Project background
Watercare is proposing to construct a new 13-kilometre-long wastewater tunnel to collect and carry wastewater from Western Springs through to the Mangere Wastewater Treatment Plant. Along the proposed route it will connect to the existing trunk sewer network to divert flows and overflows into the tunnel. If approved, this new wastewater tunnel will be called the Central Interceptor.
The concept design of the Central Interceptor was completed at the end of 2011. Watercare is applying to the Auckland Council for consent and the regulatory approval process includes public consultation.
Click here to see the latest Central Interceptor factsheet.
Why is the Central Interceptor needed?
There are three reasons:
Capacity: The Central Interceptor is needed to ensure there is enough capacity to meet planned growth and development in Auckland. Without this, there will be more overflows into the harbours and waterways.
Critical asset management: The Western Interceptor is 55-years old and is reaching the end of its economic life. The Central Interceptor will replace it.
Wastewater overflow control: There are over 100 locations in central Auckland that overflow during wet weather. Although overflows will not be eliminated, the Central Interceptor is a cost-effective option to significantly reduce these overflows.
What will it cost?
The Central Interceptor is a significant investment into the security of wastewater services in Auckland. The current estimated cost is around $620 million with an additional $180 million required for overflow control works.*
Funding for the project comes from a combination of revenue generated from wastewater charges and through long-term structured borrowing. The Central Interceptor has an expected operational life of more than 100 years. Its benefits will be shared by several generations of Aucklanders, so it makes sense to spread the costs over time.
When is construction planned?
The concept design of the Central Interceptor was completed at the end of 2011. Watercare is applying to the Auckland Council for consent. If approved, construction is planned to start in 2017, with completion planned for 2023.
What are the alternatives and what do they cost?
Duplicate the existing network: Duplication of the existing network would involve pipe laying through built-up areas with associated major traffic and community disruption. In addition to the traffic and community disruption, this option was costed at around $870 million.
Build a new wastewater treatment plant for Central Auckland: The Three Waters study investigated the feasibility of building a new treatment plant in central Auckland and concluded that it was not practicable from the perspectives of the availability of land, community impact, disposal of solids/treated wastewater.
Utilise the Central Interceptor for wastewater only: The Central Interceptor could carry wastewater only and not be used for overflow control. This would save around $100 million in Central Interceptor costs and $200 million in overflow control works. However, estimates have shown that an additional $800 million would need to be spent to continue with an earlier sewer separation programme that began under the former Auckland City Council.
What about stormwater flood protection?
The Central Interceptor will reduce combined stormwater and wastewater sewer overflows but the council will need to provide separate stormwater solutions to address flooding, erosion and contaminant issues in parts of the area served by the Central Interceptor.
* Note: all cost estimates are in 2011 dollars.