Appendix C: Development of total concentration and leachability limits for Class A and Class B landfills

In general, leachability criteria are derived using a target concentration in the receiving environment (drinking water, aquatic ecosystems) and a factor (dilution attenuation factor, or DAF) to account for dilution and attenuation between the landfill and receptor. The criteria adopted for this guideline are as follows.

1. Where the US EPA has developed criteria, these have been adopted:
   
   1. Target concentration: US Primary Drinking Water Standards
   2. DAF: 100 for all contaminants.
   3. Additional contaminants to be included were selected based on common analytical suites (VOC, SVOC, metals) and the availability of appropriate guideline criteria to be used as target concentrations.
2. Where additional contaminants were considered to be soluble in landfill leachate:
   
   1. Target concentration: The lower of the NZ Drinking-water Standard or ANZECC freshwater quality criteria
   2. DAF: Constituent-specific DAF based on a 'standard' Class A landfill.

Where contaminants were considered to be insoluble in landfill leachate, leachability criteria are inappropriate and total concentration criteria were developed. These were based on the concentration at which free product would be present in the waste (and therefore likely to be present in the leachate).

6. DAF = Dilution Attenuation Factor.

7. US Drinking Water Standards (National Primary Drinking Water Standards).

8. Australian Drinking Water Standard.

9. National Environmental Protection (Assessment of Site contamination) Measure, NEPC 1999. Industrial/ commercial land use.

10. LC50 = Lethal Concentration 50, the concentration of a chemical which kills 50% of a sample population

11.Landfill Classification and WAC for Hydrocarbon Contaminated Soil, Report for SMF Project 4153 (unpublished), March 2001.>

12. Health and Environmental Guidelines for Selected timber Treatment Chemicals, Ministry for the Environment and Ministry of Health, 1997.