A critical analysis of the comparative techniques of aquifer protective capacity studies in part of Southeastern Nigeria

An extensive assessment of aquifer vulnerability was conducted utilizing the DRASTIC, GOD, and IEC techniques to improve understanding of the behaviour of the hydrogeological resources in and around Owerri to contamination. The approach adopted for the aquifer vulnerability studies included a combination of hydrogeological data, parameter ratings, and vertical electrical soundings. These techniques used were adopted with the objectives of defining the influence of contaminant infiltration on the electrical resistivity data of the subsurface, assessing the aquifer’s vulnerability to pollution from the surface, determining the aquifer’s geometric properties, estimating the time of contaminant percolation, and defining groundwater protection zones. Owerri and environs is defined by a relatively level terrain, moderately high groundwater recharge, the predominance of sandy facies with little clay intercalation, and the occurrence of gravel in some areas. Near already-existing boreholes within the study area, forty (40) vertical electrical soundings (VES) were carried out utilizing the ABEM Terrameter SAS 4000. The VES data were analyzed and processed using a combination of computer iterative modelling and curve-matching techniques. Based on the deductions from all the models utilized in this study, the research region is a zone of moderate to high vulnerability. Sand and gravel units contain very little clay and clay-sized particles, which may indicate that the units’ capacity for absorption is limited. The GOD model revealed that 5% of the study area displayed low vulnerability, 90% displayed moderate vulnerability, and the remaining 5% was characterized by high vulnerability. The DRASTIC model revealed that 30% of the study area is of moderate vulnerability (within a range of 101–140), while 70% of the study area fell under the zone of high vulnerability (within 141–200). The vulnerability index revealed by the IEC method was further used for comparison. It was found to be < 500 mS, indicating extremely high vulnerability, and a percolation time of several months, indicating that it would take a contaminant at the surface several months of infiltration to reach the aquifer. The groundwater vulnerability map produced from the integration of the models revealed that Owerri and its vicinity are of moderate to high vulnerability, indicating a high sensitivity to groundwater pollution.