Work begins next week on removing a 180 metre underwater section of the Orewa Wastewater pipeline not seen on the surface since it was built in 1971.
It’s part of the now decommissioned pipeline that took treated wastewater from the Orewa oxidation ponds, down through the Orewa estuary before discharging it out to sea.
The pipeline hasn’t been used since late last year and the section in question has deteriorated to the point that it could become a navigation hazard if not removed.
The Rodney District Council, which is commissioning the project, says a team of specialist divers will operate from a barge over the pipeline to inspect the anchor systems, prepare the pipe section for removal and bring it to the surface. The pipe section floats of its own accord when not anchored to the sea floor.
A large tow truck will tow the pipe section ashore in one section, where it will then be cut down, lifted on to trucks and removed for recycling.
The dive team consists of three divers and two support personnel. The divers are trained in underwater demolition. The dive team normally works supporting oil rigs and associated operations in SE Asia and the Indian Ocean.
A ‘Notice to Mariners’ will be in place for the duration of the work. This will exclude vessels and water users from the area around the pipeline, barge and diver operations. The work area will be marked by yellow buoys at each end and will have yellow flashing lights at night, visible from 1nautical mile. All vessels and water users are requested to keep clear.
The work is planned to commence on Monday 29th June and intended to take approx five days. Work is highly weather dependant. The planned day to tow the pipeline ashore will be determine during the early stages of the operation, taking into account the weather and time required to free the pipeline from the seabed and its anchoring system.
Following the operation divers will swim the seabed picking up any loose debris remaining. The anchoring system will be removed where possible, while anchors that are effectively buried and cannot be lifted free will be cut flush to the seabed.
Local project managers, GHD Ltd, say that if all goes well and the weather is kind the project should be finished by the weekend.