Skip to main content.

Closed landfill assessment (section 4 in the Guide)

The recommended approach for evaluating environmental and human health risk related to closed or closing landfills, and for subsequent management decision-making, is as follows.

  1. Review available data (setting, construction, contents, monitoring).
  2. Make a preliminary assessment of potential risks.
  3. If the preliminary assessment indicates that low potential for risk exists, undertake no further investigation and consult the relevant regulatory agency.
  4. If moderate or high risk is indicated, or if there is a high level of uncertainty, initiate appropriate investigations to collect further information.
  5. Carry out more structured risk assessment(s) as further information becomes available.
  6. Initiate management or remediation action in consultation with the relevant regulatory authority.

Additional guidance, or formal requirements may be imposed by regional or district plan rules. Early liaison with council staff is recommended.

Review available data

Sources of information on closed landfills include Regional Council files, operators, aerial photos, GIS records, topographical maps and geological maps. It is also important to visit the site prior to making any assessment of the potential risks.

Hazard assessment

Analysis of environmental and human health risk typically follows a tiered approach, ranging from a simple, low cost and conservative guideline comparison to more complex and expensive, but precise, modelling options. At each stage, the results are reviewed and if there is significant uncertainty about the potential for effects further investigations may be required. The questions to be answered include:

Landfill Gas

  • Is the site generating significant quantities of landfill gas
  • Is there potential for accumulation and migration of landfill gas and the presence of an ignition source
  • Will people or biota be susceptible to asphyxiation or explosion

Leachate

  • Are there significant volumes of leachate being generated and/or high concentration of contaminants in leachate
  • What are the flow paths for leachate
  • Are there sensitive areas near the site such as estuarine, aquatic or marine environments, highly visible ground areas

Physical contact with landfill contents

  • Is the a significant number of sharps or pathogens in landfill or cover material
  • Is there exposure or potential for exposure (cap erosion or failure)
  • What is the level of pedestrian traffic, particularly where ground contact is likely

Simple guideline criteria such as ANZECC Water Quality Guidelines, NZ Drinking Water Standards and OSH Workplace exposure standards (for landfill gas) can be used in an initial evaluation of risk.

Visit the Landcare Ecological Risk site for an ecological risk evaluation model being developed for New Zealand.

Risk evaluation

Many management options for closed landfills are very costly. It is important to put landfill-related risks in context, to ensure risk acceptance and spending are compatible with those in comparable infrastructure areas, such as roading and wastewater management.

Because of the range of issues involved in landfill management, risk evaluation should where possible be carried out in a way that allows comparison of risks with different levels of quantification and non-risk issues.

Depending on the amount of data available, this can be done very simply; for example, Yes/No for each element if data is limited or dealing with a single landfill, or by using a number of comparative rating systems for a larger number of sites. Two illustrative examples of comparative rating approaches are included in the guide.

Previous | Contents | Next

Last updated: 17 September 2007