The company detailed its plans in a project modification submitted to the NSW Department of Planning.

Under the expansion project, the American coal giant aims to ramp up Metropolitan’s run-of-mine production by more than 1 million tonnes to 3.2Mt per annum in a couple of years, plus extend the mine life by 23 years.

Engineering studies identified some issues with the previous plan to upgrade the mine’s existing drift and mains conveyor system.

Peabody said upgrading the drift and conveyor capacity while the mine continued to operate would be technically challenging.

The company also said the risk of production outages due to “potential construction related accidents during the upgrades” would be high.

Peabody determined a less costly and risky option would be to develop a replacement underground drift and associated main conveyor system while the existing drift and conveyor continued to operate.

This new construction work is expected to take 30 months and add another 30 jobs to the peak construction workforce of 80 for the mine expansion.

Minor clearing and part demolition of two buildings will be required to make space for the new drift portal while a new substation to provide more power will be built.

Once the work is complete, the existing drift and conveyor system will be decommissioned.

Peabody is targeting an average of 25 metres a week for the development of the new drift which will stretch for 2.7 kilometres.

A roadheader will excavate the drift with an LHD transporting the rock until there is room to set up a small 160-kilowatt drive drift conveyor, which will be replaced by a bigger twin drive system about a year afterwards.