Geochemical decoupling between dissolved uranium and gamma radiation.

Monitoring dissolved uranium in groundwater is essential for protecting drinking-water quality, particularly in regions with elevated natural radioactivity. This study reveals spatial and geochemical decoupling between gamma radiation levels and dissolved uranium concentrations across the Chittorgarh aquifer system (Rajasthan, India). The analysis of 96 groundwater samples spanning Precambrian metamorphic, granitic, and sedimentary geological formations revealed that dissolved uranium varied nearly 100-fold (0.51-51.3 μg/L) whereas ambient gamma radiation showed relatively limited variability (65-131 nSv/h, mean 93.6 ± 13.8 nSv/h). Geostatistical mapping showed that the ambient gamma radiation dose-rate pattern may reflect contributions from the surrounding geological matrix, whereas dissolved uranium transport was associated with local mineralogical and hydrochemical conditions. The results revealed no statistically significant relationship between ambient gamma radiation dose rate and dissolved uranium concentration across the investigated sampling locations. Under the hydrogeological conditions and measurement approach applied in the Chittorgarh aquifer system, ambient gamma radiation dose-rate measurements alone did not reliably reflect spatial variations in dissolved uranium concentration. Therefore, direct uranium analysis remains necessary for assessing groundwater uranium occurrence in the study area.