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PUMPS to deal with acid mine drainage (AMD) in Joburg have been ordered by the national department of water affairs.

Remnants of the city's mining pastRemnants of the city's mining pastTwo pumps will treat some 72 megalitres of water daily, says Sydney Nkosi, the director of natural resource management in the City’s department of environmental management.
The pumps are step one of a three-stage attack on AMD, he confirms. Stage two involves a neutralisation plant, to treat the toxins in the water. Stage three will be a desalination plant, taking the salts out of the water before it is released into the water systems flowing through Joburg.

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.

One of the reef’s major mining companies, DRD Gold, is investigating whether its neutralisation plant can be refurbished and used, at an estimated cost of R60-million. Some R150-million would be needed for a desalination plant.

It is expected that the pumps, which are being imported, will arrive at the end of July.

Task team
A task team has now been set up by the City, and includes Johannesburg Water, the Johannesburg Roads Agency, Johannesburg City Parks, the Johannesburg Property Company, City Power, Emergency Management Services, and the departments of housing, environmental health, environmental management, community development, economic development, and development planning and urban management.

Contaminated waterA neutralising plant will be built to treat contaminated water“The City of Joburg will be commissioning a city-wide risks assessment on the extent of the mine void as well as potential risks posed to the city’s infrastructure such roadways, bulk service infrastructure, buildings and socio-economic impacts,” explains Nkosi.
While mining was operational, mining companies had infrastructure in place to pump water out of the mines. But as they closed down from the 1950s, the underground voids created have continued to fill as pumping operations ceased. Accumulated water has flowed into adjacent mines and is filling up the entire void, from the western basin across to the eastern basin.

There are three basins within the Witwatersrand reef, which stretches 50km from Krugersdorp on the west rand to Boksburg on the east rand. Johannesburg sits over the central basin. In this basin the water level has been rising by 59cm daily since July 2009. By mid-2010 the water level was around 500m below the surface, and expectations are that by March 2013 the water will have reached the surface.

The team’s work is multi-pronged. It needs to do an assessment of the mine void in relation to the topography of the region to locate possible ingress and especially decant points; it needs to assess the vulnerability of flooding of the City’s infrastructure, particularly sewers, storm-water tunnels, roadways, electricity, water, green infrastructure, building and boreholes; it needs to assess the vulnerability of building basements close to the mining zone; and finally, it needs to establish its own mine void water level monitoring programme.

Professor Terence McCarthy from the school of geosciences at Wits University estimates that the void will be completely filled by mid-2013.

Two levels of intervention

A mining rigA mining headgearThere are two levels of intervention in the approach to AMD in Joburg, stresses Nkosi. Three national government departments – water affairs, environmental affairs and mineral resources – are working together with the City’s task team.
“National departments are currently undertaking studies to monitor the underground mine water levels within the central basin by the Team of Experts and Monitoring Committee,” states Nkosi.

“These processes are running parallel and complementing each other,” adds Nkosi.

The department of water affairs (DWA) has appointed the Trans Caledonian Tunnel Authority as the implementing agent, says Nkosi. This state body was established in 1986 to implement the South African side of the Lesotho Highlands Water Project. It now manages the long-term funding and risk management of the project, as well as advising other water projects and water management institutions.

The DWA has budgeted R225-million over the next three years for the management of AMD. That money will be spent “in a particular basin depending on the specific infrastructure needs or urgency of interventions”, says Nkosi.

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