Posted by: Saving Water SA (Cape Town, South Africa) – partnered with Water Rhapsody conservation systems – 08 March 2010
Anthony Turton, vice-president of the International Water Resource Association, explains how our water problems can be solved to benefit the economy.
The phrase “acid mine drainage” (AMD) has been bouncing around in the media for months. It is caused by disused mine workings being flooded, which brings water into contact with the pyrite base of the ore body. Bacteria attack the pyrite, a sulphide compound, releasing sulphate and, through a complex chemical reaction, oxygen. The oxygen feeds back into the process, making it a self-sustaining reaction, much like fire feeds off fresh air.
The resulting product is a toxic cocktail of heavy metals, including arsenic and uranium, all dissolved in this highly acidic stream of water known as AMD. This is clearly not a good thing, because the volumes are substantial and the toxic loads are high. AMD from Witwatersrand gold mines is also radioactive.
Is this good news for the South African economy? Clearly not when you consider that the water decanting from the Witwatersrand mining basin will contribute about 5% of the flow volume of the Vaal River and will increase the load of toxic salts in the river by 20%.
The increased salinity of the water will eventually destroy all agriculture downstream of where the salts enter the river. But the way you frame the question dictates the answer you get, so let’s be clever and redefine the problem.
The general problem we face as a nation is that we have run out of water for economic growth. We have managed water scarcity in the past by building dams, but our losses to evaporation are massive. In the Orange and Limpopo river basins, two of our most important at the national level, we lose 95% of the rainfall to evapo-transpiration (evaporation off the dam and transpiration of water through vegetation). If we can reduce evaporation, even by only 5%, then, in effect, we would double the volume of water we have available for economic development.
This is where the AMD debate becomes interesting, because under the Witwatersrand mining basin is a void stretching from Springs to Randfontein that has a combined volume equivalent to five times that of Lake Kariba. But the really good news is that, if we chose to store water there, it would not be subject to evaporative losses. This is amazing because it does two very important things for us as a nation.
Firstly, it gives us hope for the future by growing our national economy in a way that ensures social stability. Secondly, it helps the embattled gold mining industry to solve its environmental remediation problems.
Recent work by Chris Hartnady, a respected geologist, indicates that the gold reserves left in the ground are less than the environmental liability, which means that, if the mining companies have to pay for remediation, then in effect they will go out of business.
So let us apply our minds to this new solution. Let us stop bickering over who is liable for environmental remediation of the AMD spill that will hit Johannesburg in January 2012 and let us instead collectively start to think about how to use the mine void for strategic storage that benefits the whole country.
Strategic storage of this magnitude, without evaporation, means we will have masses of water for future use. More important, we do not need to actually use that water, because it will be a strategic reserve for use only in emergencies. This will mean that existing dam operating rules can be changed.
At present, we manage our dams to keep them as full as possible, which has the unintended consequence of increasing evaporative losses from them. We can then draw the dams down to lower levels, reducing evaporative loss, but also creating more economic activity and thus prosperity, secure in the knowledge that, when drought hits us, we have a strategic reserve five times the volume of Lake Kariba.
This also means that we can optimise our water resources at the national level, and not just at the sectoral level, which in turn means more benefits to more people, but importantly also a larger pool from which to cover costs.
This optimisation at a level above that of the mining sector alone will mean that we can afford the very best technology, reverse osmosis and ion exchange, which produces the purest water. So if we ever need to drink this AMD, we can do so in full confidence that it will be safe.
South Africa is going through a transition from an extractive economy, in which costs of production were externalised onto society, to a new beneficiation economy, in which full life-cycle costing will be the norm, with benefits accruing to a wider segment of society.
This is being smart! All it needs is a new collective vision, supported by leadership with integrity, and the South African nation can face the challenge of AMD with confidence.