Repairing the ruptured pipeline that carries jet fuel to Auckland is too hazardous to be rushed, Refining NZ says.
The pipeline had to be shut down after a leak was discovered, and has caused dozens of flights in and out of Auckland to be delayed or cancelled.
Between 60,000 and 80,000 litres of jet fuel spilled. Refinery staff who noticed the drop in pressure immediately turned off the tap, but about two tanker-loads of fuel spilled and collected in a nearby culvert.
Refining NZ chief executive Sjoerd Post said a 30-strong team has been working 24 hours a day over the past four days and most of the fuel has been recovered from the leak site.
"Much of the jet fuel had leaked into a culvert on the property."
No waterways, other than culvert/drainage channel into which it flowed and in which it was contained, were impacted. ^PH 2/3— Refining NZ (@Refining_NZ) September 17, 2017
Mr Post confirmed that excavation around the leak had revealed the extent of the damage.
"Inspection has shown clear signs of the pipe being dented and the protective coating removed by heavy equipment. The pipe is located in boggy terrain and it is certain that the acidic nature of the soil will have contributed to the corrosion and subsequent tear in the pipe.
"What's not clear is when this section of the pipe may have been damaged."
Mr Post said an engineering team was preparing to insert a new section of pipe.
"All going to plan, we expect to deliver jet fuel into Wiri between midday Sunday and midday Tuesday. From that point we estimate it will take another 30 hours for the jet fuel to settle, for recertification to be obtained, and to transport to Auckland International airport."
Mr Post said the area needed to be decontaminated.
"The job to fix it is first we need to make it safe and we've had a leak of jet fuel there so fixing it involves welding so you need to make sure that you have decontaminated.
"We are in the process of making the site safe. We are digging the holes where we will actually cut the pipeline. Part of our plan B is we have spare sections of pipe."
There is still highly explosive fuel and vapour in the pipeline between Ruakaka and South Auckland, which has to be allowed to drain and settle before repairs can start.
Spokesman Peter Heath said any spark from welding gear or even a digger could cause an explosion.
Northland Regional Council staff are going to the scene today to assess the extent of the contamination. The council said there was no threat to waterways or the bird sanctuary at the Ruakaka estuary.
In a market update to the NZX, Refining NZ estimated the cost to the company at $10 to $15 million in revenue.
"The company expected that the repair could be effected within two days by installing a clamp on the damaged section of the pipe. However, closer inspection after excavating the pipeline has shown that the damaged section needs to be replaced. Our team is now preparing for this work.
"After the repair the pipeline will be run at a reduced (70-80 percent) capacity initially," the market update said.