Joburg safe from acid mine water - study

Cape Town - There is no risk of acid mine water flooding the deep basements of high-rise buildings in the Johannesburg central business district, according to a geo-technical risk assessment study released on Monday.

"The study has just been completed, and it was concluded that no risks of mine water flooding any basement structure in the CBD of Johannesburg exist," the Mine Water Research Group, headed by Professor Frank Winde, said.

The research group is based at the North West University's campus in Potchefstroom.

The study is highly critical of the acid mine drainage (AMD) report prepared last year for the government by a team of specialist scientists, and presented to an inter-ministerial committee tasked to deal with the threat of rising mine water under South Africa's biggest city.

Among the risks identified in the government report is that the rising water could lead to the "flooding of underground infrastructure... close to urban areas".

It also warns, among other things, of increased seismic activity, the threat of groundwater contamination, serious negative ecological impacts and localised flooding.

The research group said it was difficult to avoid the impression that the government report was "a premature, somewhat hasty response to a largely media and interest group-driven campaign that appears to have inflated, misrepresented and exaggerated possible risks associated with the filling of the mine void".

On the flooding risk posed by the rising mine water to buildings in central Johannesburg, it finds no evidence for this.

"Using the pile levels of the ABSA Tower East as the deepest of the bank buildings considered in the Johannesburg CBD, it was calculated that the maximum elevation to which the mine water table can rise in the Central Basin mine void is 90 metres below the base of these piles.

"For the new admin building of Standard Bank, which according to the latest issue of 'You Magazine' is already being flooded, the safety margin is 106 m," it says.

The risk-assessment was commissioned by the two banking groups.

Acid mine drainage

While the study focuses mainly on assessing the flooding risk, it also examines other aspects of acid mine drainage.

Here, too, it differs in its findings from the government report.

"The main findings of the Winde report differ in a number of crucial aspects from the AMD report tabled to the cabinet.

"This includes newly-identified ingress sources, a slower rise of the mine water table resulting in a later date of decant (despite the unusual heavy rains in late 2010 and early 2011), a significant reduction of the expected decant volume (with possible implications for proposed treatment options) and much less severe impacts of the untreated decant water on the quality of receiving streams."

It calls for "a more sustainable, low-cost, low-energy solution" to the problem, "as opposed to the currently proposed high-cost, high-energy, pump-and-treatment-option likely to be subsidised ad infinitum by society".

The government has set aside R400m to build pumping stations and treatment works to deal with the acid mine drainage problem.

The study says decanting mine water should be seen as an opportunity.

"Given the shortage of water in Gauteng, the most water-stressed province in South Africa that relies heavily on water imported from Lesotho at great costs, the anticipated decant from the mine void should be seen not as a threat, but rather as an opportunity of using water which for a couple of years went unused to fill the void.

"Untreated acidic mine water has been used in the past by municipal sewage works in the Central Rand to aid nitrate digestion... Given the number of sewage works in Johannesburg, and the volume of sewage to be treated, this alone could perhaps accommodate most, if not all, of the decanting water, resulting in no treatment costs, while saving clean water otherwise used for this purpose."

This was but one example of other possible uses for the water.

"In this context, it appears that the AMD report to the inter-ministerial committee and the cabinet, concerning the Central Rand, lacks a thorough analysis of available data and leaves many crucial aspects superficially covered.

"This includes key issues such as the volume of the expected decant, the compilation of sources of the ingressing/decanting water, water quality and relationship to rainfall, the rate of rise of the mine water table and date of decant, as well as the spectrum of associated risks," it says.