The building of Sydney's Western Harbour tollway could expose some of Sydney's suburbs to toxic sediment and excessive construction noise according to a high-level study marked "cabinet-in-confidence" that has been obtained by the ABC. The report reveals some key problems with the pending development slated for completion in 2024.

According to NSW Transport Roads and Maritime Services, the Western Harbour Tunnel project will connect to WestConnex at the Rozelle Interchange, cross under Sydney Harbour between the Birchgrove and Waverton areas, and connect with the Warringah Freeway at North Sydney. It will include upgrades to the Warringah Freeway.

This report was prepared for the NSW Government ahead of its announcement of the preferred option for the project and refers to four alternative routes for the tollway. One is a replacement for Mosman's Spit Bridge.

The report (seen only by the ABC) says the final project will deliver time savings for commuters and have the least possible disruption to locals during construction. It also points out there could be noise implications for residents in Balmain, Pyrmont and Rozelle. And because half-a-million tonnes of contaminated sediment will need to be dredged and removed - mostly from White Bay - the result could be toxic plumes of water that might have an impact on aquatic life. This could potentially affect recreational harbour users, shipping and tourism.

According to the ABC the document proposes most of the tollway run underground via one tunnel between Rozelle and Waverton and another from Crows Nest to Balgowlah. There will also be two underwater tunnels near Balmain and Seaforth that will be created from watertight concrete tubes laid on the harbour floor.

There are more than a dozen suburbs that could potentially be affected by construction, including White Bay, St Leonards Park at North Sydney, Anzac Park at Cammeray, Flat Rock Baseball Diamond at Naremburn, the Spit Reserve at Mosman and Yurulbin Park at Birchgrove. It's predicted all of these areas will experience heavy noise from a high volume of trucks (between 60 to 120) moving between work sites each day.

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The ABC also reports that the mass movement of contaminated sediment will affect more than 70 different wildlife species. It could also destroy fragile seagrasses that support more than 20 species of endangered seahorses and sea dragons. Critically endangered black cod, dolphins, sea turtles and little penguins are also potential threats.

Broadsheet reached out to Melinda Pavey, the Minister for Roads, Maritime and Freight, but she was unable to comment on the issues raised in the documents at time of publishing.

A full environmental impact statement is scheduled for release later this year.

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