Hydrochemical appraisal of groundwater evolution within the Lower Pra Basin, Ghana: a hierarchical cluster analysis (HCA) approach

The most relevant controls on groundwater quality within the Lower Pra Basin in Ghana were assessed
using Q-mode hierarchical cluster analysis (HCA). The objective was to determine the chemical characteristics of the various water groups and subgroups responsible for the groundwater evolution and identify the groundwater recharge and discharge zones within the basin. The Q-mode HCA have characterized hydrochemical data from a total of sixty-eight (68) boreholes and two (2) streams within the basin into four (4) water groups and five (5) subgroups. Results showed that, Group 1 waters had the
lowest mean pH (5.6 pH units) with EC and TDS in the range 64.9–295 lS/cm and 32.5–162.0 mg/L respectively, while, Group 4 waters had intermediary mean pH (6.3 pH units) with highest EC and TDS in the range 1,221.2–1,601.0 lS/cm and 661–691 mg/L respectively. Two main water types—the Na–HCO3 and Ca–Mg–HCO3 with Na–Cl and Ca–Mg–Cl as minor water types have also been delineated. Results also showed that, Groups 1 and 2 waters both represents transition zones between Ca–Mg– HCO3/Na–HCO3 and Na–Cl/Ca–Mg–Cl type waters and therefore, can be regarded as transition zones between
naturally circulating groundwaters which have not undergone pronounced water–rock interaction/aggressive recharging alkali carbonate waters and limited recharging local rain/permanent hard water. Thus, groundwater within the basin perhaps evolves from fresh- Ca–Mg–HCO3/Na–
HCO3 type waters to permanent hard- Ca–Mg–Cl type waters and limited recharging local rain- Na–Cl type waters along its flow paths principally due to ion-exchange reactions. However, Zion Camp areas may be serving as discharge areas to groundwater within the basin.