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1.0 low INTRODUCTION The following Human Health Risk Assessment for the former Yellow Freight System, Inc. (YFS) Terminal in Stockton, California has been prepared to evaluate potential health risks and potential groundwater quality impacts posed by the residual petroleum hydrocarbons in soil. This risk assessment has been performed using the approach in the March 1995 Workplan written by Woodward-Clyde Consultants (WCC) and submitted to the San Joaquin County, Environmental Health Division (SJCEHD) for N`" review and approval. The results presented in this risk assessment specifically address potential health risks associated with ingestion of groundwater, inhalation of volatiles at the surface, dermal exposure to groundwater, and soil ingestion. Potential impact to groundwater at the existing water supply well on site was evaluated for both the average groundwater elevation and the seasonal high groundwater elevation. 1.1 OBJECTIVES The primary objective of this risk analysis was to evaluate the potential impacts to groundwater and human health risks due to potential exposure to low levels of residual petroleum hydrocarbons which remain in the soil. The analysis was conducted in a "worst-case" manner to evaluate what the reasonable maximum groundwater concentrations might be at the existing site water supply well. Site-specific data were used whenever possible. This approach is consistent with the recently issued guidance by the U. S. Environmental Protection Agency (EPA) Risk Assessment Council stressing the use of site-specific data to evaluate potential health risks (EPA 1992a,b). Another objective was to follow the Risk Assessment Council's guidance for risk characterization limiting discussion of information to risk assessment instead of including any risk management discussions, identifying key uncertainties and 'IWO their potential to under- or overestimate risk, and including information on a range of exposure. While the reasonable maximum exposure (RME) is designed to be a measure `- of "high-end" exposure and is used by risk managers in making remedial decisions (if any) to be protective to human health, the average or central tendency risks are SALDOYELLOAPT May 4, 1995 1-1 v..