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3-D Electrical Resistivity Imaging (ERI) was used to map the subsurface lithology with the aim of delineating leachate migration path within the dumpsite at Ijagun, southwest Nigeria. Dipole –dipole and Wenner electrodes configurations were adopted to establish five and nine 2-D profiles respectively. The starting electrode spacing (a) for the dipole-dipole array was 3m while that of the Wenner array was 1m at n=1,2,..., 5. The measured resistivity values were input into ZONDRes3D resistivity & IP inversion software to generate the inverted 3-D resistivity models. The data obtained showed resistivity values from the Wenner array ranged from (1.0Ωm -120Ωm), (3.0Ωm -84Ωm), (2.0Ωm -73.0Ωm), (0.9Ωm -150Ωm), (1.2Ωm -59.0Ωm), (2.0Ωm-100Ω), (4.0Ωm -99.0Ωm), (3.0Ωm -58Ωm), (4.0-78.0Ωm) for profile 1-9 respectively. On the other hand, resistivity values of the Dipole-dipole array are (90.0Ωm-200.0Ωm), (5.0Ωm-300.0Ωm), (5.0Ωm-60.0Ωm), (11.0Ωm-300.0Ωm) and (6.0Ωm-60.0Ωm) for profile 1-5 respectively. The 3-D Resistivity Images of the two arrays were examined as the depth slices, resistivity inlines and crosslines. The depth slices showed that leachate infiltration were more up to 3m and decreased with depth while the slice view at various distances showed different level of infiltration. Of note is the presence of non-contaminated sandy layer at the center of the image with resistivity higher than 500Ωm except by the side of the flanks where the leachate successfully infiltrates down to 15.0m. Interpretation of resistivity model generated in relation to geological inference reveal decrease in leachate migration in both site down the profile. However, the Wenner resistivity image which investigated shallower depth showed intense leachate migration compare to that of the Dipole-dipole array. The present of clayey layer between the topsoil and sandy layer interpreted from the Dipole-dipole image is thought to be the protective material from leachate infiltration in areas where the leachates were not visible at the center of the image.

Keywords: Leachate, Resistivity, Imaging, 3-Dimension, Dumpsite, Wenner, Dipole-dipole