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 Summary of 2010 Annual Monitoring and Sampling January 31, 2011 5.6.6 TBA Concentrations of TBA are generally detected on the L&M OU and on the Water Front Towers' parking lot. Based on data collected during 2010, TBA is generally delineated; however, the City of Stockton did not sample their wells on the UOU or MOU during 2010, therefore, TBA could not be delineated to the east. 5.7 B-ZONE ISOCONCENTRATION TRENDS Deeper zone (B-Zone) isoconcentration trends are discussed below. Figures from 1Q10, 2Q10, and 3Q10 are provided in Appendix I. 5.7.1 TPHg Concentrations of TPHg are generally detected on the L&M OU, the Water Front Towers' parking lot, and partially on the Delta View apartment property. Concentrations of TPHg were detected south of the Mormon Slough, in well MW-29. Based on data collected during 2010, the TPHg plume is generally delineated, except to the east. 5.7.2 TPHd Concentrations of TPHd are generally detected, at relatively low concentrations, across the B-Zone wells. Based on data collected during 2010, the TPHd plume was generally delineated to the northwest, west, and south. There were a few concentrations of TPHd detected in groundwater from well MW-29 during 2010. 5.7.3 TPHo Concentrations of TPHo are generally detected on the L&M OU property, Delta View apartment property, Water Front Towers' parking lot, and south of the Mormon Sough. Based on data collected during 2010, TPHo was delineated during 2Q10, 3Q10, and 4Q10. During 1Q10, TPHo was only delineated to the west. 5.7.4 Benzene Concentrations of benzene are generally detected, in small concentrations, on the Water Front Towers' parking lot. During the 2Q10 and 4Q10, benzene was not detected at or above the MRL, therefore, was considered delineated. During the 1Q10 and 3Q10, benzene was delineated, except to the northwest. Benzene has historically been centered in the vicinity of wells MW-17, MW-43, MW-47 through MW-50, and MW-52; however, these wells were not sampled during 2010 due to measurable SPH or sheen present in the well. 5.7.5 MtBE Concentrations of MtBE are detected in two distinct areas, on the eastern portion of the Water Front Towers' parking lot and near the Mormon Slough. On the Water Front Towers' parking lot, MtBE was delineated to the west and south only, during 1Q10 and 4Q10. During the 2Q10 and 3Q10, MtBE was delineated, except to the east. Near the Mormon Slough, MtBE was delineated, except to the southwest during 1010, 3Q10, and 4Q10. I:\Tidewater\TW Stockton(Parcel 2A-0415)\Reports\QMR\2010\4010-Annual\4Q10 and Annual OSSRQRSRQMR Stockton_FINAL.doc 5.5