Abstract
An integrated geophysical and hydro-chemical investigation was carried out in the area around the Stadium-Apollo Market waste dump located in Igboya area of Ile-Ife. It was with the aim of determining the geoelectric characteristics and groundwater chemistry which were used in delineating the subsurface sequence and evaluating the possible pollution of groundwater in the area. Eight Vertical Electrical Sounding (VES) stations were occupied along two traverse lines trending North-South and East-West directions. Dipole-Dipole profilings were also carried out along same traverses. Eight water samples were collected from hand dug wells and analyzed for some chemical elements such as total acidity, major ions (Na+, K+, Cl-, Mg2+, Ca2+), NO3- and heavy metals (Cd, Cu, Fe, Hg, and Pb). Results of the investigation indicate that a maximum of four subsurface layers- the top soil, clay/sandy clay unit, the weathered layer and the basement bedrock exist in the area. The weathered layer constitutes the main aquifer unit with thicknesses of between 7 and 38 m. From the 2-D resistivity structures, contaminant plumes characterized by relatively low resistivity values (< 150 ohm-m) were identified down to depth of about 40 m in some places. Hydro-chemical results showed that the total acidity and concentration of Na+ Cl- and heavy metals (Cd, Cu, Fe, Hg and Pb) in wells closest to and down slope of the waste dump (total acidity 5.1-10.0 mg/l; Na+ 8.92-11.07 mg/l; Cl- 127.62-297.78 mg/l; Cd, 0.006-0.009 mg/l; Cu, 0.330-1.840 mg/l; Fe, 2.300-4.600 mg/l; Hg, 1.247 mg/l and Pb, 0.260 Mg/l) are higher than concentrations in distant wells, and most of them (Cl-, Cd, Cu, Fe, Hg, and Pb) exceeded national and international drinking water quality standards. It can be concluded that the groundwater in the area had been contaminated and the plume had migrated to a significant depth.KEYWORDS: Geophysical, Hydro-chemical, Waste Dump, Groundwater Quality, Pollution
Highlights
One of the common ways of waste disposal is by open dump
Low resistivity zones ( ∠ 150 ohm-m in green colours) with significant depth extent of up to 40 m, suspected to be leachate impacted zones, are found between distances 50 and 80 m; 130 and 160 m and 185 and 200 m. These areas correlate with the actual location of the waste dump which lies between distances 47 and 206 m along the traverse
The results show that wells closest to the waste dump and those located down slope of the waste dump have higher concentrations of the analyzed parameters
Summary
One of the common ways of waste disposal is by open dump. The primary consequence of solid waste disposal in open dump is the potential for gas and leachate generation due mainly to microbial decomposition of the waste materials. The Stadium-Apollo Market waste dump is located along Ife Township Stadium road off Obafemi Awolowo University Road 7 in Igboya area of Ile-Ife, Osun State. The nature of waste mix disposed in the dump is heterogeneous and widely varied. The inhabitants of Igboya area and environs depend mainly on groundwater from wells to meet most of their daily water needs. Since these wells are generally shallow and located within the vicinity of the waste dump, there is the possibility that the groundwater in the area may have been contaminated through leachate percolation. O. Olorunfemi, Department of Geology, Obafemi Awolowo University, Ile-Ife, Nigeria.
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