Once Australia’s pit mines are out of commission, what will be done with the massive voids left behind?
We’re here to see the Hazelwood mine, but it’s the looming presence of the Yallourn power station in the distant west that serves as a constant reminder of the scale of mine pit rehabilitation needed in the LaTrobe valley in the coming years.
This single site is enormous, but the dilemma facing Australia is this same problem is affecting nearly all states.
The Hazelwood mine rehabilitation project has been described as an “experiment”, as federal and Victorian state regulators play catchup with the enormity of both the job and community expectations, but it’s following a well trodden path.
Boating is good, deaths are bad
The Berkeley Pit in Butte, Montana, is the cautionary tale everyone wants to avoid.
The 1.6km-by-800m copper mine closed in 1982 and gradually filled with water irreversibly contaminated with sulphuric acid, copper, arsenic, cadmium and zinc from the surrounding rock.
In 2016, some 3000 migrating snow geese were killed when they landed on the toxic brew. The US Environmental Protection Agency (EPA) must pump out and treat the water – forever.
The good news story is in the East German Lusatia region. When the Berlin Wall fell and Germany reunited, all Lusatian brown lignite coal mines closed leaving a scarred moonscape and a toxic legacy.
In 1994, the new German government launched a decades-long plan to clean up the area, creating 140 artificial lakes that flush contaminated water out of the area. Today, 24 are open for swimming and fishing. This path has not been without challenges: in 2013 the Spree River turned rust-orange after heavy rains flushed iron hydroxide from old mines.
Closer to home, the Stockton and Kepwari pit lakes in the Western Australia Collie river valley are open to recreational use. But the 13 Collie pit lakes also have their failures: the Black Diamond lake has seen two drowning deaths and several serious injuries.
“All the closed mines will pose a danger, there is always risk,” Mine Lakes Consulting director Dr Cherie McCullough told Cosmos Weekly.
“But what we can do is evaluate that risk and make a considered decision about whether or not that risk is acceptable.”
McCullough, an internationally known pit lakes expert, says water quality is the biggest factor in determining whether a lake is a success or not. The safety of the site itself – steep sided voids can create drowning risks and ground instability – and its usefulness to the local community are also critical.
She says a dry pit void brings geotechnical issues: in the case of the LaTrobe Valley, three separate mines dip below the water table. Groundwater pushes on the sides, destabilising the walls and risking landslides that would undermine roads and towns, requiring round-the-clock pumping to keep them dry.
Many regs to rule them all
McCullough says mining states Western Australia, Queensland and the Northern Territory have world class rules, and the federal government issued new guidelines in 2016. But New South Wales (NSW) and Victoria are playing catch-up with both funding for watchdogs and the very rules that guide closures.
Five years after the devastating 45-day fire at Hazelwood in 2014, the Victorian government birthed the more muscular Mineral Resources (Sustainable Development) Amendment Act, adding to it in 2022 to manage the rehabilitation risks of mining sites. NSW changed its Mining Act in 2021 to make it clear rehabilitation is not to be left to the last minute.
Victoria and NSW are running hard as a swathe of coal mine closures are coming.
Consultancy EY and community land protection group Lock The Gate say 17 mines will close in NSW’s Hunter Valley in the next two decades. There are at least 45 voids pot-holing the state today.
In Victoria’s LaTrobe Valley, Hazelwood is the first.
Neighbouring Yallourn is set to close in 2028; owner Energy Australia is also planning a pit lake for its comparably shallow void of less than 90m. The Loy Yang mine, enormously deep at 200m deep and 2km wide, may close when AGL shuts the power plant in 2035 but co-owner of the mine, Alinta, hasn’t committed to that date; they are also proposing a pit lake.
Unlike in the US, where backfilling is mandatory for mine pits (a policy that also often results in abandonments due to the cost), there are no requirements in Australia to take this more expensive route.
In NSW, this may not be a bad thing: just two years ago Australia Institute researchers discovered that filling all of NSW’s coal voids would cost $12-25 billion, yet the government only held $3.3 billion in environmental bonds.
Late last year, the Victorian government demanded the owners of the three LaTrobe Valley coal mines kick 100% of the expected rehabilitation costs into its bond fund.
Devil in the detail
Hazelwood is not the first coal mine in Australia to be rehabilitated nor, at 130m, is it the deepest. But with a void spanning 1,281 ha across, it may be the vastest attempt globally.
The owner, Engie, wants to cap the toxic fly ash dump at the north end of the void with a combination of clay and geomembrane liner, and flood the hole with more water than is in Sydney Harbour: 638 gigalitres (GL) of groundwater, surface water, and “other” water sources. It inherited this plan from the government when, as GDF Suez, it bought the power plant in 1997.
Community campaigning nudged the Victoria government to require an Environmental Effects Statement (EES) in 2022. It’s a comprehensive assessment process that will take between two and four years, according to Engie EES lead Adam Moran. In April, the federal government also said it would take a look at the effect of using so much water on local wetlands, threatened species and the community.
Community organisers like Hayley Sestokas from Environment Victoria say these are necessary to extract the information the Morwell community needs to be assured the site is safe.
“From the start, the LaTrobe Valley was told we’d get Lake Como. But people aren’t going to be able to swim in that [due to the potential for water contamination from the ash dump],” she told Cosmos Weekly.
“We’re not in opposition to the pit lake, but we have serious concerns. We want to know what the other options are and we want to investigate what’s going to happen to the ash in there, and we want to investigate other water sources.”
Sestokas is talking about the other options noted in the final report of the inquiry into the 2014 mine fire, which looked at five possibilities. The pit lake option being pursued by Engie was found to have “critical” and “high” risks of collapse and water contamination, and partially backfilling the void was rated more highly, but both met the basic criteria.
But the report queried where the water would come from in the climate-stressed Gippsland Catchment – particularly given Yallourn and Loy Yang are also pencilled in to become pit lakes.
Engie environmental expert David McGavin, who has worked on mine rehabilitation projects in Queensland, says to remove the 1 million cubic metres, or 143,000 truckloads, of ash they’d need a new landfill somewhere in a state already nervous about contaminated soil.
“The nature of our landfill is we’re licensed. The specific wording of that licence says you cannot remove it because of the environmental risks,” he told Cosmos Weekly.
“The sheer scale of this just increases the complexity.”
What happens now will depend on what emerges from the EES.
Moran says filling the void entirely would require 2.5 billion cubic metres of solid material – effectively another mine. He called backfilling an “extreme solution” because of the sheer volume of material needed.
These enormous new landforms will be in place for hundreds, perhaps thousands of years and are therefore unlike anything our species has done from an engineering perspective before.
The challenge is ensuring the generations who come after the resource extractors, are left with a legacy they can live with.
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Originally published by Cosmos as The dilemma of rehabilitating Australia’s mine pits
Rachel Williamson is a business and science journalist based in Melbourne.