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ENM. _
<br /> ENSR International
<br /> 10411 Old Placerville Road
<br /> Suite 210
<br /> July 12, 2004 Sacramento, CA 95827 2508
<br />' (916)362 7100
<br /> FAX (9 16)362 8100
<br /> www ensr com
<br />' Mr James L Barton �� Y[EU
<br /> California Regional Water Quality Control Board `J
<br />' Central Valley Region JUL 1 5 2004
<br /> 11020 Sun Center Drive, Suite 200
<br /> Rancho Cordova, CA 95670-6114 ENVIRONMENT HEALVI
<br /> PERMIT/SERVICES
<br />' RE. Updated Site Conceptual Model, Monitoring and Remediation Status Report,
<br /> Second Quarter 2004, 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 Second Quarter 2004 Monitoring and
<br />' Remediation Report for the subject site The former site facilities were located at the former
<br /> Montgomery Ward, LLC (Wards) site located at 5400 Pacific Avenue and the former Union Oil
<br /> Company of California (Unocal) site located at 5606 Pacific Avenue, Stockton, California
<br /> (Figure 1) Groundwater monitoring was conducted pursuant to requirements of Cleanup and
<br /> Abatement Order No 5-00-707, issued to Wards, Unocal, Surry California Limited Partnership,
<br /> and Stone Brothers and Associated General Partnership on September 8, 2000, by the
<br /> California Regional Water Quality Control Board, Central Valley Region (RWQCB) (Section
<br />' 1 1 5) The locations of former and current site features are illustrated on Figure 2 The work
<br /> was performed in accordance with the field methods and procedures included in Attachment A
<br />' Groundwater Level Measurements
<br /> Depth to groundwater measurements were recorded in onsite and offsite monitoring wells on
<br />' April 12, 2004 There are four water bearing zones identified beneath and immediately
<br /> surrounding the subject site Unit A, Unit B, and Unit C Unit A wells include MW-10A, MW-14A,
<br /> MW-18, MW-19S, MW-21S, MW-22S, and MW-25S and are screened from approximately 30 to
<br />' 50 feet below grade surface (bgs) Unit B wells include MW-1 through MW-7, MW-9 through
<br /> MW-17, MW-18D, MW-19D, MW-21 D, MW-22D, MW-250, AS-26, and MW-27 and are screened
<br /> from approximately 50 to 70 feet bgs Unit C wells include MW-23S and MW-24S and are
<br /> screened from approximately 85 to 90 feet bgs Unit D wells include MW-8D, MW-23D, and
<br />' MW-24D and are screened from approximately 97 to 103 feet bgs
<br /> Groundwater measurements recorded on April 12, 2004 from wells screened in Unit A were used
<br /> to construct the groundwater elevation contour map included as Figure 3 On April 11, 2004, the
<br /> groundwater flow direction for Unit A was generally to the northeast, with the hydraulic gradient
<br /> ranging from approximately 0 002 feet per foot (ft/ft) to 0 007 ft/ft
<br /> Groundwater measurements recorded on April 12, 2004 from wells screened in Unit B were used
<br /> to construct the groundwater elevation contour map included as Figure 4 On April 12, 2004, the
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