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Stockton 99 Speedway <br /> Preliminary Endangerment Assessment Workplan <br /> April 92,2067 <br /> 3.0 PRELIMINARY CONCEPTUAL SITE MODEL <br /> To develop a conceptual understanding of the Site, information regarding .potential chemical sources, <br /> chemical release and transport mechanisms, locations of potentially exposed human receptors, and <br /> potential exposure routes are assessed. The conceptual Site model (CSM) associates sources of <br /> chemicals with potentially exposed human and ecological receptors and associated complete exposure <br /> pathways. In this way, the CSM assists in quantifying potential impacts to human and ecological <br /> receptors. This preliminary CSM may be refined and modified based on additional data obtained during <br /> the PEA process. <br /> As defined by USEPA (1989), all of the following four components are necessary for a chemical <br /> exposure pathway to be considered complete and for chemical exposure to occur: <br /> • A chemical source and a mechanism of chemical release to the environment; <br /> • An environmental transport medium (e.g., soil)for the released chemical;, - <br /> • A point of contact between the contaminated medium and the receptor (i.e., the exposure point); <br /> and <br /> • An exposure route (e.g., dermal contact with chemically-impacted soils) at the exposure point. <br /> The following sections describe.these components and provide a basis for the preliminary CSM. <br /> 3.1.1 Initial Characterization of Potential Source Areas <br /> The first component necessary for an exposure pathway to be complete, chemical source(s) at the Site, <br /> are discussed in this section. Historical information reviewed indicates that the Site has been used for <br /> automotive racing since at least 1947. The primary chemicals used on the Site include petroleum oils <br /> and fuels. <br /> Based on a review of available Site investigation data, six areas of concern (AOCs) have been identified <br /> that require additional soil investigation (Figure 4). These areas include: <br /> •Debris Fill Area - A number of samples have been collected by Kleinfelder and SGI to assess the <br /> lateral and vertical extent of fill material located in the Debris Fill Area. Soil samples collected <br /> during the test pit investigation conducted by SGI revealed the presence of arsenic, cadmium, <br /> and lead in concentrations that exceed their respective CHHSL. Miscellaneous construction <br /> debris was also observed during the test pit investigation. <br /> PEA woxplanTi lda 3-1 The Source Group,Inc. <br />