By Paul Kurtz

PHILADELPHIA (CBS) -- A Philadelphia law firm is celebrating a court victory over the Tennessee Valley Authority, in what's being called the largest environmental disaster on US soil ever to go to trial.

Hundreds of residents of a riverside community in suburban Knoxville, Tenn. sued after the TVA's Kingston Fossil Plant burst in 2008, sending about one billion gallons of fly ash into a river.

Philadelphia attorney Paul Brandes (right) and his firm represented about 80 households.

"The dykes failed. They were improperly constructed, they were neglected by poor maintenance and poor inspections, and there were many red flags warning TVA that this was going to happen," he says.

Federal judge Thomas Varlan ruled that TVA was negligent in its conduct and will be liable for damages.

Brandes says an amount will be determined during the next phase of the trial -- if both sides get there.

"If TVA wants to come to us and discuss settlement, that's fine.  But we're not banking on that.  We pushed the first phase as aggressively and forcefully as we could and we came up with a fantastic result for our clients, and in the second phase we plan to do the same thing."