Hydrogeophysical Survey and Vulnerability Assessment of some Communities in Okigwe Local Government Area, South-east Nigeria

Detailed hydrogeophysical and vulnerability studies of the aquifer systems in Okigwe area with focus on communities such as Aku, Agbobu, Ihube and Umulolo was carried out using the vertical electrical sounding (VES) method and the DRASTIC model. A total of twelve (12) vertical electrical sounding (VES) were acquired using the digital Omega Terrameter 0198. The Schlumberger configuration with a maximum current electrode spacing (AB) of 800meters was used to acquire the data. Computer Iteration was carried out using IPI2 win computer software. Layer parameters were obtained and used to estimate Aquifer Hydraulic parameters Lithologs were generated for the VES locations from which cross-sectional profiles were analysed. Results reveal the presence of four geoelectric layers with the resistivity of the first layer ranging from 18.45Ωm-773Ωm and thickness of 0.9m-0.29m representing the top soil. The second Geoelectric layer representing laterite has resistivity range of between 3.17Ωm and 5299Ωm and thickness of 0.78m to 588m. The third layer representing clay/shale has resistivity range between 2.8Ωm to 5475Ωm and thickness of 4.56m to 55.6m. Depth to the water table range from 43.6m to 59.5m. Aquifer thickness of the study area varies from 25.2m to 61.3m with a mean value of 43.7m. Transmissivity value ranges from 1679.4m2/day to 4755.2m2/day. Estimates of aquifer vulnerability rating indicates that about 46.5% of the study area has low groundwater vulnerability index to contaminants while 53.55% of the area indicated moderate aquifer vulnerability using the DRASTIC model