The City of Cambridge is an older, highly developed, post industrial City. The infrastructure system reflects that history. The original sewer system was built over 150 years ago as a combined system, i.e. both sanitary flow and stormwater flows are carried in a single pipe, and were originally discharged directly into the rivers. Today, combined sewer flows are conveyed to the Massachusetts Water Resources Authority’s (MWRA) Deer Island Treatment plant. During certain rainfall events Combined Sewer Overflows (CSOs) can occur and discharge untreated sewerage into the Charles River and/or the Alewife Brook.

In the late 1930’s separation of the combined sewer system began. Separated systems convey stormwater to the rivers and sanitary waste is conveyed to the treatment plant. Separation of the combined sewer systems continues today. The City‘s collection systems include approximately 115 miles of sanitary sewer, 78 miles of stormwater drains, 43 miles of combined sewer (sanitary sewerage and stormwater) and around 10,000 assorted sewer and drainage structures (manholes, catch basins, regulators, overflows, etc.) Today 40% of the City has been separated. Construction and rehabilitation of the sewer and drainage systems has been accomplished through the use of Federal, State and local funds.

During the past 20 years the City’s approach to sewer separation and stormwater management has become more rigorous. Over the past 5 years the City has begun to construct sewer separation and stormwater management projects that address community flooding problems and water quality issues. The goals of sewer separation and stormwater management include:

• Improving the quality of Cambridge’s waterways
• Eliminating and/or reducing combined sewer overflows (CSOs)
• Alleviating flooding in residential and commercial neighborhoods, and
• Reducing/eliminating sanitary sewer backup problems throughout the City.

The City’s actions have resulted in cleaner rivers and diminished flooding.