GROUNDWATERS OF THE EASTERN DESERT OF EGYPT

Chemical and isotopic compositions of groundwater samples from the Eastern Desert of Egypt were analyzed (cations, anions, stable isotope ratios of H, O, and Cl, tritium, and 36-Cl). Samples were collected from production wells, monitoring wells, and hand-dug wells in wadis. Two principal end-member water compositions can be identified from stable isotope compositions: (1) isotopically enriched water, most likely representing recharge by infiltration of rainwater during flash-flood events, is found widely in the Precambrian basement region of the Red Sea Hills, and (2) isotopically depleted water, similar in its chemical and isotopic characteristics to Pleistocene paleowater from the Nubian aquifer, is found in areas where the Nubian sandstone is present. Groundwaters between the Nile Valley and the Red Sea Hills are dominated by the Nubian aquifer end-member. Where the Nubian Aquifer is present beneath alluvial deposits, mixed waters are likely to be produced in high yield. Within the Precambrian terrane of the Red Sea Hills, recent runoff from impermeable basement rocks is concentrated in wadis and may recharge reservoirs contained in thick alluvial deposits or highly fractured rock in shear zones. Chemical compositions of isotopically enriched groundwaters reflect salt enrichment typical of evaporative processes in arid climates. Age of recharge for the isotopically enriched groundwaters is in some cases less than 50 years as indicated by the presence of tritium. Nubian aquifer paleowaters are believed to have ages in excess of 50,000 years based on comparison with 36-Cl and 81-Kr studies in the Western Desert. Further exploration is needed to evaluate the distribution and sustainable production yield of substantial groundwater reserves within the Eastern Desert of Egypt.