The New York Times reports that "a study of tainted drinking water in areas where natural gas is produced from shale shows that the contamination is most likely caused by leaky wells rather than the process of hydraulic fracturing used to release the gas from the rock."
"The study looked at seven cases in Pennsylvania and one in Texas where water wells had been contaminated by methane and other hydrocarbon gases. Both states have extensive deposits of gas-bearing shale that have been exploited in recent years as part of a surge in domestic energy production. Some environmental groups have suggested that hydraulic fracturing, or fracking, could cause the gas to migrate into drinking water aquifers."
The piece continues: "...in their analysis , published Monday in The Proceedings of the National Academy of Sciences, the researchers found no evidence that fractured shale led to water contamination. Instead, they said cement used to seal the outside of the vertical wells, or steel tubing used to line them, was at fault, leading to gas leaking up the wells and into aquifers."
Adds Fuel Fix : "Contrary to some suspicions, the researchers found, methane in the water reservoirs did not seep up from horizontal drills working deep underground. Instead, the gas leaked from a source much closer to the water: faulty casings and cement rings used to insulate the central shaft of a gas well."
"The results, the researchers said, help clarify the industry’s role in water pollution."