Writing in the Proceedings of the National Academy of Sciences, researchers said they found drinking-water wells in northeastern Pennsylvania within a half mile of high-volume hydraulic fracturing, or fracking, had methane concentrations six times greater, on average, than in wells farther away, the Los Angeles Times reported.
Fracking is a technique used to shatter rock formations deep underground and unlock oil and gas trapped inside by injecting large volumes of water mixed with sand and chemicals at high pressure into the earth.
Methane is known to occur naturally in the Pennsylvania aquifers studied, but the researchers said they found the chemical composition of methane in wells close to the drilling sites was the same as the natural gas extracted in the area.
"We need to understand why, in some cases, shale gas extraction contaminates groundwater and how to keep it from happening elsewhere," the researchers wrote.
There is a lack of research into the effects on human health of prolonged exposure to methane, said the study's lead author, Robert B. Jackson, professor of environmental sciences at Duke University.