A lengthy consultants’ assessment of Eraring’s plan notes trace metals in groundwater beneath the dam “have, on occasion, been recorded in concentrations in excess” of drinking water standards.
The report also notes “water appears to be flowing from the ash dam into the mine workings”, and that “artesian flow of mine water would be expected into several tributaries of Dora Creek” that feed into the lake.
An appendix to the report also identifies “major hazards”, including the potential for sinkholes to form if there are roof failures or pillar collapse in the mine. There is already one sinkhole identified in the expansion area.
Consultants SCT Operations said a second hazard was “the potential for surface water to flow from the ash dam into the mine workings and eventually into nearby tributaries of Dora Creek”.
Origin says there is no evidence heavy metals or other toxins are leaching from the ash dam itself through the mine and into the nearby lake.
“The protection of groundwater is of paramount importance to Origin,” a spokesman said, adding the company had an extensive monitoring program.
Pumping of water and other changes “have helped reduce the potential for material to migrate off site,” he said. “We will increase these activities if the expansion of the ash dam goes ahead.”
The EPA has given its conditional approval of the expansion while noting a review of the plant’s environment protection licence is now underway.
Mr Winn said the onus should be on Origin to prove the unlined ash dam was not already contaminating nearby waterways.
Brad Smith, a senior energy campaigner with the Nature Conservation Council, said the single-page EPA submission meant it “blithely rubber-stamped the expansion”.
“Origin should not make the community and future generations clean up its mess,” Dr Smith said.
Jeremy Buckingham, Greens mining spokesman, said expanding the dump over an underground mine was “a recipe for disaster”.
“This issue demonstrates some of the hidden environmental and financial costs of coal, and is yet another reason we should rapidly transition from coal to renewable energy,” Mr Buckingham said.
The expansion may need to be revisited in several years with the extra dam capacity likely to be used up by 2024.
One issue is that a 2007 planning guideline for the plant to reuse 80 per cent of the ash by 2015 has not been met.
Instead, only about 40 per cent of the ash is being recycled for cement or other uses, and that target has now been pushed back to the end of 2021.
Lake Macquarie Council said it raised “no objection” to the proposal, provided impacts to the environment, including from land clearing, were “acceptable”
The Planning Department said Origin would have to respond to the submissions.
Peter Hannam is Environment Editor at The Sydney Morning Herald. He covers broad environmental issues ranging from climate change to renewable energy for Fairfax Media.