Sinkhole in Parnell Photo: Watercare
Watercare is set to begin work today on laying a bypass pipe to reduce wastewater overflow caused by a broken pipe in Auckland's Parnell last week. Meanwhile, wastewater continues to flow into the Waitematā Harbour.
The blockage and collapse of the wastewater pipe in Parnell last week left a 13m-deep sinkhole in a carpark on St Georges Bay Road.
Over the weekend, another 10 tonnes of material had been removed from the blockage as crews continued to work around the clock to remove grit through hydro-jetting.
Watercare chief operations officer Mark Bourne told Morning Report workers were halfway through clearing the blockage.
"What is left behind are very large rocks and boulders that we're going to have to remove by an alternate technique as part of the repair process."
Bourne said the design of the 400m-long bypass was done over the weekend, with several possible routes for the piping.
It was designed to move the sewage, which was currently sitting in main sewer and causing the overflow, around the blockage and to the wastewater plant for treatment.
He said they would decide on the final route this morning, and that the first sections of the pipe were expected to be laid this afternoon, using material that was available in Auckland.
The rest of the pipes, which were being built in Whanganui, were expected to arrive in Auckland early this week.
"We're planning to have the whole thing completed within 10 days" - Watercare chief operations officer Mark Bourne
Bourne said they had an ambitious goal to complete the bypass by early next week, but he could not confirm the exact timeline yet.
"The works are very ambitious - but we are expecting the whole thing to be completed in 10 days."
He said they had been closely monitoring the two locations where wastewater was continuing to overflow into the harbour - one at the middle of Mechanics Bay, and another at the western end of Viaduct Harbour, near Freemans Bay.
Bourne said it was too early to say when they would again be swimmable.
"We started monitoring on the day the blockage first occurred, and expanded that to more than 40 different bathing beaches.
"Initial sampling showed that eight locations were above safe bathing guidelines, but we are taking a precautionary approach and have black pinned all of the inner harbour beaches in the Safeswim programme."
Typically, beaches were safe to swim between 48 and 72 hours after an overlfow event, he said.
"But in this instance, because of the scale and duration of the overflow problem, it may be a little longer than that, and we'll be undertaking a comprehensive sampling programme."
Bourne said Watercare was "proactive" about monitoring of sewers and water mains to prevent sinkholes around the extensive network.
"There are some 9000km of buried sewers and a further 9000km of water mains around the city, and monitoring includes (looking) inside pipes for defects."
The last time the Parnell pipe was surveyed, in 2019, it was in good condition so had gone into the standard five-year inspection programme, he said.
A diagram showing the impact of the Parnell sinkhole on the Ōrākei main sewer. Photo: Watercare
Auckland deputy mayor Desley Simpson, who was also the councillor for Ōrākei, said she was concerned about the continued overflow.
"The repair of the pipe is one thing, but for me the bigger concern is the environmental aspect, going into the Waitematā Harbour, which we spend so much time on trying to improve the water quality," she said.
Simpson said she had been told by Watercare that there were hundreds of litres of wastewater going into the Waitematā Harbour every second.
She said despite Watercare's assurances about the urgent work on the bypass, the overflow was still worrying.
"That's still a hang of a long time for waste to be flowing into the harbour and in my opinion I think that the devastation that could cause could be really quite serious," she said.
Simpson said the council's environmental scientists told her over the weekend that there would limited adverse effects on fish and birdlife in the short term, some of which would migrate to more suitable waters.
She said there would, however, be losses of some non-mobile species such as oysters and mussels and reminded Aucklanders to stay clear of the areas that Safeswim had marked unsafe.