STRUCTURAL CONTROL ON THE MIGRATION OF NATURAL HYDROCARBON BRINES INTO GROUNDWATER AQUIFERS IN SOUTH-CENTRAL NEW YORK

Amid growing optimism for increased US domestic energy production, the concerns over compromised drinking-water quality related to drilling have tempered the enthusiasm for shale gas development in New York State. In neighboring Pennsylvania, some workers suggest that shale gas drilling is responsible for stray gas contamination in a subset of wells (Osborn et al, 2011; Jackson et al, 2013), while others suggest that methane is controlled by natural hydrogeological factors (Molofsky et al, 2011; 2013). In the absence of pre-drill data, this controversy has been difficult to resolve. In many groundwater wells the presence of methane coexists with elevated salt content. These diluted geological brine components also have elevated levels of toxic metals (e.g., barium). Thus, it is critical to understand the geological factors that control the presence of methane in these areas independent of the shale gas controversy. This study examines the gas (hydrocarbon and noble gas) and water (salt and metals) chemistry of 65 domestic groundwater wells in south-central NY in order to: 1) establish a pre-drill baseline of groundwater chemistry and 2) investigate the hydrogeological context for gas-rich or salty groundwater. We identify significant co-variations in natural gas and dissolved brine constituents in our study area. Importantly, these components appear to be concentrated at low elevations along fault zones within major structurally-controlled valleys. We provide geochemical data that along transects of 2 major N-S trending strike-slip faults and an associated E-W trending thrust fault; the latter is a regional fault that ramps up from the Salina decollement. Our data suggests that these fault systems likely served as conduits for the natural migration of hydrocarbon-rich brines during the Alleghanian orogeny.