Acid Mine Drainage

Author: Philip J Hobbs -CSIR Senior Research Hydrogeologist

( Article Type: Overview )

Mine water pollution has been identified by the Department of Environmental Affairs and Tourism (DEAT, 2008) as an emerging issue; that may affect the future state of the environment" and, as such, qualifies for inclusion in the next state of the environment (SoE) reporting cycle. The reality, however, is that contaminated mine water, also known as acid mine drainage (AMD), has already manifested itself as a clear and present danger to the environment. The much publicised (and televised) situation in the Wonderfontein Spruit catchment arising from gold mining activities and in the Oliphant's River catchment due to coal mining activities testifies to this.
In a certain sense, South Africa finds itself in a similar position to that which faced Germany after reunification in 1990. The lignite and uranium mining activities practised in the Federal States of Saxony and Thuringia in the former East Germany (German Democratic Republic), as well as the chemical industries in the Bitterfeld area, left behind a devastated landscape and environment. The responsibility for the rehabilitation of these legacies fell to the Federal Republic and the respective Federal States.

AMD describes the process whereby acidic water generated in the mining environment enters the surrounding landscape. The acidic nature of this water derives from water-mineral chemical interactions that occur in defunct underground mine workings and in waste rock piles, sand dumps and tailings dams on surface. These processes are well understood, as is the character of the contaminants that are contained in this water. Acid mine water is a pernicious contaminant that carries trace elements such as heavy metals and radionuclide's in concentrations that are potentially hazardous to all forms of life. Whilst manageable in small quantities, the potential volume resulting from more than 100 years of gold and coal mining is alarming. For example, the volume of acid mine water currently coming to surface in the West Rand goldfield near Krugersdorp is sufficient to fill at least 10 Olympic-size swimming pools (each holding 2,500 m3) every day.
The daily salt load in this water is equivalent to almost 140 tons, the mass equivalent of 70 medium size sedan cars. These values can quite readily be multiplied tenfold to obtain a conservative order of magnitude number for the entire Witwatersrand Basin comprising five goldfields. In addition to the West Rand goldfield already mentioned, these are the East Rand, the Central Rand, the Far West Rand and the KOSH (Klerksdorp-Orkney-Stilfontein- Hartebeesfontein) goldfields. By comparison, the Oliphant's River catchment witnesses roughly double the West Rand goldfield values from defunct coal mines in the Witbank coalfield. The situation in the other coalfields (e.g. Highveld and Ermelo) located in the catchment of the Vaal Dam is still largely unknown, as is that pertaining to the burgeoning platinum mining industry on the eastern and western limbs of the Bushveld Complex. Similarly, little is known of the processes that neutralise the acidity, that prevent metals and other trace elements from accruing in the water and about the fate of these contaminants in the receiving environment.
Clearly, the potential volume of poor quality mine water threatens to significantly reduce the utility of the already stressed freshwater resources of the economic engine-room of the country. Further, the impact of mine water quality on humans is largely unknown and has not yet been studied in South Africa. To consider once more the similarities with Germany following die Wende (The Turning Point) in 1990, and South Africa's own democracy in 1994, the negative externalities associated with historical mining activities and the imposition of these costs on society demonstrate an alarming similarity.

Apart from recognising the threat posed by AMD as a matter of utmost urgency, the relevant authorities at all levels of Government need to leverage and mobilise the scientific and technological expertise offered by the various statutory research councils (e.g. CSIR, Council for Geoscience and the Agricultural Research Council), academic institutions and the private sector, as well as the strategic support provided by institutions such as the Water Research Commission. These organisations need to be regarded as allies and partners if the threat posed by AMD is to be addressed in an effective and solution-driven manner that fosters cooperative governance. It is also required that a clearly defined programme be implemented, supported by the necessary level of funding. It is important that such a programme recognises the multidisciplinary nature of the research that is required, and is predicated on collaborative teamwork across a wide range of specialist fields. Measures to meet the challenge of AMD are already being developed by researchers and industry. These include the development and implementation of water treatment processes that aim to turn the threat of AMD into an opportunity in the form of potable or industrial grade process water, with the value of the by-products an added economic benefit. It is also evident, however, that no single solution will meet the challenge of AMD.
Finally, it is not the obvious negative impact of AMD on the total environment that is the overriding concern, but the contextualization of the impact from mining (both current and defunct/abandoned) with all its ramifications within the bigger picture of national water resource scarcity