High stakes on Wellington’s South Coast
Sludge trucks prevent an ecological disaster.
High stakes on Wellington's South Coast
By Jim McNaughton
‘Sludge’ is the term for the solids produced from the wastewater treatment process. More than a million litres of sludge per day is usually piped 9km from the wastewater treatment plant at Moa Point to Carey’s Gully sludge dewatering plant at the Southern Landfill as a slurry. Once most of the water is removed, about 45 tonnes of solids are buried in the landfill and the water returned to Moa Point via the wastewater network.
Two high-pressure pipes normally work together in a primary and back-up combination to carry that sludge from Moa Point to the landfill. When both pipes failed deep under Mt Albert in January 2020, an ecological disaster loomed. Because the pipes were not accessible for immediate repair, this sludge threatened to overflow from Moa Point and discharge into Cook Strait.
While the sludge pipes are encased in concrete so the flow was contained, and the Moa Point plant had capacity to store several days of sludge overflow, it was urgent that trucks start running the sludge to landfill—with great care on a narrow winding road.
The scenic south coast is popular with drivers, cyclists, runners and surfers, and features a marine reserve.
From 23 January until 24 May 2020, when the sludge-pipes were repaired, the slow and steady procession of sludge trucks averaged five trips an hour, 24 hours per day, seven days a week along the narrow and winding coastal road, without a single major incident.
The operation may not have looked—or smelled—like success at the time, but the pressure to truck the sludge in trucks was unrelenting and the stakes were high. To prevent an environmental disaster that would adversely impact the health of local marine life and safety of local beaches, drivers had to transport up to 1200m³ (1.2M litres) of sludge every 24 hours from Moa Point to the landfill, a distance of approximately 13 kilometres.
Dave Neru of Hydrotech, who led Wellington Water’s trucking operation, said that the route was very challenging. “It’s a narrow and windy road popular with beach goers, surfers, cyclists and scenic drivers. It’s also a bus route with bus stops in live lanes, and on top of that, an exposed coastal environment prone to wild weather.”
Dave said the operation needed the right people. “They had to have experience in the sewer industry and have local knowledge. They needed to be able to work in a collaborative environment, focused on clear objectives. And they had to be prepared for the commitment and demands required of a 24/7 operation.”
The operation’s health and safety standards were of a level that meant no changes were required when Covid-19 lockdown was imposed.
Lots of things had to come together for the operation to succeed, including the inclusion of all stakeholders and supporting experts from NZTA, Wellington City Council Roading and the Southern Landfill in the planning of the operation. Adaptation to change had to be swift and any new risks identified quickly, and measures put in place. A high level of planning and preparation were necessary, as were constant reviews on performance and information.
Dave said that looking back, the operation was an amazing feat. “We averted a disaster. The operation was a successful extended marine environment rescue mission and I’m proud to have been a part of it.”
Wellington Water CE Colin Crampton with Dave Neru of Hydrotech, Derek Falvey of Veolia, and Wellington City Councillor Sarah Free at an event to celebrate the successful trucking operation.
- The operation ran for 123 days or 4 months and 2 days
- 165 people worked in the operation
- 128,814m³ (129 Million litres) of sludge were moved, the volume of 51.6 Olympic swimming pools (on average 1050m³/day)
- 27,670 Truck movements
- 332,040 kilometres travelled (or 8.2 times around the circumference of the earth)
- On average 5 trucks per hour, 24 hours a day, 7 days a week.