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Public Works

Stormwater Management Program History and Objectives


The Clean Water Act, Stormwater, and the National Pollutant Discharge Elimination System (NPDES) Managing storm drainage is an integral component of a comprehensive package of public services that Douglas County provides. Stormwater runoff is a valuable resource if handled wisely, with increased water supply volumes and enhanced open space quality being just two of the benefits. Inadequate stormwater management can result in flooding, infrastructure a,nd property damage, excessive soil erosion, degraded open space, unacceptable water quality in potable water supply reservoirs and other water bodies with decreased recreational and/or fish and wildlife values, and excessive financial burdens placed upon Douglas County due to flood damage repairs or increased operation and maintenance costs.


Douglas County is committed to taking a proactive role in managing stormwater runoff in the County as part of the overall goal of providing quality services to its citizens. To that end, Douglas County is required by federal regulation to take actions that minimize or prevent stormwater pollution under the County’s “NPDES municipal stormwater permit.”  “NPDES” stands for National Pollutant Discharge Elimination System. The NPDES permit system is a federal permit system based on the Federal Clean Water Act (CWA). These permits were initially developed to regulate sewage treatment plants and industrial discharges. While much pollution was prevented through such permits, many studies found that significant pollution is picked up in stormwater, the water that flows over the ground after it rains or snows.

In 1987, amendments to the CWA expanded the NPDES permit system to include stormwater discharges from municipalities (i.e., cities and counties), large construction sites, and many industrial sites. Within Colorado, the NPDES permit system is administered by the Water Quality Control Division (WQCD) of the Colorado Department of Public Health and Environment (CDPHE). The state NPDES program is called the Colorado Discharge Permit System (CDPS). In March 2003, the WQCD issued a CDPS Phase II Stormwater Permit to Douglas County. In March 2008, the WQCD reissued the Phase II Stormwater Permit to Douglas County for a second 5-year permit term. After the WQCD administratively extended the second permit term from March 2013 through June 2016, the third 5-year term CDPS Phase II Stormwater Permit was reissued effective July 1, 2016, and was administratively extended on June 30, 2021, and remains in effect until such time that a new MS4 Permit is issued.

The primary function of storm sewer systems, including natural channels, is the collection, conveyance, and storage of stormwater runoff. In a watershed-based approach to urban stormwater management, the municipal separate storm sewer system, or MS4, including both structural (e.g., pipes, inlets, and outlets) and natural drainage ways is a critical structural component. The MS4 serves multiple functions, such as storm drainage facilities, areas for recreation, and for open space and biodiversity conservation. While all of these aspects are important and need to be addressed as part of a comprehensive stormwater management program, the hydraulic function of the overall MS4 takes precedence.


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MS4 Permit Program

Douglas County manages a comprehensive stormwater program that covers the following Minimum Control Measures (MCMs) required by the Phase II Standard Municipal Separate Storm Sewer System (MS4) Permit. The MCMs include:

Douglas County’s stormwater program provides public education, outreach on the impacts of nutrients in the water bodies, and other focused outreach which provides information on the proper disposal of yard waste and other pollutants for businesses and residents.

Douglas County staff ensures that illicit or unpermitted discharges are eliminated, cleaned up properly, and reported to the proper agency when applicable.

The Grading, Erosion, and Sediment Control Manual (GESC/DESC) provides the requirements for temporary erosion and sediment controls and final stabilization for regulated construction activities.

The Storm Drainage Design and Technical Criteria Manual provides guidance to design engineers for the effective management of stormwater and construction design elements of stormwater systems. Operation and Maintenance templates are provided for the long-term post-construction management of stormwater facilities.

Inadequate stormwater management can result in flooding, infrastructure and property damage, excessive soil erosion, degraded water quality in potable water supply reservoirs and other water bodies, and can negatively impact recreational fish and wildlife resources.

The Program Description Document (PDD) is available upon request for public review and comment. Requests can be made in person during normal business hours through Public Works Engineering, 100 Third St. Castle Rock, CO 80104, or via email [email protected]

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As an integral part of Douglas County’s vision of providing its citizens with the highest quality services at the best value will focus on the following objectives for stormwater management:


  • Safeguard the public welfare through the proper collection, conveyance, and storage of stormwater runoff in a non-damaging and non-life threatening manner.
  • Ensure compliance with all applicable water quality regulations related to stormwater runoff, including and in particular, both the WQCD’s Stormwater Phase II program and the Cherry Creek Reservoir and Chatfield Reservoir Control Regulations, respectively.
  • Ensure that all County stormwater facilities are functioning and well maintained, including applicable open channels (i.e., stable physical characteristics).
  • Ensure sound management and regulation of County floodplains, particularly with respect to Federal Emergency Management Agency requirements.
  • Protect overall water quality of the County’s water resources.
  • Provide Healthy and diverse natural habitats for plants and animals in applicable drainage ways and County open space.
  • Integrate recreational opportunities and facilities into drainage way planning, where feasible.


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