NASHVILLE (AP) — The nation's largest public utility has agreed to dig up and remove about 12 million cubic yards (9.2 million cubic meters) of coal ash from unlined pits at a Tennessee coal-burning power plant.

Prompted by two environmental groups, the state sued the Tennessee Valley Authority in 2015 over pollution from coal ash dumps at the Gallatin Fossil Plant. Court documents show pollutants leech from the ash into the groundwater and then enter the Cumberland River, a source of drinking water for Nashville.

On Thursday, the Tennessee Department of Environment and Conservation and the environmental groups announced a settlement with TVA.

The utility will excavate a majority of coal ash at Gallatin and recycle it or remove it to a lined, permitted landfill. TVA will also develop a plan for the remaining coal ash.