SITE INFORMATION AND CORRESPONDENCE 1995-2004

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Section 8 Environmental Risk Assessment 8.1 Objective The objectives of the environmental risk assessment (ERA) of the Stockton MGP site were to conduct a qualitative screening of the site to identify wildlife habitats or sensitive plant populations in the site vicinity and to determine the likelihood of site-related chemicals reaching, and adversely affecting, these populations. Protection of the general population, the community, and the ecosystem was the primary focus of the ERA, with special attention given to species of special regulatory status and critical habitat. The ERA was prepared in accordance with the Risk Assessment Guidance for Superfund, Volume II, Environmental Evaluation Manual (U.S. EPA, 1989c) and the EPA ECO Update, Developing A Work Scope For Ecological Assessments, Intermittent Bulletin, Volume 1, Number 4 (U.S. EPA, 1991d). The ERA includes the following sections: `'• Characterization of Site and Potential Receptors Chemicals of Potential Concern • Exposure Assessment • Ecological Effects Assessment • Risk Characterization Site characterization is conducted to identify areas of potential concern that support native vegetation and wildlife. Chemicals of potential concern (COPC) are those chemicals detected during sampling activities with known environmental toxicity. COPC and areas of potential concern are the focus of the exposure characterization and toxicity assessment. The exposure assessment involves assessing exposure pathways and routes of exposure (e.g., ingestion, dermal contact, etc.) and identifies populations that may be exposed to COPC. Potential receptors are characterized by identifying potentially exposed habitats and species. The ecological effects assessment discusses the acute and chronic effects of the COPC on vegetation and wildlife. Finally, information gathered during this entire process is incorporated into the risk characterization, which addresses the relative impacts from plausible exposure pathways. 8.2 Scope The ERA is based on a field reconnaissance conducted on June 18, 1992, and analytical data collected from soil and groundwater sampling conducted between December 16, 1991, and September 1992. No biological sampling has been conducted. Specific information pertaining to sampling activities and results is discussed in Sections 3 and 5. Critical habitat and threatened or endangered species potentially in the area are discussed in Section 8.4.4. 10010427.SFO 8-1