The letter details fears dams are losing up to 25 million litres of water a day because of subsidence and diversions caused by underground mining. Contamination from exposed iron and other metals adds to the damage.
Other concerns include “valley bulging”, some of which may already be occurring at South32’s Dendrobium mine, with the result that water is being diverted around and below reservoirs and watercourses, according to the letter signed by researchers including Pete Dupen, formerly the mining manager for state agency WaterNSW.
“The solution is to modify or to curtail the [coal extraction] longwalls to the point the water loss is negligible,” he said.
Mining within 800 metres of the Cataract dam, meanwhile, shifted its wall 3 centimetres. While the shift did not result in damage, “that movement of this kind can occur gives cause for concern”, the letter said.
The extent of risks, though, remains hard to assess in part because of poor access to miners’ data. Monitoring systems themselves lack necessary scale and complexity, while failed groundwater instruments “are typically not replaced”.
“Coal mining in the Special Areas diverts and consumes water at its source, and irreversibly damages and degrades that source,” Peter Turner, a mining projects officer with the National Parks Association (NPA), said.
A Planning spokeswoman said the department was continuing to assess the proposed expansions of the Russell Vale and Dendrobium coal mines. “Once the department’s assessment is complete, both applications will be referred to the Independent Planning Commission for determination.”
A spokeswoman for one of the miners, South32, said the company was “committed to the highest environmental standards and understand the sensitivities of working within the Metropolitan Special Area”.
“Dendrobium Mine operates under a regulatory framework, which includes strict performance criteria and comprehensive monitoring and reporting requirements,” she said.
Separately, environmental groups say the government is poised to approve an extension of Dendrobium that could threaten the 25-metre high Sandy Creek waterfall in the catchment.
South32 is seeking approval to start its longwall 19 section but has not opened the process to public comment, the NPA and Lock The Gate say.
The mine is located adjacent to Lake Cordeaux and beneath an ecologically significant and endangered swamp, dubbed 15a, which feeds Sandy Creek and its waterfall.
“Based on the damage that’s occurred so far to endangered swamps due to this mine, it’s clear the only way to protect the swamp is for there to be no mining near it,” Nic Clyde, a spokesman for Lock the Gate NSW, said.
South32’s spokeswoman said the company “does not longwall mine beneath dams, named watercourses or key feature streams – including waterfalls over five metres high”.
“The public has had an opportunity to comment on the plans,” she said.
The Planning spokeswoman said the department was reviewing the extraction plan for longwall 19.
Peter Hannam writes on environment issues for The Sydney Morning Herald and The Age.