NASHVILLE (AP) - The Tennessee Valley Authority is liable for a huge spill of toxin-laden sludge in 2008 in Tennessee, a federal judge ruled Thursday.

The decision is a victory for hundreds of plaintiffs who sued after a containment dike at TVA's Kingston Fossil Plant burst in 2008. About 5 million cubic yards of ash spilled out of a storage pond, flowed into a river and spoiled hundreds of acres in a riverside community 35 miles west of Knoxville.

U.S. District Court Judge Thomas Varlan said in a written opinion that TVA was negligent in its conduct and will be liable for damages to be determined later.

TVA officials said they didn't have an immediate reaction to the decision but would respond later Thursday. TVA had argued at a trial last October that the spill was caused by factors outside the utility's control, including a "slime" layer of loose ash and silt under the dike.

Varlan said the spill was caused by a combination o f TVA's dike design, continued wet coal ash storage at the plant and geological conditions.

"Had TVA followed its own mandatory policies, procedures, and practices, the subsurface issues underlying the failure of North Dike would have been investigated, addressed, and potentially remedied before the catastrophic failure of December 22, 2008," he wrote.

TVA is continuing a $1.2 billion cleanup of the spill the Environmental Protection Agency described as one of the worst environmental disasters of its kind.

The spill drew national attention to coal ash and its toxic contaminants. Coal ash contains arsenic, boron, cadmium, chromium, lead, mercury and other metals, according to the Environmental Protection Agency. EPA officials began looking into regulating coal ash as a hazardous waste but haven't yet issued any regulations.

TVA reported in December that it paid nearly $11 million on outside legal help to battle lawsuits from the spill. About $600,000 of that was spent on outside lawyers to assist with this trial, which ended in October. The rest of the trial work was done by in-house lawyers, and TVA said it couldn't provide a total of in-house legal costs.

Ratepayers have had to pay for the spill in the form of higher power costs. TVA announced earlier this month that it wasn't raising rates for the year beginning Oct. 1.