JOHANNESBURG (miningweekly.com) – JSE-listed Group Five has started the construction of high-density treatment works, pump station and monitoring shafts to tackle acid mine drainage (AMD) in the Witwatersrand Central basin.

The group, which was awarded the R319-million contract by State-owned Trans-Caledon Tunnel Authority (TCTA) in December, started site clearing activities on the Germiston-based South West Vertical Shaft site in January and was expected to pour first concrete on Monday.

The project was in line with the TCTA’s mandate – by the Department of Water Affairs (DWA) – to tackle AMD and implement emergency AMD interventions in the Central, Western and Eastern basins of the Witwatersrand mining areas.

The construction group had ten-and-a-half months from the January 8 contract signing to complete construction, with pumping expected to start in October, TCTA project manager Craig Hasenjager told Mining Weekly Online.

The current level of AMD was said to be 256 m and it was expected to breach the environmental critical level (ECL) by September or October this year if pumping operations did not start.

The treatment plant would contain the rising water table below the ECL of 186 m below the surface at the Central basin.

Hasenjager was confident of meeting this target, despite the normal duration of such an undertaking being about two years.

Group Five had, albeit at a higher cost, mobilised all operations at once and started simultaneously the various aspects of the required operations.

Pumping operations in the Western and Central basins stopped during 1996 and 2008 respectively, while operations in the Eastern basin were halted in 2011.

The volume of AMD that needs to be treated in the Western, Central and Eastern basins was 27 Mℓ/d, 57 Mℓ/d and 82 Mℓ/d respectively.

WESTERN BASIN
The ECL for the Western basin had already been breached, reaching 0.88 m below collar level.

The TCTA noted that AMD had reached the surface in 2002 and started flowing untreated down the Tweelopiesspruit, causing environmental damage along the stream and polluting the groundwater in the Zwartkrans compartment.

The water authority’s main aim now was to draw down the water to the 165 m ECL.

The TCTA prioritised the upgrade of Rand Uranium’s existing water treatment plant to 36 Mℓ/d from its capacity of 12 Mℓ/d as an immediate solution for the Western basin.

The upgrade was expected to be complete by September. Two pumps, at a cost of R60-million, had been ordered and were due to be delivered in November.

The uncontrolled decant in the basin, barring 600 000 ℓ/d during a one-day incident, had been stopped.

The water quality in the Tweelopiesspruit had also improved.

The short-term solutions to the challenge of AMD in the region had proved too costly, however, compelling TCTA to review long-term solutions while undertaking further upgrades.

The DWA in January invited stakeholders to propose a possible long-term solution to the management of AMD in all three basins.

EASTERN BASIN
Meanwhile, as a result of financial constraints, the DWA decided to postpone the treatment of the AMD from the Eastern basin to a later stage, as its situation was less critical.

The Eastern basin’s AMD levels were recorded at 423 m, with an ECL of 290 m. It was expected that AMD would breach the ECL by November 2014.

The TCTA expected the tender for the construction of the AMD solutions in the Eastern basin to be published in April or May and hoped to start the 18-month treatment plant construction in November this year – subject to securing funding and access to land and infrastructure.