New borehole into Pike River mine could investigate cause of explosion

Tuesday, 15 December 2020

Pike River Recovery Agency staff open and walk through doors at the 170m seal. (Video first published December 17, 2019)

A camera may be fed down a new borehole at the Pike River mine to investigate one of the possible causes of the explosion that killed 29 men.

Police are still investigating any criminal culpability for the 2010 disaster with the help of a $50 million Government-funded re-entry of the mine’s access tunnel (or drift).

The re-entry will be completed early next year and the mine handed over to the Department of Conservation, which will add a memorial walk to the Paparoa Track in April or May.

However, police may continue their investigation at the mine using new boreholes to examine one of the possible causes listed by the royal commission into the disaster.

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A piece of debris recovered from the Pike River mine drift, believed to be a piece of the mine’s main ventilation fan.

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A map of Pike River mine from the royal commission, which shows the area called the goaf.

A briefing to Minister Responsible for Pike River Re-entry Andrew Little, released publicly on Tuesday, says the aim of the boreholes was to get “additional information on mine infrastructure and conditions, and on the location of other evidence”.

The boreholes would be drilled by contractors after the mine drift was recovered, it says.

A police spokesperson said an “initial high-level feasibility study” had been done to investigate whether more boreholes were needed to support the ongoing investigation.

Police would now look at a more detailed timeline and cost, she said.

She did not answer questions about whether robots would be used or how many boreholes would be drilled or where they would be drilled.

Flames burn from a ventilation shaft above the Pike River mine after the November 2010 explosion.

Pike River widow Anna Osborne said she understood a possible new borehole would look at an area called “the goaf” to examine whether it had collapsed.

The royal commission into the disaster, held in 2011, said mining experts found a substantial volume of methane fuelled the explosion.

“The area most likely to contain a large volume of methane was a void (goaf) formed during mining of the first coal extraction panel in the mine,” it said.

“A roof fall in the goaf could have expelled sufficient methane into the mine roadways to fuel a major explosion.”

It also found Pike River Coal had ignored raised methane levels in the weeks leading up to the explosion, and the Government failed in its regulatory oversight of health and safety at the underground coal mine.

Osborne said it was important to confirm whether the goaf’s roof collapsed or not.

“It hopefully will answer questions. I’m very happy that the police are exploring the options and taking their job seriously,” she said.

A roof fall in the goaf could explain how a large volume of methane fuelled the explosion while the ignition source remained a mystery.

The commission listed potential ignition sources as arcing in the mine electrical system, a diesel engine overheating, contraband taken into the mine, electric motors in the non-restricted part of the mine, or frictional sparking caused by work activities.

Bernie Monk, whose son Michael died in the mine, said he hoped robots would be sent down any new boreholes so more of the mine workings could be explored.

He said police could also use an open pipeline leading from the drift into the mine workings to deploy a robot. He hoped it would find the site of the explosion, as well as any bodies of the 29 men.

“We have so many questions that can be answered if they look further into the mine. I hope the police do the right thing and put a camera and a robot down. If they don't, the cover-up continues,” he said.

State-owned mining company Solid Energy, which took ownership of Pike River mine in 2012, completed a comprehensive design study in 2017 exploring whether they could use a borehole vehicle that could travel up to 300 metres in any direction. The study was published on the Pike River Recovery Agency website.

A briefing to Little in 2017 estimated drillholes would cost between $200,000 and $500,000 each, excluding the cost of the robot.

The agency recovery team was close to reaching the Rocsil plug installed 2.2 kilometres up the drift. It would then use breathing apparatus to explore the area between the plug and a rockfall, as well as 600m of roadway in an area off the drift called pit bottom in stone, which held key electrical equipment.

The briefing to Little says the agency had no mandate to explore or enter the main mine workings beyond a “major” roof fall at the end of the drift. The agency would be disestablished in 2021.

It had a $50.5m budget, including $4.2m of contingency funding, and had spent $40m so far.