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EXECUTIVE SUMMARY <br /> This risk assessment evaluates the potential site-related environmental and human health <br /> impacts associated with the presence of petroleum hydrocarbons in soil beneath the Santa <br /> Fe Railway Company site in Stockton, California. Potential impacts have been evaluated <br /> by estimating the migration of petroleum hydrocarbons in site soil. <br /> This report follows the risk assessment guidelines suggested by the United States <br /> Environmental Protection Agency and the California Environmental Protection Agency In <br /> addition, the methodology recommended in the California Leaking Underground Fuel Tank <br /> (LUFT) Manual to predict chemical migration in soil and groundwater was followed <br /> This risk assessment is based upon extensive site-specific data including 1) soil <br /> investigations, 2) soil geophysical data, and 3) partitioning studies Previous soil <br /> investigations have characterized the horizontal and vertical extent of petroleum <br /> hydrocarbon-impacted soil. Soil samples were obtained to determine site-specific <br /> geophysical parameters such as bulk density, intrinsic permeability, moisture content, and <br /> organic carbon contents Partitioning studies were conducted to simulate the migration of <br /> petroleum hydrocarbons through soil by determining the chemical constituents of the <br /> petroleum hydrocarbons which may partition into percolating water These studies were <br /> developed to provide an overestimate of the amount of chemicals partitioning into <br /> percolating water <br /> SESOIL, an environmental fate and transport model, was used to predict migration of <br /> petroleum hydrocarbons through the soil column This model couples the hydrogeologic <br /> cycle with soil- and chemical-specific parameters to predict the migration of dissolved phase <br /> hydrocarbons in water percolating through the soil The straight-chained alkane, <br /> tetradecane, the smallest and most water soluble chemical found in the water from the <br /> partitioning studies was modeled as a conservative chemical surrogate for the entire <br /> petroleum hydrocarbon mixture Other components of petroleum hydrocarbons would be <br /> expected to move much slower than tetradecane The area of soil containing the petroleum <br /> hydrocarbons was conservatively assumed to be approximately 127 square meters The <br /> northern and southern boundaries of this area were delineated by sampling locations at <br /> which total petroleum hydrocarbons (TPH)were nondetectable Delineation of the western <br /> 0 baMIMAWAF6 FNL{LdOS 26 93 ES-1 cnewR,.t- Ivy <br />