Missoula County Public Works and the Missoula Valley Water Quality District are working to reduce pollution caused by stormwater runoff. The County is permitted under a stormwater general permit, formally known as the Municipal Separate Storm Sewer System, or MS4 permit.

The Environmental Protection Agency and Montana Department of Environmental Quality regulate Municipal Separate Storm Sewer Systems, also called MS4s. This permit requires urbanized areas (populations of 10,000 people or more) to establish six specific methods of improving storm water quality:

1. Public education and outreach
2. Public involvement/participation
3. Illicit discharge detection and elimination
4. Construction site runoff control
5. Post-construction runoff control
6. Pollution prevention 

Illicit discharge is anything that is dumped into a storm drain system that isn’t entirely composed of stormwater. Essentially, anything other than water falling from the sky is illicit discharge! 

Examples include a leaking sewage pipe, a fuel or oil spill or any other pollutant that flows into the storm system when conditions are dry (no precipitation). There are some exceptions of course, like when groundwater or drinking water enters a storm system. Illicit discharge can often be prevented by best management practices such as storing chemicals safely, conducting inspections, installing dry-well protection and education. Prevention is much cheaper than cleaning polluted water!

To anonymously report inappropriate use of the stormwater system, such as illicit discharge, fill out this online form or contact the Missoula Valley Water Quality District at 406-258-4890.

• 2022-2027 General Permit
• 2022-2027 Storm Water Management Plan (SWMP)
• Map of MS4 boundaries (shaded in blue)