ARCHIVED REPORTS_HUMAN HEALTH SCREENING EVALUATION 2012

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1 Human Health Screening Evaluation US Can—Welty Road March 19,2012 this HHSE. SAIC and others collected 77 soil samples from 55 locations at depths between 0 and 10 feet bgs. These samples were used to evaluate risks and hazards from exposure to COPCs in soil. Detection limits in the soil samples ranged from 0.0003 to 6 mg/kg. SAIC and others collected 35 groundwater samples from 35 borings and monitoring wells to evaluate risks and hazards from BTEX and PAHs. Detection limits in the groundwater samples ranged from 0.0050 to 1,000 micrograms per liter. SAIC performed this HHSE after the Central Valley RWQCB was satisfied that the Site had been adequately characterized. Consequently,uncertainties in this HHSE were reduced to an acceptable level. The on-site soil and groundwater impacts are believed to be well characterized; therefore, EPCs were evaluated as the UCL of the mean soil concentration for each COPC evaluated in this HHSE. The UCL is a conservative estimate of the mean concentration, and is unlikely to lead to underestimation of exposure concentrations. However, when the detection frequency is very low(less than four to five percent), it may not be possible to calculate a UCL. SAIC used the sample median as the EPC in these cases, as recommended by the ProUCL guidance. The sample median was used as the EPC for benzene, acenaphthene, benzo(k)fluoranthene ,dibenz(a,h)anthracene, and indeno(1,2,3-cd)pyrene in this evaluation. The cancer risks for benzene,benzo(k)fluoranthene, dibenz(a,h)anthracene, and indeno(1,2,3-cd)pyrene in on-site soils were estimated at 2.0E-09, 3.5E-09, 1.2E-08, and 3.5E-09,respectively. Acenaphthene is not a carcinogen; and the non-cancer hazard index associated with acenaphthene in on-site soils was estimated at 3.6-07. Although the uncertainty associated with use of the sample median to represent an EPC is high,benzene, acenaphthene, benzo(k)fluoranthene, dibenz(a,h)anthracene, and indeno(1.2.3-cd)pyrene are insignificant contributors to human health effects at the Site; therefore, the use of the sample median does not affect the conclusions of this HHSE. Results from several samples collected during investigations conducted between 1995 and 1998 were not used in preparation of this HHSE. Sample locations from the 1995 investigation were chosen in support of an investigation of VOCs stored at the Hunter Container facility. The samples were collected primarily from the ground surface to assess a surface spill. The ' HPP-BTR pipelines were buried several feet below grade. Analytical results from several samples were omitted from this HHSE because the detection limits of`non-detect' results were not listed in the parent report. Eliminating these data did not affect the HHSE results or conclusions. The on-site groundwater impacts are also believed to be well characterized; however, there is a large degree of uncertainty associated with evaluating vapor intrusion from groundwater with regards to future buildings at the Site. Future buildings may alter the conditions of the subsurface. The quality of the building materials and construction may also have a significant 1 and unpredictable impact on the potential for vapor intrusion at the Site. SAIC used the most conservative assumptions and EPCs to evaluate risks and hazards from exposure to on-site groundwater for these reasons. SAIC selected the maximum detected value of each COPC in on-site groundwater to be the EPC, as recommended in the Vapor Intrusion Guidance, which is unlikely to lead to underestimation of exposure concentrations. SAIC did not include groundwater sample results from GMX-6, as Geomatrix determined that the presence of benzene and naphthalene at this location is likely due to an off-site source(Geomatrix, 2000). 13 SAIE 1