Whanganui District Council pipe replacement project coming to an end after more than two years

Stage one of the project involved replacing the pipe as far down as 8m.

A new wastewater pipe along Nixon Street in Whanganui East is nearing completion after over two years of work.

Contractors from Loaders have reached the final intersection, with nearly 900m of pipe laid since the project got under way at Anzac Parade at the start of 2022.

It is replacing a pipe that was installed in 1910.

Whanganui District Council senior stormwater engineer Kritzo Venter said leaving it in place did “not bear thinking about”.

“If it broke at a depth of 8m, that [would become] quite a big issue to sort out.

“It’s an ambulance at the bottom of the cliff. We want to make sure we are at the top of the cliff.”

Stage one of the project, 549m from Anzac Parade to Moana St using micro-tunnelling, was slowed by unstable soil and the discovery of 4575-year-old tōtara between 6-8m down.

Every time the boring machine used by contractors Parkinson and Holland hit timber, a shaft had to be sunk to get it off.

That stretch of pipe cost $2.39 million to replace.

Last December, council signed off $ 1.5m of unbudgeted funding to get stage two finished as quickly as possible, with Loaders adding 326m of sewer main from Moana St to the five-road junction of Raine St, Wakefield St, Nixon St, Burton Avenue and Duncan St.

Loader contractors have reached the Wakefield St junction as stage two of the project nears its end. Photo / Mike Tweed

Parts of Nixon St have been closed to traffic since work began.

Venter said, for the most part, residents were understanding of the disruptions.

“There have been a couple of issues, but the contractors have been good at trying to work with people.

“I think they realise it has to be done.”

Loaders is using a traditional open trenching method for stage two as the pipe is not so deep.

Venter told the Chronicle last year the original pipe was laid entirely by digging trenches.

”It must have been pretty scary, because the only thing we can come up with is they must have used timber shoring to sure up the sides of the trenches.

“Then, they would have sent people down there to lay the pipe. I’d imagine It would have all been hand-dug.”

Stage one is now 95% complete and stage two is at 75%.

“There is another stage required but it’s not as intensive as these works - putting in a rider sewer on the first block [of Nixon St],” Venter said.

“That is at a much shallower level. It picks up the local houses and drains them to a manhole, which drops it into the new sewer main.”

The pipe was identified for replacement through the use of a CCTV (closed-circuit television) camera.

“The company that does the maintenance for our water and drainage network, Veolia, has a robotic camera that goes down the pipe and takes a high-quality survey,” Venter said.

“From there, the pipe gets assessed. We look at structural integrity and prioritise the ones at the highest risk of failure.

“Nixon St has been that one.”

Mike Tweed is a multimedia journalist at the Whanganui Chronicle. Since starting in March 2020, he has dabbled in everything from sport to music. At present, his focus is local government, primarily Whanganui District Council.