Study on groundwater quality in parts of Rajasthan with special reference to uranium contamination

Issues of declining water levels and groundwater contamination are reported in parts of Rajasthan in recent times. One of the major contaminants present in the groundwater was found to be uranium. This study was carried out to determine the level of uranium contamination in Jaipur and Dausa districts of Rajasthan state and to evaluate its correlation with physicochemical parameters and stable isotopes (δ2H and δ18O). Results indicate that the dissolved uranium concentration ranges from 5 to 145 µg/l with an average concentration of 49 µg/l. Correlations of dissolved uranium with depth, physico-chemical parameters and stable isotopes were used for deducing the source of U in groundwater and release mechanism. Stable isotope data indicate three major sources of groundwater recharge; (i) evaporative surface water or contribution from irrigational return flow, (ii) evaporated rainwater and (iii) direct precipitation without evaporation. Vertical correlation of EC in groundwater indicates flushing of the local groundwater by regional groundwater flows. No correlation was observed between dissolved U and the corresponding δ18O composition. Hydrochemical and isotopic results infer that leaching of minerals present in the subsurface is the main cause for elevated levels of U in the study area.