The site of the broken pipe. Photo / Georgina Campbell
Wellington Water has managed to block and isolate a broken water pipe in a race against the clock to prevent wastewater spewing into the harbour.
A pipe burst at the intersection of Victoria and Mercer Sts yesterday.
The break is in a 300mm diameter cast iron pipe that was built in the early 1900s.
Wellington Water chief executive Colin Crampton told the Herald the pipe was reaching the end of its useful life and was in the company's programme for renewal or replacement in 2-3 years' time.
The hole or split is a relatively modest size in terms of the actual defect, but is problematic because the area is pressurised, Crampton said.
"Wastewater comes from businesses and residents and it flows down to the harbour edge, where it's contained in tanks and is pumped back up to the main tunnel that goes to the wastewater treatment plant.
"So, because it's under pressure, it means it gets forced out of that defect and is obviously much more tricky than if it was just a gravity flowing main."
Crampton said they had hoped to complete the repair overnight, but it was more complex than first thought and would now take three days.
This morning their focus changed to digging down in a different place to block and isolate the broken section of pipe, which was successfully completed this afternoon.
This means some pumps can resume removing wastewater from tanks underneath the Michael Fowler Centre and send it to a treatment plant.
Earlier today Crampton described the situation as having reached a "very fine line".
"We're on the cusp at the moment of filling all of our storage up and so if we can't get this stopper put into the pipe and resume pumping during today, we will find it very hard not to cause an overflow into the harbour, he said.
"We see it as a matter of hours now and we have all of our people down there on site ready to get into gear if that was to occur."
Sucker trucks are on site to help manage the risk.
Wellington Water thanked residents and businesses who reduced wastewater flow during the day by flushing the toilet only if essential and not using inside drains.
Some will have to continue taking these measures, although the affected area of the CBD has been significantly reduced.
It's expected the network will neutralise by this evening.
There will be some disruptions for local residents and businesses for a few more days, and Wellington Water is continuing to monitor harbour waters.
The Whairepo lagoon and diving platform are still closed as a precaution.
Mercer St remains closed and no traffic on Victoria Street can travel past Harris St.
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