Coal Dust from Rail Transport
Prepared for:
Navajo Generating Station Application Studies
Salt River Project Agricultural Improvement and Power District
Black Mesa and Lake Powell Railroad
Prepared by:
Kirk Winges and Richard Steffel
Ramboll Environ US Corporation
19020 33rd Avenue, Suite 310
Lynnwood, Washington 98036
425-412-1800
Date:
January 2016
Ramboll Environ Project Number:
06-32922C2
Coal Dust from Rail Transport
Contents
Page
Introduction ................................................................................................................................ 1
What is Coal Dust? .................................................................................................................... 1
Coal Dust, Air Pollution, and Applicable Regulations ................................................................. 2
Coal Dust from Rail Transport .................................................................................................... 3
Wind-Related Mechanisms Affecting Coal Dust................................................................. 4
Near-Track Ambient Air Quality Measurement Studies .............................................................. 9
Katestone and Ryan Studies ............................................................................................. 9
Jaffe Study .......................................................................................................................10
Railcar Coal Loss Control Measures .........................................................................................11
Project-Specific Railcar Information ..........................................................................................12
Conclusions ..............................................................................................................................13
About Ramboll Environ
Ramboll Environ US Corporation (Ramboll Environ) is an international consultancy created in late 2014
when ENVIRON International Corporation (founded 1982) joined the Ramboll Group (founded 1945) to
form the Environment and Health (E&H) Global Practice division of the merged company. Ramboll
Environ works with clients to help resolve their most demanding environmental and human health
issues. We combine resources across geographic boundaries and technical and scientific disciplines to
provide clients with the best, most responsive team—whether responding to existing challenges,
evaluating opportunities to improve performance, or seeking to reduce future liabilities. Clients around
the world benefit from our unique ability to bring clarity to issues at the intersection of science, business
and policy.
Since ENVIRON's inception over 30 years ago, we have successfully pursued a core mission of applying
the highest level of technical and strategic expertise to our clients' most critical environmental and
human health issues. In response to the increasing complexity of these issues, we have continuously
extended our capabilities and geographic reach, evolving into a truly global partnership with more than
1,400 professionals working from a network of more than 90 offices across the Americas, Europe,
Australia, and the Asia-Pacific region.
About the Authors
Kirk Winges is a Principal Consultant with Ramboll Environ. He has degrees in Geophysics and Chemical
Engineering from MIT and the University of California at Berkeley. He has 37 years of experience in air pollution
consulting and has been actively involved in the study of fugitive dust emissions from coal mining, handling,
transport, and use for his entire career. He is a nationally-recognized expert on coal dust and has previously
testified before the Under-Secretary of the Interior and the Director of the Office of Surface Mining on coal dust
topics. He has briefed a Congressional delegation, including two US Senators and a US Congressman on coal dust
issues.
Richard Steffel, a Principal at Ramboll Environ has 35 years of experience evaluating environmental impacts and
mitigation measures related to mobile and area air pollution sources. His experience includes transportation and
general conformity assessments under state and federal air quality rules. He has conducted hundreds of air quality
studies, many of which have included reviews and documentation required by the Washington and the National
Environmental Policy Acts.
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Introduction
Coal is mined at the Kayenta Mine Complex in Northeastern Arizona and transported by the
Black Mesa and Lake Powell (BM&LP) railroad; a dedicated, private, electric railroad to the
Navajo Generating Station (NGS). The potential for emissions of dust is always an
environmental concern for any such coal use/transport project due to the large volumes of coal
that must be handled to sustain power generation at a large generating station. Of particular
concern is the dust that can be released from open-top railcars due to the potential for members
of the public to be close to the rail lines. This white paper considers this issue and presents
information to allow an understanding of coal dust, its potential for emissions during rail
transport, the potential for impacts from such emissions, and what can be done to control such
emissions.
What is Coal Dust?
Coal dust is made up of small particles of coal; in some cases these particles are microscopically small. Airborne coal dust is small particles of coal that have become suspended in the
air via some process. The term "suspended" is not an absolute, but rather a relative concept
that refers to how small particles of solid material can remain in the air for long periods of time
despite the fact that they are usually heavier and denser than the air around them. The following
paragraphs explain this complex particle behavior.
Particles of any type can be characterized based on two properties: the weight of the particle
and the surface area of the particle. In general, as particles get smaller both their weight and
their surface area decrease. But particle weight decreases much more rapidly than surface area
because the weight goes down in proportion to the cube of the particle size (d3), while the
surface area decreases in proportion to the square of the particle size (d2). This is important in
this discussion because moving air affects particles based on their surface area, while gravity
influences particles based on their weight. So as particles get smaller, the force of air movement
on the particles (which tends to move the particles – to drag them along with the air) becomes
relatively greater than the force of gravity (which tends to hold the particles in place, or return
them quickly to the surface if disturbed). This makes smaller particles more susceptible to being
lifted off a surface by wind to become suspended in the air, while larger particles are both
harder to lift in the first place and more likely to rapidly settle back to the surface due to gravity.
Particles do not float in the air like a balloon filled with helium that is less dense than the air
around it. Instead, because even the smallest particles are denser than air, if they stay airborne
for any period of time, it is due to the force of air movement on the surface of the particle overwhelming the force of gravity. For example, consider the fall of a dropped baseball versus the
fall of a tiny speck of dust. The baseball cannot stay airborne because the force of gravity is
much greater than the opposing drag force imparted on the ball by the air through which it is
moving, so the baseball rapidly returns to earth. The dust speck, however, may be so small that
the drag force imparted by the air is much greater than the gravitational force on the particle, in
which case the particle's net movement towards the ground may be very small, and the particle
can remain suspended in the air and travel with the wind for long periods of time.
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Although there are many ways that coal particles can become suspended in the air, these
mechanisms can be generally divided into two categories:
1. Mechanical, where the coal particles are lifted, thrown, or dropped in the air, such as a
tire rolling over a surface that physically picks up particles and casts them into the air, or
2. Wind erosion, where a surface containing coal particles is exposed to moving air, and
where the force of the air over the surface lifts particles into the air.
This paper focuses on the latter of these two processes because the concern addressed here is
the potential for dust particles blowing off the surface of coal in an open railcar.
It is important to note that coal dust also can be emitted from any coal-handling process that
occurs in the open air. But once the coal is situated in the bed of a railcar, it is generally the
action of air moving over the surface of the coal that results in any coal dust being released from
the moving railcar.
Coal Dust, Air Pollution, and Applicable Regulations
Particles in the air are part of a normal, natural environment. Particle emission sources such as
volcanic activity, wildfires, desert dust storms, and others are part of nature. The term "air pollution," however, as typically applied to particles, refers to man-made or human-activity-generated
particles suspended in the atmosphere. Particulate matter caused by human activity is a major
air quality issue, and numerous laws, regulations, and rules have been established to control
particulate pollution. These restrictions apply to coal dust just as they do to other types of
particles caused by human activity.
There are many types of particles in the atmosphere, including soot from combustion, dust from
exposed soil, and even particles that form in the atmosphere from gases, including gases
resulting from human activity, such as vehicular exhaust. For this reason, most air pollution laws
treat particles collectively as "particulate matter," rather than regulating specific types of
particles. While there are some exceptions for especially toxic particle types (e.g., asbestos),
most particle types are not regulated specifically. Coal dust is seen as an occupational safety
issue, and there are rules and regulations concerning occupational coal dust exposure in worker
safety laws. (1) Coal-workers' "black lung," or pneumoconiosis is not, however, considered an
environmental threat to the general public because it is found almost exclusively in coal mine
workers or others who have been regularly exposed to extremely high levels of coal dust over
long periods of time. (2) Such occupational exposure is addressed with specific limits that are
much higher than the ambient air quality standards intended to protect the general public. The
EPA and other air quality agencies charged with protecting the public from air pollution have not
seen the need to develop air quality regulations aimed specifically at coal dust, but to instead
rely on rules for particulate matter as a whole. As such, there are no federal, tribal, or Arizona
State laws or regulations applying to coal dust, specifically. Rather, airborne coal dust is
addressed through laws and regulations that apply to particulate matter as a whole.
(1)
Criteria for a Recommended Standard: Occupational Exposure to Respirable Coal Mine Dust
http://www.cdc.gov/niosh/docs/95-106/
(2)
U.S. Centers for Disease Control, http://www.cdc.gov/niosh/topics/pneumoconioses/
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When first regulated, airborne particulate matter rules were based on concentrations of "total
suspended particulate," (TSP) which included all sizes of particles that could be considered
suspended in the air. In practice this meant particles smaller than about 30-50 micrometers (µm)
in diameter. As air sampling technology has improved and the importance of particle size and
chemical composition have become more apparent, ambient air quality standards have been
revised to focus on the smaller particle sizes thought to be most dangerous to human health.
Based on the most recent studies, EPA has defined two categories of particle sizes and set
standards for particulate matter based on "fine" and "coarse" inhalable particulate matter. There
are currently health-based ambient air quality standards for PM10, or particles less than or equal
to about 10 µm in diameter, as well as for PM2.5, or particulate matter less than or equal to
about 2.5 µm in diameter. Most coal dust emissions result from the handling and storage of bulk
coal and are comprised of PM10 and larger, with only a small percentage, typically around 15
percent, being in the PM2.5 size range. (3)
Coal Dust from Rail Transport
Coal and railroads have been linked since the beginning of the industrial revolution. Coal
transport typically uses large open-top railcars holding more than 100 tons of coal each. The
cars are loaded from the top, often using large vertical silos such as the one in the Powder River
Basin shown in Figure 1. Coal is typically loaded using a telescoping chute or other specialized
device. At the conclusion of the rail journey to the customer, coal is typically unloaded from the
railcar through a bottom gate or using a rotary railcar dumper.
There is an important difference in the process used
at the Kayenta mine to fill coal trains for transport by
the dedicated BM&LP rail line to the Navajo
Generating Station compared with other more
common operations in the United States (e.g.,
Figure 1). Coal is often transported many hundreds
or even thousands of miles from the mines, and
travels over a shared rail system where it must
compete with other rail traffic. For this reason, the
cargo load of each railcar is maximized, and the cars
are filled to a safe maximum capacity that typically
involves part of the coal load extending above the top of
Figure 1. Typical Coal Silo
the railcar as can be seen in the figure. In contrast,
because the BM&LP railroad is a dedicated facility, any capacity issues can be addressed by
adding railcars, and there is no need to maximize the quantity of coal in each car. Accordingly,
cars are not filled to capacity and the surface of the coal remains below the top of the car. (4) As
a result, some of the potential issues related to overfilling coal cars discussed below are not an
issue for BM&LP.
(3)
(4)
EPA Document "Compilation of Air Pollutant Emission Factors" Document No. AP-42, Appendix B.2 Generalized
Particle Size Distributions, Category 3, page B.2-13. http://www.epa.gov/ttn/chief/ap42/appendix/appb-2.pdf
Navajo Generating Station Project, Project Description, 7/3/2014
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Coal railcar loading from silos as at the Kayenta Mine allows coal dust to be controlled through
enclosure and capture. Coal trains move very slowly as the coal is loaded, so there is little coal
blown off the exposed top surface of the car as the train moves through the silo. Once outside
the coal silo, the train continues to move very slowly, and unless there is significant wind, little
coal is lost as the remaining cars are loaded.
Once the train leaves the mine and begins the journey to the customer, coal can be lost from
the railcars through a variety of mechanisms. These include the following:
 Spillage – over-filled cars can result in coal falling off the
stacked coal and over the side of the car
 Sill and other surface loss – the edges (sills) of the railcar
as well as other top surfaces on the railcar can be
catchments for coal and can lose coal due to vibration as
the trains move (see Figure 2), again noting that this issue
is not representative of trains loaded at the Kayenta Mine)
 Hatch loss – some railcars are bottom dumpers with
hatches, that if not well maintained, may not close
completely and can spill coal, and
Figure 2. Example of Overloaded Railcar
 Wind-related loss – the exposed surface at the top of the car is subject to the effects of air
as it moves over the coal resulting in coal dust blowing off the top of the car
Spillage and sill loss are not an issue in the current project because the railcars are not filled to
capacity. (4) Although these cars are bottom dump cars, the dedicated nature of this facility and
active maintenance program is effective at preventing loss through bottom hatches. As a result,
the remainder of this document focuses on potential wind-related loss mechanisms.
Wind-Related Mechanisms Affecting Coal Dust
Wind-related particle movements on surfaces result from
the shearing force moving air imparts to the surface over
which it moves. The movement of the air with respect to
the coal surface is the net effect of the movement of the
cars as well as the movement of the air over the ground.
The combined train and wind motion can lead to velocities of air of 60 miles per hour or more. (5) Note that rail
speeds on the BM&LP rail line are much lower than
typical public rail lines. As air flows over the surface of
the coal, it imparts a force to the coal particles. If the
force is sufficient, it can cause the particles of coal to
move. In the absence of controls, this force can cause
three types of particle motion, as shown in Figure 3: (6)
Figure 3. Schematic Indicating Different Wind
Mechanisms
(5)
Nimerick, K.H. and G.P. Laflin, In Transit Wind Erosion Losses of Coal and Methods of Control, Mining
Engineering, August 1979, pp1236-1240
(6)
http://oceanworld.tamu.edu/resources/environment-book/aeoliantransport.html
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 Creep
 Saltation
 Suspension
Creep refers to the process where the wind rolls the particles along the surface. In saltation,
the particles can be picked up for brief periods of time only to return to the surface. Saltation is
often described as particles "bouncing" along the surface. As they re-strike the surface, these
bouncing particles can impact and dislodge other particles and especially smaller particles, and
in some instances the impact can break larger particles to create smaller ones. Finally, if the
particles are small enough, they can be fully entrained by the wind and become suspended in
the air and carried larger distances.
The suspension of particles in the atmosphere is regulated by the EPA and other air pollution
agencies under standards and permits for dust sources. (7) Typically, the term "fugitive dust" is
used to reflect that such dust does not emanate from a stack or other confined release point, but
rather from an open area, in this case the surface of coal in a railcar. Fugitive dust is considered
an air pollutant by EPA and other regulatory agencies. (8) Creep and saltation particles do not
result in air pollution because the particles do not become suspended in the atmosphere, and
such particles are too large to be regulated by EPA under air quality laws. (9)
This is an important distinction because many studies and discussions of coal loss from intransit railcars refer to the total loss of coal via wind processes, but not all this coal loss results
in air pollution. Creep and saltation particles are much more massive than suspension particles
(e.g., a pea-size particle that might be subject to creep or saltation has a mass equivalent to 1
billion 10 micrometer particles that might become suspended). (10) So while the larger creep and
saltation particles can be a nuisance and might possibly adversely affect the railroad bed
ballast, such particles are too large to be inhaled into the human lung and do not pose a human
health hazard.
Older studies that considered coal dust losses from railcars attempted to estimate the total
mass lost from railcars in the absence of any form of controls. Most of the reported mass
consisted of larger saltation and creep particles that cannot become suspended in the atmosphere. For example, one of the earliest studies of this issue was performed by Nimerick and
Laflin in the 1970s. (11) They exposed open trays of coal to high velocity winds in a wind tunnel.
They conducted sieving analysis on the coal samples before and after exposure and saw most
of the mass lost was from large particles.
(7)
(8)
(9)
(10)
(11)
http://cfpub.epa.gov/ncea/isa/recordisplay.cfm?deid=216546
http://www.epa.gov/ttn/chief/ap42/ch13/final/c13s02.pdf
http://www.epa.gov/air/particlepollution/
3
For example: A particle with a diameter of 1.0 cm has a volume of V = 4/3π(d/2) where d is the diameter,
3
3
computes to (4/3)(3.14)(1.0/2) = 0.524 cm , while a 10 micrometer (µm) particle (0.001 cm) has a volume of
3
0.000000000524 cm , or 1,000,000,000 times smaller. With densities the same, the 1 cm particle will have a mass
about one billion times larger than the 10 µm particle.
Ibid. footnote #5
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With such large particles, once they fall off the moving railcar, they fall to the ground and are too
heavy to become suspended in the air. Consequently, such particles don't travel far from the
track. Typically, they are found in close proximity to the mine where the coal had been loaded
into the railcars. In the case of BM&LP rail hauling, it would be very difficult for creep or saltation
sized particles to escape the railcars because the surface of the coal is kept below the sills of
the cars, so the walls of the car prevent virtually all creep particles and the majority of saltation
particles from escaping the cars.
The issue of how much coal may be lost during transit has been infrequently studied, and there
is not a wealth of literature on the topic. Furthermore, reviewing historical work on this issue is
complicated because it is not always clear whether the interest was coal loss, or emissions to
the atmosphere. For example, Dow Chemical Company, an early supplier of dust treatment
chemicals for railcar bulk commodity surfaces, funded research in the 1970s aimed at quantifying the degree to which coal was lost from railcars, and how much loss could be prevented by
application of dust suppressant materials. Nimerick and Laflin, the authors of a previouslymentioned paper, were both Dow Chemical employees. Another oft quoted paper is that of
Denton, et al. (12) whose investigation focused on the effectiveness of applying a Dow Chemical
product to the surface of the coal. Many of the coal loss estimates seen in publications, even
recent publications, originate from these very old studies.
Specific estimates of the quantity of coal emitted from railcars vary widely. For example, a
BNSF website at one time reported that from 500 to 2,000 pounds of coal dust can be lost from
a single railcar and that some historical studies found total losses of as much as 3% of the coal
in transit. (13) BNSF has not published the data that form the basis for this claim, and has since
removed this statement from their website. The 3% loss claim has been seen elsewhere in the
literature, and is referenced in a report for the Environmental Protection Service in Canada and
in a second report for the Canadian Council of Ministers of the Environment (CCME). (14,15)
The actual reported finding to which most papers refer is a loss ranging from 0.5% to 3.0% and
appears to date back, in part, if not entirely, to the Nimerick and Laflin 1979 paper. (16) Nimerick
and Laflin (1979) mention this 3% loss factor, but their research indicated 0.5% to 2% of coal
lost from untreated samples. Note that these were not tests on fully loaded railcars, but were
rather based on wind tunnels tests using 1-2 inch deep trays, of the typical size used in baking.
(12)
(13)
(14)
(15)
(16)
Denton, G.H., R.E. Hassel, and B.E. Scott, Minimizing In Transit Windage Losses, Mining Congress Journal,
58(9), 49 (1972)
This statement was made on a BNSF website that was subsequently revised to no longer include this claim. The
complete statement from the website was as follows: "The amount of coal dust that escapes from PRB coal trains
is surprisingly large. While the amount of coal dust that escapes from a particular coal car depends on a number
of factors, including the weather, BNSF has done studies indicating that from 500 lbs. to a ton of coal can escape
from a single loaded coal car. Other reports have indicated that as much as 3% of the coal loaded into a coal car
can be lost in transit."
Cope, D., D. Poon, E. Wituschek, et al., 1986, Report on the Emission and Control of Fugitive Coal Dust from
Coal Trains, Environmental Protection Service, Pacific Region, s.l. Regional Program Report 86-11.
Cope, Douglas L. and Kamal K. Bhattacharyya, 2001, A Study of Fugitive Coal Dust Emissions in Canada, for The
Canadian Council of Ministers of the Environment, November 2001
Ibid. footnote #5
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It is thus unclear how well these tests on small container samples would apply to full size
railcars.
Examination of the CCME (2001) paper indicates that a variety of particulate matter emission
factors were developed during this effort, most of which addressed "controlled" emission rates
from railcars with coal treated with a dust control chemical. The Canadians also did wind tunnel
studies similar to those of Nimerick and Laflin, and developed emission factors in the range of
0.9% to 1.76%. Like those of Nimerick and Laflin, these wind tunnel tests were based on total
weight loses from sample trays, without consideration of particle size or the potential for
emissions becoming airborne.
The oft quoted 0.5% to 3% coal loss factor, however, was not the ultimate conclusion of the
more recent Canadian analysis. (15) Instead, they developed an emission factor equation based
on travel distance, a control factor, a precipitation factor, and other factors. The ultimate recommended emission factors from this paper for a 1,000-mile travel distance and 99% control (that
the authors feel is typical of spray operations) was 0.003% for particles smaller than 10 µm
(PM10) and 0.0013% for particles smaller than 2.5 µm (PM2.5).
In the early 1990s, Simpson Weather Associates, in cooperation with Norfolk Southern Corporation, conducted a four-year study of coal dust loss from railcars. (17) They used a combination
of techniques to estimate coal loss during transit, including scale-weight changes and real-time,
on-board monitoring systems. The scale-weight changes showed an average weight change of
0.36 tons per car under high-stress conditions (e.g., high winds). The real-time monitoring did
not yield accurate dust loss estimates, but provided some information regarding the conditions
under which coal dust loss was observed. It should be noted that these data were for ungroomed, untreated coal cars. In addition, the coal considered was metallurgical-grade coal, not
steam coal, and the researchers stated they thought the metallurgical coal was likely to be
dustier than other types of coal. They also concluded that cars treated with a dust palliative
compound and properly groomed surface had emissions reduced by 95% or to levels of 0.018
tons per car. For a typical 100-ton car, this equates to 0.00018%, much less than any values
mentioned previously. Finally, recall that values based on car weight losses do not necessarily
equate to dust emissions, since some of the weight loss is likely due to particles too large to
become airborne dust particles.
In 2003, researchers in Portugal did experiments with full-size railcars. (18) The total emission
rate documented in the Portuguese study was about 0.005% loss from the railcar over a 350
kilometer (220 miles) travel distance. These data were based on actual dust measurements,
although the size range of the particles is not known.
(17)
(18)
Calvin, E.M., G.D. Emmitt, J.E. Williams, A Rail Emission Study: Fugitive Coal Dust Assessment and Mitigation,
Simpson Weather Associates and Norfolk Southern Corporation, 1993, http://www.powerpastcoal.org/wpcontent/uploads/2011/08/a-rail-emission-study-fugitive-coal-dust-assessment-and-mitigation.pdf
Ferreira, A.D., D.X. Viegas and A.C.M. Sousa, Full-scale Measurements for Evaluation of Coal Dust Release from
Train Wagons with Two Different Shelter Covers, Journal of Wind Engineering and Industrial Aerodynamics, 91
(2003) 1271-1283
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An Australian group conducted a literature review of available release factors for coal dust loss
from trains and acknowledged the 0.5% to 3.0% factors reported by others. (19) They attribute
that factor to the Canadian group, D. Cope Enterprises, although the original source is likely the
Nimerick and Laflin paper from 1979. The Australian review did not acknowledge that the
Canadians have since moved on from this estimate to an emission factor equation that
produces much lower percentage loss results when typical airborne dust size ranges (i.e., PM10
and PM2.5) are considered. The Australian study does, however, point out that the 0.5% to 3.0%
estimates are inconsistent with ambient measurements. They contend that if the estimates of
coal loss were accurate, concentrations of ambient particulate matter measured in the air near
railroads would be many orders of magnitude higher than actual observed concentrations. They
also conducted their own wind tunnel studies, with the findings consistent with the Portuguese
group. They concluded that the 0.5% to 3.0% loss rate is a gross overstatement, and that actual
losses are on the order of 0.01% or less.
The potential for untreated or improperly loaded coal to be lost due to wind erosion is greatest
during the initial transport near the mine, not during later stages of rail transport. Scientific
studies with wind tunnels have shown that exposed surfaces of particles have what is known as
a "threshold velocity" where winds have to attain a certain speed before particles begin to be
blown off. In addition, any surface has a "finite availability of erodible material" that limits how
much material can be lost from a surface. (20) A pertinent quote from EPA's emission factor
reference document, AP-42 is as follows:
…sources typically are characterized by nonhomogeneous surfaces impregnated with nonerodible elements (particles larger than approximately 1 centimeter [cm] in diameter). Field
testing… using a portable wind tunnel has shown that… particulate emission rates tend to decay
rapidly (half-life of a few minutes) during an erosion event. In other words, these aggregate
material surfaces are characterized by finite availability of erodible material (mass/area) referred
to as the erosion potential. Any natural crusting of the surface binds the erodible material,
thereby reducing the erosion potential.
It is clear that air velocities over the surface of the coal in untreated, improperly loaded railcars
can be sufficient to exceed this threshold, particularly when the train is in motion. Under these
conditions, coal would be lost in the initial part of the travel. This is consistent with BNSF claims
concerning railcar coal dust since they have observed the coal dust problem mainly in the
immediate vicinity of the mines in the Powder River Basin but not elsewhere on the many
thousands of miles of track where coal is hauled throughout the US. (21)
The Nimerick and Laflin study quoted previously also shows this clear pattern. (22) Figure 4
(Figure 3 from the paper) reproduced from the Nimerick and Laflin paper plots the total loss as a
function of time after exposure. It is clear from their tests that the coal loss starts immediately
after the untreated coal is placed in the wind, and rapidly levels off to the final loss total in a few
hours.
(19)
(20)
(21)
(22)
Connell Hatch, Interim Report, Environmental Evaluation of Fugitive Coal Dust from Coal Trains, Goonyella,
Blackwater and Moura Coal Rail Systems Queensland Rail Limited, 31 January 2008, Reference No. H_327578
US Environmental Protection Agency, Compilation of Air Pollutant Emission Factors, Document AP-42, Fifth
Edition, Section 13.2.5, Industrial Wind Erosion, November, 2006. P1
http://www.bnsf.com/customers/what-can-i-ship/coal/coal-dust.html
Ibid. footnote #5
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This happens due to a phenomena called
"armoring" that is commonly used in impeding
water-caused erosion using large rocks to protect
an underlying surface of finer material from
erosion (for example the placement of large rocks
called "riprap" on coastal areas to prevent wave
erosion). The same process occurs with wind
erosion where, after an exposure to high winds,
the smaller particles capable of being eroded are
lost from the surface, and what remains on the
surface are the larger particles not capable of
being eroded by the wind. Small particles still exist
in abundance in the material below the surface,
but the large particles block the wind from
reaching these smaller particles.
Figure 4. Figure 3 from Nimerick and Laflin
Near-Track Ambient Air Quality Measurement Studies
Katestone and Ryan Studies
Two recent Australian studies involved measuring particle concentrations in the air near a coal
haul transport corridor to assess whether coal dust was being emitted from the railcars and
whether any such emissions would result in particulate matter concentrations that would be
considered potentially harmful to human health. These studies indicated that coal-hauling by
trains is unlikely to result in greater particulate matter emissions than from other freight trains.
Katestone conducted monitoring in 2012 and 2013 to collect four size fractions of particulate
matter (TSP, PM10, PM2.5, and PM1) over a two month period near a coal hauling rail corridor in
Australia. (23) They collected data for more than 1,900 loaded and unloaded coal train passbys.
Ryan and Wand peer reviewed and expanded upon the Katestone data analyses to include a
more sophisticated analysis. (24) Together these reports provide strong evidence that coal trains
do not result in any more emissions than any other freight-hauling trains. Ryan's findings were
as follow: (25)
1) Found clear evidence that particulate levels were elevated for the several minutes during
and after trains passed the monitoring station.
2) Effects were strongest and of a similar magnitude (approximately 10% increase above
background levels) and highly statistically significant for freight and coal trains, both
loaded and empty. (Emphasis added.)
(23)
(24)
(25)
Katestone Environmental Pty Ltd's Pollution Reduction Program 4.2 Particulate Emissions from Coal Trains,
Prepared for Australian Rail Track Corporation Pty Ltd May 2013
Ryan, Louise and Matthew Wand, 2014, Re-analysis of ARTC Data on Particulate Emissions from Coal Trains,
Author: Prof Louise Ryan, on behalf of access:UTS Pty Ltd for NSW Environment Protection Authority, 25
February 2014 [a peer review and re-analysis of Katestone study]
Ibid. page 12
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3) There was no evidence that loaded coal trains produced more dust than empty coal
trains. (Emphasis added.)
4) Non-statistically significant results indicated particulate levels associated with passing
unloaded coal trains were higher than those associated with loaded coal trains and
freight trains. (an anomalous finding if loaded railcars are emitting coal dust).
5) The effects were apparent for all measured particulate size fractions which included
TSP, PM10, PM2.5, and PM1, especially for freight and coal trains (loaded and empty).
Passenger train effects were non-significant for PM1 and only marginally significant for
PM2.5. Since coal dust is likely to be reflected in the larger particle fractions (i.e., TSP
and PM10), this finding suggests that other contaminants such as diesel exhaust may be
larger contributors to the somewhat elevated PM levels than coal dust.
6) Particulate matter concentration increases during train passages were moderate, with
TSP increases of about 2.4 to 2.8 µg/m3 over background during freight and coal train
(loaded and empty) passbys. Corresponding increases for PM10, PM2.5 and PM1 were
approximately 2.0, 0.7, and 0.12 µg/m3, respectively. In other words, there was about a
10% increase in the various kinds/sizes of particulate measured associated with freight
and coal trains.
It is noteworthy that while some of the cars on the more than 900 loaded coal trains considered
in the Katestone/Ryan studies may have had shaped loads that would reduce wind related coal
loss, few if any would have had surfactant applied. (26) This is a significant finding since the coal
loads for the current project, unlike those from the Powder River Basin, are not sprayed with a
chemical binding agent or surfactant. Although the use of such products is considered effective
for railcars where the surface of the coal extends above the top of the railcar and is more
exposed to the wind, it may not be a necessary step for the BM&LP railcars since they are not
filled above the sills of the car.
Jaffe Study
A study published by Jaffe, et al. (27) in 2014 reported finding evidence of coal dust emissions
from railcars in Washington State. Measurements of different sizes of particulate matter were
taken 25 meters from an active rail line. Similar to the Katestone/Ryan study noted above, Jaffe
found higher concentrations of particulate matter in the air during and immediately following the
passage of trains of all types.
The Jaffe study findings agree with Katestone/Ryan that the majority of particulate matter
observed (more than 75% for all types of trains) was composed of particles smaller than one
micrometer in size (PM1), suggesting a combustion source like diesel for the particles. However,
Jaffe observed that the ratio of PM1 to TSP was slightly lower for coal trains than for other types
(26)
27
ENVIRON was involved in the pilot studies that preceded the Katestone work and has direct knowledge of the
conditions under which coal is shipped in the study area. Email exchange indicated that although coal load
treatments vary by source, in general, few trains use surfactants and most (not all) use load profiling. Personal
communications: Michelle Manditch, ENVIRON Australia Pty Ltd, to Richard Steffel, ENVIRON International
Corporation, 3/18/2014
Jaffe, D.A., G. Hof, S. Malashanka, J. Putz, J. Thayer, J.L. Fry, B. Ayers, and J. Pierce, Diesel Particulate Matter
Emission Factors and Air Quality Implications from In-service Rail in Washington State, USA, Atmospheric
Pollution Research, Volume 5, Issue 2, April 2014 pp 344-351
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of freight trains (77% for coal trains versus 87% for freight trains). He interpreted this higher
fraction of large particles to mean coal dust was present. He cautioned that no chemical or other
types of analyses were performed to confirm that any of the larger particles were in fact
composed of coal dust, and there was only this inference to suggest coal dust in the samples.
Jaffe's interpretation of the PM1/TSP ratio as indicating the presence of coal dust is one
possible explanation of these data, but not the only one. For example, he also compared carbon
dioxide (CO2) and PM1 concentrations and showed that the ratio of PM1 to CO2 for coal trains
was lower than for freight trains. This suggests the diesel locomotives hauling coal operate
somewhat differently than those hauling freight, which might mean the size distribution of diesel
exhaust particles shifts for trains hauling heavy loads to more TSP and less PM1 than for freight
trains. Accordingly, another possible explanation for the higher fraction of TSP with coal trains is
that coal train diesel exhaust particulate has less PM1 and more TSP than freight trains and
thus not attributable to coal dust.
The small fractional difference of the PM1/TSP ratio between coal and freight trains, in the
absence of any other data, does not provide sufficient evidence to conclude the difference is
due to the presence of coal dust in the wake of the trains. Further examination of the Jaffe data
would be necessary to determine why the Jaffe study, which was shorter in duration and
involved only 49 coal trains, or fewer than 3% of the number of coal trains considered in the
Australian studies, reached such a diametrically opposed conclusion.
Because Jaffe's paper does not present his full data set, but rather provides examples, it is
difficult to determine if the presumed property is real. Any effect is very small. For example,
Figure 6 from the Jaffe report shows the double peak associated with the passing of the
locomotives and the passing of the remainder of the train. During the locomotive pass, the PM1
comprises 96% of the observed particulate, while during the remainder of the train passage, the
PM1 comprises 86% of the observed particulate. Since the coal dust would be expected to
produce little to no PM1 this slight (10%) decrease in the PM1 fraction is difficult to interpret as
evidence of coal dust. Presumably, this example was selected because it provides the best
example of Jaffe's presumed conclusion. It is unclear whether this is a loaded coal train or an
unloaded coal train or whether this same slight shift in PM1 fraction is seen for unloaded coal
trains as well as loaded coal trains, which would clearly suggest it is not associated with coal
dust. It is unclear whether this same effect happens for freight trains as well, as was found in the
Australian study.
Railcar Coal Loss Control Measures
Some railroad companies have instituted programs in which the mines and/or customers adopt
new measures for reducing coal loss during rail transport from Wyoming's Powder River Basin
(the largest coal mining area in the United States). It is highly likely that the precedents being
set in Wyoming will become Best Available Control Technology (BACT) for long-haulage of coal
in the US. (28) The methods used in these programs would not be applicable to the BM&LP
(28)
BACT determinations during air quality permitting establish precedents for all subsequent cases related to similar
projects and technologies. Once set, BACT must be applied in similar circumstances, and essentially becomes
the "default" control technology. See for example: http://www.epa.gov/ttncatc1/rblc/htm/welcome.html
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railroad because it is a private railroad and not a long haul railroad. However some discussion
of the control provisions is included here for completeness.
Compliance with these provisions is verified by on-track monitoring of airborne dust. These
measures have been recently incorporated in BNSF Tariff 6041-B. (29) Costs of these control
measures are ultimately to be passed on to the consumer of the coal or the energy derived from
the coal. The effectiveness of these measures was documented in testing conducted by BNSF
known as the Super Trial. (30) The results of this trial reportedly indicated that implementation of
these measures was very effective at reducing coal dust emissions.
Under the BNSF tariff, all coal leaving Powder River Basin mines on BNSF tracks must comply
with coal-loss control requirements for railcars. (31) The elements of this program are twofold:
 The coal loading facilities must conform with loading requirements specified in BNSF tariff
documents that call for a "profile" (i.e., load shape) for the top surface of the coal to limit
spillage and reduce wind erosion. This is sometimes referred to as "shaping" or "grooming"
the surface of the coal; such shaping is accomplished through coal-loading equipment at
the mines. This refers to the portion of the load that extends above the railcar, not relevant
to the current project since the BM&LP railcars are not filled above the top of the car sills.
 BNSF conducts track-side monitoring to ensure track-side dust levels stay below certain
thresholds. Many mine operators and customers apply additional steps beyond the coal
profiling to ensure these levels are not exceeded. These measures can include application
of a surface coating to the top of the loaded railcar. Surfactants and other proprietary
products are used for this purpose.
It is generally agreed that the effectiveness of these two measures is very good. BNSF's testing
with a particular product showed more than a 75% reduction in the coal loss rate. (32) Later
statements by BNSF have indicated a coal dust emission reduction would be 85%. (33) As
discussed above, the Canadians have routinely used 99% reduction to represent the
combination of control using shaping and surface coating.
Project-Specific Railcar Information
The project-specific details that follow are from the project description. (34) The BM&LP railroad
transports coal from the Kayenta mine to the NGS. The track extends 78 miles northwest across
the Navajo Reservation. The BM&LP is a private railroad and a closed system that does not
connect with any other railroads. The railroad right of way corridor contains a fence line
approximately 50 to 100 feet from each side of the tracks with the exception of open crossings.
When NGS is operating at full capacity, the train runs 24 hours a day 7 days a week and
(29)
http://newdomino.bnsf.com/website/prices.nsf/55abb888cb03db6286256d7100515608/1482f7444c40d655862575c3006e9544/$FILE/BNSF%206041-B%20eff%205-27-09.pdf
(30)
http://www.bnsf.com/customers/pdf/coal-super-trial.pdf
(31)
http://domino.bnsf.com/website/updates.nsf/f9928a818a7c00b986256b030057f787/5615b91cd7920132862575c500689ba1?OpenDocument
(32)
BNSF Ballast Fouling Mitigation 2-13-07
http://www.nationalcoaltransportation.org/events/BallastFoulingMitigation_2_13_07.pdf
(33)
http://www.bnsf.com/customers/what-can-i-ship/coal/coal-dust.html#4
(34)
Ibid. footnote #4
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completes three round-trips per day, delivering approximately 8,000 tons of coal per trip. A
round trip normally takes 6 to 7 hours.
The BM&LP is powered by overhead electrical lines, and thus uses no diesel-powered locomotives. As a result, particulate matter emissions from the train are less than emissions from
conventional diesel locomotive powered trains. As the previous studies have shown, the vast
majority of emissions associated with rail hauling of coal are from the locomotives. Coal dust, if
it is present at all, is comprised of large particles that do not travel far from the rail line itself.
Even with diesel locomotives, studies in Australia and elsewhere have shown that increases in
PM10 and PM2.5 are on the order of 2 micrograms per cubic meter. When it is considered that
80%-90% of the particulate in these studies is likely from locomotive exhaust, the maximum
potential increase in particulate concentrations during the passage of a coal train are much less
than 1 microgram per cubic meter, well below any level considered to be significant.
Continuation of the ongoing practice to load coal railcars to a level where the load does not
extend above the top sills of the car serves to reduce the potential for wind-related coal dust
emissions. In addition, an active program of railcar maintenance to ensure bottom dump doors
close completely also reduces the potential for on-track spillage of coal.
A separate review conducted by SRP was provided to us showing an analysis of residential
locations along the rail corridor. The vast majority of the railroad travels through open country,
with no habitation nearby. There are a few areas with some residences, but in the entire 78 mile
corridor roughly 100 dwellings or structures were identified within about ¼ mile of the track. The
average distance of these dwellings from the rail line was approximately 300 meters, with the
closest location being 74 meters, and only this one location closer than 100 meters. This fact
can be contrasted with many urban locations in the US where active coal transport is in many
cases on the order of 20 meters from the rail line. The large separation distance combined with
the 50-100 foot fence that prevents closer access leads to the conclusion that public exposure
to coal dust is very low in this instance.
Conclusions
Coal dust lost from railcars has been found to be a serious issue in the past at locations near
railcar-loading facilities because the coal is thought to interfere with the structural integrity of the
track ballast and may have contributed to train derailments. However, this issue can be
addressed through improvements in coal loading methods and coal surface treatment, and this
issue is not a problem along the BM&LP rail line because railcar loading techniques at the
Kayenta Mine fill the cars to a level below the car sills to minimize spillage and reduce exposure
to the wind during transport. In addition, any observed spillage during the loading process is
cleaned up after the train leaves the coal silo load out area.
As regards potential coal dust emissions during rail transport between the Kayenta Mine and the
Navajo Generation Station, a summary of conclusions follows:
 Mitigation measures are available and effective for control of railcar dust. One such
measure that is an ongoing practice at the Kayenta Mine is to load railcars to a level below
the car sills to minimize exposure to wind during transport and reduce the potential for
wind-related emissions.
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 Even with untreated and improperly loaded railcars, coal product losses are most likely to
occur only in the early parts of the coal trains' journey, close to the mine, because the coal
surface in the railcar rapidly becomes armored and little is lost later in the trip.
 The most recent studies of full-size railcars indicate total weight loss is low and that
emissions of airborne particulate matter are miniscule.
 The findings of near-track particulate matter monitoring studies support the contention that
coal dust lost from cars in transit is minimal.
Based on this review, and assuming continued use of effective control measures, coal dust
impacts due to wind erosion from loaded railcars are unlikely to occur along the rail haul route
between the Kayenta Mine and the Navajo Generation Station.
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