“It is clear that there have been procedural deficiencies with the ... process,including an inadequate[environmental impact statement],incomplete environmental risk analysis ... and lack of transparency,” she said.
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However,Transport for NSW has argued that strict measures will be in place to manage the risk as the buried contaminants are unearthed.
Professor Byrne warned that the sediments at both ends of the tunnel corridor at Birchgrove and Waverton were highly contaminated,containing among the highest levels of dioxins.
She said the severity of the impact on marine life would depend on how sediments,and the chemicals,moved in the harbour.
But she said there was no way that Transport for NSW’s proposed use of silt curtains,and a backhoe dredger fitted with a closed bucket,would contain the sediments due to swift currents in the area.
Dr Pat Hutchings,who has worked extensively on the biodiversity of Sydney Harbour,also argued that sediments would be washed “up and down” Parramatta River,and become trapped in the upper reaches of bays.
“That’s where a lot of the human activity occurs,but those are the areas where we’re seeing re-establishment of seagrasses and kelp beds,” she said.
The project comprises twin 6.5-kilometre tunnels from Rozelle to the Warringah Freeway at North Sydney. Large prefabricated concrete tubes will be lowered from barges into a trench on the harbour floor to build the road tunnels.
Bill Ryall,one of NSW’s leading contamination experts,agreed that the risks to marine life from the project were severe,partly because planned silt curtains to contain sediment would be too shallow,extending only about two to three metres from the harbour surface.
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“The disturbance of the sediment obviously takes place at the seafloor,which is some eight metres at least below the level of silt curtain,” he said.
Dr Ryall,who lives near the project area at Birchgrove,believes the risks could be significantly reduced by anchoring silt curtains to the harbour floor,and remediating highly contaminated sediment in watertight areas at Birchgrove and Waverton. “Then there’s negligible impact from contaminated sediments to the waters of Sydney Harbour,” he said.
The government’s most recent timetable for the start of major construction of the Western Harbour Tunnel has beensometime next year,which is later than original plans for it to begin in 2020-21.