MS4 Program

The National Pollutant Discharge Elimination System (NPDES) program was established by the federal government to control discharges of water pollution. The NPDES Permitting and Compliance Programs of Pennsylvania’s Department of Environmental Protection (PA DEP) is responsible for administering the program for the state.

Under the NPDES Stormwater Program, operators of large, medium and small regulated Municipal Separate Storm Sewer Systems (MS4) are required to have a MS4 permit to discharge stormwater.

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What is an 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; and
  • Not part of a Publicly Owned Treatment Works (sewage treatment plant).

What are Best Management Practices (BMPs)?

Best Management Practices (BMPs) are activities, facilities, designs, measures, or procedures used to manage stormwater impacts from regulated activities, to meet state water quality requirements, and to promote groundwater recharge.

Stormwater BMPs are commonly grouped into one of two broad categories or measures: structural or nonstructural.

Nonstructural BMPs are operational and/or behavior-related practices that attempt to minimize the contact of pollutants with stormwater runoff.

Structural BMPs consist of a physical device or practice that is installed to capture and treat stormwater runoff. Structural BMPs include, but are not limited to, a wide variety of practices and devices, from large-scale retention ponds and constructed wetlands, to small-scale underground treatment systems, infiltration facilities, filter strips, low impact design, bioretention, wet ponds, permeable paving, grassed swales, riparian or forested buffers, sand filters, detention basins, and manufactured devices. Structural stormwater BMPs are permanent appurtenances to the project site.

6  Minimum Control Measures (MCMs)

The MS4 Program contains six elements called Minimum Control Measures which help to reduce pollutants discharged into our rivers and creeks. These 6 MCMs include:

  1. Public Education and Outreach – Educate the public about stormwater and the importance of protecting water quality.
  2. Public Involvement – Involve the public in developing, implementing, and reviewing MS4 management programs and describes ways to reduce stormwater pollution.
  3. Illicit Discharge Detection and Elimination – Identifying and eliminating illicit discharges and spills to storm drain systems.
  4. Construction Site Runoff Control (Erosion and Sedimentation Control) – Address stormwater runoff from active construction sites.
  5. Post-Construction Stormwater Management – Address stormwater runoff after construction activities have ended through use of structural and non-structural Best Management Practices (BMPs).
  6. Pollution Prevention and Good Housekeeping – Aims to reduce water pollution through prevention and good housekeeping practices related to municipal operations.

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