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