Human impacts on groundwater flow and contamination deduced by multiple isotopes in Seoul City, South Korea.

The influence of human activities on the flow system and contamination of groundwater were investigated in Seoul City, South Korea, one of the largest Asian cities, using a combination of isotopes (deltaD, T, delta15N, delta18O, delta34S, and 87Sr/86Sr). Eighteen representative groundwater and river water samples, which were collected over a wide area of the city, were compared with previously reported data. The distribution of stable isotopes (deltaD and delta18O) with groundwater potential data shows that recharged groundwater from either the surrounding mountainous area as well as the Han River and other surface streams discharged towards the northern-central part of the city, where a subway tunnel pumping station is located. It is suggested from T values (3.3 to 5.8 T.U.) that groundwater was recharged in the last 30 to 40 years. The delta34S and delta15N of SO4(2-) and NO3- data were efficiently used as indicators of contamination by human activities. These isotopes clarified that the contribution of anthropogenic contaminants i.e., industrial and household effluents, waste landfills, and fertilizers, are responsible for the enrichment by SO4(2-) (>30 ppm as SO4(2-)) and NO3- (>20 ppm as NO3-) of groundwater. The 87Sr/86Sr values of groundwater vary (0.71326 to 0.75058) in accordance with the host rocks of different origins. Mineral elements such as Ca are also suggested to be derived naturally from rocks. The groundwater under Seoul City is greatly affected by transportation of pollutants along the groundwater flow controlled by subway tunnel pumping, contributing to the degradation of water quality in urbanized areas.