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v <br /> 1 <br /> A S S O C I A T E S I N C <br /> SB2 and MW1) Analytical results obtained from soil samples were utilized to calculate the upper <br /> 90% confidence limit (UCL) of the mean source concentration The UCL of mean concentrations <br /> 1 of CDCs beneath the site were estimated to be y <br /> Soil <br /> 1 0 0 0025 milligrams per kilogram (mg/kg) benzene, <br /> 0 0 044 mg/kg ethylbenzene, <br />' o 0 057 mg/kg toluene, <br /> 0 0 12 mg/kg total xylenes, and <br /> 0 0 05 mg/kg methyl tertiary butyl ether <br /> 1 Groundwater <br /> 0 0 00064 milligrams per liter (mg/L) benzene, <br /> 0 0 0012 mg/L ethylbenzene, <br /> 0 0 00032 mg/L toluene, <br /> o 0 00063 mg/L total xylenes, and <br /> 0 0 0025 mg/L methyl tertiary butyl ether <br /> Using these concentrations, soil leaching to groundwater, groundwater ingestion, and <br /> outdoor/indoor air pathways for volatilization of soil and groundwater were evaluated When <br /> known, site-specific parameters were used, otherwise conservative default parameters were used <br /> for the remainder of the model input Default target health risk values of 1 OE-6 for Class A & B <br /> and 1 OE-5 for Class C were utilized in the RBCA modeling process <br /> 1 A summary of the parameters utilized is included in Appendix D <br /> Model Output <br /> 1 Under Tier 2, SSTLs for soil leaching to groundwater and soil vapor were determined The <br /> results are presented below in comparison to the representative COC concentrations <br />' Soil <br /> Constituent of Sod Leaching to Indoor Outdoor Representative Required <br /> Concern Groundwater Inhalation Inhalation Concentration CRF <br /> (Resid on site) (Comm on site) (Comm on site) <br />' SSTL m SSTL m SSTL ftMgk� <br /> Benzene 00091 0 005 41 00025 <1 <br /> Ethylbenzene 86 60 >Res 0 044 <1 <br />' Toluene 230 360 >Res 0 057 <1 <br /> Xylenes >Res >Res >Res 0 12 <1 <br /> MTBE 0 78 420 >Res 0 05 <I <br /> Notes >Res indicates the risk-based target concentration Is greater than the constituent residual saturation value(see Tier 2 <br /> Worksheet 9 2,Appendix D) <br /> w 114885`reportslNFA-Rcqucs1 doc 10 <br />