NASHVILLE (AP) — The state agency charged with protecting the environment is suing the Tennessee Valley Authority over its coal-burning power plant in Gallatin.

The lawsuit, filed Wednesday by the Tennessee Department of Environment and Conservation, claims unlined storage ponds used to dispose of coal ash are leaking contaminants into local groundwater.

The lawsuit asks the Davidson County Chancery Court to issue a permanent injunction that requires TVA to comply with laws governing solid waste disposal and water quality. It also seeks civil penalties of up to $17,000 per day for violations. Those penalties could be issued retroactively for violations that stretch back years.

TVA said in a statement that it welcomes the state's assistance in managing its ash disposal. It notes that the problems cited in the lawsuit came from TVA's own monitoring data. The utility also downplays the importance of at least one leaky pond, saying, "TVA studies, prepared at the direction of TDEC, conclude this poses little if any risk of health or environmental impacts."

Last month, the U.S. Environmental Protection Agency for the first time issued national standards on coal ash disposal. Environmentalists had hoped it would be classified as hazardous, but the rules treat it more like household garbage.

The TDEC lawsuit was prompted by environmental groups that in November threatened to sue if the state agency declined to act, claiming that the coal ash ponds were seeping toxic chemicals into the Cumberland River, a drinking source for millions.

Stephanie Durman Matheny is an attorney for the Tennessee Clean Water Network, one of the groups that threatened the citizens' lawsuit. In a statement released Wednesday, Matheny said TDEC's lawsuit appears to address the most serious coal ash problems at the Gallatin ponds.

"While we appreciate the state taking this action today, ultimately it will be the environmental results that count," she said.

TVA was responsible for the largest coal ash disaster in the country in 2008 when a containment dike burst at the Kingston Fossil Plant in East Tennessee. That spill released more than 5 million cubic yards of sludge into the Emory and Clinch rivers and destroyed homes in a nearby waterfront community.

The utility has spent $1.2 billion on cleanup and restoration there. It also has agreed to convert all of the wet storage ponds for coal ash to dry storage, a $1.5 billion effort that includes work at the 1950s-era Gallatin Fossil Plant, about 45 minutes northeast of Nashville.

According to the utility, "At Gallatin in particular, TVA has received a permit and is constructing a new dry landfill and is in the process of dewatering the active wet pond ash management system."

Because of Clean Air Act violations, TVA recently had to choose whether to close the plant, retrofit it with scrubbers, or convert it to use a different fuel. The utility decided in August 2012 to add scrubbers and continue burning coal.