POTENTIAL IMPACTS on FRESHWATER AQUIFERS OF CARBON DIOXIDE LEAKS FROM DEEP GEOSEQUESTRATION

Carbon Capture and Storage employs technologies for separating, transporting and storing carbon dioxide from industrial facilities. If CO₂ is stored broadly, small CO₂ leaks (<0.1%/yr) could pose a risk to overlying potable groundwater in some locations. We sought to characterize this risk by 1) performing laboratory incubations of CO₂ infiltration of four overlying drinking-water aquifers, measuring changes in pH and chemistry; 2) developing methods to select sequestration sites to minimize potential human health risks; and 3) identifying geochemical signatures for early leak detection. Sediment samples from the Mahomet (IL), Ogallala (TX), and unconfined Atlantic coast aquifer systems (VA and MD) were incubated in water with CO₂ for >300 days. CO₂ caused the pH of the water to drop by 1-2 units across all aquifers. All baseline alkali and alkaline metal concentrations increased, but the transition metals Mn, Co, Ni, and Fe generally increased the fastest. However, other transition metal concentrations, including As and Al, decreased in the Mahomet and Ogallala samples, while U and Ba increased. Because Mn, Fe and Ca all increased rapidly with CO₂ additions—at least an order of magnitude above the control—these elements could be early geochemical markers for the presence of a CCS leak.