IntroductionMassive efforts are underway to clean up hazardous and radioactive waste sites located throughout the United States. To help determine cleanup priorities, computer models are being used to characterize the source, transport, fate, and effects of hazardous chemicals and radioactive materials found at these sites. Although the U.S. Environmental Protection Agency (EPA), the U.S. Department of Energy (DOE), and the U.S. Nuclear Regulatory Commission (NRC) have provided preliminary guidance to promote the use of computer models for remediation purposes, no agency has produced directed guidance on models that must be used in these efforts. As a result, model selection is currently done on an ad hoc basis. This is administratively ineffective and costly, and can also result in technically inconsistent decision-making. To identify what models are actually being used to support decision-making at hazardous and radioactive waste sites, a project jointly funded by EPA, DOE, and NRC was initiated. The purpose of this project was to: (1) identify models being used for hazardous and radioactive waste site assessment purposes; and (2) describe and classify these models. This report presents the results of this study. A mail survey was conducted to identify models in use. The survey was sent to -550 persons engaged in the cleanup of hazardous and radioactive waste sites; 87 individuals responded. They represented organizations including federal agencies, national laboratories, and contractor organizations. The respondents identified 127 computer models that were being used to help support cleanup decision-making.There were a few models that appeared to be used across a large number of sites (e.g., RESRAD). In contrast, the survey results also suggested that most sites were using models which were not reported in use elsewhere. Information is presented on the types of models being used and the characteristics of the models in use. Also shown is a list of models available, but not identified in the survey itself.KEY WORDS: Computer models; cleanup decision-making; hazardous wastes; radioactive wastes.plished at many of these sites will be based on initial studies [e.g., Remedial InvestigationFeasibility Studies (RIFS)] resulting from formally or informally negotiagency, In these evaluations, models (e.g,, computerized environmental pathway or engineering) are often used to characterize the source, transport, fate, and efidentified at the sites. The models may also be used to Massive efforts are underway to 'lean hazardous ated agreements bemeen the site and the governing and radioactive wastes found at contaminated sites throughout the United States [e.g., U.S. Environmental Protection Agency (EpA) Superfund Sites and the Nusites.] The nature and extent of cleanup to be accom-Commission (NRC) decommissioning fects of hazardous chemicals and radioactive materials characterize benefits of alternative remediation options.The EPA,(181-183) the U.S.
