Laserfiche WebLink
i 0 <br /> • ESTiMATES FOR HYDROCARBON VAPOR EMISSIONS 29`} <br /> 29B PETROLEUM CONTAMINATED SOILS <br /> 100 <br /> H C�x. <br /> Ci ti°4= (3) <br /> I(H(A'Acoli)+Om+k,l Benzene Vapor Equation(3) � � ' <br /> where Concentration <br /> H = Henry's law constant (=a,P,•M„H41RT) Equation(4) 1 <br /> C,,,,,,, = residual contamination level of i jmass-trmass-Ford 10 <br /> � r <br /> $b = soil moisture content (mass-H2Olmass-soil) <br /> In the high residual contaminant concentration limit Equation 2 becomes <br /> Ci��=XY11 M.... (4) Full Model- Equation(1) <br /> RT T=24'C <br /> where x, is the mole fraction of component i in the free-liquid residual phase 1100 1000 10" <br /> For mixtures composed of compounds with sermlar molecular weights, x, is <br /> CSldllal Soil Concentration <br /> roughly equal to the mass fraction of compound r. <br /> Equations 3 and 4 arc the two most commonly incorporated in vapor transport (mg-gasolineft-soil) <br /> models Note that Equation 3 predicts vapor concentrations that are proportional <br /> to the residual soil concentration of each species and are independent of the rela- 1000 <br /> tive,concentrations of each chemical species in the contaminant,while the vapor <br /> concentrations of each chemical species in lie contaminant,while the vapor con- BTEX* Vapor 00 <br /> centrattons pnedtrted by Equation 4 are independent of residual sail concenira- Concentration Equation (3) ------t` <br /> tion levels and depend only on the relative concentrations of species Due to its (mgr i <br /> mathematical characteristics, Tallier than any model validation, transient trans- 100 .40 <br /> port models6" most often incorporate Equation 3 Steady-state landfill emissionEquation(d) top <br /> models'often utilize Equation 4 It is important to recognize that these models <br /> are only valid for specific limitmg conditions, and generalization to other con- <br /> centration ranges can produce very misleading results- For example, Equation <br /> 3 predicts that vapor concentrations always increase is A increasing residual con- 10 <br /> tarninant levels,but realistically the equihbnum vapor concentration of an}comLOOOO <br /> - <br /> pound ern not exceed its saturated .apor concentration {=P,`M,v,IRTI <br /> Figure I compares vapor concentrations precled by Equations 1, 3, and 4 Full Mode!-Equation{1) <br /> di <br /> for the regular gasoline defined by Table I The required chemical parameters T�2il C <br /> (vapor pressures, octan!-,.vater partition coefficients,water sotubilti} values)can 1 <br /> be found in Johnson et at 9 Example model parameters for a sandy soil are- 100 two 10(KR) <br /> Residual Soil Concentration <br /> f, = organic carbon fraction = 0 002 (ing-gasoline ft-soil) <br /> ON = soil moisture cornenl = 5 <br /> *d <br /> t-1 = fatal void fraction = d 35 iiiuies uK mm of 6eor+me,tatuene,da}7t�rnxene,rite Yrs►apo cagtealrYEwMs <br /> po,, = soil bulk density = 160 glcmi Figure 1 Comparison of vapor concentration prediction models <br />