AW EVALUATION OF THE AIR POLLUTION ASPECTS
II OF THE
PROPOSED STEAM-ELECTRIC PLANT
AT
OAK PARK, MINNESOTA
by
DonaM F. Walters
Supervisory Chemical Engineer
and
Delance 0. Martin
Meteorologist
Revised and amended
February 17, 1965
Technical Assistance Branch
Division of Air Pollution
U.S. Public Health Service
Cincinnati, Ohio
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PREFACE
A report entitled "An Evaluation of the Air Pollution Aspects of
the Proposed Steam-Electric Plant at Oak Park, Minnesota" was prepared and
presented to the Minnesota State Health Department on December 3, 1964.
Subsequently, a more detailed analysis of the inversion breakup fumigation
case was made. This analysis indicated the possibility of sulfur dioxide
ground level concentrations in excess of the ambient air quality levels used
as guidelines in the original report.
A need was also indicated for additional meteorological study to
obtain a more precise estimate of the frequency of inversions of pertinent
depth and intensity. The study, which requires computer programing to
procure and process data from St. Cloud, Minnesota, has been initiated and
will take about 3 months to complete.
On the basis of the calculated ground level of sulfur dioxide
resulting from inversion breakup fumigations, an addendum to the original
report was prepared and sent to the health departments of Minnesota and
Wisconsin. In this addendum, it was recommended that the permit to con-
struct the proposed power plant at Oak Park Heights, Minnesota, be held
in abeyance until the St. Cloud meteorological data could be evaluated.
This revised report incorporates the results of additional calcula-
tions for the inversion breakup fumigation case as well as other minor
corrections, with the resulting modifications to the conclusions and
recommendations of the original report.
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BACKGROUND STATEMENT
The U. S. Public Health Service received several letters from citizens
in Minnesota and Wisconsin concerning a proposed steam-electric power plant
to be built by Northern States Power Company on the St. Croix River at
Oak Park, Minnesota. The Minnesota and Wisconsin State Health Departments
were informed of these letters. The Minnesota State Health Department
requested assistance in evaluating the air pollution aspects of the proposed
power plant, To this end a staff member of the Technical Assistance Branch,
Division of Air Pollution, U. S. Public Health Service, met with representa-
tives of the Minnesota Department of Health and the Northern States Power
Company on September 2, l$6k. At this meeting various aspects of the
proposed installation were discussed and information was obtained from the
company to permit evaluation of the air pollution aspects of the new plant.
Following this discussion, the proposed plant site was visited. There was
further discussion with officials of the Minnesota State Health Department
and it was agreed that a report would be submitted to that Department by the
U. S. Public Health Service.
PLANT DESIGN AND OPERATING DATA
It is our understanding that there will be two units built at the
Oak Park site. The first unit will be operational in 1968, and the second
unit will be built at a later date. Data obtained from Northern States Power
Company for the first unit is as follows:
1. Capacity: First plant - 550,000 kilowatts (normal)
630,000 kilowatts (peak)
Date of operation: February,1968
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2. Furnace design: Babcock and Wilcox cyclone furnace, 3*500 pslg,
1000° F throttle temperature, 1,000° F single reheat.
Efficiency: 9,000 Btu/kw-hr
3. Load factors: first 10 years 0.91
overall life 0.68
k. Fuel: Coal only
(a) Coal with maximum of 3*5 percent sulfur and 10 percent
ash from Western Kentucky and Southern Illinois. Beating value:
10,^00 Btu/lb. No particular coal field win supply all of the
fuel.
(b) Coal use: .2^0 tons/hr (normal)
270 tons/hr (maximum)
(c) Coal storage: Approximately 1.5 million tons — a pile
2,UOO ft. by 1,200 ft. by 50 ft. high. Barged in 31 weeks/year.
5. Stack design:
height 785 ft.
diameter ^o*^'
temperature 290 F.
velocity 60 ft/sec
height above
plant buildings (785-200) » 585 ft.
one stack for each plant
6. Control of dust emissions: electrostatic preclpitator
design inlet leading 1.5 grains/scf
design outlet loading .01 to .02 grains/scf
design efficiency 99 percent
3he collected dust will be reinjected to furnace.
Note: The data on coal composition and heating value do not appear
to be consistent. Die heating value of 10,500 Btu/pound
appears low for a 10 percent ash coal, unless there is ,-•
20-30 percent water in the coal. A high vater content coal
would probably not be barged long distances. Thus it seems
likely that an ash content of 10 percent is a minimum figure
rather than an average or maximum.
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Northern States Power Company indicates that the second unit at the
Oak Bark location will have a normal operating capacity of 750,000 kilowatts.
Operating and design data for the second unit were not obtained. Preliminary
calculations indicated that the combined emissions from these two units
might present air pollution problems. Therefore, estimates of design and
operating conditions were made for the second unit as shown in Appendix A.
It is emphasized that the data for the second plant are only our .estimates,
but will serve to Indicate the relative magnitude of the problems involved.
ESTIMATES OF TOTAL AIR POLLUTION
The hourly emission rate for the common air pollutants from coal
combustion were estimated for the first proposed unit of 550 megawatt
capacity. These estimates are shown in Table 1. There will be a few
occasions during the year when the unit will be run at the higher capacity
(630 mw.) to meet peak loads. On these occasions the pollutant emission
rate will be increased by about 15 percent.
Similar estimates of pollutant emissions were made for both the 550
megawatt and the 750 megawatt units operating at normal loads. These estimates
are given in Table 2.
In the case of the 550 megawatt unit, the major potential pollutants
are sulfur oxides, nitrogen oxides, and particulate matter. It is proposed
to control particulate emissions with an electrostatic precipitator with a
design efficiency of 99 percent. This type of control Is probably the best
that can be applied within the economic framework of the utility industry.
The design efficiency of 99 percent was used in calculating emissions, although
this efficiency is subject to fluctuation because of soot blowing, load changes,
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Bible 1. ESTIMATED EMISSIONS PROM PROPOSED POWER PLANT
550 MEGAWATT UNIT
(Pounds Per Hour)
Air pollutant
GASEOUS
Sulfur oxides (as SO.)
Nitrogen oxides (as NO.)
Carbon monoxide
Hydrocarbons
Aldehydes
PARTICULATE MATTER
Without controls
With control *
Normal operation
(550 mw)
31,400
4,720
24
47
1
4,720
47
Maximum operation
(630 mw)
35,900
5,400
27
54
1.4
5,400
54
Control assumed to be 99 percent efficient.
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Table 2. ESTIMATED EMISSIONS FROM PROPOSED POWER PLANTS
550 AND 750 MEGAWATT UNITS
(Pounds Per Hour)
Mr pollutant
GASEOUS
Sulfur oxides (as S0_)
Nitrogen oxides (as NO.)
Carbon monoxide
Hydrocarbons
Aldehydes
PAKTICULATE MATTER
Without controls
With control *
Assumed Noxmal Operating Capacity. Megawatts
Unit 1
550 mr
3i,too
4,720
24
47
1
4,720
47
Unit 2
750 nw
42,600
6,400
32
64
2
6,too
64
Total
1,300 mr
74,000
11,120
56
111
3
11,120
111
* Control assumed to be 99 percent efficient.
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electrode rapping, electrode failure, and numerous other possibilities. It
seems likely that the average operating efficiency for the precipitator
will be somewhat less than 99 percent.
There will be no positive control for the major gaseous pollutants,
but a tall stack is proposed to reduce ground level concentrations of
sulfur and nitrogen oxides. Up to this time, the use of a tall stack has
been the only method used by power plants to reduce ground level concentra-
tions of gaseous pollutants.
To put the total emissions from the proposed 550 megawatt unit in
perspective, they can be compared with air pollutant emissions from other
sources. For example, the sulfur oxide emission from this unit is roughly
equivalent to the annual sulfur oxide emission from 260,000 households burning
coal in a northern city.
However, in the case of particulate matter, these same 260,000
households would probably contribute about 1*7,000 tons of particulates per
year to the atmosphere while the proposed power plant would emit (under
ideal conditions) about 185 tons/year.
While black smoke is not usually a problem with a modern power plant,
there will be, under certain conditions, a visible non-black plume from
the stack of the unit. Because of the prominence of an 800-foot stack, the
visible emission will undoubtedly draw attention to the plant operation and
will offend the aesthetic values of some people.
Aside from combustion emissions, there also exists the possibility of
wind blown dust from the large coal storage area. The extent of the nuisance
complaints that might arise from this source cannot be assessed at this time,
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however, it would seem desirable to provide barriers around the storage area.
Experience may dictate the use of water or oil sprays for dust suppression.
Other possible dusty operations will be barge and railroad car unload-
ing, as well as conveyor belt loading, unloading and transfer points. If it
is found that these sources tend to create a nuisance, conventional collec-
tion hoods with exhaust systems vented to dust collectors can be employed.
AMBIENT AIR LEVELS OF SULFUR DIOXIDE USED. IN. EVALUATING
AIR POLLUTION ASPECTS OF THE PROPOSED POWER PLANTS
For the purposes of this evaluation the following ambient air limitations
for sulfur dioxide have been used as guides:
0.5 ppm for one half hour - maximum at any time
0.3 ppm for one half hour - 1 percent of the time
0.1 ppm average for 2k hours - not to be exceeded
on more than one day in any three consecutive months
(1.0% frequency).
These levels are based on the premise that the possibility of chronic
injury to vegetation must be minimized. If some damage to sensitive vegeta-
tion is permissible, the above limitation could be made less restrictive.
Aside from vegetation damage there must also be consideration of the
human threshold perception which is 0.3 ppm to 1.0 ppm. If ground level
concentrations reach this range even for very short periods there could be
nuisance complaints from some people so exposed. Although at the present
time some of the areas that will be affected are sparsely populated, consider-
ation should be given to the effect that future land use and population growth
will have on the potential problem of sulfur oxide pollution.
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ESTIMATION OF GROUND LEVEL CONCENTRATIONS OF SULFUR DIOXIDE
As previously noted in Tables 1 and 2, the two largest gaseous
emissions are sulfur oxides and nitrogen oxides. For this evaluation,
estimates were made of ground level concentrations of sulfur oxide only.
Calculated ground level concentrations are those expected over a
three to fifteen minute sampling period. A sampling time of one hour
would yield results that would be one half to one third those calculated.
The accuracy of the estimates is about a factor of 2 up to 0.5 mile
distance from the emission source; a factor of 5 up to 5 miles, and a
factor of 10 at 5 to 50 miles.
There are three atmospheric stability conditions considered
herein that are usually important in estimating pollutant dispersion.
These are:
1. Neutral stability (coning plume)
2. Unstable (looping plume)
3. Break-up of inversion (fumigation).
The calculations for the neutral and unstable cases are summarized
in a series of curves shown in Figures 1 through 3. Calculations for the
inversion breakup fumigation case are summarized in Table 3. In -'"igures
1-3 the curves labeled I + II represent addition of the individual esti-
mates for the proposed units of 550 megawatt and 750 megawatt capacity,
respectively. This procedure will give high results close to the plant
during a cross wind. For other wind directions the addition provides rea-
sonable estimates.
Wind persistence data, that is the tendency for the wind to blow in
a given direction for a given length of time, are available from Rochester,
Minnesota. These data were used as a guide in estimating the frequency
at which maximum concentrations will occur in a given location.
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10'
I I I I I III
I I I I I I III
I I-
—at
U.
•4h*<
r* 10
w
IOH
I I I I M I 11
Emlnlon rat«*i
I 3.96 R 10* grams /t*cond
D 9.96nlO'gromt/MCOnd.
I * 0 9.32 «10* gramt/Mcond.
Battd on plant capacity
I S50 mtgowottt
750 megawatt*
burning 3.5 % sulfur content coal
CONING
WIND SPEED 2 meters/second
(4.5 miles/hour)
I I I I I i I I
I I
10*
DISTANCE (meters)
Figure 1
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10'
,-s
o
x
o
o
oa
u
|0-e
_' I I I I
—0.3 w
— 0.2 §7
—O.I w
I It II
I I I I I I
i+n
n
i
Emission rottst
I 3.96 x 10* groms/MCond
n 5.36 x 10'groms/stcond.
I»D 9.32xlO*grams/MCond.
Based on plant capacity
I 550 megawatts
n 750 megawatts
burning 3.5 % sulfur content coal.
CONING
WIND SPEED 6 meters/second (13.5 miles/hour)
I I I M I I I
I
I I I I I II
10*
DISTANCE (meters)
10'
10
-------
ID'
10"
KT
— 5.0
— 2.0
— 1.0
I I I I I I I I
— O.I
II I I I I '-
Emission roton
I 3.96»IO»grom»/tocoi«l.
II 5.36 * 10* grams/socond.
1«II 9.32 • 10* gromt/socond.
Bosod on ptant copoelty
I SSO mogovrotts
Q 750 mtgowottt
burning 3.5 % tulf or content cool.
LOOPING PLUME
WIND SPEED 2 imttrs Mcond (4.S milos hour)
CONVECTION LIMITED TO 1500 motors
I I I I I I II
I
i i t i i in
I I I I I 111
I01
I01
10'
DISTANCE (motors)
10"
Figure 3
11:
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Table 3. ESTIMATED MAXIMUM GROUND LEVEL SULFUR DIOXIDE
CONCENTRATIONS IN INVERSION BREAKUP FUMIGATION
Unit 1
550,000
kilowatts
Unit 2
750,000
kilowatts
Distance , miles
SO concentration, ppm
Plume elevation , ft .
Plume width, ft.
Distance , miles
SO concentration, ppm
Plume elevation, ft.
Plume width, ft.
WJ.UU speeu a.o s uacjs. iiexgiiu, mpu
H.5
12.9
1.25
1,250
7,500
15. U
1.36
1,360
8,650
9
16.5
0.62
1,010
9,100
19.1
0.69
1,080
10,400
13.5
19. ^
0.39
905
10,500
22.0
O.U6
955
11,800
18
21.8
0.27
QkO
11,600
2U.1*
0.3H
880
12,900
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Wind direction data at stack height indicates calm conditions about
two or three percent of the time with wind speeds of 18 miles per hour or
more over 50 percent of the time in the fall season, UO percent of the time
in summer, and about 50 percent of the time during winter and spring seasons.
The prevailing wind direction at stack height is from the south in summer
and from the northwest during other seasons. The strongest winds are also
from these directions. This means that air pollutants from the proposed
power plant will often be transported into Wisconsin.
The calculations for the first power plant unit (550 megawatts) are
briefly summarized as follows:
1. Coning plume (Neutral stability)
The peak S0p concentration will be about 0.1 ppm at a
distance of about eleven miles from the plant. Examination
of wind persistence data indicates that the average daily S0_
concentration will be less than 0.1 ppm. It also appears
unlikely that concentrations exceeding 0.3 ppm for one half
hour for one percent of the time will be experienced. The
neutral or near-neutral atmospheric stability is a condition
which can be expected to occur in this area 60 percent to 70
percent of the time.
2. Looping plume (unstable)
For this case it is seen that the peak concentrations
of S0p will be higher and will occur closer to the plant than
in the case of neutral stability. It is estimated that this
atmospheric condition will occur about one or two percent of
the time. Under these conditions it appears unlikely that
the criteria set forth on page 7 will be exceeded. It should
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be noted, however, that it is possible for transient "puffs"
of stack effluent to exceed the S0? perception threshold for
some people.
3. Inversion breakup
In evaluating the inversion breakup fumigation, the rate
of growth of the surface-based mixing layer and its maximum depth
are uncertain; therefore, these estimates of ground concentra-
tions can be in error by a relatively large factor (say 10).
Wind speeds of less than 4.5 miles per hour are not likely to
occur during an inversion breakup period. It is more likely
that a wind speed of 8 or 10 miles per hour will exist. Even
at these speeds, a level of 0.5 ppm for one-half hour or more
may be exceeded at a distance of about 16 miles from the plant.
(See Table 3).
The estimated duration of fumigations is an additional •
uncertainty. Durations of 30 minutes or more over open coun-
try have not been documented but appear reasonable from theo-
retical considerations.
It is estimated that an inversion breakup fumigation
may occur as many as 10 or 15 times in both spring and fall
seasons for a total of 20 to 30 such events per year. Because
of the narrow, elongated shape of the fumigating plume and
the absence of controlling geographic features, such as a
deep valley, repeated fumigations of a particular segment of
the area should be infrequent, i.e. one to five events per year.
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Examination of radiosonde data from St. Cloud, Minnesota,
about 80 miles distant from Oak Park Heights, will permit
more precise determination of the frequency and intensity
of these conditions.
Assuming the installation and operation of both the 550 megawatt
and 750 megawatt units, the calculations are briefly summarized as
follows:
1. Coning plume (neutral stability)
For this case there is a small probability of ex-
ceeding the ambient air criteria for S0? set forth on page 7-
2. Looping plume (unstable)
It is indicated that there is a good possibility of
exceeding the limitation of 0.5 ppm for one-half hour. The
possibility of exceeding the 0.1 ppm average for 2k hours
for 1% of any 3 month period seems unlikely although it may-
be a borderline case. It should be noted that while the
looping plume does not reside in one spot very long, there
is the possibility of trapping part of the plume by trees
or buildinp..
3. Inversion breakup
Earlier statements regarding inversion breakup for
the 550 mw pxum, apply generally to the simultaneous opera-
tion of both plants, except that the expected ground level
concentrations of S0? could roughly double those expected
with one plant in operation. The maximum ground level
concentrations of S0? will occur at about the same distances
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indicated in Table 3 for the larger plant.
Therefore, under the conditions of inversion breakup, the
operation of both units could result in S0p ground level concen-
trations in excess of the ambient air criteria set forth on page
7.
As previously noted further study of the radiosonde data
from St. Cloud, Minnesota is required for more precise determin-
ations.
For coals with sulfur contents of other than 3.5 percent, the cal-
culated ground concentrations will vary directly with the sulfur content.
For example, if a 3 percent sulfur coal were used, ground level concentra-
tions given herein would be multiplied by -r^-z- of 0.857 to get the new estimated
ground concentrations.
The calculation method and assumptions are explained in somewhat more
detail in Appendix B. Meteorological data used in this evaluation are attached
as Appendix C.
SUGGESTED POSSIBLE ACTION TO BE TAKEN NOW TO
PREVENT FUTURE PROBLEMS
Since power plants are designed to have a useful life of twenty to
thirty years, it seems prudent to look ahead to the time when both of the
proposed generating units are in operation and, indeed, to the possibility
of additional units at the Oak Park site. Steps that can be initiated now
include:
1. Determine the availability and costs of lower sulfur coals and
the possibility of removing sulfur from coals presently
contemplated for use.
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2. Determine the availability and costs of lower" sulfur fuels
other than coal.
3. Provide space at the plant site for installation of sulfur
oxide removal from the plant effluent gases.
k. Provide for the supply and storage of low sulfur fuels to
be used during those periods when atmospheric conditions
are conducive to the build-up of air contaminant concen-
trations .
5. Design the furnaces such that higher stack gas temperatures
can be realized for short-term emergencies.
Jhese suggestions are not meant to be all inclusive, but do indicate
some possible action that can be started now with a view to obviating
future problems.
If the 550 megawatt unit is built and operated, a continuous air
monitoring plan should be designed and implemented whereby SO concentrations
are determined over a long period of time. Oils program would not only
provide data relating to the 550 megawatt unit, but would also provide
valuable information for use in estimating probable concentrations if
additional units were built. At this site the monitoring program could
probably best be carried out by the Northern States Power Company, with
participation by public agencies in Minnesota and Wisconsin. The U. S.
Public Health Service, Division of Air Pollution, could assist in the design
of such a monitoring program.
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SUMMARY AND CONCLUSIONS
The installation and operation of the 550,000 kilowatt steam-electric
plant at Oak Park, Minnesota, will generate large quantities of air pollutants,
principally sulfur oxides, nitrogen oxides, and particulate matter. The
particulate emissions will be controlled by an electrostatic precipitator
with a design efficiency of 99 percent. Thus the minimum particulate
emission will be about 0.56 ton/2U-hour day. It can be expected that this
emission will be somewhat higher in actual operation.
A 785-foot stack will be installed to permit dispersion and dilution
of gaseous pollutants. Calculations indicate that ground level concentrations
of sulfur dioxide may cause acute damage to vegetation. However, existing
information is inadequate to predict with assurance whether long-term
chronic effects will be experienced by long-lived vegetation such as trees.
It is expected that the human perception threshold for SO will be exceeded
occasionally. Inversion breakup fumigation may produce ground level con-
centrations exceeding the human perception threshold at distances of ten
miles or more.
It is recommended that the decision to grant a permit to construct
this plant be held in abeyance pending evaluation of the study of meteoro-
logical data from St. Cloud, Minnesota.
The installation and operation of a second unit of 750,000 kilowatt
capacity will more than double air pollution emissions. It should be
expected that some damage to sensitive vegetation could occur. It can
also be expected that S0? ground concentrations will exceed the threshold
perception limits more often than with only the 550,000 kilowatt unit in
operation.
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If the 550,000 kilowatt unit is built and operated, a SO monitoring
network should be activated. This will assist in determining the effects of
S0? on the surrounding vegetation and people, as well as provide guides for
future installation design.
Prevailing winds in this area are such that air pollutants will
often be carried into Wisconsin. Therefore, officials of that State
should take part in air pollution activities connected with the proposed
plant.
Plans and studies should be started now to obviate future air
pollution problems indicated by plans for expansion of this plant beyond
the initial 550,000 kilowatt capacity.
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APPENDIX A
Assumptions relating to the 730,000 kv power plant:
Normal capacity 730,000 kv-hr
Efficiency 9000 Btu/kw
Fuel used Coal (no other fuel assumed)
Heating value of fuel 11,000 Btu/pound
Coal usage 320 tons/hour
Sulfur content of coal 3.3 percent (by weight)
Stack height 800 feet above grade
Stack diameter. 28 feet
Stack gas velocity 60 feet/second
Stack gas temperature 300° Fahrenheit
Dust collector Electrostatic precipitator
10$ of the ash in the fuel goes to dust collector
Efficiency of dust collector 99 percent'(by weight)
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APPENDIX B
Holland's equation was used to estimate the effective stack rise
from the proposed power plant. Emissions under two stability conditions
were considered for each of the two proposed units. In the charted data
emissions from the initial, 550 megawatt, unit are shown as I, and from
the second, 750 megawatt, unit as II. No attempt was made to allow
for merging of plumes in computing effective rise. Any such effect
would be highly variable, and dependent upon horizontal spacing between
stacks, wind direction, and wind speed.
For computing stack rise, a diameter of 24 ft. was used for the
initial unit and 28 ft. for the second, to allow the same stack velocity.
The physical stack height, 785 ft., was reduced in diffusion computations
to r^v) ft., since the stack is to be In a valley about 200 ft. below
_/''
/surrounding terrain.
The diffusion estimates made here are based on Pasqulll's
estimates as modified by Oifford (Nuclear Safety 196l), and are repre-
sentative of sampling times between 3 and 15 minutes. For longer
sampling Intervals, concentrations will generally be less (about one-half
to one-third these values for an hour sample) due to fluctuating wind
directions.
No loss of S02 in its downwind travel is assumed, either in the
atmosphere or at the ground, and complete eddy reflection at the ground
is assumed. These assumptions tend to yield higher estimated values.
The accuracy of the estimates for coning conditions is thought to be
within a factor of 2 of true concentrations for downwind distances up
to 1/2 mile, a factor of 5 up to 5 miles, and a factor of 10 at distances
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of 5 to 50 miles. Somewhat less confidence should be placed in the
estimates for looping conditions, with the more likely error for the
highest predicted concentrations.
Concentration values shown on the di agrams are for ground-level
beneath the mean plume. The summed value (I and II) is a simple addition.
At a distance of about 1/2 mile or less when the wind is such that the
stacks are oriented cross-wind, this will give a slightly excessive
value. For other wind directions, the addition should be valid. This
minor variation will be significant only for unstable or very unstable
(looping) conditions.
The Weather Bureau has compiled wind directional persistence
data based on surface wind records for a number of places. Directional
persistence for these compilations is defined as the tendency of the
wind to blow continually from a specific direction for a number of
hours. This tendency is illustrated by seasonal directional persistence
diagrams. The percent value shown is obtained by dividing the number
of times the wind persisted in a particular direction (± 11.25 )
for at least the specified number of hours by the number of times the
wind blew from that direction (periods of time, not total hours). A
calm hour is recorded as an interruption of persistence, and the per-
sistence of calm periods is also shown. Except for calms, wind speeds
are not considered. The data shown here is for Rochester, Minnesota,
the nearest point to Minneapolis-St. Paul for which this information
has been assembled. This data is considered sufficiently representative
for our present purpose.
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Examination of the data shown, reveals a persistence of 2 hours
or more as high as 50 percent only for winds from the west-northwest
or northwest in fall or winter. Extending the averaging time from
the 3 to 15-minute period to 2 or more hours during a period of such
directional persistence, is estimated to reduce maximum ground concen-
trations under coning conditions (neutral stability) to one-half or
less. Extended persistence under looping (very unstable) conditions
is extremely unlikely.
Ground level concentrations under looping (very unstable) conditions
are computed for a wind speed of 2 raps (1+.5 mph). Looping conditions
may be expected only a small part of the time, possibly as little as 1
or 2 percent, and almost entirely on mid-summer afternoons. Wind di-
rections are transitory under these conditions and the concentrations
are more likely representative of shorter sampling times. It is also
worthy of note that the peak value is near the source (about 5/8 mile
or less), and that a ground-level concentration of 0.5 ppm is not
indicated beyond a distance of h km (less than 2-1/2 miles) even with
both units operating.
Maximum ground level concentrations under coning (neutral) con-
ditions are less than 0.2 ppm for either unit operating alone, but is
approximately 0.25 ppm for both operating together at a wind speed
of
6 mps (13.5 mph). An increase in wind speed lowers this value due to
direct dilution, and a decrease in wind speed decreases it due to
greater plume rise. Coning conditions are likely to be present between
50 and TO percent of the time.
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. The following statements apply to fumigation conditions. Ground-
based inversions may extend to 2 or 3 thousand feet, but even in an in-
version, with the light winds encountered under stable conditions, the
plume will rise to 2 thousand feet or higher from the smaller of the
two units. In winter this is well above the mean maximum mixing depth,
and in summer it is near the top of most ground-based inversions. The
diagrams of concentrations under looping conditions are extended to
indicate concentrations in a case where vertical convection is limited
to 1500 meters, typical of summertime maximum mixing depths, and pro-
bably representative of the nearest approach to true fumigation likely
to occur.
Ground based inversions, or inversions based below 500 ft.,
are present in this area 29 percent of the time in spring and summer,
35 percent of the time in fall, and 38 percent of the time in winter.
In many of these cases, the plume(s) will rise through the inversion
and diffuse upward (lofting) with no measurable concentrations reaching
the ground. Since the physical stack reaches at least into the inversion,
the plume(s) will remain aloft with a possible approach to a fumigation
condition as mentioned above when the inversion dissipates.
Upper air wind rose data indicates calm conditions (l mps, 2.2 mph,
or less) at stack height only 2 to 3 percent of the time, and wind speeds
of 8 mps (l8 mph) or more over 50 percent of the time in the fall, about
kO percent of the time in summer, and about 50 percent of the time during
winter and spring. The prevailing (most frequent) direction at stack
-It-
-------
height is from the south in summer and from the northwest during the
other seasons, but with secondary maxima from the south. The strongest
winds at stack height are also from these directions.
-5-
-------
APPENDIX C
Meteorological Data
-------
Inversion Frequency by Category.
(percent of time)
Season
Winter
(1948-1952)
Summer
(1940-1944)
Time
CST
2100
0900
2100
0900
Cases
306
310
243
182
Inversion category*
per cent of cases
A B C D E
28 18 52 1 1
24 11 63 0.3 1
37 23 21 6 12
2 1 53 10 35
All summer inversion data were obtained from records at St. Paul
for the months of July and August in the period 1940-1944.
All winter inversion data were obtained from records at St. Cloud
for the months of December and January in the period 1948-1952.
Maximum number of cases possible is 310.
^Inversion Category gefinitions
A Surface-based inversion; no other inversion
below 2 kilometers (6,562 ft.).
B Main inversion! above surface but below 2
kilometers; no other inversion existent.
C Surface-based inversion concurrent with
main inversion.
D Inversion based above 2 kilometers and
below 500 millibars (18,300 ft.).
E No inversion below 500 millibars.
-------
Average Height (Meters) of Surface-Based Inversion
Tops and Main Inversion Bases
Season
Winter
(1948-1952)
Summer
(1940-1944)
Time
CST
2100
0900
2100
0900
Surface-based
inversion
(category A)*
Top
866 (84)*»
936 (75)
329 (90)
229 ( 2)
Surface-based Inversion
with main inversion
(category C)*
Surface-based
inv. top
350 (54)
418 (35)
232 (56)
115 ( 1)
Main inv*
base
895 (54)
1056 (35)
1352 (56)
595 ( 1)
Main
inversion
(category B)*
Base
524 (161)
405 (196)
1081 (53)
946 (96)
All summer inversion data were obtained from records at St. Paul for the months
of July and August in the period 1940-1944.
All winter inversion data were obtained from records at St. Cloud for the
months of December and January in the period 1948-1952.
Maximum number of cases possible is 310.
**Figures in parentheses are the number of cases
inversion Category Definitions
A Surface-based inversion; no other inversion
below 2 kilometers (6,562 ft.).
B Main inversion} above surface but below 2
kilometers; no other inversion existent.
C Surface-based inversion concurrent with
main inversion.
D Inversion based above 2 kilometers and
below 500 millibars (18,300 ft.).
E No inversion below 500 millibars.
-------
10%
10%
Minntopolis-St. Pool
Wind speed in
miles per hour
—— less than 6
8 or more
Per cent calm given in center circle
Frequency of Wind Direction, percent of time.
-------
UPPER XIR VXHD HOSES
; 000 Meters Above Sea Level)
For December, January, February
2-7 8-11* 15-21 >
10
16
METERS PER SECOHD
20 20 90 '9ft
PER CENT
-------
UPPER AIR WIND ROSES
(50O Met em Above Sea Level)
For March, April, May
2-7 8-lU 15-2i: > 81
MEIERS PER SECOND
PER CENT
-------
T',
UPPER AIR WIND ROSES
($00 Meters Above Sea Level)
For June, JUly, August
METERS PER SECOND
10 18 80 28 90 58
•"*•••
MBM-w«JHBBMBB
PCR CENT
-------
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UPPER AIR WIND
(500 Meters Above Sea Level)
September, October, November
2-7 8-OA 15-21 > 21
METERS PER 8E30HD
10 18 20 25 90 33
PER CENT
-------
SPRING
2 Mrs. !• 53%
3 Mrs. *• 37%
5 Mrs. - 19%
DIRECTIONAL PERSISTENCE OF THE SURFACE WIND
(see appendix B for discussion)
-------
SUM MER
DIRECTIONAL PERSISTENCE OF THE SURFACE WIND
(see appendix B for discussion)
-------
FALL
2 Mrs. - 57%
3 Mrs. - 36%
DIRECTIONAL PERSISTENCE OF THE SURFACE WIND
(see appendix B for discussion)
-------
3 H(
-2O
2 Mrs. - 44%
3 Hrs. • 26%
5 Hrs. - 13%
PERSISTENCE OF THESURFCE WIND
^
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Bibliography for Meteorological Data and Computations
1. Gifford, F.A. , Jr., "Use of Routine Meteorological Observations
for Estimating Atmospheric Dispersion." Huclear Safety, Vol. 2,
Ho. 1), 1961.
2. Holland, J.Z. A Meteorological Survey of the Oak Ridge Area, Oak
Ridge, Tenn. , Atmoic Energy Commission, 1953. (Publication ORO-99)
3. Slade, D.V. , Directional Persistence, unpublished data, U. S.
Weather Bureau, Washington, D. C.
it. Airway Meteorological Atlas for the United States, U. S. Department
of Commerce, Weather Bureau, New Orleans, La.,
5. An Appraisal of Air Pollution 'in 'Minnesota, Minnesota Department
of Health, Minneapolis, Minn., 196l.
6. Pooler, F. , Jr., Mote on Potential Pollution from Large Power
Plants , U. S. Weather Bureau Research Station, Robert A. Taft
Sanitary Engineering Center, Division of Air Pollution, U. S.
Public Health Service, Cincinnati, Ohio, 1962.
7. Frisby, E.M. , Review of Climatologies.! Observations Taken at the
Pathfinder Atomic Power Plant Site near Sioux Falls, South Dakota,
May 1, 1958 to April 30, 1959, Northern States Power Company,
Minneapolis, Minn., 1959.
8. ------ Report on a-' Second Year of Hourly Climatological
Observations Taken at the Pathfinder Atomic Power Plant Site near
Sioux Falls, South Dakota, May 1, 1959 to April 30, I960, Northern
States Power Company, Minneapolis, Minn., I960.
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