Somerville is teeing up a big sewer separation job along the Mystic River, and neighbors are getting a front row seat next week. The city is hosting two public events next Wednesday on a major sewer separation plan meant to cut neighborhood flooding and reduce sewage discharges to the Mystic. City staff and consultants will lead a site walk at 11 a.m. at the intersection of Shore Drive and Temple Road, then return in the evening for a Zoom community meeting. The outreach is part of the Mystic River Outfall and Sewer Separation project, which officials say will modernize aging pipes and move stormwater out of the combined sewer system.
What the city plans to build
According to the City of Somerville project page, the plan calls for a new stormwater outfall to the Mystic River, drainage upgrades, and rehabilitation of the neighborhood’s sanitary sewers so stormwater no longer overloads the combined system. The work focuses on the area west of Foss Park and is designed to route separated stormwater to a new "trunk drain" and outfall instead of into the treatment system. City staff and consulting partners have been running field investigations and gathering resident feedback since early 2024.
Numbers and expected benefits
Engineering documents and city presentations show the project will add roughly 1.7 miles of storm pipe, including a large trunk drain, to carry stormwater to the new outfall. Project modeling estimates the work could cut annual combined sewer overflow volumes by about 50 million gallons and reduce discharges to the Mystic by roughly 55 percent, Project Manager Gina Cortese told The Somerville Times. Cortese also told the paper that municipal modeling suggests some neighborhood flood depths could fall dramatically: "With this project, a lot of that flooding goes away, close to 95 percent," she said. The team has identified potential green infrastructure sites to filter runoff and expects to prioritize roughly 15 locations for bioretention and infiltration where they are feasible.
Regional context
Somerville’s plan plugs into a broader regional push to curb combined sewer overflows and protect water quality in the Mystic and Charles watersheds. Even so, state and regional plans leave some big-storm risk on the table and will require expensive fixes, as reporting from storms keep turning Boston rivers into “sewage soup” and others notes. That backdrop helps explain why Somerville is leaning into sewer separation, a fix that reduces neighborhood flooding while cutting the volume that reaches MWRA facilities, even as advocates keep pushing for more aggressive, more costly alternatives. Residents should still expect tradeoffs: separation and green infrastructure take time and money, and some overflows during extreme storms may continue.
How to participate
The city will lead a project site walk at 11 a.m. next Wednesday, with neighbors asked to meet at Shore Drive and Temple Road, followed by a virtual community meeting from 6 to 8 p.m. that evening. Residents can register to attend the Zoom session or find materials on the project website. For background reporting and earlier design details, see The Somerville Times. Questions can be emailed to [email protected] or routed through 311 (617-666-3311 from outside Somerville).
MEPA review and next steps
The project is in the middle of state environmental review. The city has submitted an Enhanced Environmental Notification Form, and the work will require MEPA review and other permits, according to the Massachusetts MEPA advance-notice materials. State staff note the project could trigger a Chapter 91 license and other regulatory thresholds. The city says MEPA staff will attend the March 25 events and that public comments on the filing are due by April 10, 2026, as announced on the City of Somerville project page.
Design and permitting are still active, so construction timing and neighborhood impacts will depend on the MEPA review, final designs, and funding. The city plans to post updated materials after the March 25 meetings, and the state MEPA office will continue to take public comments on the filing. Neighbors who want a say in how the work lands on their blocks should plan to join the site walk or the virtual meeting and check the project materials afterward.
