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boring B-32/MW-1 at 111 feet bgs Relatively high concentrations of GRO (900 mg/Kg) and benzene (3 4 mg/Kg) were reported for the soil sample collected from boring B-42 at 98 feet bgs in 2004 Both of these samples were collected immediately below the base of sand zone 2 Petroleum hydrocarbons were reported for soil samples collected between 17 and 114 feet bgs (boring B-39), 51 and 113 feet bgs (boring B-40), 49 and 97 feet bgs (boring B-41), and 54 to 98 feet bgs (boring B-42) in the 2004 off-site investigation For the samples collected from recently advanced borings B-44 through B-48, petroleum hydrocarbons were only reported in one soil sample (benzene at 0 006 mg/Kg, boring B-46, 106 feet bgs) Given the findings of the soil samples collected from borings B-44 through B-48, the vertical and lateral extent of petroleum hydrocarbon impact also appears to be adequately characterized off-site Increased residual petroleum hydrocarbon concentrations were generally observed for soil samples collected near sand zone 1 and sand zone 2 in borings B-39 through B-42, suggesting that these stratum may be providing a preferential pathway for subsurface movement of the petroleum hydrocarbon impact Soil analytical data collected from borings B-33 through B-42 appears to show that the vertical extent of subsurface petroleum hydrocarbon impact does not extend more than approximately 10 feet deeper than the base of sand zone 2 Based on this observation, the fine grained soils situated immediately beneath sand zone 2 appear to be of sufficiently low permeability to impede additional vertical migration of the petroleum hydrocarbons at these depths iOff-site MTBE and 1,2-DCA impact to soil appears to be limited MTBE was only reported for the soil samples collected from boring B-39 between approximately 17 and 45 feet bgs, at concentrations ranging from 0 008 mg/Kg to 0 35 mg/Kg 1,2-DCA was reported for the samples collected from boring B-39 at approximately 45 feet bgs (0 027 mg/Kg) and 64 feet bgs (0 014 mg/Kg) 34 Extent of Petroleum Hydrocarbon Impact to Groundwater Shallow Screened Wells Free product has historically been measured in wells MW-4 (sheen), VW-I (sheen to 1 3 feet in thickness) and VW-4 (sheen to 0 21 feet in thickness) The lateral extent of free product in the subsurface appears to be adequately characterized in the shallow screened wells Relatively high concentrations of GRO and benzene were reported for samples collected from on-site wells MW-4 (280,000 micrograms per liter [µg/L] and 3,800 pg/L, respectively), and VW-3 (29,000 µg/L and 96 µg/L, respectively), at the time of the first quarter 2006 sampling event MTBE was not reported above laboratory reporting limits for samples collected from the shallow screened wells during the first quarter 2006 GRO, benzene, and MTBE concentrations in the shallow screened monitoring well samples collected during the first quarter 2006 are depicted on Figure 9 K 5Bp Arco for URS%1001Repurts56100 assessment rpt&scm update duc Page 10 5-MATus