The PRESTO-EPA MODEL - A user friendly, comprehensive, efficient, and accurate health effects simulation model for assessing low-level radioactive waste disposal sites

This paper presents the characteristics of the PRESTO-EPA-CPG model with emphasis on its application features, efficiency and accuracy. The original model published in 1985 was designed to assess the maximum individual dose to a critical population group and the genetic and somatic health effects to the general population due to the disposal of radioactive wastes in near surface trenches. This model was subsequently modified to improve its efficiency and accuracy and to expand its potential application to various practices, including waste disposal soil cleanup, and agricultural land application of waste materials. Accuracy of analysis was emphasised as one of the important goals of the model design. To achieve this goal a dynamic infiltration submodel, a multi phase leaching submodel and a dynamic well mechanics submodel was used. As a result model complexity was considerably increased. To reduce the complexity and to increase the efficiency of the model simplified equations were used. For instance, the original partial differential equation system for the infiltration submodel was transformed into an ordinary differential equation system by dividing the soil moisture into three components; gravity water, pellicular water, and hygroscopic water. The transformed model was validated using field data obtained from Barnwell, South Carolina. In addition, an Ad Hoc leaching submodel was also developed based on results obtained using EPA's multiphase leaching model. Hung's one-dimensional ground water model was adopted for the groundwater submodel, which has greatly simplified the simulation, especially with daughter nuclide ingrowth effects built in. A one-dimensional model could inherit significant theoretical errors relative to a three-dimensional model. However, these theoretical errors can be minimised in normal PRESTO-EPA model applications, as verified in a recent benchmarking study on solute transport. The PRESTO-EPA Operation System also includes interface software to assist users in preparing input-files, executing the simulation model, and displaying results. This interface program has considerably improved the operation of the system. Further improvements are expected from converting the existing interface program from a DOS to a Windows-95 environment