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Stantec L & M OPERABLE UNIT- FOURTH QUARTER AND ANNUAL 2012 SITE STATUS, REMEDIAL SUMMARY, AND GROUNDWATER MONITORING REPORT Summary of 2012 Annual Monitoring and Sampling February 1, 2013 1 Q1 2 only. Based on data collected historically and during 2Q12 and 3Q12, the TPHo plume is generally delineated; however, the City of Stockton did not sample their wells on the UOU or MOU during 2012; therefore, TPHo could not be delineated to the east. During 2Q12, a detection southwest of the Mormon Sough (MW-30) was also observed. During 4Q12, the TPHo plume was delineated to the north and northwest only due to select wells not sampled per MRP. 5.6.4 Benzene Concentrations of benzene are generally detected on the L&M OU property. Based on data collected during 2012, the benzene plume is delineated; however, during 2Q12, 3Q12, and 4Q12, benzene could not be delineated to the east due to the City of Stockton not sampling their wells on the UOU or MOU during 2012. During 4Q12, the benzene plume was delineated to the north, northwest, and west only due to select wells not sampled per MRP. 5.6.5 MtBE Concentrations of MtBE are generally detected on the L&M OU property. Based on data collected historically and during 2012, MtBE is delineated; however, during 4Q12, MtBE could not be delineated to the east due to the City of Stockton not sampling their wells on the UOU or MOU during 2012. During 4Q12, the MtBE plume was delineated to the north and northwest only due to select wells not sampled per MRP. 5.6.6 TBA Concentrations of TBA are generally detected on the L&M OU. Based on data collected historically and during 2012, TBA is delineated; however, during 4Q12 TBA could not be delineated to the east due to the City of Stockton did not sample their wells on the UOU or MOU during 2012. During 4Q12, the TBA plume was delineated to the north and northwest only due to select wells not sampled per MRP. 5.7 B-ZONE ISOCONCENTRATION TRENDS Deeper zone (B-Zone) isoconcentration trends are discussed below. Figures from 1 Q12, 2Q12, and 3Q12 are provided in Appendix K. 5.7.1 TPHg Concentrations of TPHg are generally detected on the L&M OU property, west of the Water Front Towers' parking lot, and southwest of the Mormon Slough. During 1Q12 and 2Q12, concentrations of TPHg were detected southwest of the Mormon Slough, in well MW-29. Based on data collected historically and during 2012, the TPHg plume is generally delineated, except to the east. During 1Q12 and 4Q12, TPHg plume was delineated to the northwest, west, and south only. 5.7.2 TPHd Concentrations of TPHd are generally detected on the L&M OU property and sporadically across the rest of the B-Zone wells. During the 1Q12, the TPHd plume was delineated to the I:\Tidewater\TW Stockton(P2A)\QMRs\2012\4Q12-Ann ual\4Q12 and Annual QSSR QRSR QMR Stockton_FINAL.doc 5.4