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MS4 general permits

Municipal separate storm sewer system (MS4) permits are issued for discharges of urban stormwater into streams, rivers, and lakes. This permitting process helps keep state waters clean enough to support recreational use and aquatic life. Our MS4 brochure provides more information.

In Colorado, the department has issued three general MS4 permits: statewide small MS4s, statewide non-standard MS4s, and small MS4s within the Cherry Creek Reservoir Basin. General permits are written to cover a group of permittees. Each permittee must submit an application to be covered by the general permit. Please visit our MS4 individual permits webpage to learn more about MS4 permits issued to a single permittee.

Qualifications for coverage under an MS4 small general permit

In Colorado, we issue general permits for small MS4s. These permits are for small MS4s as defined by EPA in the Phase II Regulations and in Colorado regulations. These permittees are generally government entities that serve a
population of less than 100,000 and are located in an “urban area with a population of 50,000 or more people” as defined by the US Census Bureau. These permittees can also include non-traditional MS4s such as public universities, schools, transportation districts, hospitals, and prison complexes.

Our urban area maps webpage provides maps of urban areas with a population of 50,000 or more people.

Statewide standard MS4 general permit (COR090000) qualifications
 
Statewide Non-Standard MS4 General Permit (COR070000) qualifications
Cherry Creek Reservoir Basin MS4 General Permit (COR080000) qualifications

Qualifications for coverage under an MS4 small general permit

In Colorado, we issue general permits for small MS4s. These permits are for small MS4s as defined by EPA in the Phase II Regulations and in Colorado regulations. These permittees are generally government entities that serve a population of less than 100,000 and are located in an “urban area” with a population of 50,000 or more people as defined by the U.S. Census Bureau. These permittees can also include non-traditional MS4s such as public universities, schools, transportation districts, hospitals, and prison complexes. 

Maps of urban areas with a population of 50,000 or more people can be accessed on our urban area maps webpage. 

Governmental entities such as cities, towns, and counties that serve a population of less than 100,000 and are in an urbanized area. 

If one portion of a city or town is considered an urbanized area, that allows the entire municipality to meet the qualifications of a small MS4. The entire city or town would be the permitted area.

Counties will determine their permitted area based on their urbanized areas. Counties do not have to implement this permit outside of the permitted area.
 

Publicly-owned systems similar to MS4s in cities and counties that are designed for a maximum daily user population (residents and individuals who come there to work or use the MS4 facilities) of at least 1,000, located in an urbanized area. 

These permittees are school districts, colleges/universities, metropolitan districts, health authorities, transportation authorities, recreation districts, urban stormwater districts, etc.

Publicly-owned systems and governmental entities that would require either a standard or non-standard MS4 general permit that are within the Cherry Creek Watershed. This permit was created to encompass additional requirements stemming from Regulation 72, which regulates the Cherry Creek Reservoir Basin. 

Other permitting information

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Contacts

MS4 permits are handled by the Permits Section, Unit 1.

Please contact either