A technically challenging project to remediate an abandoned mine site by treating heavy metal contamination has recently been completed.
Tui Mine, 2km from the Te Aroha township, was abandoned in 1975 and became one of the most contaminated sites in NZ. The underground workings, waste rock stockpiles, former processing plant and tailings dam all contributed to adverse affects on the surrounding environment.
The site was operated as an underground mine from 1967 to 1973, extracting metals such as copper, lead, zinc, silver and gold.
“T&T staff have played a major role in bringing a successful conclusion to this project,” says Waikato Regional Council Chief Executive, Bob Laing.
T&T provided project technical support, peer review and ongoing technical advice that influenced the way the mine has been successfully remediated.
T&T also made a significant and influential contribution to the success of the project as Engineer to the Contract and Engineer’s Representative; so far undertaking more than 180 site inspections over the last two and a half years. These roles have included:
- Contract management of two construction contracts totalling over $15M
- Health and safety monitoring
- Quality control monitoring
- General construction supervision
- Provision of technical advice
- Provision of project management support.
Before the remedial work, the mine's tailings dam could have collapsed in an extreme weather event or a moderate earthquake, sending toxic waste toward the town of Te Aroha, requiring residents to be evacuated.
The tailings dam was de-constructed and re-shaped into a solid and stable landform. Another dam was constructed out of concrete within the mine and now retains up to 50m of water, flooding the lower levels of the mine.
The clean-up required more than 170,000 tonnes of contaminated material to be treated on-site. Approximately 10,000 tonnes of cement, 8000 tonnes of lime, 14,000 tonnes of rock and gravel, 10,000 tonnes of clay and 10,000 tonnes of topsoil were transported to the site.