Geophysical and hydrogeochemical investigations of Nubian sandstone aquifer, South East Sinai, Egypt: Evaluation of groundwater distribution and quality in arid region

Abstract

The expansion in human activities, the absence of running water in South Sinai province in northeastern Egypt and the high cost of seawater desalination render groundwater the essential source for potable water in this arid region. This contribution represents the integration of geophysical and hydrochemical investigations to delineate groundwater distribution and evaluate the water quality of the Cretaceous sandstone aquifer of Wadi Barqa area, Southeastern Sinai. The locations of sites, suitable for geophysical sounding measurements, were selected using digital elevation map. Vertical electrical sounding (VES) and time-domain electromagnetic sounding (TEM) measurements were carried out to determine the depth and thickness of the unsaturated and water-saturated zones as well as the groundwater quality, which were verified by calibrating the estimated electrical resistivity values with the design and logs data of eleven drilled wells next to the sites of geophysical soundings. The VES and TEM data revealed the presence of relatively thick zoned aquifer, overlain by unsaturated zone with variable thickness (83-65 m). The upper aquifer zone (25–43 m thick) is characterized by higher resistivity values (16–163 Ohm.m), reflecting fresh water signature, whereas the lower aquifer zone (122–150 m thick) has lower resistivity values (16–24 Ohm.m), indicating saturation with semi-fresh to relatively brackish water. Water samples, collected from wells taping the Nubian Sandstone aquifer, have average total dissolved solids (TDS) value of 544 mg/l. The hydrochemical parameters of these samples are consistent with NaCl water type with the majority of samples belonging to high salinity with low sodium categories. This suggests that the groundwater of the aquifer was dominated by old meteoric origin. The compositional characteristics of the groundwater of the investigated aquifer indicate suitability for domestic and irrigation purposes. However, due to the arid nature of Southeastern Sinai province, it is recommended to use this groundwater as potable water.