Geochemical Characterization of Rock-Water Interaction in Groundwater at the KURT Site

Abstract

Geochemical composition of fracture filling minerals and groundwater was investigated to characterize geochemical characteristics of groundwater system at the KURT site. Minerals such as calcite, illite, laumontite, chlorite, epidote, montmorillonite, and kaolinite, as well as I/S mixed layer minerals were detected in the minerals extracted from the fracture surfaces of the core samples. The groundwater from the DB-1, YS-1 and YS-4 boreholes showed alkaline conditions with pH of higher than 8. The electrical conductivity (EC) values of the groundwater samples were around 200 S/cm, except for the YS-1 borehole. Dissolved oxygen was almost zero in the DB-1 borehole indicating highly reduced conditions. The Cl-concentration was estimated around 5 mg/L and showed homogeneous distribution along depths at the KURT site. It might indicate the mixing between shallow groundwater and deep groundwater. The shallow groundwater from boreholes showed Ca-HCO 3 type, whereas deep groundwater below 300 m from the surface indicated Na-HCO 3 type. The isotopic values observed in the groundwater ranged from-10.4 to-8.2 for 18 O and from-71.3 to-55.0for D. In addition, the isotope-depleted water contained higher fluoride concentration. The oxygen and hydrogen isotopic values of deep groundwater were more depleted compared to the shallow groundwater. The results from age dating analysis using 14 C indicated relatively younger (2000 6000yr old) groundwater compared to other european granitic groundwaters such as Stripa (Sweden).