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' 16 October 2014 AGE Project No. 13-2675 ' Page 8 of 9 ' established Commercial California Human Health Screening Level (CHHSL) of 122 pg/m3 for benzene in soil gas (Table 3). ' • Toluene, ethylbenzene, and total xylene concentrations detected in B4-Vapor, 135-Vapor and 136-Vapor were all significantly below the established SFBRWQCB Commercial ESLs and the established Commercial CHHSLs for soil gas (Table 3). • PCE concentrations detected in 135-Vapor and 136-Vapor were significantly below the established SFBRWQCB Commercial ESL of 2,100 pg/m3 for PCE in soil gas I ' and the established Commercial CHHSL of 603 pg/m3 for PCE in soil gas (Table 3). ' • None of the sixteen additional VOCs detected in B4-Vapor, B5-Vapor and B6-Vapor were above their respective SFBRWQCB Commercial ESLs (Appendix B). ' • Tracer compound, IPA was detected at a concentration of 18,000 pg/m3 in sample 135-Vapor and at a concentration of 63 pg/m3 in sample 136-Vapor; IPA ' was not detected above laboratory reporting limits in sample B4-Vapor. IPA was detected in 136-Vapor just above the reporting limit of 50 pg/m3; and IPA was detected in 135-Vapor approximately seven (7) times greater than the reporting ' limit of 2,500 pg/m3. 1 Based on the document, Advisory Active Soil Gas Investigations — April 2012, prepared by the California EPA, Department of Toxic Substance Control (DTSC), Los Angeles RWQCB, and the SFBRWQCB, if the t concentration of the leak check compound is greater than or equal to 10 times the reporting limit, the corrective action is necessary. IPA was not detected at concentrations greater than 10 times the reporting limit in any of the soil-vapor ' samples collected from the site. Based on the findings from the previous investigation performed in October 2013 and the most recent investigation in October 2014, there is minimal or diminimis risk to human health from residual petroleum hydrocarbon impacted soil and groundwater or from soil-vapor intrusion, under the current site conditions. We do not recommend further investigation at the site. LIMITATIONS ' AGE's professional services were performed using that degree of care and skill ordinarily exercised by environmental consultants practicing in this or similar localities. The findings were based primarily upon analytical results provided by an independent ' laboratory. Evaluations of the geologic/hydrogeologic conditions at the subject property for the purpose of this investigation were made from a limited number of available data points (i.e., soil borings and soil-vapor and groundwater samples) and subsurface Advanced GeoEnvironmental,Inc.