Mangere BNR Upgrade


Building Civil Electrical Fabrication Mechanical Pipelines

McConnell Dowell, in joint venture, is building a Biological Nutrient Removal (BNR) facility for Watercare as part of its expansion of processing facilities at the Mangere WWTP, which is presently the largest wastewater plant in New Zealand and one of the most advanced plants in Australasia. The scope of work involves the construction of two new reactors, two clarifiers, a blower building, a splitter box (including connections for future duplication of reactors in 10 years), two secondary effluent pipelines, sludge storage tanks, a gravity belt thickener facility and interconnecting pipework to provide additional secondary treatment capacity of approximately 250,000 people. We successfully installed the twin secondary effluent pipes under Greenwood Road using a pipejacking method, which required precision in execution due to a whole manner of services, including the main fuel pipeline from Marsden Point to Auckland/Auckland Airport, 11kV power cables, a high pressure gas main, water and telephone lines, running along the alignment.


  • 100,000m3 of earthworks
  • 15,000m3 of concrete poured
  • Over 90km of cable pulled
  • 15,000 plus terminations
  • 100% pass rate on SGS weld tests
  • 5,500m of stainless pipework and over 10,000m of pipework in total
  • 176 60 tonne reactor panels poured onsite and installed with JV equipment


Customer: Watercare Services Ltd
Location: Mangere, South Auckland
Contract Type: Design and Construct


Construction of the Mangere BNR Upgrade involves works in both greenfield and constrained brownfields environments adjacent to and within the operational Mangere plant. Works are continually in close proximity to critical services such as tanks, process lines, trunk sewers, fibre optic cables and underground HV lines that all need to be protected as any interruption in service would have a significant effect on the wastewater treatment capacity for Auckland. We have developed a strong safety culture, robust permitting procedures and implemented a thorough training and awareness programme to ensure all staff understand and strive to mitigate safety risks associated with working in this high hazard environment.

A challenge throughout the greenfield construction has been the poor ground conditions encountered at this coastal site. Earthworks for the construction of the main reactors and clarifiers amounted to the removal of around 90 000 m3 of peaty material. Ground Improvement piling for the major structures involved driving 2,400 UC piles up to 18 m long and weighing 500 kg each. This amounted to almost 42 km of “pile” installed.

The mechanical fit out was self-performed by the Joint Venture and included the largest wastewater installation in New Zealand in the last 15 years. Proactive procurement processes ensured clear communication with suppliers and open interaction with Watercare and their designers to ensure all equipment met the project requirements. The installation included large bore painted steel pipe as well as over 5.5 km of stainless steel pipe from 25 mm to 1000 mm in diameter. As the size and complexity of this project was unique in the water industry, resources were drawn from other industries using McConnell Dowell’s experience and contacts to establish a team founded on key staff, but providing knowledge and experience from power generation and petrochemicals.


The JV team has worked collaboratively with Watercare and their designers to enhance the programme, manage the risks and provide alternate solutions in a culture driven by a key concept of ‘Together Doing it Better’. This message has become the project tag line, sits on the shared space between the shared project facilities and really has been the key focus behind this successful delivery model.

The project had a number of design-build elements including the main process units, the reactor and the clarifier tanks. The JV chose lightweight post-tensioned precast concrete structures for both of these units. The drive was for resilient, watertight and quick to erect structures. The floors of the reactors and clarifiers were post tensioned slabs with the reactor floor poured in sections, each 1200 m3, or over 220 concrete trucks.

Large precast concrete panels up to 60 tonnes each were cast on site and erected using large cranes to form the tank walls. Pre-casting these panels resulted in a quick erection of the tanks, whilst safer construction methods could be employed by reducing the work at heights requirements.


As with all large projects success lies in the essence of the team. The relationship between the three parties, the JV, Watercare and CH2M Beca was paramount to being able to work through any issues that arose. The experience and drive of the members of the Joint Venture team, which numbered more than 200 at times resulted in a successful outcome. Coordination and sequencing of the works, a focus on quality and a team dedicated to Health and Safety has been key to success.

Due to the hazardous nature of the work we have implemented a number of safety initiatives to enable us to develop and maintain a strong safety culture and achieve an excellent safety record to date. Project safety initiatives have included visible leadership, regular safety talks, undertaking the LJM safety culture survey, and holding Project Refresh events and meaningful toolbox sessions.


The Mangere BNR Upgrade is due for completion in April 2018.