Last Updated 07/21/2026
Colorado’s Stormwater Permitting Program
The Colorado Water Quality Control Act (25-8-101 et seq., CRS 1973, as amended) established the Colorado Water Quality Control Commission (CWQCC) within the Colorado Department of Public Health and Environment (CDPHE) to develop water quality regulations and standards, classifications of state waters for designated uses, and water quality control regulations. The Act also established the Colorado Water Quality Control Division (CWQCD) to administer and enforce the Act and administer the discharge permit system, among other responsibilities. Violations of the Act are subject to significant monetary penalties, as well as criminal prosecution in some cases.
Colorado’s stormwater management regulations have been implemented in two phases and are included in Regulation No. 61 Colorado Discharge Permit System (CDPS) Regulations (CWQCC 2009). After the 1990 EPA “Phase I” stormwater regulation became effective, Colorado was required to develop a stormwater program that covered specific types of industries and storm sewer systems for municipalities with populations of more than 100,000. Phase I affected the City of Colorado Springs, Denver, Aurora, Lakewood, and the Colorado Department of Transportation (CDOT). Phase 1 requirements included inventory of stormwater outfalls, monitoring and development of municipal stormwater management requirements, as well as other requirements. Construction activities disturbing five or more acres of land were required to obtain construction stormwater discharge permits.
Phase II of Colorado’s stormwater program was finalized in March 2001, establishing additional stormwater permitting requirements. Two major changes included regulation of small municipalities (≥10,000 and <100,000 population) in urbanized areas and requiring construction permits for sites disturbing one acre or more. The Phase II regulation resulted in a large number of new permit holders including MS4 permits for El Paso County, City of Fountain, Town of Monument, and City of Manitou Springs. In addition, there are also non-standard MS4 permittees that include entities that are not cities or counties. Non-standard MS4 permittees include entities such as Academy School District 20, Widefield School District 3, Pikes Peak Community College, Harrison School District 2, Falcon School District 49, Cheyenne Mountain School District 12, University of Colorado at Colorado Springs, and Colorado Springs School District 11.
MS4 permit holders are required to develop, implement, and enforce a CDPS Stormwater Management Program designed to reduce the Stormwater Management and Planning Designed to reduced the discharge of pollutants from the MS4 to the maximum extent practicable, to protect water quality, and to satisfy the appropriate water quality requirements of the Colorado Water Quality Control Act (25-8-101 et seq., C.R.S.) and the Colorado Discharge Permit Regulations (Regulation 61). Non-standard MS4 permittees may elect to comply with their construction program and post-construction program requirements by following the requirements of the City’s or County’s construction and post-construction programs.
CDOT is required to comply with the requirement of the CDOT Colorado Municipal Separate Storm Sewer System (MS4) permit. CDOT’s MS4 permit authorizes discharges from the municipal storm sewer system within the permit area. The permit requires CDOT to use control measures to prevent or reduce the discharge of pollutants to state waters. The permit does this by requiring CDOT to comply with seven MS4 programs. CDOT has several different programs to make sure the amount of pollutants being discharged is reduced, as part of the permit that allows discharges from the roadway storm drain system. These include:
Construction Sites
The MS4 permit requires CDOT to implement a program to reduce or prevent the discharge of pollutants to the MS4 from covered construction activities. The requirements include assuring adequate design, implementation, and maintenance of Control Measures at CDOTs construction sites.
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Illicit Discharges
The Illicit Discharge Detection and Elimination (IDDE) Program requires CDOT implement a program to detect and remove (or advise the discharger to the MS4 to obtain a separate CDPS permit for) illicit discharges and improperly disposed materials into the MS4.
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Industrial Facilities
CDOT requires all facilities that discharge stormwater into CDOT’s storm drain system to obtain a specific authorization. The program prioritizes education to promote minimization of pollutants in the stormwater that the facilities are contributing to the system.
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Permanent Water Quality (PWQ)
This program is required under CDOT’s Municipal Separate Storm Sewer System Permit MS4). Each CDOT Region is responsible for evaluating new construction and redevelopment sites in the CDOT MS4 permit area to determine if stormwater controls are required. These controls are referred to as Permanent Water Quality Control Measures (PWQ CM) or permanent Best Management Practices (BMP).
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Pollution Prevention and Good Housekeeping
CDOT prioritizes minimization of pollutants in stormwater by developing runoff control plans for maintenance facilities, requiring the proper application of herbicides, pesticides and fertilizers, maintaining permanent BMPs, and operating public streets, roads, highways, and parking lots to promote both safety and stormwater quality protection.
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Public Education and Outreach
CDOT must implement a public education program to promote behavior change by the public to reduce pollutants in discharges from the MS4. CDOT conducts a variety of outreach activities for employees and the public. Outreach activities include brochures, fact sheets, posters, newsletters, workshops, conferences, and this website.
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Frequently Asked Questions
Who enforces stormwater compliance in Colorado?
The Colorado Water Quality Control Division, within the Department of Public Health and Environment. The Division administers and enforces the state’s discharge permit system under the Colorado Water Quality Control Act, while the separate Water Quality Control Commission develops the underlying water quality regulations and standards. Violations of the Act carry significant monetary penalties and, in some cases, criminal prosecution.
What size construction project needs a stormwater permit in Colorado?
One acre or more, under current Phase II rules. That’s actually a change from the original Phase I program, which only required permits for construction disturbing five acres or more. Phase II, finalized in March 2001, lowered that threshold to one acre and brought in a wave of new permit holders as a result.
Why do some Colorado cities have MS4 permits and others don't?
It comes down to population and Phase I versus Phase II timing. Phase I originally applied only to municipalities over 100,000 people, covering cities like Colorado Springs, Denver, Aurora, and Lakewood along with the Colorado Department of Transportation. Phase II extended coverage to smaller municipalities between 10,000 and 100,000 people in urbanized areas, which is what brought entities like El Paso County and the City of Fountain into the permit system.
What is a non-standard MS4 permittee in Colorado?
It comes down to population and Phase I versus Phase II timing. Phase I originally applied only to municipalities over 100,000 people, covering cities like Colorado Springs, Denver, Aurora, and Lakewood along with the Colorado Department of Transportation. Phase II extended coverage to smaller municipalities between 10,000 and 100,000 people in urbanized areas, which is what brought entities like El Paso County and the City of Fountain into the permit system.
What does an MS4 permit holder in Colorado actually have to do?
Develop, implement, and enforce a CDPS Stormwater Management Program designed to reduce pollutant discharge from the MS4 to the maximum extent practicable, while satisfying the water quality requirements of both the state Water Quality Control Act and Regulation 61. That’s a broad, ongoing obligation rather than a one-time construction requirement.
Does the Colorado Department of Transportation have its own stormwater program?
Yes, a fairly extensive one, since CDOT holds its own MS4 permit for the roadway storm drain system. That permit requires seven distinct programs covering construction sites, illicit discharge detection and elimination, industrial facility authorization, permanent water quality controls for new construction and redevelopment, pollution prevention and good housekeeping at maintenance facilities, and public education and outreach.
If my facility discharges into a Colorado state road's storm drain system, do I need a separate permit?
Possibly. CDOT requires any facility discharging stormwater into its storm drain system to obtain specific authorization, and the program prioritizes education to help those facilities minimize the pollutants they contribute. If your property sits near a state highway or CDOT-maintained drainage system, that’s worth confirming directly.
How can AQUALIS help my property navigate Colorado's stormwater permitting program?
AQUALIS helps Colorado property owners determine whether their project falls under Phase I or Phase II requirements, prepare construction and post-construction stormwater programs for MS4 permit holders and non-standard permittees alike, and manage authorization requirements for facilities discharging into CDOT’s storm drain system.
The information on this page is provided for general informational purposes only and is not legal advice. Regulations change frequently — AQUALIS makes no warranty as to the accuracy or completeness of this content, and any reliance on it is at your own risk. Consult a qualified professional or your local regulatory authority to confirm requirements applicable to your specific property.
