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Soil Vapor Sampling SOP Page 9 of 11 Stantec Rev. 1.0 Apr 2019 Percent Helium = Parts Per Million (ppmv)x 0.0001 8.3 Purging After the sampling equipment passes the vacuum test, the implant or well is purged to remove internal air from the sample train (tubing and vapor implant only). Three volumes will be purged from each sampling location. Purge volumes will be calculated by: Volume to be purged=Number of purge volumes x(4.46 ml/foot of 0.25 in. OD tubing x depth) If each purge volume is anticipated to be less than 50 mL, purging may be performed using a gas-tight syringe'. The flow rate during purging will be approximately equivalent to the flow rate during sampling, which is set by the flow controller provided by the laboratory. Purge data for each implant/well will be recorded on the soil vapor sampling log. 8.4 Collecting Soil Vapor Samples 8.3.1 Connecting Soil Vapor Sampling Equipment The initial vacuum of each canister will be measured using the laboratory-supplied vacuum gauge. In no case will a canister be used if the initial vacuum is measured to be at or less than 25 in Hg. Following inspection, the vapor implant tubing will be routed through a dedicated opening in the shroud, the tubing cap removed and a compression fitting attached. The tubing will then be connected to the Summa T°"canister. With the leak test shroud still in place, collection of soil vapor samples from a particular probe will begin within 10 minutes of purging. Each sample from the soil vapor wells will be collected in a 1-L batch-certified2 Summa TM canister at an approximate collection rate of less than 200 ml/min. • The valve on the Summa TM canister is opened. • The pressure gauge on the flow controller will be observed to verify that the vacuum in the canister is decreasing over time. If the flow controller is working correctly, it will take approximately 20 minutes for the vacuum to decrease to 5 in Hg for sub-slab soil vapors samples and approximately 5 to 10 minutes for shallow soil vapor samples; however, the actual sampling duration may be slightly more or less. The Summa TM canister valve will be closed and sampling will cease when a vacuum of 5 in Hg is obtained. ' Alternatively the purge may be performed at each location using a purge Summa canister. An approximate 1-inch of mercury(in Hg)drop in vacuum pressure in the 6-L purge canister corresponds to an approximate purge volume of 200 mL. z`Batch certification' means that 10 percent of the canisters processed(i.e.,cleaned using a combination of dilution, heat and high vacuum)in a given batch were sampled and analyzed by GUMS,and that concentrations of target compounds in the tested canisters were below 0.2 parts per billion vapor(ppbv). THIS INFORMATION FOR AUTHORIZED COMPANY USE ONLY STANTEC CONSULTING