Multivariate and spatial statistical analysis of radon and uranium distribution in groundwater from the central-western region of Gangwon Province, Korea

초록

This study statistically investigated the behavior of radon and uranium in 249 groundwater samples collected from the Chuncheon-Hongcheon area of Gangwon State, Korea. Both substances showed right-skewed distributions, and elevated concentrations were generally observed in granitic areas. Radon concentrations by lithology followed the order of granite > igneous rock > alluvium > metamorphic rock > sedimentary rock. The relatively high radon levels in alluvium were interpreted to reflect its spatial arrangement, as many alluvial deposits are adjacent to or linearly intercalated with granite bodies. In addition, elevated concentrations of both radionuclides were also identified near lithologic boundaries adjoining granite, suggesting that spatial proximity to granite is an important controlling factor. Approximately 77% of the high-radon sites (>= 148 Bq/L) were concentrated in areas underlain by Mesozoic granitic rocks. Radon was interpreted to primarily reflect geological signals derived from uranium-bearing minerals associated with these granites, including biotite, muscovite, zircon, and apatite. Its associations with Si and U further supported this geology-dominant pattern. Spatial clustering analysis focusing on sites with radon concentrations >= 148 Bq/L identified high-high (HH) clusters, indicating priority areas for monitoring and management. In contrast, high-uranium sites (>= 30 mu g/L; n = 7) were limited to only a few locations. This suggests that even in lithologies with high uranium contents, such as two-mica granite, lithology alone does not necessarily lead directly to high dissolved uranium concentrations in groundwater. Rather, uranium enrichment appears to occur only when the source potential of the host rock is accompanied by favorable hydrogeochemical conditions, such as oxidizing environments, bicarbonate availability, pH, and weathering reactions. Overall, radon behavior primarily reflects the distribution of source rocks containing uranium-bearing minerals, especially granite, together with their associated spatial structure, whereas uranium appears to be selectively mobilized and enriched only where suitable hydrogeochemical conditions are superimposed on this geological background.

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