Moa Point Sludge Pipelines
Update 5 February
Thanks to the local community for their continued patience and understanding as we continue with our trucking operations from the Moa Point treatment plant and the Southern Landfill.
We will be adjusting the route due to Island Bay’s Day in the Bay this weekend, with the trucks following an alternative route along State Highway 1 and up through Brooklyn (pictured below). Trucks will use this route from 6am-6pm on Saturday and Sunday, with trucks following the existing route outside of these hours. We expect about 5 to 6 trucks each way per hour during this period.
From Thursday through to Sunday, we will also be staggering the truck movements, as well as reducing the number of trucks on the road.
We apologise for any inconvenience this additional traffic may cause, but we are working to prevent the need to discharge the sludge into Cook Strait while we work to repair the pipeline to the Southern Landfill.
Update 29 January
We are continuing with our investigations into the tunnel and sludge pipelines. As part of these investigations, we are testing air valves along the pipelines in the tunnel.
As air valves are located along the pipeline, these investigations may result in noticeable odour areas surrounding the tunnel that runs under Mt Albert. We apologise for any odour issues that arise as part of this work.
Update 28 January
We have begun CCTV through the Mt Albert tunnel, which is an essential part to our investigations, helping us to understand the extent of the fault and look into solutions for the long term repair.
Trucks continue their operations 24/7, transporting sludge from the treatment plant to the landfill. The drivers have been greeted with a positive response from the community, with the sign pictured appearing on the route to the landfill.
We will be sharing weekly updates on the Moa Point situation as works continue. However, we will provide further updates should anything change.
Update 27 January
Trucks continue to work around the clock, transporting sludge from Moa Point to the landfill. We have managed to reduce the number of trucks and still continue to keep up with demand, meaning we are avoiding discharge into the Cook Strait.
We understand truck movements may be inconvenient to residents along the route, and we thank them for their understanding. We are briefing truck drivers to ensure they are keeping themselves and the public safe by reducing their speed.
The picture below shows an example of the sludge/slurry that is taken to the landfill for dewatering. This process removes the water, which then is piped back to the treatment plant through the wastewater network. The leftover solids are then put in the landfill.
Update 24 January
The trucking operations that have been operating this week, continue to prevent sludge from being discharged into the Cook Strait. The alternative operation means trucks on 24 hour rotation collect the wastewater treatment byproduct at the Moa Point Treatment Plant, taking it to the landfill at Carey’s Gully.
The operation was today refined by reducing the amount of trucks on the road and splitting them into two shifts of 6-7 trucks each. These trucks are continuing to keep up with demand, and are operating efficiently.
The fault in the pipeline was located yesterday, and we are continuing to plan a repair with a temporary bypass, as well as a long term fix. The location appears to be about 200m inside the tunnel under Mt Albert.
We are working with the local community at Moa Point, and are holding a community meeting on Sunday to update them on the project and address any concerns residents may have.
We will provide further update on Monday 27 January.
Update 23 January
Trucking operations are continuing as an alternative to the sludge pipeline between Moa Point Treatment Plant and the landfill at Carey’s Gully.
The pipeline failed last week, and a repair could be a month away or longer. No wastewater or sludge was discharged to the environment as a result of the failure, which occurred in a wastewater tunnel beneath Mt Albert.
Investigations have located the point of failure and work is under way to plan a repair with a temporary bypass, as well as a long term fix. It will be a complex job, because wastewater also flows within the tunnel towards Moa Point, making for dangerous working conditions.
With the pipeline out of action, there is a risk that if the trucking option is interrupted for 24 hours or more, some sludge may need to be discharged via the long outfall pipe that carries treated wastewater out to Cook Strait.
When the plant was built, the intended alternative to pumping sludge to the landfill in the event of a significant failure was to discharge it via the long outfall. Public expectations have changed since then however, and Wellington Water and teams of contractors are making every effort for this not to happen.
The trucking system is keeping up with daily demand, but because treatment operations at the plant and the landfill were not designed to load and unload sludge from trucks, there remains a risk that we may have to discharge sludge from the outfall.
Wellington Water is also working across a number of other options for the pipeline repair and to manage the sludge volumes.
- The treatment plant discharges over 70 million litres of treated water a day.
- Just over a million litres of sludge is produced at the plant a day. This is being transported by truck to the landfill.
- The sludge pipeline from the treatment plant to the landfill runs for 9km. It consists of two pipes, which operate one at a time, to allow for maintenance. It is highly unusual that they both have failed.
Investigations are under way for repairs to two pipes that convey a wastewater treatment byproduct – generally known as sludge – from Moa Point Treatment Plant to the council’s Southern Landfill in Carey’s Gully.
The pipes were installed in the mid-1990s, when the treatment plant was built (prior to that, wastewater was discharged to the sea at Moa Point via a short outfall pipe). They were designed to last for 80 years or more, and we believe these repairs are the result of an installation defect.
Only one pipe is operating at a time, but in this case, repairs are necessary on both. The pipes are under very high pressure when operating, and pass through a tunnel beneath Mt Albert. This is where the repair will be carried out.
While we carry out the repairs trucks will be used to convey sludge from the plant to the landfill. About a million litres of sludge a day is generated at the plant, and trucks may need to operate around the clock from time to time.
A similar repair, also due to a defect in the concrete in which the pipes are embedded, was carried out in 2013 and took about five weeks to complete.
We’ll provide more information on the repair timeline and truck schedule as we learn more.