『Abstract
　The nitrate of groundwater in the Gimpo agricultural area, South Korea, was characterized by means of nitrate concentration, nitrogen-isotope analysis, and the risk assessment of nitrogen. The groundwaters belonging to Ca-(Cl+NO3) and Na-(Cl+NO3) types displayed a higher average NO3^- concentration (79.4 mg/L), exceeding the Korean drinking water standard (＜44.3 mg/L NO3^-). The relationship between δ¹⁸O-NO3^- values and δ¹⁵N-NO3^- values revealed that nearly all groundwater samples with δ¹⁵N-NO3^- of +7.57 to +13.5‰ were affected by nitrate from manure/sewage as well as microbial nitrification and negligible denitrification. The risk assessment of nitrate for groundwater in the study area was carried out using the risk-based corrective action model since it was recognized that there is a necessity of a quantitative assessment of health hazard, as well as a simple estimation of nitrate concentration. All the groundwaters of higher nitrate concentration than the Korean drinking water standard (＜44.3 mg/L NO3^-) belonged to the domain of the hazard index ＜1, indicating no health hazard by nitrate in groundwater in the study area. Further, the human exposure to the nitrate-contaminated soil was below the critical limit of non-carcinogenic risk.

Keywords: Nitrate; Groundwater; Nitrogen isotope; Agricultural area; Geochemistry; Risk assessment』

Introduction
Study area
Methods of sampling and chemical analyses
Results and discussion
　Nitrate contamination and origins of the groundwater
　Risk assessment of nitrate in groundwater
Conclusions
Acknowledgments
References