In 2018, the National Academies of Sciences, Engineering, and Medicine issued an Interim Report evaluating the general viability of the U.S. Department of Energy's National Nuclear Security Administration's (DOE-NNSA's) conceptual plans for disposing of 34 metric tons (MT) of surplus plutonium in the Waste Isolation Pilot Plant (WIPP), a deep geologic repository near Carlsbad, New Mexico. It provided a preliminary assessment of the general viability of DOE-NNSA's conceptual plans, focused on some of the barriers to their implementation. This final report addresses the remaining issues and echoes the recommendations from the interim study. Table of Contents Front Matter Summary 1 Introduction 2 Background 3 Plans to Dilute and Dispose 4 Implementation Challenges 5 System Vulnerabilities References Appendix A: Committee and Staff Biographies Appendix B: Meetings Appendix C: How Salt Repositories Work Appendix D: Legal and Regulatory Requirements for Transportation Appendix E: States' Active Partnership Role in Safe Transportation Appendix F: High-Risk Items Within the Risk and Opportunity Analysis Report Appendix G: Acronyms and Abbreviations Appendix H: Interim Report