Geophysical and hydrogeological investigation was employed in Ero, Southwestern, Nigeria in order to evaluate the groundwater potential and its vulnerability to contamination. The aim of the project is to map the groundwater resources of the study area through delineation of hydrogeologic structures and evaluation of the vulnerability of these structures to near-surface contaminants. The survey utilized the Schlumberger depth sounding method integrated with hydrogeological measurement such as the static water level, well depth measurement in collaboration with hydrochemical analysis of wells in the study area. The geophysical investigation shows three to five distinct geoelectric units which include the topsoil, weathered layer, weathered basement, fractured basement and fresh bedrock. The top soil resistivity is in the range of 24 to 1112 Ohm-m with thicknesses 0.4 to 1.3m while the weathered layer ranges from 12 to 1402 Ohm-m with a thickness range of 0.7 to 10.2m. The weathered basement has resistivity values in the range of 575 to 913 Ohm-m with a thickness range of 0.4 to 3.5m while the fractured basement resistivity is in the range of 61 to 533Ohm-m with a thickness range of 3.5 to 16.2m. The fresh basement resistivity is in the range of 1020 to ∞ Ohm-m. The overburden thickness ranges between 1.7m to 40m. The resistivity distribution values of the aquifer units in combination with the thicknesses of the aquifer units and overburden shows that most of the study areas have low groundwater potential. The hydrogeological measurements reveal that water column thickness ranges between 0.1 - 1.7 indicating relatively thin water column in the sampled area. The groundwater in the study area flows from the northern and southwestern part into the southeastern and western part of the sampled area. The longitudinal unit conductance values which are corroborated by the top soil resistivity and vadose zone thickness was employed in the aquifer vulnerability assessment of Ero. It was revealed that the overburden protective capacity of the area can be classified into poor, weak and moderate protective capacity zones. The hydrochemical analysis reveals that the physico-chemical parameters in the three wells is portable because the results falls within the recommended safe value for drinking water by WHO and other health organizations.

Groundwater, Hydrochemical, Geoelectric, Vadoze Zone, Unit Conductance