CHEYENNE, Wyo. (AP) — The U.S. Geological Survey plans to release results Wednesday from new groundwater tests in Wyoming where another agency linked hydraulic fracturing to contaminants found in two water wells and residents complained of chemicals polluting their well water.

The new USGS data come from samples taken in April at one of the test wells near Pavillion in central Wyoming. The other test well didn't produce enough water to yield samples deemed large enough to test.

Hydraulic fracturing, or "fracking," is the petroleum industry practice of pumping water, sand and chemicals down well bores to crack open fissures and boost the flow of oil and gas.

Environmental groups have sounded the alarm about fracking for years — but with few, if any, examples of verified pollution. Petroleum industry officials say the lack of verified pollution, out of many thousands of wells fracked in the U.S. over the past few decades, proves the process is safe.

The U.S. Environmental Protection Agency, the state of Wyoming, the USGS and two American Indian tribes collaborated on the latest sampling, which followed previous testing done solely by the EPA.

The EPA theorized a fracking-pollution link in a draft report released in December. The report drew heavy skepticism from petroleum industry and state officials, including Wyoming Gov. Matt Mead, who characterized the finding as a flimsy one.

Wyoming officials — whom the EPA briefed on its findings more than a month ahead of the report's release — also grumbled that the EPA hadn't kept them in the loop about what the federal agency was up to during the previous testing.

"Gov. Mead felt that this process was an improvement on how the first draft report from the EPA was done. It was more transparent. The team had input throughout the process," Mead spokesman Renny MacKay said Tuesday.

Even so, the EPA plans to post its own data separately, EPA Region 8 spokesman Rich Mylott said.

"All EPA data have gone through the agency's quality assurance process," Mylott said by email Tuesday.

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EPA spokeswoman Alisha Johnson in Washington said Wednesday she did not know what data the EPA might release or when that might happen.

Testing by the EPA this past spring included new samples from five domestic water wells in the Pavillion area. That sampling happened outside the collaborative process.

One person each from the EPA, the Wyoming Department of Environmental Quality, and the Northern Arapaho and Eastern Shoshone tribes on the Wind River Indian Reservation near Pavillion peer-reviewed the collaborative data, according to MacKay.

A full peer review of the sampling and findings to date will occur later.

MacKay said Mead wants "science and a good process" to guide any new findings.

"The governor's position has always been he wants this investigation to play out and whatever it finds, you move on from there," he said.