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A geochemical study was carried out on the CO2-rich water occurring in granite areas of Chungcheong Province, Korea. In this area, very dilute and acidic CO2-rich waters [62–242 mg l−1 in total dissolved solid (TDS), 4.0–5.3 in pH; group I) occur together with normal CO2-rich waters (317–988 mg l−1 in TDS, 5.5–6.0 in pH; group II). The concentration levels and ages of group I water are similar to those of recently recharged and low-mineralized groundwater (group III). Calculation of reaction pathways suggests that group I waters are produced by direct influx of CO2 gas into group III type waters. When the groundwater is injected with CO2, it develops the capacity to accept dissolved solids and it can evolve into water with very high solute concentrations. Whether the water is open or closed to the CO2 gases becomes less important in controlling the reaction pathway of the CO2-rich groundwater when the initial pco2 is high. Our data show that most of the solutes are dissolved in the CO2-rich groundwater at pH > 5 where the weathering rates of silicates are very slow or independent of pH. Thus, groundwater age is likely more important in developing high solute concentrations in the CO2-rich groundwaters than accelerated weathering kinetics because of acidic pH caused by high pco2. [ABSTRACT FROM AUTHOR]