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Acid mine drainage: Solution not seeping out Financial Mail

Acid mine drainage: Solution not seeping out

Written by  Charlotte Mathews Friday, 22 April 2016 17:02
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THE last season’s below-average rainfall slowed the flow of toxic water from old mine workings, but has not deferred the urgent need to address it.

With no sign yet of the long-awaited government decision on a permanent solution to halt acid mine drainage (AMD), water quality around Johannesburg continues to deteriorate, even if the poisonous tide rising to street level — as some scientists warned — has not actually materialised.

 

If government were to make a decision in the next week, it would still have to be followed by practical implementation, which would take months and possibly years, depending on the solutions it chose.

AMD comes from water rising through defunct underground gold mines stretching from the far west to far east of the Witwatersrand after mining companies closed and stopped pumping. In contact with the old workings, the water becomes acidic and eventually spills out onto the surface, starting in lower-lying areas. For years it has been visible close to the Krugersdorp Game Reserve.

Several years ago the department of water & sanitation allocated R225m to the Trans Caledon Tunnel Authority (TCTA) for the first phase of treating AMD, which involves pumping it out, neutralising part of it and discharging it into the environment.

Because it is only partly treated, it is adding to the salinity and heavy metals in the water catchment areas. A second, more comprehensive treatment is needed.

Anthony Turton, a professor at the Centre for Environmental Management at the University of the Free State, says that on the Western basin, which he has been monitoring, the drought has reduced the outflow of AMD to below average levels, but has not stopped it completely.

Government has spent money to neutralise the water flowing out of No 8 shaft at the old West Rand Consolidated Mine. But the water flowing into the Tweelopiespruit is not completely treated and the pumping at that shaft is not enough to bring the level of tainted water down to environmentally critical levels, he says.

“There is about a decade of underground mining still possible if environmentally critical levels can be reached as intended. This has significant job creation implications,” Turton says.

Mariette Liefferink, CEO of the Federation for a Sustainable Environment (FSE), says TCTA is currently using high-density sludge treatment on about 100 megalitres a day of AMD on the western and central basins, and a similar amount of untreated water is flowing into the environment. The treatment process merely changes the acidity of the water, solidifying the heavy minerals in it. If the acidity increases again, the heavy metals will revert to a soluble form.

Since October 2015, water and sanitation minister Nomvula Mokonyane has been promising to release the report on the long-term solution imminently. In February she said it would be announced within two months. Sputnik Ratau, the departmental spokesman, said on April 14 he could not give a date for its release as it had to be presented to cabinet first.

Liefferink says taxpayers forked out R25m for this feasibility study, which was fast-tracked and completed in 2013. But all FSE’s requests for the report to be released have been ignored.

“The failure to implement the long-term treatment of AMD is resulting in the prolonged reliance upon funding from the general fiscus, increase of the salt load in the Vaal River, which can only be mitigated by releases from the Vaal Dam, and the subsequent deficit in the Upper Vaal, which is now having severe economic impacts because of the drought,” she says.

Turton says government’s selected long-term solution is believed to be desalination, which has complex implications and might explain the delay in implementing it.

Complexities include the fact that desalination is energy-intensive and, if used to treat AMD, generates a potentially hazardous stream of waste.

The waste could be sent to four high-density sludge storage facilities, one for each basin, each of which would cost government about R1bn and would have to be maintained in perpetuity. Alternatively, the waste could be used by mining companies in proven tailings water treatment technology, resulting in a neutral product that could be deposited underground to fill mining voids permanently.

The business model would either require government to appoint an agent who would treat the water to potable standards and sell it to Rand Water, a process which offers opportunities for patronage, or allow mining companies to use AMD as part of the process of extracting the remaining gold in surface tailings dams.

When the gold price was high this would be self-funding, but if the gold price fell below a certain level, those operators would have to be subsidised to treat AMD. They would be held accountable for targets and rehabilitation standards.

 

The model where the state bears all the costs would be about three times more expensive than one using mining companies, Turton says. The mining company solution also does not require selling the idea of treated AMD in drinking water to the public, which is likely to provoke resistance.

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