Researchers say the decline reflects a reduced demand for coal and extension of Consol Energy Inc.'s Bailey Mine into parts of West Virginia. But John Pippy, CEO of the Pennsylvania Coal Alliance, says there are multiple factors at play aside from market conditions.

At some mines, “once that area is mined out, then (it) shifts to a different operation,” Pippy said. “Our operators are becoming more and more efficient. They're capturing more from the seams and the sites. It's a mixture of all things.”

Forty-six mines operated over the latest reporting period, from 2008 to 2013, down from 50 in the 2003 to 2008 report.

The report examined underground bituminous coal mines and the land and water above them. It is the fourth in a series of reports mandated by Act 54, which requires the state to monitor mine subsidence and hold mining companies responsible for damage to water supplies.

The report was released by the Department of Environmental Protection and was conducted by researchers at the University of Pittsburgh. Pitt researchers could not be reached for comment.

The report also found that a procedure to level the land, known as gate cutting, has been successful in reducing pooling and improving the quality of streams.

Gate cutting may improve some aspects of a stream, but it often does not account for the full impact of mining, nor prevent damage, said Patrick Grenter, executive director of the Center for Coalfield Justice, an environmental advocacy group based in Washington, Pa.

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