Dr Stuart Blanch, the World Wildlife Fund Australia's Land Clearing and Restoration Senior Manager, said the state government should have more stringent processes when assessing developments - especially after thousands of koalas and hectares of habitat were wiped out in NSW and across the country during the summer bushfires.

He said six years was the average lifespan of a koala and in that time the population at the Brandy Hill Quarry could have drastically changed.

In fact, an Australian Koala Foundation study in 2000 found populations on Quail Island and at Sandy Point had actually doubled in under four years.

"The state government should have requested updated surveys using a wide range of techniques that are available," Dr Blanch said.

"The cumulative impact of lots of bad decisions can add up to drive species to extinction at a landscape scale."

The NSW Office of Environment and Heritage and the NSW Department of Planning and Environment looked at the project before it went to the NSW Independent Planning Commission, which gave it the green tick of approval in July.

It was approved even though quarry owner Hanson provided 2014 koala survey results throughout the process as part of its biodiversity assessment.

The updated Biodiversity Assessment Reports created in 2016 and 2019, which were submitted to the government, referred to a koala survey undertaken in 2014. Those results found there were koala droppings on the site but no breeding female koalas were spotted.

Read more: Two sides to the koala on either side of this fence

In the determination statement the Department of Planning and Environment said the quarry's assessment "over-estimates" the impact on the koala population even though the expansion could displace individual koalas.

The Mercury contacted the department to find out why an updated koala survey was not sought and if the 2014 survey was an adequate representation of the population in that area.

The department chose to provide an off-the-record response.

"There should have been a halt on any decision making after the fires and after the Upper House inquiry report about koalas was released, to make sure that they were on the side of caution and the state government failed to do that," Dr Blanch said.

The NSW Independent Planning Commission, which became involved due to the number of objections, said the biodiversity assessment was performed in accordance with government policies and the project had been designed to "avoid, mitigate and manage biodiversity impacts where practicable." It also said the impact on biodiversity would be "managed, mitigated and/or offset".

The project, which has been defined as a State Significant Development, is now in the hands of the Federal Environment Minister Sussan Ley and her department.

A decision is expected on September 8.

"The planning commission and state government have failed to take into account these recent events and protect the koala," Dr Blanch said.

"What other disasters need to happen before governments stop approving the destruction of koala habitat?"

Residents who live near the quarry are concerned the 2014 koala survey doesn't reflect the current population of koalas, or the demand for the trees in the area that has been proposed for clearing.

They have urged their neighbours, and supporters, to write to Ms Ley and urge her to ask for an updated koala survey before she makes a decision.

Documents submitted to the state government as part of Hanson's application process show the land earmarked for clearing is koala habitat. It's also home to other threatened species, although the koala will face most of the impact. The quarry wants to clear 52 hectares of land to increase its production to a maximum of 1.5 million tonnes per year.