Geophysical Characterization of Basement Rocks and Aquifer Potentials of Odeda General Hospital and it Environ in Abeokuta, Ogun State, Southwestern, Nigeria

Groundwater of the continent are found beneath the earth surface which are water found in the rocks, consolidated or unconsolidated, that are permeable enough to permit usable quantities of water to move into wells. For the assessment of Groundwater there is need for investigation of the potentiality which triggered the application of Very Low Frequency- Electromagnetic (VLF-EM) as Reconnaissance survey for Fractures which are five (5) Traverse within the study area and Vertical Electrical Sounding (VES) for the confirmation of the yield rate. Ten (10) VES were carried out using schlumberger electrode arrangement and their results are interpreted using computer iteration technique. Interpretation of VES curves has led to the classification of the curves into five (5) types which are HH, HHA, KHH, AAH and H. The curves are of four to five layers with varying resistivities and thickness. The results of the interpretation revealed six distinct layers viz Topsoil, sand clay, clayey sand, lateritic, weathered basement (sand) and fresh basement (sand stone). The topsoil is generally lateritic and is characterized by relatively high layer resistivity values. The underlain material is mostly sandy clay or clayey sand with reasonable resistivity values. The third layer consist of clayey sand or sandy clay or shale and sand (weathered/fractures) in some with reasonable resistivity values also. The fourth and fifth layer are made up of fractured and fresh basement and is characterised by high layer resistivity values. The results of this research indicate that the sandy clay and sand (weathered or fractured) constitutes the major aquifer material and the occurrence of thick aquifer in term of the weathered/fractured basement are responsible for existence of good groundwater prospect in the study area.