Use of stable isotopes to identify sources of methane in Appalachian Basin shallow groundwaters: a review

Abstract

Development of unconventional shale gas reservoirs in the Appalachian Basin has raised questions regarding the potential for these activities to affect shallow groundwater resources. Geochemical indicators, such as stable carbon and hydrogen isotopes of methane, stable carbon isotopes of ethane, and hydrocarbon ratios, have been used to evaluate methane sources however their utility is complicated by influences from multiple physical (e.g., mixing) and geochemical (e.g., redox) processes. Baseline sampling of shallow aquifers prior to development, and measurement of additional geochemical indicators within samples from across the Appalachian Basin, may aid in identifying natural causes for dissolved methane in shallow groundwater versus development-induced pathways.