WASHINGTON — The Environmental Protection Agency on Thursday linked hydraulic fracturing with groundwater contamination in Wyoming — a first-of-its-kind conclusion by the federal agency that could trigger new scrutiny of the practice used to extract oil and natural gas nationwide.

The EPA announced its findings as part of a three-year probe into possible water pollution in Pavillion, Wyo. The agency said it had discovered synthetic chemicals associated with gas production and hydraulic fracturing fluids inside deep water wells in the region.

Although the study is limited to a gas field in west central Wyoming and is only in a draft form, the EPA's finding could be a game changer for the oil and gas industry, which has insisted that hydraulic fracturing is safe and should be regulated solely by state officials, rather than the federal government.

The report is sure to stoke calls for stepped-up regulation of fracturing and natural gas drilling, even as some states already move to clamp down on the practice. New York regulators are considering new rules for natural gas drilling. State Department of Environmental Conservation spokeswoman Emily DeSantis told the Associated Press that New York's well-casing rules and proposed setbacks from water supplies would prevent contamination like that in Pavillion.

About a third of U.S. natural gas production now comes from the hydraulic fracturing process, which involves blasting mixtures of water, sand and chemicals deep underground and at high pressures to break up dense shale rock and unlock trapped hydrocarbons.

Energy analysts say the technique is key to recovering a 100-year supply of natural gas from shale formations nationwide, including the Marcellus in New York and Pennsylvania and the Eagle Ford in Texas.

Environmentalists have long warned that the chemicals used in the process could contaminate local drinking water supplies and that natural gas can leach out of poorly designed and cemented wells to pollute groundwater.

Until now, EPA officials said they had found no convincing evidence of such contamination. At Congress' direction, the agency has launched a three-year study of the intersection of hydraulic fracturing and water.

The EPA said its draft report would be available for public comment and submitted to an independent scientific review panel.

"We look forward to having these findings in the draft report informed by a transparent and public review process," said Jim Martin, EPA regional administration based in Denver.

In the Pavillion case, the EPA monitored the region from March 2009 through April 2011. After initially discovering methane and dissolved hydrocarbons in some water samples, the EPA broadened testing of groundwater from wells in the area and installed its own deep monitoring wells.

Ultimately, the agency discovered high concentrations of benzene, diesel range organics and other chemicals in groundwater samples taken from monitoring wells near 33 surface pits used to hold wastewater and drilling material — indicating that they could be a source of contamination.

Other synthetic compounds associated with hydraulic fracturing fluids also were detected in the groundwater. Those included chemicals tied to components of materials often used as part of the fracturing process — including at least one the EPA said "is not expected to occur naturally in ground water."

The agency insisted that it considered a range of explanations, but that "the data indicates likely impact to groundwater that can be explained by hydraulic fracturing."

Other results showing elevated levels of gas in the area's groundwater — possibly because it had migrated from wells that the EPA said had only "sporadic" barriers or, in some cases, no cement at all over large vertical stretches.

The agency stressed that the findings are limited to Pavillion, where fracturing has taken place both in and below the drinking water aquifer and very close to drinking water wells — conditions that are not common elsewhere in the U.S. The region has been home to oil and gas drilling since the 1950s, and some of the 169 gas production wells in the area were fractured at points some 1,220 feet below the surface.

By contrast, energy companies are extracting natural gas from Texas' Eagle Ford shale formation at depths ranging from 4,000 to 14,000 feet below the surface.

Industry representatives and their allies on Capitol Hill blasted the EPA's report, with Sen. James Inhofe, R-Okla., calling it politically motivated and "premature."

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"It is irresponsible for EPA to release such an explosive announcement without objective peer review," Inhofe said.

Chris Tucker, a spokesman for the industry group Energy In Depth, said the report was flawed with "a lot of basic things wrong." "Unfortunately, in the funhouse mirror world of anti-fracturing advocacy, some will attempt to use this as a justification to shut down an entire industry, even if the issues out there have nothing to do with it," Tucker said.