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ADVISORY — ACTIVE SOIL GAS INVESTIGATIONS TABLE 2 Preferred Analytical Methods and Modifications* Method/ Parameter GC/MS Methods GC Methods COMMENTS Modified USEPA 8260 Modified USEPA TO-15 Modified USEPA TO-17 Modified USEPA 8015 and Modified USEPA 8021 Applicability/Analytes Most VOCs: confirmation sampling for naphthalene should be performed by USEPA TO-17. Most VOCs: confirmation sampling for naphthalene should be performed by USEPA TO-17. Most VOCs: approximate concentrations should be known prior to sampling, VOCs: gasolineiTPH be performed by Limited number of most VOCs: confirmation sampling for naphthalene should USEPA TO-17. See Appendix F of this guidance for discussion. Sample Introduction Technique Modified Purge-and-trap (USEPA 5030). Samples collected in passivated canisters: VOCs are concentrated on sorbent trap. Samples pulled through sorbent pack, thermally desorbed into GC. Modified purge-and- trap (USEPA 5030). See Appendix F of this guidance for discussion. Sample Size Purge-and-trap: 5 to 250 mL (cc) (See Appendix F for discussion). To be determined by sample delivery technique and sample concentration; typically 1 to 6 liters, To be determined by a combination of factors: sorbent selected, tube length, humidity, temperature; 50 to 250 ml of sample suggested. Purge-and-trap: 5 to 250 mL (cc) (See Appendix F for discussion). See Appendix F of this guidance for discussion. Dilution may be needed if high concentration is suspected. ( Method Validation 1) As per Section 8.4 of USEPA 8000B. As per Section 8.4 of USEPA 8000B. As per Section 8.4 of USEPA 8000B. As per Section 8.4 of USEPA 8000B. Initial Calibration Minimum of 5 levels, lowest at reporting level. Use method acceptance criteria, Minimum of 5 levels, lowest at reporting level. Use method acceptance criteria, Minimum of 5 levels, lowest at reporting level. Use method acceptance criteria. Preloaded certified standard tubes may be used for calibration, Minimum of 5 levels, lowest at reporting level. Use method acceptance criteria. Vapor-phase standards are preferred. Liquid standards may be used for USEPA Methods 8260, 8015, 8021 and TO-17 provided calibration curve is validated. See Appendix F of this guidance. Continuing Calibration Mid-level calibration standard run every 12 hours. Use method acceptance criteria. Mid-level calibration standard run every 24 hours. Use method acceptance criteria. Mid-level calibration standard every 10 sample batch (Section 12 of USEPA 10-17). Mid-level calibration standard run every 12 hours. Use method acceptance criteria. Calibration Validation At minimum, vapor-phase validation check standard (2) analyzed and evaluated for each new calibration curve (% difference 5 20%). Not Applicable. No vapor-phase standard validation needed for liquid standards. At minimum, vapor- phase validation check standard (2) analyzed and evaluated for each new calibration curve (% difference 5 20%). Validation not needed if calibration curve is prepared with vapor-phase standards. 36