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Overflowing inbox: Combined sewer overflow

Part of the dock at Chelsea's Mary O'Malley State Park was submerged by the Mystic River on Jan. 3.Roseann Bongiovanni

Rethinking our approach to stormwater

Thanks to the Watershed Associations of the Charles and Mystic Rivers for calling attention to combined sewer overflows, (“The cleanup of Boston Harbor is incomplete,” Opinion, April 4). Since 1988, the Massachusetts Water Resources Authority has reduced CSOs by more than 2.8 billion gallons annually.

The Wastewater Advisory Committee agrees that the MWRA, to which we provide independent advice, still has work to do. A little less than 125 million gallons still overflows into the Charles, Alewife, Mystic, and Mystic Basin in a typical year. More than 90 percent of that flow is screened and disinfected before it hits the rivers or Boston Harbor.


Yet even if the MWRA were to eliminate all combined sewer overflows from the Charles and Mystic rivers, these rivers would still be polluted. Combined sewage from MWRA outfalls contributes 0.1 percent of total bacterial load to the Charles and 0.01 percent to the Mystic. The bulk of the bacteria entering both rivers enters via stormwater.

As global warming increases, so will the intensity of the storms that cause these overflows. Stormwater control is imperative. To make this happen, New England communities need to rethink our approach to stormwater. We need green, distributed infrastructure to deal with rainfall before it reaches drains and sewers. Instead of verges, think bioswales (runoff systems); instead of gardens, rain gardens; instead of tree islands, tree wells.

The pending infusion of federal funds is a once-in-a-lifetime opportunity to restore the hydrology of the urban landscape — reducing stormwater at the source. And we need to act quickly, both for the health of the rivers and to prevent local flooding.

Wayne A. Chouinard


Wastewater Advisory Committee to the MWRA

Sourcing bacteria in our waterways

I respect the advocacy of Emily Norton, executive director of the Charles River Watershed Association, and Patrick Herron, executive director of the Mystic River Watershed Association, as demonstrated in their op-ed, “The cleanup of Boston Harbor is incomplete.”


We all share in the desire for cleaner Charles and Mystic rivers and acknowledge all branches of government need to do more. However, idealistic hopes must be balanced with realistic, responsible, well-thought-out, cost-effective solutions.

That is the reason the MWRA has sought and received extensions on its final combined sewer overflow assessment plans, so as to further evaluate the causes and sources of pollutants.

What is already known is that even if the MWRA magically ended all CSO flow into the rivers, the problem would not be solved. Upstream stormwater and illegal connections contribute most of the bacterial loads. Combined systems, of which 94 percent are treated, contribute less than 0.1 percent of the pollutant loadings. The MWRA is not the source of the problem. Stormwater drainage systems of individual communities are the problem.

Green infrastructure sounds great if you have the acreage. In order to detain the flow, you need approximately three acres for every 1 million gallons. Secondly, effectiveness of these “green measures” is still being determined.

Let’s continue to collect and analyze data and ultimately develop solutions that solve the problem, not just pass it off to the MWRA.

Joe Favaloro

Executive director

MWRA Advisory Board

Sewage-contaminated water in our backyards

The opinion piece “The cleanup of Boston Harbor is incomplete” raises important awareness that the Boston Harbor cleanup work is not done.

However, a related aspect of this is that many waterways that feed into the harbor are also polluted with sewage. The problem is the combined sewer overflows that release sewage into those waterways. Some of these waterways are also next to where people live and can flood into their homes and onto their properties.


An especially troublesome area is Alewife Brook between Arlington and Cambridge and Somerville. There are currently six active CSOs along this slow-moving brook that are adjacent to many residential areas. For example, 5,000 people live in the 100-year flood plain of Alewife Brook, many of them in environmental justice communities. In 2021, about 50 million gallons of sewage-contaminated water were discharged into this brook.

With climate change this is likely to get worse. Thus, for many reasons the Alewife Brook should be a high priority for the elimination of the CSOs.

David White and Kristin Anderson


Save the Alewife Brook