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

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, quartzschist and biotite-hornblende granite. Twenty-Four Vertical Electrical Sounding (VES) were probed using Schlumberger array with maximum current electrode spacing (AB/2) of 100 m 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 (72.4-1735.6 Ω m), clay/clayey sand/sand/laterite (18.9-1349.5 Ω m), fractured basement (430.7-1021.4 Ω m) and the fresh basement (433.3-7146.4 Ω m). The plotted isopach map showed an overburden thickness range of 4.9-28.2 m with values greater than 20 m at the southeastern and southwestern 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 > 13 m and reflection coefficient < 0.8); medium (overburden thickness > 13 m and reflection coefficient ≥ 0.8); and low (overburden thickness < 13 m 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.

Investigating groundwater corrosion and overburden protective capacity in a low latitude crystalline basement complex of southwestern Nigeria

“…In contrast, the overburden protective capacity rating using the TDS computed from Equation (12), employing the total longitudinal unit conductance as is standard in most literature (e.g. Oladapo et al 2004;Ayolabi 2005;Oladapo and Akintorinwa 2007;Atakpo and Ayolabi 2009;Obiora et al 2015;Bayewu et al 2018), based on Henriet (1976), is given in Table 5. It indicates the overburden protective capacity ratings show fair agreement (moderate/Good-fair) at a total longitudinal conductance interval of 0.2-0.69 mho.…”

“…Furthermore, while the calibration in the current study was based on values for the parameters obtained in a typical crystalline basement environment, Henriet's (1976) application was for a set of carboniferous limestone basins but had been used in different geologic terrain, basement complex (e.g. Oladapo et al 2004;Oladapo and Akintorinwa 2007;Obiora et al 2015;Bayewu et al 2018) and sedimentary environment (e.g. Ayolabi 2005;Atakpo and Ayolabi 2009).…”

“…Longitudinal conductance has been used to assess the protective capacity of the overburden units (e.g. Henriet 1976;Oladapo et al 2004;Obiora et al 2015;Bayewu et al 2018). However, rather than calibrating the longitudinal conductance using either in situ or laboratory measured parameter(s), it is usually measured in absolute terms without determining the infiltration time (e.g.…”

“…Kalinski et al 1993) through unsaturated groundwater protective layers and compared with values obtained by Henriet (1976), especially in sub-Sahara Africa (e.g. Oladapo et al 2004;Ayolabi 2005, Oladapo andAkintorinwa 2007;Atakpo andAyolabi 2009, Obiora et al 2015;Bayewu et al 2018) the contributions of the anthropogenic sources or local geology were not also considered. In the current study, the overburden protective capacity, computed as total longitudinal conductance of the overburden material using geoelectrical layering parameters obtained from iterative interpretation of VES data acquired near well bores in Ogbomoso North, southwestern Nigeria, has been calibrated.…”

Application of Electromagnetic and Electrical Resistivity Methods for Borehole Siting in Low-Grade Metavolcanic and Metasedimentary Rocks, Sunyani West, Ghana

“…The presence of the fresh-looking baobab trees a few distance away from the VES points suggested a high groundwater potential at station A70. Three quantities (the basement rock resistivity, overburden thickness and nature of the modelled curve) are usually considered in determining a suitable site for borehole drilling (Manu et al, 2019;Bienibuor et al, 2016;Bayewu et al, 2018). All these quantities were considered, making this site very suitable for drilling.…”