Combined Estimation of Hydrogeologic Conceptual Model, Parameter, and Scenario Uncertainty with Application to Uranium Transport at the Handford Site 300 Area

摘要

A methodology was developed and applied to systematically and quantitatively assess predictive uncertainty in ground-water flow and transport modeling. The methodology considers the combined impact of hydrogeologic uncertainties associated with the conceptual-mathematical basis of a model, model parameters, and the scenario to which the model is applied. The methodology is based on an extension of a Maximum Likelihood implementation of Bayesian Model Averaging. Model uncertainty is represented by postulating a discrete set of alternative conceptual models for a site with associated prior model probabilities. The prior model probabilities reflect a subjective belief about the relative plausibility of each model based on its apparent consistency with available knowledge and data. Posterior model probabilities are computed and parameter uncertainty is estimated by calibrating each model to observed system behavior. Scenario uncertainty is represented as a discrete set of alternative future conditions affecting boundary conditions, source/sink terms, or other aspects of the models. A joint assessment of uncertainty results from combining model predictions computed under each scenario using as weights, the posterior model and prior scenario probabilities. The uncertainty methodology was applied to modeling of ground-water flow and uranium transport at the Hanford Site 300-Area. Results demonstrate the feasibility of applying a comprehensive uncertainty assessment to large-scale, detailed ground-water flow and transport modeling.