South African Water: Greater intervention needed to tackle acid mine drainage
23 mars 2012
Mining Weekly - March 23, 2012
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.