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Groundwater Monitoring ARCADIS Report for the Semiannual Period from January 1 through June 30,2012 Lincoln Center,Stockton, California 2.4 QMQC Sample Review ARCADIS performed a Level III validation of the analytical data in accordance with the data validation levels presented in Table C-7 of the Quality Assurance Project Plan (CAPP, LFR 1998). Data from the Alpha sample delivery group(SDG)ARC12062923 were reviewed.The samples associated with this SDG were collected on June 27,2012. A review of the QA/QC sample analytical results provided by Alpha for the reporting period revealed the following: • The matrix spike(MS)recoveries were within compliance criteria,and the relative percent difference(RPD)between the MS and the MS duplicate(MSD)results was within the MS RPD criteria.The MSD recovery(146%)for 1,1-dichloroethene exceeded the laboratory upper control limit of 130%.However, 1,1-dichlorcethene was not reported in any of the corresponding primary samples,and no data qualification was necessary. The sample temperatures,surrogate recoveries,field blanks, laboratory control samples,laboratory blanks, and holding times for the field samples were all within compliance criteria,which are included in the CAPP. • The RPD between the primary and field duplicate sample results for PCE at MW-123A-L was 48%, exceeding the compliance criterion of 30%specified in the QAPP.As discussed above,the laboratory MS/MSD results were generally within control limits, suggesting that the RPD exceedance in the field duplicate samples may be indicative of sample heterogeneity. Because the primary and field duplicate sample results are of the same order of magnitude, and because RPD exceedances were not observed for the other detected analytes(i.e.,TCE and cis-1,2-DCE),the PCE results for MW-123A-L were still considered usable.All other field duplicate resWts were within compliance criteria. 7. Summary of Groundwater Monitoring Activities Planned for the Next Semiannual Period In accordance with the schedule presented in Section 1.3,the next groundwater level measurement and groundwater sampling event is scheduled for December 2012. Results of the upcoming water level measurement and groundwater sampling events will be summarized in the next semiannual report,which is due to be submitted to the RWQCB on February 15,2013. M u,wi,cw a,912...6I%d.t 11