50 Million Gallons of Sewage Released into Massachusetts' Alewife Brook in 2021

Jan. 17, 2022

The Alewife sub-watershed is prone to flooding and is densely developed with impervious surfaces

50 million gallons of sewage contaminated storm water were discharged into the Alewife Brook from the cities of Cambridge and Somerville, Massachusetts in 2021.

According to websites for those two cities and the Metropolitan Water Resources Authority, there was as much sewage-contaminated water discharged into the Alewife Brook last year as in 1997. This is before the implementation of a $200 million plan to modernize the area’s antique combined sewer systems, reported Cambridge Day.

The Alewife sub-watershed is prone to flooding and is densely developed with impervious surfaces including pavement, rooftops and sidewalks. According to Cambridge Day, during major flood events when the Mystic River rises, it flows backward into the Alewife Brook. This reverses the brook’s direction, taking the contaminated flood water which contains untreated sewage back upstream.

This ultimately impacts neighborhoods in North Cambridge and East Arlington, as the water flows into the Little River and Belmont, and into residents’ homes, yards and parks. 

According to Cambridge Day, in the past 20 years Cambridge has completed more than 20 large sewer separation and storm water holding tank projects.

The landmark Conservation Law Foundation Boston Harbor cleanup court case in the 1980s resulted in the EPA enforcing the Clean Water Act and requiring that the CSO pollution end. The Long Term CSO Control Plan split this work into seven large projects that took more than a dozen years to complete and was finished by 2015.

2021 saw the same volume of hazardous pollution as before the investments, as well as CSO activations that are six times worse than the original plan promised, however, reported Cambridge Day.

“The latest data I’ve seen shows 2021 was the 16th wettest year on record, and July was the wettest on record since 1895,” said Kathy Watkins, the city’s assistant commissioner for engineering, reported Cambridge Day. “The [work since 1997] has been an incredible success, but the work is not done.”

Cambridge staff has made decreasing flooding a priority with the installation of a dozen storm water tanks. A project that is slated for the future is a 1.3 million gallon tank and 100,000-gallon bioretention basin at the Tobin School campus, reported Cambridge Day.

Cambridge and Somerville have been sending untreated sewage mixed with storm water directly into the Alewife Brook through sewer outfalls. The combined sewer system carries storm water, industrial wastewater and untreated domestic sewage away in a single pipe out to the Deer Island water treatment plant, reported Cambridge Day. Rains, tides and river currents then carry the pollution to Boston Harbor via the Mystic River.

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