Effect of the leachate head on the key pollutant indicator in a municipal solid waste landfill barrier system.

In previous studies of municipal solid waste (MSW) landfill barrier systems, chemical oxygen demand has been found to be the key pollutant indicator when estimating the breakthrough time for. However, the leachate head in a municipal solid waste landfill can be very high (>10 m in some Chinese landfills). The key pollutant indicator could be different at different leachate heads. The leachate head will continuously change during the use of a landfill. Different pollutants have different transport characteristics in the leachate, so it is necessary to determine whether changes in the leachate head change the key pollutant indicator for identifying breakthrough in a landfill barrier system. In this study, numerical models were used to investigate transport of common leachate pollutants through four typical landfill barrier systems with different leachate heads. Chemical oxygen demand reached the breakthrough threshold before the other pollutants, irrespective of (1) the leachate head and (2) changes in the leachate head. It was therefore clear that the leachate head did not affect the selection of the key pollutant indicator for identifying breakthrough in a landfill barrier system.

Leachate breakthrough mechanism and key pollutant indicator of municipal solid waste landfill barrier systems: Centrifuge and numerical modeling approach.

Groundwater pollution by leachate leakage is one of the most common environmental hazards associated with municipal solid waste (MSW) landfill sites. However, landfill leachate contains a large variety of pollutants with widely different concentrations and biotoxicity. Thus, selecting leachate pollutant indicators and levels for identifying breakthrough of barrier systems are key factors in assessing their breakthrough times. This study investigated the transport behavior of leachate pollutants through landfill barrier systems using centrifuge tests and numerical modeling. The overall objective of this study is to investigate breakthrough mechanism to facilitate the establishment of a consistent pollutant threshold concentration for use as a groundwater pollution alert. The specific objective of the study is to identify which pollutant and breakthrough threshold concentration should be used as an indicator in the transport of multiple pollutants through a landfill barrier system. The threshold concentration from the Chinese groundwater quality standards was used in the analysis of the properties of leachates from many landfill sites in China. The time for the chemical oxygen demand (COD) to reach the breakthrough threshold concentration at the bottom of a 2m compacted clay liner was 1.51years according to centrifuge tests, and 1.81years according to numerical modeling. The COD breakthrough times for single and double composite liners were within the range of 16 and 36.58years. Of all the pollutants, COD was found to consistently reach the breakthrough threshold first. Therefore, COD can be selected as the key indicator for pollution alerts and used to assess the environmental risk posed by MSW landfill sites.