Danger below: Underground acid mine water levels on the Eastern basin pose a threat
The rising levels of underground acid mine water on the East Rand have breached the environmental critical level (ECL) but there are “no worries” about it discharging on the surface for the moment, according to the state-owned entity in charge of its management and control.
Last month, the Mail & Guardian reported on how all three deep-level abstraction pumps at the government’s R1-billion Eastern basin acid mine drainage (AMD) treatment plant in Springs are no longer operational.
Acid mine drainage is harmful to humans, plants and animals because it is acidic, and it carries heavy metals, atoms that emit radiation and salts in hazardous concentrations.
The environmental critical level is defined as the highest water level within the mine void where no acid mine drainage flows out of the mine workings into the surrounding groundwater or surface water systems.
The Eastern basin plant is supposed to pump between 70- and 100-million litres of the polluted water a day to maintain the environmental critical level and to protect dolomite and groundwater sources, before it is neutralised and discharged into the Vaal River system.
“The environmental critical level of the Eastern basin has been placed at 106m below ground level and the current water level is 62m below ground,” the Trans Caledon Tunnel Authority (TCTA) told the M&G.
“Due to pumps being unavailable at present, we are unable to stop the current rate of rise. However, TCTA is monitoring the footprint of the plant through the boreholes that surround it, to monitor groundwater quality on a monthly basis.”
Poisonous legacy
Acid mine drainage is the poisonous legacy of more than a century of gold mining on the Witwatersrand. During underground mining operations, water was pumped to the surface to enable mining to take place, explains Mariette Liefferink, the chief executive of the Federation for a Sustainable Environment.
“As mining stopped, the pumping of underground water ceased and the mine voids started filling with water. The sulphide minerals in the rocks were exposed to water and oxygen, which resulted in acid mine drainage forming.”
The mining voids progressively filled with acidic water. In April 2011, the then-department of water affairs instructed the TCTA to act as the agent for the design and implementation of the short-term measures to manage and control acid mine drainage in the Western, Central and Eastern basins of the Witwatersrand goldfields.
Seismic effects
The breach of the environmental critical level on the Eastern basin has implications and is “very worrying”, Liefferink said. “The concern is not only about the AMD decanting on the surface. If you read all the government reports, they show that the ECL must not be breached because then it affects surface and groundwater and it can have seismic impacts.
“Besides that, the mines won’t be able to mine because their mine workings will flood.”
The TCTA said it is in the process of receiving necessary spare parts from Germany to start repairs on the pumps, which is expected to lead to a restart of operations by June. Similar problems had been experienced on the other mining basins.
“The motors on the Eastern basin were running from 2016 until early 2021 without any failures. We did experience motor problems in the Central basin about two years ago.
“The plant operations have not experienced any more challenges since. Both pumps are currently operating at capacity. We have had failures on the Western basin, as a result, we are currently running on the second motor. The plant uses only one pump at a time. The plant still has a spare motor.”
Concerned that the plant challenges may not be isolated to the Eastern basin, the TCTA said that as a precautionary measure, it had approached the German supplier and manufacturer, Andritz, to “assist in defining the cause of the motor failures and to provide a sustainable solution to prevent further failures”.
Andritz, the TCTA said, had “indicated that a potential solution has been identified for implementation across all the basins”.
(John McCann/M&G)Delays
Andritz had confirmed that the necessary copper wire for the motor windings has been manufactured in Germany but its transportation is being delayed. “They have not supplied the date of delivery, as yet. If any further delays are experienced, TCTA fears that this may also have a negative impact on the expected deadline on repairs to the plant,” it said.
The TCTA believes the “real environmental degradation” will happen if the basin starts to decant — when the flooded system “daylights” and flows into the receiving environment. “We remain positive the plant will be recommissioned well before the risk of decant materialises.”
A raft of reports, Liefferink said, had highlighted the key concerns with the cessation of pumping and flooding of the Eastern basin, among them that “AMD extensively contaminates surface streams and could incur devastating ecological impacts”.
Rising water levels, she said, could flood urban areas and result in geotechnical impacts that may jeopardise the integrity of urban infrastructure and may lead to an increase in seismic activity, presenting serious safety risks to deep underground mining ventures and some risk to safety and property on the surface in the vicinity of the mines.
The department of mineral resources and energy said the water in the Eastern basin mine void “has a circumneutral pH and should therefore not pose a risk due to dissolution of dolomite”.
Liefferink countered this. “The reports that I have is that the AMD dissolves dolomite.”
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