Groundwater Ages and Flow Paths at a Coastal Waste Repository Site in Korea, Based on Geochemical Characteristics and Numerical Modeling

Groundwater flow paths and groundwater ages at a radioactive waste repository located in a coastal area of South Korea were evaluated using the hydrochemical and hydrogeological characteristics of groundwater, surface water, rain water, and seawater, as well as by numerical modeling. The average groundwater travel time in the top layer of the model, evaluated by numerical modeling and groundwater age (34 years), approximately corresponds to the groundwater age obtained by chlorofluorocarbon (CFC)-12 analysis (26-34 years). The data suggest that the groundwater in wells in the study area originated up-gradient at distances of 140-230 m. Results of CFC analyses, along with seasonal variations in the δ18O and δD values of groundwater and the relationships between 222Rn concentrations and δ18O values and between 222Rn concentrations and δD values, indicate that groundwater recharge occurs in the summer rainy season and discharge occurs in the winter dry season. Additionally, a linear relationship between dissolved SiO2 concentrations and groundwater ages indicates that natural mineralization is affected by the dilution of groundwater recharge in the rainy summer season.