RICHMOND, Va. (AP) — Arsenic is illegally flowing out of one of the sites where Virginia's biggest utility stores coal ash, polluting surrounding waters, a federal judge ruled Thursday.

Though U.S. District Judge John Gibney Jr. found Dominion Virginia Power had violated federal law with the discharges from a retired power plant in Chesapeake, he didn't impose a civil penalty, saying he saw no evidence the discharge was harmful.

Nor did he order the utility to remove the ash from the water's edge to a synthetically lined landfill as the Sierra Club, the plaintiff in the lawsuit, wanted.

"The ponds and landfill convey arsenic directly into the groundwater and, from there, directly into the surface water" in violation of the U.S. Clean Water Act, Gibney wrote.

He went on to say it was not possible to determine how much arsenic is going into the surrounding waters, but said "the discharge poses no threat to health or the environment."

The judge cited an expert hired by Dominion who "found no human health or environmental concerns" in water, sediment and fish surrounding the plant — data he said the Sierra Club did not dispute at a four-day bench trial last July.

The judge ordered Dominion to do more tests and collaborate with the Sierra Club on a remediation plan.

"Dominion is pleased that the court has confirmed there has been no threat to health or the environment resulting from the coal ash stored at its former Chesapeake Energy Center," a company statement said.

Deborah Murray, an attorney from the Southern Environmental Law Center who represented the Sierra Club, said she's pleased that Dominion has been found to be breaking the law, but "disappointed the court did not order a full cleanup."

Dominion burned coal for decades at the Chesapeake Energy Center, which sits on a peninsula between a creek and the Elizabeth River, near the mouth of the Chesapeake Bay. It stored ash laden with toxic heavy metals in ponds and a landfill at the site.

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The Sierra Club argued that the site should be fully excavated. Dominion called that unnecessary and extraordinarily expensive, and the judge agreed, saying the "draconian" request would not serve the public's interest.

"Dominion receives income through rates charged to its customers; those rates would likely rise to pay for the Sierra Club's proposal. Moreover, the Sierra Club has not even attempted to itemize the collateral environmental effects of moving this much coal ash," he wrote.

The judge also wrote that the utility had cooperated with state regulators. "Dominion has been a good corporate citizen, not a chronic violator of water laws," Gibney wrote.

Still, Seth Heald, chair of the Sierra Club's Virginia chapter, said the ruling is "important for all Virginians who seek to hold the utility responsible for its mishandling of toxic coal ash.

"Now we must push Dominion to do the right thing and get this toxic ash out of the groundwater and away from the river, which is highly susceptible to disastrous flooding from sea-level rise and other climate-change effects," he said.