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E11��t® <br /> ' ENSR International <br /> . 10411 Old Placerville Road <br /> February 11, 2005 Suite 210 <br /> ' Sacramento,CA 95827-2508 <br /> (916)362-7100 <br /> FAX (916)362-8100 <br /> Ms. Margaret Lagorio REDeCTnVE§)nsr.com <br /> San Joaquin County Public Health ServicesF <br /> 304 East Weber Avenue, 3`d Floor EQ <br /> ' Stockton, CA 95201-0388 ENVIRON 1 5 Za05 <br /> HE <br /> RE: Quarterly Groundwater Monitoring and Ozone Microsparge PER ENT ALTy <br /> ' System Status Report, Fourth Quarter 2004, VICES <br /> Former Unocal Station No. 0187 <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 microsparge <br /> system status at the site located at 437 East Miner Avenue, Stockton, California (Figure 1). <br /> This report presents the results of quarterly groundwater monitoring and ozone microsparge <br /> system status through the fourth quarter 2004. Fourth quarter monitoring was coordinated with <br /> Shaw Environmental, consultants for the former Vintage Car Wash located at 601 East Miner <br /> ' Avenue. The work was performed in accordance with the field methods and procedures <br /> included in Attachment A. The locations of former and current site features are illustrated on <br /> Figure 2. <br /> Groundwater Level Measurements <br /> Depth to groundwater measurements were recorded in groundwater monitoring wells U-1 through <br /> U-26 and triple completion piezometer wells NP-1 and NP-2 (Table 1). <br /> Three groundwater-bearing zones (zone A, zone B, and zone C) exist below the subject site and <br /> ' surrounding area. Zone A is screened from approximately 15 to 60 feet below ground surface <br /> (bgs), zone B is screened from approximately 60 to 80 feet bgs, and zone C is screened from <br /> approximately 108 to 120 feet bgs. <br /> ' Groundwater measurements from wells and piezometers screened in water bearing zone A <br /> (U-1 through U-9, U-11, UV-1 through UV-3, NP-1-22 and NP-2-22) beneath the Unocal site and <br /> ' from wells located at the former Vintage Car Wash, approximately 450-feet northeast of the <br /> Unocal site, were used to construct the zone A groundwater elevation contour map included as <br /> Figure 3. During the fourth quarter 2004 monitoring event, the groundwater flow direction for <br /> water bearing zone A was generally northeast with an average hydraulic gradient of approximately <br /> ' 0.005 feet 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, and NP-2-60) and zone B wells at the former Vintage Car Wash site were used to <br /> ' construct the groundwater elevation contour map included as Figure 4. The groundwater flow <br /> i <br /> ' J:Trojecl:A694010187-325ftorkinglReportMG187 4th Qtr 04-QMR RSR.doc <br /> Celebrating 35 Years of Excellence in Environmental Services <br />