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Additional Site Assessment Report 324 East I 1 th Street Tracy,CA October 8, 2014 Sample Analyses Select soil and groundwater samples were analyzed for the following: ■ Total extractable petroleum hydrocarbons (TPH as diesel and TPH as motor oil) by EPA Method 8015B. ■ Total petroleum hydrocarbons as gasoline(TPHg),benzene,toluene,ethylbenzene,xylenes(BTEX) and methyl tert-butyl ether(MTBE)by EPA Method•8015Bm/8021 B. SITE ASSESSMENT RESULTS Field Observations During field screening of soil and groundwater samples,hydrocarbon odors were observed in soil in all site borings. However, the hydrocarbon odors observed in borings B-8 and B-10 were noted as slight and very slight,respectively.Observations are included on the boring logs in Appendix C. Soil Analytical Results Soil analytical results are summarized on Table 1.The laboratory analytical reports are included in Appendix D.The maximum TPHg and TPHd concentrations detected during this investigation were 2,600 milligrams per kilograms (mg/Kg) and 800 mg/Kg, respectively, in boring B-7 at a depth of approximately 1 ft. The only benzene concentrations detected in soil were 3.6 mg/kg and 0.096 mg/Kg in boring B-7 at depths of approximately 1 ft and 5 ft,respectively. Grab Groundwater Analytical Results Groundwater analytical results are summarized on Table 2. Key hydrocarbon results for this investigation are summarized on Figures 2 and 3.The laboratory analytical reports are included in Appendix D.The maximum TPHg and benzene concentrations in groundwater were detected in onsite boring B-7S at 410 micrograms per liter(µg/L)and 32µg2,respectively.The maximum TPHd concentration was detected in boring B-713 at 280 pg/L.TPHmo was not detected in groundwater in any site borings.Benzene was not detected in groundwater in borings B-9 and B-10. The lack of significant benzene concentrations in the most recent site borings indicates that the extent of the benzene plume is limited. 4