Delineation of contamination plume around oxidation sewage-ponds in Southwestern Nigeria |
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Authors: | A A Adepelumi B D Ako O Afolabi J B Arubayi |
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Institution: | (1) Department of Geology, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria;(2) Department of Physics, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria |
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Abstract: | Integrated surface electrical resistivity and electromagnetic (EM) surveys were conducted in a hard-rock terrain of Southwestern
Nigeria in the vicinity of active oxidation sewage treatment ponds. The aim was to detect soil contamination due to the spread
of sewage effluent, locate possible leachate plumes and conductive lithologic layers, and access the risk of groundwater pollution
in the vicinity of the sewage-ponds. Dipole–dipole resistivity profiling and very low frequency (VLF) data were acquired at
10-m intervals along five 200-m long east-west geophysical traverses. Resistivity sections obtained revealed four subsurface
geologic layers comprised of lateritic clay, clayey sand/sand, weathered/fractured bedrock, and competent bedrock. A distinct
low resistivity zone corresponding to the contamination plume (labeled B) was delineated from all the resistivity sections.
This low zone extends into the weathered bedrock and possibly suggests contamination of this layer. The filtered real component
of the processed VLF data detected three distinct anomaly zones that are representative of fractured zones filled with conductive
fluids and/or lithologic boundaries that possibly serve as conduits for the movement of contaminated effluents. The results
obtained from the two methods suggest possible contamination of the subsurface soil layers and groundwater in the vicinity
of the sewage-ponds. The existence of this contaminated plume poses a serious threat to the ecosystem and health of the people
living in the vicinity of the sewage-ponds. |
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Keywords: | Sewage Contamination Electrical resistivity Very low frequency Soil Nigeria |
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