Interpretation of Geoelectric Pseudo-Section of a Profile Across a Functional Borehole Located in-between Two Non-Functional Dug-Wells

Abstract

Electrical resistivity imaging survey was carried at Agban, Kaura Area of Kaduna State Nigeria. A profile of 500m length was deliberately selected to cut across a functional borehole located averagely 100m in-between two non-functional dug-wells. Ten (10) VES Points were sounded along the profile in the N-S direction. Terrameter SAS300 was the instrument used. The tomogram of the profile shows that the area is underlain by four layers; the first layer is sandy clay with resistivity range of 200-500Ωm. This is taken as the Overburden. The second layer is the weathered basement which constitutes of Sandy soil and water. This is taken to be the aquifer which varies along the profile. The third layer comprise of coarse grain sand which is the fractured basement of resistivity range of 1000-2000Ωm. The fourth layer of resistivity greater than 2000Ωm is the fresh basement. The image also shows a U-shaped fracture zone within the subsurface, the borehole was drilled through this fracture which contains water. This fracture causes water to migrate from the locations of the wells and accumulate at the borehole site. This research has gone a long way to establish the facts that since the dug wells are shallow; they failed at the end of the dry season when groundwater levels fall. It is a common knowledge that little specialist equipment is used for the construction of a well even though it is difficult to construct hand dug wells in hard rock. On the basis of the results of this study, we therefore recommend that thorough geophysical survey should always be carried out in the basement complex before constructing dug wells for them to be sustainable.

Keywords: Resistivity1, Kaura2, Well