| dc.description.abstract | Methane (CH₄) in the atmosphere accounts for 18% of the climate warming attributed to greenhouse gases. The majority of CH₄ emitted is due to natural mechanisms (biogenic CH₄), but even the smaller contribution of anthropogenically sourced CH₄ (thermogenic CH₄) will have a deleterious effect on global temperatures. A portion of this human-derived methane stems from the rapid growth in high volume hydraulic fracturing (HVHF) technologies used to procure natural gas from the subsurface. In order to address growing concerns, we measured the flux and carbon isotope composition of CH₄ emitted from the soil into the atmosphere in eastern Tennessee (Morgan
Co.). These measurements were made with cavity ring down spectroscopy (CRDS); CRDS permitted the collection of in situ and rapid (1 Hz) measurements of CH₄ emissions. We designed
our study by making identical sets of measurements at three HVHF wells and four geologically similar corresponding comparison sites, where HVHF activity was absent. The primary objective
was to better understand the strength of the connection between HVHF activity and the increasing concentration greenhouse gases in the atmosphere.
Through measurements made during two different field sessions (10 Oct 2015 and 29 Feb-01 Mar 2016), we found elevated background concentrations (> 2.0 ppm) of CH₄.
Through measurements made during two different field sessions (10 Oct 2015 and 29 Feb-01 Mar 2016), we found elevated background concentrations (> 2.0 ppm) of CH₄ at the test sites relative to the comparison sites. Furthermore, our data, though not significantly different, showed positive CH₄ fluxes (from soil into the atmosphere) at the test sites, whereas CH₄ fluxes were generally negative at comparison sites. These results suggest excess CH₄ in the soil that may be connected
to leakage contributed by HVHF activity. Evidence from stable carbon isotope analysis of the emitted CH₄ supports the conclusion of the presence of thermogenic gas at two of the three wells measured. at the test sites relative to
the comparison sites. Furthermore, our data, though not significantly different, showed positive CH₄ fluxes (from soil into the atmosphere) at the test sites, whereas CH⁴ fluxes were generally negative at comparison sites. These results suggest excess CH₄ in the soil that may be connected to leakage contributed by HVHF activity. Evidence from stable carbon isotope analysis of the emitted CH₄ supports the conclusion of the presence of thermogenic gas at two of the three wells measured. | |
