As requested by Solid Waste Management (SWM), this report documents the Savannah River National Laboratory's (SRNL's) evaluation of updated Naval Reactor waste container and inventory projections and proposes a Naval Reactor Component Disposal Area (NRCDA) groundwater (GW) pathway modeling approach for the next E-Area Low-Level Waste Facility (LLWF) Performance Assessment (PA).Two areas within the E-Area LLWF are used as disposal sites for reactor components from the U.S. Navy. Currently, components arrive by rail and are moved by crane to the 643-26E at-grade gravel disposal pad. Prior to operational closure, reactor components were stored and ultimately disposed in-place on the 643-7E NRCDA (Wilhite and Flach 2004). Naval Reactor (NR) waste is comprised of highly radioactive components consisting of activated corrosion-resistant metal alloy contained within welded thick steel casks, and auxiliary equipment primarily contaminated with Activated Corrosion Products (sometimes referred to as "crud" by the U.S. Navy) at low levels and contained within thinner-walled bolted containers. The 643-7E disposal pad, which contains 41 casks and has an interim soil cover, is closed to future receipts. The latest NR waste projections for the 643-26E disposal pad are substantially different from the original estimates due to a change in reactor maintenance. The original estimate was for 50 heavily shielded, welded casks and 50 thinner-walled bolted containers (primarily shield blocks). Currently, NR Programs project 33 heavily shielded, welded casks, of which 31 are already in-place on the 643-26E pad, and 381 thinnerwalled bolted containers.In addition to new waste form projections, there have been changes in facility layout and closure plans as well as PA modeling improvements. This report documents these changes as well as key NRCDA recommendations from the 2015 PA Strategic Plan (Butcher 2016). Key findings and recommendations are summarized inTable 0-1 below. SRNL-STI-2018-00633 Revision 0 vii Table 0-1. Comparison of Proposed Modeling Approach with 2008 E-Area LLWF PA. Model Feature-Aspect New Approach 2008 PA Approach Justification Number of NR Containers on 643-26E Open ended 100 cask limit Requested by SWM Type of Analysis Limits analysis -model unit curie of each rad for comparison with Performance Objectives Preliminary closure analysismodeled dose impact of projected inventory supplied by NR -scaled results for limits Requested by SWM 643-7E Perform closure analysis on final inventory from 41 containers Applied results of 643-26E model to 643-7E performance Changes in flow paths due to new aquifer model Limits Separate limits -ACP and activated metal, bolted and welded casks Single set of limits -combined all forms of inventory into a representative Knolls Atomic Power Laboratory core barrel/thermal shield cask Revision viii Revision 0 10 Table 4-2. 643-26E Projected Inventories by Waste Type Activated Metal (FY40) ACP (FY40) ISOTOPE Activity (Ci) ISOTOPE Activity (Ci)

The work described in this report is part of an effort to update the General Separations Area (GSA) regional groundwater flow calibration targets to incorporate additional well data, emphasizing Z-Area, and consideration of Mixed Waste Management Facility groundwater plume monitoring data. This work utilizes a modified version of the Excel-based Well Hydrograph Analysis Tool (WHAT), previously detailed by Hiergesell and coworkers (2015a and 2015b), to evaluate the water level measurements obtained from the Environmental Restoration Data Management System (ERDMS) database. The original version of WHAT did not correctly compute median well water level, and occasionally the minimum and maximum values.Initially, well data were downloaded from B, F, H, UTR, Z, and GSA site groupings utilizing the initial date from the time slice developed in Hiergesell 2015b (January 1, 2004) to the present (May 2, 2018). After removing records from wells with missing elements (i.e. missing measurement result), wells outside the GSA footprint, and wells having less than four data points, 731 wells were investigated and will be discussed within this report. Well hydrographs are presented in Appendix A. An analysis of the selected target wells, by location, was conducted to determine an appropriate weighting factor to associate with each target well during automated flow model calibration. Each well's mean water level is taken to be the "target" water level that will ultimately be utilized in the re-calibration of the GSA groundwater model. For each well, the suite of statistical quantities and coordinates are presented in Appendix C and each well's weighting factors are given in Appendix D.

This report documents the development and benchmarking of the E-Area Low-Level Waste Facility (ELLWF) GoldSim Engineered and Slit Trench (ET and ST) vadose zone models. Subsequent activities (beyond the scope of this effort) will couple the GoldSim-based vadose zone models to the GoldSim aquifer model, with the intent of performing stochastic analyses that couple all pertinent fate and transport processes from the ground surface up to the 100-m Point of Assessment (POA). The benchmarking presented within this report focuses on the Slit Trench 06 (ST06) hydrostratigraphic location that resides within the center set of slit trenches. These GoldSim-based vadose zone models are generic models capable of being benchmarked to any of the other trench locations within E-Area. This is a key component of the effort to include uncertainty quantification and sensitivity analysis (UQSA) in the next revision of the E-Area Performance Assessment (PA). This report describes the model and shows results obtained from benchmarking the GoldSim transport simulations under a deterministic mode (using nominal best estimate parameter settings) to best-estimate deterministic results obtained using the PORFLOW vadose zone model. The P PORFLOW model is three-dimensional while the GoldSim model represents a simplified one-dimensional treatment. The GoldSim ET and ST vadose zone models were able to reproduce PORFLOW peak fluxes, with acceptable accuracy for ET Case01 (Intact) and ST Case01 (Intact), as shown in Table ES-1 and Table ES-2, respectively. The GoldSim ET and ST vadose zone models were able to reproduce PORFLOW peak fluxes, with acceptable accuracy for ET Case11b (Subsided) and ST Case11b (Subsided), as shown in Table ES-3 and Table ES-4, respectively. The detailed comparison of radionuclide and tracer fluxes from the waste zone and to the water table are discussed in Section 5 and summarized in Section 6. Note that the parameter settings established are universal in nature and are independent of radionuclide and its progeny. The close agreement between the two models provides confidence that GoldSim will provide adequate results that will reflect the behavior of vadose zone transport under off-nominal operating conditions for sensitivity and uncertainty analysis. Table ES-1. Comparison of GoldSim and PORFLOW peak fluxes to the water table and peaks times ET Case01 (Intact).

Case 2 Isotherm Case 10a Isotherm Case 2 (4.95E-6 M Cs + ) Case 10a (1.97E-5 M Cs + ) Case2 (1.97E-5 M Cs + ) Case 10a (4.

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