The former Fluffy asbestos dump site in near Palmerston and Crace Gungahlin is believed to contain about 5550 drums, 1700 crates, shipping containers and a range of other contaminated materials buried when the loose-fill asbestos was removed from the ceilings of homes 25 years ago.
The northern part of the block, block 789 Gungahlin, is the site of the planned extension of Nudurr Drive, which runs between Crace and Palmerston, linking Gundaroo Drive and Gungahlin Drive.
The ACT government commissioned Robson Environmental to test the site for contamination before the road is built, and tabled the findings last week.
Robson said the site was used to dump the asbestos insulation removed from more than 1000 Canberra homes between 1985 and the early 1990s. The loose asbestos was placed in steel drums and shipping containers, to be buried three metres below ground.
Planning directorate records showed there were about 122 containers, 5544 drums, 1681 crates, 187 pallets, 100 plastic bags, 76 doors, 49 packages, 22 poly bundles, 14 boxes, 13 air-conditioning ducts, seven plastic containers, six pantek loads of tiles, five pieces of equipment, four telecom drums, four city crates, three tanks, one boiler and fire doors, according to the Robson report.
The site was believed not to have any special leachate controls in place, with officials at the time considering the ground had a high clay content and low permeability.
Robson found no evidence that the loose Mr Fluffy asbestos had contaminated the site.
But it said the three to four metres of clean fill that was supposed to have capped the site probably was not as thick or as clean as claimed.
There were discrepancies in reports of how high the asbestos cells extended, the capping layer might have been compromised by subsequent filling, and it appeared that some of the capping material was in fact other landfill waste.
Robson found general waste at the surface across the site, indicating there was only a shallow cap on top of household waste.
The company said its soil and groundwater tests indicated the site was "unlikely to present a significant risk to current users of the site and adjacent residents".
"However, the current capping layer over the landfill material and asbestos within the landfill is inadequate and asbestos may potentially be exposed at the surface of the landfill in the future due to soil and wind erosion," it said, recommending proper capping and a management plan.
The landfill area had also not been fully delineated to the south, east and northwest of the site, Robson found, also recommending more work be done to determine the extent of the dumping area.
Robson dug 48 test pits down as deep as four metres below ground. It found metal, brick, concrete and glass at the surface or near the surface in numerous locations. It found fragments of bonded asbestos sheeting and friable asbestos, probably due to the bonded sheeting degrading, in 10 of the test pits. The asbestos was found at 90cm or lower.
Soil samples recorded concentrations of asbestos above the site limits in eight test pits, at depths of 1.9m or more below ground. But it found no evidence of Mr Fluffy asbestos in the top three metres of landfill material, with the contamination found believed to be from other asbestos dumped there.
Robson concluded the northern strip was suitable for the Nudurr Drive extension, as long as a management plan was in place, and as long as work did not extend south of the embankment.