Modelling the Reactive Mineralogy of Groundwater Aquifers in the Densu River Basin, Southwestern Ghana

Abstract

Groundwater plays a fundamental role in the domestic water delivery system in the Densu River Basin, Ghana. The resource has sometimes been rendered unsuitable for use due to contamination from various sources such as leaching of source rocks and anthropogenic activities. Multivariate statistical techniques and mass balance modelling were applied to hydrochemical data to investigate groundwater hydrochemical evolution in the study area. The groundwater was weakly acidic, moderately mineralized, fresh to brackish with conductivity ranging from 120 μЅ/cm north of the basin to 35600 μЅ/cm south of the basin. The order of relative abundance of major cations in the groundwater is Na+ > Mg2+ > Ca2+ > K+, while that of anions is HCO3- > Cl- > SO42- > F- > NO3-. Conventional graphical technique showed that groundwater hydrochemistry in the study area is largely controlled by water rock-interaction and ion exchange reactions processes. Two main hydrochemical facies such as Na-HCO3 and Mg-Ca-HCO3 watertype were identified in the area. These facies are dominated by Na+ and HCO3-, since they plot closer to the lower corner of the diamond field. Hydrochemical analysis suggests that the dissolved ions in the groundwater may have resulted from leaching and weathering of source rocks, cation exchange and anthropogenic activities. Hierarchical Cluster Analysis (HCA), results revealed four spatial groundwater sub-groups with defined hydrochemical facies and evolutionary patterns. PHREEQC modelling and mineral stability diagrams suggest that, the most stable silicate mineral phases in the area are kaolinite and montmorillonite. Thus, suggesting restricted groundwater flow owing to the limited interconnectivity of the fracture systems that control the hydrogeological properties of the aquifers in the Densu River Basin.