By Jon Hurdle

The announcement by the U.S. Environmental Protection Administration that it has found chemical contaminants in domestic well water near natural gas-drilling rigs raises more questions about the safety of a method of gas extraction called hydraulic fracturing. For a story, click here.)

The EPA’s finding, based on tests in rural Pavillion, Wyoming, marks the first time the federal agency has tested water in response to growing complaints from around the U.S. that gas drilling is polluting groundwater with toxic substances.

Canadian energy giant EnCana, which operates almost 250 gas rigs in the area, notes that the industry is just one possible source of the contamination, a point echoed by the EPA itself, which has been at pains to point out that it has reached no conclusion about the source of the chemicals.

The agency will conduct more tests to determine how the substances got into 11 of 39 wells tested during March and May this year.

But the test results, first released to local residents on Aug. 11, are a boost to opponents of hydraulic fracturing or “fracking” who have been struggling to prove their case because the oil and gas industry doesn’t have to disclose what it puts in its drilling fluids, thanks to an exemption passed during the Bush administration to a federal clean water law.

Energy companies contend that the chemicals used in “fracking” — which are forced deep underground along with water and sand — are heavily diluted, encased in layers of steel and concrete, and injected so far below drinking-water aquifers that there’s no significant chance of an escape.

Congress, goaded by public disquiet about gas drilling, is considering a bill that would require drillers to disclose what they are putting in the ground, and remove the loophole that has allowed them to argue that publicizing the composition of drilling fluids would put them at a competitive disadvantage.

But it may be tough to resist pressure to maximize the flow of a clean-burning fuel that the Obama administration sees as key to U.S. energy policy.