Contamination in red zone worse than expected

Wednesday, 10 May 2023

Asbestos, coal tar, lead paint and other contaminants buried under Christchurch’s red zone will cost more than the $12.1 million budgeted for clean-up.

A new report to be considered by city councillors today warns that contamination in the red zone – correctly known as the Ōtākaro Avon River Corridor,​ – is worse than expected.

The budgeted figure for contamination testing and remediation was $12.1 million.

The council’s head of parks Andrew Rutledge said it would be “hard to quantify” the shortfall because it depended on the extent of contamination and methods of treatment. ​

“However, it has become clear that if we were to identify and pull out all contamination and truck it to Kate Valley [landfill], we would be significantly short,” he said.

Removing roads and backfilling on just the first phase of the City to Sea Pathway (between Fitzgerald Ave and Porritt Park)​ had been estimated to cost $4.5m – and this has carbon costs as well, said Rutledge.

There were several types of contamination in the red zone. One was called “coal tar”, which was a by-product of coal gasification and used as a roading material into the 1980s.

It contained “polycyclic aromatic hydrocarbons”, some of which cause cancer in humans. The council had spent about $70,000 looking for coal tar so far.

Coal tar was not water-soluble and would not end up in the river, the council asserted.

It was seeking consent to leave some of the substance in place. If earthworks were not required for projects, the council would “encapsulate” the road, meaning it would be left “in place with suitable control measures to prevent leaching”, Rutledge said.

“Generally the advice from our experts is that it is safe to leave as is.”

The road would be covered with soil, planted and monitored, he said.

“Complete removal is not affordable and would result in a considerable carbon cost,” said a second document, a red zone quarterly update, that will also be discussed today.

The leave-coal-tar-behind approach was used at the Avon Loop, a red-zoned area near Kilmore St and Fitzgerald Ave, where an old road was stopped and turned into a recreational walking and cycle path.

If earthworks were required, the roads would be removed and the material landfilled.

Other types of contaminant were found in former residential soils – lead paint that was scrapped off buildings, or when somebody buried a stash of asbestos decades ago, for example.

About 5500 homes were demolished in the 602-hectare red zone after the 2010-13 earthquakes.

“It is not possible to accurately test all residential soils,” stated the draft strategy.

As a result, the council had consent from Environment Canterbury or itself to test probably contaminated sites – former petrol stations and mechanic’s garages – that were listed on ECan’s Listed Land Use Register.

And where projects required earthworks, testing would occur at an early stage and remediation undertaken as needed.

Where earthworks were not required, they would leave contaminants in place and follow “accidental discovery protocols”, when pollutants were unexpectedly uncovered.

The council was also creating a “heat map of relative risk”, a digital tool that would indicate where soil contamination was likely.