The Christchurch City Council is analysing a list of more than 300 properties it owns that may be contaminated.
Affected properties include social housing, parks, reserves and cemeteries identified by Environment Canterbury (ECan) and added to its Listed Land Use Register in May.
Council strategic property analyst Tim Priddy said the original list provided by ECan included 394 entries.
He had whittled it down to 315 properties but was still grappling with duplication and other anomalies.
The Barbadoes St Cemetery shows up on the list under three different addresses.
A Linwood social housing complex called Sandilands comprises 25 separate addresses while other social housing complexes are listed as a single address.
"We're focused on housing for obvious reasons," Priddy said.
The council has hired consultants to undertake preliminary site investigations at its social housing sites. Some of them were identified as potentially contaminated about 10 years ago and were tested. Some were remediated.
Some Ministry for the Environment standards had since tightened and desktop work would determine whether more on-site work was needed, Priddy said.
ECan identified the council-owned sites as part of a city-wide effort to alert landowners that their land was potentially contaminated but stressed inclusion on the register did not mean those sites were at risk.
Health officials warn affected residents should take precautions, such as washing hands and vegetables before eating.
Priddy said many of the council-owned sites were listed as parks, including local, regional and sports parks. "We're working through the list," he said.
If preliminary work show concerns, the council would investigate further, Priddy said.
"The cost goes up significantly but if we need to, we will do it."
Among the council-owned sites suspected of contamination are a block in Ferrymead between Ferry Rd and the Heathcote River. It was known as Ferry Road Landfill No 67 and in the 1920s as McGregors Tip.
ECan notes show it the site of a "large toxic waste industrial dump" in which oils, chemicals, concrete roading, Sumner gas works refuse and "possibly some domestic rubbish" was tipped.
- The Press