Physical, Hydraulic, and Transport Properties of Sediments and Engineered Materials Associated with Hanford Immobilized Low-Activity Waste

Abstract

Current plans for treatment and disposal of immobilized low-activity waste (ILAW) from Hanford's underground waste storage tanks include vitrification and storage of the glass waste form in a near-surface disposal facility. This Integrated Disposal Facility (IDF) is located in the 200 East Area of the Hanford Central Plateau. Performance assessment (PA) of the IDF requires numerical modeling of subsurface flow and reactive transport processes over very long periods (thousands of years). The models used to predict facility performance require parameters describing various physical, hydraulic, and transport properties. This report provides updated estimates of physical, hydraulic, and transport properties and parameters for both near-and far-field materials, intended for use in future IDF PA modeling efforts. Previous work on physical and hydraulic property characterization for earlier IDF PA analyses is reviewed and summarized. For near-field materials, portions of this document and parameter estimates are taken from an earlier data package. For far-field materials, a critical review is provided of methodologies used in previous data packages. Alternative methods are described and associated parameters are provided. For far-field materials, consisting of both sand-and gravel-dominated facies underlying the IDF, a particular model has been used in previous PA modeling efforts to represent the saturation-dependent anisotropy of unsaturated hydraulic conductivity. We recommend that this model be replaced with a more recent and general tensorial pore-connectivity-tortuosity (TCT) model for saturation-dependent anisotropy. Simulation results from both the TCT and the earlier anisotropy model have been compared with observed data from a controlled vadose zone field injection experiment performed just south of the 200 East Area. The TCT model was shown to predict observed flow behavior at this site as well as or better than the model used in previous PA efforts, and with many fewer added model parameters (one versus eight). Recommended parameter estimates for the TCT model are presented. Previous estimates of dispersivities for vadose zone sediments were based on stochastic theory developed for saturated aquifer materials. An extensive literature review is presented that suggests these estimates may not be appropriate for unsaturated conditions. An alternative approach based on more fundamental physical property information is described and updated parameter estimates are presented.

Sensitivity Analysis of Contaminant Transport from Vadose Zone Sources to Groundwater

“…In laboratory characterization studies, hydraulic conductivity calculations are typically made for the vertical direction only, due to the vertical orientation of core samples. Therefore, moisture-dependent anisotropy can usually only be inferred from field observations and theoretical calculations (Rockhold et al 2015). In contrast, aquifer characterization studies are usually targeted at determining hydraulic conductivity or transmissivity in the horizontal direction, owing to the use of wells for injection/ withdrawal/monitoring.…”

“…Simulations were performed using baseline values of K s shown in Table 3.1 for the vertical direction, but increasing the K s values applied to the x-and y-directions by a factor of four (4X) for the H1, H2, and H3 subunits. In addition to anisotropy in K s , the combined effects of anisotropy in K s plus anisotropy in unsaturated hydraulic conductivity were evaluated using a tensorial connectivity-tortuosity (TCT) model (Zhang and Khaleel 2010;Rockhold et al 2015). The TCT model parameters that were used are listed in Table 3.1.…”

“…Note that some of the spikes in flux-averaged concentrations shown previously for Tc-99 in Figure 4.11 are modulated or smoothed in Figure 4.12 as a result of lateral spreading of the simulated plumes. This is especially evident for Model_03, which includes anisotropy in K s as well as anisotropy in unsaturated hydraulic conductivity generated using the TCT model (Zhang and Khaleel 2010;Rockhold et al 2015). Table 3.1) were used as baseline parameters for these and subsequent simulations.…”

Immobilized Low-Activity Waste Glass Release Data Package for the Integrated Disposal Facility Performance Assessment

“…1 The reactive transport code, such as STORM, STOMP, and eSTOMP 2 , requires input of two general classifications of data: 1) multiphase flow and 2) reactive transport. Hydraulic properties for multiphase flow simulations have been identified in data packages for both the near-and far-field (Meyer and Serne 1999;Meyer et al 2004;Rockhold et al 2015). Experimentally derived input related to conducting geochemical analyses is defined within this data package.…”

Secondary Waste Cementitious Waste Form Data Package for the Integrated Disposal Facility Performance Assessment

“…This data package compiles available data necessary for modeling the performance of cementitious waste forms for aqueous waste streams as part of the IDF PA and is an update to and supersedes the cementitious waste form data package prepared by Cantrell (2015). Other data packages have been prepared in the past for the ILAW glass and cementitious waste forms and have recently been updated (Krupka et al 2004;Rockhold et al 2015, Last et al 2015, Pierce et al 2004, Freedman et al 2015. A separate data package is being prepared for solid secondary wastes encapsulated in cementitious waste forms (Flach et al 2016).…”