This page intentionally left blank. Contents Acronyms .........................................................................................................................................xxv Executive Summary......................................................................................................................ES-1 1. Introduction and Methodology .......................................................................................1-1 1.1 SSFL Description and Background ..........................................................................1-1 1.1.1 SSFL Facility Information............................................................................1-1 1.1.2 SSFL Environmental Programs...................................................................1-3 1.1.3 Scope and Objectives of the Group 3 RI Report .......................................1-8 1.2 Physical Setting of the Reporting Area..................................................................1-11 1.2.1 Climate and Meteorology..........................................................................1-11 1.2.2 Physiography ..............................................................................................1-11 1.2.3 General Geology and Hydrogeology at the Santa Susana Field Laboratory .............................................................................................................1-12 1.2.4 SSFL Surface Water Features ....................................................................1-17 1.2.5 Habitat..........................................................................................................1-18 1.3 Previous Investigations, Interim Actions, and Monitoring ................................1-20 1.4 Group 3 Data Evaluation Process...........................................................................1-22 1.4.2 Data Presentation........................................................................................1-22 1.4.3 Risk Assessment .........................................................................................1-23 1.5 Remedial Investigation Approach .........................................................................1-23 1.5.1 Presentation of Site Background and History ........................................1-23 1.5.2 Source, Nature, and Extent of Contamination........................................1-24 1.5.3 Human Health Risk Assessment Overview and Methods ...................1-24 1.5.4 Ecological Risk Assessment ......................................................................1-44 1.5.5 Deviations from SRAM..............................................................................1-64 1.6 Fate and Transport Evaluation Approach Overview for Group 3 ....................1-67 1.6.1 CSM: Contaminant Sources, Release Mechanisms, and Migration Pathways......................................................................................................1-67 1.6.2 Potential Routes of Migration...................................................................1-67 1.6.3 Contaminant Persistence ...........................................................................1-67 1.7 Data Quality Evaluation Summary........................................................................1-69 1.7.1 Data Quality Evaluation Summary..........................................................1-69 2. Building 204 Area .......................................................................................................................2-1 2.1 Building 204 Site Background and History.............................................................2-1 2.1.1 SWMUs and AOCs.......................................................................................2-1 2.1.2 Site History....................................................................................................2-1 2.1.3 Site Chemical Use Areas..............................................................................2-3 2.1.4 Site Conditions..............................................................................................2-3 2.1.5 Site Habitats/Land Cover ...........................................................................2-4 2.1.6 Historical Document Reviews ....................................................................2-4 MGM09-SSFL/GROUP 3 RI/FRONTMATTER.DOC DRAFT III CONTENTS (CONTINUED) 2.2 RI Characterization Activities.....................................................................................2-4 2.2.1 Sampling Objectives.....................................................................................2-5 2.2.2 Sampling Scope.............................................................................................2-5 2.2.3 Key Decision Points......................................................................................2-5 2.3 RI Characterization Results.......................................................................................2-5 2.3.1 Soil Matrix and Soil Vapor Findings..........................................................2-5 2.3.2 Groundwater Findings ................................................................................2-6 2.3.3 Surface Water Findings ...............................................................................2-9 2.3.4 Completeness of Characterization .............................................................2-9 2.4 Building 204 Area Nature and Extent....................................................................2-10 2.4.1 Surface Soil Nature and Extent..................................................................2-10 2.4.2 Subsurface Soil Nature and Extent ..........................................................2-14 2.4.3 Soil Gas Nature and Extent.......................................................................2-18 2.5 Conceptual Site Exposure Model ...........................................................................2-18 2.6 Fate and Transport Analysis for Chemicals Detected in Surficial Media.........2-19 2.6.1 Contaminant Sources and Release Mechanisms....................................2-19 2.6.2 Potential Routes of Migration...................................................................2-19 2.6.3 Contaminant Persistence...........................................................................2-19 2.6.4 Contaminant Migration.............................................................................2-20 2.6.5 Surface Soil Contaminants ........................................................................2-20 2.6.6 Subsurface Soil Migration .........................................................................2-21 2.6.7 Soil-to-Groundwater Migration ...............................................................2-21 2.7 Human Health Risk Assessment for Building 204 Area.....................................2-22 2.7.1 Identification of Chemicals of Potential Concern ..................................2-22 2.7.2 Exposure Assessment.................................................................................2-23 2.7.3 Risk Characterization.................................................................................2-24 2.7.4 Uncertainty Discussion..............................................................................2-29 2.8 Ecological Risk Assessment for Building 204 Area..............................................2-30 2.8.1 Problem Formulation .................................................................................2-30 2.8.2 Analysis........................................................................................................2-31 2.8.3 Risk Characterization.................................................................................2-32 2.8.4 Conclusions and Recommendations........................................................2-35 2.9 Summary of Findings and Recommendations for the Building 204 Area........2-36 2.9.1 Nature and Extent of Contamination Summary....................................2-36 2.9.2 Risk Assessment Summary .......................................................................2-37 2.10 Recommendations for Building 204 Area .............................................................2-39 3. Storable Propellant Area (SPA) .......................................................................................3-1 3.1 SPA Background and History...................................................................................3-1 3.1.1 SWMUs and AOCs.......................................................................................3-1 3.1.2 Site History....................................................................................................3-1 3.1.3 Site Chemical Use Areas..............................................................................3-2 3.1.4 Site Conditions..............................................................................................3-2 3.1.5 Site Habitats/Land Cover ...........................................................................3-2 3.1.6 Historical Document Reviews ....................................................................3-3 3.2 RI Characterization Activities.....................................................................................3-3 3.2.1 Sampling Objectives.....................................................................................3-3 IV DRAFT MGM09-SSFL/GROUP 3 RI/FRONTMATTER.DOC CONTENTS (CONTINUED) 3.2.2 Sampling Scope.............................................................................................3-3 3.2.3 Key Decision Points......................................................................................3-4