What is an MS4?

The U.S. Environmental Protection Agency’s (EPA) Stormwater program was created under the Clean Water Act (CWA).  Phase I uses National Pollutant Discharge Elimination System (NPDES) Permit coverage to manage Stormwater from different sources, including MS4 communities.

MS4 stands for “Municipal Separate Storm Sewer System.”  “Municipal” refers to a unit of local government like a town or a city, but may also refer to an organization responsible for the administration of a developed area. The number “4” represents the four words that start with the letter “S” – “Separate,” “Storm,” “Sewer,” “System.”

MS4 Area Map

Auburn Notice of Intent under MS4 Permit

Auburn Authorization for USEPA

Annual Reports

Stormwater Regulation

EPA’s Stormwater Phase II Rule establishes an MS4 Stormwater management program that is intended to improve water quality of waterways by reducing the quantity of pollutants.

Phase II of EPA’s Storm Water Regulation requires operators of MS4s in urbanized areas and operators of small construction sites, through use of NDPES Permits, to implement programs and practices to control polluted stormwater runoff.  Phase II is intended to further reduce adverse impacts to water quality and aquatic habitat by instituting the use of controls on the unregulated sources of stormwater discharges that have the greatest likelihood of causing continued environmental degradation.  The Permit is comprised of the following six elements that, when implemented in concert, are expected to result in signifigant reduction of pollutants discharged into receiving waters:

  • Public Education and Outreach
  • Public Involvement / Participation
  • Illicit Discharge Detection and Elimination (IDDE)
  • Construction Site Stormwater Runoff Control
  • Post Construction Stormwater Management in New Development and Redevelopment Projects
  • Pollution Prevention / Good Housekeeping for Municipal Operations

Pursuant to the requirements of the Environmental Protection Agency (EPA)’s “National Pollutant Discharge Elimination System (NPDES) General Permit for Storm Water Discharges from Small Municipal Separate Storm Sewer Systems (MS4)” the Town is responsible for implementing and performing various items and activities related to stormwater management. 

As an operator of an MS4, the Town is required to develop, implement, and enforce a Stormwater Management Program (SWMP). The SWMP is a 'living document' intended to be revised and updated as needed, but at a minimum, annually. The primary goals of the SWMP are to reduce the discharge of pollutants from the MS4 to the maximum extent practicable, to protect water quality, and to satisfy the appropriate water quality requirements of the Clean Water Act (CWA).