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Assessing landfill leachate quality and leachate treatment efficiency using good sampling practices

A number of the compounds detected in landfill leachates have proved to be harmful to humans and to the natural environment. As a result, appropriate landfill leachate treatment methods must be developed, with the aim to reduce harmful concentrations of pollutants to levels which do not impose a threat to the natural environment. The complex nature of the leachates makes it difficult to select the most appropriate set of treatment methods for a specific landfill, and the actual efficiency of a treatment plant is measured in situ by comparing the quality of the water entering the plant with the quality of the water leaving the plant. The complex nature of the leachates puts high demands on the sampling, handling of sample before analyses, and analyses, as the character of the sample must not be altered. The demands increase with decreasing concentrations of the targeted compounds (µg/1 level or less). Despite this, no standard protocols for sampling and handling of leachate samples exist. The purpose of this study was to give examples of good sampling practices. Important aspects to consider during sampling and handling of samples are; i) sampling of nonhomogenized water bodies, ii) contamination, and iii) alterations of samples during collection and storage. It was found that a number of substances are enriched in the surface layer of a water body, why it was concluded that the surface layer is an important matrix to consider, both concerning the presence and the transport of harmful compounds. The risk of contamination during sampling was evaluated with the use of a field water blank, which was handled as a true water sample. It was found that despite careful handling contaminants were found at low concentrations (µg/1 level) in the field water blank, which indicated a severe risk of contamination during leachate sampling, handling of sample and/or analyses. Also in this study, the alteration of leachate samples during transport and storage was assessed. The results showed that preservation with 0.2 weight-% sodium azide immediately after sampling and storing at 48° C for a maximum of seven days in borosilicate glass bottles, resulted in the lowest loss of organic compounds from the samples. It has been evident since long that the reported character of sampled landfill leachates varies significantly. The variations can been assumed to sometimes origin from the sampling procedures used. In conclusion, the choice of sampling, transport, storage, and sample preparation before analyses is more crucial for the outcome of leachate characterisation studies than sometimes conceived.