Hydrogeochemistry of seepage water collected within the Youngcheon diversion tunnel, Korea: source and evolution of SO₄‐rich groundwater in sedimentary terrain

Abstract

Abstract:In the Youngcheon Diversion Tunnel area, South Korea, 46 samples of tunnel seepage water (TSW) and borehole groundwater were collected from areas with sedimentary rocks (mainly sandstone and shale) and were examined for hydrogeochemical characteristics. The measured SO 4 concentrations range widely from 7Ð7 to 942Ð0 mg/l, and exceed the Korean Drinking Water Standard (200 mg/l) in about half the samples. The TDS (total dissolved solid) content generally is high (171-1461 mg/l) from more shale-rich formations and also reflects varying degrees of water-rock interaction. The water is classified into three groups: Ca-SO 4 type (61% of the samples collected), Ca-SO 4 -HCO 3 type (15%) and Ca-HCO 3 type (24%). The Ca-HCO 3 type water (mean concentrations D 369 mg/l Ca, 148 mg/l HCO 3 and 23 mg/l SO 4 ) reflected the simple reaction between CO 2 -recharged water and calcite, whereas the more SO 4 -rich nature of Ca-SO 4 type water (mean concentrations D 153 mg/l Ca, 66 mg/l HCO 3 and 416 mg/l SO 4 ) reflected the oxidation of pyrite in sedimentary rocks and fracture zones. Pyrite oxidation resulted in precipitation of amorphous iron hydroxide locally within the tunnel as well as in high concentrations of Ca (mean 153 mg/l) and Na (mean 49 mg/l) for TSW, and is associated with calcite dissolution resulting in pH buffering. The pyrite oxidation required for the formation of Ca-SO 4 type water was enhanced by the diffusion of oxygenated air through the fractures related to the tunnel's construction. The subsequent outgassing of CO 2 into the tunnel resulted in precipitation of iron-bearing carbonate.

Hydrogeochemistry of sodium-bicarbonate type bedrock groundwater in the Pocheon spa area, South Korea: water–rock interaction and hydrologic mixing

“…However, little is known about the relationship between hydrochemical characteristics of the groundwater and hydrogeologic conditions in the aquifer (Yun et al, 1998;Chae et al, 2001;Choi et al, 2005). In this study, we performed a hydrogeochemical and environmental isotope study on bedrock groundwaters in the Pocheon spa area (Fig.…”

Reaction path modeling of hydrogeochemical evolution of groundwater in granitic bedrocks, South Korea

“…In South Korea, previous studies on the hydrogeochemistry of shallow and deep groundwaters in crystalline bedrocks have been mostly performed at the local scale for the purpose of groundwater and geothermal resource development (Chae et al, 2001(Chae et al, , 2006aKim et al, 2005;Park et al, 2006;Yun et al, 1998). Researches to evaluate the potential of these bedrocks to become safe repository sites for long-lived radioactive waste have started only recently (Koh et al, 1996).…”