197 International Engineering Conference on Hot Arid Regions (IECHAR 2010) Al-Ahsa, KSA, March 1-2, 2010 Abstract— Direct Current (DC) resistivity techniques of geophysical exploration are popular and proved to be successful and have many implications in the fields of engineering, geoenvironment and hydrogeology. In this paper, the electric resistivity technique proved to be successful method for mapping of Quaternary aquifer conditions in the East Nile Delta, Egypt and in Wadi Ham, United Arab Emirates (UAE). The application of this technique gave excellent information, about the aquifers lithology, their thicknesses, salinity, contamination and other valuable information. In the Eastern Nile Delta area, a detailed Vertical Electrical Soundings (VES) were implemented to explore the Quaternary aquifer subsurface conditions at this area. While at Wadi Ham, UAE, Two Dimensional (2-D) earth resistivity imaging survey was conducted to delineate the seawater intrusion for this coastal aquifer. The interpretation of the acquired resistivity data with aid of the available borehole information at both areas helped in the deduction of interesting inferences for East Nile Delta and Wadi Ham areas.The relevant geoenvironmental implications for this study at East Nile Delta are deduced concerns the main sandy aquifer. As in some sites across the area the overlying clayey cap is extremely thin. Thus, the reduced thickness of the clay cap enhances contamination of the sandy aquifer through infiltration. The major sources of groundwater contamination in this populated and urbanised area include septic tanks, sewage ditches, drainage canals, industrial sewage disposal wells and spreading of chemical fertilisers, pesticides and herbicides on the land. The Quaternary aquifer of Wadi Ham, UAE, has been overexploited during the last two decades to meet the increasing water demands. As a result, the dynamic balance between freshwater and seawater has been disturbed and the quality of the groundwater has deteriorated. Along the 2-D resistivity tomograms three zones of water-bearing formation (fresh, brackish, and salt-water zones) are identified. Along the 2-D resistivity profiles, the depth to the fresh-brackish interface exceeded 50 m at the western part of Wadi Ham and was in the order of 10 m or less in the eastern side near the shoreline. Depth to the brackish-saline water interface reached about 70 m in the western side and was in the order of 20 m in the eastern side. The thickness of the fresh water zone decreases considerably in the farming areas toward Kalba and thus the degree of seawater intrusion increases. Keywords — Contamination, Environmental/Engineering Geophysics, Quaternary Aquifer, Nile Delta, Seawater intrusion, Wadi Ham 1. INTRODUCTION urface-geophysical methods offer quick and inexpensive means to characterize the subsurface hydrogeology [1], [2]. They provide information on the subsurface properties, such as thickness of layers and saturation zones, depth to bedrock, location and orientation of bedrock fractures, fracture zones and faults. Surface and borehole geophysical methods may form a part of preliminary site evaluation for groundwater investigation. The data from geophysical surveying can guide the selection of the sites of test borings and provide data to correlate between them. The electrical methods, in general, include different techniques and instruments depending on the nature of the method used in prospecting. Some of these methods make use of natural currents and others depend on injection of artificial currents into the earth. For more details about these different techniques reference is made to [3] to [8]. The DC- resistively methods of geophysical exploration are popular and proved to be successful and have many implications in the fields of geoenvironment and hydrogeology. Electrical resistively methods were developed in the early 1900s, but have become widely used since the 1970s, primarily due to the availability in the search for suitable groundwater sources. These methods have also been used to monitor types of groundwater pollutions; in engineering surveys to locate sub-surface cavities, faults and fissures permafrost, mineshafts and in archaeology for mapping out the real extent of remnants of buried foundations of ancient buildings, amongst many other applications. One of the new developments in recent years is the use of 2-D electrical imaging/tomography surveys to map areas with moderately complex geology [9]. A more accurate mode of the subsurface is the two-dimensional (2-D) model, where the resistivity changes in the vertical direction, as well as in the horizontal direction along the survey line are recorded. Earth resistivity methods have a wide application on shallow groundwater resources. The application of surface resistivity methods to delineate the contaminated zones has the following advantages: (1) reduced need for intrusive techniques and direct sampling (2) relatively inexpensive and can be used for rapid and economical monitoring of large areas and optimization of the required number of monitoring wells; and (3) electrical conductivity/resistivity are intrinsic properties of ground-water chemistry that are readily interpreted in terms of the degree of ground-water contamination [10] to [12]. In this paper, two case studies of using geoelectric resistivity investigations for mapping of Quaternary aquifer conditions in two arid countries. The first case is using the Vertical Electrical Sounding (VES) technique in the East Nile Delta, Egypt. Tthe second case study shows the result Mapping of Aquifer Contamination Using Geoelectric Resistivity: Case Studies A. El-Mahmoudi S Manuscript received December 31, 2009. F. A. Author is with the National Institute anuscript received December 26, 2009. A. S. El-Mahmoudi is with the Water Studies Centre, King Faisal University, P.O. Box 420, Al Hofuf, 31982, KSA , E-mail: mahmoudi@kfu.edu.sa, Tel/Fax:+96635816611