Sewer Separation

Significant infrastructure challenges are common to the evolution of a modern post-industrial city. In Cambridge the original sewer lines were engineered over 150 years ago as a combined system: sewage and rain water ran through the same pipes and discharged directly into the Charles River through tide gates.

Historic Sewer Construction Photo Thumbnail Historic Sewer Construction Photo Thumbnail Historic Sewer Construction Photo Thumbnail
Historic Sewer Construction Photo Thumbnail Historic Sewer Construction Photo Thumbnail Historic Sewer Construction Photo Thumbnail

Click to view historic sewer construction and original river reconfiguration images.


Separation of the combined sewer system began in the 1930’s. Separated systems are designed and constructed to convey only stormwater to the rivers and only sanitary waste to a treatment plant. Sewer separation continues today and the city‘s collection system currently include approximately 110 miles of sanitary sewer, 94 miles of stormwater drains, and 41 miles of combined sewer. Approximately 40% of the collection system owned and maintained by Cambridge has been separated.

During the past twenty years the City has increased its sewer separation and stormwater management efforts because of stricter environmental compliance regulations and a desire to provide a better quality to residents' daily lives. Over the ten years the City has addressed localized flooding problems and stormwater quality issues within the design of sewer separation contracts. The goals of sewer separation and stormwater management include:


Improving the quality of waterways in Cambridge
Reducing or eliminating combined sewer overflows
Reducing or eliminating sanitary sewer backups
Reducing flooding


Combined Sewer Diagram Thumbnail Separated Sewer Diagram Thumbnail

Click to view detailed diagrams of each configuration.


Since the 1800's thousands of hours of engineering and millions of dollars of construction have been allocated to realize a more efficient and environmentally-friendly system. The City’s efforts have resulted in measurably cleaner rivers and significantly reduced street flooding. Today, dedicated sewer lines and the remaining combined sewer lines are conveyed to the Massachusetts Water Resources Authority’s Deer Island Treatment Plant through 15 miles of high-capacity state-owned combined sewer interceptors. During significant rainfall events combined sewer overflows can still occur and discharge untreated sewerage into the Charles River or the Alewife Brook.

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Dept of Public Works

147 Hampshire St
Cambridge MA 02139


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Monday: 8:30am-8pm
Tuesday-Thursday: 8:30am-5pm
Friday: 8:30am-12pm