Stormwater (MS4)

The Merrimack River from Arms Park (Manchester)
The Merrimack River from Arms Park (Manchester)

A Municipal Separate Storm Sewer System, or MS4, is a conveyance or system of conveyances of stormwater that is not part of a combined sewer or sewage treatment plant. MS4s in urban areas are regulated to reduce stormwater runoff and pollution. The U.S. EPA requires applicable operators of an MS4 to comply with National Pollutant Discharge Elimination System (NPDES) program permits for stormwater discharges.

This NH Stormwater Regional Coalition represents affected communities in New Hampshire. The group is composed of the separate New Hampshire Seacoast Stormwater and the Nashua/Manchester Regional Stormwater Coalitions.

MS4 permits apply to several different areas:

  • Municipalities in urbanized areas as defined by the Census Bureau, densely settled areas of 50,000 or more people and an average density of at least 1,000 people per square mile
  • Larger federal- and state-owned properties
  • Institutions such as hospitals and universities

New Hampshire’s new MS4 permit was released on January 18, 2017. The MS4 permit applies to 8 of the 14 communities in the SNHPC region: Auburn, Bedford, Derry, Goffstown, Hooksett, Londonderry, Manchester, and Windham. Communities will have 17 months to establish budgets and make preparations including  creating a roadmap of steps to comply with the permit.

This permit replaces the 2003 small MS4 general permit for MS4 operators within the State of New Hampshire. For more information on communities within New Hampshire that are automatically designated and may require permit coverage see: NH regulated communities. For more information on MS4 and stormwater management, visit the Department of Environmental Services' stormwater page as well as NH-MS4 Regional Stormwater Coalitions.