The Supreme Court will hear its first major environment case of the term on Wednesday, with lawyers set to clash over the power of the Clean Water Act to police polluters.
The case involves a dispute arising from a decades-old wastewater treatment plant in Maui.
A ruling could have broad ramifications on the reach of federal water rules that were put in place in the early 1970s in response to growing public outcry over the nation's dirty waterways.
At the center of the dispute is the Lahaina Wastewater Reclamation Facility, which treats millions of gallons of waste each day and then injects it into deep wells underground. A 2013 study ordered by the EPA showed that 90% of that waste ultimately ends up in the Pacific Ocean, after traveling through groundwater.
A collection of environmentalist groups sued Maui over the matter in 2012, arguing that waste from the plant was damaging a nearby reef and hurting marine life. In response, Maui argued that it was not liable for the damage because it is not required to get federal permits for pollution that travels through groundwater.
The Clean Water Act requires polluters to get federal permits for pollution that enters navigable waters, which includes waterways like the Pacific but does not include groundwater. The central question in the case is whether the pollution's transit through the earth before hitting ocean absolves the county of the need to acquire a federal permit.
The federal appeals court that reviewed the matter sided with the environmentalists. Circuit Judge Dorothy Wright Nelson, writing for a three-judge panel of the 9th U.S. Circuit Court of Appeals, reasoned that because the pollution was "fairly traceable" to the plant, "the discharge was the functional equivalent of a discharge into the navigable water."
The Supreme Court agreed to review that decision in February.
The case has generated significant buzz and forceful arguments from businesses and organizations on both sides.
The Trump administration, which has pushed to limit environmental regulations across the board, has also weighed in, filing briefs in support of Maui with the top court. Malcolm Stewart, the Justice Department's deputy solicitor general, is scheduled to participate in Wednesday's arguments.
The EPA has appeared to flip sides in the matter. The agency, which sided with the environmentalists in a brief filed with the 9th Circuit, released a new interpretation of the Clean Water Act in April that was in line with Maui's arguments.
Three former EPA administrators who served under both Democratic and Republican presidents said the EPA's announcement in April marked a reversal of decades of precedent that "would open an enormous loophole" in the law.
The former government officials sought to explain the complicated, technical case to the top court using an archery metaphor.
"If an archer shot an arrow from Main Street to Elm Street, her release of the arrow would be the proximate cause of damage inflicted by the arrow's landing, even though the arrow traveled through air and space to get from the beginning of its journey to its end," the administrators wrote in a brief with the justices.
The situation was the same with pollutants "when the pollutant travels through groundwater with a direct hydrological connection to the receiving surface waters," they wrote.
It is not clear how the justices will rule. The current composition of the Supreme Court includes five Republican appointees and four Democratic appointees, but the justices do not always vote along partisan expectations.
A ruling is expected by the end of June.
The case is County of Maui, Hawaii v. Hawaii Wildlife Fund, et al. No. 18-260.