Around 80 people gathered at the abandoned Tui Mine in the Waikato as the mine's clean-up project moves into its second and most critical phase.

Environment Minister Nick Smith and Green Party MP Catherine Delahunty joined the delegation at the old mine site to learn about proposed works.

Preparation works started at the end of last year for the big clean-up. (Ministry for the Environment)

The works aim to mitigate the present risks to community safety and health, and environmental damage to the mountain, streams and rivers.

Waikato Regional Council's river and catchment services group manager Scott Fowlds says the final phase of the work involves stabilisation and remediation of the tailings impoundment area.

'The waste rock and ore (tailings) from the old mine site will be shaped into a stable landform, drained and capped to secure the site.

'The tailings dam is 25 metres high and includes around 110,000 cubic metres of waste material, which will be treated with lime.”

In the latter part of the second phase the former tailings area will be landscaped, replanted and converted into a useable space for the community.

'The phase two work, projected to cost $16.2 million, started yesterday and is scheduled to finish at the end of 2013. But it won't end there. Ongoing monitoring and maintenance will run through until 2045.”

Phase two is to be funded by the Ministry for the Environment ($15.2 million), Waikato Regional Council ($800,000 in cash), and Matamata-Piako District Council ($200,000).

The Tui mine produced base metals including copper, lead and zinc over seven years before being abandoned in 1973.

Since then the mine and tailings dam have continued to leach heavy metal contaminants into the nearby Tui and Tunakahoia streams, which flow into the Waihou River and downstream into the Firth of Thames.

Scott says the Waikato Regional Council has been working in partnership with the Ministry for the Environment, Department of Conservation, Matamata-Piako District Council and iwi since 2007 to remediate the site and improve the area's water and soil quality.

'The $5.5 million first phase of the remediation project started in October 2010 and is due to be completed in December this year.”

He says this phase has involved detailed investigations, designs and consents, and the underground treatment of polluted mine tunnels and surrounds.