Groundwater prospecting utilizing vertical electrical sounding technique in Obafemi-Owode local Government area South-West Nigeria

Abstract

Investigation for groundwater resource potentials in terms of its hydrological variation and consequent impact on the subsurface water quality using electrical resistivity method was undertaken at Obafemi-Owode Local Government Area, South-West Nigeria with the principal aim of evaluating groundwater potentials and overburden units in the area. Twenty seven (27) vertical electrical sounding (VES) were carried out utilizing Schlumberger configuration with the maximum electrode spacing of 100m at each point using OMHEGA Allied Resistivity meter. The data were consequently interpreted using partial curve matching techniques and computer iteration program using WINRESIST. The geoelectric sections revealed three (3) to five (5) geoelectric layers. The weathered layer which comprises of Sandy Clay/Clayey Sand/Clay/Shale whose layer resistivity value ranges from 16.7Ωm in VESOB6 and VESOB8 with depths of 3.1m and 4.36m respectively to VESOB21 possesses the highest resistivity value of 5545.6 Ωm with a depth of 3.5m in VESOB24, underlying this layer are the fractured basement with the lowest resistivity value of 155.3Ωm in VESOB4 and the highest resistivity value of 1061.2Ωm in VESOB5. The fresh basement displayed resistivity values that range from 432.8 Ωm in VESOB21 to 22,388.7Ωm in VESOB16; the corresponding depths are undetermined due to current termination. The reflection coefficient range is between 0.02 and 0.98 while groundwater potentials of the area were classified as high areas; high (overburden thickness >13m and reflection coefficient less than < 0.8); medium (overburden thickness ≥13m and with reflection coefficient ≥ 0.8) and low (overburden thickness < 13m and reflection coefficient ≥ or ≤ 0.8). The study has therefore identified favourable groundwater potentials of the area with < 1.5 coefficient of anisotropy values.