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.

"Since the spill in December 2008, TVA's commitment has not wavered _ to clean up the spill, protect the public health and safety, restore the area, and, where justified, fairly compensate people who were directly impacted," the utility said in a statement.

TVA is the nation's largest public utility and also serves customers in Alabama, Georgia, Kentucky, Mississippi, North Carolina and Virginia.

Utility officials 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 of 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. TVA also provided $43 million to the Roane County Economic Development Foundation for use by communities in the affected area.

An estimated 500,000 cubic yards of ash remain at the bottom of the Emory and Clinch rivers nearly four years later. A decision will be made later this year to leave the submerged ash alone, dredge it up or cap it.

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.

The litigation involves more than 60 cases and more than 800 plaintiffs.

"People have been harmed through the actions of TVA, in some cases irreparably," one of the plaintiffs' attorneys, Nashville-based Beth Alexander, said in a statement. "TVA did its best to avoid financial responsibility for the harm it has done, but there was no merit or justification for it to be given such extraordinary protection. TVA spent millions of dollars in legal fees fighting to be cleared of responsibility for what they did wrong instead of compensating the people whose property was damaged."

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.

TVA said it has bought more than 180 properties and settled more than 200 other claims from people living near the spill.

"TVA remains committed to the full restoration of the community directly impacted by the spill, while being mindful of our responsibility to manage ratepayer dollars," the utility said in a statement.

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.

The plaintiffs have alleged that the spill not only damaged their property but caused an unsightly smell and scum on their shorelines adjacent to the water and rendered their property useless for recreation. Varlan said the next phase of the case will determine what each plaintiff will be entitled to, and the judge asked the parties to submit recommendations for how the next phase of the case should be handled.