ARCHIVED REPORTS_SITE INVESTIGATION AND WELL DESTRUCTION PERMIT

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CRA MEMORANDUM Page All samples submitted for VOCs, and TPH determinations were spiked with the appropriate number of surrogate compounds prior to sample extraction and analysis. Surrogate recoveries were assessed against laboratory control limits. All surrogate recoveries met the above criteria. 10.0 Internal Standards (IS) Analyses Internal standard data were evaluated for all VOC sample analyses. To ensure that changes in the GC/MS sensitivity and response do not affect sample analysis results, internal standard compounds are added to each sample prior to analysis. All results are then calculated as a ratio of the internal standard responses. The sample internal standard results were evaluated against the following criteria: i. The retention time of the internal standard must not vary more than±30 seconds from the associated calibration standard ii. Internal standard area counts must not vary by more than a factor of two (-50 percent to +100 percent)from the associated calibration standard All internal standard recoveries and retention times met the above criteria. 11.0 Laboratory Control Sample (LCS)Analyses LCSs are prepared and analyzed as samples to assess the analytical efficiencies of the methods employed, independent of sample matrix effects. For this study, the LCS was analyzed at a minimum frequency of 1 per 20 investigative samples and/or 1 per analytical batch. The LCS contained all compounds of interest. All LCS recoveries were within the laboratory control limits, demonstrating acceptable analytical accuracy. 12.0 Matrix Spike/Matrix Spike Duplicate (MS/MSD) Analyses To evaluate the effects of sample matrices on the extraction or digestion process, measurement procedures, and accuracy of a particular analysis,samples are spiked with a known concentration of the analyte of concern and analyzed as MS/MSD samples. The relative percent difference (RPD) between the EQUN EMPW MENTO"ORMNIT EMKOM