Application of Multi-dimensional Electrical Resistivity and Electromagnetic Induction Techniques to Explore the Groundwater Occurrences at El-Salloum Basin, Northwestern Coast, Egypt

Abstract

Saltwater intrusion into shallow coastal aquifers, exacerbated by excessive groundwater withdrawals, is a major environmental problem along the coastal strip of the western desert of Egypt. This leads to a loss of freshwater resources, mandating alternative, costly water supply methods. Understanding and developing groundwater resources in El Salloum Basin along the northwestern coast of Egypt remains a challenging issue.Since groundwater cannot be easily located, a variety of scientific techniques are needed to provide information concerning its occurrence and location. Groundwater is considered as one of the main sources for both rural and agriculture water supplies in many areas in Egypt especially in the desert regions. Over recent years, increasing abstraction to meet rising demand for domestic supplies and expansion in reclamation in desert fringes has raised concerns for the sustainability of the groundwater resource and the livelihoods it supports. Near-surface electrical methods are a promising technology to evaluate groundwater resources as they are sensitive to physical and chemical variations of the subsurface associated with changing groundwater quality.Vertical Electrical Resistivity Sounding (VES), 2D Electrical Resistivity Imaging (ERI) and Very Low Frequency (VLF) electromagnetic have been applied, to investigate the hydrogeological framework of El Salloum basin with the aim of determining the potential of the review for providing potable water. A depth of investigation (DOI) index was used to constrain the information content of the images at depths up to 100 m. VLF- EM surveys identified major geological interfaces suspected to be faults/fractured zones across the study area. A combined analysis of the datasets suggests that the subsurface geology is related to four/five major resistivity layers. Resistivity tomographic images have shown a decrease of resistivity by going deeper (possibly representing clay rich limestone/ saline water impacted fractured limestone) and towards the coastal region where the sea water intrusion may take a place. The equivalent geologic layers suggest that the Oolitic Limestone (Pleistocene age) at the north and the underlain fractured limestone (Middle Miocene) southward areas of coastal plain as the aquifers layers. Sites that will provide appreciable volume of water were suggested base on vertical and lateral extent of the layers. The most promising locations for drilling productive wells

are in the south and southeastern parts of the region, where the potential for potable , groundwater increases substantially. The results from this research demonstrate the capability of integrated 1D-VES, 2D-ERI and VLF-EM techniques to understand and delineate the groundwater occurrence in heterogeneous/ karsts environments.