STRUCTURAL CONTROL ON MARCELLUS BRINE MIGRATION INTO SHALLOW UPPER DEVONIAN AQUIFERS OF SOUTH-CENTRAL NY

The Marcellus Shale formation within the south-central New York counties of Steuben, Chemung, Tioga and Broome contains an economically viable reserve of thermally mature unconventional natural gas. However, concerns regarding the environmental impacts to groundwater have halted the northward expansion of horizontal hydraulic fracturing from northern PA into southern NY. Recent studies in northeastern Pennsylvania have suggested that many groundwater wells have naturally elevated levels of brine constituents which tend to be located in valley bottoms (Osborn et al., 2012; Molofsky et al., 2013). A recently developed technique combines isotopic and molecular hydrocarbon chemistry, inorganic chemistry and noble gas ratios within shallow Upper Devonian groundwater aquifers to confirm the presence of hydrocarbon bearing brines due to natural migration processes (Darrah et al., in review). This study applies this new technique to examine the chemistry of 65 domestic water wells in the 4 county region of southern NY in the context of its geological setting. Samples from well locations with a known or suspected fault show evidence of naturally occurring Middle-Devonian brine inputs. However, noble gas ratios suggest less migration occurred with a diminished brine signal relative to Pennsylvania, likely due to shallower basin conditions and lower associated temperatures. Importantly, a subset of samples with brine-type constituents were not located in valley bottoms, but did have an association with a suspected fault. The correlation of naturally present hydrocarbon-brines in faulted Upper Devonian aquifers is significant as it suggests that these faults likely served as conduits for the migration of Marcellus- sourced fluids.