Integration of Geologic and Geoelectrically Derived Parameters for Aquifer Vulnerability Assessment in Akure Metropolis, Southwestern Nigeria

Abstract

Assessment of aquifer vulnerability was carried out in the northwestern part of Akure, Southwestern Nigeria where the presence of  automobile workshops is the major source of pollution using integrated methods of multi-criteria approach and physico-chemical investigations. 187 vertical electrical sounding (VES) data were acquired using the Schlumberger array technique with (AB/2) ranging  from 65 - 150 m. Six geologic and geoelectric parameters; surface elevation, lithology, aquifer overlying layer resistivity, aquifer overlying  layer thickness, coefficient of anisotropy and hydraulic conductivity were combined to develop an aquifer vulnerability model (AVM) for  the study area using the GIS technique. These factors were subjected to the Fuzzy Analytical Hierarchy Process (FAHP) method of weightage determination to assign weights to each criterion of the aquifer vulnerability conditioning factors (AVCFS) using GIS. The AVM  shows that the eastern and western flanks of the study area are of moderate to high vulnerability, while the central area is mainly of very low to moderate vulnerability. Fifteen (15) water samples were obtained from wells across the area for physico-chemical analyses. The  predicting accuracy of the aquifer vulnerability model was validated using one of the physiochemical parameters determined from water  samples collected across the area (lead) and longitudinal conductance. The validations from the two approaches produced an accuracy of  73% and 74% respectively which proved the reliability of the model. The produced aquifer vulnerability map can be used for precise  decision-making processes in environmental planning and groundwater management in the study area.