Municipal separate storm sewer systems (MS4s) are systems of storm sewers, gutters, storm drain inlets, and similar features that are owned by cities, counties, and other government entities. They collect and discharge stormwater to local waterbodies. The division regulates sources of pollution from pipes and drains (that do not include runoff from agricultural fields) that flow directly from qualifying municipalities to state waters. Regardless of the type of permit, there are best management practices (BMPs) that help prevent stormwater runoff from contaminating the MS4s.
There are Individual MS4 permits, where an entity is large and needs their own permit to cover the work they do, such as a large city. There are also general phase-2 permits that apply to multiple entities that have similar permit circumstances. Non-standard MS4 general permits are entities that are smaller governmental agencies, school districts, recreation districts, and similar. You can learn more about the individual and general MS4 permits below.
How to get involved
All permits are required to go to public notice, so anyone can comment and provide feedback on the permit. Permits that are up for public notice and accepting public comments can be found on the Draft Permit Actions page. Some permits have more public interest and a more robust engagement process. You can find those on the Water Quality Engagement page.
Some ways you can get involved:
- Submitting comments on draft permits that are on public notice. Please make sure to submit these comments by the deadline.
- Submitting comments on other permitting actions that may be out for public notice, like draft policies or draft Clean Water Act Section 401 certifications for EPA permits in Colorado.
- Participating in a stakeholder process for a large-scale general permit, regulatory changes, or other issues.
- Participating in one of our quarterly permittee webinars, which provide updates on permitting issues. These are focused on permittees but anyone is welcome.