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E11kit. ENSR International 4 10411 Old Placerville Road Suite 210 April 12, 2004 Sacramento,CA 95827 2508 D C r D (916)362 7104 D FAX (916)362 8100 www ensr cam ' Ms Margaret Lagono APR 14 2004 San Joaquin Public Health Services Mi,,ji4lVli-IJ HEALTH ' 304 East Weber Avenue, 3rd Floor PEK,1i T/SLRVICES Stockton, CA 95201-0388 ' RE Quarterly Groundwater Monitoring and Ozone Pilot Test Status Report, First Quarter 2004 Former Unocal Facility No 2859 ' 1665 Pacific Avenue, Stockton, California ' Dear Ms Lagorio 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 first 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 February 26, 2004 (Table 1) Groundwater measurements from ' wells screened across water bearing zone A (MW-1 through MW-11, MW-13, MW-15, MWA 7, and MW-21) were used to construct the groundwater elevation contour map included as Figure 3 On February 26, 2004, the groundwater flow direction for water bearing zone A was generally east northeast with an average hydraulic gradient of approximately 0 0025 Groundwater 1 measurements recorded on February 26, 2004, from wells screened across water bearing zone B (MW-12, MW-14, MW-16, MW-18 through MW-20 and NP-1) were used to construct the groundwater elevation contour map included as Figure 4 On February 26, 2004, the groundwater flow direction for water bearing zone B was generally north-northwest with an average hydraulic gradient of approximately 0 017 feet per foot 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 February 26, 2004,from wells MWA 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, total petroleum hydrocarbons as gasoline (TPHg) by EPA Method 8015 Modified Groundwater samples collected from wells MWA through MWA 1, MW-20, J 4Proiects10694012859-3571FinaAReportsllst Qtr 2004 uMR-RSR doc V, 35 Years of Excellence in Environmental Services