SITE INFORMATION AND CORRESPONDENCE

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Lee Higgins -2- 10 August 2011 Chevron Tracy Byron Road of the project, respectively. The risk scenario for Areas 1 and 2 were evaluated in accordance with an onsite child or adult residential concept. Since affected soil in Area 3 lies predominately beneath the UPRR, Byron Road and/or active pipeline easement(s), SAIC considered the most likely exposure risk scenario to be for a construction worker. According to the Report, the HHSE was developed in accordance with the Preliminary Endangerment Assessment (PEA) Guidance Manual (California Environmental Protection Agency [Cal EPA] Department of Toxic Substances Control [DTSC], 1999, and the California Cancer Potency Factors and Chronic Reference Exposure Levels (Cal EPA - Office of Environmental Health and Hazard Assessment [OEHHA], 2011). An incremental lifetime cancer risk of 1 E-06 (i.e., 1 in 1 million), in accordance with the National Contingency Plan, is used as a point of departure for the HHSE. SAIC's HHSE findings determined that the potential onsite cancer risk and non-cancer health hazard exposure for the three areas as follows: • Area 1 - the total potential cancer risk to a hypothetical resident from oral, dermal, and inhalation exposures to onsite soil was determined to be 3E-06. This level of risk is above the de minimus level of 1 E-06, but is at the lower end of the risk management range of 1 E-6 to 1 E-04: The potential oral, dermal, and inhalation non-cancer health hazards from direct contact exposures to onsite soils for chemicals of potential concern for a hypothetical resident were summed; the non-cancer health hazard was determined to be 0.004 which is below the hazard index of 1. • Area 2 - the total potential cancer risk to a hypothetical resident from oral, dermal, and inhalation exposures to onsite soil was determined to be 9E-07. This level of risk is below the de minimus level of 1 E-06. The potential oral, dermal, and inhalation non-cancer health hazards from direct contact exposures to onsite soils for chemicals of potential concern for.a hypothetical resident were summed; the non-cancer health hazard was determined to be 0.005 which is below the hazard index of 1. • Area 3 - the total potential cancer risk to a hypothetical construction worker from oral, dermal, and inhalation exposures to onsite soil was determined to be 4E-07. This level of risk is below the de minimus level of 1 E-06. The potential oral, dermal, and inhalation non-cancer health hazards from direct contact exposures to onsite soil for chemicals of potential concern by a construction worker were summed; the non-cancer health hazard was determined to be 0.04 which is below the hazard index of 1. The shallow background water quality at the project exceeds State and Federal standards for total dissolved solids (TDS) for some drinking water and agricultural purposes. SAIC concluded the Site groundwater is not likely to be used as a drinking water source. Thus, the