Modelling the cost-effectiveness of sanitary landfill leachate control systems

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Abstract
Leachate leakage is a major risk associated with sanitary and hazardous waste landfills. This paper describes how two simple performance models, time to breakthrough and leachate leakage flux, can be used in conjunction with a cost model to develop cost-effectiveness relationships which can be used to assist the leachate control system design and planning decision-making process, and, thereby, reduce this risk. Sensitivity and marginal analyses indicate that time to breakthrough (tb) is most sensitive to liner hydraulic conductivity and thickness and that increasing liner thickness yields increasing marginal returns to fb. Leachate leakage flux (qL) is sensitive to liner hydraulic conductivity and the leachate collection pipe spacing-liner thickness ratio. For a given pipe spacing, increasing liner thickness yields decreasing marginal returns to qL. Hypothetical cost-effectiveness relationships for tb and qL are developed analytically and numerically. As a means of introducing the concept of risk, a probability density function for liner hydraulic conductivity is introduced into these relationships.