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12066.002.000 San Joaquin County Environmental Health Department November 30, 2018 Mountain House Neighborhood A, Units 3 and 4 Revised January 22, 2019 SOIL GAS CHARACTERIZATION REPORT Page 3 For the purposes of this characterization, the three soil gas samples were analyzed for the following: Volatile Organic Compounds (VOCs), including TPH-g, by EPA Test method TO-15. January 10, 2019 Sampling Event Based on review of the November 2018 ENGEO soil gas data, San Joaquin County Environmental Health Department (SJCEHD) expressed concerns regarding a leak check compound, 1,1-difluoroethane (DFA), detected at sample location SG-5. The reported DFA concentrations were greater than 10 times the detection limit for Benzene. Based on DTSC guidelines, this could suggest a potential bias in the soil gas data for SG-5. The SJCEHD has requested retesting of the SG-5 location to confirm soil gas results. In addition, it was agreed that two additional locations would be sampled northeast of the pipeline ROW, proximate to the graded residential lots, to determine if potential lateral migration of soil gas has occurred (Figure 2). To further delineate the extent of VOCs in soil gas on the Property, sampling was performed at three locations (SG-5, SG-11, and SG-12 @ 10') (Figure 2). Consistent with the November 2018 event, the soil gas samples were recovered in accordance with Department of Toxic Substances Control (DTSC) Final Advisory Active Soil Gas Investigations (July 2015). 2-propanol (IPA) was used as a leak check compound. The soil gas samples will be recovered from each of the three locations at a depth of 10 feet below the existing ground surface. For the purposes of this characterization, the three soil gas samples were analyzed for the following: Volatile Organic Compounds (VOCs), including TPH-g, by EPA Test method TO-15. In addition to the soil gas sampling, grab groundwater sampling was attempted within a separate boring adjacent to SG-5; however, refusal was encountered at a depth of 37 feet, with no groundwater encountered. ANALYTICAL RESULTS Soil Gas Samples November 20, 2018 Sampling Event Seven discrete samples reported detectable concentrations of TPH-gasoline, ranging from 210 micrograms per cubic meter (ug/m3) to 1650 ug/m3 in samples SG-5 at 5 feet and SG- 6 at 10 feet, respectively. These concentrations are below applicable RWQCB Tier 1 Environmental Screening Levels (ESLs). TPH-Gasoline was reported as non-detectable in the three discrete samples SG-8 at 5 feet, and in both SG-9 samples at 5 and 10 feet. Multiple samples reported low-level concentrations of several VOCs; the following are the maximum concentrations observed for these analytes: Acetone (400 ug/m3), Carbon Disulfide (12 ug/m3), Benzene (33 ug/m3 ), Toluene (36 ug/m3 ), 4-Methyl-2-Pentanone (MIBK) (17 ug/m3), Xylenes (14.6 ug/m3), Styrene (4.9 ug/m3), Hexane (40 ug/m3), 2-Hexanone (9.9 ug/m3), 2-Butanone(MEK) ( 110 ug/m3 ),Tetrahydrofuran (240 ug/m3), Napthalene (3.0 ug/m3), and tert-Butanol (13 ug/m3 ). All of these concentrations reported are below applicable RWQCB Tier 1 ESLs, DTSC Modified Screening Levels, and USEPA RSLs.