PREDICTION AND EVALUATION OF HYDROGEOCHEMICAL CHANGES IN SHALLOW GROUNDWATER SYSTEMS DUE TO GEOLOGIC STORAGE AND LEAKAGE OF CARBON DIOXIDE

The objective of this study is to predict and evaluate quantitatively impacts of leakage of deep groundwater (brine), which may occur during and after geologic storage of carbon dioxide, on hydrogeochemistry of shallow groundwater systems (groundwater and aquifer). In order to achieve this objective, a series of numerical modeling of hydrogeochemical changes in a shallow groundwater system under leakage of deep groundwater was performed using a non-isothermal multiphase reactive hydrogeochemical transport model TOUGHREACT (Xu et al., 2004, 2006, 2012). In this study, abandoned wells and faults are considered as main leakage pathways for deep groundwater leakage into the shallow groundwater system. The initial chemical compositions of deep and shallow groundwater are obtained from the data of the Pohang Basin, Korea. The initial mineralogical composition of the shallow aquifer is also obtained from the data of the Pohang Basin, Korea and the work of Birkholzer et al. (2008). The numerical modeling results show that the pH and TDS (total dissolved solids) and the concentrations of Ca²⁺, Mg²⁺, Na⁺, SO₄^2-, Cl^-, and HCO₃^- of the shallow groundwater increase, whereas the concentrations of Fe²⁺ and AlO₂^- decrease during the deep groundwater leakage period in terms of mixing of deep groundwater and shallow groundwater. However, the values of these water quality indicators remain below the drinking water standards of Korea except that of Fe²⁺ since the concentration of Fe²⁺ is initially exceed the drinking water standard. The numerical modeling results also show that the mineralogical composition of the shallow aquifer almost does not change during the deep groundwater leakage period because deep groundwater leakage cannot cause a pH decrease, which is essential for dissolution of the primary minerals of the shallow aquifer. These numerical simulation results suggest that deep groundwater leakage have less impacts on hydrogeochemistry of shallow groundwater systems compared with CO₂ leakage because CO₂ leakage cause significant pH decrease and thus dissolution of the primary minerals of the shallow aquifer. This work was supported by the Geo-Advanced Innovative Action (GAIA) Program funded by the Korea Environmental Industry and Technology Institute (KEITI), Ministry of Environment, Republic of Korea.