According to a July 19, 2013 article by Kevin Begos of The Associated Press, a landmark federal study on hydraulic fracturing, or fracking, shows no evidence that chemicals from the natural gas drilling process moved up to contaminate drinking water aquifers at a western Pennsylvania drilling site, the Department of Energy told The Associated Press.

After a year of monitoring, the researchers found that the chemical-laced fluids used to free gas trapped deep below the surface stayed thousands of feet below the shallower areas that supply drinking water, geologist Richard Hammack said.

Although the results are preliminary – the study is still ongoing – they are the first independent look at whether the potentially toxic chemicals pose a threat to people during normal drilling operations. But DOE researchers view the study as just one part of ongoing efforts to examine the impacts of a recent boom in oil and gas exploration, not a final answer about the risks.

Drilling fluids tagged with unique markers were injected more than 8,000 feet below the surface at the gas well bore but weren't detected in a monitoring zone at a depth of 5,000 feet. The researchers also tracked the maximum extent of the man-made fractures, and all were at least 6,000 feet below the surface.

That means the potentially dangerous substances stayed about a mile away from surface drinking water supplies, which are usually at depths of less than 500 feet. "This is good news," said Duke University scientist Rob Jackson, who was not involved with the study. He called it a "useful and important approach" to monitoring fracking, but he cautioned that the single study doesn't prove that fracking can't pollute, since geology and industry practices vary widely in Pennsylvania and across the nation.