The go-ahead has been given to dredge Whangārei Harbour so bigger crude oil cargoes can come in to the Marsden Point oil refinery.
Resource consents have been approved for Refining NZ (RNZ) to take 3.7 million cubic metres of sand off the seabed to deepen and realign the current channel.
Massive Suezmax tankers already visit the refinery but can only do so 90 per cent full because of the current channel's depth.
A deeper channel would see half of all crude oil imports — around 20 million barrels a year — brought in on ships carrying around a million barrels at a time. Cargoes arriving at the refinery at the moment are typically 600-700,000 barrels.
RNZ said the six-month dredging job would be scheduled to start in 2020. As well as the $37 million cost of dredging, RNZ would spend $20m on extra tanks to store the increased volume of crude oil.
Commissioners Sharon McGarry (chairwoman), Dr Rob Lieffering and Sheena Tepania heard the company's applications on behalf of the Northland Regional Council (NRC) over seven days during late February and March. Their decision has been released in a 140 page report.
They approved 13 consents, most valid for a 35-year period with those relating to navigational aids given 25-year consents.
Of 49 submissions to the RNZ application that was publicly notified in September last year, 18 were in support, 29 opposed and two were neutral.
Supporters said the project would have positive economic and environmental benefits for Whangārei and Northland, and there would be less environmental impact or danger with fewer tankers visiting the harbour. It was not a view shared by all who made submissions.
Opponents' wide ranging concerns included a lengthy list of cultural issues and fears the risks of oil spills or accidents would increase with the fully laden tankers.
They expressed concern that real impacts might differ from RNZ computer models and would not be ''minor''.
They also questioned the effects of the project on local commercial and recreational fisheries. Some said there had been inadequate consultation on those associated areas.
A major issue was the stability of nearby Mair Bank, with concerns about the proximity of dredging and spoil disposal sites to the already fragile and compromised Mair Bank, the Motukaroro Marine Reserve or other sensitive ecosystems.
The commissioners said the project was "unlikely to have any significant adverse effects on the environment and is generally consistent with the relevant statutory planning documents and provisions".
They said they paid particular regard to potential cumulative effects and the importance of maintaining the long-term stability of Mair Bank.
"In taking into account the existing environment, we conclude that the applicant's final proffered conditions, as changed by us in this decision, adequately avoid, mitigate or remedy the actual and potential effects [to] a level that they are not significant and are, in our view, acceptable.''.
The decision is subject to appeal for 15 working days.