Hydrogeological evaluation of geological formations in Ashanti Region, Ghana

The success of groundwater exploitation in an area largely depends on prior knowledge of existing hydrogeological parameters such as borehole yield, overburden thickness, depth of boreholes, static water level, specific capacity and the quality of water. This study, therefore, employed Geographical Information System to assess some of these hydrogeological parameters in the Ashanti Region using the ordinary kriging interpolation method. Data on 2,788 drilled boreholes in the region were used and the assessment focused on the various geological formations in the region that comprised the Birimian, Granitoids, Tarkwaian and Voltaian formations. The study results indicate that the Birimian formation is generally within medium to high yielding potential zones (30 – 60 l/min or higher) with a high drilling success rate of 91% and average borehole depth of 53 m. The Granitoids are, mostly, within the low yielding zone (< 30 l/min) with isolated high yielding boreholes and have average borehole depth and drilling success rate of 50 m and 72 % respectively. The Tarkwaian formation, on other hand, is within the medium yield zone with a drilling success rate of 80 % whilst the Voltaian formation is mainly classified to fall within low yield zone with about 60% success rate although significant high yield zones occur within the sandstone formation underlying its westernmost part in the region. Groundwater in the region is generally potable except in a few locations within the Birimian and ranitoids,where there are problems with levels of iron, nitrate, manganese and pH. Keywords: Groundwater; Hydrogeological parameters; Geological formations; Geographical Information System; Ashanti Region