What is MS4?

The Municipal Separate Storm Sewer System (MS4) is a federal program overseen by the Environmental Protection Agency (EPA).  MS4’s are conveyances or systems of conveyances including roads with drainage systems, catch basins, curbs, gutters, ditches and man-made channels, or storm drains that are owned or operated by a public entity.  MS4s are not part of a sanitary sewer system.  A municipality is bound by EPA regulations when the municipalities falls within an Urbanized Area as determined by the US Census Bureau.

Communities subject to the MS4 program must obtain a National Pollutant Discharge Elimination System (NPDES) permit and develop and implement a stormwater management plan according the terms of the permit.   In Pennsylvania, the MS4 program has been delegated to Pennsylvania Department of Environmental Protection (PADEP) which manages and administers this program on behalf of EPA.  Both agencies have enforcement powers over this program.