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Fate and Transport Modeling Methods <br /> The RBCA Spreadsheet System contairis a series of fate and transport models for predicting COC <br /> • conceitrattons at the point of exposure (POE) for indirect exposure pathways,such as air and <br /> groundwater. Under Tier 2. relatively simple analytical models are to be employed for this <br /> calaiiation,representing a nunor incremental effort relative to Tier 1.The spreadsheet modeling <br /> system is consistent with Appendix X3 of ASTM E-1739,although selected algorithms and default <br /> parameters have been updated to reflect advances in evaluation methods. <br /> The idealized schematic shown on Figure A.2 illustrates the steps rmcluded in the RSCA software <br /> for predicting transport of contaminants from the source zone to the POE for air and groundwater <br /> exposure pathways.(Please note that POE attenuation E u==and surface water exposure pathways <br /> are tat included to the software at this Bunce See Volume 1,Figure 10)Each element in Figure A2 <br /> represents a step-specific attenuation factor,corresponding to either a cross-anedia tramfer factor <br /> (CM)or a lateral transport factor(LT).The effective NAF value for each COC on each pathway is <br /> then calculated as the arithmetic product of the various attenuation factors occurring along the flow <br /> path from source to receptor. These steady-state NAF values are then used for calculation of <br /> baseline risks and back-calculation of Sete-Specific Target Levels(SSML as discussed in Section A.2 <br /> above.Please note that fate and transport modeling is not required for direct exposure pathways, <br /> such as sod ingestion or dermal contact,where the source and exposum concentrations are equal <br /> (La.. NAF- 1) Analytical models used for conservative estimation of each transport factor are <br /> described below <br /> CROSS-MEDIA TRANSFER FACTORS <br /> Exposure pathways involving transport of COCl from one medium.to another(e.g.,soil-to-air,sod.- <br /> to-groundwater) require estimation of the corresponding cross-meds transfer factor Various <br /> analytical expressions are available for estimating soil-to-atr valattlrzatwn facmrs as a function of site <br /> soil characteristics and the physical/chemical properties of volatile organic COCl. Leaching factors <br /> for organic and inorganic constituent releases from soil to groundwater can similarly be estimated <br /> as a function of COC characteristics, soil conditions,and annual rainfall infiltration. Cross-media <br /> transfer equations incorporated in the RSCA Spreadsheet System are presented in Figure A3 <br /> beginning on Page A-11 Detailed discussion of each of these cross-media factors is provided below <br /> 1 I C=AMVr:3 � R1aI1Ni4 <br /> AY <br /> owt�Sam <br /> �Yaaa <br /> Yaismizown MArlecM Lamlal Ak M <br /> ER�6weM to am ou" ChP Fm=A VFX.FES <br /> aff <br /> Fs-- -- <br /> YF <br /> YaWlYraoole y <br /> 41 FW fine? <br /> 1a4• <br /> saw AdeCted <br /> m mower ant � Faaot IYF��I U'� <br /> --------- -------------- - - - -------------------- ------ ------ <br /> 10 Sel6oearlaeo Ak <br /> am <br /> rw� <br /> vomm emn 3e sas wMyFRan Sins F 'ner2 <br /> ------'- - ----------- - - ----- <br /> MW <br /> GtOlrldwariM- AgaCtad o r:aoon 1AMM Alt I�w q <br /> VF ,an <br /> to amowa aae FaVeaor INFwamot fAOFi ~ A-7 <br /> to <br /> •VaMprtauono�y� SP�s 'A. VF, ? <br /> sp=4 vo�t��� <br /> Fa <br /> alat jVF,Nay at PW <br /> Ww.werwr, <br /> geauiewawo k an.vw sod m u.a�u« LAMM Q,o,�alm LnF x OAF <br /> C -'-Pwoon -------�� m" ------M _K°W_. <br /> aonaa Fw aw iK.n,,,l Fwwr(LOM FWW <br /> ANOCted <br /> Grounowarw G Causal(3tountlwawt wrw OAF <br /> MOM <br /> k1l"Wa am fir aonma w.csr FO�� <br /> at A09 <br /> FIGURE A-L NAF G1lCULATION SCHEMATIC FOR 11,40tRfCT EXPOSURE PATHWAYS IN ROCA <br /> SPREADSHEET SYSTEM <br /> 71 Q A i G.eidopea t�E�Lilaq.[)acc9 Canveaw Aae3aw <br /> aGemmawnscr samees LI&(Grit.1"L AA nim momveS <br />