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 Groundwater Monitoring and Sampling January 31, 2011 is delineated for 4Q10. Benzene and TBA had no detections at or above the MRL; therefore, are considered delineated in B-Zone groundwater, during 4Q10. Dissolved TPHg, TPHd, MtBE, and TBA in C-Zone groundwater are delineated, except to the east, during 4Q10. Dissolved TPHo in C-Zone groundwater is delineated to the south and southeast only, during 4Q10. Benzene is located in two separate sections of the site (north and south) in C-Zone groundwater, during 4Q10. In the northern section of the site, benzene is delineated in the central section of the site, except to the north. In the southern section of the site, benzene is delineated to the north and west only. Dissolved TPHg, TPHd, and benzene in D-Zone groundwater are delineated to the south and west, during 4Q10. Dissolved TPHo in D-Zone groundwater is delineated, except to the northwest, during 4Q10. MtBE in D-Zone groundwater is delineated, during 4Q10. TBA in D-Zone groundwater is delineated, except to the east, during 4Q10. The extent of petroleum-affected deeper (B-, C-, and D-Zones) groundwater has not been investigated by the SRDA 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 F. 2.9 PURGE WATER STORAGE AND DISPOSAL Between October 18 and 21, 2010, 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 C. 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 January 24, 2007. The RWQCB-CVR agreed to provide a revised MRP for the Site. During previous discussions with the RWQCB-CVR (most recently second quarter 2009), Stantec was I:\Tidewater\TW Stockton(Parcel 2A-0415)\Reports\QMR\2010\4010-Annual\4Q10 and Annual OSSRQRSRQMR Stockton_FINAL.doc 2.24