EVALUATING CHANGES IN FRESHWATER QUALITY IN AREAS OF NATURAL-GAS DEVELOPMENT WITHIN THE MARCELLUS SHALE PLAY

The Marcellus Shale has been rapidly developed since 2006 and is now the largest producing shale gas reservoir in the world. This rush to extract natural gas from the Marcellus, as well as from other shale gas plays, has outpaced careful consideration of the potential impacts to freshwater resources. Impairment of groundwater quality in areas of shale gas extraction has been reported, although causes remain unclear and contested due to inadequate baseline (pre-drill) water-quality data and insufficient knowledge of legacy contamination, industry operations, and local hydrogeology. To help address this issue, we are making chemical and hydrological measurements in freshwater aquifers and streams in Susquehanna County, PA, a “sweet spot” of the Marcellus Shale Play. Through analysis of these measurements, we intend to (i) elucidate the spatial and temporal variations in trace metal concentrations, major ions concentrations, hydrocarbon concentrations, and isotope chemistry prior to commencement of gas extraction activities; (ii) quantify perturbations in groundwater flow that occur naturally or that are attributable to any step in the process of shale gas development; and (iii) evaluate changes (if any) in groundwater chemistry and isotopic composition induced by hydraulic fracturing and other stages of shale gas extraction. In winter 2015, we installed multi-level groundwater monitoring wells within a 15 km² area that encompassed four shale gas pads, from which seven horizontal gas wells were drilled and subsequently hydraulically fractured through the spring, summer, and fall of 2015. The monitoring wells, which have been sampled on a monthly basis since their installation, were sited at hilltops immediately adjacent to gas well pads and in valleys above vertical projections of the gas well laterals. Water samples from four streams within the study area and hydrocarbon samples, frac fluids, and flow back from the gas wells have also been collected and are being analyzed. Findings from this sampling program show that methane isotopic composition, as well as concentrations of trace metals, major ions, and hydrocarbons, exhibit significant variations in space and time. We will present our interpretation of these data in the context of local geology, hydrology, and the timing of shale gas extraction stages.