The tunnels will be built in a trench on the harbour floor, and large prefabricated concrete tubes lowered into place from barges above. Concerns were raised last year by the Port Authority of NSW about the movement of toxic sludge that will be dug up during construction of the tunnel.
The authority said the handling of the contaminated material would be occurring within 150 metres of homes, suggesting odour and volatile emissions could become a problem.
The government has undertaken testing at the proposed site of the tunnel, while a dedicated team of environmental specialists have been assigned to the project.
“The plan for the Western Harbour Tunnel and Warringah Freeway upgrade project is based on expert peer-reviewed advice, past experience and world’s best practice,” a Transport for NSW spokesman said.
Among concessions made to the project in order for its approval are a new pedestrian and cycle path through the Cammeray Golf Club (the existing one will be destroyed) as well as offsets to the marine environment, according to government documents seen by the Herald.
Transport Minister Andrew Constance said the tunnel, which will run three lanes of traffic in each direction, would cut travel times between North Sydney and Olympic Park by up to 20 minutes.
“This city-shaping piece of infrastructure will deliver a vital boost to the NSW economy, with the tunnel and freeway upgrade, along with Beaches Link, expected to support around 15,000 full-time equivalent jobs,” Mr Constance said.
Planning Minister Rob Stokes said any trees removed need to be replaced at a ratio of two-to-one.
“Community feedback on the project has been valuable in helping understand and deliver positive changes to the design and plan, and we will continue to work closely with local communities as the project gets underway,” Mr Stokes said.
He described the Warringah Freeway as “one of Sydney’s busiest and most complex road corridors”.
The government warned last year, in an environmental impact statement, that parts of the Warringah Freeway, used by as many as 250,000 vehicles a day, will be temporarily shut overnight during construction.
Partial or complete closures of the Warringah Freeway were outlined in the report, which indicated most would occur after 10pm, or during off-peak times.
Transport for NSW confirmed late last year that the government was searching for a “development partner” to assist with the procurement and delivery.
A shortlist was announced in December, comprised of Bechtel Infrastructure, Laing O’Rourke and Harbour West Partners, a consortium comprising Macquarie Capital, Jacobs and RPS.
The Warringah Freeway upgrade will run towards a new Beaches Link, which is likely to be completed two years later than first anticipated, in 2027-28.
Tom Rabe is Transport Reporter with The Sydney Morning Herald.