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

Elevated levels of methane (CH₄) in groundwater can lead to accumulation of gas in enclosed areas, resulting in potentially explosive environments. A recent study in northeastern Kentucky identified dissolved methane to be a widespread phenomenon, with 28% (n= 51) of analyzed domestic wells in the “warning” and “immediate action” level ranges. The wells with nearby mining activities were more likely to have elevated methane levels (CH₄ > 1 mg/L). In contrast, a study in southeastern Kentucky observed significantly lower concentrations and an inverse correlation between CH₄ concentration and proximity to mining activities. CH₄ concentrations showed no correlation with distance to oil and gas wells in either study. However, recent evaluations of horizontal drilling and hydraulic fracturing as options to develop two major oil and gas plays in eastern Kentucky have increased interest in understanding baseline groundwater chemistry in the overlying shallow Pennsylvanian sandstone aquifers. Furthermore, even though large variations in chemical and isotopic composition observed over short distances are consistent with a dissected topography and limited hydrologic communication, local trends in chemical parameters and different solute availability could explain some of the observed differences in CH₄ concentrations. We sampled 18 groundwater wells for bulk chemistry and isotopic composition in an unanalyzed region located between previous studies. Initial results of major cations, anions, dissolved gas concentrations, δ¹³C_DIC, δ²H, δ¹⁸O, δ¹³C_CH4 and δ²H_CH4 suggest a biogenic source of methane for wells where sulfate (SO₄^2-) concentrations are low. δ³⁴S_SO4 and δ¹⁸O_SO4 data should elucidate sulfate sources for a subset of wells with high sulfate. Additionally, we compile and show trends in chemical and isotopic composition of groundwater in Eastern Kentucky and how they relate to methane concentrations. Further geospatial and statistical analysis of data in relation to anthropogenic activities (mining, oil and gas development) should elucidate methane and sulfate dynamics and any geochemical processes associated. We anticipate this study to improve our understanding of groundwater geochemical zones and processes, as well as the effects of previous and future resource development in Eastern Kentucky.