Ecological Research Series
MERCURY DISTRIBUTION IN SOIL AROUND
A LARGE COAL-FIRED POWER PLANT
Environmental Monitoring and Support Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Las Vegas, Nevada 89114
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
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vironmental technology. Elimination of traditional grouping was consciously
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The nine series are:
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This document is available to the public through the National Technical Informa-
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EPA-600/3-77-063
May 1977
MERCURY DISTRIBUTION IN SOIL AROUND A LARGE COAL-FIRED
POWER PLANT
By
Alan B. Crockett and Robert R. Kinnison
Monitoring Systems Research and Development Division
Environmental Monitoring and Support Laboratory
Las Vegas, Nevada 89114
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
LAS VEGAS, NEVADA 89114
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DISCLAIMER
This report has been reviewed by the Environmental Monitoring and Support
Laboratory-Las Vegas, U.S. Environmental Protection Agency, and approved for
publication. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
ii
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FOREWORD
Protection of the environment requires effective regulatory actions which
are based on sound technical and scientific information. This information
must include the quantitative description and linking of pollutant sources,
transport mechanisms, interactions, and resulting effects on man and his
environment. Because of the complexities involved, assessment of specific
pollutants in the environment requires a total systems approach which trans-
cends the media of air, water, and land. The Environmental Monitoring and
Support Laboratory-Las Vegas contributes to the formation and enhancement of
a sound integrated monitoring data base through multidisciplinary, multimedia
programs designed to:
develop and optimize systems and strategies for moni-
toring pollutants and their impact on the environment
demonstrate new monitoring systems and technologies by
. applying them to fulfill special monitoring needs of
the Agency's operating programs
The report presents the data collected in a study of mercury residues in
soil around a large coal-fired power plant. Detailed soil sampling and
analyses indicate low residue levels and no statistically significant dif-
ferences in mercury distribution patterns within 30 kilometers (km) of the
plant. These data will be considered by EPA and others in making decisions
concerning regulations of mercury emissions from coal-fired utilities. For
additional information, please contact the Pollutant Pathways Branch, Environ-
mental Monitoring and Support Laboratory-LV, P- 0. Box 15027, Las Vegas,
Nevada 89114.
George B. Morgan
Director
Environmental Monitoring and Support Laboratory
Las Vegas, Nevada
iii
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INTRODUCTION
The toxicity and hazards of mercury are well established and its distri-
bution throughout the environment has been documented (Peakall and Lovett,
1972). Due to the known hazards, a number of reports have focused on the
sources of mercury resulting from man's activities. The combustion of coal
is often cited as a significant mercury source and various emission estimates
have been calculated (Horn, 1975; Joensuu, 1971; Billings and Matson, 1972).
The amount of mercury released to the atmosphere by coal-fired electric
utilities can be estimated from the amount of coal consumed using the average
mercury content of the coal and a release factor. Coal combustion by the
electric utilities in the United States was about 365 X 10^ kilograms (kg)
in 1975, and is projected to increase to 854 X 10^ kg by the year 2000
(Merrit, 1976). The mercury level in U.S. coal has been estimated from
different data bases to average 1,000 parts per billion (ppb) (Joensuu, 1971),
300 ppb (Billings and Matson, 1972), 200 ppb (Horn, 1975), and 150 ppb (Magee
et^ £il., 1973). The latter figure, representing the most recent data, was
compiled from the largest data base and is probably the more accurate. Not
all mercury in coal is released during coal combustion and a reasonable re-
lease factor appears to be 0.9 (Billings et_ a±., 1973; Kalb, 1975; Bolton
et al., 1973). Therefore, the 1975 estimated mercury release from U.S. coal-
fired electric utilities was about 49,000 kg.
The fate of this released mercury has not been extensively studied. Klein
and Russell (1973) studied heavy metal fallout around a 650 megawatts (MW) coal-
fired power plant equipped with a 120-meter (m) stack. They state that the
soils around the plant are enriched in mercury, but present no statistical
proof. Bolton et al. (1973) conducted a major study of trace elements at the
870 MW coal-fired Allen Steam Plant and found no significant evidence of ele-
mental accumulation. Cannon and Anderson (1972) reported on elements around
the Four Corners Power Plant in New Mexico, but showed no significant elevation
of mercury levels in plants or soil. The lack of statistical treatment, the
small number of samples involved, and the terrain and background levels of
mercury limit the usefulness of these studies. For these reasons, and as a
part of a project to select a biological monitor, an investigation was con-
ducted to determine whether a mercury gradient exists around coal-fired power
plants.
The selection of a power plant was based upon the estimated potential for
contamination. This report focuses on the soil sampling portion of this study.
All samples were collected in December 1974.
The Four Corners Power Plant was selected because of its size (>2,150 MW) ,
its coal consumption (6.3 X 10^ kilograms per year (kg/y)), its length of
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operation (since 1963), and its relatively short stacks (two are 76 m and two
are 91 m). In addition, the surrounding arid terrain (15 to 20 centimeters
per year (cm/y) percipitation) is undisturbed by cultivation and the soils
are low in most elements including mercury.
Estimates of the mercury concentration of the coal burned by the plant
vary considerably. Based upon a very limited sampling, Billings et al.
(1973) estimated the mercury concentration to be 300 ppb. Green and Robinson
(1971) sampled five coal blending piles as well as the mine and found the
average mercury concentration to be 375 ppb. However, the U.S. Geological
Survey analyzed 21 coal samples from the mine and reported an average value
of 90 ppb (Swanson, 1972). The latter analyses were made using proven modern
methods in an attempt to provide precise quantitative data under a strong
quality control program. Assuming the figure of 90 ppb to be the most accurate,
it can be calculated that the Four Corners Power Plant emitted over 1 percent
of all mercury released by coal-fired power plants in the United States for
1974.
CONCLUSIONS
Detailed soil sampling and analyses for mercury residues indicate no
significant differences in mercury residue levels within 30 km of a large
coal-fired power plant. Other recent data indicated emissions of 589 and
1,372 kg of mercury by a coal-fired power plant and a smelter, respectively,
and pose no health hazard relative to air contamination (Horn, 1975). These
data should be considered in making decisions concerning regulation of
mercury emissions from coal-fired power plants. Horn (1975) indicates that
U.S. coal-fired utilities emit 9 percent of all human-related releases to
the atmosphere in the U.S. In 1974, utility emissions amounted to only
4 percent of the natural degassing mercury loss in conterminous United
States (calculated from Horn, 1975).
SAMPLING AND ANALYSIS
The sampling design selected was a radial grid employing 16 evenly
spaced radii and five logarithmically spaced circles, concentric around
the power plant (Figure 1). The radii of the circles (A-E) were 1.0, 2.9,
6.8, 14.6, and 30 kg. From the 80 sites on the grid, only 70 composite soil
samples were collected since some sites fell on stripped land or in the cool-
ing pond. Each sample was a composite of 10 subsamples collected 15 m apart.
The upper 1 to 2 cm of soil was collected by trowel and stored in pint glass
jars.
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RADII OF CIRCLES- 1.0. 2.9. 6.8, 14.6 & 30.0 km.
4- POWER PLANT
• SITES SAMPLED
Figure 1. Soil sampling sites around the Four Corners Power Plant
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The samples were dried at 60°C, sieved to 10 mesh, and 5 replicates of
150 to 200 milligrams (mg) were analyzed using an Isotope Atomic Absorption
spectrometer (Hadeiski and Mclaughlin, 1975). The geometric mean of the
replicate standard deviations was 1.9 ppb with a range of 0.2 to 21 ppb.
The standard deviation of the replicates could probably have been reduced
if the samples had been pulverized to homogenize the sample. Eleven percent
of the samples was randomly selected and reanalyzed for quality control pur-
poses. Of the eight reruns, seven were within ±1 ppb of the original value
while the eighth was off by 7 ppb.
The standard regression line of nanograms of mercury versus the digital
millivolt reading was calculated using 60 analyses of five liquid standards
and a blank. The regression was verified using a U.S. Environmental Protec-
tion Agency liquid standard and two National Bureau of Standards (NBS) Stan-
dard Reference Materials, orchard leaves (#1571) and coal (#1632). The
lower limit of detection was 5 ppb.
RESULTS
The overall arithmetic mean (the data did not exhibit significant depar-
ture from normality) for the 70 samples was 16 ppb with a range of 6 to 45 ppb
and an overall standard deviation of 6.7 ppb (see Table 1). Initially the
data were subjected to a two-way analysis of variance test using the analyti-
cal replicates. The residual error was therefore a measure of laboratory
precision only. Since the program used cannot accommodate missing samples,
six of the radii were dropped from the data analysis. The analysis of vari-
ance on the ten remaining radii showed the following:
1. A highly significant difference between circles (i.e., soil
mercury levels are related to distance from the power plant).
2. A highly significant difference between radii (i.e., soil
mercury levels are related to compass direction from the power plant).
3. A highly significant interaction effect (i.e., the type of effect
due to radii varies significantly from circle to circle, or the type of
effect due to circles varies significantly from radii to radii).
Attempts at subdividing the data to eliminate the interaction effects were
not successful.
Since it was possible that the analytical error was insignificant rela-
tive to field sampling error, a second approach was attempted. A nested two-
way analysis of variance was employed in which radii were grouped in twos
or fours which provided a residual error term composed of both analytical
and field sampling errors. The grouping of radii was conducted since it was
felt that small changes in compass direction would have an insignificant
effect on residue levels. The results of these analyses of variance were
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TABLE 1. MEAN MERCURY RESIDUES IN
SOIL BY
SITE (PPB)
Radius
Number Direction
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
MEAN
STANDARD
DEVIATION
NNE
NE
ENE
E
ESE
SE
SSE
S
SSW
SW
WSW
W
WNW
NW
NNW
N
A
—
45
30
22
21
16
23
12
14
15
27
20
24
16
—
—
22
8.7
Concentric Circle
B
6
9
13
11
13
14
—
20
20
26
22
24
23
15
14
7
16
6.3
C
12
12
13
10
10
10
9
—
12
14
23
15
18
16
13
23
14
4.4
D
10
13
11
11
10
14
6
14
—
21
14
13
22
26
—
30
15
6.8
E
—
19
9
9
12
11
14
11
12
14
21
12
17
11
—
—
13
3.7
Mean
9.3
20
15
13
13
13
13
14
14
18
21
17
21
17
14
20
16
Standard
Deviation
3.1
15
8.4
5.3
4.5
2.4
7.4
4.0
3.8
5.3
4.7
5.1
3.1
5.5
0.7
1.2
6.7
— = no sample.
Radii of circles A - E are 1.0, 2.9, 6.8, 15 and 30 km, respectively.
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similar to those encountered previously. Highly significant effects due to
circles, radii and interaction were again discovered. Since the interaction
effect could not be eliminated, it must be concluded that the distribution of
mercury residues around the plant is very complex. Therefore, no statement
based on statistical analysis can be made concerning the relationship of
mercury residue levels relative to direction or distance from the plant.
In an attempt to discern a distribution pattern of mercury, a plot was
made of mean mercury residues by site. Lines of iso-mercury residues were
then plotted as shown in Figure 2. Aside from a couple of small scattered
sites exceeding 20 ppb, there are three areas with levels exceeding 20 ppb.
The area due west of the plant may be related to the ash ponds located in
this section. The 25 ppb high to the north-northwest cannot be accounted for
by the wind direction, but another power plant (350 MW, 13 k north-northeast)
is located in that area. The samples with the highest mercury levels detected
were collected from an undisturbed island located in the cooling pond, sites
2A and 3A.
DISCUSSION
The 70 soil samples collected on a radial grid around the Four Corners
Power Plant probably represent the most intensive sampling effort to date at
that site. No statistically significant differences in mercury residue levels
were detected although some distribution patterns are evident. The levels of
mercury detected are quite low, but in good agreement with soil data compiled
by Cannon and Anderson (1972). They reported an average value of 0.02 (20
ppb) ppm compared to 16 ppb in this study. Shacklette et al. (1971) reported
the average mercury concentration of the Western United States to be 83 ppb
which is nearly twice as high as the maximum and five times higher than the
mean value reported here.
The question then arises as to the fate of mercury emissions from the
plant. The estimated annual release of mercury through stack emissions is
510 kg based upon a release factor of 0.9, a coal consumption of 6.3 X 109
kg/y and a mercury concentration of 90 ppb. This value is in agreement with
Arizona Public Services' (1975) emission estimate of 76 grams per hour (g/h)
plus or minus a factor of two for the plant operating at full load. Convert-
ing and using an operating factor of 70%, the estimate becomes 466 kg of
mercury per year. The total amount of mercury emitted by the plant since it
began operating is about 3,600 kg.
If all this mercury was evenly deposited within 5 or 10 km of the plant
and remained in the top 2.54 cm of soil, the average soil concentration would
have increased by 122 ppb or 30 ppb, respectively. The average mercury levels
in soils around the power plant are considerably below these figures. Obvious-
ly, the emitted mercury is ultimately being deposited over a much larger area.
It is possible, however, that mercury is being deposited and rapidly revolati-
lized in aerobic terrestrial environments (Rogers, 1975).
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N
14
11
10
15
WIND ROSE (WILLIAMS, 1976)
10%
• SITES SAMPLED
* ASH PONDS
* POWER PLANT
Figure 2. Distribution of mercury residues in soil around Four Corners
Power Plant (PPB)
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REFERENCES
Arizona Public Services and Utah International Incorporated. Four Corners
Power Generating Plant and Navajo Coal Mine, Environmental Report. March
1975."
Billings, C. E. and W. R. Matson. "Mercury Emissions from Coal Combustion."
Science 176:1232. 1972.
Billings, C. E., A. M. Sarco, W. R. Matson, R. M. Griffin, W. R. Coniglio,
and R. A. Harley. "Mercury Balance in a Large Coal-Fired Furnace." Journal
of Air Pollution Control Association 23:773. 1973.
Bolton, N. E., R. I. Van Hook, W. Fulkerson, W. S. Lyon, A. W. Andrew, J. A.
Carter, and J. F. Emery. Trace Element Measurements at the Coal-Fired Allen
Steam Plant, Progress Report June 1971-January 1973. ORNL-NSF-EP-43, 83 pp.
March 1973.
Cannon, H. L., and B. M. Anderson. "Trace Element Content of the Soils and
Vegetation in the Vicinity of the Four Corners Power Plant," Part III,
Appendix J, Southwest Energy Study, Report of the Coal Resources Work Group,
U.S. Geological Survey, U.S. Department of Interior, February 1972.
Green, J. A., and S. Robinson. Mercury Emissions from the Four Corners Power
Plant. Preliminary Report to the Interior and Insular Affairs Committee of
the United States Senate. May 1971.
Hadeiski, T., and R. D. McLaughlin. "Isotope Zeeman Atomic Absorption."
American Laboratory, August, p. 57. 1975.
Horn, V. H. Materials Balance and Technology Assessment of Mercury and Its
Compounds on National and Regional Basis. Prepared by URS Research Company
for U.S. Environmental Protection Agency. EPA 560/3-75-007. October 1975.
Joensuu, 0. I. "Fossil Fuels as a Source of Mercury Pollution," Science 172;
1027. 1971.
Kalb, G. W. "Total Mercury Mass Balance at a Coal-Fired Power Plant,"
Trace Elements in Fuel, P. Babu, Ed. American Chemical Society. Washington,
D.C. 1975.
Klein, D. H., and P. Russell. "Heavy Metals: Fallout Around a Power Plant,"
Environmental Science and Technology 7;357. 1973.
Magee, E. M., H. J. Hall, and G. M. Varga, Jr. Potential Pollutants in Fossil
Fuels, prepared by Esso Research and Engineering Company for U.S. Environmental
Protection Agency. EPA-R2-73-249. June 1973.
Merritt, P. C. "Productivity" and "Politics—Key Words for Coal Men in '75,
'76" Coal Age 82. February 1976.
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Peakall, D. B., and R. J. Lovett. "Mercury: Its Occurrence and Effects in the
Ecosystem," BioScience 22;20. 1972.
Rogers, R. D. "Methylation of Mercury in a Terrestrial Environment,"
U.S. Environmental Protection Agency. EPA-600/3-75-014. 1975.
Shacklette, H. T., J. G. Boerngen, and R. L. Runer. "Mercury in the
Environment Surficial Materials of the Conterminous United States,"
U.S. Geological Survey Circular 644, USDI. 1971.
Swanson, V. E. "Composition and Trace Element Content of Coal and Power
Plant Ash," Southwest Energy Study, Part II, Appendix J. Report of the
Coal Resources Work Group, U.S. Department of Interior, January 1972.
\
AU.S. GOVERNMENT PRINTING OFFICE: 1977 - 784-680/93 Region No. 9-1
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/3-77-063
3. RECIPIENT'S ACCESSIOI*NO.
4. TITLE AND SUBTITLE
MERCURY DISTRIBUTION IN SOIL AROUND A LARGE COAL-
FIRED POWER PLANT
5. REPORT DATE
May 1977
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Alan B. Crockett and Robert R. Kinnison
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Environmental Monitoring and Support Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Las Vegas, Nevada 89114
10. PROGRAM ELEMENT NO.
1HD620
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency-Las Vegas, NV
Office of Research and Development
Environmental Monitoring and Support Laboratory
Las Vegas, Nevada 89114
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/600/07
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Seventy soil samples were collected on a radial grid employing sixteen evenly
spaced radii and five logarithmically spaced circles, concentric around the
Four Corners power plant. The soil samples were analyzed for total mercury
using a Zeeman Atomic Absorption spectrophotometer. Residue levels were quite
low compared to average soil residues and no statistically valid differences
in mercury residue levels were detected between circles or radii using two-
way analysis of variance techniques. F-ratios indicated: significant differences
between circles, significant differences between radii, and significant complex
interaction which could not be eliminated. Contours of iso-mercury concentrations
show a relative high west of the plant near the ash ponds and another just east
of the plant. The fate of the 510 kg of mercury emitted per year is not known,
but it is not accumulating near the plant. Mercury emissions by U.S. coal-fired
power plants amount to only 4% of the natural degassing loss in the U.S., and
levels near power plants appear low. The significance of mercury emissions by
power plants should be evaluated on a regional basis since the evidence shows
no significant local elevation of mercury in soils or air.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
COSATI Field/Group
Mercury*
residues
monitoring
soil*
power plants*
Four Corners, NM
coal-fired power plants
07B
08M
10B
18B
18H
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)'
UNCLASSIFIED
21. NO. OF PAGES
16
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
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