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Frontier Transportation B23502.01A January 2, 1996 Page 2 • Evaluate the field and analytical data and assess the extent of PPC migration in soil and groundwater; • In the event that the work scope outlined in the plan does not accomplish our purpose stated above, we will assess the need for additional site characterization and/or identify appropriate corrective action(s) ; and • Prepare a technical report documenting the investigative procedures, summarize the findings, and presenting conclusions and recommendations. 3.0 BACKGROUND A description of the site, the geologic and hydrologic characteristics, and the project history are summarized in the following subsections. 3.1 Site Description: The site is located in Tracy, California at 425 Larch Road (APN 212-200-08) in the northwest quarter of Section 16, Township 2 South, Range 5 East, Mount Diablo Baseline and Meridian. Drawing 1 is a site location map. The Frontier Transportation facility consists of a single story metal frame on slab building and parking areas. The gasoline USTs were located immediately east of the northeast corner of the building. The diesel USTs were located southeast of the southeast corner of the building. The site is located in an industrial park and is bound on the east by Industrial Way, south by Larch Road, and west by a single story office building. Drawing 2 is a site plan depicting site features. 3.2 Geologic and Hydrologic Characteristics: The following subsections summarize the geology and hydrology of the Tracy area. 3.2.1 GeoloQv: The site is located on the boundary of the Sacramento Valley and the San Joaquin Valley within the central portion of the Great Valley geomorphic province of California. The Great Valley is a nearly flat northwest to southeast trending structural basin approximately 450 miles long by 50 miles wide. The Great Valley has been filled with a sequence of older to younger alluvium of Pliocene to Holocene age which overlie sedimentary rocks of Cretaceous to Tertiary age. These sedimentary units, in turn, overlie a crystalline basement of Paleozoic and Mesozoic metamorphic and igneous rocks. The shallow subsurface geology in the site vicinity is a heterogeneous mix of gravel, sand, silt, and clay (Hackel, 1966) . 3.2.2 Hydroloev: Sediments containing fresh groundwater are largely unconsolidated silts and sands deposited as river channel, flood plain, and alluvial fan deposits of Pliocene to Recent age (Davis and others, 1959).