CHEYENNE, Wyo. (AP) — The U.S. Geological Survey plans to release new test results from a Wyoming gas field where the U.S. Environmental Protection Agency has linked hydraulic fracturing to groundwater contamination.

The data to be released Wednesday comes from samples taken in April near Pavillion in central Wyoming. The EPA, Wyoming, USGS and two American Indian tribes collaborated on the sampling.

Fracking is the petroleum industry practice of pumping water, sand and chemicals underground to crack open fissures and boost the flow of oil and gas. Last year, the EPA tested samples from two wells specially drilled to check for contaminants and announced that fracking may have caused groundwater pollution.

Some residents requested the EPA testing, saying their well water turned foul after gas drilling picked up in their neighborhood several years ago.

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