The future of the Burwood landfill site was a hot topic for this forum!
The first presentation was made by Grant Gillard of CCC. He discussed the history of Burwood landfill and that it had served as a municipal solid waste (MSW) landfill from 1984‐2005. He also discussed its role as a disposal location for waste material following the Canterbury earthquake sequence in 2010‐ 2011, for which it reopened in 2011.
Post earthquakes, various waste streams were accepted (C&D waste, liquefaction silt, contaminated soils and hydrovac waste) and were stored in different areas of the landfill. Currently between 5,000‐30,000 tonnes of contaminated soil is received at the landfill per month at a cost of $20 per tonne. The cost of disposing of this type of material at Kate Valley landfill is $300 per tonne.
The landfill is due to finally close in December 2020. The impact of the closure of this facility on development in the area is likely to be significant. It is planned to plant over 10,000 natives over the area and use it as a recreational reserve with walking and mountain bike tracks. The landfill has been capped with an evapotranspiration type cap which allows a proportion of the landfill gas (LFG) to vent passively.
LFG has been collected at Burwood landfill since 2002. The gas is composed of between 47‐55% methane, 33‐36% CO2 and the remainder is made up of various other gasses. Initially the gas was flared off but was subsequently used as an energy source for municipal buildings in the city. A gas pipeline extends 17km from the landfill to the Bromley waste water treatment plant and then into the city to the Art Gallery and Te Honoaga Civic offices. The gas field produces between 200‐600m3/hr of LFG and it is thought likely to produce enough LFG to meet demand until 2027.
The second presentation was given by Joanne Ferry of Tonkin + Taylor, who discussed the generation of LFG in general terms and the factors that affects it. By far the most important factor in methane generation in a landfill is the percentage of the organic content of the waste being disposed of. The type of organic matter also affects the rate of methane production and the length of time over which it is produced. LFG production extends well beyond 30 years.
Certain type of organics, such as wood waste, degrade slowly and produce LFG for long periods of time. This type of waste should be considered for diversion from landfills and thus have an impact from a carbon credits and economic perspective. There is currently no regulatory requirement to manage LFG emissions once a landfill has closed. The future of landfill site selection was also discussed. There is the option to repurpose existing quarries, to develop greenfield sites or to consider alternatives such as waste to energy and other new innovations. With greenfield developments it allows for better site selection and for a best practice landfill to be designed and constructed. Repurposing of existing quarries has a host of problems including leachate management and aesthetic effects. Currently, New Zealand does not have the scale to construct a waste to energy plant.
Landfills can produce LFG for much longer than is commonly thought. A site in New Zealand which has been closed for nearly 100 years is still producing landfill gas.
The ligering question is, what is available to replace Burwood landfill?
Finally, all agreed that new innovations are needed to deal with our waste going into the future.
Presenter Name |
Presenter Company |
Grant Gillard |
Christchurch City Council (CCC) |
Joanne Ferry |
Tonkin + Taylor (Auckland office) |
30 July 2019 NZ event report by Cecilia Gately – GHD Limited
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