The expansion, which covers an additional 12 longwall blocks at the Hunter Valley mine, is currently waiting for approval from the New South Wales Department of Planning and plans are being publicly exhibited until December 19.

Recent media reports have stated the mine and its Stage 3 plans are facing local lobbying over subsidence fears.

Cessnock Greens councillor James Ryan told the Herald newspaper that a lot of people living above the mine were worried about subsidence effects on the Sandy Creek and Cony Creek waterways and were lobbying to halt the expansion.

However, Austar general manager Frank Fulham told ILN that at this stage he had not seen any indications there would be lobbying against the mine’s expansion.

“When the councillor spoke he said if the reports say that cracking of the bedrock were to occur, then people would have concerns but it is not definitive,” Fulham said.

“The subsidence report indicates that cracking of the creek bed is unlikely due to the massive nature of the underlying Branxton Formation that extends down to the Greta coal seam.”

He said Austar’s detailed subsidence impact assessment, conducted by Mining and Subsidence Engineering Consultants (MSEC), used two parameters for subsidence, the first being predicted maximum subsidence based on an Incremental Profile Method and the second being upper bound subsidence.

He added the latter was developed for risk assessment purposes and based on subsidence being equivalent to 65% of the effective seam thickness.

Austar is currently completing its second panel, and as the only mine in Australia currently using LTCC, there is no historical data on LTCC-related subsidence statistics at the Department of Primary Industries.

“We believe that the maximum upper bound subsidence is unlikely to be more than 50 per cent of the effective seam thickness rather than the 65 per cent that has been adopted,” Fulham said.

“Subsidence predictions indicate that all buildings and structure within the Stage 3 area will remain within safe, serviceable and repairable criteria.

“A separate peer review subsidence report assessed the MSEC prediction for maximum predicted subsidence and considered it to be needlessly conservative.”

Stages 1 and 2 of the mine’s expansion have already received state government approval and cover five longwall blocks.

“Stage 3 is [longwall blocks] six to 17, so by the time we have completed Stage 2 we will have further information gathered based on LTCC subsidence,” Fulham said.

“The other thing to take into account is as these longwall panels progress the workings are getting deeper each time. At the moment we’re 450 metres deep in Stage 1, we’ll go to a maximum of 550 metres deep in Stage 2, and up to 740 metres in Stage 3.

“The strata in this area is dominated by the Branxton Formation which is a very competent sandstone conglomerate strata unit which is hundreds of metres in thickness.

“So it’s a little bit different than any other underground Hunter Valley mine. The Branxton Formation is sufficiently massive to be strong enough to span the longwall panel voids without collapsing resulting in a controlled compression of the chain pillars, so the landform will subside in a relatively uniform manner.”

Stage 3 approval by the department is expected around the end of April with the next step being ministerial approval.

Fulham expects the approval process to be complete by the end of the first half of 2009 or the start of the second half. Mining in the Stage 3 area is expected to start in 2012.

Fulham confirmed the mine’s expansion plans would have Austar hiring an extra 60 people in the construction phase and increasing its mining workforce by 75 to 275.