AVI- and GOD-based vulnerability assessment of aquifer units: a case study of parts of Akwa Ibom State, Southern Niger Delta, Nigeria

Vulnerability assessment of aquifer units is vital in groundwater management and development. In this study, aquifer vulnerability was assessed via surficial resistivity measurements in Obot Akara Local Government area of Southern Nigeria using the GOD and AVI methods. In all, 19 vertical electrical soundings (VES) were made in the area using the Schlumberger electrode configuration with maximum current electrode spreads varying from 600 to 1000 m. The area is shown to comprise 3–4 geoelectric layers within the limit of the electrode spread utilized. The third geoelectric layer, interpreted as gravelly sands at some locations and sandy clay at other locations constitutes the major aquifer units in the area and has a thickness of 56.0–68.9 m. Based on the GOD index and AVI results, the hydrogeological units in the area are adjudged to have low to moderate vulnerability to contaminants. The little percentage high-vulnerability zone has been demarcated.