Suggestions for improvement of the methodology and use of MEPAS, the Multimedia Environmental Pollutant Assessment System. Environmental Restoration Program

The Multimedia Environmental Pollutant Assessment System (MEPAS) has been evaluated for the purpose of determining if the current ranking of waste sites is realistic and reliable. There are two main reasons for the uncertainty of the rankings identified in this study: the use of the hazard potential index (HPI) and the user input. The HPI contributes to unreliable rankings because risks to human populations are summarized in a single numerical value. A final result from MEPAS should include risks to the maximally exposed individual, average individual, and the population (noting the population size) so that users can evaluate and weigh these risks. Examination of user input indicates that exposure pathways and exposed populations were sometimes arbitrarily selected. Users must be better informed about the characteristics of the waste site and its potential interaction with human populations for realistic input to the MEPAS model to be developed. Without realistic and consistent input to the MEPAS, or any model, reliable results cannot be expected and any prioritizations based on the results will be questionable.