A PROPOSAL to convert Hunter coal mine voids into lakes to "drought-proof" regional NSW areas has received cautious support as a private company seeks NSW Government funding to test its feasibility.
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Hunter Valley Lakes Corporation has briefed government ministers about a plan to have an artificial lake system stretching 60 kilometres from Muswellbrook to Broke, which it said would "provide water security, jobs, irrigation and drought-proofing".
The corporation points to a model in the Lusatian Lake District in the former East Germany where brown coal pits that were closed in the 1990s have been converted to a series of more than 20 recreational lakes, tourist attractions, cycle paths and water sports.
The Lusatian area was redeveloped when the united German government established a government-owned corporation to steer the project, and invested billions of euros.
Hunter Valley Lakes Corporation director Greg Story said the proposal had the potential to be "the modern day Snowy River hydro scheme underpinning economic, social and environmental progress for northern NSW".
The company is reported to be in negotiations with mining companies over three voids in Hunter sites where mining has ceased, or approvals end in the next few years.
Some of the Hunter's largest open cut mine sites such as Mt Arthur at Muswellbrook and Mount Thorley Warkworth at Singleton have approvals to mine for nearly two decades.
The NSW Minerals Council supported turning Hunter mine voids into lakes in 2016 after environmental groups turned their focus to the legacy of Hunter open cut mining, and more than 40 voids that will be left when coal mining ceases.
The lakes proposal was floated when environmental groups criticised the NSW Government for failing to require multinational mining companies to backfill voids, as occurs in America.
Muswellbrook mayor Martin Rush said his council believed that leaving voids was no longer best practice mining in NSW.
Companies seeking to expand or intensify mines should be required to back-fill voids with appropriate soil strata and micro-relief and return the landscape, as near as possible, to its original condition.
But he gave cautious support to using legacy voids for water storage, which would have to be explored on a case by case basis.
Muswellbrook Council, Idemitsu and AGL are currently working to re-purpose a Muswellbrook Coal legacy void as the lower reservoir of a 250MW pumped hydro energy system to provide renewable energy storage to every home in the Hunter.
Mr Rush said a major issue facing a Hunter artificial lakes proposal, that was not an issue for the German lakes system, is that annual evaporation exceeds rainfall.
"The only source of water for storage, therefore, is saline ground water or flood water inflow," he explained.
"Some of the voids, however, are at sufficient depth and proximity to the Hunter River to store flood water during increasingly intense flood events to return the water to the environment or agriculture during increasingly intense droughts."
The permeable nature of Hunter coal mine voids would require considerable work to prepare voids to store water, he said.
Mr Rush said the former Drayton coal mine voids are the only substantial voids that could be re-purposed within the next five years which sit relatively high in the landscape and away from the Hunter River.
While the Drayton voids could be considered as artificial lakes "it is more likely that these legacy voids will be re-purposed for ash disposal or left permanently on the landscape with a light vegetation cover".
In 2016 a Hunter Communities Network-commissioned report, The Hole Truth: The mess coal companies plan to leave in NSW, said some Hunter coal mines had pits extending at least 150 metres below the natural water table and already draw down local groundwater to form lakes.
But water quality in the final void lakes becomes increasingly saline, with one study estimating that one large void in the Hunter may contain 1 million tonnes of salt after 500 years.
The report's author, Energy and Resource Insights principal researcher, Adam Walters, said filling Hunter voids with water was not the answer. Water was far more plentiful in Germany than the Hunter, and Hunter mine voids had been designed to be "terminal sinks", where evaporation rates exceed rainfall and groundwater inputs, he said.
"It would certainly be possible to somewhat speed up the filling of the voids with water, and possibly, some lakes could be made. But creating lakes that can be used for recreation or aquaculture requires high water quality," Mr Walters said.
Monash University head of environmental engineering, Dr Gavin Mudd, said many unknowns remained about the long-term fate and behaviour of mine voids, despite industry and government assurances.
Dr Mudd said Mr Walters' report identified the serious gaps in scientific knowledge and the lack of regional studies integrating current and former mines.
Lock the Gate Alliance spokesperson Georgina Woods said she was pleased to see someone talking about the future landscape of the Hunter after coal mining, but "this idea seems a little half-baked".
"The government has given almost no thought to what this region will look like in 20 years. It has approved excessive coal production and given mining companies permission to leave this productive and beautiful region pockmarked with pit lakes that will be highly saline and possibly laced with heavy metals," Ms Woods said.
"Ideas like this, coming out of the blue from Sydney, really highlight the dearth of planning for this region's future.
"Why hasn't the regional water strategy been finalised? Where is our region-wide synoptic plan for post-mining land use? Where is the industry plan for new job opportunities when coal mining winds down?"
The German Government-owned company rehabilitating Lusatia's empty mine pits is required to treat and clean water polluted by mining, in a project ultimately estimated to cost $10 billion.
NSW Minerals Council chief executive Stephen Galilee said the Upper Hunter Mining Dialogue was looking at a range of mine closure opportunities, "including specifically examining the experience of Germany, where the lakes district has been developed".
