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Lee Higgins -2 - 25 January 2011 Catellus Property Tracy, San Joaquin County between depth of 0 and 10 feet bgs are considered COPCs. Analytical data for 60 soil samples collected from 51 borings were evaluated for the HHSE. • Data provided in the HHSE describes exposure point concentrations (EPCs) that were used to calculate the upper confidence limit (UCL) for the mean soil concentration of each COPC. If a high number of non-detect (ND) results occur, it may not be possible to calculate a UCL. The United States Environmental Protection Agency (US EPA) recommends that if this condition occurs, to use the sample median as the EPC. • Potential residential exposure to chemicals in onsite soils were estimated for oral, dermal, and inhalation- routes following algorithms in the California Department of Toxic Substances Control (DTSC) Preliminary Endangerment Assessment (PEA) Guidance Manual. The algorithms incorporate health protective default exposure parameters promulgated by DTSC and US EPA that represent reasonable maximum exposure for health hazards and health risks. Cancer risks and non-cancer health hazards were estimated using PEA Guidance Manual equations. • An incremental lifetime cancer risk of 1 E-06 (i.e., one in one million), in accordance with the National Contingency Plan is used as a point of departure. A cancer risk equal to or below this threshold is considered to be insignificant. If the excess cancer risk is within the acceptable range between 1 E-06 to 1 E-04, a site-specific risk management decision may be considered by the lead regulatory agency. • The additive oral, dermal, and inhalation total potential onsite residential cancer risk determined at 4E-06 is within the range of risk management level of 1 E-06 to 1 E-04. A conservative approach for an onsite residential receptor scenario was utilized in the HHSE. The most likely future onsite use will be for commercial/industrial purposes and/or maintenance trench worker(s). • For non-cancer hazard indices, a hazard index of 1 or less is considered an acceptable health hazard level; the non-cancer hazard index was determined to be 0.003. If regulatory criteria are exceeded based on the findings, the HHSE identifies the chemical and exposure pathways contributing to the elevated risks or hazards. The risks can be more precisely assessed in a site-specific refined health risk assessment, if warranted. • Since soil and groundwater were delineated, and the characterization dataset adequately describes Site conditions, EPCs were calculated as the UCL of the mean soil concentration for each COPC. • BTEX and PAHs were detected in shallow groundwater samples collected during characterization activities. Benzene was detected in only one of 43 samples analyzed, and the concentration reported was below the maximum contaminant level (MCL). Toluene and some PAHs were detected at very low concentrations indicating the potential risks associated with this pathway are low.