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Massachusetts Water Resources Authority
April 15, 2010
mwra original logo cambridge seal somerville logo

Ria Convery, Communications Director
Massachusetts Water Resources Authority
(617) 788-1105 or

Owen O’Riordan, Cambridge Department of Public Works
(617) 349-4845

Robert Staaf, Somerville Department of Public Works
(617) 625-6600 ext. 5410


Alewife Brook Combined Sewer Overflows Progress Update


cover of cso annual report 2009

MWRA 2009 CSO ANNUAL REPORT PDF (Released March, 2010)

map of cso outfalls alewife brook

Map of CSO Outfalls Along
the Little River/Alewife Brook
(larger image)

This notice, required by Massachusetts Department of Environmental Protection (DEP), is an annual update on the progress of Combined Sewer Overflow (CSO) control measures undertaken to improve the water quality of Alewife Brook.

This notice is for residents whose property lies in the extended floodplain of Alewife Brook as established and currently in effect by the Federal Emergency Management Agency (FEMA).

The water quality of Alewife Brook is often impaired due to bacteria and other pollutants from a number of sources, including cross connections between sanitary sewers and storm drains, urban stormwater runoff and CSOs.  During both wet and dry weather, Alewife Brook generally fails to meet state bacteria standards for fishing and swimming.

Portions of Cambridge and Somerville are served by combined stormwater and sanitary sewer systems common in older cities.  There are now eight CSO outfalls along Alewife Brook that release untreated discharges during moderate and heavy rainfall.  These discharges relieve the sewer system, preventing sewage backups into homes, businesses and streets.

As part of the Boston Harbor Case (D. Mass. C.A. No. 85-0489-RGS), the Massachusetts Water Resources Authority (MWRA) is required to undertake certain corrective actions to reduce or eliminate CSO discharges along Boston Harbor, the Mystic, Charles and Neponset Rivers and Alewife Brook.  MWRA, in conjunction with the Cities of Cambridge and Somerville, is currently in the process of designing and constructing several CSO projects that, when completed, will significantly reduce CSO discharges to the Alewife Brook.

Work already completed by the MWRA, Cambridge and Somerville has noticeably reduced the number of CSO events and the total volume discharged to the brook.  MWRA estimates that average annual CSO discharge to Alewife Brook has been reduced by 34% since 1987, when MWRA accepted responsibility for developing and implementing a long-term control plan.  MWRA and Somerville closed four CSO outfalls several years ago as part of these CSO control efforts.

After lengthy delays in the permitting process, including more than two years of project delay due to wetlands permit appeals commencing in 2005, the City of Cambridge resumed final design in October 2008 for projects in the CSO control plan related to Alewife Brook.  Since then, Cambridge has made substantial progress and has been able to move certain projects into construction.

Cambridge combined two of the Alewife Brook CSO projects into one construction contract which commenced in January 2010.  The work of this contract will separate common storm drain and sewer manholes in the neighborhoods near Massachusetts Avenue and Alewife Brook Parkway and will also upgrade city sewer system connections to MWRA’s interceptor sewer and provide floatables control at CSO outfalls along Alewife Brook near Massachusetts Avenue.  The contractor plans to complete this work by the end of 2010.

Cambridge is also nearing the completion of final design for the stormwater outfall and wetland basin in the DCR Alewife Reservation that is necessary to accommodate stormwater flows that will be removed from the sewer system in subsequent contracts.  The basin will attenuate the stormwater flows to avoid contributing to Alewife Brook flood levels. Cambridge plans to commence this construction contract in the summer of 2010, and the work of this contract is scheduled to be complete by the summer of 2012.  Cambridge and MWRA have worked closely with DCR during development and environmental review of the Alewife Brook CSO control plan to ensure that the new facilities are compatible with DCR’s Master Plan for the Alewife Reservation.

Cambridge plans to commence design of a fourth project, involving sewer separation in the area east of Fresh Pond Reservation, in the summer of 2010.  MWRA plans to commence design of the fifth and last Alewife project in 2012.  It involves improvements related to MWRA’s CSO outfall to Alewife Brook (Outfall MWR003), located behind the Alewife Station, as well as improvements to the City of Somerville’s Tannery Brook Conduit connection to MWRA’s system and Somerville’s related CSO outfall (Outfall SOM01A). 

Construction of all five projects is scheduled to be completed by December 2015.  Together, the projects are predicted to reduce average annual CSO volume to Alewife Brook by 85% and bring CSO discharges into compliance with water quality standards 98% of the time on average.

For more information on CSOs and the CSO control program, contact MWRA at (617) 660-7971 or visit MWRA’s website at, or visit the Cities of Cambridge and Somerville websites at  and

It is important to understand that floodwaters in all cases can present health risks, and proper precautions are necessary to minimize these risks during flooding events.  Public health officials recommend avoiding contact with the brook during rainstorms and for 48 hours afterwards, as there may be increased health risks due to bacteria or other pollutants.  DEP has developed guidance for homeowners for responding to flooding or sewer backups, which can be found at

Available on-line at: and


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