Groundwater vulnerability assessment was carried out at Igbara Oke Southwestern Nigeria, with a view to classify the area into vulnerability zones, by applying the electrical resistivity method, using Schlumberger electrode arrays with maximum electrode separation (AB/2) of 65 m in (41) different locations for data acquisition. Geoelectric parameters (layer resistivity and thickness) were determined from the interpreted data. The study area comprises four geoelectric layers (topsoil, lateritic layer, weathered/ fractured layer and fresh basement). The geoelectric parameters of the overlying layers across the area were used to assess the vulnerability of the underlying aquifers to near-surface contaminants with the aid of vulnerability maps generated. Three models were compared by maps using geo-electrically derived models; longitudinal conductance, GOD (groundwater occurrence, overlying lithology and depth to the aquifer) and GLSI (geoelectric layer susceptibility indexing). The total longitudinal conductance map shows the north central part of the study area as a weakly protected (0.1-0.19) area, while the northern and southern parts have poor protective capacity (<0.1); this is in agreement with the GOD method which shows the northern part of the study area as less vulnerable (0-0.1) while the southern part has low/ moderate (0.1-0.3) vulnerability to contamination. The longitudinal conductance exaggerates the degree of susceptibility to contamination than the GOD and GLSI models. From the models, vulnerability to contamination can be considered higher at the southern part than the northern part and therefore, sources of contamination like septic tank, refuse dump should be cited far from groundwater development area.

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The research was conducted to unravel the aquifer protective capacity and groundwater yield of the environment of a mining site at Ijero-Ekiti, Nigeria. The electrical resistivity method was employed and data gotten were used in combining the conventional longitudinal conductance and a new approach that indexes the resistivity and thickness considering some layers which could be protective and have low resistivity like clay material. The area is characterized by the Nigeria Basement Complex consisting of Precambrian rocks, made up of the migmatite gneiss, amphibole schist, quartzite, calc gneiss, schist biotite gneiss, biotite-schist, epidiorite, pegmatite and granite. A total of 9 points were sounded with maximum current electrode separation of 50 – 80 m. The sounding data were interpreted with the aid of partial curve-matching and computer iteration. Result of the interpretation of the geophysical data shows that the area is composed of variable subsurface layering that ranges from three to four layers. Groundwater potential zones were delineated based on the geo-electrical data. The study reveals that VES 1, 3, 4, 5 and 8 have high to medium groundwater potential. However, VES 2, 6 and 9 are characterized by low groundwater potential. The distinct aquifer protective zones identified in the study area using longitudinal conductance and geoelectric layer susceptibility indexing are poor and weak. The study has been able to detect the groundwater yield and the protective capacity of the overburden in the northeastern part of Ijero-Ekiti where a mining site is located using electrical method. Geochemical analysis of water and soil samples from the area is recommended to understand the right treatment required for some of the groundwater sources for drinking.