Parsons Brinckerhoff is conducting the study for the proposed coal mine, near the Pages River.

According to ABC News, residents opposed to the development say the company has discovered more coal in the area and now wants to mine 150 million tonnes over 50 years.

A spokeswoman for the consultants, Mary Diab, said although extracting all the coal available could take longer and might involve underground mining, the current proposal was still for an opencut mine operating over 25 years.

Diab said a number of options were being looked at, which included two pits within the Bickham site. She said if results showed there was a negative impact, the proposed mining area would be assessed, ABC News reported.

Development of the 45-50Mt Bickham reserve was thrown into the spotlight late last year when a NSW government study found no new underground mining should take place in the Upper Hunter Valley.

Only two opencut sites were deemed suitable by the report for potential mining in the area over the next 15 years; one of those sites was Bickham's reserve.

Once the Parsons Brinckerhoff study has been approved, Bickham can then undertake other environmental studies before submitting a formal development application for the mine.

Diab said the potential economic benefits of any new coal mine were carefully assessed against the risks of significant environmental amenity or social impacts.