On March 4, 2025, the U.S. Supreme Court issued a 5-4 decision in City and County of San Francisco v. Environmental Protection Agency, narrowing the Environmental Protection Agency’s (EPA) authority under the Clean Water Act (CWA) to impose outcome-based permit conditions—termed “end-result” requirements by the Court—on entities discharging pollutants into U.S. waters. The majority held that the CWA does not authorize the EPA or states to enforce permit provisions that make permittees responsible for the quality of receiving waters absent specific, quantifiable effluent limitations. This decision has immediate implications for the National Pollutant Discharge Elimination System (NPDES) permitting framework, particularly regarding the enforceability of narrative water quality standards.
Legal Background
Enacted in 1972, the CWA establishes a comprehensive framework for regulating the discharge of pollutants into U.S. waters, primarily through the NPDES permitting program. Under the CWA, EPA and authorized state agencies issue permits that impose “effluent limitations”—specific, quantifiable restrictions on the “quantities, rates, and concentrations” of pollutants discharged by permit holders. These permits also typically include monitoring, recordkeeping, and reporting requirements, as well as best management practices designed to minimize pollution. Notably, the CWA’s “permit shield” provision protects permittees from liability under the Act, provided they comply with their permit terms.
This case addressed the validity of “end-result” requirements, which condition a permittee’s compliance on the quality of the receiving water rather than on adherence to specific effluent limitations. These provisions effectively impose liability for water quality standard exceedances whether or not a permittee’s discharge is the proximate cause of a violation.
Factual and Procedural Background
San Francisco operates two combined sewer systems: the Bayside facility, which discharges into San Francisco Bay, and the Oceanside facility, which empties into the Pacific Ocean. The Oceanside facility occasionally overflows during heavy rainfall, releasing untreated wastewater, including raw sewage, into the ocean. In 2019, the EPA incorporated two end-result requirements into the Oceanside facility’s NPDES permit: (1) a prohibition on discharges that “contribute to a violation of any applicable water quality standard,” and (2) a ban on discharges that “create pollution, contamination, or nuisance” as defined by California law. San Francisco challenged these provisions, arguing that they imposed vague and unattainable obligations, exposing the city to enforcement actions for water quality standard exceedances beyond its control.
San Francisco appealed these provisions to the EPA’s Environmental Appeals Board, which upheld them, and then petitioned for review in the U.S. Court of Appeals for the Ninth Circuit. A divided panel of the Ninth Circuit deferred to the EPA’s interpretation of the CWA, holding that Section 301(b)(1)(C) authorizes the agency to impose “any” limitations necessary to achieve water quality standards. The Supreme Court reversed.
The Court’s Opinion
Writing for the majority, Justice Samuel Alito, joined by Chief Justice Roberts and Justices Thomas, Kavanaugh, and, in part, Neil Gorsuch, held that the CWA does not authorize the EPA to impose end-result requirements. The Court’s analysis rested on the statutory text, legislative history, and the overall regulatory framework. The Court focused on Section 301(b)(1)(C), which authorizes “any more stringent limitation” necessary to meet water quality standards, concluding that this provision requires EPA to include specific, quantifiable effluent limitations in discharge permits rather than open-ended directives tied to ambient water quality. Justice Alito reasoned that end-result requirements undermine the CWA’s objective of providing clear, ex ante compliance obligations by exposing permittees to liability for conditions beyond their control, such as pollution from upstream sources.
The Court also examined the evolution of federal water pollution regulation, noting that Congress deliberately rejected the pre-1972 framework, which held permittees liable for water quality exceedances, in favor of a discharge-based regulatory system. The majority concluded that end-result requirements effectively reintroduced the discarded approach Congress sought to eliminate. Finally, the Court identified two structural features of the CWA that conflict with end-result requirements: (1) the permit shield provision, which would be rendered ineffective if permittees could be held liable for water quality violations despite full compliance with permit terms, and (2) the absence of a statutory mechanism for apportioning liability among multiple dischargers contributing to water quality exceedances.
Justice Amy Coney Barrett, joined by Justices Sotomayor, Kagan, and Jackson, dissented. While acknowledging the importance of regulatory specificity, Barrett defended the EPA’s use of narrative standards as a necessary “backstop” when precise effluent limitations alone fail to protect water quality. She cautioned that the majority’s decision could constrain the EPA’s ability to craft effective permits, particularly in cases where permittees fail to disclose critical discharge data.
Implications
The ruling has significant implications for the EPA, regulated entities, and broader water quality enforcement efforts. Industry groups and municipal authorities hailed the decision as a win for regulatory certainty, as it requires the EPA to establish clear, quantifiable permit conditions rather than ambiguous, outcome-based standards. This shift may mitigate compliance risks and reduce regulatory exposure for businesses and municipalities. Conversely, environmental advocates have expressed concerns that the decision could weaken the CWA’s ability to protect water quality, particularly in complex, multi-discharger scenarios. The ruling could also lead to delays in the permitting process, as EPA will need to compile more detailed discharge data to establish specific effluent limitations.
Looking ahead, the EPA and delegated states must replace vague “don’t violate water quality standards” directives in CWA permits with specific technologies and conditions necessary to meet water quality standards during the five-year permit renewal cycle. Whether the EPA can muster the resources for this demanding task remains unclear. Entities with NPDES permits should examine their permits to identify any problematic “end-result” provisions.