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amec'9 <br /> Mr. Howard Hold <br /> California Regional Water Quality Control Board <br /> Central Valley Region <br /> April 27, 2010 <br /> Page 8 <br /> CONCLUSIONS <br /> At the Lathrop Facility, groundwater concentrations of total and dissolved Cr and dissolved <br /> Cr VI have been at or below the CDPH MCL of 50 pg/L for Cr since the commencement of the <br /> monitoring program in 2002. TPH-diesel has not been detected above the reporting limit of <br /> 50 pg/L in any of the groundwater samples since November 2007. The removal of the stockpile <br /> material at the Lathrop Facility was completed in October 2007, and the vadose zone soil <br /> assessment was completed in November 2007 (Geomatrix, 2007).' The findings of the vadose <br /> zone assessment indicated that the low concentrations of Cr and Cr VI detected in soil at the <br /> Lathrop Facility did not pose a significant risk to groundwater quality and that soil remediation <br /> was not warranted (Geomatrix, 2007). Since the removal of the stockpile in October 2007, and <br /> in compliance with RWQCB requirements that eight groundwater sampling events be completed <br /> prior to submittal of a request to terminate groundwater monitoring and rescind the Order <br /> (as specified during the October 22, 2009, meeting with the RWQCB), groundwater sample <br /> concentrations at wells LPW-1, LPW-2, and LPW-3 appear to be stable or decreasing <br /> F:inures 6 through. "1;. <br /> We appreciate your review of the recent groundwater monitoring results for the Lathrop Facility. <br /> As discussed during our meeting with you on October 22, 2009, we are proceeding with <br /> preparation of a letter requesting site closure for the Lathrop and French Camp Facilities. If you <br /> In ave any questions regarding the recent groundwater monitoring events at the Lathrop Facility, <br /> as documented in this letter, or would like to discuss the request for site closure letter, please <br /> contact us at (949) 642-0245. <br /> Sincerely yours, <br /> AMEC Geomatrix, Inc. �S\ONAL GFp <br /> Linda Conlan, PG No.6943 <br /> Senior Geologist Exp, S 31 /0 <br /> �F CA��F <br /> 7 Geomatrix Consultants, Inc., 2007, Soil Investigation Report, MonierLifetile LLC, Lathrop Facility, <br /> Lathrop, California, December 31. <br /> P:\10626.000.0\Docs\Semi-Annual Groundwater Monitoring&Sampling\Lathrop Monthly Groundwater Monitoring\Ltr_042710.doc <br />