EPA 541-R97-134 1997 EPA Superfund Record of Decision: Castle Air Force Base (6 Areas) OU 5 Merced, CA 05/21/1997 <IMG 971340> <IMG 97134A> Final Record of Decision Comprehensive Basewide Program-Part 1 (Groundwater) Castle Air Force Base 31 January 1997 FINAL RECORD OF DECISION COMPREHENSIVE BASEWIDE PROGRAM-PART 1 (GROUNDWATER) CASTLE AIR FORCE BASE TABLE OF CONTENTS Tab Section/Page 1.0 INTRODUCTION . 1-1 2.0 DECLARATION FOR THE RECORD OF DECISION . 2-1 2.1 SITE NAME AND LOCATION . 2-1 2.2 STATEMENT OF BASIS AND PURPOSE . 2-1 2.3 ASSESSMENT OF THE SITE . 2-2 2.4 DESCRIPTION OF THE REMEDY. 2-2 2.4.1 Selected Remedy: Main Base Plume . 2-3 2.4.2 Selected Remedy: East Base Plume . 2-4 2.4.3 Selected Remedy: Castle Vista Plume. 2-5 2.4.4 Selected Remedy: Other Plumes. 2-5 2.5 STATUTORY DETERMINATIONS . 2-6 2.6 SIGNATURES FOR LEAD AND SUPPORT AGENCIES . 2-6 3.0 DECISION SUMMARY . 3-1 3.1 SITE NAME, LOCATION AND DESCRIPTION. 3-1 3.1.1 Site Name and Location. 3-1 3.1.2 Land and Water Use. 3-1 3.1.3 Regional Topography . 3-1 3.1.4 Geology/Hydrology . 3-2 3.2 SITE HISTORY AND ENFORCEMENT ACTIVITIES. 3-6 3.3 HIGHLIGHTS OF COMMUNITY INVOLVEMENT. 3-9 3.4 SCOPE AND ROLE COMPREHENSIVE BASEWIDE-PART 1 . .3-10 3.5 NATURE AND EXTENT OF GROUNDWATER CONTAMINATION . .3-11 3.5.1 Shallow Hydrostratigraphic Zone (HSZ) . .3-12 3.5.2 Upper Subshallow HSZ. .3-13 3.5.3 Lower Subshallow HSZ. .3-13 3.5.4 Confined HSZ. .3-13 3.5.5 Deep HSZ. .3-14 3.6 SUMMARY OF GROUNDWATER PLUME RISKS . .3-14 3.6.1 Human Health Risk Assessment. .3-14 3.6.2 Ecological Risk Assessment (ERA). .3-23 3.6.3 Screening of Contaminants and Groundwater Plume Regions . .3-23 3.7 DESCRIPTION OF THE ALTERNATIVES. .3-29 3.7.1 Alternative 1 No Action . .3-31 3.7.2 Alternative 2 Impacted Area Well-Head Treatment/Well Destruction and Monitor . .3-32 3.7.3 Alternative 3 Extraction with TCE Capture Objective of 5 Ig/L . .3-34 3.7.4 Alternative 4 Extraction with TCE Capture Objective of 0.5 Ig/L . .3-37 3.7.5 Alternative 5 Extraction with TCE Capture Objective of 3 Ig/L . .3-39 3.7.6 Alternative 6 Extraction for Plume Control Combined with Potential Well-Head Treatment . .3-41 3.8 DETAILED AND COMPARATIVE ANALYSES OF REMEDIAL ALTERNATIVES . .3-43 3.8.1 Main Base Plume Regions . .3-45 3.8.2 East Base Plume Region. .3-50 3.8.3 Summary of Analysis and Selected Remedy . .3-54 3.9 STATUTORY DETERMINATIONS . .3-61 3.9.1 Main Base Plume . .3-61 3.9.2 East Base Plume . .3-62 4.0 LIST OF APPLICABLE OR RELEVANT AND APPROPRIATE REQUIREMENTS (ARARs) AND TO-BE-CONSIDEREDS (TBCs). 4-1 4.1 CHEMICAL-SPECIFIC ARAR AND TBCs. 4-2 4.1.1 Federal Chemical-Specific ARAR and TBCs . 4-2 4.1.2 State Chemical-Specific ARAR and TBCs . 4-2 4.2 LOCATION-SPECIFIC ARAR AND TBCs. 4-3 4.2.1 Federal Location-Specific ARAR. 4-3 4.2.2 State Location-Specific ARAR. 4-4 4.3 ACTION-SPECIFIC ARAR AND TBCs. 4-4 4.3.1 Federal ARAR. 4-4 4.3.2 State ARAR and TBCs . 4-4 5.0 RESPONSIVENESS SUMMARY . Tab 5 APPENDIX A: ADMINISTRATIVE RECORD INDEX . Tab 6 TABLES . Tab 7 FIGURES. Tab 8 Reference List for Castle Air Force Base Comprehensive Basewide-Part 1 Record of Decision 1. Castle Air Force Base Draft Comprehensive Basewide Groundwater Remedial Investigation/Feasibility Study - Part 1, Jacobs Engineering Group Inc., December 21, 1995. 2. Castle Air Force Base Final Comprehensive Basewide Groundwater Remedial Investigation/Feasibility Study - Part 1, Jacobs Engineering Group Inc., June 12, 1996. 3. Interim Record of Decision, Operable Unit No. 1, Castle Air Force Base, Merced County, California, August 7, 1991. 4. Record of Decision, Operable Unit No. 2, Castle Air Force Base, Merced County, California, November 1993. 5. Interim Guidance on Preparing Superfund Decision Document: The Proposed Plan, the Record of Decision, the Explanation of Significant Difference, the Record of Decision Amendment, U.S. Environmental Protection Agency, Office of Emergency and Remedial Response, EPA/540/G-007, July 1989. 6. The Water Quality Control Plan (Basin Plan) for the California Regional Water Quality Control Board Central Valley Region, The Sacramento River Basin and the San Joaquin River Basin, Third Edition, 1994. 7. Castle Air Force Base Long Term Groundwater Sampling Plan, Jacobs Engineering Group Inc., January 1996. 8. Draft Revised Design Basis Report for Castle Airport, Jacobs Engineering Group Inc., January 1996. 9. Final Revised Design Basis Report for Castle Airport, Jacobs Engineering Group Inc., August 1996. 10. Castle Air Force Base Comprehensive Basewide Program - Part 1: The Proposed Plan for Remedial Action of Groundwater, Booz, Allen & Hamilton Inc., June 1996. 11. United States Air Force Installation Restoration Program Castle Air Force Base Community Relations Plan, Gutierrez-Palmenberg Inc., May 1995. FINAL RECORD OF DECISION CASTLE AIR FORCE BASE COMPREHENSIVE BASEWIDE PROGRAM-PART 1 1.0 INTRODUCTION This decision document presents the remedial actions (RAs) selected for the comprehensive cleanup of groundwater at the formerly active Castle Air Force Base (AFB), Merced County, California. The RAs under this Comprehensive Basewide Program-Part 1 (CB-Part 1) are being carried out to complete the cleanup of all groundwater plumes at Castle AFB as the first of a two part process leading to the final comprehensive cleanup of all soil and groundwater contamination at the site (CB-Part 2). The selected RAs for CB-Part 1 were developed in accordance with the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA), as amended by the Superfund Amendments and Reauthorization Act of 1986 (SARA) and, to the extent practicable, the National Oil and Hazardous Substances Pollution Contingency Plan (NCP). These decisions, documented herein, are based on the information contained in the Administrative Record File for Castle AFB. The Administrative Record Index (Appendix A) identifies documents that were considered or relied upon to make these decisions. The purpose of this Record of Decision (ROD) is to decide the appropriate level of groundwater remediation necessary to protect human health and the environment, and to determine what requirements are applicable or relevant and appropriate requirements (ARARs) based on the groundwater beneficial use designation and site-specific conditions. This ROD has been divided into five sections to address the selected RAs for groundwater remediation at Castle AFB. These five sections are: • Section 1.0 Introduction. This section serves as an overall introduction to the ROD. • Section 2.0 Declaration For The Record of Decision. This section documents the Ras selected for groundwater cleanup at Castle AFB and serves as an abstract for the key information contained in the ROD. It provides signatures of concurrence by the U.S. Air Force (AF), the U.S. Environmental Protection Agency (EPA), and the State of California Environmental Protection Agency (Cal/EPA). • Section 3.0 Decision Summary. This section provides an overview of the site characteristics, the alternatives evaluated, and the analysis of those options. It also identifies the selected remedy and explains how the remedy fulfills statutory requirements. • Section 4.0 Listing of Applicable or Relevant and Appropriate Requirements (ARARs) and To-Be-Considereds (TBCs). This section describes the Federal and State ARARs required to be complied with under this ROD. • Section 5.0 Responsiveness Summary. This section contains a summary of comments received during the public comment period and responses to those comments. In addition, a summary of agency comments on the Preliminary Draft and Draft Final ROD, and responses to these comments, are included. The Responsiveness Summary can be found at Tab 5. Appendix A provides the Administrative Record Index and can be found at Tab 6. Figures and tables referenced in the ROD can be found at Tabs 7 and 8, respectively. 2.0 DECLARATION FOR THE RECORD OF DECISION This section documents the RAs selected for groundwater cleanup at Castle AFB and serves as an abstract for the key information contained in the ROD. It provides signatures of concurrence by the AF, the EPA, and the Cal/EPA. For the groundwater plumes selected for RAs under CB-Part 1, the following determinations are in effect: • Statutory Preference for Treatment as a Principal Element is Met and a Five-Year Review is Required for the Main Base and Castle Vista Plumes. • Statutory Preference for Treatment as a Principal Element is Not Met and a Five-Year Review is Required for the East Base Plume. 2.1 SITE NAME AND LOCATION Castle AFB (currently known as Castle Airport) is a National Priorities List (NPL) Site located in Merced County, California. 2.2 STATEMENT OF BASIS AND PURPOSE This ROD presents and documents the RAs selected for the cleanup of groundwater at Castle AFB. CB-Part 1 is intended to address the full range of contaminated groundwater under both the Castle AFB site and the contiguous areas where contaminated groundwater has migrated off base. The objective of the Castle AFB CB-Part 1 RAs is to capture the contaminated groundwater plume(s) within the Maximum Contaminant Level (MCL) boundary of the most restrictive contaminant present, and clean up the contaminated groundwater to MCL levels. This ROD supersedes previous groundwater RODs (i.e., the Operable Unit (OU) 1 Interim ROD and the OU 2 ROD), and the ongoing and planned actions under these two prior RODs are integrated into the selected remedy for the comprehensive cleanup of Castle AFB groundwater contamination.