Hydrochemical characterization of groundwater in the Accra plains of Ghana

Chemical and isotopic analyses are used to characterize and identify the relevant water-rock interactions, which are responsible for the poor groundwater quality in the Accra Plains. Four main water types are identified. Processes that singly or in combination influence the chemical composition of each water type include halite dissolution carbonate dissolution and precipitation, seawater intrusion, cation exchange, evaporative concentration of solutes and aluminosilicates dissolution. These processes contribute considerably to the concentration of major ions in the groundwater. Stable isotope contents of the groundwater suggest mainly direct integrative recharge. A few samples plot along the meteoric-seawater mix line which is coincidentally the evaporative line. The Cl-/Br- ratios of some of these are close to 300 confirming marine origin, others probably concentrated by evaporation have their Cl-/Br- ratios significantly lower than 300. Groundwater is qualitatively good for drinking purposes only along the foothills of the Akwapim Togoland ranges.