Rogue bore gets sealed off

Contracted workers set about sealing off the bore in the service lane between Amohau and Eruera streets. Photo / Stephen Parker

A rogue bore which exploded in the city recently has been killed, the council says.

The abandoned bore in the service lane between Amohau and Eruera streets sprang to life this month, spraying water and steam 15m into the air.

A sudden air pressure change, coupled with ground movement over time that loosened the ground around the bore, caused the explosion, said Garry Brown, general manager of Rotorua Well Drilling.

"The bore was 94 metres down into the ground but was a relatively low pressure bore.

"We've dealt with a few of these over the years. It's nothing new for Rotorua - but this one was pretty stubborn."

Mr Brown said his team had to get cold water flowing to the bore to quench it before they could get down the hole to seal and re-grout it.

Rotorua Lakes Council geothermal inspector Peter Brownbridge said about two incidents like this occur per year.

"We've monitored it since last Friday, no sign of heat or gas coming up, so with the grouting now done we're confident we've killed the bore."

Geoff Rice, who owns 1144 to 1152 Eruera St, said it was lucky there was not a car parked or person over the bore at the time of the explosion, but was content with the council's response.

"They seem to have gotten on top of it and that's the main thing - it's definitely sealed."

Mr Brownbridge said the bore's location was noted by the council who would now reinstate the alleyway, which would be finished in a few days.

"Shutting this bore down has been quite a job. We're pleased it's now done."

Exploding bore

* Exploded on August 9, spraying water and steam 15m in the air.

* Air pressure change and loosening of the ground behind the explosion.

* The bore was 94m deep and was drilled in 1974.

* Council workers had to quench the bore by pouring cold water over it, before grouting a fine cement, which was forced into the bore under pressure.

* The council deals with about two incidents like this per year.