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L & M OPERABLE UNIT- FIRST QUARTER 2012 SITE STATUS, REMEDIAL SUMMARY, AND GROUNDWATER MONITORING REPORT Groundwater Monitoring and Sampling April 30, 2012 I:\Tidewater\TW Stockton (P2A)\QMRs\2012\1Q12\1Q12 QSSR QRSR QMR Stockton_FINAL.doc 2.19 Validation issues with report number 80085: It should be noted that the MRL for chloromethane was raised in sample MW-70 due to the presence of an interfering compound. Validation issues with report number 80108: The MS associated with sample MW-73 for the analyte tertiary butyl alcohol was outside of the stated QC limits for percent recovery, due to the analyte concentrations already present in the un-spiked sample. 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. Validation issues with report number 80125: The RPD values associated with sample MW-72 for the analyte dissolved chromium was outside of the stated QC limits by approximately 0.3 percent. This may indicate a possible bias for the reporting precision. The LCS and LCSD percent recoveries were within QC limits indicating accuracy in reporting. Since there is no RPD value to confirm precision in reporting, the reported dissolved chromium may be biased; however, dissolved chromium values are within historical limits. 2.7 FIRST 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. SPH or sheen has historically been reported in well 2AMW-14 since May 2002 (Table 3, Figure 9). Historical thickness of SPH in well 2AMW-14 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.