EPA Proposes Landmark Stormwater Regulation in Massachusetts

The US Environmental Protection Agency (EPA) has proposed a new draft general stormwater permit that, once finalized, will impose potentially onerous new requirements on more than 4,000 properties in the Charles, Neponset, and Mystic River watersheds in Massachusetts. The permit will impact commercial, industrial, and institutional (CII) properties with one acre or more of impervious surface—including office parks, shopping malls, hospitals, and private colleges and universities—in over 60 communities in the Boston metropolitan area.

EPA’s new permit brings a wider swath of property within EPA’s stormwater permitting purview while also imposing additional requirements on properties already covered by a separate National Pollutant Discharge Elimination System (NPDES) permit: for example, properties already covered under EPA’s multisector general permit (MSGP), which authorizes stormwater discharges from certain industrial activities, may also be subject to this new general permit. 

The MSGP covers only industrial stormwater discharges and, as such, does not address stormwater discharges from nonindustrial activities. Properties within the covered watersheds that are currently covered by an MSGP with one acre of nonindustrial impervious cover (such as roofs, parking lots, and sidewalks) will also have to seek additional coverage under the new general permit. 

NEW PERMIT REQUIREMENTS

EPA is requiring property owners subject to the new permit to reduce phosphorous loads from stormwater discharges by an aggressive 60% to 65%. The permit specifically regulates phosphorous as an indicator pollutant because the Charles, Neponset, and Mystic River watersheds are all impaired by pollutants commonly found in stormwater runoff, including nutrients (phosphorous and nitrogen), bacteria, and pathogens. Owners of impacted properties will have to implement best management practices to meet the phosphorous reduction requirements. Permittees will have up to 12 years to comply under a compliance schedule set forth in the draft permit. 

EPA initially announced that it would issue the new permit in September 2022 in response to petitions and subsequent litigation filed by the Conservation Law Foundation (CLF) demanding that EPA exercise its residual designation authority to address excess nutrients and bacteria in the three watersheds. EPA is accepting public comments on its proposed draft permit through January 29, 2025 and will hold a series of virtual public hearings in January 2025. EPA is specifically seeking public comment on whether to include multifamily residential properties in the final permit and whether the 12-year compliance schedule is appropriate, among other topics.

EPA’S RESIDUAL DESIGNATION AUTHORITY

EPA proposed the sweeping new stormwater regulation under its rarely used residual designation authority (RDA). Clean Water Act regulations (40 CFR § 122.26(a)(9)(i)(C) and (D)) allow EPA to exercise its RDA to require NPDES permits for specific categories of stormwater discharges on a case-specific basis if the discharges contribute to a violation of water quality standards, are a significant contributor of a pollutant to a navigable waterway, or must be controlled based on wasteload allocations that are part of total maximum daily loads that address the pollutants of concern. 

EPA’s Massachusetts action is part of a recent trend of EPA utilizing its RDA to expand its regulation over stormwater. In another recent example, on November 20, 2024, EPA Region 9 finalized its designation of certain CII sites in two watersheds in Los Angeles County: the Alamitos Bay/Los Cerritos Channel Watershed and the Domingues Channel and Los Angeles/Long Beach Inner Harbor Watershed. This regulatory action responds to two 2015 petitions that led to the court decision in Los Angeles Waterkeeper v. Pruitt, 320 F. Supp. 3d 1115 (C.D. Cal. 2018), which held that EPA acted contrary to the Clean Water Act by declining to regulate stormwater discharges from CII sites in the Los Angeles region. 

EPA may also exercise its RDA to regulate stormwater discharges in other New England watersheds in the near future. In 2023, CLF filed a petition asking EPA to regulate stormwater discharges to the Great Bay Estuary in southern New Hampshire. As of August 2024, EPA stated that it is still evaluating whether it is appropriate for the agency to exercise its RDA to regulate stormwater discharges in the Great Bay watershed. 

EPA’s authority to expand its stormwater permitting requirement via the agency’s RDA could be challenged in light of the US Supreme Court’s 2024 Loper Bright decision curtailing agency deference. EPA’s recent actions to regulate stormwater discharges in Massachusetts and Los Angeles may also be rolled back in the incoming Trump-Vance administration’s deregulation efforts.