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. Updated Corrective Action Plan—Tosco (76)Service Station No 11192, Stockton, California — <br /> June 26,2002 <br /> additional oxygen(t a through ozone mtcrosparging)would allow the degradation sequence to continue <br /> to completion <br /> 2. The hydrogeologic characteristics of the site and the surrounding area where the <br /> unauthorized release has migrated or might migrate: <br /> The most recent monitoring and sampling event at the site was conducted on February 18, 2002 This <br /> event included point monitoring with the former Shell station located across Pershing Avenue from the <br /> site On this date, the measured depth to groundwater in the monitoring wells ranged from 1186 to <br /> 15 92 feet below TOC The groundwater flow direction at the site was toward the north-northeast,with <br /> a relatively flat gradient of 0 002 ft/ft <br /> Previous subsurface exploration events indicate that the site is predominantly underlain by clay and <br /> clayey sand with lesser amounts of silt to approximately 3 toll feet bgs Underlying the clayey zone is <br /> sand and silty sand to a depth of approximately 27 feet bgs From approximately 27 to fib feet bgs,clay <br /> with silty clay and clayey silt was recorded Underlying this clay, sand was encountered to 75 feet bgs, <br /> the total depth explored A detailed description of the site geology is presented in Section 2 3 of this <br /> report <br /> 3. The proximity and quality of nearby surface waters, wetlands, or groundwater, and the <br /> current and potential beneficial uses of these waters: <br /> Surface Waters <br /> Based on the USGS Topographic Map for this area, the nearest surface water bodies are Smith Canal <br /> located approximately 1,300 feet south of the site and the Calaveras River,located approximately 3,500 <br /> feet north of the site Both of these waterways are channeled,flow generally southwest, and drain into <br /> the Stockton Deep Water Channel <br /> • 140245 08 6 <br />