GEOLOGY
Measuring surface and shallow gas flux and composition as a prelude to geologic carbon sequestration in eastern
Kentucky. THOMAS (MARTY) PARRIS*, MICHAEL P. SOLIS, and KATHRYN G. TAKACS, Kentucky
Geological Survey, University of Kentucky, Lexington, KY 40506.
Geologic carbon sequestration, the process of capturing and injecting CO 2 into subsurface reservoirs, is
being evaluated as a mechanism to mitigate anthropogenic greenhouse gas emissions in Kentucky and worldwide.
The goal is to sequester CO2 underground for geologically significant periods. Monitoring and verifying the fate of
injected CO2 is critical and requires a portfolio of monitoring technologies, including soil gas geochemistry. The
motivation for using soil gas geochemistry is, should injected CO2 leak (microseepage), it might cause a
perturbation that is geochemically distinct compared to background soil gas flux and composition. Measurements
were made that characterize background soil gas flux and composition at 29 locations, having various degrees of
human disturbance, distributed among four representative sites in eastern Kentucky.
Fluxes of CO2 and CH4 at the soil-atmosphere interface were measured using closed chamber methods.
Bulk and isotopic composition of atmospheric and surface and shallow soil gases were measured using gas
chromatography and mass spectrometry. Soil gas CO2 concentrations down to 100 cm were one to two orders of
magnitude greater than atmospheric (390 to 400 ppmv). The difference provides the driving force for CO2 flux from
the soil to the atmosphere. High CO2 concentration in the soil is likely the product of root and microbe respiration,
which is supported by depleted carbon isotope values (δ13C= −21 to −24‰). In contrast, soil gas CH4 values were
typically an order of magnitude lower than atmospheric (~1.9 ppmv), thereby providing a driving force for CH 4 flux
from the atmosphere into the soil.