RESUMEN
A baseline hydrochemistry of the above zone aquifer was examined for the potential of CO2 early detection monitoring. Among the major ionic components and stable isotope ratios of oxygen, hydrogen, and carbon, components with a relative standard deviation (RSD) of <10 % for the seasonal variation were selected as relatively stable. These components were tested for sensitivity to the introduction of 0.1 mol/L CO2 (g) using the PHREEQC simulation results. If the relatively stable components were sensitive to the introduction of CO2, then they could be used as indicators of CO2 leakage into the above zone. As an analog to the zone above CO2 storage formation, we sampled deep groundwater, including geothermal groundwater from well depths of 400-700 m below the ground surface (bgs) and carbonated springs with a high CO2 content in Korea. Under the natural conditions of inland geothermal groundwater, pH, electrical conductivity (EC), bicarbonate (HCO3), δ18O, δ2H, and δ13C were relatively stable as well as sensitive to the introduction of CO2 (g), thus showing good potential as monitoring parameters for early detection of CO2 leakage. In carbonated springs, the parameters identified were pH, δ18O, and δ2H. Baseline hydrochemistry monitoring could provide information on parameters useful for detecting anomalies caused by CO2 leakage as measures for early warning.