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ATC Associates Inc. 1117 Lone Palm Avenue, Suite 201 Modesto,California 95351 209-579-2221 fax:209-579-2225 ASSOCIATES INC. Shut In Test A shut in test will be conducted prior to collecting conformation samples from each of the proposed soil gas sampling point locations. This test consists of applying a vacuum of approximately 10 to 15 inches of mercury to the soil gas sampling apparatus used for collecting soil gas samples with a Summa canister. The applied vacuum will be monitored for approximately 10 minutes to evaluate the integrity of the sampling apparatus. Once the vacuum has shown to be consistKe soil gas sampling apparatus wil be used to collect confirmation samples from each soil gas sampling point using a Summa canister. The soil gas sampling point will be purged prior to collecting the confirmation sample. Leak Test To ensure leakage of ambient air is not diluting the soil gas sample, a leak test utilizing the vapor leak check compound 1,1-difluoroethane (1,1-DFA) will be conducted at each location of potential ambient air intrusion including sample system connections, surface bentonite seals, and the top of the temporary soil gas point. The leak check compound will applied during purging and sampling activities at each soil gas point location. The flow rates will be monitored to ensure a sampling rate of 100 to 200 mL/min. Since 1,1-DFA is less dense than ambient air, a shroud will be emplaced around the downhole tubing to contain the 1,1-DFA. The shroud atmosphere will be monitored using a flame ionization detector(FID) since 1,1-DFA can not be detected using a PID. Collection of Soil Gas Samples Soil gas samples will be collected from each of the soil gas sampling points using a glass syringe for the mobile laboratory. The sampling equipment will be dedicated to each soil gas point. Prior to the collection of soil gas samples, the appropriate number of purge volumes will be removed from each soil gas point as determined by the stepped purge test. A leak detector compound will be applied to evaluate the potential for sample dilution by ambient air and to ensure sample integrity. Confirmation samples will be collected in Summa canisters from each of the soil gas sampling points to be analyzed by an off-site laboratory. Soil gas samples will be collected in accordance with the DTSC guidelines entitled Advisory-Active Soil Gas Investigations dated January 28, 2003 and Interim Final — Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air dated December 15, 2004, revised February 7, 2005. Chemical Analyses Soil gas samples collected from the soil gas sampling points will be immediately transferred under chain-of-custody procedures to a mobile laboratory to be located on site. The samples will be analyzed for total petroleum hydrocarbons as gasoline (TPHg), benzene, toluene, ethylbenzene, and xylenes (BTEX), MTBE, tertiary butyl alcohol (TBA), DIPS, tertiary amyl methyl ether (TAME), ETBE, 1,2-DCA, and EDB using EPA Method 8260B. Additionally, selected soil gas samples will be analyzed for methane by EPA Method 8015M and for oxygen and carbon dioxide by an appropriate EPA Method using a gas chromatograph (GC) and/or a thermal conductivity detector (TCD). The mobile laboratory will primarily be used as a screening tool. S:\Environmental\25847\38\Workplans\2010 May SGS.doc 5