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Pollution treatment equipment for vehicle fumes pumped from motorway tunnels through Waterview in Auckland could add $140 million to the cost of the $1.89 billion-plus project, says the Transport Agency.
Neighbours of proposed venting stacks at each end of the 3.2km twin tunnels are alarmed the agency is considering pumping out untreated fumes, while predicting a "negligible" impact on local air quality after these are dispersed from a height of 25m.
Waterview Primary School principal Brett Skeen says parents remain sceptical about the level of certainty offered by computer modelling, especially given Auckland's changeable weather patterns.
"Ultimately we want it treated - that's our bottom line," said Mr Skeen, whose school has a boundary 38m from the site of a northern venting stack.
Property developer Greg Burgess, who holds resource consents to build 83 town-houses on land 70m from a proposed southern stack west of Richardson Rd in New Windsor, says his development has been frozen by the agency's plans.
"Having a big smokestack next to a school and next to a housing development is just incompatible," he said. "How can I build houses when they're looking straight up to a smokestack blowing untreated contaminants?"
Mr Burgess, who bought his land in Valonia St in 1989 and gained resource consents three years ago to develop it, asked why it was not included in a list of 29 "sensitive receptor" sites, where the computer modelling predicts air quality would in most cases be improved by tunnels to siphon traffic off surface roads.
Transport Agency principal project manager Clive Fuhr said consultants relied on World Health Organisation guidelines in assessing sites where children or elderly people gathered, and those nearest the venting stacks were probably best off, given that vehicle emissions would be dispersed upwards.
But he said the agency was looking forward to more dialogue with the community before its board could decide by the end of next month whether the emissions needed treatment.
Treatment stations at each end of the Waterview link to the Northwestern Motorway would add between $100 million and $140 million to the cost of the project, which is already estimated at $1.89 billion for two-lane tunnels or $2.14 million for three lanes each way.
"I don't think the agency is going to want to do anything that's clearly prejudicial to health, but the evidence is suggesting that it [untreated venting] won't be."
Waterview school parent Margie Watson said concentrating the fumes at two venting sites gave the road-builders an ideal opportunity to treat it, even if overall pollution from tunnels proved less than from surface roads.
But Mr Fuhr said there may be more cost-effective ways to reduce pollution, such as through vehicle engine efficiency or better fuel standards.
He said consultants were still conducting "sensitivity" modelling to determine whether there would be any marked benefits from changing the venting stack locations.
Mr Burgess wants the southern stack moved to industrial land east of Richardson Rd, but Mr Fuhr noted the proximity of that site to another school, as well as a need to protect volcanic cone sight lines.
