Factors controlling the spatial and temporal variability in groundwater 222Rn and U levels

Abstract

Radon (222Rn) and uranium (U) measurements were conducted in 98 groundwater samples in Yongin area, Korea to identify the factors controlling their levels and spatial distributions. Groundwater samples were obtained from the different depth of wells used for drinking water and irrigation. 222Rn and U concentrations were measured using a liquid scintillation counter (LSC) equipped with a pulse-shape analyzer and inductively coupled plasma mass spectrometers (ICP-MS), respectively. Large variations were observed in groundwater concentrations of 222Rn and U, ranging between 0.6 ± 0.1-673.7 ± 8.7 Bq L-1 and 0.02-117.00 μg L-1, respectively. Correlation analysis revealed no significant relationship between field parameters (temperature, electrical conductivity, pH, and dissolved oxygen) and 222Rn or U concentrations. The fact that 222Rn and U concentrations were higher in granite areas than gneiss areas suggests that lithology plays a significant role in controlling the levels and spatial distributions of the two radionuclides. Furthermore, groundwater 222Rn and U behaviors have been affected by the existence of fault and well depth. Especially, the temporal monitoring of 222Rn suggests that 222Rn concentrations in the shallow groundwater may be controlled by variation in rainfall and artificial effects such as water curtain cultivation conducted in the winter season in this study area.