Major ions geochemistry and environmental isotope study of the Nubian aquifer system, Dakhla Oasis, Western Desert, Egypt

Among the hydrochemical studies, the original marine solution of the NaCl t ype and the continental Na2SO4 type of meteoric genesis, are the dominant w ater types in the Nubian sandstone aquifer. The hydrochemical facies of sod ium-calcium-chloride-sulfate are due to leaching, mixing, dilution processe s, and removal of the marine solution by meteoric flows under oxidation-red uction potentialities. The hydrochemical facies and marine-meteoric boundar ies show that the groundwater flows from SW to NE across the Dakhla depress ion. The determination of the saturation index (SI) indicated that anhydrit e, aragonite, calcite dolomite, and magnesite are undersaturated with respe ct to the groundwater, and the minerals might dissolve. The studies of stable isotopes reveal that the groundwater samples are plot ted exactly along the sand-evaporation line (delta D = 2.9* delta(18)O - 54 ). Radioactive isotopes show that tritium values fall below 2.6 Tu, which i ndicates that no recent infiltration water reached the aquifer due to high potential evaporation. The application of carbon-14 dating indicates that t he age of the groundwater is < 14 000 years B.P., i.e. of post-pluvial time .