Mine water has polluted the Klipspruit. Photo: Delwyn Verasamy/M&G
When huge volumes of contaminated mine water gushed out of the flooded mining basin in the West Rand goldfield near Krugersdorp about 20 years ago, it had devastating consequences — acutely toxic rivers and radioactive dams.
Mariette Liefferink was one of the activists who sounded the alarm about the threat of acid mine drainage and spent the next decade highlighting the risks of this poisonous, polluted water seeping from mining areas into the waterways of Gauteng.
Reports at the time of the flooding warned that acid mine drainage would affect the stability of infrastructure in the centre of Johannesburg, flood the tourist mine shaft at Gold Reef City, harm the Cradle of Humankind World Heritage Site, cause health problems and pollute rivers and drinking water sources.
For Liefferink, these fears were not entirely unfounded — acid mine drainage is a “pernicious” contaminant that carries metals, radio-nuclides (atoms that emit radiation) and salts in concentrations hazardous to all forms of life.
She said the potential volume of acid mine drainage resulting from more than 130 years of gold and coal mining in South Africa is alarming.
In 2011, the minister of water affairs directed the Trans-Caledon Tunnel Authority to implement short-term interventions to deal with acid mine drainage. This included the upgrading of the Western Basin acid mine drainage treatment plant in Randfontein in 2012 and the construction of the Central (Germiston) and Eastern (Springs) basins treatment plants, in 2014 and 2016 respectively.
The plants pump about 180-million litres of acid mine drainage every day from the three underground basins, neutralise the acidic water and then discharge it into the Vaal River system and the Crocodile West river system.
Danger: Treating the mines’ acid water is successful in the short-term. But if mines are not rehabilitated the threat will become worse.
‘Threat to economic engine’
Although the short-term treatment reduces the high salt load in the water, the neutralised mine water still contributes 362 tons of total dissolved solids — salts — a day to the Vaal Barrage, a dam on the Vaal River near Vanderbijlpark..
“This additional salinity creates water security risks for the Integrated Vaal River System,” said Liefferink. “If 150-million litres of the neutralised acid mine drainage … are released in the Vaal Barrage, 60 million litres of clean water will have to be released from the Vaal Dam to dilute the salinity.”
Diluting the salinity requires more water than the volume of water in the Vaal Dam, which means it will eventually have to be augmented by the Tugela-Vaal and the Lesotho Highlands Water Project 2 — which may only be completed by 2027 or later.
“The biggest challenge is the threat of acid mine drainage to the already stressed freshwater resources of the economic engine room of the country,” Liefferink said.
Water expert Anthony Turton, agrees. “The acid mine drainage problem is bigger today than it has ever been, but has simply fallen off the media news cycle. The core problem has always been — and will continue to be — the increase in salt load into the national water resource.
“This destroys what little water resource we have left for economic use, and drives up the cost of water treatment while also hastening the onset of localised Day Zero type of structurally-induced water scarcity.”
Bashan Govender, the project manager of mine water at the department of water and sanitation, said the concern is the salinity, which can typically range from 1 800mg to 2 400mg per litre of water. The regulatory limit is 600mg per litre.
“But what we’ve established is that the impact of the discharges that come out of the Central Basin and Eastern Basin, that eventually report to the Vaal Barrage, is not triggering a dilution requirement from the Vaal Dam into the Barrage,” he said.
But Liefferink emphasises that these high salt loads are “unsustainable in the long term”.
Suvania Naidoo, who did her doctorate on the socioeconomic effects of acid mine drainage, said: “Acid mine drainage is not as big a problem as sewage pollution is at the moment. But the concern is, do we know what’s going to happen in the future if we continue to discharge water with such high levels of sulphate?”
The pH — which is used to measure how acidic water is — of the corrosive mine water is very low (acidic). In the short-term treatment, the pH is adjusted using lime to make the water more alkaline.
Most of the metals drop out, but if the neutralised water becomes acidic, the metals could become mobilised again, Liefferink points out.
Disposing of the sludge after treatment is a problem because it cannot be beneficially used.
‘Clogged up’
“In the Western Basin, it is disposed of in an unlined pit; in the Central Basin, on a mine dump; in the Eastern Basin, the sludge was being disposed into boreholes until the boreholes clogged up,” she said.
Even though huge volumes of acid mine water are being pumped out of the Central and Eastern basins, the amount of toxic water is increasing. And monitoring has shown that the water quality of the raw mine water has not improved.
“It was previously assumed that, in time, the poor quality water will separate from the better quality water and stay deep in the basins and the water closer to the surface will be of a better quality. But this is not the case,” Liefferink said.
“This confirms the mine water cannot be allowed to flood the mine voids and decant [spill out] since it will have significant impacts on Johannesburg and downstream water users.
“Pumping and treatment of mine water will have to continue.”
Govender added: “What we’ve realised is the amount of acid mine drainage requiring pumping on a daily basis is a little more than what was originally predicted. The plants are running at full cycle to ensure an adequate amount of water can be pumped up.
“There are specific levels we need to maintain and the moment we pass those levels, then we run the risk of polluting groundwater resources.
“If it rises even further and there’s no intervention put in place to arrest that water, that’s when there will be a surface decant,” he said, adding, however, that the plants are equipped for the volumes.
(John McCann/M&G)
Rising risk
Increased coal mining, coal-fired power generation and uranium mining means the risk of acid mine drainage will increase.
Although the gold mining industry is in decline, the post-closure decant of acid mine drainage is an “enormous threat”, which could worsen if mining rehabilitation is delayed or not implemented, Liefferink said.
The liquidation of mining companies such as Mintails, Blyvooruitzicht and the Grootvlei mines, has exacerbated the effects in Gauteng, she said. “Liquidation of mines allows for the externalisation of the pumping and treatment of polluted water to neighbouring mines, the state and future generations.”
Unclosed mines are a risk to water resources. “But mine closure is currently very poorly implemented.”
What is acid mine drainage?
It is caused when water flows over or through sulphur-bearing (pyrite) materials forming solutions of acidity. It comes mainly from abandoned gold and coal mines, and currently active gold and coal mining. It is characterised by a low pH (as corrosive as battery acid), an excessive concentration of dissolved metals and sulphate salts and, in some cases, elevated levels of radioactivity.
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