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Work Plan Frontier Transportation { July 23, 2001 J i Site Layout Map) . Soil samples were collected every five feet. Laboratory analysis of soil r samples identified no detectable concentrations of TPH-g, BTEX, or MTBE. Groundwater samples were subsequently collected. Results are tabulated in Table 1 . In January 2000, BEII advanced two borings (13-5 and B-6), installed four additional groundwater monitoring wells (MW-8 through MW- 11), and collected nine soil vapor samples for a soil vapor survey as part of an additional site assessment (See Figure 2). Soil sample analysis identified no detectable concentrations of petroleum hydrocarbons with the exception of boring 13-6. Maximum contaminant levels in B-6 were identified 100 mg/kg as TPH-g, 2,343 is µg/kg as BTEX, and 10,600 µg/kg as MTBE at 10 ' bg. Maximum soil vapor concentrations f "j were identified at sample point V5 at 4 ' bg. Groundwater samples were subsequently collected ` JJ from all monitoring wells . Groundwater results are tabulated in Table 1 and soil vapor sample results are presented in Table 2. -� 3.0) SITE GEOLOGY/HYDROGEOLOGY The site is located on the boundary of the Sacramento Valley and the San Joaquin Valley Ij within the west-central portion of the Great Valley Geomorphic province of California. The Great Valley has been filled with a sequence of older to younger alluvium of Pliocene to Holocene age which overlay sedimentary rocks of Cretaceous to Tertiary age. These sedimentary units, in turn, overlay 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 (Reference; Site Characterization Report, Twining Laboratories, October 16, 1996) . BEII encountered clay and a heterogeneous mix of clay from 0' to 25' bg in January of 1998. '- First subsurface water was encountered at depths from I F to 12' bg during tank removal and monitoring well installation at this site in 1995 and 1996 . Since then, shallow subsurface Jwater has been encountered between 6' and 10' bg. The flow of groundwater is generally in a western direction beneath the site (See Figure 3 , Groundwater Gradient Map) . Il 4.0) PROPOSED SCOPE OF WORK -� BEII proposes to excavate approximately 280 cubic yards of potentially impacted soil in the former UST area. Monitoring well MW-3 will be abandoned under permit and inspection of the SJCPHS-EHD prior to soil excavation. In addition, BEII proposes to install a deeper monitoring well to identify the lateral extent of MTBE as identified by boring B-6 and will act as a replacement well for MW-3 . 2 L.1