Shellfish warnings to end soon

Permanent signs in Tomahawk Rd, near Smaills Beach in Dunedin, that warn against collecting shellfish should be removed this year, as work to clean up Dunedin's sewage nears completion.

The signs were expected to be taken down by September, when the second stage of the Tahuna outfall and secondary treatment plant was due to be completed.

But construction delays and technical issues mean the plant's complex biological filter, which clarifies the sewage stream so the ultraviolet disinfection system can have more effect, was commissioned only this week.

Dunedin City Council water and waste services manager Dr Laura McElhone said the ultraviolet treatment system itself was commissioned late last year and test results showed it was disinfecting more than 99% of the sewage stream.

She said the council wanted to be totally confident the biological filter was working as it should before warning signs were removed from beaches. An exact date for that to happen was not available yesterday.

Since the $37 million, 1.1km Tahuna outfall pipe was commissioned in January 2009, regular tests of water from between Second Beach, near the St Clair pool, and Smaills Beach have shown the water is safe for swimming.

Dr McElhone warned, however, that while beaches should no longer be contaminated by sewage, there might still be issues with pollution from other sources after the treatment plant was fully operational.

A perfect example came yesterday as swimmers and surfers were warned to avoid the waters around Lawyers Head until further notice, after testing revealed high bacteria levels that were probably due to natural environmental conditions, such as hot weather and a high number of sea birds in the area. There was no indication the contamination was linked to the treatment plant, she said.

The council has previously warned there could be contamination from farming activities and run-off into the ocean, especially during heavy rains, once the signs are removed.

- debbie.porteous@odt.co.nz