Māngere Wastewater Treatment Plant Diversion Chamber

Our client entrusted us with complex, multi-disciplinary works to construct a new diversion chamber around two major sewer interceptors entering the Māngere Wastewater Treatment Plant (WWTP). The interceptors are part of a vast new underground tunnel network that will alleviate pressure on stormwater and wastewater systems, leading to a cleaner Tāmaki Makaurau Auckland.  

Seipp’s brief includes the controlled, staged deconstruction of existing interceptor chambers, the installation of 36m-deep bored pile foundations to a new confluence chamber, and the connection of the new twin DN1400 rising mains and existing Western Sewer Interceptor to the confluence chamber. The project is currently scheduled for completion in July 2024.  

While this is formally a build-only project, Seipp – in a joint venture with Ghella Abergeldie JV – has interacted closely with the designer, focusing on constructability and temporary works.

‍

Crucial health and safety protocols

With safety and wellbeing at the heart of our company culture, our strong reporting practices are essential to this high-risk project.

Our team is working on existing infrastructure in varied states of disrepair, so we have focused on planning and contingency. In a constrained site, we have minimised entries required to the existing sewers and established exclusion zones and designated walkways.

‍

‍

Seipp’s self-perform reputation

Our Auckland Regional Manager, Drew Griffen, says the ‘pure complexity’ of the project makes it a high-risk challenge for Seipp. ‘We have taken great care not to damage the aged existing infrastructure. Plus we had to coordinate the temporary works required to divert these large-diameter sewer trunk mains.’

Seipp has a proven track record in self-performing construction work. Doing it ourselves enables us to pre-plan carefully, manage risk effectively, realise efficiencies, mitigate our carbon footprint, enhance health and safety, and generally improve outcomes – often passing on a cost saving to the client, too.

With our extensive self-perform capabilities, we are able to complete all piling works, excavations, temporary steel and mechanical works, and the sewer bypass. Drew says, ‘We’ve essentially completed everything except for the bored piles, with a specialist contractor doing that.’