An Isotopic Perspective On Water And Carbon Sources In Complex Geochemical Settings Of The Appalachians
Sack, Andrea L. 1
1 Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO; Geology and Geography, West Virginia University, Morgantown, WV
Understanding sources of water and carbon are important for tracking recharge sources as well as assessing any changes in water quality associated with shale gas drilling and/or coal mining in the Appalachian region of the United States. Environmental stable isotopes have become an increasingly useful tool for determining sources and cycling of water, carbon, nutrients and other trace elements. The variations in water-rock interactions, recharge sources, recharge pathways, and age can impart unique isotopic signatures to different water sources. The main objectives of this study were to use stable isotopes of water (d18O H2O and d2H H2O) and DIC (d13C DIC) to delineate sources of water and carbon in natural springs, coal mine discharges and brines co-produced during Marcellus Shale gas drilling in Appalachia. Preliminary data indicates that stable isotopes can be used in conjunction with routine geochemistry to understand sources of carbon and water at each site.
Additionally, gas and water samples were collected from gas producing wells in the region from Upper Devonian sands and Middle Devonian Marcellus Shale in southwestern Pennsylvania and north-central West Virginia to asses the water quality and any hydrologic connections during Marcellus Shale drilling. Initial conclusions suggest that the oxygen and hydrogen isotope composition of water, carbon isotope composition of dissolved inorganic carbon, and carbon and hydrogen isotope compositions of methane in Upper Devonian sands and Marcellus Shale are very different compared with shallow groundwater aquifers, coal-mine waters, and stream waters of the region. Therefore, spatiotemporal stable isotope monitoring of the different sources of water before, during, and after hydraulic fracturing can be used to identify migrations of fluids and gas from deep formations that are coincident with shale gas drilling.