Auckland Council says its entire wastewater network could be compromised if water removed from SkyCity's convention centre's basement enters the system with strong toxins.
Firefighters battling the blaze at the SkyCity convention centre in central Auckland say they are moving into a recovery phase, but there is still eight million litres of water in the basement to get rid of.
Council staff are testing the water to find out if it is safe enough to pump into the city's wastewater network, rather than the storm water network.
Auckland Council's SafeSwim programme manager Nick Vagar told Checkpoint that getting the water out of the basement was definitely "urgent".
He said they're concerned about combustion products as a result of the fire, for example volatile organic compounds and hydrocarbons, which they are running tests for at the moment.
"Also our concern around the basement is that as cars start to float, that we'll potentially get more contamination than we have at the moment, so part of this is managing risk to minimise any more contamination to that water.
"We understand this is causing a hazard for the firefighters in the basement ... they’ve advised us the need to get the water out as rapidly as possible."
The initial test results will help them discuss with Watercare the best course of action, depending on the quality of the water. If they decide to discharge into the wastewater network then it will have be treated first.
But that comes with risks too, Mr Vagar said, because it will eventually end up at the Mangere Wastewater Treatment Plant which uses biological reactors to remove contaminants.
"They’re a key part of the wastewater network, and the risk for Watercare is if there are toxins in that water that will effectively kill off the microorganisms in those reactors, then that will compromise the whole wastewater system.
"So that’s the key issue we’re addressing at the moment in terms of whether we can put it into the wastewater [system]."
Some of the immediate test results are expected tonight and tomorrow morning, but meanwhile to contain the health and safety issue, Mr Vagar said the untreated water has for the past couple of days been going into the city's stormwater network and discharged into the Viaduct basin.
"We have to keep discharging to remove the immediate hazard ... and it’s needed to proceed with the recovery. Obviously, as soon as that immediate problem is gone we’ll stop pumping but in the meantime we have to continue to do it.
"We think that the risk of that is relatively low, there’s obviously potentially some toxins in there but our main concern at the moment is the proportion of the water that’s ended up in the basement of the carpark, which because it’s made its way down through the fire areas of the convention centre, we’re concerned that it’ll have a high level of toxic compounds in it."
And they are taking precautions to minimise any hazard and avoid pumping any contaminated sediments out of the basement, he said.
There's also a safeswim hazard alert on the Viaduct area to warn people that the water is potentially contaminated, he said.
'We don't take it lightly to pump it out into the environment'
Earlier this afternoon at a press conference, Fire and Emergency's Murray Billing said Fletchers was largely coordinating the water being pumped out and that today the amount of water entering the building had been significantly reduced.
Mr Billing said the water in the basement was about one-and-a-half metres in depth.
Auckland Council's SafeSwim manager Nick Vigar told reporters at this stage they do not know the level of contamination.
He said they were looking to pump the water over to the wastewater network.
"We don't take it lightly to pump it out into the environment and as soon as we can stop pumping it out into the environment we will."
Equipment from Ports of Auckland is being hauled in to pump out millions of litres of water flooding the basement of the building.
Fire and Emergency said it was talking with Fletcher Building and Auckland Council about how to dispose of the water, which had built up over the last three days.
An Auckland Council spokesperson said the water was being tested and NIWA and Watercare were also on the scene.
Close to 100 cars in the convention centre's carpark had been affected by water damage, SkyCity has confirmed.
It said cars parked on level B4 belonged to SkyCity employees and it would cover costs that were a result of water damage and employees would be fully compensated.