p.1 

OAR Box 1875 

Prepped by Ollie Stewart 

Document Number: 

4DII-E-59 

Docket Number: 

A-90-19 

Printed 12/1/200811:12:46 AM Sheet 41 of 86 
P.2 

AUG T 1991 

A-90-19 

ll-E-59 

a , r : < 

DEC :• 0 /992 ' 

MEMORANDUM ^tk^lSkkll '"OX):' 

SUBJECT: Roundtable Discussion on Bubbling of Section 112 (MACT) 

Standards 

FROM: Doug Bell, Chief 

Standards Development Branch, ESD (MD-13) 

TO: Roundtable Participants 

Regional Air Division Directors 

This memorandum summarizes the mini-roundtable MACT bubble 

discussion held June 19, 1991 in Bill Rosenberg's office at 

Waterside Mall, Washington, D. C. Meeting materials and a list 

of participants are attached. 

Bruce Jordan, Director of the Emission Standards Division, 

Office of Air Quality Planning and Standards (OAQPS), opened the 

meeting with a brief introduction regarding the purpose and what 

he hoped the meeting would accomplish. In summary, he wanted to 

elicit ideas and views on bubbling MACT standards from the 

different perspectives and experiences represented at the 

meeting, to narrow the range of viable bubble options, and to 

sharpen and focus on the real issues associated with those bubble 

options. 

After describing the goals of the meeting, Mr. Jordan then 

asked the participants to introduce themselves, whom they 

represented, and to summarize their philosophy on bubbling MACT 

standards. Industry representatives unanimously favored the 

concept of bubbles and were interested in seeing the concept work 

in practice. In contrast, the nonindustry representatives were 

generally not in favor of bubbles citing enforcement, 

implementation, and administrative problems, and the possibility 

that a bubble could result in significant emission increases over 

what the standards would have otherwise achieved. 

Following the introductions, Nancy Mayer of OAQPS summarized 

EPA's current policy on bubbling National Emission Standards for 

Hazardous Air Pollutants (NESHAPs) as laid out in EPA's Emission 

Trading Policy Statement (ETPS) (51 FR 43814; December 4, 1986). 
P.3 

She described how current policy does not allow bubbling to be 

used to meet proposed or promulgated NESHAP. The participants 

noted that the current policy would have to be revised in order 

to accommodate bubbling in MACT standards. Several participants 

were interested in obtaining a copy of the policy. A copy of the 

policy is attached. 

The first major issue discussed was whether standards should 

first be developed and then bubbled, or whether the bubble should 

be considered in the development of the standards themselves. If 

the bubble were part of the standards development, EPA could 

consider any cost savings at that time, and account for bubble 

stringency and implementation and enforcement problems within the 

framework of the standard. The standard itself would encompass 

multiple emission sources, but would not specify emission limits 

for each source. Instead, a single limit would be designated, 

and the regulation would describe how emissions from each point 

would be determined and converted to compare to the overall 

limit, considering emission rate, capacity utilization, and hours 

of operation. 

Several possible types of bubbles were discussed. A mass 

emission bubble would sum the allowable emissions from the 

individual sources at a facility and designate that sum as the 

overall bubble limit for that facility, e.g., 5 Mg/yr. The owner 

or operator would then adjust the emissions from each source to 

his liking as long as the sum of those emissions did not exceed 

the 5 Mg/yr. 

An emission rate bubble would explicitly tie the bubble 

limit to production rate, i.e., as production fluctuated, so 

would the aggregate bubble limit the owner or operator would have 

to meet. The bubble limit would be expressed in terms of mass of 

emissions per mass of product. Both the mass emission and 

emission rate bubbles would be based on allowable emissions, 

i.e., those allowed by the standards. If an owner or operator 

achieved greater reductions than allowed, he would be able to 

take credit for the difference and use that difference to offset 

other emissions elsewhere in the bubble. It was acknowledged 

that even without a bubble, an owner or operator would likely do 

better than the standard, but that under a bubble he would get a 

credit that he otherwise would not have had. This concern was 

raised by nonindustry representatives and is discussed below. 

A third type of bubble was the emission point bubble. Under 

this bubble no credit could be taken for operating a given 

control device better than the efficiency assigned to that device 

in developing the standard. For example, an incinerator rated at 

a 98 percent emission reduction efficiency could not take credit 

for operating at 99.99 percent, even though it might really be 

doing so. Additional reductions would have to be achieved 
P.4 

through process changes, a different but more efficient kind of 

control device, or production curtailments. 

A central issue was identifying where the offsetting 

emissions for bubbling, or "credits," would come from. The group 

identified two potential sources of credits, but came to no 

agreement on whether or not they should be allowed: (1) 

additional reductions achieved by the installed control device 

beyond what the standard requires and.(2) additional reductions 

achieved by controlling a source not otherwise required to be 

controlled. The emission credit generated by (1) was 

characterized by one participant as a "windfall" in that these 

reductions would have occurred anyway. He explained that 

standards are set at a relatively loose level and that controls 

installed to meet the standards do significantly better. He was 

concerned that allowing those reductions that would have occurred 

anyway to be used to balance other emission points with less 

control would result in greater overall emissions. He described 

an example where a VOC standard was set for coating operations at 

a level that would have forced installation of the desired 

technology which was designed for greater emission reductions. 

Some operators, in response to the standards, however, completely 

reformulated their coatings for some lines and acquired large 

"credits" that were then used to bubble with uncontrolled coating 

lines. If the bubble had not been allowed, all the lines would 

have been controlled to the level of the standard, resulting in a 

greater overall emission reduction than achieved with the bubble. 

He felt that those owners and operators had "gamed" the system, 

taking advantage of the way the standards were set to 

substantially under-control, and that such situations could have 

been better dealt with if considered directly in the standardssetting process. 

In response, industry representatives noted that the 

resultant net emissions were no different than those allowed by 

the standards, but that the emission reductions were achieved in 

a more cost-effective way. However, the nonindustry participant 

contended that such "paper credits" should not be available 

because they were an artifact of where the standards were set and 

not what the actual control level would have been. He made the 

point that credits should only arise from additional control 

above and beyond control that would have been achieved in 

practice, and not that level beyond what was required. It was 

also noted that the ETPS does not allow the difference between 

required and actual to be used as a credit. 

Industry participants disagreed with the "windfall" 

descriptor and believed that such a scheme would encourage plant 

operators to do better than the standard and find innovative ways 

to increase the efficiency of their controls. They also pointed 

out that after application of a MACT standard, there will be 

little "wiggle room" to gain additional reductions. One industry 
P.5 

participant indicated that his company most likely would consider 

controlling sources that would not be controlled by the 

regulation (because of small size or throughput), but which may 

be less costly for him because of plant-specific factors. This 

prompted the suggestion by a nonindustry participant that cutoffs 

in the standards may, therefore, be drawn in the wrong place and 

that the standards should have no cutoffs in return for a bubble; 

that way the source would decide where the appropriate cutoffs 

would be for its specific configuration. 

The conversation then turned to how a bubble could be 

developed, using a specific example. The example was a mix of 

emission points at a plant (process vents, storage tanks, 

transfer operations, and wastewater), each with different kinds 

of standards, e.g., percent reduction, equipment, and 

concentration. A number of problems were identified: (1) how to 

translate standards with different formats into a common emission 

basis, (2) how to translate sources with differing emission rates 

into a common basis (i.e., how to bubble batch and continuous 

processes), (3) what would be the averaging period for 

compliance, and (4) how would emissions be determined for 

compliance? It was observed that if a bubble were not 

considered, one would not have to determine the mass emissions 

from a percent reduction, equipment, or.work practice standard, 

but that under a bubble such a calculation would be necessary. 

It was also noted that a bubble would increase the 

administrative and enforcement burden on both industry and the 

reviewing authority, although no agreement was reached on the 

degree. One of the nonindustry representatives expressed the 

opinion that a bubble would make compliance "an order of 

magnitude" more complicated and that compliance determinations 

would be significantly more difficult. He cited the resource 

burden of additional training of permit writers, additional time 

in negotiating permits, and the complexity of enforcing a permit 

on emission points which had different permitted emission levels 

and emission formats from those specified in the MACT standards. 

Another participant expressed concern over how one would keep 

track of emissions within the bubble over time to compare it with 

the total emissions allowed under the bubble, especially when 

production was variable. All emission calculations would have to 

be made on the same basis. Conversion calculations would have to 

be well-documented and equivalent emissions demonstrated. 

Additional resources would be necessary to evaluate these 

conversions and approve bubbles. Enforcement personnel were of 

the opinion that the averaging time to determine compliance with 

a bubble should be the same as for determining compliance with 

the MACT standard, and that the averaging times should be short 

enough to be enforceable. Interest was also expressed by the 

group in learning more about Region II's recordkeeping problems 

with New Jersey's bubble, mentioned in the meeting materials. 

These recordkeeping problems were alluded to during a visit by a 
P.6 

headquarters EPA representative to Region II, but no details were 

provided. Information on these problems will be sought and 

provided to the group when available. Industry participants, 

however, perceived the burden of implementing a bubble as 

relatively small compared with the additional requirements that 

would be imposed by the permitting process itself, and agreed to 

work on approaches that would allay concerns of the nonindustry 

participants. 

Another issue discussed was the possible creation of a 

disincentive to participate in the Early Reduction Program if 

bubbling MACT standards were allowed. One of the advantages of 

the Early Reduction Program is that a source can bubble many 

unrelated emission points. If a MACT bubble were also available 

it was believed that some sources may pass up Early Reductions 

and institute a MACT bubble directly, if it could acquire the 

same bubbling advantage. However, the participants generally 

agreed that the Early Reduction program still provided a 

significant advantage to sources seeking to delay compliance with 

a MACT standard, perceived as likely being more stringent, and 

that bubbling MACT standards would be an option they could still 

do at a later time, e.g., the programs were not related and 

participating in one would not affect participation in the other, 

and both programs offered benefits. After a brief discussion, it 

appeared that the availability of a MACT bubble would not likely 

have an impact on a source's incentive to participate in the 

Early Reduction Program. 

The final issue discussed was that of bubbling different 

pollutants. One industry participant stated that he was thinking 

of one-for-one trades, but would not oppose including some sort 

of indexing to allow for pollutant toxicity. Conversely, the 

nonindustry participants wanted to limit bubbling only to the 

same pollutant. They were concerned with trading pollutants with 

different toxicities, even if a weighting scheme were instituted, 

and because different pollutants are not controlled to the same 

degree, even with the same control device. A major concern with 

bubbling across pollutants was that speciation of emissions and 

quantification of individual pollutants would be necessary to , 

determine relative weighting for toxicity and to account for 

different control efficiencies for different pollutants. Another 

concern with bubbling across pollutants was the environmental 

impact of emissions from different kinds of emission points. 

While this is also a concern in bubbling the same pollutant, the 

effect could be greatly magnified if a lower toxic pollutant from 

a heated, elevated source were bubbled with a higher toxic 

pollutant from a cooler, ground-level source that would result in 

much higher ambient concentrations. 

Near the end of the meeting, next steps were discussed. Mr. 

Jordan expressed his desire to narrow things down to better focus 

on the issues, and observed that the group seemed to prefer the 
P.7 

~ P " 

"emission point" bubble over the other possible bubble options 

outlined in the meeting materials (see attached). The emission 

point bubble would reduce nonindustry concerns over taking credit 

for the difference between actual emissions and what are allowed 

by the standards by assigning a nominal efficiency (e.g., 98 

percent for an incinerator) to a particular control device 

regardless of what it achieved in practice. This option would 

thus spur credits through the use of more stringent controls or 

process changes, or prompt a source to control emission points 

that it would have not otherwise been required to control. The 

participants favored a followup meeting to discuss in more detail 

the emission point bubble in light of the issues and with respect 

to EPA's ETPS. It was noted that the "emission point" bubble 

needs a more appropriate descriptor. 

Mr. Jordan closeei the meeting by again asking the 

participants their view of bubbling and whether or not those 

views had changed over the course of the meeting. The industry 

participants were pleased that the discussions had been initiated 

and that they were better able to understand the issues and 

concerns associated with a bubble. As a result they believed 

they were better able to address the problems and to help devise 

a workable bubble that would not be environmentally detrimental. 

The nonindustry participants reiterated that their concerns must 

be satisfactorily addressed before they would accept a bubble. 

They felt it necessary that the Office of General Counsel address 

as soon as possible the legal issues of whether or not the Clean 

Air Act allows MACT bubbling and if bubbling across pollutants is 

permitted. The nonindustry participants indicated that some form 

of bubble may be acceptable if it adhered to restrictions in the 

ETPS, did not extend to new sources, and was environmentally 

neutral or resulted in a net benefit to the environment over not 

having a bubble. 

The OAR staff thinks that a reasonable and workable bubble 

will be advantageous to the environment and would allow more 

cost-effective compliance with MACT standards. We are working 

with other offices within the Agency to develop a position on 

MACT bubbles. We are planning another discussion in September to 

present this position. This roundtable may include additional 

participants and be expanded to include discussion of other 

issues related to the Hazardous Organic NESHAP. You will receive 

details concerning this roundtable in the near future. If you 

have questions, please contact Bruce Jordan at (919) 541-55723 or 

me at (919) 541-5568. 

Attachments 

bcc: Ron Campbell 

Tom Helms 

OAQPS:ESD:SDB:RColyer:JStevens:FTS 629-5262:MD-13(Mutual):8-7-91 
•1 

MACT Bubble 

June 19, 1991 

Name 

Larry Weinstock 

Bob Strieter 

Reg Modiin 

Brian Taranto 

Nancy Cookson 

David Doniger 

Cheryl Sutterfield 

Chuck Grigsby 

Rick Colyer 

Doug Bell 

Bruce Jordan 

Andrew Otis 

Jane Engert 

Daniel Fort 

Carl Mazza 

Patricia Embrey 

Michael Winer 

Kathy Kaufman 

Barry Elman 

Don Theiler 

Nancy Mayer 

Jim Weigold 

John Silvasi 

David Sprague 

Linda Chaput 

Lydia Wegman 

Roundtable Participants 

Room 939, EPA West Tower 

Oraanization 

OAR-10 

API 

MVMA 

Exxon Chem 

CMA 

NRDC 

PMA 

SOCMA 

EPA/OAQPS 

EPA/OAQPS 

EPA/OAQPS 

EPA/OPPE 

EPA/OAQPS 

EPA/OTS 

EPA/OAR 

EPA/OGC 

EPA/OGC 

EPA/OAR 

EPA/OPPE 

Wisconsin 

EPA/OAQPS 

EPA/OAQPS 

EPA/OAQPS 

EPA/OAQPS 

EPA/OAQPS 

EPA/OAQPS 

(CMA) 

(Phone 

(Phone 

(Phone 

(Phone 

(Phone 

(Phone 

(Phone 

Phone 

202-382-2174 

202-682-8337 

313-956-5502 

713-870-6117 

202-887-1241 

202-624-9334 

202-835-3548 

201-397-2808 

919-541-5262 

919-541-5568 

919-541-5572 

202-245-3749 

703-308-8684 

202-382-3694 

202-382-7403 

202-382-7625 

202-382-7606 

202-475-8950 

202-382-2727 

hookup) 

hookup) 

hookup) 

hookup) 

hookup) 

hookup) 

hookup) 

P.8 
P.9 

MACT BUBBLES 

MINI-ROUNDTABLE DISCUSSION 

JUNE 19, 1991 

10:00-4:00 

BILL ROSENBERG'S OFFICE 
P.10 

MACT BUBBLES 

A MACT bubble would allow some or all sources subject to MACT 

standards at a contiguous facility to find the best "fit" in terms of emission 

reductions and cost without exceeding what total emissions would have 

been at the facility had each source subject to a MACT standard been 

required to comply with each individual standard. To determine a bubble, 

one would sum the emissions allowed under MACT for each emission 

ooint and require the owner or operator of the facility to meet the sum 

emission number any way he chooses. Such an approach would 

-.heoretically result in over-control of some sources and under-control of 

others, providing the owner or operator maximum flexibility to achieve his 

emission reduction in the most cost-effective manner possible. 

Regulations under development in response to the 1990 Clean Air 

Act Amendments do not explicitly preclude the use of bubbles. However, 

there are many legal, technical, and policy issues that must be resolved 

before EPA can set a bubble policy for MACT. These issues, identified at 

a May 29. Workgroup meeting, are outlined below. The scope, options, 

and issues are not intended to be exhaustive, and others may be 

developed. 
P.11 

BUBBLE SCOPE OPTIONS 

•» All sources covered by a MACT standara within_contiguous facility. 

An industrial site with a number of different emission-causing 

operations would be subject to multiple MACT standards. -£c_Lgxam^le. 

reactor process vents, storage tanks, etc.. could be coyejg^at^a_giyf>n 

point in time by separate MACT standards: whereas other operations 

such as degreasing or surface coating may notjge. Only those sources 

covered by a MACT standard would be included in the bubble. As MACT 

standards were set for the other sources, the bubble would grow. 

• Bubble defined in each MACT standard (case-by-case). 

Assuming a general bubble policy is adopted, the specifics on what 

ana how each source covered by a MACT standard could be bubbled 

with other sources within a contiguous facility would be spelled out in 

each standard. This would be a case-by-case approach, and would 

address any special situations peculiar to each source. 

• Bubble sources within same MACT standard. 

This option would limit bubbling to all sources to which the same 

MACT standard applies within the facility, e.g., all storage tanks with the 

same MACT standard couid be bubbled, but storage tanks and process 

vents could not. 

• All emission points within same process unit or subcategory. 

This option would limit bubbling across a collection of integrated 

X equipment that results in a product or across a defined subcategory. In 

the HON. for example, one would bubble across all emission sources in a 

butadiene production unit, i.e.. storage tanks, process vents, wastewater. 

transfer, and equipment leaks. 

• Bubble across Early Reduction or other non-MACT sources. 

This option would greatly increase flexibility to an owner or operator 

by allowing him to bubble sources subject to MACT against sources with 

an Eariy Reduction extension or even sources not yet regulated. 
P.12 

^ ISSUES/CONSIDERATIONS 

LEGAL 

• Can sources within a bubble be allowed to control to less than their 

applicable MACT standards and/or tloors? 

A MACT bubble would allow an owner or operator to over-control 

some sources and under-control others at the facility. Thjs_wguld result in 

a[lowinq the under-coctrolled sources to meet something less than thp 

MACT standar^jQ£4hosaja0urces, something less than-the-MAST-Uooj^ 

or no control at all. 

Can we allow toxicity-weighted trading among hazardous pollutants? 

Shouid we give special consideration to high risk pollutants? 

The Act does mention toxicity as a factor in both early reductions 

and modifications, but does not for setting MACT standards. If it is 

determined that bubbling based on weighted toxicity is acceptable and 

desirable, we must then develop a scheme that may or may not resemble 

that for modifications or early reduction. Such a scheme would generally 

reguire greater than 1 -for-1 reductions of more toxic pollutants over less 

toxic pollutants. 

POLICY 

Allowing bubbles could create a disincentive to participate in Early 

Reduction Program. 

The Early Reduction Program is designed to offer sources a more 

cost-effective emission control solution than what they otherwise may 

have to comply with under MACT. Under the Early Reduction Program, 

sources that achieve a 90_p_ircent reduction before proposal of an 

applicable MACT standard_can get a 6-vear compliance extejpsi__iJo.r 

meetinjthejy]^1^andard. The Early Reduction Program results in 
P.13 

—r— 

significant additional emission reduction than would have otherwise 

occurrea. A source may perceive that the ability to bubble MACT 

standaras is an attractive alternative to the Early Reduction Program and 

wouid cnoose not to participate, resulting in a loss of the emission 

reductions that wouid otherwise have occurred. 

TECHNICAUADMINISTRAT1VE/ENFORCEMENT 

How to bubble different kinds of standards, i.e., performance, work 

practice, equipment? 

/y 

c 

A Standards based on performance or emissions standards are 

statutorily preferred, but work practice or equipment standards are a "last < 

reson" when emissions cannot be reasonably captured and measured, 

and consequently, the actual control efficiency and emissions are difficultL. 

to determine. Estimates are made for the purposes of assessing impacts/" 

of the standard, but these are generally composed of industry-wide r " 

average numbers that do not easily translate into individual facility X 

numbers. Determining emissions-associated with equipment orworkr' 

practice stanoards afTspecificJacilitv is difficult, anrLdetemwttntr"" ^- ^ 

omissions for the purpose of a bubble would be even mo-redifficult,jC"- _ 

because the o__ner or operatQLwgu|di ^antlo apply a differenrgquipmeet^ 

ojiwonc-practirp other than MACT for whjchjeiiT^sslonsjiiay^^ \ 

been calculated. -*•—^ 

Shouid Droduction curtailments or shutdowns be allowed in bubble 

calculations? 

Shutdowns or curtailments in production can create problems if fully 

creditea in all situations. For example, assume that MACT is based on 

98 percent reduction and 2 process units running at the same production 

rate were bubbled, one achieving 97 percent and the other 99 percent. If 

the 99 percent unit shut down and the production transferred to a different 

facility, the bubble would then be achieving only 97 percent reduction, and 

the facility with the new 99 percent unit would be allowed to bubble it 

against another unit achieving less than MACT. However, one could 

aroue that a curtailment or shutdown is a real emission reduction and 
P.14 

shouid be alloweo. even though it does not appear to reflect what MAC" 

is intended to represent. 

Should we allow fugitive equipment leaks in the bubble? 

The standard for equipment leaks has already been negotiated 

among EPA, industry, environmental groups, and State and local 

agencies. The rule has been formally agreed to by all parties with the 

understanding that EPA will propose and promulgate the rule agreed to 

by the committee. The negotiated rule represents a delicate balance of 

competing interests, providing both the environmental protection 

demanded by the States and environmentalists, and protection to the 

industry from enforcement actions if they failed to meet specified 

performance levels. If EPA were to allow a plant to do something less 

than required by the rule, it could be interpreted by the negotiating parties 

that EPA has reneged on the agreement, opening the rule up for 

litigation, and throwing EPA's Reg Neg program into disarray. In addition, 

any of the negotiating parties would be able to sue the Agency on the 

basis that it did not live up to its end of the agreement. 

Would bubbling result in overall emission increases? 

Bubbling could result in overall emission increases for 2 reasons" 

First, where an over-controlled source (99.5 percent) within a 98-percent 

bubble shut down, leaving an under-controlled source (96.5 percent), and 

rebuilt at 98 percent control by itself or within another bubble, a net v— -

incEeaseJn emissions would resultjf total emissions were not tied to ^ 

-production. Second, because sources required to meet a 98-percent 

MACT would probably control to a greater degree anyway (a 98-percent 

efficient incinerator is a least common denominator for most organic 

pollutants and most actually achieve greater efficiencies with a properly 

operating control device), we would be allowing the source to use the 

_difference as an offset for greater enrnssjgns__alsewher8 at theiacjjjty. 

One way to correct for this would be to charge a "premium" tc bubble. 

Such a scheme would disallow one-for-one bubbling, i.e., 10 lbs. for 10 

lbs., and would require some additional percentage, e.g., 20 percent. 

Therefore, should an owner or operator want to bubble, he must achieve 

12 lbs. instead of 10 lbs. reduction. 
.it should also be noted that EPA's current Emission Trading Policy 

Statement (ETPS) does not allow the difference between required and 

actual to De used as a credit; and also suggests charging a "premium" to 

bubble. The ETPS funher states that bubbles should not increase 

emissions of hazardous or toxic air pollutants. (51 FR 43814: December 

4. 1986) 

What is additional enforcement/administrative burden associated with 

bubbling? 

The basic tenant underlying bubbling is that an owner or operator 

would over- and under-control the various MACT sources within the 

bubble to achieve the same net emission rate had he controlled each 

source to the MACT standard. Consequently, additional information is 

necessary to determine the extent of over- and under-control of each 

source to ensure that they balance. 

For example, assume that a facility has bubbled a number of similar 

process vents to determine a single overall emission limit or rate. 

Althougn the bubble has a single emission limit, determination of 

compliance would have to be made on a point-by-point basis, and then 

summed to compare with the bubble limit. Testing or other short-term 

compliance determinations would not translate easily into an longer-term 

bubble limit, especially when production fluctuates. Furthermore, the 

owner or operator must keep track of different limits for each vent, each 

perhaps with its own monitoring, recordkeeping, and reporting scheme, 

especially when different control devices are used. 

in addition, to the extent that changes in production rates due to 

market demands (closure or curtailment), malfunctions, or maintenance 

occur, it may be necessary to adjust the bubble limit and thus redefine the 

limit for each vent. Furthermore, the owner or operator must readjust the 

bubble each time he adds a new vent. Every adjustment to the bubble 

that results in new limits for each vent wouid require an additional 

compliance determination to ensure that the new limits were being met. 

if bubbling across pollutants is limited, or toxicity indexing is used. 

the weighted averaging necessary to define and readjust the bubble 

would add another dimension of complexity in keeping track of the 

different limits for each vent. 
P.16 

BUBBLE OPTIONS 

NO BUBBLE. 

Bubbling would not be allowed, and sources would have to meet 

the emission limits established in the MACT standard for that source. 

PRO: In practice bubbles are not easily implemented. The major 

problems have been outlined above. These problems and issues were 

identified by those on the Workgroup with experience in trying to 

administer and enforce various kinds of bubbles, specifically the STAPPA 

representative, Office of Enforcement, and the Stationary Source 

Compliance Division. Concern was expressed about gamesmanship and 

not knowing whether or not a facility was in compliance. Region II 

officials, in a subsequent discussion, described New Jersey's attempt at 

implementing a bubble as a recordkeeping nightmare. 

CON: Bubbling can provide a cost-effective way to meet MACT 

standards. 

TOTAL MASS EMISSION BUBBLE. 

A total mass emission bubble would be based on actual emissions 

for all sources covered by a MACT standard within a contiguous facility, 

e.g., 1 ton/year. This would be a bubble in its purist form. Under this 

option, the emissions from each source covered by a MACT standard 

would be summed and the aggregate mass emission number would 

become the bubble limit that the facility would have to achieve. 

PRO: An owner or operator would have flexibility to over-control or 

under-control any source within the bubble as long as the overall mass 

limit(s) was met. 

CON: Recordkeeping and compliance determination with single 

bubble limit more difficult due to different controls on similar sources (i.e.. 

over-control and under-control of identical vents) and to emission changes 

because of production fluctuations. 

8 
P.17 

EMISSION RATE BUBBLE. 

An emission rate bubble based on production, e.g., 1 ton/1.000 

tons product. An overall facility emission rate limit would be established 

under this option, also, but would be directly related to production. 

PRO: Would account for changes in production. As production 

increased or decreased through shutdowns or curtailments, so would the 

bubble limit. 

CON: In addition to emission data, this option would also require 

production data. Would become more difficult to determine compliance at 

facilities with many products (e.g., DuPont's Chambersworks Plant makes 

750 different products). 

AMISSION POINT BUBBLE. 

Under an emission point bubble control equipment is assigned a 

nominal efficiency, regardless of the actual efficiency in the specific 

application. An owner or operator would have to over-control by using a 

more stringent control device, or by contolling a source that would not 

have otherwise been required to control (e.g., a vent above a Total 

Resource Effectiveness cutoff or a tank below a size cutoff). In return, he 

could choose to under-control or not control certain sources. However, 

because a nominal efficiency would be assigned, additional bubble credits 

could not be gained by using the same control device more efficiently. 

PRO: Because each control device wouid have its own assigned 

efficiency, a source test would not be necessary as long as the device 

were operating properly. 

CON: However, because the same control device may not result in 

the same efficiency in different applications, the EPA would have to make 

some determination as to the appropriate efficiency for each application, 

or require testing. 
Theoretical MACT Bubble 

59 (MACT Bubble limit) 

/ 5/8 

f 

TO 

5/2 

TO 

TO = Transfer operation 

ST = Storage tank 

PV = Process vent 

Emissions / Emissions 

Before bubble/ After bubble 

10/12 

ST 

10/5 

ST 

MACT Standard 

95% 

Equipment 

98% 

10/8 

ST 

3/1 

PV 

J 

10/15 

ST 

/ 

Chemical plant 

3/6 

PV 

3/2 

PV 

• / 

00