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1 December 22, 1998 Harding Lawson Associates 4034405 Margaret Lagorio, Supervising RENS San Joaquin County Public Health Services Environmental Health Division ' Page 9 samples from boring SB-1 but were not encountered in the 20 foot sample TPHd and TPHmo concentrations ranged from 120 mg/kg to 1,900 mg/kg and from 600 to 1,500 mg/kg, respectively The maximum TPHd and TPHmo concentrations both occurred in the 10-foot sample These data indicate that near the source impacted soil extends to depths of at least 15 feet bgs but were not detected in the sample from 20 feet bgs Another objective, was to further assess the lateral extent of soil contamination Cross-sectional views of the vertical and lateral and vertical extent of TPHd-impacted soil are shown in Plates 7 and 8 Courtyard walls are present in close proximity 6 5 feet wost and 4 feet south of the sumps and USTs The basement ' walls extend to depths of at least 10 to 15 feet based on available information These walls constrain the lateral extent to the east and south of the USTs/sump location The northerly ' extent of impacted soil is constrained by boring NSA-3, neither sample from NSA-3 contained detectable TPHd The lateral extent to the east is constrained by boring SB-2, none of the samples from SB-2 exhibited subjective hydrocarbon odors or elevated PID readings With the exception 2 0 mglkg of TPHd detected in the 15 0 foot sample (repotting limit of 1 0 mg(kg), TPHd, TP1Imo, and BTEX were not detected in either sample from boring SB-2 Therefore, the vertical and lateral extent of impacted soil have been determined To assess the potential threat to groundwater quality from the impacted soils, sample SB-1-10 0, which possessed the maximum concentrations of TPHd and 1 PHmo, was analyzed for the soluble fractions of TPHd, TPHmo, and BTEX using the appropriate methodology and deionized water as the leaching liquid No detectable soluble TPHd, TPHmo,benzene, ethylbenzene, or total xylenes were reported in the ' leachate (Table 1) Although 5 3 ug/L of toluene (reporting limit 5 0 ug/L) was detected in the leachate, this is less than the USEPA primary maximum contaminant limit (MCL) for toluene of 1,000 ug/L and the CAL-EPA primary MCL of 150 ug/L These soluble data indicate the remaining impacted soils do not threaten groundwater quality Additional soluble data collected during the removal of the 210,000-gallon, # six fuel UST formerly located in the southeast corner of the Site (Plate 2), corroborate the above conclusion (Table 3) Six soil samples with concentrations of TPHd and TPHmo ranging from 230 to 8,100 mg/kg and from 540 to 9,600 mg/kg, respectively, were analyzed for soluble fractions of TPHd and TPHmo with the WET procedure using deionized water and silica gel filtration of the extract These six samples were of similar soil types (clayey silt/silty clay) to those encountered is the courtyard and collected at similar depths (8 5 to 11 0 feet bgs) No detectable concentrations of soluble TPHd or TPHmo were reported for any of these samples These soluble data and the soluble data from the courtyard strongly support the conclusion that rthe remaining impacted soils do not threaten groundwater quality Some residual fuels contain PAHs which include some carcinogenic compounds To assess potential threat to health and safety from the remaining impacted soils, the sample containing the highest I concentration of TPH (SB-1-10 0) was also analyzed for PAHs None of the PAH analytes were detected above the normal respective method reporting limits Therefore, the remaining impacted soils do not contain PAHs and therefore do not pose a potential threat to health and safety associated with PAHs ' The work plan indicated that, if groundwater was encountered in boring SB-1 near the sump, a . groundwater grab sample would be collected rhe analyses of the Hydropunch groundwater sample from boring SB-1 would suggest that, although no BTEX was detected, groundwater near the source may be ' impacted with TPHd and TPHmo However, these data are suspect Considering that the 20-foot soil r ��