Hydrogeophysical Evaluation of Groundwater Potential and Aquifer Protective Capacity in Akerebiata, Ilorin, Nigeria

Abstract

Groundwater potential and aquifer protective capacity in Akerebiata and its environs, Ilorin South, Nigeria, were evaluated using the Vertical Electrical Sounding (VES) method. The study was motivated by the absence of a functional municipal water supply and increasing reliance on shallow hand-dug wells that are often unreliable and vulnerable to contamination. Six VES stations were acquired using the Schlumberger electrode configuration with a maximum current electrode spacing of 200 m. Apparent resistivity data were processed and interpreted through partial curve matching and iterative inversion to delineate subsurface geoelectric layers and infer hydrogeological conditions. The results reveal three to five geoelectric layers across the study area, comprising topsoil, weathered basement (saprolite), fractured basement (saprock), and fresh basement. Groundwater occurrence is primarily associated with the weathered and fractured basement units, while the fresh basement is largely non-aquiferous. Weathered layer thickness varies significantly across the area, ranging from less than 5 m to over 14 m. VES stations 2 and 3 exhibit the most favorable groundwater conditions, characterized by thick saprolitic layers (>14 m), moderate resistivity values, underlying fractured basement, and moderate aquifer protective capacity. VES stations 4 and 5 show moderate groundwater potential, whereas VES 6 is considered unsuitable for groundwater development due to shallow bedrock and limited storage capacity. The study demonstrates that groundwater potential in Akerebiata is highly localized and structurally controlled. Borehole drilling to depths exceeding 18 m is recommended to ensure adequate penetration of productive aquifer zones. The integration of VES interpretation with longitudinal conductance analysis proves effective for groundwater assessment and vulnerability evaluation in crystalline basement terrains.