Interpretation of vertical electrical sounding points around two boreholes at samaru college of agriculture, A.B.U., Zaria-Nigeria

摘要

Vertical Electrical Sounding (VES) was carried out around a functional and non-functional borehole at the Samaru college of Agriculture, Ahmadu Bello University, Zaria-Nigeria, with the target to investigate the causes of failure of one of the boreholesThis paper focus on the VES Points taken around the two boreholes (A and B). VES Points 1, 2 and 3 were taken around borehole A, while VES Points 4 and 5 were taken around borehole B. The sounding curves for VES 1,2 and 3 shows a four-layer geoelectric structure. The first layers for the three VES Points shows a range of resistivity values of 280ohm-m to 360ohm-m. This moderately high resistivity values could be as a result of the presence of laterites. VES 4 and 5 were made around borehole B. The sounding curves indicate a 5-layer geoelectric structure. This is in fairly good agreement with the borehole log. The high resistivity values at VES Points 4 and 5 around borehole B is an indicative of low conductivity in the subsurface structures. The VES Points 1, 2 and 3 around the existing and functional borehole A has large aquifer thickness and low depth to water table. This finding is a proof that there is a correlation between the depth to basement and depth to water table. On the other hand, the VES Points 4 and 5 around the non-functional borehole B, has small aquifer thickness and large depth to water table which could be a possible reason why the borehole failed not up to two years after it was drilled.