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December 22, 1998 Harding Lawson Associates 4034405 Margaret Lagorio, Supervising REHS San Joaquin County Public Health Services Environmental Health Division Page 6 concentrations will not exceed RBSLs in the future) then no remediation is warranted at the level of risk associated with the RBSLs The results of HLA's RBCA evaluation for this site are presented below ' RESULTS OF INVESTIGATION 1 Subsurface Conditions- Soil Profile Boring logs are presented in Plates 4, 5, and 6 As presented in the boring logs, the upper 12 feet of soils consists of brown to dark gray clay, silty clay, and clayey silt The dark gray and dark grayish brown colors were associated with TPH-impacted soils Beneath the uppei clay-rich horizon were brown clayey silt in boring SB-1 and brown clayey fine-grained sand in boring SB-2 Saturated soils were first encountered in the 20 0 foot soil samples and static water levels rose to approximately 16 feet in borehole SB-1 Blow counts are recorded on the boiing logs presented in Plates 5 and 6 IAnalytical Results- Soil Samples Analytical results from six soil samples are listed in Table 1 Sample selection was based on the depth distribution of impacted soil encountered in previous borings, the objective of assessing the vertical extent of impacted soil near the source, and subjective field criteria including odors, discoloration, and PID readings These field criteria are recorded on the boring logs presented in Plates 5 and 6 Sample nomenclature indicates the boring number and depth of the sample (e g , SB-1-5 0 indicates the 5 0-foot sample from boring number SB-1) Three samples (SB-1-5 0, SB-1-10 0, and SB-1-15 0) from boring SB-1 exhibited subjective hydrocarbon odors (slight to moderate) and the same three samples exhibited elevated PID readings (0 8 to 9 0 ppm) None of the samples from SB-2 exhibited subjective hydrocarbon odors or elevated PID readings TPHd was detected in four samples and TPHmo was detected in three of the six samples submitted for ` analyses Maximum TPHd and TPHmo concentrations of 1,900 mg/kg and 1,500 mg/kg, respectively, were detected in sample SB-1-10 0 In boring SB-1, TPHd concentrations ranged from 120 mg/kg to 1,900 mg/kg and TPHmo concentrations ranged from 600 to 1,500 mg/kg Benzene was not detected above ' normal reporting limits of 0 0050 mglkg in any of the soil samples Toluene, ethylbenzene, and total xylenes were detected in two (SB-1-5 0, SB-1-10 0) of the six samples at maximum concentrations of 0 1 mg/kg, 0 011 mg/kg, and 0 019 mg/kg, respectively In boring SB-2, with the exception 2 0 mg/kg of TPHd ' detected in the 15 0 foot sample, TPHd, TPHmo, and BTEX were not detected in either sample Sample SB-1-10 0, which possessed the maximum detected concentrations of TPHd and TPHmo, was analyzed for the soluble fractions of TPHd, TPHmo, and BTEX using the appropriate methodology and 1 deionized water as the leaching liquid Soluble TPHd, TPHmo, and BTEX were not detected above the normal respective method reporting limits Sample S13-1-10 0, with the maximum detected concentrations of TPH was also analyzed for PAHs None of the PAH analytes were detected above the normal respective method reporting limits ' ti