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Alewife Brook sewage: Today vs. 1997, pre-Boston Harbor cleanup

Caption: Worst Offender: Somerville’s SOM01A Combined Sewer Overflow (CSO)Worst Offender: Somerville’s SOM01A combined sewer overflow.

This viewpoint was submitted by Precinct 13 Town Meeting member Kristin Anderson, who is monitoring the combined sewer overflows into the Alewife Brook. The following is from the Save the Alewife Brook newsletter.

So far, this year, a total of 50 million gallons of sewage-contaminated stormwater has been discharged into the Alewife Brook from combined sewer overflows, as shown immediately below, in data sourced from the permittes' websites (see references at end).

The kind of sewage that we are talking about here is the kind that you flush. It contains hazardous human waste which can cause disease.

CSO data

There have been a total of 45 combined sewer overflow (CSO) activations in the Alewife Brook in 2021.

Rainstorms producing as little as an inch of rain can trigger a CSO discharge into the Alewife Brook.

The 2021 CSO discharge numbers are significant because they show ZERO reduction in the volume of discharges, as compared to the original 1997 assessment. That predates any improvements that were made as part of the Boston Harbor Cleanup case to close the CSOs.

The CSO Final Variance Permit** from the Mass. Department of Environmental Protection that allows the permittees (Somerville, Cambridge, and MWRA) to discharge sewage contaminated water into Alewife Brook, provided the public with a promise that there would be an 85% reduction in discharges after the work was done,*** as part of the Long Term Control Plan (LTCP).

But an 85% reduction would mean that we would experience 7 CSO activations and 7.3 million gallons, annually. The reality this year is SIX TIMES WORSE than what the Variance Permit predicted.

Close up of the kiosk sign at the Alewife Stormwater Wetland in CambridgeCloseup of the kiosk sign at the Alewife stormwater wetland in Cambridge.

While there has been a lot of rain this year there still should have been some improvement. Also, with climate change we can expect more rainfall and more severe storms.

Note that this variance permit places no maximum limit on the number of annual activations. It places no maximum limit on the annual volume of discharges. It is not concerned about any maximum amount of bacteria in the water. However, the Final Variance Permit does require that the permittees (Somerville, Cambridge, & MWRA) have in place a Long Term Control Plan (LTCP) and that they are making improvements. But the Alewife Brook LTCP was completed in 2015 and, to the best of our knowledge, there have been no improvements since then, other than regular maintenance.

There’s an opportunity, now, for a new Alewife Brook CSO Long Term Control Plan to be developed. It appears that the previous improvement efforts are unexpectedly losing ground to an increase in precipitation, an increase in stormwater, and an increase in sanitary sewage, resulting in more CSO activations. Since we expect that the future will bring more precipitation and more dramatic storms, the new Alewife Brook CSO Long Term Control Plan must consider all these factors. It should be a plan to close all the CSOs in the Alewife Brook.

The Alewife Basin is prone to flooding.**** When there is flooding, Arlington’s most vulnerable and diverse neighborhoods receive flood waters over the bank of the Alewife and into parks, yards, and neighborhood homes, right through the back door. This is not percolating ground water flooding. It is flood water that is mixed with sewage. To make matters worse, the Alewife reverses direction during some flood events, sending that contaminated flood water back to North Cambridge, towards Cambridge’s most diverse and vulnerable neighborhood.

The Alewife Brook CSOs are an environmental justice issue.

What can you do about this?

Please reach out to your state representative today and ask them for federal funds to address this problem.

Sign the Save the Alewife Brook petition to close the CSOs in the Alewife Brook.

Please join the Save the Alewife Brook online Zoom meeting on Dec. 13, to discuss our vision for a safe, clean, and beautiful Alewife Brook and to plan our public response to the upcoming regulatory milestones.


Combined Sewer Overflow Reporting – City of Cambridge, MA (

Alewife Brook Combined Sewer Overflow (CSO) Control | City of Somerville (

MWRA’s CSO Reporting Page

** The DEP’s Final Variance Permit, see page 12

*** 3 See page 3: 2019 Alewife Mystic Final Fact Sheet (

**** Massachusetts Sea Level Rise and Coastal Flooding Viewer (

***** Massachusetts 2020 Environmental Justice Populations 


Oct. 20, 2021: 'Horror' tour of Alewife Brook sewage outfalls leads to letter plea 


This viewpoint, from the Save the Alewife newsletter, was published Tuesday, Nov. 23, 2021.

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