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