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SIMULATING RADIONUCLIDE FATE AND TRANSPORT IN THE UNSATURATED ZONE: EVALUATION AND SENSITIVITY ANALYSES OF SELECT COMPUTER MODELS
Citation:
Chen, J., R. Drake, Z. Lin, AND D G. Jewett*. SIMULATING RADIONUCLIDE FATE AND TRANSPORT IN THE UNSATURATED ZONE: EVALUATION AND SENSITIVITY ANALYSES OF SELECT COMPUTER MODELS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/R-02/082 (NTIS PB2003-104288), 2003.
Impact/Purpose:
Information.
Description:
Numerical, mathematical models of water and chemical movement in soils are used as decision aids for determining soil screening levels (SSLs) of radionuclides in the unsaturated zone. Many models require extensive input parameters which include uncertainty due to soil variability and unknown future meteorological conditions. The impacts of uncertain model parameters upon pertinent model outputs are required for sound modeling applications. Model users need an understanding of these impacts so they can collect the appropriate parameters for a given site and incorporate the uncertainties in the model predictions into the decision making process. This report primarily summarizes the findings which address the uncertainties and sensitivities of model outputs due to uncertain input parameters. The report also addresses the sensitivity of simulated results to conceptual model selection, and the comparison of sensitivity results between models, illuminating numerical differences and errors.
Five models were evaluated in this study: CHAIN, MULTIMED_DP 1.0, FECTUZ, CHAIN 2D, and HYDRUS. The models span a range in detail and intended use. This report presents information on the sensitivity of these codes to model conceptualization of radionuclide transport in the vadose zone, to numerical differences and errors, and to changes and uncertainties in input parameters, as well as presenting information concerning the analysis and interpretation of certain modeling components. The report does not intend to assess the appropriateness of any model for a particular use nor the uncertainty due to the model chosen, but it does indicate the problems and limits of using certain modeling components for certain physical applications. This study identified the limitations and advantages of using the selected codes for assessing the transport and fate of radionuclides in the unsaturated zone. The study also assessed the degree of uncertainty that exists in various model output parameters due to the combination of sensitivities of input parameters, high parameter variabilities, model type with its particular set of components, and the specific properties of the radionuclides.