Boral is under investigation over allegations it doctored lab reports to understate the level of toxic chemicals coming from its Berrima factory, south of Sydney.
Blue Circle Southern Cement (BSCS) has a licence to fire its cement kilns with "alternative fuels", including old tyres, used oil and carbon from aluminium electrodes.
A July 2006 report into emissions showed arsenic levels in the kiln stack were up to 15 micrograms per normal cubic metre of gas.
Antimony - a common component of coal and petroleum - were up to 20 micrograms.
In a later draft of the same report, obtained by The Daily Telegraph, the stated levels of both hazardous substances had been changed to indicate concentrations were up to just 4 micrograms.
But both drafts relied on the same samples taken during tests run over two days in April 2006 - before the company was given approval to burn tyres and used oil.
The Department of Environment and Climate Change (DECC) said it was concerned about the allegations raised.
"We are in the midst of organising an independent audit of monitoring results," a department spokesman added.
The consultancy that prepared the reports, Queensland-based firm New Environmental Quality (newEQ) , admitted Blue Circle sent the initial report back and asked for changes.
"That’s not uncommon," newEQ managing director David Arbuckle said. "All our clients are always keen to get draft reports."
BSCS agreed it had asked for changes to the report but insisted the process was transparent.
"BCSC became aware of some errors in the report and, in December 2006, arranged for an independent expert review of the report to be conducted," a Boral spokeswoman said.
"This review identified a small number of errors in some of the report data. BCSC requested that newEQ correct the report based on the errors identified."
The DECC began investigating Blue Circle after concerns raised by a local group, Residents Against Dioxins.
Source: Daily Telegraph - Sydney, New South Wales, Australia