Abstract

Aquifer potentials characteristics and its impacts on the groundwater subsurface protection of the aquiferous zone using electrical resistivity method of hydrogeophysical prospecting was carried out at Obafemi-Owode Local Government Area, Ogun State South-West Nigeria with the principal purpose of evaluating and rating aquifer protective capacity of the overburden units in the area. Twenty seven (27) vertical electrical sounding (VES) were probed using Schlumberger configuration with the maximum electrode spacing of 100m at each point using Allied OMHEGA Resistivity meter. The data were interpreted using partial curve matching techniques and computer iteration program using WINRESIST. Parameters such as aquifer resistivity, aquifer thickness, overburden thickness, basement resistivity, reflection coefficient and longitudinal conductance were calculated and used for evaluating the groundwater yields and vulnerability of the aquiferous zone to contaminant seepages. The reflection coefficient range is between 0.02 and 0.98 while protective capacity range is between 0.00135 and 0.510. Groundwater potentials of the area were classified as high Areas with 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. Also, the study area shows a very poor, poor, and moderate protective capacity rating. Seven (7) VES stations have very poor protective capacity, eighteen (18) VES stations shows poor protective capacity and only two (2) VES stations shows a moderate protective capacity rating. Since the longitudinal conductance illustrates the impermeability of the confining layers which is generally ˂ 1.0 Siemens; values ˃1.0 Siemens would indicate zones in which the confined aquifer would be protected; the revelations of the study area are possible indications that the groundwater quality status may have been impaired which necessitated the need for borehole water to be randomly sampled for contaminant loads based on this investigation.