[2021 AR] MS4 Permittees

2021 Report

Regulated Stormwater- MS4 Permittees

All municipalities with Municipal Separate Storm Sewer Systems (MS4s) permits from the Colorado Department of Public Health and Environment (CDPHE) in the watershed have adopted stormwater programs, consistent with Regulation 72, for construction projects within their jurisdictions. The requirements in Regulation 72, in some cases, go above and beyond the MS4 Permit requirements in Regulation 61 Colorado Discharge Permit System Regulations.

In 2020, the MS4 permittees conducted 13,418 inspections of 2,681 construction sites. In addition, the MS4 permittees required that construction site owners/operators install 81 new permanent control measures that are designed to reduce pollutants in stormwater before it enters Cherry Creek or its tributaries.

In 2021, the MS4 permittees conducted over 14,450  inspections (an increase of over 7% from 2020) of over 2,800 construction sites. In addition, the MS4 permittees required that construction site owners/operators install 36 new permanent control measures that are designed to reduce or eliminate pollutants in stormwater before it enters Cherry Creek or its tributaries.

Further information on each MS4’s program can be found in their annual reports in the links below.

Find Out More About MS4 Permittees' programs

MS4 Permittee Annual Reports

Annual reports are submitted to the Division by March 10 (Phase II MS4 permittees) and April 1 (Phase I MS4 permittees)  

(coming soon)

Public Education

In addition, to regulating construction sites in the Cherry Creek reservoir basin, the MS4 permittees also have programs to educate the public, respond to and eliminate illicit discharges, and reduce or eliminate pollutants in stormwater from municipal operations.


Grass Swale

Above & Beyond

SEMSWA Approach to Regional Water Quality

Each of the MS4 permittees in the Cherry Creek Basin has sophisticated programs and projects, as evidenced by the Southeast Metro Stormwater Authority (also called SEMSWA) Approach to Regional Water Quality and Arapahoe County's Water Action Plan. 

SEMSWA Projects 2021

Arapahoe County Water Action Plan and Turf Removal Project

Through the Arapahoe County Sustainability Initiative, the County wrote a new Water Action Plan in 2021. The Water Action Plan seeks to “improve County facilities’ resource conservation through a workplace culture focused on sustainability and economics.” The short term goal is to reduce total water use by 3.4 million gallons per year or 5% below 2019 baseline within 2 years. The long-term goal is to reduce total water use by 5 million gallons per year or 8% below 2019 baseline.

One way the County will accomplish these goals is by reducing landscape water associated with County facilities. The first project is converting 3 acres of rarely-used turf grass to nonirrigated native grass at the Administration building in Littleton. The County plans to save 1.5 million gallons of irrigation water a year. In addition to removing the Kentucky Blue Grass in 2021, the County will stop fertilizing the field. Eliminating the fertilizer stops nutrient runoff from the field during storm events.

2021 Stormwater Permits and Inspections for Construction and Post-Construction Development

1Reinspection fees issued
2SCMs with Final Acceptance after 2007
3 Inspections of SEMSWA owned/operated SCMs
4CDOT Construction Sites: 2 CDOT capital Improvement projects. 3 Local Agency Federal Funded projects were reviewed by the locals and through the CDOT review process. The Local Agencies will report these three projects to CCBWQA.
No new PWQ have been installed since last reported in 2021. Please note, that many of the PWQ may be maintained by Local Agencies and not CDOT.
Castle Pines has 5 permanent BMPs/CMs per 2008/2009 WQ regulations and 4 BMPs/CMs per the COR080000 requirements (one facility is a pond for a small, less than 1 acre, disturbance area) (note: several permanent BMPs/CMs are in the process of being built and being accepted by the City in 2021)