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Work plan forAdditional GroundwaterAssessment <br /> Former Chevron Service Station 94054 <br /> March 19, 2010 <br /> 2.2 REGIONAL GEOLOGY/HYDROG;EOLOGY <br /> The Stockton area is part of the Great valley physiographic province and is underlain by <br /> Holocene age alluvium and the Victor Formation to a depth of approximately 150 feet below <br /> grade. The formations are comprised of unconsolidated Quaternary age deposits and are <br /> heterogeneous consisting of laterally discontinuous lenses of sand and gravel with varying <br /> amounts of sand and silt interstratified with units of clay and silt. <br /> Surface water bodies present in the vicinity of the site include. the Smith Canal, located <br /> approximately 1,200 feet to the south, Deep Walker Channel, locatedapproximately 2,250 feet <br /> to the south and Calaveras River, located approximately 4,250 feet to the north. <br /> 2.3 SITE GEOLOGY <br /> Site-specific monitoring well boring logs indicate that the site lithology is consistent with regional <br /> lithology. Site-specific lithology is comprised primarily of clay and silt with discontinuous lenses <br /> of poorly to well graded sand and gravel. Monitoring well boring logs for MW-1, MW-1A, <br /> MW-1B, MW-1C, MW-2, MW-213, MW-2C, MW-3, MW-4, MW-413, MW-4C, MW-4D, MW-5, <br /> MW-6, MW-7, MW-8, MW-9, -MW-9B, MW-9C, MW-9D, MW-10, MW-11, MW-12, MW-12B, <br /> MW-12C and MW-12D are included in Attachment C. <br /> Four water bearing zones have been identified underlying the site: the A zone (screened from <br /> approximately 5 to 35 feet below ground surface [bgs]), the B zone (screened from <br /> approximately 40 to 51.5 feet bgs), the C zone (screened from approximately 65 to 81.5 feet <br /> bgs) and the D zone (screened from approximately 95 to 101 feet bgs Monitoring well screen <br /> intervals are provided in Table 2. Depth to water at the site generally ranges from 3.33 to 23.41 <br /> feet below ground surface. The predominate groundwater flow direction observed in each of the <br /> water bearing zones is as follows (ARCADIS, 2010 — Second Semiannual 2009 Groundwater <br /> Monitoring Report): <br /> • A zone —northwest <br /> • B zone—west-northwest <br /> • C zone— north-northeast <br /> • D zone — northeast, however there is an insufficient number of monitoring events to <br /> summarize the predominant flow direction in the D zone. <br /> A Groundwater flow direction rose diagram for the B zone is included as Attachment D. <br /> ':',CA5FP\Data\Aprolect\ENV\CHEVRCN\94054\6 DeliverablesANork Plans\2010\Temp\Work Plan for Site Assessmene.4821010950.coc 2 <br />