Environmental assessment of Durban Navigation Colliery discard dumps in the Klip River coalfield, Kwazulu-Natal Province of South Africa

Durban Navigation Colliery (Durnacol) occurs in the Klip River coalfield, the Dumps Nos. 1 and 2 of which were used as disposal sites shortly after the mine started in 1895. Both dumps are relatively small in size (<150,000 m²) in terms of South African mine standard and partially burnt or still burning. This study aimed to conduct a comprehensive geochemical assessment of the potential environmental impact from the two dumps. The methodologies used included field observation; field tests (Fizz, pH, EC), sampling; analyses of mineralogy (XRD), geochemistry (XRF), water quality (AA and ICP-MS), particle size distribution and Acid–Base Accounting (ABA). The field investigation indicated no toe seepage around the two dumps. Fizz rating of burnt material was higher than that of unburnt material on both dumps and paste pH proved to be neutral (pH 6–7). This study further indicated that the combustion/burning of coal discard slightly increased both pH and alkalinity, but no trend was identified. The ABA results indicated that both dumps had the potential to turn acidic, as the majority of the samples taken had sulphide-sulphur higher than 0.25%. It is also noted that there is potential for heavy metal leaching out, specifically Al, Fe, Mn, and Zn from the dumps. A continuous monitoring of the boreholes in the vicinity of the dumps was recommended to establish the potential development and migration of a pollution plume around the dump in future.