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OAR Box 1830 

Prepped by Ollie Stewart 

Document Number: 

34) IV-B-32 

Docket Number: 

A-87-11 

Printed 11/13/2008 7:20:52 AM Sheet 34 of 232 
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USBJ 

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

ANN ARBOR. MICHIGAN 48105 

JAN * 0 199* 

MEMORANDUM 

SUBJECT: 

FROM: 

T O : 

DJjLLUJLg 

lUij JAN 241994 Wj 

OFFICE OF 

AIR AND RADIATION 

Review and Analysis of Sierra Research Report 

Glenn W. Passavant, Chief ^ycS^c-w. (JJ -^fcKAJ^uu^ZA^ 

Special Regulatory Projects Branch 

Public Docket A-87-11 

I. Introduction 

On November 5, 1993 EPA received a letter from the American 

Automobile Manufacturers Association (AAMA) transmitting a report 

entitled "A Comparative Study of the Effective of Stage II Refueling 

Controls and Onboard Refueling Vapor Recovery" . The report had been 

prepared by Sierra Research, Inc. for AAMA. The most recent comment 

period on the proposed onboard refueling vapor recovery (ORVR) 

requirement closed on August 22, 1993. This report was received 

more than six weeks after the close of the comment period. However, 

in the spirit of maximizing the consideration of public input on the 

rulemaking decisions, we are assessing the contents of the report 

in the course of the final rulemaking deliberations. 

The remainder of this memorandum is divided into four sections. 

Section II reviews the fundamental issues, analytical approach and 

conclusions of the Sierra Report. Section III describes general and 

specific points of disagreement between the Sierra report and EPA's 

Regulatory Impact Analysis (RIA). Section IV compares the Stage II 

and ORVR effectiveness values as derived from the Sierra Report and 

EPA's RIA and discusses the differences. Finally, Section V 

presents discussion and conclusions on ORVR controls benefits 

incremental to Stage II based on EPA's analysis. 

II. Summary of Sierra Report 

The Sierra report identified three fundamental issues to be 

assessed in the report: These included: 

1. Identifying which approach, Stage II or ORVR, is best for 

improving air quality; 

2. Determining what, if any, incremental air quality 

benefits will result from a combination of Stage II and 

ORVR controls relative to the implementation of only 

Stage II systems; and 
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3. Assessing what impact a phase-out of Stage II controls 

would have on refueling emissions after ORVR systems are 

in widespread use. 

Sierra then identified three steps to assess these concerns as 

shown below. 

1. Identification of areas required by the CAAA to implement 

Stage II controls; 

2. Determination of the status of Stage II implementation in 

areas where it will be required and estimation of the 

percentage of refueling emissions that will be eliminated 

in each area by Stage II systems during the 1993, 1994, 

and 1996 ozone seasons; and 

3. Performance of an emissions inventory analysis over a 20-

year period, based on EPA's MOBILES.Oa emission factor 

model, to compare the benefits of Stage II, ORVR, and 

combinations of Stage II and ORVR systems in three areas 

representative of moderate (Phoenix, Arizona), serious 

(Boston, Massachusetts), and severe (Houston, Texas) 

ozone nonattainment areas. 

After gathering the desired information and making assumptions 

when necessary Sierra conducted an analysis comparing the 

effectiveness of Stage II and ORVR controls. Based on the separate 

analyses for Stage II and ORVR controls Sierra reached the following 

conclusions. 

1. Implementation of Stage II systems without ORVR will 

eliminate 75-85% of the sum of refueling and fuel 

spillage VOC emissions by 1996, reaffirming that Stage II 

systems will eliminate the bulk of refueling emissions 

before the sale of the first ORVR-equipped vehicle. 

2. Implementation of ORVR systems on passenger cars alone 

would, in the absence of Stage II controls, eliminate 

only 50-60% of refueling emissions by the year 2015, 

based on EPA's ORVR assumptions. MOBILE5.0a runs based 

on more realistic assumptions regarding ORVR 

effectiveness indicate that ORVR systems on passenger 

cars will reduce refueling emissions, by only 30-45%. 

Therefore, ORVR on passenger cars alone will provide 15-

55% less control than implementation of Stage II systems 

alone. 

3. Implementation of ORVR systems on all gasoline-fueled 

vehicles, in the absence of Stage II controls, would 

ultimately result in greater control of refueling 

emissions than implementation of Stage II systems alone, 

using EPA's optimistic assumptions regarding ORVR 

performance in customer service. However, this would not 

occur until some time after 2005, more than 10 years 
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after the time by which full implementation of Stage II 

requirements could have occurred in most ozone 

nonattainment areas. Further, the incremental reduction 

in refueling emissions would be no more than about 10% 

for any of the three cities considered in this analysis. 

In contrast, the analysis based on more realistic 

assumptions of ORVR effectiveness indicates that the use 

of ORVR on all gasoline-fueled vehicles would provide 

less control of refueling emissions that Stage II through 

at least 2015. 

4. Implementation of ORVR on either passenger cars or all 

gasoline-fueled vehicles in combination with Stage II 

requirements would result in greater control of refueling 

emissions than Stage II alone if EPA's ORVR assumptions 

are used in the analysis. However, even if the 

optimistic EPA assumptions are used, the incremental 

reductions in refueling emissions are small for ORVR 

implementation on passenger cars and even smaller for the 

extension of ORVR requirements to light-duty trucks and 

heavy-duty vehicles. More importantly, these benefits 

may be illusory because when breathing loss effects are 

considered, the use of ORVR in combination with Stage II 

systems leads to less control of refueling emissions than 

with Stage II alone. (This counter-intuitive result 

occurs because ORVR-equipped vehicles prevent Stage II 

systems from returning vapors to the underground storage 

tank. Without the return of the vehicle tank vapors, the 

underground tank must breathe in fresh air, which leads 

to additional vaporization of liquid fuel.) 

5. If a phase-out of Stage II requirements, provided for by 

the CAAA, was to occur in 2010 with ORVR implemented only 

on passenger cars, it would result in a 15-55% increase 

in refueling emissions relative to the level of control 

provided by Stage II systems alone. The Stage II phaseout would, however, have little impact on refueling 

emissions relative to the ORVR-only case where ORVR is 

required on all gasoline-powered vehicles. 

III. EPA Critique of Sierra Report 

EPA disagrees with both the general issues raised by Sierra as 

the areas for analysis and some specifics of the Stage II and ORVR 

analyses conducted by Sierra to assess these issues and reach their 

conclusions. Each of these if discussed below. 

A. General 

As a result of the Clean Air Act Amendments of 1990 both Stage 

II and ORVR controls are required. By the time ORVR controls begin 

in the 1998 model year, Stage II will be in place in all serious and 

worse ozone NA areas and many moderate areas will have voluntarily 

implemented Stage II controls as well. However, ORVR controls on 
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light-duty vehicles (LDVs) are also required under the Act, with EPA 

holding the statutory authority to require ORVR controls for lightduty trucks (LDTs) and/heavy-duty vehicles (HDVs) under section 

202(a) (1) . 

Thus, the question is not Stage II vs ORVR as suggested by 

Sierra, but which is the better choice for the long term, retaining 

Stage II solely for the purpose of capturing LDT/HDV refueling 

emission or requiring LDT/HDV ORVR controls with the eventual phaseout of Stage II controls as allowed under section 202(a)(6) of the 

Act. 

In making such a decision the comparison should be made on 

which strategy is the most effective (gets the greatest of refueling 

emission reductions overall) and on which strategy is the most cost 

effective in the long term. The Sierra report addresses neither the 

absolute tons of emission reduction or the cost effectiveness of 

controlling LDT/HDV refueling emission by either Stage II or ORVR 

controls. Thus, its utility as an input to decision making is 

limited. 

B. Specific Concerns 

In preparing the RIA for the ORVR rule, EPA and Sierra 

considered many of the same points. While there are some minor 

differences between the EPA and Sierra analyses of the effectiveness 

of Stage II and ORVR controls, the key differences are identified 

below. 

• EPA and Sierra do not agree on the number of moderate 

ozone NA areas which will have Stage II. It is not 

required nor will it be installed in all moderate NA 

areas. 

• The gasoline/service station throughput distributions in 

Table 7 of the Sierra report weight fuel distribution too 

much toward larger stations. The EPA metro distribution 

is appropriate for most NAAs, but in the case where Stage 

II is required through an entire state, the nationwide 

distribution is considered more representative. 

• The ORVR in-use efficiency rate ignores the positive 

impacts of full life useful life and onboard diagnostic 

systems. 

• The liquid seal ORVR system entrainment rate used by 

Sierra is off by a factor of 2. Even GM in their 

comments indicated a value of 25 percent. 

• For the reasons discussed in the Summary and Analysis of 

Comments, the assertion that ORVR controls will negate 

the claimed effectiveness of Stage II in reducing 

emptying loss emissions is exaggerated if not unfounded. 
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IV. Comparison of Sierra and EPA Effectiveness Estimates for Stage 

II and ORVR 

A. Stage II 

Sierra compared the effectiveness of Stage II and ORVR plus 

Stage II for three areas, Phoenix, AZ (moderate), Boston, MA 

(serious), Houston, TX (severe), and drew its conclusions based on 

that analysis. Sierra projected Stage II efficiencies of 80.2, 

85.5, and 85.5 percent for these three areas, respectively. 

EPA's analysis was not done on an area by area basis, but 

rather on a combined basis for all areas. To simplify, EPA used an 

86 percent efficiency (annual enforcement) for all areas and a 10/10 

exemption level as indicated in the 1991 EPA Stage II Technical 

Guidance document. On an overall basis, these simplifications were 

conservative, since they lead to higher Stage II effectiveness 

values. Also as was mentioned above, EPA used a metro service 

station throughput distribution for all areas except for situations 

where Stage II is a statewide requirement, such as is the case in 

Massachusetts. In those states EPA used a nationwide service 

station throughput distribution. EPA's estimate of the average 

Stage II effectiveness (80.7 percent), falls well within the 

distribution of state-by-state Stage II effectiveness values found 

in Table 9 of the Sierra report. However, EPA does not believe that 

Stage II implementation will be as widespread as indicated by 

Sierra. 

B. ORVR 

Sierra's estimate of the in-use effectiveness of ORVR controls 

is found in Appendix C of the Sierra Report. Sierra estimates a 

value of about 80 percent assuming 

- a 97 percent efficiency for a properly operating system 

- a 6.2 percent in-use failure rate 

- a 50 percent increase in emissions from failed systems 

due to the liquid seal 

- an attribution of a claimed increase in emptying loss 

emissions to ORVR systems 

In calculating the effectiveness Sierra used an emission rate 

of 4.54 g/gal for refueling emissions and .454 g/gal for emptying 

losses. The calculation is shown below: 

(1-.062) (.97) (4.54) + (0M.454) + (. 062) (. 5) (4 . 54) = 

(4.54) + (.454) 

EPA's estimate of the in-use effectiveness of ORVR systems is 

described in the RIA. EPA expects that ORVR systems will be 
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designed for essentially zero emissions at certification. The 

effectiveness of a properly operating integrated system will depend 

on the fuel RVP, temperatures, and amount of fuel dispensed during 

any given event. When these factors are taken into account, EPA's 

best estimate is about 97 percent in ozone NA areas and 93 to 95 

percent nationwide, depending on what fuel temperature distribution 

is assumed for the southeast US. 

These values are decreased by in-use failures. However, as is 

discussed below, EPA's estimate of in-use failures, based on 

evaporative emission experience, is much less than that used by 

Sierra. 

There are two types of system failures common to evaporative 

control, system pressure failures and purge failures. System 

pressure failures are not expected to impact ORVR efficiency because 

of the short duration of refueling events and the high system 

pressure and vapor flow rates during refueling. However, as is 

discussed below onboard diagnostics (OBD) and enhanced I/M would be 

helpful in dealing with pressure failure related emissions should 

they be significant. 

With regard to purge system failures, current evaporative 

system purge failure rates are about 3.5 percent for 50,000 miles. 

Such a high failure rate would not be expected with ORVR systems for 

several reasons. The full life useful life requirement will upgrade 

component reliability. Based on this requirement EPA expects a 

purge system failure rate over the full life to be similar to that 

seen over the half-life (3.5%). Furthermore, enhanced I/M and OBD 

will reduce this failure rate, since both systems will check the 

functionality of the purge system. Data available to EPA suggests 

that enhanced I/M and OBD will reduce these failures by 80 percent 

in NAAs. However, in areas without enhanced I/M, OBD alone will be 

less effective. At least 80 percent of failures will be identified 

by the system, but only 60 percent of the failed vehicles (3/4 of 

the identified failures) will be corrected. On a weighted basis, 

the failure rate is abut 1.2 percent. 

Enhanced I/M and OBD will discourage system tampering. 

Furthermore, tampering will be discouraged by movement of the 

canister from the engine compartment to the rear of the vehicle as 

manufacturers indicate is likely in many ORVR systems. 

As is discussed in the RIA, liquid seals may increase vapor 

generation in ORVR system with failed purge systems by 25 percent. 

This increases the effect of the failure rate to about 0.9 percent 

in NAAs and 1.5 percent overall. 

Unlike the Sierra report, EPA's analysis includes no detriment 

for emptying losses. As is discussed more fully in the Summary and 

Analysis of Comments, emptying loss emissions are not well 

characterized or understood. It is not clear if and when emptying 

losses occur in conventional tanks, if and how effective Stage II 

is in reducing emptying losses, and what effect ORVR would have on 
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this control. Even with these uncertainties, there is an 

alternative control strategy available should it be deemed 

necessary. A pressure/vacuum vent valve or limiting orifice which 

will contain emissions can be placed at the outlet of the vent pipe 

from the underground storage tank. When used, this technology would 

be effective on conventional and Stage II equipped fuel dispensing 

systems. Given these uncertainties and alternative approaches it 

is not necessary or appropriate to include emptying losses in the 

ORVR system effectiveness evaluation. 

Thus, in summary, EPA predicts an ORVR system efficiency of 

about 95 percent in ozone NA areas and 92-95 percent overall 

depending on what is assumed about the dispensed fuel temperature 

in the southeast U.S. 

V. Discussion/Conclusion 

The discussion above and the analysis in the RIA support a 

number of conclusions. With exemptions, Stage II will control about 

80 percent of refueling emissions in the areas where it is 

installed. This control will largely be in place before ORVR 

controls begin and will be effective on most gasoline-powered 

highway vehicles. 

ORVR controls are expected to provide emissions control at a 

level of about 95 percent in ozone NA areas. If installed on all 

vehicle classes it will cover essentially all of the consumption 

Stage II would control and the extra emissions control in the long 

term would be about 15 percentage points in these areas. Even a 

modest decrease in the scope of the ORVR program or a decrease in 

system efficiency would not affect the conclusion that ORVR controls 

would provide grater emission reductions than Stage II in the long 

term. However, if ORVR controls are not applied to LDTs / HDVs the 

reduction of benefits would be dramatic, since together they 

comprise about 40 percent of refueling emissions. The benefits of 

LDT/HDV controls incremental to Stage II are in the same 15 percent 

range in areas where Stage II is installed, but substantially 

greater in the ozone NAAs where there is no Stage II. 

However, in areas where Stage II is installed, the benefits of 

a full ORVR program would not exceed Stage II until about 2010. At 

that point, it would be appropriate to consider Stage II phase-out 

since there would be few benefits, and the cost effectiveness of 

those benefits would be very unattractive. EPA' RIA contains a full 

discussion of the costs, emission reductions, cost effectiveness, 

and benefit-cost ratio of LDT/HDV ORVR controls incremental to Stage 

II and compares it to retaining Stage II solely for controlling 

LDT/HDV refueling emissions. As can be seen in that analysis the 

ORVR option is superior in the long term.