Rains will increase rate of rising acid water

Posted by: Saving Water SA (Cape Town, South Africa) – partnered with Water Rhapsody conservation systems – 26 November 2010

Unless millions of litres of acid mine water beneath Johannesburg are decanted soon, low-lying areas in the city could be flooded, Prof Terence McCarthy of the University of the Witwatersrand warns.

He said if pumping does not begin by October next year, many sites, including tourist attraction Gold Reef City — which he described as a “national treasure” — could flood.

Prof McCarthy was speaking at the launch of his new study, The Decanting of Acid Mine Water in the Gauteng City-Region — Analysis, Prognosis and Solutions, published by the Gauteng City- Region Observatory, a partnership between Wits University and the Gauteng government.

“The void beneath the Witwatersrand, which has been created by gold mining activity over the last 120 years, is filling with water which is rising by about 15m a month,” said Prof McCarthy.

In October 2008, East Rand Proprietary Mines stopped pumping and the space created by the mine’s rock extraction began to fill with water.

“Currently, the water level in the void lies at a depth of about 600m below the surface, but this could rise faster during the rainy season,” Prof McCarthy said.

If it is not pumped out, the water will spill out of the ground and find its way into the Klip River catchment area, which flows into the Vaal River.

Mine water is generally toxic and corrosive, but Prof McCarthy said when it reaches the deeper parts of the mine void, it is deprived of oxygen and the chemical reactions cease, which caps the levels of pollution.

“Ultimately, the decant water may become of sufficient quality that it could be used to augment the region’s drinking water supply, although we have no idea how long that could take,” he said.

“But in the immediate term, the water that will decant is potentially toxic. The uranium in the water is poisonous.”

Prof McCarthy said two pumping stations needed to be established, in Germiston and Florida in Johannesburg.

Pumping “will not necessarily be a perpetual cost”, he said.

Source: Business Day

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