General MS4 Information

What is the MS4 Program?

Stormwater regulations associated with the Federal Clean Water Act (CWA) are administered under the Municipal Separate Storm Sewer System (MS4) Program.  In Pennsylvania, the MS4 program is managed by the Pennsylvania Department of Protection (PADEP). 

Storm Drain

Storm Drain

What is an MS4?

EPA defines an MS4 as “a conveyance or system of conveyances that is:

  • Not part of a Publicly Owned Treatment Works (sewage treatment plant);
  • Owned by a state, city, town, village, or other public entity that discharges to waters of the U.S.;
  • Designed or used to collect or convey stormwater (including storm drains, pipes, ditches, etc.); and
  • Not a combined sewer.”

Who is an MS4?

MS4 regulations were rolled out in two phases:

  • Phase I, issued in 1990, requires medium and large cities or certain counties with populations of 100,000 or more to obtain NPDES permit coverage for their stormwater discharges.
  • Phase II, issued in 1999, requires regulated small MS4s in urbanized areas, as well as some small MS4s outside the urbanized areas, to obtain NPDES permit coverage for their stormwater discharges. 

What is Required under the MS4 Program?

Operators of a small MS4 must obtain an NPDES permit and develop and implement a stormwater management plan (SWMP) according to the details of their specific permit.  Mandatory elements of the SWMP include six (6) Minimum Control Measures (MCMs); each MCM has a number of associated BMPs

The MCMs are:

  1. Public Education and Outreach on Stormwater Impacts,
  2. Public Involvement / Participation,
  3. Illicit Discharge Detection and Elimination,
  4. Construction Site Stormwater Runoff Control,
  5. Post-Construction Stormwater Management in New and Re-Development Activities,
  6. Pollution Prevention / Good Housekeeping for Municipal Operations

MS4s in the SPC Region

As of December 2014, there are 207 municipalities within the 10 county SPC-Region that hold an MS4 permit.  Click here to view a map of MS4 municipalities in the SPC region
To learn more about the MS4 program, visit the following sites:


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General MS4 Information Public Education & Outreach Public Involvement & Participation Illicit Discharge Detection & Elimination Construction Site Stowmwater Runoff Control Post-Construction Stormwater Mgt in New & Redevelopment Activities Pollution Prevention/Good Housekeeping for Municipal Operations