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Workplan for Additional Assessment and Subslab Gas Sampling Tracy Office Plaza 324 E. l 1 th Street,Tracy, CA November 22, 2013 and the maintenance of the initial vacuum in the sampling manifold system.After shut in testing,the probe will be connected to the sampling assembly using a Swagelok fitting and Teflon tubing, then a shroud will be placed over the probe and Helium will be introduced to a concentration of 20 to 30%. The helium concentration will be monitored periodically using a helium detector and the vacuum pump will be started to purge the manifold/probe assembly. During purging, vapor from the probe will be routed to a Tedlar bag within a vacuum chamber to check for helium within the probe/sampling assembly and to qualitatively screen for volatile contaminants using a PID.Upon completion of purging of approximately three times the ambient volume of air in the assembly/probe and void space,the sampling Summa canister will be opened for sample collection. The pre-set valve will regulate the vapor flow to approximately 150 milliliters of air per minute, which equates to approximately 5 minutes to fill the I-liter canister.Sample collection is typically discontinued when the vacuum decreases to between 5 and 4 inches of mercury. For further quality assurance,a duplicate sample will be collected at each sampling event. Additionally, Tedlar bag samples are collected after sample collection to check for helium in the sampling assembly. This method allows Pangea to monitor for leaks from the sample probe before and after sample collection and correct problems before sending the samples to the laboratory.The subslab gas sampling will be conducted in general accordance with procedures described in Pangea's Standard Operating Procedures (SOPS)for Subslab Gas Sampling(Appendix B). Task 4—Waste Management and Disposal Soil cuttings and other investigation-derived waste will be stored onsite in Department of Transportation (DOT)-approved 55-gallon drums. The drums and their contents will be held onsite pending laboratory analytical results. Upon receipt of the analytical reports, the waste will be transported to an appropriate disposal/recycling facility. Task 5—Report Preparation Upon completion of assessment activities,Pangea will prepare a technical report.The report will describe the investigation activities, present tabulated analytical data,and offer conclusions and recommendations. 5