NASHVILLE (AP) - Environmental groups say the coal ash stored at a Gallatin plant is illegally seeping toxic chemicals into the Cumberland River, a drinking water source for millions.

On Monday afternoon, the groups sent a 60-day notice of intent to sue to the Tennessee Valley Authority. The utility operates the 1950s-era Gallatin Fossil Plant, about 45 minutes northeast of Nashville.

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.

The Monday letter accuses TVA of violating the Clean Water Act. It also claims the Tennessee Department of Environment and Conservation has declined to take action on the violations.