Potential for a Process-based Monitoring Method above Geologic Carbon Storage Sites using Dissolved Gases in Freshwater Aquifers

The process-based method is a new technique for monitoring CO2 storage permanence in the vadose zone above geologic carbon storage (GCS) sites. This method uses ratios of coexisting gas species to understand geochemical processes rather than comparing CO2concentrations with large baseline data sets, thereby making monitoring more efficient. In the vadose zone, ratios among coexisting gases (CO2, O2, N2 and CH4) have been used to distinguish biologic respiration, water-rock-CO2 interaction, and methane oxidation from a leakage signal. We report the preliminary results of a feasibility test conducted in July 2012 at the Zero Emission Research and Technology Center (ZERT) controlled release site in Montana, USA to discern whether the method could be applied to dissolved gases in groundwater, thereby enhancing groundwater monitoring. Preliminary results are favorable, making the process- based approach potentially useful for monitoring shallow freshwater aquifers above GCS sites.