This paper presents a radically new approach for evaluating hazardous waste leachability. In the past, leachability has been measured through conductance of laboratory leaching tests, either batch or column, using experimental conditions that attempt to simulate field conditions. An approach is proposed in which measured intrinsic properties of a waste are used in mathematical models to infer the long-term leachability.

To provide background information, laboratory leaching tests are reviewed with emphasis on interpretation of the results. It is argued that results of bench-scale tests are difficult to scale up to field disposal conditions and that they do not lend themselves to extrapolation over time.

Leaching from wastes takes place via solubilization of contaminants inside the matrix and transport through the matrix pore system to the surrounding aqueous solution. Intrinsic properties that determine leaching rates can be categorized as chemical or transport phenomenon. Chemical properties include those factors that determine a contaminant's solubility, for example, chemical speciation, precipitation, adsorption, kinetics of reaction, buffering capacity, and so forth. Transport properties include structure of the pore system, factors affecting diffusion of ions in the pores, and hydraulic conductivity. Laboratory methods to measure these properties are briefly described.

A mathematical model, developed to predict leaching of toxic metals from solidified wastes under acidic conditions, is described. The model uses measured properties of wastes to predict leaching rates under a variety of conditions. Verification experiments are presented and the merits and limitations of the model for long-term predictions are discussed.