Cherry Creek Reservoir Drainage Basin, Colorado Municipal Separate Storm Sewer Systems, Phase II Stormwater Permit

Watershed-Based Permitting Case Study Cherry Creek Reservoir Drainage Basin, Colorado Municipal Separate Storm Sewer Systems, Phase II Stormwater Permit Permitting Authority Contacts: Other Stakeholders: Colorado Department of Public Health and Environment (CDPHE) Cherry Creek Basin Water Quality Authority Water Quality Control Division www.cherrycreekbasin.org/cc_home.asp 4300 Cherry Creek Drive South Cherry Creek Stewardship Partners Denver, CO 80246-1530 www.cherry-creek.org/ Nathan T. Moore (303) 692-3555 Pollutants and Indicators Addressed in Permit: [email protected] Phosphorus, pollutants associated with storm sewer discharges, chlorophyll a Dick Parachini Permit Information: (303) 692-3516 Permit: www.cdphe.state.co.us/wq/PermitsUnit/stormwater/ [email protected] 2008MS4080000permit.pdf Permit Type: General permit for small municipal separate storm Rationale: www.cdphe.state.co.us/wq/PermitsUnit/stormwater/ sewer systems 2008MS4080000rat.pdf Effective Date: March 10, 2008 Expiration Date: March 9, 2013 Watershed: Cherry Creek (Colorado) Overview and Highlights Key Water Quality Concerns: Phosphorus, chlorophyll a The Colorado Department of Public Health and Environ- ment (CDPHE) developed a watershed-based Phase II Stakeholder Involvement Techniques: Stormwater permit for Municipal Separate Storm Sewer • Permittees and other stakeholders worked Systems (MS4s) with discharges to the Cherry Creek closely with state to develop requirements. Reservoir drainage basin in Colorado. The permit includes • Permit terms revised through public triennial requirements for the Phase II Six Minimum Measures review process for reservoir Control Regulation. for all permitted discharges (Public Education, Public • MS4s coordinate compliance activities across Involvement/Participation, Illicit Discharge Detection and the watershed and within jurisdictions. Elimination, Construction Site Stormwater Runoff Con- Case Study Issues of Interest trol, Post-Construction Stormwater Management, and Pollution Prevention/Good Housekeeping [5 CCR 1002- POTW Discharges 61.18(11)(a)(ii)(A)-(F)]) as well as additional best man- Industrial Process Wastewater Discharges agement practice (BMP) requirements and implementa- Concentrated Animal Feeding Operations tion schedules under the Public Education, Construction, and Post-Construction BMP measures. Municipal Separate Storm Sewer System Discharges ✔ Construction Site Stormwater Discharges The permit requirements are based on the Cherry Creek Reservoir Control Regulation No. 72 (Control Regulation), Industrial Facility Stormwater Discharges which aims at protecting the reservoir’s beneficial uses. Sources of Point Type Combined Sewer Overflows The watershed-based requirements of the permit imple- Statewide Watershed Approach ment the Control Regulation, and, therefore, the permit requirements are modified through Colorado’s triennial Implementation of Water Quality Standards review process for the Control Regulation. This process Implementation of Total Maximum Daily Loads or Other ✔ provides for collaboration among permittees, the permit- Watershed Pollutant Reduction Goals ting authority, and watershed stakeholders to review and Permit Coordination/Synchronization modify requirements every 3 years if needed. Integrated Municipal Requirements Successful implementation of the permit, which is in its Point Source—Point Source Water Quality Trading second cycle, has been attributed to effectively educating Point Source—Nonpoint Source Water Quality Trading permittees and stakeholders and early cooperation among Discharger Association permittees, CDPHE, and the Cherry Creek Basin Water Highlighted Approach(es) Quality Authority (Basin Authority) to develop requirements Coordinated Watershed Monitoring 1 Watershed-Based Permitting Case Study Cherry Creek Reservoir Drainage Basin, Colorado that are consistent with the regulations and feasible for standard. According to permittees to accomplish. This process has also fostered col- the Basin Authority’s Stormwater Phase II laboration among permittees both across the watershed and 2006 Annual Report, the Minimum Measures within jurisdictions to streamline compliance activities. annual phosphorus loads to the reservoir since the 1. Public Education Permitting Background early 1990s have been 2. Public Involvement/ lower than the TMAL, Participation Watershed Description but the chlorophyll a 3. Illicit Discharge Detection Cherry Creek flows north through the 245,500-acre Cherry standard was achieved in and Elimination Creek Reservoir drainage basin toward its confluence with only 3 of the previous 15 4. Construction Site Storm- the South Platte River, the point that marks the original years. The phosphorus water Runoff Control settlement of Denver, Colorado. The 850-acre Cherry Creek goal was never achieved 5. Post-Construction Storm- Reservoir was built at the north end of the watershed for during the same pe- water Management flood control, but its proximity to the Denver metropolitan riod. The revised Control 6. Pollution Prevention/ area makes it a popular destination for swimming, boating, Regulation introduced Good Housekeeping and other recreational activities. The Cherry Creek State a phased approach to Recreation Area surrounding the reservoir receives more than implementing the phos- 1 million visitors each year. phorus TMAL to facilitate the additional investigations necessary to recalculate the Water Quality and Regulatory History TMAL to meet the new chlorophyll a standard. Cherry Creek Reservoir is designated for warm water aquatic Other revisions to the Control Regulation incorporated the six life, primary recreation, water supply, and agriculture uses. minimum measures required under the newly implemented In the early 1980s, a study identified phosphorus as the Phase II stormwater regulations. Furthermore, consistent with nutrient critical to algal productivity in the reservoir. To the phosphorus TMAL, the Control Regulation includes spe- prevent eutrophication and protect the reservoir’s beneficial cific requirements for regulated stormwater discharges in the uses, CDPHE adopted the Control Regulation in 1985. The Cherry Creek Basin to control the discharge of nutrients to Control Regulation established a total phosphorus numeric the Cherry Creek Reservoir. The Control Regulation contains water quality standard for the reservoir and introduced a requirements based on Colorado’s Phase II Municipal Guid- total phosphorus total maximum annual load (TMAL) and ance (Phase II Guidance, available at www.cdphe.state.co.us/ implementation plan for the reservoir. wq/PermitsUnit/stormwater/ms4guide.pdf) and the Basin In 1988 legislative declaration (Colorado Revised Statutes Authority’s 2000 Cherry Creek Reservoir Watershed Storm- 25-8.5-101 et seq.) established the Basin Authority to water Quality Requirements (Cherry Creek Basin Stormwater develop and implement plans for water quality controls for Requirements, available at www.cherrycreekbasin.org/pdf/ the Cherry Creek Basin. The Basin Authority is a quasi-mu- SW%20Req.pdf). nicipal corporation and political subdivision of Colorado that has primary responsibility for water quality in the Cherry Permit Development Creek Basin. The Basin Authority reviews and makes recom- In 2002 CDPHE initiated a watershed-based permitting ap- mendations for technical specifications for new projects in proach in conjunction with the Basin Authority to implement the Cherry Creek Basin and also implements its own work the Phase II stormwater provisions of the Control Regulation plan. The Control Regulation requires the Basin Authority to within the context of the phosphorus TMAL. The general per- spend at least 60 percent of its funding on constructing and mit, originally issued in March 2003 and reissued in March maintaining pollutant-reduction facilities. 2008, reflects the requirements of both the Phase II Guidance and the Cherry Creek Basin Stormwater Requirements. Permit In 2000 CDPHE replaced the total phosphorus standard for requirements that apply to all permitted discharges are based Cherry Creek Reservoir with a new water quality standard on the Phase II. Additional permit requirements for discharges for chlorophyll a along with a total phosphorus goal, rather to the Cherry Creek Reservoir drainage basin are based on the than a standard. CDPHE decided to use a response variable Cherry Creek Basin Stormwater Requirements. (chlorophyll a level) rather than a causative variable (total phosphorus) as the water quality standard because it more More than 300 stakeholders were involved in developing the directly relates to the reservoir’s beneficial uses. CDPHE permit, but the public process for the permit addressed only then requested cooperation from the Basin Authority in the Phase II stormwater provisions. The watershed-based considering amendments to the existing Control Regulation permit provisions are strictly for implementing the Control to implement the new standard for the Cherry Creek Basin. Regulation; therefore, stakeholder involvement that helped Revisions to the Control Regulation in 2001 recognized that shape the terms of the watershed-based permit provisions Cherry Creek Reservoir was not attaining the chlorophyll a occurred primarily during CDHPE’s triennial review process 2 Watershed-Based Permitting Case Study Cherry Creek Reservoir Drainage Basin, Colorado for the Control Regulation. During the review process, the requirements for discharges to the Cherry Creek Basin to Basin

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