JSE-listed Group Five has started the construction of high-density treatment works, pumpstations 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 expected to pour first concrete before the end of February.

The project is in line with the TCTA’s mandate from 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 has 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 tells Engineering News.

The current level of AMD is said to be 256 m and it is expected to breach the environmentally critical level (ECL) by September or October if pumping operations do not start.

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

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

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

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 volumes of AMD that need to be treated in the Western, Central and Eastern basins are 27 Mℓ/d, 57 Mℓ/d and 82 Mℓ/d respectively.

The ECL for the Western basin has already been breached, having reached 0.88 m below collar level.

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

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

The TCTA has 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 is expected to be completed by September. Two pumps, at a cost of R60-million, were ordered and are due to be delivered in November.

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

The water quality in the Tweelopiesspruit has also improved.

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

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

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

The Eastern basin’s AMD levels have been recorded at 423 m, with an ECL of 290 m. It is expected that AMD will breach the ECL by November 2014.

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