Cleaning up a historic mine site to make it safe for visitors

Historic Waiuta Gold Mine Site Remediation

Once in full operation during the early 1900s, the Prohibition Mine at Waiuta township processed arsenic-bearing ore by heating it to release gold. Abandoned in 1951, the mine’s now surrounded by mining relics and a ghost town. The gold processing area is a historic site that the Department of Conservation wanted to open to the public. The challenge? The site was heavily contaminated by high concentrations of accumulated arsenic on the ground and in the surface water—and the Department needed to make the site safe for visitors.

We provided detailed engineering and scientific oversight for the Prohibition Mine Contaminated Site Remediation project. Performing a technical peer review of previous remedial works, we identified any knowledge gaps and analyzed possible remediation options for the site—identifying and assessing six options. The preferred choice? A composite of on-site excavation, deposition, and in-situ covering, with the most heavily contaminated soils removed for off-site disposal. On-site waste rock tailings, known as mullock, from the original mine shaft were used as compacted site cover. A set of clean-up objectives was established for arsenic in site soils and in surface water leaving the site.

The outcome? The final remediated site meets all the remediation objectives—it’s aesthetically pleasing and safe for visitors to observe the historic mining features.