Hydrochemical evolution and source controls of groundwater quality in the voltaian aquifers of East Mamprusi, Northern Ghana

In many rural communities in Ghana, groundwater is the main domestic water source, but its quality is shaped by aquifer geology, mineral dissolution, residence time and local human inputs. This study assessed the hydrochemical evolution, drinking-water suitability and source controls of Voltaian aquifers in East Mamprusi using 55 groundwater samples. Hydrochemical facies, Gibbs and ionic-ratio plots, Comprehensive Pollution Index (CPI), Water Quality Index (WQI), PHREEQC saturation modelling, sensitivity analysis and Positive Matrix Factorisation (PMF) were applied. Groundwater was generally alkaline, with pH ranging from 6.39 to 8.82, and was dominated by Na+K-HCO₃ facies, representing 74.5% of samples. Gibbs plots showed rock dominance in 83.64% of samples, while Na-normalised weathering ratios indicated that 96.36% of samples reflected carbonate buffering, silicate weathering, and ion exchange. CPI indicated low pollution: 16.36% clean, 41.82% sub-clean, 36.36% slightly polluted and 5.45% moderately polluted. However, WQI classified 30.91% as unsuitable for drinking, mainly due to elevated fluoride and boron. Fluoride ranged from 0.01 to 13.29 mg/L and was linked to alkaline, Na-rich, HCO₃-dominated groundwater. PHREEQC showed complete supersaturation with calcite, aragonite and dolomite, with 61.82% supersaturated with fluorite. PMF resolved geogenic fluoride-boron enrichment, anthropogenic nitrate input and Na-HCO₃-TDS mineralisation, supporting targeted monitoring, borehole screening and treatment.