Horizontal drilling and hydraulic fracturing have enhanced energy production but raised concerns about drinking-water contamination and other environmental impacts. Identifying the sources and mechanisms of contamination can help improve the environmental and economic sustainability of shale gas extraction. Using a combination of water and dissolved gas chemistry I will address two questions: 1) Are elevated levels of hydrocarbon gas in drinking-water aquifers near gas wells natural or anthropogenic? and 2) If fugitive gas contamination exists, what mechanisms cause it? Using noble gas and hydrocarbon tracers, we distinguish natural sources of methane from anthropogenic contamination and evaluate the mechanisms that cause elevated hydrocarbon concentrations in drinking-water near natural-gas wells.The data implicate leaks through annulus cement (four cases), production casings (three cases), and underground well failure (one case) rather than gas migration induced by horizontal drilling or hydraulic fracturing deep underground.
