RECORD OF DECISION HANFORD 100 AREA SUPERFUND SITE 100-DR-1, 100-DR-2, 100-HR-1, 100-HR-2, and 100-HR-3 OPERABLE UNITS July 2018 ii Table of Contents PART I: DECLARATION OF THE RECORD OF DECISION ........................................................... 1 1.0 Site Name and Location .................................................................................................... 1 2.0 Statement of Basis and Purpose ........................................................................................ 1 3.0 Assessment of the Site ...................................................................................................... 1 4.0 Description of Selected Remedy ....................................................................................... 1 4.1 Overall Site Cleanup Strategy .................................................................................... 1 4.2 Principal Threat Wastes at the Site ............................................................................. 2 4.3 Major Components of the Selected Remedy .............................................................. 2 5.0 Statutory Determinations................................................................................................... 6 6.0 ROD Data Certification Checklist ..................................................................................... 7 7.0 Authorizing Signatures ...................................................................................................... 8 PART II: DECISION SUMMARY ....................................................................................................... 11 1.0 Site Name, Location, and Brief Description ................................................................... 11 2.0 Site History and Enforcement Activities ......................................................................... 11 2.1 Site Operational History ........................................................................................... 11 2.2 Previous Investigations and Interim Actions ............................................................ 13 2.3 CERCLA Regulatory and Enforcement Activities ................................................... 15 3.0 Community Participation ................................................................................................ 16 4.0 Scope and Role of the Response Action ......................................................................... 17 5.0 Site Characteristics .......................................................................................................... 19 5.1 Site Features and Land and Groundwater Use .......................................................... 19 5.2 Nature and Extent of Contamination ........................................................................ 22 5.3 Conceptual Site Model ............................................................................................. 25 6.0 Current and Potential Future Land and Water Uses ........................................................ 26 6.1 Current Onsite and Surrounding Land Use............................................................... 26 6.2 Anticipated Future Land Use .................................................................................... 26 6.3 Current Ground and Surface Water Uses ................................................................. 27 6.4 Potential Future Groundwater Beneficial Uses ........................................................ 27 6.5 Expected Timeframes for Beneficial Groundwater Use ........................................... 27 6.6 Location of Anticipated Groundwater Use in Relation to Contamination................ 27 7.0 Summary of Site Risks .................................................................................................... 27 iii 7.1 Summary of Human Health Risk Assessment .......................................................... 27 7.2 Summary of Ecological Risk Assessment ................................................................ 31 7.3 Basis for Action ........................................................................................................ 32 8.0 Remedial Action Objectives............................................................................................ 33 8.1 Specific Remedial Action Objectives ....................................................................... 33 8.2 Cleanup Levels ......................................................................................................... 34 9.0 Description of Alternatives ............................................................................................. 38 9.1 Description of Remedy Components ........................................................................ 39 9.2 Common Elements of Alternatives 2, 3, and 4 ......................................................... 48 9.3 Expected Outcomes of Each Alternative .................................................................. 50 10.0 Comparative Analysis of Alternatives ............................................................................ 50 10.1 Overall Protection of Human Health and the Environment ...................................... 52 10.2 Compliance with Applicable or Relevant and Appropriate Requirements ............... 52 10.3 Long-Term Effectiveness and Permanence .............................................................. 52 10.4 Reduction of Toxicity, Mobility, or Volume through Treatment ............................. 53 10.5 Short-Term Effectiveness ......................................................................................... 53 10.6 Implementability ....................................................................................................... 55 10.7 Cost ........................................................................................................................... 56 10.8 State Acceptance ....................................................................................................... 56 10.9 Community Acceptance ............................................................................................ 56 11.0 Principal Threat Waste .................................................................................................... 57 12.0 Selected Remedy ............................................................................................................. 57 12.1 Summary of the Rationale for the Selected Remedy ................................................ 57 12.2 Detailed Description of the Selected Remedy .......................................................... 59 12.3 Summary of the Estimated Remedy Costs ............................................................... 67 12.4 Expected Outcomes of the Selected Remedy ........................................................... 68 13.0 Statutory Determinations................................................................................................. 68 13.1 Protection of Human Health and the Environment ................................................... 69 13.2 Compliance with ARARs ......................................................................................... 69 13.3 Cost Effectiveness .................................................................................................... 80 13.4 Use of Permanent Solutions and Alternative Treatment Technologies to the Maximum Extent Practicable ................................................................................... 80 13.5 Preference for Treatment as a Principal Element ..................................................... 81 iv 13.6 Five-Year Review Requirements .............................................................................. 82 14.0 Documentation of Significant Changes ........................................................................... 82 PART III: RESPONSIVENESS SUMMARY ........................................................................................ 83 1.0 Introduction ..................................................................................................................... 83 2.0 Community Involvement................................................................................................. 83 3.0 Comments and Responses ............................................................................................... 83 ACRONYMS ............................................................................................................................................ 107 REFERENCES ......................................................................................................................................... 109 Appendix A .... Comments Received During Public Comment Period on Proposed Plan for Remediation of the 100-DR-1, 100-DR-2, 100-HR-1, 100-HR-2, and 100-HR-3 Operable Units ........................... A-i Figures Figure 1. Hanford Site River Corridor ................................................................................................. 12 Figure 2. Features of the 100-D/H Area ............................................................................................... 13 Figure 3. Stratigraphy and Hydrogeologic Units of 100-D/H .............................................................. 20 Figure 4. 100-D/H Water Table Map (March 2011) ............................................................................ 21 Figure 5. Groundwater and Surface Water Interactions at 100-D/H .................................................... 22 Figure