United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-93/159 October 1993
? EPA Project Summary
Airborne Asbestos
Concentrations During Buffing of
Resilient Floor Tile
A study was conducted to determine
the level of airborne asbestos concentra-
tions during routine spray-buffing of as-
bestos-containing floor tiles at 17 schools
in northern, central, and southern New
Jersey. Although the schools selected do
not represent a statistical random sample,
they do represent a cross section of floor
conditions and floor-care maintenance
practices. Increased airborne asbestos lev-
els during spray-buffing were measured
at 12 of the 17 schools. The increase was
statistically significant at 7 of the 17
schools. Overall, the mean relative increase
in airborne asbestos concentrations dur-
ing spray-buffing with the high-speed ma-
chines (1000 to 1500 rpm) was statistically
significantly higher than that during buff-
ing with low-speed machines (175 to 330
rpm). Machine speed appeared to have a
significant effect on the structure mor-
phology of the airborne asbestos struc-
tures generated during spray-buffing. Re-
sults of the study indicate that spray-buff-
ing can generate asbestos-containing par-
ticles from the surface of asbestos-con-
taining resilient floor tile. The estimated 8-
hr time-weighted average (TWA) of total
fiber concentrations (0.093 f/cm2 maximum)
in the breathing zone of the machine op-
erators (as determined by phase contrast
microscopy [PCM]) did not exceed the
Occupational Safety and Health Adminis-
tration (OSHA) action level of 0.1 fibers
per cubic centimeter (f/cm3), 8-hr TWA.
This Project Summary was developed
by EPA's Risk Reduction Engineering
Laboratory, Cincinnati, OH, to announce
key findings of the research project that is
fully documented in a separate report of
the same title (see Project Report order-
ing information at back).
Introduction
Although no longer manufactured in the
United States, asbestos-containing resilient
floor tiles are installed in residential dwellings,
institutions, commercial and public office build-
ings, and industrial facilities. The organic ma-
trix in floor tiles may be either asphalt or
polyvinyl chloride, and their dimensions are
either 9 in. by 9 in. or 12 in. by 12 in. The
asbestos in nearly all floor tiles is chrysotile,
which is dispersed throughout the thickness
of the tile. Although these floor tiles are con-
sidered nonfriable, the frictional forces ex-
erted on these materials during routine floor-
care maintenance operations can generate
asbestos-containing particles.
The principal types of maintenance per-
formed routinely on resilient floor tiles include
spray-buffing and dry burnishing, and wet
scrubbing and stripping followed by refinish-
ing. The U.S. Environmental Protection
Agency (EPA), school districts, and the Resil-
ient Floor Covering Institute have monitored
airborne asbestos levels during wet stripping
of asbestos-containing floor tiles. These stud-
ies have shown elevated levels of asbestos
structures in the air during the stripping op-
eration (based on transmission electron mi-
croscopy [TEM]), but the 8-hr TWA concen-
trations (based on PCM) were below the
OSHA permissible exposure limit and action
level of 0.2 and 0.1 f/cm3 of air, respectively. If
the action level is exceeded, periodic per-
sonal air monitoring, employee training, and
medical surveillance are required (29 CFR
1910.1001). The results of the two analytical
techniques differ mostly because PCM does
-------
not detect the smaller fibers (<5 (am in length
and <0.25 pm in width) as measured by
TEM. Also, the OSHA methodology requires
a length to width ratio (aspect ratio) of 3:1 or
greater whereas the TEM methodology has
an aspect ratio of 5:1 or greater. In response
to concerns raised by school districts and
building managers regarding the release of
asbestos structures during stripping opera-
tions, the EPA issued interim guidance on
appropriate procedures for the stripping of
asbestos-containing floor coverings.
Little data are available for evaluating the
extent of asbestos structures released during
other floor-care maintenance procedures, such
as spray-buffing. Spray-buffing is the restor-
ative maintenance of a previously polished
floor by use of a suitable floor-polishing ma-
chine immediately after the surface has been
mist-sprayed with an appropriate product
whereby the wet application is buffed to dry-
ness. The levels of airborne asbestos struc-
tures released during spray-buffing could be
higher than those during wet stripping, espe-
cially if the floor has been poorly maintained
(i.e., minimal wax layer), is worn, or is other-
wise damaged.
The Risk Reduction Engineering Labora-
tory (RREL) of the U.S. EPA and the Environ-
mental Health Service (EHS) of the New
Jersey Department of Health (NJDOH) con-
ducted a study to evaluate airborne asbestos
concentrations during routine spray-buffing of
asbestos-containing floor tile. The primary ob-
jectives of this study were (1) to determine
the airborne asbestos concentrations during
routine spray-buffing of asbestos-containing
resilient floor tile in a cross section of schools
in northern, central, and southern New Jer-
sey, and (2) to compare the fiber concentra-
tions measured by PCM during routine spray-
buffing of asbestos-containing floor tile with
the OSHA action level of 0.1 f/cm3 of air, 8-hr
TWA(29CFR1910.1001).
Study Sites
This study was conducted at 17 schools,
distributed among eight school districts, in
northern, central, and southern New Jersey.
Although these schools do not represent a
statistical random sample, they do represent
a cross section of floor conditions and floor-
care maintenance operations.
Access to the schools was coordinated
directly by the Environmental Health Service
of the New Jersey Department of Hearth (EHS-
NJDOH). The EHS-NJDOH collected bulk
samples of all floor tiles; and documented
floor-care practices, floor conditions, and char-
acteristics of the floor-buffing equipment and
materials in each school, as well as other
variables that might have an effect on the
release of asbestos structures.
In all of the schools, the existing custodial
staff performed the floor-care maintenance
operations. The floors were prepared (i.e.,
dry and/or wet-mopped) and spray-buffed in
accordance with established practices and
procedures at the respective schools.
Sampling Strategy
The first study objective was to determine
whether airborne asbestos concentrations in-
creased during the spray-buffing of floor tile.
This was addressed by collecting air samples
before and during floor-buffing operations. A
maximum of two distinct areas were tested in
each school studied. Immediately before buff-
ing operations began, three baseline, fixed-
station, area air samples were collected in
each test area under normal building condi-
tions (i.e., no intentional air disturbance be-
yond that attributable to normal occupancy
activity in the area). Three personal breath-
ing-zone samples were collected during buff-
ing operations for comparison with the baseline
samples. These samples also were taken
under normal occupancy conditions (i.e., no
air disturbance beyond that attributable to the
buffing itself). These samples were collected
in the breathing zone of the buffing machine
operators so they would be representative of
airborne asbestos levels during spray-buffing
operations. The three baseline and three per-
sonal breathing zone samples were analyzed
by TEM.
The second study objective was to com-
pare total fiber concentrations during buffing
operations with the OSHA action level of 0.1
f/cm3, 8-hr TWA. This was achieved by col-
lecting one sample in the breathing zone of
the machine operator during the spray-buff-
ing in each area. These samples were col-
lected in accordance with OSHA sampling
protocols and analyzed by PCM.
To confirm the percentage and type of
asbestos in the floor tile, bulk samples of
each type of floor tile present in each school
were collected.
Sampling Methods
Fixed-Station Area Air Samples
The baseline, fixed-station, area air samples
were collected on open-face, 25-mm-diam-
eter, 0.45-)um-pore-size, mixed cellulose es-
ter (MCE) filters with a 5-jim-pore-size MCE
diffusing filter and a cellulose support pad
contained in a three-piece cassette. The filter
cassettes were positioned on tripods approxi-
mately 5 ft above the floor, with the filter face
at a 45° angle toward the floor. The filter
assembly was attached to an electric-pow-
ered (110 VAC) 1/6-horsepower vacuum
pump operating at a flow rate of approxi-
mately 9 L/min. Air volumes ranged from 564
to 916 L The sampling pumps were cali-
brated with a precision rotameter both before
and after sampling.
Personal Breathing Zone Air
Samples
Three personal breathing zone air samples
were collected on the same filters described
in the previous section and were analyzed by
TEM. A fourth personal breathing zone sample
was collected on a 25-mm-diameter, 0.8-nm-
pore-size MCE filter, and a cellulose support
pad contained in a three-piece cassette with
a 50-mm conductive extension cowl. This
fourth personal breathing zone sample was
collected in accordance with OSHA protocols
and analyzed by PCM.
The four filter cassettes were positioned in
the breathing zone of the buffing machine
operator. Each filter was attached to approxi-
mately 50 ft of Tygon tubing that was at-
tached to an electric-powered (110 VAC) 1/6-
horsepower vacuum pump operating at a
flow rate of approximately 9 L/min. Air vol-
umes ranged from 617 to 970 L To achieve
the target air volume of 600 L in the time
required to spray-buff the test area, traditional
battery-powered, personal sampling pumps
could not be used because of their limited
airflow rates (approximately 2 L/min with the
0.45-nm-pore-size MCE filter).
Bulk Floor Tile Samples
Bulk samples were collected of each type
of floor tile present in each school. Each
sample consisted of a 2-in. by 2-in. section of
floor tile. A 2-in. by 2-in. template was used to
delineate the area on the floor tile. A hammer
and wood chisel were used to remove the
tile, which was then placed in a labeled Ziploc
plastic bag. The exact location of the sample
was recorded on a plan drawing of the build-
ing.
Analytical Methods
Air Samples
The 0.45-|om-pore-size MCE filters were
prepared and analyzed in accordance with
the non mandatory TEM method specified in
the Asbestos Hazard Emergency Response
Act (AHERA) Final Rule (October 30, 1987;
40 CFR Part 763). Each of the 0.8-nm-pore-
size MCE membrane filters was analyzed by
PCM. These 0.8 urn sample filters were pre-
pared and analyzed according to the NIOSH
7400 protocol (Revision 3, June 5, 1989,
-------
National Institute of Occupational Safety and
Health Manual of Analytical Methods).
Bulk Floor Tile Samples
The type and percentage of asbestos in
the floor tile were determined by polarized
light microscopy analysis in accordance with
the EPA test method "Interim Method for
Determination of Asbestos in Bulk Insulation
Samples" (EPA 600/M4-82-020). A confirma-
tory analysis was performed on floor tile from
8 of the 17 schools. The samples were ana-
lyzed by TEM in accordance with Chatfield's
Method (SOP-1988-02, Revision No. 1: Analy-
sis of Resilient Floor Tile). Portions of a freshly
fractured edge of the bulk samples were ana-
lyzed by scanning electron microscopy to
examine the condition of the floor tile surface.
Statistical Methods
Descriptive statistics were calculated for
each school and each area within a school.
These descriptive statistics included the
sample size; arithmetic mean, minimum, and
maximum airborne asbestos concentrations;
and the arithmetic standard deviation.
A two-factor analysis of variance (ANOVA)
was used to compare airborne asbestos con-
centrations before and during floor buffing.
Each school was considered separately. The
experimental factors in the ANOVA analysis
were the sample period (baseline, during)
and area within a school (A or B). If only one
area was studied at a school, the analysis
was reduced to a one-factor ANOVA, which
is equivalent to a Student's t-test.
Quality Assurance
Specific quality assurance procedures out-
lined in the AHERA rule were used to ensure
the precision of the collection and analysis of
air samples; these included filter lot blanks,
open and closed field blanks, and repeated
sample analyses (replicate and duplicate
analyses).
Results and Discussion
Study-Site Characteristics
Resilient Floor Tile
The resilient flooring in the 28 study sites
(representing 17 schools) included mostly 9-
in. by 9-in. tiles and some 12-in. by 12-in.
tiles. Although the asbestos content of the
tiles ranged from 1% to 38%, the content of
most of the tiles exceeded 10%. The spray-
buffed areas ranged from 727 to 3386 ft2; the
average area was approximately 2150 ft2.
Any floor areas with damaged (e.g., broken)
or missing tiles were isolated to prevent their
contact with the buffing machine.
Floor Care Maintenance Practices
Sixteen of the 17 schools used a black pad
for stripping the floors, whereas EPA's interim
procedure guidelines for the stripping of resil-
ient floor coverings recommend the use of
the "least abrasive pad possible". The schools
wet-stripped and refinished the floors one to
three times a year (during the summer, win-
ter, or spring breaks).
The floors were dry- and/or wet-mopped
before they were spray-buffed. All of the
schools dry-mopped the floors, and nine of
the schools both dry and wet-mopped the
floors. The floors are typically spray-buffed
once a year; however, some schools spray-
buffed the floors one to three times each
week.
Buffing Equipment and Materials
Twelve of the schools used buffing ma-
chines operating at 1000 to 1500 rpm and
five used buffing machines operating at 175
to 330 rpm. The appropriate buffing pad (i.e.,
a white pad with high-speed machines and a
red pad with low-speed machines) was used
at all of the schools except two: school No. 1
used a red pad with a high-speed machine,
and school No. 13 used a green pad (de-
signed for heavy scrubbing and light stripping
applications) with a low-speed machine.
Airborne Asbestos Concentrations
Before and During Spray-Buffing
Three samples were collected before and
three during routine spray-buffing of asbes-
tos-containing floor tile in each area within a
school. Table 1 presents the descriptive sta-
tistics (i.e., mean, minimum, maximum, and
standard deviation) separately for each school/
area combination and each sampling period
(i.e., baseline and during spray-buffing). Fig-
ure 1 shows the average airborne asbestos
concentrations at each area before and dur-
ing spray-buffing.
Increased airborne asbestos levels during
spray-buffing were noted at 12 of the 17
schools. The increase was statistically signifi-
cant at seven of these schools (Nos. 1, 5, 6,
7, 12, 14, and 17). When compared with
baseline measurements taken before buffing,
airborne asbestos concentrations were quali-
tatively the same or lower during buffing at
the remaining five schools (Nos. 2, 4, 9, 10,
and 16).
Overall, the mean relative increase in air-
borne asbestos concentrations during spray-
buffing with the high-speed machines (1000
to 1500 rprn) was significantly higher
(p=0.0326) than the relative increase during
spray-buffing with the low-speed machines
(175 to 330 rpm). On average, airborne as-
bestos concentrations were approximately 5
times higher during spray-buffing than before
spray-buffing with the higher speed machines;
whereas, spray-buffing with the lower-speed
machines showed a 2-fold increase.
Airborne Asbestos Concentrations
Based on Frequency of Spray-
Buffing
Spray-buffing is routinely performed (one
or more times weekly) at 7 schools, whereas
spray-buffing is performed less frequently
(once per month to once per year) at the
remaining 10 schools. The mean airborne
asbestos concentrations measured before
buffing at the schools in which spray-buffing
is routinely performed (0.035 s/cm3) was sig-
nificantly greater (p=0.0004) than the mean
baseline concentration measured at schools
in which spray-buffing is performed less fre-
quently (0.007 s/cm3).
Personal Breathing Zone
Concentrations of Total Fibers
Table 2 presents total fiber concentrations
measured in the machine operator's breath-
ing zone during spray-buffing, as determined
by PCM. The actual time spent buffing the
floors ranged from 64 to 97 min.
School maintenance workers do not typi-
cally spray-buff floors for a full 8-hr work shift.
According to school custodians at the five
sites (Nos. 6A, 10A, 11 A, 13B, and 16B) that
showed measured levels above 0.1 f/cm3, the
average time spent buffing floors on a typical
day ranges from 1.5 to 2.5 hr. Assuming that
a maintenance worker spends no more
than 2.5 hr/day buffing the floor and has
no additional exposure to asbestos for the
remainder of the day, the estimated 8-hr
TWA concentrations for all of these sites
would be less than the OSHA action level
of 0.1 f/cm3, 8-hr TWA. The maximum
estimated 8-hr TWA exposure concentra-
tion (0.093 f/cm3, 8-hr TWA) was mea-
sured at Site 11 A.
Morphology and Size
Distributions of Asbestos
Structures
The TEM analysis of the 163 samples
collected before and during spray-buffing
yielded a total of 4598 asbestos struc-
tures, of which more than 99% were
chrysotile and less than 1% were amphib-
ole. The asbestos in nearly all floor tiles is
chrysotile. Overall, the asbestos structures
were primarily matrices (approximately
80%) and to a lesser extent, fibers, clus-
ters, and bundles.
The structure morphology for asbestos
structures observed before (i.e., baseline)
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i/e 1. Summary of Airborne Asbestos Concentrations Measured By TEM Before and During Buffing of Floor Tile
Asbestos Concentration, s/cm3 (N=3)
Baseline DurinQ Buffino.
Site
1A
1B
2A
3A
3B
4 A'
5A
6A
6B
7A
7B
8A
8Bf
9A
10A
10B
11 A
11B
12A
12B
13A
13B
14A
15A
16A
16B
17A
17B
Mean
0.004
0.001
0.006
0.001
0
0
0.009
0.030
0.029
0.003
0.008
0.011
0.041
0.010
0.086
0.038
0.033
0.029
0.012
0.065
0.015
0.194
0.006
0.094
0.001
0.003
0.001
0.050
Minimum
0
0
0
0
0
0
0.005
0
0.015
0
0.005
0.005
0
0
0
0.030
0.020
0.005
0.009
0.029
0
0.051
0.005
0.058
0
0
0
0.024
Maximum
0.009
0.005
0.010
0.005
0
0
0.014
0.076
0.054
0.010
0.014
0.020
0.103
0.020
0.254
0.045
0.0i4
0.069
0.014
0.113
0.040
0.390
0.010
0. 126
0.005
0.005
0.005
0.065
Standard
Deviation
0.005
0.003
0.006
0.003
0
0
0.005
0.040
0.021
0.006
0.005
0.008
0.055
0.010
0.145
0.008
0.018
0.034
0.003
0.043
0.022
0.175
0.003
0.034
0.003
0.003
0.003
0.023
Mean
0.014
0.013
0.003
0.011
0.003
0
0.107
0.163
0.205
0.145
0.414
0.025
-
0.003
0.067
0.032
0.056
0.077
0.067
0.096
0.082
0.290
0.052
0.151
0.001
0
0.056
0.114
Minimum
0.010
0.005
0
0
0
0
0.088
0.065
0.137
0.097
0.379
0.015
.
0
0.033
0.029
0.015
0.067
0.043
0.062
0.015
0.225
0.020
0.102
0
0
0.052
0.035
Maximum
0.019
0.019
0.005
0.025
0.009
0
0.123
0.302
0.291
0.179
0.464
0.030
_
0.009
0.094
0.035
0.097
0.090
0.113
0.151
0.206
0.329
0.087
0.216
0.004
0
0.059
0.189
Standard
Deviation
0.005
0.007
0.003
0.013
0.005
0
0.018
0.123
0.078
0.043
0.044
0.009
_
0.005
0.031
0.003
0.058
0.012
0.039
0.048
0.040
0.057
0.034
0.059
0.002
0
0.004
0.077
' Summary statistics are based on two samples (N=2).
f The samples collected during spray-buffing were too heavily loaded with paniculate to count.
low-speed buffing was comparable with
that observed during low-speed buffing.
That is, similar percentages of fibers,
bundles, clusters, and matrices were ob-
served both before and during low-speed
buffing. The structure morphologies for as-
bestos structures observed during high-
speed buffing, however, were distinctly dif-
ferent; these morphologies showed that
the percentage of asbestos fibers observed
during high-speed buffing was approxi-
mately 2.5 times greater than the percent-
age of fibers observed before buffing. In
contrast, the percentage of asbestos ma-
trices were greater before high-speed buff-
ing than during buffing. One possible ex-
planation for a decrease in the number of
asbestos matrices during buffing is that
the high-speed buffing pulverizes any as-
bestos-containing particles lying on the sur-
face of the floor and/or any particles con-
tained in the wax layer on the floor tile.
This could also explain the increase in the
percentage of asbestos fibers during high
speed buffing. Another possible explana-
tion for the increase in the percentage of
asbestos fibers during high-speed buffing could
be the abrasion of surficial fibers from the floor
tile.
Overall, less than 1% of the asbestos fibers
measured before and during were greater than
5 yum in length. Although comparable structure
size distributions were observed before and
during low-speed buffing, a larger percentage of
the structures observed during high-speed buff-
ing were less than 1 jam compared to structures
observed before high-speed buffing. The in-
creased number of structures less than 1 jum in
length could result from (1) the pulverization of
asbestos structures on the floor surface and/or
asbestos structures contained in the wax layer,
and/or (2) the abrasion of surficial fibers from
the floor tile.
Conclusions
Spray-buffing can cause asbestos structures
to be generated from the surface of asbestos-
containing resilient floor tile. Increased airborne
asbestos concentrations during spray-buffing
were measured at 12 of the 17 schools studied.
The increase was statistically significant at seven
of these schools.
Overall, the mean relative increase in air-
borne asbestos concentrations during spray-
buffing with the high-speed machines (1000 to
1500 rpm) was significantly higher than the
relative increase during spray-buffing with the
low-speed machines (175 to 330 rpm). On
average, airborne asbestos concentrations were
approximately 5 times higher during than before
spray-buffing with the high speed machines;
whereas, spray-buffing with the low-speed ma-
chines showed a 2-fokd increase.
Machine speed appears to have a significant
effect on the structure morphology of the air-
borne asbestos structures generated during
spray-buffing. The percentage of asbestos fi-
bers observed during high-speed buffing was
approximately 2.5 times greater than that be-
fore buffing; whereas, the percentage of asbes-
tos fibers observed during low-speed buffing
was approximately 1.3 times greater. The per-
centage of asbestos matrices measured during
high-speed buffing were approximately 12 times
lower than before buffing; whereas, the percent
-------
Sampling period
Baseline [ During buffing
1
CO
3
co
e
0.1
0.01
1B 2A 3A 3B 4A 5A 6A 6B
Study Site
Figure 1. A verage airborne asbestos concentrations (measured by TEM) before and during buffing of asbestos-containing resilient floor tile (continued).
Sampling period
Baseline j During buffing
i
3
I
•^
0.001
78 8A 9A 10A 10B 11A
0.01
11B 12A 12B
Figure 1. (continued).
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1
§
I
0.1
0.01
0.001
Sampling period
Baseline I I During buffing
13A
17B
Figure 1. (concluded)
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Table 2. Total Fiber Concentrations During Buffing of Resilient Floor Tile (As Measured by PCM)
Site
Total Fiber Concentration,
f/cm3
1A
1B
2A
3A
3B
4A
5 A'
6A
6B*
7A
7B*
8A*
8B*
9A
10A
10B
11 A
11B
12A
12B
13A
13B
14A
15A
16A
16B
17A
17B
0.033
0.034
0.078
0.077
0.076
0.024
.
0.130
-
0.048
-
_
.
0.030
0.133
0.061
0.295
0.065
0.067
0.070
0.085
0.220
0.042
0.076
0.080
0.104
0.027
0.055
age of asbestos matrices measured during low-
speed buffing was essentially unchanged (i.e.,
<0.4% bwer).
The estimated 8-hr TWA of total fiber con-
centrations (0.093 f/cm3 maximum) in the breath-
ing zone of the machine operators (as deter-
mined by PCM) did not exceed the OSHA
action level of 0.1 f/cm3, Siir TWA.
Recommendations
Further research is recommended to study
the effect of buffing methods on the release of
asbestos structures from the surface of asbes-
tos-containing resilient floor tiles. A study should
be designed to evaluate the extent of asbestos
release during application of the two buffing
methods (low-speed spray-buffing and high-
speed dry-buffing) on three levels of floor care
(poor, intermediate, and good). The results of
this study would define the need for and nature
of guidance for the buffing of asbestos-contain-
ing resilient floor tiles.
The full report was submitted in fulfillment of
Contract No. 68-D2-0058 by Environmental
Quality Management, Inc. under subcontract to
Pacific Environmental Services, Inc. through the
sponsorship of the U.S. Environmental Protec-
tion Agency.
' Samples were all too heavily loaded with par-
ticulate to count.
•trV.S. GOVERNMENT PRINTING OFFICE: 1993 - 750-071/800*2
-------
This Project Summary was prepared by the staff of Environmental Quality
Management, Inc., Cincinnati, OH 45240 and Environmental Health Service,
New Jersey Department of Health, Trenton, NJ 08625
Aaron R. Martin is the EPA Project Officer
Alva Edwards is the Technical Project Officer (see below)
The complete report, entitled "Airborne Asbestos Concentrations During Buffing
of Resilient Floor Tile," (Order No. PB93-227 551/AS; Cost: $27.00,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The Technical Project Officer can be contacted at
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-93/159
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