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Steven Sasson -3- February 5, 1996 results of the confirmatory soil samples, CRC concluded that the area identified with hydraulic fluid-contaminated soil had been adequately excavated to the extent technically feasible or practical. The ground water results also indicated that the ground water had not been impacted by the soil contamination (CRC 1995) In response to the CRC's January 19, 1995 report entitled Soil Excavation Report and Groundwater Investigation, the SJCPHS requested that a risk assessment of the residual hydraulic fluid in the soil be performed (SJCPHD 1995) This letter report is ENVIRON's response to that request. 2.0 Risk Assessment for the Bridges Specialty Center Site A risk assessment can be used to determine whether the release of particular chemicals have the potential to cause harm to human health or the environment A risk assessment, as it applies to this site, can also be used to determine the potential for risk to human health as a result of exposure to hydraulic fluid in the soil, as well as the potential for migration of hydraulic fluid to ground water resources These two issues will be addressed separately in this report in Sections 2 1 and 2 2, respectively. 2.1. Human Health Risk Assessment • In accordance with the California Environmental Protection y (Cal/EPA)A encartment of g - Department Toxic Substances Control's (DTSC's) guideline "Preliminary Endangerment Assessment" (PEA), a risk assessment has been performed by ENVIRON for the Bridges Special Center to estimate the potential for adverse health effects from residual levels of hydraulic fluid in the soil. The PEA Guidance Manual, prepared by DTSC (DTSC 1994), provides basic information for determining if there has been a release of a hazardous substance that presents a risk to human health or the environment The PEA provides a mechanism of determining if known or potential hazardous substance sites require immediate or long-term remedial actions by the DTSC or DTSC oversight. The PEA presents a methodology to perform a human health screening risk evaluation. This screening evaluation conservatively assumes that the land use of the site will be residential, regardless of the current use and zoning for the site (DTSC 1994) Consistent with PEA guidance, this human health risk assessment is performed in four steps (1) data evaluation and chemical selection, (2) exposure assessment, (3) dose-response (toxicity) assessment, and (4) risk characterization These four steps, as applied to this site, are described in the following sections I 2.1.1 Data Evaluation and Chemical Selection The purpose of this section is to identify the chemicals of potential concern which are evaluated in this health risk assessment. The selection of chemicals to be included in this report is based upon the analytical results from previous soil investigations conducted at the site, as well as the history of the release at the site As recommended by DTSC (DTSC 1994), the maximum concentration