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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 A RPD for TPHo is estimated at about 46.2 percent, (based on MDL of 0.05 mg/L) during 4Q12. The RPD values for TPHo are greater than the recommended range of RPD (20 percent) for QC purposes. This may indicate a possible bias for reproducibility and precision. The TPHo analytical results are within historical values; therefore, the reported values are not anticipated to be affected. 2.6.2.4 General Laboratory Notes The laboratory validation issues are consistent with the D-Zone quality assurance and quality control. Each set of issues corresponds directly with the denoted report. All laboratory reports are included in Appendix E. Validation issues with report number 82960: The MS/MSD and RPD values associated with samples MW-69 and MW-70 for the analyte benzene were outside of the stated QC limits. The samples were 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 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 MW-71 through MW-74 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. 2.7 FOURTH QUARTER 2012 SEPARATE PHASE HYDROCARBONS AND HYDROCARBON CONCENTRATION TRENDS 2.7.1 Shallow Zone The following sections summarize trends for detected petroleum hydrocarbons, fuel oxygenates, and observed SPH for shallow(A-Zone) groundwater beneath the Site. 2.7.1.1 Separate Phase Hydrocarbons Measurable SPH or SPH-sheen has historically been observed in shallow A-Zone wells MW-10, 2AMW-13, 2AMW-14, MW-19, and DPE-1 through DPE-13. Due to the quantity and viscous nature of the SPH, and the presence of emulsified SPH and groundwater in some of these wells, the depth to groundwater/SPH interface and corresponding SPH thickness have historically been difficult to accurately measure. This is evident by the inability to obtain SPH thickness measurements from wells 2AMW-14 and DPE-4 in December 2002, from well DPE-8 in February 2004, and from wells DPE-8 and DPE-10 in May 2005. Variations in measured depth to water/SPH and SPH thickness are apparent in several of these wells from quarter to quarter. This may also be attributed to seasonal fluctuations in groundwater levels. I:\Tidewater\TW Stockton(P2A)\QMRs\2012\4Q12-Ann ual\4Q12 and Annual QSSR QRSR QMR Stockton_FINAL.doc 2.12