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i Work Plan Frontier Transportation Page 2 through MW-7) to assess the extent of subsurface contamination beneath the site (See Figure 2, Site Layout Map). Soil samples were collected every five feet. Laboratory analysis of soil samples identified no detectable concentrations of TPH-g, BTEX, or MTBE from 5 ' bg to 25 ' bg. Groundwater samples were subsequently collected. Results are tabulated in Table 1 . In January 2000, BEII advanced two borings (B-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, Site Layout Map for well locations). Soil sample analysis identified no detectable concentrations of petroleum ` hydrocarbons with the exception of boring B-6. Maximum contaminant levels in B-6 were identified 100 mg/kg as TPH-g, 2,343 µg/kg as BTEX, and 10,600 µg/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 . Results are tabulated in Table 1 . - On May 17, 2002, BEII supervised the well abandonment of MW-3 in order to perform excavation in that area. From May 20 through 24, BEII excavated a total of 325 tons of soil near the former UST area. The excavation pit measured 30 feet by 30 feet by 15 feet deep. The soil e ,I consisted of heterogeneous clays with some fine-grained silty sand stringers at groundwater depth. Groundwater was encountered in the silty sand at approximately 13 ' bg. The excavation pit was terminated at 15 ' bg to avoid collapsing of the pit from the entry of silty sand and groundwater. Soil sample results identified the highest concentrations below the encountered - - - groundwater. 1 On May 30 and 31 , 2002, BEII supervised the installation of one replacement groundwater monitoring well (MW-3R) and two deeper groundwater monitoring wells (MW- 12 and MW-13) to help define the extent of dissolved petroleum hydrocarbons beneath the site (See Figure 2 for well locations). Monitoring well MW-3R was advanced to 20 ' bg while MW- 12 - and MW43 were advanced to 40 ' bg. See Table l for groundwater results. 3.0) SITE GEOLOGYIHYDROGEOLOGY 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 p, 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, L October 16, 1996). BEII encountered clay and a heterogeneous mix of clay from 0' to 25' bg in January of 1998. F , W , First subsurface water was encountered at depths from I P to 12' bg during tank removal _ ! ) and monitoring well installation at this site in 1995 and 1996. Since then, shallow subsurface f i 2 �J