A GEOELECTRIC ASSESSMENT AND CLASSIFICATION OF THE AQUIFER SYSTEMS IN A TYPICAL BASEMENT COMPLEX TERRAIN;

A geoelectric assessment and classification of the aquifer types and systems in a basement complex terrain of Ekiti state, southwestern Nigeria have been carried out as part of a continuing effort at the groundwater potential appraissal of the state. The study involved the electrical resistivity method using the Vertical Electrical Sounding (VES) field technique was adopted. A total of four hundred and thirty-one (431) VES stations were occupied using the Schlumberger electrode configuration. The interpretation and analysis of the data revealed that the study area is underlain by five geoelectric layers which are topsoil, laterite, clay/sandy clay/clayey sand/sand, weathered layer, partly weathered/fractured basement and the presumably fresh basement. The clay/sandyclay/clayey sand/sand, the weathered layer and the partly weathered/fractured basement constitutes the two (2) primary aquiferous units. These primary aquifer units were observed to have combined to form five (5) secondary aquifer systems, these include the weathered aquifer; the weathered/partly weathered/fractured (unconfined) aquifer; the weathered/fractured (confined) aquifer; the weathered/fractured (unconfined)/fractured (confined) aquifer and the fractured (confined) aquifer. The weathered aquifer represents the predominant aquifer type in the study area, having about 51 % occurrence. It has its highest and least occurrences on migmatite and charnockite respectively. The groundwater potential of each of the lithologic units in the stud