Geoelectric Sounding to Delineate Shallow Aquifers in the Coastal Plain Sands of Okitipupa Area, Southwestern Nigeria

In Okitipupa area, southwestern Nigeria, the aquifers of the Coastal Plain sands are largely Quaternary porous sediments, but without records of their subsurface disposition. In this study, 50 Schlumberger soundings were conducted over the study area, aimed at delineating the boundaries, depth range of the shallow aquifer units and assess their vulnerability to near-surface contaminants. The study delineated two major aquifer units within the area: The upper/surficial aquifer system, which occur at depths ranging from 5.8m (around Agbabu) to 61.5m (around Ikoya) and with materials of higher average resistivity (504.7 m), suggestive of gravelly/coarse to medium-grained sand and the intermediate aquifer system, characterised by depth range of 32.1-127.5 m, average resistivity of 296.8 m, typical of medium-grained sand saturated with water. The highly resistive, impermeable materials overlying the aquifer units around Ajagba, Aiyesan, Agbetu, Ilutitun, Igbotako and Erinj suggests that the aquifer units are less vulnerable to near-surface contaminants than in Agbabu, Igbisin, Ugbo and Aboto where aquifers are overlain by less resistive materials. This study enabled the delineation of shallow aquifers, their subsurface disposition and promising areas for elaborate groundwater development in the area.