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• ENSR International JAN 1 7nng 10411 Old Placerville Road January 26, 2005 Suite 210 ' ENVIRONMENT HEALTH Sacramento,CA 95827-2508 PERMIT/SERVICES (916)362-7100 FAX (916)362-8100 www ensr com ' Mr James L Barton California Regional Water Quality Control Board Central Valley Region ' 11020 Sun Center Drive, Suite 200 Rancho Cordova, CA 95670-6114 ' RE Updated Site Conceptual Model, Quarterly Monitoring and Remediation Status Report Fourth Quarter 2004 Former Unocal Facility No. 5098 ' 5400 and 5606 Pacific Avenue, Stockton, California ' Dear Mr Barton ENSR Corporation (ENSR) has been authorized by Union Oil Company of California (Unocal) to ' prepare an updated Site Conceptual Model (SCM) and Fourth Quarter 2004 Monitoring and Remediation Status Report for the subject site The former site facilities were located at the former Montgomery Ward, LLC (Wards) site located at 5400 Pacific Avenue and the former Unocal site located at 5606 Pacific Avenue, Stockton, California (Figure 1) Groundwater ' monitoring was conducted pursuant to requirements of Cleanup and Abatement Order (CAO) No 5-00-707, issued to Wards, Unocal, Surry California Limited Partnership, and Stone Brothers and Associated General Partnership (Stone Bros ) on September 8, 2000, by the ' California Regional Water Quality Control Board, Central Valley Region (RWQCB) (Section 1 1 5) The work was performed in accordance with the field methods and procedures included in Attachment A The locations of former and current site features are illustrated on ' Figure 2 Groundwater Level Measurements ' Depth to groundwater measurements were recorded for onsite and offsite monitoring wells on October 18, 2004 Four water bearing zones identified beneath the subject site and vicinity ' Unit A, Unit B, Unit C and Unit D This nomenclature was developed by Environmental Resolutions, Inc (ERI) and is based on site conditions presented in ERI's Work Plan for Supplemental Environmental Investigation report dated November 12, 1998 Unit A wells include MW-10A, MW-14A, MW-18, MW-19S, MW-21S, MW-22S, and MW-25S which are screened ' from approximately 30 to 50 feet below grade surface (bgs) Unit B wells include MW-1 through WVV-7, i►nvv-9R, WVV-i u tnrougn MVv-i 7, gvv-181D, MW-19 7, MW-21 D, MW-22D, MW-25D, AS- 26, and MW-27 through MW-30 which are screened from approximately 50 to 70 feet bgs Unit C wells include MW-235, MW-24S, and MW-31 which are screened from approximately 85 to 90 feet bgs Unit D wells include MW-8D, MW-23D, MW-24D, and MW-32 which are screened from approximately 97 to 103 feet bgs Groundwater measurements recorded on October 18, 2004 from wells screened in Unit A were used to construct the groundwater elevation contour map included as Figure 3 The groundwater J LProiects10694015098-2931Wor1unglReports15098 4th Qtr 04 QMR doc I _ Celebrating 35 Years of Excellence in Environmental Services