A "quagmire" of a Clean Water Act ruling that Justice Antonin Scalia wrote more than 13 years ago could now play a central role in the outcome of the U.S. Supreme Court's most important environmental case this term.

In County of Maui v. Hawaii Wildlife Fund, lawyers for each side, including the United States as amicus, find support in Scalia's plurality opinion in Rapanos v. United States. At issue is whether the federal clean water law requires certain permits when pollutants are conveyed from one source via groundwaters to navigable waters.

In the background, an internal fight has raged between Maui's mayor, the county council and the corporation counsel over whether there's even a live dispute for the justices to resolve. Although the Supreme Court was informed of a possible settlement, no questions were asked about it during arguments Wednesday.

Under the Clean Water Act, the definition of the term "discharge of a pollutant" includes "any addition of any pollutant to navigable waters from any point source." The case involves the discharge of pollutants from injection treatment wells in Maui.

During Wednesday's arguments, Elbert Lin, partner at Hunton Andrews Kurth, argued Maui is not violating the act's permit requirements when pollutants from its wells reach navigable waters via groundwaters. The act, he said, is concerned only with "point source" pollution—an identifiable source of the pollution—and groundwater is a conveyance, not a "point source" of the pollution.

Rapanos was a fractured 4-1-4 decision in which Scalia adopted a hydrographic test to define the Clean Water Act's jurisdiction over waters. The relevant part of his opinion for the Maui case is that the act "does not forbid the 'addition of any pollutant directly to navigable waters from any point source,' but rather the 'addition of any pollutant to navigable waters.'"

Lin's argument " sounds like the 'directly' [to navigable waters] argument that Justice Scalia's opinion rejected," Justice Brett Kavanaugh told him.

"Yes, your honor, the Rapanos plurality that Justice Scalia wrote, we think it's factually consistent with our reading," Lin said, responding to Kavanaugh. "We think he was concerned about point source-to-point source pollution."

But David Henkin, counsel to the wildlife fund, countered that the Clean Water Act does not limit permits only to point source-to-point source pollution.

"The Clean Water Act prohibits unpermitted additions of pollutants to navigable waters from any point source," Henkin said. "This prohibition is not limited to pollutants that flow directly from a point source to navigable waters. The word 'directly' is nowhere in the text. For three decades, EPA interpreted the Clean Water Act prohibition this way."

A major concern raised by several justices during Wednesday's arguments was whether there is some "limiting principle" for whichever way they rule on the ground water question. For example, if Henkin wins, what would protect a homeowner with a leaking septic tank from the hassle and expense of a permit and fines of $50,000 per day for violations? And if Lin prevails, how is a polluter stopped from evading permits by using groundwater as a conveyance?

Lin said the federal law requires states to have nonpoint source management programs and that there are grants and incentives in place for states to regulate. States also, as a "water quality backstop," are required every two years to identify waters failing to meet water quality standards.

But Justice Elena Kagan responded, "The question is not whether there's a possible state backstop. The question is what Congress was doing in this statute." The pollution here, she added, is from a point source, which is the well, and it's to navigable waters, which is the ocean, and it's an addition. How does this statute not apply?"

And Chief Justice John Roberts Jr. was skeptical of Henkin's limiting principle: The pollution must be fairly traceable to the point source and that source be the proximate cause. Fairly traceable, he said, depends on the sophistication of instruments identifying and tracing the pollution and proximate cause is "notoriously manipulable."

The United States supported the plaintiffs in the lawsuit in the lower courts, but in April the government changed its position. An amicus brief by a bipartisan trio of former EPA administrators, represented by former assistant to the solicitor general Sarah Harrington, partner at Goldstein & Russell, urged the justices to reject the solicitor general's "newly discovered and misguided interpretation" of the Clean Water Act.

Besides the United States, the case has drawn numerous amicus briefs from business, industry, environmental , former EPA officials, legal organizations, and others, represented by such major law firms as Mayer Brown, Kirkland & Ellis, Beveridge & Diamond, Gibson, Dunn & Crutcher, Hogan Lovells, Crowell & Moring, and Robbins, Russell, Englert, Orseck, Untereiner & Sauber.