Comparison of leachate attenuation characteristics of colliery spoils in field, column and batch tests

摘要

Waste Management paper 26B (DoE, 1995) recognises the validity of site specific designs to remove the leachate hazard to surface and ground water posed by landfills, and thus decrease the problem of "over engineering" of low-risk landfill sites. This includes the consideration of materials in landfill systems to attenuate the hazardous components of leachate before they reach vulnerable ground or surface waters. The process of leachate attenuation includes; physical (e.g. dilution), physicochemical (e.g. sorption, ion exchange), chemical (e.g., precipitation and complexation), and microbial (e.g. degradation). However, before leachate attenuation is considered in the risk assessment procedure for andfill design a thorough understanding of the processes governing the attenuation of leachate are required. Coal mining and associated coal utilising industries have led to waste material often referred to as colliery spoil. Colliery spoils have been used in construction of landfill liners due to the large redundant volumes of little economic use. However, previous investigations into the attenuation capacity of spoil are limited, and due to its inherent variability a large number of samples may need to be tested during material selection to ensure adequate performance. Rapidity of the test becomes significant when comparing a large lumber of samples, which would be the case during material selection in the quality assurance phase of landfill liner construction. The two main types of laboratory test used in leachate attenuation investigations are batch equilibrium and column flow tests. Both tests are used to obtain contaminant retention parameters for use in risk assessment studies of contaminant transport from landfill sites. Laboratory tests are more frequently performed than field based tests due to better control on the test conditions and relative ease of test monitoring Batch tests are routinely used in the laboratory in preference to column tests because of the relatively short test time, reduced need for leachant sample analysis, and better test precision. However, column tests are considered to be more realistic than batch tests in determining sorption parameters since they simulate the migration of contaminants in the field more accurately. This paper aims to discuss the use of batch and column tests for assessing colliery spoil as a leachate attenuating material within landfill liner systems. The results of a large-scale field test are also presented for comparison with laboratory test results.