This could contaminate water for South Africa's neighbours, Namibia, Botswana, Zimbabwe and Mozambique.
But although the problem will cost government and the public billions in the years ahead, campaigners argue that one group is unlikely to pay: the mining companies that caused the problem in the first place.
A stinking stream
In some parts of the Witwatersrand, on which Johannesburg and its satellite towns are built, the pollution has already arrived. A government report puts the problem in cold, clinical language: "Following cessation of mining in the area in 1998, the mine void in the Western Basin filled with water and finally began to decant on surface in 2002." The once pristine Tweeloopies Spruit is today a stinking, fetid bright orange stream. The pollution is what the scientists term Acid Mine Drainage – the result of oxygenated water coming into contact with iron pyrites, during the mining process. When this wells up onto the surface the impact is devastating.
As the report by the Department of Water Affairs puts it: "Where the river cascades over falls or rapids, thick crusts of iron and manganese oxides have formed. Over the years since surface decant commenced, the extent of this iron precipitate has extended progressively further downstream. The water is toxic and has a profound impact on aquatic biodiversity." In the Krugersdorp Game Reserve into which the river flows, only the hippo now survive.
A century old legacy
Gold mining, for the past 120 years the bedrock of the South African economy, is today in decline. As the mines closed pumping of the water found underground ceased. Gradually the disused mine shafts filled with water – rising at between 0.3 and 0.4 metres per day. But the streets of central Johannesburg, or the homes in Soweto are not about to be flooded by a filthy flood – its effects are far more insidious.
"On a knife edge"
The water table is threatened when what the scientists term the "Environmental Critical Level" is crossed.* This is estimated to be 1,520 metres below the surface. Marius Keet, Regional Manager for Water Affairs for the region, says the ECL breach will take place in September or October this year.
There is now a race against time to try and prevent this taking place. Two pumps, donated by Central Rand Gold, are awaiting assembly in Germany. These will have to be shipped out and installed before pumping can begin. Mr Skeet estimates installation will be completed in October or November. "We are on the edge," he said in a phone interview. "This is walking on very thin ice."
Breaching the Environmental Critical Level would be deeply worrying, but not an immediate danger to health, says Marius Skeet. "The level is set conservatively," he says. But action is needed now to prevent long-term environmental damage.
Years of warnings
Certainly there have been plenty of official warnings. The first report on the issue dates back to 1957 and subsequent investigations have highlighted the issue at regular intervals. In December 2010 a report by government scientists to an Inter-Ministerial Committee on Acid Mine Drainage called for immediate action. Pumping was needed across the region "as a matter of urgency."
So far – says environmental campaigner, Mariette Liefferink – the response has been completely inadequate. Ms Liefferink, who sits on an official liaison committee with government, says "The tardiness of Government to act has created the current emergency."
Ms Lifferink, who has campaigned on the issues for years, says the proposed treatment of the Acid Mine Water would remove some of the toxic and radioactive metals, however, the sulphate levels would remain "unacceptably high." She points out that the neutralised Acid Mine Water e.g. contains 2,500mg per litre of sulphates – against a World Health Organisation standard for sulphates in drinking water of 200 mg per litre.
"The Government has allocated Rand 433 million ($46 million) for the treatment of AMD. What is required, however, is Rand 6 billion (£633 million)," says Ms Liefferink.
Who pays for the clean-up?
There is no question that coping with the pollution will cost billions and the clean-up will have to continue for generations. The problem is that many of the main perpetrators have long since left South Africa. Companies like the giant mining conglomerate, Anglo-American, have re-listed on the London stock exchange. They have also sold or 'de-bundled' their assets.
In May 2005 the Financial Mail – South African equivalent of The Economist – printed an article entitled: "Last Man in Hot Water." The article quoted Cathy Reichardt, of the University of the Witwatersrand School of Mining Engineering as saying "There's been a culture of denial around dewatering issues and a lot of head-in the-sand activity." As the ore body of mines is gradually worked out, the mines get sold on, and she cited the example of the Grootvlei mine.
Grootvlei once belonged to Gengold, a major mining house. But Gengold sold it to Harmony. It was then sold on, from Petmin to Bema Gold to Pamodzi Gold, which went into liquidation. The assets of Grootvlei were bought by Aurora Mines. This was run by Zondwa Mandela, a grandson of former President Mandela. Aurora chairman was Khulubusa Zuma, nephew of the current president. They promptly turned off the pumps, allowing the mine to flood and sold off the mine infrastructure.
As the then director-general of the Department of Water Affairs, Mike Muller pointed out in 2005, the costs should be carried by the mining companies. "We understand that over the next decade or so, many of the gold mines may cease to be operational. The mines must carry the costs of closure measures, even if they are no longer operational, since it is their activities that have created the pollution hazard by exposing chemically active rock formations to the water."
But with their assets sold off and their headquarters moved outside of South Africa, its highly unlikely the major mining houses will be willing to shoulder the burden. The South African government is in the process of preparing a report on this – apportioning the liabilities for the clean-up. For the present this is confidential, but, says Marius Skeet, it should be available to the public in the next two to three months, "depending on what our legal team decides."
* Environmental Critical Level (ECL), being the level in the mine void above which the water should not be allowed to rise, to protect specific environmental features, including groundwater resources
Author Profile: Martin Plaut is senior research fellow at the Institute of Commonwealth Studies and former BBC World Service News' Africa editor, with special focus on South Africa, the Horn and Sudan.
Photo Credits: Hippos in contaminated water. Acid mine drainage coats the hippos at Hippo Dam at the Krugersdorp Game Reserve. Courtesy of Mariette Liefferink.