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1 %TC A S S O C I A T E S .I N C . applicable risk limits at potential points of exposure. The software uses simple analytical.models in:copiunction with additional,site data to calculate Tier 2 SSTLs in a manner consistent with the ASTM standard. Model Input As described above there does not appear to be an complete athwa s at the subject site. The - ,. PP Y P -pathways J U only secondary sources are 1) the subsurface-soil which may lead to soil leaching to groundwater or volatilization from subsurface-soil to:outdoor or indoor air and 2) the dissolved groundwater plume which may lead to groundwater ingestion or volatilization to outdoor or indoor air-. Constituents of Concern According to the ASTM standard, TPH is not .to be .modeled when performing a RBCA evaluation. The following.000s were therefore identified for the site: , • . benzene; L? • ethylbenzene; { • toluene; and �"'� • total xylenes; and • methyl`tertiary butyl ether. Representative COC soil concentrations.of the source zone were calculated using soil analytical data from only soil borings advanced within the delineated zone of contamination (borings SP-1 and MWi). Analytical results obtained from soil samples were utilized to calculate the upper 90% confidence limit (UCL)of the mean source concentration. The UCL-of mean-concentrations of CDCs beneath the-site were estimated to-be: Soil • 0.0085-milligrams per kilogram(mg/kg)benzene; • 0.14 mg/kg ethylbenzene; • 0.12 mg/kg toluene; • 0.3 mg/kg total xylenes and L • 0.029 mg/kg methyl tertiary butyl'ether. Groundwater L • 0.041 milligrams per liter(mg/L)benzene; • 0.0032 mg/L ethylbenzene; • 0.015 mg/L toluene; L • 0.064 mg/L total xylenes; and l • 0.052 mg/L methyl tertiary-butyl ether. 4 L w:\62574.05VcporU\cloawrrFS3.dac 9