HR: 11:50h
AN: H32B-06    [Abstracts]
TI: Uncertainty and the Conceptual Site Model
AU: * Price, V
EM: vprice1@alltel.net
AF: Van Price, Advanced Environmantal Solutions, LLC 407 West Main Street, Lexington, SC 29072, United States
AU: Nicholson, T J
EM: tjn@nrc.gov
AF: Thomas J. Nicholson, Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, Two White Flint North, 11545 Rockville Pike, Rockville, MD 20852, United States
AB: Our focus is on uncertainties in the underlying conceptual framework upon which all subsequent steps in numerical and/or analytical modeling efforts depend. Experienced environmental modelers recognize the value of selecting an optimal conceptual model from several competing site models, but usually do not formally explore possible alternative models, in part due to incomplete or missing site data, as well as relevant regional data for establishing boundary conditions. The value in and approach for developing alternative conceptual site models (CSM) is demonstrated by analysis of case histories. These studies are based on reported flow or transport modeling in which alternative site models are formulated using data that were not available to, or not used by, the original modelers. An important concept inherent to model abstraction of these alternative conceptual models is that it is "Far better an approximate answer to the right question, which is often vague, than the exact answer to the wrong question, which can always be made precise." (Tukey, 1962) The case histories discussed here illustrate the value of formulating alternative models and evaluating them using site-specific data: (1) Charleston Naval Site where seismic characterization data allowed significant revision of the CSM and subsequent contaminant transport modeling; (2) Hanford 300-Area where surface- and ground-water interactions affecting the unsaturated zone suggested an alternative component to the site model; (3) Savannah River C-Area where a characterization report for a waste site within the modeled area was not available to the modelers, but provided significant new information requiring changes to the underlying geologic and hydrogeologic CSM's used; (4) Amargosa Desert Research Site (ADRS) where re-interpretation of resistivity sounding data and water-level data suggested an alternative geologic model. Simple 2-D spreadsheet modeling of the ADRS with the revised CSM provided an improved match to vapor-phase tritium migration. Site-specific monitoring coupled to these alternative CSM's greatly assists in conducting uncertainty assessments. (Work supported by USNRC contract NRC-04-03-061.)
DE: 1829 Groundwater hydrology
DE: 1847 Modeling
SC: Hydrology [H]
MN: 2007 Fall Meeting