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EARM. MMEMSEM ENSR International ' 10411 Old Placerville Road Suite 210 February 5, 2004 Sacramento,CA 95827-2508 (916)362-7100 FAX (916)362-8100 www ensr com Ms Margaret Lagorio 0 14 San Joaquin Public Health Services IECE.� ��`—�'�� ' 304 East Weber Avenue, 3`d Floor FEB 0 5 2004 Stockton, CA 95201-0388 ENVIRONMEW IIrALTH RE Quarterly Groundwater Monitoring and Ozone Pilot Test Status ReporpERMIT/SERVICES Fourth Quarter 2003 Former Unocal Facility #2859 ' 1665 Pacific Avenue, Stockton, CA 1 Dear Ms Lagono 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 fourth quarter 2003 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 November 25, 2003 (Table 1) Groundwater measurements from wells screened across water bearing zone A (MW-1 through MWA 1, MW-13, MW-15, MW-17, and MW-21) were used to construct the groundwater elevation contour map (Figure 3) On November 25, 2003, the groundwater flow direction for water bearing zone A was generally northeast with an average hydraulic gradient of approximately 0 003 Groundwater measurements ' recorded on November 25, 2003 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 November 25, 2003, the groundwater flow direction for ' water bearing zone B was generally north-northwest with an average hydraulic gradient of approximately 0 002 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 from November 26, 2003, through December 3, 2003 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 (TPH) as gasoline by EPA Method 8015 Modified, and fuel oxygenate compounds methyl tertiary butyl ether (MTBE), tertiary-amyl methyl ether (TAME), tert butanol (TBA), diisopropyl ether (DIPE), ethyl tertiary butyl ether (ETBE) using EPA Method 8260B Additionally, groundwater samples were analyzed for lead scavengers J\Projects\469401357-2859NFinal\Reports\4th Qtr 2003-QMR-RSR doc ' C 35 Years of Excellence in Environmental Services