15 years, $107m: Celebrating Tauranga City Council's Southern Pipeline

Southern Pipeline project director Steve Wiggill. File photo

The conclusion of what's thought to be the biggest infrastructure project Tauranga City Council has ever completed was celebrated last night.

The Southern Pipeline project took 15 years and cost $107 million, with more than 500 people having a hand in bringing it to fruition.

It was designed to accommodate future growth in several suburbs including Welcome Bay, Hairini, The Lakes, Pyes Pa and Tauriko, providing capacity through to 2050.

It would also take the pressure of the Chapel St wastewater treatment plant, reducing the risk of an overflow of raw sewerage into the Tauranga's streets or harbour.

Early planning work started in the 1990s with the first contract for professional services signed in 2005 and construction starting in 2009.

The pipeline was commissioned in October last year, taking the first of what people in the wastewater business discretely refer to as "flows".

Some of the key players who worked on the project gathered at Baycourt last night to have a drink, remember the journey and celebrate the completion of the work.

In all, the project involved laying about 10km of pipelines connecting the city's two wastewater treatment plants at Te Maunga and Chapel St, as well as building new pump stations.

Cranes lined up to lay pipe for Southern Pipeline in July 2018. File photo

About 1.5km of that 10km crossed the Tauranga Harbour in a horizontally drilled tunnel up to 35m underground between Matapihi and Memorial Park.

It was by far the riskiest portion of the project and caused contractors many headaches, according to project director Steve Wiggill.

Wiggill, an engineer specialising in water, joined the project in 2016, just as the harbour crossing was about to start.

The crossing was beset by challenges that put the project behind schedule by around 10 months.

The most devastating, Wiggill said, was when a reamer in the drilling rig struck a piece of 51,000-year-old timber deep under the harbour and broke.

That problem, and many others - big and small - were overcome to bring the project to a conclusion.