Geochemical approach to safeguard water supply

RURAL communities in the water poor Olifants River Valley in the Klein Karoo of South Africa is heavily dependent on the Klein Karoo Rural Water Supply Scheme (KKRWSS) introduced in the early 1990s. A total of 39 000 people benefit from about one million cubic meters of groundwater pumped from 18 boreholes every year, mainly through better employment due to improved farming conditions.

Now the scheme is under threat because high iron levels in the groundwater form iron precipitate on oxidation, causing boreholes and pipes to clog. Pumping becomes more difficult and the flow of water is reduced.

Dr Alakendra Roychoudhury, a senior lecturer and environmental geochemist at UCT's Department of Geological Sciences, believes that a geochemical approach will provide a cost-effective solution to the problem that will probably include chemical, biological and mechanical measures.

Currently a very expensive technique developed in the United States is being used by the Department of Water Affairs and Forestry to fix affected holes.

It involves the pumping of large volumes of heated chemicals into the hole, takes three to five days and can cost up to R70 000.

The treatment improves the water supply from the hole for approximately two years before repeated clogging makes the hole ineffective again.

As these costs are seriously threatening the sustainability of the water supply scheme, Roychoudhury and PhD student Meris Smith are working in conjunction with the Council for Scientific and Industrial Research (CSIR) to investigate why the groundwater has high iron concentrations, and to study to which extent bacteria are responsible for the problem.

The geochemistry of the water and the chemical composition of the rock formations through which the water flows are being analysed, in an attempt to pinpoint the source of the iron.

Laboratory experiments will soon be set up to replicate the conditions in the borehole, so that the behaviour of iron in the system can be understood. The knowledge gained will help to identify factors that control iron oxidation and to find ways to prevent or limit the problem. New and improved methods of borehole rehabilitation can be tested in the laboratory, and then in the borehole.

Roychoudhury says the results of this new mechanistic approach will not only enable the KKRWSS to operate more sustainably to the benefit of the community in the Olifants River valley, but could be applied in other parts of southern Africa and the world where similar oxidation problems are being experienced.

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