The Oct. 11, 2000, spill from the mining company's containment pond poured 300 million gallons of coal sludge into water supplies in Kentucky and West Virginia.

"The Bush administration came in and the scope of our investigation was considerably shortened," Spadaro, who helped investigate the spill for the Mine Safety and Health Administration, said on the CBS show.

He called it "interference with a federal investigation of the most serious environmental disaster in the history of the eastern United States."

CBS said the Richmond, Virginia company was a "generous" contributor to the Republican Party.

The official said his investigation found Massey Energy, which owned the impoundment, knew the containment was weak and had leaked once before.

He said the company could have faced large fines and criminal charges.

But he said the MSHA curtailed his report and cited the company for two violations rather that the eight he sought. Spadaro said he refused to sign the report and resigned from the investigation.

This year, a judge with the federal Mine Safety and Health Review Commission set a fine for the company at $5,500. It faced a possible fine of $55,000 by the Labor Department.

In 2002, the company agreed to pay $3.25 million to the state of Kentucky and a $225,000 fine to its Department of Fish and Wildlife Resources.

The company also reached an undisclosed settlement with residents who said their property was damaged in the spill.

CBS said Massey Energy, the head of the mine administration and Secretary of Labor declined to be interviewed. Representatives for the Labor Department and Massey were not immediately available for comment on the CBS report.