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This groundwater places destabilising pressure on the floor of the mine pit, which can only be mitigated by constant groundwater pumping.
“The best way to do this [rehabilitation] from a safe, stable and sustainable perspective is to apply [lake] water, which counteracts the pressure in the groundwater, keeps the batters stable, and covers the coal,” says Moran.
Environmentalists have warned that plans to flood the former Hazelwood coal mine to create a pit lake risk water security and possible contamination. Credit: Justin McManus
Globally, this approach has been widely used where brown coal deposits are below the water table, he says.
Engie has existing water contracts with Gippsland water it would use to fill the pit lake, as well as applying for additional surface waters, from the Morwell River. The company’s existing contracts have clauses that reduce and even limit water use in times of drought, says Moran.
“We want to tweak them so that they are representative of what we need, but also representative of climatic conditions,” he says.
Environmentalists are concerned about potential contaminants from a large coal-ash dump at one end of the pit. Engie proposes to cap this, using earth or concrete, and it would be inundated.
Internal advice recently provided to the federal Department of Climate Change, Energy, Environment and Water recently said there was a risk of creating a large pit lake with deteriorating water quality that would be unsuitable for swimming for coming decades.
If approved, the proposed pit lake would cover the former coal mine site. Credit: Justin McManus
Other risks include “serious or irreversible environmental damage” to the downstream Ramsar-listed Gippsland Lakes and insufficient flows to meet the huge volumes of water required to fill the lake, it found.
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Environmental Justice Australia lawyer Chloe Badcock had said alternatives to diverting rivers – such as using recycled and desalinated water – should be considered.
“This half-baked rehabilitation plan will drain water resources, create a filthy, toxic pit lake, and choke the water supply to the Gippsland Lakes,” she said.
Moran disagrees that water contamination poses a substantial risk, saying independent auditors would be required to ensure the site, from the mine void to ash landfills, are legally compliant.
The proposal is currently being assessed for its potential environmental impacts.
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