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E11�"R� <br />' ENSR International <br /> 10411 aid PlacervilleSuite 210 <br />' Sacramento,CA 95827-2508 <br /> July 28, 2005 (916)362-7100 <br /> X IL 2 9 2005 FAX (916)362-8100 <br /> www ensr corn HEAL? <br /> IMr James L Barton PEhiAII/SERVICES <br /> California Regional Water Quality Control Board <br /> Central Valley Region <br /> 11020 Sun Center Drive, Suite 200 <br /> Rancho Cordova, CA 95670-6114 <br />' RE: Request for Reduction in Sampling <br /> Former Unocal Facility No 5098 <br />' 5400 and 5606 Pacific Avenue, Stockton, California <br />' Dear Mr Barton <br /> ENSR Corporation (ENSR) has been retained by Union Oil Company of California (Unocal) to <br />' conduct activities related to the remediation activities at the above-referenced site Former site <br /> facilities that are the subject of this report were located both at the former Montgomery Ward, <br /> LLC (Wards) site located at 5400 Pacific Avenue and at the former Unocal site located at <br /> 5606 Pacific Avenue, Stockton, California (Figure 1) Groundwater monitoring is conducted <br /> pursuant to requirements of Cleanup and Abatement Order (CAO) No 5-00-707, issued to <br /> Wards, Unocal, Surry California Limited Partnership, and Stone Brothers and Associated <br /> General Partnership (Stone Bros ) on September 8, 2000, by the California Regional Water <br /> Quality Control Board, Central Valley Region (RWQCB) (Section 1 1 5) The locations of former <br />' and current site features are illustrated on Figure 2 <br /> In the Second Quarter 2005 Monitoring and Sampling (M&S) Report, ENSR. requested <br /> reductions in sampling for groundwater and for vapor from select extraction wells The content <br /> of that request was Included in the Recommendations section of the M&S Report The following <br /> sections summarize ENSR's formal request for a reduction in the current sampling program for <br />' the site <br /> Request for Reduction in Groundwater Samplina <br /> In the Second Quarter 2005 Monitoring and Sampling Report, ENSR included an updated Site <br /> Conceptual Model (SCM) In that SCM, ENSR made the following conclusions <br /> S The existing groundwater monitoring well network defines the limits of the SCM The <br /> TPHg and benzene plumes appear to be reducing In size, stable, and well defined within <br /> J IProiectsW6940L5098-2931WorkinglReportslLetter Requesting Reduction in Samping15098 Letter Requesting Reduction in Sampling doc <br /> Celebrating 35 Years of Excellence in Environmental Services <br />