Effects of groundwater residence time and recharge rate on nitrate contamination deduced from δ18O, δD, 3H/3He and CFCs in a small agricultural area in Chuncheon, Korea

Stable isotopes of water, chlorofluorocarbon (CFCs), and 3H/3He were applied in combination with hydrogeochemical data to analyze recharge patterns and nitrate contamination of shallow groundwater systems in a small agricultural area, Yupori, Chuncheon (Korea), where the eastern part is on hill slopes and the western part is low lands. The values of δ18O and δD indicated that groundwater is derived mainly from summer precipitation, which is more pronounced in the western part than in the eastern part. The apparent groundwater ages using CFC-113 and 3H/3He ranged from 13 to 31 yr, and are younger in the western part than in the eastern part. Dispersion models fit concentrations of 3H and CFC-113 for most wells of the eastern part with intermediate dispersion parameters. Nitrate concentrations were higher in the western part than the eastern part due to the land use pattern and topography. Stable isotopes of water and groundwater ages indicated that higher recharge rate affected by multiple sources of contamination is dominant in the western part whereas limited recharge with weak nitrate sources is considerable in the eastern part. This groundwater flow pattern corresponds to the different nitrate concentrations in the western and the eastern part. Groundwater residence time and recharge rate play an important role in the spatial distribution of NO3 concentration in the study area as well as land use pattern.