This study evaluated the effects of CO₂ leakage on the geochemical composition of groundwater in various geological media through long-term column experiments. Four columns were set up with soil representing a silicate aquifer; clean sand; a sand and limestone mixture; and alluvium soil, respectively. The experiments were conducted under the same experimental conditions for approximately one year. As the CO₂-saturated synthetic groundwater was introduced into the columns, a decrease in pH and increases in electrical conductivity (EC), alkalinity, and concentrations of cations and trace elements were observed in all geological media. However, different patterns of changes were also observed depending on the mineralogical and physico-chemical characteristics of each material. As the column operation continued, while the pH decreased and low alkalinity values were more evident in the silicate soil and clean sand columns, the carbonate column continued to show high alkalinity and EC values in addition to high concentrations of most cations. The alluvium soil showed distinctive cation-exchange behaviors during the initial introduction of CO₂. The results indicate that changes in the geochemical composition of groundwater will depend on the characteristic of the geological medium such as pH buffering capacity and cation exchange capacity. This study can be useful for monitoring and managing the impacts of CO₂ leakage in various aquifer environments.