About This Project:
The Somerville Marginal New Pipeline Connection is an ongoing infrastructure project aimed at improving the performance of the sewer system in the Somerville and Medford area. It is part of a broader effort by the Massachusetts Water Resources Authority (MWRA) to reduce Combined Sewer Overflows (CSOs) where untreated wastewater is discharged into local waterways during heavy rainstorms.
This project plays a key role in MWRA’s Long-Term Control Plan, developed in response to the Boston Harbor cleanup case, which requires significant reductions in these overflows to protect water quality.
The project serves the communities of Somerville and Medford, as well as areas near the Upper Mystic River and downstream at Prison Point. It involves building a new relief pipe equipped with a remotely controlled valve. This pipe will connect two major sewer lines, allowing the system to better handle excess flow during storm events by using available capacity further downstream.
Once complete, the project is expected to reduce the number of overflow events in this area from 30 to 17 per year and cut the volume of discharged wastewater from about 100 million gallons to 62 million gallons annually. Another nearby outfall is also expected to see improvements, with overflow events dropping from 5 to 3 per year, and volumes decreasing from 4.5 million gallons to 3.6 million.
Overall, the project will result in a major environmental benefit by significantly reducing the amount of untreated wastewater that reaches the Upper Mystic River and Boston Harbor.
Work Includes:
The work included in this project is centered around improving water flow management and CSO control. It features the construction of a new pipe connection and the installation of a remotely operated control valve between two major sewer interceptors. These improvements are designed to better manage flow between systems during heavy rain events, thereby reducing stress on the CSO facility and its nearby outfall. The project includes targeted system performance upgrades that will reduce CSO discharges specifically at the Somerville Marginal CSO Facility and the adjacent outfall to the Upper Mystic River. By taking advantage of downstream capacity under certain conditions, the project will help mitigate overflows during high tide and storm events, reducing the number of activations and the volume of discharges. This strategic approach to system optimization also contributes to downstream benefits, including reduced overflow events at the Prison Point facility.
Schedule:
The project is expected to begin in the Spring of 2026 and be completed in the Summer of 2026.