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S E C OR <br /> • 4.6 Arsenic <br /> Arsenic concentrations in selected shallow and deep zone wells within the hydrocarbon plume <br /> and within perimeter wells are evaluated for historical trends on a semi-annual basis during the <br /> first and third quarters. <br /> During the first quarter 2008, arsenic concentrations ranged from 0.0072 mg/L (MW-21) to 0.30 <br /> mg/L (MW-18) in the shallow zone wells, and from 0.0086 mg/L (MW-35) to 0.059 mg/L <br /> (MW-51) in the deep zone wells. Arsenic concentrations over the past two years appear to be <br /> relatively consistent. Graphs depicting arsenic trends in selected shallow and deep zone wells <br /> within the petroleum hydrocarbon plume (shallow wells MW-9, MW-32, 2AMW-13, DPE-9 and <br /> deep zone well MW-17) and shallow and deep well pairs along the perimeter of the dissolved <br /> plume (MW-34/MW-35, MW-25/MW-26, and MW-27/MW-28) are included in Appendix G <br /> (Appendix G; Figures 1 through 8). <br /> 4.7 Purge Water Storage and Disposal <br /> During the first quarter 2008 monitoring and sampling event, approximately 460 gallons of purge <br /> water was discharged between January 22 and January 25, 2008 into the secondary <br /> containment sump and subsequently flushed through the onsite remediation system to be <br /> treated and discharged to the sanitary sewer under the waste water discharge permit for West <br /> Weber Avenue and North Lincoln Street, Stockton, CA. Field data sheets for calculating purge <br /> volume are included in Appendix C <br /> • 4.8 Requested Changes to Monitoring and Reporting Program <br /> Based on review of historical and recent groundwater monitoring and sampling data, SECOR <br /> recommended that sampling frequency be reduced for some of the up-gradient and outlying <br /> wells for the Site and that some of the analysis currently being performed be eliminated from <br /> select wells. The requested changes were submitted 3Q06 and a meeting to discuss these and <br /> additional changes was conducted with the CRWQCB-CVR on January 24, 2007. The <br /> CRWQCB-CVR agreed to provide a revised MRP for the Site. At a later meeting with the <br /> CRWQCB-CVR, SECOR again discussed the reduction of sampling frequency and analysis for <br /> wells associated with the L&M OU MRP and was assured that the CRWQCB-CVR was currently <br /> proceeding with that effort. CEMC and COP look forward to the draft MRP from CRWQCB-CVR <br /> for review and future implementation. <br /> F <br /> 5., <br /> • <br /> 1Q08QSSRQRSRQMR.Final.doc 26 April 30,2008 <br /> 7TFW.26397.42.1307 <br />