ARCHIVED REPORTS_SEMI-ANNUAL GROUNDWATER MONITORING REPORT AUGUST 2010

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ameO Total Cr was detected in the groundwater samples from wells FCW-1, FCW-2, and FCW-3 at concentrations of 10 pg/L, 12 pg/L (FCW-2 duplicate at 13 pg/L), and 49 pg/L, respectively. Dissolved Cr also was detected in the groundwater samples from wells FCW-1, FCW-2, and FCW-3 at concentrations of 4.8J pg/L, 12 pg/L (FCW-2 duplicate at 12 pg/L) and 32 pg/L, respectively. Total Cr and dissolved Cr concentrations in the groundwater samples from wells FCW-1, FCW-2, and FCW-3 were within the range of historical concentrations for these wells. The reported total and dissolved Cr groundwater sample concentrations were below the CDPH MCL of 50 pg/L. Dissolved Cr VI was detected in the groundwater samples from wells FCW-1, FCW-2, and FCW-3 at concentrations of 3.5 pg/L, 10 pg/L (FCW-2 duplicate at 10 pg/L), and 27 pg/L, respectively. Since May 2004, dissolved Cr VI has not been detected in the groundwater samples from well FCW-1 above the laboratory reporting limit of 0.5 pg/L, with exceptions in November 2007, November 2008, November 2009, and August 2010. The dissolved Cr VI concentrations observed in the groundwater samples from wells FCW-1, FCW-2, and FCW-3 during this sampling event were within the range of historical concentrations for these wells. The reported dissolved Cr VI groundwater sample concentrations were below the CDPH MCL of 50 pg/L. Since the removal of the stockpile in November 2005, almost five years of groundwater monitoring has been conducted at the French Camp facility (nine groundwater sampling events), and groundwater sample concentrations from the three wells appear to be stable or decreasing (Figures 12 through 17). 4.3 QUALITY ASSURANCE AND QUALITY CONTROL RESULTS AMEC Geomatrix followed specific QA/QC procedures during this groundwater monitoring event. A summary of the field and laboratory QA/QC procedures and results are presented in this section. To assess field data precision, one blind field duplicate sample was collected at each Facility during the August 2010 groundwater monitoring event. The blind duplicate samples were analyzed using the same EPA methods used for the primary groundwater samples. Equipment blanks were not deemed necessary because dedicated disposable bailers were used for purging and sampling the groundwater monitoring wells. Data precision is estimated by comparing analytical results from duplicate samples. The comparison is made by calculating the relative percent difference (RPD) for the analytical results from each duplicate sample pair. The typical QA/QC goal for precision is that the RPD for any detected constituent in a duplicate sample pair should not exceed 30%, unless AMEC Geomatrix, Inc. P:\10626.000.0\Docs\Semi-Annua1 Groundwater Monitoring&Sampling\Semi-Annual 1-10 9