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Before the site was sealed in 2005, about 300cum of tar was removed from three above-ground tar holding tanks, stabilised with lime and cement, and disposed of in a hazardous waste cell at the Green Island Landfill.
No additional hazardous waste from the gasworks tar pit had been deposited at the Green Island landfill, the spokesman said.
The council decided to manage the material in situ while it was assessing options for the remediation of the site, he said.
A feasibility study for the site notes the council prefers a remediation option that uses offsite disposal because that method could ‘‘completely remove the contaminants from the site and therefore ensure the environment is protected’’.
The study assesses disposal at Green Island, Burnside Landfill in Dunedin, AB Lime at Winton, Kate Valley Landfill in North Canterbury, and Redruth Landfill in Timaru.
The Green Island Landfill receives the lowest score in the study.
Burnside Landfill receives the highest score.