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Municipal Separate Storm Sewer Systems

Municipal Separate Storm Sewer Systems (MS4s) + Stormwater Management

Krystal Paisley

July 29, 2020

Water is one of our most precious resources. That is one of the many reasons we must all do our part in protecting our ponds, rivers, streams, lakes, and oceans.


One issue our water sources face is pollution. And, one of these sources of pollution is stormwater runoff.


As rain falls and travels down our streets, parking lots, and sidewalks, it picks up pollutants—such as trash, motor oil, chemicals, and more—and then often travels through municipal separate storm sewer systems or MS4s. Often times, this water then flows, untreated, into local bodies of water.

MS4 Programs + Stormwater Management

According to the EPA a municipal separate storm sewer system (MS4) is “a conveyance or system of conveyances that is:


  • owned by a state, city, town, village, or other public entity that discharges into U.S. waters,
  • designed or used to collect or convey stormwater,
  • not a combined sewer, and
  • not part of a sewage treatment plant or publicly owned treatment works.”


To prevent pollutants from traveling into our waterways through these MS4s, MS4 owners/operators are required to develop a stormwater management program, often labeled SWMP, and obtain a National Pollutant Discharge Elimination System (NPDES) permit.


Stormwater management programs and the NPDES permits go hand-in-hand. The stormwater management program details the stormwater control practices that align with the NPDES permit requirements. The goal? Reducing the number of pollutants discharged from the MS4.

Developing a Stormwater Management Program

A successful, and compliant, stormwater management program describes how the program will reduce pollutant discharge from the sewer system, or MS4.


The U.S. EPA outlines these program areas addressed by successful MS4 programs:


  • Construction Site Runoff Control: reducing pollutants from construction activities
  • Illicit Discharge Detection and Elimination: detecting and eliminating illicit discharges
  • Pollution Prevention/Good Housekeeping: minimizing pathways for carrying runoff
  • Post-Construction Runoff Control: managing stormwater after construction
  • Public Education and Outreach: informing and educating the public
  • Public Involvement/Participation: involving and gaining input from the public in your program
  • Program Effectiveness: identifying measurable goals and analyses
  • Total Maximum Daily Loads: addressing the approved Total Maximum Daily Load (TMDL) if necessary

The Importance of a Compliant MS4 Program

A compliant MS4 Program is incredibly important for the community, the public, and the future of our water. It provides safe and sustainable water for now and in the future.


For owners/operators of an MS4, it ensures that you are compliant with rules and regulations and won’t face unnecessary fines.


Compliant MS4 is also the right thing to do. Doing what we can to keep pollutants out of our water is the best thing we can do to protect this essential resource.


Need help getting your MS4 program compliant? Interested in learning about ways you can improve? Contact us at, we’d love to help.