The broken jet fuel pipeline currently disabling many flights in and out of Auckland Airport could be fixed as early as Sunday.
However, Refining NZ says it would then take about 30 hours for the oil to settle before it could be put back into the supply chain for aircraft that were carrying out varying degrees of refuelling detours before or after landing at the country's biggest airport.
The announcement will be welcome news to the thousands of travellers affected since the discovery was made at Ruakaka on Thursday.
The Northland Regional Council said it had been working with Refining NZ on the clean-up and it hasn't ruled out a prosecution.
Refining NZ chief executive Sjoerd Post this morning said that a 30-strong team had been working 24 hours a day over the last four days to recover the leaked fuel from the site.
"Much of the jet fuel had leaked into a culvert on the property. Quick action by our team, working alongside environmental staff from the Northland Regional Council, meant we were able to contain the leak and prevent it from moving into waterways."
The contaminated soil was being removed. Heavily contaminated soil is being transported to the refinery for remediation, while lightly contaminated soil is being taken to a secure landfill.
Post confirmed that excavating around the leak had revealed the pipeline had been dented at some stage.
"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. While further analysis of the metal is to be carried out, we are concluding that this incident is a 'one-off'.
Post said that the refinery's engineering team is preparing to insert a new section of pipe and is working to a tight timeframe to return the pipeline to service.
"All going to plan, we expect to deliver jet fuel into Wiri between midday Sunday the 24th and midday Tuesday the 26th. 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."
In a post on its Facebook page, the company responded to questions about why the repair would take so long.
"We need to be absolutely clear that it is safe to work in before we can start welding in the new section of pipe. The second point is that the work site is in a boggy, peaty area, made even more challenging to work in by the recent heavy rains. Rest assured that we are working as quickly as humanly possible to fix the pipe," they wrote.
Meanwhile, Air New Zealand's chief operations integrity and standards officer Captain David Morgan today labelled the incident "extremely disappointing".
"The shut-down is currently impacting all airlines operating into and out of Auckland Airport and limiting the volume of jet fuel able to be uplifted to 30 per cent of normal usage.
"It's estimated around 2000 Air New Zealand customers will be affected by flight cancellations today as the airline works to consolidate passenger loads and minimise fuel usage."
An airport spokesperson said there have been a few new domestic cancellations, however due to the volume of flights between Wellington, Auckland and Christchurch many passengers would likely be put on other flights. A Blenheim flight has also been affected.
The spokesperson said there were currently 14 international or domestic flights cancelled.
However, when put in context that an average of more than 460 flights went in and out of the airport daily, the impact hadn't been too bad.
"I think contextually wise, we have 465 flights that operate at the airport daily so if you look at it with that context there's not a huge amount of flights that have been cancelled.
"What that shows is that airlines have responded and have put in mitigation and are refuelling and using other measures."
A Northland Regional Council said an investigation would be carried out to see whether any enforcement or prosecution was needed under the Resource Management Act.
In the meantime, staff would get samples from groundwater bores to establish existing water quality parameters but council didn't believe they would be impacted "given the prompt nature of the containment, recovery and clean-up".
"At this stage, council is satisfied the refining company acted promptly and appropriately, both in its notification of - and subsequent response to - the leak."