Balancing Progress, Partnership, and Practicality
Over the next two months, the Massachusetts Water Resources Authority (MWRA) will finalize a draft update to its Combined Sewer Overflow (CSO) Long-Term Control Plan — a blueprint that could shape regional water quality, infrastructure, and ratepayer costs for decades. For MWRA communities, the decisions made this winter will influence not just how we meet environmental goals, but how we sustain affordability, fairness, and local livability in the process.
Why This Matters Now
Under the Boston Harbor case, MWRA addressed 86 overflows through 35 projects completed by 2015, boosting Deer Island treatment and yielding major water quality gains.
Since the 1980s, MWRA’s investments have reduced combined sewer discharges by nearly 88 percent and ensured that 94 percent of what remains receives treatment before entering our rivers. The results are visible: Boston Harbor and its tributaries are among the cleanest urban waterways in the nation.
Yet six “variance” outfalls — clustered along the Charles River, Alewife Brook, and Upper Mystic River — still trigger limited discharges during heavy rain. With climate change projected to bring longer, wetter storms, MWRA’s updated plan applies a new “2050 Typical Year” rainfall model — the first of its kind in the nation — to test future performance. The goal: maintain today’s progress under tomorrow’s conditions.
On November 19, the MWRA Board of Directors will consider the staff’s recommended alternatives. By December 31, the draft plan will be submitted to state and federal regulators, opening a formal public comment period in 2026.
A Collaborative Path Forward
This update marks an unprecedented partnership. MWRA, the City of Cambridge, and the City of Somerville — known collectively as the Partners — could each have filed their own plans; instead, they chose to align modeling, scoring, and cost-sharing to submit a single, coordinated recommendation.
That decision reflects months of joint technical work, community outreach, and policy alignment — a rare level of intergovernmental coordination for a program of this complexity.
Listening at Scale
Over the past three years, MWRA, Cambridge, and Somerville have undertaken one of the most open and expansive planning efforts of its kind. Public meetings, direct sessions with advocacy groups such as the Mystic River Watershed Association and the Charles River Watershed Association, as well as targeted outreach to environmental-justice communities have brought a wide range of voices, perspectives, and ideas to the table.
Those perspectives have been heard and reflected throughout the process — in the modeling priorities, in how alternatives were scored, and in how community impacts were weighed. The Partners deserve credit for an unusually robust public process — one that invited real dialogue and gave advocacy groups and residents an opportunity to shape how the issues were understood.
Still, it’s important to recognize that engagement and agreement are not the same thing. The goal of those discussions was to inform the evaluation, not to negotiate it. The Partners’ responsibility was to listen carefully, weigh every idea against consistent technical, regulatory, and fiscal criteria, and recommend what best serves the entire system and its ratepayers.
Every idea deserves consideration; not every idea merits action when weighed against its real-world impact, cost, and feasibility.
What MWRA Is Proposing
After evaluating 39 location-specific alternatives across four levels of control, MWRA has recommended one balanced option for each basin:
(For members and partners seeking a deeper explanation of how MWRA and its Partners evaluated alternatives, balanced trade-offs, and shaped the final recommendation please check out the resources on our CSO Resources Page.)
Balancing Progress and Pragmatism
The Advisory Board’s perspective is grounded in pragmatic stewardship — the idea that environmental progress and fiscal responsibility are not opposing goals but shared obligations that must be carefully balanced. As U.S. District Judge Richard Stearns, who continues to oversee MWRA’s CSO program under the federal consent decree, noted in 2023
“[T]here may come a point of diminishing return at which spending an additional $100 for a $1 incremental benefit would make no sense from a public-policy view.”
Pursuing the most aggressive option might sound ideal, but it would carry extraordinary trade-offs: decades of deep construction through parklands and riverfront neighborhoods — from the Esplanade to Magazine Beach to Alewife Brook — along with years of noise, traffic, and limited public access. That generational loss would fall hardest on communities already living near these rivers.
Even a quick look at MWRA’s cost modeling shows how quickly the numbers climb. The most stringent CSO control option — roughly $7 billion across all partners, including about $3 billion borne by MWRA’s ratepayers — would drive over one billion dollars in combined added assessments through 2050, with more costs to follow as borrowing continues. Boston alone would shoulder about $350 million, Cambridge more than $65 million, and even a smaller community like Watertown would face more than $20 million in added costs over that period.
By contrast, MWRA’s more measured proposal — the roughly $870 million hybrid plan — keeps systemwide increases far more manageable, with typical community impacts a fraction of those extreme scenarios. That difference is exactly what’s at stake: the line between progress that’s sustainable and progress that strains the very ratepayers who fund it. A fuller breakdown of projected community impacts is available on our CSO Resources Page.
The recommended hybrid approach reflects the same values that have guided MWRA’s success over the past three decades: protect water quality, sustain affordability, and respect the communities that live beside and pay for the system. It achieves meaningful additional control while preserving financial capacity for other critical investments — from interceptors to treatment-plant upgrades — that safeguard both environmental and fiscal health.
Water Quality Reality Check
CSO control is only part of the water-quality equation. MWRA’s modeling shows that even if all CSOs were eliminated, bacteria standards would still be exceeded in many reaches of the Charles and Mystic because of stormwater runoff and upstream pollution.
In other words, “zero CSOs” does not automatically mean “swimmable rivers.”
Moreover, aggressive sewer-separation programs can unintentionally cause sanitary sewer overflows (SSOs) — releases of concentrated, untreated sewage during major storms. Effective solutions must balance environmental benefits with the realities of an aging urban system.
The path forward requires continued investment in inflow and infiltration (I/I) removal, stormwater management, and watershed-level planning — not simply larger tunnels.
Our Role and Partnership
The Advisory Board plays a distinctive role under the same enabling legislation that created the MWRA: independent oversight, fiscal advocacy, and collaborative partnership.
We commend MWRA staff and leadership for maintaining transparency and keeping member communities closely informed throughout this process. That openness enables us to fulfill our responsibility to ensure every dollar spent reflects the same balance of environmental care and fiscal responsibility that defines our stewardship of the system.
Next Steps and How to Engage
- November 19: MWRA Board expected to vote on the draft plan for regulatory submission.
- December 31: Draft submitted to MassDEP and EPA.
- Early 2026: Public-meeting series and formal comment period.
Once the draft is released, the Advisory Board will publish a more detailed policy impact analysis outlining what the proposed alternative means for member communities — including financial, operational, and policy implications — and why we support MWRA’s recommended approach over the more extreme, higher-cost levels of control.
To support members during the public-comment period, we’ll also provide Member Toolkits designed to make complex issues easier to communicate and advocate for locally. The toolkit is expected to feature materials such as:
- Template letters for both local officials and legislators;
- Talking points and plain-language summaries to help explain the plan and its impacts to stakeholders unfamiliar with CSOs or wastewater planning; and
- Presentation materials and briefing sheets for community meetings and local boards.
Members: Stay engaged. Review updates on our CSO Resources Page. Share this brief with your local officials, and use the upcoming Member Toolkit to help your community and legislators understand what these decisions could mean for local budgets and ratepayers.
Decisions of this scale come once in a generation. By engaging now, we can help ensure MWRA’s next phase of CSO control remains both “Green and Fair” — protecting the environmental health of our shared waterways and the fiscal health of the communities that fund them.
