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The sediment cycle option is important at sites where surface water runoff may potentially carry the indicator chemical from the surface to off-site locations Because surface runoff at the Santa Fe Railway Company site is not a significant mode of chemical transport, for the purposes of this assessment, the sediment cycle options were not employed The chemical fate cycle accounts for the following processes • advection • diffusion • volatilization adsorption and desorption • chemical degradation • biological transformation, and • other processes The model is based on a user-specified soil column and simulates chemical transport in the vadose zone (the column of soil from the surface to the top of the water bearing zone) Site-specific parameters are incorporated into the model using SESOIL's application, climate, and soil input files Chemical-specific parameters are incorporated into the model using the application and chemical input files Values from measurements at the site were used whenever possible to reflect actual site conditions. Where site data were unavailable, conservative assumptions were made based on ChemRisk®'s understanding of the site. The following subsections outline the specific input parameters used for the SESOIL modeling of the Santa Fe Railway Company site Application File The application file describes the parameters which are specific to each soil layer at the site A"soil layer" is a homogeneous subsurface soil zone Parameters in this file consist of layer thicknesses, variability of parameters between layers, area and depth of petroleum hydrocarbon-impacted soil, and chemical loading Layers were selected and described based upon site-specific data Boring logs for the site were reviewed to identify the different stratigraphic layers present One distinct soil type was identified silty-clay from 0 to 55 feet bgs C V0600 MSAWAFE FNL\ks&W 26 93 4-7 C}wnRme 1993