The U.S. Supreme Court has waded in again on the issue of how wide the reach of the Clean Water Act is. The high court on Nov. 6 heard oral arguments in a case that deals with whether pollutants from a Maui wastewater treatment plant that are discharged into groundwater and eventually end up in the Pacific Ocean are covered by federal permits that govern specific facilities, or “point sources.”

The County of Maui, Hawaii—and the federal government—contend that discharges into groundwater should be excluded from such National Pollutant Discharge Elimination System, or NPDES, permits. On the other side, the Hawaii Wildlife Fund and other environmental groups strongly disagree.

See more case details, updates and broader implications here and here.

Attorney Elbert Lin, representing the county, argued that a NPDES permit is mandated “only when a point source or series of point sources is the means of delivering pollutants to navigable waters.” Groundwater “is a nonpoint source,” said Lin, a former West Virginia solicitor general. [View transcript of oral arguments here.]

But Justice Stephen Breyer said that the county's approach would amount to “an absolute road map for people who want to avoid the point source regulation.” For example, he said, companies could build discharge pipes from the treatment plant to a point “five feet” from a body of water.

The justices seemed to be wrestling with how to draw a regulatory line that would be tough enough to dissuade people from trying to get around the clean water statute but on the other hand wouldn't require many thousands of homeowners to get a federal permit to install septic tanks.

Larry Liebesman, senior adviser with water resources firm Dawson & Associates—who attended the court's session—said that the county's and government's position for categorically excluding discharges into groundwater from having to get NPDES permits didn’t seem to carry the day.

Liebesman, a former Justice Dept. senior trial attorney specializing in environmental cases, said in an interview, “Frankly, I think the justices, just about all of them, weren’t buying that argument.” He added, "I think the environmental groups are likely to prevail on that point.”

David Henkin, an Earthjustice senior attorney, who represented the environmental groups before the court, said in an interview, “I was very happy that the justices were honing in on the really big-ticket question here, which is whether people can evade the Clean Water Act simply by using groundwater as a sewer to pollute navigable waters.”

Liebesman added, “On the flip side, I think the justices, including the more liberal ones, are very concerned about a limiting principle"—what sort of standard to devise. There was no consensus on what that benchmark should look like.

Henkin suggested a standard involving traceability of pollutants and the "proximate cause" of moving the pollution. But Chief Justice John Roberts was skeptical about that. He said he would like to see a "limited principle" for when groundwater carrying pollution moves to federally regulated waters, like the Pacific.

Breyer also felt Henkin's suggestion fell short. He said that "I am worried about 500 million people or something suddenly discovering that they have to go apply for a permit [from] the EPA."

At one juncture during the proceedings, the justices were discussing how to trace pollution from a group of homeowners' individual septic tanks. For Roberts, the difficulty in tracking down the polluter sparked a literary reference. "It's like an Agatha Christie novel," he said. "You have 20 people and they shoot the gun at the guy at the same time."

A decision in the case is expected during the court's current term, but it isn't clear when.