Stormwater Management

  • Stormwater Management

  • Annual Reports

The City of Somerville's sewer and drain collection systems consists primarily of combined stormwater and sewer systems. Some areas of the City along the Alewife Brook and the Mystic River have separate systems. Combined systems are common in older cities such as Somerville. During significant rainstorms, combined sewer systems may fill up beyond their capacity with a mixture of sanitary waste and rainwater. Combined Sewer Overflows (CSO) act like a relief valve allowing sewerage to discharge into waterways preventing sewerage backups into homes, businesses, and streets. Somerville’s combined sewer system ties into the Massachusetts Water Resources Authority's (MWRA) wastewater collection system which is treated and discharges at Deer Island. During periods of heavy rain, both MWRA and Somerville’s wastewater systems can become overwhelmed by rainwater releasing CSOs into both the Mystic River and the Alewife Brook.

Municipal separate storm sewer systems (MS4) use separate pipes for sanitary sewage and stormwater flows. Combined sewer systems (CSS) use the same pipes.
Graphic, Washington D.C. Department of Energy and Environment

NPDES / Stormwater Management Program

As part of the Environmental Protection Agency (EPA) National Pollutant Discharge Elimination System (NPDES) permitting program, Somerville is required to take steps to reduce the impact of stormwater pollution. Portions of Somerville's stormwater drainage system operate as a Municipal Separate Storm Sewer System (MS4) under this permit.

The City's program includes the following elements:

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

2016 General Permit

The EPA issued a new, updated general permit effective July 1, 2018. This permit replaces the 2003 permit and contains updated and new requirements that the Town will have to meet. The entire contents of the permit are available at the EPA’s website:

June 2020 Efforts

Somerville developed an updated stormwater management plan which outlines the steps the City is undertaking to comply with the new permit requirements in greater detail than in the Notice of Intent (NOI).