NSPS SUBPART DD COALITION 

VIA ELECTRONIC MAIL 

September 21, 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.: TWO NEW ISSUE PAPERS DEVELOPED BY RTP ENVIRONMENTAL ASSOCIATES 

ON CERTAIN NSPS SUBPART DD ISSUES 

Bill: 

During June and August 2010, the NSPS Subpart DD Coalition provided you via e-mail with 11 

papers developed by RTP Environmental Associates (RTP) (Raleigh, NC) on certain issues 

related to EPA's ongoing review of New Source Performance Standard (NSPS) Subpart DD for 

Grain Elevators. By this letter, we providing you with two new “issue papers,” which RTP has 

developed. These issue papers, like those I provided you in 2010, reflect the conclusions of 

RTP, as reviewed and endorsed by the Coalition. 

The two papers address: 

• Barge/Ship Unloading Systems, where RTP concludes that, “... based on the results 

of ... survey data, there is no indication that alternative forms of barge/ship unloading 

are of environmental significance and, therefore, it is not appropriate to regulate 

these forms of barge/ship unloading under a new NSPS, particularly when, as the 

Coalition has emphasized separately, state/local air pollution control agencies can be 

expected to adequately address significant emissions, if any, from new barge/ship 

unloading equipment, even in the absence of Subpart DD;” and, 

• Wire Screen Column Dryers, where RTP concludes that “Given the relatively small 

rate of emissions from these dryers (i.e., only about 25% of the emissions from a 

comparably-sized column grain dryers) and the fact that most of these dryers do not 

create any new emissions (i.e., most are replacement units), this subcategory of 

sources should be considered insignificant and, therefore, should not be regulated 

under any revised NSPS. In any event, state/local air pollution control agencies can 

be expected, as the Coalition has emphasized in its petition for repeal of Subpart DD, 

to address PM emissions from new “rice” dryers appropriately, even in the absence 

of Subpart DD.” 

These issue papers supplement company-specific information on these issues provided you 

earlier this week by two companies the Coalition represents, Bunge North America and 

Riceland Foods, respectively. 

304-A West Millbrook Road 

Raleigh North Carolina 27609

(919) 845-1422

Memorandum 

To: Jess McCluer (NGFA) and Dave Ailor (NOPA) 

CC: Peter Wyckoff, NSPS Subpart DD Coalition 

From: Jack Burke – RTP Environmental Associates, Inc.

Date: September 21, 2012

Re: Review of Data on Barge/Ship Unloading Systems

This memorandum builds on an assessment of barge/ship unloading issues related to Subpart DD 

addressed in my memorandum of June 28, 2010.1 I have prepared this document at the request 

of the NSPS Subpart DD Coalition (the “Coalition”). Two general topics are addressed herein. 

The first topic is a brief summary of the conclusions provided in RTP’s June 2010 memorandum. 

The second topic is an assessment of data recently provided by Coalition member companies 

regarding present and planned barge/ship unloading operations at Subpart DD grain elevators.2

Summary of Previous Analysis

RTP’s previous review of the provisions in §60.302(d) and the relevant rulemaking record 

reached the conclusion that Subpart DD requirements apply only in those situations where an 

affected barge/ship unloading operation employs a bucket elevator unloading leg (i.e., a Marine 

Leg) to remove grain from a barge or ship at a Subpart DD grain elevator. Other types of barge 

and ship unloading operations are not subject to any specific requirements under Subpart DD. 

 

1

 See “Applicability of and Alternatives to the Current NSPS Subpart DD Barge Unloading Standard” to Jess 

McCluer (NGFA) and David Ailor (NOPA) from Jack Burke, RTP Environmental Associates, June 28, 2010. 

2

 I use the term “Subpart DD grain elevators” here as shorthand to describe grain storage elevators with a 

permanent storage capacity of 1 million bushels or more and grain terminal elevators with a permanent capacity of 

2.5 million bushels or more. 
Review of Barge/Ship Unloading Data 

21 September 2012 

Page 2 of 5 

This interpretation is consistent with the data and information U.S. EPA used as the basis for the 

unloading station requirements in Subpart DD. 3

Previous discussions between the Coalition and U.S. EPA indicated that the Agency may be 

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 

an April 2010 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 were obtained 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). 

Summary of September 2012 Survey Data

At your request, RTP conducted a voluntary survey of the nine Coalition member companies 

who responded to U.S. EPA’s original §114 Subpart DD information request. This confidential 

survey requested information on barge/ship unloading activities at the companies’ Subpart DD 

grain elevators. Of the nine companies surveyed, I received responses from eight of them. Some 

results of this survey are summarized in Table 1. The data in this table show that: 

 Only about 6% of the surveyed Subpart DD grain elevators have barge/ship unloading 

stations; and 

 Few new barge/ship unloading stations are planned for the next five years. 

 

3

 §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). The inherent design differences 

are the basis for RTP’s conclusion that such unloading systems are not currently regulated under Subpart DD. 
Review of Barge/Ship Unloading Data 

21 September 2012 

Page 3 of 5 

Table 1. Summary of New Survey Data on Barge/Ship Unloading 

Survey Question Response 

Number of Subpart DD Elevators 296 

Number of Subpart DD Elevators with Barge/Ship Unloading 17 

Number of Existing Barge/Ship Unloading Stations 20 

Number of Planned Barge/Ship Unloading Stations (next 5 years) 2 

The survey also requested data on the types of barge/ship unloading systems currently employed 

at the companies’ Subpart DD grain elevators. The results of the survey in this regard are 

summarized in Table 2. As the data in Table 2 show, CBUs and marine legs are the most 

commonly employed types of unloading systems and they have the highest average installed 

capacities. Combined, these two types of unloading systems account for over 90% of the 

installed barge/ship unloading system capacity at the Subpart DD grain elevators surveyed. 

Except for a few of the clam shell unloading systems, all of the unloading systems shown in 

Table 2 have the conveying equipment ventilated to a baghouse for emissions control. 

Table 2. Summary of New Survey Data on Barge/Ship Unloading 

Type of Unloading System Number of 

Systems 

Nominal Average 

Capacity of Systems 

(tons/hr) 

CBU 6 2,400 

Clam Shell 4 300 

En-masse Conveyor 2 200 

Marine Leg (Bucket Elevator) 6 1,100 

Other 2 400 

Analysis of September 2012 Barge/Ship Unloading Survey Data

RTP’s previous assessment of barge/ship unloading issues raised the threshold question of 

whether alternative means of barge/ship unloading warranted regulation at all. The results of the 

survey data described herein provide information that can be used to help answer this question. 

Specifically, the future plans of the survey respondents provide one perspective on the answer to 

the question of whether alternative forms of barge/ship unloading should be regulated under any 

future revision of Subpart DD. As indicated in Table 1, only two new barge/ship unloading 

stations are planned at the 296 Subpart DD grain elevators included in the survey. These 

planned new stations are to be Marine Legs. Consequently, the survey data suggest that 100% of 
Review of Barge/Ship Unloading Data 

21 September 2012 

Page 4 of 5 

the new barge/ship unloading stations to be constructed in the next five years at Subpart DD 

elevators are already regulated under the current rule. This result argues for no new regulation of 

barge/ship unloading stations. 

The new survey data provide another perspective on the answer to the threshold question 

regarding regulation of barge/ship unloading stations. From the survey data, it is clear that 

CBUs are on a par with Marine Leg unloading systems in terms of installed capacity at existing 

Subpart DD elevators. So answering the question of whether CBUs are worthy of regulation will 

help answer the question of whether Subpart DD should address alternative forms of barge/ship 

unloading at all. 

Figure 1 is a photo of the unloading end of a CBU in operation. Aspiration of the casing 

surrounding the buckets in a CBU to a baghouse provides control of some emissions. However, 

as evident from Figure 1, it is not feasible to enclose these units to the center line of the bottom 

pulley as required for Marine Legs under the current Subpart DD regulations. 

Figure 1. Continuous Barge Unloader 
Review of Barge/Ship Unloading Data 

21 September 2012 

Page 5 of 5 

Conclusions

Table 3 shows the potential uncontrolled particulate emissions from a CBU and a Marine Leg. 

As this table shows, CBU emissions on a “pound per ton” basis are significantly less than those 

from a Marine Leg. Given the ratio of average capacities shown in Table 2, these data 

demonstrate that emissions of PM and PM10 from an average sized CBU are of lesser 

significance than from an average sized Marine Leg (i.e., about half) and on par with an average 

sized Marine Leg with respect to PM2.5 emissions. However, the limited number of CBUs in 

existence at Subpart DD grain elevators, the fact that none of the survey respondents has plans to 

install a new CBU in the next five years, and the fact that all of the CBUs in the survey are 

ventilated to a baghouse lead to the conclusion that CBUs do not warrant regulation under 

Subpart DD. 

This conclusion can be extrapolated to other forms of barge/ship unloading by considering their 

relative insignificance when compared to Marine Legs and CBUs. Based on the results of the 

September 2012 survey data, there is no indication that alternative forms of barge/ship unloading 

are of environmental significance and, therefore, it is not appropriate to regulate these forms of 

barge/ship unloading under a new NSPS, particularly when, as the Coalition has emphasized 

separately, state/local air pollution control agencies can be expected to adequately address 

significant emissions, if any, from new barge/ship unloading equipment, even in the absence of 

Subpart DD. 

Table 3. CBU and Marine Leg Emissions4

Pollutant CBU 

(lb/ton) 

Marine Leg 

(lb/ton) 

CBU-to-Marine Let 

Ratio 

PM 0.029 0.15 19% 

PM10 0.0073 0.038 19% 

PM2.5 0.0019 0.0050 38% 

It is also important to re-emphasize the conclusion of RTP’s prior analysis in regards to CBUs, 

en-masse conveyors, pneumatic unloaders and certain other forms of barge/ship unloading. 

These types of unloading systems were not considered in the original Subpart DD rulemaking 

process and, therefore, they are not “unloading legs” as this term is defined in Subpart DD (i.e., 

these units are not subject to regulation under the current version of Subpart DD). 

 

4

 Source: AP-42, Table 9.9.1-1, 3/2003. 
304-A West Millbrook Road 

Raleigh North Carolina 27609

(919) 845-1422

Memorandum 

To: Jess McCluer (NGFA) and Dave Ailor (NOPA) 

CC: Peter Wyckoff, NSPS Subpart DD Coalition 

From: Jack Burke – RTP Environmental Associates, Inc.

Date: September 21, 2012

Re: Review of New Data on Wire-Screen Column Dryers

Background

In a previous assessment of column-type grain dryers that employ woven wire screens (“rice 

dryers”) as the column walls, RTP Environmental Associates, Inc. (RTP) concluded that: 

 This type of dryer is not currently regulated by 40 CFR Part 60, Subpart DD because it 

does not meet the regulatory definition of either a column or rack dryer and these are the 

only types of grain dryers regulated by Subpart DD; and 

 Based on a projected rate of wire-screen dryer construction and the emissions of fine 

particulate (i.e., PM10 and PM2.5) from such dryers, this type of dryer should not be 

regulated under any revised form of Subpart DD. 

On August 28, 2012, Riceland Foods (Riceland) received an email from Roy Oommen of ERG 

(U.S. EPA’s technical support contractor for the Subpart DD regulatory review) soliciting 

additional information on the rice dryers at Riceland’s facilities. Riceland has provided ERG 

with a response to its questions. The data in Riceland’s response raise some questions in regard 

to RTP’s previous analysis of the environmental significance of wire screen rice dryers. The 

purpose of this memorandum is to revisit RTP’s original assessment in light of the data Riceland 

has recently provided to ERG. 

Rice Production

One conclusion of RTP’s original assessment of wire screen dryers was that “rice production was 

relatively static between 2002 and 2009.” Figure 1 is an updated graph of rice production data 
Review of New Data on Wire-Screen Column Dryers 

21 September 2012 

Page 2 of 5 

through July 2012. As this figure shows, U.S. rice production continues to remain at a relatively 

constant level, fluctuating between 400 million and 550 million bushels per year with no upward 

trend in production rates. These data suggest that there is no underlying trend in place that 

would drive an expansion in rice drying capacity in the U.S. 

Figure 1. Recent US Rough Rice Production 

(source: http://www.ers.usda.gov/data-products/rice-yearbook-2012.aspx) 

Size of U.S. Rice Dryer Population

RTP made an estimate of the U.S. rice dryer population in 2010 based on the following 

assumptions: 

 Average Rice Dryer Size = 5,000 bushels 

 U.S. Rice Crop = 450 million bushels 

300

350

400

450

500

550

600

Annual US Rough Rice Production (million bushels)
Review of New Data on Wire-Screen Column Dryers 

21 September 2012 

Page 3 of 5 

 Average Annual Rice Dryer Operating Hours = 2,000 hours 

 Percent of Rice Crop Dried = 90% 

 Number of Drying Passes per Bushel = 3 

 Rough Rice Bulk Density = 46 lb/bushel 

Using these assumptions, the U.S. dryer population was estimated at around 120 units. 

Riceland’s response to ERG’s recent questions demonstrates that this estimate is likely low by a 

significant amount. After discussion with Neil Washburn of Riceland, it appears that RTP’s 

prior estimate of the dryer population, which was derived using average values, did not properly 

account for the peak demand for rice drying that occurs during the harvest season. Thus, any 

estimate of rice dryer population must take the peak drying demand into account. 

Riceland processes about 20% of the U.S. rice crop. A simplistic way to estimate the U.S. rice 

dryer population based on the rice dryer population in Riceland’s facilities would be to scale the 

Riceland rice dryer population upward, assuming that the remaining 80% of U.S. rice processed 

by other companies requires a proportional number of rice dryers. A review of data from one 

rice dryer vendor suggests that this simplistic approach appears reasonable. To RTP’s 

knowledge, there are two primary dryer vendors that supply rice dryers: Shanzer and GSI (Grain 

Systems Inc). Assuming that these vendors have about equal market share yields an estimate of 

approximately 56 new rice dryers installed between 2001 and 2011.1

 Riceland installed 11 new 

rice dryers during this period, or approximately 20% of the estimated total. Since Riceland 

processes about 20% of the U.S. rice crop, Riceland’s share of rice dryer purchases appears to 

mirror its share of the U.S. rice crop. Using a 20% factor to approximate Riceland’s share of the 

U.S. rice dryer population results in an estimate of approximately 600 rice dryers in the U.S. 

Rice Dryer Construction Rates

Given the fact that Riceland’s rice dryer population appears to be representative of the U.S. rice 

dryer population, then Riceland’s past rice dryer purchases can be used as the basis for 

estimating total U.S. rice dryer purchases. As stated above, from 2001 through 2011, Riceland 

purchased 11 new rice dryers.2

 Assuming this value represents 20% of the U.S. market results in 

an estimate of 55 rice dryers constructed between 2001 and 2011, or 5.5 dryers per year. This 

 

1

 Shanzer’s experience list indicates that it supplied 28 rice dryers during this period. 

2

 The term “new” is used here to represent both replacement dryers and additional dryers installed by Riceland. 
Review of New Data on Wire-Screen Column Dryers 

21 September 2012 

Page 4 of 5 

value is slightly higher than RTP’s previous estimate of 4 new rice dryers per year.3 Note 

however, that most of these dryers are likely replacement units.4

 Thus, for the most part, they do 

not result in new emissions from existing facilities. Also, it is RTP’s understanding that not all 

of these dryers are wire screen dryers (i.e., some are NSPS Subpart DD column dryers). 

Rice Dryer Emissions

RTP reviewed the background documentation for the development of AP-42 Section 9.9.1.5

 This 

review, which provided information on grain dryer emission factors specific to wire-screen 

column rice dryers, shows that these emissions are 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, or about 25% of the AP-42 general 

grain column dryer emission factor of 0.22 lb/ton.6

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

hours per year. 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.7 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. 

Conclusion

The current version of Subpart DD does not apply to wire-screen column dryers. If a revised 

Subpart DD were to regulate such dryers, as many as 5 or 6 dryers per year could become subject 

to the NSPS (if all of the new dryers are constructed at Subpart DD affected grain elevators). 

 

3

 See Column Grain Dryers Using Woven Wire Screens as the Column Walls, memorandum from Jack Burke, RTP 

Environmental Associates, Inc. to Jess McCluer and David Ailor, June 15, 2010. 

4

 As discussed in Neil Washburn’s response to ERG’s August 28, 2012, questions, 100% of Riceland’s new dryers 

installed in the last five years were replacement units and two-thirds of the dryers planned for the next five years 

will be replacement units. 

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

Report, RTI International, April 2003. 

6 Ibid, Tables 4-13 and 4-16. 

7

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

about 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. 
Review of New Data on Wire-Screen Column Dryers 

21 September 2012 

Page 5 of 5 

Given the relatively small rate of emissions from these dryers (i.e., only about 25% of the 

emissions from a comparably-sized column grain dryers) and the fact that most of these dryers 

do not create any new emissions (i.e., most are replacement units), this subcategory of sources 

should be considered insignificant and, therefore, should not be regulated under any revised 

NSPS. In any event, state/local air pollution control agencies can be expected, as the Coalition 

has emphasized in its petition for repeal of Subpart DD, to address PM emissions from new 

“rice” dryers appropriately, even in the absence of Subpart DD