Sanitary Sewer Overflows (SSOs)

Impact Areas: Town-wide, but generally in low laying areas of town. A Sanitary Sewer Overflow (SSO) is an unintentional discharge of wastewater to the environment prior to reaching a treatment facility. SSOs occur infrequently when the capacity of the sewer system is exceeded, usually due to extreme conditions such as heavy rainfall or an obstruction or break in sewer lines. When an SSO occurs in Arlington a notification will be posted on this page (above in the News section). An email notification will also be sent via the SSO Notification Email list. Subscribe to this email list on the email subscription page.

Learn more about SSOs at MWRA's website.

Combined Sewer Overflows (CSOs)

Impact Areas: Along Alewife Brook. A combined sewer overflow (CSO) occurs when a large storm overwhelms the combined sewerage system causing rainwater to mix with wastewater and discharge to a nearby water body.  This relief measure prevents sewage backups into homes and businesses.  Cambridge, Somerville, and the MWRA own combined sewer outfalls that discharge to the Alewife Brook.  When a CSO occurs from an outfall these entities own, there will be a notification displayed on their website. These pages also include locations of their CSOs and additional information.

Cambridge CSO Notifications
Somerville CSO Notifications
MWRA CSO Notifications

Learn more about CSOs at MWRA's website

This page is part of the Town's Sanitary Sewer Overflow Public Notification Plan, established on July 6, 2022 in compliance with Mass Department Environmental Protection regulation 314 CMR 16.00.