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EALIt® <br /> ENSR International <br /> 10411 Old Placerville Road <br /> April 26, 2004 Suite 210 <br /> Sacramento, CA 95827-2508 <br /> 047 (916)362-7100 <br /> FAX (916)362.8100 <br /> Mw.ensr.com <br /> ' Ms. Margaret Lagorio <br /> San Joaquin County HEMMED <br /> Public Health Services <br /> 304 East Weber Avenue, 3rd Floor APR 2 9 2004 <br /> Stockton, CA 95201-0388 <br /> ENVIRONMENT HEALTH <br /> PERMIT/SERVICES <br /> RE: Quarterly Groundwater Monitoring and Ozone Pilot.Test Status R9port, ;7,. <br /> First Quarter 2004, Former Unocal Station No. 0187y <br /> ' 437 East Miner Avenue, Stockton, California <br /> Dear Ms, Lagorio: <br /> ENSR Corporation (ENSR) has been authorized by Union Oil Company of California Unocal to <br /> prepare this report summarizing quarterly groundwater monitoring and ozone pilot test status at <br /> I� the site located at 437 East Miner Avenue, Stockton, California (Figure 1). This report presents <br /> the results of quarterly'groundwater monitoring-and ozone pilot test status through the first <br /> quarter 2004. First quarter monitoring was coordinated with Shaw"Environmental, consultants <br /> for the former Vintage Car Wash located at 601 East Miner Avenue. The work was performed'' <br /> in accordance with the field methods and procedures included in Attachment A. The locations <br /> of former and current site features are illustrated on Figure 2. <br /> ' Groundwater Level Measurements <br /> ENSR subcontracted the first quarter 2004 groundwater monitoring and sampling event to Doulos <br /> ' Environmental (Doulos), of Orangevale, California. Doulos performed the groundwater monitoring <br /> on February 16, 2004. Depth to groundwater measurements were recorded in groundwater <br /> monitoring wells U-1 through U-26 and triple completion piezometers NP-1 and NP-2 (Table 1). <br /> ' Three groundwater-bearing zones (A, B, and C) exist below the subject site and surrounding area. <br /> Zone A is screened from:,-approximately 15 to 60 feet below ground surface (bgs), k6e B is <br /> screened from approximately 60 to 80 feet bgs, and zone C is screened from approximately, 108 <br /> to 120 feet bgs. <br /> Groundwater measurements from wells and piezometers screened in water bearing zone A (U-1 <br /> through U-9, U-11, UVA through UV-3, NP-1-22 and NP-2-22) beneath the Unocal site and from <br /> wells located at the former Vintage Car Wash, approximately 450-feet northeast of the Unocal site, _ <br /> ' were used, to construct the zone A groundwater elevation contour map included as Figure 3. <br /> During the first quarter 2004 monitoring event, the groundwater flow direction for water bearing <br /> zone A was generally northeast with an average hydraulic gradient of approximately 0.004-feet <br /> l per foot (ft/ft). <br /> Groundwater measurements from wells screened in zone B (U-13, U-14, U-16, U-18, U-20, U-22, <br /> U-24, NP-1-65, NP-2-60) and B zone wells at the former Vintage Car Wash site were used to <br /> J:1Projects10694010187-3251FinallReportslist Qtr 04-QMR RSR10187 1st Qtr 04-QMR RSR.doc <br /> ® 35 Years of Excellence in Environmental Services <br /> s <br />