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 The TPHo results associated with sample MW-68 and QCDUP-6 have a percent difference of +/- 57.5 percent. 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. 2.6.2.7 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 C. Validation issues with report number 75022: MS/MSD results associated with samples MW-68, MW-69, and QCDUP-6 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. 2.7 FOURTH QUARTER 2010 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. SPH or sheen has historically been reported in well 2AMW-14 since May 2002 (Table 3, Figure 9). Historical thickness of SPH in that well has ranged from 0.02 ft reported during the first quarter 2005 to a maximum thickness of 2.99 ft reported during the fourth quarter 2003. Well 2AMW-14 was not assessed during the third through fourth quarters of 2004 due to its connection to a free product removal system. However, well 2AMW-14 has been accessible for the last 24 consecutive quarters and has contained sheen only for the last 10 quarters. SPH or sheen has historically been reported in well MW-10 since February 2004 and has ranged in I:\Tidewater\TW Stockton(Parcel 2A-0415)\Reports\QMR\2010\4010-Annual\4Q10 and Annual OSSRQRSRQMR Stockton_FINAL.doc 2.17