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#. ( v <br /> ! ATC <br /> A S S O C I A T E S I NC <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. An overall target health risk value of 1.0E-5 was utilized in <br /> the RBCA modeling process. <br /> A summary of the parameters utilized is included in Appendix C. <br /> Model Output <br /> V <br /> 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 /> #: ate .......... Svc. 1 .......:.:.:.:. ::.:::::.:: ± sr::::,,,:,. ............................ ... <br /> ..................................................,...........:.:.:..:::_:::::. .......::::::::. <br /> ..::::::::::::::::' ►:::::::::::::::::::.Iltti�a ►:::;::;::;::>;:Y # :::::::::.Ylr►ihAixt ►:>::>::>::>:: r :«<:::<:»: <br /> .............. <br /> E. .. .:....t...........,.?t ... ............................;.;..................................:.:..,..............................................................................,....................... <br /> �•s{ :.........p. <br /> :.......:;;::;,ttttttt;;•:;-: ..#...... � .:::.;:.:1tifl <br /> :t,........ <br /> •:....>:..:..:....:..............::::.t>:;•t� <br /> . . . : <br /> : <br /> �ppt�s. �, .;,;.:.:;,.:+;;:SS:`:;::;.r;;;;t;.................. <br /> Benzene >Res 0.52 0.13 320 450 0.0085 <1 <br /> Etbylbenzene >Res >Res 130 >Res >Res 0.14 <1 <br /> Toluene >Res >Res 51 >Res >Res 0.12 <1 <br /> Xylenes >Res >Res >Res >Res >Res 0.3 <1 <br /> L MTBE >Res 3.7 430 >Res >Res 0.029 <1 <br /> Notes: >Res indicates the risk-based target concentration is greater than the constituent residual saturation value(see Tier 2 Worksheet 9.2, <br /> Appendix C). <br /> Groundwater <br /> er : -:;PA a <br /> . d :::::: tuor :....�.7....... <br /> d <br /> . ... .;. : : � :::.:..::::bill tF;;:.;..:>::uafi # .. <br /> « :Calfa► s» ':>`':>>': v » »» <br /> �.. <br /> ::::.:::.::::.... :. <br /> S ' ....1 :. ............t3............... ........ <br /> Benzene >Sol 0.029 2.0 >Sol 0.041 1.0 <br /> Ethylbenzene >Sol 10 >Sol >Sol 0.0032 <1 <br /> Toluene >Sol 20 >Sol >Sol 0.015 <1 <br /> b— Xylenes >Sol >Sol >Sol >Sol 0.064 <1 <br /> MTBE >Sol 51 4,700 >Sol 0.052 <1 <br /> Notes: >Sol indicates the risk-based target concentration is greater than the constituent solubility value(see Tier 2 Worksheet 9.3,Appendix C). <br /> v <br /> When the COC's representative concentration is greater than the calculated SSTL, this indicates <br /> that the selected target level has been exceeded. As shown in the above table, the representative <br /> concentration of benzene was above its respective SSTL of 0.029 mg/L (groundwater ingestion <br /> on site). For benzene to fall below the SSTL value of 0.029 mg/kg, the representative <br /> r <br /> w:\62574.05\reports\closure-FS3.doc 10 <br /> a.. <br />