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Stantec February 18, 2011 Mr. Ken Sommers Page 4 of 6 Reference: Phase II Environmental Site Assessment. Task 5 — Soil Vapor Sampling Weather Conditions The sampling of the soil vapor probes will not be conducted during or within five days of a significant rain event (1/2 inch or greater). The majority of the Calpine Site, with the exception of some minimal landscaping, is covered by asphalt and concrete. The soil sample borehole locations will be selected in areas free of standing or ponded water for at least five days prior to sampling. Soil vapor sampling will also not be conducted during barometric pressure fluctuations associated with the passage of frontal systems. The frontal systems can introduce atmospheric air into the shallow vadose zone. Shut-In Test Prior to purging or sampling the soil vapor well, a shut-in test will be conducted. The shut-in test checks for leaks in the above ground fittings. The shut-in test will consist of assembling the above-ground apparatus (e.g., valves, lines and fittings), and evacuating the lines to see if there is any observable loss of vacuum. The fittings will be adjusted as needed until the vacuum in the above- ground portion of the sample train does not noticeably dissipate. Leak Check A leak test will be conducted to evaluate if a good seal is established in the sampling train, ground surface, and probe interface. A leak test will be conducted at every vapor sampling point. Isopropyl alcohol will be used as the leak check compound. Isopropyl alcohol will be applied to towels or clean rags and placed around all connections in the sampling train in order to evaluate potential leaks of ambient air into the sampling train. A shroud will be placed over the sampling equipment. The isopropyl alcohol concentrations detected in the soil vapor samples will be reported in the analytical report and will be discussed in the report, if any. Purge Volume Test The purge volume test ensures that stagnant and/or ambient air is removed from the sampling equipment, and that subsequent samples are representative of the native subsurface conditions. The actual purge volume removed will be based on the total of the sample probe, the internal volume of the sample tubing, the annular space around the soil vapor probe tip, and the dry bentonite in the annular space. Three purge volumes will be selected as the default volume for the soil vapor probes since SUMMA® canisters will be used to collect the soil vapor samples. The purge volume test will be conducted at a flow rate between 100 to 200 milliliters per minute (ml/min). (:\Projects\Calpine\Lodi\Work Plan\CalpineLodi.Work Plan.docx