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NASHVILLE, Tenn. — A federal appellate panel on Monday overturned an order that would have required the nation’s largest public utility to unearth and remove a massive amount of coal ash at one of its Tennessee power plants.

In a 2-1 decision, the 6th U.S. Circuit Court of Appeals wrote that leaks from unlined coal ash pits through groundwater into the Cumberland River are a “major environmental problem” at the Tennessee Valley Authority’s Gallatin Fossil Plant. But, the ruling continued, the Clean Water Act isn’t the “proper legal tool of correction” to address it.

The cleanup would have involved digging up and moving almost 14 million cubic yards of coal ash, a byproduct of burning coal for power that contains heavy metals like arsenic, mercury and lead. Though Monday’s decision was a defeat for environmental interests, state regulators still have a lawsuit pending over similar environmental complaints at Gallatin.

The environmental investigation by state regulators will help TVA determine how to dispose of the ash, said utility spokesman William Scott Gureck.

The case drew plenty of outside interest over how the Clean Water Act was applied. Eighteen largely Republican states, the U.S. Chamber of Commerce, national coal industry interests and more than a dozen other groups weighed in against the lower court’s cleanup ruling, saying it would have wide-reaching, expensive consequences, particularly for ratepayers. Environmental groups and Tennessee regulators were skeptical that rate hikes would have been necessary.

Democratic attorneys general for four other states warned that overturning the order would threaten the Clean Water Act and give polluters incentive to skirt regulation by rerouting discharges to groundwater.

In his dissent to Monday’s decision, Judge Eric Clay said the ruling lets polluters escape Clean Water Act liability by moving their drainage pipes a few feet from the riverbank. He wrote that two other circuit courts have ruled in the opposite manner.

DJ Gerken, managing attorney of the Southern Environmental Law Center, said his group is determining next steps with its client, Tennessee Scenic Rivers Association, which is one of the groups that sued TVA.

“In a week where neighboring states around the Southeast have dealt with catastrophic floods that inundated coal ash lagoons, it’s a reminder that storing highly toxic coal ash in unlined, leaking pits next to our rivers and lakes is irresponsible,” Gerkin said in a news release. “It’s past time for utilities to move their coal ash to dry, lined storage away from our waterways.”

TVA initially said the Gallatin cleanup project would cost $2 billion, though later estimates factoring in an onsite landfill ranged below $1 billion. The federal utility’s timeline has said it would take 24 years to move the ash to an onsite landfill, an estimate the state and environmental groups questioned.

In August 2017, a district judge ordered the coal ash to be excavated and removed at Gallatin, about 40 miles (65 kilometers) from Nashville. He cited Clean Water Act violations of pollutants leaking into the Cumberland River, but said there was scant evidence of harm done by the pollution so far.

Gureck, the TVA spokeswoman, said Monday’s ruling provides clarity on the Clean Water Act and confirms the utility isn’t violating it. He said TVA will correct any impacts that state regulators identify at TVA’s Tennessee ash ponds, in addition to its plans to convert from wet to dry coal ash storage by 2022.

Previously, the utility has contended that capping the waste where it sits would be less expensive and avoid a possibly larger spill from moving the ash. But capping the ash wasn’t an option under the court order.

TVA powers 9 million customers in parts of seven Southern states.