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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).

PennDOT's MS4 Permit

PennDOT has an Individual MS4 Permit covering stormwater conveyances operated by PennDOT and used for collecting or conveying stormwater runoff associated with PennDOT's roads, bridges, and related structures, such as maintenance facilities. PennDOT's previous MS4 permit expired on July 14, 2015 and had been administratively extended until the new permit was approved.  The current permit became effective on November 1, 2021 and expires on October 31, 2026.  An Annual MS4 Report is due by September 30 each year.  

The MS4 Permit is designed to help reduce the discharge of pollutants from the regulated small MS4, to the maximum extent practical, to protect water quality, and to satisfy the appropriate water quality requirements of the Clean Water Act and the Pennsylvania Clean Streams Law. The permit requires the development and implementation of a Storm Water Management Program (SWMP). The SWMP features six Minimum Control Measures (MCMs). Each MCM requires implementation of specific Best Management Practices (BMPs) to meet measurable goals according to an approved schedule.

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