The dismantling of the former Marsden Point oil refinery is on track to finish by the middle of next year.

The refinery closed and became an import-only terminal earlier this year.

The owners Channel Infrastructure have budgeted $220 million for decommissioning the site.

Chief executive Naomi James said the project is more than 70 percent complete.

"And then ultimately the facilities will be left in a state when they are safe and ready for demolition, and then at a future date there will be a demolition and removal of the structures that remain."

James said groundwater remediation is also ongoing.

The company's testing shows contamination is reducing onsite, she said.

The closure of the refinery has raised questions about New Zealand's future fuel security.