The Deer Island Treatment Plant, which handled wastewater from the Massachusetts Water Resources Authority's 43 sewer communities in FY2025, is still operating under a federal discharge permit that expired in 2005. EPA and MassDEP issued a draft renewal in May 2023, but as of October 21, 2026 no final permit had been issued and none was scheduled.
What the draft would change
The 2023 draft adds seasonal Enterococcus limits. Until it is made final, the old permit continues administratively. On flow, the plant has room to spare: its 365-day average dry-day flow was 257.1, 250.5 and 245.5 mgd in the three months of the fourth quarter of FY2026, against a limit of 436 mgd.
A violation after years without one
Deer Island had one permit violation in FY2026, having reported none from FY2020 to FY2024. The smaller Clinton Treatment Plant had five violations in FY2026, after seven in FY2025 and eleven in FY2024.
Overflows in court
The permit is one of three open regulatory questions. On May 15, 2026, MWRA asked the federal court in the Boston Harbor Case to declare its overflow obligations met, including at eight outfalls that missed their long-term goals at the end of 2024; the motion was pending as of September 23, 2026. A draft Updated CSO Control Plan, costed at about US$1.3 billion, is due in final form in 2027.
Spending on the plant
MWRA is rebuilding Deer Island while it waits. The Clarifier Rehabilitation Phase II contract (US$298,197,238.72 after Change Order 4, July 2026) was 46.2% billed at June 30, 2026, with completion set for June 10, 2028.
MWRA's finances, tariffs, supply, energy position and forward milestones are summarized in the reference profile. The full report, Utility Intelligence Profile: Massachusetts Water Resources Authority, is available for USD 99. For a free overview, read the Massachusetts Water Resources Authority Utility Snapshot.