The agency charged with overseeing the Pike River Mine re-entry is considering creating a new tunnel into the drift to act as a second escape route and help with ventilation.
In a statement, the Pike River Recovery Agency chief executive Dave Gawn said creating a new tunnel was one of three re-entry scenarios being considered by technical experts in Greymouth who had met over the past two days.
The tunnel would have a 2m diameter and be about 200 metres long. The other two options included drilling a large borehole or re-entering the main drift as it is with no second exit point.
Gawn said if the tunnel was possible it would provide ventilation, a second means of egress and quicker access to areas of interest to help find out what had happened and to recover any remains.
Drilling a large borehole would assist ventilation and possibly act as a means of escape. The proposals were being worked on further.
Gawn said the agency would continue its planning while it waited for the Minister Responsible for the Pike River Re-Entry to decide whether to give the go-ahead based on an earlier plan sent to him.
"The Pike River families have been waiting for more than seven years now and it's important that we keep the pace up, while not sacrificing any finer details around health and safety," Gawn said.
Family Reference Group representatives Bernie Monk and Anna Osborne were optimistic about the plan.
"These guys are working from a position that we will be re-entering, and a lot of this is standard mining practice around the world. It's been fascinating and positive to hear the details of how they're planning to expel the methane, introduce the nitrogen and then bring in fresh air," Anna says.
A procurement process was underway to find a contractor for the work.
Those carrying out the work would be involved in recovery planning and risk analysis, as well as mine sealing and rehabilitation works at the end of the project.
Little set up the Pike River Recovery Agency earlier this year to plan for a manned re-entry into the drift access tunnel of the mine in which 29 men died following an explosion in 2010.
There has been no entry into the mine since then and Labour campaigned on a re-entry in the last election after the former National Government said it was too risky.
The re-entry attempt is aimed at trying to get further evidence of the explosion and recover any remains that might be in that area.
Gawn said this week a team considering the re-entry looked at ventilation and geotechnical engineering for the re-entry plan.
It consisted of seven technical experts contracted by the agency, the Pike River family representatives and two of their expert advisors, Agency staff, the Minister's Independent Advisor Rob Fyfe, and representatives from the Department of Conservation, Worksafe and New Zealand Mines Rescue.
"The input of ventilation and engineering experts, with the detailed chemistry and geological engineering knowledge in the room, combined with hundreds of years of mining experience, has enabled us to get closer to finalising a preferred option," Gawn said.