Recent development of horizontal drilling and hydraulic fracturing in Pennsylvania has contributed to increased public concern over water and public safety. Cases of methane migration into water supplies have been observed as a result of shale gas development. Methane migration into water supplies and the atmosphere is a concern for multiple reasons: methane is a stronger greenhouse gas than carbon, it is an explosion hazard, and it can create anaerobic conditions at depth. Very few studies have documented the effects of methane leakage on natural waters. A technique to detect methane migration into surface water has been implemented on Sugar Run in Lycoming County, Pennsylvania near a suspected leaking unconventional gas well. Surface water measurements, atmospheric methane measurements and aqueous cation and anion concentration measurements were completed along the stream. Surface water shows methane concentrations as high as 76 ppb in the stream body and 4,600 ppb in two seeps (area where groundwater directly comes to the surface) located along this stretch. Average streams unaffected by biogenic and thermogenic sources in Pennsylvania exhibit methane concentrations of ~1 ppb. Isotopic analysis of stable carbon isotopes (δ13C in CH4) in Sugar Run indicates a thermally mature thermogenic source (-42 to -10.3), most likely sourced from Marcellus Formation at depth. Additionally, using a Los Gatos greenhouse gas analyzer, atmospheric methane concentrations around the seep locations were measured to be as high as 100 ppm. In comparison, average global atmospheric methane concentrations are about 2 ppm. Results from the seep and adjacent stream samples show higher concentrations of metals such as Mn, Fe, Co, Ni and As. In contrast, U is beneath detection. High aqueous methane concentrations in the seep and heavy isotopic δ13C in CH4 are both consistent with leaking thermogenic methane. High methane could create a reducing environment at depth as indicated by mobilization of metals such as Fe and Mn. A reducing environment and an increase in metal concentrations related to unconventional gas exploration could adversely affect fish and wildlife present in the watershed. Research is needed to understand the effects of both natural and anthropogenic sources of methane on stream environments.

Effect of methane leakage on metal mobilization near a shale gas well

253rd National Meeting (2017)

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