Acid mine drainage in the Witwatersrand: an intergenerational problem

On the 2^nd of March 2012 Professor Fred Ellery of Rhodes University Environmental Science Department gave a stimulating lecture on the acid mine drainage (AMD) problem facing the Witwatersrand.

Fred first became interested in this subject when working on the Klip River wetland south of the Witwatersrand ridge. He stated that this wetland is “undoubtedly the most valuable wetland in South Africa in terms of the ecosystem services it provides – particularly as a trap for harmful solutes produced by mining and other activities, which would otherwise enter the Vaal River”. The Klip River wetland is a sink for many pollutants generated by mining activities as well as wastewater treatment works South of Johannesburg.

Johannesburg or “Egoli” (the city of gold) has depended primarily on gold for its economic development, and indeed much of the wealth of the entire country is linked to activities in this economic hub. Ellery argued that in fact, the history of the country as a whole was shaped by the discovery of gold by the Australian geologist George Harrison in 1886. “Uitlanders” flocked to the Witwatersrand in the years that followed, heightening tensions between them and the residents in the Zuid Afrikaanse Republiek (ZAR), leading to the orchestrated Jameson Raid and ultimately the Second Anglo Boer War.

This problem of AMD occurs in many areas where gold mining takes place, but the geology of the Witwatersrand Basin and younger rocks of the Transvaal Supergroup has exacerbated this threat. The occurrence of high concentrations of iron pyrite (FeS₂) in the gold-bearing strata has contributed directly to the AMD problem. Iron pyrite is a waste product of mining and is disposed of following extraction of gold, giving the mine dumps of the Witwatersrand their golden colour. As this iron pyrite is oxidised, sulphuric acid forms, which enters groundwater and surface water aquatic ecosystems, where the pH of water is often less than 3. Sulphuric acid also brings heavy metals into solution, such that these become toxic for aquatic ecosystems and possibly humans.

The dolomite rocks of the Transvaal Supergroup host many underground caves with massive volumes of water. In order to enable mining at considerable depths, these aquifers were dewatered. As these mines are no longer economically viable and being abandoned, water is no longer being pumped out of underground aquifers. As a result, the water table is rapidly recharging and rising. Data reveals that the groundwater is rising at more than 50 cm per day such that where groundwater is 200 m below surface, it is likely to reach the surface in about a years time. When this happens in low-lying areas of the Witwatersrand, problems will be severe as surface water will pose a risk to infrastructure and human health. Already in the Wonderfontein Spruit, a tributary of the Mooi River, there are warnings about polluted water. Could this be a grim indication of what is to be expected more widely on the Witwatersrand in the near future?

It has become vital that management strategies be developed to prevent decanting of hazardous water onto the surface. Pumping groundwater into existing watercourses and addressing the water quality issues by treatment is a vital first step. Whatever strategy is developed to ameliorate this problem will be expensive. It is hoped that the South African government will realise the weight of the problem and how much higher the cost would be to do nothing.

The take home message that Fred wanted the audience to ponder was the importance of having a good understanding of how systems worked and why they might collapse, as well as the need for high quality data. The outcomes of both present and future actions need to be managed, and it is vital that an awareness that fosters action is created. As a society, we need to realise that there is an intergenerational aspect to our actions: the lack of foresight by gold mines over the last 100 years has created a very real social, economic and environmental concern for us today. Things that we do today will have known as well as unforeseen impacts for future generations. Fred challenged us as postgraduates at Rhodes University to consider the kinds of expertise that are needed to face these sorts of problems, and to carefully contemplate what we at Rhodes should be doing in our studies to adequately equip us with the knowledge, skills and attitudes to face similar issues now and in the future. Interdisciplinary action is needed, and urgently, as this is a problem that is not going to be easy to solve without people from diverse disciplines working together!