Delineation of Groundwater at Iseyin, South Western Nigeria

Aims: This research was carried out to determine: the variation in resistivity of the different soil profiles in the area, the depth and thickness of the weathered basement, the depth and thickness of the aquifer, the depth to basement, and to establish areas suitable for borehole development. Materials and Methods: Vertical Electrical Sounding (VES) was carried out using Schlumberger electrode array. A pair of potential and current electrodes was arranged in such a way that the potential electrodes were positioned in between the current electrodes and the positioning of the electrodes was set out using the measuring tape. The Ohmega resistivity meter was used for the data collection which measures the apparent resistivity of the subsurface. Results and Conclusions: The results showed that the area is composed of four (4) to five (5) layers, namely; the topsoil, clay, sandy clay/clayey sand, sand, and dry sand. The top soil has apparent resistivity ranging from 134.2 to 790.9 \(\Omega\)m with thickness and depth between 0.4 and 2.4 m. Clay is found mainly in traverses 1, 7, and 8. It has apparent resistivity ranging from 37 to 77.4 \(\Omega\)m , thickness between 2.9 and 1.9 m and depth within 5.0 and 16.9 m. Sandy clay/ clayey sand are concentrated in traverses 1, 3, 5 and 8 with apparent resistivity range between 18.4 and151.8 \(\Omega\)m ; thickness of about 1.3 to 18.8 m , and depth ranging from 2.3 to 35.7 m. The sand has apparent resistivities of about 226.2 to 610.8; thickness between 0.4 and 7.7 m, and depth ranging from 1.0 to 12.2 m. They are found in traverses 2, 3, and 4. Dry sand/ dry sand (with quartzite) have apparent resistivities ranging from 407.8 to 924.3 \(\Omega\)m . It has thickness ranging from 0.8 to 3.2 m and depth between 0.8 and 5.1 m. Perched aquifer could be found in sand and sandy clay. Wet sand contains both confined and unconfined aquifers while clayey sand harbours confined aquifer.