Mining and Metal Pollution: Assessment of Water Quality in the Tarkwa Mining Area

Abstract

The quality of water in mining communities is uncertain since metals associated with acid mine drainage are known to saturate these waters. Previous studies in Tarkwa, an area noted for gold and manganese extraction, have reported large concentrations of aluminium, arsenic, cadmium, copper, lead, manganese and mercury in water samples. This research aimed at investigating the chemistry of groundwater with special focus on the contamination status of trace elements. It also compared levels of metal concentration with those that were determined in previous research works, to identify changes that might have occurred. Thirty-eight water samples from boreholes, hand-dug wells and streams, within the Tarkwa area were obtained and analysed. Results show that 90 % of water in the area is acidic and Eh was determined to be positive, depicting oxidizing conditions. Mean groundwater temperature was 28.9 ºC. Thirty-two samples had either temperature or pH values falling outside the range recommended by the World Health Organisation (WHO). Thirty samples had at least one metal concentration exceeding the WHO guideline values. Among the list of elements that exceeded the guideline, arsenic, manganese, nitrate, nitrite and iron were the most predominant. The dominant ions in the samples were sodium and bicarbonate. High concentrations of Fe and SO₄^2- in some parts of the study area point to the influence of acid mine drainage (AMD). Comparisons of results of metal concentrations with findings from previous research in the area showed a reduction in concentration. Hydrochemical modelling with PhreeqC attributed this reduction to sorption processes. Comparison of levels of metal concentration in the different water supply facilities (borehole, hand-dug well and stream) showed no significant variations.

Keywords: Water Quality, Drinking Water, Hydrochemical Modelling, Heavy Metals