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Soil Gas Sampling Procedures <br /> Soil gas samples will be collected from each of the deep soil borings at two depths, one <br /> immediately below the "A" Clay(30 to 35'bgs) and the second immediately above the water <br /> table (approximately 45 to 50'bgs). Once the sampling depth interval has been reached the drill <br /> bit and slide hammer will be removed from the hollow-stem auger system. <br /> A soil gas implant probe will be lowered through the hollow-stem auger to the bottom of each <br /> soil boring at the depth of sampling interest through a series of 3/4" diameter hollow soil gas <br /> sampling rods. The probe will then be driven approximately one foot below the base of the hole <br /> into undisturbed soil. A six to twelve inch interval of bentonite slurry will be placed by tremie <br /> pipe into the bottom of the hole to form a seal between the hollow stem auger and base of hole. <br /> A wait time of about 20 minutes will be allowed in order for the vapor concentrations in <br /> disturbed and undisturbed soil to equilibrate. <br /> The sampling rod will then be pulled back in order to expose the probe to the formation where <br /> in-situ soil gas will be sampled. One liter volume Summa canisters shall be prepared using <br /> procedures described in Appendix 4, Air Sampling and Analysis, Canisters and Tedlar Bags, <br /> fifth edition provided by Air Toxics Ltd. <br /> The sample tubing and sampling apparatus shall be purged of at least one purge volume prior to <br /> sample collection. The flow rate during sample purging shall be maintained between 100 and <br /> 200 milliliters per minute, and the flow rate shall be measured and recorded. Photoionization <br /> detector(PID)measurements of the soil vapor will be collected from the boring immediately <br /> following the removal of the first purge volume. PID measurements will continue to be collected <br /> until the concentration of VOCs measured in the purged vapor stabilizes or a maximum of three <br /> purge volumes is reached. <br /> A soil gas sample will be collected using the flow regulator attached to the Summa canister, a <br /> process that should take approximately 6 to 10 minutes. To check for system leaks, a leak <br /> M ain\D:AEnvironmentaI\LN CV\10152007.wpd 35 <br />