The U.S. Supreme Court reaffirms the scope of the Clean Water Act in a case brought against the County of Maui, HI.

WASHINGTON, D.C.—On April 23, the nation’s highest court dealt a significant blow to the Trump administration’s attempt to dismantle the Federal Water Pollution Control Act, commonly known as the Clean Water Act (CWA).

That law, passed by Congress almost 50 years ago, prohibits the unpermitted discharge of pollutants from a point source—such as a factory’s wastewater discharge pipe—to surface waters. Unless the discharger has obtained, and is complying with the terms of, a permit authorizing such discharge, it is flatly illegal.

Indeed, the permitting requirement is perhaps the CWA’s central feature, as the permit incorporates the pollution limits and reporting requirements mandated by the various provisions of the statute.

Until recently, the U.S. Environmental Protection Agency (EPA) had taken the sensible position that pollutant discharges from a point source that reach surface waters through hydrologically connected groundwater are subject to the CWA’s permitting requirement. In 2019, however, after receiving requests from industry groups, the agency issued an “interpretive statement” disavowing its earlier interpretation, and filed an amicus curiae (friend of the court) brief with the United States Supreme Court urging it to dismiss a CWA suit brought against the County of Maui, Hawaii, for discharging sewage through groundwater to the Pacific Ocean. Discharges to surface waters through groundwater, EPA argued, are outside of the CWA’s permitting requirements.

In a 6-to-3 opinion, the Supreme Court pointedly disagreed. “We do not defer here to EPA’s interpretation of the statute,” the court ruled, noting that “EPA itself has changed its mind” about the very issue in question. “[T]o follow EPA’s reading,” the court reasoned, “would open a loophole allowing easy evasion of the statutory provision’s basic purposes. Such an interpretation is neither persuasive nor reasonable.”

The loophole the court had in mind is easy to envision. In the court’s own words: “Where a pipe ends a few feet from navigable waters and the pipe emits pollutants that travel those few feet through groundwater (or over the beach), the permitting requirement clearly applies.”

The court did not hold that any discharge through groundwater is covered by the CWA permitting requirement, but rather only those that are the “functional equivalent of a direct discharge” to surface waters. The court identified a number of factors that could enter into this functional equivalency analysis, including the distance between the point source and the surface waters and the time it takes for pollutants to travel from the point source to those waters. “If the pipe ends 50 miles from navigable waters,” the court explained, “and the pipe emits pollutants that travel with groundwater, mix with much other material, and end up in navigable waters only many years later, the permitting requirements likely do not apply.”

Plainly, however, the court has reaffirmed the purpose of the CWA’s permitting requirement, and has sent a message to the federal courts—and to EPA and the states—that the attempted “loophole” has been closed.