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4 <br /> Workplan for Soil Gas Study—Subslab Sampling Cardno� <br /> 807 N. Hunter Street Stockton,California <br /> November 25,2014 ATC <br /> Shaping the Future <br /> pillar to keep it out of the path of the building's inhabitants. Proposed soil vapor probe construction details are <br /> shown on Figure 4. Sampling equipment will be dedicated to each soil gas probe. To protect the integrity of the <br /> probe until sampling is complete, the aboveground portion of the probe will either be installed in a clearly marked <br /> protective container or attached to a wall or pillar to keep it out of the path of the building's inhabitants. <br /> A Cardno ATC field geologist will be present to observe the advancement and installation of the soil gas sampling <br /> points and to grade the subslab soils evacuated from approximately three inches below the base of the concrete <br /> slab flooring using a vacuum. A photo-ionization detector(PID)will be used as a field screening device for the <br /> detection of petroleum hydrocarbon vapors during the advancement and installation of the temporary subslab vapor <br /> points. Soil samples will not be collected. <br /> 2.3 Collection of Soil Gas Samples <br /> Cardno ATC will follow guidelines established in the following documents: Advisory—Active Soil Gas <br /> Investigations, dated April 2012, and Final— Guidance for the Evaluation and Mitigation of Subsurface Vapor <br /> Intrusion to Indoor Air, dated October 2011. These guidelines have been established by the Los Angeles and San <br /> Francisco Regional Water Quality Control Boards (LA RWQCB and SF RWQCB) and the California Department of <br /> Toxic Substances Control (DTSC). <br /> 2.3.1 Shut In Test <br /> A shut in test will be conducted prior to collecting a confirmation sample from the proposed soil gas sampling point <br /> location. This test consists of applying a vacuum of approximately 7 inches of mercury to the soil gas sampling <br /> apparatus for approximately 10-15 minutes to evaluate the integrity of the sampling apparatus. <br /> 2.3.2 Leak Testing <br /> A tracer compound, typically difluoroethane or iso-propanol, is used to test for leaks around the tubing at the <br /> ground surface and in the sampling system. The tracer is placed under the shroud during sample collection. If the <br /> tracer is detected per CA-EPA advisory specifications, another sample is collected <br /> 2.3.3 Soil Gas Sample Collection <br /> The process begins with the soil gas being withdrawn from the end of the tubing that runs from the sampling tip to <br /> the surface connected via an on-off valve. The probe tip and sampling tubing are nominally purged of three internal <br /> dead volumes. A sample of the stream of in-situ soil gas is then withdrawn to be sampled. The soil gas sample will <br /> be collected in summa canisters. <br /> 3 LABORATORY ANALYSIS <br /> A state certified laboratory will analyze the vapor samples collected. Summa canisters will be shipped following <br /> COC protocol to a State certified laboratory for testing. <br /> The samples collected in summa canisters will be delivered to the lab following COC protocol and analyzed using a <br /> modified EPA Method TO-15 GC/MS method appropriate for soil vapor. Cardno ATC will request detection limits <br /> for the analytes of interest that are less than or equal to the residential scenario screening levels provided in Table <br /> E of the Environmental Screening Levels (ESLs)for Indoor Air and Soil Gas (Vapor Intrusion Concerns) as <br /> published by the RWQCB San Francisco Bay Region in November 2007. <br /> Compounds of interest(COI)will include the following: <br /> • PCE <br /> • chloroform <br /> • dichlorodifluoromethane <br /> • vinyl chloride <br /> www.cardnoatc.com <br />