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. hydrocarbon migration through the soil column and the potential to reach the groundwater <br /> aquifer <br /> The Seasonal Soil Compartment Model (SESOIL) (USEPA, 1984) was used to estimate <br /> diesel migration through the soil SESOIL is a seasonal soil compartment model developed <br /> under contract for the USEPA SESOIL predicts the total mass of a chemical that may <br /> migrate through a user-specified soil column due to percolating water <br /> The methodology for using environmental fate and transport models to predict the migration <br /> of chemicals through the soil to a groundwater aquifer and the subsequent dispersion within <br /> the aquifer is consistent with strategies suggested and commonly used in the State of <br /> California For example, the Leaking Underground Fuel Tank (LUFT) Manual (California <br /> State Water Resources Control Board, 1989) employs the same protocol used in this <br /> procedure This evaluation is consistent with a LUFT "Alternative Risk Appraisal" in that <br /> site-specific soil characteristics have been collected and used to estimate petroleum <br /> hydrocarbon migration at the Santa Fe Railway Company site The use of site-specific data <br /> provides a greater level of confidence (less uncertainty) that the migration has been <br /> appropriately estimated <br /> 4 41 Modeling Strategy <br /> A strategy must first be developed to estimate the potential migration of petroleum <br /> hydrocarbons through the vadose zone Three distinct approaches are possible to evaluate <br /> the environmental fate and transport of hydrocarbon mixtures The first is to simulate the <br /> environmental fate of a subset of "worst-case" indicator chemicals The second method is <br /> to evaluate the environmental fate and transport of surrogate constituents The third <br /> method involves the simulation of the environmental fate of the hydrocarbon mixture as a <br /> whole. <br /> In order to select the most appropriate method for use in environmental fate and transport <br /> simulations, the following factors must be considered <br /> • the availability of information on the mixture, <br /> • the quality of information on the mixture, <br /> • the mobility/toxicity of the mixture, and <br /> • the availability of site information <br /> 0+~17ZArrrwFe FNauw.es 26 93 4-5 ChcmRuN IM <br />