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Tracer Research Corporation <br /> The sampling manifold attached to the end of the probe, forming an air tight <br /> ' union between the probe and the silicon tubing septum. The septum connect the <br /> manifold to the pump vacuum line and permits syringe sampling. <br /> ' This sampling system allows the sample to be taken upstream of the sampling <br /> pump, manifold, and septum. Since cross contamination of sampling equipment can <br /> be a major problem, Tracer Research replaces the materials (probe and syringe), <br /> between sampling points, that contact the soil gas before or during sampling. If the <br /> P g <br /> equipment is contaminated, all the components are replaced. At the end of each day <br /> ' the manifold is cleaned with soap and water and baked in the GC oven. <br /> -Sampling Probes <br /> ' Steel probes are used only once each day. To eliminate the possibility of <br /> cross contamination, they are washed with high pressure soap and hot water spray, or <br /> steam-cleaned. Enough sampling probes are carried on each van to avoid the need to <br /> re-use any during the day. <br /> -Glass Syringes <br /> Glass syringes are usually used for only one sample a day and are washed and <br /> baked out at night. If they must be used twice, they are purged with carrier gas <br /> (nitrogen) and baked out between probe samplings. <br /> - Polyethylene Tubing and VOA Vials <br /> Polyethylene tubing and VOA vials used for the collection of groundwater <br /> samples are used only once and then discarded to avoid cross contamination. <br /> ' -Sampling Efficiency <br /> Soil gas/groundwater pumping is monitored by a vacuum gauge to ensure that <br /> ' an adequate flow of gas from the vadose zone is maintained. A reliable gas sample <br /> can be obtained if the sample vacuum gauge reading is.at least 2 inches Hg less than <br /> ' the maximum measured vacuum of the vacuum pump. <br /> May 22,1992 Page 7 1-92-358 <br />