Abstract

The study investigates the electro-geophsysical method's application to assess corrosivity, competence, and aquifer vulnerability in Njaba and its environs, in southeastern Nigeria, aiming to determine soil suitability for engineering constructions and estimate aquifer vulnerability. Urbanization in the area has led to increased man-made structures and surface pollution exposure. Twenty-three geo-electric resistivity soundings were conducted using ABEM Terameter SAS-4000 and Schlumberger configuration with a maximum half-current electrode spacing of 500 m. Results indicate undulating topography with elevations ranging from 361 to 1336.9ft. Soil resistivity assessment reveals 43.5% moderate competence, 26.1% competent, and 26.1% highly competent zones, with the remainder exhibiting incompetent clay lithology. Corrosivity assessment shows 73.9% essentially non-corrosive and 26.1% mildly corrosive topsoil. The study identifies a semi-deep aquifer system with depths ranging from 79.2 to 115 m and thickness from 23.4 to 48.5 m. Aquifer resistivity ranges from 28700 to 990 Ωm, indicating clean sand to sand with clay admixtures. Hydraulic conductivity varies from 0.0852 to 27.90068 m/day, suggesting clean sand. Aquifer vulnerability assessment indicates a high to moderately low protective capacity, making most of the area suitable for engineering construction and groundwater development. The study highlights the reliability of geological and geo-electric methods in delineating hydraulic conductivity and lithostratigraphic units. It recommends corrosion-resistant pipes in mildly corrosive areas to prevent pipe rupture within a depth of approximately 1.1 m.

Keywords: Competence, corrosivity, hydraulic conductivity, aquifer vulnerability.