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Ell�yt® ENSR International 10411 Old Placerville Road Suite 210 July 16, 2004 Sacramento,CA 95827-2508 (916)362-7100 FAX (916)362-8100 www ensr com ' Ms Margaret Lagorio 0 (� San Joaquin Public Health Services RECEUf ID 304 East Weber Avenue, 3rd Floor ap Stockton, CA 95201-0388 J U L_�W2004 RE Quarterly Groundwater Monitoring and Ozone Pilot Test Status Report, ENVIRONNIEN'1 11L ALTH ' Second Quarter 2004 PERMIT/SERVICES Former Unocal Facility No 2859 ' 1665 Pacific Avenue, Stockton, California Dear Ms Lagorlo ENSR Corporation (ENSR) has been authorized by Union Oil Company of California (Unocal) to prepare this report summarizing quarterly groundwater monitoring and ozone pilot test status at ' the site located at 1655 Pacific Avenue, Stockton, California (Figure 1) This report presents the results of quarterly groundwater monitoring and ozone pilot test status through the second quarter 2004 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 in monitoring wells MW-1 through MW-21, and piezometer well NP-1 on April 5, 2004 (Table 1) Groundwater measurements from wells ' screened across water bearing zone A (MW-1 through MW-11, MW-13, MW-15, MW-17, and MW-21) were used to construct the groundwater elevation contour map included as Figure 3 On April 5, 2004, the groundwater flow direction for water bearing zone A was generally east ' northeast with an average hydraulic gradient of approximately 0 002 feet per foot (ft/ft) Groundwater measurements recorded on April 5, 2004, from wells screened across water bearing zone B (MW-12, MW-14, MW-16, MWA 8 through MW-20 and NP-1) were used to construct the groundwater elevation contour map included as Figure 4 On April 5, 2004, the groundwater flow ' direction for water bearing zone B was generally north-northeast with an average hydraulic gradient of approximately 0 009 ft/ft Copies of the groundwater sampling information sheets are included in Attachment B A summary of groundwater elevations measured to date is presented ' in Table 1 Groundwater Sampling and Analytical Results Groundwater samples were collected April 5, 2004, from wells MW-1 through MW-21 and NP-1 The groundwater samples were submitted to California Laboratory Services (CLS) in Rancho ' Cordova, California for analyses of benzene, toluene, ethylbenzene and total xylenes (BTEX) by EPA Method 8021, and total petroleum hydrocarbons as gasoline (TPHg) by EPA Method 8015 Modified Groundwater samples collected from wells MWA through MW-11, MW-20, MW-21 and J 1Proiects10694012859 3571FinaMeportsl2nd Qtr04 QMR RSR12nd Qtr 04 QMR doc t 35 Years of Excellence in Environmental Services