Sea life in Sydney Harbour faces a severe threat from a “cocktail of chemicals” set to be dispersed from the construction of a multibillion-dollar motorway tunnel, marine biologists warn.
The biologists joined contamination experts and community groups in raising serious concerns about the proposed Western Harbour Tunnel and Beaches Link motorways during a parliamentary inquiry into the projects on Friday.
Maria Byrne, from the Australian Marine Sciences Association, said the risk to marine life from dredging for the harbour tunnel was severe because it would disturb a “cocktail of chemicals” contained in sediment on the harbour floor.
High levels of toxins have been discovered in Berrys Bay, where tunnel dredging will occur.Credit: Dominic Lorrimer
“Highly toxic chemicals will be released. We’ve got a long harbour, and if you ever see the way the currents move ... there are lots of opportunities for contaminants to go west and east,” she told the inquiry.
“The movements between Berrys Bay, Snails Bay, White Bay and the Rozelle rail yards have a high potential to disturb and redistribute sediments.”
The project will result in the dredging of almost a million cubic metres of sediment, the equivalent of about 400 Olympic-sized swimming pools.
Professor Byrne, who specialises in marine biology at Sydney University, argued that the project risks reversing a significant improvement in the water quality of Sydney Harbour in recent decades, citing the return of seagrasses and kelp.
She was highly critical of Transport for NSW’s report on the environmental impact of the project, saying it failed to adequately consider the effect the new tunnel would have on marine species.
“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.
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.
Dr Bill Ryall has voiced major concerns about the Western Harbour Tunnel project.Credit: Dean Sewell
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.
“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 been sometime next year, which is later than original plans for it to begin in 2020-21.
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