Last year's ANZAC Day oil spill was an accident waiting to happen says Judge Jeff Smith in Tauranga District Court today.

Mobil was fined $288,000 for the April 27, oil spill, in which between three and six tonnes of heavy fuel oil flowed into Tauranga harbour from under the Mount Maunganui wharf.

Mobil is fined $288,000 for the Anzac oil spill. Photo: File.

The oil company pleaded guilty to a single charge of discharging into the environment in December 2015.

Ninety per cent of the fine will go to the Bay of Plenty Regional Council to help offset the more than $300,000 cost of the prosecution. The shortfall will be met by the ratepayer.

'There may need to be some review of the legislation,” says the judge.

The under wharf bunker fuel system comprising a main 250mm pipe about 2.7km long, with offshoot laterals to the 11 Mount Maunganui berths could only be shut off at the main pump.

When a ship at the northern end of the wharf was being refuelled as was the case on April 27, 2015, the whole system including all 21 laterals to the berths was pressurised to 100psi for the main pipe.

The pipe leaking the estimated 3-6 tonnes of heavy fuel oil into the harbour was 30 years old and was flagged in two separate reports by oil and gas technologies specialist and a Tauranga engineering company.

Also in the agreed summary of facts, a council officer John Holst told the Mobil terminal manager, the part of the pipe leaking along with the associated valve was evidence in the council's investigation. When it was cut from under the wharf it was to be stored in a locked council storage facility at the port, where it could be analysed by both the council and Mobil experts.

The council officer thought he would be contacted as soon as the damaged pipe was cut free. Instead it was taken to Mobil's yard. On April 29, the regional council obtained a search warrant and took the pipe.

When the regional council required from Mobil, all the documentation it possessed on the pipes. The two reports recommending the work were not included and were only provided later on specific request, says Judge Smith.

Systemic failure by Mobil Oil NZ was discussed Judge Smith and the lawyers for both the Regional Council and Mobil before setting the amount of the fine.

The failure was either in Mobil Oil, a company that either did not know the significance of cracking and swelling in a steel pipe carrying hot oil under pressure and ignoring the reports – or it was systemic in the reports were not included with the rest of the pipeline documentation, and maybe the company didn't know the state of the pipeline.

Mobil Oil NZ has so far paid $1.187 million for the regional council clean-up costs with a $600,000-$700,000 bill from the Tauranga Bridge Marina yet to be paid.

Mobil Oil has since carried out major modifications to its under wharf bunkering system. The number of laterals has been reduced from 21 to seven.

Each lateral pipe now has an isolation valve so when a ship is being refuelled, only the single line is pressurised. Mobil has sought and obtained resource consent for the new system.