The Tennessee Valley Authority denied that amount of coal ash water had entered the river (though it did acknowledge some historical contamination during a recent site visit). Walter Kutschke, an engineer for Aecom, an engineering firm contracted by the authority, confirmed the 27 billion-gallon figure, however, under cross-examination.
While the plant’s history is not at issue in the current trial, lawyers for the environmental law center cited it in arguing that smaller coal ash leaks were still occurring at Gallatin.
The authority has had more recent challenges in dealing with coal ash: In 2008, an ash pond dike at its Kingston Fossil Plant in eastern Tennessee collapsed, releasing just over a billion gallons of coal ash water into the Emory River, which flows into two other rivers, including the Tennessee.
The slurry released in that spill, which has been called the largest environmental disaster of its kind, buried 300 acres of land in toxic sludge. That sludge was taken to an unlined landfill in Alabama, just outside a predominantly African-American community, prompting challenges under federal civil rights law.
The spill helped spur the E.P.A. to create new rules regulating coal ash storage, and the Tennessee Valley Authority has begun to comply by draining and capping many of its ash ponds and storing future coal ash in dry landfills.
Gallatin’s coal ash problems do not approach the scale of earlier disasters, but people and communities are still affected. The City of Gallatin, which gets its drinking water from the river, at a spot about a mile downstream from the plant, said in a 2014 report that the coal plant represented a threat to its water supply.
John Kammeyer, the Tennessee Valley Authority’s vice president for civil projects, who manages its coal ash storage, said the state had acknowledged the issue of seepage from coal ash ponds, which is allowed in certain circumstances.
“If we thought we were doing anything unsafe or untoward, we wouldn’t do it,” Mr. Kammeyer said.