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' 26 March 2015 • • AGE Project No. 14-3289 ' Page 3 of 4 Following sample collection, each boring was permanently sealed to prevent vertical migration of potential contaminants. Soil borings were abandoned by backfilling with Portland cement from the total depth to surface grade. 3.0. FINDINGS ' Hydrocarbon odors were not encountered in any of the eight soil-vapor samples collected. Contaminants of concern were not detected above laboratory reporting limits ' in SV1 and SV2. Soil-vapor samples SV3 and SV4, collected adjacent to the southwest corner of the community center and in the southwest corner of the subject property, respectively, contained the following volatile organic compounds: ' • Toluene was detected at 1.9 ug/L at five feet bsg in SV3 and 2.3 ug/L at five feet bsg in SV4. ' • Total xylenes were detected at concentrations of 1.4 ug/L, 3.4 ug/L, and 1.2 ug/L, in samples SV3-5, SV3-10, and SV4-5, respectively. ' • 1,3,5-Trimethylbenzene and 1,2,4-Tri methyl benzene were detected at a concentration of 1.1 ug/L and 2.8 ug/L in sample SV3-10. • Naphthalene was detected at a concentration of 1.2 ug/L in SV3-5. Analytical results of the soil-vapor samples are summarized in Table 1. Laboratory ' reports (CT214-1503069), QA/WC reports, and chain of custody forms are included in Appendix B. t4.0. CONCLUSIONS Based on the data collected from this investigation, AGE concludes: • The detected compounds, including, toluene, xylenes, 1,2,4-trimethylbenzene, ' 1,3,5-trimethylbenzene and naphthalene, are typical constituents in fuel hydrocarbons and are likely related to former leaking underground storage tanks on and near the subject property. • The naphthalene concentration detected in SV3-5 (1.2 ug/L) is above regulatory soil vapor guidelines for residential properties. The typical guidelines used are the California Human Health Screening Levels (CHHSLs), developed by the California EPA, and the Environmental Screening Levels (ESLs), developed by the Regional Water Quality Control Board — San Francisco Bay Region. The ' CHHSL and ESL for naphthalene in soil gas for residential scenarios are 0.032 ug/L and 0.036 ug/L, respectively. The exceedance by two orders of magnitude could indicate a possible vapor intrusion issue. Additional investigation is ' warranted. ' Advanced GeoEnvironmental,Inc.