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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 2.27 wells MW-29 and MW-44 for MtBE. Analytes detected in well MW-29, across the Mormon Slough, are not anticipated to be assocated with a historic release at the L&M OU. Low level dissolved TPHd in B-Zone groundwater was delineated to the west during 1Q12. Dissolved TPHo in B-Zone groundwater was observed to the north in the Water Front Tower’s parking lot (MW-57 and MW-58) and to the south along the Delta View Apartments and south of the Mormon Slough. Dissolved benzene in B-Zone groundwater was not reported at concentrations at or above the laboratory MRL, with the exception of one minor detection in well MW-58 (0.0067 mg/l) located northeast in the Water Front Towner’s parking lot. Dissolved TBA in B-Zone groundwater samples had no detections at or above the MRL; therefore, was considered delineated during 1Q12. Dissolved TPHg in C-Zone groundwater was delineated to the north, west, and southwest, during 1Q12. Dissolved TPHd was not delineated during 1Q12; however, only low level detections were observed. TPHo in C-Zone groundwater was observed to the north in the Water Front Tower’s parking lot in wells MW-62 and MW-63 and to the southwest of the Site in well MW-67 during 1Q12. Dissolved benzene in C-Zone groundwater was delineated to the west during 1Q12. Dissolved MtBE in C-Zone groundwater was delineated to the northwest, west, and south, during 1Q12. Dissolved TBA in C-Zone groundwater was delineated, except to the east during 1Q12. Dissolved TPHg and TBA were delineated to the northwest, west, and south during 1Q12. Dissolved TPHd was delineated, except to the east during 1Q12. Dissolved TPHo in D-Zone groundwater was observed to the north in the Water Front Tower’s parking lot in wells MW-68 through MW-70 and south of the Site in wells MW-73 and MW-74, during 1Q12. Dissolved benzene in D-Zone groundwater was delineated to the west and south during 1Q12. Dissolved MtBE in D-Zone groundwater was delineated during 1Q12. The extent of petroleum-affected deeper (B-, C-, and D-Zones) groundwater has not been investigated by the city of Stockton at the UOU and MOU to the east. 2.8 ARSENIC Arsenic concentrations in selected shallow and deep zone wells within the hydrocarbon plume and within perimeter wells are evaluated for historical trends on a semi-annual basis during the first and third quarters. Arsenic concentrations over the past three years appear to be relatively consistent with the exception of A-, and B-Zone wells MW-25/MW-26 where a slight increase has been observed. Stantec will continue to evaluate and perform trend analysis through additional periods of groundwater fluctuation before it is determined if the trend is certain. Graphs depicting arsenic trends in selected A-Zone and B-Zone wells within the petroleum hydrocarbon plume (shallow wells MW-9, MW-32, 2AMW-13, DPE-9 and deep zone well MW- 17) and shallow and deep well pairs along the perimeter of the dissolved plume (MW-34/MW- 35, MW-25/MW-26, and MW-27/MW-28) are included in Appendix G.