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Assessing Local Deposition of Mercury
Associated with
Coal-Fired Power Plants
T. Sullivan1, B. Bowerman1, J. Adams1,
F. Lipfert2,
1 Brookhaven National Laboratory
2 Independent Consultant
Presented at the
DOE/NETL Mercury Control Technology R&D Program Review
Pittsburgh, PA July, 15, 2004
Brookhaven Science Associates
U.S. Department of Energy
Background
Mercury regulation is on its way.
EPA has suggested a Cap-and-Trade Program
Impacts of local deposition are perceived to be
an issue of concern for Cap-and-Trade
• Secretary McGinty (PA – DEP) “Unlike most pollutants,
mercury is highly toxic and does not disperse easily, creating
“hot spots” of contamination.” July 04
• Secretary Cipriano (IL – EPA) “Specifically, we are
concerned that local "hot spots" of elevated mercury may
result or worsen, especially if the required reduction levels
are not sufficiently strict.” Feb 04
Brookhaven Science Associates
U.S. Department of Energy
Background
Modeling studies suggest some increased local
deposition, however, few measurement studies.
Local deposition of reactive gaseous mercury
and any particulate mercury is expected during
precipitation events. Elemental mercury enters
the global cycle.
Data are needed to asses local impacts.
Brookhaven Science Associates
U.S. Department of Energy
Approach
Select a coal-fired power plant for analysis.
Perform deposition modeling based on plant
specific parameters and meteorological
conditions.
Design soil and vegetation sampling program to
look for excess deposition within 10 Km of the
plant and determine the validity of modeling.
Examine data for correlation with model
predictions and look for hot spots.
Brookhaven Science Associates
U.S. Department of Energy
Coal-Fired Power Plant
A large sized power plant in the Midwest was
selected for study.
Annual emissions of Hg 340 kg/yr
Fraction of Hg(+2) = 0.18 (61kg/yr of Hg(+2))
Large stack height (200 m), lower deposition
locally.
Brookhaven Science Associates
U.S. Department of Energy
Deposition Modeling
• Use plant specific parameters (emission
rates, stack height, etc.).
• Examine meteorological records over 10
year period. Select most representative year.
• Model deposition over the course of 1 year.
Brookhaven Science Associates
U.S. Department of Energy
Wind and Rain Rose
Wind Rose Rain Rose
Brookhaven Science Associates
U.S. Department of Energy
Deposition Modeling Results
N
Power Plant
Background wet
deposition of
5 – 10 ug/m2/yr
Deposition unit
ug/m2/yr
Brookhaven Science Associates
U.S. Department of Energy
Final Sampling Grid
8 km
Brookhaven Science Associates
U.S. Department of Energy
Sampling
Cover an area of 64 km2 primarily south west of plant
At each of the 51 grid locations collect:
• 3 soil samples from top 5 cm (3 meter spacing)
• 1 deep soil sample from 5 – 10 cm
• 1 vegetation sample
Brookhaven Science Associates
U.S. Department of Energy
Analysis
All samples shipped back to
BNL
Samples analyzed on Direct
Mercury Analyzer (DMA-80).
(Moisture determined
separately.)
Each sample measured 3
times to verify homogeneity.
Blank analysis every 10th
sample
NIST Standard every 10th
sample Associates
Brookhaven Science
U.S. Department of Energy
Results
51 Sample Sites
Average 28.7 ng/g 1
Probability of being less than soil Hg level
• Median 27.4 ng/g 0.9
0.8
• Standard Deviation – 7 0.7
Probability
0.6
ng/g 0.5
0.4
0.3
• Maximum – 55 ng/g 0.2
0.1
• Minimum – 11.6 ng/g 0
0 10 20 30 40 50 60
Soil Hg (ng/g)
Brookhaven Science Associates
U.S. Department of Energy
Soil Results
Effects of deposition are
subtle and there is
variability in the spatial
distribution of Hg in soils.
Statistically significant
agreement between
model and data not
found.
No clear definition of
background.
Brookhaven Science Associates
U.S. Department of Energy
Results (deep vs. surface samples)
80
Deep
70 Samples
Surface
60
Mercury (ng/g)
50
40
30
20
10
0
0 10 20 30 40 50
Locxation (1=A6, 48=J3)
Brookhaven Science Associates
U.S. Department of Energy
Results (deep vs. surface samples)
Difference in Surface soil versus Deep soil Concentration
30
25
Difference in concentration (ng/g)
20
15
10
5
0
-5
-10
-15
-20
I6
I7
B2
B3
B6
B7
F2
F3
F6
F7
B4.1
B4.2
B5.1
B5.1
F2.1
A6
C.a3
C2
C3
C4
C5
C6
C7
D.a3
D3
D6
D7
E.a3
E.a4
E.a5
E3.1
E3.2
E3
E4.2
E4
E5.1
E5
E6
G4
G5
H3
H4
H5
H6
C3.
C4.
C5.
J3
Location
Brookhaven Science Associates
U.S. Department of Energy
Vegetation Results
Vegetation mercury levels (ng/g) versus
Effects of deposition are predicted deposition
similar and there is much 2000
larger variability than in
the soil samples. 0
-2000
Same general pattern as
Soil samples. -4000
-6000
-8000 -6000 -4000 -2000 0 2000 4000 6000
10.70 to 22.90
22.90 to 31.50
31.50 to 84.40
84.40 to 691.10
Brookhaven Science Associates
U.S. Department of Energy
Comparison of deposition modeling and
data on mass deposition
Three estimates obtained:
• Mass deposited = Excess in surface soils versus
deep soils (0.7 ng/g)
• Mass deposited = Surface soil average minus
average of the lowest 1/3 of the samples (8.4 ng/g).
Lowest 1/3 taken as pre-operational background.
• ISCT model annual deposition prediction multiplied
by plant life.
Brookhaven Science Associates
U.S. Department of Energy
Estimates of Mass Deposited
Case Total Mass Percentage of Percentage of
Required total Hg reactive Hg
over plant life emission emissions
time of 23
years (g)
Deep vs. 2700 0.04 0. 2
Surface Soils
Lowest 1/3 as 30000 0.4 2.1
background
(upper bound)
Deposition 9400 0.12 0.7
Modeling (23
years)
Brookhaven Science Associates
U.S. Department of Energy
Conclusions
At the power plant under study a small fraction
(< 0.5%) of mercury appears to be deposited
within 5 miles of the plant.
No evidence for ‘hot spots’ in soil.
General agreement between estimates of total
mass deposited between data and model.
Agreement between data and model in terms of
spatial pattern is not statistically significant.
Next step: Repeat at another plant
Brookhaven Science Associates
U.S. Department of Energy
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