Exploration of Shallow Basement Aquifers for Cost-Effective Groundwater Exploitation Using Electrical Resistivity Profiling and Vertical Electrical Sounding in Minna, Nigeria

Abstract

Geoscientific exploration is a prerequisite for groundwater development through borehole drilling in the Basement Complex. With advances in model drilling technologies that increase drilling depth, accompanied by uncertainties, the cost of drilling boreholes has increased, especially where shallow groundwater zones are poorly explored. Horizontal Electrical Resistivity Profiling (HERP) and Vertical Electrical Sounding (VES), employing the Schlumberger configuration, were used to investigate the lateral and vertical resistivity variation of the study area. 5 profile lines, each consisting of 5 to 7 sounding stations, were established. Low resistivity points on the profiles were selected for further prospecting employing the VES with 50 m maximum current electrode half separation (AB/2). The HERP reveals lateral variation of the resistivity distribution associated with the subsurface weathered and fractured Basement rock units. Relatively low resistivity values (0.12 Ω to 0.17 Ω and 30.0 Ωm to 41.9 Ωm) were delineated in the north-western and south-western portions of the study area. These portions are interpreted as weathered, fractured, and water-saturated lithologies with shallow groundwater potential. In contrast to low resistivity zones, high resistivity zones, which represent relatively unfractured, fresh Basement lithology, observed along parts of profile 3 are considered unsuitable zones for shallow groundwater exploitation. VES interpretation reveals predominantly H-model curve type comprising 3 geoelectric layers (ρ₁ > ρ₂ < ρ₃). These layers represent the unsaturated topsoil, the weathered materials, and the fractured/fresh Basement rock units. The fractured Basement rock layer defines the shallow aquiferous zone within the depths of 30 m to 50 m.