A federal judge in Virginia could soon decide a potentially landmark case determining whether power plants can be held accountable for contaminating surface waters with toxic chemicals that leached into the ground from coal ash pits.

U.S. District Court Judge James Gibney Jr. heard four days of testimony last month in a lawsuit brought by the Sierra Club accusing Dominion Virginia Power of fouling the Elizabeth River with arsenic that seeped via ground water from coal ash pits at the company’s now-closed Chesapeake Energy Center in Chesapeake, VA.

Hydrologists, chemists and other experts for Sierra testified that contaminants from coal ash could travel from longstanding pits through ground water to nearby waterways. Dominion, though, disputes that it is the source of arsenic found in the river, asserting that Sierra did not prove that pollutants from the plant can or would reach surface waters.

A fundamental issue in the case is whether the Clean Water Act applies to pollution of surface waters via ground water.  The 1972 federal law regulates pollution discharges via pipes or from storm runoff from non-agricultural land. The Virginia Department of Environmental Quality is delegated by the U.S. Environmental Protection Agency to enforce that law.

Patrick Parenteau, an environmental law professor at Vermont Law School, said the applicability of the Clean Water Act to pollution from ground water has been a subject of controversy for a long time — and one that could take this case as far as the Supreme Court.

“In a larger sense, this is really dealing with the ugly legacy of the coal era,” he said. “This is one of the first of these cases under the Clean Water Act to go to trial, which is unusual.”

Gibney indicated on June 24 at the conclusion of the trial that he would issue a ruling in a matter of weeks after reviewing both sides’ legal filings this month.

If the Sierra Club prevails, the ruling could affect how Dominion and other power plant owners go about closing out the impoundments they used for decades to hold the ash residue from burning coal for electricity.  But legal experts say the environmental group faces an uphill struggle to make its case.

Dominion already has state-issued permits and has begun discharging water from coal ash pits at power plants it has on the Potomac and James rivers.  The company plans to drain the impoundments at those sites and three other facilities it owns in Virginia, then cover the coal ash residue with impermeable caps to prevent leaching of contaminants.

The question at stake in this case is whether the coal ash pits could be polluting nearby waters by virtue of being near them through the “hydrological connections” in the ground water.

The Sierra Club, represented in the case by the Southern Environmental Law Center, alleges that arsenic from Dominion’s coal ash ponds and from a landfill is leaching through the ground water to surrounding surface waters, which are protected under the Clean Water Act.

Dominion’s own reports to DEQ show arsenic is present in the ground water near the coal ash pit at the facility, though at levels allowed by its permit at the time, according to testimony at the trial. SELC is seeking to prove those contaminants are a likely source of arsenic found in the Elizabeth River.

“The proof of causation is a hurdle,” said Robert Percival, director of the environmental law program at the University of Maryland, who said courts have been split on similar cases. “How do you prove that toxics came directly from this source?”

Parenteau said he once got a court to order a dye tracer test to link contamination downhill from a granite mine to the operation. The tests were inconclusive at the time, he said. Dominion also used dye testing last winter to trace oil spilled at a substation in Crystal City, VA, through underground storm sewers to Roaches Run and the Potomac River. The company subsequently took responsibility for the oil slick on the river and cleaned it up.

Though dye testing was not done in the Chesapeake Energy case, SELC lawyer Brad McLane said a hydrologist and a geochemist retained by Sierra testified that based on what is known about ground-water movement at that site, the arsenic detected in monitoring wells there would be flowing to nearby surface waters. McLane said his experts’ testimony “supports Dominion’s liability.”

But Dominion spokesman Rob Richardson reiterated the company’s defense that any contamination in the Elizabeth River had to come from another source.

“We know there are levels of arsenic in the Elizabeth River. It’s an industrial area,” Richardson said. “We are in compliance with all of our permits at Chesapeake Energy Center.”

Unlike many other coal-fired power plants, the Chesapeake facility has also stockpiled coal ash in a lined landfill, which sits atop a one-time ash pond that had been drained. The facility stopped burning coal at the end of 2014. Dominion is seeking a permit from the DEQ to drain another ash impoundment at the Chesapeake Energy Center, which still holds water, and then to cap it.

Sierra’s lawsuit contends that polluting via ground water is no different than discharging pollutants through a pipe. At a minimum, the environmental group says, Dominion ought to be required to obtain a discharge permit from regulators for the leaching contaminants.  But Sierra wants much more – to force Dominion to excavate the coal ash and transport it inland to a lined landfill, eliminating it as a source of contamination to the river.

Though utilities in North Carolina, South Carolina and Georgia are being required to take such steps in the wake of catastrophic ash pit spills in the South, Judge Gibney seems unlikely to go that far, based on comments he made in a partial transcript of the trial that was provided by Dominion. The company estimates that excavating the Chesapeake Energy Center landfill and ash pits would cost hundreds of millions of dollars.

“As I look at the case right now,” Gibney said, “(you) need to think of something other than spending a couple hundred million dollars to fix this problem.

“It may be that, at some stage, we have to come back here and consider remedy at a later date, if there is a violation, and I’m not saying that there is,” the judge said, according to the transcript.