# ATTACHMENT D-4

Emission Reduction Calculations for Gasoline Storage Tank Pressure-VacuumVent Caps

R .C .S.A
. Section 22a-174-30 Back2round The amendment to R

.C.S.A
. Section 22a-174-30 reduces emissions of volatile organic compounds (VOCs) by requiring the use of "pressure-vacuumvent caps" (P-V vent caps) on stationary gasoline storage tanks at facilities that are subject to the Stage II vapor control regulation
. The amendment also requires the use of a two-point closed systemfor the transfer of gasoline froma gasoline tanker truck to an stationary storage tank; improves Stage II systemmaintenance; clarifies testing requirements and increases testing frequency
. The P-Vvent cap requirement becomes effective as of May 10, 2005
. Emission Calculations P-Vvent caps act to limit the amount of breathing losses that occur daily due to barometric pressure changes and gasoline evaporation enhanced by fresh air replacement when gasoline is drawn fromthe stationary tank
. The Department's emission calculations focus on the reductions resulting fromthe new requirement for P-Vvent caps at all Stage II gasoline service stations
. Additional reductions expected fromthe requirements for two-point closed systemare not quantified at this time
. The requirements for more comprehensive performance testing and improved maintenance procedures are expected to result in greater rule effectiveness
. 2007 Uncontrolled Emissions Uncontrolled emissions at Stage II equipped operations in 2007 due to stationary tank breathing are estimated to be: Eunc = EFUnc X Q1999 X Fr x Gr x CF Where: E , = 2007 uncontrolled emissions (tons/day) EFunc = 1 .0 lbs VOC/1000 gallon throughput Q1999 = gasoline sold in CT 1999 (thousands of gallons/year) = 1,431,153.91 (from

CT's 1999 Periodic Inventory) Fr = fraction of gasoline sold at Stage II service stations = 0 .95 (based on data in the Department's 1996 & 1999 Periodic Inventories) Gr = growth in gasoline sales from1999 to 2007 = 1 .10 (surrogate, developed fromthe Connecticut Department of Transportation VMT estimates for 1999 and 2007) CF = (1 ton/2000 lbs) x (1 year/365 days) Application of this formula yields : 2007 Uncontrolled Emissions = 2 .0 tons/day

### 2 D-4 2007 Emissions with Connecticut's P-VVent Cap Requirement The California Air Resources Board (CARB) estimates that P-Vvent caps reduce breathing losses fromstationary storage tanks by 90% .1 Connecticut's R

.C.S.A
. Section 22a-174-30 requires vent caps on all Stage 11-equipped operations dispensing 10,000 gallons or more of gasoline in any calendar month. The Department has previously determined that more than 95% ofthe gasoline sold in Connecticut is dispensed through Stage 11-equipped pumps. Resulting controlled emissions in 2007 are: " Assuming 100%rule effectiveness: 2007 Emissions with EPA Rule and the Connecticut Rule = 2.0 tons/day (1 - (0.9 * 1 .0)) = 0 .2 tons/day " Assuming 80%

rule effectiveness: 2007 Emissions with EPA Rule and the Connecticut Rule = 2.0 tons/day (1 - (0.9 * 0 .8)) = 0 .6 tons/day Incremental Shortfall Credit Due to Connecticut's Regulation Reductions creditable toward the shortfall are the difference between uncontrolled and controlled emissions in 2007
. Accounting for a range of possible rule effectiveness: " Assuming 100%rule effectiveness:

Shortfall Credit = 2.0 tons/day - 0 .2 tons/day = 1 .8 tons/day " Assuming 80%

rule effectiveness : Shortfall Credit = 2

.0 tons/day - 0

.6 tons/day = 1 .4 tons/day Based on the above analysis, the P-Vvent valve requirement of R .C.S.A. Section 22a174-30will result in between 1 .4 and 1 .8 tons/day additional VOC reduction beyond those incorporated into the Department's ozone attainment plan and EPA's calculation of Connecticut's emission reduction shortfall
. By the end of 2004, the Department plans to complete a mid-course review evaluating progress toward attainment of the 1-hour ozone standard in Connecticut
. That document will include a discussion of how the combined reductions fromthe P-V vent valve regulation and other adopted control measures are sufficient to meet EPA's shortfall requirement for Connecticut
.

1 CARB's estimate of P-V vent cap control efficiency was cited in an attachment to a July 19, 2000 letter fromDavid Conroy (EPA Region 1) to David Wackter (CTDEP)
.