14 Oct 2019

Research findings on Selebi Phikwe tremors have revealed that there is a good correlation between the recorded seismicity and the rise in underground water level at the closed BCL Mine.

The three-month research was undertaken by Botswana Geo Science Institute (BGI) and two consultants; Aqualogic and OHMS,  which kick-started end of June to establish the source of the vibrations, the frequency and the magnitude of the vibrations.

“We have a high level of confidence that the events are coming from the South Eastern section of the closed BCL Mine beyond the depth of 980m level below surface,” says one of the consultants and also the director and consulting mine seismologist at OHMS Mr Vlok Visser.

Mr Visser informed the Stakeholder meeting in Selebi Phikwe on Wednesday that the data recorded suggests that seismic events with magnitudes between -3.2 and 2.0 were recorded between June 28 and September 24.

To determine the likelihood of the recorded seismic activity to have caused structural damage in the town of Selebi Phikwe, he said the data showed that no individual event could have caused structural damage.

However, he said since the data was only recorded over a period of three months, the possibility of historic or future structural damage could not be excluded as a potential hazard.

The study recommended that a professional opinion of a structural engineer should be obtained, with experience in ground vibrations analysis to assist in quantifying the potential of the seismic events to cause structural damage to buildings in Selebi Phikwe.

Since seismicity has been identified as a potential hazard, the study also recommended that the risk associated with it should be managed.

This could be done through continuous monitoring of the hazard and periodic analysis of the seismic data.

The research also revealed that most tremors occurred between June and July from midnight up to 5am with a substantial reduction of tremors recorded from August to September.

“We associate this reduction of tremors to the pumping out of ground water at the BCL Mine,” added Botswana Geoscience Institute manager of Applied Geoscience Mr Koketso Botepe.

Pumping of ground water at BCL Mine was stopped around October last year and resumed end of July this year when the water head reached the 1000m mark.

Mr Botepe said the liquidator at the time decried that pumping out water was costly, hence it  flooded the South East shaft against Department of Mines’ warnings.

He said the water was left to reach 1000m mark so that pumping could begin.

Mr Botepe also informed stakeholders that  government had given out P3.5 million for BGI to carry on with monitoring.

He said BGI would install infrastructure to enable his team to do extensive monitoring and in addition he was going to ensure that stations were spread out optimally.

For his part, the chairperson of Safe Phikwe committee Mr Arone Sefho expressed dissatisfaction with the report.

He said BCL Mine had been there for a long time, but Selebi Phikwe residents never experienced any tremors.

He said the number of tremors recorded in the final draft report was lower than the number of tremors recorded during the study.

Another member of Safe Selebi Phikwe committee Mr Steven Tawanana accused the government of taking the residents of Selebi Phikwe for granted, adding that the government took a long time to address the problem.

He said flooding the mine was done against regulations and advice from Department of Mines, therefore BCL Mine should be held accountable for the damage caused by the tremors.

The district commissioner for Central District Mr Rapetse Mathumo reiterated that the government had the interest of the nation at heart, hence it sent a team of experts to carry out intensive investigations on the tremors experienced in Selebi Phikwe.

He said it was important for the study to be undertaken to enable the government to make informed decisions, adding that the government could not make decisions based on assumptions.

Mr Mathumo further informed the meeting that  government  had a problem with the former liquidator and acted swiftly by replacing him with another liquidator. ENDS