Investigation of Geophysical Signatures for Successful Exploration of Groundwater in Highly Indurated Sedimentary Basins: A Look at the Nasia Basin, NE Ghana

An integrated geophysical and geological approach to ensure improved success rates in groundwater development has been proposed for a partially metamorphosed sedimentary basin in Ghana and other areas of similar lithology. The development of groundwater resources in the Voltaian Sedimentary Basin has been constrained by poor success rates estimated to be below 56%. This can be attributed to the inappropriate deployment of geophysical surveys and corresponding erroneous interpretation of results as well as inadequate knowledge of the characteristics of the major lithologies and their characteristic geophysical signatures. In this study, an integrated geophysical investigation using 2D electrical resistivity tomography surveys, electromagnetic conductivity surveys and geophysical borehole logging was employed to determine the geophysical characteristics of the diverse lithological units of the Kwahu–Bombouaka and Oti–Pendjari Groups underlying the study area. This includes mapping the lateral and vertical extents of weathering and fracturing in the subsurface. This study finds that a concerted approach to successful groundwater development should encompass the integration of multiple geophysical techniques with interpretations guided by a priori information on the geology. Such interpretations should also focus on the differences in structural trends and field relationships at each location and not solely on the contrasting magnitudes of geophysical signatures. In line with that, the contact zones between formations, bedding planes and the weathered zone should be targeted during siting as these locations hold promise for groundwater resources development. For example, within the Bimibilla Formation, thicker weathered zones appear to give indications of higher groundwater storage potentials.