The Coal Terminal Action Group (CTAG) in New South Wales (NSW) and the Greens Party are accusing the NSW government of altering an environmental study on the impact of dust from coal trains.

They said 15 out of 18 conclusions in the Particulate Emissions from Coal Trains report made for the Australian Rail Track Corporation (ARTC) were doctored between the submission of the draft version dated May 24 and the version published after seven days.

James Whelan, chair of the dust and health committee of the CTAG, pointed out that the leaked draft version said air pollution levels were high when loaded and unloaded coal rail wagons passed a monitoring station versus situations with no rail traffic.

"By deleting or inserting the word 'no' or 'not', a very different picture of the impacts of coal trains on air quality in Newcastle and the Lower Hunter is reached ... Other conclusions were modified to significantly downplay the pollution levels associated with coal trains," Mr Whelan was quoted by Yahoo News.

He warned that Barry Buffier, the chair of the Environmental Protection Agency, may have been very gullible and too speedy in making policy announcements based on an altered report.

However, the ARTC insisted that the report went through a final review process and it is accurate.

"The environmental consultants that prepared the report discovered an error in the calculations while preparing the final report and they adjusted the findings accordingly," the ARTC said in a statement.

The report was made in response to an attempt to double the number of coal trains through Hunter Valley and Newcastle in anticipation of a proposed fourth coal export terminal at the port city.

But CTAG said 30,000 residents who live within half kilometers of the coal rail route will face more health risks with the planned addition of trains.

It wrote to NSW Premier Barry O'Farrell to seek a special investigation into the alleged doctoring of the report which was compiled by Katestone consultants.

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