ARCHIVED REPORTS_THIRD QUARTER 2011 SITE STATUS, REMEDIAL SUMMARY, AND GROUNDWATER MONITORING REPORT

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Stantec L & M OPERABLE UNIT- THIRD QUARTER 2011 SITE STATUS, REMEDIAL SUMMARY, AND GROUNDWATER MONITORING REPORT Groundwater Monitoring and Sampling October 28, 2011 the Water Front Towner's parking lot. Low level concentrations of MtBE in B-Zone groundwater samples were detected in two separate sections of the Site; northeast (wells MW-42. MW-51, MW-58, and MW-59) and southwest (wells MW-29 and MW-44). Dissolved TBA in B-Zone groundwater samples had no detections at or above the MRL; therefore, was considered delineated during 3Q11. Dissolved TPHg in C-Zone groundwater was delineated to the north, west, and southwest, during 3Q11. Dissolved TPHd and TPHo in C-Zone groundwater were delineated to the northeast, east, south, and southwest, during 3Q11. Dissolved benzene in C-Zone groundwater was delineated to the west, during 3Q11. Dissolved MtBE in C-Zone groundwater was delineated to the south, west, and northwest, during 3Q11. Dissolved TBA in C-Zone groundwater was delineated, except to the east during 3Q11. Dissolved TPHg, benzene, and TBA in D-Zone groundwater were delineated to the west and south during 3Q11. Dissolved TPHd and MtBE in D-Zone groundwater were delineated during 3Q11. Dissolved TPHo in D-Zone groundwater was delineated to the east only during 3Q11. 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. 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. 2.9 PURGE WATER STORAGE AND DISPOSAL Between Julyl 18 and 21, 2011, approximately 500 gallons of purge water was transferred to the on-site remediation system to be treated and discharged to the sanitary sewer under the waste water discharge permit for West Weber Avenue and North Lincoln Street, Stockton, CA. Field data sheets for calculating the estimated purge volume are included in Appendix D. 2.10 REQUESTED CHANGES TO MONITORING AND REPORTING PROGRAM Based on review of historical and recent groundwater monitoring and sampling data, Stantec recommended that sampling frequency be reduced for some of the up-gradient and outlying wells for the Site and that some of the analysis currently being performed be eliminated from select wells. The requested changes were submitted during the third quarter of 2006 and a meeting to discuss these and an additional change was conducted with the RWQCB-CVR on Iffidewater7W Stockton(P2A)\QMRs\2011\3Q11\3011 QSSR QRSR QMR Stockton_FINAL.doc 2.26