Correspondence/Rebuttal pubs.acs.org/est
Comment on “Geochemical Implications of Gas Leakage associated with Geologic CO2 StorageA Qualitative Review”
T
he critical review by Harvey et al.1 summarizes the current knowledge about the geochemical impact of a CO2 intrusion into potable shallow aquifers. Harvey et al.1 identify the unknown CO2 leakage rate as one important factor influencing geochemical processes in groundwater. There seems to be the general assumption that CO2 will intrude into thick aquifers at low leakage rates. Hence, the CO2 dissolves completely in the groundwater and an increasing leakage rate causes enhanced aqueous CO2 concentrations which can intensify geochemical reactions. However, in confined groundwater systems, which are typically used for drinking water supply, the development of a separate CO2 gas phase is much more likely.2,3 In confined aquifers the CO2 gas phase rises buoyancy driven from the leakage location at the bottom of the aquifer to the top. It will accumulate below the aquitard, spread in direction of the steepest inclination, and potentially pool in an anticlinal structure. The thickness of these gas phase bodies underneath impermeable layers outside an anticlinal structure can be very thin (
