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I <br /> ESTIMATES FOR HYDROCARBON!VAPOR EMISSIONS 34 <br /> WS PETROLEUM CONTA♦'1i HATED SOILS <br /> Qua„ Cl vrtn Qa'r Ci.v <br /> Vapor Emissions `��— -�- Air+Frit:-liquid Producl{h <br /> A A h Air In `^ �""� Arr+Grotmdwster Out <br />' � Air In-�` <br /> Vacuum <br /> puniP vapor <br /> a Diffuser <br /> Stack <br /> Vapor <br /> Wellkv- ` <br /> =_� , <br /> Vapor Flow �� t i t Vapor flow ` <br /> may,• - �.�. I �x <br /> kc 2 _ABLY <br /> Groundwater <br /> Greiisndwates <br /> I <br /> Flgure 3. Soil venting operation <br /> As mentioned above, the most conservative emissions estimates for venting Injector <br /> Imps <br /> operations are obtained by using Equation 17 for the emission rate and Equation <br /> 4 for the vapor concentrations While this approach might provide good estimates Figure 4 Pump and treat operation <br /> of the emission rate al the start of venting, vapor concentrations decrease with <br /> time during venting due to changes in the composition of the residual and due <br /> to mass-transfer resistances 9 To account for this behavior, we calculate a time- by displacing fluid with air, and as the fluid is driven to a collection and tre.lt <br /> averaged ernisston rate, E„,&, and average it apor ooncenlration, C,,,1,, based on menl system aboveground,the air is allowed to escape unn=tcd to the atmoThe'C <br /> the time period for remediation, and the mass of compound t removed dur- The air flowrate(at 1 a(m), Qo,r, requited to obtain a given fluid pumping tate <br /> ing this period, m. Qr, is <br /> =rnf r. (19) Q., + Him] I Qr(pumping groundwater) <br /> c„Ve=mi,Qvmy 10 3 m <br /> l2 i� <br /> Typical venting vapor Ilowrates are 10<Q,,,,,<200 ft'Fmin For gasoline spill Q w I 1 + I Qr (pumping free-liquid hydrocarbon) <br /> remediation, typical total hydrocarbon vapor concentrations can be as great as Q. <br /> 12 9 m <br /> 300 mgfL at start-up, but hien usually decrease to <50 mgiL <br /> where His the depth to groundwater expressed in in The maximum,*apor el1w, <br /> li 2d Emissions from Groundwater Pump and Treat Operations sions, &A r..,, from the pumps will then be <br /> and Free-Uquid Product Recovery _{//{���� <br /> C.PUW—Qa1f C/, (4l 1I <br /> A pumping operation is pictured in Figure 4,where groundwater and free-liquid <br /> product are being removed If submersible electric pumps arc used, then em's- v%here C,, again denotes The hydrocarbon vapor concentrations in the air Thcti1 <br /> sions will be minimal Often, however, inleclor pumlis arc used Riese work 1L(1nSCr%.itive t'niccinn e%tn'htIe% air r'hl,iu't,il b% .1SStnnrnr tint vapid Anil 11(111111 <br />