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L & M OPERABLE UNIT- FIRST QUARTER 2012 SITE STATUS, REMEDIAL SUMMARY, <br />AND GROUNDWATER MONITORING REPORT <br />Groundwater Monitoring and Sampling <br />April 30, 2012 <br />I:\Tidewater\TW Stockton (P2A)\QMRs\2012\1Q12\1Q12 QSSR QRSR QMR Stockton_FINAL.doc 2.15 <br />2.5.2.6 Quality Assurance/Quality Control Samples <br />Duplicate sample QCDUP-5 was collected from L&M OU C-Zone well MW-62 during 1Q12 <br />sampling event. A comparison of the samples is shown below. <br />Analyte Sample # <br />MW-62 <br />Sample # <br />QCDUP-5 % Difference <br />TPHg (mg/L)<0.05 <0.05 0% <br />TPHd (mg/L)0.54 0.51 +/-5.7% <br />TPHo (mg/L)0.15 0.11 +/-30.8% <br />Benzene (mg/L)<0.0005 <0.0005 0% <br />MtBE (mg/L)<0.0005 <0.0005 0% <br />TBA (mg/L)<0.005 <0.005 0% <br />2.5.2.7 General Laboratory Notes <br />The laboratory validation issues are consistent with the C-Zone quality assurance and quality <br />control. Each set of issues corresponds directly with the denoted report. All laboratory reports <br />are included in Appendix D. <br />Validation issues with report number 80108: <br />The MSD associated with sample MW-61 for the analyte benzene was outside of the stated QC <br />limits for percent recovery, due to the analyte concentrations already present in the un-spiked <br />sample. This may indicate a possible bias for the reporting accuracy. The LCS percent <br />recovery was within QC limits indicating accuracy in reporting. RPD values were within QC <br />range in the MSD indicating precision in reporting. The reported values are considered valid. <br />The MS associated with samples MW-66 and MW-67 for the analyte tertiary butyl alcohol was <br />outside of the stated QC limits for percent recovery, due to the analyte concentrations already <br />present in the un-spiked sample. This may indicate a possible bias for the reporting accuracy. <br />The LCS percent recovery was within QC limits indicating accuracy in reporting. RPD values <br />were within QC range in the MSD indicating precision in reporting. The reported values are <br />considered valid. <br />It should be noted that the MRL for chloromethane was raised in sample MW-66 due to the <br />presence of an interfering compound. <br />Validation issues with report number 80125: <br />The RPD values associated with sample MW-65 for the analyte dissolved chromium was <br />outside of the stated QC limits by approximately 0.3 percent. This may indicate a possible bias <br />for the reporting precision. The LCS and LCSD percent recoveries were within QC limits <br />indicating accuracy in reporting. Since there is no RPD value to confirm precision in reporting, <br />the reported dissolved chromium may be biased; however, dissolved chromium values are <br />within historical limits.