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AECOM Environment <br /> Because minor leakage around the probe seal should not materially affect the usability of the <br /> soil vapor sampling results, the mere presence of the tracer gas in the sample should not be a <br /> cause for alarm. Consequently, portable field monitoring devices with detection limits in the low <br /> ppm range are more than adequate for screening samples for the tracer. If high concentrations <br /> (> 20%) of tracer gas are observed in a sample, the probe seal should be enhanced to reduce <br /> the infiltration of ambient air. <br /> During the initial stages of a soil vapor sampling program, tracer gas samples should be <br /> collected at each of the sampling probes. If the results of the initial samples indicate that the <br /> probe seals are adequate, the project manager can consider reducing the number of locations <br /> at which tracer gas samples are employed. At a minimum, at least 10% of the subsequent <br /> samples should be supported with tracer gas analyses. When using permanent soil vapor <br /> probes as part of a long-term monitoring program, annual testing of the probe integrity is <br /> recommended. <br /> APM 2010 <br />