Central Interceptor - ISCouncil

Central Interceptor

Project Details

  • Project Owner: Watercare Services Ltd
  • Rating Type: As Built Design
  • Registered Date: March 2020
  • Location: NZ
  • Assessor Name: Olivia Philpott
  • Stakeholders: Ghella-Abergeldie Joint Venture, Jacobs

This project by Watercare Services Ltd has achieved a V 1.2 Leading Design Rating .


The Central Interceptor is New Zealand’s largest wastewater tunnel project, consisting of a 14.7 km main tunnel, multiple shafts, a major pump station and substantial wastewater network infrastructure. It is located in Auckland and will run underground from Grey Lynn, to Watercare’s Māngere Wastewater Treatment Plant.

A Tunnel boring machine will be employed to build the underground tunnel, which lies between 15-110 m below the surface and has an internal diameter of 4.5 m. Most of the construction will be underground and includes structures at the connection points such as access shafts, drop shafts, flow control structures, overflow structures, grit traps, air vents and air treatment facilities. The construction period for this project is expected to be 6 years.

The Central Interceptor will reduce combined wastewater and stormwater overflows that currently flow into urban waterways and beaches. It will also duplicate a critical section of our network under the Manukau Harbour.

Key Achievements

  • Applying the IS design rating to a completed design retrospectively and achieving the highest possible rating.
  • Whole-of-life energy reduction of 41%
  • Whole of life water reduction of 40%
  • Whole-of-life materials reduction of 15%
  • Development of an ecology quantification method to apply percentage increases of ecological enhancement to individual initiatives and overall net enhancement.
  • Design of a wastewater re-use plant for ‘fit for purpose’ construction water.
  • Single-Pass segmental tunnel lining methodology with corrosion protection. This initiative reduces materials, energy, water, construction programme, cost, and significantly improves the safety and working conditions of the workers.
  • Mates in Construction foundation partnership funding a full-time field officer who will look after a portfolio of New Zealand projects as well as the Central Interceptor to address mental health and suicide in the construction industry.
  • Developing a training centre for all site staff to improve skills in risk awareness, identification, and response. This includes health and safety factors but also things like spill response, setting up sediment traps, and how to respond to archaeological finds all through kinesthetics learning.
  • Utilising tunnel spoil from the Central Interceptor toward rehabilitation of a Maori heritage landmark, Te Motu a Hiaroa (Puketutu Island)

 Project Highlights

Highlight 1 - Development of an ecological enhancement quantification methodology

With our ecologist, Boffa Miskell, the project has developed a methodology to allocate numerical value to individual ecological initiatives and enhancements to be able to measure the percentage of net enhancement. To the best of the projects knowledge, quantification of ecological enhancements, as opposed to quantifying the planted land area of offsets, had not been done on an ISCA project previously. The Central Interceptor are happy to discuss this approach with other projects as it received high praise from design rating verifiers.

Highlight 2 - Water Resource Focus

Major initiatives that contributed toward the reductions in whole of life water include:

  • Piloting wastewater re-use for construction water. This is the first time in New Zealand that wastewater will be re-used for construction. As well as minimising potable water use on the project, the CI are working with Watercare to investigate the resource recovery potential and alternative water sources for Auckland in the long-term in light of climate projections for changing rainfall patterns.
  • Utilising non-potable effluent for the dampening of odour treatment beds throughout operations. As the operation of the asset does not have any requirements for potable water, we have a focus on ‘fit for purpose’ water.

Replacing twin-shafts (vortex drop and de-aeration/access shaft) with a single cascade drop shaft at various sites. A significant reduction in materials and spoil excavation comes with a reduction in energy and water. This design initiative had a significant reduction in resource use.

Highlight 3 - Supported local communities and social enterprise

Creation of a laundry business

Construction sites pose the risk of exposing employees to potentially harmful substances. These substances have the potential to be carried on workers Personal Protective Equipment (PPE) posing a risk to their families at home. The Central Interceptor project has found an answer that provides a safe solution for workers and their families while providing employment and work experience opportunities to local communities in the form of creating a laundry service. This provides an opportunity for the community to gain new skills and employment through running a business. While CI will be the main customer to begin with, the project will assist the laundromat to find new business. Following the completion of the project the laundry service will be handed over to those who have run it to continue the legacy of the project. The laundromat initiative helps meet the Mangere-Otahuhu Local Board Plans desired outcome of creating a strong local economy.

Make, Give, Live initiative

Make, Give, Live is a social enterprise focussed on easing isolation and improving mental health and wellbeing in the community. For every knitted item they sell, they donate a knitted item to a kiwi in need.

The Central Interceptor purchased a number of knitted beanies for our construction site staff. We had also begun identifying how we could help other Kiwis along the tunnel route. We raised the idea of donating woollen garments to May Road School in Mt Roskill, which is very close to one of our construction sites. The outcome we achieved highlights our one family approach to work and has helped us built a quality community relationship.

The project has reached out to a number of schools along the CI route, asking them how we can be a good neighbour. May Road School has a number of challenges as a lower-decile school. One of these is keeping pupils warm in the classroom so they can concentrate on their studies. The school was delighted when we approached them and felt the greatest need was for slippers to keep pupils’ feet warm and dry. In addition, we wanted to support a worthwhile local charity to set up closer links with schools: with our established relationships in this area, we can help Make, Give, Live with this goal.

In August 2020, the CI alongside Make, Give, Live delivered 200 colourful pairs of lovingly knitted slippers to the school. This donation now means every child has a pair of slippers, kept for them in the classroom, to slip into each day when they arrive for lessons. Now another Make, Give, Live knitting group has a great relationship with a local school.



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