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The original $1.2b cost rose to $1.32b when the scope of the project extended from Western Springs to Grey Lynn, and connections to service new developments in Mt Roskill, along with improving water quality on the the western isthmus.
Watercare is blaming “unprecedented inflation since late 2021″ resulting in higher labour costs for a 15.5 per cent increase of $204 million to complete the works, bringing the total budget to $1.523b.
The new cost was approved by the Watercare Board on November 7.
“The increase covers the construction of the tunnel to Tawariki St, Grey Lynn (due for completion mid-2026) and includes provision of $109m to address the impacts of ongoing inflation to the end of the project. This is based on current inflation forecasts. If cost increases are less than predicted, then the full provision won’t be utilised,” Watercare said in a statement.
Watercare Central Interceptor executive programme director Shayne Cunis said construction was progressing safely and efficiently across all 16 sites, with 72 per cent of work now completed.
Watercare's tunnel boring machine, Hiwa-i-te-Rangi, has broken through to a shaft in May Rd, Mt Roskill, on its 14.7km journey to central Auckland.
“Hiwa-i-te-Rangi, our tunnel boring machine, has broken through to a shaft in May Rd, Mt Roskill, and is more than halfway on her 14.7km journey to central Auckland,” Cunis said. “We’ve completed one link sewer and will finish the first drive for a second link sewer at the end of the month. Milestones are coming thick and fast.
“We absorbed the costs incurred through the Covid-19 pandemic and we had an allowance for inflation within the original budget, but with the level of inflation that has been experienced, it became clear that these rising costs would exceed our budget allowance. Additional funding will come from within Watercare resources and not Auckland Council and will allow us to complete the project as planned at the end of 2026.”
The Central Interceptor tunnel will connect with combined stormwater/wastewater networks in older suburbs such as Blockhouse Bay, Mt Roskill, Grey Lynn and Mt Albert, taking flows to Māngere Wastewater Treatment Plant for processing, resulting in an 80 per cent reduction in wet-weather discharges into local waterways. It is the largest wastewater infrastructure project in New Zealand history.
The Central Interceptor, being built by Watercare Services and joint venture partners Ghella (Italy) and Abergeldie (Australia), will reduce overflows into central Auckland waterways, streams and beaches and stop the wastewater from being mixed with stormwater. The project will also upgrade an antiquated wastewater network and cater for growth over the next 100 years.
The tunnel, an immense 4.5 metres in diameter, is designed to hold a capacity of 226,000 cubic metres – equivalent to 90 Olympic swimming pools – and control the flow rate into the Mangere Wastewater Treatment Plant.
For many years, Watercare has stuck to the $1.2b cost for the giant tunnel.
The cost of the City Rail Link has risen from $4.4b to $5.5b.
In March this year, it was announced the city’s biggest project, the 3.4km City Rail Link between Britomart and Mt Eden stations, rose in cost from $4.4b to $5.5b.
Auckland Council and the Government are partners in the CRL, sharing the cost.
Watercare is funding the Central Interceptor through water bills.
Bernard Orsman is an Auckland-based reporter who has been covering local government and transport since 1998. He joined the Herald in 1990 and worked in the parliamentary press gallery for six years.
