A mining expert has told the Queensland floods inquiry that many thousands of mines continue to pose significant threats to public safety and the environment.
But a mining expert has told the Queensland Floods Commission of Inquiry many thousands of abandoned and operating mines continue to pose significant threats to public safety and the environment.
Queensland's summer of natural disasters cost the state $7 billion in coal production last financial year.
Queensland Resources Council chief executive Michael Roche told AAP that export figures for the September quarter were down 16 per cent from what they were in the months before 70 per cent of the state flooded last summer, killing 35 people.
He said there was currently a 'Sydney Harbour's worth of water spread across the 50-odd coalmines' and that production was still impaired.
Coalmines in Queensland typically seek to prevent tailings and storage dams overflowing by discharging water from those dams into flowing streams for dilution.
But in the lead-up to the last storm season, streams were not flowing, preventing mines from being able to reduce dam levels.
The Department of Environment and Resource Management (DERM) regulates the volume and timing of the releases, as well as the allowable salinity.
Mr Roche said release conditions had been revised in the lead-up to another potentially troublesome storm season to give mines more flexibility to discharge water in scenarios where there was no risk of enhanced environmental harm'.
'It will enable mines to better handle what's thrown at them in the upcoming wet season,' he said.
'But the changes weren't so generous as to really help mines make big inroads into the legacy of water that was built up over the last two wet seasons.'
Many environmental experts opposed to the use of natural streams say the controlled discharge of unwanted water from tailings dams is the cheapest disposal method but bad for the environment.
They argue there are plenty of other more environmentally friendly options available to mining companies.
'Some mines are trialling various water treatment technologies, and they are very expensive ... the mines report that there is no silver bullet,' Mr Roche said.
University of New South Wales (UNSW) consultant mining engineer David Lawrence outlined some of those methods for the inquiry on Monday.
The impact of flooded mines on public health and safety and the environment varied 'depending on the type of mine and any associated mineral processing or ancillary activity', he said in a statement tendered to the inquiry.
He said floods in 2008 and last summer caused significant sediment issues.
'There were challenges in emptying flooded pits due to the elevated salt and solids content,' he said.
'The impact on downstream aquatic life including fish populations would be expected to be potentially severe,' he said, adding that people were also at risk of drowning in abandoned mine shafts.
Mr Lawrence outlined several interstate cases in which the clean-up from a serious leak had cost several million dollars.
Mr Roche, whose organisation also made a submission to the inquiry, said coal was an inert resource that did not, in itself, pose a significant threat to the environment.
The relaxed conditions do not relate to metalliferous mines.
The commission, which entered its final week of hearings on Monday, made 175 recommendations in its interim report in August and will deliver its final findings in February.
