The treatment site of the Central Basin Acid Mine Drainage (AMD) plant has been significantly affected by the recent increased rainfall in Gauteng, the Trans-Caledon Tunnel Authority (TCTA) said on Monday.

TCTA, on behalf of the Department of Water and Sanitation (DWS), operates and maintains three AMD plants within three basins, namely Central basin in Germiston, Eastern basin in Springs and Western basin in Randfontein.

The Central Basin AMD Plant, designed for a water treatment capacity of 84 Mℓ/d, with a current treatment average operating capacity of 60 Mℓ/d, including planned outages and shutdowns calculated over a year, has not been operating at full capacity owing to challenges with the AMD pumps that abstract water from the mine void and the scaling on the discharge line to the Elsbergspruit.

“The plant has been operating without any major interruptions for the past year, averaging 60 Mℓ/d, 18% below the operating capacity, and the shaft level was maintained well below the decant point,” says TCTA project management and implementation executive manager Johannes Mavuso.

The excessive rain experienced during the current rainy season has caused a spike in the water level in the Central basin and, as a result, the possibility of a decant remains high at or around the South-East Vertical Shaft, west of Farrar Park, in Boksburg.

“Though indications are that the current situation could lead to a possible decant of AMD, there is no imminent danger at this stage, and the public will be kept informed of any major developments,” he assures.

To mitigate the risk of decanting on the plant, TCTA in partnership with mining group DRDGold, has implemented an interim measure, which will increase the capacity of the discharge pipeline to enable the AMD plant to operate at a peak capacity of about 72 Mℓ/d.

In addition to this, there has also been an increase in the current pumping and treatment capacity from 60 Mℓ/d to about 68 Mℓ/d, effective from late January 2023. The impact of this measure against the rise of water levels is being monitored daily.

“TCTA has been experiencing technical challenges with the AMD pumps and the sludge discharge pipeline, thus preventing the AMD Plant from operating at the desired capacity,” he continues.

However, permanent solutions are being implemented to get the Central Basin AMD Plant to operate at the desired capacity, including the construction of the sludge discharge pipeline, which has started and is planned for completion in June 2023.

Further, the temporary pump will be replaced with a larger rebuilt pump to increase the AMD total pumping capacity to 82 Mℓ/d, with completion expected in March 2023.

While the pumps will be able to pump 84 Mℓ/d, the full capacity of the plant will only be achieved once the discharge pipeline has been completed.

“The implementation of the interim and permanent solutions will enable the AMD Plant to pump and treat at the peak operating capacity of 82 Mℓ/d by end of March 2023 and we hope that the level of rainfall will ease up to give the plant an opportunity to stabilise the pumping levels,” Mavuso concludes.