Whangaparaoa, New Zealand

Army Bay Ocean Outfall

Watercare Services Limited


This wastewater treatment plant (WWTP) upgrade and ocean outfall replacement project consists of a new outfall pipeline capable of conveying 1.4 cubic meters per second (49 cfs) from Army Bay WWTP to the consented marine discharge location. The project also provides a high-level emergency overflow from the effluent storage ponds to the new outfall pipeline, an upgrade of the Discharge Pond Pump Station pumps and rising main, an upgrade of the UV Disinfection Facility, and an upgrade to supporting electrical and control systems.

Fast Facts
  • 1.9 kilometers (1.2 mi) of single-drive trenchless pipeline using the Direct Pipe® system with wet recovery
  • Approximately 900 meters (2,953 ft) of marine pipeline
  • The project utilized the state-of-the-art Herrenknecht Direct Pipe® system for the first time in New Zealand

Scope of Work

The project was delivered to Watercare as a design+construct (design-build) contract by McConnell Dowell constructors. Delve Underground provided detailed design (temporary and permanent elements) services for McConnell Dowell and supported the client with construction phase services throughout.

Challenges & Innovations

Several innovations were delivered on this project. On the trenchless section, the Herrenknecht Direct Pipe® system, which combines microtunnelling and horizontal directional drilling (HDD) techniques, was used for its ability to install long terrestrial outfall pipeline in a single drive, safely and with speed. The use of this system reduces environmental impacts, making it ideal for working in sensitive spaces with limited access such as the regional park and New Zealand Defence Force lands that overlie the alignment on land. This was the first Direct Pipe drive in New Zealand, and it set a world record for longest drive by Direct Pipe. On the marine section, bespoke pipe ballast blocks were designed to avoid rocks impacting the outfall pipeline and to lower drag on the outfall during installation. A single point diffuser was designed instead of a multipoint diffuser to minimize future inspection and maintenance requirements.