x'/EPA
United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S7-81-087 July 1982
Project Summary
Trace Element
Characterization of Coal
Wastes—Fifth Annual
P rog res^flejpo rt
.
R. C. Heaton, Lf/fy Wangen, P. i. W$«s4j, J. M. Williams, E. F. Thode, M. M.
Jones, A. M. NyitrayV'P^Wagner, and J>P. Bertino
During the past year we continued
our research on environmental control
technologies as they relate to coal
preparation wastes and extended our
assessments to include studies of high-
sulfur Appalachian coal cleaning
wastes.
The most promising control tech-
nology for dealing with high-sulfur
coal wastes consists of sequential
slurry coating of the waste with lime
and limestone. In the configuration
tested (0.35% lime and 1.1% lime-
stone), this technique controlled the
waste effluent quality for 4 months;
the effluent pH remained between 7.3
and 7.6, and the trace element con-
centrations (Al, Ca, Mn, Fe, Co, Ni,
Cu) were reduced by 40 to 99-plus %.
Codisposal of coal wastes and alkaline
soils or mine overburdens is partly
effective in controlling the leachate
quality under steady-state conditions.
However, none of the materials tested
could control the highly acidic efflu-
ents obtained under intermittent leach-
ing conditions.
Comparisions between trace ele-
ment concentrations predicted by
chemical equilibrium models and those
obtained in experiments with coal
waste leachates yielded good agree-
ments for the major cations (Al, Ca,
Fe) but, except for fluoride, the major
anions were not well accounted for.
The observed trace element concentra-
tions were all significantly lower than
predicted.
Calcination experiments have shown
that high-sulfur coal waste from
Appalachia (Plant K) behaves differ-
ently than other wastes we have
studied. The high cost of this technol-
ogy ($1.39 to $9.84/ton product)
places it outside the realm of economic
feasibility at this time.
We have also completed an assess-
ment of the Plant K coal wastes. These
materials are similar to those from the
Illinois Basin and their leachates are
often very acidic, with pH values
sometimes less than 2. Several trace
elements have shown discharge sever-
ities greater than unity (Fe. As. Ni, Mn,
Al), but iron is by far the worst
offender, with values sometimes
greater than 100.
Results of the EPA extraction pro-
cedure, used to classify solid wastes
under the Resource Conservation and
Recovery Act, compare favorably with
those of our own leaching experiments
for those elements analyzed (Ag, As,
Ba, Cd, Cr, Hg, Pb, Se). However, coal
wastes release substantial quantities
of other trace elements not included in
the protocols at present (Fe. Al, Ni,
Mn, Zn, Cu).
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This Project Summary was develop-
ed by EPA's Industrial Environmental
Research Laboratory, Research Trian-
gle Park, NC, to announce key findings
of the research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
In the past, our research on coal and
coal wastes focused on identifying trace
elements released in hazardous
amounts during weathering and leach-
ing of high-sulfur coal refuse from the
Illinois Basin, and on evaluating control
technologies for this problem. Present
efforts are directed toward further devel-
opment of these control technologies
and extension of trace element assess-
ments to the drainages from high-sulfur
coals and coal wastes from Appalachia.
The drainages from many coal waste
dumps are often highly contaminated
with trace or inorganic elements. How-
ever, until recently there has been little
concrete information on the quantities
released, the controlling chemistry in-
volved, or the ways to control these
releases. Accordingly, the principal ob-
jectives of our program are to:
(1) Assess the nature and magnitude
of trace element releases of envi-
ronmental concern.
(2) Reveal experimentally the chem-
istry controlling trace element
releases.
(3) Evaluate and recommend appro-
priate pollution control technol-
ogies or necessary research and
development programs.
The studies under way are a continu-
ation of experimental efforts begun in
1976, which were directed toward
identifying and quantifying the trace
element releases from high-sulfur coal
wastes from the Illinois Basin. We now
have a good quantitative understanding
of the environmental concerns associ-
ated with these wastes and their drain-
ages. In FY 1979 we began in-depth
experimental evaluations of various
technologies for controlling them.
Among the methods considered were
codisposal of the coal waste with neu-
tralizing or attenuating agents, contain-
ment of waste leachates coupled with
water treatment techniques, and altera-
tion of the waste to yield an environ-
mentally inert material. Cost analysis
showed the last of these technologies to
be too costly, while the first two were
only partially effective, at least in the
configuration studied. In FY 1980 we
have continued to evaluate and improve
these technologies, emphasizing those
we consider to be the most promising;
namely, sequential slurry treatment of
the coal waste with lime and limestone
and certain codisposal techniques. We
also extended our trace element assess-
ments to include coals and coal wastes
from Appalachia.
Technical accomplishments of FY
1980 fall into three general areas: (1)
studies of control technologies for high-
sulfur coal wastes from the Illinois
Basin, (2) evaluation and assessment of
coal wastes from Appalachia, and (3)
continuing development of procedures
and techniques.
Environmental Control
Technologies
Studies performed over the past sev-
eral years show that the drainages from
uncontrolled piles of high-sulfur coal
wastes typically are very acidic (pH
values less than 2 have been observed)
and contain environmentally significant
concentrations of several trace ele-
ments. This contamination is caused by
sulf uric acid generated within the waste
to oxidation of pyrite. To eliminate the
contamination one must prevent the
formation of the acid within the waste,
neutralize the acid in situ after it is
formed, or allow the leaching to take
place and treat the effluents to remove
the acid and trace element contami-
nants. Each of these approaches has
advantages and disadvantages.
Acid formed in a waste pile can be
neutralized in situ by mixing the coal
refuse with alkaline materials either
before or during disposal. We have
demonstrated that if the pH of the waste
effluents is maintained in the proper
range, the trace element concentrations
also stay within acceptable limits. The
initial pH of the waste effluent can be
easily controlled by adding hydrated
lime to the waste, but this treatment is
only temporary because any excess lime
is quickly washed out of the solid refuse.
Ground limestone is more durable, since
it is not soluble in neutral solutions, but
it cannot control the high initial acidities
of high-sulfur coal waste. Although
neither the lime treatment nor the lime-
stone treatment alone is an adequate
control technology, a combination of the
two, using a small amount of lime to
control the initial acidity and a larger
amount of limestone to control the
slowly generated acid within the pile,
promises the advantages of both without
the limitations of either. Experiments
completed during FY 1980 show that
this approach is very effective in con-
trolling coal waste effluents for up to 4
months.
Leachates from high-sulfur coal
wastes obtained from the Illinois Basin
(Plant B) typically have pH values of
approximately 2.0 or less when sub-
jected to long-term laboratory weather-
ing experiments. However, when the
same wastes were sequentially treated
with 0.35% lime and 1.0% limestone
and subjected to artificial weathering
conditions equivalent to intermittent
rains totaling 39 in. per year, the waste
effluents had pH values between 7.3
and 7.6 for nearly 4 months. In addition
the trace element releases were reduced
by 40 to 99-plus %. Figure 1 shows the
effectiveness of this treatment in con-
trolling trace element releases from this
waste. Cost analyses carried out in 1978
show that sequential lime/limestone
slurry treatment would cost between 22
and 500 per ton of cleaned coal (1978
dollars), which is competitive with the
technologies already in use.
Although the lime/limestone slurry
treatment has provided some very en-
couraging results, it lasts for only about
4 months under the conditions of the
laboratory weathering tests. In fact,
because the amount of limestone added
is chemically equivalent to only about
10% of the pyrite in the waste, this
treatment cannot be permanent unless
oxidation of the waste is somehow
prevented. However, we believe this
treatment of the waste, followed by
disposal in an anaerobic environment,
would be useful as a comprehensive
waste disposal strategy. The lime/lime-
stone treatment would neutralize the
acid initially present in the waste and
control the trace element releases until
the permanent anaerobic disposal could
be implemented.
Some uncertainties remain concern-
ing the lime/limestone treatment. Be-
cause this treatment has been evaluated
with only one coal waste, we must
determine if the observed performance
is a general phenomenon or if it is
unique to the material we tested. In
addition, no attempt was made to opti-
mize the treatment parameters. The
effects of compaction of the waste pile
or freeze/thaw cycles have not been
studied. Finally, the mechanism by
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Cu
0.001
0.01
1 10
Discharge severity
100
Figure 1. Discharge severities (leachate concentration/100 x Minimum Acute
Toxicity Effluent/MATE) for selected trace elements in drainages from
high sulfur coal preparation wastes - untreated wastes (unshaded} and
lime/limestone treated wastes (shaded).
which this process works is only par-
tially understood. All of these questions
warrant study and will be addressed in
the coming year.
Another way to neutralize acid in situ
in coal wastes is to mix the refuse with
alkaline soils or mine overburdens either
before or during deposition in the waste
dump. Alkaline process wastes, such as
fly ash, could also be used. This possi-
bility is attractive because it would be
easy to implement and the required
materials are inexpensive and readily
available. Laboratory studies conducted
this year with a variety of soils and
process wastes showthat alkaline mate-
rials are partly effective in controlling
effluent quality when mixed with the
coal waste or placed downstream of the
waste. Concentrations of Al, Ni, F, and
As (and the acidity) were all lower in the
leachates for samples treated with the
alkaline materials. Furthermore, the
concentration decreases coincided with
the increases in pH. However, the con-
centrations of Mn and Fe were higher in
the leachates from the treated samples,
probably because these elements were
leached from the codisposed materials
themselves. None of the materials tested
could produce acceptable leachates
during the initial leaching of the sample.
The same was true after regeneration of
the waste pile by the passage of air
through the waste. Therefore, codis-
posal of coal waste with these types of
materials, at least by itself, is not likely
to constitute a workable control tech-
nology. However, information gained
from these studies will be useful in
evaluating the effects of the mineralogy
and underlying structure of potential
disposal sites on the waste effluents.
We are continuing these investigations
to determine which soils or underbur-
dens are most beneficial and which are
most harmful to effluent quality.
The most widely used control tech-
nology for coal waste effluents is col-
lection of the acidic drainages coupled
with water treatment, usually alkaline
neutralization. This approach is simple
and uses proven technology. Also, cost
analyses carried out in 1978 showed
that this approach typically costs be-
tween 7 and 55C per ton of cleaned coal,
so it is also relatively inexpensive. The
obvious disadvantage is that water
treatment must be continued as long as
the waste pile retains any acid-
generating potential, which can be
hundreds of years. Nevertheless, be-
cause this technique is so widely used,
and because its principle, alkaline neu-
tralization, is the same as that behind
the best control technologies so far
devised, additional investigation is war-
ranted.
To study the chemistry of the neutral-
ization process, we titrated a coal waste
leachate with calcium hydroxide to
various pH values and determined the
concentrations of the trace elements
left in solution. We then calculated the
expected concentrations using a com-
plex equilibrium code. The calculated
and experimental values compare well
for the major cations [calcium, alumi-
num, Fe(ll) and Fe(lll) ]. However, the
behaviors of the anions of major interest
(sulfate, arsenate, borate, and fluoride)
are not well accounted for in the thermo-
dynamic model, except for fluoride. In
addition, the important trace element
concentrations are all lower than the
calculated values. We speculate that
these elements (As, Cd, Co, Cr, Cu, Mn,
Ni, and Zn) are adsorbed on the hydrated
iron and aluminum hydroxide precipi-
tates. This behavior suggests that alka-
line neutralization of coal waste leach-
ates may actually be more effective in
controlling the release of trace metal
cations than thermodynamic calcula-
tions predict. Although these theoretical
calculations cannot yet describe such
complex chemical systems, they are
valuable in identifying the factors con-
trolling the solubilities of potential pol-
lutants. Therefore, we will continue this
line of investigation next year.
The formation of acid in the coal
waste can be prevented in two ways.
One is to dispose of the waste in an
anaerobic environment (nonoxidizing)
so that the pyrite cannot oxidize. This is
essentially a return of the coal waste to
the type of environment from which it
originally came. Disposal of the waste in
this way is simple in principle, and once
the anaerobic conditions are estab-
lished, no further treatment is required
to control the waste effluents as long as
the disposal site is not disturbed. How-
ever, it takes a significant length of time
to properly structure such a disposal
site, and during this time, the acid
generated in the pile must be controlled.
We believe that combining anaerobic
disposal with a short-term method, such
as the lime/limestone treatment, offers
an acceptable solution to coal waste
disposal.
The second way to prevent acid gen-
eration is to destroy the pyrite so that,
even under oxidizing conditions, the
waste has no acid-generating capability
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In past studies we have shown that
calcining, which destroys pyrite, is
effective in controlling the teachabilities
of the trace elements in high-sulfur coal
wastes from the Illinois Basin. Calcining
is a one-time permanent treatment.
Thus, the treated materials can be
disposed of conventionally without con-
cern for their potential behavior in the
distant and unforeseeable future. How-
ever, calcining merely exchanges one
problem for another. The coal wastes
are rendered innocuous because cal-
cining drives off the sulfur, which
eliminates the acid-generating capacity
of the waste. The solid: are left inert, but
the evolved sulfur must be dealt with,
either by flue gas desulfurization or by
some technique of retaining the sulfur
in the solid waste. Also, costs are high—
not only for the control of the evolved
sulfur, but also for the energy required
to heat the mineral matter to the re-
quired temperatures. In fact, our cost
studies show that the cost of calcining
coal wastes can be as high as $10.00
per ton of cleaned coal (March 1978),
clearly placing this technology beyond
the realm of economic feasiility. Never-
theless, we recently conducted some
experiments to determine if waste from
Plant K calcines in the same manner as
that from Plant B. We found that trace
releases from Plant K mineral wastes,
when calcined at the optimum condi-
tions for Plant B, are not as well
controlled. The discharge severities for
Mn and Ni remained larger than unity
after calcining, and significant discharge
severities (0.1 < DS < 1.0) were ob-
served for Al, Cu, and Fe. These results
were quite unexpected in view of the
similarity of the mineral makeup of the
wastes. Conditions may have not been
optimum for these wastes, or other
factors may be involved, but we have not
initiated the experimental program re-
quired to determine the reasons. We
believe that, because the treatment is
very expensive, additional intensive
study is unwarranted.
Assessment of High-Sulfur
Appalachian Coal Wastes.
During the past year we have system-
atically studied the refuse from two coal
cleaning plants in western Pennsyl-
vania. These plants. Plants I and K,
process high-sulfur Appalachian coal,
although they use different processes.
The laboratory work has been completed
for both plants, but because the data are
complete only for Plant K, the results for
Plant K are presented in this report;
results for Plant I will be presented in
the next annual report. Plant K is a jig
operation and is unusual among the
plants we have studied because the
fines are not cleaned, but are sent
straight through the plant and combined
with the clean coal. Consequently, the
plant output consists of cleaned coal,
coarse mineral matter, and a 60-mesh
slurry effluent. In this study, we have
examined only the-coarse refuse, the
cleaned coal, and the raw feed coal.
In general, the mineral content of the
waste from Plant K is comparable to that
previously studied from the Illinois
Basin. The Plant K material has a slightly
lower sulfur content, but slightly higher
concentrations of Li, Cl, As, Cd, Sb, and
Lu. Except for Zn and Rb, which are
slightly lower in the Plant K waste, all
the remaining elements are present in
comparable concentrations. No marcasite
was detected, but the pyrite concentra-
tions (~25%) are typical of the high-
sulfur coal wastes of siderite (FeCO3).
This is the first time we have found this
mineral in coal wastes. The Ca content
of the Plant K refuse is low, which
suggests that little or nocalcite is present.
This material has little or no self-
neutralizing capacity.
Before chemical and mineralogical anal-
yses, the refuse from Plant K was
separated into seven fractions, based on
the gross external appearances of the
various pieces. Examination of these
fractions along with the composite
waste permitted us to derive some very
useful information about the relation-
ships between some of the trace ele-
ments and the various mineral phases.
Most of the teachable trace elements
tend to concentrate in those fractions
containing the highest concentrations
of clays and other silicate minerals.
However, certain elements (Se, As, Sb,
Cd, and Fe) are associated with the
pyritic minerals. These elements are
undoubtedly present in the form of
sulfides (or selenide) and some of them
are important because of their toxico-
logical properties. Leaching studies
(described below) suggest that the chem-
istry of these elements in the waste pile
effluents is somewhat different than
that of the rest of the trace elements.
We performed micromineralogical
studies of these coal wastes, using
electron microscopy coupled with ener-
gy dispersive spectrometry. Because
this technique observes such a small
fraction of the sample at any one time,
the results must be interpreted carefully.
Nevertheless, one can perform elemen-
tal analyses while retaiing the spatial
resolution of the microscope. This is
difficult, if not impossible, with other
techniques. These studies confirmed
our observations that most of the trace
elements are associated with various
types of clays. In addition, the trace
elements seem to be present as discrete
mineral phases, rather than in chemical
associations with the gross minerals.
We performed static leaching experi-
ments in which the coal waste was
shaken with deionized water for from 1
to 50 days. The mixtures were then
filtered, and the filtrate was analyzed for
acidity, specific conductance, and trace
element content. All these measure-
ments increased with leaching time.
Often, the leachates were very acidic,
with pH values less than 2, indicating
that this waste could generate drainages
of environmental concern. Fe, As, Ni,
Mn, and Al had discharge severities
greater than unity, indicating sufficient
concentrations in the waste effluents to
be of environmental concern. Zn, Cd,
and Cu had discharge severities be-
tween 0.5 and 1.0, suggesting that these
elements may be cause for concern
under certain circumstances.
The concentrations of several trace
elements increase sharply with in-
creased time, and they continue to
increase even after most of the other
elemental concentrations have reached
steady-state values. These elements.
As, Se, and Cd, are associated with
sulfide mineral phases, possibly as
sulfides (or selenide). We surmise that
the mobilization of these elements
depends not only on the pH of the
leachate, but also on the rate at which
the respective mineral phases are oxi-
dized.
In addition to the static leaching
experiments, we also performed a series
of dynamic leaching experiments with
the coal wastes by placing the coal
waste into glass columns and pumping
deionized water through the columns at
a slow and constant rate. The effluents
from the columns were sampled and
analyzed peiodically for acidity, specific
conductance, and trace element concen-
trations. After all these values had
reached steady state, the leachate flows
were stopped for 2 weeks and air was
forced through the columns. The leach-
ate flows were then resumed and the
experiment continued as before until
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the trace element concentrations in the
effluents again reached steady state.
This experiment is designed to simulate
the weathering of an uncontrolled waste
pile that is intermittently exposed to wet
(rain) and dry cycles. The initial leach-
ates are very acidic when they emerge
from the waste column, with pH values
from 1.9 to 2.2 As the leachate flow
continues, these decay to more moder-
ate values (~4). After the columns are
"regenerated" by passing air through
them, the initial pH values are again
very low (—2.3-2.4). Continuation of the
leachate flow also causes these values
to decay to moderate steady-state values
(~4). Trace element concentrations be-
have in exactly the same way as the
solution acidity (Figure 2). This behavior
can be explained. Before the experiment
the coal waste is exposed to air in the
normal course of handling and sample
preparation. This causes some oxidation
to take place. The oxidation of pyrite in
the waste leads to the formation of
sulfuric acid, which accumulates in the
waste until it is washed out by the
leachate early in the leaching experi-
ment. As the leaching proceeds, both
the acidity and the trace element con-
centrations decay to more moderate
steady-state values. However, when the
leachate flow is interrupted and air is
forced through the column, oxidation
again takes place and the resulting acid
accumulates in the waste until leaching
is resumed. Thus when water is again
allowed tof low through the column, the
initial effluents are very acidic and the
trace element concentrations are very
high. Our observations of very acidic
leachates after air regeneration of the
waste column suggest that this waste
has strong acid-generating tendencies,
and that the acid-drainage problem
associated with this waste, significant
even under steady-state conditions, is
aggravated when the leaching is inter-
mittent.
The initial discharge severities of Fe,
Ni, and Mn were all greater than unity,
but Fe, with a discharge severity of more
than 100, was by far the worst offender.
In addition, Zn, Cd, Al, and Cu had initial
discharge severities between 0.5 and
1.0. These elements may pose problems
of environmental concern under certain
weathering conditions. In past reports
in this series, we showed that trace
element concentrations in the leachates
are controlled by the pH. However, in
certain cases (Pb, As, and possibly Co
and Al), other factors are involved. The
most important of these is probably
oxidation of the minerals containing
these elements.
In summary, the experimental evi-
ence seems to indicate that the high-
sulfur waste from Plant K may pose
problems with serious environmental
consequences unless it is properly dis-
posed of. These problems are caused by
the high acidities and the high concen-
trations of several trace elements in the
waste effluents. Although our laboratory
leaching conditions may be somewhat
Al
Mn
Fe
0.001
0.01
100
1000
Discharge severity
Figure 2. Discharge severities (leachate concentration/100 x MATE) for selected
trace elements in leachates from Plant K coal preparation wastes as
determined by dynamic leaching experiments—initial (unshaded) and
steady-state (shaded).
more severe than those encountered in
a large waste pile, it is clear from our
field work that there is cause for concern
in the disposal of these solid wastes.
The behaviors of these materials exactly
parallel those of the high-sulfur wastes
from the Illinois Basin. While there is
every reason to believe that the same
control technologies will work for each
of these coal wastes, we plan to test
some of the more promising techniques
with this waste as well as that from
plants in the Illinois Basin.
Leaching Procedures
Throughout our investigation of coal
waste, we have attempted to devise
leaching tests that provide meaningful
information on the environmental be-
havior of these materials. Accordingly,
we have developed several procedures
and have used the results of these tests
as the basis for our predictions on the
weathering behaviors of coal cleaning
wastes. However there remains the
question of how these procedures com-
pare with those used by other research-
ers and, in particular, how they relate to
the EPA extraction procedure used to
classify wastes under the Resource
Conservation and Recovery Act (RCRA).
We addressed this question by compar-
ing the results of our leaching proce-
dures to those obtained using the EPA
extraction procedure.
Seven mineral wastes from coal prep-
aration plants in the Illinois Basin,
Appalachia, and the western U.S. were
leached in accordance with the EPA
extraction procedure published in the
Federal Register of May 19, 1980. This
amounts to using 100 g of waste, ground
to pass through a 9.3-mm standard
sieve (-3/8 in.), adding 1600 ml of
deionized water to the waste, and agi-
tating for 24 h in an extractor designed
to ensure that all sample surfaces are
continuously brought into contact with
well-mixed extraction fluid. The pH
values of the mixtures are monitored
during the extraction and, if the pH is
greater than 5, adjustment must be
made by adding 0.5/V acetic acid. After
24 h, the solids are removed by filtra-
tion, and the concentrations of eight
elements (Ag, As, Ba, Cd, Cr, Hg, Pb, and
Se) in the filtrate are determined.
The primary differences between our
leaching procedures and that prescribed
by EPA are the use of a higher liquid-to-
sol ids ratio in the EPA test, the exam ina-
tion of a different set of elements by the
EPA test, and the requirement that
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alkaline systems be acidified in the EPA
procedure. Compared to leaching tests
that we have used over the past several
years in our research on coal wastes,
the results of the EPA procedure com-
pare favorably with those of our proce-
dures for elements examined by both.
Among the samples that we leached
according to the EPA procedure, only
the western coal waste required addi-
tion of acetic acid to maintain the pH
below 5. Judged according to the criteria
in the Federal Register, all the coal
waste leachates had trace element
concentrations below the maximum
values set by EPA.
R. C. Heaton, L E. Wangen, P. L. Wanek. J. M. Williams. E. F. Thode, M. M.
Jones, A. M. Nyitray. P. Wagner, andJ. P. Bertino are with the Los Alamos
Scientific Laboratory, University of California, Los Alamos, NM 87545.
David A. Kirchgessnor is the EPA Project Officer (see below).
The complete report, entitled "Trace Element Characterization of Coal Wastes—
Fifth Annual Progress Report," (Order No. PB 82-219 379; Cost: $12.00,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
•U8.QOVERNMENT PRINTING OFFICE:1M2-55«-M2-425
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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Fees Paid
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