Hydrogeochemical characterization and assessment of groundwater quality in the Kwahu-Bombouaka Group of the Voltaian Supergroup, Ghana

The Kwahu-Bombouaka Group of the Voltaian Basin, which defines the northern fringe of the basin, constitutes a significant part of the North East Region of Ghana. Most of the inhabitants in the region depend on groundwater for domestic and irrigation purposes. Therefore, a geochemical characterization and assessment of groundwater quality in the area was carried out using hydrochemical, GIS-based ordinary kriging interpolation and multivariate statistical methods on fifty-five (55) borehole water samples. The aim of this study was to determine the concentrations and spatial distribution of various ions, groundwater quality issues and the geochemical processes contributing to groundwater chemistry. The area is largely underlain by sandy shales and mudstones of the Poubogou Formation and feldspathic, quartzitic sandstones with conglomeratic lenses of the Panabako Formation. The abundance of major cations in the groundwater is in the order: Na+ > Ca2+ > K+ > Mg2+ whereas that of the major anions vary in the order: HCO3- > SO42- > Cl-. Na-HCO3 water type is common in the area, which may be due to dissolution from silicate minerals (albite and microcline) in the basement rocks. The results indicate that fluoride (0.01-8.40 mg/L, mean of 0.58 mg/L) and boron (0.01-4.81 mg/L, mean of 0.28 mg/L) contamination is a threat to groundwater quality with respect to their guideline values provided by the World Health Organization. The groundwater chemistry is primarily controlled by ion exchange reactions, weathering of silicate minerals residing in the Panabako Formation and anthropogenic activities from agriculture. Groundwater in the area is largely suitable for drinking purposes although some few boreholes in the northwestern and southeastern parts have high fluoride and boron concentrations. The sodium percentage (11-99%, mean of 70%), magnesium ratios (2.05-57, mean of 29) and sodium adsorption ratio (0.15-38, mean of 4.72) are quite high in some of the communities in the southeastern part of the area. This suggests that water in this part of the area is not entirely suitable for irrigation