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ADVISORY — ACTIVE SOIL GAS INVESTIGATIONS <br />When comparing the results from field duplicate/replicate samples, a wider allowance <br />should be given for the differences (e.g., 50 percent Relative Percent Difference [RPD]) <br />because of the inherent variability associated with soil gas samples. The specific <br />guideline for the RPD should be based on DQ0s and be specified in the QAPP. <br />6.3.3 Laboratory Control Samples <br />Laboratory Control Samples (LOS) are optional as described in Appendix F. <br />6.3.4 Split Samples <br />The regulating agency may request split samples be collected and analyzed by a <br />separate laboratory. <br />6.3.5 Holding Times <br />Holding times for soil gas samples should be specified in the workplan. All soil gas <br />samples should be analyzed pursuant to container-specific holding times, as follows: <br />TABLE 1 <br />Soil Gas Sample Holding Time <br />Container Holding Time Comments <br />Glass syringes 30 minutes <br />Polymer gas sampling <br />bags <br />6 hours <br />Glass bulbs 24 hours Must have surrogate added within 15 <br />minutes of collection <br />Passivated stainless <br />steel canisters <br />30 days <br />Sorbent Tubes 30 days Sulfur and nitrogen compounds and bis- <br />chloromethyl ether should be analyzed <br />with one week. <br />Hydrogen sulfide See Section 7.1 <br />6.4 ANALYTICAL METHODS <br />There are no approved USEPA methods specifically designed to analyze soil gas <br />samples. Consequently, modified versions of existing USEPA methods were adopted. <br />Numerous modifications of USEPA methods are being used for soil gas analysis. Each <br />modification has advantages and disadvantages. Soil gas analysis should be performed <br />in accordance with the protocols noted in the respective USEPA method(s) concurrently <br />with the specific recommended practices for soil gas samples outlined in Table 2. <br />July 2015 34