Johannesburg - is acid water a threat?

Could the City of Gold’s foundations be rocked by acidic water eating away at the ground it stands on?

It is no secret that Johannesburg’s fortunes have been built on the backbone of gold mines and gold mining, although rewarding, contains many dangers. One of these dangers are the acid water created while mining in the world’s largest gold deposit.

Like every good debate, there are two camps on this matter.

A report released in 2011 by a group of experts entitled “Mine Water Management in the Witwatersrand Gold Fields with Special Emphasis on Acid Mine Drainage,” suggested that rapidly-rising acid mine water under Johannesburg would start flooding the lower levels of Gold Reef City’s tourist mine by March 2012.

Professor Frank Winde headed a study which was also released in 2011 however suggested that Johannesburg’s CBD was safe from being flooded by acid water. This report conducted by the group headed by Winde had said that “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.”

Fast forward to March 2012 and you would find that although the acid water hadn’t flooded Gold Reef City as predicted, but meetings were being held to approve emergency measures for the treatment of acid water.

These emergency measures are being put in place as it would waste time to build proper acid mine water purification infrastructure that would offer a permanent solution.

The rising acid water in the Central Basin has reached a level of about 200m below the critical environmental level.

The critical environmental level is where the acid mine water starts to erode underground dolomitic structures and shortly afterwards start to pollute the natural groundwater as well as points of egress, such as fountains.

This process takes several months, after which the water eventually begins to emerge on the surface.

The environmentally critical level in the Central Basin is 150m below the surface at the South-Western vertical shaft of the old ERPM mine in Germiston – the shaft selected years ago by Western Utilities ­Corporation is the best point for the acid mine water in the Central Basin to be pumped out and properly purified to the quality of drinking water.

The acid water is currently 350m below the surface at the South-Western vertical shaft.

A year ago scientists, who had been researching the underground ingress of water for more than a decade, predicted that acid mine water would reach the environmentally critical level by February this year, but in the 12 months to February rainfall in the Central Basin, which includes ­Johannesburg and the neighbouring East Rand, was considerably below the average for the previous five years.

This reduced the rate at which the water was rising in the hundreds of old mine passages and other excavations.

The Caledon Tunnel Authority, which acts as the state body to deal with the impending crisis, proposed that three water installations be built rapidly to pump out the rising water, treat it temporarily with lime and then release it into the environment.

However, environmental groups are upset because this process merely reduces the acidity of the water and does not remove the toxic heavy metals it contains.

In the Western Basin – where it is hopelessly too late to prevent pollution because the acid water has been flowing out since October 2002 at a rate of 15.7 megalitres a day – the Caledon Tunnel Authority now wants to construct an installation such as this on the premises of the Randfontein Estates Mine, where the water is being treated with lime and then discharged into the already contaminated Tweelopiespruit.

Public meetings where the public could comment on these proposals were held in Krugersdorp last weekend and in Germiston on Friday to discuss the Central Basin installation.

It is predicted that the eventual outflow will be 57 megalitres a day. The new plant is envisaged close to the previous one used by DGRGold to counteract the problem by pumping out and treating the water at the South-Western vertical shaft. These pumps ceased operating because the shaft was closed down by mine inspectors after a mining accident.

In the Eastern Basin a new installation is being planned at the old Grootvlei No 3 shaft.

The last update we could obtain was from three days ago, when it was reported that the government was working with the mines to reduce the rising acid water levels. But on where they are exactly in executing the plans are still shrouded in mystery.

The big question of whether Johannesburg was in danger or not? The answer it seems is that yes, if nothing is done in time then Johannesburg could be in danger from rising acid water levels.

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