Interim White Paper - Midwest RPO Candidate Control Measures
3/10/2006 Page 6
percent in-use efficiency for a Stage II program. If inspections occur annually, the efficiency is estimated to be 77 percent. Minimal inspections reduce the in-use efficiency to 56 percent.
The U.S. EPA issued regulations requiring onboard vapor recovery (ORVR) standards for the control of refueling emissions in 1994. ORVR works by routing refueling vapors to a carbon canister on the vehicle and are expected to achieve from 95-98 percent reduction of the vehicle refueling emissions. Vehicle manufacturers were required to begin phasing in ORVR beginning in 1998, with 100 percent phase-in to be achieved by 2006. Once ORVR control systems are in widespread use through the vehicle fleet, then the U.S. EPA may exempt areas from Stage II vapor recovery system requirements.
As ORVR equipment is being phased in for new vehicles, there is some concern regarding the compatibility of ORVR controls and Stage II controls. When an ORVR-equipped vehicle refuels at GDF with Stage II VRS, the amount and composition of the vapor returned to the UST by the Stage II control system can be impacted. An increase in the amount of air (in lieu of gasoline vapor) returned to the vapor space of the UST will lead to gasoline evaporation, or vapor growth, in the UST and lead to excess emissions from the UST vent. A larger amount of air is returned to the UST vapor space for some Stage II vacuum assist VRS when refueling vehicles with ORVR controls, and therefore, the excess emissions are greater for some vacuum assist systems.
CARB has promulgated a new program in California in 2001 called Enhanced Vapor Recovery (EVR). The program includes six main modules, including changing the control efficiency requirement to 98 percent for Stage I vapor recovery, requiring P/V valves on all systems, improving the Stage II compliance certification process to increase effectiveness from 90 to 95 percent, and measures to improve ORVR compatibility. Initially, CARB believed full compliance could be achieved within four years. EVR is now being implemented over a period of eight years (full compliance in 2008) to allow time to develop and certify vapor recovery systems to the regulations’ technology-forcing standards, as will as to provide a four-year window for existing facilities to upgrade equipment to meet the new standards.
CANDIDATE CONTROL MEASURES
The most promising reductions beyond current requirements can be obtained by increasing the required control efficiency of Stage I vapor recovery systems from 90 to 98 percent in areas with existing Stage I programs and requiring Stage I vapor recovery systems in areas that currently do not have Stage I vapor recovery requirements. Additional reductions could be obtained by requiring Stage I vapor recovery in counties bordering 8-hour ozone nonattainment areas. The Stage I requirements could be based on the CARB EVR Module 1 requirements, which changes the control efficiency requirement to 98 percent, requires P/V valves on all systems, and contains additional specifications to prevent leaks.
For Stage II emissions, the percentage of ORVR vehicles on the road will continue to increase as older vehicles are replaced by new ones. Adding new Stage II controls at gasoline stations will produce less reductions (at a higher cost) in the future. Additional reductions beyond current Stage II and ORVR requirements can be obtained by increasing the required control efficiency of Stage II vapor recovery systems from 90 to 95 percent in areas with existing Stage II programs and requiring Stage II vapor recovery systems in areas that currently do not have Stage II vapor recovery requirements. The Stage II requirements could be based on the CARB EVR Module 2 requirements.
For underground storage tank breathing losses, there is a commercially available membrane vapor recovery system to recover gasoline vapors and return them to the storage tank. One system is the OPW Vaporsaver™ system, which reduces VOC emissions by 95-99%. When the pressure in the tank reaches
Disclaimer: The control measures identified in this document represent an initial set of possible measures. The Midwest RPO States have not yet determined which measures will be necessary to meet the requirements of the Clean Air Act. As such, the inclusion of a particular measure here should not be interpreted as a commitment or decision by any State to adopt that measure. Other measures will be examined in the near future. Subsequent versions of this document will likely be prepared for evaluation of additional potential control measures.