The Department of Conservation has 305 potential or fully identified contaminated sites across the West Coast.

And of those - either contaminated or potentially unsafe - 246 are associated with historic mining activity and 27 with landfills.

Western South Island acting statutory manager Scott Freeman told the West Coast Conservation Board’s May meeting that there were a lot of “potentially” contaminated sites across the region.

There were 305 “that we know of” and which were tagged and mapped within the department’s internal GIS system.

At the same time it had begun work on some of those sites.

The contaminated former Prohibition gold mine workings at Waiuta along with the nearby Prohibition site were the most prominent to date.

Freeman said that at the same time there were 19 landfill sites in the region yet to be assessed which in light of “climate change issues” was going to require a higher focus.

DoC Western South Island director Mark Davies said the West Coast sites were part of a nationwide programme by the department and would take years to be systematically addressed by the department.

 “The highest priority on the West Coast is the Snowy River site. This is very much a matter for DoC and the West Coast Regional Council.

“All I can say is the programme is a very high priority for the department. We have got a funding programme sitting behind it.”

Board member John Taylor noted the contaminated list included coal mine sites.

Davies said this only applied to those sites where “contamination has been identified”.

“All I can assure the board is our database is absolutely complete.”

A condensing tower at what was this country's most toxic site, the historic Prohibition gold mine at Waiuta. Photo / DoC

Taylor, a geological engineer for many decades, said he believed he knew of other sites not yet on the database but was happy to share that knowledge.

Freeman’s report to the board noted “numerous potentially” contaminated sites in the region on land administered by DoC.

“These sites have been used for mining, fuel and chemical storage, cemeteries, landfills and a range of other potentially contaminating activities,” he said.

But given the rich geological diversity in the region, there would be numerous sites where contaminants occurred naturally “at significantly elevated concentrations.

“Nearly all these sites are yet to be investigated, so the potential risk to natural and historic heritage, ecosystems, the health of conservation workers, and or visitors to the conservation estate is largely unknown.”

Freeman’s report noted two types of site: contaminated, and potentially contaminated.

The first were sites already investigated and confirmed to contain contaminated soil from past hazardous material or activity.

The second were sites with potential contamination and included on the Hazardous Activities and Industries List (HAIL) - which were required by regulation to be investigated.

 “Both contaminated sites and HAIL sites are registered on council databases.”

All sites on DoC-administered land had been identified and registered.

“There are 305 contaminated/HAIL sites in the Western South Island.”

For the Prohibition site the department undertook a $2.6 million clean-up from 2016-18 of what had been assessed as the most toxic mine site in New Zealand and the second most arsenic-contaminated site in the world.

Some of the identified landfills include old dumps previously used by the small communities scattered along the 650km West Coast.

A well-known example is the former Westland District Council Fox Glacier dump which spilled into the Fox River in March 2019 during a weather bomb - sparking a major environmental disaster.

The dump’s contents were strewn down 21km of the Fox riverbed through the Westland Tai Poutini National Park and then along 64km of coastline.

The subsequent massive clean-up cost over $3.3 million.