Deployment of Electrical Resistivity Method for Evaluation of Sustainable Groundwater Resources in Lapai, Niger State, Nigeria

Abstract

Groundwater accessibility in basement complex terrains is governed by the hydraulic properties of weathered and fractured aquifer systems. Despite growing demand driven by rapid urbanisation, systematic hydrogeophysical characterisation of such aquifers remains limited across central Nigeria. This study deployed the Schlumberger vertical electrical sounding (VES) technique using the SYSCAL Pro resistivity meter (IRIS Instruments, France) at twelve stations to evaluate the groundwater potential of Lapai, Niger State, underlain by the migmatite-gneiss basement complex. Acquired data were processed through partial curve-matching and computer-assisted iterative inversion to determine subsurface resistivity distribution, aquifer depth, and groundwater prospectivity. All interpreted VES curves exhibit the H-type configuration (ρ₁ > ρ₂ < ρ₃), confirming a three-layer subsurface model. The uppermost lateritic layer ranges in thickness from 2 to 6 metres. The second layer, with resistivity values of 60–140 Ωm occurring at depths of 2–23 metres, is interpreted as a saturated weathered basement aquifer. The third layer represents fresh, locally fractured basement encountered at depths of 30–60 metres, constituting a secondary aquifer target. The study concludes that sustainable groundwater development is technically feasible through boreholes drilled to approximately 70 metres, targeting both the weathered and fractured basement aquifer units.