ARCHIVED REPORTS_VAPOR INTRUSION SURVEY - SOIL GAS SAMPLING REPORT

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t ' reading was from the test sample after purging one-sampling train volume. Therefore, the subsequent samples were collected after removing one purge volume from each soil gas sampling location. The calculations for the purge volumes are presented on the Soil Gas ' Purge Volume Calculation Table in Appendix D. PSC performed a 10-minute leak check on the sampling manifold prior to purging or collecting the soil gas sample for each location. The guidelines do not specifically indicate how much of a vacuum drop is considered acceptable. After 10 minutes had passed upon charging the vacuum gauge among the seven primary sampling trains, two sample locations had vacuum drops greater than 2 inches of mercury. PSC deemed a drop of 2 inches or less to be acceptable. Sample location SG-2 had incurred a 4-inch drop and SG-4 had incurred a 12-inch drop. For sample SG-2, the environmental technician retightened the compression fittings and proceeded with the vapor purge. Sample SG-2 did not decrease vacuum pressure after allowing the appropriate time to purge the sample train. This indicated that the sampling train 1 did not have a leak. Rather upon further investigation,it was determined that the compression fitting was over tightened and pinched closed the opening to the sample tubing. PSC refit the compression fitting, performed an additional 5-minute leak check, a successful purge, and then collected a successful soil gas sample. PSC did not record a successful leak test for sample SG-4. It was determined that the leak may have been with the connection of the manifold to the purge canister. PSC retightened the manifold compression fittings. The purge appeared successful. However, the sample volume collected for soil gas sample SG-4 was not sufficient. The field sampler recorded the final SUMMA canister vacuum reading at 22 inches after allowing the appropriate sample collection time. However, the canister should have had only 5 inches of vacuum remaining. The sampler stopped collecting the sample at 22 inches assuming that the gauge was incorrect. However, the laboratory confirmed that the actual vacuum remaining in the SG-4 canister was 21 inches. Therefore, it appears as though only 250 mLs was actually collected instead of approximately 900 mLs. The unusually slow sample collection may have been due to the over-tightened/pinched tubing or to less permeable conditions in the sampling zone. The laboratory had to pressurize the canister to 21 inches of mercury (well beyond the normal 5 inches) in order to analyze the sample. This resulted in a dilution factor approximately three times greater than the other samples. Analysis of this diluted sample produced results that were biased high. The reporting limits were approximately three times greater than the other samples due to sample dilution. Therefore, the sample results are not representative and thus unusable. This rejected sample does not disqualify the overall soil vapor intrusion survey. The remaining five exterior samples and the one interior sample indicate with a high level of confidence that the risk of soil vapor intrusion does not exist for the facility. ' 2.5 Soil Gas Analytical Results The analytical results of the soil gas samples collected and submitted for analysis have been tabulated and are presented on Tables 1 and 2 and on figure 4. A copy of the analytical data is included in Appendix F. A detailed discussion of the analytical results are presented as follows. Vapor Intrusion Survey Soil Gas Sampling Report ' Prepared For:Sara Lee Bakery Group,Inc. Prepared By:PSC Industrial Outsourcing,LP Sam Lee—Lincoln Street\2009_03_31-Soil Gas Sampling Raport.doc March 31,2009 10