Hydrochemical Evolution of Groundwater Within the Amansie and Adansi Districts of the Ashanti Region (Ghana)

Fifty-nine (59) boreholes and twelve (12) hand-dug wells were collected for quality assessment to delineate the soil–water–rock interactions responsible for the chemical evolution of groundwater within the Amansie and Adansi Districts. Results show that silicate weathering and ion-exchange reactions are the major processes influencing groundwater chemistry within the Districts. Groundwater within the districts is acidic as 62% of groundwaters had pH which ranged  from 3.6 to 6.0 pH units, attributable predominantly to natural processes than mining activities. The study also show that about 98% of groundwater is fresh (EC < 500μS/cm) with EC values which ranged from 22.8 to715 μS/cm, and a mean value of 179.8 μS/cm. Groundwater TDS ranged between 14.9 and 393.9 mg/L with a mean value of 110.4 mg/L. The relative abundance of cations and anions are in the order of: Ca²⁺ > Na⁺ > Mg²⁺ > K⁺ and HCO₃⁻ > Cl⁻ > SO₄²⁻, respectively. Two principal hydrochemical water types: Ca-Mg-HCO₃ and Na–Cl have been delineated, with Ca-Mg-SO₄, Na-Mg-Ca-HCO₃ and Na-Cl-SO₄ as minor water types. The study further shows that the surface waters are chemically the least evolved of the waters investigated since they are principally Ca–Mg–HCO₃ type waters. The surface waters thus could be serving potentially as recharge reservoirs to groundwater within the districts. Groundwater within the districts principally evolves from fresh Ca–Mg–HCO₃ type water into Na–HCO₃ type water into Ca–Mg–Cl type water into Na–Cl type water along its flow-path due to ion-exchange reactions.