Characterization of the groundwater flow and nitrate contamination using 3H/3He and CFCs residence time in an agricultural area

Tritium, CFCs, and dissolved gases in groundwater were analyzed in combination with hydrogeological data to determine the groundwater residence time and to understand the mechanisms controlling the hydrology of an agricultural site, Chuncheon (Korea). The apparent ages estimated from concentrations of CFCs ranged 15 to 25 years and the apparent ages based on tritium/helium-3 (3H/3He) were in the range of 2-18 years. The concentrations of reconstructed initial tritium (measured 3H + measured tritiogenic 3He) and CFC-113 were compared to estimate groundwater mixing using simple mixing models; piston-flow model, exponential mixing, and binary-mixing model. A conceptual model of groundwater flow using measured apparent 3H/3He and CFC- 113 age will be developed to understand the hydrological processes of the site. The combined use of the hydrogeochemical data and the groundwater residence time will be evaluated to characterize the hydrology of the study area and to assess nitrate contamination history. The residence time from environmental tracers can supply useful information on the groundwater recharge and the contaminant transport history in aquifer system.