Acid Mine Drainage: the environmental and social risks in the Witwatersrand gold fields

Written by  Mariette Liefferink Tuesday, 12 January 2016 18:54
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South Africa is at the transition point of “peak water.” This is the moment when the economy transitions from a demand-driven state to a supply-constrained state. Peak water means that supply will be limited. This will affect economic growth and may result in social instability.

 

By 2025, the Orange, Limpopo and Vaal River system will transition into water scarcity. For example, the Limpopo River Basin is already over-allocated by about 120%, and is facing a 241% increase in demand by 2025. Even in 2013, the Minister briefed parliament that 52 villages had no water in Limpopo.

The right of every person to water of sufficient quality and quantity is enshrined in the Bill of Rights. The notion of basic supply has been determined in regulations issued by the Department of Water Affairs. These provide that the minimum standard for basic water supply services include: a minimum quantity of potable water of 25 litres per person per day or six kilolitres per household per month, available within 200 metres of a household and with a value such that no consumer is without a supply for more than seven full days in any year. In many cases this Right is violated.

The Vaal River system is in crisis

The Vaal River System supplies water to 60% of the economy and 45% of the population of South Africa. A multi-pillar strategy has been devised to ensure the future availability of sufficient water of good quality. One of the measures involves re-using treated effluent (waste water), starting with mine water by 2014/2015. Mine water has been prioritised because of the many hazards of acidic water.

The serious ramifications of AMD in the West Rand Basin (one of three mining basins in Gauteng) was first recognised in 2002. AMD in this region threatens the Cradle of Humankind World Heritage Site as well as the 11,491 downstream landowners and agricultural activities that are largely or wholly dependent on groundwater for drinking and economic use. For the next 10 years, up to August 2012, raw or untreated AMD continued to flow into dams, rivers and streams with devastating consequences.

As well as water pollution, AMD is associated with degradation of soil quality, harming aquatic sediments and fauna, and heavy metals seeping into the environment. In addition, radioactive metals such as uranium (U) also occur in the discarded mine water. There is  a marked increase in U-levels in water resources of the whole catchment since 1997.

Long-term exposure to AMD-polluted drinking water may lead to increased rates of cancer, decreased cognitive function and appearance of skin lesions. Metals in drinking water could compromise the neural development of the foetus, which can result in mental retardation.

Sludge

Sludge is the thick soft, wet Mud (or a similar viscous mixture of liquid and solid components) left over after refining processes. Currently, two high density sludge projects are operational for the immediate treatment of AMD. They are in the Western (West Rand) Basin and the Central Basin. These plants are presently treating (neutralising) around 100 million litres (Ml) of AMD daily. An equivalent volume of the neutralised water is then discharged to the environment.

However, the metal sludge is currently disposed of in unlined pits and on storage facilities for the ore waste of mines (known as ‘tailings’ – what we call mine dumps). The numerous open pits in the West Rand Goldfield have been identified as a major single source of entry into disused mines.

Combating salinity 

The  water  quality  results  of  the supposedly neutralised AMD were supplied to the Federation for a Sustainable Environment by the Department of Water Affairs in 2013. They showed sulphate levels of between 2,395 and 3,012 mg/l. The World Health Organisation’s standard for sulphate in drinking water is 200mg/l. Sulphate concentrations of 600 mg/l and more cause diarrhoea in most individuals and adaption may not occur. 

The highest cost burden of combating salinity is currently being carried by the household sector and not, as might be expected, by industry in accordance with the ‘polluter pays principle’

If AMD is not treated to a level where the salt load is removed, the Upper Vaal will go into deficit. In drought conditions, this is what will happen:

  • Restrictions will be placed on domestic users in the Upper Vaal; or
  • The dilution standard at Vaal Barrage will be relaxed, resulting in very poor quality water reaching the users in the Middle and Lower Vaal (Kosh area, Free State Goldmines and all the mining activity in the Northern Cape on the Vaal Gamagara Scheme);
  • With the Upper Vaal in deficit there would then be no possibility of transferring water into the Olifants-, Crocodile West/Marico and Limpopo catchments, and economic activities in six provinces could be affected if water consumption is curtailed

Limited plans

There are many sources of AMD such as seepage from tailings storage facilities, contaminated wetlands and rivers, open pits, waste rock dumps, and secondary sources of contaminants that remain in the soil after a dump has been removed. They are not addressed in the current treatment of AMD. 

Very few specialist investigations appear to have been done to identify the status of the geohydrological regime,  the extent of contamination, preferential pathways and predictions regarding long– term migration. As a result there are very limited mitigation or management options that specifically deal with the containment or rehabilitation of contaminated groundwater.

There are no proactive management plans in place by the South African government to cope with the flooding and possible decant [overflow] of water from the Far Western Basin, the Free State goldfields and the Kosh Basin.

What should be done?

The cost of water has increased drastically because of the cost of energy. There are more affordable and reliable technologies. Both of these factors make local solutions much more viable. The Department of Water and Sanitation’s decision to “pump and treat” should be revisited since this will result in pumping the polluted water for ever, at excessive cost. It has been suggested by respected academics (such as Prof. Dr. Habil Frank Winde) that the disused mines should be allowed to fill. This will require no deep pumping. As a result, less AMD will be produced and so there will be a smaller quantity of AMD to be treated. A prerequisite will be effective surface reclamation and land re-use.

Combating salinity

The  water  quality  results  of  the supposedly neutralised AMD were supplied to the Federation for a Sustainable Environment by the Department of Water Affairs in 2013. They showed sulphate levels of between 2,395 and 3,012 mg/l. The World Health Organisation’s standard for sulphate in drinking water is 200mg/l. Sulphate concentrations of 600 mg/l and more cause diarrhoea in most individuals and  adaption may not occur. 

If AMD is not treated to a level where the salt load is removed, the Upper Vaal will go into deficit. In drought conditions, this is what will happen:

  • Restrictions will be placed on domestic users in the Upper Vaal; or
  • The dilution standard at Vaal Barrage will be relaxed, resulting in very poor quality water reaching the users in the Middle and Lower Vaal (Kosh area, Free State Goldmines and all the mining activity in the Northern Cape on the Vaal Gamagara Scheme);
  • With the Upper Vaal in deficit there 
  • Innovative technologies must be investigated and piloted to find the best practicable environmental option. That is, the option that causes the least damage to the environment at a cost acceptable to society in the short and long term. Sibanye Gold, for example, has a research facility and works with the University of Cape Town and Mintek on value recovery solutions, using precipitation, ion-exchange, reverse osmosis, and organisms.

It is imperative that mining companies implement zero effluent strategies and treat AMD from its source.

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