Hydrogeochemical study on the contamination of water resources in a part of Tarkwa mining area, Western Ghana

Abstract

The aim of this study was to investigate the groundwater chemistry with special concern to metal pollution in selected communities in the Wassa West district, Ghana. In this mining area, 40 ground water samples, mainly from drilled wells, were collected. The groundwaters have generally from neutral to acidic pH values and their Eh values indicate oxidising conditions. The dominating ions are calcium, sodium, and bicarbonate. The metal concentrations in the study area are generally lower than those typically found in mining regions. Only 17 wells show metal concentrations exceeding WHO guidelines for at least one metal. The main contaminants are manganese and iron, but arsenic and aluminium also exceed the guidelines in some wells probably affected by acid mine drainage (AMD). Metal concentrations in the groundwater seem to be controlled by the adsorption processes. Hydrogeochemical modelling indicates supersaturation of groundwater with respect to several mineral phases including iron-hydroxides/oxides, suggesting that adsorption on these minerals may control heavy metal and arsenic concentrations in groundwater. The area is hilly, with many groundwater flow divides that result in several local flow systems. The aquifers therefore are not strongly affected by weathering of minerals due to short groundwater residence times and intense flushing. The local character of groundwater flow systems also prevents a strong impact of acid mine drainage on groundwater systems in a regional scale.