The geochemical evolution of very dilute CO2-rich water in Chungcheong Province, Korea: processes and pathways.

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]