### BULK GASOLINE STORAGE TANKS

Date Initiated: August 10, 1998 Dates Modified / Updated : April 25, 2008 PROCESS DESCRIPTION: Gasoline bulk storage tanks release ROG vapor s containing listed substances into the atmosphere. The majority of emissions can be categorized as bulk storage tank fitting losses, rim seal losses, working losses, deck seam losses, degassing releases, and refilling losses. Emission rates are highly dependent upon the storage tank size, construction, and design as well as annu al fuel throughput. Most bulk gaso line storage tanks in San Diego County are equipped with either internal or ex ternal floating roofs. Fixed roof tanks are best quantified with the standard gasoline dispensing and storage procedures which can be modified to apply to any indivi dual site's equipment and procedures. The primary components of the gasoline emissions are benzene, hexane, toluene, xylenes, and a mixture of other nonmet hane hydrocarbons. Additional emissions occur at the bulk terminal loading racks and vapor processing units which are quantif ied separately from the bulk tanks. Emission estimation techniques for the bulk storage tanks are based upon procedures p ublished by the EPA (AP-42, Section 7.1, (9/ 97). Additional equipment and emission speciation information was obtained from the San Diego APCD permit files and CAPCOA publications. District estimation t echniques for emission inventory purposes are as follows:

Overall Emissions: Overall bulk storage tank emission s are the sum of rim seal, deck fitting, working, deck seam, degassing, and refilling losses. Indi vidual compounds are quantified using a standard vapor speciati on profile for reformulated / oxygenated gasoline; Ea = (Lr + Lwd + Lf + Ld + Ldg + Lrf) x Ci Eh = Ea / H Where: Ea = Annual g asoline emissions, lbs/ y ea rEh = Maximum hourly gasoline emissions, lbs/hour Lr = Rim seal losses, lbs/year Lwd = Withdrawal losses, lbs/year Lf = Deck fitting losses, lbs/year Ld = Deck seam losses, lbs/year Ldg = Degassing emissions, lbs/year Lrf = Refilling emissions, lbs/year Ci = Concentration of each listed subs tance in the gasoline vapor, lbs/lb

Calculation of emissions from each of the contributing processes listed above depends upon several somewhat complex estimation pr ocedures which must be performed for each individual storage tank. These specific cal culation procedures are also from AP-42; Rim Seal Losses: Emissions from the rim seals around the edges of the bulk storage tank floating roof depend primarily upon the diameter of the tank (i.e.; length of seal), the type of seal, and the type of roof (internal or external). An empi rical procedure is provided in AP-42 to calculate these emissions along with 'seal factors' necessa ry to fit the data. Lr = (K Ra + (K Rb x V^n)) x D x Mv x Kc x P* x Ci Where: Lr = Rim seal losses, lbs/year K Ra = Zero wind speed rim seal loss fact or, lb-mole/ft yr, (Table 7.1-8) K Rb = Wind speed dependent rim seal loss factor , lb-mole/(mph)^n ft yr, (Table 7.1-8) V = Average ambient wind speed at tank site, mph, (Table 7.1-9) = 6.9 mph for San Diego County

n = Seal related wind speed exponent, dimensionless, (Table 7.1-8) D = Tank diameter, ft Mv = Average vapor molecular weight, lbs/lb-mole = 66.0 for gasoline vapor RVP 10Kc = Product factor = 0.4 for crude oil = 1.0 for all other organic liquids P* = Vapor pressure function, dimensionless = (P va / P a ) / [1 + (1 - (P va / P a )^0.5)^2] = 0.122 for gasoline bulk storage in San Diego County P va = Vapor pressure at daily average liqui d surface temperature, psia, (Table 7.1-2) = 5.7 for Gasoline RVP 10 at 65 F P a = Atmospheric pressure, psia = 14.7 psia at sea level Ci = Concentration of each listed subs tance in the gasoline vapor, lbs/lb

Withdrawal Losses: Emissions caused by the withdraw al of gasoline from the bulk storage tanks consist primarily of liquid fu el remaining on the exposed interior wall surface after the lowering of the floating roof. The emission rate depends upon the storage tank dimensions (exposed surface ar ea per gallon of fuel withdrawn) and the interior wall condition (shell clinkage factor). An esti mation procedure is provided in AP42 to calculate these emissions along with repr esentative 'clinkage factors' necessary to p redict the amount of fuel retained on the wall surface. Lwd = [(0.943 x Q x C x W l ) / D] x [1 + (N c x F c / D)] x Ci Where: Lwd = Withdrawal losses, lbs/year 0.943 = Units conversion factor (constant), 1000 ft 3 - gal/bbl 2 Q = Annual gasoline throughput, bbl/yr, (Note 1 barrel = 42 gallons) C = Shell clinkage factor, bbl/1000 ft2, (Table 7.1-10) W l = Average organic liquid density, lbs/gal = 6.1 lbs/gal for gasoline D = Tank diameter, ftN c = Number of fixed roof support columns, dimensionless F c = Effective column diameter, ft Ci = Concentration of each listed substa nce in the gasoline vapor, lbs/lb Deck Fitting Losses: Emissions of gasoline vapor from bulk storage tank deck fittings depend upon the number and type of fittings on the floating roof of each individual tank. An empirical procedure is pr ovided in AP-42 to predict these emissions along with the 'deck fitting loss factors' necessary to estimate vapor emissions from each type of fixture. Lf = Ff x P* x Mv x Kc x Ci Where: Lf = Deck fitting losses, lbs/year Ff = Total deck fitting loss factor, lb mole/year = [(N F1 x K F1 ) + (N F2 x K F2 ) + ... + (N Fnf x K Fnf )] N Fi = Number of deck fittings of a particular type (i = 0, 1, 2,..., nf), dimensionless

nf

= Total number of fitting types, dime nsionless, (Tables 7.1-11 to 7.1-15) K Fi = Deck fitting loss factor for a pa rticular type of f itting, lb mole/year = [K Fai + (K Fbi x (K v x V)^m i )] K Fai = Zero wind speed loss factor for fitti ng type 'i', lb mole/year, (Table 7.1-12) K Fbi = Wind speed dependent loss factor for fitting type 'i', lb mole/year, (Table 7.1-12) K v = Fitting wind speed correction factor, dimensionless = 0.7 for external floating roof tanks = 0.0 for internal and domed external floating roof tanks V = Average ambient wind speed, mph = 6.9 mph for San Diego County

m i = Loss factor for a particular type of deck fitting, dimensionless, (Table 7.1-12)P* = Vapor pressure function, dimensionless = (P va / P a ) / [1 + (1 - (P va / P a )^0.5)^2] = 0.122 for gasoline bulk storage in San Diego County P va = Vapor pressure at daily average li quid surface temperature, psia, (Table 7.1-2) = 5.7 for Gasoline RVP 10 at 65 F P a = Atmospheric pressure, psia = 14.7 psia at sea level Mv = Average vapor molecular weight, lbs/lb-mole = 66.0 for gasoline vapor RVP 10 Kc = Product factor = 0.4 for crude oil = 1.0 for all other organic liquids Ci = Concentration of each listed subs tance in the gasoline vapor, lbs/lb

Deck Seam Losses: Internal floating roof tanks with bolted decks may have deck seam losses from vapors escaping th rough gaps. An empirical procedure is provided in AP-42 to predict these emissions along with the 'd eck seam loss per unit seam length factor' necessary to estimate emissions from bolted decks. Since there are no remaining bolted floating roof decks in San Diego County, the EASIER inventory data forms and calculation procedures om it this calculation. Ld = K D x S D x D^2 x P* x Mv x Kc x Ci Where: Ld = Deck seam losses, lbs/year K D = Deck seam loss per unit seam le ngth factor, lb mole/ft year = 0.0 for welded floating roof decks = 0.14 for bolted floating roof decks S D = Deck seam length factor, ft/ft2= L seam / A deck L seam = Total length of deck seams, ft A deck = Total deck surface area, ft2 D = Tank diameter, ft P* = Vapor pressure function, dimensionless = (P va / P a ) / [1 + (1 - (P va / P a )^0.5)^2] = 0.122 for gasoline bulk storage in San Diego County P va = Vapor pressure at daily average liquid surface temperature, psia, (Table 7.1-2) = 5.7 for Gasoline RVP 10 at 65 F P a = Atmospheric pressure, psia = 14.7 psia at sea level Mv = Average vapor molecular weight, lbs/lb-mole = 66.0 for gasoline vapor RVP 10 Kc = Product factor = 0.4 for crude oil = 1.0 for all other organic liquids Ci = Concentration of each listed subs tance in the gasoline vapor, lbs/lb

Degassing Emissions: Occasionally, bulk gasoline storag e tanks must be emptied and degassed to allow for repair activities both inside the tank and on the floating decks. Degassing bulk storage tanks results in orga nic emissions from both the evacuated vapor space and any evaporated liquid remaining on the walls, floor, or deck. The San Diego County APCD Vapor Recovery staff has deve loped the following calculation procedure to estimate these emissions; Ldg = (L vapor space + L walls + L roof + L floor ) x Ci Where: Ldg = Degassing emissions, lbs/year= [(0.462 x D^2) + (0.707 x D)] x Ci D = Bulk storage tank diameter, ft Ci = Concentration of each listed subs tance in the gasoline vapor, lbs/lb L vapor space = Vapor space evacuation losses, lbs/year

= 0.315 x D^2 (assuming the following information) = (3.14 x D^2 / 4) x H x (1/385) x Mv x 0.39 where; 3.14 = Pi, (dimensionless mathematical fu nction used to calculate interior tank volume) D = Bulk storage tank diameter, ft H = Average height of roof when tank is vented, ft, (Assume 6 ft) (1/385) = Conversion factor, lb moles gas/ft3 Mv = Molecular weight of gasoline vapor, lbs/lb mole, (Use 66.0 for gasoline vapor) 0.39 = Mole fraction of gasoline vapor in vented space assuming a liquid temperature of 65 F and a partial pressure of 5.7, (i.e.; 5.7 psia / 14.7 psia) L walls = Liquid evaporation losses from the side walls of the vented tank, lbs/year

= 0.707 x D (assuming the following information)

= 3.14 x D x H x 0.25 x 0.15 where; 3.14 = Pi, (dimensionless mathematical func tion used to calculate wall surface area) D = Bulk storage tank diameter (a lso twice the radius), ft H = Height of roof when tank is vented, ft, (Use 6 ft if unknown) 0.25 = Assumed average thickness of liquid on tank walls after draining, millimeters 0.15 = Conversion factor for gasoline liquid, lbs/mm ft2 L roof = Liquid evaporation losses from the inside roof of the vented tank, lbs/year= 0.029 x D^2 (assuming the following information)

= (3.14 x D^2 / 4) x 0.25 x 0.15 where; 3.14 = Pi, (dimensionless mathematical func tion used to calculate roof surface area) D = Bulk storage tank diameter, ft H = Average height of roof when tank is vented, ft, (Assume 6 ft) 0.25 = Assumed average thickness of li quid on interior roof after draining, millimeters 0.15 = Conversion factor for gasoline liquid, lbs/mm ft2 L floor = Liquid evaporation losses from the fl oor of the vented tank, lbs/year

= 0.118 x D^2 (assuming the following information)

= (3.14 x D^2 / 4) x 0.1 x 1.5 where; 3.14 = Pi, (dimensionless mathematical func tion used to calculate floor surface area) D = Bulk storage tank diameter, ft H = Average height of roof when tank is vented, ft, (Assume 6 ft) 0.1 = Assumed average thickness of liqui d on floor after draining, centimeters 1.5 = Conversion factor for gasoline liquid, lbs/cm ft2

Refilling Emissions: After degassing and repairing th e bulk gasoline storage tanks, a refilling operation must occu r which generates gasoline vapor emissions. Liquid fuel surges into the tank from below and forces vapors out the vents until the liquid surface meets the floating roof and be gins to raise the structure. The San Diego County APCD Vapor Recovery staff has developed the follow ing calculation procedure to estimate these emissions;

Lrf = (3.14 x D^2 / 4) x H x (1/385) x Mv x 0.39 x Ci = 0.315 x D^2 x Ci Where:Lrf = Refilling emissions (after degassing ope rations), lbs/year 3.14 = Pi, (dimensionless mathematic al function used to calculate interior tank volume) D = Bulk storage tank diameter, ft H = Average height of r oof when tank is vented, ft, (Assume 6 ft) (1/385) = Conversion factor, lb moles gas/ft3 Mv = Molecular weight of gasoline vapor, lbs/lb mole, (Use 66.0 for gasoline vapor) 0.39 = Mole fraction of gasoline vapor in vented space assuming a liquid temperature of 65 F and a partial pressure of 5.7, (i.e.; 5.7 psia / 14.7 psia) Ci = Concentration of each li sted substance in the gasoline vapor, lbs/lb

Hourly Emission Estimates: Average hourly emissions are estimated by dividing annual emissions by the hours of operation (Note: gasoline vapor contains no compounds currently deemed acutely hazardous). Eh = (Ea x Ci) / Hrs where: Eh = Hourly emission estimate, lbs/hour Ea = Annual emission estimate, lbs gasoline vapor/year Ci = Concentration of each listed subs tance in the gasoline vapor, lbs/lb Hrs = Hours of bulk storage tank operation, hours/year

EMISSIONS INFORMATION: Emission estimation procedures and factors are based on information from EPA AP-42 (Section 7.1). Gasoline speciation data is from both the EPA (NESHAPS Document 453/R-94-002a) and CAPCOA (Air Toxics Hot Spots Industry wide Risk Assessment Guidelines).ASSUMPTIONS / LIMITATIONS: - Emission estimation procedures are ba sed upon AP-42 methods for floating roof storage tanks containing organic liquids. Fixed roof storage tanks may not be accurately quantified with these procedures. - Gasoline vapor speciation is base d on information in the EPA NESHAPS Document for the Gasoline Distribu tion Industry (vapor speciation for reformulated / oxygenated fuel) and the CAPCOA Industry wide Risk Assessment Guidelines (liquid speciation). - Emissions of organic vapo rs containing listed subs tances from tanks storing diesel, distillate oil, kero sene, jet fuel, motor oil, lubricants, machining oils, and residual oil are assumed to be below re porting levels. Aviation gas, however, should be considered equi valent to gasoline unless site specific information indicates otherwise. - Retail gasoline storage and dispensing equipment should not be evaluated with these estimation techniques. Separate calcu lation procedures have been developed for these processes and equipment. - Facilities tend to misreport the annual "tank refilling" activities needed to complete the above equations. Refilling emissions are calculated by the District only after a degassing operation when the ta nk vents are left open to properly raise the floating roof. Emissions fr om typical refilling operati ons with closed vents are included in the rim seal and withdrawal estimates. To avoid overestimating refilling emissions, the database calcu lation procedure uses the "number of degassing events" to estimate refilling emissions. FORMS: Use the reporting form for all sizes of bulk gaso line storage tanks. Verify the accuracy of the permit equipment description. Do not report diesel, distillate , or jet fuel fuel storage. Due to the complexity of rim seal and fitting losses, emission rates for these releases are

Gasoline Speciation Data Weight % Vapor Weight % Liquid Benzene 0.4 % 1.0 % Ethyl Benzene 0.1 % 1.6 % Hexane, Isomers of 1.4 % 1.8 % Toluene 1.1 % 8.0 % Xylene, Isomers of 0.4 % 2.4 % 2,2,4-Trimethylpentane 0.7 % 0.8 %typically calculated separately and entered into the database as constants (lbs released / year) and (lbs released / hr) . Since the em ission rates are only dependent upon tank size and design, the emissions are unaffected by throughput. The District database is not currently programmed to perform th ese tank specific calculations.