Biotic Components, Processes and Characteristics Central to Biotic Transport Modeling of Soils at the Nevada Test Site. M. M. Hooten, J. T. Markwiese, T. G. Myles, B. Crowe, A. Colarusso, P. Black, R. Ryti, J. Tauxe, K. Ostler, and D. Hansen; Neptune and Co., Inc., University of Toronto, Los Alamos National Laboratory, and Department of Energy, Nevada
The potential for biotic mixing of soils leading to upward transport of buried contaminants has emerged as a significant sensitivity in performance assessments (PAs) of low-level radioactive waste at the NTS. To date, uncertainties and large gaps in biotic information have required undue conservatism in probabilistic models of biotic transport processes. This overestimates the probable radiological releases from disposal systems at the NTS and does not facilitate effective decision-making. A comprehensive literature search addressed biological assumptions of probabilistic biotic transport models for soils and identified plants and animals of the NTS capable of accessing and/or mixing waste when buried under less than 3 to 5 m of soil cover. Plants bioaccumulate contaminants in their tissues, thus leading to redistribution of contaminants with the loss of shed materials or the death of the plant. Animals primarily mix contaminants in near-surface soils as a result of nesting, foraging, and burrowing activities. We have developed conceptual models and a corresponding numerical (probabilistic) model befitting the details of biotic soil transport modeling in arid systems using the information provided in this paper. The numerical model will be used as a basis for creating summary statistics of model parameters, identifying data deficiencies, and performing sensitivity analyses to identify parameters that require further data collection. These efforts will clarify existing data gaps and uncertainties that to date, have been obscured by a lack of biotic information regarding soil-mixing processes. This work serves as a basis for future research and fieldwork for biotic transport modeling at the NTS and in the U.S. desert southwest. The results of this research provide useful information to decision makers and waste disposal managers for estimating waste-isolation integrity over time and for identifying optimal waste disposal options in the future.
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