The first of the Mt Albert sludge pipelines to be repaired using a high-strength liner has been returned to full operation, following a comprehensive testing programme and reconnection to the wastewater network. The high-pressure pipeline is now once again transporting sludge between the Moa Point Wastewater Treatment Plant and the Southern Landfill, enabling the interim trucking operations to be stopped.
Wellington Water has also successfully completed a related major project to repair the Moa Point Interceptor, another critical asset in the wastewater network which had suffered damage to its concrete interior due to build-up of corrosive gases. The damaged section of the tunnel has been fitted with a new corrosion-resistant lining and is being put back into operation.
Wellington Mayor Andy Foster says delivering these significant projects under any circumstances is a major achievement, but particularly during the lockdown conditions we have been facing.
“Covid-19 created a number of challenges for these critical and highly technical major projects, from the border closure and disruption of international freight through to the need for social distancing protocols on-site. In that context, Wellington Water and its contractor partners have has done a fantastic job to reach these milestones, while simultaneously duplicating their frontline teams to ensure our essential water networks were safely protected and maintained throughout every level of the lockdown.”
Both projects had unique challenges, with the 1.8km Mt Albert sludge pipeline in particular requiring one of the largest-scale installations of the innovative pipe liner product anywhere in the world.
“I particularly want again to record our gratitude to the team from Amex Sanivar who left home and family and came half way around the world during the Covid crisis, to install the pipeline,” Mayor Foster said. “I also want to thank the rest of the team on the job, as well as neighbours of the tunnel-end worksites in Kilbirnie and Island Bay, and residents along the sludge trucking route for their patience while this essential work was carried out.”
Wellington Water Chief Executive Colin Crampton said it was a great result to have the first pipeline back up and running, and the sludge trucks off the road, without having had any discharge to the sea.
“Meeting the engineering challenges of this project has required a high degree of ingenuity from both local contractors and international specialists, as well as skilled work in often difficult conditions from the crews on the ground.”
“We’re also deeply appreciative of the patience and understanding shown by the residents who’ve had sludge trucks going past their homes, which provided us the opportunity to repair the pipeline and ensure sludge did not have to be discharged to the ocean,” says Mr Crampton.
“The repair solution also improves the durability of the pipeline within the tunnel, minimising the risk of the pipe failing is such a difficult-to-reach place again. The extra lifespan gives Wellington City Council and the region more time to consider options for a more sustainable approach to managing sludge than disposal into landfill.”
The liner for the second pipeline has arrived from Germany and preparatory works for its installation have already begun. It is expected to be operational in approximately three weeks.
“The success of the first pipeline certainly gives us confidence going into the second, but as with any complex engineering project, there are ongoing risks to manage and we’ll be proceeding carefully and methodically,” says Mr Crampton.
While one pipeline provides sufficient capacity to allow sludge trucking to cease immediately, the second is designed to act as a backup and, operating in combination with the first, allows higher volumes of sludge to be transported more efficiently.
Max Vollenbroich of German firm Amex-Sanivar helps guide the folded and taped high strength liner towards the sludge pipe. Over 1.8km of liner was drawn through a damaged 150mm diameter, concrete-encased pipe in an 8-hour operation that will leave the pipe stronger and much less likely to fail than before. Once in place, the liner is inflated using compressed air to break the tape and form a tubular shape within the old pipe.
The 1.8km- long liner was manufactured in Germany and shipped here under urgency for the repair during the Covid-19 Level 4 lockdown. A second liner arrived in New Zealand last week, and will be drawn through the companion pipe in a similar operation getting under way this week. Five specialist technicians flew to New Zealand to oversee the installation, spending two weeks in quarantine prior to carrying out the work. They will return in mid-June.
Mayor Foster and Councillor Sean Rush visit the site with Josh Wright and Elliot Altham (right) from consulting engineers Stantec.