Nitrate vulnerability of groundwater in Jeju Volcanic Island, Korea

Groundwater is the sole source of water for about 670,000 residents of Jeju Island, which is a volcanic Korean island. Since the 1990s, nitrate contamination of groundwater has emerged as a major environmental issue. To ensure the sustainability of water resources, this study aimed to develop a vulnerability model for nitrate contamination as a preventive measure. Based on intrinsic vulnerability determined using the DRASTIC model, the effects of anthropogenic parameters related to NO₃ sources and groundwater use (land use and the hydraulic gradient, respectively) on contamination were tested using a geographic information system (GIS). The correlation between groundwater nitrate distribution and vulnerability was considerably stronger compared to the DRASTIC method, with the correlation coefficients (r) increasing from -0.048 to 0.562 and -0.069 to 0.481 in the western and eastern regions, respectively. However, in the southern and northern regions, nitrate concentrations in groundwater are low, likely due to the heavily paved land surface that resulted from urbanisation, such that groundwater vulnerability appeared negligible. To prevent further nitrate contamination in coastal groundwater, management policies for land use and groundwater exploitation should be enacted along with continuous groundwater monitoring at the regional scale.