Changes in geochemical and carbon isotopic compositions during reactions of CO2-saturated groundwater with aquifer materials

[Display omitted] •CO2 leakage causes increases of cation concentrations and alkalinity.•Spatial aqueous chemistry provides insights regarding reaction mechanisms.•Carbon isotopic composition changes as aquifer materials are dissolved.•A carbon isotopic fractionation modeling is a useful tool for detecting CO2 leakage. This study evaluated impacts of CO2 leakage on a shallow groundwater system through laboratory column experiments, which simulated field push-and-pull and natural-gradient tests. The sediment and groundwater were collected from the Environmental Impact evaluation Test (EIT) facility in the Korea CO2 Storage Environmental Management (K-COSEM) test site, and temporal and spatial changes in aqueous chemistry at different stages were monitored. The results showed that as CO2-saturated groundwater was passing through the columns, the concentrations of cations, electrical conductivity (EC), and alkalinity increased, indicating dissolution of primary silicate minerals and perhaps trace amounts of undetected carbonate minerals. There was a significant difference in carbon-13 isotope ratios between the background and CO2-saturated groundwater, and isotopic composition change (with an enrichment factor of 1‰) occurred as CO2-saturated groundwater reacted with the aquifer materials. This study suggests that detailed temporal and spatial geochemical changes are helpful providing insights into the underlying geochemical mechanisms. Also, the isotopic fractionation modeling applied in this study is useful for detecting a small degree of carbon fractionation during the reactions of leaked CO2 and aquifer materials.