Infrequently, the combined sewer at Alewife and Mystic rivers will overflow during heavy storm events.

The water quality in Alewife Brook is often impaired due to bacterial and other pollutants from a number of sources, including stormwater runoff, CSOs and cross connections between sanitary sewers and storm drains.  Water quality in the brook during both wet and dry weather 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 to the brook.

Portions of Cambridge and Somerville are served by combined stormwater and sanitary sewer systems, common in older cities.  There is one Somerville CSO outfall and seven Cambridge CSO outfalls on Alewife Brook, (see the attached plan) 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.  In addition, bordering communities also have separate drainage pipes that collect stormwater runoff and carry it to the brook. Discharges from CSOs and from separate stormwater pipes include bacteria and other pathogens, oxygen-demanding pollutants, solids and other contaminants.

Public health officials recommend avoiding contact with the brook during and for 48 hours following rainstorms, 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.

A Storm Fact Sheet is available on the Massachusetts Department of Public Health web site. Updated information on water quality in the Alewife Brook watershed can be found at a "real time" site co-sponsored by the City of Somerville at www.mysticriveronline.org. 

SOM001A Plan