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The preceding approach was used to accurately and conservatively quantify the vertical migration potential of tetradecane to represent petroleum hydrocarbons Because it is assumed that physically the maximum concentration in a layer is uniform throughout that layer, migration will begin at the bottom of that layer This can be simulated in SESOIL by loading the very top portion of the following layer TABLE 4-1 presents the loading mass derivation. The study area was conservatively delineated by using soil borings in which petroleum hydrocarbons were not detected Where a soil boring was not present, the maximum lateral distance that could reasonably be expected to contain petroleum hydrocarbons was used. The area of soil containing the diesel fuel was conservatively assumed to be approximately 127 square meters This area encompasses the former tank area and the former vault This study area is presented in FIGURE 2-3 The indicator chernical, tetradecane, was used to conservatively represent the physical and chemical properties of TPH at the site TABLE 4-2 summarizes the application file input parameters that were used to represent the presence of tetradecane at the Santa Fe Railway Company site Loading of the chemical was begun in year five This was done to ensure that the water balance in the soil column was in equilibrium pnor to loading The modeling must account for rain water, which begins infiltration in year one, to "fill-up" the soil column Therefore, when chemical loading is begun, the water balance in the soil column is in equilibrium Climate File SESOIL uses monthly climatological data to model the hydrologic cycle Parameters from the Sacramento, California climate file provided as part of the SESOIL model program were used. This file was used as a representation of rainfall that occurs in Stockton, California. Percolation of water through the soil is estimated based on the average monthly rainfall minus the amount of rain that evaporates Rainfall is estimated from the average storm cycle of the area using values for precipitation per storm, number of storms, and duration of storms Evaporation rates are estimated for the site based on the climate file for the area Evaporation rates were calculated by the model based on monthly average temperature, percent humidity, percent cloud cover, and albedo (reflectivity) G'060D7MAWAFEFNVkaM2693 4-10 Ch=Rkoe, 1993