) Evaluation of groundwater aquifer vulnerability in Ilorin Metropolis Using Electrical Resistivity Method of Geophysics

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Date

2019

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Publisher

European Water resources Associiation

Abstract

An area of 321.97 km2 in Ilorin Metropolis has been studied, using 312 Vertical Electrical Sounding data obtained in an intensive Electrical Resistivity Survey. The goal of the study is to evaluate the vulnerability of groundwater in the area to contamination with a view to advise Kwara State Government on the safe sites for locating the planned public water project in the different parts of Ilorin. VES data acquired in the area were subjected to manual and computer-aided interpretations to delineate the different geo-electric layers, their hydrogeological significance, and vulnerability of the aquifer. The area was divided into zones, namely, A, B and C. Results of the study revealed presence of five geo-electric layers and two groundwater aquifer layers. The first aquifer corresponds to weathered rock layer, has hydraulic conductivity ranging from 0.1 and 3.0 m/day, lies at shallow depths ranging between 2 and 36 m, and has overburden material whose protective capacity (𝑠) against groundwater contamination is weak (𝑠≤0.19), except in few places in zone C where protective capacity is moderate (0.2≤𝑠≤0.69). The second aquifer layer corresponds to fractured basement rock, lies at depths ranging between 5.0 and 53 m, has overburden layer whose protective capacity against groundwater contamination ranges from moderate (0.2≤𝑠≤0.69) to good (0.7≤𝑠≤4.9). Groundwater in fractured basement rock aquifers is more protected against contamination from dumpsite leachates and anthropogenic wastes than the groundwater in the weathered rock aquifers. Joint interpretation of hydro-dynamic properties of the overburden and aquifer layers of the three zones showed that zone C has the highest groundwater protection capacity, while zone A has the least protection capacity against contamination. Different safe spots were identified for citing boreholes for potable water supply in the three zones. The study recommended that all boreholes for portable water supply, except in few places in zone C, should penetrate the fractured basement rock aquifers to avoid the supply of contaminated groundwater in the future.

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Keywords

groundwater vulnarability, aquifer protective capacity, longitudinal conductance, Geo-electric layer, Electrical resistivity method

Citation

Raji, W. O. Abdulkadir, K. A. and Rahman, R. A. (2019) Evaluation of groundwater aquifer vulnerability in Ilorin Metropolis Using Electrical Resistivity Method of Geophysics. Water Utility Journal, 23, 27 -33

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