The Tui mine in Te Aroha, the most contaminated site in New Zealand, has been cleaned up. The work took 2½ years and cost almost $22 million.
The mine, which extracted copper, lead and zinc sulphides, has been leaching heavy metals since it was closed in 1973.
Radio New Zealand's environment reporter said enough concrete to build a 50-storey building, eight thousand tonnes of lime, 14,000 tonnes of rock and gravel, and 20,000 tonnes of clay and topsoil were needed to stabilise the mine.
Cement and lime was also injected into the old underground workings to reduce the amount of contaminants leaching into the Tui and Tunakohoia Streams.
The clean-up had been planned for 15 years and began in 2011 when the Government agreed to pay $21 million towards the cost. The remainder was covered by councils.
The mine was in operation for only five years. It closed when its owners went into receivership, and has not been mined since.
Between 1967 - 1973 copper, lead and zinc sulphides were extracted. Waste, rock ore dumps and mine tailings, made up of zinc and cadmium, were left behind.
The site is now grassed over.