Municipal Separate Storm Sewer System - MS4

NPDES Permit No. PAG136221

Annual Reports:


Municipal Separate Storm Sewer System

Pennsylvania’s Storm Water Management Act (Act 167) was enacted in 1978. This Act was in response to the impacts of accelerated stormwater runoff resulting from land development in the state. It requires counties to prepare and adopt watershed based stormwater management plans. It also requires municipalities to adopt and implement ordinances to regulate development consistent with these plans. Ross Township is part of the North Hills Council of Governments, which has a comprehensive Act 167 Management Plan.

View a map of the Release Rates.

In response to the 1987 Water Quality Amendments to the Clean Water Act, the EPA published the rules for Phase I of the National Pollutant Discharge Elimination System (NPDES) stormwater program in 1990. The Phase I program requires municipalities with populations of 100,000 or greater to implement a stormwater management program as a means to control discharges from the “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 stormwater (including storm drains, pipes, ditches, etc.)
  • Not a combined sewer
  • Not part of a Publicly Owned Treatment Works (sewage treatment plant)

The Municipal Separate Storm Sewer System (MS4) Program was administrated through the Federal Clean Water Act (CWA) in 1999. Pennsylvania implemented state regulation of the MS4 permit in 2003. The underlying goal of the MS4 program is to prevent stormwater pollution from entering streams, lakes, ponds, rivers, etc. Municipalities are required through the EPA and PA DEP to implement a stormwater management program comprising of 6 minimum control measures (MCMs).

The NPDES stormwater program is a permit-based program that established requirements that municipalities must meet to discharge storm water from MS4s to the nation’s surface waters. Under the conditions of the permit, Ross Township is required to possess the legal authority to control storm drain system pollutants, continue mapping its storm sewer system, monitor stormwater discharges, and develop and implement comprehensive management programs. The permit also increases impervious area treatment goals, requires the implementation of trash reduction strategies, and environmental site design for new and redevelopment projects.

Stormwater management programs for both Phase I and Phase II require that communities reduce the discharge of pollutants to the “maximum extent practicable.” The regulations require that the management programs address a minimum of six elements, that when implemented are expected to result in significant water quality benefits. The six elements are:

  • Public Education and Outreach - Educate and outreach to inform citizens about the impacts that stormwater runoff has on water quality.
  • Public Participation / Involvement - Provide opportunities for citizens to participate in the stormwater management program or other programs which improve water quality.
  • Illicit Discharge Detection and Elimination - Develop and implement a plan to detect and eliminate non-stormwater discharges into the stormwater system.
  • Construction Site Runoff Control - Develop, implement, and enforce an erosion and sediment control program for construction site activities that disturb 1 acre or greater.
  • Post-Construction Runoff Control - Develop, implement, and enforce a program that addresses post-construction stormwater runoff from new development or redevelopment sites.
  • Good Housekeeping for Municipal Facilities - Develop and implement a program that reduces or prevents pollutant runoff from municipal operations.

It is important for residents to understand their responsibility with stormwater management. When rain falls, typically one does not think about the entire course of events regarding the water flows and the pollutants that enter our water during each rainfall.

If you are a homeowner and have stormwater issues, you may refer to the EPA's Green Infrastructure Page for reference to help determine what the best option is for your home.