A Generation-Shaping CSO Decision: From Recommendation to Regulatory Review
On February 25, the MWRA Board of Directors voted unanimously to authorize submission of the Draft Updated Combined Sewer Overflow (CSO) Long-Term Control Plan to the Massachusetts Department of Environmental Protection (MassDEP) and the U.S. Environmental Protection Agency (EPA) by the newly extended deadline of April 30, 2026.
During the discussion, Board members emphasized both the rigor of the analysis and the gravity of the decision. Secretary Rebecca Tepper thanked staff for the “enormous amount of work, thought and analysis” that shaped the recommended alternative and described the approach as a practical balancing of neighborhood impacts, construction realities, long-term costs, and environmental goals.
Board member Brian Swett similarly noted that the recommended alternative represents a “better and more well thought out approach,” underscoring the depth of technical work completed since the fall. He described the plan as a “base plan” — one that preserves flexibility and adaptability as climate projections and regulatory expectations evolve over time.
When submitted on April 30, the draft will formally advance into regulatory review — marking a pivotal milestone in a process that will shape regional water quality, infrastructure investments, and sewer assessments for decades to come.
As Secretary Rebecca Tepper noted during the meeting, the vote authorizes submission of a draft plan, but it is “not a final decision — it is the beginning of a process.” Final requirements will ultimately be shaped through DEP and EPA review, including a five-month public comment period and additional regulatory evaluation.
For MWRA communities, the upcoming submission represents the transition from internal evaluation to public and regulatory scrutiny. The framework is nearing completion. The next phase will determine how the balance between environmental progress and fiscal responsibility is ultimately codified.
What the Board Authorized
The Board authorized staff to complete and submit a Draft Updated CSO Control Plan consistent with the recommendations presented on February 4 and summarized again on February 25.
The recommended alternatives for the Alewife Brook, Upper Mystic River, and Lower Charles River basins are designed to:
- Achieve zero CSO discharges in a 2050 Typical Year,
- Reduce discharges in larger storm events beyond the 2050 Typical Year, and
- Balance water quality improvements, construction impacts, affordability, and long-term adaptability.
The joint plan includes approximately $764 million in MWRA spending, in today’s dollars, as part of a coordinated $1.28 billion program across the three Partners: MWRA, the City of Cambridge, and the City of Somerville.
MWRA leadership underscored the strength of this partnership in advancing a coordinated, jointly developed submission rather than separate filings. That alignment reflects extensive technical collaboration and policy coordination across jurisdictions.
Climate Reality and the 2050 Typical Year
A defining feature of this plan is its “First in the Nation” use of a forward-looking “2050 Typical Year” rainfall model designed to reflect projected increases in storm intensity and volume due to climate change.
Modeling presented to the Board showed that without additional projects, CSO activations and volumes would increase under future rainfall patterns. The recommended alternatives are intended to preserve today’s progress under tomorrow’s conditions.
Board member Brian Swett emphasized that the recommended alternative functions as a base plan — one that preserves adaptability should future conditions require additional capacity. In a program expected to extend through mid-century and beyond, that flexibility was described as essential.
Importantly, the modeling also reaffirmed a central reality: eliminating CSOs within the MWRA system alone would not automatically produce “swimmable” rivers in all conditions. Stormwater runoff, upstream sources, and watershed-level dynamics continue to influence water quality outcomes.
CSO control is necessary, but it is not the sole driver of environmental progress.
Financial Impacts: The Trade-Offs in Plain Terms
MWRA currently has approximately $6 billion in planned capital spending over the next decade, roughly $5 billion of which is dedicated to asset protection, resiliency and system expansion — investments considered essential to maintaining reliability and regulatory compliance.
Mandated CSO spending does not occur in isolation. Once required spending is added to the capital plan, it competes directly with other infrastructure priorities for debt capacity and financial flexibility.
During Board discussion, Board member Henry Vitale asked what “might have to give” if capital demands become constrained — underscoring the reality that additional mandated spending inevitably competes with other projects.
In practical terms, required CSO spending risks crowding out other capital needs. When borrowing capacity is finite, every dollar directed to new mandated projects limits the Authority’s ability to pace or prioritize other investments.
Under the recommended plan:
- Household sewer charges are projected to more than double by 2050 under baseline capital needs alone.
- Additional CSO spending would further increase those projections.
- Higher levels of control, such as full elimination in larger 2050 storm scenarios, would drive materially greater assessment impacts.
Bond coverage ratios, which protect the Authority’s financial standing and borrowing capacity, are also sensitive to additional capital layering. Maintaining stability in those metrics is essential to preserving long-term affordability.
As MWRA finance leadership noted, debt service already represents roughly half of the Authority’s annual budget. Careful pacing and prioritization remain critical.
Advisory Board Perspective: What the Vote Means
The MWRA Board’s vote authorizes staff to submit a draft plan built around the recommended alternatives discussed over the past several months.
This plan:
- Achieves zero CSOs in a 2050 Typical Year,
- Preserves environmental gains under future climate conditions,
- Maintains financial capability across the service area, and
- Preserves long-term flexibility should future standards evolve.
The vote itself does not yet send the plan into regulatory review. That step occurs when the draft is formally submitted to MassDEP and EPA by the extended April 30th deadline.
What the vote does do is give Advisory Board staff a defined proposal to begin reviewing in detail.
Decisions at this scale — more than a billion dollars in projected infrastructure investment, with some alternatives reaching several billion — are precisely the kind of moment where the Advisory Board’s statutory role comes into focus. Our charge is simple: keep affordability and long-term impacts on communities and ratepayers front and center as major system decisions move forward.
That work is already underway.
Now that a preferred path has been identified, staff can begin examining the assumptions behind the plan and the long-term financial implications for the communities that ultimately fund the system.
One issue we will be looking at closely is how projected costs extend beyond the modeling horizon presented to the Board. Infrastructure decisions of this scale shape ratepayer costs long after the model ends, and understanding those longer-term impacts will be an important part of the conversation moving forward.
We expect to share the results of that analysis in the months ahead.
Decisions of this scale do not happen often. When they do, they deserve clear analysis and a full understanding of both the environmental benefits and the long-term costs.
Green — and Fair.
What Happens Next
- April 30, 2026: Draft Updated CSO Long-Term Control Plan submitted to MassDEP and EPA.
- Following Submission: Public hearings and formal comment period administered through DEP and EPA review.
- Final Plan: Revised as necessary following public input and regulatory feedback.
The Advisory Board will continue its independent analysis of the Draft Plan and will submit comments as part of the regulatory review process.
