A report on the risks associated with New Zealand's most toxic site will go to the Government soon, for a decision on funding its clean-up.
The Tui Mine, near Te Aroha in Waikato, was a copper, zinc and lead mine that was closed in 1973.
Since then it has been leaching contaminants into nearby waterways, and the tailings dam is unstable.
Waikato Regional Council says $4.5 million has been spent on engineering investigations and trials in phase one of the clean-up of the mine.
Council project manager Ghassan Basheer says another $13 million will probably be required to complete the work.