Impacts of CO2 leakage into shallow formations on groundwater chemistry

Abstract Geological storage of CO 2 is one option for mitigating atmospheric emissions of carbon dioxide. However, the injected CO 2 has the possibility of leakage. The leaked CO 2 may move upward into shallow formations and thereby affects shallow groundwater. To investigate this effect, 27 tonnes of gaseous CO 2 was injected into an aquifer about 180 m below a surface. Periodic groundwater samples were studied to identify shift of hydro-chemical parameters, including pH, TDS, ORP, Ca, Mg, Na, HCO 3 , Cl, SO 4 , Pb, Fe, and F. The results indicated that CO 2 dissolution and reaction concurrently reduced aquifer pH levels and increased concentrations of TDS, Ca, Mg, HCO 3 , and F. ORP level and SO 4 concentration remained static. Pb and Fe concentrations were lower than the detection limit 1 mg/L and 0.02 mg/L, respectively. After the CO 2 breakthrough, Cl concentration increased to a stable level slightly higher than the background concentration. The shift in groundwater levels of Ca and Mg was attributed to dolomite (or Mg-rich calcite) and calcite-dominant dissolution processes. Results indicated linear approximations between concentrations of F vs. HCO 3 (slope 0.0036) and F vs. Ca (slope 0.013). Additionally, the TDS and the total molar concentration of Ca and Mg showed linear correlations with increased levels of HCO 3 .