Koppers Wood Products, a multinational corporation, treated timber using a combination of copper, chrome and arsenic at a 20-hectare block in Hume from the the early 1980s to 2005.

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One report put the contamination of groundwater at 2430 times the safe level.

It was revealed in March the corporation had failed in its obligations to send in regular groundwater tests to the government.

The Environment Protection Authority’s scrutiny of the company’s activities was also found to be haphazard.

Fears were aired by a former environment protection chief Bob Dunn that the contamination could spread from the site, which sat uphill from Jerrabomberra Creek, connecting to the Jerrabomberra Wetlands and Lake Burley Griffin.

The revelations prompted the government to order urgent testing to ensure the contamination had not shifted off the site since the last comprehensive audit in 2007.

Early results, released by Environment Minister Simon Corbell in April, were promising, showing the contamination was still contained.

Now, a more comprehensive independent report conducted by expert environmental consultant Coffey International had found the contamination did not pose a risk to the community.

The Coffey report stated the toxic plume was "unlikely to present an unacceptable risk to human health or the environment now and into the foreseeable future”.

It found migration of the toxins off the site was unlikely, and that direct contact with the contamination was also not a risk because it was deep below the surface and at low concentrations.

It noted land owners were unlikely to want to use the groundwater, and would need a licence regardless.

Coffey found the discharge of the toxins into surface water was also not likely.

It recommended that no further investigation of the site was needed, but warned a review should be conducted if future tests didn’t match up with the trends it had predicted.

It also said there was no risk to using land around the site that it was being released by the government for industrial use.

Mr Corbell said the government would continue to monitor closely the remediation of the site by its new owners.

"It is very important that Canberrans have access to the most recent information and are reassured the surrounding land in Hume is safe and that the government is very serious and fully committed to protecting our environment," he said.

Koppers avoided any responsibility for the clean-up of the contamination following an extensive court battle with the land’s new owners.

It was not prosecuted for the pollution or disciplined for the missing groundwater test results, although the government maintains it takes an educative, rather than punitive, approach in such scenarios, particularly where there is no risk to human health or the environment.

Very few prosecutions of polluters have occurred in the ACT, and the Environmental Defender’s Office has previously said the EPA is under-resourced and failing to properly enforce environmental law.

The EDO, which has had federal funding cuts, says only four prosecutions were launched for breaches of environment laws in the 15 years between mid-1998 and mid-2012.

Shadow environment spokeswoman Nicole Lawder said she was glad the opposition forced the government to be transparent about the site.

She said residents could now have peace of mind that the contamination was contained.

“The chemicals in question have the potential to be very dangerous and have adverse impacts on human and animal health so it was vital that we forced the government to have this independent report completed."