Southeastern Section - 67th Annual Meeting - 2018

Paper No. 3-6
Presentation Time: 10:10 AM


SZYNKIEWICZ, Anna1, LEDOUX, St. Thomas Majeau2, FAIIA, Anthony M.1 and MAYES, Melanie3, (1)Earth and Planetary Sciences, The University of Tennessee, 602 Strong Hall, 1621 Cumberland Ave, Knoxville, TN 37996, (2)Earth and Planetary Sciences, University of Tennessee, Knoxville, 1412 Cricle Drive, Knoxville, TN 37996, (3)Climate Change Science Institute and Environmental Sciences Division, Oak Ridge National Laboratory, PO Box 2008, MS 6038, Oak Ridge, TN 37917

Previous research has demonstrated that hydraulic fracturing has the potential to contaminate shallow aquifers with methane (CH4) from deeper formations. This study compares concentrations and isotopic compositions of CH4 sampled from domestic groundwater wells in Letcher County, Eastern Kentucky in order to characterize its relation to neighboring hydraulically fractured natural gas wells. The studied groundwater shows elevated CH4 concentrations ranging from 0.05 mg/L to 10 mg/L (mean: 4.92 mg/L). However, this is considerably lower compared to the northern Appalachian Basin (e.g., Marcellus Shale) where the CH4 concentrations reach as high as 70 mg/L. The measured δ13C values of CH4 range from -66 ‰ to -16 ‰ (mean: -46 ‰), and δ2H values range from -286 ‰ to -86 ‰ (mean -204 ‰). The occurrence of CH4 is not correlated with proximity to hydraulically fractured natural gas wells. Generally, CH4 occurrence corresponds with Na-Cl-HCO3-rich and more reducing groundwater, and with low concentrations of SO4. Additionally, groundwater in greater proximity to surface mining is more likely to be oxidized and contains less CH4. We infer that mining activities increase the probability of CH4 oxidation in shallow groundwater of Letcher County. Our results suggest that hydraulic fracturing does not increase the likelihood of stray gas migration into the groundwater of eastern Kentucky, although CH4 concentrations can be elevated in this region. Local residents have reported occasional accidents of domestic well combustion as a result of excessive CH4 accumulation. The isotopic values of CH4 suggest an immature thermogenic and mixed biogenic/thermogenic origin rather than thermogenically mature shale gas. More research is needed to explain the distribution of CH4 concentrations. Future studies should include more intensive sampling within a smaller area as the region's mountainous terrain creates relatively isolated valleys, making the chemical and isotopic results spatially heterogeneous.
  • 2018 04 10 GSA_groundwater Appalachia.pdf (3.1 MB)