Hydrochemical characterization of groundwater in the Akyem area, Ghana

The Akyem area is a small farming community located in southeastern Ghana. Groundwater samples from wells in the area were analyzed for concentrations of the major ions, silica, electrical conductivity and pH. The objective was to determine the main controls on the hydrochemistry of ground-water. Mass balance modeling was used together with multivariate R-mode hierarchical cluster analysis to determine the significant sources of variation in the hydrochemistry. Two water types exist in this area. The first is influenced most by the weathering of silicate minerals from the underlying geology, and is thus rich in silica, sodium, calcium, bicarbonate, and magnesium ions. The second is water that has been influenced by the effects of fertilizers and other anthropogenic activities in the area. Mineral speciation and silicate mineral stability diagrams suggest that montmorillonite, probably derived from the incongruent dissolution of feldspars and micas, is the most stable silicate phase in the groundwaters. The apparent incongruent weathering of silicate minerals in the groundwater system has led to the enrichment of sodium, calcium, magnesium and bicarbonate ions as well as silica, leading to the supersaturation of calcite, aragonite, dolomite and quartz. Stability in the montmorillonite field suggests restricted flow conditions and a long groundwater residence time, leading to greater exposure of the rock to weathering. Cation exchange processes appear to play minor roles in the hydrochemistry of groundwater.