Pressure is increasing on the federal government to refuse the expansion of Brandy Hill quarry after evidence was uncovered that shows the area is a koala breeding ground.
The state government approved the expansion in July but federal environment minister Susan Ley will have the final say because it is likely to have a significant impact on a matter of national environmental significance.
Ms Ley is due to make a ruling under the 1999 Environment Protection and Biodiversity Conservation Act on Tuesday.
Koala rescuer Kai Wild, who rescued more than 100 koalas on Kangaroo Island during the black summer bushfires, visited the area on Saturday to show support for the community campaign to stop the quarry expansion.
Mr Wild was present when locals with the assistance of a scat detection dog found scat from a mother and joey within a kilometre of the quarry's boundary.
"Now that it has been identified as a breeding population I would hope the NSW government will rescind its approval and don't wait for Susan Ley to reject it. I would hope they understand the significance of the site given what has happened with the bushfires," he said.
A report authored by University of Newcastle wildlife conservation scientist Ryan Witt and conservation biologist John Clulow determined the expansion would sever an east-west corridor between other patches of preferred koala habitat and result in a significant barrier to koala movement.
The report, Commissioned by the Brandy Hill and Seaham Action Group, report notes that the NSW Independent Planning Commission, which recommended the project be approved, relied on outdated data when assessing the project and failed to take into account the "current and declining status" of koalas, which was drastically affected by the 2019-20 bushfires.
Dr Witt said the loss of around a quarter of koala habitat on public land during the 'black summer' bushfires increased the significance of the koala habitat that would be destroyed by the proposed expansion, but this had not been factored into the IPC's decision.
"The site of the proposed expansion contains some of the best habitat in an area that did not burn. It has high suitability to support the remaining koalas in the state," he said.
"It's not an appropriate time to approve projects that will affect koala populations and habitat when the impact of the 2019-20 bushfires hasn't yet been factored into planning instruments."
The report is based on analysis of relevant policy documents and fieldwork conducted on properties neighbouring the quarry, where the fieldwork team spotted a healthy female koala and a bellowing male nearby.
"I spent three nights conducting fieldwork on properties neighbouring the quarry, and within that time we observed a healthy female koala, and a bellowing male koala within 100 metres. A short time later, another bellowing male koala was heard a bit further way," Dr Witt said.
"It's clear the expansion would have a critical impact on the local koala population, especially considering the likelihood of healthy males and females utilising that habitat."