Quick action to contain and recover fuel-soaked earth and water near the ruptured oil pipeline at Ruakaka appears to have prevented widespread contamination.
Refining New Zealand has been in charge of collecting and removing the material and monitoring the site for hydrocarbons, in preparation for a complex operation to remove and replace a short section of failed pipeline.
Northland Regional Council staff have also been monitoring the effects of the leak and the recovery process to ensure it carried out appropriately and a suitable remediation plan is implemented.
At this stage that is the council's primary focus, a spokesman said.
"The council remains satisfied the clean-up and repair operation is being carried out appropriately in the circumstances."
Council staff have sampled groundwater bores and ditches in the vicinity to establish existing water quality parameters.
"Yesterday was the first time we have collected water samples for analysis."Earlier there had been a layer fuel still sitting on top of the water, making sampling for its presence unnecessary.
It could be 10 days before the required test results are known.
NRC staff are planning a water sampling programme but it is not known yet for how long.
Several of the bores tested had not been working for some time and were abandoned, while others were still being used.
Department of Conservation (DoC) staff have conducted a visual inspection of the Ruakaka Wildlife Refuge on the coast two kilometres away and are confident there is no contamination from the air fuel spill.
DoC will continue to monitor the situation and work with NRC.