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r <br /> ADVISORY-ACTIVE SOIL GAS INVESTIGATIONS <br /> I <br /> 6.3.2 Field Duplicate/Replicate Samples <br /> Duplicate samples are collected simultaneously, whereas replicate samples are <br /> collected sequentially. At least one duplicate/replicate sample should be collected and <br /> analyzed per 20 samples or per batch, whichever is more often. <br /> Duplicate/replicate samples should be collected from contaminated areas at a <br /> frequency based on the project DQOs. The workplan should state the <br /> duplicate/replicate collection frequency. <br /> Duplicate/replicate samples should be collected in separate sample containers at the <br /> same location and depth. Replicate samples can be collected immediately after the <br /> original sample, or a duplicate sample can be collected simultaneously by use of a T- <br /> splitter at the point of collection to divide the sample stream into two separate sample <br /> containers. <br /> The field replicate mentioned in this section should not be confused with the laboratory <br /> replicate (see Table 2 in Section 6.5, and the QA/QC Section of Appendix F). <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 DQOs and be specified in the QAPP. <br /> a <br /> 6.3.3 Laboratory Control Samples <br /> 1 <br /> Laboratory Control Samples (LCS) 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 /> 1 <br /> i <br /> j April 2012 31 <br />