The contaminated site covers half a hectare and was inherited by the Department of Conservation (DoC) when it was formed in 1987.
Ms Adams said the Government had committed $28 million towards cleaning up contaminated sites and the Prohibition site would cost $600,000 to fix.
"Clean-ups have been completed on the old pesticide plant at Mapua and more recently on the Tui Mine site at Te Aroha in the Waikato. This Prohibition Mine site is now our top priority for clean-up."
The clean-up plan being developed by DoC is likely to involve cleaning the condensing tower, removing arsenic-contaminated soil, securing it in sealed barrels in a watertight pit and capping the surface around the pit and tower.
The remediation will also involve a water treatment plant.
The cost will be equally split between the Environment Ministry's contaminated sites remediation fund and DoC.