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Stantec L & M OPERABLE UNIT- FOURTH QUARTER AND ANNUAL 2012 SITE STATUS, REMEDIAL SUMMARY, AND GROUNDWATER MONITORING REPORT Groundwater Monitoring and Sampling February 1, 2013 Analyte Sample# Sample# % Difference MW-9 QCDUP-1 TPHg (mg/L) 0.82 1.2 +/-37.6% TPHd (mg/L) 2.8 3.5 +/-22.2% TPHo (mg/L) 0.071 0.089 +/-22.5% Benzene (mg/L) 0.0058 0.0099 +/- 52.2% MtBE (mg/L) 0.00098 0.0011 +/- 11.5% TBA (mg/L) 0.028 0.032 +/- 13.3% A relative percent difference (RPD) for TPHg, TPHd, TPHo, and benzene are estimated at 37.6, 22.2, 22.5, and 52.2 percent, respectively, during 4Q12. The RPD values for TPHg, TPHd, TPHo, and benzene are greater than the recommended range of RPD (20 percent) for quality control (QC) purposes. This may indicate a possible bias for reproducibility and precision. The TPHg, TPHd, TPHo, and benzene analytical results are within historical values; therefore, the reported values are not anticipated to be affected. 2.3.2.5 General Laboratory Notes The following validation issues are consistent with the shallow zone quality assurance (QA) and QC. Each set of issues corresponds directly with the denoted report (Appendix E). Validation issues with report number 82960: The matrix spike (MS) and matrix spike duplicate (MSD) and RPD values associated with sample QCEB-2-RM for the analyte benzene were outside of the stated QC limits. The sample was affected by the analyte concentrations already present in the un-spiked sample. This may indicate a possible bias for the reporting accuracy and precision. The laboratory control spike (LCS) percent recovery was within QC limits indicating accuracy in reporting. Since there is no RPD value to confirm precision in reporting, the reported benzene may be biased; however, benzene values are within historical limits. The MS/MSD associated with samples QCDUP-4, QCTB-1, QCTB-2, QCEB-1-PV, QCEB-2-PV, and QCEB-1-RM for the analyte P + M xylene was outside of the stated QC limits for percent recovery. This may indicate a possible bias for the reporting accuracy. The LCS percent recovery was within QC limits indicating accuracy in reporting. RPD values were within QC range in the MSD indicating precision in reporting. The reported values are considered valid. 2.4 FOURTH QUARTER 2012 B-ZONE GROUNDWATER RESULTS 2.4.1 B-Zone Groundwater Gradient B-Zone groundwater elevations at the Site ranged from 6.34 ft below MSL in well MW-35 to 1.28 ft above MSL in well MW-44 (Table 3 and Figure 10). Groundwater gradient during 4Q12 in the B-Zone was calculated for two sections of the site (central and western). Along the I:\Tidewater\TW Stockton(P2A)\QMRs\2012\4Q12-Ann ual\4Q12 and Annual QSSR QRSR QMR Stockton_FINAL.doc 2.5