MWRA CSO Report Provides No Solution to Alewife’s Problems

On December 30, 2021, the Massachusetts Water Resource Authority (MWRA) published its anticipated Final CSO Performance Assessment, as part of a series of regulatory reports that have been submitted to the U.S. Environmental Protection Agency (EPA) and the Massachusetts Department of Environmental Protection. These reports are a requirement of the landmark Boston Harbor Cleanup Case. Here, the MWRA has attempted to demonstrate that it has achieved the levels of Combined Sewer Overflow (CSO) control, “including as to frequency of activation and as to volume of discharge specified in its Long-Term CSO Control Plan” as stated in the court ruling.1

What the MWRA Final CSO Performance Assessment Report Says:

  1. The Boston Harbor Cleanup has been extremely successful for the Boston Harbor.2 There really has been a miraculous transformation in the Boston Harbor that everyone involved can be proud of.
  2. SOM001A, Somerville’s Alewife Brook CSO is not in compliance3 and there is no plan proposed to get SOM001A into compliance4. SOM001A is the Tannery Brook CSO, which discharges combined sewage from Davis Square.

What the MWRA Final CSO Performance Assessment Report Doesn’t Say:

  1. Based on modeling, rather than real data, the report claims that there were a total of 6.26 million gallons of CSO discharge in the Alewife Brook in 2021.5 The reality is that in 2021 there was a total of 50 million gallons of sewage water discharge into the Alewife Brook. The true data is eight times worse than the MWRA’s modeled data. The MWRA’s CSO report is off by 43 million gallons!
Actual, Real, True, Measured Data from the CSO Reporting Websites.6
  1. The report does not provide actual CSO discharge volumes in the Alewife Brook. It only includes measured 2021 CSO discharge volumes for the first half of the year. For the second half of 2021, the MWRA used modeling, rather than actual measured discharge volumes.6
  2. Cambridge, Somerville, and the MWRA have reported the actual measured data for the entire year on their CSO Activations reporting websites.7 Given the disproportionate health impact that the CSOs have on our most vulnerable Environmental Justice populations in the Alewife area, it is not equitable to publish untrue, modeled data that has no basis in reality. The true numbers demand that more work is done to control the CSOs. If the true data is published, then this report can be used to better improve the community health problems of hazardous sewage-contaminated floodwater that enters the homes, yards, and parks of Alewife area neighborhoods.
  3. The report basically evaluates modeled performance of the CSOs for a “typical” year which was determined over twenty years ago based on historical data. It is this modeled data that is then used to evaluate compliance. The “typical” year assumption needs to be re-evaluated and likely updated to represent current conditions including the effects of climate change.8
  4. The actual data is used for model calibration but not for assessing compliance. This is a potential disconnect between what is actually happening and what the model is saying.
  5. The Final CSO Performance Assessment report does not account for the effects of Climate Change and its continual increase in precipitation.9 It says nothing about how Climate Change’s increase in wet weather is resulting in an increase in CSO activations. The report makes no mention about the fact that future conditions will be even worse, not only because of the increase in precipitation, but also because of sea level rise, and more frequent and dramatic storm events.
  6. Missing from the MWRA’s Final CSO Performance Assessment report is any information whatsoever about the Alewife Basin’s topography and how it is prone to flooding. It says nothing about how close to sea level the Alewife is. And it says nothing about the number of people who live within the Alewife’s 100-year flood plain and how hazardous sewage-contaminated flood water enters the homes, yards and parks of the area’s most vulnerable, Environmental Justice populations. The report says nothing about how unsafe it is to live near the Alewife Brook because of CSO sewage water that floods neighborhood homes.
  7. And, alarmingly, although it does list other pathogens, the CSO Final Performance Assessment report says nothing about COVID-19 in the CSO sewage water and what health risk the Alewife’s hazardous COVID-19 contaminated flood water carries when it enters residents’ homes, yards, and parks. The MWRA is already doing an amazing job of testing their wastewater for COVID-19. That data should be included in their CSO report.10


The Boston Harbor Cleanup has been a great success for the Boston Harbor. The Alewife Brook is a small waterbody by comparison, but it should be treated it as the unique tributary that it is. The flat topography of the low-lying Alewife watershed ensures that CSOs have a disproportionate impact on the folks living in this flood-prone area. A review of FEMA flood maps reveals there are an estimated 1200 East Arlington residents, 3500 Cantabrigians, and 300 Belmont residents living in the Little River – Alewife Reservation’s 100-year flood plain. Because of flooding, the CSOs make the Alewife Brook an unsafe place to live near. The neighborhoods around the Alewife include the area’s most diverse and vulnerable populations, which makes this an Environmental Justice issue, since these are Environmental Justice populations.11 Because of the elevated health risks associated with sewage water entering the homes of Alewife residents, the Alewife’s CSO control design should exceed the EPA & MWRA’s 85% improvement goal as part of the Boston Harbor Cleanup case.

The great achievements from the first Long Term CSO Control Plan, which closed half the CSOs in the Alewife Brook, are losing ground to Climate Change, with its wetter rain season, and more frequent and dramatic storms. What we once thought would be an 85% reduction in CSO discharges is now completely eclipsed by the effects of Climate Change, in addition to other factors such as the increase in impervious surface. In 2021, there have been 50 million gallons of sewage-contaminated water discharged into the Alewife Brook. This is the same volume of sewage contaminated stormwater discharge as for the base year of 1997, which is the year that the MWRA chose as the design year in its original Long-Term CSO Control Plan.

The MWRA’s CSO Performance Assessment provides no path forward towards solving the critical community health problems that Alewife Brook CSOs present. As an example, there is currently no plan for compliance of Somerville’s SOM001A CSO. For this CSO, which MWRA has flagged as being out of compliance, there should be a plan that includes (1) full sewer separation and elimination of the SOM001A CSO, (2) gray infrastructure that includes an underground stormwater tank at Dilboy Park, (3) another Pumping Station to convey sewage out to Deer Island, and (4) green infrastructure that includes a stormwater wetlands to clean Somerville’s stormwater, bioswales and rain gardens, (5) Alewife Brook restoration, and (6) possible daylighting of the Tannery Brook.

Somerville, Cambridge, and the MWRA will benefit when their CSOs are no longer polluting the community surrounding Alewife Brook. There is federal funding available to do this work now, making the project an economic win. Somerville, Cambridge, and the MWRA should stop pushing the costs downstream on MWRA rate payers in Everett and Chelsea who cannot afford it. By closing the CSOs, they will prevent unsafe, contaminated discharge into Alewife Brook and into the flood water that enters neighborhood homes, yards, and parks. Half of the CSOs have already been closed, now is the time to close those that remain.


1 CSO Post-Construction Monitoring and Performance Assessment (
2 Taking Back Boston Harbor – CLF
3 P. 2-4, Table 2-2 Report NPDES 2018-07-27 (
4 P. 2-10, Table 2-4, P. 4-18, 4-19 Report NPDES 2018-07-27 (
5 P. 2-4, Table 2-2, Q4-2021 SYSTEM CONDITIONS, Report NPDES 2018-07-27 (
6 P. 2-1, Report NPDES 2018-07-27 (
7 Combined Sewer Overflow Reporting – City of Cambridge, MA (
Alewife Brook Combined Sewer Overflow (CSO) Control | City of Somerville (
MWRA’s CSO Reporting Page
8 P. x of the Definitions. Based on historical data for 1949-1987 and 1992. Report NPDES 2018-07-27 (
10 MWRA – Wastewater COVID-19 Tracking
11 Massachusetts 2020 Environmental Justice Populations (
In Massachusetts, a neighborhood is defined as an Environmental Justice population if one or more of the following four criteria are true: the annual median household income is not more than 65 per cent of the statewide annual median household income; minorities comprise 40 per cent or more of the population; 25 per cent or more of households lack English language proficiency; or minorities comprise 25 per cent or more of the population and the annual median household income of the municipality in which the neighborhood is located does not exceed 150 per cent of the statewide annual median household income.

Leave a Reply

%d bloggers like this: