A PRELIMINARY MANUAL FOR THE DESIGN OF COAL MINE PITLAKES AS AN ENVIRONMENTALLY STABLE CLOSURE OPTION IN SOUTH AFRICAN MINES

South Africa has been mining coal since the early 1800s, initially by conventional underground methods, but since 1950 the majority of the coal production has been from open cast mines. Coal is the major component of the South African Power supply network and this is predicted to continue into the latter half of the 21st century. Open cast coal mines generally leave a final void because of the mining method, insufficient overburden to fill the voids created by removal of the coal and /or to manage water. Once mining operations cease, these voids fill with water forming a lake which is generally referred to as a “pitlake”. The author has estimated that there are over 200 pitlakes in the three major South African coal fields namely the Mpumalanga/Witbank/Highveld, KwaZulu-Natal and Waterberg areas. The research study evaluates the environmental sustainability of using pitlakes as a closure option for old and proposed coal mines in South Africa. The current South African mining and environmental legislation states that all pitlakes should be backfilled for the mine to achieve mine closure. The major factors which determining environmental sustainability of pitlakes are the water balance and water quality. Positive water balances result in discharge onto surface. The water quality of a pitlake determines the future use and the environmental risk. Pitlake water quality varies depending on the geology, mining method and catchment characteristics. In general, pitlake water quality may not comply with legislated catchment water quality standards. This investigation concentrated on the two major drivers of pitlake sustainability (quantity and quality), whilst investigating four different pitlakes; The pitlakes were selected on the basis that they are representative of the major South African coal fields considering variances in geology, climatic conditions and mining methods. Sufficient data was collected in the study to allow for the development of a guideline for the design of coal mine pitlakes in the South African coal fields. This preliminary design manual considered the water balances of the pitlakes and the biological and chemical process that drive the water quality of pitlakes. The aim of this manual is to provide guidelines for the design of coal mine pitlakes for the pitlake to be a sustainable closure option.