Acid mine drainage

The Trans-Caledon Tunnel Authority (TCTA) says that its acid mine drainage (AMD) water treatment plant in the Western Basin couldn’t be re-opened as planned on 4 June 2019 due to an escalating security threat in the Mintails Gold Treatment plant area.

The AMD Western Basin has been out of commission since 24 May 2019 due to cable theft and general vandalism caused by illegal miners in the neighbouring Mintails Gold Treatment plant area.

The theft and vandalism led to a power failure at the pump station on 9 Shaft, leading to the shutdown.

The situation arose when illegal miners took possession of the Mintails mining site, adjacent to 9 Shaft which houses the AMD pump station. The Mintails site was previously secured, however, when it was placed under business rescue the appointed liquidators withdrew the security services, paving the way for illegal miners to step in.  

The Eskom substation which supplies power to the pump station is located on the Mintails site.

TCTA reported through a local newspaper on Saturday 1 June 2019, that it expected to have the plant re-opened by 04 June 2019. TCTA, in collaboration with Sibanye-Stillwater, at the time had been in the process of rerouting the cable line through an overhead power line, meant to make the cables inaccessible to cable thieves and as a means to speed up the repair process.

However, as of Monday 3 June 2019, the solution had to be abandoned due to the deteriorating safety situation in the neighbouring area.

Contractors working on the line could not complete the work as a result of the rapid and drastic escalation of crime activity in the area. Most of the connection points at the Eskom substation had also been vandalised during this period, further placing doubt on the sustainability of the proposed solution.

“The area has become extremely dangerous for contractors and security personnel, with armed and dangerous illegal miners (zama-zamas) running unhindered in the area and out-numbering the security personnel on the ground. The place is like a warzone”, says TCTA Executive Manager: Project Management and Implementation Johann Claassens,

A possible solution in sight

A new proposed plan is to draw electricity from an identified substation that is 3.7 km from the pump station.

“It is expected that this solution will take approximately three to four weeks to be fully implemented, due to the distance and the virgin territory that must be prepared for the purposes of the new power line,” says Claassens.

TCTA and Sibanye-Stillwater management had also looked at the possibility of installing a generator in order to reduce downtime, however, due to the power needs of the AMD plant and pump station this was considered unviable in the short to medium-term as the size of the generator required is not readily available and would be costly.  

Environmental threat

The water table is currently at approximately 8 600 mm below surface, rising at an average of 100 mm/day. It is expected that by the time of operation the water level will have risen by about 2 100 mm putting it at approximately 5 860 mm below surface. This would still be within the safe margins.

However, with the water table rising there is a risk of limited seepage of acid mine water into the wetland area downstream of the abstraction point due to the pumps located in the wetland also being impacted by the power outage.

Of the three basins managed by the TCTA (AMD Eastern, AMD Central and AMD Western Basins) the Western Basin remains the most vulnerable due to the closing of the Mintails mines and the growing security threat posed by the illegal gold mining activities in the area.

TCTA says that it is working closely with Sibanye-Stillwater and Eskom to speed up the process of restoring power to the AMD Western Basin plant.

“We continue to strictly monitor the water levels during this period and will implement all possible measures necessary to prevent decant of AMD into the environment,” Claassens concludes.