Investigators are looking into claims highly toxic waste has been buried in unmapped sites at Tiwai Point's aluminium smelter.
This includes spent cell liner waste that contains cyanide and toxic fluoride, that is banned from being buried untreated in both the US and Australia.
The claims come from former smelter workers detailed in a regional council report.
Phil Pennington has been reading the report. He spoke to Susie Ferguson.
