Geochemical sensitivity to CO 2 leakage: detection in potable aquifers at carbon sequestration sites

Various approaches to groundwater monitoring for CO 2 leakage detection and potential impacts of groundwater quality in the above potable aquifers at geological carbon sequestration sites have been reported in literature and briefly reviewed in this study. Although geochemical para‐meters have been proposed as indicators of CO 2 leakage in potable aquifers, assessing sensitivity of geochemical parameters to CO 2 leakage in groundwater is needed. In this study, we present a methodology, using a geochemical model, to simulate responses of aqueous geochemistry to CO 2 leakage into a potable aquifer and then to assess sensitivities of the proposed monitoring geochemical parameters based on their relative changes to initial values. The geochemical model was used to simulate CO 2 leakage into carbonate‐poor and carbonate‐rich aquifers. Results of calculated sensitivities show that dissolved CO 2 and dissolved inorganic carbon in groundwater are most sensitive to CO 2 leakage in all settings. Alkalinity is moderately sensitive, with the best response in the presence of carbonates in the aquifer sediments while groundwater pH shows best response in the aquifer sediments with little carbonates. Impacts of initial (or baseline) groundwater chemistry on sensitivity of geochemical parameters to CO 2 leakage, compared to impacts of aquifer mineralogy, appear to be minor. For monitoring purpose, dissolved CO 2 and dissolved inorganic carbon are better indicators than pH and alkalinity in potable aquifers at geological carbon sequestration sites.