David Dahl still remembers the fire in the summer of 2008, the one that caused coal-tar sludge to seep from an old storage tank at Tonawanda Coke.

The fire was bad enough, the company supervisor told a federal court jury Wednesday, that 10 to 15 tons of sludge escaped from the tank that day.

Dahl also remembers the sludge still being there a year later. “It was still there in the area outside the tank,” he said of a cleanup effort in 2009.

Dahl’s testimony, much of which was echoed by a state inspector who also testified Wednesday, offered a glimpse into what federal prosecutors claim was Tonawanda Coke’s practice of illegally storing and disposing of hazardous waste.

The company is facing 18 separate charges of polluting the air and ground on and around its Town of Tonawanda plant, and three of them have to do with its handling of coal-tar sludge, one of the byproducts of its coking operation.

Prosecutors Aaron J. Mango and Rocky Piaggione also claim that the company improperly disposed of sludge by dumping it on piles of coal on the plant’s grounds.

Defense lawyers countered Wednesday by suggesting that sludge from the old storage tanks predated Tonawanda Coke and that state inspectors went years without citing the company for violations.

“Some of that material seeped out before Tonawanda Coke owned the facility,” Thomas Corbett, a retired inspector with the state Department of Environmental Conservation, acknowledged Wednesday.

Corbett also testified about the company’s practice of mixing sludge with coal, and despite suggestions from the defense that the practice might be allowable under the law, he insisted it was improper.

“No,” he said, “I didn’t believe it was in compliance.”

Gregory F. Linsin, a lawyer for the company, argued that Tonawanda Coke’s practice of mixing sludge with coal is part of a larger effort to recycle its byproducts.

The trial before Chief U.S. District Judge William M. Skretny continues today.