CAUSES AND EXTENT OF ELEVATED METHANE CONCENTRATIONS IN THE GROUNDWATER OF EASTERN KENTUCKY

Across Eastern Kentucky, methane is observed in groundwater wells at concentrations above the immediate action level (>1 mg/L) as outlined by the Environmental Protection Agency. In many rural areas, groundwater is the only potable water source, making identification of the controls of methane contamination important for mitigation efforts. In this study, groundwater from 24 wells in Eastern Kentucky were analyzed for methane, trace metals, alkalinity, sulfide, sulfate, ferrous iron, and water quality parameters. The sample locations, spanning three counties, build off previous studies in the northeastern and southeastern corners of the state. Mining, along with oil and gas extraction, occur throughout the region. By combining a complete water chemistry profile with methane concentrations and isotopes, we identified if the methane was controlled by oil and gas exploration, natural bacterial processes, and/or influenced by local mining activity.

Methane isotope ratios were consistent with microbially derived methane, with a small portion migrating into the shallow strata from deeper thermogenic sources. Interestingly, proximity to extensive coal mining appeared to suppress methane production. We hypothesize this is the result of an increase in sulfate production by pyrite oxidation, limiting methanogenesis. This was illustrated in a clear relationship between sulfate concentrations and isotopes. Overall, these results suggest that anthropogenic activities directly and indirectly influence geochemical conditions and methane distribution in groundwater in eastern Kentucky. Similar isotopic relationships would be expected in areas with different levels of mining and oil and gas development, constraining the contribution of mining and drilling activities to changing subsurface geochemistry.