Abstract
Waste management is one of the most important problems in developing countries. The major concern in this regard is waste dump sites, to both environmental scientists and the general public. At Al Misk (Buraiman) Lake, all the domestic and industrial waste of Jeddah was dumped without any treatment. A concrete dam was constructed to block the migration of contaminants from the lake. The purpose of this research is to determine the efficiency of geophysical methods in delineating the contaminant emanating from the seepage of sewage water from Al Misk Lake to the wadi downstream of the concrete dam. The geophysical studies are used, including the electrical resistivity and induced polarization techniques in conjunction with in-situ hydrogeological studies to define the extension of contamination in both sides of the dam. Two subsurface layers were identified by geophysical techniques. The most of the contamination is restricted in the first layer which is interpreted as a salty sandy layer with high porosity. The average thickness of contaminated layer is about 8 m and has very low resistivity (<10 Omega.m) due to the increase of contaminated water. The second layer shows the relative high resistivity values (>30 Omega.m) than the first layer due to the presence of boulders and gravels with silty sand and, in some places, accumulation of basement boulders also found with high resistivity values (>700 Omega.m). Induced polarization helps to differentiate between the clay and contaminated sandy layer due to the variation of their chargeability values. Induced polarization results show the presence of low resistivity and low chargeability values in the first layer and high chargeability in some parts of the second layer duo to the presence of clay. The contaminations may extend to the deep layers, in the areas of faults and more porosity sediments. The results of electrical conductivity (EC), total dissolved solids analysis, temperature, and pH reveal that the total dissolved solids are very high in the front and the back of the dam, which affect the other parameters. The results concluded that the contaminant plume exists on either side of the dam with the same degree of contamination.