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MS4 Stormwater
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What is a Municipal Separate Storm Sewer System (MS4)?

Municipal storm water sewer systems (MS4s) that are located within the boundaries of a Census Bureau defined "urbanized area" are regulated under EPA's Phase II Storm Water Rule. This requires MS4s to develop a storm water management program that will reduce the amount of pollutants carries by storm water during storms events to water bodies tot he "maximum extend practicable". The goal of the program is to improve water quality and recreation use of waterways.

MS4 storm water programs have six elements called Minimum Control Measures (MCM) that when implemented together, are expected to result in a reduction of pollutants discharged into water bodies.

What are impacts of storm water runoff?

Storm water adversely impacts the quality of our surface waters, as it carries with it various pollutants, sediments, and other debris from the surfaces over which it runs off. Storm water also creates quantity problems which results in flooding, stream bank erosion, sanitary sewer overflows (SSO), basement flooding, and sewer backups.

What is Storm Water Pollution?

Any toxic discharge that enters into the storm water sewer system, as storm water flows (or snow melts); it picks up debris, chemicals (such as fertilizers, pesticides, dirt, cigarette butts, and other pollutants). This discharge enters a storm sewer system and is discharged to a lake, stream, river, wetland, or coastal water.