Mine plans need to be best practice to take risk out of final voids

UNSW representatives at Mine Rehabilitation Conference

Where once discussions about mine rehabilitation were concentrated on just that, repairing the land as open cut mines progressed, now the talk has turned to what do we do once mining has ceased.

The coal industry downturn is providing new opportunities for those with an interest both in research and practical applications for restoring and developing the land post-mining. 

One such researcher is Wendy Timms who is based at the University of NSW, Australian Centre for Sustainable Mining Practices (ACSMP), School of Mining Engineering.

Raised in the Hunter Valley Dr Timms is a geologist and water engineer who has worked in Australian and Canada on issues relating to water and waste in mining and agriculture. She was one of the guest speakers at the recent Mining Rehab Conference held in Singleton as part of the Coal Festival.

 Warkworth Mine near Bulga

Now in its sixth year the event organised by the University of Newcastle’s Tom Farrell Institute attracted more than 260 people – a record for the conference. One topic creating more interest than others these days is what to do with the final void –quiet literally the hole in the ground left once open cut mining ceases. The voids can range in size from a couple of hundred hectares to nearly 1000 hectares in the case of the one expected to be left once mining ceases at Rio Tinto’s Warkworth mine near Bulga.

Dr Timms said a recent pilot study looking at the Hunter Valley’s open cut mines revealed the estimate of land covered by the region’s 30 final voids would be 3,840ha or 0.18 per cent of the region’s total land area. And although that may not sound too troublesome Dr Timms said it was always best to minimise the size of the void to reduce potential problems.

She said their research showed well designed mine plans could lead to smaller and less risky voids. “With modern mining practices the backfilling and rehabilitation of the sites is the number one aim and it progresses as the mine develops,” she said.

“But we can improve on those outcomes by using the latest engineering and computer modelling when it comes to planning the mine.

“We used six generic plans on our pilot study and found the voids could be improved by better design. That meant having voids that were either shallower and dryer or deeper and wetter for water storage and wetlands – depending on the particular location of the mine.

“Its all about getting the planning right before the mine is developed.”

Dr Timms said there were great examples of voids being used in Europe and Western Australia. She suggested they could be adapted for water storage even flood mitigation in the Hunter Valley or for wetlands and carbon sequestration.“There are plenty of good news stories from rehabilitation of final voids,” she said.

Dr Wendy Timms

But she also warned there were risks due to poor designs that result in overflows and issues with water quality. Her major concern is to ensure proper planning takes place in particular an understanding of the surface area relative to depth. Get that wrong and Dr Timms said there maybe serious risks. “We must design better landform outcomes including the slope of the highwall,” she said.

Dr Timms was optimistic that with further research and better designs the risks associated with voids can be minimised and the development of their economic uses were attainable. 

This article was first published in the Singleton Argus.

Related article 'Future scenarios for mine voids from open cut mining in the Hunter Valley' was published on the Australian Centre for Sustainable Mine Practices site in January.