The multi-million-dollar Bylong Valley coal mine has been refused development consent by an independent planning panel, citing concerns about "long-lasting environmental, agricultural and heritage impacts".

Key points: Construction of the Bylong Valley coal project was supposed to start this year

Construction of the Bylong Valley coal project was supposed to start this year It was referred to NSW's independent planning panel, which rejected the proposal

It was referred to NSW's independent planning panel, which rejected the proposal The company behind the project could still challenge the rejection in court

South Korean company Kepco was behind the project, north-east of Mudgee, and claimed it would inject more than $300 million into the state economy, extracting 120 million tonnes of coal over 25 years.

The mine — which Kepco claimed would have created 650 jobs during construction and 450 during production — was referred to the NSW Independent Planning Commission for determination in October last year on the back of significant community opposition.

In its determination released today, the commission raised "significant concern" about the longer-lasting environmental impacts of the mine.

The commission acknowledged the mine's economic and social benefits, but said it was not in the public interest as it was contrary to the principles of "ecologically sustainable development".

"While the commission found the mine's predicted air quality, biodiversity, noise, subsidence and visual impacts are acceptable and/or can be effectively managed or mitigated, it raised significant concern about other longer-lasting environmental impacts," the commission said in its determination.

"The predicted economic benefits would accrue to the present generation but the long-term environmental, heritage and agricultural costs will be borne by the future generations."

In summary, it found:

The groundwater impacts would be unacceptable

The groundwater impacts would be unacceptable No evidence to support the (Kepco's) claim that the impacted Biophysical Strategic Agricultural Land (BSAL) can be rehabilitated post-mining to BSAL-equivalent

No evidence to support the (Kepco's) claim that the impacted Biophysical Strategic Agricultural Land (BSAL) can be rehabilitated post-mining to BSAL-equivalent Given the expected level of disturbance to the existing natural landscape, the commission did not consider that a recreated landscape post-mining would retain the same aesthetic, scenic, heritage and natural values; and

Given the expected level of disturbance to the existing natural landscape, the commission did not consider that a recreated landscape post-mining would retain the same aesthetic, scenic, heritage and natural values; and Greenhouse gas aspects of the project remain problematic

Farmers relieved 'war' is over for now

Graham Tanner, a farmer whose 800 acres borders the Kepco site, said he is "ecstatic and shell-shocked" by the decision.

"This is good farming area, it's been a seven-year battle but it looks like we won the war," he said.

Farmer Graham "Tag" Tanner and Warwick Pearse from the Bylong Protection Society. ( ABC News: Liv Casben )

Mr Tanner said there was already insufficient water in the valley for farming.

"The water that the mine would take would suck the valley dry."

But the NSW Minerals Council has slammed the decision by the "faceless" commission as an "utter failure of the NSW planning system".

In a statement, CEO Stephen Galilee said it represented a lost opportunity for the local region, in particular the communities of Kandos and Rylstone, where investment and jobs are desperately needed.

"This refusal comes after more than seven years of assessment, including repeated changes to the assessment processes and requirements during this period, highlighting just how difficult and complicated the current NSW planning system has become," he said.

Kepco, which claims it has spent $700 million developing the project and buying land in the area, could still challenge the judgment in court and is reading through the 146-page decision.

A spokesperson said the company was "disappointed with the decision, and is reviewing the statement of reasons".

Kepco has been working on the project since 2010 and construction was originally proposed to commence this year.