The owner of the former Hazelwood coal mine in Victoria's Latrobe Valley expects to spend about $1 billion filling it with water, but a conservation group says it has serious concerns about the plan.
The Hazelwood mine and adjacent power station ceased operating in 2017 and its owner — French energy giant Engie — wants to rehabilitate the site by turning the mine into a lake.
If approved, the lake would contain 725 gigalitres of water — more than Sydney Harbour.
The project is being reviewed by the Victorian and federal governments, with the state government ordering Engie to produce an environmental effects statement (EES).
Environmental groups fear there will not be enough water available in local waterways to fill the mine over the coming decades.
They are also worried about the potential for contamination of local waterways if the proposal goes ahead.
Of particular concern is the site's ash landfill, which stores the toxic by-products of coal-fired power generation.
Engie environmental expert David McGavin said the company was working through its plan to prevent ash from the landfill leaching into the mine.
"Subject to the outcomes of the EES … what we need to do here is make something that's non-polluting," Mr McGavin said.
"So if there are any options that we're looking at, that are going to create pollution, whether that be of surface water, groundwater, then we simply can't do it."
He said a variety of methods could be used to cap the landfill, including using clay.
If the mine is filled with water, the landfill will sit below the waterline.
The Victorian planning minister is expected to review the ESS after public hearings next year.
Water concerns
Engie believes it can fill the mine using commercially available water and its existing entitlements from the Latrobe River system.
There is currently 98 gigalitres of water in the mine, which sits above two aquifers that naturally fill it.
But Environmental Justice Australia lawyer Chloe Badcock said the plan was a short-term solution with detrimental consequences for the environment, as it would drain water resources and pollute nearby water systems.
"We've heard an expert say what the life span of this project and of the pit lake will look like," she said.
"What they're saying is the life span is so short-term, that it will be so contaminated in 50 years that humans won't be able to come near it."
Meteorologists are predicting extreme heat and dry conditions this year and beyond, as three years of wet weather — a result of the most recent La Niña weather pattern — come to an end.
Ms Badcock said her organisation was concerned the proposed lake would put more stress on nearby water systems, at a time when water shortages were projected for the next few years.
"Future protections on water availability indicate there will be insufficient water available to meet minimal environmental demands, even if the project wasn't going ahead, as well as insufficient water available to meet the volumes required to fill the mine void," she said.
Ms Badcock said the scoping requirements released by the state government for the environmental effects statement revealed there were safer and more viable alternatives that needed to be considered by Engie.
"All we're asking is for a better rehabilitation option that protects the community and our river systems and safer alternatives to diverting the Morwell River," she said.
"[The could include] the use of recycled or desalinated water, or considering other rehabilitation options as well."
