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i <br /> SAFEWAY MEAT PACKING FACILITY, STOCKTON, CALIFORNIA <br /> TIER II RISK BASED CORRECTIVE ACTION <br /> FEBRUARY 26, 1996 <br /> PAGE 4 - 2 <br /> 4.1 Site Parameters <br /> Table 4 presents the site parameters value and the bases for the selected values The values used <br /> were either measured site characteristics, estimated values based on site and area characteristics, <br /> engineering evaluations, or default values found in the RBCA standard <br /> Measured Site Characteristics: The parameters based on measured values were depth to <br /> groundwater, width of source area parallel to the groundwater flow, depth to the subsurface soil <br /> source, and groundwater gradient (used to estimate the groundwater velocity) <br /> Estimated Site Characteristics Literature values for the following site characteristics were <br /> based on the predominant soil type found at the Stockton site, that is a salt to silty clay soil bulk <br /> density (1 38 g/cm3), total porosity (0 46), hydraulic conductivity (3 3 x 10"5 cm/s for a sandy <br /> clay used for average case and 2 5 x 10"5 cm/s for a salt clay soil, based on data in USEPA 1988, <br /> this value is used to estimate the groundwater velocity), and height of the capillary fringe for the <br /> average case (150 cm) were based on median values of literature references for clay soil <br /> (Specific references are provided in Table 4 ) The moisture content of the vadose zone soil has <br /> not been measured, however the boring logs indicate that the soil is moist Based on this <br /> characteristic, it was assumed that the soil is at field capacity Data in the Superfund Exposure <br /> Assessment Manual (USEPA, 1988) indicates that at field capacity the mean moisture content of <br /> salt loam is 0 33 cm3/cm3 and for a salty clay is 0 387 cm3/cm3 Using an estimated moisture <br /> content in this range would indicate that 70% or more of the pore volume would be occupied by <br /> water and would result in low estimates of soil gas emissions So that vapor emissions would <br /> not be underestimated, it was assumed that half the pores in the vadose zone soil are filled vvath <br /> water <br /> o131CnJ? <br />