Hydrochemical variations in selected geothermal groundwater and carbonated springs in Korea: a baseline study for early detection of CO₂ leakage

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.