Concentrations of copper, lead and zinc were generally raised across all locations tested by Tonkin + Taylor in an investigation of Kettle Park at St Clair.
Several samples had very high concentrations, the environmental and engineering consultancy said.
Most results for the three metals exceeded screening criteria for a Ministry for the Environment class-A landfill or the private Burnside landfill.
The results indicated landfill materials would require some form of pre-treatment to reduce leachability.
Pre-treatment options would also need to consider the management of asbestos in soil.
Excavating the site has been flagged by the Dunedin City Council as one possible long-term remedy for Kettle Park, but the cost could run to tens of millions of dollars.
Options are to be weighed up when the council considers its 2024-34 long-term plan.
Short-term options included continuing to protect the toe of the sand dune by the park while monitoring the dune face, a council spokesman said.
Councillors were due to discuss the Tonkin + Taylor study today.
A council staff report said contaminants in the landfill and capping materials were at concentrations that presented a potential health risk, but they were covered by layers of topsoil and turf.
The health risk for users of the sports fields remained low.
Kettle Park operated as a landfill from about 1900 to the 1950s.
The landfill was capped in the 1960s and sports fields were developed there.
A series of storms in the past 10-15 years had eroded the dune system and continued erosion presented risks of exposing the waste itself, Tonkin + Taylor said.
Its latest report included analysis of samples from 60 bore holes down to a maximum depth of 7m.
The landfill site was both larger and closer to the sea than the council had thought.
The consultancy’s report and its drilling programme cost $128,000.
The additional cost of further investigations was yet to be confirmed.
