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Stantec <br /> L & M OPERABLE UNIT- FOURTH QUARTER AND ANNUAL 2010 SITE STATUS, <br /> REMEDIAL SUMMARY, AND GROUNDWATER MONITORING REPORT <br /> Summary of 2010 Annual Monitoring and Sampling <br /> January 31, 2011 <br /> 5.6 A-ZONE ISOCONCENTRATION TRENDS <br /> Shallow zone isoconcentration trends are discussed below. Figures from 1Q10, 2Q10, and <br /> 3Q10 are provided in Appendix I. <br /> 5.6.1 TPHg <br /> Concentrations of TPHg are generally detected on the northern section of the L&M OU and on <br /> the eastern side of the Water Front Towers' parking lot. Based on data collected historically and <br /> during 2010 for the shallow zone wells, the TPHg plume is generally delineated; however, the <br /> City of Stockton did not sample their wells on the UOU or MOU during 2010, therefore, TPHg <br /> could not be delineated to the east. <br /> 5.6.2 TPHd <br /> Concentrations of TPHd are generally detected on the L&M OU property and the Water Front <br /> Towers' parking lot. Based on data collected historically and during 2010, the TPHd plume is <br /> generally delineated to the west, south, and northwest. The City of Stockton did not sample <br /> their wells on the UOU or MOU during 2010; therefore, TPHd could not be delineated to the <br /> east. There were a few concentrations of TPHd detected in groundwater from well MW-30 <br /> during 2Q10, 3Q10, and 4Q10. <br /> 5.6.3 TPHo <br /> Concentrations of TPHo are generally detected on the L&M OU property, and very seldom <br /> detected on the Delta View apartment property. Based on data collected during 2010, the TPHo <br /> plume is generally delineated; however, the City of Stockton did not sample their wells on the <br /> UOU or MOU during 2010, therefore, TPHo could not be delineated to the east. <br /> 5.6.4 Benzene <br /> Concentrations of benzene are generally detected on the L&M OU property, and on the eastern <br /> side of the Water Front Towers' parking lot. Based on data collected during 2010, the benzene <br /> plume is delineated; however, the City of Stockton did not sample their wells on the UOU or <br /> MOU during 2010, therefore, benzene could not be delineated to the east during 1Q10 and <br /> 2Q10. <br /> 5.6.5 MtBE <br /> Concentrations of MtBE are generally detected on the L&M OU property, and on the Water <br /> Front Towers' parking lot. Very seldom, concentrations of MtBE were detected on the Delta <br /> View apartment property, near well MW-23. Based on data collected during 1Q10, MtBE is <br /> generally delineated, except to the northwest where a low concentration was observed in well <br /> MW-20. During 2Q10, MtBE was delineated. During 3Q10 and 4Q10, MtBE was delineated, <br /> except to the east. The City of Stockton did not sample their wells on the UOU or MOU during <br /> 2010; therefore, MtBE could not be delineated to the east. <br /> I:\Tidewater\TW Stockton(Parcel 2A-0415)\Reports\QMR\2010\4010-Annual\4Q10 and Annual OSSRQRSRQMR Stockton_FINAL.doc 5.4 <br />