ARCHIVED REPORTS_FOURTH QUARTER AND ANNUAL 2010 SITE STATUS, REMEDIAL SUMMARY, AND GROUNDWATER MONITORING REPORT

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Stantec L & M OPERABLE UNIT- FOURTH QUARTER AND ANNUAL 2010 SITE STATUS, REMEDIAL SUMMARY, AND GROUNDWATER MONITORING REPORT Groundwater Monitoring and Sampling January 31, 2011 2.5.2.6 Quality Assurance/Quality Control Samples Duplicate sample QCDUP-5 was collected from L&M OU C-Zone well MW-62 during 4Q10 sampling event. A comparison of the samples is shown below. Analyte Sample # Sample # % Difference MW-62 QCDUP-5 TPHg (mg/L) 0.065 0.055 +/- 16.7% TPHd (mg/L) 0.98 0.87 +/- 11.9% TPHo (mg/L) 0.20 0.14 +/- 35.3% Benzene (mg/L) <0.0005 <0.0005 0% MtBE (mg/L) <0.0005 <0.0005 0% TBA (mg/L) <0.005 <0.005 0% 2.5.2.7 General Laboratory Notes The laboratory validation issues are consistent with the C-Zone quality assurance and quality control. Each set of issues corresponds directly with the denoted report. All laboratory reports are included in Appendix C. Validation issues with report number 75022: MS/MSD results associated with samples MW-61 and MW-63 for the analytes MtBE and TBA were outside of the stated QC limits for percent recovery. This may indicate a possible bias for the reporting accuracy. The RPD values for MtBE and TBA are within range indicating precision in reporting. The LCS percent recoveries were within QC limits, for the analytes MtBE and TBA, indicating accuracy in reporting; therefore, the reported values are considered valid. The TPHd and TPHo surrogate octacosane was out of QC limits for MW-63. This could have been due to matrix interference. The sample outlier is not anticipated to affect the reported values. In addition, RPD values are within QC limits for TPHd and TPHg demonstrating precision in reporting. 2.6 FOURTH QUARTER 2010 D-ZONE GROUNDWATER RESULTS 2.6.1 D-Zone Groundwater Gradient Data D-Zone groundwater elevations at the Site ranged from 8.62 ft below MSL in well MW-55 to 7.89 ft below MSL in well MW-73 (Table 3 and Figure 24). Groundwater flow direction during 4Q10 was to the north-northwest with an approximate hydraulic gradient of 0.001 ft/ft (Figure 24). The highest D-Zone groundwater elevation (7.89 ft below MSL) was reported in well MW-73, located in the southeast corner of the L&M OU site behind the remediation system. Historical groundwater flow direction and gradient data are summarized in Table 8, and vertical I:\Tidewater\TW Stockton(Parcel 2A-0415)\Reports\QMR\2010\4010-Annual\4Q10 and Annual QSSRQRSRQMR Stockton_F I NAL.doc 2.14