GEOELECTRIC SURVEY FOR BOREHOLE SITING IN THE BASEMENT COMPLEX TERRAIN OF AJAOKUTA, SOUTHWESTERN NIGERIA

Abstract

The location of a Steel Rolling Mill and a Gas Turbine Power Plant at Ajaokuta, Kogi State, has drastically increased the growing population of the area. The existing surface water facilitie groundwater resource in order to meet the water demand of the people. This study is aimed at determining the geoelectric sequence of the area, the overburden thickness, aquifer geoelectric characteristics and nature of the bedrock with a view to develop groundwater through borehole drilling. Horizontal resistivity profiling (HRP) was conducted along eight (8) traverses with station separation of 30 m using the Wenner array. The results of the HRP were presented as profiles and loc further investigated with Vertical Electrical Sounding (VES) technique. Twenty occupied with the Schlumberger array of half current electrode spacing AB/2 ranging from 1 m to10 data were acquired using PASI Digital Resistivity Meter (16 GL), presented as sounding curves and interpreted by partial curve matching and computer assisted 1D forward modelling using WinResist software. The results of the VES interpretation were use geoelectric sections revealed four major geoelectric layers which are the topsoil, weathered basement, partly weathered basement and fresh basement. The topsoil has resistivity value that varies from 6 ohm ohm-m and thickness of between 0.5 m and 4 m. The weathered basement has resistivity values that range from 16 ohm-m to 250 ohm resistivity value of 32 to 410 ohm values that vary from 154 ohm the results, one test borehole at VES 9 and two (2) observatory wells at VES 5 and 4 were pumping test analysis conducted on the wells revealed a yield of 25 was significant correlation between the geoelectric sections and the borehole logs.