Assessment of the wastewater effect on the shallow subsurface soil at Farafra Oasis, Egypt, by using geoelectrical and geochemical data analysis

Abstract

Geoelectrical techniques have been used to detect the subsurface stratigraphy and structures around Farafra Oasis, Egypt. 1D inversion approaches have been applied to interpret the geoelectrical data obtained at six vertical electrical soundings (VES’s) using the well-known Schlumberger array with half-current electrode spacing (AB/2) varying from 3 to 400m in successive steps.A preliminary quantitative interpretation of the sounding curves was achieved firstly by using two-layer standard curves and generalized Cagniard graphs. The final models were obtained in 1D using IPI2WIN program. The modeling results were used to construct two geoelectrical sections.Two geoelectrical units were identified: the superficial geoelectrical layer is composed mainly of shale (Dakhla Shale Formation). It is characterized by relatively very low electrical resistivity values (3–5Ωm) with a maximum thickness of about 17.58m.The second layer reveals moderate electrical resistivity values (17–98Ωm). It is extended from the surface layer to the end of the investigated section and represents the Sandstone (upper aquifer) in the study area.