A $113,000 statistical report has backed New Plymouth District Council claims city beaches are safe while it discharges partially treated effluent this summer.
Since December 3, half of all effluent discharged through New Plymouth's Waiwhakaiho outfall has been screened and disinfected but not biologically treated. This is necessary while an upgrade is carried out on one of the two aeration basins at the Waste Water Treatment Plant.
The move initially alarmed surf lifesaving clubs and recreational users of the city's beaches and even prompted a Tui Beer billboard insinuating raw sewage had been seen on Fitzroy Beach.
Now a statistical assessment carried out by Niwa, as part of council's resource consent for the project, shows the risk to swimmers and beach users of getting sick is minimal and within "Ministry of Environment guidelines".
The study's results are desktop figures but physical testing of water quality is to be regularly undertaken by the Taranaki Regional Council at Fitzroy, Bell Block and Waiwhakaiho river.
"The best part from my point of view is what has been done is very comprehensive and I am satisfied with the monitoring and the checks and balances that have been put into place," said Taranaki Surf Lifesaving club development officer Andy Cronin.
The statistical analysis concluded the risk of gastrointestinal illness attributable to the outfall to be less than one per cent for swimmers and recreational users of the beaches.
When combined with existing and potential sources of contamination such as stormwater the water quality at the beaches can be classified as "good". The only higher level is "very good".
The news for shellfish is not so great. Council has already erected signs warning against collecting shellfish while the upgrade work is under way and the statistical analysis confirms that was the right move.
The risk is worst around Bell Block where the individual illness rates from eating raw shellfish could be as much as 13 per cent. At East End beach that risk drops to just over five per cent. When the treatment plant is back running at full capacity these statistical risks will reduce to 5.4 per cent and 1.8 per cent respectively.
Regional Council officers will also be monitoring shellfish for faecal indicators during the upgrade at Bell Block, Fitzroy and a control site in Oakura.
Council water and waste manager Mark Hall said work on the upgrade of the first aeration basin at the treatment plant was expected to be finished by March.
Up to two months after that the second aeration basin will undergo the same upgrade, during which time partially treated effluent will have to be discharged again he said.
- © Fairfax NZ News
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