Selection and Traceability of Parameters To Support Hanford-Specific RESRAD Analyses -- Fiscal Year 2008 Status Report

Abstract

In fiscal years 2007 and 2008, the Hanford Site Groundwater Remediation Project, formerly managed by Fluor Hanford, Inc., requested the Pacific Northwest National Laboratory (PNNL) to support the development and initial implementation of a strategy to establish and maintain, under configuration control, a set of Hanford-specific flow and transport parameter estimates that can be used to support Hanford Site assessments. The motivation for this work was the realization that previous site assessments have used different parameters, and that published references often do not provide direct traceability of the parameters back to the raw data and analytical approaches used to derive the assessment parameters.The goals of the work described in this report are to improve the consistency, defensibility, and traceability of parameters and their ranges of variability, and to ensure a sound basis for assigning parameters for flow and transport models. The strategy was to identify the existing parameter data sets most recently used in site assessments, documenting those parameter data sets and the raw data sets on which they were based, and use the existing parameter sets to define best-estimate parameters for use in the RESRAD code. The RESRAD code is a computer model designed to estimate radiation doses and risks from RESidual RADioactive materials. The Hanford-specific assessment parameters compiled for use in RESRAD are traceable back to the professional judgment of the authors of published documents. This document provides a summary of those efforts, culminating in a set of best-estimate Hanfordspecific parameters for use in place of the default parameters used in the RESRAD code.

Evaluation of Soil Flushing for Application to the Deep Vadose Zone in the Hanford Central Plateau

“…The general stratigraphy of lithologic units beneath the 200 West Area (Figure 3.1) was based on that described by Last et al (2009a) and Last et al (2009b) and use the layer identification nomenclature from these reports. The mean thicknesses of layers provided in these reports were used in the simulation.…”

“…Representative hydraulic properties from sediment classes in Last et al (2009b) were assigned to each hydrostratigraphic unit. Hydrologic parameter values for each of these sediment classes were derived from Last et al (2006) and Last et al (2009b).…”

“…Hydrologic parameter values for each of these sediment classes were derived from Last et al (2006) and Last et al (2009b). Last et al (2006) provided statistical distributions of van Genuchten model (van Genuchten 1980) parameters (α, n, θr, θs) and saturated hydraulic conductivity (Ks).…”

“…Last et al (2006) provided statistical distributions of van Genuchten model (van Genuchten 1980) parameters (α, n, θr, θs) and saturated hydraulic conductivity (Ks). Bulk density data were derived from laboratory data contained in a prototype hydraulic properties database (Last et al 2009b). When a geological unit contained more than one sediment class, only one of the sediment classes was selected in the simulations.…”

“…The typical saturated hydraulic conductivity values for these layers listed in Tables 3.1 and 3.2 reflect the averaging scheme used by Last et al (2009aLast et al ( , 2009b and may not reflect the values beneath a specific waste site. For example, a thin caliche layer, which has very low hydraulic conductivity, is often present in the 200 West Area.…”