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Additional Site Assessment Report and Human Health Risk Screening Evaluation www.arcadis.com 7 facility for disposal on January 8, 2020, March 10, 2021 and March 16, 2022. The waste manifests are provided in Appendix E. 4 Quality Assurance/Quality Control The overall quality assurance/QC objective for field activities and laboratory analyses was to produce data of sufficient quality to evaluate site conditions. To verify laboratory results, one duplicate soil sample was collected and analyzed; the duplicate sample (DUP1) was associated with primary soil sample B-16. Additionally, one duplicate soil vapor sample was collected and analyzed; the duplicate sample (DUP-1) was associated with primary soil vapor sample B-16. The duplicate samples were analyzed for the same constituents as their associated primary samples. USEPA-mandated sample holding times and preservation were observed. The data are considered acceptable for their intended purposes (Section 5.3). 5 Analytical Results This section describes the soil and soil vapor analytical results for samples collected between 2019 and 2022. For the site assessment, residents were identified as the most likely and sensitive on-site receptor. Soil and soil vapor analytical results were compared to residential environmental screening levels (ESLs; San Francisco Bay Regional Water Quality Control Board [SFBRWQB] 2019) and the Low-Threat Underground Storage Tank Case Closure Policy (LTCP; State Water Resources Control Board [SWRCB] 2012) residential screening levels. If LTCP screening levels were available for a given constituent, those screening levels took precedence over the SFBRWQCB ESLs. Soil analytical results are presented in Table 1 and shown on Figure 3. Soil vapor analytical results are presented in Table 2 and shown on Figure 4. Laboratory analytical reports are provided in Appendix F. 5.1 Soil Analytical Results The TPH-g, TPH-d, BTEX, and naphthalene results for the eight primary soil samples collected in December 2019, January 2020, and February 2022 are summarized below: • TPH-g (C5-C12) was detected in three of the eight primary soil samples, at concentrations up to 349 milligram per kilogram (mg/kg; B-16 from 5.5 to 6.0 feet bgs). • TPH-d (C12-C22) was detected in each of the eight primary soil samples, at concentrations up to 1,400 mg/kg (B-12 from 9.5 to 10.0 feet bgs). • Benzene and ethylbenzene were not detected in any of the primary soil samples. • Toluene was detected in one of the eight primary soil samples, at a concentration of 0.0248 mg/kg (B-16 from 5.5 to 6.0 feet bgs). • Total xylenes were detected in one of the eight primary soil samples at a concentration of 0.00210 J mg/kg (B-16 from 5.5 to 6.0 feet bgs). The J-qualifier signifies that the reported value is an estimate, less than the laboratory reporting limit.