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Determination of the Vulnerability of Water Supply Aquifers in Parts of Imo River Basin, South-Eastern Nigeria: The Case of Benin Formation

Eight locations in the study area were investigated to obtain data on the depth to water table, net recharge, aquifer media, soil media, topography, impact of the vadose zone and hydraulic conductivity. These parameters are denoted by the acronym, DRASTIC, an empirical groundwater model that estimates groundwater contamination vulnerability of aquifer systems based on the hydrogeological settings of the area. This was used to develop a vulnerability map for the study area. The vulnerability map shows that areas within Benin Formation have generally moderate vulnerability to pollution. 2 . The characteristics of these aquifers such as transmissivity, hydraulic conductivity and storage potentials are not clearly understood. Since the mid 1980's, some researchers from the academia have carried out geological/geochemical investigations. Uma (1986) carried out a study on the ground resources of the Imo River Basin using hydro-geological data from existing boreholes. He concluded that three aquifer systems (shallow, middle and deep) exist in the area (Uma, 1989). Geophysical investigations on groundwater resources in the Imo River Basin were also carried out in different sections of the basin. While the contributions made by these workers are remarkable, more work still needs to be done, particularly in the area of vulnerability of the aquifer systems. The present study is aimed at investigating the vulnerability of the hydro- geological character in Ameki and Imo shale Formations to pollution. Vulnerability assessment is more meaningful in areas where water resources are under stress due to industrial or agricultural activities, as it can provide valuable information for