Application of electrical and electromagnetic data to delineate shallow aquifer zones: a case study of Vea catchment, Ghana

Access to groundwater for use in semi-arid regions is costly due to consistent failures in borehole drilling programs attributable to either a survey not carried out before drilling or incorrectly interpreted geophysical results. Thus, this study aims at delineating the geometry of the shallow weathered crystalline basement aquifer of the Vea catchment, northern Ghana, to aid in the assessment of its groundwater storage potential. Integrated electromagnetic and electrical resistivity surveys within the study area and borehole logs were integrated to delineate the aquifer zones of the study area. The study results revealed the interface between the bedrock and the overlying weathered subsurface as the most transmissive aquifer zone, with the saturated weathered subsurface making up 90% of the total volume of aquifers in the subsurface. The aquifer material in this zone predominantly includes varying proportions of sandy clay and weathered granite, with apparent resistivity ranging from 100 to 500 Ωm in the subsurface. Also, the results indicated that the weathered bedrock interface is irregular, and the water strike zone of the shallow aquifer in the weathered zone mimics the water table and the landscape of the area. Therefore, the study findings could improve the success rate of borehole drilling within the catchment and similar geological terrains.