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Stockton 99 Speedway Preliminary Endangerment Assessment Workplan April 12,2007 (USEPA, 1989; 1991; 1998; 2004), and California Environmental Protection Agency (CaIEPA, 1992; 1994; 1996). The human health screening assessment for the Site will include a screening-level risk evaluation (SLRE), which is conducted by comparing Site data to appropriate risk-based screening levels. This will provide a basis for evaluating whether action is warranted to mitigate potential health effects from exposure to contaminants in the subsurface at a Site. The SLRE will identify any chemicals of potential concern (COPCs) to be further evaluated under a formal, Site-specific screening evaluation. This assessment uses specific equations and exposure factors to quantify doses received by potentially exposed populations of receptors via various exposure routes. The human health risk assessment will quantify associated potential adverse noncancer health effects and excess cancer risks associated with the COPCs. The Site is currently zoned for commercial/industrial use. Future land-use may include residential, commercial, or mixed residential/commercial use. The planned future land use will be defined in greater detail during the risk assessment. Consistent with the PEA framework, a qualitative ecological screening evaluation (ESE)will be performed for the Site. During the PEA process an ecological survey will be performed to assess whether ecological receptors could contact site-related contaminants, in order to evaluate whether a screening- level analysis is warranted. The initial conservative screening evaluation focuses on literature-based exposure and toxicity information (e.g., benchmark concentrations) in combination with analytical data on potentially impacted soil. The ESE will evaluate whether further investigation and assessment is ✓ necessary. Screening criteria used in the SLRE will include background levels (for metals) and regulatory criteria. In an effort to focus on those chemicals that are expected to account for the majority of the estimated health and ecological impacts at the Site, a screening level evaluation will be conducted to identify COPCs. Under the screening level evaluation, a chemical will be identified as a COPC if the following conditions applied: • A detected concentration exceeding relevant background (ambient) concentration (metals only); and • A detected concentration exceeding applicable risk-based screening levels. USEPA (1989) and CaIEPA (1992) recommend that metals detected at background (ambient) levels not be identified as COPCs at a site. For this evaluation, background levels will be obtained from soil samples collected in Parking Lot A Area. No fill material has been deposited in this area and Site-related activities are not expected to have impacted the area. A metal will be considered present at background/ambient levels and will not be evaluated further if the maximum detected concentration within each area is below its upper bound background level. In cases where background levels are not PEA WorWan.Firutdoc 3-7 The Source Group,Inc.