The government agency responsible for protecting NSW’s drinking water has opposed a coal mine extension which it says threatens Sydney’s second-largest dam.
Key points:
- WaterNSW opposes Dendrobium mine extension, saying it will cause ‘irreversible’ environmental damage
- The agency said the extension could cause ‘cracks’ to form in Sydney’s second-largest dam, Avon Dam
- He says the new mine design does not adequately address the reasons why the IPC initially rejected the project
The NSW Planning Department is assessing a revised plan to extend the Dendrobium colliery, which has been declared State Significant Infrastructure (SSI) following its rejection by the Independent Commission planning (IPC).
WaterNSW opposed the original proposal due to its impact on water supply. The agency maintained its opposition in its latest submission on the environmental impact statement (EIS) of the revised plan.
“The submitted proposal is considered unacceptable to WaterNSW in its current form due to impacts on water quantity, water quality and ecological integrity in the metropolitan special area,” it said.
In its latest submission, WaterNSW revealed that the mine extension posed a risk to the stability of the Avon Dam, the main water source for the Illawarra region.
“WaterNSW, as owner and operator of the dam, is very concerned that the safety of the dam may be compromised by the proposed longwall mining.
“The differential movement on the dam walls could cause cracks to open in the dam walls. »
The agency said subsidence from longwall mining at the dam is expected to be between 35 and 40 millimeters.
This is eight times more than the subsidence observed by continuous monitoring from 1970 to 2021.
WaterNSW claimed that the impact of longwall mining on the dam had not been assessed by a suitably qualified dam engineer, and that the impacts of subsidence in the EIS were “grossly underestimated”. “.
Debate over the extent of water loss
WaterNSW said that despite the mine’s footprint being reduced by 60%, work on the proposed underground mine would still result in the removal of 70 gigaliters of water over the next 17 years.
South32’s developers said in its latest mine plan that it had reduced surface water losses by 78% based on revised groundwater modeling.
But WaterNSW expressed concern about the accuracy of the surface water loss predictions mentioned in the EIS.
“Surface water losses are likely to be underestimated compared to other estimates and modeling available. »
He said water losses are also expected to continue long after the mine has ended.
“Surface water losses will be long term and potentially in perpetuity as the mine will not be completely sealed off.
“The proposed continuous release of a partially sealed Dendrobium in Zones 2-5 has been estimated at approximately 1.2 megaliters per day. »
Claims for environmental damage
South32 said its revised plan avoided major streams and groups of swamps, but WaterNSW said the longwalls would still pass under or near 16 upland swamps and several major waterways.
The agency argued that the proposed rollbacks for key streams were aimed at repairing environmental damage rather than avoiding it altogether.
WaterNSW said remediation “will not restore the function and values of a watercourse system”, and that the damage in some cases will be permanent.
“The proposed mine design is likely to cause significant or irreversible damage to environmental features, including many waterways and wetlands. »
Requirements of IPC Recommendations
The project is the first mine to be granted SSI status, a statement which came after a motion was passed by the NSW Legislative Council endorsing the elevated status of the project.
The motion was passed with the requirement that the revised proposal take into account the recommendations of the IPC.
In its statement of its opposition to the project, WaterNSW claimed in several instances that the miner had failed to do so.
” [The mine design] does not adequately address questions raised by IPC, IAP and WaterNSW about previous mining projects in Zones 5 and 6, i.e. a mine design that minimizes impacts above and below the surface. »
The IPC noted a lack of consideration of the environmental assessment of alternative mine designs.
WaterNSW disagreed with the developer continuing to include 305m wide long walls, claiming that narrower long walls would reduce surface water loss through subsidence.
South32 says there is no material water loss
A spokesperson for South32 said independent reviews of underground mining on the catchment “have revealed that there have been no observed material impacts on the drinking water supply due to mining. underground mining in these watersheds”.
“Our expert assessment reports have revealed that there will still be no significant watershed-scale water loss, nor any significant change in water quality at the watershed level. of a watershed following the Dendrobium mine extension project. »
Based on its modelling, the mining company said there was no expected impact to WaterNSW infrastructure.
“The ground fracturing and water flow information and data described in our Environmental Impact Statement has been peer reviewed and is based on best practice modeling undertaken by independent, data-informed professionals. in-depth monitoring.
“Based on similar peer-reviewed work, no significant subsidence impacts are expected to occur to WaterNSW’s existing water supply infrastructure as a result of the project. »