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May 30, 2018 Page 4 of 7 Reference: Data Gap Assessment Report, Former Chase Chevrolet, 424 North Van Buren Street, Stockton, California Soil Vapor Sample Collection - After allowing the soil vapor probes to equilibrate for approximately 72 hours, soil vapor samples were collected using 1-liter Summa canisters with dedicated flow controllers set at approximately 175 milliliters per minute. Batch-certified Summa canisters were provided by Eurofins Air Toxics and were observed to arrive with a vacuum of approximately 30 inches of mercury (in Hg). Canisters and flow controllers were connected to the soil vapor probe tubing using a Swagelock connector, and approximately two probe volumes (calculated based on length of tubing and annular space of the sandpack) were purged using a syringe connected via a 3-way valve. After purging, the sample train was connected to the probe tubing, and a shut-in test was performed by applying approximately 28 in Hg vacuum, isolating the system via an in-line valve, and confirming no loss of pressure over a period of two minutes. Sampling was performed under a shroud using helium as a leak- check compound, and an atmosphere of approximately 35 percent helium was maintained beneath the shroud, as confirmed using a field helium detector. Soil vapor sampling was considered complete when the vacuum on the Summa canister reached approximately 5 in Hg. Summa canisters were returned to the laboratory in their original shipping containers under COC protocol. ANALYTICAL PROGRAM Soil and groundwater samples were analyzed for gasoline range organics (GRO), benzene, toluene, ethylbenzene, and total xylenes (BTEX), methyl tertiary-butyl ether (MTBE), and naphthalene by United States Environmental Protection Agency (USEPA) Method 8260B. A quality control trip blank sample provided by the laboratory accompanied the samples and was analyzed for BTEX, MTBE, and naphthalene. Soil vapor samples were analyzed for GRO, BTEX, MTBE, and naphthalene using USEPA Method TO-15 Modified, and for the presence of atmospheric gases carbon dioxide (CO2), methane (CH4), and helium using American Standard Testing Materials (ASTM) Method D-1946 Modified. Laboratory analytical reports and COC records are included as Attachment C. WASTE MANAGEMENT AND DISPOSAL Soil cuttings generated during borehole advancement and soil sampling were placed in a Department of Transportation-approved 55-gallon drum and stored onsite pending characterization, removal and disposal by a waste management contractor. RESULTS AND DISCUSSION Soil Stratigraphy - Surface materials consisted primarily of lean clay to a depth of approximately three to five ft bgs. Silt with sand, interspersed with layers of well-graded sand, was encountered from Design with community in mind