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I Mr. Jim Barton RWQCB March 29, 2013 Page 12 4) Record the recovery time, which is the time for the system to return to zero vacuum after purging. Tracer Gas After purging, a tracer compound (isopropanol or isopropyl alcohol)will be applied to all locations where ambient air could enter the sampling system. A shroud will be placed over the aboveground sample train (pump, Sample T, and SUMMA canister). Placement of the isopropanol will be as follows: 1) Towels wetted with the tracer liquid will be placed: a) On top of the bentonite sealing the annular space between the direct-push rod or auger flight and the ground surface. b) On top of the bentonite sealing the annular space between the auger or direct-push rod and the sample tubing. c) Inside the shroud. 2) Record PID readings under the shroud while.sampling. a) Record the highest reading and convert to parts per billion (ppb) using the following calculation: i) PID reading X 6 =ppm X 1,000=ppb ii) This calculated concentration of tracer gas will be compared against isopropanol concentrations found during sample analysis to determine whether the sample was contaminated and is, therefore, unusable. b) If soil vapor analytical results have greater than 10 percent tracer gas contamination compared to tracer gas concentration within the shroud, then the sample results will be considered suspect. Soil Gas Sample Collection Once purging is completed and the tracer gas had enough time to diffuse throughout the shroud, sampling will commence, as follows: 1) Leave the valve to the sample tubing open and close other open valves on the Sample T (should be the valves'to the pump and to the SUMMA canister; the third valve on the.unused arm of the Sample T should already be closed). 2) Open the SUMMA canister valve and record the vacuum reading from the gauge on the SUMMA canister stem onto the Soil Gas Sample Data Sheet, Surface/Downhole Probe Samples Form. 3) Slowly open the valve on the SUMMA canister. I xMS