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A contamination assessment of the Cadbury factory was commissioned by its owner, Mondelez New Zealand, in 2017, and has just been released to the Otago Daily Times by the land’s new owner, the Ministry of Health, under the Official Information Act.
It found, as expected given the land had a long history of industrial use even before the advent of the Cadbury factory, that soil contamination was widespread.
"The concentration of contaminants do not, however, suggest a site-wide level of significant risk to human health or to the environment."
Investigators focused on 11 potential hazardous practices that had taken place on the land, in 13 different locations.
In two of those, heavy metals were found in levels potentially dangerous to human health, but in the others chemical levels did not exceed relevant guidelines.
A high level of lead was discovered in a historical foundry and current workshop site, and excessive arsenic was found where a historical sawmill stood and a range of industrial processes took place.
"Overall, on the assumption that the site remains as an industrial use and therefore is likely to be capped by concrete over the areas of contamination risk, use of the site for an industrial purpose is considered low risk for human health."
Should the land use change, the affected areas would need suitable capping or mediation, the report said.
"Capping of contaminants that do not present a vapour risk is considered to mitigate the risk associated with the lead and arsenic heavy metals human health risk for the end site user.
"However, management in construction and soil disposal will likely be required."
The report did not consider asbestos risk - the building is known to have asbestos. Remediation work was carried out by the ministry at the start of the demolition process.
Nor was groundwater tested, partly due to none being found on site at the depths drilled to.
"There remains a potential for soluble contaminants to migrate through groundwater into Otago Harbour," the report said.
"However, the approximately 170 years of industrial activities on the site, contaminants with an affinity to migrate are likely to largely have already done so."
Mondelez announced in February 2017 it would close the Dunedin Cadbury factory the following year.
Beca began work on the contamination assessment about August 2017, and delivered its report to Mondelez that October.
The factory stopped production in March 2018. The ministry officially became the owner of the factory in November that year, having paid $11.6 million for the property.
The report charted a long history of industry on the land, which included an iron and brass foundry, a soap works, a boiler maker, a tannery and a wool scourer.
Timber and coal yards formerly stood on the site, which was also used to store kerosene and petrol.