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In this July 27, 2011, file photo, workers stand behind the top of a pump for the hydraulic fracturing process in the Marcellus Shale layer to release natural gas at a Range Resources site in Claysville, Pa. (AP Photo)

In this July 27, 2011, file photo, workers stand behind the top of a pump for the hydraulic fracturing process in the Marcellus Shale layer to release natural gas at a Range Resources site in Claysville, Pa. (AP Photo)