ARCHIVED REPORTS_SEMI-ANNUAL GROUNDWATER MONITORING REPORT AUGUST 2010

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ameO 6.0 CONCLUSIONS At the Lathrop facility, groundwater concentrations of total Cr and dissolved Cr and dissolved Cr VI have been at or below the CDPH MCL of 50 pg/L for Cr-since the commencement of the monitoring program in 2002. Diesel-range petroleum hydrocarbons have not been detected above the reporting limit (50 pg/L) in any of the groundwater samples since November 2007. The removal of the stockpile material at the Lathrop facility was completed in October 2007, and the vadose zone soil assessment work was completed in November 2007 (Geomatrix, 2007a). The findings of the vadose zone assessment indicated that the low concentrations of Cr and Cr VI detected in soil at the Lathrop facility did not pose a significant risk to groundwater quality and that soil remediation was not warranted (Geomatrix, 2007a). Since the removal of the stockpile in October 2007, almost three years of groundwater monitoring has been conducted at the Lathrop facility (nine groundwater sampling events), and groundwater sample concentrations at wells LPW-1, LPW-2, and LPW-3 appear to be stable or decreasing (Figures 6 through 11). At the French Camp facility, diesel-range petroleum hydrocarbons were not detected in the groundwater samples from wells FCW-1, FCW-2, and FCW-3. All other groundwater sample concentrations were below the CDPH MCL of 50 pg/L for Cr. As reported previously, stockpile material was removed from the French Camp facility in November 2005, and the vadose zone soil assessment work was completed in January 2006 (Geomatrix, 2006a). The findings of the vadose zone assessment indicated that the low concentrations of Cr and Cr VI detected in soil at the Facility did not pose a significant risk to groundwater quality and that soil remediation was not warranted (Geomatrix, 2006a). 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). In accordance with the request for site closure letter (AMEC Geomatrix, 2010b), MonierLifetile has met the requirements for both Facilities as outlined by the RWQCB in the October 22, 2009 meeting for rescinding the Order. Once the Order has been rescinded, MonierLifetile will destroy the groundwater monitoring wells at each Facility. AMEC Geomatrix, Inc. P:\10626.000.0\Docs\Semi-Annua1 Groundwater Monitoring&Sampling\Semi-Annual 1-10 13