Greater intervention needed to tackle acid mine drainage

The environmental risks and hazards associated with acid mine drainage (AMD) and radioactivity within South Africa’ Witwatersrand goldfields are issues that need to be tackled more seriously, despite current initiatives by government, reports environmental protection group Federation for a Sustainable Environment CEO Mariette Liefferink.

In February, Mining Weekly reported that the Department of Water Affairs (DWA) had confirmed the initiation of a R17-million feasibility study to assess longer-term solutions for South Africa’s AMD problem. The investigation began in December and should be completed over a maximum period of 18 months.

The department also intends to probe solutions over and above those identified as so-called ‘immediate’ and ‘short-term’ solutions for implementation by the Trans-Caledon Tunnel Authority (TCTA) across the Witwatersrand goldfields.

Last year, the authority indicated that up to R924-million might be required to deal comprehensively with the threat of AMD by imple- menting emergency and near-term projects designed to deal with the problem.

Initially, the TCTA was allocated R225-million, which the National Treasury increased by a further R208-million after both the TCTA and the DWA made representations.

Therefore, the funding shortfall for the project was estimated at R492-million; however, in his 2012 budget speech, Finance Minister, Pravin Gordhan allocated R433-million for short-term interventions to tackle AMD.

As early as 1987, the US Environmental Protection Agency recognised that “. . . problems related to the ecological risk of mining waste may only be rated as second to that of global warming and stratospheric ozone depletion”.

Liefferink notes that, if this is the case, the Witwatersrand gold-mining area, which comprises the Kosh, Far East, Central Rand, Western and Far West basins, as well as the Free State gold mines, is at serious risk.

“There is wide acceptance that AMD is responsible for the most costly environmental and socioeconomic impacts, such as surface and groundwater pollution, soil degradation, destruction of aquatic habitats and allowing heavy metals like cadmium, cobalt, copper, [molybdenum should read arsenic and uranium – FSE’s comment] and zinc to seep into the environment,” says Liefferink, who is on the Gauteng Department of Agriculture and Rural Development’s steering committee for the reclamation and rehabilitation of mine residue areas within the Witwatersrand.

She explains that the destruction of ecosystems caused by AMD is generally irreversible. In many cases, the polluted sites may never be fully restored, as AMD pollution is so persistent that there is no available remedy. “AMD threatens South Africa’s scarce water sources, and, as a result, also threatens human health and food security in mining areas.”

Liefferink notes that, as at 1997, South Africa produced an estimated 468-million tons of mineral waste a year.

“The potential volume for AMD for the Witwatersrand goldfield alone amounts to an estimated 350 Mℓ/d. This represents 10% of the potable water supplied by water utility Rand Water to municipal authorities for urban distribution in Gauteng and the surrounding areas, at a cost of R3 000 for every one-million litres,” she says.

The South African gold-mining industry is in decline but the postclosure decant of AMD is an enormous threat and could become worse if remedial activities are delayed or not implemented.

The Witwatersrand basin has been mined for more than a century and is the world’s largest gold- and uranium-mining basin, comprising more than 120 mines, from which 43 500 t of gold has been extracted in one century and 73 000 t of uranium has been extracted between 1953 and 1995.

The basin covers an area of 1 600 km2, of which 400 km2 is used for mine residue deposits also known as tailings dams. These tailings dams contain six-billion tons of iron pyrite tailings, the waste produced by gold mining, which contain 430 000 t of low-grade uranium.

These tailings dams are mostly unlined and many are not vegetated, providing a source of extensive dust, water and soil pollution. It is estimated that 6 000 km2 of soil is affected by gold mining on the Witwatersrand basin alone.

“If inhaled, uranium particles pose various health risks, as uranium is chemically toxic and has radioactive daughter particles.

“In South Africa, 1.6-million people live in informal settlements adjacent to or directly on top of mining residue areas despite the Chamber of Mines’ guideline, which states that each tailings deposit should be surrounded by a 500 m buffer zone, where no human settlement is allowed,” Liefferink points out.

Most, if not all, of these areas have no fencing or warning signs.

Water in some of these areas has been tested for heavy metals, with shocking results, she says.

The residents are also affected by chemicals like radon and radon gas rising from abandoned open mine shafts. According to a report by the Mine Water Research Group of the North West University, radon and radon gas are a leading cause of lung cancer in uranium miners.

An airborne radiometric survey of the West Rand and Far West Rand basins was carried out by parastatal science council the Council for GeoScience on behalf of the DWA and found that many of the residential areas like Carl- toneville, Kagiso, Randfontein, Khutsong and Westonarea fall within areas of high-risk radio- activity contamination.

The Central Rand basin is currently flooding at 60 Mℓ/d (0.9 m), which will contaminate all groundwater and decant on surface in a densely populated area (Boksburg) at three times the rate of the Western basin.

In 2002, in the Krugersdorp-Randfontein area, water started to decant from a number of shafts into the Tweelopiesspruit and Wonder- fonteinspruit streams. The water has a pH level of 2.2. The normal pH level for water is 7.3.

“The combination of the pH and reduction- oxidation-driven reactions resulted in a measured uranium concentration of 16 mg/ℓ for the Robinson lake, near Randfontein, and resulted in the lake being identified as a radiation area,” says Liefferink.

DWA regulations for drinking water state the uranium concentration should not exceed 0.07 mg/ℓ and 0.01 mg/ℓ for irrigation.

Long-term exposure to AMD-polluted drinking water may lead to increased rates of cancer, decreased cognitive function and skin lesions, says Liefferink.

In July last year, government proposed neutra- lisation to treat AMD in South Africa. Neutra- lisation involves adding lime to AMD to adjust the pH level of the water. Although neutralisation removes most of the heavy metals from acid mine water, it does not remove the sulphates.

The World Health Organisation’s standard for sulphates in drinking water is 200 mg/ℓ. Water treated by neutralisation will contain levels closer to 2 500 mg/ℓ, while every 25 Mℓ of water treated will result in 100 t/d of salt being deposited into the country’s rivers.

“If AMD is not treated to a level where the salt load is removed, the Upper Vaal’s water supply will go into deficit. If there is a drought, restrictions will be placed on consumers in the Upper Vaal or the dilution standard at the Vaal Barrage will be relaxed, resulting in poor-quality water reaching the consumers in the Middle and Lower Vaal,” she says.

With the Upper Vaal in deficit, there would then be no possibility of transferring water into the Olifants catchment, and mining activities in six provinces could be affected by the curtailed water consumption.

Edited by: Tracy Hancock

CEO Mariette Liefferink discusses AMD and tailings dams – Creative Commons License

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