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April 15, 2004

Help on the Way to Relieve Alewife Brook of Combined Sewer Overflows

Joint press release: Massachusetts Water Resources Authority, Cambridge Department of Public Works and Somerville Department of Public Works

Help is on the way for water quality in Alewife Brook. The Massachusetts Water Resources Authority (MWRA) and the Cities of Cambridge and Somerville are finalizing plans for a $75 million series of projects to significantly reduce combined sewer overflows (CSOs) into the brook.  After receiving final approval from the state Environmental Policy Act office last spring, design of the project is well underway.

The first piece slated to move ahead is Cambridge’s planned stormwater outfall and treatment wetland associated with sewer separation work in the neighborhood east of Fresh Pond Reservation. The City has submitted a Notice of Intent to the Cambridge Conservation Commission for work in or near wetland areas, and hearings are currently ongoing.

Construction of this project is scheduled to begin in July 2005.  The water quality of Alewife Brook is often impaired due to bacteria and other pollutants from a number of sources, including CSOs, cross connections between sanitary sewers and stormwater runoff. 

During both wet and dry weather, the brook generally fails to meet state bacteria standards for fishing and swimming.  Contaminant sources originate in the watershed communities of Belmont, Arlington, Cambridge and Somerville, all of which are undertaking programs to identify and control the sources of pollution.Portions of Cambridge and Somerville are served by combined stormwater and sanitary sewer systems, common in older cities. 

There are eight CSO outfalls on Alewife Brook, which discharge untreated CSO (a mixture of wastewater and stormwater) during moderate and heavy rainfall to relieve the system and prevent sewer backups into homes, businesses, and streets. 

Public health officials recommend avoiding contact with the brook during and for 48 hours following rain storms, as there may be increased health risks during these periods. 

Contact with floodwaters should also be avoided as they may contain similar contaminants and pose associated health risks.As part of a federal court order, MWRA working with the Cities of Cambridge and Somerville are implementing an ambitious CSO abatement program to minimize the impacts of these CSO discharges by reducing discharges by an estimated 84%. Earlier sewer separation work and other system improvements by Cambridge and Somerville, done in the 1990’s, have already significantly reduced the CSO discharges to the Alewife Brook.The $75 million project consists primarily of “sewer separation.” 

By removing stormwater from the combined system, sewer separation creates more room in the sewer pipes during storms, thereby reducing the amount that overflows. The newly separated stormwater is then redirected through new pipes to the Alewife Brook. Cambridge’s sewer separation work will involve state-of-the-art measures to improve the quality of the stormwater flows as well as to attenuate, or dampen, these flows to avoid increases to Alewife Brook stream levels. 

Flooding along Alewife Brook has long been a problem, so Cambridge has taken great care to ensure that flows from the new stormwater outfall project will not worsen the existing flooding situation. 

In addition to the sewer separation work, “hydraulic relief” of sewer system constrictions at key connection points will allow more flow from the local systems to get into the MWRA pipes, thereby reducing the overflow amounts. The main elements of the current project are:

  • Separating stormwater from the combined sewer system in neighborhoods east of Fresh Pond to eliminate CSO discharges from a major Cambridge outfall (CAM004) located near Fresh Pond.  (Early phases of this work were completed in 2002.)  This work will ultimately include constructing a new stormwater outfall and an innovative 3.4-acre stormwater wetland to attenuate peak flows to the Little River/Alewife Brook and improve stormwater quality.
  • Separating common manholes in the CAM400 area (bounded by Alewife Brook Parkway, Whittemore and Massachusetts Avenues) to reduce CSO discharges.
  • Increasing the size of connections between local sewers and the MWRA interceptor to reduce CSO discharges.
  • Increasing the size and capacity of MWRA’s Rindge Avenue siphon to reduce CSO discharges.
  • Installing mechanisms at all remaining Alewife Brook CSO outfalls to control floatable materials.

In accordance with the current state water quality variance, MWRA submitted the Final Alewife Brook/Upper Mystic Variance Report in July 2003.  The Massachusetts Department of Environmental Protection (DEP) and the United States Environmental Protection Agency (U.S. EPA) are expected to make a final decision on the appropriate level of CSO control and water quality standards for the Alewife Brook after a public review process. 

The regulatory agencies’ determination is currently scheduled to be issued in September 2004. MWRA’s CSO program is also overseen by a federal judge as part of the Boston Harbor court case. MWRA, along with the CSO communities, is implementing 25 different CSO control projects along Boston Harbor and the Mystic, Charles and Neponset Rivers.As noted above, final design of the Alewife project is now underway and construction will take several years to complete. 

While the CSO project will reduce bacteria levels in the brook after rainstorms, there will continue to be sources of pollution in the watershed during both dry and wet weather conditions.  Each community and various watershed organizations are working to identify and reduce these contaminant sources, and to try to understand and address the causes of local flooding conditions as well.For more information on CSOs and the CSO abatement program, contact MWRA at 617-788-1170 or visit their website at or visit the Cities of Cambridge and Somerville websites at and Updated information on water quality in the Alewife Brook watershed can be found at the Mystic River Watershed Association (MyRWA) website, and at a “real time” site co-sponsored by the City of Somerville and MyRWA at on the Web at:  and Date: April 15, 2004