Ten Year Sewer and Drain Infrastructure Plan

The City has developed a strategic plan to manage the infrastructure improvements of the sewer and storm water mains, manholes, catch basins, pumping stations and CSO outfalls that carry waste and storm water to treatment plants and discharge locations. This 10-year plan serves as a guidance document to prioritize construction and rehabilitation of these complex systems.

The goals of the 10 Year Plan are to:

Address high-risk infrastructure conditions
Remove inflow/infiltration (I/I) from sewer systems
Eliminate sanitary sewer overflow (SSOs) and reduce CSOs
Manage stormwater quality and quantity
Reduce flooding and protect neighborhoods
Address fats, oils, and grease (FOG) in the sewer system
Conduct operation and maintenance activities

Projects are prioritized by considering:

Aging infrastructure reaching the end of its service life and needs replacement or rehabilitation
Planned private development projects
Climate change impacts
Public health impacts
Available budget/funding
Projects planned as part of the 5 Year Sidewalk and Street Reconstruction Plan
Regulatory initiatives and enforcement actions or permit requirements that change

Frequently Asked Questions

How much of the City's sewer system is already separated from stormwater drains?

Cambridge's sewer system is approximately 55% separated, where sewage goes directly to the MWRA for treatment and the stormwater discharges directly into Alewife Brook or the Charles River. The remaining system is combined sewer, where the sewer and stormwater share a common pipe and can be directed to the MWRA for treatment during dry and wet weather, and to the Alewife Brook or the Charles River during wet weather CSOs.

What is a CSO?

Combined Sewer Overflows (CSO) act like a relief valve allowing sewerage to discharge into waterways preventing sewerage backups into homes, businesses and streets. Cambridge’s combined sewer system ties into the Massachusetts Water Resources Authority's (MWRA) wastewater collection system which is treated and discharges at Deer Island. During periods of heavy rain both MWRA and Cambridge’s wastewater systems can become overwhelmed by rainwater releasing CSOs into both the Charles River and the Alewife Brook.

Combined System (left) versus a Separated System (right)

Diagram of a Combined Sewer System Diagram of a separated sewer system