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Additional Site Assessment Report and Human Health Risk Screening Evaluation www.arcadis.com 8 • Naphthalene was detected in one of the eight primary samples at a concentration of 0.0634 mg/kg (B-16 from 5.5 to 6.0 feet bgs). All reported TPH-g, TPH-d, BTEX, and naphthalene concentrations in soil were less than the applicable LTCP (SWRCB 2012) residential screening levels and SFBRWQCB residential soil ESLs (SFBRWQB 2019), with the exception of TPH-d. Concentrations of TPH-d exceeded the SFBRWQCB residential soil ESL (260 mg/kg) in five of the eight primary soil samples. The exceedances are further addressed in Section 7. 5.2 Soil Vapor Analytical Results The following section discusses the analytical results for TPH, VOCs, and fixed gases for soil vapor collected in January 2020 and April 2022. 5.2.1 Total Petroleum Hydrocarbons and Volatile Organic Compounds The TPH-g and VOC concentrations in soil vapor are summarized below: • TPH-g was detected in both analyzed samples at concentrations of 140,000 micrograms per cubic meter (µg/m3; B-13 at 5 feet bgs) and 14,000,000 µg/m3 (B-13 at 8 feet bgs). • Benzene was detected in one of the three primary samples at a concentration of 2.1 J µg/m3 (B-16 at 5 feet bgs). • Ethylbenzene, toluene, and xylenes were not detected in any of the soil vapor samples. • A total of 14 other VOCs were detected in the soil vapor samples. All reported TPH-g and VOC concentrations in soil vapor were less than the applicable LTCP (SWRCB 2012) residential screening levels and SFBRWQCB residential ESLs (SFBRWQCB 2019), with the exception of TPH-g. Concentrations of TPH-g exceeded the SFBRWQCB residential ESL in both samples. The exceedances are further addressed in Section 7. 5.2.2 Fixed Gases Oxygen concentrations in soil vapor ranged from 0.85 percent (B-13 at 8 feet bgs) to 21 percent (B-16 at 5 feet bgs and the associated duplicate). Nitrogen concentrations in soil vapor ranged from 9.3 percent (B-13 at 8 feet bgs) to 96 percent (B-13 at 5 feet bgs). Methane concentrations in soil vapor ranged from 0.040 percent (B-13 at 5 f eet bgs) to 80 percent (B-13 at 8 feet bgs). Carbon dioxide concentrations in soil vapor parent samples ranged from 0.098 percent (B-16 at 5 feet bgs) to 9.8 percent (B-13 at 8 feet bgs). Carbon dioxide was also detected in the duplicate sample. Helium was not detected in any of the soil vapor samples; helium concentrations were within the acceptable leak limit of 5 percent (refer to Section 3.2.3 for more detail on the helium leak test).