The Alewife Brook flows through neighborhoods in Arlington, Belmont, Cambridge, and Somerville and is a popular recreational and commuter area. However, persistent overflows of untreated combined sewage are leading to poor water quality and an environmental hazard to those who live and spend time near the brook.
Alewife Brook received a D on this year’s water quality report card, meaning that the stream complies with water quality standards for swimming and boating less than half of the time. In fact, in wet weather – when a quarter inch of rain has fallen in the previous 48 hours – Alewife Brook meets swimming standards only 4% of the time. Much of this contamination is due to Combined Sewer Overflows (CSOs) — when untreated sewage is released into this small brook — during heavy rainstorms.
““CSOs are not the only way that bacteria get to rivers and streams, but they are the most intense and dramatic. In 2023, over 26 million gallons of untreated combined sewage overflowed into Alewife Brook alone. But this problem is fixable, and there are many ideas on the table for eliminating them. I hope we have the collective political will to make that happen.””
Alewife Brook starts at Fresh Pond and runs underground to the Alewife T station, where it is met by the Little River and begins to form the border between Arlington and North Cambridge and then the border between Arlington and West Somerville along the Alewife Brook Parkway until it joins the Mystic River about a mile south of the Mystic Lakes.
The brook flows next to densely populated residential areas in East Arlington, North Cambridge, and West Somerville. It also runs alongside the popular Alewife Greenway Path, where people run, bike, and walk their dogs. And yet it remains the site of the highest concentration of untreated sewage pollution in Greater Boston.
Photo: Isaiah Johnson
CSOs occur primarily during very wet weather. Image adapted from EPA.gov
Combined Sewer Overflows (or CSOs) are intentional sewage discharges into rivers, lakes, and streams. They are part of old drainage systems that process stormwater and sewage in the same pipe network. During very wet weather, the amount of water coming through the system is more than the pipes can handle, so they are designed to overflow directly into waterways rather than back up into people’s homes.
Some Combined Sewer Overflows are at least partially treated before being released, but all six CSOs that discharge to the Alewife Brook are completely untreated.
In 2023, 26 million gallons of combined sewage and stormwater were discharged into Alewife Brook. Compared to the main stem of the Mystic River, the Alewife Brook is a small stream, which makes the pollution problem even more concentrated. If you were to stand by the brook in average conditions, you would have to stand there for five days straight for 26 million gallons to pass through the channel. So far in 2024, more than 18 million gallons have been discharged.
Map of Combined sewer overflow locations in the mystic river watershed - Red dots represent active csos
CSOs are harmful to people, habitat, and wildlife. Research has shown that in municipalities bordering a CSO-impacted river in Massachusetts, extreme CSO events are associated with higher risk of acute gastrointestinal illness within four days of CSO exposure. The largest CSO events are associated with increased risk of acute gastrointestinal illness regardless of drinking water source.
CSOs remain a pressing issue for everyone who lives, works, and recreates near our rivers and streams. In fact, the Alewife Brook can overflow its banks during the very same storms that cause CSO discharges, sending sewage-laden water into backyards and the popular Alewife Brook commuter path. Resident David Stoff, a member of the local grassroots advocacy group, Save the Alewife Brook, captured this photo last summer of an unknowing resident pushing a baby stroller through a puddle containing raw sewage from the brook.
Photo courtesy of Save the Alewife Brook
CSOs represent an environmental justice tragedy in Massachusetts. On average, if a watershed has twice as many people in poverty, it will have 3.4 times as much sewage discharge. And on average, if a watershed has twice as many people of color, it will have 4.4 times as much sewage discharge. The Alewife Brook is adjacent to environmental justice neighborhoods as defined by the EEA. These neighborhoods are among the top 10% in the country in terms of their exposure to and proximity to toxic wastewater in streams, according to the US-EPA EJ screening tool.
For those residents who continue to be directly exposed to the hazards of CSOs and for the health of our ecosystems and waterways, we must continue to advocate for the full elimination of CSOs across Greater Boston.
“Raw sewage flooding into Alewife Brook Reservation (a state park) and neighboring yards and homes may be an abstraction to some, but for those of us living within smelling distance, the situation is very real. The Alewife community, including our significant Environmental Justice populations, expect our environmental health to be protected. My neighbors and I became sick after having untreated sewage floodwater in our homes. We need overflows of untreated sewage to stop.”
The Mystic River Watershed Association is committed to this goal. We are working alongside Save the Alewife Brook and the Charles River Watershed Association to engage with an ongoing process organized by the Massachusetts Water Resources Authority (MWRA) and the cities of Somerville and Cambridge to control CSOs in the our watersheds. Over the past four decades, many CSOs have been closed and more CSOs are being partially treated before they are released into our waterways.
“The next couple of years will be crucial in determining whether our area will fulfill the promise of The Clean Water Act, and finally solve the problem of the remaining CSOs in greater Boston. The Mystic River and Alewife Brook flow through the most densely populated watershed in New England. We owe it to the people of these communities to find the will to make the long-term investments in infrastructure we need to protect public health and restore our rivers.””
HOW CAN YOU HELP?
Add Your Voice to the CSO Conversation
Subscribe to the MyRWA e-news to receive updates about CSOs in the Mystic and to stay in the loop about opportunities for public involvement in the CSO Long-Term Control Plan.
Contact your legislators to let them know that you care about CSOs and want to see investment in the improvement of stormwater infrastructure. Find your legislator here.
When the opportunity arises, vote yes on increased stormwater funding in your municipality. Better stormwater infrastructure can reduce the flow of rainwater through combined systems and help mitigate CSOs.
Stay Informed: Sign up for CSO Notifications
Use the MWRA notification sign up. You need to create an account – but then you will be notified of any CSOs in the area. The cities of Boston, Cambridge, Chelsea, and Somerville manage their own combined sewer outfalls, including CSO reporting, so you can sign up for those alerts separately through their respective websites.
