Geoelectric Investigation of Aquifer Vulnerability within Afe Babalola University, Ado -Ekiti, Southwestern Nigeria.

Abstract

Many investigation techniques are commonly employed with the aim of estimating the spatial distribution of transmissivity and protective capacity of groundwater resources. Unfortunately, the conventional methods for the determination of hydraulic parameters such as pumping tests, permeameter measurements and grain size analysis are intrusive and relatively expensive. A non-intrusive and less-expensive geoelectric investigation involving vertical electrical sounding was carried out in some parts of the campus of Afe Babalola University, Ado Ekiti, Ekiti State, Nigeria. A total of fifty-nine (59) vertical electrical sounding (VES) data were acquired using R 50 D.C. resistivity meter within the campus which is underlain by the Precambrian basement rock of southwestern Nigeria. Following the interpretation of the VES data, maps and 2D-sections were generated. The geoelectric sections enabled the subsurface to be characterized into five geoelectric layers namely: Topsoil, clayey/sandy-clay, weathered layer, fractured basement and fresh basement. The assessment and analysis of the materials above the aquifers showed that longitudinal conductance (S) values ranged from 0.08438 to 0.73449 mhos; thus the area is classified into weak (0.1 – 0.19 mhos), moderate (0.2 – 0.69 mhos) and good protective capacity (0.7 mhos and above). The major aquifer delineated is the weathered/fractured basement aquifers. These aquifers are characterized by thick overburden, moderate/good protective capacity, moderate to relatively high value coefficients of anisotropy and low transverse unit resistance. This suggests that the materials above the aquifers act as seal, thus protecting the major aquiferous units. However, the aquifer matrix itself is relatively permeable. Areas with weak protective capacity are therefore vulnerable to infiltration of polluting fluid.