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Closure and post-closure management (section 5 in the Guide)

Once a landfill or a landfill cell reaches its capacity, it should be progressively closed by constructing a final cover (or cap), which is the key component to minimising:

  • infiltration of rainfall to control quantity of leachate produced, thus minimising groundwater impacts
  • the potential for refuse to come in contact with humans and other ecological receptors
  • vermin access and impact
  • discharge of LFG and fire/explosion potential
  • odours
  • erosion, while providing a surface to sustain landscaping and improve visual aesthetics.

At the time of closure:

  • A final cap should be installed
  • A summary should be prepared of the operational history of the site, any remedial measures that have been undertaken, the location of any bores and monitoring points, and the final cap details.
  • The site should be fenced and locked to prevent access, and signs established advising of the alternative disposal location(s).
  • Any existing issues such as vermin should be carefully monitored.

Final capping

Design considerations

  • Landfill design - if the liner and leachate collection system are capable of significantly reducing seepage of leachate a cap using natural soils is appropriate, in other situations a final cap consisting of compacted clay or using geomembrane or geosynthetic clay liner systems should be used.
  • Climate - in areas with high rainfall, comp-acted clay or geosynthetic systems should be used, in arid or semi-arid climates other solutions maybe appropriate.
  • Slope stability - limit final slope to 1V:4H
  • Desiccation and freeze thaw - avoid crack formation by using less plastic (less clay, more silt) soils and using adequately thick soil layer over clay layer.
  • Settlement - allow for settlement in capping design
  • Erosion - use final slope less than 1V:4H and cut-off drains at approximately 6 m vertical increments.

Final cap designs

Recommended design

  • 150 mm topsoil, 600 mm compacted barrier, 300 mm subgrade or foundation layer.
  • Focus on minimising infiltration

Potential alternatives include:

Capillary Barrier

  • 150 mm topsoil, approx 500 mm finer grained soil, approx 500 mm coarser grained soil
  • appropriate for arid or semi arid climates, less issues with freeze/thaw cracking
Geosynthetic Barrier
  • geosynthetic clay liner and/or geomembrane in cap
  • geosynthetic barriers should be considered where there are shallow or sensitive aquifers underneath the landfill, hazardous waste is present or the site does not have a leachate collection system.

Post-closure care

A post closure care and management plan should be prepared and should include:

  • start and estimated end dates of the post-closure care period
  • detailed description and basis of the monitoring parameters and frequencies for monitoring
  • periodic and incidental maintenance
  • a health and safety plan
  • corrective action measures if adverse impacts (for example, surface water or groundwater contamination, odour, fire) are observed
  • a contingency plan (for fire, earthquake, flood event, etc.)
  • an end-use plan for the landfill.

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Last updated: 17 September 2007