WestConnex officials have confirmed there will be three exhaust stacks on the 9km long new M5 tunnel.
They will be located at Kingsgrove, Arncliffe and St Peters.
A WestConnex spokeswoman said on Thursday, "The New M5 preferred design has one ventilation outlet at Kingsgrove, one ventilation outlet at Arncliffe, and one ventilation outlet at St Peters Interchange.
"The design and operation of each of these three outlets will be detailed in the new M5 environmental impact statement, due for public display later this year."
A residents group was alarmed by incorrect media reports based on Mr Gay's statement.
“I was absolutely shocked to learn there would be two stacks in Kingsgrove, another two in Arncliffe, and two more in St Peters,” said WestCONnex Action Group spokeswoman and Beverly Hills resident Kathryn Calman.
“This isn’t just bad news for the residents of these suburbs.
"Every stack has a dispersal radius of about 2km, so this will leave hundreds of thousands of people across south-west Sydney choking on concentrated, toxic pollution.
“Duncan Gay says there will be no changes to air quality next to these stacks.
"But no environmental impact studies have been conducted, and exposure to traffic pollution has been linked to cancers, respiratory diseases and irreversible lung damage in children."
Ms Calman said confirmation that Kogarah Golf Club at Arncliffe would be the location for a stack would also be "another nail in the coffin" of an endangered Green and Golden Bell Frog colony.
The frogs were "unlikely to thrive on huge plumes of toxic pollution", she said.
Ms Calman criticised the the government's plan to sign the $5 billion construction contract before the environmental impact statement was approved.
She said a parliamentary inquiry should be established to look into the full business case for the project before more was "wasted".
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