Results of the field PPTs will be interpreted using reactive transport modeling based on CORE2D and TOUGHREACT. Numerical simulations will be used to reproduce breakthrough curves for the ions and trace elements so that mechanisms that may control groundwater quality change and mobilization of tracer elements after CO2 is introduced into shallow aquifers can be understood. Different processes will be examined, including ad/desorption of elements from clay and/or iron oxide surfaces that may coat the grains and dissolution of minerals. More detailed solid-phase mineralogy and chemical analyses will be conducted to supplement the reconnaissance data available and to support the modeling analyses. Mass balance will be calculated for injected versus dissolved CO2 in groundwater during the test. This combination of field and modeling analyses will allow determination of potential impact of CO2 on mobilization of major and trace elements and transience of mobilization. This study will provide a valuable test of modeling analyses from previous studies indicating that As and Pb are the primary trace elements mobilized by dissolution of arsenopyrite and galena (Wang and Jaffe, 2004; Apps et al., 2009; Zheng et al., in press).
Data from the field and modeling studies will provide valuable information on which geochemical parameters can be used to fingerprint CO2 leakage into aquifers. Previous studies suggest pH, HCO3, As, and Pb (Carroll et al., 2009; Zheng et al., in press); however, these results are all based on modeling analyses that may not be reliable. Information on fingerprints of CO2 leakage is crucial to developing monitoring systems in USDWs above geologic sequestration sites. Data from these tests will provide information critical to risk assessments of commercial CO2 sequestration sites.