If there is a lucky side to the break in the Ruakaka to Auckland oil pipeline, it is that it happened only a few kilometres from the Refining New Zealand plant at Marsden Point.

Another stroke of luck in an otherwise disastrous situation is that the thinner pipe bringing natural gas to Northland, which shares the same underground corridor, wasn't damaged in whatever incident first snagged the oil pipe.

That much was evident in a site visit for media yesterday, led by the refinery's chief executive Sjoerd Post. The parallel pipes lie 2m underground, 50cm from each other.

Mr Post confirmed a digger tooth was found near the damaged pipe. Experts from insurance giant Lloyds had confirmed "scrapes" but believed the damage happened some years ago, he said.

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Had the damage happened at a more inaccessible part of 175km-long Ruakaka Auckland Pipeline (RAP) the task of bringing in specialist equipment, heavy machinery, truckloads of gravel to give traction in the wet conditions and transporting workers would have added to the nightmare.

A break happening in a more built-up area would present more safety problems.

The Ruakaka site is hundreds of metres from most houses although several residents, including a household only 50m from the break, have been relocated to motels and other accommodation.

It has direct access off a major road and is near where many of the refinery staff working on the job live.

The smell of jet fuel seemed to permeate the air at the site yesterday where two crews of 40 people have been working around the clock for a week to repair the pipe.

It was not vapour, however, causing the smell but high piles of contaminated peat soil that had been dug from 2m deep and wide trenches on either side of the now fragile pipe.

Those trenches are cambered to have water run away from the pipe, to be collected, put in large ponds and trucked from the site to the refinery.

Despite the reek, monitoring equipment indicates low levels of escaped or uncollected hydrocarbon contaminated materials.

Stringent work safety rules are in force on the site where removal or isolation of volatile soil was the priority until the damaged section of pipeline could be prepared for the specialist cutting, stopping and rewelding job.

A plug has already been inserted at one end of a section of the pipe, and water will flush any hydrocarbons away from the weld-site. At the other end, the same will happen in the opposite direction. The isolated section will also be filled with water for the welding of new pipe.

If the work goes to plan, the pipeline should be in operation again on Sunday.

Meanwhile, frustratingly, there are thousands of cubic metres of fuel lying in the pipeline waiting for delivery to Wiri, South Auckland, including 6800cu m of jet fuel.

That fuel will require a settling period and recertification before it can redistributed, scheduled for Tuesday or Wednesday.

The pipeline repair task is being carried out under peer review and utilising international experience and procedures used to repair fuel pipelines and containers in many other countries, Mr Post said.

The $15 million to $20m he quoted earlier this week as the cost is an estimated profit loss, not the repair bill.

"That's forfeited profit margins, so the shareholders will ultimately carry the cost of this."

Other costs, and the full price, would not be counted up until the system was up and running again, he said.