Hydrogeochemical characteristics of surface water and groundwater in areas underlain by black shales and slates of the Okchon zone, Korea

摘要

The purpose of this study is to investigate the hydrogeochemical characteristics and the potential contamination of surface water and groundwater in areas underlain by black shales and other metasedi-mentary rocks in the Okchon zone, Korea. Surface water and groundwater samples were collected from the Duk-Pyung, Chu-Bu, Bo-Eun, I-Won and Geum-Kwan areas of the Okchon zone, and the in-situ measurement and chemical analysis of dissolved constituents were performed. All water samples have Ca~(2+)-HCO_(3~-) and Ca~(2+)-(Cl~--SO_(4~(2-))) compositions due to the dissolution of calcite and Mg-carbonates and the oxidative dissolution of sulfide minerals from black shale and slates. The increase of concentrations of Ca~(2+), Mg~(2+), HCO_(3~-), Na~+ and SiO_2 from surface water to groundwater indicates progressive water-rock interaction as supported by hydrogeochemical modeling and phase stabilities of related minerals. High concentrations of K~+, Cl~- and NO_(3~-) are also found in groundwater due to the inflow of external contaminants. From the results of statistical analysis, it could be concluded that the factors controlling the hydrogeochemical characteristics of surface water and groundwater are the inflow of external contaminants, the dissolution of carbonates, the weathering of silicates and the oxidation of sulfides.