Geochemical processes controlling groundwater quality in Pushkar Valley, Rajasthan, India

Knowledge of the geochemical processes controlling the groundwater quality in semi-arid areas is useful to the judicious utilization of the resources available and for preventing further desertification. The investigations presented in this paper highlight the geochemical evolution of groundwater in Pushkar (fresh water lake) Valley, located towards the eastern margin of the Thar desert. The highly saline water is of Na-Cl type. Medium salinity water is of Na-HCO3-Cl type or Ca-Mg-HCO3 type or Ca-Mg-Na-HCO3 type. The data suggests that the groundwater is derived mainly from recharge by rainfall, and has moved through aquifers rich in Na and Cl during regional salinization. Highly saline groundwater with low sulphate content indicates localized SO42- reduction, and that with high sulphate concentration may be related to a long history of evaporation. The hydrochemical analyses indicate that carbonate weathering is predominant and the groundwaters require alkalies (Na+K) which can be supplied by either silicate weathering or by dissolution of alkaline soil salts to balance the carbonate alkalinity. However, contributions of Na from silicate weathering is insignificant.