Ashton is proposing to modify the development consent to maintain safe working conditions in the underground mine and integrate gas management across the underground and use the methane for power generation, it says.

The modification includes the construction and operation of a central gas drainage plant and gas flaring facility compound, measuring approximately 25m x 75m, located on the ground surface in the north eastern corner of the underground mine area.

The 80 gas bores would distributed across the underground mine area, where the construction of the bores will be staged over the remaining 10-12 year life of the underground mine.

A pipeline network to convey gas from the gas bores to the central gas drainage plant and gas flares would also need to be constructed as would minor associated works where required for access and electrical power.

“Gas (predominantly methane) is liberated from coal during mining, and can accumulate in the underground workings creating a significant safety risk and constraining mine development and efficiency,” the company said in its environmental assessment.

“Generally, mine ventilation systems are capable of managing low gas levels However, where gas levels exceed the capabilities of the ventilation system, additional infrastructure and gas management measures are required.

“As proposed by this modification, an effective and commonly used approach at other underground coal mines, including NSW, is to drain the gas from mined goaf areas and pipe this to a central location for management.”

In June 2011, the Planning Assessment Commission approved a development consent modification application for the development and operation of 15 gas bores over longwall panels 6B, 7A, 7B and 8 in the Pikes Gully seam of the underground mine.

It was noted in the environmental assessment for MOD 7 that a more substantial gas drainage arrangement would be required to effectively manage gas levels in the deeper seams of the multiseam underground mine.

“This modification describes the more substantive gas drainage arrangement,” the company said.

“This will ensure safe and efficient mining operations for the remaining 10 to 12 years of mine life in the three deeper coal seams; that is the Upper Liddell, Upper Lower Liddell and Lower Barrett seams.

The flaring of the drained gas will significantly reduce the Scope 1 fugitive greenhouse gas emissions of the mine.

“The proposed modification will not alter the overall area of the ACP or the mining method, the company said.

“Further, there will be no increase in the rate of coal extraction, production or frequency of rail loading and offsite rail transport to that already approved.”