Wednesday, April 2, 2008 : 3:20 p.m.

Incorporating Scenario Uncertainty within a Hydrogeologic Uncertainty Assessment Methodology

Philip D. Meyer1, Thomas Nicholson2, Ming Ye, Ph.D.3, Shlomo P. Neuman4 and Mark L. Rockhold1, (1)Pacific Northwest National Laboratory, (2)US Nuclear Regulatory Commission, (3)Florida State University, (4)University of Arizona

We describe the development and application of an uncertainty methodology that specifically incorporates hydrologic scenario uncertainty.  We discuss the definition and representation of hydrologic scenarios, which contribute to uncertainty in future system states.  The methodology quantifies estimates of predictive uncertainty for ground-water flow and radionuclide transport modeling while considering the combined impacts of uncertainties associated with the conceptual-mathematical model, model parameters, and the scenarios being applied.  The methodology is based on an extension of Maximum Likelihood Bayesian Model Averaging (MLBMA) to include scenario uncertainty.  Scenario uncertainty is represented as a set of alternative future conditions affecting boundary conditions, source/sink terms, environmental processes and events, or other aspects of the model.  Each scenario has a prior scenario probability based on a subjective understanding and judgment of the plausibility of the scenario's occurrence and conditions.  A joint assessment of uncertainty results from combining MLBMA model predictions computed under each scenario using prior scenario probabilities as weights.  Mutually exclusive, alternative scenarios are generated by defining scenarios as possible combinations of non-mutually exclusive events.  Scenario probabilities are determined from estimates of the marginal and conditional probabilities of these events.  We demonstrate the application of this methodology to modeling of ground-water flow and uranium transport at the 300 Area of the U.S. Department of Energy's Hanford Site in central Washington State.  Two scenarios representing alternative future behaviors of the Columbia River adjacent to the site were considered.  Predictive simulations carried out with the calibrated models illustrate how model- and scenario-averaged predictions are computed. The results display the individual contributions from the conceptual model, model parameter, and scenario uncertainties in estimating predictive uncertainties of the numerical transport model.  This application demonstrates the usefulness of the methodology for assessing uncertainties in modeling ground-water flow and radionuclide transport, and understanding the possible sources of the model's inherent uncertainties.

Philip D. Meyer, Pacific Northwest National Laboratory Philip D. Meyer is a Sr. Research Engineer at Pacific Northwest National Laboratory. He received a B.A. degree in Physics from Cornell University and M.S. and Ph.D. degrees in Civil Engineering from the University of Illinois at Urbana-Champaign. Dr. Meyer has 20 years experience in applying models of flow and transport through unsaturated and saturated porous media to the solution of engineering problems, including the estimation and interpretation of hydrologic uncertainties in dose/risk assessment, analysis of flow and transport in soil covers, engineered barriers, and the near-field environment at waste disposal facilities, and groundwater monitoring network design under uncertainty.

Thomas Nicholson, US Nuclear Regulatory Commission Thomas Nicholson is a Senior Technical Advisor in the Office of Nuclear Regulatory Research of the U.S. Nuclear Regulatory Commission (USNRC). He has served in the research office for 25 years, and has worked at the USNRC for 30 years. His principal responsibilities are as the agency technical advisor in hydrogeology and radionuclide transport at nuclear facilities. He formulated and directed research studies in unsaturated and saturated flow and radionuclide transport monitoring and modeling. He holds a B.S. in geological sciences from Pennsylvania State University and a M.S. in hydrogeology from Stanford University, and is a registered professional geologist.

Ming Ye, Ph.D., Florida State University Dr. Ming Ye is an Assistant Professor in the School of Computational Science and Department of Geological Sciences of the Florida State University. Before joining the Florida State University, he was an Assistant Research Professor of the Desert Research Institute, and post-doc of the Pacific Northwest National Laboratory. He received his Ph.D. in hydrology from the University of Arizona in 2002, and a B.S. in geology from Nanjing University, China, in 1997. His research interests include groundwater modeling in saturated and unsaturated porous and fracture media, parameter estimation, applied geostatistics, and uncertainty analysis of groundwater modeling.

Shlomo P. Neuman, University of Arizona Regents' Professor of Hydrology, B.Sc. (1963) Geology Hebrew University Jerusalem, M.S. (1966) and Ph.D. (1968) Engineering Science UC Berkeley, Member U.S. National Academy of Engineering, Fellow American Geophysical Union and Geological Society of America.

Mark L. Rockhold, Pacific Northwest National Laboratory Mark L. Rockhold is a Sr. Research Scientist at Pacific Northwest National Laboratory. He received a B.S. degree in Geology from Kansas State University, an M.S. degree in Soil Physics from Kansas State University, and a Ph.D. degree in Bioresource Engineering (Water Resources) from Oregon State University. Dr. Rockhold’s research interests include measurement and modeling of physical, chemical and biological processes and interactions in soils and groundwater systems, characterization of subsurface heterogeneity, and parameterization for field-scale flow and reactive transport modeling.


2008 Ground Water Summit