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TO E RO E K SOP No.021,REV.1 „ SOIL GAS SAMPLING METHODS ASSOCIATES,INC. PAGE 8 3. Place tracer compounds around the soil gas well at the ground surface and at all connections in the aboveground sampling system train. Tracer compound is emplaced by wetting or spraying a paper towel or rag and wrapping around the area of the connation where leaks could occur. 4. Collect samples as describe in previous sections and use analytical results to determine if the tracer compound has leaked into the sample. 2.9 DECONTAMINATION Sampling probes should be decontaminated before the first sample is collected and between sampling points. Probes that are grossly contaminated should be decontaminated using a high-pressure steam cleaner. Probes that are not grossly contaminated can be decontaminated by brushing off loose soil particles, then heating the probes until they are warm to the touch to drive off any volatile contaminants. Heating times of 7 to 10 minutes are generally sufficient for this purpose. This brushing and heating method greatly reduces the generation of decontamination fluids. Syringes must be decontaminated between each use. Sampling syringes must be disassembled and baked at 240°C for a minimum of 15 minutes or at 120°C for a minimum of 30 minutes, or must be replaced. All canisters must be properly decontaminated by the laboratory as specified by appropriate EPA methods. If Y-branched tubing or any other sampling equipment is to be reused, it must also be decontaminated between sampling locations. 2.10 SAMPLE TRANSFER After collection, each sample container will be transported to the designated laboratory for analysis. In many cases, samples will be analyzed on site in a mobile laboratory. 2.11 ADVANTAGES AND DISADVANTAGES OF EACH SAMPLING METHOD Tedlar®bags are relatively inexpensive to use but can only be used once and then must be disposed of. If the soil formation being sampled has a low porosity and permeability, such as clay or silty clay, it may not be possible to inflate the Tedlar®bag with soil gas. Some regulatory agencies do not recommend use of Tedlar® bags to collect soil gas for VOCs analysis. Due to short holding times, Tedlar®bags should typically only be used for on-site or near-site analysis.