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i r EbM® ENSR International MA&WiAPR 3 0 2004 ti 10411 0!d Placerville Road April 26, 2004 ENVIRuNMENT HEALTH Suite 210 PERMIT/SERVICES Sacramento,CA 95827-2508 (916)362-7100 l } FAX (916)362-8100 www ensr com F1 Mr Mike Infurna San Joaquin County I ( i Environmental Health Division FJ 304 E Weber Avenue, Third Floor I Stockton, CA 95201 I ( � RE Updated Site Conceptual Model, Monitoring and Remediation Status Report First Quarter 2004, Former Unocal Facility No 5098 5400 and 5606 Pacific Avenue, Stockton, California l � Dear Mr Infurna I [ I ENSR Corporation (ENSR) has been authorized by Union Oil Company of California (Unocal) to prepare an updated Site Conceptual Model (SCM) and First Quarter 2004 Monitoring and Remediation 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 Union Oil Company of California (Unocal) site located at 5606 Pacific Avenue, Stockton, California (Figure 1) Groundwater monitoring was conducted pursuant to requirements of Cleanup and fj L Abatement Order No 5-00-707, issued to Wards, Unocal, Surry California Limited Partnership, and Stone Brothers and Associated General Partnership on September 8, 2000, by the California Regional Water Quality Control Board, Central Valley Region (RWQCB) (Section 1 1 5) The locations of former and current site features are illustrated on Figure 2 The work l was performed in accordance with the field methods and procedures included in Attachment A _ I Groundwater Level Measurements Depth to groundwater measurements were recorded in onsite and offsite monitoring wells on -February-26,-2004 —There-are_three water bearing zones identified beneath and_ immediately surrounding the subject site Unit A, Unit B, and Unit C Unit A wells include MW-10A, MW-14A, MW-18, MW-19S, MW-21S, MW-22S, and MW-25S and are screened from approximately 30 to 50 feet below grade surface (bgs) Unit B wells include MW-1 through MW-7, MW-9 through MW-17, MW-18D, MW-19D, MW-21 D, MW-22D, MW-25D, AS-26, and MW-27 and are screened from approximately 50 to 70 feet bgs Unit C wells include MW-23S and MW-24S and are rr screened from approximately 85 to 90 feet bgs Unit D wells include MW-8D, MW-23D, and LL MW-24D and are screened from approximately 97 to 103 feet bgs Groundwater measurements recorded on February 26, 2004 from wells screened in Unit A were L! used to construct the groundwater elevation contour map included as Figure 3 On i February 26, 2004, the groundwater flow direction for Unit A was generally to the northeast, with the hydraulic gradient ranging from approximately 0 002 feet per foot (ft/ft) to 0 007 ft/ft Groundwater measurements recorded on February 26, 2004 from wells screened in Unit B were � used to construct the groundwater elevation contour map included as Figure 4 On J\Protects\0694015098-293\Final\Reparts\lst Qtr'04-QMR RSR doc IL( i 35 Years of Excellence in Environmental Services