What is MS4?

Municipal Separate Storm Sewer Systems (MS4s) are collection systems designed to transport rainwater and snow melt through a series of drains, pipes, ditches and open channels to our streams and rivers. The water that flows into the storm sewer system is called stormwater runoff. Before entering the system, it becomes contaminated by oil and grease from roadways, pesticides from lawns, sediment from construction sites, and carelessly discarded trash, such as cigarette butts, paper wrappers and plastic bottles. In a separate storm sewer system, stormwater runoff is not treated; therefore, all of the pollutants it carries flow directly into our waterways, where they can contaminate drinking water supplies and interfere with the habitat for fish and other aquatic organisms.

To prevent harmful pollutants from being washed or dumped into MS4s, certain operators are required to obtain NPDES permits and develop stormwater management programs (SWMPs). The SWMP describes the stormwater control practices that will be implemented consistent with permit requirements to minimize the discharge of pollutants from the sewer system.

Castle Shannon Borough was issued a Municipal Separate Storm Sewer System (MS4) Permit through the Pennsylvania Department of Environmental Protection (PADEP) and the Environmental Protection Agency.  Implemented through the Clean Water Act, the permit’s numerous requirements are through six Minimum Control Measures (MCMs).  These six MCMs consist of the following:

Minimum Control Measures (MCMs):

  1. Public Education and Outreach – Distribute educational materials and conduct outreach to inform citizens about the impacts that stormwater runoff has on water quality.
  2. Public Involvement/Participation – Provide opportunities for residents to participate in the stormwater management program or other programs which improve water quality.
  3. Illicit Discharge Detection and Elimination – Develop and implement a plan to detect and eliminate non-stormwater discharges into the stormwater system.
  4. Construction Site Runoff Control – Develop, implement and enforce an erosion and sediment control program for construction site activities that disturb one acre or greater.
  5. Post Construction Site Runoff Control – Develop, implement and enforce a program to address discharges of post-construction stormwater runoff from new development or redevelopment areas.
  6. Pollution Prevention/Good Housekeeping – Develop and implement a program that reduces or prevents pollutant runoff from municipal operations.

How Can You Be Stormwater Smart?

  • Use fertilizers sparingly and sweep up driveways, sidewalks, and gutters
  • Never dump anything down storm drains or in streams
  • Vegetate bare spots in your yard
  • Compost your yard waste
  • Use least toxic pesticides, follow labels, and learn how to prevent pest problems
  • Direct downspouts away from paved surfaces; consider a rain garden to capture runoff
  • Take your car to the car wash instead of washing it in the driveway
  • Check your car for leaks and recycle your motor oil
  • Pick up after your pet
  • Have your septic tank pumped and system inspected regularly

Stormwater Management Resources:

Quick Resource Guide to MS4 Program
Homeowner’s Stormwater Guide
Homeowner’s Guide to Stormwater
When It Rains, It Drains
PA Department of Environmental Protection
Three Rivers Wet Weather
Western Pennsylvania Conservancy




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