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E11C�yt® COME= Mr James L Barton ' December 2, 2004 Page 3 ' In May 2002, the RIW was replaced The new Delta College Irrigation well became operational in July 2002 In July 2004, three wells (MW-28 through Mw-30) were Installed to assist in defining the lateral extent of petroleum hydrocarbons in groundwater south and east of the site In August 2004, well MW-9 was abandoned and replaced with MW-9R in order to facilitate ' planned construction activities to expand the shopping mall In November 2004, two wells (MW-31 and MW-32) were Installed to assist In defining the vertical and lateral extent of petroleum hydrocarbons in deeper aquifer zones beneath the site Well survey data and groundwater analytical data for these wells were not available for this report IGEOLOGY & HYDROGEOLOGY Regional According to information provided by Environmental Audit Inc (EAI), in their Supplemental Investigation Report Problem Assessment Report, and Work Plan dated October 12, 2000, the site is located near the center of the Great Central Valley of California The Central Valley is a large northwestward-trending asymmetrical trough, which was formed by filling of a large structural trough in the bedrock formation The trough Is situated between the Sierra Nevada Mountains on the east and the Coast Range Mountains on the west The sediments that filled the trough originated as erosion debris from the adjacent mountains and foothills The bedrock complex Is composed of metamorphosed marine sediments The overlying sediments exhibit a fairly complete stratigraphic section of Cretacious, Tertiary, and Quanternary deposits which have a maximum thickness of approximately 9,000 feet beneath the Stockton area The recent sediments were apparently deposited by flooding of the major rivers (i e , San Joaquin) The sites are located In the San Joaquin River Basin The Basin covers approximately 15,880 square miles and includes the entire area drained by the San Joaquin River It includes all watersheds tributary to the San Joaquin River and the Delta south of the Sacramento River and south of the American River watershed The principal streams in the Basin are the San Joaquin River and its larger tributaries the Cosumnes, Mokelumne, Calaveras, Stanislaus, Tuolumne, Merced, Chochilla, and Fresno Rivers The sites are located between the Calaveras River to the south and Bear Creek located approximately four miles to the north Further, the sates are located in the Lower Mokelumne Hydrologic Area of the North Valley Floor Hydrologic Unit of the San Joaquin Hydrologic Basin Site Specific Sediments beneath the site are fluvial deposits associated with the San Joaquin River and Its tributaries, particularly the Calaveras River which Is located approximately one mile south of the site Based on available logs of boring and wells associated with the Wards and Unocal sites, 11QcsacramentolprojectslProjects10694045098 293final\Reports15098 R5E Results Report doc