Uranium content and uranium isotopic disequilibria as a tool to identify hydrogeochemical processes

This paper studies the uranium content and uranium isotopic disequilibria as a tool to identify hydrogeochemical processes from 52 groundwater samples in the province of Granada (Betic Cordillera, southeastern Spain). According to the geological complexity of the zone, three groups of samples have been considered. In Group 1 (thermal waters; longest residence time), the average uranium content was 2.63 +/- 0.16 mu g/L, and U-234/U-238 activity ratios (AR) were the highest of all samples, averaging 1.92 +/- 0.30. In Group 2 (mainly springs from carbonate aquifers; intermediate residence time), dissolved uranium presented an average value of 1.34 +/- 0.13 mu g/L, while AR average value was 1.38 +/- 0.25. Group 3 comes from pumping wells in a highly anthropized alluvial aquifer. In this group, where the residence time of the groundwater is the shortest of the three, average uranium content was 5.28 +/- 0.26 mu g/L, and average AR is the lowest (1.17 +/- 0.12). In addition, the high dissolved uranium value and the low AR brought to light the contribution of fertilizers (Group 3). In the three groups, U-235/U-238 activity ratios were similar to the natural value of 0.046. Therefore, U-235 detected in the samples comes from natural sources. This study is completed with the determination of major ions and physicochemical parameters in the groundwater samples and the statistical analysis of the data by using the Principal Component Analysis. This calculation indicates the correlation between uranium isotopes and bicarbonate and nitrate anions.

Automated summary

This study investigates uranium content and isotopic disequilibria in 52 groundwater samples from the province of Granada in southeastern Spain to identify hydrogeochemical processes. Results show significant differences in uranium content and isotopic ratios among different types of groundwater, which are related to geological backgrounds and hydrological characteristics.