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H 1031

An Act relative to combined sewer overflows

194th Legislature (2025-2026) Introduced by Marjorie Decker and 3 co-sponsors

Prohibits untreated CSO discharges in MWRA areas during large storms from 2035, requiring solids removal and bacteria deactivation as treatment standards.

Reporting date extended to Wednesday, March 18, 2026
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Bill Summary · H 1031

Summary of H.1031: An Act relative to combined sewer overflows

Purpose and intent

  • Establishes a framework to address combined sewer overflows (CSOs) in Massachusetts, with a prohibition on untreated CSOs in MWRA sewer service areas for specific storm conditions.
  • Aims to ensure CSO discharges include solid removal and bacterial deactivation, updating standards as technology and climate considerations evolve.

Key provisions added

  • New definitions (Chapter 21, Section 27B):
    • Combined Sewer System: a single-pipe system receiving sanitary wastewaters and stormwater for treatment.
    • Combined Sewer Overflow (CSO): discharge from a Combined Sewer System to a water of the Commonwealth before a Publicly Owned Treatment Works (POTW) treatment plant.
    • Publicly Owned Treatment Works (POTW): treatment works owned by a state or municipality, including facilities defined under the Clean Water Act and the MWRA system.
    • POTW Treatment Plant: portion of POTW designed for at least secondary treatment (including recycling/reclamation), including Deer Island’s MWRA plant.
    • Untreated CSO: CSO discharge that does not include removal of solids and treatment to deactivate bacteria.
  • Prohibition timeline:
    • Beginning January 1, 2035, there shall be no untreated CSO in any 25-year 24-hour storm event or smaller storm event in MWRA sewer service areas (as defined by Acts of 1984, ch. 372, §8).
  • Regulatory implementation:
    • Within 18 months, the Massachusetts Department of Environmental Protection (MassDEP) must adopt regulations to implement Section 27B.
    • Regulations must define:
    • A 25-year 24-hour storm event (and update it over time for climate change).
    • A definition of CSO treatment that, at minimum, removes solids and deactivates bacteria (and updates with advancing technology).

Scope and affected entities

  • Applies to the MWRA sewer service areas (as referenced in the 1984 statute) and to facilities defined as POTWs, including the MWRA treatment plant at Deer Island.
  • Affects municipalities, MWRA member communities, and utility/utility-scale wastewater operators responsible for CSOs.

Timeline and procedural details

  • Regulatory development: MassDEP must adopt implementing regulations within 18 months of enactment.
  • Climate/adaptation consideration: Definitions, including the 25-year storm and CSO treatment standards, are to be updated as technology and climate science evolve.
  • Reporting status: The bill’s status shows an extended reporting date to Wednesday, December 31, 2025.
  • Legislative actions noted:
    • Referred to the Senate/House Environment and Natural Resources committees on 2025-02-27.
    • Hearing held/work scheduled in mid-June 2025.
    • Senate concurrence noted in the document path.
  • Related matters: Similar prior filing exists (HD 886 of 2023-2024); HD 2758 is listed as related/replacing.

Potential impact and considerations

  • Drives a long-term infrastructure and treatment standard for CSOs, potentially requiring substantial capital investments in storage, conveyance, treatment upgrades, or CSO control technologies.
  • Establishes uniform, regulation-backed expectations for reducing untreated CSO discharges in response to storm events, aligning with public health and water quality goals.
  • Creates a regulatory timetable that municipalities and the MWRA must plan around, including climate-adaptive definitions for storm events and treatment requirements.

Compiled from official sources — confirm details with the bill’s official record.

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