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\..� %Wwl Mr Michael J. Infurna Jr. P.G., S.R.E.H.S. February 14, 2006 Page 4 DISCUSSION The soil profile encountered in all four borings consisted of silt, silt with clay, and clayey silt over a clay layer and a competent, laterally continuous hard pan at 3.3 feet to 3.5 feet bgs. This suggests that the soil profile naturally displays a relatively low permeability which would impede or reduce potential leaching of soil hydrocarbons into the groundwater beneath the Site. The analytical results indicate that TPHd and TPHmo were present in the soil samples collected 2 feet bgs at concentrations that range from 11 to 110 mg/kg. The highest concentrations of both TPHd and TPHmo were reported for sample SB-1/SB-1@2'. To evaluate the potential threat to groundwater posed by these hydrocarbons, SECOR requested that the soluble fraction of TPHd and TPHmo in sample SB-1/SB-1@2' be chemically analyzed. SECOR directed Kiff Analytical to perform the Waste Extraction Test (WET) on sample SB-1/SB-1@2' and to analyze the resulting extract for TPHd and TPHmo. The results of these analyses are shown in Table 1. The soluble fractions of TPHd and TPHmo were not detected at concentrations equal to or greater than method reporting limits. In addition, the TPHd chromatograms suggest the diesel range hydrocarbons do not appear to represent typical diesel fuel, but rather, may be more similar to that of hydrocarbons found in asphalt. CONCLUSIONS AND RECOMMENDATIONS Based on the results presented in Table 1 and discussed above, SECOR presents the following conclusions and makes the following recommendations. TPHd (11 to 33 mg/kg) and TPHmo (50 to 110 mg/kg) are present in the soil samples collected 2 feet bgs where PG&E had formerly used a con-vault to store and dispense diesel and gasoline fuels to fleet vehicles . Soluble fractions of TPHd and TPHmo were not detected at concentrations equal to or greater than the method detection limits in the sample with the highest concentrations, indicating that these hydrocarbons are unlikely to leach into the subsurface and impact the groundwater. The soil profile includes fine-grained soils (silts and clays) and a competent hard pan that appears to be continuous between borings, which further reduces the potential for leaching of the hydrocarbons into the groundwater. Based on the low permeability soil profile and the lack of soluble TPHd and TPHmo fractions, the relatively low concentrations of TPHd and TPHmo measured in the soil samples collected 2 feet bgs do not appear to pose a threat to groundwater at the Site. SECOR recommends that no additional investigation of hydrocarbons in the soil is warranted in the area where PG&E formerly used the con-vault. I:\PG&E\report\Final Phase 11 report.doc