KEY POINTS:
Neighbours of Auckland's proposed $1.9 billion Waterview motorway tunnels are fuming over a consultant's report questioning the effectiveness of filtering polluted air from them.
Beca Infrastructure has told the Transport Agency that the reduction of contaminants vented from overseas tunnels by using conventional treatment technology such as electrostatic precipitators has been "so marginal that it has not been possible to demonstrate a measurable improvement in external air quality".
It says in its report that an initial proposal by the agency to manage pollution from a 3.2km pair of twin tunnels between Mt Albert and Waterview by high-velocity discharges from venting stacks - so the pollution will disperse high into the atmosphere - would meet "common international practice".
But that has upset residents near the route, especially parents of pupils at Waterview Primary, which has a boundary within 40m of the site for a fume stack above the northern portals.
A property developer at the other end of the tunnels has asked the Transport Agency to consider installing a stack on industrial land further east.
School board member Rob Black said the Beca report failed to make recommendations about international best practice or include any cost-benefit analysis based on minimising health risks from venting untreated vehicle fumes.
He said that was despite a call in June by Transit NZ for a report on air-quality management "to benchmark the proposed approach incorporated in the design work to date against international best practice".
Neither was there any apparent consideration in the report of a recommendation from Auckland City for the venting stack to be built at least 1km away from the school.
The city and the Waitemata District Health Board want fumes to be treated before being pumped out of the tunnels.
Mr Black's partner, Margie Watson, said the report's conclusions seemed at variance with a statement in it that electrostatic precipitators were about 70 per cent effective in removing potentially carcinogenic fine particles from in diesel fumes.
Transport Agency principal project director Clive Fuhr said the Beca report was simply a background review of overseas practices, and not intended as a recommendation.
The leading document would be an air-quality effects report, which had yet to be completed but would be discussed at community workshops next month before forming the basis of a recommendation to the agency's board.
It would cover computer modelling of traffic volumes and meteorological patterns to determine the best height and location of the venting stacks.
Mr Fuhr said a Niwa scientist had assured residents they would be "far better off having those cars using a tunnel and having that air released into the higher atmosphere, rather than having those cars driving through your community".
Asked about the proximity of the proposed venting stack to the school, Mr Fuhr said: "The nature of the dispersal is that if you're closer to the dispersal point, it's probably the safest place to be, because it disperses it up."
