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SOP No.021,REV.1 TO E RO E K SOIL GAS SAMPLING METHODS „ AssoCI ns INC. PAGE S 6. If less than 0.25 liters is collected after 4 minutes of sampling, raise the soil gas probe 0.5 feet (if possible, i.e., when using a temporary probe). Continue to evacuate the vacuum chamber for another minute. If the minimum required soil gas is not collected, repeat the procedure again. If the minimum required volume of soil gas is still not collected, abandon the collection process. All steps conducted must be accurately recorded in a field logbook. 7. Remove the top of the vacuum chamber after the soil gas sample is collected in the Tedlar®bag. 8. Close the valve on the Tedlar® sampling bag, clamp the Tygon® tubing, and remove the Tedlar® sampling bag. 9. Turn off the pump. 10. Follow the leak check procedures described in Section 2.8. 11. Label the Tedlar®bag and its corresponding field data sheet(Figure 1)with the sample number. 12. Fill out the rest of the field data sheet and record all information in the field logbook. 13. Ship samples to the laboratory for analysis. Tedlar® samples do not need to be chilled after collection or during transportation. 2.4 SAMPLE COLLECTION USING SYRINGES Soil gas also can be collected for chemical analysis in a syringe for on-site analysis. The system is purged and the sample is collected using the following procedures: 1. Connect the syringe to the probe tubing using a 3-way valve. 2. If the syringe is connected directly to the probe implant or tip (shallow applications only), no purging is required. 3. Open the valve and collect the sample by pulling on the syringe piston to extract the desired volume. Close the valve, then remove and cap the syringe. 4. Follow the leak check procedures described in Section 2.8. 5. Document the sample collection in a field logbook. 6. Analyze samples immediately (maximum holding time is 30 minutes); samples do not need to be chilled prior to analysis. 2.5 SAMPLE COLLECTION USING SUMMA CANISTERS Soil gas also can be collected for chemical analysis in a stainless steel, evacuated canister, or Summa canister. Often,these expensive canisters are used to collect duplicate samples for off-site analysis from locations where field screening analysis using Tedlar®bags or syringes is in use. When this method is used, the canister sampling train is connected directly to the purged Tygon®