Delineation of leachate at a dumpsite using geo-electrical resistivity method: a case study of Abule Egba, Lagos, Nigeria

This study presents the application of the dipole-dipole and the Schlumberger electrode arrays of electrical resistivity techniques to map the extent of leachate migration and its possible impact on groundwater at Abule Egba, dumpsite, Lagos. The uncontrolled mode of refuse disposal in Lagos over the years is worrisome because it reduces the potential sources of potable water for the growing population. This informed the evaluation of leachate migration to groundwater in the study area. To achieve this, 2-D resistivity imaging data was acquired along five traverses and was integrated with VES data acquired along the established traverses. The 2-D resistivity imaging and VES data were processed using DIPPRO and WINRESIST software respectively. The interpretation of the geo-electrical measurements was constrained by borehole data obtained within the study area. The results of the 2D and VES revealed five (5) geoelectric layers which correspond to the topsoil, clay, sandy clay, clayey sand and sand. The topsoil has layer thickness of 0.5-2.7 m and resistivity values within range of 9.8-133.3 Omega m. The clay has layer thicknesses between 1.7 m to 33.1 m and resistivity values ranging from 4.8 to 67.9 Omega m. The sandy clay layer has thickness of 1.0-14.5 m and resistivity values ranging from 13.5 to 128.8 Omega m. The clayey sand layer has thickness 1.9-44.4 m and resistivity values ranging from 16.3 to 129.0 Omega m. The sand delineated has thickness of 5.7-81.7 m and resistivity values ranging from 1.9 to 1230 Omega m. The fourth layer with low resistivity values of 1.9-2.4 Omega m at depth range 14.5-29 m is suggestive of leachate contamination when compared with the delineated sand of resistivity values of 419-916 Omega m in VES 19-24 which serve as control. The study revealed that some regions around the dumpsite have been contaminated by leachate which could infiltrate to the unconfined aquifers in the area if not properly monitored and regulated. Thus, this study shows the efficacy of electrical resistivity method in mapping leachate generated from solid wastes in the dumpsite.