Geo-electrically and hydrogeologically derived vulnerability assessments of aquifer resources in the hinterland of parts of Akwa Ibom State, Nigeria

Abstract

The study aims at employing geo-electrically and hydrogeologically derived indices to assess the vulnerability in an alluvial environment of Obot Akara and Nsit Atai counties in the hinterland of Akwa Ibom State, Southern-eastern Nigeria. Vulnerability maps have been generated using seven indices: depth to groundwater (D); net groundwater recharge (R); aquifer media (A); soil media (S); topography (T); impact of vadose zone (I) and hydraulic conductivity acronymized as DRASTIC. The DRASTIC vulnerability index (V) was computed as the sum of the product of weights and ratings. The results indicate that, for Obot Akara site, about 20% of the aquifer is classified as medium vulnerability, about 40% is high vulnerability and very high vulnerability. . For Nsit Atai, about 60% of the aquifer is classified as medium vulnerability while 20% represents high and very high vulnerability respectively. The results of the vulnerability assessment shows that the DRASTIC quality category in percentage is contributory from the seven parameters and hence avoidable anthropogenic activities leading contamination of groundwater should be avoided while the vulnerability maps should be employed to avoid locating boreholes in areas with very high vulnerability. With appropriate software programmes, ground-based geophysical data, hydrogeological and environmental inputs, the vulnerability assessment has been made to cover both the present and future exploitable groundwater resources for the healthy and economic benefits of human existence.