MS4 Program

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Missoula County is an active participant of the storm water general permit requirement, formally known as the MS4 General Permit. MS4, meaning Municipal Separate Storm Sewer System, and the permit are administered by the Environmental Protection Agency (EPA). In 2005, the EPA delegated the Montana Department of Environmental Quality (MDEQ) to implement these permits in urbanized areas of Montana with populations of 10,000 or more as determined by the US Census.


The permit requires the county to implement and enforce a storm water management program to reduce pollutants from entering waterways and help protect water quality as it is outlined in the Montana Water Quality Act. In doing so, the county has partnered with the Missoula Water Quality District to assist with implementing the program and its six minimum control measures. Please call 406.258.4753 or visit for more information.