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16 <br /> intrinsic permeability of 5 x 10-11 cm2 (equivalent to a hydraulic conductivity of 5 x 10-6 <br /> CM/sec) is considered conservative since the soil type, CH, in the critical area below the <br /> residual chemicals indicates a much lower permeability Furthermore, the silt below the fat <br /> clay is very dense as indicated by the blow counts measured during standard penetration tests <br /> ' The standard penetration tests were performed while drilling the monitoring well boring MW- <br /> 1 Blow counts vaned from 18 to 47 which indicates Very Stiff to Hard soils <br /> The disconnectedness index for silt and clay, 12, is specified as recommended by the SESOIL <br /> documentation This index is a dimensionless number, generally ranging from 3 7 to 12 <br /> Higher values indicate less-connected pore space and hence greater resistance to flow <br /> ' The effective porosity for silt, 0 27, is specified as recommended <br /> 1� by the SESOIL <br /> documentation. The effective porosity is defined as the ratio of the pore space through which <br /> ' flow can occur to the total volume <br /> Cation exchange capacity is specified as zero SESOIL determines retardation based on <br /> ' organic carbon content alone when the cation exchange capacity is specified as zero Cation <br /> exchange modeling is typically utilized for heavy metal transport <br /> ' SESOIL employs the general Freundlich equation to model soil sorption processes The <br /> equation includes an exponent know as the Freundlich exponent In the absence of chemical <br /> specific data, a value of 10 is recommended in the SESOIL user manual for the Freundlich <br /> exponent With the Freundlich exponent input as 1 0, the Freundlich equation then defines a <br /> linear partitioning isotherm <br /> ' 5.3.5 Chemical Properties <br /> The SESOIL software package from General Science Corporation includes chemical data files <br /> for eight common contaminants of concern including benzene, toluene, and ethylbenzene The <br /> recommended values were compared to values found in multiple references (see the Reference <br /> section below) The solubility constants compare closely but the SESOIL chemical file value <br /> for Ethylbenzene's Henry's constant does not agree by three orders of magnitude with the <br /> value reported in reference no 1 (0 0079 m3-atm/mole) or reference no 5 (0 0087 m3- <br /> atm/mole) Ethylbenzene is assigned a Henry's constant of 0 0079 m3-atm/mole because it is <br /> the more conservative value All four contaminants of concern are aromatic non-halogenated <br /> volatile organics. <br /> The organic carbon adsorption coefficients for benzene, toluene, and ethylbenzene provided <br /> with the SESOIL software package are more conservative than the similar values reported in -- _--- - <br /> _ - references no 2 and reference no 5 (for benzene). The SESOIL recommended values are <br /> approximately one-half to one-third of the reference no 2 values The more conservative <br /> SESOIL recommended values are specified <br /> w 19411ftcportslsew,,doc 8 <br /> i <br /> SMTN <br />