Evaluation of a Prototype Decision Support System for Selecting Trench Cap Designs

A computer-based prototype decision support system (PDSS) to assist the risk manager in selecting an appropriate trench cap design for waste disposal sites is evaluated. The selection of the "best" design among feasible alternatives requires consideration of multiple and often conflicting objectives. The methodology used in the selection process consists of: selecting and parameterizing decision variables, using data, simulation models, or expert opinion; selecting feasible trench cap design alternatives; ordering the decision variables and ranking the design alternatives. The simulation models incorporated in the PDSS are the Hydrologic Evaluation of Landfill Performance (HELP) model which is used to simulate the trench cap water balance and the Chemicals, Runoff, and Erosion from Agricultural Manage ment Systems (CREAMS) erosion component that is used to simulate trench cap erosion. The decision model is based on multi-objective decision theory and uses a unique approach to order the decision variables and rank the design alternatives. The PDSS is evaluated using the Hill Air Force Base landfill cover demonstration project. The water balance and surface erosion of four alternative landfill cover designs were monitored for a 4-yr period. Two of the cover designs were used to calibrate and test the simulation models. The results ofthe PDSS, using both data from all four designs and long-term simulations from two of the designs, illustrate the relative advantages of each of the cover designs and which cover is the "best" alternative for a given set of criteria and a particular importance order of those