NASHVILLE (AP) — A federal utility is appealing a judge's order to excavate and move its coal ash at a Tennessee power plant.

In Nashville federal court Monday, the Tennessee Valley Authority filed its appeal notice over its Gallatin Fossil Plant outside Nashville.

TVA says the cleanup would take 24 years and cost $550 million using a lined landfill onsite, or up to $2 billion and possibly a different timeline with an offsite landfill.

The Southern Environmental Law Center, representing an environmental group in the lawsuit, says TVA overestimates the time and cost.

A judge ordered the cleanup in August, saying coal ash storage is leaking pollutants into the Cumberland River and violating the Clean Water Act.

The judge said there's scant evidence of concrete harm beyond the risk and presence of pollutants.