Leaving a final void once open cut mining ceases should not be considered best practice.
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That is the opinion of academic Phillip Geary, who has been bothered by the practice for many years and is now calling on governments to change the rules that allow finals voids to be approved.
The Associate Professor, Environmental Science at the University of Newcastle said the idea final voids became best practice probably developed 40 years ago.
“But now we can and must do better. It is no longer acceptable to think leaving a final void is best practice, “ he said.
Prof. Geary said back in the 1970s when the first voids were being approved the depth and surface area was smaller but today’s voids had depths of 300 metres and covered more than 1000 hectares.
Commenting on suggestions the voids could be utilised for such things as theme parks or aquaculture Prof Geary said such ideas were ridiculous.
“Other than putting a fence around them there is nothing they can be used for in the Hunter,” he said.
“They are big unsafe toxic water holes that affect the surrounding hydrology. Water in the voids is contaminated by the low ph levels.”
Of particular concern given the size of the voids now being approved is their impact of groundwater.
According to Prof. Geary the void has the ability to ‘suck in’ water from surrounding areas. Near a watercourse this could prove very problematic.
Prof Geary said the voids should be backfilled and that backfilling should become the new best practice for post-mining.
“When mining companies prepare their cost benefit analysis on new mining projects it must include the cost of backfilling, “ he said.
“That way the community knows the true cost of developing and operating an open cut mine.”
If this doesn’t happen the Professor considered the legacy of these voids will become the community’s responsibility and already the state has 500 disused mine sites that need remediation.
The NSW government allocated $4.276million for rehabilitation of derelict mines in 2013-14 and that fell to just over $4m in 2014-15, he said.
But the mining sector generated $1.5billion in income for the government in 2013-14, he said.
Prof.Geary is concerned the powerful lobbying by the minerals industry is preventing the government from instituting the requirement for backfilling.
“They might argue it’s too costly but leaving a void is too costly for any community, “ he said.
“Anyway mining companies can afford to develop the mine and factor in no income during that development period so now they should factor in the cost of backfilling post-mining.”
