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�r <br /> E M-K <br /> • _ ENSR International <br /> 10411 Old Placerville Road <br /> " Suite 210 <br /> 2005 APR 18 AN 9=' S56acramento,CA 95827-2508 <br /> April 12, 2Q05 SAN J 0 A 0 tJ I H COUNTY FAX (916)362-8100 <br /> ENWIPONMENTAL www ensrcom <br /> HEALTHOEPARTHENT <br /> Mr James L Barton <br /> California Regional Water Quality Control Board <br /> 1 Central Valley Region <br /> 11020 Sun Center Drive, Suite 200 <br /> Rancho Cordova, CA 95670-6114 <br />' RE Updated Site Conceptual Model, Quarterly Monitoring and Remediation Status Report <br /> First Quarter 2005 <br /> Former Unocal Facility No 5098 <br /> 5400 and 5606 Pacific Avenue, Stockton, California <br />' Dear Mr Barton <br /> ENSR Corporation (ENSR) has been authorized by Union Oil Company of California (Unocal) to <br /> prepare an updated Site Conceptual Model (SCM) and a First Quarter 2005 Monitoring and <br /> Remediation Status Report for the subject site Former site facilities that are the subject of this <br /> report were located both at the former Montgomery Ward, LLC (Wards) site located at 5400 <br /> Pacific Avenue and at the former Unocal site located at 5606 Pacific Avenue, Stockton, <br /> California (Figure 1) Groundwater monitoring has been conducted pursuant to requirements of <br />' Cleanup and Abatement Order (CAO) No 5-00-707, issued to Wards, Unocal, Surry California <br /> Limited Partnership, and Stone Brothers and Associated General Partnership (Stone Bros ) on <br /> September 8, 2000, by the California Regional Water Quality Control Board, Central Valley <br /> Region (RWQCB) (Section 1 1 5) The work was performed in accordance with the field <br /> methods and procedures included in Attachment A The locations of former and current site <br /> features are illustrated on Figure 2 <br /> Groundwater Level Measurements <br /> Depth to groundwater measurements were recorded for onsite and offsite monitoring wells on <br />' January 10, 2005 Four water-bearing zones have been identified beneath the subject site and <br /> vicinity Unit A, Unit B, Unit C and Unit D This nomenclature was developed by Environmental <br /> Resolutions, Inc (ERI) and is based on site conditions presented in ERI's Work Plan for <br /> Supplemental Environmental Investigation report dated November 12, 1998 Unit A wells include <br /> MW-10A, MW-14A, MW-18, MW-19S, MW-21 S. MW-22S, and MW-25S which are screened from <br /> approximately 30 to 50 feet below ground surface (bgs) Unit B wells include MWA through MW- <br /> 7, MW-9R, MW-10 through MW-17, MW-18D, MW-19D, MW-21D, MW-22D, MW-25D, AS-26, <br /> and MW-27 through MW-30 which are screened from approximately 50 to 70 feet bgs Unrt C <br /> wells include MW-23S, MW-24S, and MW-31 which are screened from approximately 85 to 90 <br /> feet bgs Unit D wells include MW-8D, MW-23D, MW-24D, and MW-32 which are screened from <br /> approximately 97 to 103 feet bgs <br /> • <br /> J TrotectsM94015098 2930orkinglReports150981st Qtr 05-QMR doc <br /> Geiebrarrng 35 Years of Excellence in Environmental Services <br />