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Independent Report Backs Council's Actions

Thursday 13 December 2012, 2:17PM

By New Plymouth District Council

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NEW PLYMOUTH

A statistical assessment of microbes in the sea during the New Plymouth Wastewater Treatment Plant upgrade has been released by New Plymouth District Council.

The quantitative microbial risk assessment (QMRA) was carried out by NIWA, with input on ocean current models by local firm Met Ocean Solutions Ltd, as part of the Council’s resource consent conditions associated with the NPWWTP upgrade.

The report confirms the Council’s advice about swimming and shellfish collecting during the months when the plant’s aeration basins are being upgraded: That the risk to swimmers at local beaches during the basins’ bypass periods is within Ministry of the Environment guidelines, and that shellfish collecting in the area should be avoided while NPDC’s warning signs are in place.

“It’s good to have this confirmation that we have taken the right precautionary actions during the months when the aeration basins are offline,” says Manager Water and Wastes Mark Hall.

In the QMRA, the report writer notes that New Plymouth’s beaches are rated ‘good’ under the Ministry for the Environment’s Microbiological Water Quality Guidelines – the highest rating possible for beaches with a treatment plant outfall nearby.

The report identified that there could be a small elevated health risk in shellfish beds along the New Plymouth coastline during the treatment plant’s normal operations. “It should be noted however that the risk is derived from a desktop modeling exercise which takes a precautionary approach, not from actual monitoring results,” says Mr Hall.

The Council will undertake monitoring once the upgraded plant is fully operational to determine whether norovirus exists.

In response to a request by some submitters during the resource consent hearings, the QMRA included a section of the effectiveness of ultraviolet light treatment of effluent.

The report noted that a UV system would increase the efficiency of treatment of noroviruses. However NPDC has no plans to install a UV system as the plant’s current treatment system already results in a high level of disinfection which meets resource consent requirements.

“Our current treatment system has another 30 years of life before a full replacement becomes necessary and a UV system would cost about $3.5 million – a significant expense when we have a suitable treatment system in place,” says Mr Hall.

Related link

QMRA report (27 pages 1.1MB PDF)