SITE INFORMATION AND CORRESPONDENCE

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M. Scott Mansholt - 3 - • 26 March 2008 990 Beechnut-Tracy The report states that analytical results for the onsite soil samples were evaluated in a two- tiered process; the first tier used a conservative site-wide risk approach by comparing maximum detected chemical concentrations to direct contact ESLs for residential receptors and commercial/industrial workers, respectively. The soil concentrations were converted to equivalent soil vapor concentrations, which were then compared to residential and commercial/industrial soil vapor ESLs for vapor intrusion concerns. In the second tier, chemical concentrations were compared to ESLs on a sample-by-sample basis; Geomatrix indicated this risk evaluation process identifies areas of concern and can be used to help identify locations that need further evaluation. Thus, Geomatrix's report stated that the sum of the ratios of the detected concentrations relative to the ESLs represents a conservative estimate of the cancer risk or the hazard index. The U. S. EPA and other agencies generally believe and have reported this approach overestimates the potential for non-carcinogenic health affects due to simultaneous exposures to multiple chemicals because it does not account for different toxic end points. However, Geomatrix states this approach can be used as a screening tool to rapidly identify those exposure scenarios for which exposure to multiple chemicals does not pose a non- carcinogenic health risk. The maximum concentrations are not present at the same exposure point and a potential receptor will not be exposed to all maximum onsite COPCs at the same time. According to the State of California Fish and Game Natural Diversity Database, 2007, no endangered, threatened, or sensitive species identified by state or federal agencies were located within one-half mile radius of the site. The review concluded that the site is located in an urbanized area of Tracy, consisting primarily of commercial/industrial properties, residencies to the west. Therefore, according to the database that due to lack of sensitive species in the immediate vicinity of the site, no ecological risks were identified or evaluated. Based on the Screening Health Risk Assessment, using the tier-one evaluation approach, the Geomatrix report identified six separate onsite boring/sampling locations where: • Elevated concentrations of TPH compounds with an unacceptable cancer risk, include carcinogenic PAHs via direct contact to soil, and naphthalene and ethylbenzene via inhalation exposures to indoor air; • Direct dermal contact with TPH as crude oil in soil was the primary chemical contributing to exceeding the cumulative hazard index of 1 .0; • Results exceed the total theoretical estimated lifetime cancer risk and hazard index for direct contact of COPCs in soil by residents; and, the total theoretical estimated cancer risk and hazard index for vapor intrusion exceeds the COPCs for residents; and, • The results exceed the total theoretical estimated lifetime cancer risk and hazard index for direct contact in soil of COPCs by commercial/industrial workers; and, the total theoretical estimated cancer risk and hazard index for vapor intrusion exceeds the COPCs for commercial/industrial workers.