Starting in January 2025, the Cities of Cambridge and Somerville and the Massachusetts Water Resources Authority (MWRA) will be holding more public meetings on Combined Sewer Overflows (CSOs) in the Mystic and Charles Rivers and their tributaries. These meetings come as our region moves into the next phase of its Long Term Control Plan to manage CSOs in Boston Harbor – part of the decades-old Federal District Court Order in the Boston Harbor Case that requires that the MWRA undertake certain corrective actions to reduce or eliminate CSO discharges to Boston Harbor, the Mystic, Charles, and Neponset Rivers and Alewife Brook. The Mystic River Watershed Association, Charles River Watershed Association, and Save the Alewife Brook, along with other advocates, have been at the table, weighing in on options for large-scale engineering solutions to the region’s CSO problem.
This coming January we need you to get involved with us to advocate for CSO controls.
At the next public meeting, scheduled for Jan 22, 2025, engineers and city planners will present an “alternatives analysis” — engineering proposals and their relative costs and benefits — along with an evaluation of their “affordability.”
Staff from MyRWA will be at the meeting, but it’s important that many people show up and show they care about this important pollution and infrastructure issue.
The CSO Long Term Control Plan is the most important tool we have for collectively influencing a positive outcome. This is a once-in-a-generation opportunity to show a groundswell of public support for investments in infrastructure that protect our rivers and streams, and the public health of our neighbors and ourselves.
In greater Boston, we have already made great strides in achieving the promise of the Clean Water Act, and it is now time to finish the job. Here is what you need to know about CSOs and the processes underway to minimize them.
CSOs in wet and dry weather. Adapted from EPA
What are Combined Sewer Overflows?
Combined Sewer Overflows are intentional outflows of sewage and rainwater discharged into rivers and streams during very wet weather. They are the result of outdated water infrastructure that is built with a connected sewer and storm drain system. During dry weather, this system works just fine, sending wastewater down the pipe and off to a treatment facility — specifically the facility at Deer Island — where waste and pollutants are removed. During very wet weather, though, especially when a lot of water falls in a very short period of time, the amount of water coming through the system is more than the pipes can handle, so they are designed to overflow rather than back up into people’s homes, sending both the stormwater and the sewage into rivers and streams. These events are called Combined Sewer Overflows, and they pose a risk to the health of both the people and the ecosystem downstream.
CSOs are a public health risk and represent an environmental justice tragedy, disproportionately affecting low-income, minority, and linguistically isolated communities. You can learn more about Combined Sewer Overflows, where they occur, and the risks associated with them at our website, mysticriver.org/csos.
how did we get here?
For much of the last century, Boston Harbor was considered the most polluted harbor in the country. Back then, it was hard to imagine the Charles and Mystic Rivers being used for recreation in the way they are today. Much of this pollution in the harbor came from the persistent outflow of sewage from old pipe networks built as the city grew.
In the 1980s, the Conservation Law Foundation and the EPA sued the Commonwealth of Massachusetts for violating the Clean Water Act of 1972. This litigation catalyzed the cleanup of Boston Harbor and led to the creation of the Massachusetts Water Resources Authority (MWRA), which was charged with establishing a long-term plan to control and eliminate CSOs alongside polluting municipalities. Before the cleanup, 1.7 billion gallons of polluted wastewater were discharged into the Mystic and the Charles every year.
The CSO Long Term Control Plan sets benchmarks that the MWRA must meet. Though progress toward these benchmarks has been made, many still have not been met. For example, in 2023 more than 200 million gallons of combined sewage were still dumped into the Mystic River and 26 million gallons were discharged — completely untreated — into Alewife Brook.
Right now we must continue to advocate for the MWRA and the cities of Cambridge and Somerville to finish the job and clean up the remaining CSOs discharging into our water bodies.
Who Manages the Combined Sewer Systems in the Mystic River?
Stormwater pipes are managed by both local cities and by the MWRA. In the Mystic, CSOs are present in systems managed by the Cities of Boston, Cambridge, Chelsea, and Somerville, and by the MWRA. These entities are required to notify the public when a CSO occurs. You can sign up for CSO alerts via the links above. The current CSO Long Term Control Plan focuses on the CSOs remaining in Cambridge and Somerville, some of which are managed by the MRWA.
Who is responsible for fixing CSOs?
The Commonwealth of Massachusetts has a responsibility to protect public health and the environment. The continued discharge of sewage through CSOs violates the Clean Water Act, which is enforced by the Environmental Protection Agency (EPA). As such, the local governing bodies — specifically the MWRA and polluting cities — are responsible for solving the issue of CSOs. The EPA is the final authority that can determine whether or not the state and cities have done enough to fix the problem.
What are the possible solutions?
Ultimately, CSOs will be solved by separating sewage lines from stormwater lines so that the sewage can all go to a treatment plant and the stormwater can discharge to the river without sewage pollution. Unfortunately, large-scale sewer separation across the whole network is very expensive and disruptive. Thankfully, there are other ways to mitigate CSOs.
Green Stormwater Infrastructure - One possible partial solution to CSOs is the incorporation of Green Stormwater Infrastructure. This includes features like rain gardens, permeable pavement, and other installations that help keep rainwater where it falls, mimicking the way rain drains in nature. Green infrastructure comes with many additional benefits, including increased greenery and nutrient pollution reduction.
Fixing Old Pipes - Some pipes in the network are old and leaky and receive extra stormwater from the ground and other unintended sources. We can invest in fixing these pipes so they work more efficiently and reduce the load on the system. (Sometimes referred to as “Inflow/Infiltration” or “I and I”).
Storage - We can build big pipes, tunnels, and tanks to temporarily store stormwater underground when it falls. This keeps the water from overwhelming the system during big storms and can lead to a reduction in CSOs. After a storm, storage systems can release stormwater to Deer Island.
Bigger Pipes - CSOs happen because there is too much water entering the system at once for the pipes to handle. We can upgrade pipes, as well as pumps and pump stations, to be able to handle more water at once, which would improve the flow through the system and reduce overflows. (Sometimes referred to as “Conveyance”).
Treatment - While we can’t always build another Deer Island, we can treat or partially treat sewage before it is discharged at smaller facilities in other parts of the system, removing bacteria, solids and sediments, trash, and other pollutants before the water goes into the river.
Why is this Moment so Important?
Over the course of the next few years, the MWRA, Cambridge, and Somerville will be considering and evaluating all of these potential solutions, their effectiveness, and the costs and disruptions associated with them before putting together a plan for the next stage of CSO mitigation. The decisions made now will be set in stone.
CSOs are a pressing issue with a disproportionate impact on environmental justice communities. Nobody deserves sewage in their rivers, parks, and backyards, and your zip code should not determine whether or not you are exposed to pollution. This is a once-in-a-generation opportunity to tell the cities and the MWRA that it’s time to finish the job and to demonstrate that the public supports making the investments needed to get there.
What is MyRWA’s Position Going into the Next Public Meeting?
MyRWA's role as advocates for the elimination of CSOs in the Mystic River and the Alewife Brook is to aggressively push the cities and the MWRA to come away from this next phase of CSO control with the best possible outcome that protects public health and local ecology. We are waiting to learn more information about the various solutions that these groups are exploring as part of this process. Our primary responsibility is to our residents, who continue to bear the adverse impacts of CSOs on their neighborhoods and communities.
A resident pushes a stroller through sewage-laden water from Alewife Brook. Photo courtesy of Save the Alewife Brook
How Can I Support?
The next public meeting for CSOs will be held on Wednesday, January 22nd in the evening. We will let you know as soon as registration information becomes available and will post the meeting to our calendar. In the meantime, you can sign up for our email newsletter and visit our website to learn more about why CSOs are a problem.
Important Acronyms
There can be a lot of confusing acronyms that come up in the CSO conversation. Here’s what some of the most important ones stand for:
CSO - Combined Sewer Overflow
LTCP - Long Term Control Plan
MyRWA - Mystic River Watershed Association
MWRA - Massachusetts Water Resources Authority
BWSC - Boston Water and Sewer Commission
CRWA - Charles River Watershed Association
StAB - Save the Alewife Brook
CLF - Conservation Law Foundation
(US) EPA - (United States) Environmental Protection Agency
(Mass) DEP - (Massachusetts) Department of Environmental Protection
I&I - Infiltration and Inflow (see fixing old pipes)
GI - Green Infrastructure
GSI - Green Stormwater Infrastructure
EJ - Environmental Justice
