Designing Alternative Landfill Covers Using Parametric Uncertainty Analysis

This presentation describes a comprehensive effort to address landfill cover design using innovative numerical estimation methods with site-specific data. The sensitivity of predicted cover performance was evaluated while incrementally changing engineering variables including cover thickness, soil type, and percent plant cover. For each of the 72 different combinations of these variables, a Monte Carlo technique was used to vary soil hydraulic properties for 1000 simulations, with a statistical range determined by laboratory analyses of soil samples collected from the site. The multiple simulations represent a stochastic technique that allows for the variability of measurement results to be included in numerical predictions. Modeling results demonstrated that a minimum thickness for covers of all soil types and the presence of at least a minimum plant cover were necessary to prevent drainage of more than 0.5 cm/yr. Variations in both cover thickness and percent plant cover showed the presence of threshold values for each soil type tested, beyond which incremental additions added little to cover performance. The methods developed demonstrate innovative uses for numerical simulations, which can provide for cost effective cover designs and contribute to improved decision making by improving the technical basis for negotiating final cover systems with regulatory authorities.