HYDROGEOLOGICAL INVESTIGATION FOR GROUNDWATER POTENTIALS IN AJAOKUTA AREA, KOGI STATE NIGERIA USING ELECTRICAL RESISTIVITY SURVEYS (original) (raw)

Abstract The objective of this geophysical survey is to evaluate the hydrological characteristics of the study area. This includes the availability of groundwater, depth of aquifer, determining whether the underlying geology is competent basement/weathered basement or fractured bedrock and the delineation of the subsurface into various geo-electric layers. The availability of groundwater in an area is controlled by varying geological factors such as hydrogeological units, stratigraphical faults/folds, and geological sequences The methodology used is the direct current method using the schlumberger configuration. In this electrical resistivity method, artificially-generated electric currents are introduced into the ground and the resulting potential differences are measured at the surface. Deviations from the expected pattern of potential differences from homogeneous ground provide information on the lithological formations and electrical properties of subsurface anomalies. A total of 10 vertical electric sounding was carried out on the study area, which covers the entire community and the data plotted and computer software designed by Vander Velpen BPA was used to iterate the result. This removes the noise and field errors incorporated in the data. The result of the VES curve reveals that there are three major geoelectric layers The fist layer has an intermediate resistivity implying a sandy soil. Very low resistivity corresponds to clayey/clayey sand (VES 4, VES 5, and VES 6) while exceedingly high resistivity (VES 10) implies a lateritic cover. The second layer is the weathered layer sub-divided into minor geoelectric layers such as clays, gravels and weathered rocks. The weathered layers have low resistivity values, possibly due to the presence of conduction fluids such as water. The third layer is the basement or bedrock which may be fractured basement or fresh bedrock. Ajaokuta has more of fresh unfractured bedrocks except in some cases (VES 2 and VES 4) The resistivity of topsoil varies from 12.6Ω to 3247.9Ω with a mean of 657.1Ω ± 947.7. The thickness of topsoil is within the range of 0.4m to 14.9m with a mean of 2.2m ± 4.2. The resistivity of weathered layer ranges from 27.9Ω to 175.5Ω with a mean of 59.2Ω ± 43.5. The thickness of the weathered layer is from minimum of 5.8m to maximum of 37.0 m having a mean of 12.4m ± 9.5. The depth to basement varies from 6.2m to 37.5m with a mean of 13.38 ± 9.07. The resistivity of the basement in the area varies from 183.3Ωm to 4294.2Ωm with a mean 0f 905Ωm ± 1170.The thickness of the topsoil is very low except for (VES 4) The average depth to basement is 13.38m±9.07. Keywords: Boreholes, Ajaokuta, schlumberger configuration, resistivity, VES