Municipal Separate Storm Sewer System (MS4)

Documents and Brochures available to the public about MS4s:

MS4_Fact Sheet 1 of 7_Overview
MS4_Fact Sheet 2 of 7

MS4_Fact Sheet 3 of 7
MS4_Fact Sheet 4 of 7
MS4_Fact Sheet 5 of 7
MS4_Fact Sheet 6 of 7
MS4_Fact Sheet 7 of 7

Homeowner Guides and Information:

Homeowners Guide to Stormwater BMP Maintenance
Downspout Disconnection
Downspout Disconnection – Poster

Swimming Pool Discharges
How to create a rain garden

For Kids:


Additional Links to Other Sites:

PA Department of Enviromental Protection (DEP)

Environmental Protection Agency (EPA)

Why is storm water sewer management important?

Pollutants in storm water is one of the largest concerns surrounding water runoff.  Because storm water ultimately works its way into local streams and creeks, the quality of the water is affected by any pollutants that run off into the storm sewers along with water.  Here are some common, every day pollutants that affect storm water runoff:

  • Dog waste
  • Yard Fertilizers
  • Swimming pool discharge

Pollutants are not the only concern, however.  Storm water runoff that is not managed properly can negatively impact the environment and wildlife.  Stormwater flows much faster down a road than it does in woods.  The faster moving water picks up pollutants and sediments that are carried to creeks and streams.  The result of this unmanaged runoff is:

  • flooding
  • sediment build-up
  • polluted streams and creeks
  • land erosion
  • uninhabitable environments for fish and other animals

It’s easy to notice flooding after large rain storms, but smaller rains also have an impact as well.  95% of rainfall volume occurs from smaller rain events.  Over time,  even with smaller volume rainstorms, streams and creeks lose their natural bends and tend to become warmer over time, decreasing the amount of dissolved oxygen which can be harmful to fish.

What is the MS4 Program?

The MS4 Program is administrated by the Pennsylvania Department of Environmental Protection.  The EPA defines MS4 as “A conveyance or system if conveyances that is not part of a public water treatment plant or other public entity that collects water in storm drains, ponds, etc., and not a combined sewer”.

What is a Rain Garden?

A rain garden is an landscaped area that is specifically designed to accept water runoff and soak into the ground.  A rain garden is not much different than a flowering garden of perennial plants and shrubs.  It often is a unique and inexpensive way to beautify your property with one exception – it effectively uses water runoff.


Who uses MS4 Programs?

MS4 regulations, issued in the early to late 1990’s required population centers of varying sizes, to permit for coverage of stormwater discharges.  Permits for small population centers, as well as urbanized population centers must be obtained from the National Pollutant Discharge Elimination System (NPDES).

What is required under an MS4 Program?

All Ms4 programs that are permitted by NPDES must include six Minimum Control Measures (MCMs).  The MCMs are:

    1. Public Education and Outreach on Stormwater Impacts
    2. Public Involvement and Participation
    3. Illicit Discharge detection and Elimination
    4. Contruction Site Stormwater runoff Control
    5. Post – Construction Stormwater Management in new and re-developed areas
    6. Pollution Prevention / Good Housekeeping for Municipal Operation

MS4s in the Southwestern Pennsylvania Region

As of late 2014, there were 207 municipalities within the 10 county region that MS4 permits.