Municipal Separate Storm Sewer System Program

MS4 is an acronym for a Municipal Separate Storm Sewer System. It's a system of stormwater conveyances and structures owned or operated by a public agency that does not connect to the sanitary sewer system and does not lead to a wastewater treatment plant. It discharges untreated water into local drainageways, streams, and rivers. 


Pennsylvania's MS4 program is implemented by the Pennsylvania Department of Environmental Protection (DEP), which fulfills this role to comply with federal mandates under the Clean Water Act. The Environmental Protection Agency (EPA) has an oversight role because they are the federal agency charged with managing the Clean Water Act. 

National Pollutant Discharge Elimination System Permit

The authorization that MS4 communities get from the DEP to legally discharge stormwater into local streams and rivers is called an "NPDES" permit which stands for National Pollutant Discharge Elimination System. To meet the terms of their NPDES Permit, communities need to develop what's called a "Stormwater Management Program" (SWMP). Communities that discharge stormwater into the Chesapeake Bay Watershed, such as Lower Paxton Township, are also required to develop a "Pollutant Reduction Plan" (PRP).

Control Measures

There are 6 Minimum Control Measures (MCM) that make up Lower Paxton Township's Municipal Separate Stormwater System (MS4) program. These 6 MCMs are:

  • Construction site runoff management
  • Good housekeeping and pollution prevention for municipal operations
  • Illicit discharge and detection
  • Post-construction stormwater management
  • Public education
    • Public Education includes distributing informational posters, meeting with the public, providing links on the web page to related information, and providing a means for reporting suspected pollution concerns.
  • Public involvement


Construction activities have sediment runoff rates 1,000 to 2,000 times greater than forested land and 10 to 20 times greater than agricultural lands. The Dauphin County Conservation District has the primary responsibility for managing construction runoff. 

Conservation District

Lower Paxton Township works closely with the Conservation District to mitigate construction runoff through regulations to control construction activities and penalties for non-compliance; review of construction plans to ensure site-specific needs are addressed, and site inspections to ensure necessary control measures have been installed and maintained.

  1. Good Housekeeping & Pollution Prevention for Municipal Operations
  2. Illicit Discharge & Detection
  3. Post-Construction Storm Water Management
  4. Public Involvement