Management of Leachate from Waste Rock Dump: A Case Study at Newmont Ghana Gold Limited – Ahafo Kenyasi

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Concentrations of heavy metals –i.e. Fe, Mn, Cu, As, Zn, Ni and Cd- and physical parameters in surface and ground waters at some controls and compliance points within the NGGL’s concession at Ahafo South were assessed. Water samples were taken from seven sampling locations within the mining area between the months of October 2011 and March 2012. Heavy metals’ concentrations were determined using the AAS whilst those of physico-chemical parameters were determined using standard methods for examination of water. Mean concentrations of the heavy metals in rainfall samples were 0.02, 0.02, 0.00, 0.003, 0.003, 0.00 and 0.00 mg/L respectively, and those in groundwater were respectively 0.197, 0.280, 0.00033, 0.064, 0.0067, 0.00 and 0.0012mg/L. Surface water recorded 0.470, 0.041, 0.002, 0.0017, 0.00, 0.00 and 0.00003 mg/L, respectively. Mean manganese and arsenic concentrations in groundwater at two control points exceeded EPA Ghana standards of 0.1mg/L for mining water discharge. The mean values of the physico-chemical parameters in surface and ground waters were within acceptable limits of EPA Ghana standards; sulphate in surface water just at the threshold. The study indicates that pyrite oxidation from the waste rock is evident, causing high concentrations of sulphate, above the Ghana standards, to leach directly from the waste rock. However, there is no potential for acid generation due to the high carbonate content of the rocks acting as a buffering material.
A thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology in partial fulfilment of the requirement for the award of Master of Science degree in Environmental Science.