30 | Nelson City Council: York Valley Landfill Upgrade T T Richard Loader Landfill upgrade to deliver stability The project includes the construction of a major buttress 40 metres tall by 120 metres wide at the toe of the front face of the landfill. REGIONAL DEVELOPMENT The Nelson City Council and Tasman District Council have embarked on a $7.9 million project at the York Valley Landfill that will provide stability in the event of a maximum credible earthquake during a 500-year horizon, preventing significant environmental damage. The project includes the construction of a major buttress 40 metres tall by 120 metres wide at the toe of the front face of the landfill. Located just a few kilometres south of Nelson City, York Valley Landfill is the only active regional landfill in the Nelson & Tasman regions. The waste catchment area includes all of Nelson and Tasman and currently all of Buller. In the region of 80,000 tonnes of waste is delivered to the landfill each year, and includes residential waste from trucks and transfer stations, as well as skips and bins from demolition and work sites including production factories. Just over three years ago the joint Councils’ Nelson Tasman Regional Landfill Business Unit (NTRLBU) identified that the risk analysis around landfill stability from a geotechnical and earthquake type event had been based around the active life of the landfill and needed review. Nathan Clarke, General Manager of Regional Services for Nelson City Council and Tasman District Council, had joined the NTRLBU and felt that basing risk analysis around the landfill’s active life was inappropriate. “The reality was that the landfill would be there for a thousand years after it had been filled to capacity,” says Nathan. “We changed our paradigm and instead of looking at it over a thirty-year period, we looked at it over a five-hundred-year period. That told us that the probability of a very large earthquake hitting the landfill during that period shifted from being quite low to quite high, making the risk of the landfill’s failure significantly higher. “From that risk assessment, we identified ways to mitigate the risk, and one of them is the construction of a large buttress, essentially a dam, at the front of the landfill where the waste is placed and compacted. “That dam will add a significant amount of weight to the landfill, so that if it shakes through a seismic event the base will be held and waste cannot slide forward.” Environmental and Engineering Consultancy Tonkin + Taylor has been the principal designer for this latest package of work, while DS Project Solutions was engaged for procurement and to manage the overall programme of work. Planning and design for the project commenced in 2020, and the project is being undertaken over five stages. Stages one and two were the construction of upper buttresses and stormwater channels completed over 2022/23. Stages three, four and five commenced September this year and are being undertaken as one package of work. Mike Edridge Contracting was appointed as lead contractor, following a competitive tender process. Stage three is the relocation of the access road and services away from the base of the landfill, while stage four is rebuilding and increasing the resilience of the leachate management systems. “In a landfill you get water generated that has to be removed otherwise it destabilises the waste material. We’re adding to the existing drains, pipes and wells to get that leachate out.” The fifth stage is putting in 120,000 tonnes of bulk fill in the front, to form the buttress. That material is being sourced from the landfill itself, by digging out some spurs in valleys to reduce the instability in those areas. It is expected stages three, four and five will be completed by the end of April next year. “The completed project will give the Nelson City and Tasman District Council confidence that the landfill will be stable under a maximum credible earthquake event during a 500-year horizon.” Nathan says a key driver for the project was mitigation of the risk of a possible environmental catastrophe should the York Valley Landfill fail following a major seismic event in the region, and waste or leachate spilling into the streams and causing environmental damage. “If that were to happen under a big storm event it might result in waste plastics and leachate getting into the stream and into the sea. In addition to the environmental benefits, the buttress will also give us confidence that we can fill the landfill to its design capacity. “The landfill has a value of around $300 million in respect to the amount of waste it can accommodate. “To reduce the amount of waste able to be accepted in the landfill would reduce its value to the region significantly.” ATEC specialises in weighing and information reporting systems. If you need to scan it, weigh it, track it and report on it, we have a solution. We supply, service, build hardware, software and provide unique solutions for a wide range of industries. ATEC are proud to be a iliated with Nelson City Council. 3 Nayland Road, Stoke, Nelson 03 547 6159 www.atec.co.nz
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