SITE INFORMATION AND CORRESPONDENCE

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Human Health Screening Evaluation Former Vernalis Pump Station September 2,2010 The evaluation of risk associated with the soil-exposure pathways is limited to the upper 10 feet of on-site soils, consistent with the on-site residential land-use scenario as described in the PEA Guidance Manual. Only analytical results from soil samples collected between 0 and 10 feet bgs are included in this HHSE (Tables 1 and 2). Groundwater samples were also collected and analyzed for constituents of potential concern (COPCs) during previous site characterization studies and during groundwater monitoring activities. The analytical results for benzene,toluene, ethylbenzene, and total xylenes (BTEX); and polynuclear aromatic hydrocarbons (PAHs) for all groundwater samples are provided in Tables 3 and 4, respectively. A sample from an existing water-supply well at the site did not contain site-related COPCs at or above laboratory reporting limits. Total dissolved solids (TDS) concentrations in shallow groundwater samples collected at the site ranged from 1,220 milligrams per liter(mg/L)to 1,390 mg/L (see Table 5), which exceed three or more of the following current California Department of Public Health(CDPH) maximum contaminant levels (MCLS; CDPH, 2004) and Central Valley RWQCB Water Quality Goals (WQG; Central Valley RWQCB, 2000) for drinking water: • CDPH MCL: 500 mg/L, recommended; 1,000 mg/L, upper; 1,500 mg/L, short term. • Central Valley RWQCB WQG, CDPH, and EPA drinking water standards: 500 mg/L. • Central Valley RWQCB WQG, Agricultural Water Quality Goal: 450 mg/L. • Central Valley RWQCB WQG, EPA Ambient Water Quality Criteria for Taste and Odor or Welfare: 250 mg/L. A sample from an existing water-supply well at the site also exceeded two of the above standards; however, the well is likely screened in a deeper water-bearing zone, and is thus beyond the scope of this evaluation. The affected shallow groundwater on site exceeds State of California and federal TDS standards for drinking water as well as agricultural-use criteria; as a result, the shallow groundwater at this site is not likely to be used as a drinking-water source. For these reasons, SAIC-Benham considered the groundwater exposure route incomplete and was not evaluated quantitatively(see Figure 3). Volatile compounds, including benzene, toluene, acenaphthene, fluorene, and naphthalene, were detected in groundwater samples at relatively low concentrations (Tables 3 and 4). Several semi- volatile compounds were also detected in groundwater at low concentrations (Table 4). While vapor intrusion of volatile and semi-volatile chemicals from groundwater to indoor air is possible, potential risks associated with this pathway are not expected to be significant due to the low concentrations of these chemicals in groundwater at the site. SAIC-Benham did not quantitatively evaluate the vapor intrusion pathway for this reason. 3 � The Benham Companies,LLC A Wholly Owned Subsidiary From S mxt to Sotanwls