Chemical and isotopic constraints on the origin of Wadi El-Tarfa ground water, Eastern Desert, Egypt

We evaluated the use of the renewable ground water resources of the Eastern Desert to develop sustainable agriculture in Upper Egypt, an alternative that could alleviate some of Egypt's dependence on water from the Nile River, Ground water from shallow aquifers in the Eastern Desert of Egypt, near the intersection of Wadi El-Tarfa and the Nile River, was analyzed for chemical compositions, stable isotope ratios, and tritium activities. The ground water has a range in total dissolved solids of 300 to 5000 mg/L, Values of delta D and delta(18)O range from -10 to +34 parts per thousand and -2 to +5.2 parts per thousand, respectively, and defines a line having a slope of 5.7 that intersects the meteoric water line at about delta D = -15 parts per thousand on a plot of delta D versus delta(18)O. These findings indicate that the water might have been derived by a combination of evaporation of and salt addition to regional precipitation. Only one sample could have been derived directly by evaporation and transpiration of modern Nile River mater. Salinization of the ground water could have occurred through dissolution of marine aerosol dry fallout, carbonate minerals, gypsum, and other trace evaporitic minerals at and near the ground surface. Tritium activities ranged from 0.04 to 12.9 TU (tritium units), indicating that all but one of the samples were derived at least partly from precipitation that occurred within the last 45 years. These data indicate that Nubian Aquifer paleowater is not a significant component of the shallow aquifers of this portion of the Eastern Desert. The most likely source of this ground water is sporadic flash flood events yielding locally voluminous recharge that accumulates in coarse sediments and fractured rock beneath alluvial channels. The magnitude of this renewable ground water resource and its potential for supporting sustainable agriculture require further investigation.