One of the most intensive debates on the environmental safety of shale gas exploration and hydraulic fracturing is the possible contamination of drinking water wells in areas of extensive shale gas operation. Our previous study in northeastern Pennsylvania has shown elevated levels of methane in wells located near (1 km) from these areas had much lower methane concentrations [6].
contamination is based on the different isotopic (δ13C-CH4; δ2H-CH4) and In contrast, it was argued that relatively high methane in this part of the Appalachian Basin is due to natural flux of methane and is not linked to the shale gas drilling [13]. The ability to delineate methane sources and thus the distinction between natural flux and anthropogenic geochemical (propane/methaneratios)compositions of thermogenic relative to biogenic methane sources. It was shown that the elevated methane in drinking water wells near the shale gas wells had a thermogenic composition (e.g., heavier 13C-CH4) than wells located 1 km away from shale gas sites with an apparent mixed thermogenic-biogenic composition. New emerging noble gas data reinforce the carbon isotopes and hydrocarbon ratios data and indicate that the high levels of meth ane exceeding the hazard level of 10 mg/L are indeed related to stray gas contamination directly linked to shale gas operation. The most probable mechanism for stray gas contamination is leaking through inade quate cement on casing or through well annulus from intermediate formations