Appendix 2E Evaluation of Soil Excavation Volumes and Footprints
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If you need help accessing this document, please contact us at [email protected]. Appendix 2E Evaluation of Soil Excavation Volumes and Footprints This page intentionally left blank. TECHNICAL MEMORANDUM Evaluation of Soil Excavation Volumes and Footprints, Santa Susana Field Laboratory, Ventura County, California PREPARED FOR: National Aeronautics and Space Administration (NASA) PREPARED BY: CH2M HILL, Inc. (CH2M) Introduction This technical memorandum documents the methodology used to estimate soil excavation volumes and footprints for the following cleanup alternatives, which are discussed in the Draft Supplemental Environmental Impact Statement for Soil Cleanup Activities at Santa Susana Field Laboratory: Soil Excavation Soil Excavation Soil Excavation Volume Footprint Average Depth Alternative (yd3) (acres) (ft bgs) Alternative A: 870,000 220 2.45 AOC Cleanup Alternative B: 384,000 78 3.05 Revised LUT Levels Cleanup Alternative C: 247,000 36 4.25 Suburban Residential Cleanup Alternative D: 176,500 26 4.21 Recreational Cleanup AOC = Administrative Order on Consent ft bgs = feet below ground surface LUT = Look-Up Table yd3 = cubic yards The soil excavation volumes and footprints listed in the table were calculated based on a rigorous analysis of soil analytical data, regulatory and risk-based criteria, site topography (slopes, rock outcrops, drainageways, and roads), and site operations (structures, features, and activities). For all alternatives, the NASA-administered property at the Santa Susana Field Laboratory (SSFL) is divided into the following individual areas or operational sites: • Former Liquid Oxygen (LOX) Plant • Area II Landfill • Expendable Launch Vehicle (ELV) Area • Ash Pile/Sewage Treatment Plant (AP/STP) • Alfa Area • Bravo Area • Alfa/Bravo Fuel Farm (ABFF) • Storable Propellant Area (SPA) • Building 204 Area • Skyline Road Area • Hazardous Waste Storage Area (HWSA) FES0218201216MGM 1 TECHNICAL MEMORANDUM: EVALUATION OF SOIL EXCAVATION VOLUMES AND FOOTPRINTS, SANTA SUSANA FIELD LABORATORY, VENTURA COUNTY, CALIFORNIA • Coca Area • Delta Area • Propellant Load Facility (PLF) • Coca/Delta Fuel Farm (CDFF) • R-2 Ponds Alternative A: AOC Cleanup During the field efforts documented in the NASA Soil Data Summary Report for Santa Susana Field Laboratory (NASA, 2017b), estimated remediation areas (ERAs) and extended remediation areas (XRAs) were generated using field sampling results. The ERAs (AOC-Based Estimated Remediation Areas) represent the estimated extent of contamination based on site conditions and analytical data for all chemicals of concern (COCs). The XRAs (AOC-Based Extended Remediation Areas) represent the potential extent of contamination for two parameter classes that could not be delineated through field sampling: dioxins/furans and total petroleum hydrocarbons (TPHs). The lateral extents of the ERAs were located by evaluating the degree of exceedances above the screening levels through field samples. Boundaries for the AOC cleanup were generated by identifying samples that did not have reported criteria exceedances (non-detected data). In some cases, however, step-out samples1 were not feasible because of the presence of limiting topographic and/or site-related features. When a step-out sample was infeasible, the ERA was adjusted to extend to the limiting feature or professional judgement was exercised to determine the estimated lateral extent of contamination. However, an alternate delineation method, that is, the XRA, was necessary for dioxins/furans and TPHs. Sampling with step-out samples was not effective in delineating the extent of contamination for these COCs, because the AOC LUT values are significantly below conventional laboratory capabilities for detection. Laboratories failed to identify the difference between the minimum reporting limit and the AOC LUT value, resulting in endless “detected” samples. The XRA approach is used to assess the existing terrain around known contamination sources and identify natural barriers for chemical transport (slopes, rock outcrops, drainageways, roads). The XRAs are conservative and show the potential extent of dioxins/furans and TPHs based on the AOC LUT values. The XRA approach was presented to DTSC in the NASA Soil Data Summary Report for Santa Susana Field Laboratory (NASA, 2017b), which was accepted by DTSC in May 2019. For Alternative A: AOC Cleanup, AOC LUT XRA and ERA extents were used to generate the remediation area. The average depth of contamination and corresponding volume was then determined for each soil remediation area. The following steps describe the process used to calculate the estimated cleanup volume per site for Alternative A: AOC Cleanup: • Step 1: Based on the determination of the XRAs, the boundary for each soil remediation area was delineated around soil samples with analytical data that exceeded the AOC LUT values. • Step 2: Average depth of contamination for each soil remediation area was determined based on the samples inside the boundary. • Step 3: Excavation volume for each soil remediation area was obtained by multiplying the excavation footprint by the average depth. • Step 4: Total excavation volume for a given site was obtained by adding the excavation volumes for all the individual soil remediation areas. 1 A step-out sample is used to further delineate the extent of contamination around a sample location exceeding the LUT value. 2 FES0218201216MGM TECHNICAL MEMORANDUM: EVALUATION OF SOIL EXCAVATION VOLUMES AND FOOTPRINTS, SANTA SUSANA FIELD LABORATORY, VENTURA COUNTY, CALIFORNIA The overall soil excavation volume and footprint for Alternative A: AOC Cleanup (all sites combined) are 870,000 yd3 and 220 acres, respectively, which correspond to an overall average depth of 2.45 feet. These calculations were performed in the excel workbook provided in Attachment 1. Alternative B: Revised LUT Levels Cleanup For Alternative B: Revised LUT Levels Cleanup, seven soil COCs were given revised LUT values using the California Environmental Protection Agency (Cal EPA) Office of Environmental Health Hazard Assessment, Los Angeles County screening levels and U.S. Environmental Protection Agency (EPA) screening levels. All other current AOC LUT values remained the same. These seven COCs were chosen because they resulted in the greatest disproportionate level of cleanup between the COC LUT values and the environmental agency cleaning levels. The following steps describe the process used to calculate the estimated cleanup volume per site for Alternative B: Revised LUT Levels Cleanup: • Step 1: Individual soil remediation areas were developed for each operational site based on a data comparison. The boundary for each soil remediation area was delineated around soil samples with analytical data that exceeded the revised AOC LUT values. • Step 2: Average depth of contamination for each soil remediation area was determined based on the samples inside the boundary. • Step 3: Excavation volume for each soil remediation area was obtained by multiplying the excavation footprint by the average depth. • Step 4: Total excavation volume for a given site was obtained by adding the excavation volumes for all the individual soil remediation areas. The overall soil excavation volume and footprint for Alternative B: Revised LUT Levels Cleanup (all sites combined) are 384,000 yd3 and 78 acres, respectively, which correspond to an overall average depth of 3.05 feet. These calculations were performed in the excel workbook provided in Attachment 2. Alternative C: Suburban Residential Cleanup For Alternative C: Suburban Residential Cleanup, established suburban residential risk-based cleanup levels were compared to the soil data at each operational site. Site-specific, risk-based cleanup levels for soil contaminants at SSFL have been developed based on standard risk assessment procedures and equations provided in the DTSC-approved Standardized Risk Assessment Methodology (SRAM), EPA risk assessment guidance (RAG), and Cal EPA RAG. The following steps describe the process used to calculate the estimated cleanup volume per site for Alternative C: Suburban Residential Cleanup: • Step 1: Individual soil remediation areas were developed for each operational site based on a data comparison. The boundary for each soil remediation area was delineated around soil samples with analytical data that exceeded the suburban residential risk-based cleanup levels. • Step 2: Average depth of contamination for each soil remediation area was determined based on the samples inside the boundary. • Step 3: Excavation volume for each soil remediation area was obtained by multiplying the excavation footprint by the average depth. • Step 4: Total excavation volume for a given site was obtained by adding the excavation volumes for all the individual soil remediation areas. FES0218201216MGM 3 TECHNICAL MEMORANDUM: EVALUATION OF SOIL EXCAVATION VOLUMES AND FOOTPRINTS, SANTA SUSANA FIELD LABORATORY, VENTURA COUNTY, CALIFORNIA The overall soil excavation volume and footprint for Alternative C: Suburban Residential Cleanup (all sites combined) are 247,000 yd3 and 36 acres, respectively, which correspond to an overall average depth of 4.25 feet. These calculations were performed in the excel workbook provided in Attachment 3. Alternative D: Recreational Cleanup For Alternative D: Recreational Cleanup, recreational risk-based cleanup levels were compared to the soil data at each operational site. Site-specific risk-based cleanup levels for soil contaminants