Abstract
A shallow electromagnetic study (electrical conductivity and magnetic susceptibility measurements) and laboratory conductivity sampling of the flood plains of Oluwatuyi/Oshinle area of Akure have been undertaken. This is with the aim of correlating the terrain conductivity mapping with laboratory measurements to establish the effectiveness of the induced secondary currents in determining the effects of infiltrating leachates occasioned by heaps of refuse dumped in the course of River Elegbin in the study area. Quadrature and in-phase measurements in vertical and horizontal dipole modes were undertaken on seventeen traverses of various lengths. Laboratory conductivity measurements were conducted on twenty one water samples obtained from hand-dug wells. The horizontal dipole measurements exhibit higher conductivity values suggesting contamination of the upper strata from the ubiquitous refuse in the area. The lower conductivity values obtained from the vertical dipole mode may be due to the high retarding capability of abundant clay in the area to contaminant flow. The similarity in conductivity distribution obtained from field and laboratory studies show that terrain conductivity is strongly influenced by saturating fluid. The high magnetic susceptibility values obtained in northern course of the river suggests predominantly ferromagnetic dumps while the low values characterizing the central and southern course indicate predominantly domestic waste in the zone.
Highlights
Dealing with contaminated site is a major problem in urban areas because conventional site characterization typically involves intensive field programmes of drilling and core sampling, downhole geophysical logging, well monitoring, and hydrochemical analysis
Terrain conductivity mapping and laboratory sampling of 21 water wells in Oluwatuyi/Oshinle area of Akure has been undertaken in this study to determine the level of contamination occasioned by ubiquitous refuse in the area
The higher conductivity values obtained from horizontal dipole measurements is indicative of level of upper strata contamination occasioned by leachates associated with massive refuse dump
Summary
Dealing with contaminated site is a major problem in urban areas because conventional site characterization typically involves intensive field programmes of drilling and core sampling, downhole geophysical logging, well monitoring, and hydrochemical analysis. Effective characterization of urban sites with elaborate field programmes is usually inhibited by limited available space to work and the presence of ambient electrical noise. Site characterization in such urban centres can be rapidly and perhaps effectively implemented with the use of shallow electromagnetic field study. Chief among the reasons for utilizing shallow electromagnetic method especially in urban areas is the ability of the method to work around the limitations. The method adopted in this study was utilized by Lanz et al (1998) to carry out a geophysical investigation on landfill delineation and characterization. The full detailed electromagnetic survey revealed a labyrinth of subsurface pipes about 1 m deep together with a number of anomalously low conductivity regions
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