Aquifer Vulnerability Assessment at Ipinsa-Okeodu Area, Near Akure, Southwestern Nigeria, using GODT

Aquifer vulnerability assessment has been undertaken at Ipinsa and Oke-Odu area, southwestern Nigeria using geoelectrically derived GODT model. One hundred and two (102) vertical electrical soundings (VES) data utilizing Schlumberger array were carried out at half-current electrode separation (AB/2) varied between 1-150 m. Qualitative interpretation of the VES data using partial curve matching and computer-aided inversion techniques yielded geo-electric parameters (layer resistivity and thickness) that were used in delineating the aquifers in the area and evaluating their vulnerability to pollutants. The geoelectric sections revealed that the area is underlain by three to four geo-electric layers namely the topsoil, weathered layer, partly weathered/fractured basement and fresh basement. The weathered layer and partly weathered/fractured basement constitute the major aquifers in the area. The GODT vulnerability model depicts that the area is characterized by four vulnerability zones which are very low, low, moderate and high vulnerable zones. According to the model, about 10% of the area is highly vulnerable while about 35% is of moderate rating. The low and very low ratings constitute 40% and 15% of the area respectively. Keywords: Aquifer vulnerability, GODT model, vertical electrical sounding and geoelectric parameters