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Municipal Separate Storm Sewer System (MS4)

An MS4 is a conveyance or system of conveyances that is:

  • 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 storm water (including storm drains, pipes, ditches, etc.).
  • Not a combined sewer.
  • Not part of a publicly owned treatment works (sewage treatment plant).

The general requirement is to develop and implement a Storm Water Management Program (SWMP) of Best Management Practices (BMPs) to reduce the discharge of pollutants from your regulated small MS4 to the Maximum Extent Practicable (MEP).

*PennDOT’s current permits began on July 17, 2011 and are active through July 16, 2016.


Minimum Control Measures (MCMs)

The six MCMs are:

  1. Public education and outreach
  2. Public participation/involvement
  3. Illicit discharge detection and elimination
  4. Construction site runoff control
  5. Post-construction runoff control
  6. Pollution prevention/good housekeeping


Reporting is required in the first, third and fifth permit years and includes additional requirements of identification and screening of Dry Weather Flow sites (flow that continues greater than 72 hours after a rain event). Each MCM requires implementation of BMPs to meet measurable goals according to an approved schedule.