November 14, 1995 

MEMORANDUM 

SUBJECT: Calculating Potential to Emit (PTE) and Other 

Guidance for Grain Handling Facilities 

FROM: John S. Seitz, Director 

Office of Air Quality Planning and Standards (MD-10) 

TO: Director, Office of Ecosystem Protection, Region I 

Director, Air and Waste Management Division, 

Region II 

Director, Air, Radiation, and Toxics Division, 

Region III 

Director, Air, Pesticides, and Toxics Management 

Division, Region IV 

Director, Air and Radiation Division, Region V 

Director, Multimedia Planning and Permitting 

Division, 

Region VI 

Director, Air, RCRA, and TSCA Division, Region VII 

Assistant Regional Administrator, Office of 

Pollution 

Prevention, State and Tribal Assistance, Region VIII 

Director, Air and Toxics Division, Region IX 

Director, Office of Air, Region X 

The purpose of this guidance is to address the 

determination of PTE for grain elevators and other issues for 

grain handling facilities. 

Background 

In a memorandum dated January 25, 1995, the Environmental 

Protection Agency (EPA) addressed a number of issues related 

to the determination of a source's PTE under section 112 and 
2 

title V of the Clean Air Act (Act). [Memorandum from John

Seitz to EPA Air Directors entitled “Options for Limiting the

Potential to Emit (PTE) of a Stationary Source Under Section

112 and Title V of the Clean Air Act,” hereinafter referred to

as the “January 25 memorandum”]. One of the issues discussed

in the memorandum was the term "maximum capacity of a

stationary source to emit under 

its physical and operational design," which is part of the

definition of "potential to emit." The memorandum clarified

that 
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inherent physical limitations and operational design features 

which restrict the potential emissions of individual emission 

units, should be taken into account. This clarification was 

intended to address facilities for which the theoretical use 

of equipment is much higher than could ever actually occur in 

practice. For such facilities, if their physical limitations 

or operational design features are not taken into account, the 

potential emissions could be overestimated and the source 

owner could be subject to the Act requirements affecting major 

sources. Although such source owners could accept enforceable 

limitations restricting the operation to its designed level, 

the EPA believes this administrative requirement to be 

unnecessary and burdensome. 

On the topic of "physical and operational design," the 

January 25 memorandum provided a general discussion. In 

addition, the EPA committed to providing technical assistance 

on the type of inherent physical and operational design 

features that may be considered acceptable in determining the 

potential to emit for certain individual small source 

categories. The EPA is currently conducting category-specific 

analyses in support of this effort, and hopes as a result of 

these analyses to generate more general guidance on this issue 

as well. The purpose of this memorandum is to address the 

issue as it relates specifically to grain elevators, and to 

provide EPA guidance on other issues related to grain handling 

facilities. 

The policies set forth in this memorandum represent 

official EPA guidance on this issue and are intended to 

provide guidance to State regulators on methods that the EPA 

believes are appropriate for sources whose potential emissions 

are, as a practical matter, restricted by inherent operational 

limitations. The policies set forth in this memorandum are 

intended solely as guidance, do not represent final Agency 

action, and cannot be relied upon to create any rights 

enforceable by any party. 

In addition to today’s guidance, there are two additional 

recent EPA activities that relate to emission calculations for 

grain elevators and other grain handling facilities. First, 

the EPA recently issued a policy memorandum entitled 

“Definition of Regulated Pollutant for Particulate Matter for 

Purposes of Title V,” (Lydia Wegman to Regional Offices, 

October 16, 1995.) In this memorandum, the EPA recognizes PM10 as the only regulated form of particulate matter for 
4 

purposes of determining applicability to title V major source 

requirements. Second, the EPA is issuing revised emission 

calculation methods (interim update to AP-42, section 9.9.1, 

“Grain Elevators and Processes”) The combined result of the 

October 16 memorandum and the revised emission calculation 

methods is a substantial reduction in the particulate emission 

estimates from a given grain elevator and grain handling 

facilities. 

Guidance for Grain Elevators 

For purposes of today's guidance, a "country grain 

elevator" means any grain elevator that receives more than 50 

percent of its grain from farmers in the immediate vicinity 

during the harvest season, and a grain terminal is an elevator 

that receives grain primarily from other elevators. 

Grain elevators emit particulate matter, including PM-10, 

during the receiving, handling, and shipping of grain. The 

rate of particulate matter emitted is directly proportional to 

the amount of grain handled by the elevators. 

The EPA recognizes that country grain elevators are 

clearly constrained in their operation, to the extent that 

they are designed to service, and as a matter of operation 

only service, a limited geographic area from which a finite 

amount of grain can be grown and harvested. Moreover, the 

principal determinant of which given elevator will be used by 

a farmer is the proximity of the elevator to the harvest. 

Consequently, a single elevator services essentially the same 

geographic area from year to year. The EPA believes that this 

constraint is "inherent" to the operation of the elevator 

(i.e., operation of the grain elevator is directly linked to a 

specific and definable harvest area). The grain handling and 

storage facilities at grain elevators are designed to handle 

very large amounts of grain in a relatively short period of 

time (i.e., at harvest). Although the physical capability 

exists to handle large amounts of grain throughout the year, 

such a year-round operation is clearly unachievable as a 

practical matter and does not occur in reality. Although the 

amount of grain harvested during any 1 year will vary 

somewhat, the EPA believes that an estimable and reasonable 

upper bound can be determined which would never be exceeded 

absent extraordinary circumstances. 
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For existing country grain elevators, the EPA has 

determined that a reasonable and realistic "upper-limit" 

estimate of the number of bushels of grain projected to be 

delivered to the elevator may be considered in identifying the 

"maximum capacity" of such elevators for the purpose of 

estimating their PTE. Consequently, the EPA does not 

recommend basing the potential to emit calculation for 

existing country grain elevators on a throughput estimate 

based upon year-round operation of the elevator at its maximum 

rate of operation. 

Instead, the EPA recommends that the PTE be determined 

based upon a more realistic estimate of the maximum amount of 

grain that could be received during a record crop year in the 

geographic area served by the elevator. The EPA believes that 

the highest amount of grain received during the previous 5 

years, multiplied times an adjustment factor of 1.2, will 

constitute a realistic upper bound on the amount of grain a 

country elevator could receive. The adjustment factor of 1.2 

is designed to take into account additional considerations 

that might affect the maximum harvest including: (1) the 

possibility that the number of acres harvested in the local 

area could increase, (for example, if an increased percentage 

of acres in the growing region became available for planting 

because of changes in government policy); and (2) increases in 

crop yields. 

The EPA expects that there may be rare cases where the 

future grain receipts in a given year could exceed the 1.2 

times the historical production figure. Where this is the 

case, the maximum receipt estimate should be recalculated. 

Example : The maximum amount of grain received during the

previous 5 years for a given elevator is 2 million

bushels. Consequently, the estimate of maximum receipt,

to be used for purposes of determining the facility’s

potential to emit, is 2 x 1.2, or 2.4 million bushels. 

In some future year, 2.6 million bushels are received. 

At this point, the maximum receipt estimate becomes 2.6 x

1.2, or 3.1 million bushels. 

The EPA believes that this guidance, in combination with 

the previously mentioned updates to emission calculation 

methods, will result in few, if any, country grain elevators 

exceeding the major source threshold for PM-10. 
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Permitting of Nonmajor Sources 

In response to recent questions, the EPA wishes to 

clarify the requirements of the title V program for nonmajor 

source grain elevators subject to section 111 or 112 

standards. This issue is addressed in 40 CFR part 70, 

paragraph 70.3(b)(1), which allows States to exempt nonmajor 

sources from title V permitting until such time as the EPA 

completes a rulemaking to determine how the program should be 

structured in the future for nonmajor sources. 

For grain elevators over a certain size, there is an 

existing new source performance standard (i.e., a section 111 

standard) that was promulgated during the late 1970s. This 

same standard also applies to additional agriculturallyrelated facilities such as flour mills, corn mills (human 

consumption), and rice mills. Some sources covered by this 

standard may have potential emissions less than the major 

source threshold. For these nonmajor sources, as indicated in 

section 70.3(b)(1), the EPA has granted a temporary exemption 

from title V permitting. As noted, this temporary exemption 

from title V permitting is set to expire when the EPA 

completes a further rulemaking addressing permitting of 

nonmajor sources. However, it is the EPA’s intent that this 

rulemaking or a separate rulemaking will establish a permanent 

exemption for grain elevators, feed mills, and other grain 

handling facilities that are nonmajor sources. 

There are currently no applicable section 112 standards 

for the grain and feed industry. As indicated by paragraph 

70.2(b)(2), the EPA will, for any future section 111 or 112 

standards that may apply, determine whether to exempt any or 

all nonmajor sources from the requirement to obtain a title V 

permit at the time the standard is promulgated. 

Facilities with Low Actual Emissions 

The EPA also believes it useful to reiterate its policy 

guidance with respect to sources with low annual rates of 

actual emissions. In the January 25 memorandum, the EPA 

announced a 2-year transition policy for plant sites emitting 

less than 50 percent of the major source threshold. Under 

this transition policy, sources emitting less than this 

amount, and keeping adequate records, are not required to be 

treated by States as major sources for purposes of determining 
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applicability of title V and section 112 requirements. The 

transition period in the memorandum expires in January 1997. 

The EPA intends to promulgate rulemaking amendments that 

would extend permanent relief to low-emitting sources, 

excluding such sources from being classified as “major 

sources” for purposes of title V permitting. (The exact 

cutoff for what constitutes a low-emitting source would be 

determined in the rulemaking process). Such amendments are 

scheduled for completion before the end of the 2-year 

transition period. (If the amendments are not promulgated by 

January 1997, the transition period will be extended for the 

facilities addressed in this document until the abovementioned amendments are finalized). 

The EPA believes that these provisions for low-emitting 

sources will ease the regulatory burden for grain elevators, 

feed mills, and other agriculturally-related facilities. 

Using the recently adopted (November 1995) interim emission 

factors for PM-10, even on an uncontrolled basis, the EPA has 

determined that grain elevators with an actual throughput less 

than the values listed in Attachment 1 will not exceed 50 

percent of the major source threshold. So long as adequate 

records of annual throughput are kept, sources handling less 

than those levels are considered by the EPA to be emitting 

less than the 50 percent cutoff and can be exempted from title 

V. Because these facilities are often well controlled, many 

grain terminals with greater throughputs will not be subject 

to title V permitting. In addition, preliminary calculations 

indicate that only the largest of feed mills are likely to 

exceed this cutoff. 

Consideration of Control Measures 

The effect of control devices and measures in grain 

handling facilities can be taken into account in determining 

whether a source can be considered a “low-emitting source” as 

described above, so long as adequate records are kept 

documenting the proper operation and maintenance of the 

control devices and measures. 

The EPA and the grain industry are working to develop 

estimates of the effectiveness of oil addition as a control 

measure. The results of this effort should be available by 

later this year or early next year. Interim guidance on the 
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effectiveness of oil addition is available in the abovedescribed revisions to section 9.9.1 of AP-42. Consistent 

with the provisions affecting other types of control devices 

or measures, the effectiveness of oil addition can be taken 

into account in determining whether actual emissions are below 

the cutoff for “low-emitting” facilities as described above. 

For sources whose actual emissions exceed the cutoff 

described above, consistent with the EPA’s general PTE policy, 

the effect of control measures (including oil addition) can be 

taken into account where those control devices and measures 

are subject to enforceable limits or are inherent to the 

operation of the facility. [Control measures that are 

“inherent” are those which are always being operated and 

maintained for reasons other than community air quality 

protection. Examples of inherent control measures would 

include (a) product collection devices for which the value of 

the product collected greatly exceeds the cost of the 

collection device, and (b) devices for which the primary 

purpose is to improve product quality control, to recover 

product, or to enhance production operating efficiency (for 

example, product recovery cyclones associated with operations 

such as pellet cooling at feed mills).] 

There are a number of grain elevators that have “closed 

loop” systems in which conveyors are completely enclosed 

essentially from the grain unloading point to the point at 

which grain is deposited to the bin. Where this is the case, 

some agencies (for example, the State of Michigan) have made 

adjustments in the emission estimate to take this into 

account. The EPA agrees that such adjustments are 

appropriate, particularly in estimating emissions from the 

“headhouse” or “internal” portions of the emission factors. 

Further, in the case of feed mills, there are certain 

operations which can be totally enclosed. Where this is the 

case, the emission calculations should take this into account. 
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Cautions 

This guidance is not intended to replace the 

establishment of operational limitations in permits to 

construct or operate when such limitations are deemed 

appropriate or necessary, such as the establishment of PTE 

limits in a minor source preconstruction permit for sources 

not yet in operation. (For such sources, there may not be a 

historical data base on crop production). Additionally, this 

memorandum is not intended to be used as the basis to rescind 

any such restrictions already in place. 

This guidance should not be interpreted as having any 

effect on whether new source performance standards apply to a 

given elevator. The guidance is not intended to prevent any 

control agency from imposing requirements designed to provide 

for attainment of the national ambient air quality standards. 

Distribution/Further Information 

The Regional Offices should send this memorandum to 

States within their jurisdiction. Questions concerning 

specific issues and cases should be directed to the 

appropriate Regional Office. Regional Office staff may 

contact Tim Smith of the Integrated Implementation Group at 

919-541-4718. The document is also available on the 

technology transfer network (TTN) bulletin board, under "Clean 

Air Act, Title V, Policy Guidance Memos." (Readers unfamiliar 

with this bulletin board may obtain access by calling the TTN 

help line at 919-541-5384). 

Attachment 

cc: Chief, Air Branch, Regions I-X 
Grain Throughput associated with Uncontrolled PM-10 emissions 

of 50 tons/yr 

Type of 

shipping/receiving 

Grain Total throughput 

(bushels) 

Truck or rail 

receiving/truck or 

rail shipping 

Wheat 

Corn/soybeans 

Milo (sorghum) 

32 million 

14 million 

20 million 

Truck or rail 

receiving/barge 

shipping 

Wheat 

Corn/soybeans 

Milo (sorghum) 

24 million 

10 million 

15 million 

Barge 

receiving/ship 

shipping 

Wheat 

Corn/soybeans 

Milo (sorghum) 

10 million 

4.0 million 

6.1 million 

Truck or rail 

receiving/ship 

shipping 

Wheat 

Corn/soybeans 

Milo (sorghum) 

17 million 

7.1 million 

10 million 

Notes: 

1. This table indicates, based upon the EPA’s 

recommended interim emission factors, the throughput 

associated with 50 tons per year of uncontrolled PM-10 

emissions, which is 50 percent of the major source threshold 

for PM-10. (For a small number of geographic locations 

designated as serious PM-10 nonattainment areas, the major 

source threshold is 70 tons per year. For any elevators 

located in such areas, the above number should be multiplied 

times 0.7). 

2. The estimates take into account: (a) receiving, (b) 

internal grain handling emissions, (c) bin vents, and (d) 

shipping. These are the sources that are generally present 

at a given terminal. If there are other significant sources 

of PM-10 at a given terminal, these would need to be 

considered. 

3. Calculations assume density of wheat = 60 lb/bushel. 

Density of corn, soybeans, milo (sorghum) = 56 lb/bushel.