SkyCity convention centre fire: Contaminated Auckland harbour mud to be entombed in concrete

Mud sediment in Auckland's harbour contaminated with arsenic and other chemicals from the SkyCity fire will be dredged, mixed with concrete and disposed of on land. 

Auckland Council Safeswim programme manager Nick Vigar said on Friday afternoon that 10 days after the fire erupted on the roof of the convention centre, it was back to business as usual for water quality around the city. 

Ecotoxicology testing showed no long term impacts for marine life and water quality, he said. 

However, there was a possibility of significant contamination of sediments within 10-100m of stormwater outlets with heavy metals, such as cadmium and arsenic.

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The sediment was set to be dredged for the upcoming America's Cup and would not be dumped at sea, Vigar said.

Instead, it would be mixed with sand and concrete and transformed into "Mudcrete", before being disposed of on land at specialist facilities. 

"None of the sediments from here are going to the marine environment."

Council principal freshwater scientist Coral Grant said the major risk from the contaminated water was cadmium and arsenic being taken up by shellfish.

Test results showed "low to moderate toxic effects very localised to the outfalls", she said. 

However, a public health warning against collecting shellfish near urban areas was already in place.

"We don't encourage people to collect shellfish down here anyway."

Vigar said of the 27 million litres of water to fight the fire, 15-20 million reached the waterfront.

Of the most concern was the 1.8 million litres pumped out of the basement to the stormwater system before it was found the Māngere wastewater treatment plant could handle the water, and it was pumped into the wastewater system. 

Stuff asked whether in hindsight authorities should have held off pumping the water out of the basement until it was known whether it could be handled by the wastewater system. 

Vigar was firm in his response, saying Fire and Emergency and Fletcher had an "immediate hazardous situation in the basement" and a responsibility to get rid of that hazard quickly, as was authorised by the Resource Management Act.