Napier Awatoto Outfall

McConnell Dowell is working with Napier City Council in an Early Contractor Involvement (ECI) contract to develop the design for an efficient and affordable new outfall for the Awatoto Wastewater Treatment Plant.

The current scope includes designing and constructing:

• A new outfall pipeline from the Awatoto Wastewater Treatment Plant (WWTP) to the consented location.
• A control chamber between the existing WWTP works and the outfall.
• A diffuser: a section of pipeline attached to the outfall that will help dilute and discharge the treated effluent, prevent fish from entering the outfall and ensure the outfall complies with existing consent conditions, which specify a 1:100 dilution.

Our marine tunnelling specialists and designers from Delve are assessing three micro-tunnelling options with the Council. Two use Direct Pipe® and traditional pipe-jacking, with pipeline diameters ranging from 1200 mm to 1800 mm.

About 93% of Napier’s wastewater is treated at the Awatoto Wastewater Treatment Plant and is discharged after treatment off the coast into Hawke Bay via a 1.6 km long outfall built in 1973.

The outfall is reaching the end of its design life and has needed extensive repairs in 1984, 2012 and 2020. Each repair is complex and expensive, and the treatment plant must be shut down when the pipe is out of action. The new outfall will reduce risk and maintenance costs and increase capacity to enable future development.

The aim is to have a new outfall in operation by 2029.

For more information about the project, visit the Napier City Council website: https://www.napier.govt.nz/napier/projects/wastewater-outfall-replacement/

Example of Direct Pipe tunnelling set up