This paper demonstrates the operation of EXPAR, a knowledge-based system designed to assist in preparing a set of data for a contaminant transport model. The accompanying evaluation exercise provides preliminary indications of the usefulness of EXPAR. The exercise tested the ability of participants to simulate the distribution of three organic compounds at a hazardous waste site near Ottawa, Canada. A modest set of basic information was provided together with one of four sets of supplementary data. The embedded knowledge in the EXPAR system appeared to provide valuable assistance in modeling, and the system itself met our expectations in terms of the user-friendliness and robustness. Additional work will be required to remove the weaknesses found in the evaluation particularly with respect to biodégradation data and guidance in establishing flow directions. The results of the project have shown that knowledge-based systems show promise in solving problems associated with the implementation of a transport model.