Posted on: November 26, 2010 Posted by: Diane Swarts Comments: 0

‘Pump and treat’ stations east and west of Johannesburg could keep acid mine drainage below groundwater level, to give the city clean water within a decade.

South Africa’s government would have to act in 2011 to save the last remaining Johannesburg gold mine at Central Rand Gold, and Gold Reef City historic gold mine, or act by 2012 to save Witwatersrand Reef wetlands, Klip River, and Vaal River system, says Prof Terence McCarthy.

Abandoned mine shafts are filling up and toxic springs are already releasing highly acidic (low Ph) water with high ‘salts’ content, including iron sulfide and heavy metals oxides, into groundwater and small streams.

Surface water ingress into the mining void, could eventually ensure riverless Johannesburg and Pretoria of a water supply, replacing Vaal River water from 80km away, but surface pollution and poorly maintained sewage works would have to be fixed and securely maintained to ensure clean ingress water.

Uranium bio-toxin

Uranium content is high in the West Rand basin, adding a strong bio-toxin to the groundwater mix, and down the Tweelopies Spruit, via Krugersdorp Game Reserve, where the stream is ‘completely dead and deadly’, according to Mogale City parks official Stefan Du Toit.

Uranium’s bio-toxicity is a much larger problem than radio-activity, that could vary, and is not a good indicator of uranium levels in acid mine drainage, said Prof McCarthy at a media conference at Wits University.

Surface pollution

Some West Rand decant is going north to the Hartbeespoort Dam, already polluted by sewage, fertilisers, and effluent from a nickel and magnesium plant in Magaliesburg.

Some low lying areas already feel the brunt of the rising sheet of toxins from two ‘hollow sheets’ of mined out reefs, Main Reef Leader, and the other, smaller Witwatersrand reef, named ‘Kimberley Reef’, after the origin of the financiers who pioneered Johannesburg’s mining industry when prospectors reached the limits of adit workings.

Acid mine drainage also arises from mine dumps leachate, Prof McCarthy told during a conference at Wits University in Senate House. Natural bio-remediation by reed beds had broken down due to drainage channels in most wetlands.

“Johannesburg sewage works discharge poorly treated water into the Klip River that rises in Soweto, bearing sulfides and heavy metals to the Vaal River near the barrage.

“Poor quality discharge would require release of some Vaal Dam water, upstream from the barrage, depleting the very water reserve that Johannesburg depends on,” Prof McCarthy said.

Ingress pollution hot spots occur where surface streams cross major cracks down to mine workings, as occurs at a site on Main Reef Road in Florida.

Bio-remediation waste residue

Asked about the Rhodes Biosure process and other bio-remediation methods based on a controlled process of mixing acid mine drainage (AMD) and partially treated sewage, Prof Mc Carthy commented to that these processes reduce sulfides and precipitate metals into a peat, leaving a substantial waste stream that requires further treatment and disposal.

“I do not like bioremediation in principle, I recommend standard technology, with acidity treatment by adding lime, and flocculation, leaving a smaller waste stream

Buildings would not ‘dissolve’

Some specialists had warned that acid water could slowly dissolve concrete foundations and basements of highrise buildings, but Prof McCarthy says there is no reason for panic.

From the 11th floor of Wits University Senate House, several low lying areas of potential toxic springs are visible, like Newtown near the Market Theatre.

Health, environmental and social impacts of groundwater filling Johannesburg’s old mine shafts should not lead to hysteria and panic, says the veteran geology academic.

Prof McCarthy addressed a public lecture on decanting of acid mine drainage, detailing effects on some authorities, businesses, industries and residents.

Prof McCarthy has written extensively on the geology of gold bearing rocks of the Witwatersrand basin, bounded by a massive crescent from Evander, the Reef, Carletonville, and Orkney, to Welkom and the Free State gold fields.

Water sale funding

Pumping would have to continue indefinitely, funded at first by the state, which had been contributing to pumping for decades, and funded later by waster sale for industrial and domestic use.

Due to discontinuations and strictures between mine shafts and mined out areas, mainly at hundreds of dykes, water flow in the two mined out sheets is slow, leading to disparate local levels.

These levels are influenced locally by ingress rates and pumping. One pumping station would not be sufficient to save Johannesburg or the reef from AMD decant. Prof McCarthy recommends two pumping stations, at sites where treatment and release would be most convenient.

Periodic sampling of water at disused mine shafts, reveals a rapid recent rise at Gold Reef City, and more erratic rise on the East Rand and West Rand.

Water quality is also affected by local conditions, like age of water contact, extent of underwater tunnel collapse due to rotting wooden stays, flow rate, ingress rate, and prospective pumping rate.

Grootvlei scare

Periodic public and media frenzy about immanent decanting of acid mine drainage (AMD) from toxic springs in places like Nigel, City Deep, or Randfontein, are fuelled by certain assumptions about groundwater movement, and the effects of marginal mines closing down and stopping to pump out groundwater seepage from mining sumps.

Among the AMD impact hot spots is Grootvlei mine, an economic hot potato involving liquidations, well connected BEE bidders, maintenance failures, illegal miners, scavengers, international funding, and appeals for state funding.

PHOTO THUMB; A single pump station could not solve a linear reef acid mine drainage (AMD) problem, due to water migration slowed by thousands of obstructions, exceeded by the speed of inflow at distant ends. Dual pump and treatment stations may save Johannesburg and Gauteng from AMD.

PHOTO DISPLAY; Prof Terence McCarthy.

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