Sutherland Shire Council says US coal giant Peabody proposed expansion of its Helensburgh mine presents unacceptable risks to the Woronora drinking water catchment, Royal National Park and associated threatened ecological communities.
The council unanimously agreed at its last meeting to oppose the proposal following a motion by Cr Melanie Gibbons.
As well as making a formal submission to the NSW Department of Planning, Housing and Infrastructure's brief public consukltation process, the council also decided to write to the appropriate ministers and shire MPs, advising them of the council's position and calling for refusal of the modification in its entirety.
Metropolitan Collieries proposed to extend the mine into previously unmined areas near the Woronora drinking water reservoir.
The proposal, called Modification 4 - Longwalls 317 and 318, is being assessed as a NSW Major Project and also requires federal government approval, which can be given without a separate assessment.
A Peabody spokesman said Metropolitan Mine was more than 500 metres underground and used some of Australia's narrowest longwall paths to minimise subsidence impacts.
"Two independent scientific panels have confirmed there is no connective cracking to the surface as result of mining activities at Metropolitan Mine," he said.
"Last year, the operations contributed $73.5 million in wages, over $200 million in spending with local suppliers and provided a $324 million return for the NSW economy."
Sutherland Shire Environment Centre and the Protect Our Water Alliance are among groups that have strongly opposed the application.
SSEC spokesman Cooper Riach said mining had already caused damage to the catchment.
"We are concerned about the strength of the NSW Government approval process for this expansion, especially since Peabody [has] already caused irreparable damage to the upland swamp ecosystems in our protected drinking water catchment," he said.
Protect Our Water Alliance said the Woronora Catchment was a critical drinking water source for more than five million people, including Sutherland Shire residents.
"The longwall panels are located alarmingly close to the Woronora Reservoir, which is a crucial asset for regional water security," the group said.
"Longwall mining is known to cause subsidence, fracturing of rock layers, and irreversible damage to watercourses, reservoirs, and upland swamps."