Impact assessment of the effects of the former uncontrolled landfill of Sidi Yahya Oujda (Morocco) on groundwater using physicochemical, geological and electrical triple approaches

Abstract

This study is part of the geophysical mapping of the former site of the uncontrolled Sidi Yahya Oujda landfill. It also aims to show the contribution of the integrated interpretation of geological and geophysical data in the diagnosis of illegal dump sites. The application was made on the rehabilitated site of the former uncontrolled Oujda landfill located in Sidi-Yahya, which was closed in 2005. Geological and geophysical studies by electrical resistivity tomography (TRE) were carried out at the site level. Nine 475 m long TRE profiles with an investigation depth of up to 110 m were generated to image the subsoil. Analysis of the physicochemical and metallic composition of the leachate from this site and the groundwater taken from 3 nearby wells revealed significant pollution of the leachate with a COD of 12780 mg. O2/L and a BOD5 of 525.34 mg. O2/L. The groundwater had high electrical conductivity (average of 3.9 mS/cm), chloride content (710 mg/L average) and nitrate content (74.62 mg/L average). The metal concentrations in the leachate and groundwater far exceeded the Moroccan standards, with high average values for zinc (619.22 μg/L), copper (318.12 μg/L), nickel (233.76 μg/L), chromium (169.16 μg/L), L) and iron (12940 μg/L). Geologically, a context was highlighted with lateral lithological variations and the presence of faults. The waste/leachate layer has low resistivity values (<10 Ω m) and a thickness of up to 25 m. It rests on terrains of different geological natures. In the southern part of the site, there is a layer of red clay with a thickness of up to 50 m and low resistivities (<10 Ω m), which overlies a layer of limestone with high resistivity values (>100 Ω m). In the northern part, we encounter a discontinuous and thin layer of fractured dolomites with resistivities greater than 50 Ω m. This layer of dolomite rests on a layer of clays.