Assessment of groundwater contamination using geographic information systems

In this study two sites were selected in order to investigate groundwater contamination and spatial relationships among groundwater quality, topography, geology, landuse and pollution sources. One site is the Asan area, an agricultural district where pollution sources are scattered and which is mainly underlain by granite of Cretaceous age. The other site is the Gurogu area of Seoul city, an industrial district where an industrial complex and residential areas are located and which is mainly underlain by gneiss of Precambrian age. Groundwater samples collected from these districts were analysed for chemical constituents. An attribute value files of chemical constituents of groundwater and the spatial data layers were constructed and pollution properties were investigated to establish out spatial relationships between the groundwater constituents and pollution sources using geographic information systems (GIS). Relatively high contents of Si and HCO3- in the groundwater from the Asan area reflect the effect of water-rock interaction whereas high contents of Cl-, NO3- and Ca2+ in the groundwater from the Gurogu area are due to the pollution of various sources. The significant seasonal variation of SiO2, HCO2- and Ca2+ contents, and that of Ca2+ content were observed in the Asan and the Gurogu areas, respectively. Seasonal variation of pollutants such as Cl-, NO3- and SO42- was not observed in either area. Pollution over the critical level of the Korean drinking water standard has been investigated from 15 sampling sites out of 40 in the Asan area, and 33 sampling sites out of 51 in the Gurogu area. Pollution by NO3-, Cl-, Fe2+, Mn2+, SO42- and Zn2+ in the groundwater from the industrial district (Gurogu area) and that of NO3-, SO42- and Zn2+ in the groundwater from the agricultural district (Asan area) were observed. The principal pollutant in both areas is NO3-. Deep groundwater from the Asan area is not yet contaminated with NO3- except for one site, but most of the shallow groundwater site occurring near the potential point sources is seriously contaminated. From the result of buffering analysis, it seems clear that factories and stock farms are the principal pollution sources in the Asan area. The groundwater from the Gurogu area has already been seriously polluted considering the fact of NO3- contamination of deep groundwater. Chlorine pollution of shallow groundwater in the Gurogu area was also observed. Spatial relationship between pollution level and its source was clarified in this study by using GIS, which will be applicable to the effective management of groundwater quality.