$1.2b Central Interceptor wastewater tunnel to keep Auckland beaches clean
Thursday, 14 March 2019
Construction is set to begin on a $1.2 billion tunnel that aims to reduce Auckland wastewater overflows, with the signing of a construction contract due on Thursday.
The so-called Central Interceptor will run for 13km between Western Springs and the Māngere Wastewater Treatment Plant. Auckland Council's water utility body Watercare will work with infrastructure firm Ghella Abergeldie Joint Venture to deliver the project by 2025.
At 4.5m in diameter, the project will be Auckland's largest wastewater tunnel and the biggest wastewater project ever undertaken in New Zealand. The tunnel is expected to reduce wastewater overflows in the central city by 80 per cent.
Watercare chief executive Raveen Jaduram said the project would allow Aucklanders to enjoy cleaner beaches by reducing wastewater overflows during storms.
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'In older parts of central Auckland, wastewater and stormwater flow into a combined network of pipes. When it rains, stormwater overwhelms these pipes, which are designed to overflow into waterways,' he said.
'We want everyone to be able to enjoy clean waterways, beaches and estuaries – that's why we're building the Central Interceptor. It will run underground from Western Springs to the Māngere Wastewater Treatment, collecting wastewater along the way via link sewers and drop shafts.'
The central wastewater network currently overflows to local waterways and the Waitematā Harbour at more than 100 locations and to the Manukau Harbour at 14 locations.
The Central Interceptor will address wet weather overflows by collecting the wastewater and stormwater from these overflow points and transporting it to Māngere for treatment.
It will cross Manukau Harbour about 15 metres below the seabed and along a route connect to the existing wastewater network, which will divert flows and overflows into the tunnel.
While the tunnel is being built Watercare plans to deliver further projects in the area such as separating stormwater and wastewater pipes. The largest of these projects is the Grey Lynn wastewater tunnel which is a 2km extension of the Central Interceptor.
'We are delighted to announce that the Grey Lynn wastewater tunnel has been included in our construction contract with Ghella Abergeldie Joint Venture,' Jaduram said.
'This is an extremely good outcome for Aucklanders because it means a better result for the environment without any extra cost for customers. Together, the Central Interceptor and our western isthmus projects will reduce overflows in the area by at least 80 per cent.'
The Central Interceptor will support the existing wastewater pipeline that passes under the Manukau Harbour which was built in 1964 and is reaching the end of its operational life. Damage to, or failure of, this pipe could result in a significant discharge of untreated wastewater into the Manukau Harbour.
It will also include back-up generators at the new Māngere Pump Station in case of an extended power outage.
Watercare's board of directors approved the motion to move forward on the project with contractors Ghella Abergeldie Joint Venture in November last year.
Watercare has previously completed projects like an upgrade to the Mangere Wastewater Treatment Plant in 2005 and building a wastewater tunnel running from Parnell to Orakei.
Construction of the Central Interceptor will start with site works in August with the project is expected to be completed by 2025.