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1 September 30, 1999 Harding Lawson Associates 47491 1 Margaret Lagono, Supervising REHS San Joaquin County Public Health Services Environmental Health Division Page 6 a vertical thickness of impacted soil of approximately 7 feet Therefore, the lateral extent of approximately 350 square feet and the vertical thickness of 7 feet yields an volume of approximately 90 cubic yards Assuming a ' weight of 3,000 pounds per cubic yards, this is approximately 270,000 pounds or 122,725 kilograms Assuming an average concentration of 250 mg/kg in the remaining impacted soil this is an approximate TPHd mass of 30 7 kilograms, or approximately 9 7 gallons of diesel ' SUMMARY AND CONCLUSIONS ' This letter report provides additional information in support of no further action at the Newark facility These data were requested by PHS/EHD in their correspondence to Newark dated February 25, 1999 The PHS/EI-1D request was issued following HLA's submission on December 22, 1998 of the reports entitled Closure Report 210,000-gallon UST Removal Project and Summary Report Limited Phase II Investigation, Courtyard Tanks and Sump,which presented results of environmental investigations in two areas within the Newark facility Courtyard Tanks and Sump Presented above are calculations of the remaining contaminant mass in impacted soils In summary,the remaining TPHd mass near the courtyard tanks and sump is approximately 215 kilograms, or approximately 68 gallons of diesel As discussed in detail in HLA's Summary Report(HLA, 1998c), analytical data, with normal reporting limits, collected from the courtyard soil sample with the highest TPHd concentration • Did not contain detectable concentrations of benzene, O Did not contain detectable concentrations of any of the PAH analytes, and • Did not contain detectable concentrations of soluble TPHd These data, and those cited above and in HLA's Summary Report(HLA, 1998c) strongly support the ' conclusion that the remaining impacted soils do not pose a threat to groundwater quality Former 210,000-Gallon UST As presented in detail above, the remaining TPHd mass at the former 210,000 gallon UST location totals approximately 31 kilograms, or 10 gallons of diesel As discussed in detail in HLA's Closure Report, 210,000-gallon UST Removal Project(HLA, 1998b), the following information was presented • The remaining impacted soils do not contain detectable concentrations of BTEX P • Soluble analyses on six soil samples with TPHd concentrations up to 8,100 mg/kg show that these soils do not contain detectable concentrations of soluble TPHd , and therefore do not pose a potential threat to groundwater quality ' These data, and those presented above and in HLA's Closure Report(HLA, 1998b) strongly support the conclusion that the remaining impacted soils do not pose a threat to groundwater quality 1