The Planning Assessment Commission has been told millions of dollars in wages will be lost if the Mount Thorley Warkworth mine does not go ahead.
A third public hearing into the controversial mine expansion got underway in Singleton yesterday.
The main argument supporting the development stems from the potential economic benefits of the project, such as the ongoing employment of 1,300 workers.
Rio Tinto has stated in its submission that the expansion is earmarked to contribute $1.5 billion to the state's economy over the next 20 years.
Managing Director of BAEconomics Brian Fisher said that should not be downplayed.
"According to our calculations, around $1.5 billion in net present value terms," he said.
"That is made up of a number of components.
"One of the biggest ones is a $612 million worth of contribution to employees and contractors above what they otherwise would be able to earn."
But Lock the Gate Alliance co-ordinator Georgina Woods insists the benefits of the mine expansion have been inflated.
"In our submission to the Planning Assessment Commission, we revealed that proper analysis of the coal resource at Warkworth shows that there are many more years worth of mining at the current extraction rate available to Rio Tinto.
"Nobody's jobs depend upon this project getting approved."
Increased dust, water supply issues and noise pollution have topped the list of environmental concerns presented to the PAC on its first day of hearings.
Residents of Bulga says the ecological detriment's linked to expanding mining operations would also lead to negative health impacts.
Disruption to natural wildlife habitats and local woodlands were also been highlighted.
Environmental Justice Australia researcher, Doctor James Whelan says dust levels are already dangerously high.
"If you compare the particle pollution level close to where this coal mine is being assessed, we can see that they regularly exceed the national health standard, getting as high as 70 micrograms per cubic metre," he said.
"The current standard is just 50 micrograms per cubic metre.
"Even without the expanded coal mine, particle pollution levels are well over the national standard."
Recent mining engineering graduate Brianna Milgate said the project's employment benefits will be significant.
"I graduated at the end of last year and with the current state of the industry, there's really not many jobs going at all," she said.
"Of my graduating class, probably only about 20 per cent have secured jobs.
"The other 80 per cent are now looking for work in other industries, or working in places such as Coles or Woolies.
"Some have even been forced to go on the dole."
The public hearing continues this morning in Singleton.