Environmental group Coromandel Watchdog says companies involved in the ownership of the Tui Mine, near Te Aroha, have a moral obligation to contribute to the cost of cleaning up the site.
The former zinc, lead and copper mine near Te Aroha in Waikato is regarded as New Zealand's most contaminated site.
The Government has agreed to boost to $15.2 million its total spending on stabilising the mine, while the Matamata-Piako District Council and Waikato Regional Council will jointly contribute $1 million.
The consortium that once owned the mine went into liquidation and the mine was closed in 1973.
As that was before the Resource Management Act came into force, the company had not been required to file a bond to help cover any pollution problems.
John Drummond, of Coromandel Watchdog, says companies that were part of the consortium are still operating today and they should take some of the responsibility - though he doubts there's much chance of getting any money out of them.
Environment Minister Nick Smith says it's incredibly frustrating that taxpayers have to pick up the tab, but the advice he has from officials is that there is no reasonable legal prospect of being able to recover any of the clean-up costs.
Meanwhile, Tui Mine clean-up project leader Ghassan Basheer says while the technology to be used on the mine hasn't been tried before on an abandoned site, it has been used overseas with success.