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ADVISORY - ACTIVE SOIL GAS INVESTIGATIONS Surrogates; Method blank; and Field blank. All surrogate recovery data should comply with laboratory-derived control limits. Control limits should be included in the laboratory reports for reference. Surrogate recovery limits should be approximately 70 percent to 130 percent (30 percent deviation). The laboratory-derived recovery limits may be wider or narrower than the 30 percent figure depending on sample introduction technique and compound used. If a compound-specific recovery limit is not selected, an explanation should be provided to justify the recovery limit used. See Appendix F for surrogate introduction techniques. 6.3.1 Sample Blanks Method Blanks: Method blanks should be used to verify the effectiveness of decontamination procedures in the laboratory, and to detect any possible interference from ambient air; Trip Blanks for Off-site Shipments: Trip blanks should be included in the shipping containers when collecting USEPA TO-17 samples; Material Blanks: Prior to soil gas sampling, an assembled soil gas probe, tip and tubing should be blank tested at a frequency of one analysis per new batch of tubing or material used; and Equipment Blanks: Equipment blanks should be collected from decontaminated equipment before reuse at a frequency specified in the workplan. One equipment blank should be collected and analyzed for each batch of 20 samples, or at least one per day, whichever is more often. 6.3.2 Field Duplicate/Replicate Samples Duplicate samples are collected simultaneously, whereas replicate samples are collected sequentially. At least one duplicate/replicate sample should be collected and analyzed per 20 samples or per batch, whichever is more often. Duplicate/replicate samples should be collected from contaminated areas at a frequency based on the project DQ0s. The workplan should state the duplicate/replicate collection frequency. Duplicate/replicate samples should be collected in separate sample containers at the same location and depth. Replicate samples can be collected immediately after the original sample, or a duplicate sample can be collected simultaneously by use of a T- splitter at the point of collection to divide the sample stream into two separate sample containers. The field replicate mentioned in this section should not be confused with the laboratory replicate (see Table 2 in Section 6.5, and the QA/QC Section of Appendix F). July 2015 33