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A new USGS study reports that shale-gas production in northern Pennsylvania has not currently caused widespread hydrocarbon contamination in the upland aquifer zone used for domestic supply.

The study focused on groundwater in upland settings—high or hilly land—where natural processes are less likely to contribute methane and other hydrocarbons to shallow groundwater. Untreated water samples were collected and analyzed from 35 domestic wells in northeastern Pennsylvania where shale gas is under production, and from 15 domestic wells in southern New York where shale gas is not in production. Methane concentrations in the Pennsylvania wells were not significantly different from those in the New York wells.

Twenty of the 50 sampled domestic wells were located within 1 kilometer of a gas well. Methane was detected in 1 of these 20 wells, suggesting that shale-gas production resulted in some contamination of shallow upland groundwater. Sources of methane were teased out by looking at the isotopic signatures of this compound. A second well within 1 kilometer of a gas well contained trace amounts of other hydrocarbons, such as benzene, that could be associated with shale-gas production. However, the age of the groundwater, which pre-dates shale-gas production, indicates that the effects of shale-gas production on groundwater quality cannot yet be fully assessed because groundwater potentially affected by land-surface sources of contamination associated with gas production has not yet reached the wells.

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