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The ageing pipe that takes treated wastewater from the Army Bay treatment plant out into the Tiri Channel is to be replaced at an estimated cost of $28 million.
Watercare Services expects to apply for construction consents early next year to install a replacement pipeline, using ‘trenchless technology’ – which basically means there won’t be any digging. Instead, either horizontal directional drilling or pipe jacking (in which pipes are assembled in an access shaft and pushed into position by hydraulic jack) will be used to install the pipe so that all the machinery used will be land-based.
No decision has yet been made regarding the future of the existing pipe but in the interim it will be maintained as a back-up.
The Army Bay Wastewater Treatment Plant services the population of Whangaparaoa Peninsula, Orewa, Hatfields Beach and Silverdale. Treated wastewater from the plant is discharged via a 1.8 kilometre pipe that extends into the fast-flowing Tiri Channel at a depth of approximately 25 metres.
The treatment plant has been operating with the existing outfall since 1982.
An earlier proposal for an outfall near Wellington Reef was considered in 2012, but following more detailed investigations and public feedback the trenchless pipline was proposed instead.
The replacement pipe will discharge treated wastewater to the same location as the existing pipe. It will be sized to accommodate future growth, reduce overflows and help improve the operation of the treatment plant. The plant will continue to operate under its existing resource consent.
Design work is underway with construction proposed for late 2016 to 2018, subject to consents.
Most of the work will take place on New Zealand Defence Force land.
