A decision whether to approve the project, which would have a significant impact on the Port Stephens koala population with the loss of 52 hectares of prime koala habitat, is due to be handed down on Tuesday, September 8.

The expansion of the quarry, owned by concrete giant Hanson, was granted by the Independent Planning Commission in July, but Ms Ley will have the final say because the project has been deemed likely to have a significant impact on a matter of national environmental significance.

Now a new scientific report commissioned by the Brandy Hill and Seaham Action Group and authored by University of Newcastle wildlife conservation scientist Dr Ryan Witt and conservation biologist Associate Professor John Clulow, has found that the area is indeed used by breeding female koalas.

"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 found.

The report noted that the IPC had relied on outdated data when assessing the project and failed to take into account the "current and declining status" of koalas, which was drastically affected by the 2019-20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.

"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."

The '30 days to save Port Stephens Koalas' campaign was launched on August 9 and has attracted more than 3000 supporters as it counts down the days until a (September 8) decision. The name of the group changes as the number of days until a decision is made counts down. As of Thursday, September 3 the page is called '5 days to save Port Stephens Koalas'.

Campaign spokesperson Chantal Parslow Redman, who lives with her family on a property near the quarry, said it was deeply disappointing that a community group was forced to fund an independent environmental assessment in order to provide the government with an adequate evaluation of the impact of a development on a threatened species.

"It should not be possible to approve a project that will have a significant impact on a threatened species on the basis of data collected in 2014 and before planning instruments have been updated to take into account the fact that koalas in NSW are set to be extinct by 2050," she said.

"Port Stephens is home to one of the last remaining koala populations on the east coast of Australia, including a population hub at Brandy Hill/Seaham. There are only a few hundred koalas left in Port Stephens, after a huge decline in numbers over the past two decades."

A spokesperson for Hanson had previously told the Examiner that the Biodiversity Conservation Division assessment reported that the removal of koala habitat could be offset through suitable biodiversity offset credits.

"As part of operations, areas of native vegetation will be retained within land owned by Hanson to the north east, north west and west of the development area, which contain habitat opportunities for koalas similar to that within the quarry site," the spokesperson said.

"Additionally, land close by to the property is the subject of two separate BioBanking Agreement, which [will] improve or maintain the condition of native vegetation to support the koala habitat."

Port Stephens State MP Kate Washington said that the report had demonstrated "just how weak and inadequate Gladys Berejiklian's koala protection laws are".

"The government's laws are so weak, even their own planning commission wants them strengthened," she said.

"Thank goodness my community cares about koalas so much that they've been prepared to fight for their survival in the face of a government that couldn't care less.

"This expert report lays waste to the government's pathetic koala protection laws. Now it's up to federal minister Sussan Ley to step in and protect this vital breeding habitat."