Pike River plan cheapest and ‘least complex’

A plan to re-enter the Pike River mine drift with no second means of escape is technically feasible and achievable safely, backers say.

The Pike River Recovery Agency – a stand-alone government department set up in November 2017 – recommended the single-entry plan approved yesterday by minister Andrew Little.

It includes breaching the two seals at 30 metres and 170m, purging methane using nitrogen, and bringing fresh air into the tunnel up to the rockfall blocking the mine workings at about 2.3km. Three boreholes would be drilled to help ventilation.

Specialists, including a forensic search team and experienced underground miners, would then enter the tunnel in stages.

The agency’s report to Little says the single-entry option has

118 high-level risks and 308 hazards. It is the cheapest option at $36 million – $13m over the original budget. The small tunnel would have cost $49m and the borehole option would have been

$41m.

Mines rescue staff have previously walked up to 300m into the mine, while robots with cameras have been up to 1500m. The unexplored section, where it is possible bodies could be found, is about 800m. The main forensic area of interest, where electrical and circuitry equipment that may point to a cause is, is about 1900m.

The other two re-entry options were a second small tunnel and a large diameter borehole, which would have provided a second means of escape for recovery specialists in the event of tunnel collapse or fire.

Agency chief executive Dave Gawn, chief operating officer Dinghy Pattinson, the families’ expert Tony Forster and Bathurst Mining chief executive Richard Tacon had all agreed single-entry was the best option.

Pattinson said the announcement was ‘‘fantastic news’’. He was part of the mines rescue team that went into the drift as far as

300m, and put in a seal at 170m. ‘‘I think it’s a good solid plan we’ve got. For me, it’s been unfinished business.

‘‘When I went in to put in the

170m seal we left a note on the wall to say we’d be back, so this is the start of it.’’

The borehole option – opposed by the families’ expert – did not meet requirements to be classed as a second exit, he said.

‘‘The single-entry plan is not without its challenges but the risks can be managed,’’ Pattinson said.

The single-entry plan could be done by December 2019, and the site handed back to the Department of Conservation by June 2020.

Police have said they would do a risk assessment of the plan before making a decision on whether their staff would enter the mine.