NSPS SUBPART DD COALITION 

VIA ELECTRONIC MAIL 

September 20, 2012 

Mr. William Schrock 

U.S. Environmental Protection Agency 

Office of Air Quality Planning and Standards 

109 T.W. Alexander Drive 

Mail Code: E143-03 

Research Triangle Park, NC 27709 

Re: Follow-up to the July 25 Meeting of the NSPS Subpart DD Coalition with EPAOAQPS 

Dear Bill: 

On July 25, 2012, representatives of the NSPS Subpart DD Coalition1

 met in your offices to 

discuss the status of EPA’s efforts in revising the grain elevator new source performance 

standard (NSPS) found at 40 CFR Part 60, Subpart DD. We are submitting this letter on behalf 

of the Coalition in order to comment on three issues that arose during the July 25 meeting: 

1. Whether it would be appropriate to distinguish between permanent grain storage and 

temporary grain storage on the basis of the number of turnovers in a year; 

2. Whether some fraction of the grain storage capacity of a temporary grain storage facility 

(TSF) should count toward quantifying the total “permanent” storage capacity at a given 

grain elevator; and, 

3. What distinguishes emergency storage from a TSF. 

We are submitting this letter also to provide you with an inventory and summary of the 11 “white 

papers” that the Coalition has submitted previously on technical matters. 

This letter does not signal any change in the Coalition’s overarching views. The Coalition as a 

first priority continues to urge EPA to repeal Subpart DD for the reasons detailed in its February 

6, 2012, petition. Also, in the event EPA were to deny that petition and move towards revising 

Subpart DD, the Coalition would continue to urge EPA to exclude TSFs from Subpart DD 

altogether. In the Coalition’s view, it would not be “appropriate” within the meaning of section 

111 of the Clean Air Act to regulate by means of an NSPS the future addition of TSFs to grain 

elevators. TSFs do not present a nationally significant risk to air quality and, therefore, do not 

warrant a federal response in the form of an NSPS. Just as state/local air pollution control 

agencies can adequately address grain elevators (as the Coalition’s February 6, 2012 petition 

shows), they can also adequately address new TSFs. 

 

1

 The members of the NSPS Subpart DD Coalition include the Corn Refiners Association, the North American Millers’ Association, 

the National Council of Farmer Cooperatives, the National Grain and Feed Association, the National Oilseed Processors 

Association and the USA Rice Federation.
Mr. William Schrock 

Follow-up to the July 25 Meeting of the NSPS Subpart DD Coalition with EPA-OAQPS 

September 20, 2012 

Page 2 of 6 

1. Distinguishing Between Permanent Grain Storage and Temporary Grain Storage on 

the Basis of the Number of Turnovers per Year 

The fundamental purpose of a TSF is for bulk storage of grain on a temporary basis. 

TSFs generally experience a single turnover annually. In 2010, the Coalition’s technical 

consultant, RTP Environmental Associates, Inc. (RTP), analyzed Coalition member 

companies’ responses to a 2009 EPA §114 survey. The responses collectively contained 

data for 121grain elevators, including data representing 119 storage-unit-years2

 of TSF 

operation. Of these, three TSFs reported a total of five storage-unit-years with more than 

one turnover per year; the maximum number of annual turnovers reported was two. At 

two of the three TSFs reporting more than one annual turnover, it appears that these TSFs 

were used to store two different grains in a single year, rather than being used as an 

“active” storage unit. In sum, according to the §114 data, annual turnovers for TSFs 

average about 0.9, with a few units experiencing as many as two turnovers annually. That 

low rate of turnovers makes sense, given that filling and emptying a TSF are laborintensive, time-consuming processes and not something routinely done on a daily, weekly, 

or even monthly basis. 

In stark contrast, the rate of turnovers at permanent grain storage is much higher – 

averaging about 9.3 per year, based on the §114 data. That relatively high rate of 

turnover makes sense as well, because permanent storage and grain handling obviously 

are structured to operate much more efficiently and rapidly than TSFs. 

These major differences in turnover rates and structure are so great, and so well 

substantiated by the §114 data, that there is no need for Subpart DD applicability 

purposes to build a turnover rate into a definition of TSFs in order to distinguish them from 

permanent capacity. There is, moreover, a risk in attempting to restrict the universe of 

TSFs by means of a turnover rate. While the §114 data clearly show that the vast majority 

of TSFs typically experience a single annual turnover, it is conceivable that due to 

weather extremes or other unforeseen factors, there may be periods when a larger fraction 

of the TSF population could experience multiple annual turnovers. But, even if they did, 

that would not materially diminish the reality that TSFs are structurally, functionally and 

operationally completely different from permanent storage. Accordingly, the Coalition 

maintains that the most appropriate definition of a TSF remains the generally accepted 

one which posits four key elements: (a) a base consisting of asphalt, concrete or similar 

material; (b) rigid, self-supporting sidewalls; (c) an aeration system; and, (d) a tarp or 

similar cover. 

2. Counting Some Fraction of a TSF’s Capacity as Permanent Storage Capacity 

As noted above, RTP’s previous analysis of the §114 data determined that from 2005-

2007, the number of annual turnovers in permanent storage units averaged about 9.3, 

while the annual turnovers for TSFs averaged only about 0.9. RTP previously developed 

an emissions model to estimate the relative significance of temporary and permanent 

storage. This model suggests that the uncontrolled emissions from both types of storage 

 

2 The term “storage unit year” is used here to refer to each year of storage/throughput data for an individual TSF. For example, if a 

single TSF reported data for three years, these data represent three storage-unit-years of operation.
Mr. William Schrock 

Follow-up to the July 25 Meeting of the NSPS Subpart DD Coalition with EPA-OAQPS 

September 20, 2012 

Page 3 of 6 

facilities are similar when compared on the basis of a unit of throughput.3 Given the 

temporary-to-permanent storage throughput ratio from the survey data, however, this 

emissions model indicates that an uncontrolled bushel of temporary storage has 

approximately 10 times less environmental significance than a bushel of permanent 

storage. 

Contrary to the facts discussed above, EPA’s Office of Enforcement and Compliance 

Assurance (OECA) has issued an opinion that for purposes of determining NSPS 

applicability, the storage capacity of a TSF is considered to be “permanent storage 

capacity” as this term is defined in Subpart DD.4

 While the OECA opinion disavows any 

binding effect on other EPA offices, state/local agencies or the regulated industry, in some 

cases this opinion is being treated as binding by both EPA regional offices and state/local 

permitting authorities in determining Subpart DD applicability for grain elevators. The 

Coalition believes that on the basis of the Subpart DD rulemaking record and the §114 

data, TSF capacity is clearly not the same as permanent storage capacity and, therefore, it 

should not be considered at all in making Subpart DD applicability determinations. Indeed, 

as noted above, the Coalition believes that TSFs should be excluded from Subpart DD 

altogether. 

The Coalition understands that, based on the §114 data, EPA’s Office of Air Quality 

Planning and Standards (OAQPS) is considering treating TSFs in the upcoming 

Subpart DD rulemaking in a manner that differs from the OECA opinion. One option that 

we understand OAQPS is considering is to have TSF capacity count towards permanent 

storage capacity at a fractional level (i.e., one bushel of temporary storage capacity is 

equivalent to a fraction of a bushel of permanent storage capacity). This concept was 

discussed during the July 25 meeting between Coalition representatives and OAQPS. 

Since that meeting, the Coalition has considered this concept specifically. We believe that 

TSF capacity should not be considered in applicability determinations either now or in the 

future, for the following reasons: 

• As discussed above, TSFs are starkly different from permanent storage capacity in 

all key respects, namely: structure, function, operation, and annual emissions of 

particulate matter (PM). There is no commonality that justifies grouping TSF 

capacity with permanent capacity from the standpoint of the logic of section 111 of 

the Clean Air Act. TSFs are not a “subcategory” of permanent storage capacity 

within the meaning of section 111. 

• TSF are truly temporary. They are intended to handle intermittent surges and 

surpluses and, hence, are not used necessarily every year. The current year is a 

good example. Low yields in 2012 will likely result in less use of TSFs. 

 

3

 The estimated uncontrolled PM10 emissions factors for permanent storage and temporary storage facilities are 0.077 pound per 

ton of throughput and 0.084 pound/ton, respectively (see “Analysis of 114 Survey Data by the Subpart DD Coalition” presented to

EPA on February 24, 2010). 4 See letter from Michael S. Alushin, Director, Compliance Assessment and Media Programs Division, Office of Compliance, EPA 

to Mr. Kendall Keith, President, National Grain and Feed Association, November 21, 2007.
Mr. William Schrock 

Follow-up to the July 25 Meeting of the NSPS Subpart DD Coalition with EPA-OAQPS 

September 20, 2012 

Page 4 of 6 

• As can be seen in the §114 data, the amount of permanent storage capacity 

nationwide exceeds the amount of temporary storage capacity by an order of 

magnitude, thereby underscoring the concept that future TSFs, if any, do not pose a 

significant risk to air quality justifying regulation at the national level in the form of an 

NSPS. In other words, TSF capacity is too environmentally insignificant to be a 

rational basis for triggering Subpart DD applicability. State/local air pollution control 

agencies are able to address TSFs satisfactorily. 

• Finally, the underlying data indicate that TSF emissions are too environmentally 

insignificant to justify regulation at the national level in the form of an NSPS, 

including having TSF capacity count towards permanent storage capacity at a 

fractional level. As noted above, the ratio of turnovers and, hence, emissions of 

TSFs versus permanent storage is roughly 1-to-10. But that is only a comparison of 

one bushel of TSF as against one bushel of permanent storage. Since Subpart DD 

is a national-scale rule, logic calls for taking also into account the ratio of TSF 

capacity nationally to permanent storage nationally, as reflected in the §114 data. 

That ratio is also less than 10 percent, meaning that on a national basis, uncontrolled 

TSF emissions amount to less than 1% of the uncontrolled emissions associated 

with permanent storage. Emissions of such a small magnitude would not be worth 

regulating by means of an NSPS or of counting any fraction of TSF as “permanent” 

capacity. 

In sum, on the basis of the Subpart DD rulemaking record and the §114 data, TSF 

capacity is clearly not the same as permanent storage capacity and, therefore, it should 

not be considered at all in making Subpart DD applicability determinations. The Coalition 

urges EPA to exclude TSFs from Subpart DD altogether, and certainly from any 

quantification of permanent capacity. 

The Coalition very much agrees with the view you expressed during the July 25 meeting 

that, assuming EPA does not repeal Subpart DD and instead revises it, the revised version 

and the old version should treat TSFs in the same way. From the Coalition’s standpoint, 

that means that TSFs should be excluded from Subpart DD altogether. As the Coalition 

explained in its May 14, 2010, petition to rescind the OECA opinion, that opinion is 

incorrect in concluding that TSFs are a form of permanent storage. Based on the record 

for the original rulemaking, EPA could not have intended Subpart DD to apply in any way 

to TSFs when Subpart DD was promulgated. While TSFs have now come into 

widespread use, it is clear from the §114 data that they are too inconsequential to warrant 

national regulation in the form of an NSPS. State and local agencies can address them 

adequately. 

The Coalition repeats the request in its May 14, 2010, petition that EPA squarely address 

the Coalition’s arguments in that petition against the OECA opinion and propose to rescind 

it as part of the Agency’s “review” of Subpart DD. The OECA opinion is an unavoidable 

part of that “review.” EPA at some point will have to respond to those arguments. 
Mr. William Schrock 

Follow-up to the July 25 Meeting of the NSPS Subpart DD Coalition with EPA-OAQPS 

September 20, 2012 

Page 5 of 6 

3. Emergency Grain Storage Operations and How an Emergency Grain Storage Pile 

Differs from a TSF 

“Emergency grain storage” is a grain storage practice used by grain elevator operators 

during bumper-crop years and for other unique circumstances in “emergency” situations 

where there is no better alternative for grain storage. This practice, which involves 

outdoor piling of grain, is not regulated under Subpart DD. Emergency storage differs 

from temporary storage in an important way - it lacks one or more of the four key 

characteristics of TSFs. For instance, emergency storage often lacks sidewalls, a cover 

and, sometimes, aeration. 

The amount of particulate matter emissions from emergency storage piles may be similar 

to that of TSFs (on a “pounds per bushel of throughput” basis) during times when 

emergency storage piles are actually used. However, emergency piles are used 

infrequently and only in “emergency” situations where there is no better alternative for 

grain storage. Storage of grain in emergency piles is significantly less desirable when 

compared to storage in a TSF or permanent storage facility because of the potential for 

loss of inventory and degradation of the grain quality. Simply put, emergency storage 

piles represent storage of last resort for grain elevator operators. Thus, emergency 

storage piles should not be considered equivalent to TSFs in terms of environmental 

impacts and it is appropriate to continue the historical practice of not regulating such 

infrequently used sources under Subpart DD, nor should such sources be considered in 

determining applicability of Subpart DD at a given facility. 

4. Issues and Concerns That the Coalition Has Previously Discussed with the Agency 

Coalition representatives met with EPA representatives and representatives from EPA’s 

contractor ERG several times during 2010 to discuss a number of issues and concerns 

with NSPS Subpart DD. As a result of these discussions, the Coalition had RTP prepare 

11 “white papers,” which provided analysis of certain of the issues discussed at these 

meetings as well as suggested revisions to Subpart DD language to address these issues. 

Electronic copies (PDF files) of these 11 white papers were provided (via email) to EPA in 

June and August of 2010. 

EPA is now renewing its efforts to revise and update Subpart DD. One purpose of this 

letter is to summarize the issues described in the previously submitted white papers. 

A brief summary of the issues addressed in the previously submitted white papers is 

included in Table 1, along with the title and date of each paper submitted to EPA. Note 

that the intent of the summary is not to replace the information in the white papers 

themselves, but to provide a quick reference guide to facilitate EPA’s review and 

consideration of these documents. Copies of the individual white papers are included with 

this letter, following Table 1. 

* * * * * * * 

1 

Table 1. Summary of 11 Previously Submitted “White Papers” Developed by RTP on behalf of the Coalition 

File Name 

Date 

Submitted to 

EPA 

Status Summary 

Barge Unloading Paper 2010-06-28.pdf 06/29/2010 Only version submitted 

This paper identifies the fact that alternative barge unloading systems are not regulated under Subpart DD, identifies the fact that very little opacity data exist for such systems, and raises the question as to whether alternative barge unloading operations are significant enough to be regulated at all. 

Dry Mill Clarification 2010-06-25.pdf 06/25/2010 Only version submitted 

This paper identifies an issue that has occurred where some state/local permitting authorities have incorrectly applied Subpart DD to dry corn mills that produce fuel ethanol and suggests rule language that would clarify Subpart DD applicability at these sources. 

Grain Dryer Paper 2010-06-15.pdf 06/15/2010 Initial submittal 

This paper demonstrates that Subpart DD does not currently apply to wire-screen (rice) dryers. It provides an estimate of the U.S. population of wire-screen dryers and their emissions. It demonstrates that wire-screen dryers are an insignificant 

emissions source and that they should not be regulated under 

Subpart DD. It determines, based on available data, that if an opacity limit is imposed, it should be at least 10%. 
2 

Table 1. Summary of 11 Previously Submitted “White Papers” Developed by RTP on behalf of the Coalition 

File Name 

Date 

Submitted to 

EPA 

Status Summary 

Grain Dryer Paper V2 2010-07-31.pdf 08/02/2010 Supplement al 

This paper outlines a proposed design standard for wire-screen dryers that is arguably more stringent than the present standard for perforated-plate column dryers. Assuming that EPA determines that wire screen dryers are "significant" and, therefore, should be regulated under Subpart DD, the use of the design standard and definition outlined in this paper should be considered as the basis for such regulation. 

Grain Elevator Definition 2010-06-25.pdf 

06/25/2010 Initial submittal This paper is completely superseded by the July 31, 2010, version below. 

Grain Elevator Definition V2 2010-07-31.pdf 

08/02/2010 Replacemen t submittal 

This paper provides suggested language revisions to Subpart DD to address problems that some Coalition members have experienced with permitting authorities misinterpreting what constitutes the “grain handling operations” affected facility. It also provides suggestions to address situations where more than one grain elevator may exist at a single location. 

Grain Handling Opacity Testing 2010-06-15.pdf 

06/15/2010 Only version submitted 

This paper provides suggested language revisions to Subpart DD to address situations where opacity measurements are required for equipment that is fully enclosed. The intent of this suggested language is to avoid expending resources on opacity measurements for equipment that, by design, cannot have visible emissions. 
3 

Table 1. Summary of 11 Previously Submitted “White Papers” Developed by RTP on behalf of the Coalition 

File Name 

Date 

Submitted to 

EPA 

Status Summary 

Grain Unloading 2010-06-25.pdf 06/25/2010 Only version submitted 

This paper provides suggested language revisions to Subpart DD to clarify the boundaries of grain loading and grain unloading stations. Such clarification is needed to ensure 

consistent evaluations when determining whether a capital expenditure occurs or whether an affected facility is 

reconstructed. 

Mineral Oil Paper 2010-06-15.pdf 06/15/2010 Only version submitted 

This paper addresses the potential applicability of mineral oil as a control technique for reducing emissions from TSF 

operations. It concludes that the control cost-effectiveness of 

using mineral oil is excessive. Note that in June 2012, as Coalition representatives alerted EPA on July 25, 2012, the European Food Safety Authority (EFSA) published a scientific 

opinion on dietary exposure in humans to mineral oil hydrocarbons. EPA needs to be mindful of this opinion in any requirements it might impose that implicate the use of mineral oil as a control technique for reducing emissions from TSF operations. 

Representative Testing 2010-06-25.pdf 06/25/2010 Initial submittal This paper is completely superseded by the July 31, 2010, version below. Representative Testing V2 2010-07-31.pdf 08/02/2010 Replacemen t submittal 

This paper provides suggested changes to Subpart DD to allow affected facilities to conduct representative testing on "identical affected facilities." It also suggests a minor clarification to the language in §60.303(b)(1). 
304-A West Millbrook Road 

Raleigh North Carolina 27609

(919) 845-1422

Memorandum 

To: Jess McCluer and Dave Ailor 

CC: Peter Wyckoff, NSPS Subpart DD Coalition 

From: Jack Burke – RTP Environmental Associates, Inc.

Date: June 28, 2010

Re: Applicability of and Alternatives to the Current NSPS Subpart DD Barge Unloading 

Standard

 

Background

Subpart DD defines each barge unloading station as an affected facility. The term “barge 

unloading station” is not specifically defined, but the term “grain unloading station” is defined as 

“that portion of a grain elevator where the grain is transferred from a truck, railcar, barge, or ship 

to a receiving hopper.” 

Subpart DD regulates fugitive particulate matter emissions from certain barge unloading 

operations through a design/work practice standard at §60.302(d): 

“The owner or operator of any barge or ship unloading station shall operate as follows: 

(1) The unloading leg shall be enclosed from the top (including the receiving hopper) to the 

center line of the bottom pulley and ventilation to a control device shall be maintained on 

both sides of the leg and the grain receiving hopper. 

(2) The total rate of air ventilated shall be at least 32.1 actual cubic meters per cubic meter of 

grain handling capacity (ca. 40 ft3

/bu). 

(3) Rather than meet the requirements of paragraphs (d)(1) and (2) of this section the owner 

or operator may use other methods of emission control if it is demonstrated to the 

Administrator's satisfaction that they would reduce emissions of particulate matter to the 

same level or less.” 

To aid in understanding the scope of this requirement, RTP reviewed the record for the original 

Subpart DD rulemaking. In regards to barge unloading, the “Standards Support” document for 

the 1977 proposed rule states: 

“Grain is received by barge at inland terminal and port terminal elevators. The unloading 

areas are generally open to the weather. In most cases grain is unloaded with a bucket 
Applicability of and Alternatives to the Subpart DD Barge Unloading Standard 

28 June 2010 

Page 2 of 3 

elevator (leg) that is lowered into the barge. Their capacities range from 15,000 up to 75,000 

bushels per hour; the average is about 30,000.”1

And in the proposed rule, EPA states: 

“All of the bucket elevators (legs) observed by EPA at barge and ship unloading stations 

during the development of the proposed standards had various types of enclosures and were 

ventilated. A facility with the leg enclosed from the top (including the receiving hopper) to 

the center line of the bottom pulley appeared to perform with the least emissions. This 

facility was observed in operation with and without the ventilation system in operation. 

Visible emissions were observed to be significantly lower when the ventilation system was 

operating than when it was not. EPA concluded that this system represents the best 

demonstrated system of emission reduction (considering costs) and proposes an equipment 

standard based on the design of' this system.” [42 FR 2845] 

There were no changes in the barge unloading provisions between the proposed and the final 

rules.2

 In RTP’s view, the above statements demonstrate that Subpart DD is focused on 

regulating fugitive emissions from bucket elevator unloading legs used for barge unloading. 

§60.302(d)(3) provides for equivalency determinations in situations where it is not possible to 

meet the design standards in §60.302(d)(1) and (2). There are several types of barge unloading 

equipment that have been developed since Subpart DD was promulgated, which appear to fall 

into this category. Specifically, continuous barge unloaders (CBUs) and en-masse style drag 

conveyors could conceivably be considered to have “unloading legs” and, therefore, be subject to 

the provisions of Subpart DD. However, neither of these unloading systems is a “bucket 

elevator” as the term is used in the original Subpart DD rulemaking record. These unloading 

systems differ significantly in design from the unloading legs referenced in §60.302(d). 

Based on discussions with Coalition members, RTP has determined that there is some confusion 

among both elevator owners and permitting authorities as to how alternative unloading systems 

(i.e., systems that do not employ a bucket elevator unloading leg) are regulated under 

Subpart DD. In some cases, members of the Coalition have applied for equivalency 

determinations under the provisions of §60.302(d)(3), even though their unloading system does 

not include a bucket elevator unloading leg. And in some cases, Coalition members have had 

difficulty in obtaining equivalency determinations. The Coalition has expressed a desire to have 

Subpart DD modified to address these issues. 

 

1

 “Standards Support and Environmental Impact Statement Volume 1: Proposed Standards of Performance for 

Grain Elevator Industry,” EPA·450/2·77·001a, January 1977. 

2

 “Standards Support and Environmental Impact Statement Volume 2: Promulgated Standards of Performance for 

Grain Elevator Industry,” EPA-450/2-77-001, April 1978. 
Applicability of and Alternatives to the Subpart DD Barge Unloading Standard 

28 June 2010 

Page 3 of 3 

Analysis

A careful review of the provisions in §60.302(d) and the relevant rulemaking record leads one to 

conclude that the Subpart DD requirements apply only in those situations where an affected 

barge unloading operation employs a bucket elevator unloading leg to remove grain from a barge 

or ship. Other types of barge and ship unloading operations (e.g., barge unloading using a clam 

shell) are not subject to any specific requirements under Subpart DD. This interpretation is 

consistent with the data and information EPA used as the basis for the requirements in 

Subpart DD. 

It would be helpful for EPA to eliminate the confusion surrounding the scope and applicability of 

the barge unloading provisions in Subpart DD. Additionally, it would be desirable for the 

Agency to streamline the equivalency determination process in situations where such a 

determination is required. 

Based on a May 6th meeting between RTP, EPA and ERG, it appears the Agency is considering 

an opacity limit as an alternative to the design standard in the current rule. Based on discussions 

with and information received from Coalition members, RTP believes that available data are 

inadequate for developing an opacity limit for alternative unloading designs. Through a survey 

of Coalition members, RTP obtained opacity test data for only one alternative unloading leg. 

This is an en-masse drag conveyor at Bunge’s Cairo, Illinois facility. No opacity test data have 

been identified for a CBU and only two opacity tests were obtained for barge unloading 

operations that do not involve unloading legs (e.g., a clam-shell unloader). 

Because alternative unloading systems (i.e., unloading systems that do not use a bucket elevator 

unloading leg) were not considered in the original Subpart DD rulemaking, the threshold 

question that must be addressed going forward is whether such alternative systems are a 

significant source of emissions (i.e., Is it appropriate to regulate these sources under Subpart 

DD?). RTP understands that the Coalition is prepared to work with U.S. EPA in addressing this 

question. 

 
304-A West Millbrook Road 

Raleigh North Carolina 27609

(919) 845-1422

Memorandum 

To: Jess McCluer and Dave Ailor 

CC: Peter Wyckoff; NSPS Subpart DD Coalition Members 

From: Jack Burke – RTP Environmental Associates, Inc.

Date: June 25, 2010

Re: Dry Mill Clarification to Grain Storage Elevator Definition in NSPS Subpart DD

Issue: 

§60.301(f)(2) of Subpart DD defines a “grain storage elevator” as: 

“any grain elevator located at any wheat flour mill, wet corn mill, dry corn mill (human 

consumption), rice mill, or soybean oil extraction plant which has a permanent grain 

storage capacity of 35,200 m3

 (ca. 1 million bushels).” [emphasis added] 

Some permitting agencies have interpreted this threshold incorrectly to apply to dry corn mills 

that do not produce products destined for human consumption (i.e., fuel ethanol plants). To 

eliminate confusion, the NSPS Subpart DD Coalition would like EPA clarify the definition of 

“grain storage elevator” to specifically exclude dry corn mill plants that produce fuel ethanol. 

Suggested Clarifications to Subpart DD: 

To eliminate confusion regarding dry corn mills, the following change to the definition of grain 

storage elevator at §60.301 is suggested: 

(f) Grain storage elevator means any grain elevator located at any wheat flour mill, wet corn 

mill, dry corn mill (human consumption), rice mill, or soybean oil extraction plant which has 

a permanent grain storage capacity of 35,200 m3

 (ca. 1 million bushels). Grain elevators at 

dry corn mills that produce ethanol for fuel use are not grain storage elevators.
304-A West Millbrook Road 

Raleigh North Carolina 27609

(919) 845-1422

Memorandum 

To: Jess McCluer & Dave Ailor 

CC: Peter Wyckoff, NSPS Subpart DD Coalition 

From: Jack Burke – RTP Environmental Associates, Inc.

Date: June 15, 2010

Re: Column Grain Dryers Using Woven Wire Screens as the Column Walls

Introduction and Summary

This memorandum summarizes RTP’s analysis of issues associated with the possible regulation 

of column grain dryers that use woven wire screens instead of perforated plates. RTP has 

reviewed available data on this type of dryer. Based on this review, the rate of emissions from 

these dryers is low and the rate of construction, modification, and reconstruction of such dryers 

is also low. The combination of these factors means that such dryers are an insignificant 

subcategory of equipment at grain elevators from an emissions perspective and, therefore, are not 

appropriate for regulation under Subpart DD. RTP also found no data to support the position 

that these dryers can meet a 0 percent opacity limit. The limited data available suggest any 

opacity limit should be at least 10 percent. 

Background

Subpart DD regulates emissions from certain column dryers. Figure 1 is a simplified crosssection sketch of a column dryer. In this type of dryer, wet grain is fed to the dryer at the top and 

flows by gravity through a packed column to the bottom of the dryer. Heated air is introduced 

on the inside of the columns and flows out through the grain to the atmosphere. The grain 

columns are contained by parallel walls constructed of perforated plates or wire mesh screens, 

depending on the application. Air moving through the grain columns dries the grain but also can 

entrain particulate matter, which may be emitted to the atmosphere. 

Subpart DD only regulates emissions from certain types of column dryers. The rule defines a 

column dryer to be “any equipment used to reduce the moisture content of grain in which the 

grain flows from the top to the bottom in one or more continuous packed columns between two 

perforated metal sheets.”[emphasis added] Thus, column dryers that contain the grain column 

between walls made of something other than perforated metal sheets (e.g., woven wire screens) 

are not considered column dryers for purposes of Subpart DD. 

 
Wire Screen Dryer Review 

15 June 2010 

Page 2 of 6 

Figure 1. Simplified Schematic of Grain Column Dryer 

 
Wire Screen Dryer Review 

15 June 2010 

Page 3 of 6 

Under Subpart DD, any “column dryer” with a column plate perforation exceeding 2.4 mm 

diameter (ca. 0.094 inch) must meet a 0 percent opacity standard. Otherwise, Subpart DD 

contains no specific emission limits or other requirements for column dryers. The standard was 

established in this way because, during the 1977-1978 rulemaking process, EPA concluded that 

add-on controls for column dryers were not cost effective.1

 The structure of the rule language is 

such that meeting a design standard (e.g., a dryer having column plate perforations less than or 

equal to 2.4 mm in diameter) effectively exempts regulated column dryers from the 0 percent 

opacity standard. 

At the time the column dryer standard was developed, there may have been relatively few dryers 

that employed wire screens as walls to contain the grain columns in the dryer.2 Wire screen 

walls are preferred for rice drying because they offer greater durability, result in less kernel 

damage, and provide for more efficient dryer operation. Figure 2 contains photographs of the 

two types of column dryer walls. 

Figure 2. Woven Wire and Perforated Plate Materials 

RTP has examined the database compiled from the responses by Subpart DD Coalition members 

to U.S. EPA’s September 2009 Section 114 information request. Of the 28 column dryers that 

 

1

 See “Standards Support and Environmental Impact Statement Volume 1: Proposed Standards of Performance for 

Grain Elevator Industry;” U.S. EPA, OAQPS, January 1977. One reason that controlling grain dryers is 

expensive is because typically they are only used for relatively short periods each year as grain is harvested. In 

some years the dryers are not used at all. 

2

 Of the 28 wire screen dryers identified in the Subpart DD Section 114 survey responses, only two were 

constructed prior to 1989 and only one prior to 1980. However, RTP is aware that this type of dryer was in 

relatively common use for drying rice in California during the 1970s (see, for example, “Staff Report on 

Emissions from Rice Dryers in the Sacramento Valley Air Basin”, California Air Resources Board, April 11, 

1974). 
Wire Screen Dryer Review 

15 June 2010 

Page 4 of 6 

indicate the use of wire screen column walls, all but two are used for rice or rice and some other 

grain.3

 

RTP also contacted several dryer manufacturers to better understand the grain dryer marketplace 

in general and the market for wire screen dryers in particular. We identified two manufacturers 

who sell “rice dryers” that use wire screens as column walls.4

 Recent sales of these rice dryers 

have been limited to a one or two each year from each of these manufacturers. One of these 

manufacturers described wire screen dryers as a “niche market.” 

RTP also reviewed recent data on U.S. rice production. These data, which are plotted in 

Figure 3, show that rice production was relatively static between 2002 and 2009.5 This steady 

production rate suggests that rice dryer sales are likely driven by the need for replacement units 

rather than a large expansion in capacity due to a long-term trend of increasing rice crop 

production. 

Wire Screen Column Dryer Emissions

As part of its ongoing review of Subpart DD, U.S. EPA may be considering adding compliance 

requirements for column dryers that use wire screens (i.e., rice dryers). One issue is whether the 

expected growth of this source subcategory warrants regulation under the NSPS. To evaluate 

this issue, there are at least two questions that should be addressed. Both relate to the 

significance of column dryers as sources of emissions at grain elevators. The first question is the 

level of emissions from rice dryers. The second is the expected growth in the population of new 

and reconstructed rice dryers going forward. The discussion that follows addresses each of these 

questions. 

In an effort to assess emissions from new and reconstructed rice dryers, RTP reviewed the 

background documentation for the development of AP-42 Section 9.9.1.6

 This review, which 

provided information on grain dryer emission factors specific to screen rice dryers, shows that 

these emissions are in general lower than the final AP-42 emission factor for column grain 

dryers. According to the data in the AP-42 background report, the average particulate emissions 

from screen rice dryers is 0.051 lb/ton, as compared to the AP-42 general grain column dryer 

emission factor of 0.22 lb/ton.7

 

 

3

 RTP also determined that one of the two non-rice dryers is actually not a woven wire screen-type dryer (i.e., the 

Zimmerman dryer uses a thin sheet of stainless steel that appears to be a “screen,” but is actually a perforated 

plate). 

4

 The dryer vendors contacted by RTP include Shanzer (a Division of D & W Industries, Inc.) and GSI (a Division 

of GSI Group). 

5

 These years represent the rice crop data that are readily available on USDA’s website. 

6

 “Emission Factor Documentation for AP-42 Section 9.9.1 - Grain Elevators and Grain Processing Plants - Final 

Report”, RTI International, April 2003. 

7 Ibid, Tables 4-13 and 4-16. 
Wire Screen Dryer Review 

15 June 2010 

Page 5 of 6 

Figure 3. Recent U.S. Rice Production 

A typical rice dryer has a capacity of about 5,000 bushels per hour and operates for about 2,000 

hours per year.8

 Rough rice has a bulk density of about 45 pounds per bushel. Thus, using the 

emission factor data cited above, a typical rice dryer would be expected to emit about 5.7 pounds 

per hour of particulate emission. The PM10 and PM2.5 fractions of these emissions are estimated 

to be about 2.2 and 0.4 lb/hr, respectively.9

 For 2,000 hours per year of operation, annual 

emissions from a typical rice dryer would be about 5.7 tons of PM, 2.2 tons of PM10, and 0.4 tons 

of PM2.5. 

 

8

 Approximate average capacity and operating hours of rice dryers reported in surveys, per discussion with Neil 

Washburn, Riceland Foods, Inc. 

9

 The average PM10 fraction of screen rice dryer PM emissions is ~38 percent, and the average PM2.5 fraction is 

~6.5 percent; see “Staff Report on Emissions from Rice Dryers in the Sacramento Valley Air Basin”, California 

Air Resources Board, April 11, 1974, Figure 6. 

400

420

440

460

480

500

520

540

560

580

600

Annual Rice Production (million bushels)
Wire Screen Dryer Review 

15 June 2010 

Page 6 of 6 

RTP estimates the current U.S. population of screen rice dryers to be somewhere in the 

neighborhood of 120 units.10 Assuming these dryers have a 30-year service life, about 3 percent 

of them will be reconstructed or replaced each year. With no growth in rice crop, this translates 

to about four new or reconstructed rice dryers annually. This value is consistent with the 

anecdotal information obtained from the two rice dryer vendors contacted by RTP. Given the 

relatively low emissions from each dryer and the small number of dryers likely to become 

subject to any prospective NSPS, it is reasonable to conclude that wire screen rice dryers belong 

to a subcategory of sources that is not “significant” from the perspective of the NSPS process. 

Opacity Standards

Through discussions with U.S. EPA, RTP is aware that the Agency is considering a 0 percent 

opacity standard for screen rice dryers. This standard is based on current permit limits for 

several dryers in Arkansas. It is RTP’s understanding that these limits were imposed by the 

Arkansas Department of Environmental Quality (ADEQ) based on the Department’s 

interpretation that the dryers are subject to Subpart DD. It is also RTP’s understanding that these 

dryers may not meet a 0 percent opacity standard under all operating conditions. In particular, 

during initial startup and when the rice supply is changed, the dryers exhibit short-term visible 

emissions in excess of 0 percent opacity. Finally, it is RTP’s understanding that the dryers in 

question have never been compliance tested using Method 9, so no data actually exist to 

demonstrate the ability to comply with a 0 percent opacity standard. Limited opacity data 

provided to U.S. EPA by the Coalition show that screen rice dryers typically cannot meet such a 

limit on a short-term basis.11 If such a limit cannot be achieved in practice, then it should not 

form the basis for an NSPS. 

Conclusions

In the U.S., wire screen column dryers are used primarily for drying rice. If Subpart DD were to 

regulate wire screen column dryers, about four dryers per year would become subject to the 

NSPS, for a total of 20 dryers over the next five years. Given the relatively small rate of 

emissions from these dryers, this subcategory of sources should be considered insignificant and 

therefore, should not be regulated under the revised NSPS. 

It does not appear that a 0 percent opacity standard for wire screen rice dryers has been achieved 

in practice. Therefore, this limit should not form the basis for an NSPS for these dryers. Based 

on the data supplied to U.S. EPA in September 2009, a more appropriate limit would be 10 

percent opacity. 

 

10 This estimate is based on total U.S. rice production of about 450 million bushels in 2009, an average dryer size of 

5,000 bushels per hour, average operating hours of 2,000 hours per year, the assumption that 90 percent of rice 

production is dried, and the assumption that each bushel of rice passes through a dryer three times. Thus, the 

number of 5,000 bushel/hour rice dryers can be estimated as follows: 

(450 MM bushels/yr) x (0.9 bushels dried /bushel) x (3 passes) / (5,000 bushels/hr/dryer x 2,000 hr/yr) = 121.5 

dryers 

11 Data provided to U.S. EPA by Riceland Foods, Inc. in a presentation made in September 2009. 
304-A West Millbrook Road 

Raleigh North Carolina 27609

(919) 845-1422

Memorandum 

To: Jess McCluer & Dave Ailor 

CC: Peter Wyckoff, NSPS Subpart DD Coalition 

From: Jack Burke – RTP Environmental Associates, Inc.

Date: July 31, 2010

Re: Design Standard for Column Grain Dryers Using Woven Wire Screens as the Column 

Walls

Issue: 

In a previous memorandum dated June 15, 2010, RTP provided the Coalition with an analysis of 

rice dryers using woven wire screens as the column walls. In a discussion of this analysis during 

the Coalition’s July 8th, 2010, meeting with U.S. EPA, an alternative approach to regulating these 

dryers was identified. This approach involved setting a design standard for woven-wire screen 

rice dryers that would be analogous to the current design standard for column dryers. 

As background, Subpart DD defines a column dryer as “any equipment used to reduce the 

moisture content of grain in which the grain flows from the top to the bottom in one or more 

continuous packed columns between two perforated metal sheets.” As described in RTP’s 

June 15 memorandum, the definition of “column dryer” does not include wire screen rice dryers. 

It is my impression of the discussion of this issue with EPA, that the Agency agrees with the 

Coalition’s view regarding wire screen dryers. 

The current standard for column dryers requires that the perforations in the column walls be less 

than or equal to 2.4 mm (2,400 μm) in diameter. Otherwise, the dryer is subject to a zero percent 

opacity standard. A 2.4-mm diameter represents a cross-sectional area of 4.5 mm2

, which is 

about equivalent to a 10 mesh screen which has an opening size of 4.0 mm2. 

The suggestion was made that the definition of “column dryer” be amended to include wire 

screen dryers, and that the design standard be modified accordingly. EPA agreed to consider 

such approach and the Coalition agreed to provide EPA with additional information to aid in that 

consideration. This memorandum provides suggested revisions to the current Subpart DD 

language to address the issue of wire screen dryers using a design standard. 
Wire Screen Dryer Standard 

31 July 2010 

Page 2 of 2 

Suggested Clarifications to Subpart DD: 

First, revise the definition of column dryer in §60.301 as follows: 

 (m) Column dryer means any equipment used to reduce the moisture content of grain in 

which the grain flows from the top to the bottom in one or more continuous packed 

columns between two perforated metal sheets, two woven wire screens, or a combination 

of perforated metal sheets and wire screens. 

Next, add a design standard to §60.302(a) for woven wire screen column dryers. The intent of 

this provision is to establish a design standard for rice dryers that requires that the dryers be 

enclosed, and that the enclosure have 24 mesh control screens up to the level of the dryer 

column. Suggested language to implement this concept is added to the current NSPS language 

below: 

(a) On and after the 60th day of achieving the maximum production rate at which the 

affected facility will be operated, but no later than 180 days after initial startup, no owner 

or operator subject to the provisions of this subpart shall cause to be discharged into the 

atmosphere any gases which exhibit greater than 0 percent opacity from any: 

(1) Column dryer with an outside column plate perforation exceeding 2.4 mm 

diameter (ca. 0.094 inch).

(2) Column dryer with column wire screens provided the dryer is not in an enclosure 

having control screens with 24 mesh or smaller openings with such control 

screens at least as high as the exterior dryer column walls.

(32) Rack dryer in which exhaust gases pass through a screen filter coarser than 50 

mesh. 
304-A West Millbrook Road 

Raleigh North Carolina 27609

(919) 845-1422

Memorandum 

To: Jess McCluer and Dave Ailor 

CC: Peter Wyckoff; NSPS Subpart DD Coalition Members 

From: Jack Burke – RTP Environmental Associates, Inc.

Date: June 24, 2010

Re: Definition of Grain Elevator and Scope of Grain Handling Operations Under NSPS 

Subpart DD

Issue #1 

§60.300(a) applies to each affected facility at any grain terminal elevator or any grain storage 

elevator. This subsection identifies “all grain handling operations” as a single affected facility. 

§60.301(b) defines the term “grain elevator” as any plant or installation at which grain is 

unloaded, handled, cleaned, dried, stored, or loaded. At issue is whether two (or more) grain 

elevators at a single location (i.e., on the same or contiguous property) are considered a single 

grain elevator, or whether they are different grain elevators for purposes of the definition of the 

affected facility consisting of “all grain handling operations.” 

Consider the following example. An elevator owner constructs a second, functionally 

independent elevator (subject to the NSPS) at a different location, but on the same property as an 

existing elevator that is not currently subject to the NSPS. If the two elevators (new and 

existing) are considered a single grain elevator, then the construction of the grain handling 

operations associated with the new elevator would likely subject the grain handling operations at 

the existing elevator to NSPS requirements because of the way the affected facility is defined 

(i.e., “all grain handling operations”). None of the other activities at the existing elevator would 

be subject to the NSPS unless they are subsequently modified or reconstructed. 

Issue #2 

Some permitting authorities evaluate NSPS applicability for grain handling operations on an 

individual unit basis (e.g., a single bucket elevator), as opposed to evaluating applicability for the 

collection of “all grain handling operations” at a site, despite the plain language of the rule and 

the discussion in the preamble to the rule.1

 

1

 See 42 FR 2843. 
Grain Elevator Definition 

June 25, 2010 

Page 2 of 2 

For example, in one case, replacement of a single bucket elevator at an existing grain elevator 

has been determined to subject the new bucket elevator to Subpart DD, even though this 

replacement does not meet the definition of construction, reconstruction, or modification. This 

situation has occurred because some permitting authorities view the bucket elevator replacement 

as construction of a new affected facility, even though it really represents a change to a 

potentially affected facility (i.e., “all grain handling operations” at the elevator) and should, 

therefore, be evaluated to determine if it represents either reconstruction or modification of the 

existing affected facility. 

Suggested Clarifications to Subpart DD 

The Coalition has identified several minor changes to the Subpart DD rule language to address 

the issues outlined in this memorandum. First, clarify that the affected facility for grain handling 

operations is limited in scope: 

§60.300 Applicability and designation of affected facility. 

(a) The provisions of this subpart apply to each affected facility at any grain terminal 

elevator or any grain storage elevator, except as provided under §60.304(b). The affected 

facilities are each truck unloading station, truck loading station, barge and ship unloading 

station, barge and ship loading station, railcar loading station, railcar unloading station, 

grain dryer, and the collection of all grain handling operations at each grain elevator. 

Next, adjust the definitions to provide for the possibility of multiple grain elevators at a single 

location: 

§ 60.301 Definitions. 

(b) Grain elevator means any plant or installation at which grain is unloaded, handled, 

cleaned, dried, stored, or loaded. Grain elevators on the same or contiguous property 

and which are functionally independent, are considered separate grain elevators.

Functionally independent means a grain elevator is capable of unloading, handling, 

storing, and loading grain independently from any other grain elevator.
304-A West Millbrook Road 

Raleigh North Carolina 27609

(919) 845-1422

Memorandum 

To: Jess McCluer and Dave Ailor 

CC: Peter Wyckoff; NSPS Subpart DD Coalition Members 

From: Jack Burke – RTP Environmental Associates, Inc.

Date: July 31, 2010

Re: Definition of Grain Elevator and Scope of Grain Handling Operations Under NSPS 

Subpart DD – Revised

Introduction 

In a previous memorandum dated June 25, 2010, RTP provided the Coalition with suggestions 

for addressing several issues related to the definition of a grain elevator and scope of the grain 

handling affected facility in Subpart DD. In a discussion of this memorandum during the 

Coalition’s July 8th, 2010, meeting with U.S. EPA, a concern was identified with one part of the 

suggested language. The memorandum revises the original suggestion to address the concern 

raised during the July 8th meeting. 

 

Issue #1 

§60.300(a) applies to each affected facility at any grain terminal elevator or any grain storage 

elevator. This subsection identifies “all grain handling operations” as a single affected facility. 

§60.301(b) defines the term “grain elevator” as any plant or installation at which grain is 

unloaded, handled, cleaned, dried, stored, or loaded. At issue is whether two (or more) grain 

elevators at a single location (i.e., on the same or contiguous property) are considered a single 

grain elevator, or whether they are different grain elevators for purposes of the definition of the 

affected facility consisting of “all grain handling operations.” 

Consider the following example. An elevator owner constructs a second, functionally 

independent elevator (subject to the NSPS) at a different location, but on the same property as an 

existing elevator that is not currently subject to the NSPS. If the two elevators (new and 

existing) are considered a single grain elevator, then the construction of the grain handling 

operations associated with the new elevator would likely subject the grain handling operations at 

the existing elevator to NSPS requirements because of the way the affected facility is defined 

(i.e., “all grain handling operations”). None of the other activities at the existing elevator would 

be subject to the NSPS unless they are subsequently modified or reconstructed. 
Grain Elevator Definition - Revised 

July 31, 2010 

Page 2 of 2 

Issue #2 

Some permitting authorities evaluate NSPS applicability for grain handling operations on an 

individual unit basis (e.g., a single bucket elevator), as opposed to evaluating applicability for the 

collection of “all grain handling operations” at a site, despite the plain language of the rule and 

the discussion in the preamble to the rule.1

For example, in one case, replacement of a single bucket elevator at an existing grain elevator 

has been determined to subject the new bucket elevator to Subpart DD, even though this 

replacement does not meet the definition of construction, reconstruction, or modification. This 

situation has occurred because some permitting authorities view the bucket elevator replacement 

as construction of a new affected facility, even though it really represents a change to a 

potentially affected facility (i.e., “all grain handling operations” at the elevator) and should, 

therefore, be evaluated to determine if it represents either reconstruction or modification of the 

existing affected facility. 

Suggested Clarifications to Subpart DD 

The Coalition has identified several minor changes to the Subpart DD rule language to address 

the issues outlined in this memorandum. First, clarify that the affected facility for grain handling 

operations is limited in scope: 

§60.300 Applicability and designation of affected facility. 

(a) The provisions of this subpart apply to each affected facility at any grain terminal 

elevator or any grain storage elevator, except as provided under §60.304(b). The affected 

facilities are each truck unloading station, truck loading station, barge and ship unloading 

station, barge and ship loading station, railcar loading station, railcar unloading station, 

grain dryer, and the collection of all grain handling operations at each grain elevator. 

Next, adjust the definitions to provide for the possibility of multiple grain elevators at a single 

location: 

§ 60.301 Definitions. 

(b) Grain elevator means any plant or installation at which grain is unloaded, handled, 

cleaned, dried, stored, or loaded. Grain elevators which are functionally independent,

are considered separate grain elevators.

Functionally independent means a grain elevator is capable of unloading, handling, 

storing, and loading grain independently from any other grain elevator.

 

1

 See 42 FR 2843. 

Deleted: ¶
304-A West Millbrook Road 

Raleigh North Carolina 27609

(919) 845-1422

Memorandum 

To: Jess McCluer and Dave Ailor 

CC: Peter Wyckoff; NSPS Subpart DD Coalition Members 

From: Jack Burke – RTP Environmental Associates, Inc.

Date: June 15, 2010

Re: Grain Handling Opacity Testing Under NSPS Subpart DD

Issue: 

§60.302(c)(2) of New Source Performance Standard (NSPS) Subpart DD limits visible 

fugitive emissions from any grain handling operation to 0% opacity. §60.30(b)(3) requires 

that Method 9 be used to demonstrate compliance with this limit. A grain handling operation 

is defined as “bucket elevators or legs (excluding legs used to unload barges or ships), scale 

hoppers and surge bins (garners), turn heads, scalpers, cleaners, trippers, and the headhouse 

and other such structures.” In many grain elevators, much of this equipment is fully enclosed 

and, therefore, has no fugitive emissions. Conducting Method 9 observations on fully 

enclosed equipment is not a productive use of resources. 

Suggested Clarifications to Subpart DD: 

Two changes to the rule are suggested to address this issue. The first is to provide a 

definition of “fully enclosed” in §60.301, as follows: 

(p) Fully enclosed means a grain handling operation that is inside an enclosure that is 

designed such that it contains no openings through which dust can escape directly to the 

atmosphere. Openings for aspiration are not considered to be openings through which 

dust can escape to the atmosphere. 

The second suggested change provides an optional exemption for fully enclosed grain 

handling operations from the fugitive emissions opacity limit in §60.302, as follows: 

 (c) On and after the 60th day of achieving the maximum production rate at which the 

affected facility will be operated, but no later than 180 days after initial startup, no owner 

or operator subject to the provisions of this subpart shall cause to be discharged into the 

atmosphere any fugitive emission from: 
Grain Handling Operation Opacity Testing 

June 15, 2010 

Page 2 of 2 

(1) Any individual truck unloading station, railcar unloading station, or railcar loading 

station, which exhibits greater than 5 percent opacity. 

(2) Any grain handling operation which is not fully enclosed and which exhibits greater 

than 0 percent opacity. 

(3) Any truck loading station which exhibits greater than 10 percent opacity. 

(4) Any barge or ship loading station which exhibits greater than 20 percent opacity. 

An owner or operator of an affected grain handling operation may elect to make a onetime demonstration that any individual grain handling operation meets the definition of

fully enclosed in §60.301(p) or the owner or operator may elect to comply with the 

applicable opacity limit in (c)(2).
304-A West Millbrook Road 

Raleigh North Carolina 27609

(919) 845-1422

Memorandum 

To: Jess McCluer and Dave Ailor 

CC: Peter Wyckoff; NSPS Subpart DD Coalition 

From: Jack Burke – RTP Environmental Associates, Inc.

Date: June 25, 2010

Re: Suggested Revisions to NSPS Subpart DD Grain Unloading Station Definition 

Issue 

The current definitions of “grain unloading station” and “grain loading station” at §60.301(j) and 

§60.301(k), respectively, are intended to be generally applicable to truck, railcar, barge and ship 

unloading and loading stations. The boundaries of the “unloading station” and “loading station” 

affected facilities are a bit unclear in this definition. In addition, in some cases the termination 

point of a “grain unloading station” may not include a receiving hopper. Better definition of the 

affected facility boundaries is important when determining whether a capital expenditure occurs 

or whether an affected facility is reconstructed. 

Suggested Clarifications to Subpart DD 

The following changes to the definition of “grain unloading station” are suggested to clarify the 

intent of the definition: 

(j) Grain unloading station means that portion of a grain elevator where the grain is 

transferred from a truck, railcar, barge, or ship to a receiving hopper or to the grain handling 

equipment that connects the unloading station to the rest of the grain elevator. A grain 

unloading station includes all of the equipment, support structures, and associated dust 

control equipment and aspiration systems connected to or required to operate the grain 

unloading station. 

This suggested change clarifies that the unloading station includes all of the equipment involved 

in unloading, up to the point that the grain is transferred to either storage or to grain handling 

operations associated with storage. 
Grain Unloading Station Definition 

June 25, 2010 

Page 2 of 2 

It is also suggested that the definition of “grain loading station” be revised in a parallel construct, 

as follows: 

(k) Grain loading station means that portion of a grain elevator where the grain is transferred 

from the elevator to a truck, railcar, barge, or ship. A grain loading station includes all of the 

equipment, support structures, and associated dust control equipment and aspiration systems

connected to or required to operate the grain loading station.
304-A West Millbrook Road 

Raleigh North Carolina 27609

(919) 845-1422

Memorandum 

To: Jess McCluer and Dave Ailor 

CC: Peter Wyckoff; NSPS Subpart DD Coalition Members 

From: Jack Burke – RTP Environmental Associates, Inc.

Date: June 15, 2010

Re: Potential Use of Mineral Oil for Control of Dust from TSF Operations under NSPS 

Subpart DD

Introduction

This memorandum summarizes RTP’s analysis of issues, effectiveness and costs associated with 

the use of mineral oil as a dust suppressant for temporary storage facility (TSF) applications. 

Attached to this memorandum are excerpts from various reference documents on which the 

analysis is based. 

Summary

RTP evaluated the use of mineral oil for controlling dust emissions from the operation of TSFs. 

Putting aside the question of feasibility, or whether this application of mineral oil has been 

demonstrated in practice, the results of RTP’s evaluation demonstrate that mineral oil is not a 

cost-effective means of dust control. Estimated control costs for particulate matter (PM) are 

approximately $7,500 per ton, with PM10 and PM2.5 control costs being much higher. 

Background

Mineral oil is demonstrated to be an effective means of grain dust control for certain applications 

at grain elevators. Reported control efficiencies range from a high of near 90% to a low of 0%, 

depending on the specific circumstances of the application.1

 RTP’s review of the available data 

suggests that initial control efficiencies of 50 to 60 percent appear more typical. Some of the 

relevant factors known to influence the effectiveness of mineral oil as a dust control agent are the 

degree of mixing that occurs between the mineral oil and the grain2

 and the length of time that 

 

1

 The background document for AP-42 cites a range of 60 to 80%. Lab studies show initial control efficiencies 

resulting from mineral oil application can be close to 90%, but the effectiveness of mineral oil declines to zero 

(i.e., no control) after 9 to 12 months of storage of the grain to which it has been applied. Individual field tests 

also show a wide range of efficiencies. See Attachment A to this memorandum for additional details. 

2

 See, for example, “Emission Factors for Grain Elevators, Final Report;” Midwest Research Institute, Kansas City, 

MO; January 3, 1997, page A-1. 
Mineral Oil Control for TSF Operations 

15 June 2010 

Page 2 of 10 

has passed between the mineral oil application and subsequent handling of the grain.3

 Both of 

these factors are important when considering whether mineral oil is an applicable control 

technology for reducing dust emissions from TSFs.4

RTP has examined the Subpart DD database complied from Coalition member’s responses to 

U.S. EPA’s September 2009 Section 114 information request to owners/operators of grain 

elevators. Based on this review, we could not identify any instances where mineral oil is applied 

to TSF filling operations that are managed exclusively with portable or mobile conveying and 

unloading equipment.5 This finding is significant because such TSF operations represent a large 

fraction of the total population of TSFs. 

After examining the nature of TSF filling operations, RTP concluded that it should be possible to 

install mineral oil spray equipment on portable unloading/conveying equipment. The feasibility 

of this type of application is by no means certain, however, and the technology would at a 

minimum, require some engineering and development effort. For example, for most such 

applications, a separate mobile spray system would need to be designed and constructed because 

portable unloading/conveying equipment is typically not suited for mounting a heavy oil supply 

tank. Figures 1 and 2 are photos of this type of equipment. 

Figure 1. Portable Conveyor Serving Temporary Storage Pile 

 

3

 See “Reducing Grain Dust with Oil Additives;” F. S. Lai, et al., Transactions of the ASAE; 1981; Page 1628. 

4

 In this context, the emissions from temporary storage facilities include the activities associated with filling and 

reclaiming the storage pile, including truck unloading, pile building, pile reclaim, and truck loading. 

5

 In some cases, grain loaded onto temporary storage piles has had mineral oil applied to it during handling 

activities within the permanent elevator operations. This grain is later loaded onto temporary storage piles using 

portable equipment. 
Mineral Oil Control for TSF Operations 

15 June 2010 

Page 3 of 10 

Figure 2. Portable Auger System 

If one ignores questions regarding the feasibility of mounting mineral oil spray systems on 

portable unloading equipment, the question still remains as to how effective mineral oil 

application would be in controlling dust emissions from TSFs. There are two key reasons for 

questioning the effectiveness of mineral oil in this type of application: 

• The first reason is the limited opportunity for mineral oil to be mixed with grain as it is 

transferred from trucks onto a temporary storage pile using portable equipment. The 

best-case scenario is to apply the mineral oil immediately after the first transfer point 

(i.e., after the point where the grain drops from the truck into the ground-level hopper of 

the portable conveyor). In this situation, there would be no suppression of dust from the 

unloading operation, but dust emissions from any downstream transfer points and from 

the dropping of grain onto the storage pile would be suppressed. The effectiveness of 

mineral oil in controlling dusting would be limited due to the limited opportunity for 

mixing of the oil and grain in this operation. 

• The second reason has to do with the once-through nature of temporary storage. In most 

cases, once a temporary storage pile is filled, it is covered and it sits virtually undisturbed 

until it is time for the pile to be reclaimed. During the storage period, dust emissions are 

minimal (with or without mineral oil dust suppression). The next opportunity for mineral 

oil to be effective in suppressing dust is when the pile is reclaimed. This reclaim 
Mineral Oil Control for TSF Operations 

15 June 2010 

Page 4 of 10 

operation occurs on average about six months6

 following the pile filling operations. Tests 

show that mineral oil loses about two-thirds of its effectiveness in controlling dust 

emissions six months after the initial application.7 Because of this loss of efficiency, the 

application of mineral oil to grain entering a temporary storage pile has significantly less 

impact on emissions from subsequent handling than it would for grain that is stored for 

shorter periods of time (e.g., as it does with permanent storage, which typically 

experiences multiple turnovers annually). 

Two final concerns exist. One is that soybeans that are treated with mineral oil and are 

subsequently exported to the European Union may yield soybean oil having hydrocarbon levels 

in excess of a FEDIOL code of practice of 300 ppmw.8 A second concern, which has been 

expressed by several Coalition members, is that applying mineral oil to wheat may have 

detrimental impacts on milling operations. Both issues would have to be carefully investigated 

before a requirement that mandates mineral oil application to all grains in temporary storage 

could be considered feasible. 

Analysis 

In an effort to assess the cost-effectiveness of using mineral oil for controlling dust emissions 

from temporary storage, RTP defined a TSF emissions model and then applied reasonable 

estimates of mineral oil control efficiency to this model. The TSF emissions model, including 

expected mineral oil control efficiencies, and the basis for this model, are summarized in 

Table 1. Note that PM emissions are used in this computation to provide comparison to costeffectiveness values addressed in the Coal Preparation NSPS which EPA recently revised 

(74 FR 51950). 

The TSF emissions model shown in Table 1 results in an overall uncontrolled PM emission 

factor of 0.174 lb/ton of grain throughput. The overall mineral oil controlled emission factor is 

0.118 lb/ton which yields a decrease of 0.056 lb/ton attributable to the effect of the mineral oil. 

This is the TSF PM emissions reduction that is estimated to result from mineral oil application 

immediately after the grain receiving operation. 

 

6

 For 2007, the average TSF in the NSPS Subpart DD 114 survey was used for 22 weeks and the average turnover 

factor was approximately one. RTP interprets these data to mean that the pile was filled and then emptied about 6 

months later. This interpretation is consistent with how TSFs are used by elevator operators. 

7

 See “Reducing Grain Dust with Oil Additives;” F. S. Lai, et al., Transactions of the ASAE; 1981; Page 1628. 

8

 The EU Oil and Proteinmeal Industry is known as FEDIOL. Part of its code of practice states “that any detection 

of a level [of mineral oil] above 300 mg/kg shall mean that the [vegetable] oil shipment concerned is considered 

to be contaminated by mineral oil.” The code also states: “If the further analysis reveals a contamination by 

external mineral oil, the vegetable oil of the shipment concerned shall not enter the EU feed or food chain.” 
Mineral Oil Control for TSF Operations 

15 June 2010 

Page 5 of 10 

At a mineral oil cost of $3.5/gallon and an application rate of 0.02 weight percent, the cost of 

applying mineral oil to one ton of grain is9

: 

(2000 lb/ton) x (0.0002 lb oil/lb grain) / (6.7 lb/gallon) x ($3.5/gallon) = $0.21/ton of grain 

And the control cost-effectiveness (not including other O&M costs or capital recovery costs for 

the mineral oil system) is: 

($0.21/ton of grain) / [(0.056 lb PM/ton of grain) / (2000 lb/ton)] ≈ $7,500/ton of PM 

The control cost effectiveness for PM10 and PM2.5 is much higher since these pollutants represent 

a relatively small fraction of total particulate emissions (less than 50 percent and 10 percent, 

respectively) from TSF operations. The above control costs are in excess of values that EPA has 

recently determined are not cost-effective.10

Based on the above assessment, RTP concludes that the use of mineral oil is not a cost-effective 

means of controlling dust from TSF operations, even if one assumes its use is feasible. Also, 

note that to our knowledge, the application of mineral oil to grain in conjunction with portable 

conveyors and unloading equipment has not been demonstrated. 

Table 1. TSF Emissions Model Basis 

Activity

Uncontrolled 

PM Emissions 

(lb/ton)*

Mineral Oil 

Control 

Efficiency

Controlled 

PM Emissions 

(lb/ton)

Basis / Discussion

Receiving: 

Hopper Truck 0.035 0% 0.035 Mineral oil cannot be applied until after grain 

enters conveying equipment. 

Grain Handling 0.061 60% 0.0244 Reasonable best-case based on literature 

(see attachment). 

Pile filling 0.002 60% 0.0008 Reasonable best-case based on literature 

(see attachment). 

Storage / 

Aeration 0.013 40% 0.0078 Average between initial efficiency of 60 

percent and final efficiency of 20 percent. 

Pile Reclaim 0.063 20% 0.0504 

Assumes that efficiency declines by 2/3 over 

a six-month storage period. 

Overall 0.174 0.118 

* Uncontrolled emission factors from AP-42, as described in RTP’s presentation to U.S. EPA on February 24, 2010. 

 

 

9

 The cost for mineral oil is based on large bulk purchases and is typical of costs reported by Coalition members. 

Various mineral oil application rates have been studied. A value of 200 ppmw is used in this calculation because 

this rate represents the most common value cited in the literature. Also, the initial control efficiency of 60% is 

consistent with this rate of oil application (i.e., lower initial application rates are expected to lead to lower dust 

suppression efficiencies). 

10 See, for example, 72 FR 22904: “In addition, the incremental benefit and cost of fabric filters at a bituminous 

mine compared to application of chemical suppressants is a reduction of an additional 33 tons of PM, but the 

annual cost is an additional $200,000. Due to these high costs [$6,060/ton], we concluded that fabric filters are 

not BDT for any coal preparation plant processing bituminous coal.” 
Mineral Oil Control for TSF Operations 

15 June 2010 

Page 6 of 10 

ATTACHMENT A 

BACKGROUND INFORMATION 
Mineral Oil Control for TSF Operations 

15 June 2010 

Page 7 of 10 

“Emission Factor Documentation for AP-42 Section 9.9.1; Grain Elevators and Grain 

Processing Plants; Final Report”; April 2003, page 2-44.

The emission control methods described above rely on either process modifications to reduce 

dust generation or capture collection systems to control dust emissions after they are generated. 

An alternative control measure that has developed over the last 10 years is dust suppression by 

oil application. The driving forces for developing most such dust suppression systems have been 

grain elevator explosion control as well as emission control. Consequently, few data have been 

published on the amount of emission reduction achieved by such systems. Recent studies, 

however, have indicated that a PM reduction of approximately 60 to 80 percent may be 

achievable (see References 57 and 61 in Section 4). 

Generally, these oil application dust suppression systems use either white mineral oil, soybean 

oil, or some other vegetable oil. Currently, the Food and Drug Administration restricts 

application rates of mineral oil to 0.02 percent by weight. Laboratory testing and industry 

experience have shown that oil additives applied at a rate of 60 to 200 parts per million by 

weight of grain, or 0.5 to 1.7 gallons of oil per thousand bushels of grain can provide effective 

dust control.36 The effectiveness of the oil suppression system depends to some extent on how 

well the oil is dispersed within the grain stream after it is applied. Several options are available 

for applying oil additives. 

1. As a top dressing before grain enters the bucket elevator or at other grain transfer points. 

2. From below the grain stream at a grain transfer point using one or more spray nozzles. 

3. In the boot of the bucket elevator leg. 

4. At the discharge point from a receiving pit onto a belt or other type conveyor. 

5. In a screw conveyor. 

___________________________ 

Reference 57: Tests of Oil Suppression Of PM-10 At Grain Elevators, Test Report, Midwest 

Research Institute, Kansas City, MO, November 1994. 

Reference 61: Emission Factors for Grain Elevators, Final Report to National Grain and 

Feed Foundation, Midwest Research Institute, Kansas City, Missouri, 

January 3, 1997. 

 

 

36 Letter from Thomas C. O’Connor, National Grain and Feed Association, to Dallas Safriet, U.S. Environmental 

Protection Agency, Research Triangle Park, NC, June 30, 1997. 
Mineral Oil Control for TSF Operations 

15 June 2010 

Page 8 of 10 

“Test Of Oil Suppression Of PM-10 at Grain Elevators, Test Report”; Midwest Research 

Institute, Kansas City, MO, 1994 [AP-42 Section Number: 9.9.1; Reference Number: 16].

The Greenwood elevator applies food grade mineral oil (Amoco Superla DCO) through a spray 

system supplied by InterSystems of Omaha, Nebraska. A cost of $288.50 was quoted for a 55-gal 

drum of the oil during an October 1994 telephone conversation. 

The system sprays oil through inspection ports on the elevator legs. The spray system contains a 

check valve and cannot operate with the oil pressure less than 20 psi. Facility personnel stated 

that they typically operate the system at 25 psi. A representative of Intersystems stated that the 

spray tip used (No. 8001) delivers 0.076 gal/min at 80°F and 20 psi and 0.1 gal/min at 80°F and 

40 psi. [page 3 - 4] 

Mineral Oil Control Efficiency(%) 

Oil at 25 psi Oil at 20 psi

Grain PM-10 PM PM-10 PM

Milo 57 56 33 21

Corn 69 48 79 57

[page 13] 

It should be noted that the mineral oil control efficiency values obtained during this scoping 

study may be lower than that which can be achieved at other installations. This statement is 

based upon the fact that the Greenwood elevator applies the oil to grain in the leg. As a result, 

not all of the oil adheres to the grain and only a limited amount of mixing can occur before the 

grain hits the gallery belt. Other installations designed to spray oil during active grain tumbling 

are expected to exhibit higher control efficiency. [page 19] 

 
Mineral Oil Control for TSF Operations 

15 June 2010 

Page 9 of 10 

“Reducing Grain Dust with Oil Additives”; F. S. Lai, et al., TRANSACTIONS of the 

ASAE; 1981; Page 1628.

Chart generated from data in paper. 

 

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 2 4 6 8 10

Months from Initial Application

Dust Control Efficiency vs. Time

mineral oil @ 0.02 wt. %

Corn

Wheat
Mineral Oil Control for TSF Operations 

15 June 2010 

Page 10 of 10 

“Emission Factors for Grain Elevators, Final Report”; Midwest Research Institute, Kansas 

City, MO; January 3, 1997

Although the country elevator has an oil suppression system, it does not regularly apply oil to the 

grain received. The facility agreed to operate the system on a limited basis for testing purposes. 

Thus, the results obtained during the BD tests reference freshly oiled grains. To obtain 

information on how oil can become more effective with the greater mixing that occurs with 

repeated handling, controlled tests were conducted in pairs. The first test involved freshly oiled 

grain. Thereafter, the second test in the sequence used the same grain in a second "turn"; no 

additional oil was applied. 

The first controlled test sequence involved internal handling of wheat (tests BD-107 and 108). 

When referenced against a mean uncontrolled PM10 emission factor of 0.021 lb/ton, the first and 

second turns resulted in efficiencies of 16% and 48%, respectively. Note, however, that the 

facility reported low pressure when applying the oil. For this reason, a second wheat test 

sequence was conducted (BD-l13 and 114). Here, the oil pressure was reported as normal and the 

first and second turns resulted in 68% and 64% efficiency, respectively. 

A similar test sequence of the internal handling of oiled com was conducted at the country 

elevator. Referenced to an uncontrolled PM10 emission factor of 0.023 lb/ton, the first and 

second turns exhibited 29% and 78%, respectively. 

A second corn test sequence (BD-10 and 11) of shipping emissions was conducted. Again, the 

com was first oiled and then handled. The first turn resulted in no observable control. The corn 

was re-elevated and loaded a second time. For that test, an emission factor of 0.0203 lb/ton was 

found. This represented a 30% reduction from the uncontrolled average of 0.0295 lb/ton. Even 

more importantly, the second test represents a 60% reduction from the first turn. 

Additional controlled tests were conducted at Terminal 1. Unlike the country elevator, 

Terminal 1 routinely oils all grains at the time of receipt. Both controlled test sequences 

involved railcar shipping. Tests BE-111 and 113 were conducted on oiled wheat, and averaged 

78% control of PM10 emissions. Tests BE-109 and 110 (conducted on oiled soybeans) did not 

exhibit any observable control when referenced against the average uncontrolled emission factor 

from Tests BE-106 to 108. [page A-1] 
304-A West Millbrook Road 

Raleigh North Carolina 27609

(919) 845-1422

Memorandum 

To: Jess McCluer and Dave Ailor 

CC: Peter Wyckoff; NSPS Subpart DD Coalition Members 

From: Jack Burke – RTP Environmental Associates, Inc.

Date: June 25, 2010

Re: Representative Testing Under NSPS Subpart DD

Issue 

§60.303 of New Source Performance Standard (NSPS) Subpart DD requires testing of each 

affected facility subject to a particulate matter emissions limit in §60.302. In some situations this 

requirement means that a number of substantially identical units must be tested. A single 

representative compliance test should be sufficient in these situations. 

Suggested Clarifications to Subpart DD 

To address the issue of representative compliance testing and to clarify a minor point of potential 

confusion in §60.303(b)(1), the following revisions to §60.303 are suggested: 

§60.303 Test methods and procedures. 

(a) In conducting the performance tests required in §60.8, the owner or operator shall use as 

reference methods and procedures the test methods in appendix A of this part or other 

methods and procedures as specified in this section, except as provided in §60.8(b). 

Acceptable alternative methods and procedures are given in paragraph (c) of this section. 

(b) The owner or operator shall determine compliance with the particulate matter standards in 

§60.302 as follows: 

(1) Method 5 shall be used to determine the particulate matter concentration and the sampled

volumetric flow rate of the effluent gas. The sampling time and sample volume for each 

run shall be at least 60 minutes and 1.70 dscm (60 dscf). The probe and filter holder shall 

be operated without heaters. 

(2) Method 2 shall be used to determine the ventilation volumetric flow rate. 

(3) Method 9 and the procedures in §60.11 shall be used to determine opacity. 

(c) The owner or operator may use the following as alternatives to the reference methods and 

procedures specified in this section: 
Representative Testing 

June 25, 2010 

Page 2 of 2 

(1) For Method 5, Method 17 may be used. 

(d) An owner or operator required to determine compliance with the particulate matter 

standards in §60.302 may elect to conduct representative testing if performance tests are 

required on more than one identical affected facility.

To clarify the intent of this provision, two key terms should be defined in §60.301, as follows: 

Representative testing means testing of one affected facility in cases where two or more such 

facilities are otherwise required to be tested at a single location.

Identical affected facility means any affected facility that is substantially the same as any 

other affected facility in function, capacity, size, and design.
304-A West Millbrook Road 

Raleigh North Carolina 27609

(919) 845-1422

Memorandum 

To: Jess McCluer and Dave Ailor 

CC: Peter Wyckoff; NSPS Subpart DD Coalition Members 

From: Jack Burke – RTP Environmental Associates, Inc.

Date: July 31, 2010

Re: Representative Testing Under NSPS Subpart DD - Revised

Introduction 

In a previous memorandum dated June 25, 2010, RTP provided the Coalition with suggestions 

for addressing an issue related to testing of multiple identical affected facilities at a grain 

elevator. In a discussion of this memorandum during the Coalition’s July 8th, 2010, meeting 

with U.S. EPA, EPA indicated that any such revisions would need to be consistent with existing 

policy. The memorandum revises RTP’s original suggestions to be consistent with EPA’s 

existing policy on this issue. 

Issue 

§60.303 of New Source Performance Standard (NSPS) Subpart DD requires testing of each 

affected facility subject to a particulate matter emissions limit in §60.302. In some situations this 

requirement means that a number of substantially identical units must be tested. A single 

representative compliance test should be sufficient in these situations. 

Suggested Clarifications to Subpart DD 

To address the issue of representative compliance testing and to clarify a minor point of potential 

confusion in §60.303(b)(1), the following revisions to §60.303 are suggested: 

§60.303 Test methods and procedures. 

(a) In conducting the performance tests required in §60.8, the owner or operator shall use as 

reference methods and procedures the test methods in appendix A of this part or other 

methods and procedures as specified in this section, except as provided in §60.8(b). 

Acceptable alternative methods and procedures are given in paragraph (c) of this section. 

(b) The owner or operator shall determine compliance with the particulate matter standards in 

§60.302 as follows: 
Representative Testing - Revised 

July 31, 2010 

Page 2 of 2 

(1) Method 5 shall be used to determine the particulate matter concentration and the sampled

volumetric flow rate of the effluent gas. The sampling time and sample volume for each 

run shall be at least 60 minutes and 1.70 dscm (60 dscf). The probe and filter holder shall 

be operated without heaters. 

(2) Method 2 shall be used to determine the ventilation volumetric flow rate. 

(3) Method 9 and the procedures in §60.11 shall be used to determine opacity. 

(c) The owner or operator may use the following as alternatives to the reference methods and 

procedures specified in this section: 

(1) For Method 5, Method 17 may be used. 

(d) An owner or operator required to determine compliance with the particulate matter 

standards in §60.302 may elect to conduct representative testing if performance tests are 

required on more than one identical affected facility provided that the units are operated and 

maintained in a similar manner and the owner or operator demonstrates that the emission rate 

of the tested unit is no more than 80% of the applicable emission limit.

To clarify the intent of this provision, two key terms should be defined in §60.301, as follows: 

Representative testing means testing of only one identical affected facility in cases where two 

or more such identical affected facilities are otherwise required to be tested at the same grain 

elevator. 

Identical affected facility means an affected facility that has the same or better emissionrelated design specifications as another affected facility at the same grain elevator.