The U.S. Environmental Protection Agency in no way contends that a draft report on groundwater pollution in Wyoming could apply to hydraulic fracturing in any other part of the U.S., an EPA official told a U.S. House subcommittee.

That includes the Marcellus Shale, a vast area of booming gas drilling in Pennsylvania and other northeastern states, EPA Regional Administrator James Martin said Wednesday.

"The geologic conditions that exist with the Marcellus Shale are significantly different," Martin told the House Science Committee's energy and environment subcommittee, which held a hearing in Washington on the draft EPA report released Dec. 8.

The report theorized that gas industry activity including hydraulic fracturing, or fracking, may have caused groundwater pollution in the Wyoming community of Pavillion.

Petroleum companies frack their wells to improve the flow of oil and gas. The process involves pumping water, fine sand and a relatively small proportion of chemicals down well holes to fracture deposits and create new fissures.

More than 160 gas wells have been drilled in Pavillion. Some have been fracked as recently as 2005.

Pavillion residents have complained for years that their well water stinks of hydrocarbons, and in 2008 they asked the EPA to investigate. The EPA found suspect chemistry in two wells drilled to check for groundwater pollution.

Fracking in Pavillion occurred fairly close to where residents get their drinking water: As shallow as 1,200 feet below the surface in an area where the deepest water wells have been drilled to a depth of about 800 feet, Martin told the subcommittee.

That's quite different from the geology of the Marcellus Shale, where gas wells are 5,000 feet deep or more.

But Republican Rep. Ralph Hall, of Texas, said the Pavillion report is but one example of an anti-fracking agenda by EPA.

"It is important to recognize what EPA is doing in Wyoming is not isolated. They are going after fracking everywhere they can," Hall said.

Although the petroleum industry maintains there are no proven cases of fracking having polluted groundwater, some environmentalists have viewed the Pavillion report as justifying their worries about the practice.

A public health professor at the University of Pittsburgh, Bernard Goldstein, testified that he would support a fracking moratorium until better practices for fracking are put into place.

He said the U.S. sooner or later will extract its accessible onshore gas and there's no rush.

"It's not going anywhere," Goldstein said. "Unless the Canadians can figure out how to frack underneath Lake Erie, that's staying with us."

Other witnesses questioned the validity of the Pavillion study and the EPA's preliminary findings.

"Once misinformation gets out into the public, it takes on a life of its own and is almost impossible to correct," said Kathleen Sgamma, vice president of government and regulatory affairs for the Denver-based petroleum industry group Western Energy Alliance.

Wyoming's top state oil and gas regulator, Tom Doll, said the EPA consulted only minimally with his agency, the Wyoming Oil and Gas Conservation Commission, on research behind the report.

"We had significantly greater consultation with the state than perhaps Mr. Doll might be aware of," Martin said.

The EPA has extended a public comment period on the Pavillion report six more weeks through March 12. The agency also is seeking nominees for experts in backgrounds including petroleum engineering, geology, chemistry and hydrology to serve on an upcoming peer review panel for the report.