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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 2.11 <br />2.4.2.6 Quality Assurance/Quality Control Samples <br />Duplicate samples QCDUP-2 and QCDUP-4 were collected from L&M OU B-Zone wells MW-60 <br />and MW-32, respectively, during 1Q12 sampling event. A comparison of the samples is shown <br />below. <br />Analyte Sample # <br />MW-60 <br />Sample # <br />QCDUP-2 % Difference <br />TPHg (mg/L)<0.05 <0.05 0% <br />TPHd (mg/L)0.49 0.41 +/-17.8% <br />TPHo (mg/L)0.13 0.12 +/-8.0% <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 />Analyte Sample # <br />MW-32 <br />Sample # <br />QCDUP-4 % Difference <br />TPHg (mg/L)<0.05 <0.05 0% <br />TPHd (mg/L)0.17 0.15 +/-12.5% <br />TPHo (mg/L)0.095 <0.05 ~62.1% <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 />A percent difference for TPHo results associated with sample MW-32 and QCDUP-4 is <br />estimated at about 62.1 percent (based on MDL of 0.05 mg/L) during 1Q12 due to QCDUP-4 <br />being below the MDL. This may indicate a possible bias for reproducibility and precision. The <br />TPHo analytical results are within historical values; therefore, the reported values are not <br />anticipated to be affected. <br />2.4.2.7 General Laboratory Notes <br />The laboratory validation issues are consistent with the deep 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 80085: <br />The surrogate 2,4,6-tribromophenol was out of QC limits for sample MW-29 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 />Validation issues with report number 80108: <br />The MSD associated with samples MW-56 and MW-59 for the analyte benzene was outside of