RECONNAISSANCE PAR IMAGERIE ÉLECTRIQUE DU SITE POLLUÉ DE LA DÉCHARGE PUBLIQUE DE LA VILLE D'OUJDA (MAROC ORIENTAL)/Geophysical survey by electrical resistivity imagery of the Oujda city landfill (Eastern Morocco)

The Sidi Yahya landfill is a uncontrolled landfill of household refuse. It is located in the commune of Sidi Yahya, approximately 7 km southeast of Oujda (Eastern Morocco). The total tonnage of waste produced was about 1.2 to 1.5 million metric tons for the period of the landfill exploitation (1990-2005). The total surface which was entirely used covers 41 hectares. The groundwater (water table at about 30 m depth) circulates in post-Miocene material underlain by an impermeable substratum formed by Miocene marls. The soil is calci-magnesic, with a more or less important layer of silt and clay. Water coming from the domestic waste itself or resulting from degradation of organic matter under aerobic conditions, as well as meteoric water that percolates through the waste, combine to form a leachate enriched in various pollutants. The main objective of this study was the detection of eventual groundwater pollution and estimation of the extent of the resulting underground pollution plume. A geophysical study using Electrical Resistivity Imagery was carried out. The location of profiles obtained with a dipole-dipole array (three profiles 23 m long and one profile 475 m long) was constrained by the available space in the landfill facility. The resistivity sections show the resistivity distribution to a depth of 30 m for short profiles and 50 m for the long profile. The results show very conductive layers with very low resistivity values (< 5 Ω·m), suggesting that these areas might be saturated with migrating leachate. In the central part of the landfill the contamination reaches a depth of about 20 m.