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Abdelwahed Facility, Ultramar Site No. 13792 May 9, 2013 Stockton California NFAR Request and Well Destruction Work Plan and soil analytical data are summarized in Tables 1 and 2, respectively. Soil and groundwater analytical reports are contained in Attachment E. Soils encountered in the MW -13 boring consist of silty and sandy clay, clayey silt, and sand. No analyte concentrations were detected in the 15 and 30 -foot soil samples. The 50 -foot soil sample, collected from below groundwater level, contained concentrations of 3.4 milligrams per kilogram (parts per million or ppm) TPHd, 2.8 ppm TPHg, 0.022 ppm benzene and other aromatic compound concentrations ranging from 0.026 to 0.51 ppm. Lesser concentrations of BTEX compounds ranging from 0.14 to less than 0.0050 ppm were detected in the 55 and 60 - foot soil samples. No MTBE concentrations were detected in any soil sample. Analytical results from the groundwater sample collected from well MW -13 on 28 December 2012 indicated concentrations of 5,200 ppb TPHg and 10 ppb benzene. TPHd was not detected above the reporting limit in the groundwater sample. The most recent groundwater sample collected in May 2012 prior to the destruction of well MW -1, indicated concentrations of 75,000 ppb TPHg, 3,100 ppb benzene, and 110 ppb DCA. The most recent groundwater concentration data in well MW -13 are one to two orders of magnitude less than the concentrations detected in former well MW -I in May 2012. SOIL GAS INVESTIGATION A soil gas investigation (SGI) was conducted at the site in order to evaluate the potential for vapor intrusion into current and future site buildings and soil gas conditions toward off-site areas. The investigation was developed in accordance with guidance contained with the California Department of Toxic Substances Control (DTSC) Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air -Interim Final dated 15 December 2004 (revised 7 February 2005), and the California Environmental Protection Agency (Cal EPA) Advisory—Active Soil Gas Investigations dated April 2012. Horizon retained TEG Northern California (TEG) of Rancho Cordova (C-57 License No. 706568) to advance soil vapor probes, collect soil gas samples and analyze soil vapor samples utilizing an on-site mobile laboratory. Eurofins Air Toxics Limited (ATL) of Folsom, a State - certified laboratory (NELAP #I2282CA), was retained to provide a 250 -milliliter (ml) Summa canister and perform duplicate sample analysis. Horizon updated the Site Health and Safety Plan to address hazards related to SGI and notified Underground Service Alert to mark subsurface utilities. Soil Gas Investigation Fieldwork Fieldwork for the SGI was conducted on I I December 2012. The concrete pavement was cored at two of the four sampling locations. The locations were cleared for utilities with a hand auger to a depth of approximately 3 feet below surface grade (bsg). Soil gas probes were advanced at sampling locations SG -1 through SG -4 as shown on Figure 7. Prior to purge testing and soil gas sampling, a probe blank was collected by drawing ambient air sample through a sampling apparatus set-up. Temporary soil gas probes were advanced 1792 NFAR rpt.doc Project No. 1792.26 4 HORIZON ENVIRONMENTAL INC.