Characterization of subsurface structures across a functional borehole at Mabushi Area of Kaduna State Nigeria

Abstract

Mabushi area lies between latitudes 9⁰30' N and 9⁰45'N and longitudes 8⁰20'E and 8⁰35'E in the southern part of Kaduna state Nigeria. A Profile of 200m length was established comprising of nine (9) VES Points with a functional Borehole located betweenVESmb3 and VESmb4. The Borehole is one of the oldest in the Area. This study was aimed at characterizing the subsurface structures along the profile taken NE-SW across the functional borehole. The survey area is dominated by mainly four layers, namely: Topsoil, weathered layer, fractured layer and Fresh basement. The topsoil resistivity values varies between 100-1200Ωm. This layer is predominantly sandy clay with an outcrop of granitic rock at VESmb6. The second and third layers within the subsurface structures are taken as the aquifer constituting of sandy soil and coarse/medium grain sand with a relatively large thickness of 65m. The Borehole was sited between VESmb3 and VESmb4. It has been functional for the past twenty nine (29) years. A critical observation of the tomogram shows that the borehole was drilled to a sufficient depth of 45m and the thickness of the aquifer which is 65m where the borehole was sited is appropriate to sustain the borehole. The depth to fresh basement rock was found to be approximately 100m as calculated from the sounding curves of the VES points.

Keywords: Borehole, Aquifer, Subsurface