Sewage plant crisis closes oyster farms

By CATHY ARONSON

Twenty-eight Warkworth oyster farms have been forced to close for two months after raw sewage was pumped into the local river from the town's sewerage plant, which was contaminated by oil.

The plant pumped out untreated sewage into the Mahurangi River for two weeks at the end of June when about 200 litres of oil destroyed its ability to treat the sewage.

The farmers stand to lose about $100,000 after Auckland Public Health and MAF imposed a two-month ban on farming oysters 7km downstream in the Mahurangi Harbour.

The Rodney District Council tested local industrial sites, but has been unable to trace the source of the oil.

Wastewater manager Uys Dewet said the contamination was a disaster.

"Someone has physically dumped the oil in the sewerage line, which has created a disastrous chain of events," he said.

The oil killed the organisms that break down the sewage.

The plant returned to normal last week after the council cleaned up the oil, took the contaminated sludge to a landfill and put in extra chlorine to kill the bugs.

Public Health protection officer Leslie Breach said the ban was imposed on oyster harvesting to avoid a viral outbreak.

Oysters would store the bacteria and if they were eaten, could cause viral infections.

Viral gastroenteritis outbreaks in several Auckland restaurants last August were linked to oysters harvested in the Waikere Inlet in the Bay of Islands and dented the international reputation of the New Zealand industry.

At least 18 oyster farms were banned from harvesting their shellfish, and the Northland Regional Council suspected overflowing septic tanks as the cause.

Warkworth oyster farmers have agreed to the industry standard ban of eight weeks, but most do not believe the oysters were contaminated.

Bio Marine manager Jim Dollimore said the farmers were willing to close to protect their reputations, even though they would lose about a quarter of their annual profits.

"It hasn't been great. It maybe shouldn't have been this long but there is not much we can do.

"We do want to know who was responsible for the oil spill."

An Auckland Regional Council compliance monitor, Belinda Gillespie, said the authority was satisfied that the council was not at fault.

She said the plant's ability to handle pollutants and the district's sewage and discharge restrictions would be analysed in its application for a new resource consent.

The present 15-year-old consent expired in 1999.

nzherald.co.nz/environment