Potential Impacts of Leakage from Deep CO2 Geosequestration on Overlying Freshwater Aquifers

Carbon Capture and Storage may use deep saline aquifers for CO2 sequestration, but small CO2 leakage could pose a risk to overlying fresh groundwater. We performed laboratory incubations of CO2 infiltration under oxidizing conditions for > 300 days on samples from four freshwater aquifers to 1) understand how CO2 leakage affects freshwater quality; 2) develop selection criteria for deep sequestration sites based on inorganic metal contamination caused by CO2 leaks to shallow aquifers; and 3) identify geochemical signatures for early detection criteria. After exposure to CO2, water pH declines of 1-2 units were apparent in a I aquifer samples. CO2 caused concentrations of the alkali and alkaline earths and manganese, cobalt nickel, and iron to increase by more than 2 orders of magnitude. Potentially dangerous uranium and barium increased throughout the entire experiment in some samples. Solid-phase metal mobility, carbonate buffering capacity, and redox state in the shallow overlying aquifers influence the impact of CO2 leakage and should be considered when selecting deep geosequestration sites. Manganese, iron, calcium, and pH could be used as geochemical markers of a CO2 leak, as their concentrations increase within 2 weeks of exposure to CO2.