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V=1 INC <br /> ' that will be measured on a centimeterp er minute basis An in-line flow meter will <br /> • <br /> ' be placed in the sample stream to monitor flow rates during sampling Ideally, a <br /> vacuum of less than 2 inches of mercury (m-Hg) will be applied <br /> ' (Note If a non-adjustable vacuum pump is to be used, purge the sample point using a <br /> vacuum box and a Tedlar bag in a manner similar to the sample collection procedure <br /> outlined below ) <br /> 2 Approximately one to two tubing volumes (if using the PRT system) or probe rod <br /> volumes of vapor will be purged prior to collection of the first sample Excessive <br /> purging should be avoided, as it may draw soil gas from beyond the immediate <br /> ' area of the probe and thereby misrepresent the actual concentration of vapor <br /> encountered at the probe tip <br /> I 1 I <br /> (Note Field instrumentation [e g , flame-ionization detector (FID), oxygen-carbon dioxide <br /> meter, etc ] may be inserted into the sample train for field screening and/or optimization <br /> of purge volumes ) <br /> 3 To collect a sample, first seal the silicone adapter tubing with the adjustable clamp <br /> to prevent the back-flow of vapor at the sampling point Then attach the silicone <br /> tubing adapter to the Teflon sample-line tubing attached to the vacuum box <br /> Attach the vacuum pump to the vacuum box at the tubing adapter near the small <br /> brass valve <br /> ' (Note A gas-tight laboratory syringe can be used to sample the vapor directly from the <br /> silicone adapter tubing This method is only to be used when an onsite, mobile laboratory <br /> ' is available and the laboratory is ready to analyze the sample within 30 minutes of sample <br /> collection } <br /> APPENDIX III <br /> ' 12270020 125 8 <br />