JOHANNESBURG – The state of acid mine drainage (AMD) at some mining areas in the Witwatersrand has reached a critical point, despite short- and long-term interventions to remedy the environmental issue.
According to the Department of Water and Sanitation, when minerals with sulphides are exposed to oxygen and water this creates sulphuric acid and dissolved iron, which in turn mobilises other heavy metals like lead and uranium (radiological risks). AMD entails the outflow of this acidic, heavy-metal-containing water from surface and underground mines.
Throughout their operations, the historic gold mines in the Witwatersrand pumped out water. But as the mines closed or were abandoned over the years, ‘dewatering’ reduced and the defunct mines filled with water, exacerbating the AMD issue.
The rising water levels also bring the risk of earth tremors and the contamination of rivers and aquifers.
The Witwatersrand contains the eastern, western and central basins. The western basin covers the Krugersdorp, Witpoortjie and Randfontein areas; the central basin extends from Roodepoort in the west rand to the east rand mines; and the eastern basin covers the east rand area, including Boksburg, Brakpan, Springs and Nigel.
The western basin is considered to be “an environmental disaster” by environmental risk analyst Dr Anthony Turton, as its acid mine water levels are rising.
“The western basin environmental critical levels (ECLs) were breached in 2000. Decant [the surface discharge of water from an abandoned mine] happened in 2002 and decant has been more or less going since the exception of a couple of months last year. With all the heavy rain we had in January and February this year, it was flooding again,” Turton told Moneyweb.
Acid mine water is being pumped out of the central and eastern basins, and their water levels have been contained, says Marius Keet, senior manager for mine water management at the Department of Water and Sanitation.
There are no specific regulations on the ECLs, as various mine shafts differ in density and altitude.
Red tape has also afflicted the western and eastern basins, holding up contract agreements to resume de-watering operations. Turton says the contract for AMD treatment in the eastern basin was recently awarded after long delays which made it “physically impossible” to install pumps to prevent the breach of ECLs.
Currently, AMD water is not suitable for human consumption. Even after treatment the water is toxic, says CEO of Federation for a Sustainable Environment Mariette Liefferink, as it still contains sulphate salts.
Acid mine water is pumped from various Witwatersrand basins and released into rivers which flow into major rivers supplying the country’s drinking water, including the Vaal River.
Liefferink has raised concerns about there being no rehabilitation plans to clean rivers which become the recipient of this toxic water. “There is no management measure and funding available for rehabilitation of rivers, if you go to the west rand you will see the contaminated rivers and dams,” she adds.
Another contentious issue is the disposal of metal contents once the acid mine water has been treated – a byproduct referred to as sludge. Liefferink says there are 170 mine dumps spread throughout the Witwatersrand, which she says do not get the requisite and environmental attention which is needed.
Sludge in the western basin is discharged in a western pit, while in the central basin “we [the department] are co-disposing with one of the mining companies on a dumping facility and in the eastern basin we are currently investigating where the sludge will be pumped,” says Keet.
“Although it’s a challenge there will always be sludge, but we deal with this in the best environmental manner we can,” he adds.
Tackling the problem
From an infrastructure point of view for the treatment of acid mine water, the department in 2012 appointed the Trans-Caledon Tunnel Authority (TCTA), for the pumping of acid mine water from basins in the Witwatersrand area.
“For the central basin, the AMD water will be pumped from the South West Vertical Shaft. For the western and eastern basins, the water will be pumped from west rand 9 Shaft and from Grootvlei 3 Shaft in the western and eastern basins respectively,” says TCTA manager for stakeholder and communications Christopher Tsatsawane in an emailed response to questions.
The treated acid mine water from the central basin is released into the Elsburg River in Germiston, on an “on and off basis since May 2014,” says Tsatsawane.
TCTA, on behalf of the department, is implementing the construction of the water pumping infrastructure, which started in January 2013.
The commission to pump and treat water from the central basin to non-consumable levels is at a cost of R409 million, in what could be considered as a short-term solution to the environmental issue.
The infrastructure to pump water from central basins is supplied by TCTA and the costs of the infrastructure will be carried by South African tax payers, says Liefferink. She also says Central Rand Gold has donated the stainless steel pumps in the central basin as the mining group is on board to protect gold reserves.
Keet says the department is investigating a plan to set up a desalination plant to neutralise acid mine water, a process which involves removing sulphate salts from the treated water.
He adds: “We are recommending to the minister to appoint an implementing agent for establishing a desalination plant in the central and eastern basin”.
The idea is to have acid mine water treated for industrial and consumption purposes.
This might be an ambitious task, as Liefferink says setting up a desalination plant is an expensive exercise with the infrastructure estimated to cost R6.6 billion, operation costs coming in at R750 million and a further R250 million for maintaining the plant.
The reduction of water levels is necessary for Central Rand Gold to explore its resource base in the Witwatersrand and meet exploration targets in the central basin.
Central Rand Gold announced in a SENS announcement at the end of June, that water levels at its central basin mine had decreased, due to a successful commissioning phase of the pump project.
The company had seen water levels rising to about 165 metres below the surface up to mid-May 2014. Since the plant has been in action, “the water level within its mining area has remained relatively stable,” and had even started reducing at the time of the announcement.
The pumps used to dewater mine shafts, Central Rand Gold says, will provide the means to contain the rising water table below the environmental critical level of 186 metres below at the central basin.
The water pumps operate at a capacity limited to 400 metres below surface, which the agreement gives Central Rand Gold the option to undertake further dewatering activities.
In the announcement, CEO Johan du Toit says the company hoped to see an acceleration in the water levels dropping, so the mining areas in the Witwatersrand (which had to be abandoned due to rising water levels) could be re-accessed. Turton explains that the central basin project is a success as Central Rand Gold has a vested interest in preventing flooding of its underground resources, which has gold reserves of “20 years”.
The mining group has acquired seven prospecting rights including Western Areas A, B and E, Consolidated Main Reef, Langlaagte, Crown Mines, Anglodeeps, Village Main, Robinson Deep, City Deep and Simmer & Jack.