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amec'0 <br /> Mr. Howard Hold <br /> California Regional Water Quality Control Board <br /> Central Valley Region <br /> April 27, 2010 <br /> Page 2 <br /> BACKGROUND <br /> The groundwater monitoring and sampling activities and laboratory results presented in this <br /> letter are provided in response to our discussions with you during our project meeting on <br /> October 22, 2009. During that meeting, representatives from MonierLifetile and AMEC met with <br /> you regarding site closure for the Lathrop and French Camp Facilities. In summary, we <br /> discussed the assessment completed at the Facilities and the steps necessary to rescind the <br /> Order and close the project. The RWQCB indicated during this meeting that if the Order could <br /> not be rescinded, the RWQCB may be able to convert it to a monitoring only program. <br /> As agreed upon during the meeting, the RWQCB identified the following action items or steps <br /> (the current status of each action item is also listed): <br /> • Action Item #1: Conduct the November 2009 groundwater monitoring event as <br /> scheduled at the Lathrop and French Camp Facilities and provide the tabulated <br /> results to the RWQCB, along with concentration-time series graphs, for justification <br /> that the groundwater sample concentrations are stable or declining since the removal <br /> of the stockpiles. <br /> Status: The November 2009 groundwater monitoring event was completed as <br /> scheduled at both Facilities and the results were submitted to the RWQCB in our <br /> report titled, Semi-Annual Groundwater Monitoring Report, November 2009, <br /> Lathrop and French Camp, California, dated January 20, 2010 (AMEC <br /> Geomatrix, 2010).4 <br /> • Action Item #2: Provide analytical data from at least eight consecutive groundwater <br /> monitoring events after the removal of the stockpiles at each Facility. After <br /> completing the November 2009 sampling event, eight groundwater monitoring events <br /> were completed at the French Camp Facility. Based on the monitoring results <br /> presented in the Semi-Annual Groundwater Monitoring Report (AMEC Geomatrix, <br /> 2010), the prevailing trend of groundwater concentrations for total petroleum <br /> hydrocarbons as diesel (TPH-diesel), chromium (Cr) and hexavalent chromium <br /> (Cr VI) at the French Camp Facility is stable to non-detect. After completing the <br /> November 2009 sampling event, five groundwater monitoring events were completed <br /> at the Lathrop Facility. To meet the requirement for eight monitoring events at the <br /> Lathrop Facility (since removal of the stockpile), three additional groundwater <br /> monitoring events are required. According to our discussions with you during the <br /> October 22, 2009 meeting, the three additional sampling events for the Lathrop <br /> Facility may be conducted monthly to expedite the closure process rather than <br /> continuing on the semi-annual schedule currently in place. <br /> 4 AMEC Geomatrix, Inc.,2010, Semi-Annual Groundwater Monitoring Report, November 2009, MonierLifetile LLC, <br /> Lathrop and French Camp Facilities, California, January 20. <br /> PA10626.000.0\Docs\Semi-Annua1 Groundwater Monitoring&Sampling\Lathrop Monthly Groundwater Monito6ng\Ltr_042710.doc <br />