A Northern Virginia county and an environmental group announced Wednesday that they will appeal a Virginia state board’s decision to let two coal ash impoundments be drained into Chesapeake Bay tributaries.

The Prince William County Board of Supervisors and the James River Association joined the Potomac Riverkeeper Network in challenging Dominion Virginia Power’s authorization to discharge more than 200 million gallons of water from impoundments used to collect ash waste from the company’s coal-burning power plants.

The announcements came on the heels of news that even before the Virginia State Water Control Board approved those discharges last month, Dominion had drained nearly 34 million gallons of water last year from one of its impoundments into Quantico Creek, a tributary of the Potomac River.

Dominion officials acknowledge the discharge and say it was in compliance with its permit at the time. But the groups — already concerned about Dominion’s future discharges — say they were upset that Virginia’s Department of Environmental Quality either didn’t know about or permitted the previous draining.

The Southern Environmental Law Center will represent the James River Association in its appeal over changes to a permit at Dominion’s Bremo Power Station, 30 miles southeast of Charlottesville on the James River. The SELC is also representing the Potomac Riverkeeper Network in a separate appeal over the permit approved on the same day in January for another site, Dominion’s Possum Point Power Station on the Potomac River near Quantico.

The conservation groups’ appeals argue that the permits do not meet the requirements of the federal Clean Water Act to use the best available technology to treat wastewater before discharging it. If unchanged, the permits set a precedent for how hundreds of millions of gallons of water in coal ash impoundments across the state and region could be drained, as is required eventually under Environmental Protection Agency regulations of all unlined impoundments.

The Prince William County board, which oversees the county that includes the Possum Point station, originally asked the DEQ for more time to consider the permit changes. When that request wasn’t granted, the board opposed the permit and authorized $40,000 to research its legal options.

After the Prince William supervisors met Tuesday night, the board said Wednesday that it would file suit asking the courts to require Dominion to treat the water more extensively before draining it from its coal ash impoundments.

The board was leaning toward an appeal already, citing concerns about local water quality and human and aquatic health. Coal ash contains a variety of toxic contaminants, including arsenic, aluminum, barium and boron. According to the Physicians for Social Responsibility, human exposure to the heavy metals contained in coal ash can result in cancer, reproductive problems and birth defects.

The EPA supports draining coal ash impoundments, saying they present health and environmental risks if the contaminants in them leach into groundwater or get released in catastrophic spills. But groups appealing the state board’s decision are concerned that draining the impoundments can present the same risks if the water is not treated to reduce more of the contaminants than the current permit requires.

Those concerns were heightened earlier this week when Dominion acknowledged draining 33.7 million gallons of water last year from one of its coal ash impoundments. A consultant’s report obtained by the Potomac Riverkeeper Network shows Dominion did drain an unspecified amount of water from an impoundment at its Possum Point site into Quantico Creek in May 2015. The report says the drainage was in compliance with the station’s existing permits, but SELC lawyers want that confirmed.

“We are reviewing the terms of the prior permit for Possum Point as new information comes to light, but emptying tens of millions of gallons of polluted water from a coal ash pond certainly wasn’t part of the normal operations that were authorized,” said SELC senior attorney Greg Buppert.

When asked about the discharge, Dominion officials replied by e-mail that “everything that has been done is in full compliance and always will be.”

The DEQ has not yet responded to questions about whether Dominion was operating within its permit when it discharged the water, but Potomac Riverkeeper Dean Naujoks is demanding a formal investigation.

Last year, Dominion shifted the water in four separate impoundments at Possum Point into a larger fifth one before seeking a permit to drain that impoundment into Quantico Creek. But there was no mention of any of that water already having been drained into the creek in public notices or during hearings that preceded the state board’s approval.

“We are outraged that Dominion dumped 34 million gallons of untreated coal ash wastewater into a tributary of the Potomac River,” said Naujoks. “We are even more outraged that DEQ let this happen, and we want a full investigation.”

The Prince William County board statement said the discharge casts additional doubts on Dominion’s ability to monitor itself and comply with regulations as it prepares to drain the largest impoundment.

“This has been…a creeping crisis,” said Frank Principi, Woodbridge supervisor on the board, during an interview earlier this month. “Simply because Dominion is complying with state or federal guidelines doesn’t mean that it’s not going to contaminate our river system.”

The recent news “makes the situation even more troubling, adding to a sense that the procedure is not taking place with full transparency,” the board said in a statement on Principi’s website.