Municipal Separate Storm Sewer System (MS4)

About the Program
Municipal Separate Storm Sewer System (MS4) is a program implemented to reduce the amount of pollutants that enter the surface waters of the state. A system of drainage is considered to be a MS4 as long as it is not connected to a sewer that contains both stormwater and sanitary lines (combined sewers), or a sewage treatment plant.

A primary goal of the MS4 program is to reduce and completely eliminate illicit discharges. An illicit discharge is any discharge to a separate stormwater system that is not stormwater or groundwater. Illicit discharges occur when contaminated water is released into storm sewers rather than properly being directed to sanitary sewers. The outcome of illicit connections is polluted lakes, rivers, and streams. Many municipalities enforce the elimination of illicit discharges by prohibiting illicit discharges in their ordinance.

More Information
For more information on MS4 regulations, please visit the Michigan Department of Environmental Quality’s website.