Fire and Emergency is preparing to destroy 61,000 litres of foam concentrate it has detected nationwide.
The concentrate - enough to make half an Olympic swimming pool full of foam - is all non-approved B Class foam for fighting petrochemical fires.
Some of it may contain banned and hazardous PFAS (per and polyfluoroalkyl substances) compounds.
Some of it is old, predating a 2006 ban on some foams, and some was impossible to identify, so a cautionary approach was being taken to get rid of it, Fenz said in a statement.
"It has not been specifically tested for PFAS compounds, but is all being treated as containing PFAS for the purposes of disposal."
This follows Fenz's December 2017 moratorium on using any Class B foam concentrates that have not been tested by ESR and confirmed as PFOS (perfluorooctane sulphonate) and PFOA-free, in accordance with the Hazardous Substances and New Organisms Act standard.
It is being stored at 13 sites around the country, double bagged and in areas designed to contain any spills.
Hastings fire station, for instance, has 4000 litres of non-PFAS foam believed to have been inherited by Fenz from the petroleum industry in the 1990s.
All 61,000 litres will be exported by ship in November for controlled incineration, in the same way foams containing PFAS are.
"We are using a professional, independent certified hazardous chemicals and waste disposal company," Fenz said.