OF BMPS FOR SPILL PREVENTION AND RESPONSE (Source:Urban Storm Drainage Criteria Manual, Volume 3 (UDFCD 1999) Best Management Practice Advantages Disadvantages Drip pans pans used to contain small volumes of leaks Inexpensive; simple installation and operation; possible reuse/recycle of material; empty/discarded containers can be used as drip pans Small volumes; inspected and cleaned frequently; must be secured during poor weather conditions; personnel must be trained in proper disposal methods Covering enclosure of outdoor materials, equipment, containers, or processes Simple and effective; usually inexpensive Frequent inspection; possible health/ safety problems if built over certain activities; large structures can be expensive Vehicle positioning locating trucks or rail cars to prevent spills during transfer of materials Inexpensive; easy; effective May require redesign of loading and unloading areas; requires signage to designated areas Loading/unloading by air pressure or vacuum for transfer of dry chemicals or solids Quick and simple; economical if materials can be recovered; minimize exposure of pollutants to stormwater Costly to install and maintain; may be inappropriate for denser materials; site-specific design; dust collectors may need permit under Clean Air Act Sweeping with brooms to remove small quantities of dry chemicals/solids exposed to precipitation Inexpensive; no special training; recycling opportunities Labor-intensive; limited to small releases of dry materials; requires disposal to solid waste container Shoveling for removal of large quantities of dry materials, wet solids and sludge Inexpensive; recycling opportunities; remediates larger releases Labor-intensive; not appropriate for large spills; requires backfill of excavated areas to maintain grade Excavation by plow or backhoe for large releases of dry material and contaminated areas Cost effective for cleaning up dry materials release; common and simple Less precise; less recycling and reuse opportunities; may require imported material for backfill Dust control (industrial) water spraying, negative pressure systems, collector systems, filter systems, street sweeping May reduce respiratory problems in employees around the site; may cause less loss of material and save money; efficient collection of larger dust particles More expensive than manual systems; difficult to maintain by plant personnel; labor and equipment intensive; street sweepers may not be effective for all pollutants Signs and labels Inexpensive and easily used Must be updated/maintained so they are legible, subject to vandalism and loss Security to prevent accidental or intentional release of materials Preventative safeguard; easier detection of vandals, thieves, spills, leaks, releases; prevents spills with better lighting; no unauthorized access to facility May not be feasible for smaller facilities; may be costly; may increase energy costs due to increased lighting; dispersed locations require individual enclosures; requires maintenance Area control measures good housekeeping measures, brushing off clothing before leaving area, etc. Easy to implement; results in cleaner facility and improved work environment May be seen as tedious by employees and may not be followed

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Denver Water Quality Management Plan Chapter 7 Page 7-21 EXHIBIT 7.8 ADVANTAGES AND DISADVANTAGES OF BMPS FOR SPILL PREVENTION AND RESPONSE (Source:Urban Storm Drainage Criteria Manual, Volume 3 (UDFCD 1999) Best Management Practice Advantages Disadvantages Preservation of natural vegetation Can handle more stormwater runoff than newly seeded areas; effective immediately; increases filter capacity; enhances aesthetics; provides areas for infiltration; wildlife can remain undisturbed; provides noise buffers; less maintenance than new vegetation Planning required to preserve and maintain existing vegetation; may not be cost effective with high land costs; may constrict area available for construction activities; may require signage or fencing; subject to disturbance Temporary seeding short-term vegetative cover on disturbed areas Inexpensive and easy to do; establishes plant cover quickly in good conditions; stabilizes soils well; aesthetic; sedimentation controls for other site areas; helps reduce maintenance costs of other controls Requires soil preparation; may require mulching or reseeding of failed areas; seasonally limited; may require signage or fencing; subject to disturbance Preventative MaintenancePreventative maintenance involves the regular inspection and testing of plant equipment and operational systems. The purpose of the preventative maintenance program should be to prevent breakdowns and failures by adjustment, repair, or replacement of equipment before a major breakdown or failure can occur. Preventative maintenance should be used selectively to eliminate or minimize the spill of contaminants to receiving waters. Maintenance activities will involve the use of chemicals and fluids, so spill response information and spill cleanup materials should be kept on the site and readily available. For many industrial facilities, a preventative maintenance BMP would simply be an extension of the current plant preventative maintenance program to include items to prevent stormwater runoff contamination such as upkeep and maintenance of storage tanks, valves, pumps, pipes, and other process-water or chemical feed devices. Routine inspections and testing of equipment are required to identify maintenance needs. Typical equipment to inspect and test includes pipes, pumps, storage tanks and bins, pressure vessels, pressure release valves, process and material handling equipment, and stormwater management devices. Defective or severely worn equipment should be replaced or repaired promptly. Inspections, testing, and follow-up actions should be documented. Similar to preventative maintenance for plants, a plan for vehicles and equipment maintenance includes routine inspections and testing. All equipment should be kept clean with no excessive amounts of oil and grease buildup, and equipment and parts should be stored under cover. Storage of solvents, greases, oils, hydraulic fluids, paints, thinners and hazardous materials should be consistent with the materials storage and inventory BMP, and used oil for recycling

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Pollution Source Controls (Non-Structural BMPs) Chapter 7 Page 7-22 should be stored in self-contained labeled tanks. Used oil tanks and drums should be located away from the nearest inlet to the storm drainage system or flowing streams and preferably indoors, if possible. Care must be taken during maintenance procedures to prevent pollutant releases by implementing measures such as drip pans; proper cleanup, disposal, and recycling; and removal of fluids and batteries from salvage vehicles and equipment. Cleanup from maintenance activities includes proper disposal or recycling of used oil, lubricants, and other fluids, and cleaning any catch basins that receive runoff from a maintenance area. Use of a mop or dry sweeping compound is preferable to hosing down work areas or using concrete cleaning products. Proper maintenance activities associated with building and grounds include sweeping of paved surfaces rather than washing; routine cleaning of stormwater drainage systems; and proper disposal of wash water, sweepings and sediments. Maintenance Practices Denver implements a variety of municipal maintenance practices on a regular basis that provides opportunities for reduction of pollutant loading in stormwater. The Water Environment Federation and American Society of Civil Engineers (WEF and ASCE 1998) provide several examples of these practices: 4 Street Cleaning This involves regularly sweeping streets to physically remove pollutants from surfaces that drain to storm sewers. In Denver, streets are typically swept twice per year if debris has accumulated: once in the spring to remove deicing residuals and once in the fall to remove fallen leaves. Effectiveness of street sweeping has been shown to be highly variable in several national databases (see www.bmpdatabase.org ). Studies suggest that vacuum-type sweepers are far more effective than rotary-brush type sweepers. 4 Catch Basin Cleaning This involves cleaning catch basins and stormwater inlets to remove pollutants, reduce high pollutant concentrations during the first-flush of storms, prevent clogging of the downstream conveyance systems and restore the catch basin s sediment-trapping capacity. 4 Storm Drain Flushing Storm drains can be flushed with water to suspend and remove deposited material. This helps to ensure that pipes convey design flows and removes pollutants from the storm drain systems. This practice is most effective when the storm drain daylights in a structural BMP area where sediment is trapped or otherwise able to be cost-effectively collected. 4 Roadway and Bridge Maintenance Methods to prevent or reduce the discharge of pollutants from roadway and bridge maintenance include paving as little area as possible (i.e., minimize urban sprawl), design bridges to collect and convey stormwater, using measures to prevent run-on and runoff, properly disposing of maintenance wastes, and training employees and subcontractors.

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Denver Water Quality Management Plan Chapter 7 Page 7-23 EXHIBIT 7.9 WELL VEGETATED RIPARIAN BANK ALONG THE SOUTH PLATTE RIVER IN DENVER 4 Structural BMP Maintenance Implementing routine maintenance for structural stormwater BMPs is critical to their proper functioning, as described in Chapter 6. 4 Storm Channel and Creek Maintenance Reduction in pollutant levels can be achieved by regularly removing dumped items and material from storm drainage channels and creeks. This can include identifying illegal dumping spots, posting no littering signs and providing significant penalties for doing so, etc. Stabilizing streambanks to enable them to withstand typical storm flows is also important in urbanized areas. Under Denver s CDPS permit, Denver addresses six public street maintenance elements including snow and ice management; dry and liquid deicer storage; herbicide usage along roadways; sweeping litter and debris; sweeping streets following snow control (e.g., sanding/deicing); and disposal of sweeper waste (Denver 2002). Examples of the types of nonstructural BMPs implemented include covered storage areas for stockpile areas, applying herbicides during fair weather conditions, and street sweeping in the spring and fall. Land-Use Planning and Management Practices Development of ordinances and land planning practices that protect streams and rivers are a key non-structural BMP. Site designs that maximize infiltration, provide on-site retention, slow runoff and minimize impervious land coverage provide a variety of stormwater management benefits. A variety of mechanisms exist, and only a few are discussed herein. The challenges to land-use planning practices are often political and require significant cooperation among multiple departments and agencies. Examples of land-use controls and practices that can provide significant water quality benefits, many of which are based on WEF and ASCE (1998) guidance, include: 4 Protective Covenants provide restrictions on a variety of pollutant sources such as pesticide/fertilizer application, stream setbacks, vegetative cover requirements, etc. 4 Stream buffer requirement/riparian zone protection limit development directly adjacent to streams. 4 Floodplain restrictions limit development in the floodplain. 4 Steep slope restrictions limit clearing/grading on steep slopes. 4 Wetland protection limits development in wetland areas (also required under Section 404 of Clean Water Act).

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Pollution Source Controls (Non-Structural BMPs) Chapter 7 Page 7-24 4 Specific protection for environmentally sensitive areas limits development in certain habitat areas. 4 Upland and riparian tree cover requirements promote certain percentage of tree canopy, which helps to intercept rainfall and provide other benefits. 4 Waterway disturbance permits require roadways and utilities to cross streams in a manner to minimize their impact. 4 Community open space requirements provide additional open space and natural areas to infiltrate runoff and buffer the stream area. 4 Cluster development strategies reduce impervious area at developments by clustering development into centralized areas where stormwater can be effectively treated. 4 Green Development and Smart Growth strategies encourage developments with holistic design concepts that consider factors such as land-use issues, resource conservation, natural area and open space preservation, and community/cultural issues. A key land-planning concept that has already been discussed in Chapter 5 is Low Impact Development (LID). As previously noted, the goal of LID is to mimic a site's predevelopment hydrology by using design techniques that infiltrate, filter, store, evaporate, and detain runoff close to its source. Instead of conveying and treating stormwater in facilities located at the bottom of drainage areas, LID addresses stormwater through small, landscape features located at the lot level. With regard to application and acceptance of LID in Denver, it is important to note that LID concepts can be integrated into the first step of the UDFCD BMP selection process, which is employing runoff reduction techniques. In Denver, structural BMPs are then required to treat the remaining Water Quality Capture Volume (UDFCD 1999). Another key concept that has already been implemented in parts of Denver (e.g., Cherry Creek Basin, as discussed in Chapter 4) includes Green Development or Smart Growth strategies. These approaches are important in that they consider factors beyond the immediate development and redevelopment area, helping to minimize urban sprawl and its impacts, while recognizing the interconnectedness of the natural environment to development. Communities throughout the country have also moved toward these types of developments, including cities in Oregon, Maryland, Florida, California, Texas and others (See http://www.sustainable.doe.gov/greendev/ ). Zoning ordinances and municipal planning strategies are key components of Smart Growth and Green Development strategies and require cooperation across city departments and agencies. Denver should continue to pursue integration of these concepts due to their many benefits to both the community and the environment. Protective covenants are also a particularly noteworthy example of an effective land management strategy to minimize pollution. As an example, in the Grant Ranch and Trailmark subdivisions in Littleton upstream of Bow Mar Lake, specific guidance and restrictions were detailed in protective covenants to minimize adverse impacts to the water quality of the lake. Water quality monitoring upstream of the lake has shown that these covenants have helped to minimize the concentrations of nutrients and pesticides in runoff tributary to the lake (WWE 2004).

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Denver Water Quality Management Plan Chapter 7 Page 7-25 SUMMARY AND CONCLUSIONS Non-structural (pollutant source control) BMPs are critical to effective stormwater management in Denver and are foundational to many of Denver s CDPS permit requirements. Non-structural BMPs help to minimize the quantity of pollutants entering the storm drainage system, thereby reducing the treatment required at downstream structural BMPs. Non-structural BMPs are particularly important in areas that have already been developed. Denver has implemented many public education activities, which are necessary to the success of most non-structural BMPs. Specific opportunities for Denver that could be further developed in the future include: 1. Provide additional educational brochures and water pollution prevention resources on the Denver web site. For example, as discussed in Chapter 5, many of the national case studies provide extensive web-based resources. 2. Develop pollution prevention programs for specific industries that require further attention and/or partner with entities providing existing programs. For example, the City of Boulder s PACE program targets and provides educational information to specific industry segments including auto repair, auto body, green building, dental offices, dry cleaning, landscaping, manufacturing, printing, restaurant, and retail sectors. The City of Portland has a similar program the Eco-Logical Business Program. As an alternative to independently developing such programs, Denver can partner with professional organizations and industry groups to support their efforts in this type of training. For example, GreenCO is providing landscape BMP training for those in the landscaping industry in Colorado. Denver should support this effort and other similar efforts for other hot spot industry segments. 3. Educate developers and Denver staff on the benefits of land management strategies such as open space/natural areas preservation, riparian buffer zone protection, Smart Growth, Green Development, and Low Impact Development strategies. Many of these strategies are already practiced in the Denver area through stormwater management approaches that Minimize Directly Connected Impervious Area such as porous landscape detention, grassy swales and porous pavement. 4. Continue educational campaigns, both to the public and to Denver staff and elected officials.

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Chapter 8 Page 8-1 Chapter 8 Potential Regional Facilities Stormwater management can be handled on-site, at regional facilities, or through a combination of both. A variety of factors determine which approach is most effective. Some factors include: 4 Capital and operations/maintenance costs 4 Right-of-way availability 4 Property ownership 4 Extent of existing development 4 Extent of redevelopment 4 Extent of on-site BMPs already in place 4 Zoning 4 Land development review practices 4 Existing master drainage plans and their recommendations 4 Local drainage criteria 4 Special goals and objectives related to quantity and quality management 4 Other factors There are many benefits of larger, regional facilities such as their potential to serve as attractive, multi-purpose facilities that become true community assets. The following discussion identifies potential regional facility locations throughout Denver, especially in redevelopment areas identified in Blueprint Denver: An Integrated Land Use and Transportation Plan (Denver 2000), that could play a valuable role in protecting water quality, as well as fulfilling other objectives. All of the following discussion is provided at a conceptual level only. Considerable additional analysis will be necessary to determine if the following ideas are feasible. The Storm Drainage Master Plan Phase I Final (Matrix 2003) found the capacity of the drainage system within a majority of Denver correlates to between a 1and 5-year system. Although this limited capacity results in periodic flooding, the current systems offer opportunities for regional water quality treatment. The extensive existing drainage networks discharging through only a few outfalls provide opportunities to treat the entire basin runoff at the end-of-pipe, rather than (or in addition to) attempting to treat the runoff in a myriad of small in-tract ponds within the basin. The existing drainage systems provide adequate capacity to treat the first flush, or a storm of magnitude of -inch or less of runoff. In keeping with the major drainageways information included in the Storm Drainage Master Plan Exhibit 8.1 identifies the major Denver drainage basins. Exhibit 8.2 identifies potential opportunities for regional water quality facilities in these basins. Exhibit 2.3 in Chapter 2 should be referenced for more detailed basin locations by numeric code. A basin-by-basin discussion identifying the key drainage basin characteristics and regional water quality opportunities and constraints follows. These conceptual-level discussions will require additional follow-up work, as identified in Chapter 9, in order to make decisions regarding regional treatment.

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Denver Water Quality Management Plan Chapter 8 Page 8-7 SOUTH PLATTE RIVER Fourteen drainage basins tributary to the South Platter River are evaluated for regional stormwater treatment opportunities in this discussion, including: 4 Prairie Gateway 4 I-70 & Colorado Boulevard 4 I-70 & York 4 Lower Platte Valley 4 Central Platte Valley 4 1st & Federal 4 Valverde 4 Ruby Hill 4 Dartmouth 4 College View 4 West Belleview 4 Sloan s Lake 4 I-25 4 West Harvard Gulch Prairie Gateway (Basin 0058) EXHIBIT 8.3 BACKGROUND DATA FOR PRAIRIE GATEWAY (BASIN 0058) Location Description: 56 th and Quebec Receiving Waterway: South Platte River General Land Use: Commercial and Industrial (includes Denver Water Pump Station and Bulk Mail Facility) Drainage Basin Area: 1.59 square miles Basin Composite Imperviousness: 25% Outfalls: 100-year retention no outfall Capacity of Outfalls: 100-year pipes and detention pond Prairie Gateway is land along Quebec Street north of 56 th Avenue that was previously part of the Rocky Mountain Arsenal. The Prairie Gateway Outfall Systems Planning Preliminary Design Report (UDFCD 2003) explored options to manage stormwater runoff and determined 100-year retention systems to be the most feasible option. Opportunities All development in the drainage basin must retain and treat water quality on-site or in regional ponds. The basin is being newly developed and must adhere to the current guidelines of the Urban Drainage and Flood Control District (UDFCD) for drainage criteria.

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Potential Regional Facilities Chapter 8 Page 8-8 Constraints Commerce City s storm outfalls do not have the capacity to handle additional runoff; therefore, development must incorporate stormwater ponds into the site planning. I-70 & Colorado Boulevard (Basin 0060-01) Exhibit 8.4 summarizes key background data for the I-70 & Colorado Boulevard basin (Basin 0060-01). EXHIBIT 8.4 BACKGROUND DATA FOR I-70 & COLORADO BOULEVARD (BASIN 0060-01) Location Description: North Denver and Commerce City 35th to 64th Avenues, and York to Dahlia Streets Receiving Waterway: South Platte River General Land Use: Mix of industrial and residential Drainage Basin Area: 1,745 acres (2.73 square miles) Basin Composite Imperviousness: 68.7% Number of Outfalls and 2-Year Hydrology: 2 within Denver: 84 at 54th & Steele 581 cfs 38 at 58th & York 130 cfs Capacity of Outfalls: Generally less than 2-year Opportunities Basin 0060-01 is fully built-out with older neighborhood residential use in the upper reaches and commercial use in the lower reaches. Blueprint Denver shows the region downstream (northwest) of Vasquez Boulevard as an Area of Change, meaning that redevelopment is expected to occur in the area of the storm drain outfalls. This is an opportunity for installation of regional water quality treatment, especially since basin runoff is confined to only two outfalls within Denver. A gravel pit between 54th and 56th Avenues and Brighton Boulevard and the Railroad is an opportunity for an on-line regional water quality pond at the discharge of the 84-inch outfall. However, this site is located within Commerce City, but would primarily treat runoff from Denver. Vacant land is located northeast of Riverside Cemetery and would be an opportunity for off-line regional water quality treatment. Likewise, this site is located within Commerce City, but would primarily treat runoff from Denver. Another location for regional water quality treatment within this basin is Swansea Park. This Denver Parks land may provide an opportunity for off-line regional water quality ponds.

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Denver Water Quality Management Plan Chapter 8 Page 8-9 An alternatives analysis for combined capital improvements for Basins 0060-01 & 4400-02 found the least-cost solution included regional detention in this basin. Areas identified for regional detention exist at the Park Hill Golf Course, 48th & Colorado, 38th and Grape Street, and the former Dahlia Square. These detention ponds could also be configured for regional water quality treatment. Constraints The main constraint to regional water quality treatment is the fact that the outfalls occur outside of Denver in Commerce City. Either land areas must be identified within Denver for regional treatment, or an agreement must be structured with Commerce City for operation and maintenance of regional facilities. I-70 & York (Basin 0060-02) Exhibit 8.5 summarizes key background data for the I-70 & York basin (Basin 0060-02). EXHIBIT 8.5 BACKGROUND DATA FOR I-70 & YORK (BASIN 0060-02) Location Description: North Denver and Commerce City 42nd to 52nd Avenues, and Brighton to Colorado Boulevards Receiving Waterway: South Platte River General Land Use: Mix of industrial and residential (includes National Western Stock Show Complex) Drainage Basin Area: 936 acres (1.46 square miles) Basin Composite Imperviousness: 71.8% Number of Outfalls and 2-Year Hydrology: 12 within Denver Only large outfalls: 78 & parallel 42 at Race Court 381 cfs Capacity of Outfalls: 2-year The only major (larger than 48 inch) outfall exists at Race Court just upstream of the Burlington Ditch headgate. This outfall drains 580 tributary acres discharging via a 78-inch pipe and parallel 42-inch pipe that have a total capacity of about 410 cfs. The existing system has about a 2-year level of service.

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Potential Regional Facilities Chapter 8 Page 8-10 Opportunities Basin 0060-02 is fully built-out with older neighborhood residential use in the upper reaches and commercial use in the lower reaches. Blueprint Denver shows the industrial sites as Areas of Change, meaning that redevelopment is expected to occur in the area of the storm drain outfalls. This is an opportunity for installation of regional water quality treatment, especially since most of the basin runoff is primarily confined to the one outfall north of the National Western Stock Show complex at Race Court. Constraints If the expected redevelopment does not occur, then land acquisition would be necessary for a regional facility. No Denver Parks or Open Space land is available in this basin for regional water quality treatment. Lower Platte Valley (Basin 0062-01/4500-02) Exhibit 8.6 summarizes key background data for the Lower Platte Valley basin (Basin 006201/4500-02). EXHIBIT 8.6 BACKGROUND DATA FOR LOWER PLATTE VALLEY (BASIN 0062-01/4500-02) Location Description: North of Downtown Denver 8th to 38th Avenues, and Grant to Williams Streets, Includes Coors Field Receiving Waterway: South Platte River General Land Use: Mix of industrial, commercial and residential Drainage Basin Area: 2,858 acres (4.47 square miles) Basin Composite Imperviousness: 77.5% Number of Outfalls and 2-Year Hydrology: 16 outfalls 1 primary outfall captures 81% of the basin: 81 at 36th 1,215 cfs Capacity of Outfalls: Less than 1-year Basin 0062-01 is fully built-out with older neighborhood residential use in the upper reaches and commercial use in the lower reaches. This basin includes Lower Downtown, Coors Field, rail yards, and a number of existing residential neighborhoods. It is characterized by terrace topography in the upper portions of the basin and nearly flat outfalls near the South Platte River. This condition results in inadvertent detention near the basin headwaters and surcharge of storm sewers in lower reaches.

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Denver Water Quality Management Plan Chapter 8 Page 8-11 Opportunities There are opportunities for regional end-of-pipe water quality treatment along the South Platte River. An off-line water quality pond could be constructed near the outfall of the existing 81inch pipe in 36th Avenue. The existing pipe has capacity to convey a -inch rainfall event (i.e., water quality capture volume) and would capture runoff from 2,260 acres of a developed basin. Another opportunity for regional end-of-pipe water quality treatment is at 29 th and Broadway at an outfall to the South Platte River. An off-line water quality pond could be constructed off the existing 108-inch pipe through Coors Field. The pipe was recently constructed and receives runoff from 81 acres of the Coors Field parking lot. However, proposed improvements will extend the storm drain up 27 th Avenue and will expand the tributary area. Constraints If the expected redevelopment does not occur, then land acquisition would be necessary for a regional facility. No Denver Parks or Open Space land is currently available in this basin for regional water quality treatment. Central Platte Valley (Basin 0063-01) Exhibit 8.7 summarizes key background data for the Central Platte Valley (Basin 0063-01). EXHIBIT 8.7 BACKGROUND DATA FOR CENTRAL PLATTE VALLEY (BASIN 0063-01) Location Description: Southwest of Downtown Denver Alameda to Cherry Creek, along the South Platte River, Includes Elitch Gardens Receiving Waterway: South Platte River General Land Use: Mix of industrial, commercial and residential Drainage Basin Area: 1,342 acres (2.10 square miles) Basin Composite Imperviousness: 83.2% Number of Outfalls and 2-Year Hydrology: 32+ outfalls in total 6 primary outfalls Capacity of Outfalls: 1-year to 5-year This basin includes older neighborhood residential use in the upper reaches east of the railroad tracks and Santa Fe, and commercial use in the majority of the basin for the lower reaches. Blueprint Denver shows the majority of the basin (commercial areas) subject to change. Intercepted stormwater is discharged via at least 32 storm drainage outfalls, which are comprised mainly of local storm drains from I-25 and adjacent properties. Some of the existing larger outfalls include:

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Potential Regional Facilities Chapter 8 Page 8-12 4 Bayaud Avenue outfall is 36-inch (54-inch upstream) with 351 tributary acres 4 3rd Avenue outfall is 54-inch with 104 tributary acres 4 6th Avenue outfall is 72-inch with 273 tributary acres 4 13th Avenue outfall is 42-inch with 119 tributary acres 4 Colfax Avenue outfall is 36-inch with 53 tributary acres 4 Elitch s outfall is 48-inch with 44 tributary acres Opportunities Redevelopment of the lower industrial areas will provide an opportunity for construction of regional water quality systems. In particular, end-of-pipe water quality ponds on the larger outfalls may be possible. The 72-inch storm drain in 6 th and 7 th Avenues could be constructed with a low-flow diverter to treat runoff from 273 acres. Constraints If the expected redevelopment does not occur, then land acquisition would be necessary for a regional facility. No Denver Parks or Open Space land is currently available in this basin for regional water quality treatment. 1st & Federal (Basin 0064-01) Exhibit 8.8 summarizes key background data for the 1st & Federal basin (Basin 0064-01). EXHIBIT 8.8 BACKGROUND DATA FOR 1 ST AND FEDERAL BASIN (BASIN 0064-01) Location Description: West of Downtown Denver Between Alameda and 8th Avenue, and Between Perry Street and Bryant Street Receiving Waterway: Weir Gulch and South Platte River General Land Use: Mix of industrial, commercial and residential Drainage Basin Area: 610 acres (0.95 square mile) Basin Composite Imperviousness: 66.6% Number of Outfalls: 8 outfalls Capacity of Outfalls: 1-year to 5-year Blueprint Denver shows Federal Boulevard subject to change, along with some of the commercial/industrial area adjacent to the South Platte River. Intercepted stormwater is discharged in eight storm drainage outfalls that include two to Weir Gulch and six directly to the South Platte River.

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Denver Water Quality Management Plan Chapter 8 Page 8-13 Opportunities Redevelopment of the lower industrial areas may provide an opportunity for construction of regional water quality systems. An on-line water quality pond has been constructed and maintained on Weir Gulch at Barnum Park near 6th and Federal. Constraints Much of the industrial land is within the current South Platte River floodplain. No Denver parks or open space land is currently available in this basin for regional water quality treatment; therefore, land acquisition would be necessary to construct a regional facility. Valverde (Basin 0064-02) Exhibit 8.9 summarizes key background data for the Valverde basin (Basin 0064-02). EXHIBIT 8.9 BACKGROUND DATA FOR VALVERDE (BASIN 0064-02) Location Description: West of Downtown Denver Between Louisiana and 4 th Avenue, and Between Wolffe Street and the South Platte River Receiving Waterway: South Platte River General Land Use: Mix of industrial and residential Drainage Basin Area: 1,701 acres (2.66 square miles) Basin Composite Imperviousness: 69.2% Number of Outfalls and 2-Year Hydrology: 15 outfalls 1 outfall captures 55% of the basin: 54 x108 at Vallejo Street 309 cfs Capacity of Outfalls: Generally 2-year Basin 0064-02 is fully built-out with older neighborhood residential use in the upper reaches and commercial use in the lower reaches. Blueprint Denver shows Federal Boulevard, Alameda Avenue, and Morrison Road subject to change, along with some of the commercial/industrial areas adjacent to the South Platte River. Intercepted stormwater is discharged in fifteen storm drainage outfalls. Opportunities A regional detention facility is located at West-Bar-Val-Wood Park, which serves the largest stormwater outfall system in the basin (Vallejo Street). The detention facility provides an opportunity for water quality treatment.

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Potential Regional Facilities Chapter 8 Page 8-14 Blueprint Denver shows an area of expected redevelopment along the South Platte River. This area could provide an additional opportunity for regional water quality near the outfall of the Vallejo Street system. An existing pond in Vanderbilt Park could provide water quality treatment for the storm drain system in the southern portion of the basin along Mississippi Avenue. Constraints This basin is fully built-out with dense development, and the high cost of real estate prohibits land acquisition for regional facilities. Ruby Hill (Basin 0065-01) Exhibit 8.10 summarizes key background data for the Ruby Hill basin (Basin 0065-01). EXHIBIT 8.10 BACKGROUND DATA FOR SOUTH PLATTE RUBY HILL (BASIN 0065-01) Location Description: South Platte River Drive and West Evans Avenue in West Denver Receiving Waterway: South Platte River General Land Use: Mix of industrial and residential Drainage Basin Area: 832 acres (1.3 square miles) Basin Composite Imperviousness: 70.1% Number of Outfalls: 5 existing to South Platte River Capacity of Outfalls: 2-year to 5-year capacity for existing Currently, there are only five known outfalls into the South Platte River within this basin: 4 48-inch from West Evans outfalls at Jewell Avenue 4 36-inch by 58-inch from West Evans outfalls at Jewell Avenue 4 Direct flow from the southern basin 4 Two 36-inch outfalls This basin is fully built-out with neighborhood residential use in the upper reaches and commercial/light industrial in the lower reaches. Blueprint Denver shows the region along both sides of Federal Boulevard as an Area of Change. This is an opportunity for installation of regional water quality treatment. Two existing off-line detention and water quality ponds are located at Pacific Place and South Tejon Street. Opportunities A small portion of this basin will be redeveloped. The redevelopment area along Federal Boulevard at West Warren Avenue would be an excellent opportunity to provide water quality and detention.

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Denver Water Quality Management Plan Chapter 8 Page 8-15 Constraints Redevelopment of the site must occur before regional water quality treatment could be constructed. Coordination with private property owners must occur. Dartmouth (Basin 0065-02) Exhibit 8.11 summarizes key background data for the Dartmouth basin (Basin 0065-02). EXHIBIT 8.11 BACKGROUND DATA FOR SOUTH PLATTE-DARTMOUTH (BASIN 0065-02) Location Description: South Platte River Drive and West Dartmouth Avenue in West Denver Receiving Waterway: South Platte River General Land Use: Mix of industrial and residential Drainage Basin Area: 512 acres (0.8 square mile) Basin Composite Imperviousness: 86.8% Number of Outfalls: 1 existing to South Platte River Capacity of Outfalls: 2-year to 5-year capacity for existing Currently, there is only one known outfall into the South Platte River within this basin: 4 73-inch by 55-inch from West Dartmouth Avenue This basin is fully built-out with light neighborhood residential and commercial/light industrial. Only a very small portion of this basin is within Denver. Opportunities No opportunities for regional water quality have been identified for this basin. Constraints The majority of the basin is outside of Denver city limits.

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Potential Regional Facilities Chapter 8 Page 8-16 College View (Basin 0067-01) Exhibit 8.12 summarizes key background data for the College View basin (Basin 0067-01). EXHIBIT 8.12 BACKGROUND DATA FOR COLLEGE VIEW (BASIN 0067-01) Location Description: South Platte River Drive and West Union Avenue Receiving Waterway: South Platte River through Arapahoe County General Land Use: Mix of industrial, commercial and residential Drainage Basin Area: 960 acres (1.5 square miles) Basin Composite Imperviousness: 45.5% Number of Outfalls and 2-Year Hydrology: 2 existing to Park at Lowell and Quincy Avenue and South Federal and West Layton, 45 cfs and 166 cfs Capacity of Outfalls: 2-year to 5-year capacity for existing Outfalls include: 4 30-inch from West Quincy Avenue 4 42-inch from South Federal Boulevard This basin is fully built-out with neighborhood residential and commercial/light industrial use. Only a very small portion of this basin is within Denver. Opportunities The park at South Irving and West Quincy Street is an excellent opportunity for water quality and on-line detention. It is located directly at the outfall across Lowell Boulevard and would benefit the upstream portion of the basin. Constraints The majority of the basin is outside of Denver. Discharge agreements with the City of Sheridan would need to be in place before constructing the facility.

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Denver Water Quality Management Plan Chapter 8 Page 8-17 West Belleview Avenue (Basin 0067-02) Exhibit 8.13 summarizes key background data for the West Belleview Avenue basin (Basin 0067-02). EXHIBIT 8.13 BACKGROUND DATA FOR WEST BELLEVIEW AVENUE (BASIN 0067-02) Location Description: South Sheridan Boulevard, West Denver Receiving Waterway: South Platte River through Jefferson County General Land Use: Mix of industrial, commercial and residential Drainage Basin Area: 3,520 acres (5.5 square miles) Basin Composite Imperviousness: 52.0% Number of Outfalls and 2-Year Hydrology: 4 existing to existing storm sewers within Jefferson County: 110 cfs, 30 cfs, 16 cfs (from Grant Ranch) and 191 cfs (from South Meade Street) Capacity of Outfalls: 2-year to 5-year capacity for existing Outfalls include: 4 Future 48-inch from South Meade Street 4 Existing 24-inch to 36-inch from Grant Ranch This basin is fully developed with neighborhood residential and commercial/light industrial use. Only a very small portion of this basin is within Denver. Opportunities No new regional water quality facilities in Denver are needed for this basin because Grant Ranch has newly constructed water quality and detention facilities. Constraints The majority of the basin is outside of Denver. Existing discharge agreements with surrounding municipalities would need to be considered before any improvements could be constructed.

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Potential Regional Facilities Chapter 8 Page 8-18 Sloan s Lake (Basin 4700-01) Exhibit 8.14 summarizes key background data for Sloan s Lake basin (Basin 4700-01). EXHIBIT 8.14 BACKGROUND DATA FOR SLOAN S LAKE (BASIN 4700-01) Location Description: West of Downtown Denver Between 33 rd and Colfax Avenues, and Sheridan Boulevard and the South Platte River Receiving Waterway: South Platte River General Land Use: Mix of industrial and residential Drainage Basin Area: 1,017 acres (1.59 square miles) within Denver Basin Composite Imperviousness: 65.0% Number of Outfalls: 1 outfall 54 along Colfax Avenue Capacity of Outfalls: Less than 2-year Basin 4700-01 is fully built-out (within Denver) with older neighborhood residential use in the upper reaches and commercial use in the lower reaches and Colfax Avenue. This basin includes Sloan s Lake, which provides significant stormwater detention for a 3.7-square-mile tributary area from Lakewood, Edgewater, and Wheatridge. Opportunities Sloan s Lake could provide water quality opportunities for a large, urbanized drainage basin. The lake occupies 176.5 acres. Redevelopment of the commercial areas along Colfax Avenue could provide an opportunity for construction of more localized water quality systems below Sloan s Lake. Constraints This basin is fully built-out with dense development, and real estate acquisition would be a constraint for regional facilities.

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Denver Water Quality Management Plan Chapter 8 Page 8-19 I-25 (Basin 5000-01) Exhibit 8.15 summarizes key background data for the I-25 basin (Basin 5000-01). EXHIBIT 8.15 BACKGROUND DATA FOR I-25 (BASIN 5000-01) Location Description: Mississippi to Alameda Avenues, and I-25 to Downing Street Receiving Waterway: South Platte River across I-25 General Land Use: Mix of commercial and residential Drainage Basin Area: 802.6 acres (1.25 square miles) Basin Composite Imperviousness: 71.9% Number of Outfalls and 2-Year Hydrology: 13+ outfalls, primary outfall is a 54 at Center Street 387 cfs Capacity of Outfalls: Approximately 1-year Intercepted stormwater is discharged into the South Platte River. The outfalls include: 4 54-inch with 602 tributary acres, or 75% of Basin 5000-01 4 36-inch for the I-25 & Santa Fe intersection 4 30-inch for the Santa Fe & Alameda intersection 4 30-inch for the Alameda & I-25 intersection 4 2-24-inch for local I-25 drainage 4 2-18-inch for local I-25 drainage 4 5-15-inch for local I-25 drainage Opportunities Basin 5000-01 is fully built-out with older neighborhood residential use in the upper reaches and commercial use in the lower reaches. Blueprint Denver shows the commercial sites as Areas of Change, meaning that redevelopment is expected to occur in the area of the storm drain outfalls. This is an opportunity for installation of regional water quality treatment, especially since most of the basin runoff is primarily confined to the one outfall in Center Avenue. The regional pond could be located near the Home Depot at Santa Fe and Alameda. Smaller drain outfalls from the highway and adjacent industrial/commercial land along the Platte River Valley could be treated using ultra-urban retrofits. This may include mechanical treatment systems or other BMPs, and would require a regular maintenance program. The lack of existing BMPs on outfalls in this area may warrant these additional measures. Constraints If the expected redevelopment does not occur, then land acquisition would be necessary for a regional facility. No Denver Parks or Open Space land is currently available in this basin for regional water quality treatment.

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Potential Regional Facilities Chapter 8 Page 8-20 West Harvard Gulch (Basin 5300-01) Exhibit 8.16 summarizes key background data for the West Harvard Gulch basin (Basin 530001). EXHIBIT 8.16 BACKGROUND DATA FOR WEST HARVARD GULCH (BASIN 5300-01) Location Description: South Platte River Drive and West Yale Avenue Denver and Englewood Receiving Waterway: South Platte River General Land Use: Mix of industrial, commercial and residential Drainage Basin Area: 896 acres (1.4 square miles) Basin Composite Imperviousness: 57.1% Number of Outfalls: 1 existing directly to South Platte River Capacity of Outfalls: 2-year to 5-year capacity for existing This basin is fully built-out with neighborhood residential and commercial/light industrial. A large portion of this basin is within Englewood and is an open channel. Opportunities The open parcel at Federal Boulevard and West Vassar Avenue provides an excellent opportunity for water quality and on-line detention. It is located directly at the 54-inch outfall that serves the entire upper portion of the highly developed upstream residential area. The lower portion of the West Harvard Gulch provides a unique opportunity for water quality and detention. The gulch passes through a commercial gravel operation and is an excellent location for water quality. Constraints Discharge agreements with Englewood would need to be reviewed before constructing regional facilities. Land would have to be acquiredfor regional facilities.

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Denver Water Quality Management Plan Chapter 8 Page 8-21 FIRST CREEK First Creek (Basin 3700) Exhibit 8.17 summarizes key background data for the First Creek basin (Basin 3700). EXHIBIT 8.17 BACKGROUND DATA FOR FIRST CREEK (BASIN 3700) Location Description: Near DIA at Pena & 56 th Avenue Flows through Aurora, Adams County, Denver, Rocky Mountain Arsenal and Commerce City Receiving Waterway: Outfalls to the South Platte River at approximately East 128 th Avenue General Land Use: Commercial and residential in headwaters Open space through Rocky Mountain Arsenal Cultivated land in Commerce City Drainage Basin Area: 47.2 square miles (About 9.62 square miles in Denver) Basin Composite Imperviousness: About 48% in upper reaches Number of Outfalls: Tributary Blue Grama tributary Dogwood West tributary Capacity of Outfalls: 100-year wetland channels, pipes and detention ponds First Creek crosses Pena Boulevard just north of 56 th Avenue and then flows through the northeastern portion of the Rocky Mountain Arsenal. The upper reaches of First Creek are being developed with regional detention and water quality ponds. Toward the center of the basin, First Creek bisects Green Valley Ranch, which consists of medium-density, single-family residences. First Creek then enters Rocky Mountain Arsenal with a more incised, low-flow channel and wider floodplain areas. The lower First Creek basin consists of irrigated farmland with pockets of light industrial and residential properties. In the lower reaches, First Creek flows across the Brian Canal and the Burlington Ditch, which intercept low flow runoff. Opportunities All development in the First Creek drainage basin must detain and treat water quality on-site or in regional ponds. The Rocky Mountain Arsenal has strict agreements for the quantity and quality of stormwater runoff into the federal property. The main regional pond in the upper reaches is the Green Valley Ranch Golf Course pond, also known as the Himalaya Pond. There are also regional detention ponds adjacent to Pena Boulevard.

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Potential Regional Facilities Chapter 8 Page 8-22 Constraints Since this basin is recently developed, drainage master plans have required incorporation of regional water quality and detention into land planning. Developers must adhere to the current UDFCD drainage criteria guidelines. IRONDALE GULCH Irondale Gulch (Basins 3900 & 3901) Exhibit 8.18 summarizes key background data for Irondale Gulch basins (Basins 3900 and 3901). EXHIBIT 8.18 BACKGROUND DATA FOR IRONDALE GULCHES (BASINS 3900 & 3901) Location Description: North of I-70 and east of Quebec Flows through Aurora, Adams County, Denver, Rocky Mountain Arsenal, and Commerce City Receiving Waterway: Outfalls to the South Platte River at approximately East 96 th Avenue General Land Use: Commercial/Industrial in headwaters Residential in upper reaches Open space through Rocky Mountain Arsenal Cultivated land in Commerce City Drainage Basin Area: 26.7 square miles (about 12.48 square miles in Denver) Basin Composite Imperviousness: 50% in upper reaches Number of Outfalls: Southern tributary to Havana Lateral at Havana & 56 th Avenue Center tributary to Derby Lake in Rocky Mountain Arsenal Northern tributary to Highline Lateral for outfall to Parkfield II detention at Chambers and 56 th Avenue Capacity of Outfalls: 100-year pipes and detention ponds 10-year concrete open channels 100-year natural channels Irondale Gulch drains through the areas of Aurora s Majestic Commerce Center, Green Valley Ranch residential area, Gateway commercial and multi-family area, Silverado Subdivision, Parkfield Subdivision, Montbello Subdivision, the Rocky Mountain Arsenal and Commerce City with an eventual outfall to the South Platte River at approximately East 96 th Avenue. The drainageway throughout the basin and the Arsenal contains several lakes, ponds and detention

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Denver Water Quality Management Plan Chapter 8 Page 8-23 areas. The drainage below the Arsenal is primarily storm sewer or roadside ditches, with capacity for only minor floods. Opportunities All development along Irondale Gulch must either detain or treat water quality on-site or in regional ponds. The Rocky Mountain Arsenal has strict agreements for the quantity and quality of stormwater runoff into the federal property. Constraints Since this basin is recently developed, drainage master plans have required incorporation of water quality and detention into land planning. CLEAR CREEK Clear Creek (Basins 4300-03 & 4309-01) Exhibit 8.19 summarizes key background data for the Clear Creek basins (Basin 4300-03 and 4309-01). EXHIBIT 8.19 BACKGROUND DATA FOR CLEAR CREEK (BASINS 4300-03 & 4309-01) Location Description: Northwest Denver and Arvada Between I-76 and 32 nd Avenue Between Harlan Street and Alcott Street Receiving Waterway: Clear Creek General Land Use: Mostly residential with some commercial including golf course and Regis University Drainage Basin Area: 2,316 acres (3.62 square miles) Basin Composite Imperviousness: 56.6% Number of Outfalls: 4 (from Denver drainage systems) 66 outfall drains Berkeley Lake Capacity of Outfalls: 2-year The only major (larger than 48 inch) outfall exists at Sheridan Boulevard in Arvada. This outfall drains 1,343 tributary acres which includes the Berkeley Lake basin to the South. The outfall is a 66-inch pipe with a capacity of about 184 cfs (0.15% slope). The existing system further up in the basin and within Denver has a capacity of about 350 cfs (60 at 1.8%), which is approximately a 2-year capacity. Opportunities Berkeley Lake and Rocky Mountain Lake provide water quality treatment for the majority of tributary drainage area within Denver.

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Potential Regional Facilities Chapter 8 Page 8-24 Constraints With the exception of small outfalls at 52 nd Avenue and 50 th Avenue, the major outfalls occur outside of Denver in Arvada. SAND CREEK Four drainage basins tributary to Sand Creek are evaluated for regional stormwater treatment opportunities in this discussion, including: 4 North Stapleton (Basin 4400-01) 4 Quebec Corridor (Basin 4400-02) 4 South Stapleton (Basin 4400-03) 4 East Stapleton (Basin 4400-04) North Stapleton (Basin 4400-01) Exhibit 8.20 summarizes key background data for the North Stapleton basin (Basin 4400-01). EXHIBIT 8.20 BACKGROUND DATA FOR NORTH STAPLETON (BASIN 4400-01) Location Description: North Stapleton Quebec to Havana, and I-70 to 56 th Avenue Receiving Waterway: Sand Creek General Land Use: Redevelopment of Stapleton Airport Drainage Basin Area: 3,183 acres (4.97 square miles) Basin Composite Imperviousness: 42.4% Number of Outfalls: 1 existing to Sand Creek 3 new outfalls proposed Capacity of Outfalls: 100-year capacity Currently, drainage for areas north of I-70 flows to the north into the Rocky Mountain Arsenal. Only one formal major outfall currently exists to Sand Creek: the Colorado Department of Transportation (CDOT) storm pipe for the I-70 corridor, which flows in a storm pipe system parallel to I-70 into Sand Creek. In the future, all drainage from the basin will discharge through only three outfall locations into Sand Creek. Regional water quality treatment is proposed at these three outfalls. The Sand Creek floodplain significantly encumbers the site between Sand Creek and I-70 and will eventually become more confined via implementation of the Sand Creek Master Plan channel improvements. Little drainage infrastructure currently exists in this undeveloped basin, except for the Catellus site, west of and adjacent to Havana. Since no major outfall exists today for the area, 100-year

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Denver Water Quality Management Plan Chapter 8 Page 8-25 retention has been constructed. Water is metered-out through small storm drains to allow the ponds to dry between storms. Opportunities The East Stapleton Development Plan: The Green Book (Green Book) (Denver 1995) and Outfall Systems Plan-Stapleton Area (OSP) (Denver and UDFCD 1995) set the plan for future drainage. The current master planning document is the Infrastructure Master Plan (BRW 2000), which was approved by Denver Wastewater in April 2001 and generally adheres to the concepts in the OSP. One exception is that the OSP did not include a water quality component in the North Area regional detention basin. The OSP was predicated upon on-site MDCIA (Level 2), gross pollutant removal and water quality facilities (extended detention basins). The Urban Storm Drainage Criteria Manual, Volume 3 (UDFCD 1999) included guidelines for water quality treatment within the detention basin, and this concept has been adopted in the new Storm Drainage Master Plan updates. The land plan retains the Green Book concept of establishing a major drainageway called the North Stapleton Outfall Channel. This major drainageway receives almost all runoff generated on the North Stapleton site. The conveyance is a large channel, where multiple uses are envisioned within the proposed drainage corridor. The proposed pond at the outfall is sized to store the 100-year hydrograph without overtopping, and includes a multi-stage outlet for water quality treatment. Constraints None were identified because regional water quality treatment of this basin is already planned for when the site is redeveloped. Quebec Corridor (Basin 4400-02) Exhibit 8.21 summarizes key background data for the Quebec Corridor (Basin 4400-02). EXHIBIT 8.21 BACKGROUND DATA FOR QUEBEC CORRIDOR (BASIN 4400-02) Location Description: North Denver and Commerce City 12th to 52nd Avenues, and Quebec to Dahlia Streets Receiving Waterway: Sand Creek General Land Use: Mix of industrial and residential Drainage Basin Area: 3,206 acres (4.61 square miles) Basin Composite Imperviousness: 65.0% Number of Outfalls and 2-Year Hydrology: 1 primary within Denver: 90 & parallel 60 in Dahlia 1,161 cfs Capacity of Outfalls: Less than 5-year

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Potential Regional Facilities Chapter 8 Page 8-26 This basin is fully built-out with older neighborhood residential use in the upper reaches and commercial use in the lower reaches. Blueprint Denver shows the entire basin as an Area of Stability, inferring that Basin 4400-02 is not an area of future land use change. However, corridor studies are now being initiated for this segment of I-70 that will evaluate the need for highway and commuter rail improvements and identify related transit-oriented development (TOD) opportunities. Opportunities Redevelopment of land within these basins would generally require a 100-year drainage system and improvement of highway and rail drainage facilities for a 50-year conveyance system. It is assumed that additional locations for stormwater detention or related conveyance improvements would be planned and constructed as part of the improvement programs associated with any enhanced use within the area. An alternatives analysis for combined capital improvements for Basins 0060-01 and 4400-02 found the least-cost solution included regional detention in this basin. Areas identified for regional detention exist at the Park Hill Golf Course, 48 th and Colorado, future Denver Police Department site at 38 th and Grape Street, and Dahlia Square. These detention ponds could also be configured for water quality treatment as well. Since most of the basin is discharged though one outfall in Dahlia Street, there is an opportunity for an off-line regional water quality facility near the outfall. The pond could treat collected runoff regionally at the end of pipe before discharging into Sand Creek. However, end-of-pipe treatment would locate the pond in Commerce City. Constraints The main constraint to regional water quality treatment is the fact that the outfalls occur outside of Denver in Commerce City. Either land areas must be identified within Denver for regional treatment, or an agreement must be structured with Commerce City for operation and maintenance of regional facilities.

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Denver Water Quality Management Plan Chapter 8 Page 8-27 South Stapleton (Basin 4400-03) Exhibit 8.22 summarizes key background data for the South Stapleton basin (Basin 4400-03). EXHIBIT 8.22 BACKGROUND DATA FOR SOUTH STAPLETON (BASIN 4400-03) Location Description: South Stapleton Quebec to Havana, and Montview to I-70 Receiving Waterway: Sand Creek General Land Use: Redevelopment of Stapleton Airport Drainage Basin Area: 1,016 acres (1.59 square miles) Basin Composite Imperviousness: 70.8% Number of Outfalls: 5 existing to Sand Creek Capacity of Outfalls: 5-year capacity for existing 100-Year capacity for new systems This basin will be almost completely redeveloped. South of I-70, only water quality detention is required, provided that the full 100-year storm is conveyed directly to the receiving major drainageway without impact to downstream properties. Therefore, all new Stapleton drainage systems are designed for 100-year capacity. Opportunities The Green Book and OSP (Denver and UDFCD 1995) set the plan for future drainage. The current document is the Infrastructure Master Plan (BRW 2000), which was approved by Denver Wastewater in April 2001 and which adheres to the concepts in the OSP. Stapleton Filing No. 1 was recently developed to include in-tract water quality treatment. East of Filing 1 at Stapleton, stormwater will be directed easterly to the proposed regional outfall system discharging at Smith Road and Sand Creek (near RK Mechanical). Several proposed outfalls will be combined into one large regional water quality pond near Smith Road and Sand Creek. Approximately 285 tributary acres will be conveyed to this proposed regional water quality pond via three new storm drains. Constraints Redevelopment of the site must occur before regional water quality treatment can be constructed.

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Potential Regional Facilities Chapter 8 Page 8-28 East Stapleton (Basin 4400-04) Exhibit 8.23 summarizes key background data for the East Stapleton basin (Basin 4400-04). EXHIBIT 8.23 BACKGROUND DATA FOR EAST STAPLETON (BASIN 4400-04) Location Description: East Stapleton Havana to Peoria, and Montview to I-70 Receiving Waterway: Sand Creek General Land Use: Redevelopment of Stapleton Airport Drainage Basin Area: 1,806 acres (2.82 square miles) Basin Composite Imperviousness: 73.3% Number of Outfalls and 2-Year Hydrology: 4 existing to Sand Creek Capacity of Outfalls: 2-year to 5-year capacity for existing 100-year capacity for new systems Currently, there are only four known outfalls into Sand Creek within this basin: 4 72-inch from Aurora from the south through the Stapleton site 4 84-inch in Havana from the north, collecting drainage along Smith Road and Havana 4 Open channel in Aurora from the north 4 I-70 corridor in a parallel storm pipe system to Sand Creek Drainage on the Stapleton site is currently informal with few storm drains, relying upon infiltration, evaporation and sheet flow to drain the site to Sand Creek. A 72-inch storm drain from Aurora currently flows north though the Stapleton site and discharges to Bluff Lake. This 72-inch pipe can convey runoff only up to the 5-year event. Drainage from the jail and other properties between Smith Road and I-70 is conveyed to Sand Creek in the 84-inch pipe. This pipe has approximate capacity for the 2-year discharge. The area south of Smith Road drains to open channels in Aurora and directly to Sand Creek. Opportunities This basin will be almost completely redeveloped. South of I-70, only water quality detention is required, provided that the full 100-year storm is conveyed directly to the receiving major drainageway without impact to downstream properties. Therefore, all new Stapleton drainage systems are designed for 100-year capacity. Discussions with Denver Parks Department suggest interest in the development of Bluff Lake (in the southeastern portion of the Stapleton site) for limited use as a water quality pond. This lake was formerly fed by Sand Creek via an irrigation-style channel, but this water supply is no longer active. Management plans for Bluff Lake propose to enhance its use as a public amenity and to encourage wetlands restoration. Therefore, additional water supply is desired for the site. Proposed grading plans for the Stapleton site direct stormwater flows to Bluff Lake to enhance

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Denver Water Quality Management Plan Chapter 8 Page 8-29 its water volume. A new 7-foot x 5-foot box culvert is proposed to discharge into Bluff Lake for regional water quality treatment. Storm drainage pipes in this area will be constructed commensurate with development. Constraints A portion of this basin is within Aurora. Redevelopment of the site must occur before regional water quality treatment could be constructed. WESTERLY CREEK Four drainage basins tributary to Westerly Creek are evaluated for regional stormwater treatment opportunities in this discussion, including: 4 South Stapleton (Basin 4401-01) 4 11 th Avenue to Montview (Basin 4401-02) 4 Lowry (Basin 4401-03) 4 Upper Westerly Creek (Basin 4401-04) South Stapleton (Basin 4401-01) Exhibit 8.24 summarizes key background data for the South Stapleton basin (Basin 4401-01). EXHIBIT 8.24 BACKGROUND DATA FOR SOUTH STAPLETON (BASIN 4401-01) Location Description: South Stapleton MLK to Montview, and Quebec to Peoria Receiving Waterway: Westerly Creek General Land Use: Redevelopment of Stapleton Airport Residential use in Aurora Drainage Basin Area: 1,939 acres (3.03 square miles) Basin Composite Imperviousness: 50.6% Number of Outfalls: 8 Capacity of Outfalls: 100-year Capacity The majority of this basin has been recently constructed or will be constructed soon as part of the Stapleton Redevelopment project. The portion south of 26 th Avenue and east of Westerly Creek that lies within the City of Aurora is primarily residential. Opportunities Regional water quality has been recommended in the Stapleton Infrastructure Master Plan Water quality ponds along Westerly Creek are to be installed as development progresses. No additional water quality is proposed for this basin.

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Potential Regional Facilities Chapter 8 Page 8-30 Constraints There are no constraints for implementation of the water quality ponds shown in the Stapleton Infrastructure Master Plan 11 th Avenue to Montview (Basin 4401-02) Exhibit 8.25 summarizes key background data for Basin 4401-02. EXHIBIT 8.25 BACKGROUND DATA FOR 11 TH AVENUE TO MONTVIEW (BASIN 4401-02) Location Description: South of Stapleton, north of Lowry Quebec to Peoria Receiving Waterway: Westerly Creek General Land Use: Residential with commercial along roadway corridors Drainage Basin Area: 1,811 acres (2.83 square miles) Basin Composite Imperviousness: 62.6% Number of Outfalls: 3 existing to Westerly Creek, 1 additional proposed Capacity of Outfalls: 2-year and 5-year capacity This basin is fully built-out with older neighborhood residential and commercial uses throughout and is not an area of future land use change. Opportunities No opportunities have been identified for regional water quality treatment. Water quality will be treated in-tract commensurate with new development. Constraints This basin is fully built out with dense development, and acquisition of real estate is a constraint for regional facilities.

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Denver Water Quality Management Plan Chapter 8 Page 8-31 Lowry (Basin 4401-03) Exhibit 8.26 summarizes key background data for the Lowry basin (Basin 4401-03). EXHIBIT 8.26 BACKGROUND DATA FOR LOWRY (BASIN 4401-03) Location Description: Lowry 11 th Avenue to Alameda, Quebec to Havana Receiving Waterway: Westerly Creek General Land Use: Redevelopment of Lowry Air Force Base Mixed use of residential, commercial Drainage Basin Area: 2,246 acres (3.51 square miles) Basin Composite Imperviousness: 40.6% Number of Outfalls: 5 Capacity of Outfalls: 100-year capacity The majority of this basin has been recently constructed as part of the Lowry Redevelopment project. Opportunities Water quality has been provided as master planned in the Lowry Master Drainage Plan (BRW 1998) at two locations: Westerly Creek Pond Dam and Kelly Road Dam. All water flowing into Westerly Creek within the Lowry Redevelopment area is treated at Kelly Road Dam. No additional water quality is proposed for this basin. Constraints There are no constraints for implementation of the regional water quality ponds shown in the Lowry Master Drainage Plan.

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Potential Regional Facilities Chapter 8 Page 8-32 Upper Westerly Creek (Basin 4401-04) Exhibit 8.27 summarizes key background data for the Upper Westerly Creek basin (Basin 440104). EXHIBIT 8.27 BACKGROUND DATA FOR UPPER WESTERLY CREEK (BASIN 4401-04) Location Description: South of Lowry Alameda to Jewell, west of Havana Receiving Waterway: Westerly Creek General Land Use: Residential and commercial mix Drainage Basin Area: 1,824 acres (2.85 square miles) Basin Composite Imperviousness: 55.6% Number of Outfalls: 5 existing Capacity of Outfalls: 2-year and 5-year capacity This basin is mostly built-out with neighborhood residential and commercial uses throughout, and major redevelopment within the basin is not anticipated. Opportunities All runoff flows north to the Westerly Creek Pond Dam where it is treated for water quality. No additional water quality facilities have been proposed within the basin. Constraints This basin is fully built out with dense development, and acquisition of land is required for regional facilities.

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Denver Water Quality Management Plan Chapter 8 Page 8-33 CHERRY CREEK Four drainage basins tributary to Cherry Creek are evaluated for regional stormwater treatment opportunities in this discussion, including: 4 Central Business District (Basin 4600-01) 4 Cherry Creek Mall (Basin 4600-02) 4 Upper Cherry Creek (Basin 4600-03) 4 Upper Cherry Creek (Basin 4600-04) Central Business District (Basin 4600-01) Exhibit 8.28 summarizes key background data for the Central Business District basin (Basin 4600-01). EXHIBIT 8.28 BACKGROUND DATA FOR CENTRAL BUSINESS DISTRICT (BASIN 4600-01) Location Description: Downtown Denver 6th Avenue to the South Platte River along the lower Cherry Creek corridor Receiving Waterway: Cherry Creek General Land Use: Commercial Drainage Basin Area: 1,392 acres (2.17 square miles) Basin Composite Imperviousness: 83.2% Number of Outfalls: 42 outfalls Capacity of Outfalls: 2-year to 5-year Intercepted stormwater is discharged into Cherry Creek. Some of the major outfalls include: 4 16-foot x 4-foot box culvert from the Pepsi Center 4 10-foot x 5-foot box culvert recently constructed for the Convention Center up to 14th and Stout Street 4 96-inch pipe outfalling at 14th and Market Street draining large pipe in Larimer Street 4 54-inch pipe from Delgany Street Opportunities No opportunities have been identified for regional water quality treatment. Water quality will be treated in-tract commensurate with new development. Constraints This basin is fully built out with dense development, and the high cost of downtown real estate is a constraint for acquisition for regional stormwater facilities.

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Potential Regional Facilities Chapter 8 Page 8-34 Cherry Creek Mall (Basin 4600-02) Exhibit 8.29 summarizes key background data for the Cherry Creek Mall basin (Basin 4600-02). EXHIBIT 8.29 BACKGROUND DATA FOR CHERRY CREEK MALL (BASIN 4600-02) Location Description: 6th Avenue to Colorado Boulevard Along the Cherry Creek corridor Includes the Denver Country Club and Cherry Creek Mall Receiving Waterway: Cherry Creek General Land Use: Commercial and residential Drainage Basin Area: 2,952 acres (4.61 square miles) Basin Composite Imperviousness: 57.7% Number of Outfalls: 24 outfalls Capacity of Outfalls: 2-year to 5-year Intercepted stormwater is discharged into Cherry Creek. Some of the major outfalls include: 4 56-inch pipe at 1st and Marion Street 4 66-inch pipe from Cherry Creek Mall at University Boulevard and Cherry Creek 4 60-inch pipe from the east side of the Cherry Creek Mall near Steele Street 4 3-foot x 8-foot box culvert in Steele Street 4 48-inch x 76-inch elliptical pipe in Colorado Boulevard north of Cherry Creek 4 66-inch pipe at Garfield Street and Cherry Creek 4 42-inch pipe from University Boulevard south of Cherry Creek 4 72-inch pipe from Washington Street south of Cherry Creek draining 618 acres Opportunities No easy opportunities have been identified for regional water quality treatment. Water quality will generally be treated in-tract commensurate with new development. However, there may be an opportunity on the existing 66-inch pipe at University Boulevard that captures runoff from 44 acres of dense commercial development and parking at the mall. This storm sewer could be daylighted and detention constructed if some peripheral parking area were sacrificed. Constraints This basin is fully built-out with dense development, and the high cost of real estate prohibits acquisition for regional facilities. The many outfalls preclude construction of a few regional facilities. There are no opportunities for on-line water quality treatment within Cherry Creek.

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Denver Water Quality Management Plan Chapter 8 Page 8-35 Upper Cherry Creek (Basin 4600-03) Exhibit 8.30 summarizes key background data for the Upper Cherry Creek basin (Basin 460003). EXHIBIT 8.30 BACKGROUND DATA FOR UPPER CHERRY CREEK (BASIN 4600-03) Location Description: Denver, Glendale, and Aurora Colorado Boulevard to Quebec Along the Cherry Creek corridor Receiving Waterway: Cherry Creek General Land Use: Commercial and residential Drainage Basin Area: 3,597 acres (5.62 square miles) Basin Composite Imperviousness: 68.9% Number of Outfalls: 19 Outfalls Capacity of Outfalls: 2-year to 5-year The lower reach of this basin is outside Denver limits in the City of Glendale. The upper reaches of the basin are in Aurora. Most of this basin has been developed into neighborhood residential use and parks. Blueprint Denver shows the entire basin as an Area of Stability. No areas have been identified as Areas of Change. This basin is characterized by smaller tributaries to Cherry Creek with travel paths generally less than one mile to each outfall. This reach of the Cherry Creek basin includes the Goldsmith Gulch outfall. Opportunities No opportunities have been identified for regional water quality treatment. Water quality will be treated in-tract commensurate with new development. Constraints This basin is fully built-out with dense development, and land acquisition is necessary for regional facilities. No opportunities for regional detention were identified in this basin. The many outfalls preclude construction of only a few regional facilities. There are no opportunities for on-line water quality treatment within Cherry Creek.

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Potential Regional Facilities Chapter 8 Page 8-36 Upper Cherry Creek (Basin 4600-04) Exhibit 8.31 summarizes key background data for the Upper Cherry Creek basin (Basin 460004). EXHIBIT 8.31 BACKGROUND DATA FOR UPPER CHERRY CREEK (BASIN 4600-04) Location Description: Denver and Aurora Parker Road, I-225, Yosemite Street Along the Cherry Creek corridor Receiving Waterway: Cherry Creek General Land Use: Commercial and residential Drainage Basin Area: 3,693 acres (5.77 square miles) Basin Composite Imperviousness: 51.3% Number of Outfalls: 14 outfalls Capacity of Outfalls: 2-year to 5-year The lower reach of this basin is outside Denver limits in the City of Aurora. Most of this basin has been developed into neighborhood residential use and parks, with commercial use along major roadway corridors. This basin is characterized by smaller tributaries to Cherry Creek with travel paths generally less than 1 mile to each outfall. There are three major outfalls in the basin, all located near the point where Cherry Creek passes under Hampden Avenue. Opportunities A new stormwater detention pond is proposed in the undeveloped parcel of land owned by Denver Parks west of the intersection of Parker Road and Dartmouth Avenue, just north of the baseball fields. The parcel of land is approximately 4.6 acres in area. Incorporating water quality into a detention pond in this location would treat runoff from approximately 478 acres of land east of Parker Road prior to discharging into Cherry Creek. Two major storm sewer outfalls discharge into Cherry Creek within 1,200 feet of each other on the west side of Cherry Creek near Hampden Avenue and Dartmouth Avenue. An undeveloped parcel of land approximately 300 ft x 1,100 ft (7.6 acres) in area stretches between the two outfalls. A water quality feature in this location would treat runoff from approximately 728 acres of land to the west before it enters Cherry Creek. Constraints It is unclear if Denver Parks has plans for developing either parcels of land or if a water quality feature could be incorporated into whatever development plans they may have. Discussions with Denver Parks need to take place before either of these potential water quality treatment locations could be seriously considered.

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Denver Water Quality Management Plan Chapter 8 Page 8-37 GOLDSMITH GULCH Goldsmith Gulch (Basin 4601-01) Exhibit 8.32 summarizes key background data for the Goldsmith Gulch basin (Basin 4601-01). EXHIBIT 8.32 BACKGROUND DATA FOR GOLDSMITH GULCH (BASIN 4601-01) Location Description: I-225 and I-25 Interchange Receiving Waterway: Cherry Creek General Land Use: Mix of commercial and residential Drainage Basin Area: 4,992 acres (7.8 square miles) Basin Composite Imperviousness: 56.6% Number of Outfalls: 2 existing to Cherry Creek Capacity of Outfalls: 2-year to 5-year capacity for existing Outfalls include: 4 Open channel to Cherry Creek 4 72-inch by 120-inch from South Monaco Parkway This basin is fully built-out with neighborhood residential and commercial/light industrial. Only a very small portion of this basin is within Denver. The newly constructed I-25 and I-225 interchange includes off-line detention and water quality ponds as part of the storm sewer system. Opportunities Several existing parks and detention facilities located along Goldsmith Gulch provide an opportunity for water quality. Each park s detention facility could potentially be modified to meet the requirements for water quality. The locations of these facilities are Wallace Park, Rosamond Park, Bible Park, Iliff and Monaco, and Cherry Creek and Monaco. Constraints Each detention facility will have to be analyzed to determine the effect of modifying the facility with respect to flood attenuation. Agreements between Denver, Greenwood Village, and UDFCD would need to be in place before constructing any facilities.

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Potential Regional Facilities Chapter 8 Page 8-38 DRY GULCH AND LAKEWOOD GULCH The Dry Gulch and Lakewood Gulch basins are evaluated for regional stormwater treatment opportunities together in the following discussion. Dry Gulch is tributary to Lakewood Gulch, which is tributary to the South Platte River. Lakewood & Dry Gulches (Basins 4800-01 & 4801-01) Exhibit 8.33 summarizes key background data for the Lakewood Gulch and Dry Gulch basins (Basins 4800-01 & 4801-01). EXHIBIT 8.33 BACKGROUND DATA FOR LAKEWOOD & DRY GULCHES (BASINS 4800-01 & 4801-01) Location Description: 6 th to Colfax Avenues, and Sheridan to Federal Receiving Waterway: Lakewood Gulch and Dry Gulch, a tributary of Lakewood Gulch All tributary to the South Platte River General Land Use: Primarily residential Drainage Basin Area: Lakewood Gulch: 750 acres (1.17 square miles) Dry Gulch: 248 acres (0.39 square mile) Basin Composite Imperviousness: Lakewood Gulch: 59.6% Dry Gulch: 62.0% Number of Outfalls and 2-Year Hydrology: 1 pipe outfall larger than 24 : 39 at Lowell Boulevard 106 cfs Capacity of Outfalls: About 2-year Lakewood Gulch is a major drainageway with a 16-square-mile watershed, and Dry Gulch is a north bank tributary to Lakewood Gulch. Lakewood and Dry Gulch both discharge to the South Platte River. The gulches begin in Lakewood and terminate into the South Platte River at 14 th Avenue. Only about 10 percent of the total tributary area is within Denver. The basins are long and narrow, running west to east. The basins within Denver are fully built-out primarily with neighborhood residential use, except for commercial use along arterial transportation corridors. Blueprint Denver shows linear corridors along Dry Gulch and Colfax subject to change. There are proposed light rail and other transit-oriented improvements that may occur in these basins in the future. Runoff generally flows down the relatively steep roadways into these major drainageways. Relatively little storm pipe is necessary in these basins due to the capacity of the streets to convey stormwater. Intercepted stormwater in the pipes is discharged in small, local storm drainage outfalls to the drainageways.

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Denver Water Quality Management Plan Chapter 8 Page 8-39 Opportunities An on-line water quality pond could be constructed on Dry Gulch or Lakewood Gulch. However, due to the high peak flows, configuring a water quality pond to retain trapped sediment and trash would be a design challenge. Constraints There are no opportunities to construct a regional water quality pond at the end-of-pipe. No land has been identified within the gulches for on-line water quality ponds. WEIR GULCH Weir Gulch (Basin 4900-01) Exhibit 8.34 summarizes key background data for the Weir Gulch basin (Basin 4900-01). EXHIBIT 8.34 BACKGROUND DATA FOR WEIR GULCH (BASIN 4900-01) Location Description: West of Downtown Denver Between 9 th and Kentucky Avenues, and Sheridan Boulevard and the South Platte River Receiving Waterway: Weir Gulch General Land Use: Mix of residential, commercial, and industrial Drainage Basin Area: 1,473 acres (2.30 square miles) within Denver Basin Composite Imperviousness: 58.3% Number of Outfalls and 2-Year Hydrology: 16 outfalls Capacity of Outfalls: 2-year Basin 4900-01 tributary to Weir Gulch is fully built-out (within Denver) with older neighborhood residential use in the upper reaches and commercial use in the lower reaches. Two major tributaries outfall into Weir Gulch: 1 st Avenue and Dakota Avenue Tributaries. Opportunities An existing on-line water quality facility exists on Weir Gulch at Barnum South Park. Strip parks have been developed by the Denver Parks and Recreation Department from 1 st Avenue to Alameda Avenue along the gulch, which could be reconfigured to be utilized for regional stormwater management. Constraints This basin is fully built-out with dense development, and land acquisition is necessary for regional facilities.

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Potential Regional Facilities Chapter 8 Page 8-40 SANDERSON GULCH Sanderson Gulch (Basin 5100-01) Exhibit 8.35 summarizes key background data for the Sanderson Gulch basin (Basin 5100-01). EXHIBIT 8.35 BACKGROUND DATA FOR SANDERSON GULCH (BASIN 5100-01) Location Description: West Denver and Jefferson County South Platte River to South Pierce Street Receiving Waterway: South Platte River General Land Use: Mix of industrial and residential Drainage Basin Area: 4,864 acres (7.6 square miles) Basin Composite Imperviousness: 54.6% Number of Outfalls and 2-Year Hydrology: 1 within Denver: Open Channel at Platte River Drive See FHAD Capacity of Outfalls: 100-Year 4 Much of the Sanderson Gulch basin is tributary to Mississippi Avenue and the associated outfall. Opportunities Basin 5100-01 is fully built-out with older neighborhood residential use in the upper reaches and commercial use in the lower reaches. Blueprint Denver shows the region along both sides of Federal Boulevard as an Area of Change, meaning that redevelopment is expected to occur in the area of the storm drain outfalls. This is an opportunity for installation of regional water quality treatment, especially since basin runoff is confined to one major outfall. An undeveloped open channel section along Mississippi Avenue at Quivas Street is an opportunity for an on-line regional water quality pond at the discharge of the 4 ft x 8 ft CBC. This site is an ideal location for water quality treatment. Other locations for regional water quality treatment within this basin are Huston Lake, Garfield Lake, Ward Reservoir No. 5, and Harvey Park. These Denver Parks lands may provide an opportunity for off-line regional water quality ponds. Constraints The main constraint to regional water quality treatment is the fact that the outfall at Mississippi Gulch requires coordination with Public Service Company and private landowners. Either land areas must be identified within Denver for regional treatment, or an agreement must be structured with Public Service Company for operation and maintenance of regional facilities.

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Denver Water Quality Management Plan Chapter 8 Page 8-41 GREENWOOD GULCH Greenwood Gulch (Basin 5401-01) Exhibit 8.36 summarizes key background data for the Greenwood Gulch basin (Basin 5401-01). EXHIBIT 8.36 BACKGROUND DATA FOR GREENWOOD GULCH (BASIN 5401-01) Location Description: East Belleview Avenue and South Monaco Street, Southeast Denver Receiving Waterway: Greenwood Gulch General Land Use: Mix of industrial, commercial, and residential Drainage Basin Area: 93 acres (0.15 square mile) Basin Composite Imperviousness: 84.0% Number of Outfalls: 3 existing leaves Denver and discharge to Greenwood Gulch Capacity of Outfalls: 2-year to 5-year capacity for existing Outfalls include: 4 30-inch from West Quincy Avenue 4 42-inch from South Federal Boulevard This basin has several future developments planned. The majority of the basin is composed of residential, commercial and light industrial. The entire basin is within Denver. Opportunities Existing detention and water quality facilities are servicing this basin. No new facilities are required at this time. Constraints Any modifications to existing facilities must conform to the existing developer agreements.

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Potential Regional Facilities Chapter 8 Page 8-42 BEAR CREEK Six drainage basins tributary to Bear Creek are evaluated for regional stormwater treatment opportunities in this discussion, including: 4 Fort Logan (Basin 5500-01) 4 Upper Bear Creek (Basin 5500-02) 4 Academy Park Tributary (Basin 5500-03) 4 Marston Lake North (Basin 5500-04) 4 Pinehurst Tributary (Basin 5500-05) 4 Henry s Lake Tributary (Basin 5501-01) Fort Logan (Basin 5500-01) Exhibit 8.37 summarizes key background data for the Fort Logan basin (Basin 5500-01). EXHIBIT 8.37 BACKGROUND DATA FOR FORT LOGAN (BASIN 5500-01) Location Description: Southwest of Downtown Denver Between Yale and Union Avenues, and Between Sheridan and Federal Boulevards Receiving Waterway: Bear Creek General Land Use: Mix of residential and commercial Drainage Basin Area: 1,997 acres (3.12 square miles) Basin Composite Imperviousness: 52.8% Number of Outfalls: 9 outfalls Capacity of Outfalls: 1to 2-year Basin 5500-01 is primarily residential use on the north side of Bear Creek and a mixture of residential with Fort Logan National Cemetery and Mullen High School on the south side. Wolcott Lake, located on the northern end of the basin, does not receive enough stormwater runoff to be effective for water quality purposes. Opportunities The 2003 Fort Logan Cemetery development plan proposes two detention ponds which would provide water quality benefits for the south side of the basin. No opportunities have been identified for regional water quality treatment on the north side of Bear Creek. Water quality will be treated in-tract commensurate with new development. Constraints No Denver Parks or Open Space land is available in this basin on the north side of Bear Creek. Land acquisition would be necessary to provide regional water quality systems to this area.

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Denver Water Quality Management Plan Chapter 8 Page 8-43 Upper Bear Creek (Basin 5500-02) Exhibit 8.38 summarizes key background data for the Upper Bear Creek basin (Basin 5500-02). EXHIBIT 8.38 BACKGROUND DATA FOR UPPER BEAR CREEK (BASIN 5500-02) Location Description: Southwest of Downtown Denver Between Lakeridge Road and Lehigh Avenue, and Between Wadsworth and Sheridan Boulevards Receiving Waterway: Bear Creek General Land Use: Mix of residential, commercial, and industrial Drainage Basin Area: 1,178 acres (1.84 square miles) Basin Composite Imperviousness: 45.5% Number of Outfalls: 15 outfalls Capacity of Outfalls: 2-year Intercepted stormwater is discharged into Bear Creek. Some of the major outfalls include: 4 30-inch to an open channel at Webster Street 4 30-inch at Reed Street 4 30-inch at Newland Street 4 42-inch at Lamar Street 4 42-inch at Joslin Court 4 48-inch at Golden Way 4 30-inch at the north side of Sheridan Boulevard 4 48-inch at the south side of Sheridan Boulevard Opportunities No opportunities have been identified for regional water quality treatment. Water quality will be treated in-tract commensurate with new development. Constraints This basin is fully built-out with dense development, and acquisition of real estate is a constraint for regional facilities. The many outfalls preclude construction of only a few isolated regional facilities.

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Potential Regional Facilities Chapter 8 Page 8-44 Academy Park Tributary (Basin 5500-03) Exhibit 8.39 summarizes key background data for the Academy Park Tributary basin (Basin 5500-03). EXHIBIT 8.39 BACKGROUND DATA FOR ACADEMY PARK TRIBUTARY (BASIN 5500-03) Location Description: Southwest of Downtown Denver Between Bear Creek and Quincy Avenue, and Between Wadsworth Boulevard and Ingall Street Receiving Waterway: Bear Creek General Land Use: Mostly commercial with some residential Drainage Basin Area: 384 acres (0.60 square mile) Basin Composite Imperviousness: 67.2% Number of Outfalls: 3 outfalls Including 54 at Marshall Street Capacity of Outfalls: 2-year The majority of this basin (88%) is located within Jefferson County. Only the downstream outfall portion of the basin is located in Denver. Opportunities No opportunities have been identified for regional water quality treatment within Denver. Several small facilities associated with individual development have been constructed in the upstream (Jefferson County) portion of the basin. Constraints The basin is almost entirely located within Jefferson County.

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Denver Water Quality Management Plan Chapter 8 Page 8-45 Marston Lake North (Basin 5500-04) Exhibit 8.40 summarizes key background data for the Marston Lake North basin (Basin 550004). EXHIBIT 8.40 BACKGROUND DATA FOR MARSTON LAKE NORTH (BASIN 5500-04) Location Description: Quincy to Belleview, Kipling to Wadsworth Wadsworth to Sheridan north of Quincy Receiving Waterway: Bear Creek General Land Use: Residential and commercial mix Drainage Basin Area: 1,894 acres (2.96 square miles) Basin Composite Imperviousness: 45.0% Number of Outfalls: 1 existing to Bear Creek Capacity of Outfalls: 5-year capacity There are over 15 minor storm sewer outfalls to the Marston Lake North channel from its beginning at Lakes Lake to the channel s outfall into Bear Creek. The channel drains approximately 2.96 square miles. There is an existing detention pond called Lakes Lake located between Stanford Avenue and Balsam Way, north of Union Avenue Opportunities It is assumed that Lakes Lake was constructed with the intention of providing water quality. If that is not the case, incorporating water quality into the pond would provide treatment for the 453 acres flowing to it. There is a series of ponds in line with the Marston Lake North channel located east and west of Sheridan near the Oxford Avenue intersection. Any of these ponds could be used for water quality treatment in the lower portion of the basin. Constraints Land acquisition may be necessary for the ponds in the lower reach of the basin.

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Potential Regional Facilities Chapter 8 Page 8-46 Pinehurst Tributary (Basin 5500-05) Exhibit 8.41 summarizes key background data for the Pinehurst Tributary basin (Basin 5500-05). EXHIBIT 8.41 BACKGROUND DATA FOR PINEHURST TRIBUTARY (BASIN 5500-05) Location Description: Southwest of downtown Denver Between Bear Creek and Quincy Avenue, and Between Wadsworth and Sheridan Boulevards Receiving Waterway: Bear Creek General Land Use: Residential and commercial Drainage Basin Area: 461 acres (0.72 square mile) Basin Composite Imperviousness: 42.2% Number of Outfalls: 2 outfalls Primary outfall is 42 Capacity of Outfalls: 50-year Basin 5500-05 is primarily residential use in the lower reaches, and golf course/residential in the upper reaches. Colorado Academy is located in the central portion of the basin. Opportunities There are several existing and proposed detention/water quality systems throughout the basin. Newly constructed detention and water quality ponds exist on the Colorado Academy site. There is good opportunity for on-line water quality facilities to be constructed in the lower reaches of the channel, just south of Hampden Avenue. Constraints Land acquisition costs could be prohibitive.

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Denver Water Quality Management Plan Chapter 8 Page 8-47 Henry s Lake (Basin 5501-01) Exhibit 8.42 summarizes key background data for the Henry s Lake basin (Basin 5501-01). EXHIBIT 8.42 BACKGROUND DATA FOR HENRY S LAKE (BASIN 5501-01) Location Description: Southwest of Downtown Denver Between Bear Creek and Stanford Avenue Between Kipling Avenue and Pierce Way Receiving Waterway: Bear Creek General Land Use: Residential, commercial, golf course, undeveloped Drainage Basin Area: 864 acres (1.35 square miles) Basin Composite Imperviousness: 35.0% Number of Outfalls: 1 outfall (located in Jefferson County) Capacity of Outfalls: Not quantified The majority of this basin (95%) and the outfall are located within Jefferson County. Only 40 acres at the upstream end of the basin are located within Denver. Little Henry s Lake is located on Denver property. Opportunities A regional detention pond, Little Henry s Lake, is located just south of Henry s Lake and could provide regional water quality for Denver s 40 tributary acres. The pond is maintained by Denver s Parks and Recreation Department. RTD owns land adjacent to the existing Park N-Ride facility near Wadsworth Boulevard and Hampden Avenue in Jefferson County. RTD has expressed some interest in using the land for stormwater detention/water quality purposes. A series of on-line ponds are located in the lower portion of the drainageway (Jefferson County). Constraints The basin is almost entirely located within Jefferson County. A maintenance agreement is required for use of Little Henry s Lake as a regional water quality facility.

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Potential Regional Facilities Chapter 8 Page 8-48 DUTCH CREEK Coon Creek (Basin 5901-01) Exhibit 8.43 summarizes key background data for the Coon Creek basin (Basin 5901-01). EXHIBIT 8.43 BACKGROUND DATA FOR COON CREEK (BASIN 5901-01) Location Description: Belleview to Bowles, Kipling to Sheridan Receiving Waterway: Coon Creek General Land Use: Mixed use of residential, commercial Drainage Basin Area: 1,984 acres (3.10 square miles) Basin Composite Imperviousness: 53.2% Number of Outfalls: 2 to Coon Creek within Denver Capacity of Outfalls: 5-year capacity The majority of this basin is relatively new construction and includes on-site detention and water quality facilities. Denver s jurisdiction consists of only a narrow strip of land cutting across Coon Creek and a small tributary basin at the upstream end of the basin. The majority of this basin is located outside of Denver, including the outfall to Dutch Creek. Opportunities No opportunities have been identified within Denver for regional water quality treatment. Constraints This basin is located almost entirely within Jefferson County. SUMMARY Multiple opportunities exist for regional stormwater quality treatment facilities. Chapter 9 identifies work that needs to be completed to further evaluate and plan for regional stormwater treatment at these potential sites.

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Chapter 9 Page 9-1 Chapter 9 RECOMMENDATIONS AND IMPLEMENTATION PLAN As is the case with cities throughout the country, Denver is faced with complex regulatory requirements with regard to water quality. Denver s Phase I CDPS permit specifies stringent requirements with which it must comply or face significant penalties. Fortunately, Denver already has many sound water quality requirements in place in the form of policies and regulations. This chapter provides a summary of recommendations for future water quality protection efforts, along with a proposed implementation plan for these recommendations. RECOMMENDATIONS 1. All new and redevelopment projects must address water quality in their development plans, complying with the stormwater policies and design criteria specified in the Urban Storm Drainage Criteria Manual, Volumes 1-3 (UDFCD 1999, 2001) and in Denver s CDPS permit. Particularly critical is the four-step BMP planning process that requires: 4 Implementing stormwater runoff reduction practices. 4 Providing treatment of the Water Quality Capture Volume. 4 Implementing streambank and channel stabilization techniques for any drainageways within or adjacent to a project site. 4 Providing additional treatment for pollution hot spots. 2. Under Denver s CDPS permit, adverse impacts to receiving waters posed by urban stormwater discharges must be minimized to the maximum extent practicable. Examples of these adverse impacts can include increased pollutant loading, increased runoff rates and volumes, channel instability, modification of aquatic habitat and increased sediment loading, both during and after construction. It is essential to recognize that, despite the best efforts to control stormwater runoff, there will be some change in receiving water characteristics due to development; therefore, a zero impact policy is not realistic or attainable. As a result, Denver advocates management of stormwater through the implementation of BMPs designed in accordance with the guidelines established by UDFCD (UDFCD 1999, 2001), as summarized in #1, above. 3. Denver will continue to advocate the use of multiple BMPs, including non-structural measures, source controls, and structural BMPs, to reduce stormwater pollution. Whenever practicable, combining BMPs in series can be very effective in reducing stormwater pollution. 4. The stormwater quality BMP implementation guidelines provided in Chapter 6 of this Plan will be shared with developers and city staff alike to promote better integration of water quality into site designs, including more substantial use of runoff reduction techniques.

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Recommendations Chapter 9 Page 9-2 5. Denver will work to ensure that water quality is addressed in the very beginning of the site development process so that stormwater quality BMPs are better and more cost effectively integrated into site designs. Various Denver departments (e.g., Public Works, Planning, Parks, Environmental Health) must work together with a shared vision of stormwater quality management to accomplish this goal. 6. Urban stormwater management must be an integral part of site design and take into consideration multiple objectives. As stated in the Urban Storm Drainage Criteria Manual, Volume 1 (UDFCD 2001), the many competing demands placed on space and resources require that stormwater management strategies take into account water quality enhancement, groundwater recharge, recreation, wildlife habitat, wetland protection, protection of landmarks/amenities, control of erosion and sediment deposition, and creation of open space. In addition, the appearance of BMPs is particularly important; Denver will expect to receive site development plans that feature attractive BMPs that will be viewed as assets by the community. Denver will encourage multi-purpose usage of BMPs; however, compatibility among uses must be demonstrated (e.g., compatibility between recreational areas and detention areas). 7. Planning for water quality must proceed hand-in-hand with drainage planning for quantity (rate and volume). In urban areas, these two planning efforts are inseparable. When these issues are addressed together and early in the site planning process, more efficient, economical and attractive land uses generally result. 8. Denver will continue to review BMP designs for pubic safety and maintenance accessibility, maintainability, documentation of maintenance requirements and schedule, and assured long-term funding for maintenance. Proper maintenance is fundamental to public safety and long-term effectiveness of stormwater BMPs; therefore, Denver will take these steps to promote better long-term maintenance of BMPs: 4 Require inclusion of a simple BMP maintenance plan as part of Denver s Stormwater Quality Control Plan submittal requirements. 4 Require a legally binding description of BMP maintenance requirements and arrangements as part of development plan approval. 4 Clearly identify BMP maintenance requirements in forthcoming updates to Denver s Storm Drainage Criteria Manual 4 Prepare easy-to-understand maintenance guidance documents and brochures for both pubic and private facility owners. These documents will be based on maintenance recommendations of UDFCD and the guidelines provided in Chapter 6 of this Plan. 9. The same stormwater quality management expectations and practices that apply to projects in the private sector also apply to projects that are the responsibility of Denver, such as buildings, parks, streets, utilities, etc. When Denver is preparing plans for any such

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Denver Water Quality Management Plan Chapter 9 Page 9-3 projects or managing, maintaining and/or upgrading existing facilities, potential adverse stormwater quality effects must be evaluated and suitably mitigated. 10. Denver will continue to actively participate in regional water quality management efforts such as those being conducted by South Platte Cooperative for Urban River Evaluation (CURE), the Cherry Creek Basin Stewardship Partners, and the Barr Lake-Milton Reservoir Watershed Group. These on-going efforts emphasize the importance of Denver partnering with neighboring communities to tackle difficult water quality issues. Denver must also stay abreast of forthcoming regulatory changes that affect management of the many lakes and streams within its boundaries. 11. Denver s stormwater management strategies must be consistent with the principles, criteria, and priorities in its multiple planning and technical criteria documents, as described in Chapter 4. 12. Denver will work to remove obstacles to innovative stormwater management approaches by reviewing regulations and codes and, where practical, modifying requirements that conflict with the principles of this Plan. For example, such conflicts may arise with regard to parking lot and curb and gutter design requirements relative to some Low Impact Development approaches. 13. Denver will continue to promote managing and treating stormwater quality using aboveground facilities, rather than in subsurface, vault-type treatment devices. Nevertheless, Denver recognizes that there are some cases where the use of such facilities is necessary due to extreme space constraints in smaller redevelopment sites, such as those located in the downtown area. 14. Denver will evaluate the feasibility of collaborating with UDFCD, a university, other local governments, and other organizations to pilot-test innovative BMPs. Denver will continue to actively partner with UDFCD to develop design guidance for new BMPs for the Denver area. 15. Denver will continue to educate the public on stormwater quality issues. Additional opportunities for Denver s existing public education program include: 4 Provide additional educational brochures and water pollution prevention resources on the Denver web site. For example, as discussed in Chapter 5, many of the national case studies provide extensive web resources. 4 Develop pollution prevention programs for specific industries that require further attention and/or partner with entities providing existing programs. For example, the City of Boulder s Partners for a Clean Environment (PACE) program targets and provides educational information to specific industry segments including auto repair, auto body, green building, dental offices, dry cleaning, landscaping, manufacturing, printing, restaurant, and retail sectors. The City of Portland has a similar program. As an alternative to independently developing such programs,

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Recommendations Chapter 9 Page 9-4 Denver can partner with professional organizations and industry groups to support their efforts in this type of training. 4 Educate developers and Denver staff on the benefits of land management strategies such as open space/natural areas preservation and/or restoration, riparian buffer zone protection, Smart Growth, Green Development, and Low Impact Development strategies. 4 Continue educational campaigns on specific measures to minimize pollution at its source. These efforts will include a multi-faceted approach directed to the public, Denver staff and elected officials, and neighboring communities. 16. Based on an initial reconnaissance level evaluation (as described in Chapter 8), there are promising opportunities for regional water quality BMPs, including large retention basins and wetlands, that could reduce impacts to downstream receiving waters. Methods to finance the development and maintenance of these facilities are urgently needed. In addition, Denver will proceed with more detailed citywide planning to identify and prioritize regional BMP alternatives. As a part of any regional facility evaluation, it will be important to clearly define under what circumstances a developer can have their requirement for onsite water quality treatment waived (e.g., paying a fee-in-lieu-of treatment) due to regional treatment facilities. 17. Closely related to regional water quality facilities is the need to conduct a watershed-bywatershed evaluation of current stream and lake conditions, including steps that are necessary to improve the status quo. The purpose of such an evaluation is to identify watershed-specific goals, priorities, data gaps and practicable mitigation measures that could be developed to strategically improve conditions. It is logical to focus initially on 303(d)-listed streams (i.e., those that are considered by to be impaired for one or more pollutants) and to work closely with existing efforts such as those of South Platte CURE, the Barr-Milton Watershed Group, and Denver Public Works and Environmental Health. 18. Denver will continue to monitor approaches used throughout the country related to stormwater and watershed management. Lessons learned from case studies evaluated in this Plan will be kept in mind during decision-making and planning for Denver. Examples of common themes from communities with advanced stormwater programs include: 4 Comprehensive approaches are being used to address drainage, flooding, erosion, aquatic life, native habitat, and water quality in an integrated manner. 4 Watershed-based approaches are being used for planning and problem solving. 4 Geographic Information System (GIS) tools are being used effectively to prioritize stormwater improvements and to more effectively communicate to citizens, staff, and developers. 4 Storm runoff volume reduction practices are being used in many of these communities. These practices include a variety of runoff reduction techniques

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Denver Water Quality Management Plan Chapter 9 Page 9-5 such as grass buffers and swales, green roofs, and other landscape-based approaches. 4 The importance of sound long-term maintenance of BMPs is widely recognized, as is the need to provide pubic safety at drainage facilities. 4 Strong public education and outreach campaigns in combination with extensive web sites are substantive components of these programs. Education is being aggressively used as a key strategy to improve runoff quality. 4 Significant financial investments, often measured in millions of dollars, have been required for many communities to conduct their stormwater quality planning efforts. These communities recognize that comparable future expenditures will be required to implement their plans, and are implementing suitable methods of financing. 19. Because the water quality challenges facing Denver will require significant funding, new and potentially innovative financing strategies that capitalize on public/private partnerships will be investigated. Although this Plan provides a solid framework and foundation for effective stormwater quality management in Denver, a follow-up implementation plan and schedule are needed to ensure that the principles and practices set forth in this Plan are implemented throughout Denver. An initial Implementation Plan is outlined in the following section. IMPLEMENTATION PLAN As a result of extensive review of this Plan by both the Denver Advisory Committee and an Outside Review Committee, the need for an implementation plan identifying how the recommendations of this Plan would be implemented was identified as a top priority. In Exhibit 9.1, recommendations from this Plan have been tabulated along with identification of responsible party, timeframe, and level of financial investment by Denver. This implementation plan can be considered a road map for Denver to manage stormwater quality in the future. It is anticipated that this initial framework will be revised periodically.

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Denver Water Quality Management Plan Chapter 9 Page 9-7 EXHIBIT 9.1 IMPLEMENTATION PLAN FOR DENVER WATER QUALITY MANAGEMENT PLAN ACTION ITEMS ACTION ITEM DESCRIPTION TIMEFRAME LEAD DEPARTMENT APPROXIMATE FUNDING LEVEL 1. Update Denver sStormDrainage Criteria Manual to reflect the policies and guidelines of this Plan. Integrate the policies and strategies identified in this Plan into the DenverStorm Drainage Criteria Manual. Representative topics include integration of water quality/quantity management, BMP maintenance, consideration of regional facilities, and policies regarding multiple use facilities and new BMPs. 2005 Public Works Engineering Division $80-100,000 (Contract) 2. Update Denver sStormwater Quality ControlPlans, An Information Guideto reflect the policies of this Plan with specific emphasis on maintenance plans for BMPs. Currently, the Information Guide has no requirements for long-term maintenance plans for BMPs. The guide should be expanded to require the developer to clearly outline maintenance requirements for the facility. 2005 Public Works: Engineering and Wastewater Management $15-30,000 (Contract) 3. Update or expand Denver s Easement and Indemnity Agreement to provide specific language regarding maintenance of BMPs. Denver s current agreement should be revised to provide specific legally binding provisions with regard to BMP maintenance in accordance with the recommendations of Chapter 6 and Appendix D. Alternatively, a separate agreement can be developed focusing solely on maintenance. 2005 Public Works and City Attorney s Office To Be Determined 4. Update Denver s web site to enable easier public access to stormwater and waterquality-related information. Currently, Denver s web site provides only limited information to the public on stormwater quality and water quality management. The web site could be updated to contain more information already developed by Denver and to consolidate drainage and water-quality-related planning documents. 2005 Public Works and Communications Department To Be Determined

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Recommendations Chapter 9 Page 9-8 EXHIBIT 9.1 IMPLEMENTATION PLAN FOR DENVER WATER QUALITY MANAGEMENT PLAN ACTION ITEMS ACTION ITEM DESCRIPTION TIMEFRAME LEAD DEPARTMENT APPROXIMATE FUNDING LEVEL 5. Increase interdepartmental awareness of the policies and strategies in this Plan. This can be accomplished by two avenues: 1) presenting the information to related departments such as Community Planning and Development and Parks and Recreation through PowerPoint presentations; and/or 2) developing a condensed, fullcolor, graphically appealing version of the document for broader distribution. These presentations would emphasize the importance of planning for stormwater management early in the development review process and the necessity of these policies applying to Denver s internal projects. 2005 Public Works Wastewater Management Division To Be Determined 6.1 Evaluate regional BMP facility opportunities in more detail with regard to cost and practicality. This Plan identifies multiple potential opportunities for regional BMPs; however, it was beyond to the scope of this document to systematically evaluate these in detail. Regional facilities have significant potential for stormwater quality management, but require detailed and thorough planning and financial arrangements to be effective. 2005-2006 Public Works Wastewater Management Division and Community Planning and Development $50-100,000 (Contract) 6.2 Evaluate and develop acceptable funding strategies for regional BMPs, including the feasibility of publicprivate partnerships. In the event that regional facilities are deemed feasible for various locations in Denver, Denver needs to have a policy and financing strategy in place for these facilities. Basic research of how other communities have financed these facilities would be beneficial, followed by adaptation of these strategies to fit Denver. An example is the fee-in-lieu-of approach. Public Works Wastewater Management Division and Community Planning and Development To Be Determined

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Denver Water Quality Management Plan Chapter 9 Page 9-9 EXHIBIT 9.1 IMPLEMENTATION PLAN FOR DENVER WATER QUALITY MANAGEMENT PLAN ACTION ITEMS ACTION ITEM DESCRIPTION TIMEFRAME LEAD DEPARTMENT APPROXIMATE FUNDING LEVEL 7. Conduct watershed-bywatershed assessments to better characterize the water quality issues facing Denver for the purpose of tailoring specific mitigation strategies to actual watershed issues. Building upon and integrating with efforts already underway by regional watershed groups, Denver s Department of Environmental Health, Public Works Wastewater Management Division, the Joint Stormwater Task Force, Urban Drainage and Flood Control District and others, inventory available instream biological, chemical and physical data to better target watershed priorities and solutions. A considerable database already exists, but would benefit from integration into a GIS-based system. This type of assessment would form the basis of developing specific watershed goals where none have been developed, and promote better understanding in areas where goals have already been developed. This task should interface with Task 6.1 relating to identification of regional facilities. A three-phase program is envisioned that 1) inventories available information; 2) develops targeted strategies to address specific watershed concerns and/or fills data gaps; and 3) implements recommended strategies. 2005-Phase 1 2006-Phase 2 2007-Phase 3 (and into the future) Public Works Wastewater Management Division and Environmental Health Coordination with existing watershed groups and Urban Drainage and Flood Control District will be essential. To Be Determined 8. Continue to educate the general public and specific industry groups on stormwater quality issues. This is an on-going program under Denver s stormwater permit and the Wastewater Management Division. It is important that these activities continue and that Denver integrate with independent industry training programs where appropriate (e.g., builders). On-going Public Works Wastewater Management Division On-going Denver Program

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Recommendations Chapter 9 Page 9-10 EXHIBIT 9.1 IMPLEMENTATION PLAN FOR DENVER WATER QUALITY MANAGEMENT PLAN ACTION ITEMS ACTION ITEM DESCRIPTION TIMEFRAME LEAD DEPARTMENT APPROXIMATE FUNDING LEVEL 9. Pilot testing of innovative BMPs. This Plan describes several innovative stormwater quality management strategies including green roofs, porous landscape detention, Low Impact Development strategies and others. Denver should partner with Urban Drainage and Flood Control District in pilot tests of these BMPs, as the opportunity arises. Public Works Wastewater Management Division and Urban Drainage and Flood Control District Variable 10. Provide additional education on BMP maintenance requirements to private owners of stormwater BMPs. Given the many BMPs already in place in Denver, owners of privately owned facilities would benefit from easy-to-understand guidance regarding maintenance of BMPs. A brochure or short manual based on the maintenance guidelines in the Plan could be distributed to facilitate improved BMP maintenance. For example, a brochure could be developed for the Clear Choices for Clean Water series through the Joint Task Force with the reader directed to Denver s web site for more detailed guidance. 2005 Public Works Wastewater Management Division and Joint Stormwater Task Force To Be Determined 11. Implement recommendations of comprehensive utility review. A URS-led team of consultants will complete a fourreport comprehensive utility review. Report 1 will be a utility assessment program and definition study. Report 2 will be a utility management, administration and organizational study. Report 3 will be a cost of service study, and Report 4 will be an integrated waste management feasibility study. 2005 Public Works Wastewater Management Division To Be Determined

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References Page R-1 REFERENCES American Society for Testing and Materials. ASTM Standard E 1527-00 for Phase I Site Assessments. American Society of Civil Engineers and U.S. Environmental Protection Agency. 2004. International Stormwater Best Management Practices Database. www.bmpdatabase.org American Water Resources Research Foundation (AWWARF) and Water Environment Research Foundation (WERF). 2003. Impacts of Major Point and Non-Point Sources on Raw Water Treatability. http://www.is.ch2m.com/cwqf/ Baus, T. 2004. Wright Water Engineers Personal Communication with Terry Baus, Program Manager, Wastewater Management Division, Department of Public Works, Denver. Bergstedt, A. 2004. Water Quality Improvement in the South Platte River, Report to the Mayor Draft for Internal Review Only, June 24. BRW. 1998. Lowry Master Drainage Plan, Addendum No. 2. Denver, CO: City and County of Denver. BRW. 2000. Cherry Creek Greenway Corridor Master Plan Denver, CO: City and County of Denver. BRW. 2000. Infrastructure Master Plan Denver, CO: City and County of Denver. California Stormwater Quality Association (CASQA). 2003. California Stormwater Quality Association Stormwater Best Management Practice Handbook Cheng, M.S. and others. 2003. Hydrological Responses from Low Impact Development Comparing with Conventional Development. In Proceedings of the Protection and Restoration of Urban and Rural Streams Symposium held during the World Water and Environmental Resources Congress in Philadelphia, Pennsylvania, June 24-26, 2003 Reston, VA: American Society of Civil Engineers. Cherry Creek Stewardship Partners. 2003. Cherry Creek Watershed Water Quality and Resource Stewardship Regional Memorandum of Understanding Cherry Creek Stewardship Partners. 2003. Cherry Creek Watershed Smart Growth for Clean Water Report. Denver, CO: Cherry Creek Stewardship Partners. City and County of Denver and Urban Drainage and Flood Control District. 1995. Outfall Systems Plan-Stapleton Area Denver, CO: UDFCD. City and County of Denver, Department of Parks and Recreation. 2004. Natural Areas Program Field Guide Denver, CO: Denver Parks and Recreation.

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References References Page R-2 City and County of Denver, Department of Public Works, Engineering Division. 2002. Standards and Details for City Engineering, Section I, Minor Projects Denver, CO: City and County of Denver. City and County of Denver, Department of Public Works, Engineering Division. 2003. Storm Drainage and Sanitary Construction Detail and Technical Specifications Denver, CO: City and County of Denver. City and County of Denver, Department of Public Works, Wastewater Management Division. 1989. Denver Storm Drainage Master Plan Denver, CO: City and County of Denver. City and County of Denver, Department of Public Works, Wastewater Management Division. 1992. Denver Storm Drainage Design and Technical Criteria Manual Denver, CO: City and County of Denver. City and County of Denver, Department of Public Works, Wastewater Management Division. 1995. Standard Details Denver, CO: City and County of Denver. City and County of Denver, Department of Public Works, Wastewater Management Division. 2000. Stormwater Quality Control Plans: An Information Guide Denver, CO: City and County of Denver. City and County of Denver, Department of Public Works, Wastewater Management Division. 2003. Rules and Regulations Governing Sewerage Charges and Fees and Management of Wastewater and Chapter 56, Articles 91 through 107 of the Revised Municipal Code. City and County of Denver, Department of Public Works, Wastewater Management Division. 2004. Sanitary and Storm Sewer Easement and Indemnity Agreement Denver, CO: City and County of Denver. City and County of Denver, Department of Public Works. 2000. Standards and Details for City Engineering, Section 1, Minor Projects Denver, CO: City and County of Denver. City and County of Denver, Department of Public Works. 2001. Design Guidelines for Stapleton Water Quality: Patterns for Integrating Water Quality Treatment into the Community, An Addendum to the Stapleton Rules and Regulations. Denver, CO: City and County of Denver. City and County of Denver. 1995. East Stapleton Development Plan: The Green Book Denver, CO: City and County of Denver. City and County of Denver. 1997. Executive Order No. 121. Subject: Pesticide Use. From Mayor Wellington E. Webb to All Agencies under the Mayor. City and County of Denver. 2000. Blueprint Denver, An Integrated Land Use and Transportation Plan Denver, CO: City and County of Denver.

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Denver Water Quality Management Plan References Page R-3 City and County of Denver. 2000. Denver Comprehensive Plan 2000, A Vision for Denver and its People Denver, CO: Denver City Council. City and County of Denver. 2000. Long Range Management Framework South Platte River Corridor Denver, CO: City and County of Denver. City and County of Denver. 2001. Blueprint Denver Denver, CO: City and County of Denver. City and County of Denver. 2002. Annual NPDES Monitoring Report Denver, CO: City and County of Denver. City and County of Denver. 2003. Denver Parks and Recreation Game Plan: Creating A Strategy for Our Future Denver, CO: City and County of Denver. City and County of Denver. 2003. NPDES Stormwater Permit Annual Report for 2002 CDPS Permit No.: COS-000001 Denver, CO: City and County of Denver. City and County of Denver. 2003. Roadmap to Development Review, Permitting, and Construction Sites Program Process, Wastewater Management Division Rules and Regulations and MS4 Permit Requirements Denver, CO: City and County of Denver. City and County of Denver. 2004. Exhibit 6 Proposal of Denver International Airport for the July 12, 2004 South Platte River Basin; Laramie River Basin; Republican River Basin; Smoky Hill River Basin (Regulation #38) Rulemaking Hearing. City of Aurora Utilities Department; City of Denver Department of Public Works; City of Lakewood Department of Planning, Permits and Public Works in cooperation with Urban Drainage and Flood Control District. 1991. Stormwater NPDES Parts 1 and 3 Permit Application City of Aurora Utilities Department; City of Denver Department of Public Works; City of Lakewood Department of Planning, Permits and Public Works in cooperation with Urban Drainage and Flood Control District. 1992. Stormwater NPDES Part3 Permit Application Joint Appendix City of Austin, Texas. 2001. Watershed Protection Master Plan Phase I Watersheds Report Austin, TX: City. City of Boulder, Colorado. 2004. Partners for a Clean Environment. http://www.ci.boulder.co.us/environmentalaffairs/PACE/index.htm City of Portland, Oregon. 2000. Portland s Clean River Plan Portland, OR: Bureau of Environmental Services. City of Portland, Oregon. 2002. Stormwater Management Manual Revision 2 Portland, OR: City of Portland Environmental Services.

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References References Page R-4 City of Portland, Oregon. 2002. Maintaining Your Stormwater Management Facility: Homeowner Handbook. Portland, OR: Bureau of Environmental Services. City of Portland, Oregon. 2002. Maintaining Your Stormwater Management Facility: A Handbook for Private Property Owners. Portland, OR: Bureau of Environmental Services. City of San Diego, California, Stormwater Pollution Division. 2004. Website: www.thinkbluesd.org City of San Diego, California. 2003. Stormwater Standards San Diego, CA: City. Coffman, L. 2003. Wright Water Engineers Personal Communication with Larry Coffman, Prince George s County, MD Regarding Low Impact Development. Coffman, L.S. 2001. Low Impact Development Creating a Storm of Controversy. Water Resources Impact, 3(6): 7-9. Colorado Department of Public Health and Environment. 2003. Authorization to Discharge Under the Colorado Discharge Permit System City and County of Denver, Permit No. COS-000001. Denver, CO: Colorado Department of Public Health and Environment. Colorado Department of Public Health and Environment. 2003. Authorization to Discharge Under the Colorado Discharge Permit System Denver International Airport, City and County of Denver, Permit No. COS-000008. Denver, CO: Colorado Department of Public Health and Environment. Colorado Water Quality Control Commission. 2001. Regulation No. 31 The Basic Standards and Methodologies for Surface Water. 5 CCR 1002-31. Revised May 14, 2001. Colorado Water Quality Control Commission. 2001. Regulation No. 38 Classifications and Numeric Standards South Platte River Basin, Laramie River Basin, Republican River Basin, Smoky Hill River Basin. 5 CCR 1002-38. Revised May 14, 2001. Colorado Water Quality Control Division, Colorado Water Quality Control Commission, and the Colorado Sediment Task Force. 2002. Provisional Implementation Guidance for Determining Sediment Deposition Impacts to Aquatic Life in Streams and Rivers Colorado Water Quality Control Division. 2002. 319 Proposal Summary Sheet for the Barr Milton Watershed. Denver, CO: Colorado Water Quality Control Division. Colorado Water Quality Control Division. 2001. Antidegradation Significance Determination for New or Increased Water Quality Impacts, Procedural Guidance, Version 1.0. Denver, CO: Colorado Department of Public Health and Environment. Colorado Water Quality Control Division. 2002. Website: http://www.is.ch2m.com/cwqf/

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Denver Water Quality Management Plan References Page R-5 Colorado Water Quality Control Division. 2003. Final Section 309 Report, A study of Colorado water quality classification and standard issues under CRS 25-8-309 Denver, CO: Colorado Department of Public Health and Environment. Colorado Water Quality Control Division. 2003. The 303(d) list. Colorado Water Quality Control Division. 2004. Exhibit 1, Proposal of Water Quality Control Division for the July 12, 2004 South Platte River Basin; Laramie River Basin; Republican River Basin; Smoky Hill River Basin (Regulation #38) Rulemaking Hearing. Colorado Water Quality Form. 2004. Website: http://www.is.ch2m.com/cwqf/ Debo, T. and A. Reese. 2002. Municipal Stormwater Management 2 nd Edition. Boca Raton, FL: Lewis Publishers. Denver Regional Council of Governments. 1983. Urban Runoff Quality in the Denver Region Denver Regional Council of Governments. 1998. Metro Vision 2020 Clean Water Plan Policies, Assessments and Management Programs Denver, CO: Denver Regional Council of Governments. Denver Water Department. 2004. Website: www.denverwater.org Doerfer, J, and B. Urbonas. 1993. Stormwater Quality Characterization in the Denver Metropolitan Area Denver, Colorado: UDFCD. Doerfer, J. 2004. Wright Water Engineers personal communication with John Doerfer, Urban Drainage and Flood Control District. Dudley, M. 2004. Lake Management and Protection Plan Prepared for City and County of Denver Department of Parks and Recreation, Natural Areas Program. April. Energy Efficiency and Renewable Energy Network and U.S. Department of Energy. 2004. Green Development Introduction. http://www.sustainable.doe.gov/greendev/ Gill, L.S. and Z. Sands. 1999. Phytoremediation of MGP: History and Challenges. In Wetlands and Remediation, An International Conference edited by Dr. Jeffrey Means and Dr. Robert Hinchee. Battelle Press, Columbus, Ohio Green Industries of Colorado. 2004. Website: www.greenco.org GreenCO and Wright Water Engineers. 2004. Green Industry Best Management Practices for the Conservation and Protection of Water Resources in Colorado Denver, CO: GreenCO. Grubbs, G. 2001. Letter to Water Directors of State Water Programs, Great Water Body Programs, Authorized Tribal Water Quality Standards Programs, and State and Interstate

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References References Page R-6 Water Pollution Control Administrators, regarding Development and Adoption of Nutrient Criteria into Water Quality Standards. November 14. Hammer, D.L. 1989. Constructed Wetlands for Wastewater Treatment: Municipal, Industrial, and Agricultural. Boca Raton, FL: CRC Press. Hansen, P. and J.G. Massey. 1999. Tissue Distribution of Excess Copper in Salix Exigua (Sandbar Willow). In Wetlands and Remediation, An International Conference edited by Dr. Jeffrey Means and Dr. Robert Hinchee. Columbus, Ohio: Battelle Press. Heaney, J., Sample, D. and L. Wright. 2002. Costs of Urban Stormwater Control EPA-600/R02/021. ( http://www.epa.gov/ORD/NRMRL/Pubs/600R02021/600R02021.pdf ) Cincinnati, OH: National Risk Management Research Laboratory, Office of Research and Development, USEPA. Henry, K. 2003. Wright Water Engineers personal communication with Karen Henry, City of San Diego, CA. Horner, R.R., J.J. Skupien, E.H. Livingston, and H.E. Shaver. 1994. Fundamentals of Urban Runoff Management: Technical and Intuitional Issues Washington, DC: Terrene Institute, in cooperation with the U.S. Environmental Protection Agency. Irrigation Association. 2004. Website: http://www.irrigation.org/ Kadlec, R.H. and R.L. Knight. 1996. Treatment Wetlands Boca Raton, FL: CRC Press. Keep America Beautiful, Inc. 1987. Tips for Preventing Litter in Your Town Stanford, CT: Keep America Beautiful. Keep America Beautiful, Inc. 1990. Focus: Facts on Municipal Solid Waste. Stanford, CT: Keep America Beautiful. Landberg, T. and M. Greger. 1996. Differences in Uptake and Tolerance to Heavy Metals in Salix from Unpolluted and Polluted Areas. Applied Geochemistry 11:175-180. Lee, J. 2003. Wright Water Engineers personal communication with Joan Lee, Snohomish County, WA. Liptan, T. 2003. Wright Water Engineers personal communication with Tom Liptan, City of Portland, OR. Lord-Reeves, S.K. 2003. Letter to Chris Wiant regarding South Platte River Issues Formulation Hearing Selenium Stakeholders Proposal. October 28. Low Impact Development (LID) Center. 2003. Low Impact Development (LID) Urban Design Tools. http://www.lid-stormwater.net/

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Denver Water Quality Management Plan References Page R-7 Matrix Design Group. 2003. Denver Stormwater Drainage Master Plan Denver, CO: City and County of Denver. Mayor s South Platte River Commission. 2000. Long Range Management Framework South Platte River Corridor Denver, CO: Mayor s South Platte River Commission. McLaughlin Water Engineers, Ltd. 1995. Stormwater Outfall Systems Plan Stapleton Area. Denver, CO: McLaughlin Water Engineers, Ltd. McLaughlin Water Engineers, Ltd. 1998. Preliminary Design Report for the Upper Central Platte Valley South Platte River Restoration Denver, CO: McLaughlin Water Engineers, Ltd. Munakata-Marr, J. 2004. Wright Water Engineers personal communication with Dr. Junko Munakata-Marr, Colorado School of Mines. National Research Council. 1992. Restoration of Aquatic Ecosystems: Science, Technology, and Public Policy Washington, DC: National Academy Press. Olsen, R.L., Fuller, P.R., Hinzel, E.J. and Smith, P.L., 1986. Demonstration of Land Treatment of Hazardous Waste. Presented at the 7th National SUPERFUND Conference and Exhibition. 1986. Washington DC. Piatt-Kemper, J.E. 2003. Letter to Chris Wiant regarding Classifications and Numeric Standards for South Platte River Basin Regulation No. 38, Issues Formulation Hearing November 2003. October 28. Pima County Wastewater Management Department. 2003. Arid West Water Quality Research Project Pitt, R., Maestre, A., and R. Morquecho. 2004. The National Stormwater Quality Database (NSQD, Version 1.1). Tuscaloosa, AL: University of Alabama. Prince George s County, Maryland Department of Environmental Resources Programs and Planning Division. 2000. Low Impact Development Design Series, An Integrated Design Approach January. Prince George s County, MD: Maryland Department of Environmental Resources and Planning Division. Roesner, L.A. and B.P. Bledsoe. 2003. Physical Effects of Wet Weather Flows on Aquatic Habitats Alexandria, VA: Water Environment Research Foundation. United Kingdom: IWA Publishing (co-publisher). Rosgen, D. 1996. Applied River Morphology Pagosa Springs, CO: Wildland Hydrology Schueler, T. and H. Holland. 2000. The Practice of Watershed Protection. Ellicott City, MD: The Center for Watershed Protection.

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References References Page R-8 Science Applications International (SAIC). 2004. Municipal Separate Storm Sewer System (MS4) Program Evaluation, City and County of Denver, Colorado, April 19-22, 2004. Prepared for EPA Region 8. Denver, CO: EPA Region 8. Smith, P. L. and P. Wayland. 1999. Wetland Mitigation Sites Attenuating Solids, Salts and Metals in Irrigation Water. In Wetlands and Bioremediation, An International Conference, Conference Proceedings. Salt Lake City, Utah. Smith, P.L., Redente, E., and Hopper, E. 1987. Soil Organic Matter. In: Reclaiming Mine Soils and Overburden in the Western United States: Analytical Parameters and Procedures. Ankeny, IA: Soil Conservation Society of America. Snohomish County, Washington, Surface Water Management Division. 2001. Annual Achievement Report Snohomish County, Washington: Surface Water Management Division. Snohomish County, Washington. 2002. Drainage Needs Report Snohomish County, Washington: Surface Water Management Division. Snohomish County, Washington. 2004. Website: www.surfacewater.info South Platte Coalition for Urban River Evaluation (SPCURE). 2003. South Platte Coalition for Urban River Evaluation Denver, CO: South Platte Coalition for Urban River Evaluation. South Platte River Watershed under Colorado Discharge Permit System (CDPS) Permit No. COS-000001, which was renewed on March 20, 2003 and remains effective until April 30, 2008. Colorado Water Quality Control Division 2003. State of Colorado. Colorado Water Quality Control Act (CRS 25-8-101 through 25-8-702). State of Colorado. CRS 25-8-201 through 25-8-406. Stormtech, Inc., Beth Foy and Associates, Center for Watershed Protection and Norris and Associates, Inc. 2003. Memorandum, Evaluation of Stormwater Reduction Practices for the Milwaukee Metropolitan Sewerage District, March 1. The Trust for Public Land. 2002. Cherry Creek Basin Open Space Conservation and Stewardship Plan Denver, CO: The Trust for Public Land. U.S. Environmental Protection Agency. 1990. National Pollutant Discharge Elimination System Permit Application Regulation for Inclusion of a Stormwater Discharge Regulation, Federal Register Volume 55, No. 222. U.S. Environmental Protection Agency. 1996. Website: http://www.is.ch2m.com/cwqf/

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Denver Water Quality Management Plan References Page R-9 U.S. Environmental Protection Agency. 1998. National Strategy for the Development of Regional Nutrient Criteria. Washington, D.C.: U.S. Environmental Protection Agency Office of Water. U.S. Environmental Protection Agency. 1999. Preliminary Data Summary of Urban Storm Water Best Management Practices EPA 821-R-99-012. Washington, DC: U.S. Environmental Protection Agency Office of Water. U.S. Environmental Protection Agency. 2001. Development and Adoption of Nutrient Criteria into Water Quality Standards Under Section 304 of the Clean Water Act 66 Federal Register 1671. Washington, DC: U.S. Environmental Protection Agency. U.S. Environmental Protection Agency. 2003. Water Quality Trading Policy, January 13, 2003 Washington, DC: U.S. Environmental Protection Agency Office of Water. U.S. Environmental Protection Agency. 2003. Wetlands and West Nile Virus. EPA-843-F-03012. Washington, DC: U.S. Environmental Protection Agency. U.S. Environmental Protection Agency. 2004. Website: www.epa.gov U.S. Environmental Protection Agency. 2004. Stormwater Program Website: http://www.epa.gov/npdes/stormwater Urban Drainage and Flood Control District. 1999. Urban Storm Drainage Criteria Manual, Volumes 3 Denver, CO: Urban Drainage and Flood Control District. Urban Drainage and Flood Control District. 2001. Urban Storm Drainage Criteria Manual, Volumes 1-2 Denver, CO: Urban Drainage and Flood Control District. Urban Drainage and Flood Control District. 2003. Prairie Gateway Outfall Systems Planning, Preliminary Design Report Denver, CO: Urban Drainage and Flood Control District. Urbonas, B. and J. Doerfer. 2003. Some Observations on Atmospheric Dust Fallout in the Denver, Colorado Area of the United States. Flood Hazard News. December. Denver, CO: Urban Drainage and Flood Control District. Urbonas, B., Guo, J., and L. Tucker. 1989. Sizing Capture Volume for Storm Water Quality Enhancement. Flood Hazard News. Denver, CO: Urban Drainage and Flood Control District. Washington State Department of Ecology. 2001. Stormwater Management Manual for Western Washington Olympia, WA: Washington State Department of Ecology. Water Environment Federation and American Society of Civil Engineers. 1992. Design and Construction of Urban Stormwater Management Systems. ASCE Manual and Reports of Engineering Practice No. 77 and WEF Manual of Practice FD-20. Alexandria,VA: Water Environment Federation.

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References References Page R-10 Water Environment Federation and American Society of Civil Engineers. 1998. Urban Runoff Quality Management. WEF Manual of Practice No. 23 and ASCE Manual and Report on Engineering Practice No. 87. Alexandria, VA: Water Environment Federation. Watershed Management Institute. 1997. Operation, Maintenance and Management of Stormwater Management Systems. Ingleside, MD: Watershed Management Institute. Wright Water Engineers. 1984. South Platte River Major Drainageway Master Planning, Chatfield Dam to Baseline Road, Phase A. Prepared for the Urban Drainage and Flood Control District. Denver, CO: Wright Water Engineers. Wright Water Engineers. 1985. South Platte River Major Drainageway Master Planning, Chatfield Dam to Baseline Road, Phase B, Volume1, Preliminary Engineering Design Prepared for the Urban Drainage and Flood Control District. Denver, CO: Wright Water Engineers. Wright Water Engineers. 1985. South Platte River Major Drainageway Master Planning, Chatfield Dam to Baseline Road, Phase B, Volume II, Recreation Plan Prepared for the Urban Drainage and Flood Control District. Denver, CO: Wright Water Engineers. Wright Water Engineers. 2004. Personal Communication Regarding the Effectiveness of Covenants and other Source Controls at the Grant Ranch/Trailmark Subdivisions. Wu, M., Franz, E.H., and S. Chen. 1999. Spartina Pectinata: A Candidate Species for Constructed Treatment Wetlands. In Wetlands and Remediation, An International Conference edited by Dr. Jeffrey Means and Dr. Robert Hinchee. Battelle Press, Columbus, Ohio.

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Glossary Page G-1 GLOSSARY 1 Antidegradation Requirements : Requirements that ensure protection of water quality for a particular water body where the water quality exceeds levels necessary to protect fish and wildlife propagation, and recreation on and in the water. This also includes special protection of waters designated as outstanding natural resource waters. Antidegradation plans are adopted by each state to minimize adverse effects on water. Basin: A hydrologic unit consisting of a part of the surface of the earth covered by a drainage system consisting of a surface stream or body of impounded surface water plus all tributaries. Best Available Technology Economically Achievable (BAT): Technology-based standard established by the Clean Water Act (CWA) as the most appropriate means available on a national basis for controlling the direct discharge of toxic and non-conventional pollutants to navigable waters. BAT effluent limitation guidelines, in general, represent the best existing performance of treatment technologies that are economically achievable within an industrial point source category or subcategory. Best Available Technology/Best Control Technology (BAT/BCT): A level of technology based on the very best (state-of-the-art) control and treatment measures that have been developed or are capable of being developed and that are economically achievable within the appropriate industrial category. Best Conventional Pollutant Control Technology (BCT): Technology-based standard for discharges from existing industrial point sources of conventional pollutants including BOD, TSS, fecal coliform, pH, oil and grease. The BCT is established in light of a two-part "cost reasonableness" test which compares the cost for an industry to reduce its pollutant discharge with the cost to a POTW for similar levels of reduction of a pollutant loading. The second test examines the cost-effectiveness of additional industrial treatment beyond BPT. EPA must find limits which are reasonable under both tests before establishing them as BCT. 1 Definitions in this glossary have been compiled from several key references and websites including: Denver Wastewater Management Division Rules and Regulations http://www.denvergov.org/admin/template3/forms/Sewer%20charges.PDF Urban Drainage and Flood Control District, Volume 3 http://www.udfcd.org/usdcm/vol3.htm Blueprint Denver Glossary http://www.denvergov.org/admin/template3/forms/BD_glossary.pdf CWQCD http://www.cdphe.state.co.us/wq/ Utah APWA http://www.ulct.org/apwa/Glossary.htm USGS website, Stormwater Magazine Glossary: http://www.forester.net/sw_glossary.html EPA website glossaries http://www.epa.gov/ednnrmrl/main/gloss.htm and http://cfpub.epa.gov/npdes/glossary.cfm?program_id=0 the Low Impact Development website: http://www.lowimpactdevelopment.org/school/glossary.html the Maryland website http://www.mde.state.md.us/assets/document/sedimentstormwater/Glossary.pdf and the NRDC website http://www.nrdc.org/water/pollution/storm/gloss.asp

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Glossary Glossary Page G-2 Best Management Practices (BMPs): Schedules of activities, prohibitions of practices, maintenance procedures, and other management practices to prevent or reduce the pollution of waters of the United States. BMPs also include but are not limited to treatment requirements, operating procedures, and practices to control plant site runoff, spillage or leaks, sludge or wastewater disposal, or drainage from raw material storage. Better Site Design: A collection of site planning, design, and development strategies that help reduce adverse impacts to the natural environment by recreating, to a certain extent, the original hydrology and plant community of the predevelopment site. Biofilter: Dense vegetation designed to filter stormwater runoff as it passes through. (Also see definition of Grass Buffer and Grass Swale.) Bioretention: Also known as Rain Garden, Bio-Filter and a LID BMP. On-lot retention of stormwater through the use of vegetated depressions engineered to collect, store, and infiltrate runoff. BMP: Best Management Practice. (See definition above.) Brownfield: According to the Environmental Protection Agency, a brownfield is an abandoned, idled, or under-used industrial or commercial facility where expansion or redevelopment is complicated by real or perceived environmental contamination. Buffer Strip: Strips of grass or other erosion resistant vegetation located between a waterway and an area of more intensive land use. (Also see definition of Grass Buffer.) Buffer Zone: A designated transitional area around a stream, lake, or wetland left in a natural, usually vegetated state so as to protect the waterbody from runoff pollution. Development is often restricted or prohibited in a buffer zone. Catch Basin: An entryway to the storm drain system, usually located at a street corner. CDPS: See Colorado Discharge Permit System. Channel Stabilization: Erosion prevention and stabilization of velocity distribution in channel using jetties, drops, revetments, structural linings, vegetation, and other measures. Clean Water Act: Legislation that provides statutory authority for the NPDES program; Public law 92-500; 33 U.S.C. 1251 et seq. Also known as the Federal Water Pollution Control Act. Cluster Development: Buildings concentrated in specific areas to minimize infrastructure and development costs while achieving the allowable density. This approach allows the preservation of natural open space for recreation, common open space, and preservation of environmentally sensitive features. Colorado Discharge Permit System : The State of Colorado s system of permitting discharges (e.g., stormwater, wastewater) to Waters of the State that corresponds to the federal

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Denver Water Quality Management Plan Glossary Page G-3 National Pollutant Discharge Elimination System (NPDES) permits under the federal Clean Water Law. Combined Detention Basin: A detention basin that performs both water quality and flood control functions. Constructed Wetland Basin: A constructed wetland basin is appropriate for large catchments and is a shallow retention pond which requires a perennial supply of water to permit the growth of rushes, willows, cattails, and reeds. It treats runoff by slowing it down to allow time for settling and biological uptake. Cubic Feet Per Second (cfs): A rate of flow that is equal to a volume of water one foot high and one foot wide flowing a distance of one foot in one second. One "cfs" is equal to 7.48 gallons of water flowing each second. As an example, if a car's gas tank is 2 feet by 1 foot by 1 foot (2 cubic feet), then gas flowing at a rate of 1 cubic foot/second would fill the tank in two seconds. Culvert: A short, closed (covered) conduit or pipe that passes stormwater runoff under an embankment, usually a roadway. Design Storm: A rainfall event of specific size, intensity, and return frequency (e.g., the 1year storm) that is used to calculate runoff volume and peak discharge rate. Detention: The storage and slow release of stormwater from an excavated pond, enclosed depression, or tank. Detention is used for pollutant removal, stormwater storage, and peak flow reduction. Both wet and dry detention methods can be applied. Effective Imperviousness: The total imperviousness of a site is the weighted average of individual areas of like imperviousness. For instance, paved streets (and parking lots) have an imperviousness of 100 percent; drives and walks have an imperviousness of 96 percent; roofs have an imperviousness of 90 percent; and lawn areas have an imperviousness of 0 percent. The total imperviousness of a site can be determined taking an area-weighted average of the imperviousness of the street, walk, roof, and lawn areas. End-of-Pipe System: Any device and/or treatment system applied to stormwater, combined wastewater, municipal wastewater and/or industrial wastewater at the outlet of a collection system prior to a receiving water body. The majority of wastewater treatment systems including sanitary and combined wastewater treatment plants and many stormwater treatment schemes such as detention basins are end-of-pipe systems. Erosion: When land is diminished or worn away due to wind, water, or glacial ice. Often the eroded debris (silt or sediment) becomes a pollutant via stormwater runoff. Erosion occurs naturally, but can be intensified by land clearing activities that remove established vegetation such as farming, development, road building, and timber harvesting.

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Glossary Glossary Page G-4 Eutrophication: Excessive levels of phosphorous, nitrogen, and nutrients in the water, which leads to a decrease in oxygen levels. Often characterized by excessive growth of algae and aquatic vegetation, often resulting in deteriorated water quality and beach closings. Event Mean Concentration (EMC): A method for characterizing pollutant concentrations in a receiving water from a runoff event often chosen for its practicality. The value is determined by compositing (in proportion to flow rate) a set of samples, taken at various points in time during a runoff event, into a single sample for analysis. Extended Detention Basin: An extended detention basin is appropriate for larger sites and is designed to totally empty out sometime after stormwater runoff ends. The extended basin uses a much smaller outlet than a flood control detention basin which extends the emptying time for the more frequently occurring runoff events to facilitate pollutant removal. Fecal Coliform: Bacteria found only in the intestinal tracts of humans and animals. The major sources are animal waste, waste treatment plants, and failing septic systems. The presence of these bacteria typically indicates pollution that may pose a potential health risk. Filter Strip: Grassed strips situated along roads or parking areas that remove pollutants from runoff as it passes through, allowing some infiltration and reduction of velocity. First Flush: The condition, often occurring in storm-sewer discharges, in which a disproportionately high pollutant load is carried in the first portion of the discharge or overflow. Flow Control Structure: A structure, such as an outlet of a detention basin, that is designed to produce a specific rate of runoff in the outflow of a stormwater management facility, generally with the intent of reducing peak runoff rates from developed areas, and, for treatment BMPs, to provide an extended drain time for settling of particulates. Forebay: Storage space located near a stormwater BMP inlet that serves to trap incoming coarse sediments before they accumulate in the main treatment area. Geographic Information System (GIS): A database of digital information and data on landuse, land cover, ecological characteristics, and other geographic attributes that can be overlaid, statistically analyzed, mathematically manipulated, and graphically displayed using maps, charts, and graphs. Grading: Stripping, excavating, filling and/or stockpiling soil to shape land area for development or other purposes. Grass Buffer: Uniformly graded and densely vegetated area of turf grass. This BMP requires sheet flow to promote filtration, infiltration, and settling to reduce runoff pollutants. Grass Swale: Densely vegetated drainageway with low-pitched side slopes that collects and slowly conveys runoff. Design of longitudinal slope and cross-section size forces the flow to be slow and shallow, thereby facilitating sedimentation while limiting erosion.

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Denver Water Quality Management Plan Glossary Page G-5 Green Roof: A vegetated roof that can be used to treat precipitation and/or provide detention. Green roofs require an engineered structure that can support soils, vegetation and loads associated with rainfall, snow, people and equipment. Key components include a waterproof membrane, root barrier, drainage layer, soil/growing medium, irrigation system and plants. Greenway: A linear open space or corridor composed of native vegetation. Greenways can be used to create connected networks of open space that include traditional parks and natural areas. Hot Spot: Area where land use or activities generate highly contaminated runoff with concentrations of pollutants in excess of those typically found in stormwater. Household Hazardous Waste: Common everyday products that people use in and around their homes including paint, paint thinner and pesticides that, due to their chemical nature, can be hazardous if not properly disposed. Hydrodynamic Structure: An engineered structure using gravitational separation and/or hydraulic flow to separate sediments and oils from stormwater runoff. Hydrology: The science addressing the properties, distribution, and circulation of water across the landscape, through the ground, and in the atmosphere. Illicit Connection: Any discharge to a municipal separate storm sewer that is not composed entirely of stormwater and is not authorized by an NPDES permit, with some exceptions (e.g., discharges due to fire-fighting activities). Integrated Management Practice (IMP): A Low Impact Development (LID) practice or combination of practices that are the most effective and practicable (including technological, economic, and institutional considerations) means of controlling the predevelopment site hydrology. Impervious Area: A hard surface area (e.g., parking lot or rooftop) that prevents or retards the entry of water into the soil, thus causing water to run off the surface in greater quantities and at an increased rate of flow. Infill Development: Development of vacant lots or enhancement of existing urban properties. Infiltration: The process or rate at which water percolates from the land surface into the ground. Infiltration is also a general category of BMP designed to collect runoff and allow it to flow through the ground for treatment. Inlet: An entrance into a ditch, storm sewer, or other waterway. In-Line Storage: The use of a portion of the volume of a storm sewer or drain, combined sewer and/or interceptor sewer system that is not being used to transport combined wastewater or stormwater to accommodate the storage of additional stormwater runoff or combined wastewater. This term also applies to a storage facility, such as a tank, basin, or other reservoir,

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Glossary Glossary Page G-6 which is connected to a sewer system in such a way that all flow in the system passes through the storage facility. In the latter usage, inline storage is differentiated from offline storage which is connected in such a way that excess flow can be diverted to the storage facility, but normal flows bypass the facility. (Also see Off-Line Storage.) Integrated Pest Management (IPM): The practice of using biological, chemical, cultural, and physical measures to manage pests while minimizing or eliminating the use of chemical pesticides. Level Spreader: An outlet designed to convert concentrated runoff to sheet flow and disperse it uniformly across a slope, thereby preventing/minimizing erosion. Low Impact Development: The integration of a site s ecological and environmental goals and requirements into all phases of urban planning and design from the individual residential lot level to the entire watershed. Also see Smart Growth, Minimizing Directly Connected Impervious Area, Sustainable Urban Drainage Systems. Macroinvertebrate: An organism is visible without magnification and that lacks a backbone. Examples include snails, worms, fly larvae, and crayfish. Maximum Extent Practicable (MEP): A standard for water quality that applies to all MS4 operators regulated under the NPDES program. Since no precise definition of MEP exists, it allows for maximum flexibility on the part of MS4 operators as they develop and implement their programs. Media Filter: A filter containing sand, compost, sand peat, or perlite and zeolite designed to filter constituents (particulates, oil, bacteria, or dissolved metals) out of stormwater runoff as it passes through the filter. (Also see Sand Filter Extended Detention Basin.) Micropool: A smaller permanent pool incorporated into the design of larger stormwater ponds to avoid resuspension of particles and minimize impacts to adjacent natural features. Milligrams Per Liter (mg/L): A unit of concentration of a constituent in water or wastewater. It represents 0.001 gram of a constituent in 1 liter of water and is approximately equal to one part per million (PPM). Minimizing Directly Connected Impervious Areas (MDCIA): A variety of runoff reduction strategies based on reducing impervious areas and routing runoff from impervious surfaces over grassy areas to slow down runoff and promote infiltration. The benefits are less runoff, less stormwater pollution, and less cost for drainage infrastructure. Also see Smart Growth and Low Impact Development. Minimum Measures: Stormwater management programs required under the CDPS MS4 permit. They include public education and outreach, public participation/involvement, illicit discharge detection and elimination, construction site stormwater runoff control, postconstruction stormwater management, and pollution prevention/good housekeeping for municipal operations.

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Denver Water Quality Management Plan Glossary Page G-7 Modular Block Porous Pavement: Modular block porous pavement consists of open void concrete slab units underlain with gravel. The surface voids are filled with sand. This BMP is intended to be used in low traffic areas to accommodate vehicles while facilitating stormwater infiltration near its source. A variation of this BMP is termed stabilized-grass porous pavement, consisting of plastic rings affixed to filter fabric underlain with gravel. The surface voids are filled with sand and grass sod or seed. MS4: Municipal Separate Storm Sewer System, see below. Municipal Separate Storm Sewer System (MS4): A publicly owned conveyance or system of conveyances that discharges to waters of the United States and is designed or used for collecting or conveying stormwater, is not a combined sewer, and is not part of a publicly owned treatment works (POTW). Municipal Stormwater Permit: An NPDES permit issued to municipalities to regulate discharges from municipal separate storm sewers for compliance with EPA regulations. National Pollutant Discharge Elimination System (NPDES): The national program under Section 402 of the Clean Water Act for regulation of discharges of pollutants from point sources to waters of the United States. Discharges are illegal unless authorized by an NPDES permit. NPDES: National Pollutant Discharge Elimination System, as described above. Non-Point Source (NPS) Pollution: Pollution discharged over a wide land area, not from one specific location. These are forms of diffuse pollution caused by sediment, nutrients, organic and toxic substances originating from land-use activities and carried to lakes and streams by surface runoff. Non-point source pollution is contamination that occurs when rainwater, snowmelt, or irrigation washes off plowed fields, city streets, or suburban backyards. As this runoff moves across the land surface, it picks up soil particles and pollutants, such as nutrients and pesticides. Non-Structural BMPs: Stormwater runoff treatment techniques which use natural measures to reduce pollution levels, and do not require extensive construction efforts and/or promote pollutant reduction by eliminating the pollutant source. Off-Line: A management system designed to control a storm event by diverting a percentage of stormwater events from a stream or storm drainage system. Oil/Water Separator: A device installed (usually at the entrance to a drain) which removes oil and grease from water entering the drain. On-Line: A management system designed to control stormwater in its original stream or drainage channel. Open Space: Land set aside for public or private use within a development that is not built upon.

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Glossary Glossary Page G-8 Open-Channel Flow: Fluid flow where the bottom and sides of the flow are confined by solid surfaces and the upper surface is in contact with the atmosphere and is at atmospheric pressure. Open-channel flow occurs in rivers, streams, canals, channels, swales, and ditches, and in pipes, sewers, and culverts that are less than completely full. Outfall: The point where wastewater or drainage discharges from a sewer pipe, ditch, or other conveyance to a receiving body of water. Peak Flow: The maximum instantaneous discharge of a stream or river at a given location. It usually occurs at or near the time of maximum stage. Peak Runoff Rate: The highest actual or predicted flow rate (measured in cubic feet per second) for runoff from a site. Permeability: The ability of a material to allow the passage of a liquid, such as water through rocks or soil. Permeable materials, such as gravel and sand, allow water to move quickly through them, whereas impermeable material, such as clay, does not allow water to flow freely. Point Source Pollutant: Pollutants from a single, identifiable source such as a factory, refinery, or place of business. Pollutant (as defined by CDPS Regulation 6.3.0 [51]): Dredged spoil, dirt, slurry, solid waste, incinerator residue, sewage, sewage sludge, garbage, trash, chemical waste, biological nutrient, biological material, radioactive material, heat, wrecked or discarded equipment, rock, sand, or any industrial, municipal or agriculture waste. Pollutant Load: The quantity of pollutants carried in stormwater. Porous Landscape Detention: Porous landscape detention consists of a low lying vegetated area underlain by a sand bed with an underdrain. A shallow surcharge zone exists above the porous landscape detention for temporary storage of the WQCV. This BMP allows small amounts of WQCV to be provided on parking lots or adjacent to buildings without requiring the set-aside of significant developable land areas. Also see Rain Garden. Porous Pavement and Pavers: Alternatives to conventional asphalt that utilize a variety of porous media, often supported by a structural matrix, concrete grid, or modular pavement, which allow water to percolate though to a sub-base for gradual infiltration. See definition for Modular Block Porous Pavement. Porous Pavement Detention: Porous pavement detention consists of modular block porous pavement that is installed flat and is provided with a two-inch-deep detention zone above its surface to temporarily store the WQCV from the tributary drainage area including its own surface. Runoff infiltrates the void spaces of the gravel base course through the sand filter and slowly exits through an underdrain. Rain Garden: See bioretention and porous landscape detention.

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Denver Water Quality Management Plan Glossary Page G-9 Receiving Waters: Natural or man-made water systems into which materials are discharged. Regional Transportation District (RTD): The regional public transportation agency for the six county Denver metropolitan area. Restoration: Human activity that results in the return of an ecosystem to a close approximation of its condition prior to disturbance. Retention Pond: A BMP consisting of a permanent pool of water designed to treat runoff by detaining water long enough for settling, filtering, and biological uptake. Wet ponds may also be designed to have an aesthetic and/or recreational value. These BMPs have a permanent pool of water that is replaced with stormwater, in part or in total, during storm runoff events. In addition, a temporary extended detention volume is provided above this permanent pool to capture storm runoff and enhance sedimentation. It requires a perennial supply of water to maintain the pool. A retention pond is appropriate for larger catchments. Retrofit: The creation or modification of a stormwater management practice, usually in a developed area, that improves or combines treatment with existing stormwater infrastructure. Riparian Area: Vegetated ecosystems along a waterbody through which energy, materials, and water pass. Riparian areas characteristically have a high water table and are subject to periodic flooding. Riparian Zone: The border or banks of a stream. Although this term is sometimes used interchangeably with flood plain, the riparian zone is generally regarded as relatively narrow compared to a flood plain. The duration of flooding is generally much shorter, and the timing less predictable, in a riparian zone than in a river flood plain. Runoff Reduction Practices: Strategies to reduce runoff peaks and volumes from urbanizing areas, employing a practice generally termed minimizing directly connected impervious areas (MDCIA). Runoff: Water from rain, melted snow, or irrigation that flows over the land surface. Sand Filter Extended Detention Basin: A sand filter extended detention basin consists of a sand bed and underdrain system. Above the vegetated sand bed is an extended detention basin sized to capture the WQCV. A sand filter extended detention basin provides pollutant removal through settling and filtering and is generally suited to off-line, on-site configurations where there is no base flow and the sediment load is relatively low. Sanitary Sewer: A system of underground pipes that carries sanitary waste or process wastewater to a treatment plant. Scupper: An opening in a wall through which water can drain (i.e., from the roof of a building or a landscape area)

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Glossary Glossary Page G-10 Sediment: Soil, sand, and materials washed from land into water, usually after rain. Sediment can destroy fish-nesting areas, clog animal habitats, and cloud water so that sunlight does not reach aquatic plants. Sheet Flow: The portion of precipitation that moves initially as overland flow in very shallow depths before eventually reaching a stream channel. Slope: Angle of land measured in horizontal distance necessary for the land to fall or rise one foot, expressed by horizontal distance in feet to one vertical foot. Slotted Curbs: Curbs with slots or cut-out areas that allow stormwater to flow away from the curbed pavement into an adjacent landscape or turf area. These can reduce excessive concentration of flows and associated erosion problems. Smart Growth: Development that uses a variety of strategies to enhance existing communities and protect community character in a way that is compatible with the natural environment, as well as attracts economic development. It encourages more town-oriented, transit-focused, and pedestrian-friendly new development while restoring vitality to existing developed areas. Also see Low Impact Development. Source Control: A method of abating storm-generated or CSO pollution at the upstream, upland source where the pollutants originate and/or accumulate. Spill Prevention Control and Countermeasure Plan (SPCC): A plan prepared by a facility to minimize the likelihood of a spill and to expedite control and cleanup activities should a spill occur. Storage Capacity: The volume of fluid that can be stored in a system. For storm drainage and sewerage systems, storage capacity refers to the volume available for the temporary storage of excess storm flow or wastewater flow in a pipe, channel, basin, tank, or other facility, or in the system as a whole. Storm Drain: A slotted opening leading to an underground pipe or an open ditch from carrying surface runoff. Storm Sewer: A sewer that carries intercepted surface runoff, street wash, and other wash waters, or drainage, but excludes domestic sewage and industrial wastes except for unauthorized cross-connections. Stormwater Facilities: Systems such as watercourses, constructed channels, storm drains, culverts, and detention/retention facilities that are used for the conveyance and/or storage of stormwater runoff. Stormwater Management: Functions associated with planning, designing, constructing, maintaining, financing, and regulating the facilities (both constructed and natural) that collect, store, control, and/or convey stormwater.

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Denver Water Quality Management Plan Glossary Page G-11 Stormwater Ponds: A land depression or impoundment created for the detention or retention of stormwater runoff. See definition for Retention Pond and Extended Detention Basin. Stormwater Quality Control Plan (identified in Stormwater Quality Control Plan, An Information Guide ): The Wastewater Management Division's guidebook which identifies the submittal requirements relating to erosion, sedimentation, and water quality issues for all development, redevelopment, and other construction projects. Stormwater Quality Detention: The temporary storage of stormwater to provide stormwater quality treatment through the settlement of suspended solids. Stormwater Quantity Detention: The temporary storage of stormwater on a site to provide downstream flood control through the reduction of the runoff rate to pre-development levels. Stormwater: Precipitation that accumulates in natural and/or constructed storage and stormwater systems during and immediately following a storm event. Streetscaping: Physical amenities added to the roadway and intersections, including lighting, trees, landscaping, art, surface textures and colors, and street furniture. Structural BMPs: Devices that are constructed to provide temporary storage and treatment of stormwater runoff. Sustainable Urban Drainage Systems (SUDS): A series of techniques that are designed to manage surface water runoff as close to the source as possible in a more sustainable manner than traditional drainage systems. Typical techniques include porous surfacing, permeable paving systems, infiltration/attenuation trenches and swales. Also see Low Impact Development, Smart Growth, and Minimizing Directly Connected Impervious Area. Surface Conveyance: A means of conducting stormwater runoff aboveground rather than in underground pipes, usually involving curb and gutter, concrete V-pan, or channel. Surface Water: Water that remains on the surface of the ground, including rivers, lakes, reservoirs, streams, wetlands, impoundments, seas, estuaries, etc. Suspended Sediment: Very fine soil particles that remain in suspension in water for a considerable period of time without contact with the solid fluid boundary at or near the bottom. They are maintained in suspension by the upward components of turbulent currents. Sustainable Development: Development that meets the needs of the present without compromising the ability of the future to meet its own needs. Also: Development that maximizes efficiency and functionality of systems while minimizing the consumption of precious resources. Swale: See definition of Grass Swale. Technology-Based Effluent Limit: Permit limit for a pollutant that is based on the capability of a treatment method to reduce the pollutant to a certain concentration.

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Glossary Glossary Page G-12 Total Maximum Daily Load (TMDL): The maximum allowable loading of a pollutant that a designated water body can assimilate and still meet numeric and narrative water quality standards. TMDLs were established by the 1972 Clean Water Act. Section 303(d) of the US Water Quality Act requires states to identify water bodies that do not meet federal water quality standards. In 1996 the states developed (with EPA approval) a list of water bodies that failed to meet section 303(d) standards. These are the focus of TMDLs. Allocation of named pollutants is on percentage basis. Transit-Oriented Development: Form of development that maximizes investment in transit infrastructure by concentrating the most intense types of development around transit stations to promote increased transit use. Trash Rack: Grill, grate or other device installed at the intake of a channel, pipe, drain, or spillway for the purpose of preventing oversized debris from entering the structure. Treatment Roof: A green roof that provides stormwater quality treatment. Treatment Train: Best Management Practices that work together in series to provide stormwater quality treatment. Treatment Volume: The volume of stormwater runoff from a site requiring stormwater quality treatment. Underdrain: A perforated pipe, typically 4-6" in diameter placed longitudinally at the invert of a bioretention facility for the purposes of achieving a desired discharge rate. Urban Design: Involves the social, economic, functional, environmental, and aesthetic objectives that result in the plan or structure of a city, in whole or in part. Water Quality Capture Volume: The quantity of stormwater runoff that must be treated in stormwater quality BMPs in Denver. This volume is equivalent to the runoff from an 80th percentile storm, meaning that 80 percent of the most frequently occurring storms are fully captured and treated and larger events are partially treated. In simple terms, this quantity is about half of the runoff from a 2-year storm. Waters of the State: Any and all surface and subsurface waters which are contained in or flow in or through this State, but does not include waters in sewage systems, waters in treatment works of disposal systems, and all water withdrawn for use until use and treatment have been completed. Waters of the United States: All waters that are currently used, were used in the past, or may be susceptible to use in interstate or foreign commerce, including all waters subject to the ebb and flow of the tide. Waters of the United States include all interstate waters and intrastate lakes, rivers, streams (including intermittent streams), mudflats, sand flats, wetlands, sloughs, prairie potholes, wet meadows, playa lakes, or natural ponds. [See 40 CFR 122.2 for the complete definition.]

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Denver Water Quality Management Plan Glossary Page G-13 Watershed: That geographical area which drains to a specified point on a water course, usually a confluence of streams or rivers (also known as drainage area, catchment, or river basin). Wet Pond: See definition of Retention Pond. Wet Weather Flows: Water entering storm drains during rainstorms. Wetlands: Areas that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs, and similar areas. WQCV: Water Quality Capture Volume (see definition above). Zero-Lot-Line Development: A development option in which side yard restrictions are reduced and the building abuts a side lot line. Overall unit-lot densities are therefore increased. Zero-lot-line development can result in increased protection of natural resources, as well as reduction in requirements for roads and sidewalks.

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Denver Water Quality Management Plan Appendices Appendices

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Denver Water Quality Management Plan Appendices Appendix A Colorado Water Quality Control Commission Stream Classifications and Water Quality Standards Relevant to DenverEffective November 1, 2004(Includes Stream Segments Either in orAdjacent to Denver s Boundaries)

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STREAM CLASSIFICATIONS and WATER QUALITY STANDARDS DESIG CLASSIFICATIONS NUMERIC STANDARDS REGION: 2,3 & 4 BASIN: UPPER SOUTH PLATTE RIVER Stream Segment Description PHYSICAL and BIOLOGICAL INORGANIC mg/l METALS ug/l TEMPORARY MODIFICATIONS AND QUALIFIERS 10b. Mainstem of West Plum Creek including all tributaries, lakes, reservoirs, and wetlands from its source to Perry Park Pond. Aq Life Cold 1 Recreation 1a Water Supply Agriculture D.O.=6.0 mg/l D.O.(sp)=7.0 mg/l pH=6.5-9.0 F.Coli=200/100ml E. Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.02 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.05 NO 3 =10 Cl=250 S0 4 =WS As(ac)=50(Trec) Cd(ac)=TVS(tr) Cd(ch)=TVS CrIII(ac)=50(Trec) CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=WS(dis) Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Mn(ch)=WS(dis) Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac)=TVS Ag(ch)=TVS(tr) Zn(ac/ch)=TVS 11a. All tributaries to the East Plum Creek system, including all lakes, reservoirs and wetlands which are not on national forest lands. UP Aq Life Warm 2 Recreation 1a Agriculture D.O.=5.0 mg/l pH=6.5-9.0 F.Coli=200/100ml E. Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.06 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 As(ch)=100(Trec) Cd(ac/ch)=TVS CrIII(ac/ch)=TVS CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS 11b. All tributaries to the West Plum Creek system, including all lakes, reservoirs and wetlands, which are not on national forest lands, except for specific listings in Segments 9 and 12. UP Aq Life Warm 2 Recreation 1a Agriculture D.O.=5.0 mg/l pH=6.5-9.0 F.Coli=200/100ml E. Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.06 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 As(ch)=100(Trec) Cd(ac/ch)=TVS CrIII(ac/ch)=TVS CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS 12. Mainstem of Garber Creek and Jackson Creek from the boundary of National Forest lands to the confluence with West Plum Creek. Aq Life Cold 1 Recreation 1a Water Supply Agriculture D.O.=6.0 mg/l D.O.(sp)=7.0 mg/l pH=6.5-9.0 F.Coli=200/100ml E. Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.02 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.05 NO 3 =10 Cl=250 S0 4 =WS As(ac)=50(Trec) Cd(ac)=TVS(tr) Cd(ch)=TVS CrIII(ac)=50(Trec) CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=WS(dis) Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Mn(ch)=WS(dis) Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac)=TVS Ag(ch)=TVS(tr) Zn(ac/ch)=TVS 13. Mainstem of Deer Creek, including the North and South Forks, from the source to Chatfield Reservoir. Aq Life Cold 1 Recreation 1a Water Supply Agriculture D.O.=6.0 mg/l D.O.(sp)=7.0 mg/l pH=6.5-9.0 F.Coli=200/100ml E. Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.02 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.05 NO 3 =10 Cl=250 S0 4 =WS As(ac)=50(Trec) Cd(ac)=TVS(tr) Cd(ch)=TVS CrIII(ac)=50(Trec) CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=WS(dis) Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Mn(ch)=WS(dis) Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac)=TVS Ag(ch)=TVS(tr) Zn(ac/ch)=TVS 14. Mainstem of the South Platte River from Bowles Avenue in Littleton, Colorado, to the Burlington Ditch diversion in Denver, Colorado. Aq Life Warm 1 Recreation 1a Water Supply Agriculture D.O.=5.0 mg/l pH=6.5-9.0 F.Coli=200/100ml E. Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.06 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 NO 3 =10 Cl=250 S0 4 =WS As(ac)=50(Trec) Cd(ac/ch)=TVS CrIII(ac)=50(Trec) CrVI(ac/ch)=TVS Cu(ac/ch)=TVS*2.8 Fe(ch)=WS(dis) Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ch)=190(dis) Mn(ac/ch)=TVS Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS 15. Mainstem of the South Platte River from the Burlington Ditch diversion in Denver, Colorado, to a point immediately below the confluence with Big Dry Creek. UP Aq Life Warm 2 Recreation 1a Water Supply Agriculture D.O.* pH = 6.5-9.0** F.Coli=200/100ml E. Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.10 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =1.0 NO 3 =10 Cl=250 S0 4 =WS As(ac)=50(Trec) Cd(ac/ch)=TVS CrIII(ac)=50(Trec) CrVI(ac/ch)=TVS Cu(ac/ch)=TVS*2.3 Fe(ch)=WS(dis) Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ch)=400(dis) Mn(ac/ch)=TVS Hg(ac)=2.4(dis) Hg(ch)=0.4(dis) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS *See attached table for sitespecific Dissolved Oxygen standards. **pH=6.0-9.0 from 64 th Ave. downstream 2 miles. Temporary modifications: F. Coli=existing quality; E.Coli=existing quality. Expiration date of 2/28/10. 16a. Mainstem of Sand Creek from the source to the confluence with the South Platte River. UP Aq Life Warm 2 Recreation 1a Agriculture D.O.=5.0 mg/l pH=6.5-9.0 F.Coli=200/100ml E. Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.1 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 As(ch)=100(Trec) Cd(ac/ch)=TVS CrIII(ac/ch)=TVS CrVI(ac/ch)=TVS Cu(ac/ch)=TVS* Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac)=TVS Se(ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS Temporary modifications: Se(ch)= 19.3 g/l Se(ac)=no acute standard. Expiration date of 2/28/10. *Cu (ac/ch) = TVS *2.6 below the Sand Creek Water Reuse Facility outfall.

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STREAM CLASSIFICATIONS and WATER QUALITY STANDARDS DESIG CLASSIFICATIONS NUMERIC STANDARDS REGION: 2,3 & 4 BASIN: UPPER SOUTH PLATTE RIVER PHYSICAL and BIOLOGICAL INORGANIC mg/l METALS ug/l TEMPORARY MODIFICATIONS AND QUALIFIERS 16b. Aurora Reservoir. Aq Life Warm 1 Recreation 1a Water Supply Agriculture D.O.=6.0 mg/l D.O.(sp)=7.0 mg/l pH=6.5-9.0 F.Coli=200/100m E. Coli=126l/100ml NH 3 (ac)=TVS NH 3 (ch)=0.06 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.05 NO 3 =10 Cl=250 SO 4 =WS As(ac)=50(Trec) Cd(ac)=TVS(tr) Cd(ch)=TVS CrIII(ac)=50(Trec) CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=WS(dis) Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Mn(ch)=WS(dis) Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac)=TVS Ag(ch)=TVS(tr) Zn(ac/ch)=TVS 16c. All tributaries to the South Platte River, including all lakes, reservoirs and wetlands, from the outlet of Chatfield Reservoir, to a point immediately below the confluence with Big Dry Creek, except for specific listings in the subbasins of the South Platte River, and in Segments 16a, 16b, 16d, 16e, 16f, 16g, 17a, 17b, and 17c. UP Aq Life Warm 2 Recreation 1a Agriculture D.O.=5.0 mg/l pH=6.5-9.0 F.Coli=200/100ml E. Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.06 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 As(ch)=100(Trec) Cd(ac/ch)=TVS CrIII(ac/ch)=TVS CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS Fish Ingestion Organics Temporary modifications: East & West Toll Gate Creeks, Toll Gate Creek Se(ch)=18 g/l(dis), Se(ac)=no acute standard. Expiration date of 2/28/10. 16d. Second Creek from the source to the OBrian Canal. UP Aq Life Warm 2 Recreation 1a Agriculture D.O. (ch)=3.3 mg/l 1 pH=6.5-9.0 F.Coli=200/100ml E. Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.06 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 As(ch)=100(Trec) Cd(ac/ch)=TVS CrIII(ac/ch)=TVS CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS 1 15 th percentile of D.O. measurements collected between 6:30 a.m. and 6:30 p.m. 16e. Third Creek from the source to the OBrian Canal. UP Aq Life Warm 2 Recreation 1a Agriculture D.O. (ch)=4.0 mg/l 1 pH=6.5-9.0 F.Coli=200/100ml E. Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.06 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 As(ch)=100(Trec) Cd(ac/ch)=TVS CrIII(ac/ch)=TVS CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS 1 15 th percentile of D.O. measurements collected between 6:30 a.m. and 6:30 p.m. 16f. Barr Lake Tributary from the source to the Denver Hudson Canal. UP Aq Life Warm 2 Recreation 1a Agriculture D.O. (ch)= 1 pH=6.5-9.0 F.Coli=200/100ml E. Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.06 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 As(ch)=100(Trec) Cd(ac/ch)=TVS CrIII(ac/ch)=TVS CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS 1 When water is present, D.O. concentrations shall be maintained at levels that protect classified uses. 16g. Marcy Gulch from, including all lakes, reservoirs, and wetlands from the source to the confluence with the South Platte. UP Aq Life Warm 2 Recreation 1a Agriculture D.O.=5.0 mg/l pH=6.5-9.0 F.Coli=200/100ml E. Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.06 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 As(ch)=100(Trec) Cd(ac/ch)=TVS CrIII(ac/ch)=TVS CrVI(ac/ch)=TVS Cu(ac/ch)=TVS* Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS *Cu (ac/ch) = TVS *2.4 below the Centennial Wastewater Treatment Facility outfall 17a. Washington Park Lakes, City Park Lake, Rocky Mountain Lake, Berkely Lake. UP Aq Life Warm 1 Recreation 1a Agriculture D.O.=5.0 mg/l pH=6.5-9.0 F.Coli=200/100ml E.Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.06 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 As(ch)=100(Trec) Cd(ac/ch)=TVS CrIII(ac/ch)=TVS CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS 17b. Sloans Lake. Aq Life Warm 1 Recreation 1a Agriculture D.O.=5.0 mg/l pH=6.5-9.0 F.Coli=200/100ml E.Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.06 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 As(ch)=100(Trec) Cd(ac/ch)=TVS CrIII(ac/ch)=TVS CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS 17c. Bowles Lake, a.k.a. Patrick Reservoir or Bow Mar Lake. Aq Life Warm 1 Recreation 1a Agriculture D.O.=5.0 mg/l D.O.(sp)=7.0 mg/l pH=6.5-9.0 F.Coli=200/100ml E.Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.06 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 Al(ac/ch)=TVS As(ch)=100(Trec) Cd(ac/ch)=TVS CrIII(ac/ch)=TVS CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS

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UPPER SOUTH PLATTE RIVER SEGMENT 15 Site-Specific Minimum Dissolved Oxygen Standards UNDERLYING STANDARDS Early Life Stage Protection Period (April 1 through July 31) 1-Day 1,5,6 3.0 mg/L (acute) 7-Day Average 1.2.,4 5.0 mg/L Older Life Stage Protection Period (August 1 through March 31) 1-Day 1,5 2.0 mg/L (acute) 7-Day Mean of Minimums 1,3 2.5 mg/L 30-Day Average 1.2. 4.5 mg/L TEMPORARY MODIFICATION During the period until October 31, 2001, the Segment 15 dissolved oxygen standards from 88 th Avenue north to the end of the Segment shall be the currently existing ambient conditions as monitored in 1992, 1993, and 1994 by the Division and by the Metro District. Beginning November 1, 2001, the standards shall apply to all sections of Segment 15 south of the Brighton Ditch diversion. The standards north of the Brighton Ditch diversion shall continue to be the ambient conditions existing in 1992, 1993, and 1994. Beginning November 1, 2004, the standards shall apply to all sections of Segment 15. Footnotes 1. For the purposes of determining compliance with the standards, dissolved oxygen measurements shall only be taken in the flowing portion of the stream at mid-depth, and at least six inches above the bottom of the channel. All sampling protocols and test procedures shall be in accordance with procedures and protocols approved by the Division. 2. A minimum of four independent daily means must be used to calculate the average for the 7-Day Average standard. A minimum of eight independent daily means must be used to calculate the average for the 30-Day Average standard. The four days and the eight days must be representative of the 7-Day and the 30-Day periods respectively. The daily means shall be the mean of the daily high and low values. In calculating the mean values, the dissolved oxygen saturation value shall be used in place of any dissolved oxygen measurements which exceed saturation. 3. The 7-Day Mean minimum is the average of the daily minimums measured at the location on each day during any 7-Day period.

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4 North of the Lupton Bottoms Ditch diversion, the ELS 7-Day average standards for the period July 1 June 31 shall be 4.6 mg/L. 5. During a 24 hour day dissolved oxygen levels are likely to be lower during the nighttime when there is no photosynthesis. The dissolved oxygen levels should not drop below the acute standard (ELS acute standard of 3.0 mg/L or the OLS standards of 2.0 mg/L). However, if during the ELS period multiple measurements are below 3.0 mg/L during the same nighttime period, the multiple measurements shall be considered a single exceedance of the acute standard. For measurements below 2.0 mg/L during either the ELS or the OLS periods, each hourly measurement below 2.0 mg/L shall be considered an exceedance of the acute standards. 6. In July, the dissolved oxygen level in Segment 15 may be lower than the 3.0 mg/L acute standard for up to 14 exceedances in any one year and up to a total of 21 exceedances in three years before there is a determination that the acute dissolved oxygen standards is not being met. Exceedances shall be counted as described in Footnote 5.

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STREAM CLASSIFICATIONS and WATER QUALITY STANDARDS DESIG C LASSIFICATIONS NUMERIC STANDARDS REGION: 3 AND 4 BASIN: CHERRY CREEK Stream Segment Description PHYSICAL and BIOLOGICAL INORGANIC mg/l METALS ug/l TEMPORARY MODIFICATIONS AND QUALIFIERS 1. Mainstem of Cherry Creek from the source of East and West Cherry Creek to the inlet of Cherry Creek Reservoir. UP Aq Life Warm 2 Recreation 1a Water Supply Agriculture D.O.=5.0 mg/l pH=6.5-9.0 F.Coli=200/100ml E.Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.06 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 NO 3 =10 Cl=250 SO 4 =WS As(ac)=50(Trec) Cd(ac/ch)=TVS CrIII(ac)=50(Trec) CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=WS(dis) Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Mn(ch)=WS(dis) Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS 2. Cherry Creek Reservoir. Aq Life Warm 1 Recreation 1a Water Supply Agriculture D.O.=5.0 mg/l pH=6.5-9.0 F.Coli=200/100ml E.Coli=126/100ml Season mean chlorophyll a = 15 g/l measured in the upper three meters of the water column for the months of July through September NH 3 (ac)=TVS NH 3 (ch)=0.06 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 NO 3 =10 Cl=250 SO 4 =WS As(ac)=50(Trec) Cd(ac/ch)=TVS CrIII(ac)=50(Trec) CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=WS(dis) Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Mn(ch)=WS(dis) Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS 3. Mainstem of Cherry Creek from the outlet of Cherry Creek Reservoir to the confluence with the South Platte River. UP Aq Life Warm 2 Recreation 1a Water Supply Agriculture D.O.=5.0 mg/l pH=6.5-9.0 F.Coli=200/100ml E.Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.10 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 NO 3 =10 Cl=250 SO 4 =WS As(ac)=50(Trec) Cd(ac/ch)=TVS CrIII(ac)=50(Trec) CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=WS(dis) Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Mn(ch)=WS(dis) Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS 4. All tributaries to Cherry Creek, including all lakes, reservoirs and wetlands, from the source of East and West Cherry Creeks to the confluence with the South Platte River, except for specific listings in Segment 2. UP Aq Life Warm 2 Recreation 1a Agriculture D.O.=5.0 mg/l pH=6.5-9.0 F.Coli=200/100ml E.Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.10 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 As(ch)=100(Trec) Cd(ac/ch)=TVS CrIII(ac/ch)=TVS CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS

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STREAM CLASSIFICATIONS and WATER QUALITY STANDARDS DESIG CLASSIFICATIONS NUMERIC STANDARDS REGION: 3 BASIN: CLEAR CREEK Stream Segment Description PHYSICAL and BIOLOGICAL INORGANIC mg/l METALS ug/l TEMPORARY MODIFICATIONS AND QUALIFIERS 15. Mainstem of Clear Creek from Youngfield Street in Wheat Ridge, Colorado, to the confluence with the South Platte River. UP Aq Life Warm 1 Recreation 1a Water Supply Agriculture D.O.=5.0 mg/l pH = 6.5-9.0 F.Coli=200/100ml E.Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.06 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 NO 3 =10 Cl=250 SO 4 =WS As(ac)=50(Trec) Cd(ac/ch)=TVS CrIII(ac)=50(Trec) CrVI(ac/ch)=TVS Cu(ac/ch)=TVSx3. 66* Fe(ch)=WS(dis) Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Mn(ch)=WS(dis) Hg(ch)=0.01(Trec) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVSx1. 57* Aquatic life warm 1 goal qualifier. Temporary modification: E.Coli=261/100 ml. Expiration date of 2/28/10. 16a. Mainstem of Lena Gulch including all tributaries, lakes, reservoirs and wetlands from its source to the outlet of Maple Grove Reservoir. UP Aq Life Warm 2 Recreation 1a Water Supply Agriculture D.O.=5.0 mg/l pH=6.5-9.0 F.Coli=200/100ml E.Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.10 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.05 NO 3 =10 Cl=250 SO 4 =WS As(ac)=50(Trec) Cd(ac)=TVS Cd(ch)=TVS CrIII(ac)=50(Trec) CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=WS(dis) Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Mn(ch)=WS(dis) Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS 16b.All tributaries to Clear Creek from the Farmers Highline Canal diversion in Golden, Colorado to the confluence with the South Platte River, except for specific listings in Segments 16a, 17a, 17b, 18a and 18b. UP Aq Life Warm 2 Recreation 2 Agriculture D.O.=5.0 mg/l pH=6.5-9.0 F.Coli=2000/100ml E.Coli=630/100ml NH 3 (ac)=TVS NH 3 (ch)=0.10 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 As(ch)=100(Trec) Cd(ac/ch)=TVS CrIII(ac/ch)=TVS CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS 17a. Arvada Reservoir. UP Aq Life Cold 2 Recreation 2 Water Supply Agriculture D.O.=6.0 mg/l D.O.(sp)=7.0 mg/l pH=6.5-9.0 F.Coli=200/100ml E.Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.02 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.05 NO 3 =10 Cl=250 SO 4 =WS As(ac)=50(Trec) Cd(ac)=TVS(tr) Cd(ch)=TVS CrIII(ac)=50(Trec) CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=WS(dis) Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Mn(ch)=WS(dis) Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS Water + Fish Organics 17b. Mainstem of Ralston Creek from the source to the inlet of Arvada Reservoir, including Ralston Reservoir, and Upper Long Lake. UP Aq Life Cold 2 Recreation 1a Water Supply Agriculture D.O.=6.0 mg/l D.O.(sp)=7.0 mg/l pH=6.5-9.0 F.Coli-200/100ml E.Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.02 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.05 NO 3 =10 Cl=250 SO 4 =WS As(ac)=50(Trec) Cd(ac)=TVS(tr) Cd(ch)=TVS CrIII(ac)=50(Trec) CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=WS(dis) Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Mn(ch)=WS(dis) Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS Water + Fish Organics 18a. Mainstem of Ralston Creek, including all lakes and reservoirs, from the outlet of Arvada Reservoir to the confluence with Clear Creek. UP Aq Life Warm 2 Recreation 1a Water Supply Agriculture D.O. = 5.0 mg/l pH = 6.5-9.0 F.Coli=200/100ml E.Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.10 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 NO 3 =10 Cl=250 SO 4 =WS As(ac)=50(Trec) Cd(ac/ch)=TVS CrIII(ac)=50(Trec) CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=WS(dis) Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Mn(ch)=WS(dis) Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS 18b. Mainstem of Leyden Creek and Van Bibber Creek from their source to their confluence with Ralston Creek. Mainstem of Little Dry Creek from its source to its confluence with Clear Creek. UP Aq Life Warm 2 Recreation 2 Water Supply Agriculture D.O.=5.0 mg/l pH=6.5-9.0 F.Coli=2000/100ml E.Coli=630/100ml NH 3 (ac)=TVS NH 3 (ch)=0.10 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 NO 3 =10 Cl=250 SO 4 =WS As(ac)=50(Trec) Cd(ac/ch)=TVS CrIII(ac)=50(Trec) CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=WS(dis) Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Mn(ch)=WS(dis) Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS 19. All tributaries to Clear Creek, including lakes, reservoirs and wetlands, within the Mt. Evans Wilderness Area. OW Aq Life Cold 1 Recreation 1a Water Supply Agriculture D.O.=6.0 mg/l D.O.(sp)=7.0 mg/l pH=6.5-9.0 F.Coli=200/100ml E.Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.02 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.05 NO 3 =10 Cl=250 SO 4 =250 As(ac)=50(Trec) Cd(ac)=TVS(tr) Cd(ch)=TVS CrIII(ac)=50(Trec) CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=WS(dis) Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Mn(ch)=WS(dis) Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac)=TVS Ag(ch)=TVS(tr) Zn(ac/ch)=TVS TVS x (times) the FWER (final water effect ratio) = site-specific standard.

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DESIG CLASSIFICATIONS NUMERIC STANDARDS REGION: 2 BASIN: MIDDLE SOUTH PLATTE RIVER Stream Segment Description PHYSICAL and BIOLOGICAL INORGANIC mg/l METALS Ug/l TEMPORARY MODIFICATIONS AND QUALIFIERS 1a. Mainstem of the South Platte River from a point immediately below the confluence with Big Dry Creek to the confluence with St. Vrain Creek. UP Aq Life Warm 2 Recreation 1a Water Supply Agriculture D.O.* pH=6.5-9.0 F.Coli=200/100ml E.Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.10 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 NO 3 =10 Cl=250 SO 4 =WS As(ac)=50(Trec) Cd(ac/ch)=TVS CrIII(ac)=50(Trec) CrIII(ch)=TVS CrVI(ac/ch)=TVS Cu(ac/ch)=TVS*2.2 Fe(ch)=WS(dis) Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Mn(ch)=WS(dis) Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS *See attached table for sitespecific Dissolved Oxygen standards. Fish Ingestion Organics 1b. Mainstem of the South Platte River from a point immediately below the confluence with St. Vrain Creek to the Weld/Morgan County Line. UP Aq Life Warm 2 Recreation 1a Water Supply Agriculture D.O.=5.0 mg/l pH=6.5-9.0 F.Coli=200/100ml E.Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.10 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 NO 3 =10 Cl=250 SO 4 =WS As(ac)=50(Trec) Cd(ac/ch)=TVS CrIII(ac)=50(Trec) CrIII(ch)=TVS CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=WS(dis) Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Mn(ch)=WS(dis) Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS Fish Ingestion Organics Temporary modification: NH 3 (ch)=0.12 mg/l below confluence with Cache La Poudre River. Expiration date of 2/28/10. 2. Deleted. 3a. All tributaries to the South Platte River, including all lakes, reservoirs and wetlands, from a point immediately below the confluence with Big Dry Creek to the Weld/Morgan County line, except for specific listings in the subbasins of the South Platte River, and in Segments 3b, 4, 5a, 5b, 5c, and 6. UP Aq Life Warm 2 Recreation 1a Agriculture D.O.=5.0 mg/l pH=6.5-9.0 F.Coli=200/100ml E.Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.10 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 As(ch)=100(Trec) Cd(ac/ch)=TVS CrIII(ac/ch)=TVS CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS Fish Ingestion Organics 3b. Hayesmount Tributaries including the Upper Hayesmount Tributary from the source to the confluence with Box Elder Creek and the Lower Hayesmount Tributaries from the source to the Denver Hudson Canal. UP Aq Life Warm 2 Recreation 1a Agriculture D.O. (ch)= 1 pH=6.5-9.0 F.Coli=200/100ml E.Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.10 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 As(ch)=100(Trec) Cd(ac/ch)=TVS CrIII(ac/ch)=TVS CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS 1 When water is present, D.O. concentrations shall be maintained at levels that protect classified uses. 4. Barr Lake and Milton Reservoir. UP Aq Life Warm 2 Recreation 1a Water Supply Agriculture D.O.=5.0 mg/l pH=6.5-9.0 F.Coli=200/100ml E.Coli=126/100ml NH 3 (ac)=TVS NH 3 (ch)=0.10 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 NO 3 =10 Cl=250 SO 4 =WS As(ac)=50(Trec) Cd(ac/ch)=TVS CrIII(ac)=50(Trec) CrIII(ch)=TVS CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=WS(dis) Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Mn(ch)=WS(dis) Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS Fish Ingestion Organics 5a. Mainstems of Lone Tree Creek, Crow Creek and Boxelder Creek from their s ources to their confluences with the South Platte River, except for specific listings in Segment 5b. UP Aq Life Warm 2 Recreation 2 Agriculture D.O.=5.0 mg/l pH=6.5-9.0 F.Coli=2000/100ml E.Coli=630/100ml NH 3 (ac)=TVS NH 3 (ch)=0.10 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =0.5 As(ch)=100(Trec) Cd(ac/ch)=TVS CrIII(ac/ch)=TVS CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS Temporary modification: Lone Tree Creek NH 3 (ch)=0.26 mg/l. Expiration date of 2/28/10. 5b. Mainstem of Boxelder Creek from the confluence with Coyote Run to the Denver Hudson Canal. UP Aq Life Warm 2 Recreation 2 Agriculture D.O. (ch)=4.7 mg/l 1 pH=6.5-9.0 F.Coli=2000/100ml E.Coli=630/100ml NH 3 (ac)=TVS NH 3 (ch)=0.10 Cl 2 (ac)=0.019 Cl 2 (ch)=0.011 CN=0.005 S=0.002 B=0.75 NO 2 =10 NO 3 =100 As(ch)=100(Trec) Cd(ac/ch)=TVS CrIII(ac/ch)=TVS CrVI(ac/ch)=TVS Cu(ac/ch)=TVS Fe(ch)=1000(Trec) Pb(ac/ch)=TVS Mn(ac/ch)=TVS Hg(ch)=0.01(Tot) Ni(ac/ch)=TVS Se(ac/ch)=TVS Ag(ac/ch)=TVS Zn(ac/ch)=TVS 1 15 th percentile of D.O. measurements collected between 6:30 a.m. and 6:30 p.m.

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DESIG CLASSIFICATIONS NUMERIC STANDARDS REGION: 2 BASIN: MIDDLE SOUTH PLATTE RIVER Stream Segment Description PHYSICAL and BIOLOGICAL INORGANIC mg/l METALS Ug/l TEMPORARY MODIFICATIONS AND QUALIFIERS 6. Lost Creek from Interstate 76 south, including all its tributaries, stock ponds and wetlands. UP Aq Life Warm 2 Recreation 2 Agriculture D.O.=5.0 mg/l pH=6.5-9.0 F.Coli=2000/100ml E. Coli=630/100ml NO 3 =100 N0 2 =10 CN=0.2 S=0.002 B=0.75 As=100(Trec) Be(ch)=100(Trec) Cd=10(Trec) CrIII=100(Trec) CrVI=100(Trec) Cu=200(Trec) Pb=100(Trec) Mn=200(Trec) Ni=200(Trec) Se=20(Trec) Zn=2000(Trec)

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Site-Specific Minimum Dissolved Oxygen Standards for Middle South Platte segment 1a STANDARDS Early Life Stage Protection Period (April 1 through July 31) 1-Day 1.4,5 3.0 mg/L (acute) 7-Day Average 1.2 5.0 mg/L Older Life Stage Protection Period (August 1 through March 31) 1-Day 1.4 2.0 mg/L (acute) 7-Day Mean of Minimums 1.3. 2.5 mg/L 30-Day Average 1.2. 4.5 mg/L Footnotes 1. For the purpose of determining compliance with the standards, dissolved oxygen measurements shall only be taken in the flowing portion of the stream at mid-depth, and at least six inches above the bottom of the channel. All sampling protocols and test procedures shall be in accordance with procedures and protocols approved by the Division. 2. A minimum of four independent daily means must be used to calculate the average for the 7-Day Average standard. A minimum of eight independent daily means must be used to calculate the average for the 30-Day Average standard. The four days and the eight days must be representative of the 7-Day and the 30-Day periods respectively. The daily mean shall be the mean of the daily high and low values. In calculating the mean values, the dissolved oxygen saturation value shall be used in place of any dissolved oxygen measurement s which exceed saturation. 3. The 7-Day Mean Minimum is the average of the daily minimums measured at a location on each day during any 7-Day period. 4. During a 24 hour day, dissolved oxygen levels are li kely to be lower during the nighttime when there is no photosynthesis. The dissolved oxygen levels should not dr op below the acute standard (E LS acute standard of 3.0 mg/L or the OLS standard of 2.0 mg/L). However, if during the ELS period multiple measurements are below 3.0 mg/L during the same nighttime period, the multip le measurements shall be cons idered a single exceedance of the acute standard. For m easurements below 2.0 mg/L during either the ELS or the OLS periods, each hourly measurement below 2.0 mg/L shall be consi dered an exceedance of the acute standard. 5. In July, the dissolved oxygen level in Segment 1a may be lower than the 3.0 mg/L acute standard for up to 14 exceedances in any one year and up to a total of 21 exce edances in three years befor e there is a determination that the acute dissolved oxygen standards is not being met. Exc eedances shall be counted as described in Footnote 4.

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Denver Water Quality Management Plan Appendices Appendix B Denver s Response to April 2004 EPA Audit of Stormwater Program

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Denver Water Quality Management Plan Appendices Appendix C Water Quality Improvement in the South Platte River, Report to the Mayor

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Denver Water Quality Management Plan Appendices Appendix D Representative Stormwater BMP Maintenance Agreements

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I 70 I 70 I 25 I 25 I 25 HARLAN ST HARLAN ST SHERIDAN BLVD SHERIDAN BLVD TENNYSON ST TENNYSON ST LOWELL BLVD LOWELL BLVD FEDERAL BLVD FEDERAL BLVD ZUNI ST ZUNI ST PECOS ST PECOS ST HURON ST HURON ST BROADWAY BROADWAY FRANKLIN ST FRANKLIN ST WASHINGTON ST WASHINGTON ST YORK ST YORK ST STEELE ST STEELE ST COLORADO BLVD COLORADO BLVD DAHLIA ST DAHLIA ST HOLLY ST HOLLY ST MONACO ST MONACO ST QUEBEC ST QUEBEC ST ULSTER ST ULSTER ST YOSEMITE ST YOSEMITE ST DAYTON ST DAYTON ST N HAVANA ST N HAVANA ST N LIMA ST N LIMA ST N PEORIA ST N PEORIA ST URSULA ST URSULA ST POTOMAC ST POTOMAC ST SABLE BLVD SABLE BLVD CHAMBERS RD CHAMBERS RD LAREDO ST LAREDO ST TELLURIDE ST TELLURIDE ST TOWER RD TOWER RD DUNKIRK ST DUNKIRK ST HIMALAYA ST HIMALAYA ST LIVERPOOL ST LIVERPOOL ST PICADILLY RD PICADILLY RD BUCKLEY RD BUCKLEY RD 56TH AVE 56TH AVE 52ND AVE 52ND AVE 48TH AVE 48TH AVE 44TH AVE 44TH AVE 38TH AVE 38TH AVE 32ND AVE 32ND AVE 26TH AVE 26TH AVE 20TH AVE 20TH AVE COLFAX AVE COLFAX AVE 11TH AVE 11TH AVE 6TH AVE 6TH AVE 1ST AVE 1ST AVE ALAMEDA AVE ALAMEDA AVE EXPOSITION AVE EXPOSITION AVE MISSISSIPPI AVE MISSISSIPPI AVE FLORIDA AVE FLORIDA AVE JEWELL AVE JEWELL AVE ILIFF AVE ILIFF AVE YALE AVE YALE AVE DARTMOUTH AVE DARTMOUTH AVE HAMPDEN AVE HAMPDEN AVE MANSFIELD AVE MANSFIELD AVE QUINCY AVE QUINCY AVE UNION AVE UNION AVE BELLVIEW AVE BELLVIEW AVE Cherry Creek Cherry Creek 5200-02 0067-02 4600-04 5500-02 4600-03 5100-01 0061-01 3700-01 4400-01 5000-02 4400-02 4600-02 4601-02 3901-01 4500-01 4401-01 4601-01 5500-01 0059-01 4500-04 4401-03 3900-03 3501-01 3700-02 5901-01 4400-04 4401-02 0062-01 0060-01 0064-02 4600-01 0063-01 4900-01 4401-04 4700-01 3900-02 4309-01 4300-03 4500-02 5500-04 3900-04 4500-03 4400-03 0060-02 5501-01 5300-01 3702-01 4000-01 5000-01 0065-01 4800-01 0064-01 3901-02 5200-01 0067-01 0065-02 0058-01 4801-01 0067-03 5500-03 5500-05 5500-04 SECOND CREEK THIRD CREEK 4601-03 UPPER HAYSMOUNT BOX ELDER 3900-01 Cherry Creek Cherry Creek South Platte River South Platte River W e s t T o l l G a t e C r e e k W e s t T o l l G a t e C r e e k Irondale Gulch Irondale Gulch First Creek First Creek Second Creek Second Creek Third Creek Third Creek Box Elder Creek Box Elder Creek South Platte River South Platte River Sand Creek Sand Creek East Toll Gate Creek East Toll Gate Creek Toll Gate Creek Toll Gate Creek Clear Creek Clear Creek FILE: denexgGIS_ProjectsDenverDrainageactiveappswright_waterexhibit2.3_location_map.mxd, 1/11/2005, wilson_wheeler Exhibit 2.3 Drainage Basins Location Map 0 2 1 Miles Streets-Interstates City & County of Denver Storm Basins County Boundary Rivers/Creeks Lake Legend

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I 70 I 70 I 25 I 25 I 25 HARLAN ST HARLAN ST SHERIDAN BLVD SHERIDAN BLVD TENNYSON ST TENNYSON ST LOWELL BLVD LOWELL BLVD FEDERAL BLVD FEDERAL BLVD ZUNI ST ZUNI ST PECOS ST PECOS ST HURON ST HURON ST BROADWAY BROADWAY FRANKLIN ST FRANKLIN ST WASHINGTON ST WASHINGTON ST YORK ST YORK ST STEELE ST STEELE ST COLORADO BLVD COLORADO BLVD DAHLIA ST DAHLIA ST HOLLY ST HOLLY ST MONACO ST MONACO ST QUEBEC ST QUEBEC ST ULSTER ST ULSTER ST YOSEMITE ST YOSEMITE ST DAYTON ST DAYTON ST N HAVANA ST N HAVANA ST N LIMA ST N LIMA ST N PEORIA ST N PEORIA ST URSULA ST URSULA ST POTOMAC ST POTOMAC ST SABLE BLVD SABLE BLVD CHAMBERS RD CHAMBERS RD LAREDO ST LAREDO ST TELLURIDE ST TELLURIDE ST TOWER RD TOWER RD DUNKIRK ST DUNKIRK ST HIMALAYA ST HIMALAYA ST LIVERPOOL ST LIVERPOOL ST PICADILLY RD PICADILLY RD BUCKLEY RD BUCKLEY RD 56TH AVE 56TH AVE 52ND AVE 52ND AVE 48TH AVE 48TH AVE 44TH AVE 44TH AVE 38TH AVE 38TH AVE 32ND AVE 32ND AVE 26TH AVE 26TH AVE 20TH AVE 20TH AVE COLFAX AVE COLFAX AVE 11TH AVE 11TH AVE 6TH AVE 6TH AVE 1ST AVE 1ST AVE ALAMEDA AVE ALAMEDA AVE EXPOSITION AVE EXPOSITION AVE MISSISSIPPI AVE MISSISSIPPI AVE FLORIDA AVE FLORIDA AVE JEWELL AVE JEWELL AVE ILIFF AVE ILIFF AVE YALE AVE YALE AVE DARTMOUTH AVE DARTMOUTH AVE HAMPDEN AVE HAMPDEN AVE MANSFIELD AVE MANSFIELD AVE QUINCY AVE QUINCY AVE UNION AVE UNION AVE BELLVIEW AVE BELLVIEW AVE S o u t h P l a t t e R i v e r S o u t h P l a t t e R i v e r C h e r r y C r e e k C h e r r y C r e e k S o u t h P l a t t e R i v e r S o u t h P l a t t e R i v e r Irondale Gulch Irondale Gulch First Creek First Creek Second Creek Second Creek Third Creek Third Creek Box Elder Creek Box Elder Creek Sand Creek Sand Creek East Toll Gate Creek East Toll Gate Creek Toll Gate Creek Toll Gate Creek West Toll Gate Creek West Toll Gate Creek Clear Creek Clear Creek FILE: denexgGIS_ProjectsDenverDrainageactiveappswright_waterexhibit8.1_drainage_basins.mxd, 1/11/2005, wilson_wheeler 0 2 1 Miles Exhibit 8.1 Denver Drainage Basin Map Legend Bear Creek Cherry Creek Clear Creek First Creek Harvard Gulch Irondale Gulch Lakewood Gulch Sand Creek Sanderson Gulch Second Creek Sloan's Lake South Platte River Weir Gulch County Boundary Rivers/Creek Waterbodies Box Elder Creek Third Creek Haysmount Creek

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I 70 I 70 I 25 I 25 I 25 HARLAN ST HARLAN ST SHERIDAN BLVD SHERIDAN BLVD TENNYSON ST TENNYSON ST LOWELL BLVD LOWELL BLVD FEDERAL BLVD FEDERAL BLVD ZUNI ST ZUNI ST PECOS ST PECOS ST HURON ST HURON ST BROADWAY BROADWAY FRANKLIN ST FRANKLIN ST WASHINGTON ST WASHINGTON ST YORK ST YORK ST STEELE ST STEELE ST COLORADO BLVD COLORADO BLVD DAHLIA ST DAHLIA ST HOLLY ST HOLLY ST MONACO ST MONACO ST QUEBEC ST QUEBEC ST ULSTER ST ULSTER ST YOSEMITE ST YOSEMITE ST DAYTON ST DAYTON ST N HAVANA ST N HAVANA ST N LIMA ST N LIMA ST N PEORIA ST N PEORIA ST URSULA ST URSULA ST POTOMAC ST POTOMAC ST SABLE BLVD SABLE BLVD CHAMBERS RD CHAMBERS RD LAREDO ST LAREDO ST TELLURIDE ST TELLURIDE ST TOWER RD TOWER RD DUNKIRK ST DUNKIRK ST HIMALAYA ST HIMALAYA ST LIVERPOOL ST LIVERPOOL ST PICADILLY RD PICADILLY RD BUCKLEY RD BUCKLEY RD 56TH AVE 56TH AVE 52ND AVE 52ND AVE 48TH AVE 48TH AVE 44TH AVE 44TH AVE 38TH AVE 38TH AVE 32ND AVE 32ND AVE 26TH AVE 26TH AVE 20TH AVE 20TH AVE COLFAX AVE COLFAX AVE 11TH AVE 11TH AVE 6TH AVE 6TH AVE 1ST AVE 1ST AVE ALAMEDA AVE ALAMEDA AVE EXPOSITION AVE EXPOSITION AVE MISSISSIPPI AVE MISSISSIPPI AVE FLORIDA AVE FLORIDA AVE JEWELL AVE JEWELL AVE ILIFF AVE ILIFF AVE YALE AVE YALE AVE DARTMOUTH AVE DARTMOUTH AVE HAMPDEN AVE HAMPDEN AVE MANSFIELD AVE MANSFIELD AVE QUINCY AVE QUINCY AVE UNION AVE UNION AVE BELLEVIEW AVE BELLEVIEW AVE S o u t h P l a t t e R i v e r S o u t h P l a t t e R i v e r C h e r r y C r e e k C h e r r y C r e e k CHERRY CREEK RESERVOIR S o u t h P l a t t e R i v e r S o u t h P l a t t e R i v e r MARSTON LAKE NORTH OF RIVERSIDE CEMETERY OFF-LINE WATER QUALITY POND FROM 38" IN YORK GRAVEL PIT ON-LINE WATER QUALITY POND FROM 84" IN 54TH AVE SWANSEA PARK OFF-LINE WATER QUALITY POND 36TH AVE OFF-LINE WATER QUALITY POND FROM 81" IN 36TH AVE 48TH AVE & COLORADO BLVD DETENTION & WATER QUALITY POND PARK HILL GOLF COURSE DETENTION & WATER QUALITY POND DAHLIA ST OFF-LINE WATER QUALITY POND FROM 90" & 60" IN DAHLIA ST 38TH AVE & GRAPE ST DETENTION & WATER QUALITY POND NORTH STAPLETON DETENTION & WATER QUALITY POND SOUTH STAPLETON OFF-LINE WATER QUALITY POND EXISTING BARNUM PARK ON WEIR GULCH ON-LINE WATER QUALITY POND BLUFF LAKE ON-LINE WATER QUALITY POND STAPLETON POND #180 WATER QUALITY POND STAPLETON POND #181 WATER QUALITY POND BROADWAY OFF-LINE WATER QUALITY POND FROM 108" IN 29TH AVE CENTER AVE OFF-LINE WATER QUALITY POND FROM 54" OUTFALL BERKELEY LAKE ROCKY MOUNTAIN LAKE NORTH WESTERLY CREEK WETLAND FOR WATER QUALITY EXISTING KELLY ROAD DAM ON-LINE DETENTION AND WATER QUALITY EXISTING WESTERLY CREEK DAM ON-LINE DETENTION AND WATER QUALITY SLOAN'S LAKE WEST-BAR-VAL-WOOD DETENTION VANDERBUILT PARK GARFIELD LAKE DETENTION AND WATER QUALITY HUSTON LAKE MISSISSIPPI GULCH ON-LINE WATER QUALITY POND HARVEY PARK LAKE DETENTION AND WATER QUALITY WARD RESERVOIR NO. 5 EXISTING HARVARD PARK ON-LINE DETENTOIN AND WATER QUALITY X X COLORADO ACADEMY DETENTION AND WATER QUALITY HENRY'S LAKE LAKES LAKE MARSTON LAKE CHANNEL PONDS X X FT LOGAN CEMETERY DETENTION EXISTING WELLSHIRE GOLF COURSE ON-LINE DETENTION AND WATER QUALITY WALLACE PARK ON-LINE DETENTION AND WATER QUALITY EAST PRINCETON AVE WATER QUALITY ILIFF ON-LINE DETENTION AND WATER QUALITY 7TH AVE OFF-LINE WATER QUALITY POND FROM 72" PIPE LITTLE HENRY'S LAKE FILE: denexgGIS_ProjectsDenverDrainageactiveappswright_waterexhibit8.2_water_quality11x17.mxd, 1/11/2005, wilson_wheeler Exhibit 8.2 Opportunities for Regional Water Quality Treatment 0 2 1 Miles City & County of Denver Storm Basins County Boundary Rivers/Creeks Water Body Legend