Merriespruit, 22 February 1994

Remembering the events at Merriespruit on this day, 22 February 1994 are now particularly poignant. This year, 2019, is the 25th anniversary of the disaster that struck the people of the town. And today’s anniversary comes less than a month after the tailings dam at Brumadinho in the Brazilian state of Minas Gerais burst leaving, according to the latest available information, 169 people confirmed dead and 141 still unaccounted for.

On the evening of that day in 1994, a 2.5-metre high flood poured out of the Merriespruit No 4 tailings dam carrying 600,000 cubic metres of water and tailings over a distance of 4 kilometres through the Virginia suburb of Merriespruit. The flood engulfed 80 homes, taking the lives of 17 people relaxing or sleeping in their homes. The Merriespruit mine’s tailings dam had burst after a torrential thunderstorm that dumped an unprecedented 5 centimetres of water onto the site in the short space of half an hour. The downpour led to the dam’s wall being breached, releasing the flood of water and tailings onto an unsuspecting and peaceful suburbs.

At that time, residue dams, including that of Merriespruit, were built with conventional technology using the “semi-dry paddock” system. It is a system whereby a “daywall” perimeter is constructed and allowed to settle and to dry under supervision before slurry is deposited, normally at night into the so-called “nightpan”. Then as, now, a penstock is normally located near the centre of the dam to drain water away from the slurry as well as from natural rainfall. And this is how the Merriespruit No 4 dam had been designed in the 1970s. Houses in the Virginia suburb of Merriespruit had already been built and the community established long before any work had started to establish the dam.

The official investigation showed that No 4 dam was in an unacceptable state before its wall’s collapse. Despite legislative safety requirements at the time, the dam did not have sufficient and mandated freeboard to cope with a once-in-a-hundred-years storm. And it had been known for some years that the dam wall was sloughing, though nothing was done to rectify the situation. This was the finding of the official inquest and investigation into the catastrophe – mine management and the contractors managing the dam were found to be directly responsible for the collapse, largely because cost-cutting had reduced the number of skilled people responsible for the dam’s maintenance and because skilled people had been replaced by people with far-less experience and knowledge.

The Merriespruit disaster led to changes in the laws governing safety with a new Code of Practice for Mine Residue Deposits. This in itself derived from work by the CSIR that gave rise in 1995 to the Draft Code of Practice for the Design, Operation and Closure of Tailings Dams. Today all active dams are fitted with ring mains that carry excess water to a return-water dam that can manage sudden or excessive water flows from penstocks. Mandatory freeboard heights have been increased to ensure that perimeter walls cannot be overwhelmed and maintenance of dams cannot be delegated to individuals with inadequate experience.

In addition, new regulations were promulgated concerning the proximity of housing to tailings dams. Today, house building is only allowed if it is located at least a kilometre from a tailings dam. And it is certainly not allowed downslope of a dam. These developments are all part of the mining industry’s steady progress towards ever-safer mine operations.

The International Council on Mining and Metal (ICMM) comprising 27 of the world’s leading mining companies and more than 30 national associations, including the Minerals Council South Africa, is playing its part in this area too. Following the catastrophic tailings dam failures at Mount Polley (Canada) in 2014 and Samarco (Brazil) in 2015, the ICMM undertook a review on tailings storage facility management in 2016. The review found that a greater focus on governance is needed to assure that the extensive existing technical and management guidance is effectively applied.

The outcome was a tailings storage facility (TSF) governance framework which enhances focus on those key elements of management and governance necessary to maintain integrity of TSFs and minimise the risk of catastrophic failures.  The six key elements of this TSF governance framework are:

  • Accountability, Responsibility and Competency
  • Planning and Resourcing
  • Risk Management
  • Change Management
  • Emergency Preparedness and Response
  • Review and Assurance

For its part, following the Brumadinho disaster, the Minerals Council board resolved that all Minerals Council members should review their tailing storage facilities’ construction, maintenance and operating protocols in order to ensure the stability and safety of these facilities and the surrounding communities.

As the mining industry recalls and mourns the lives of those men, women and children whose lives were cut short on that evening of 1994, we recommit ourselves to ensuring that mining is safe for our country’s mineworkers and for their families.