INTEGRATED GEOPHYSICAL METHODS FOR GROUNDWATER POTENTIAL ASSESSMENT OF U’ BLOCK PREMISES, ADEKUNLE AJASIN UNIVERSITY, AKUNGBA AKOKO, SOUTHWESTERN NIGERIA.

Integrated very low frequency (VLF-EM) and electrical resistivity method was carried out at the Department of Earth-Science in Adekunle Ajasin University campus, Akungba Akoko, Southwestern Nigeria. A total of 62 stations were occupied for the VLF-EM survey, the study is aimed at evaluating groundwater potential of the area. Two geophysical surveys were conducted with station to station seperation of 5m along five traverses, while a total of 15 VES data were acquired at selected points guided by the VLF-EM responses. Schlumberger array of AB/2 of 65 m with a total spread length of 130 m. The VLF-EM data set were processed by inversion through Karous Hjelt to produce VLF-EM section while resistivity data were processed by partial curve matching and computer iteration techniques to obtain depth sounding curve and subsequently Geo-electric sections. Two distinct conductive zones were revealed; ; low conductive zones which indicate low geological structures/poor groundwater zones and high conductive zones which indicate high groundwater zones respectively. Four distinct Geo-electric/geological units were revealed as topsoil, weathered basement, partially weathered/fractured basement, and fresh basement columns. Resistivity of the topsoil ranges from 64 to 1500 ohm-m, and layer thickness ranging from 1.0 to 3.0 m. The weathered layer has resistivity ranging from 55.0 to 338.1 ohm-m and thickness ranging from 2.3 to 16.0 m. The partially weathered/fractured basement unit has resistivity ranging from 205.0 to 1360 ohm-m, and thickness value of 6.5 to 38.7, while the fresh basement with resistivity ranging from 1443.1 to 1715.0 ohm-m. The results generally revealed that groundwater potential zones were observed in few areas as evident in traverse one. It can be concluded that groundwater potential of the area is low arising from the limited natures of fracture at depth and thin nature of the weathered basement column in the area. It is therefore recommended that drilling program for sustainable borehole should be focused between station 18 to 25 m along traverse one, ves two and ves three in the study area.