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i • 314 PETROLEUM DONTAMINATEO SOILS ESTIMATES FOR HYDROG4RBOi+I VAPOR ElatlSSiONS 3 Zone of S"epGo Flow gasoline to creme a 5% moisture content, 10,000 Ing-gasohnelkg soil gasolin cmWiniinatedSoil contaminated sail Thts soil was placed in the tank, a hl2 sweep gas flow star ad, and effluent benzene vapor concentrations were monitored with time "11 S0711 sirf$°e vapor conoenlration data, sweep gas flowrale, and tank dimensions were us So calculate the vapor flux rates presented in Figure 10 The sweep gas velotl was 3 4 cm/s(0.08 mph),Which was determined experimentally to be great ensu to ensure that the flux was not dependent on the sweep gas fiowrate An appnu\ Sweep Gas mate analysis of'the gasoline is contained in Table 1, where the initial mole Fra �--- tion of benzene is 0 0205. The sweep gas temperature was 24'C- The 4`CThe measured benzene vapor emissions from this experiment are compar with the predictions from Equation 14 in Figure 10. For these condllions, it model reasonably predicts the observed emissions, at least to the accuracy alt is desired for emissions estimation purposes. za- W id Emissions from So# Venting Operation Figure 9 Gasoline emissions experiment apparatus Figure I 1 resents emission rates for a ran of vapor flowrates an g P � ip (Q.��J vapor concentrations (CrJ In §IV.2 we use the emission rates correspondsi: to Q„II= 1400 Umin (50 f131tnin), and the maximum benzene vapor comentr 1 tion for soils contarnimled with gasoline contauurlg 1 mole percent benzene(3 2 mg/L) The worse case is the situation in witch vapors are discharged untreated �arttl =Div l.v and there is a nondimtnishing benzene source Equations 17 and 4 predict that di Benzene emission rate gu�t,a, and vapor concentration in the exit gas C ,,,,,.. , will lir Senmic(24 C) Flux xi=002 g.M.,m=6532 gid (g/cm2-d) CT,,=o nt n'g)kg pb= 16 gJcan CY ,=3 2 x 14_a glcsnr tam=0 05 gig .01I€the vapors are treated by a vapor treatment unit with a destruction effiuency O ei U 38 rl=0 45, them the benzene emission rale b and vapor concentration to tUr, exit gas Ct � fire Q Q &,.w'-127 g1d C,.,.W=1 6 x 10-P g1c1n3 C O It r4 typically observed that vacuum-well hydrocarbon vapor concectratiow. 001decrease during venting, so the values presented above should be regarded ati lQp worst-case estimates To calculate the worst-case average vapor emissions dui 150 200 tag a roil venting project, we use Equation 19 Suppose that venting removed Time (min) 100%of the benzene from a 500 gal gasoline spill,which conlained 1%by welghi Figure 10 Comparison of measured and predicted benzene fluxes trorn gasoline conlamt- benzene, over a six-month period Then the average emission rate 9.,1,, for lltc netted soil venting operation is calculated with Equation 19 to be I