The U.S. Environmental Protection Agency announced Thursday it is abandoning its longstanding plan to have independent scientists confirm or cast doubt on its finding that hydraulic fracturing may be linked to groundwater pollution in central Wyoming.

The EPA is standing by its findings, but state officials will lead further investigation into the pollution in the Pavillion area. The area has been a focus of the debate over whether fracking can pollute groundwater ever since the EPA's initial report came out in late 2011.

The decision was detailed in a draft news release obtained by The Associated Press. EPA spokesman Tom Reynolds in Washington, D.C., confirmed the information, saying the federal agency will let state officials carry on the investigation with the EPA's support.

"We stand behind our work and the data, but EPA recognizes the state's commitment to further investigation," he told AP.

Wyoming officials have been skeptical about the theory that hydraulic fracturing played a role in the pollution, but Reynolds expressed confidence the state could lead the work from here.

Hydraulic fracturing, or fracking, boosts the productivity of oil and gas wells by pumping pressurized water mixed with sand and chemicals down well holes to crack open fissures in the ground.

Environmentalists have voiced concern about fracking causing groundwater pollution for years, but the practice has significantly boosted oil and gas production in regions such as the Bakken Shale in North Dakota and the Marcellus Shale underlying Eastern states.

The EPA's 2011 report marked the first time the agency publicly linked fracking and groundwater contamination, causing a stir on both sides of the issue.

The new research led by Wyoming officials would be funded at least in part by a $1.5 million grant from Encana Corp.'s U.S. oil and gas subsidiary, which owns the Pavillion gas field. A final report is due by late 2014.

"We think this is the most pragmatic, quickest way to help the residents of Pavilion. We're going to work hand in hand with the state to make sure this investigation moves forward," Reynolds said.

The EPA had sought nominations for experts to serve as peer reviewers for its draft report. Reviewers needed to be free from the appearance of any conflict of interest and have the necessary expertise to review the findings, according to a Federal Register announcement last year.

The EPA has extended public comment periods on the draft report three times since it came out _ twice last year and again this year. Each extension delayed the peer-review plans.

The EPA also has been conducting a study examining the relationship between fracking and groundwater in different areas of the country and is proceeding with that study.