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Soil and Groundwater Investigation Report Vernalis Pump Station August 2006 SAIC identified a total of four water supply wells within the %2-mile search area. One domestic well and two public wells were located at the site within the area of concern. The well completion reports indicate the domestic well was constructed with a minimum sanitary seal of 50 feet bgs. The public wells were constructed with minimum sanitary seals of 150 feet bgs and 200 feet bgs,respectively. The fourth supply well is an irrigation well located up gradient of the area of concern. The well completion report indicates that this well was constructed with a minimum sanitary seal of 60 feet bgs. SAIC also identified six monitoring wells and one groundwater-extraction well located within the %2-mile search radius. These wells are located on the Western Farm Service property,which is diagonally opposite the Bellini property's northern tip at the intersection of Welty Road and Highway 33. A summary of the water supply well search results is presented in Table 1. Approximate locations of the water supply wells are shown on Figure 1. 4.3 SOIL ANALYTICAL RESULTS For decision-making purposes, laboratory analytical results were compared to"action levels,"or concentrations above which further evaluation to define the extent of affected soil and groundwater is appropriate. Soil action levels are the EPA Region 9 PRGs for direct residential exposure through ingestion, dermal contact, and inhalation pathways. PRGs are risk-based tools for evaluating sites that combine current human health toxicity values with standard exposure factors, in order to estimate contaminant concentrations in environmental media(soil, air, and water)that are considered by the EPA to be protective of humans over a lifetime. Summarized in Tables 2 and 3 are the soil sample analytical results for the constituents of concern and the EPA Region 9 PRGs against which they were compared to assess whether any further characterization is appropriate. A map of soil sample analytical results is provided on Figure 3. Copies of the soil sample laboratory analytical reports are included in Appendix C, along with a data usability discussion. No soil sample analytical result collected during this investigation was greater than a PRG action level. Although eight different PAHs were detected in samples collected from the surface (i.e., 1 foot bgs) of borings SB-22, SB-23, SB-24, and SB-25,no concentration exceeded a PRG. Furthermore,no BTEX constituent was detected in any soil sample. TPHc levels of 330 mg/kg and 380 mg/kg were detected in the samples collected from 1 foot bgs at SB-22 and SB-23. However,the low levels of TPHc (and PAHs) in these shallow soil samples,as in all the surface samples containing PAHs,are likely attributable to surface spills of petroleum hydrocarbons from former site operations at SB-22 or from an unknown source off site at SB-23. Moreover,plausible sources of surface impacts off site at SB-23 do not include the OVP or TAOC pipeline, since they were buried several feet beneath the ground surface, and no TPHc, BTEX, or PAHs were found below a depth of 1 foot bgs. Based on SAIC's evaluation of the data collected during this investigation and previous investigations, the source area of affected soil at the boiler house and pump house is encircled by borings with no constituent of concern at levels exceeding the PRGs. Therefore,the lateral extent of affected soil associated is defined in the immediate vicinity of the boiler house and pump house, centered on monitoring well MW-1. 4.4 GROUNDWATER ANALYTICAL RESULTS Groundwater sample analytical results were compared to the RWQCB WQOs provided in the memorandum entitled Beneficial Use-Protective Water Quality Limits for Components of Petroleum- Based Fuels(RWQCB,2004). WQOs are used for the protection of existing or potential sources of drinking water. The WQOs include Chemical Constituents(which requires compliance with California ANNE 5 From Science to Solutions-