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0 <br /> 302 PETPEUM CONTAMINATED SOILS ESTIMATES FOR NYR • <br /> RDCAR$ON VAPOR EMISSIONS 303 <br /> vaporyenussions and C,V a is the vapor concentration of species i in equillbr ttm with the containt- <br /> i A A � nant/sod matrix,and as discussed is given by Equation 4 Experimentally meas <br /> WindIt t t h) t ured D,° values aro available in the literature for many compounds of interest, <br /> they can also be predicted reliably from kinetic theory formulas 10 The soluttaii <br /> t <br /> ���� $f 4�' .< aVz}�<j f.f7 x}•}=f. to Equation 5 is <br /> Jil A A A h <br /> Ja�+\+a J\ \ a ♦ \ \ ♦ \ ■ \ . \ \ \ . \ \ l z <br /> \ C ■/i Z � \ 1—H nor exp }� slit(itirzrH) 47) <br /> / / / / ! 1 / ! / / r J / I / / J 1 M l ► i f 2 I <br /> vapor emissions • • \ \ . \ ♦ a \ \ • a \ \ • • <br /> ■ a a \ • \ ♦ � <br /> ■Jar\Ja/�■r\ • \ ■ ♦ \ ♦ a \ ■ \ • a \ a • ♦ ■ • <br /> %J J • + / r J J ! / / / • r r / / <br /> Tank Pit rr ♦ + rrJJ ! r r l + rJ r ! <br /> aJaJ\J■J\�/\ \i r Ja/\!•J\r•J\r■/ai Ja/\r/iaJa and the corresponding vapor fiux, 1p,i, from the pit is <br /> i♦/ar■/a/a/ r }i4� �}�; lnixr�t, } � ♦ a ♦ ♦ \ \ ♦ a ■ . \ • . \ a • <br /> I • / / I �s<�'�i e�ix�Ff 1'F Yxrxa`�1� J■'\!•+\�% \J■J•r\/■raJ•/■/\J\ <br /> a J■/\/a Jti� t z ai `' �x 14} �y��` J r ! J r r J r r r r f r + <br /> ■J■ a ■ � �Yz��r.fixa; f�s "Ax7Y}/.t+J�rIJ/, l+/ er! JJ r lJ ! +al aJ.!• c7 ©l�y <br /> ti_- ^P0 exp 1 ' Gl/ J ! rrJ ! . <br /> % <br /> I J I J IM —tt7Nr, <br /> V <br /> � <br /> ■J\ sa ■ a 1 a ■ ■ 1 a • a \ <br /> } The maximum vapor flux, gp,i,,,asi► occurs at steady state (t-->at) <br /> ...,-- Soluble Groundwater Plunte _D, (9) <br /> (9) <br /> H <br /> Groundwater Flow <br /> IF(gure s Sources of Qmissiorts during excavation Note that the assumptions used in this model(nondiminishing source,zero con- <br /> ' centration boundary condition) lead to conservative emissions estimates Emis <br /> We can estimate emissions from an excavated pit by assuming that vapor trans- sions during excavation may be higher than those predicted by Equation 9 due <br /> port is limited by diffusion upwards from the pit bottom through a quasi-stagnant to the mixing within the pit induced by digging machinery For most cases, <br /> layer of air At ground surface the vaptms are Swcpt awry by the w ind For this however, Equation 9 should provide a good estimate of(he average emission\ <br /> situation, the vapor flux in tike pit can be obtained a\a solution to the diffusion during the excavation and tank replacement stage <br /> equation. 112h Emissions Associated with Exposed Piles of Contaminated Sotf <br /> ac,v_ alc,. <br /> —Do1 ? ) Estimating emissions from an excavated pile of contaminated soil requirt.s a <br /> at az more complex analysis When fresh coniamioated soil is placed on the pile,volatih <br /> subject to the following boundary and initial conditions zation occurs rapidly frorn the soil layers on the outside of(he pile As layers <br /> of soil near the surface dry out,the .apor emission matte decreases because vapors <br /> 0 must diffuse through a longer path to reach the atmosphere For this process <br /> C„ = 0 z (6) <br /> ci, ` C."q Z 0 Lf at at ay ., ay <br /> where. <br /> where— <br /> C,,, = vapor phase concentration of species i <br /> t = tune CA = air filled void fraction in soil <br /> z = distance above the pit bottom = sail bulk densit} <br /> H = depth of excavation t = time <br /> Q,° = vapor phase molecular diffusion coefficietit in air =ciTetitive pcimuS media vapor diffusion coefficient for specits i <br />