Waiuta Prohibition Mine As Good as Gold

Waiuta Prohibition Mine Site Remediation Case Study

From one of the richest gold mines on the West Coast in the early 1900’s to New Zealand’s most toxic contaminated site, remediation work on the Waiuta Prohibition Mine involved a combination of decontamination work and historic preservation.

Department of Conservation

Project Specification:
EnviroWaste was contracted by the Department of Conservation (DOC) to carry out remediation of the Prohibition mine site at Waiuta.

Project Start:
1st August 2016

Project Completion:
28th October 2016

Waiuta Prohibition Mine was opened in 1938 and was the site of a ‘roasting plant’ where arsenic-bearing ore was heated to release gold. Residue from this process contained high concentrations of arsenic which accumulated on the ground throughout the site.

The site was abandoned in 1951, but was later inherited and cordoned off by Department of Conservation (DOC) in 1987. It was not until 2005, that the full extent of the contamination from the historic mine was realised. The arsenic levels in surface water were among the highest recorded in the world, posing a serious risk to people and the environment.

EnviroWaste was contracted by DOC to carry out remediation of the Prohibition mine site at Waiuta. The remediation plan had four objectives:

Improve the water quality both on and offsite to acceptable levels,

      • Reduce the risk of exposure to contaminated soil and air to acceptable levels,
      • As far as practically possible, retain the historic fabric of the site and
      • Ensure the remediation exemplifies best practice.

Health and Safety was an extremely important aspect of this project, with a large amount of time and cost allocated to the protection of personnel health and site specific safety compliance.

The remediation of the site began on the 1st of August 2016. The work consisted of the removal of 96 drums of high level arsenic contaminated material for treatment at a hazardous waste facility, and the construction of a lined and capped containment cell, for the safe onsite disposal of lower level arsenic contaminated soil and other debris.The site was then capped with a layer of mullock to isolate any remaining residual arsenic contaminated soil, providing a safe layer of protection for the public. The concrete foundations of the historic mine were cleaned, removing contaminated dust and sediment. Some of the concrete areas which still contained elevated levels of arsenic after high pressure water cleaning, were coated with a concrete sealer to provide additional protection for visitors. Stormwater was diverted around the site via a series of swale drains, some lined with cement, to prevent further water contamination and erosion issues.

Following completion of the physical remediation works, the entire Prohibition mine remediation area was checked and validated for the presence of arsenic. Over 260 individual tests were carried out using x-ray fluorescence (XRF) soil testing technology. Results showed that arsenic levels were well below the target levels specified in the Remediation Action Plan. On-going testing of the area wlll safeguard both the surrounding environment and visitors to the site.

Feedback from Mark Davies, DOC Director Operations, Western South Island; “The EnviroWaste Technical Services team has worked in partnership with DOC, bringing their expertise, their commitment to worker and public safety, and their integrity to bear in the remediation activities for the Waiuta Prohibition mine site. They have delivered a timely and cost effective remediation solution to very high standards that paves the way for DOC to re-open the site so that visitors can safely explore, understand and appreciate its historic value.” 

Pictured: The Waiuta Prohibition Roasting Plant Site

Waiuta Mine