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