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' Page 2 Geologua l Teelinlcs liii'. Groundwater Monitoring Report Project No 989 2 November 18,2004 ' concentrations of MtBE fluctuate with groundwater elevation and that the overall MtBE concentration has decreased over time (Chart 2) 1 1.0 HYDROGEOLOGIC SYSTEM ' 1.1 Regional Structure ' Valley Wholesale Drug Company (VWDC) is located in the southwest quarter of the of Section 7, TIN, R6E, related to the Mount Diablo B&M, on the United States Geological Survey (USGS) topographic map, Stockton West Quadrangle, California, 7 5 minutes series ' A review of the USGS Topographic Map reveals that the elevation of this site is approximately 10-feet above mean sea level(AMSL) ' The site is located on the gradually sloped floor of the northern San Joaquin Valley The geologic composition of the area is characterized as fluvial deposits of the San Joaquin - Sacramento River delta system that overlay continental rocks and deposits derived from ' erosion of the Sierra Nevada Mountain Range located approximately 50 miles northeast of Modesto The southwest tilting Sierra Nevada fault block underlies the northern San Joaquin Valley area Overlying the consolidated rocks are unconsolidated sediments The lower ' consolidated batholithic and metamorphic rocks are poorly transmissive, however the overlying sedimentary layers are often quite permeable These unconsolidated layers include Pliocene/Pleistocene age continental deposits, Pleistocene age lacustrine and marsh deposits, ' and Holocene older and younger alluviums and flood-basin deposits 1.2 Regional Stratigraphy The following information comes from the United States Department of Agriculture — Soil Conservation Service (USDA) Soil Survey of San Joaquin County, California (McElhiney, ' M A , 1992), indicates the area surrounding the site is predominately made up of one general soil type • Jacktone --- Hollenbeck -- Stockton A gentle 0 to 2 percent slope, somewhat poorly ' drained and moderately well drained, fine textured soils that are moderately deep and deep to a cemented hardpan and that have been drained in some areas, on basin rims and ' in basins • The USDA Soil Survey of San Joaquin County, California (MeElhiney, M A , 1992), states the area beneath the VWDC is categorized as being urban land with the following ' description o The urban land unit consists of closely built-up areas in cities Streets, parking lots, buildings, and other structures cover more than 85 percent of the surface The landscape has been so altered by urban works that identification of the soils is � 1 k