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1 - <br /> ENSR International <br /> 10411 Old Placerville Road <br /> July 19, 2004 Suite 210 <br /> ' Sacramento,CA 95827-2508 <br /> (916)362-7100 <br /> FAX (916)362-8100 <br /> www.ensr.com <br /> MOVED <br /> Ms. Margaret Lagorio <br /> San Joaquin County JUL 0 20Q4 <br /> Public Health Services <br /> 304 East Weber Avenue, 3`d Floor ENVIRONMENT HEALTH <br /> Stockton, CA 95201-0388 PERMIT/SERVICES <br /> ' RE: Quarterly Groundwater Monitoring and Ozone Pilot Test Status Report, <br /> Second Quarter 2004, 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 pilot test status at <br /> 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 second <br /> quarter 2004. Second quarter monitoring was coordinated with Shaw Environmental, <br /> consultants for the former Vintage Car Wash located at 601 East Miner Avenue. The work was <br /> performed in accordance with the field methods and procedures included in Attachment A. <br /> The locations of former and current site features are illustrated on Figure 2. <br /> ' Groundwater Level Measurements <br /> Depth to groundwater measurements were recorded in groundwater monitoring wells U-1 through <br /> ' U-13, U-15 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), zone 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 UV-1 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 second quarter 2004 monitoring event, the groundwater flow direction for water bearing <br /> zone A was generally northeast with an average hydraulic gradient of approximately 0.005 feet <br /> ' 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 /> construct the groundwater elevation contour map included as Figure 4. The groundwater flow <br /> • J:1Projects10694010187-325T!naRReportsl2nd Qtr 04-QMR RSRN0187 2nd Qtr 04-QMR RSR.doc <br /> ' z: 35 Years of Excellence in Environmental Services <br />