Northland Regional Council has released a list of 32 sites in the region that are contaminated with chemical waste.
Councils around the country are preparing similar lists, after an ombudsman's ruling that such information should be available to the public.
The Northland council says most of the contaminated sites it has listed are garages, landfills and timber mills where petrol-based products or chemicals such as copper, chrome and arsenic have seeped into the soil.
There are also more than 500 sites where hazardous substances are kept, or have been in the past, and could cause contamination if they escaped from safe storage.
The council says it is satisfied all the sites are well-contained, monitored and managed.