The suggestion comes from a review of investigations into the historic landfill under Kettle Park for the Dunedin City Council by consultancy Beca.
The release of the review comes after the city council put about $38 million in its 2025-34 plan for the remediation of the former landfill. The review, from November last year, was released this month by the Otago Regional Council under the Local Government Official Information and Meetings Act 1987 (Lgoima).
Anecdotal evidence suggested "a wax-wrapped box of machine guns and ammunition from World War 2" was found buried next to the Dunedin Ice Stadium.
The Ocean Beach army battery and firing range were also nearby, the Beca review said.
Although explorations to date had failed to turn anything up, they recommended a desktop exercise be undertaken in order to better understand the site’s use by the New Zealand military, the consultants said.
"Remaining risk could be managed with appropriate procedures and working alongside New Zealand military or specialist third-party suppliers to control and manage the disturbance and disposal."
The city council is due to re-visit options to clean up the historic landfill along the St Clair-St Kilda coast before the end of the month.
For that reason the regional council declined to release a report entitled, "Draft Kettle Park — Review of Assessment of Remedial Options".
That report was due to be presented to the city council on August 26 and would be made public at that time, the regional council said.
However, another Beca review from late last year released by the regional council said the city council needed to better understand the impact on public access, long-term maintenance and potential changes to wildlife habitat of its forthcoming plan to deal with the toxic waste beneath Kettle Park.
Beca reviewed three options put forward to address the threats to the environment and public posed by the historic landfill — which operated from around 1900 to the early 1950s and is now under threat from coastal erosion.
A Beca senior associate said the three options provided "different levels and durations of protection".
They said all three remediation options were "generally sound" but recommended further work on "long-term sustainability, structural design to prevent future outflanking and the logistics of extensive waste removal".
"Public access, long-term maintenance and potential habitat changes should be further explored."
The three options reviewed were using "geosynthetic containers" as reinforcements, waste removal along with "dune reprofiling" or waste removal and a "backstop wall", or rock armouring.
Beca said the three options, advanced in 2023 by Tonkin + Taylor, were developed in order to align with the city council’s St Clair-St Kilda coastal plan.
Accordingly, Beca assumed there was to be no further investigation of alternative options.
Geosynthetic containers offered "an efficient and relatively quick solution" for around 20 years, but could be overtopped by waves in a one-in-10-year storm, which could result in sand dune material that contained contaminants being spilled.
The option of waste removal and reprofiling the dunes with clean sand was advanced with the suggestion that removing waste material up to 50m inland from the beach could be required.
Such extensive excavation, Beca said, could disturb neighbouring areas and measures would be required to prevent environmental contamination.
The review also said "empirical evidence" should be provided to show the new sand dunes would withstand the erosion and storms predicted with climate change.
Waste removal and the installation of rock armouring would reasonably provide a 50-year lifespan for the intervention, the review said.
"And the provision for future adaptation as a conventional seawall is sensible."
However, the review also noted the option did not include a specific plan to prevent coastal processes from "outflanking" the the rock wall.
Further, although rock walls typically offered long-term protection, once exposed they would "alter the coastal landscape and potentially impact local ecosystems", the consultants said.
City councillors discussed coastal hazards at Kettle Park and the St Clair and St Kilda beaches behind closed doors on Tuesday.
