Combined Sewer Overflow Control Planning Program - Joint efforts by Cambridge, MWRA, and Somerville

The Draft Plan is here!

The City of Cambridge, the City of Somerville, and the Massachusetts Water Resources Authority are proud to present the Draft Updated Combined Sewer Overflow Control Plan (Draft Plan) – an achievement that reflects years of collaboration, innovation, and shared commitment to a cleaner and healthier future for the receiving waters and the communities that rely on them. Grounded in rigorous data analysis and shaped by extensive public and stakeholder engagement, this forward-thinking plan balances environmental responsibility with community priorities, construction impacts, and affordability. With an estimated investment of $1.3 billion, the Draft Plan will dramatically reduce CSOs across all three waterbodies and, even in the face of increased precipitation driven by climate change, is projected to eliminate CSOs in a 2050 Typical Year. As the first CSO plan in the nation to explicitly incorporate climate change, it sets a new standard for integrated, resilient water management. Built upon four years of dedicated technical work and partnership, this plan is designed to deliver meaningful water quality improvements and positions the region as a national leader in addressing the complex challenges of CSO control, climate resilience, and long-term environmental stewardship.

A downloadable version of the Draft Plan can be found under the “Draft Plan” Header on the right toolbar. Note for mobile users, scroll down past the News Feed to view downloadable documents. Hard copies of the Draft Plan are available for viewing at local libraries, including the those in Cambridge, Somerville, all 43 Communities receiving MWRA sewer service, and the MWRA library located at 2 Griffin Way, Chelsea, MA.

The project team will host a Virtual Public Meeting on June 2, 2026 to describe the contents and details of the Draft Plan. Register for here to receive the zoom meeting link, and see more information in the News Feed section (here) below.

Written, public comments on the Draft Plan can be submitted to the project team through an online comment portal, by email, or by mail until September 30, 2026. Verbal public comment can also be made at Public Hearings. Please note, all comments are considered public record.  

Submit Comments in the Online Comment Portal 

Comments can be submitted to the project team electronically using our online comment portal hosted by Plan Engage at: https://us.planengage.com/updatedcsocontrolplan/page/home

Submit Comments by Email 

Comments can be emailed to the project team at UpdatedCSOControlPlan@aecom.com 

Submit Comments by Mail 

Electronic comments are preferred, however written comments addressed to “Draft Updated CSO Control Plan Partners” can be mailed to the project team at the following address: 

MWRA 
Attn: Draft Updated CSO Control Plan 
2 Griffin Way 
Chelsea, MA 02150 

Submit Comments by Public Hearing  

Verbal comments can be made at one of two virtual Public Hearings to be held in September 2026. More information on these Public Hearings, including registration links, will be provided as it becomes available in the News Feed section of this website.

Persons with disabilities who need auxiliary aids and services for effective communication (i.e., CART, ASL), written materials in alternative formats, or reasonable modifications in policies and procedures in order to access the programs, activities, and meetings of the City of Somerville should please contact the ADA Coordinator at 617-625-6600 x 2059 or ADA@somervillema.gov

If you need assistance translating or understanding this information, please call 311 (617-666-3311) or contact us at languageaccess@somervillema.gov

About the project

The City of Cambridge and the Massachusetts Water Resources Authority (MWRA) are collaborating to improve water quality in the Charles River, and are also collaborating with the city of Somerville to improve water quality in the Alewife Brook and Mystic River through the development of updated combined sewer overflow (CSO) control plans.

A combined sewer overflow (CSO) occurs when a large rainstorm overwhelms a combined sewer system, causing stormwater to mix with wastewater (or sewage) and discharge to a nearby river or lake.

Cambridge, MWRA, and Somerville (the team) are developing updated control plans that will reduce their respective CSOs and protect our waterways, as part of the Variances for CSO Discharges to the Lower Charles River/Charles Basin and to the Alewife Brook/Upper Mystic River Basin issued by MassDEP in 2019, .

We want to hear from you!

Public participation is a critical element in the successful development and implementation of the CSO Control Plans. The team wants to understand how the Charles River, Alewife Brook and the Mystic River affect your life and what impact potential improvements to the stormwater and sewage systems may have on your communities.

By participating in this planning process, you can weigh in on and influence key considerations, such as:

What tools should be used to reduce CSOs? And in what areas should we pursue these tools?
How should we weigh potential tradeoffs, such as the pace of CSO reduction and its relation to increases in sewer rates?

While CSO reduction and stormwater management can be highly technical, there are decisions to be made that affect your communities and neighbors. We want to hear from you whatever your level of experience is with these issues. Stay informed, attend project meetings, and keep checking this website and the team’s CSO pages at:

City of Somerville: https://www.somervillema.gov/cso
City of Cambridge: www.cambridgema.gov/CSO
MWRA: https://www.mwra.com/CSO