Groundwater geochemical evolution, origin and quality in the Lower Pra Basin, Ghana: Insights from hydrogeochemistry, multivariate statistical analysis, mineral saturation indices, stable isotopes (δ2H and δ18O) and geostatistical analysis

Abstract

In many places across the globe, including the Wassa District of Ghana, groundwater provides a significant supply of water for various purposes. Understanding the groundwater origin and hydrogeochemical processes controlling the groundwater chemistry is a major step in the sustainable management of the aquifers. A total of 29 groundwater samples were collected and analysed. Ionic ratio graphs, multivariate statistical analysis, mineral saturation indices, stable isotopes, and geostatistics methods were used to examine the sources and the quality of the groundwater. The findings describe the water types in the district as Ca–Mg–HCO₃–Cl, Ca–Na–HCO₃, Na–Ca–HCO₃, Ca–Na–HCO₃–Cl, Na–Ca–HCO₃–Cl, mix water type, Na–HCO₃–Cl, with possible evolution to Ca–Na–Cl–HCO₃, and Na–Ca–Cl–HCO₃. According to the IEWQI for drinking water, around 53.6% of the samples have good quality, whereas 10.7% have very low-quality groundwater. Only 3.45% of the samples are suitable to use for irrigation without treatment, whereas 41.4% are somewhat safe with minimal treatment. Water-rock interactions, including the dissolution and weathering of silicate minerals, cation exchange processes, and human activities like mining and quarrying, are some of the main factors influencing groundwater chemistry. Principal component analysis revealed that groundwater chemistry is influenced by a combination of natural and anthropogenic sources. The APCs-MLR receptor model quantifies the factors that play important roles in groundwater salinization, including mineral dissolution and weathering (19.4%), localised Cd (16%), Ni (14.6%), Pb (12.8%), and Fe (11.4%) contamination from urbanisation while unidentified sources of pollution account for about 26.0%. The stable isotopes revealed groundwater is of meteoric origin and water-rock interaction the major mechanism for groundwater mineralization. The results of this research highlight the need of implementing an integrated strategy for managing and accessing groundwater quality.