Recent Recharge Possibilities Determination of the Pleistocene Aquifer System of Wadi El-Assiuti Basin, Egypt Using Hydrogeochemical and Environmental Isotopic Criteria

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"Wadi El-Assiuti is one of the largest dry wadis in Middle Egypt. It comprises prolific groundwater potentialities and suitable lands for agricultural expansion. Twenty one groundwater samples are recently collected from the drilled water wells tapping the Pleistocene groundwater aquifer. The groundwater salinity values vary generally from 580 mg/l to 2445 mg/l indicating fresh to brackish water. The variation in water genesis could reflect the diversity of the recharge sources for the Early Pleistocene aquifer. The resistivity method is used where thirty vertical electrical soundings are measured in the field. It was able to delineate the groundwater aquifers and some concealed normal faults. The isotopic results of the collected surface and groundwater samples are widely varied from -8.9 to 2.81 ‰ for oxygen-18 and from -61.07 to 21.11 ‰ for deuterium. Almost 86 % of these samples fall in the depleted isotopic range, whereas the remaining percentage (14 %) is gradually enriched. Correlating the data points with respect to the Global Meteoric Water Line (GMWL) indicted the distribution of these points below the global line. The low slope and intercept values obtained from this correlation addresses the old origin of the main bulk of groundwater, which is represented by 86 % of samples. These samples carry the depleted isotopic signature of the paleowater characterizing the Eastern Desert of Egypt. The replenishment source of this water for the wadi proper could be from the local rainfalls on the upstream reaches of Wadi E-Assiuti, in addition to the underlying Nubia aquifer through a direct contact along deep seated faults. Towards the western reaches, at the entrance of the wadi (Nile Valley), the aquifer is almost recharged by the River Nile. The 14C age determination for two samples indicated that the Pleistocene water of Wadi El-Assiuti is mostly paleowater with a significant portion of relatively recent water recharging the aquifer from the rainfalls of the Red Sea mountainous area, in addition to the local ones."