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Phase II Environmental Site Assessment Report Yosemite Senior Housing 309 W.Yosemite Avenue and 105 Sycamore Avenue APNs 217-210-100 and 217-210-110 Page 5 Table 1: Tetrachloroethene(PCE)Results in Soil Gas Sample ID PCE Concentrations Indoor Air SLs divided by AF (µg/m) (0.03,µg/m) ASG-1-5.5 45 15 ASG-1-15 6.5 15 ASG-2-5.5 6.5 15 ASG-2-15 11 15 ASG-3-5.5 41 15 ASG-3-15 16 15 Notes:µg/m3=Micrograms per cubic meter;red text=exceeded attenuation applied indoor air screening level of 15 µg/m3; Indoor Air SLs=Department of Toxic Substances Control(DTSC)Human Health Risk Assessment(HHRA)Note 3 DTSC-Modified Screening Levels,June 2020,revised May 2022,Residential Indoor Air;AF=Attenuation Factor The default DTSC attenuation factor of 0.03 is likely too conservative for risk evaluations in the State of California,since it is derived from studies conducted in areas where construction design includes basements and variable climate conditions. Previously published attenuation factors of 0.001 were superseded by the updated default attenuation factor but are likely more appropriate for Site conditions.The DTSC is currently conducting studies in the State of California to obtain a more appropriate attenuation factor, as a result, it is likely the default attenuation factor of 0.003 will be updated in the future for California specific risk evaluations. 4.2 SOIL 4.2.1 Risk Assessment Concentrations of VOCs in soil were compared to the most recent USEPA RSLs or the DTSC-SLs. 4.2.2 Analytical Results One soil sample was collected from near the bottom of each boring location and analyzed for VOCs by EPA Method 8260B. The soil sample from DP-1 was collected at 27 feet bgs; DP-2 from 20 feet bgs; and DP-3 at 20 feet bgs. VOCs were not detected at or above their respective reporting limits.Reporting limits were sufficient for comparing to the USEPA RSLs or the DTSC-SLs for residential soil in most instances. The Site-specific conceptual site model(CSM)is included in Appendix F. Laboratory analytical results compared to human health risk screening levels for the collected soil samples are included on Table B,Appendix E. 4.3 GROUNDWATER 4.3.1 Risk Assessment Detected concentrations of VOCs in groundwater were compared to the San Francisco Bay Regional Water Quality Control Board's Tier 1 Environmental Screening Levels for groundwater, dated 2019 (SF-ESLs). Groundwater at the Site is not utilized for public use or consumption. 4.3.2 Analytical Results Two (2) grab groundwater samples were collected from DP-1 and DP-2 and were analyzed for VOCs by EPA Method 8260B. VOCs were not detected at or above their respective reporting limits. While not all reporting limits were sufficient for comparing concentrations to the SF-ESLs for groundwater,the exposure pathway for the COCs is by inhalation; therefore, the presence of COCs at concentrations below the C CONDOR