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Joburg moves to act on acid mine drainage. It is setting up a task team of experts and is working with the national government on the problem.
THE City of Joburg is to set up a task team, comprising experts and engineers, to conduct a “full, city-wide investigation” into the risks of acid mine drainage (AMD) on the infrastructure of the city.

City manager Mavela Dlamini (Photo: Enoch Lehung, City of Johannesburg)City will engage national government on acid mine drainage, says City Manager Mavela Dlamini (Photo: Enoch Lehung, City of Johannesburg)A March report on AMD, approved by the mayoral committee, states that the City manager, Mavela Dlamini, will engage with the national government “at a high level” to minimise any risks associated with AMD.
Acid mine drainage refers to the water that drains over the surface of acid-bearing rock which has been exposed through mining, becoming toxic as it rises to the surface of disused mines and making contact with air. It threatens the health of rivers and people who come into contact with that water.

The Witwatersrand stretches 50 kilometres from Krugersdorp on the West Rand to Boksburg on the East Rand, with a gradient of around 160 metres from one end to the other. Mining started 124 years ago on the Witwatersrand, in 1886, but from the 1950s mines across the region started closing down. In 2008, the last remaining operational mine, East Rand Propriety Mines in Boksburg, closed its operations.

While mining was operational, mining companies had ongoing infrastructure in place to pump water out of the mines. But as they closed down, the underground voids created from mining operations have continued to fill as the pumping operations have ceased. Accumulated water has flowed into adjacent mines and is filling up the entire void.

The national Department of Water Affairs has budgeted R225-million over the next three years for the management of AMD.

“We welcome the budget announcement of R225-million for AMD, and the City manager has been mandated to explore how part of that budget can be apportioned for our own requirements,” says Flora Mokgohloa, the executive director of the environment for the City.

All infrastructure in Johannesburg, including that relating to sewer, water, electricity, buildings and roads, will fall within the investigation.

It has been estimated that infrastructure must be put in place to deal with AMD within 20 months. Professor Terence McCarthy, from the School of Geosciences at Wits University, estimates that the void will be completely filled in about two-and-a-half years from now.

Risks that were highlighted in a December 2010 national government report are multiple.

“Experience in the Western Basin has shown the severe impacts that can be expected if the mine void is allowed to flood completely and decant,” indicates the City report.

As mines continue to flood with toxic water from deep below the surface, the risk of contamination of shallow groundwater means that water for agricultural use and human consumption will become contaminated.

Other risks include geotechnical impacts or subsidence. This could result in greater seismic activity – in other words, earth tremors, which could have “a moderate localised effect on property and infrastructure”.

The decant of AMD on the environment could have serious negative ecological effects, especially on rivers, which could flood, particularly in low-lying areas.

Western Basin
Already the disused mines in the Krugersdorp area, or the Western Basin, have been flooded, and AMD is decanting into the Twee Lope Spruit, which flows into the Limpopo River and ultimately into the Indian Ocean near Maputo in Mozambique.

“The existing pumping and treatment capacity is inadequate to effectively manage the impact of AMD, with the excess volume flowing untreated into the receiving aquatic environment,” according to the report.

That water comes from several sources: rainfall, ground water seepage from the old mine workings and residue deposits, and from sewage and storm water reticulation systems.

To prevent this, pumping and treating of water must continue, and if possible, it is necessary to reduce the volume of water to be pumped and treated. That can be done through canalisation of surface streams, sealing surface cracks and mine openings, and ensuring that sewage and storm water systems don’t contain leaks. If water from streams can be tapped away from the mine workings, that would also reduce the flooding of mines.

Central Basin
In the largest basin, the Central Basin over which Johannesburg is situated, the water level has been rising by 59 centimetres daily since July 2009. By mid-2010 the water level was around 500 metres below the surface. Predictions are that by March 2013 the water will have reached the surface.

“Of even greater consequence is that it will not only have flooded the shallower underground tourist facilities at Gold Reef City, but also compromised the shallow groundwater resource associated with the dolomitic strata located to the southeast of Johannesburg,” indicates the report.

Since October 2008, an increase in earth tremors has been confirmed, although the tremors are not as severe as they were when mining activity was being conducted in the Central Basin. The frequency of these tremors will be monitored.

Despite this, several developers are confident that AMD does not pose a threat to their developments in Westgate, in Ferreirasdorp in the CBD.

The landowners – the Johannesburg Land Company, Standard Bank and Iprop – are working on plans for office, residential and retail space in Westgate. The area was one of the first in Joburg to be mined, and the developers have had to fill the workings to stabilise the land.

Eastern Basin
Also of concern is the Eastern Basin, in Ekurhuleni. Pumping of mine water ceased in 2008 and as the water level rises, it risks flooding the CBD of Nigel on the East Rand in the next five years.

The Grootvlei Mine is the last mine in the region to be pumping water, but because of financial pressures, it is not treating the water like it used to – and that untreated water is being discharged into the Blesbok Spruit and a nearby protected wetland. So far, the mine has managed to maintain the water level at 700 metres below the surface.

“In light of the above, it is recommended that AMD intervention and management measures are undertaken in the Western, Central and Eastern basins as a matter of urgency,” states the report.

Various treatment options and technologies for the treatment of the AMD water have been identified. “Given the variability in water quality between the different basins and the possibility that the water quality in the mine voids will improve over time, it is likely that a suite of different technologies will be required.”

The report has several recommendations. In the Western Basin, a treatment plant needs to be established to supplement the present plants used by mines in the area. Pumping facilities need to be upgraded.

In the Central Basin, a pumping facility needs to be installed “in one or more existing mine shafts, with a treatment plant or plants nearby”.

In the Eastern Basin, the pumping capability at Grootvlei Mine must be reinforced and the existing treatment plant must be brought back into service. “The volumes of water to be managed may be reduced by the timely implementation of ingress management measures, with a resultant reduction in operating costs. The design of the pump and treat systems will need to take this into account.”

Measures to stop or reduce the entry of water into the underground workings must also be investigated.

Once the pumping and treatment of AMD is under control, conditions similar to those when mining was taking place, will be produced. In the long term this is not sustainable as it could result in excessive salt loads emptying into the surrounding water systems. It is expected that the water quality will improve in the long term.

Environmental levy
The possibility of an environmental levy to be paid by operating mines to cover the costs of past mining, is being investigated. It would be levied on all operating mines to fund the legacies of the past.

“The problems posed by AMD will have implications far into the future, with impacts likely to continue for many years. The process of management of these impacts will therefore need to continue, with ongoing assessments and adaptation as conditions change.”

The national report indicates that the state will fund and operate measures to manage AMD on the Witwatersrand. In the short term the mining industry will be expected to contribute to some of the costs of this.

There is a possibility that the private sector will be allowed to treat AMD and sell it to the market, but probably with the help of a state subsidy.

The Department of Water Affairs has agreed to install one new pumping station and upgrade a sludge treatment operation, to save Johannesburg from rising acid water.

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