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SMTH <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 1.0 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 /> 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 /> Reference information for Xylenes were more difficult to locate. _Xylenes are composed of <br /> three isomers with similar properties. According to reference no. 4, all three isomers may <br /> occur in approximately equal amounts in a gasoline when sold. Therefore, average chemical <br /> properties were calculated and input to SESOIL <br /> Water Solubility <br /> 175 mg/1 - 1,2-Xylene (page 505 of ref. 4) <br /> 146 mg/1 - 1,3-Xylene (page 516 of ref. 4) <br /> 156 mg/l - 1,4-Xylene (page 526 of ref. 4) <br /> average = 159 mg/1 <br /> Henry's Law Constant <br /> 5.1 x 10-3 atm-m3/mole - 1,2-Xylene (page 505 of ref. 4) <br /> 7.7 x 10-3 atm-m3/mole - 1,3-Xylene (page 516 of ref. 4) <br /> 7.7 x 10-3 atm-m3/mole - 1,4-Xylene (page 526 of ref. 4) <br /> average = 6.8 x 10-3 atm-m3/mole <br /> N:\150114\mode1\param.doc 4 <br />