Geophysical investigations for groundwater in the middle Precambrian province of upper Denkyira district using electromagnectic and electrical resistivity methods

Abstract

In this study, geophysical investigations were carried out in twelve (12) communities in the Up-per Denkyira District located in the Birimian and the Tarkwaian Formations of the Central Re-gion of Ghana with the aim of delineating groundwater potential zones, drilling the selected sites, and subsequently comparing the geophysical results with those of the drilling. The geo-physical methods employed included electromagnetic profiling and resistivity sounding using the Schlumberger array. Six (6) boreholes were drilled and the results revealed a lithology that con-sists of laterite, clay, sandy-clay and slightly-to-highly weathered sap-rock including phyllite as the regolith which determines the groundwater potential. Groundwater was generally found at the depth of 20.0-38.0m in the Birimian Formation and 17.0-40.0m in the Tarkwaian Forma-tion. It was found that boreholes drilled within the Tarkwaian and Birimian Formations were successful in producing groundwater, thus indicating that the area has a relatively high ground-water potential since the characteristic geological structures of the basement rocks favour groundwater transmissivity and storativity. The surface geophysical results were correctly vali-dated by the drilling results thus confirming the geophysical exploration technique as a para-mount and a pre-requisite tool for borehole siting.