Characterization of groundwater in the 'Tamnean' Plutonic Suite aquifers using hydrogeochemical and multivariate statistical evidence: a study in the Garu-Tempane District, Upper East Region of Ghana

Abstract

Abstract The 'Tamnean' Plutonic Suite aquifer is the main public water supply for the Garu-Tempane District. Thus, hydrogeochemical characterization is essential to provide valuable insights into pollution sources and the main controls on groundwater chemistry. In this regard, multivariate statistical methods, conventional hydrochemical graphical methods, and various ionic ratios complemented with PHREEQC geochemical modelling were carried out using 38 groundwater samples collected from the Tamnean Plutonic Suite aquifers, Ghana. The ionic ratio plots, the chloro-alkaline indices, and the graphical diagrams indicate that the major sources of groundwater chemistry are silicate mineral dissolution and cation exchange coupled with the leaching of domestic solid waste and nitrogen-based fertilizers. The Q-mode hierarchical cluster analysis reveals three spatial groundwater zones. Groundwater from recharge areas consists of Ca–Na–HCO3 water types in cluster 1. The intermediate zone is characterized by Ca–Mg–Na–HCO3 water types of moderate ionic compositions in cluster 2, and this evolves into a discharge zone in cluster 3 mainly of Ca–Mg–Na–HCO3–NO3 water types. The principal component analysis (PCA) reveals three factors, which account for 81% of the total variance, and this suggests most of the groundwater chemistry had longer interaction with the lithological materials. The PHREEQC geochemical modelling consisting of mineral saturation index indicates that groundwater is mostly supersaturated with respect to dolomite and undersaturated with respect to calcite, anhydrite, fluorite, gypsum, and halite. Based on the water quality index, the groundwater in the district is generally suitable for drinking water purposes. All the samples are within the World Health Organization acceptable limits for drinking water except for lower pH, elevated nitrate and bromide concentrations in some of the wells. About 10.5% of the groundwater samples are contaminated with nitrate, which may pose a health danger to the inhabitants in the communities. The finding of this study will not only contribute to solving the research paucity regarding the Tamnean Plutonic Suite aquifers in the Garu-Tempane District but will serve as a valuable document for water managers and decision-makers in Ghana.

Keywords

• Tamnean Plutonic Suite
• Groundwater chemistry
• Saturation index
• Elevated nitrate concentrations