KEPCO was "encouraged to acquire all of the land to be either directly or indirectly affected by the development", it said in a June 27 submission to the NSW Independent Planning Commission before a final decision on the controversial underground and open cut coal project in the next few weeks.

KEPCO alleged the "encouragement" to buy thousands of hectares of Bylong Valley land occurred during an on-site meeting with government and department representatives in April, 2016, but encouragement to invest in the proposal was not confined to that meeting.

"Support and consent from NSW Government" since KEPCO bought the exploration licence from Anglo American in 2010 "encouraged KEPCO to subsequently invest $180 million in exploration and mine planning", the company said in its submission.

KEPCO invested more than $750 million to establish an underground and open cut mine in the valley between Denman and Mudgee, which included $115 million to buy properties including a church, the general store, the local public school, and significant private landholdings including historic Tarwyn Park, the company said.

"At no time in the development assessment process has there been a policy shift to suggest to KEPCO that the NSW Government's coal resource in the Upper Bylong Valley should not be mined," it said.

A NSW Government spokesperson rejected the allegation a government minister encouraged KEPCO to acquire the properties at the April, 2016 on-site meeting.

The company's purchase of more than 13,000 hectares of Bylong Valley has been heavily criticised by mine critics, including Bylong Valley Protection Alliance whose spokesman Warwick Pearse called it the "silencing of dissent".

"KEPCO had already spent about half a billion dollars by the time it applied for the mine approval. That's a mighty weight of money and influence to put to a government and department assessing the project," Mr Pearse said.

A late heritage report commissioned by the Independent Planning Commission found a revised mine plan that nearly halved the amount of coal to be mined over 25 years would still have an irreversible impact on the historic valley.

"There is still considerable uncertainty about whether the historic uses of the place and its cultural significance can be successfully retained and or recovered," the heritage report found.

"Proposed changes to the significant natural and cultural landscape character for the proposal are fundamental. While some of the impacts may have changed due to the revised mine plan, the fact remains that the material impacts cannot be fully mitigated, nor are they reversible.

"The natural forces that shaped and patterned the landforms and vegetation over millennia, and the long evolving history of human land uses and management, both Aboriginal and non-Aboriginal, will be removed."

The National Trust of NSW listed Bylong Valley as a scenic landscape area in 2013.

The heritage report found impacts of the revised mine plan on the valley were "direct, indirect, visual, temporary and permanent, and physical and cultural".

In a response KEPCO rejected the heritage report conclusions and said it was a "committed custodian" of the properties it owned, including former horse stud Tarwyn Park, where Peter Andrews developed his natural sequence farming methods.

KEPCO argued only 2 per cent of the valley landscape would be modified because of the mine, but not lost. The company would not leave a final void after mining and land would be rehabilitated to blend with the landscape.

"If the revised mine plan for the project is not approved the socio-economic and other benefits which are set to flow to the Bylong valley will largely evaporate," KEPCO told the Independent Planning Commission in its final submission.

The company proposes to run an open cut and underground mine complex for 25 years and mine up to 6.5 million tonnes of coal per year for use in the domestic Korean energy market.

The project would provide 450 jobs and deliver $278 million in royalties to NSW, KEPCO said.