WASHINGTON — The U.S. Supreme Court seems uncertain about how to decide a closely watched case from Hawaii about the reach of landmark federal clean water protections.

The justices heard arguments Wednesday about whether a sewage treatment plant needs a federal permit when it sends wastewater deep underground, instead of discharging the treated flow directly into the Pacific Ocean. Studies found the wastewater soon reaches the ocean and has damaged a coral reef near a Maui beach.

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Several justices appeared to be searching for a compromise between environmental groups on one side and the Trump administration and the local Hawaii government on the other. Trump’s Environmental Protection Agency recently reversed the agency’s long-standing position.

Sewage plants and other polluters must get a permit under the Clean Water Act when pollutants go through a pipe from their source to a body of water. The question in this case is whether a permit is needed when the pollutant first passes through the soil or groundwater.

Maui injects 3 million to 5 million gallons a day of treated wastewater into wells beneath the Lahaina Wastewater Reclamation Facility, which sits about a half-mile from the Pacific shoreline. Environmental groups in Hawaii sued Maui after studies using dyes to trace the flow showed more than half the discharge from two wells was entering the ocean in a narrow area. They won a ruling from the federal appeals court based in San Francisco.

The justices seemed concerned that a ruling for Maui would provide what Justice Stephen Breyer called a “road map” for polluters to evade federal permit requirements.

Picking up on Breyer’s description, Chief Justice John Roberts asked, “Any little bit of groundwater is enough to break the chain?”

Lawyers for Maui and the administration both said it would. But Elbert Lin, representing Maui, said other federal requirements and state regulations would prevent such abuses. Lin said Colorado had stepped in to prevent a silver mine from avoiding regulation by moving the discharge of its wastes from surface water to a pipe buried in rocks.

At the same time, some justices were concerned that, in one example, individual homeowners with faulty septic tanks might find themselves facing fines of $50,000 a day if water pollution in a nearby stream could be traced to their property.

“Some clear line for the property owner, I think, is really important here,” Justice Brett Kavanaugh said.

David Henkin, the lawyer for the environmental group Earthjustice, pointed out that local regulation of septic tanks already exists to protect groundwater. “If it’s not polluting the groundwater, it’s certainly not polluting the navigable waters,” Henkin said.

Henkin also said he is not aware of any citizen lawsuit, permitted under the Clean Water Act, against an individual septic tank owner since the law’s enactment in 1972.

Twenty-two mostly Republican-led states, but also the nation’s largest wastewater utility, New York City, are siding with Maui. Home builders, energy companies and the Chamber of Commerce also are calling on the court to reverse the appeals court ruling.

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Former EPA administrators under Democratic and Republican presidents and another 13 states and the District of Columbia, mainly under Democratic control, are urging the justices to uphold the appellate ruling.

A decision in Maui v. Hawaii Wildlife Fund, 18-260, is expected by June.