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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 2.7 <br />2.3.2.7 General Laboratory Notes <br />The following validation issues are consistent with the shallow zone quality assurance and <br />quality control. Each set of issues corresponds directly with the denoted report (Appendix D). <br />Validation issues with report number 80108: <br />The matrix spike duplicate (MSD) associated with samples 2A-MW-12, QCEB-2-RG, QCTB-2, <br />and QCEB-2-PV for the analyte benzene was outside of the stated quality control (QC) limits for <br />percent recovery, due to the analyte concentrations already present in the un-spiked sample. <br />This may indicate a possible bias for the reporting accuracy. The laboratory control spike (LCS) <br />percent recovery was within QC limits indicating accuracy in reporting. Relative percent <br />difference (RPD) values were within QC range in the MSD indicating precision in reporting. The <br />reported values are considered valid. <br />The matrix spike (MS) associated with samples MW-23 and QCDUP-6 for the analyte tertiary <br />butyl alcohol was outside of the stated QC limits for percent recovery, due to the analyte <br />concentrations already present in the un-spiked sample. This may indicate a possible bias for <br />the reporting accuracy. The LCS percent recovery was within QC limits indicating accuracy in <br />reporting. RPD values were within QC range in the MSD indicating precision in reporting. The <br />reported values are considered valid. <br />Validation issues with report number 80125: <br />The RPD values associated with samples MW-9, MW-18, and MW-21 for the analyte dissolved <br />chromium was outside of the stated QC limits by approximately 0.3 percent. This may indicate <br />a possible bias for the reporting precision. The LCS and laboratory control spike duplicate <br />(LCSD) percent recoveries were within QC limits indicating accuracy in reporting. Since there is <br />no RPD value to confirm precision in reporting, the reported dissolved chromium may be biased; <br />however, dissolved chromium values are within historical limits. <br />The surrogate 2,4,6-tribromophenol was out of QC limits for sample MW-21 due to matrix <br />interference. This may indicate a possible bias for the analysis. The method blank surrogate <br />spike was within QC limits; therefore, the sample outlier is not anticipated to affect the reported <br />values. <br />It should be noted that the MRL for 1,1,2-trichloroethane was raised in samples MW-9 and <br />MW-18 and the MRL for 1,1,2,2-tetrachloroethane was raised in sample MW-9 due to the <br />presence of an interfering compound.