Watercare’s $1.2b Central Interceptor project sees busiest year

There’s nothing like a tunnel boring machine (TBM) shaft break-through to get the blood pumping. And the recent completion of the first link sewer to connect to Watercare’s main Central Interceptor tunnel was the cause of real celebration for the whole 500-strong project team.

t’s the first major construction milestone of 2023 for New Zealand’s largest wastewater project: to build a 14.7km underground wastewater tunnel from Māngere to central Auckland. The tunnel will significantly reduce wet-weather overflows into waterways by taking combined stormwater and wastewater to Māngere Wastewater Treatment Plant for processing.

Link Sewer C is the first of two connecting sewers to be completed. Watercare Central Interceptor executive programme director, Shayne Cunis says the milestone is one to savour: “We’ve been through a global pandemic, closed borders and floods. It’s a great achievement for the Ghella Abergeldie JV tunnellers to finish tunnelling safely and four weeks ahead of schedule.”

The micro-tunnel boring machine is being refurbished before starting link sewer B in late July. It will run from Rocket Park, Mt Albert to Rawalpindi St, just over one kilometre away.

Meanwhile, across town, in Hillsborough, Hiwa-i-te-Rangi is quietly building the main tunnel. She is more than five kilometres from her starting point at Māngere in 2020 and at 110 metres, is in the deepest section of the entire journey. Tunnellers travel half an hour to reach the tunnel boring machine via electric locomotive.

Elsewhere, most of the project’s 17 shafts are well underway. Large cascade drop-shafts are being installed, to dissipate the energy of wastewater as it drops from the existing wastewater network to the Central Interceptor tunnel. The liners are transported from the port at night, due their large size.

Also hitting the streets: three new Central Interceptor electric tipper trucks have joined the fleet. The e-trucks transport excavation materials to Puketutu Island, Māngere where Watercare is carrying out a rehabilitation project at a former quarry.

The e-trucks were manufactured by XCMG, a leading global e-truck manufacturer in China and have a special fast battery swap system. Each vehicle can transport up to 13 tonnes of material, with an average range of 200km and produce 79% less CO2 emissions compared with their diesel counterparts.

Shayne Cunis says they are an exciting addition: “The Central Interceptor is a stand-out project in terms of safety and expertise. The e-trucks will provide huge carbon savings through zero emissions and are performing as well as their diesel counterparts.”

In coming months, a decision to extend the Central Interceptor tunnel to Pt Erin will be known. Resource consent applications were lodged in February and the entire project is now expected to be completed in 2026. The May Rd, Mt Albert south section (including Link sewer C and the main tunnel) will be operational ahead of that deadline.