A REPORT by the Office of Environment and Heritage has raised fears about the environmental risks linked to a major Illawarra coal company's underground expansion plans.
The NSW government is considering Gujarat NRE Coking Coal's bid to modify its "preliminary works" project at Russell Vale so it can start work on a new longwall and key underground access roads.
Seven swamps exist directly above or close to the planned mining area and the surface is covered by largely undisturbed bushland.
The project falls within Sydney's drinking water catchment, and Cataract Creek, which flows into Cataract Reservoir, is also nearby.
An environmental assessment prepared for Gujarat said the impacts were likely to be "minimal" due to the nature of the works, mitigation measures and long-term land uses in the area, including mining.
But the Office of Environment and Heritage (OEH) submission identified "significant concerns" about the adequacy of the assessment and "likely high impacts" on ecological communities, threatened species and groundwater aquifers.
This could lead to "potential loss of water to nearby Cataract Creek", it said.
In particular, it raised concerns about subsidence, the impact on streams and swamps and the potential flow-on effect to habitats for threatened species including several ground-dwelling frogs.
"Virtually no baseline monitoring data has been provided ... and for some sites there is not even 12 months worth of data by which to assess impact," it said.
"Given the lack of baseline monitoring and inadequate details on type and adequacy of this monitoring or clear and effective management feedback loops ... OEH is of the view that the proposed mining in its current format adopts a 'trial and error' approach to mining impact management."
Gujarat's mining operations at Russell Vale are governed by a complex series of approvals.
OEH criticised the incremental approvals as a "piecemeal approach" that did not consider the full cumulative impacts.
The company's latest application would allow it to mine an area known as Longwall 5 and extract another 1.6 million tonnes of coking coal.
A major expansion application is being assessed separately.
Gujarat did not respond to specific questions, but said it was "co-operating and working with all government departments as part of the approval pro-cess".
The environmental assessment, prepared by Cardno, said the extent of proposed longwall mining had been refined to minimise environmental impacts and provide economic benefits.
It expected the effect on surface features to be "insignificant".
"Subsidence-induced erosion is not anticipated to occur, nor generate any significant change in the potential for ponding, scouring or erosion in the swamps," the assessment said.
"The extraction of Longwalls 4 and 5 is not anticipated to be a significant risk to Cataract Creek in regard to its stream, as the proposed works incorporate narrow longwalls and wide pillars.
"The impacts are likely to be restricted to short reaches where flow infiltrates into cracks in the bed, then re-emerges further downstream."