The Variation in the Depth of Overburden at Different Ves Points within Samaru Using D.C. Resistivity Technique

The interpretation of 32 Schlumberger vertical electrical sounding (VES) data was carried out at Samaru College of Agriculture, A.B.U, Zaria, Sabongari Local government area of Kaduna State, Nigeria. This is an attempt to investigate the groundwater potential and the geologic characteristics of the overburden of the area. Terrameter signal averaging system (SAS) model 300 was the instrument used. No booster was used as the expected depth is within the range of penetration of the instrument. In this instrument consecutive readings are taken automatically and the results averaged continuously and displayed. The schlumberger electrode configuration was used in the data acquisition. The field procedure consists of expanding AB (distance between current electrodes) while MN (distance between potential electrodes) is fixed. This process yields a rapidly decreasing potential difference across MN, which eventually exceeds the measuring capacity of the instrument; therefore a larger value for MN was taken to continue with the survey. The VES curves were interpreted using IPI2Win resistivity computer software. The survey area is dominated by mainly four layers, namely: Overburden, Weathered basement, fractured basement and Fresh basement. The overburden consists of laterites, clay and fadama loam. The results of the interpreted VES data showed that The Overburden thickness varies from 1.3 to 5.2m, with an average of 3.1m. The lowest overburden depth is at VES20 where the depth to basement is as low as 6m. A map was produced by contouring all the overburden depths at each VES point at an interval of 0.5m. The map shows the variation of the topsoil depth from one place to another within the survey Area which is an indication of the inhomogenuity of the subsurface structures. The thickness of the aquifer varied from 1-35m with an average of 18m.