The Environmental Defenders Office, representing the Bylong Valley Protection Alliance, will attempt to defend the IPC's refusal of the mine, which was knocked back in September due to concerns about its impact on productive agricultural land, groundwater and its contribution to climate change.

KEPCO, which spent a decade trying to get the greenfield mine approved before its refusal, appealed the IPC decision late last year.

The Environmental Defenders Office took on the case for the community group after the IPC declined to participate in the judicial review on the basis it may compromise its impartiality.

"This is an important case. It is the first time the IPC has refused a new coal mine because it was not in the public interest, finding the mine would contribute to climate change," EDO special counsel Rana Koroglu said.

"The Bylong community is stepping up and defending the IPC's decision to protect the area's prime agricultural land from groundwater depletion and stop the mine fuelling devastating climate change.

"We will argue on their behalf that the IPC properly considered the impacts on groundwater and correctly applied the legislation regarding preferred land uses and the assessment of greenhouse gas emissions."

KEPCO wrote off the project and nearly 700 million Australian dollars in January, marking down the value of its Bylong mining rights from $642 million to zero in a report to the South Korean stock exchange.

It also marked down the value of the 13,000 hectares of land it owns between Denman and Mudgee by $45 million, after paying $115 million for properties since 2010, when it paid more than $400 million for the mining licence.

The proposed open cut and underground coal mine would produce up to 120 million tonnes of coal over 25 years for the Korean domestic energy market.

KEPCO has said it would create more than 800 direct and indirect jobs, with nearly $280 million in royalties to the NSW Government and $600 million in annual business turnover.

Bylong Valley Protection Alliance president Phil Kennedy said the proposed mining area was "home to the top 3.5 per cent of agricultural land in the state".

"KEPCO's industrial mine places important agricultural land in jeopardy," he said.

"The Bylong Valley is a unique valley - there are underground streams between four and six metres below the surface that we're able to tap for food security and fodder production. This mine would compromise that."