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Soil and Groundwater Investigation Report Catellus Property September 2006 4.4 GROUNDWATER ANALYTICAL RESULTS Summarized in Tables 4 and 5 are the groundwater sample analytical results and the ESLs and WQOs to which they were compared to assess the presence of affected groundwater and whether any further groundwater characterization is appropriate. Maps presenting the concentrations of dissolved constituents of concern in groundwater are provided on Figures 4a and 4b. Copies of the groundwater sample laboratory analytical reports are included in Appendix E. 5. DISCUSSION OF PETROLEUM DISTRIBUTION 5.1 EXTENT OF AFFECTED SOIL For delineation purposes,soil sample analytical results were compared to the PRGs presented in the U.S. EPA Region 9 PRGs Table(U.S. EPA,2004)and the ESLs provided in the document titled Screening for Environmental Concerns at Sites with Contaminated Soil and Groundwater(Interim Final) (RWQCB, 2005). PRGs and ESLs are tools for initial,screening-level evaluations of analytical results. The PRGs and ESLs are based on standard exposure factors, in order to estimate contaminant concentrations in soil, air,and water that are considered to be protective of humans over a lifetime;they are calculated without site-specific information. The lowest, most conservative PRG or ESL constituent concentration was used. Soil sample analytical results obtained during this investigation were less than PRGs and ESLs,with the following exceptions: • TPHc was detected in borings SB-6(2,200 mg/kg), SB-15 (890 mg/kg),and SB-20(2,300 mg/kg). Additionally,the PAHs benzo(a)pyrene and naphthalene were reported for S13-5 (0.060 mg/kg and 1.4 mg/kg), and benzo(a)pyrene alone was detected in SB-6(0.040 mg/kg)and SB-15 (0.070 mg/kg). However,the lateral extent of affected soil in these borings is defined by several encircling borings. • TPHc and benzene were detected in boring SB-8 (17,000 mg/kg and 0.64 mg/kg),as were the PAHs anthracene(5.6 mg/kg),benzo(a)anthracene(1.2 mg/kg),benzo(a)pyrene(0.67 mg/kg), naphthalene(11 mg/kg),and phenanthrene(18 mg/kg). In the area of S13-8,there is apparently a source area of affected vadose zone soil. Above the water table at 9 feet bgs,benzene is present,and PAH concentrations are an order of magnitude above PRGs and ESLs. Although the lateral extent of affected soil in SB-8 is defined by encircling borings,the elevated concentrations of constituents of concern in soil warrant further investigation in this area. Since the groundwater level in borings S13-6, SB-15,and SB-20 was at or above the depth at which the affected soil samples were collected,the presence of dissolved crude-oil constituents is most likely due to groundwater transport. Therefore,the results are not indicative of a source area release into vadose zone soil. The vertical extent of affected soil was defined in all but boring S13-20,which in the sample collected at 21.5 feet bgs still contained TPHc at a concentration of 2,300 mg/kg, well above the ESL for TPHc of 500 mg/kg. However,no PAH or BTEX were detected in this sample. For more information regarding the delineation of affected soil,refer to the Appendix F,Affected Soil and Groundwater Delineation Worksheet. 5.2 EXTENT OF AFFECTED GROUNDWATER For contaminant delineation purposes, groundwater sample analytical results were compared to the ESLs and the 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 5 From Science to Solutions-