An Integrated Geophysical and Geochemical Investigation of an Open Dumpsite in a Sedimentary Formation

Abstract

The extents of migration of leachate plumes and the probabilistic assessment of human health risks were carried out on Oke-Diya dumpsite, Sagamu, Southwestern Nigeria. Geophysical methods involving Very Low Frequency-Electromagnetic (VLF-EM) and Electrical Resistivity Topography (ERT) techniques, and Atomic Absorption Spectrometric (AAS) geochemical method were used to map and detect the presence and extent of leachate migration. The VLFEM pseudo-sections revealed conductive zones of responses 25 - 50 to a depth of about 15 m and approximated distance 50 m from the study area. The 2D and 3D ERT models delineated high conductive zones with very low resistivity values ranging from 0.551-6.54 and 2.4respectively. These conductive regions were observed to depths above 13.4 m and approximated distance 60 m from the study area in the 2D models. The 3D sections comprising of the horizontal depth slices, vertical planes and volumetric displays revealed regions with higher conductivity to a depth of about 21.9 m and approximated distance 50 m from the dumpsite. The mean concentrations of heavy metals Pb, Ni, Cd, Zn, Fe and Cu in the soil samples were higher than the concentrations in the control samples. The human health risk assessment indicated unacceptable values for non-carcinogenic adverse effects for both children and adults. The probabilistic cancer risks were within the acceptable range for Pb and unacceptable for Cd for both the children and adults. Generally, this study had identified areas of concentrated plumes accumulation and migration pathways, which were in agreement with earlier studies in sedimentary terrain.