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Work Plan T ' Frontier Transportation May 31, 2001 samples identified no detectable concentrations of TPH-g, BTEX, or MTBE. Groundwater samples were subsequently collected. Results are tabulated in Table 1 . t. In January 2000, BEII advanced two borings (B-5 and B-6), installed four additional ( I groundwater monitoring wells (MW-8 through MW- 11 ), and collected nine soil vapor samples !J for a soil vapor survey as part of an additional site assessment (See Figure 3 , BEII Sample Locations). Soil sample analysis identified no detectable concentrations of petroleum hydrocarbons with the exception of boring 13-6. Maximum contaminant levels in B-6 were r identified 100 mg/kg as TPH-g, 2,343 pg/kg as BTEX, and 10,600 lig/kg as MTBE at 10' bg' Maximum soil vapor concentrations were identified at sample point V5 at 4 ' bg. Groundwater samples were subsequently collected from all monitoring wells. Groundwater results are tabulated in Table 1 and soil vapor sample results are presented in Table 2. L ] 3 .0) SITE GEOLOGY/HYDROGEOLOGY i-J The site is located on the boundary of the Sacramento Valley and the San Joaquin Valley —� 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 . JFirst 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 Iwater has been encountered between 6' and 10' bg. The flow of groundwater is generally in a lwestern direction beneath the site (See Figure 4, Groundwater Gradient Map) . f` 4.0) PROPOSED SCOPE OF WORK i BEII proposes to perform an additional soil gas vapor survey to identify the lateral extent —I of soil gas vapors identified in the previous survey performed in January 2000. BEII proposes to excavate two 5-feet deep by 3 -feet wide by 204eet long exploratory trenches at the site. The location of the trenches will be based on the results obtained from the proposed soil vapor r �I survey. Furthermore, three additional groundwater monitoring wells will be installed to define �_J the lateral extent of impacted groundwater from monitoring well MW-3 (See Figure 5 for [ Proposed Soil Vapor and Well Locations) . � ) 2 fJ