Chemicals linked to hydraulic fracturing, or "fracking," have been found again in the groundwater of a town in Wyoming that has become a flashpoint in the debate over the drilling practice.

A U.S. Geological Survey (USGS) report found traces of methane, ethane and phenol in a monitoring well in rural Pavillion, Wyo., where residents say fracking has contaminated their drinking water.

Pavillion was thrust to the forefront of the fracking debate in December of 2011, when the Environmental Protection Agency (EPA) reported finding groundwater contaminants in two wells there. That report, which drew harsh criticism from the natural-gas industry, represented the first time the U.S. government had made a connection between fracking and groundwater pollution.

Alisha Johnson, a spokeswoman with the EPA, told The Hill that the USGS findings are “generally consistent” with EPA’s earlier tests.

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But a natural-gas industry group questioned the assertion that the USGS study matched the EPA's earlier tests, noting USGS did not test one of the two monitoring wells because the water levels were too low. In March, the Bureau of Land Management issued a report warning that a small sample size, such as the one used by EPA, could create statistical bias in the groundwater samples.

Fracking is a process that injects a high-pressure mixture of water, sand and chemicals into tight rock formations to unlock natural gas. The practice has been credited with reenergizing the domestic gas industry by unlocking hard-to-reach gas deposits.

The natural-gas industry has said fracking is safe, and says studies linking it to groundwater contamination and seismic activity are false.

But environmentalists have opposed the practice and say it will have a devastating impact on water supplies. The test results in Wyoming are likely to reignite calls to halt fracking.

Steve Everley, a spokesman for natural-gas industry group Energy in Depth, said the USGS decision to disqualify one of the EPA’s two Pavillion monitoring wells showed EPA’s original analysis was faulty.

Everley said the new findings are better paired with those of the Bureau of Land Management, which told EPA its monitoring wells were insufficient for testing groundwater. It suggested adding more monitoring wells to remove possible bias from the sampling.

“Perhaps the EPA should also listen to the Bureau of Land Management, which warned months ago that the results from one of EPA’s wells couldn’t be trusted, and advised the EPA to start over,” Everley told The Hill on Thursday. “But I suppose that, like so many other facts about Pavillion, wouldn’t generate the same sorts of headlines.”

Congressional Democrats have warned about risks from fracking, and pressure on the Obama administration from Republicans and some Democrats to expedite natural-gas exports has added another element to the debate.

In a letter sent to Energy Secretary Steven Chu on Wednesday, 20 House Democrats urged the administration to conduct an environmental impact statement for the effects of fracking before approving natural-gas export agreements or facilities.

The letter signatories expressed concern over U.S. Energy Information Administration (EIA) estimates that 63 percent of export demand would be met by increased production. Of that production, 85 percent of it would come from unconventional drilling, such as fracking.