Today, in a 6-3 opinion, the U. S. Supreme Court decided one of the more closely followed environmental disputes of recent years. In County of Maui v. Hawaii Wildlife Fund, the Court considered whether injecting municipal sewage effluent into groundwater, which then travels about half a mile before discharging to the ocean, requires a permit under the Clean Water Act (CWA). The Court found that it did.

The purpose of the CWA is to "restore and maintain the chemical, physical and biological integrity of the Nation's waters." The principal tool for achieving this lofty goal is a permit system for discharges from "point sources," meaning a "discrete conveyance." The most straightforward example of a regulated discharge is that from the end of a pipe directly to a navigable waterway. In the Maui case, the discharge passed through groundwater before entering the ocean, but data showed the ocean discharge contained the same pollutants as were pumped underground.

But is such a discharge "from" the point source, i.e. municipal treatment plant, or from the groundwater? Writing for the majority, Justice Breyer announced a new test for deciding such a case. A permit is required for a point source discharge or the "functional equivalent." That is, a direct discharge and a discharge through groundwater are functionally equivalent when "the discharge reaches the same result through roughly similar means." He likened the situation to a recipe that calls for adding drippings from the meat into the gravy; no one would question that "from" in that context includes conveyance through a pan or cutting board.

The majority rejected arguments from the County, EPA and Justices Alito and Thomas in dissenting opinions, that there should be a bright line test—no discharges through groundwater should ever be subject to federal regulation. Justice Breyer reasoned that approach would create gaping "loopholes" that would prevent attainment of the CWA's conservation goals. For example, a facility could terminate a discharge pipe on the beach a few feet from the navigable receiving water, and then maintain that a permit is not necessary because the pollutants came from the soils between the pipe and waterway.

Justice Breyer acknowledged that functional equivalence will not always be easy to discern, as groundwater always eventually finds its way to navigable waters. There will be times when the presence of pollutants in navigable waters is too attenuated from the discharge to justify a permit. In Maui's situation, the injected pollutants had to travel about half a mile to the ocean. What if they had to travel 250 miles and did not emerge in the receiving waters for 100 years? The majority is content to allow future courts and agencies to refine the new test.

This decision, and the unwillingness to adopt an easy-to-apply test, reflects a recognition by the Court of the complexities that underlie jurisdictional determinations under the CWA. As noted here, the Trump Administration's attempt at rewriting the definition of "waters of the United States" (WOTUS), which is the basis for CWA jurisdiction, goes the other direction. The proposed WOTUS rule seeks to establish a simple definition based on observable, running water. In doing so it follows Justice Scalia's plurality opinion in the Rapanos case and rejects Justice Kennedy's "significant nexus" test. The latter is nuanced and involves professional judgment about the interconnectedness of natural systems. The Maui Court's "functional equivalent" test is of a kind with "significant nexus" in its focus on achieving the intent of the CWA.

While the Court's decision is sensible and promotes science-based jurisdictional determinations, it leaves a great deal of uncertainty in place. The Court expects, and we can too, that there will be many cases and administrative processes considering when discharges to groundwater require permits.