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Human Health Risk Assessment Former Mobil Oil Bulk Plant 04-343 540 East Grant Line Road Tracy, California 5.0 EXPOSURE ASSESSMENT The Exposure Assessment is the process of estimating human exposure to a chemical in the 't environment. The exposure assessment describes the magnitude, duration, timing, and route of exposure. The primary components of the exposure assessment includr. 1) identification of the ' potential exposure pathway(s), 2) identification of reasonable. exposure scenarios, and 3) prediction of chemical concentrations at points of potential exposure. Estimates of exposure in this assessment are based on measurements of existing site conditions and environmental fate modeling. ' 5.1 COMPONENTS OF AN EXPOSURE ASSESSMENT ' The exposure assessment consists of three main components: 1) exposure setting, 2) identification of exposure pathways, and 3) exposure quantificati:i't. A flowchart of the ' exposure assessment process is presented in Figure 5-1. In characterL, 'lig the exposure setting, it is important to depict the general physical characteristics of the site a,7d the populations on or near the site (EPA, 1999h). Populations are defined and described with respect to characteristics that influence exposure (e.g., location relative to site). In addition, this; step considers attributes of the current population and of potential future populations, which ma,, differ under an alternate land use (EPA, 1989b). ' The second step in the exposure assessment process is to identify potential exposure pathways. This component identifies those pathways by which human populations may be exposed. ' Exposure pathways are identified based on consideration of the sources, releases, types, and locations of chemicals at the site; the environmental fate of chemicals; and the location and activities of the potentially exposed populations (EPA, 1989b). Expoulre points and routes of ' exposure are identified for each exposure pathway (EPA, 1989b). For a pathway to exist, each of the following elements must be present: 1 A source and mechanism for chemical release ' • An environmental transport medium • A point of potential human contact with the medium • A of Pxnncµre Y ' 30-0136-11 5-1 1