Watercare says early results from its environmental monitoring of the Waitematā Harbour are reassuring and indicate the impact of the overflows from the Ōrākei Main Sewer blockage seems to be localised.

It’s been three weeks since a wastewater bypass put a stop to the high-volume overflows into the Waitematā Harbour that began when a sinkhole formed above the major wastewater pipe in Parnell and blocked it when the ground caved in.

Watercare environmental care manager Dr Nathaniel Wilson says water sampling in the harbour and oyster sampling are key components of its environmental monitoring programme.

“Our sampling programme will continue until at least Christmas, so while it is too soon to reach conclusions, what we’re seeing so far indicates the impact of the overflows is concentrated on the area in the immediate vicinity of the overflow locations – Mechanics Bay across to Wynyard Quarter.

“The nature of the harbour means there was sufficient dispersion and dilution to significantly reduce the impact to water quality at locations further from the discharge point. This dynamic harbour environment is why most of Auckland’s swimming beaches had green water quality pins on Safeswim soon after the overflows ended.

“It also appears that most of the solid matter had settled in the pipe and didn’t come out at the overflow point. This is why we haven’t seen wastewater debris washing up on beaches or visible on the surface of the harbour.”

Routine beach and harbour inspections have now stopped, although additional Safeswim testing will continue through November.

Oyster bags strategically placed at various locations in the harbour are tested fortnightly to measure build-up of bacteria, viruses and metals.

“Shellfish sampling indicates there were high levels of bacterial and viral indicators close to the discharge location while the overflows were occurring, which is to be expected. The good news is these levels dropped significantly when the overflows had stopped.

“It’s important to note that this sampling is to complement our environmental monitoring – not to demonstrate that the shellfish is safe to eat. General health advice – as specified on the Auckland Regional Public Health Service’s website – is to avoid eating shellfish from urban areas because of the risk from a wide range of contaminants.”

Dr Wilson says while the early results indicate the impact is highly localised, Watercare is committed to doing what it can to protect and enhance the wider Waitematā Harbour.

“We’re following guidance from Ngāti Whātua Ōrākei and hope to have conversations with other organisations that work to protect and restore the harbour.

“This could mean contributing to existing mussel bed restoration programmes and looking for opportunities to improve the areas immediately around the discharge locations.”

Update on the Ōrākei Main Sewer and bypass solution

Watercare head of service delivery Sharon Danks says the bypass pumping solution is working well.

“It’s been three weeks now since the high-volume overflows stopped. We do have some issues with the pumps blocking from time to time, so we are always urging our customers to only flush the 3Ps – pee, poo and toilet paper.

“We’ve also managed to partially open the ‘stoplog’ – the steel fabricated door inside Ōrākei Main Sewer – to allow low levels of wastewater flows through the pipe. This removes the risk of overflows at times of the day when flows are higher than average, and reduces the risk of overflows in wet weather.

“There are still some large boulders inside the pipe and we hope to remove these before Christmas, once all the necessary safety measures are in place.

“The design for the sewer’s repair is progressing well. We hope to have the materials for this arrive in the country before Christmas so we can start construction early in the new year.”

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