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EINL-M. ' ENSR International 10411 Old Placerville Road October 14, 2004 Suite 210 ' Sacramento,CA 95827-2508 (916)362.7100 FAX (916)362-8100 r-, w"w. corn Ms. Margaret Lagorio r r " r San Joaquin County Public Health Services OCT 18 2004 304 East Weber Avenue, 3`d Floor EIhV;1;�,;;„� i4 i f�EAI TH Stockton, CA 95201-0388 PERMIT/SERVICES ' RE: Quarterly Groundwater Monitoring and Ozone Microsparge System Status Report,Third Quarter 2004, Former Unocal Station No. 0187 ' 437 East Miner 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 microsparge system status at the site located at 437 East Miner Avenue, Stockton, California (Figure 1). ' This report presents the results of quarterly groundwater monitoring and ozone microsparge system status through the third quarter 2004. Third quarter monitoring was coordinated with ' Shaw Environmental, consultants for the former Vintage Car Wash located at 601 East Miner Avenue. 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 groundwater monitoring wells U-1 through U-26 and triple completion piezometer wells NP-1 and NP-2 (Table 1). ' Three groundwater-bearing zones (zone A, zone B, and zone C) exist below the subject site and surrounding area. Zone A is screened from approximately 15 to 60 feet below ground surface (bgs), zone B is screened from approximately 60 to 80 feet bgs, and zone C is screened from ' approximately 108 to 120 feet bgs. Groundwater measurements from wells and piezometers screened in water bearing zone A (U-1 through U-9, U-11, UV-1 through UV-3, NP-1-22 and NP-2-22) beneath the Unocal site and from wells located at the former Vintage Car Wash, approximately 450-feet northeast of the Unocal site, were used to construct the zone A groundwater elevation contour map included as Figure 3. During the third quarter 2004 monitoring event, the groundwater flow direction for water bearing ' zone A was generally northeast with an average hydraulic gradient of approximately 0.005 feet per foot Pft). Groundwater measurements from wells screened in zone B (U-13, U-14, U-16, U-18, U-20, U-22, 1 U-24, NP-1-65, NP-2-60) and zone B wells at the former Vintage Car Wash site were used to construct the groundwater elevation contour map included as Figure 4. The groundwater flow i' J:1Projectsk0694010187-325%FinanReports\3rd Qtr 04-QMR RM0187 3rd Qtr 04-QMR RSR,doc *� 35 Years of Excellence m Environmental Services