Geologic carbon sequestration could significantly impact water utilities if CO2 leaks into USDWs. EPA rules rely on modeling analyses to assess impacts of CO2 on groundwater quality; because of limitations to modeling; however, a more comprehensive evaluation of impacts based on integrated modeling, laboratory, and field studies should be used. If CO2 leakage into USDWs mobilizes trace metals, a large problem for water utilities could be created because the low MCLs for As and other trace metals could be exceeded. We need to better understand sources and mobilization mechanisms of trace metals and how CO2 may impact these processes.
Because abandoned wells could serve as primary pathways for upward movement of CO2 and brines from storage reservoirs, more detailed information on location and depths of such wells is essential to preclude CO2 leakage into USDWs. In addition, brine leakage into aquifers could also mobilize metals in aquifers. Previous studies in the High Plains aquifer in Texas show that changing water chemistry from a calcium-bicarbonate to sodium-chloride type mobilizes As and other metals caused by the counterion effect (Scanlon et al., 2009). Information on abandoned wells is essential to preventing inadvertent cross-contamination of USDWs from brines and other contaminants. Although CO2 plumes resulting from leakage from sequestration sites can displace saline formations into existing USDWs—contaminating the freshwater aquifer—or displace the USDWs, modeling analyses by Nicot (2008) suggest that such a problem should be negligible for typical Gulf Coast aquifers.