The testing of a monitoring well in the rural town of Pavillion in Wyoming showed lower levels of the carcinogen benzene, a hydrocarbon commonly associated with oil and gas development, than what the U.S. Environmental Protection Agency reported in 2011 when it linked contaminants in two water wells to hydraulic fracturing, the U.S. Geological Survey reported.
Last year's testing by the EPA showed benzene at almost 50 times the recommended EPA limit, while the new data -- from just one well -- show benzene at 3 percent of the recommended EPA limit, the USGS said.
In releasing its results the USGS made no attempt to link chemical levels to fracking.
"Interpretation was not part of the scope of the report," USGS spokesman Dave Ozman said.
A natural gas industry group said it was predictable the USGS study wouldn't match the EPA's tests, citing a Bureau of Land Management report that the EPA's small sample size could create statistical bias in the groundwater tests.
"Perhaps the EPA should also listen to the Bureau of Land Management, which warned months ago that the results from one of EPA's wells couldn't be trusted and advised the EPA to start over," Steve Everley, a spokesman for natural gas industry group Energy in Depth, said.
Environmental groups and some Wyoming residents remain opposed to the practice, calling for a halt to fracking over its alleged impact on water supplies.