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GEOMATRIX <br /> THIRD"QUARTER 2004. <br /> GROUNDWATER MONITORING REPORT <br /> UST Site No. 3 --Port.of Stockton <br /> Stockton, California <br /> 1.0 INTRODUCTION <br /> This report summarizes the third quarter 2004 groundwater monitoring event at Port of <br /> ' r <br /> i Stockton's (Port) former underground storage tank (UST) Site No. 3. Monitoring was performed <br /> on September 23, 2004, by WGR Southwest, Inc. (WGR), in accordance with directives from the <br /> local enforcement agency, the San Joaquin County Environmental Health Department (EHD). <br /> UST Site No. 3 is located near the central portion of the Port in the City of Stockton, San Joaquin_ <br /> fi County, California, approximately 50 feet north of Port Road G and about 300 feet west of Port <br /> Road 14 (Figures 1 and 2). The site is catalogued by EHD as Site Code 1282424. <br /> The site formerly contained two 12;000-gallon USTs,both of which stored unleaded gasoline <br /> (Figure 2). The tanks were removed in 1988, along with approximately 180 cubic yards of soil <br /> excavated to a depth of about I 1 feet below ground'surface (bgs). Detailed descriptions of the <br /> site, the site investigation history, and the site hydrogeologic setting are available in the Results <br /> ofAdditional Assessment and Remediation Evaluation of Petroleum Hydrocarbons in <br /> Groundwater(Geomatrix, 2003). <br /> The site is located on the delta of the San Joaquin River, approximately 2 miles east of the <br /> f confluence of the San Joaquin' and Calaveras rivers. The subsurface geology consists of a thick <br /> sequence of alluvial deposits of late Tertiary to Holocene age overlying sedimentary rocks of <br /> Cretaceous-to Tertiary age,which in turn overlie crystalline basement rocks. Site-specific data <br /> collected to a maximum depth of 49 feet bgs indicate a soil profile consisting of interbedded sand <br /> and clay layers. Since 1999, depth to groundwater beneath the site has ranged from 9 to 16 feet <br /> bgs. Groundwater beneath the site is confined to semiconfined. <br /> 2.0 FIELD-PROCEDURES " <br /> Starting with third quarter 2004, the method used to purge the groundwater monitoring wells <br /> before sampling was changed from vacuum evacuation to a dedicated submersible pump purge. <br /> I:\PROJECT\6000S\643i.00016437-2-3.doe l <br />