Geophysical Investigation for Aquifer Potential Assessment and Groundwater Development at EKSU Staff Quarters GRA Ado Ekiti, Southwest Nigeria

Abstract

Very-Low Frequency Electromagnetic (VLF-EM) and Electrical resistivity methods for  reconnaissance and detailed geophysical studies respectively have been carried out within the Ekiti-State University Staff Quarters at Onigari GRA area of Ado-Ekiti. The study’s objectives include amongst others to detect drillable points for groundwater abstraction boreholes in order to frontally address the inherent problem of scarce water supply for uses by the university staff and their families living within the quarters. Seventeen (17) East-West traverses were established along where VLF profiling were conducted at an interval of 10m. The qualitative and quantitative interpretations of the VLF-EM data revealed twenty three (23) positions along the traverses that exhibited significant conductivities which are suggestive of thick and/or fractured overburden which are favourable structures for possible groundwater accumulation, these 23 positions were selected for further detailed investigation using the Vertical Electrical Sounding (VES) technique. The Twenty-three (23) VES stations were thereafter occupied employing the Schlumberger arrangement, with half-electrode spacing (AB/2) varying from 1-150m. The quantitative interpretation of the obtained VES data were carried out using the  curve-matching and computer iteration techniques. The 3-layer (A and H); 4-layer (HK, KH, KQ and QH); 5-layer (HKH); 6-layer (AKHK and KHKH) and 7-layer (HKHKH) depth sounding curves were derived from the area. The 4-Layer type curve is predominant with 25% occurrence. The geoelectric sections mapped-out five lithologic units; including the topsoil; the weathered layer; the partly weathered/fractured basement, the fractured basement and the fresh basement. From the integrated consideration of the geoelectric parameters and inferred aquifer characteristics of the study area, it becomes clearer that the following VES postions are recommendable for the development of good yielding groundwater development schemes in order of priority,VES 20 ,  VES 12 , VES 18 ,  VES 10 , VES 8 ,  VES 7  and VES 15.

Keywords: Traverses, Depth Sounding Curves, geoelectric sections, VES stations, aquifer units, boreholes