AQUIFER RISK ASSESSMENT OF PARTS OF IWOROKO AREA, SOUTHWESTERN NIGERIA

Abstract

The demand for potable water for human consumption in Iworoko Ekiti located in the basement complex of southwestern Nigeria, is increasing due to the yearly influx of students into the area. The tremendous population growth with increasing anthropogenic activities had suggested the need for aquifer risks assessment of the area. Integrated geophysical approach using Very Low Frequency Electromagnetic (VLFEM), Electrical Resistivity (ER) Methods and water chemistry analysis were adopted to evaluate the risk of the aquifers to pollution, consequently its groundwater quality. A total of 10 VLF- EM traverses were established mostly in the east-west direction and data were obtained at 20 m station interval, fifty-six (56) Schlumberger Configuration Vertical Electrical Sounding (VES) points were occupied and sixty-eight (68) shallow hand-dug wells-water samples analyzed. The geo-electric parameters results and sections led to the delineation of four subsurface layers namely: topsoil, weathered layer, partly weathered/fractured basement and fresh basement. The respective resistivity and thickness values of these layers are 46-1071 Ωm and 0.3-3.6 m, 11-334 Ωm and 1.8-24.4 m, 314- 755 Ωm and 18-45.8 m and 986-38770 Ωm and 0.4-55.4 m depth to fresh basement. The curve types indicate the presence of weathered layer and fracture confined aquifers in the study area. Water quality index results revealed good quality groundwater except at Anglican Church (northeastern area) which was attributed to the very shallow nature of the well. The depth to aquifer in the area is mostly between 3.3 m - 25.4 m with hardpan laterite and lateritic clay dominating the layers overlying the aquifer which suggest low risk to pollutants infiltration. This is supported by the Groundwater Occurrence (G), overall lithology of aquifer (O) and depth to groundwater table (D) G.O.D index ranging from 0.1 - 0.62 indicative of low to moderate vulnerability in the study area. In addition, the physicochemical parameters of water samples measured also falls within the WHO limit for groundwater consumption. In conclusion, groundwater potential in Iworoko area is low except some isolated points around satellite town/EKSU area with moderate potential. Most of the aquifers are protected and hence, less vulnerable to pollution due to the nature of the overlying layers.