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<br /> 324 PETROLEUM CONTAMINATED SOJLS ESTIMATES FOR HYDROCARBON VAPOR EMISSIONS 325
<br /> Sceriado 12 A benzene emission rate of 109 g!d for an air-chipper treating equivalent 70-y average vapor concentrations are also presented for each scenario
<br /> groundwater containing 1 ppm baizene at a throughput rate of 761 Jinin(20 gpm) Based on these values, the only 70-y average vapor concentration >0 12 p:glml
<br /> The air flowrate through the stripper is 5660 I.rmin (200 SCFM) is due to the emissions from contaminated soils left in place(0 94 jig/W) II is
<br /> important to nate, however, that these predictions correspond to the most con-
<br /> IV 21 Emissions from Buried Gasoline-Corrraminated Sods servalwe assurnFlions(uncovered,permeable soils, noudunuushing source),and
<br /> a specific depth to-contamination It should be clear that for other soil types, sur-
<br /> In kill Ig benzene emission estimates for gasoline-contaminated soils left in- face covers, and contamination depths, the predicted aboveground vapor con-
<br /> place were calculated and preserved in Figure 13 For the air dispersion niodel- eentrahons will be lovA enough so as to not pose a significant health risk For
<br /> rag, the following situation was selected this reason, future cleanup criteria should be influenoW by site-specific environ-
<br /> mental risk assessments, which evaluate all significant migration pathways and
<br /> Scenario 13. THecase of a nondirninishing gasoline source containing I mole the potential Impacl an people and the environment
<br /> % benzene at 20°C located 5 tit below ground surface The soil is homogeneous tri summary,models have been presented for estimating the Hydrocarbon vapor
<br /> and there is no low permeability surface cover (i e , paving, clay liner)- emissions for typical service stalion remediation operations A range of example
<br /> scenarios was presented in the text, emission rates were calculated, and air-
<br /> 1V.3 "Box Model" Predictions dispersion models were used to calculate the corresponding vapor concentrations
<br /> rn nearb3 communilies It is important to remember that these models incorporate
<br /> As mentioned above,the box imodel was used to calculate ambient vapor con- conservative assumptions and are intended for use as screening tools to deter-
<br /> cenlrations close to the source Maximum vapor concetiirdttow, will be encoun- mine %Nether the emission rates or local vapor concentrations are potentially
<br /> tered an the downwind edge of an area source,and for the purpose of generating "large"or"small"as compared to values specified in regulatory requirements
<br /> very Conservative exposures, we will assume that a receptor rs located at this
<br /> downwind edge For(fie sample calculations a 2 2 m1s(5 mph) wind speed and
<br /> a 2 m box height were used The length, L, of the source in the windward since- REFERENCES
<br /> tion was taken to be the greatest "edge" length of the source For example,
<br /> 1.= 12 2 m for the excavated pit, and L=6 1 in for the contaminated soil pile I Clucu, G T, and T D Shoup '`Seal Sorption of Organo Vapors and Efti tc of
<br /> Vftlues were not computed for the slacl, sources(air-stripper,Boil veining),bocduw Humidity on Sorptne Mectidnism and Capacity," Environ Sri Technol, 19
<br /> circ feet 111111 this model is not appropriate fol such ceiurces The "Nix model" 1196 1200, 1985
<br /> predictions are listed in 1 able 3 for compdrison with the results fiorn the 1SC 2 Spencer W F Dvz[r hunon of Peehcidcc Between Soil, Witter,and Air, Pcstic rites
<br /> model As expected, the bo),model predictions are always greater than the ISC In the Sod Ecxrlogy,Dcgradation,and Movement,"Michigan State University, Last
<br /> Lansing, Mtchigtin, 1970
<br /> model predictions listed to '1sUle 3 3 Poe,S H , K IF Valsaral, 1 J Thitwdeaux,did C Springer "Equilibnunt Vapor
<br /> !'base Adsarplxin of Volatile Organic Chernicahc an Dry Soils,"J Hazard Mar
<br /> 19, 17 32, 1998
<br /> V EXPOSURE CALCULATIONS AND CONCLUSIONS 4 VaNaraJ,K T ,and L J Thibodeaux ' 13quilibrium Adsorption of Chentical Vapors
<br /> on Surlace Sods, l mditlls,and Landfarnis—A Review,"J Hazard Afar , 19,79-99
<br /> The vapor concenlratlons Meted in fable 3 can he combined with a breathing 1988
<br /> rate, body weight, duration of exposure, and potency factor to predict the adds- 5 Brauner, S , P It Emmett, arid. H 'feller J Am 0eni Sac , 611, 309, 1938
<br /> tronal human health risk due to each of the sources described In 1111~LiMpter Given 6 Jury, W A , W F Spencer, and W I Farnier ` Behavior Asses satent Modcl Ior
<br /> site current debate over Hie prober choice of poelency factors, breathing rates, Trace Orgawcs in Soil I Motel description, J F+iunm Qua! , 12,558-564, 1983
<br /> and demographics, ho%ever, calculated risks are not presented in this chapter 7 Jury,W A , W k Spencer, and W J Khmer "Behavior Assessment Model for
<br /> For comparison though, the JRIS14 potency factor for benzene(0 029 kg-d/mg), Trace Organics in Soil 11 Application of Screening Model,"J Environ Qua!, 13,
<br /> tahich Is based on a 70 y exposure for a 70 kg person, yields a >1 0 x 10-6 risk 573-579, 1984
<br /> 8 Shen,T "Esliniating Hazardous Air Emissions from Disposal Sites,"Pallunon Frr-
<br /> lor average lifetime benzene vapor concentrations >0 12 liglmt, fora 20 m 3!d gineenng, 13(8) 31-34, 1981
<br /> breathing rate In order to compare this value with the predicted concentrations 9 Johnson P C M W Kenibloa,,k4 and J D Colthart "Practical Seri-,ening Models
<br /> presented in Table 3, one trust consider that the exposure duration during any for Soil Venting Applications," in Proceedrags of the NW KWAPI ConfePrenre on
<br /> of These processes is much less than 70 v For example the maxunuin duration Yeimlrr+rrr H4d+ocxiiilropr atrrf Orga+ac{�ierrrr,ii�s rn Cresiinrtxcirrr f'rt wwrrN�►n t7i
<br /> of A'Xraistire f"Orn boil ride euue11+11tC 1e onlyll W6 y t3K9 10 111 1 ahk 3 lhciefore i+rii,ur awl lt, %feuu7r,iri Nrnr job,i 4 11 Ibmikiiu, T X logo
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