Municipal Separate Storm Sewer Systems (MS4) Permit

Urbanized Area Map
Every five years, the Maine Department of Environmental Protection (MDEP) issues a state-wide General Permit to all communities designated as small Municipal Separate Storm Sewer Systems (MS4s). The MS4 designation is based on decennial U.S. census data for "Urbanized Areas," which are generally defined as densely developed census tracts or blocks with populations of at least 50,000. The 2013-18 General Permit identifies thirty MS4 communities in Maine and requires them all to implement Minimum Control Measures (MCMs) to reduce pollution from stormwater runoff. Windham's Urbanized Area, seen in the image above, consists primarily of the North Windham shopping centers as well as destinct urban area within the town boundaries.

Minimum Control Measures

State and federal regulations require more urbanized communities like Windham to implement the following six Minimum Control Measures (MCMs) to significantly reduce the discharge of pollutants into local waterways. The Town is required to develop a detailed Stormwater Program Management Plan that describes how each of the MCMs will be implemented over the five year permit period. Each of these MCMs is targeted towards specific audiences and activities as briefly described below:

MCM1. Public Education and Outr​each: distribute educational materials and conduct public outreach to inform citizens about the impacts polluted stormwater on receiving water quality. 

MCM2. Public Participation and Involvement: provide opportunities for citizens to participate in stormwater management program development and implementation.

MCM3. Illicit Discharge Detection and Elimination: develop and implement an enforceable plan to conduct routine inspections of stormwater systems to eliminate illicit pollutant discharges to receiving waters.

MCM4. Construction Site Runoff Control: develop and implement an enforceable plan to minimize sediment transport to receiving waters from construction activities disturbing more than 1 acre of land.

MCM5. Post-Construction Runoff Control: develop and implement an enforceable plan to minimize polluted stormwater runoff to receiving waters from new development or redevelopment projects.

MCM6. Pollution Prevention / Good Housekeeping: develop and implement a training program to minimize stormwater pollution from municipal activities. 


Credit:  City of South Portland