SignificanceThis study incorporates time series sampling of groundwater before, during, and after drilling, hydraulic fracturing, and initiation of shale gas production. Using monitoring wells installed next to gas well pads and above gas well laterals, previously undocumented responses to drilling and a gas well casing breach were observed, although groundwater impacts arising from the process of hydraulic fracturing were not detected. We discover considerable temporal variability in methane concentrations in deeper horizons of freshwater aquifers and attribute this to persistent shifts in aquifer recharge that influence mixing between shallow freshwater and comparatively saline and methane-rich deep groundwater. These results have implications for attribution of groundwater contamination to specific stages of shale gas development or natural processes and improving regulatory monitoring.

We characterize the appropriation of surface water for the extraction of natural gas from Pennsylvania's Marcellus Shale, and we examine the influences of these diversions on stream flows at 300 sites. Our analysis reveals that permitted withdrawals range from 50 m3/d to more than 18,000 m3/d and that water is taken from streams of all sizes, from headwater streams to eighth‐order rivers. Flow alteration varies inversely with watershed area and, for larger streams, is compounded by upstream withdrawals. The ratio of daily permitted withdrawal to median stream flow ranges from 0.0001 to unity, although low flows in most, but not all, smaller streams are protected by pass‐by flow requirements. Temporal changes in surface water withdrawals track gas well completion activity, rather than changes in operational strategies, and while reuse of wastewater has increased since 2009, freshwater accounted for 75% of water used in hydraulic fracturing through the peak in gas well completion activity.

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Hydraulic fracturing is an increasingly common technique for the extraction of natural gas entrapped in shale formations. This technique has been highly criticized due to the possibility of environmental contamination, underscoring the need for method development to identify chemical factors that could be utilized in point-source identification of environmental contamination events. Here, we utilize comprehensive two-dimensional gas chromatography (GC × GC) coupled to high-resolution time-of-flight (HRT) mass spectrometry, which offers a unique instrumental combination allowing for petroleomics hydrocarbon fingerprinting. Four flowback fluids from Marcellus shale gas wells in geographic proximity were analyzed for differentiating factors that could be exploited in environmental forensics investigations of shale gas impacts. Kendrick mass defect (KMD) plots of these flowback fluids illustrated well-to-well differences in heteroatomic substituted hydrocarbons, while GC × GC separations showed variance in cyclic hydrocarbons and polyaromatic hydrocarbons among the four wells. Additionally, generating plots that combine GC × GC separation with KMD established a novel data-rich visualization technique that further differentiated the samples.

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