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rl <br /> • Corrective Action Plan—Tosco{76}Service Station No 11192, Stockton, California <br /> March 13, 2002 <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 monitonng and sampling event at the site was conducted on February 18, 2002 This <br /> event included joint monitoring with the former Shell station located across Pershing Avenue from <br /> the site On this date, the measured depth to groundwater in the monitoring wells ranged from 1186 <br /> to 15 92 feet below TOC The groundwater flow direction at the site was toward the north-northeast, <br /> with a relatively flat gradient of 0 002 ft/ft ��Pa,�d +To 01 �rlw,"" <br /> V A,� <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 to 11 feet bgs Underlying the clayey <br /> zone is sand and silty sand to a depth of approximately 27 feet bgs From approximately 27 to 68 <br /> feet bgs, clay with silty clay and clayey silt was recorded Underlying this clay, sand was <br /> encountered to 75 feet bgs, the total depth explored A detailed description of the site geology is <br /> presented in Section 2 3 of this report <br /> The MtBE plume beneath the site is predominantly defined Previous investigations at the site <br /> indicate that the plume is largely confined to the site, although detections of petroleum hydrocarbons <br /> in the onsite deep well and offsite Geoprobes indicate that additional vertical and lateral delineation <br /> . is necessary in the downgradient direction At the time this CAP was prepared, the analytical data <br /> from the former Shell station joint monitoring and sampling event was not available for review <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 <br /> 3,500 feet north of the site Both of these waterways are channeled, flow generally southwest, and <br /> drain into the Stockton Deep Water Channel <br /> 14024508 6 <br />