The self-certification process has left the cross-border fill dumping business open to potential manipulation and exploitation given that neighbouring NSW councils have limited resources to monitor what is being dumped, and when.

The cross-border clean fill disposal business is a financial godsend for Canberra developers escaping costly dumping fees in the ACT.

One of the biggest recent "fill" projects in neighbouring NSW is the former quarry site on the Old Federal Highway where around 74,000 tonnes of excavated material from the Canberra Metro light rail project has been dumped.

In the case of the Old Federal Highway project, the Yass Valley Council requested only application fees, a $3000 erosion control bond and a "contribution" to council of 12 cents per tonne "in respect of road maintenance".

If the same quantity of fill was dumped within the ACT where $11.65 was quoted by the government as the standard rate for the disposal of clean fill, it would have cost the developer - in this case, a consortium of businesses contracted by the ACT government - just over $1 million in fees.

Of more concern to local residents around the dump sites is that any uncertainty around the quality of the fill raises further questions about the effect on local area waterways and hydrology.

Clean fill is classified as virgin excavated natural material (VENM) but according to one experienced local contractor who could not be named, there was no evidence inspection or certification process on major building sites at which he works so "almost anything could slip through, and has".

In the case of the Old Federal Highway quarry remediation, fill dumping was stopped at least once when contamination was detected through a tip-off to council.

The Yass Valley Council's Director of Planning, Chris Berry, admitted the Old Federal Highway quarry site had experienced "ongoing issues".

"We have had irregular incidents, and not just at that site, where material going in was unapproved," he said.

"There was some material brought to the site which was not clean fill."

Dumping was stopped in April last year and the unapproved material was sifted out and removed from the site. It is not known where the unapproved fill, which photographic evidence shows contained chunks of plastic and broken steel star pickets, ended up after leaving the Old Federal Highway site.

Bill Rhodin, who operates the popular tulip farm next door to the quarry site, said he was aware that work was suspended on the site at one stage and he had concerns, too about sediment control which have since been addressed.

"The old quarry was just a hole in the ground. As long as all the proper environmental assessments are done, filling it up with Canberra clean fill made sense because the fill has to go somewhere," Mr Rhodin said.

"But there's a lot of room for improvement in the way things have been done.

"There was no communication from council to neighbours about the development, the site has been overfilled significantly because there are trees there with about one and half metres of fill up their trunks, and it took about six months to address the sediment control problem which came too late after some of the big recent rain events."

The issues around the Old Federal Highway site sharpens the focus on the most recent approval by the Yass council to allow the dumping of 90,000 tonnes of construction fill on a property at Kaveneys Road, near Hall.

The Kaveneys Road project, which was the subject of 20 objections to council, has been classified as the remediation of an eroded gully, the fifth significant project of its kind since 2014.

Access Canberra said in a statement that when material is taken into NSW, it is the responsibility of the owner of the material to seek appropriate approvals from the NSW regulatory authorities prior to the material's disposal.

However, the Queanbeyan-based branch of the NSW Environmental Protection Agency confirmed it doesn't test fill coming out of Canberra and going into NSW, nor does it engage any private certifiers to do the work. It becomes involved when complaints are made or awareness of a specific issue is raised.

Mr Berry said there was no reason to suggest that the current self-certification system and the council's checks on remediation sites wasn't working well and that using clean fill for erosion remediation is of significant benefit in improving a previously degraded environment.

"Our main concern was if there was non-approved material going into a site and whether that material carries a risk to humans or the environment. We would then make a risk assessment and if it was possible to do so, manage the issue in situ," he said.

He urged residents concerned about unapproved dumping in their area to contact the council.

"A high level of truck activity in a particular part of the shire may not, in itself, be an issue because the development application process includes projected truck movements, would limit those truck movements, and the times of those movements depending on the area," he said.

"If residents are concerned and we get complaints, we can track it back to the approval conditions and investigate."