Millions of litres of highly acidic mine water is rising up under Johannesburg and, if left unchecked, could spill into its streets in 18 months. Parliament’s water affairs portfolio committee has been told the corrosive water as the acidity of vinegar and lemon juice.
The acid water is now about 600m below the city’s surface, but is rising at a rate of between 0.6m and 0.9m a day, the South African Press Association reports. Department of Water and Environmental Affairs deputy director of water quality management Marius Keet told MPs “It can have catastrophic consequences for the Johannesburg central business district if not stopped in time. A new pumping station and upgrades to the high-density sludge treatment works are urgently required to stop disaster,” he warned.
Speaking at the briefing, activist Mariette Liefferink from the Federation for a Sustainable Environment said the rising mine water posed an “enormous threat” and would become worse if remedial actions were further delayed, SAPA said. “This environmental problem is second (in South Africa) only to global warming in terms of its impact, and poses a serious risk to the Witwatersrand as a whole. At the rate it is rising, the basin will be fully flooded in about 18 months.”
Acid water is formed underground when old shafts and tunnels fill up. The water oxidises with the sulphide mineral iron pyrite. The water then fills the mine and starts decanting into the environment, in what is known as acid mine drainage. Keet said the problem was not confined to Johannesburg. In 2002, acid mine drainage had started decanting from the Western Basin, located below the Krugersdorp-Randfontein area. The outflow grew worse earlier this year after heavy rains, prompting the department to intervene.
However, a lack of treatment capacity “compelled in-stream treatment as a short-term intervention”, he said. The department poured tons of lime into the Tweelopies Spruit in a bid to neutralise the water. This led to problems with the resulting sludge that formed in the water course.
The region’s Eastern Basin, below the town of Nigel, was also threatened. The last working mine still pumping out water in the area was Grootvlei. Keet said if the mine stopped pumping, acid water would decant into the town “within two to three years”. The department is taking legal action against the mine, after it allegedly ignored a directive to treat the pumped water before discharging it. Keet said about R220 million was needed to establish pump stations, pipelines and treatment works. “The challenge is where the money will come from,” he said.
Liefferink said if the acid mine water rose to the surface in Johannesburg’s city centre, it posed a threat to the city’s inhabitants, its buildings and the surrounding environment. She said residents of many of Gauteng’s poorer communities lived alongside, and in some cases on top of, land contaminated by mining activities.
The Mining Weekly reported in April 2008 that the West Rand decant had turned Robinson Lake (pictured) in Randfontein into a poisonous wastewater. Once a popular recreational area where fishing was a favourite pastime, the water by 2008 had a pH of 2.2 “and completely incapable of sustaining any forms of life.” In addition, the National Nuclear Regulator found a uranium concentration of 16 mg/ℓ in the water, obliging it to declare Robinson Lake a radiation area.