Modern Mining July 2022

of flooding

Unfortunately, the TCTA has also announced that the pump motors at the Western and Central Basins are experiencing similar problems to those of the Eastern Basin. Impact of pump failure on the Eastern Basin “Initially it was found that if the situation were not addressed, AMD would continue to decant from the Western Basin and could also, in time, cause the water in the Central and Eastern Basins to rise until it discharged on-surface,” explains Liefferink. The water control level for the Eastern Basin was established at 1 280 m Above Mean Sea Level (AMSL) to allow for the protection of the dolomites and the dolomite aquifers (AMD dissolves dolomites) and 1 470 m ABSL to protect groundwater sources. “It was recommended that pumping commence

delayed in getting to the country. Further to this, supply chain challenges also delayed the delivery of spare parts that would have enabled the recom missioning of the two pump sets, one in February and the other in March 2022. This meant that the planned re-commission dates were postponed to end March 2022 and end May 2022 respectively. “The first batch of spares arrived in February 2022 and repair to one of the pumps commenced. Unfortunately, a further setback occurred when, dur ing the pump testing stage, it emerged that the motor windings had failed, which necessitated a complete rewiring of the motor. Given that the copper wiring could only be delivered at end of April 2022, this again led to a postponement of the commissioning of the two pump-sets to June 2022, which meant that plant operations were suspended until June 2022,” explains Liefferink. “The breakdown of all three motors pumping acid mine water within the Eastern Basin will, if not contained soon, have serious negative impacts on the community of Nigel on the East Rand and mining operations in the area, and will pose a severe envi ronmental risk to the major river systems,” she says. According to the TCTA, which was appointed by the DWS to operate the AMD Treatment Plants, the environmental critical level of the Eastern basin was placed at 106 m below ground level. The current water level stands at 62 m below ground. The good news is that the water level in the Eastern Basin has not yet reached the danger zone of 25 m below ground level. Based on the current rate of rise and if current conditions prevail, it is estimated that this level will be reached in December 2022.

Above: The DWS constructed three plants to treat the mine water to a level that was suitable for discharge into the environment. Left: Acid mine drainage poses numerous negative environmental impacts.

Gold mining has taken place on the Witwatersrand for more than 120 years.

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