Assessment of groundwater prospect and aquifer protective capacity using resistivity method in Olabisi Onabanjo University campus, Ago-Iwoye, Southwestern Nigeria

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Abstract

Electrical resistivity investigation was carried out at Olabisi Onabanjo University campus, Ago-Iwoye, Southwestern Nigeria with the aim of evaluating groundwater potential and aquifer protective capacity of the overburden units in the area. The underlain rocks are predominantly porphyroblastic and banded gneiss, quartz-schist and biotite-hornblende granite.
Twenty-Four Vertical Electrical Sounding (VES) were probed using Schlumberger array with maximum current electrode spacing (AB/2) of 100m at each point using the OHMEGA Allied resistivity meter. The data were interpreted using the partial curve matching and computer iteration programme using WINRESIST. Parameters such as overburden thickness, basement resistivity, reflection coefficient and longitudinal conductance were calculated and used for evaluating the groundwater potential and aquifer vulnerability of the study area.
The predominant VES curve types obtained are KH, H, A, AKH, HKH and HA. The geoelectric sections show that the area is underlain by 3–5 layers: the topsoil (72.4–1735.6Ωm), clay/clayey sand/sand/laterite (18.9–1349.5Ωm), fractured basement (430.7–1021.4Ωm) and the fresh basement (433.3–7146.4Ωm). The plotted isopach map showed an overburden thickness range of 4.9–28.2m with values greater than 20m at the south-eastern and south-western parts of area. The reflection coefficient range is between 0.62 and 0.98 while protective capacity range is between 0.03 and 0.28. Groundwater potential of the area were classified as high (overburden thickness>13m and reflection coefficient<0.8); medium (overburden thickness>13m and reflection coefficient≥0.8); and low (overburden thickness<13m and reflection coefficient>0.8). The protective capacity rating falls between poor to moderate, thus, vulnerable to infiltration of leachate and other surface contaminants.
The study therefore helped in identifying favourable groundwater potential and the aquifer vulnerability of the area.

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NRIAG Journal of Astronomy and Geophysics
Volume 7, Issue 2
December 2018
Pages 347-360

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