SEPA
            United States
            Environmental Protection
            Agency
            Environmental Sciences Research
            Laboratory
            Research Triangle Park NC 27711
            Research and Development
Dispersion of Sulfur
Dioxide from the
Clinch River Power
Plant

A Wind-Tunnel
Study

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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-
gories were established to facilitate further development and application of en-
vironmental technology  Elimination of traditional grouping  was  consciously
planned to foster technology transfer and a maximum interface in related fields
The nine series are

      1   Environmental  Health  Effects Research
      2   Environmental  Protection Technology
      3   Ecological Research
      4   Environmental  Monitoring
      5   Socioeconomic Environmental Studies
      6   Scientific and Technical Assessment Reports (STAR)
      7   Interagency Energy-Environment Research and  Development
      8   "Special" Reports
      9   Miscellaneous Reports

This  report has been assigned to the ENVIRONMENTAL MONITORING series.
This  series describes research conducted to develop new  or improved methods
and  instrumentation for the identification and quantification of environmental
pollutants at the lowest conceivably significant concentrations  It also includes
studies to determine the ambient concentrations of pollutants in the environment
and/or the variance of pollutants as a function of time or meteorological factors
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia  22161

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                                             EPA-600/4-79-052
                                             September 1979
   DISPERSION OF SULFUR DIOXIDE FROM THE
         CLINCH RIVER POWER PLANT
            A Wind-Tunnel Study
                    by
             Roger S. Thompson
    Meteorology and Assessment Division
Environmental  Sciences Research Laboratory
     Research  Triangle Park, NC  27711
ENVIRONMENTAL SCIENCES RESEARCH LABORATORY
    OFFICE OF RESEARCH AND DEVELOPMENT
   U.S. ENVIRONMENTAL PROTECTION AGENCY
     RESEARCH TRIANGLE PARK, NC  27711

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                                 DISCLAIMER
     This report has been reviewed by the Environmental  Sciences Research
Laboratory, U.S. Environmental  Protection Agency, and approved for
publication.  Mention of trade  names or commercial products does not
constitute endorsement or recommendation for use.

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                                ABSTRACT
     A wind-tunnel study of the transport and dispersion of sulfur
dioxide from the Clinch River Power Plant in Virginia was performed
for periods of neutral atirospheric conditions corresponding to two
1-hour periods for which field data were available.  A 7-km x 21-km
area of the quite rugged complex terrain surrounding the power plant
was modeled at a scale of 1:1920 using a terraced construction.  Exaggerated
stack diameters were used in modeling the buoyant emissions from the
plant's two stacks.
     The most significant influences of terrain on the plume were found
to be frequent downwashing and an angle of ~30° to the mean wind direction
for the plume's initial direction.  These phenomena were produced by
the hills just upwind and downwind of the stacks.  Ground-level concentrations
measured at positions corresponding to field sampling sites compared
well with field measured values.  Comparisons of concentrations measured
above the model surface with helicopter field measurements were not
good, but the wind-tunnel measurements were shown to satisfy a conservation
of mass requirement.  The standard deviations of plume spread in the
vertical and horizontal directions were measured for various downwind
distances and compared to Pasquill-Gifford values for flat terrain.
Ground-level concentrations under the plume center!ine were compared
to Gaussian plume model estimates, given the plume path and effective
stack height determined experimentally.

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                                CONTENTS


Abstract	    iii
Figures	     vi
Tables	     ix
Symbols	      x
Acknowledgements 	     xi

       1.  Introduction	      1
       2.  Conclusions 	      3
       3.  Experimental Details and Procedures 	      7
           3.1  Field study	      7
           3.2  Selection of model scale and orientation 	      8
           3.3  Selection of periods to model	      9
           3.4  The Meteorological Wind Tunnel and modifications .  .     12
           3.5  Model construction 	     14
           3.6  Similarity criteria and constraints	     15
           3.7  Visualization and measurement techniques 	     21
       4.  Experimental Results and Discussion 	     23
           4.1  Wind-tunnel boundary layer 	     23
           4.2  Wind speed measurements	     23
           4.3  Plume visualization	     24
           4.4  Concentration measurements 	     25
           4.5  Plume spread	     31
References	     33

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                                   FIGURES
Number                                                                  Page

1       The EPA Meteorological  Wind Tunnel  without model  or              34
        modifications in place.

2       Mean velocity measurements at Pibal site in the wind             35
        tunnel compared with field pibal  measurements for July 24.

3       Mean velocity measurements at Pibal site in the wind             35
        tunnel compared with field pibal  measurements for April 28.

4       Temperature (a) and wind direction (b) from field pibal          36
        releases.

5       Schematic of the model  in the wind-tunnel test section
        showing the vortex generators, trip and roughness for            37
        boundary-layer generation, and the settling chamber.

6       Topographical map of the area modeled.  Locations of field       38
        sites and wind-tunnel sampling positions are indicated.

7       The Clinch River terrain model in the wind tunnel.  Vortex
        generators, sawtooth trip, and rows of roughness  elements        39
        are upwind.  Plant is in foreground.

8       Mean velocity measurements at various longitudinal positions     40
        in the wind tunnel for July 24, 1000-1100 EST conditions.

9       Mean velocity measurements at various longitudinal positions     40
        in the wind tunnel for April 28, 1800-1900 EST conditions.

10      Lateral homogeneity of the approaching boundary-layer flow.
        Mean velocity (a) and turbulence intensity (b) at a              4-)
        distance of 4 m from the upstream edge of the roughness.
        The velocity values are expressed in wind-tunnel  units,
        u  • 1.0 m/s.
         00
11      Mean velocity (a) and turbulence intensity (b) measured above
        Plant, Tower, and Pibal sites in the wind tunnel.  Conditions    42
        modeled are July 24, 1000-1100 EST.

12      Mean velocity (a) and turbulence intensity (b) measured above
        Nash Ford, Munsey, and Lambert sites in the wind tunnel.         43
        Conditions modeled are July 24, 1000-1100 EST.
                                   vi

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Number                                                                 Pag

13      Mean velocity (a)  and turbulence intensity  (b)
        measured above Plant, Tower,  end Pibal  sites  in  the  wind        44
        tunnel.  Conditions modeled are April  28,  1800-1900  EST.

14      Mean velocity (a)  and turbulence intensity  (b) measured
        above Nash Ford, Munsey, and  Lambert sites  in the  wind          45
        tunnel.  Conditions modeled are April  28,  1800-1900  EST.

15      Photographs of the plume from one stack at  the Clinch           46
        River Power Plant on July 24, 1977.

16      Photographs of the plume from one stack at  the Clinch           47
        River Power Plant on July 24, 1977.

17      Flow visualization in the wind tunnel  of July 24,  1000-         48
        1100 EST conditions.

18      Ground-level concentrations on the face of  the hill             &q
        just downwind of the plant for July  24, 1000-1100  EST
        conditions.

19      Ground-level concentrations at a distance of  x = 0.64  km        50
        downwind of the stacks for July 24,  1000-1100 EST
        conditions.

20      Lateral ground-level concentration profile  at a  distance        51
        of x = 3.2 km downwind of the stacks for July 24,  1000-1100
        EST conditions.

21      Lateral concentration profiles at a  distance  of  x  =  1.2 km     52
        downwind of the stacks for July 24,  1000-1100 EST
        conditions.  Gaussian curve fits are drawn  with  the  a  's
        specified.                                          y

22      Lateral concentration profiles at a  distance  of  x  =  2.3 km     53
        downwind of the stacks for July 24,  1000-1100 EST  conditions.
        Gaussian curve fits are drawn with the o 's specified.
        Field helicopter data are also shown for^a  slightly  later
        sampling period.

23      Lateral concentration profiles at a  distance  of  x  =  4.8 km     54
        downwind of the stacks for July 24,  1000-1100 EST  conditions.
        Gaussian curve fits are drawn with the o 's specified.

24      Lateral concentration profiles at a  distance  of  x  =  8.2 km     55
        downwind of the stacks for July 24,  1000-1100 EST  conditions.
        Gaussian curve fits are drawn with the o 's specified.
        Field helicopter data are also shown for^a  slightly  later
        sampling period.
                                   vii

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 Number
                                                                       Page
25      Ground-level concentrations under the plume centerline          55
        (Figure 6) for July 24, 1000-1100 EST conditions and
        April 28, 1800-1900 conditions.

26      Ground-level concentrations measured under plume centerline     57
        in wind tunnel compared with flat-terrain Gaussian model:
                                  n
        c - (Q/iro ozu)exp(-i|(H/oz) ), with c  and o^ calculated for

        C stability.

27      Vertical concentration profile above Couch Cemetery for         58
        July 24 conditions, x = 1.65 km.  Gaussian az - 290 m.

28      Vertical concentration profile above Tower site for July 24     58
        conditions, x = 3.2 km.  Gaussian o  = 318 m.

29      Vertical concentration profile for July 24 conditions,          59
        x - 4.8 km, y s 0.4 km.  Gaussian  cr  = 439 m.

30      Vertical concentration profile for July 24 conditions,          59
        x = 8.2 km, y = 0.4 km.  Gaussian a  = 659 m.

31      Vertical concentration profile above Nash Ford site for         60
        July 24 conditions, x * 10.2 km.  Gaussian oz = 857 m.

32      Vertical concentration profile for April 28 conditions,         60
        x = 1.2 km, y = 0.4 km.  Gaussian a  = 192 m.

33      Vertical concentration profile for April 28 conditions,         61
        x = 2.3 km, y = 0.4 km.  Gaussian 
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Number
                                 TABLES
           Summary of Field Conditions  for the  Clinch  River          10
           Power Plant and Field  Sampling  Sites,  July  24,  1977,
           1000-1100 EST.
           Summary of Field Conditions  for the  Clinch  River  Power
           Plant and Field Sampling  Sites, April  28, 1977,
           1800-1900 EST.

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                                SYMBOLS
A          plume cross section area
c          concentration of pollutant
cn,a        maximum concentration for a given profile
 max
D          stack diameter
g          acceleration due to gravity
H x        effective source height including plume rise
L          length scale of model
LB         buoyancy length parameter of plume
LM         momentum length parameter of plume

N          number of layers used in approximating integral
Q          emission rate of pollutant from source
T_         ambient air temperature
 o
T          stack gas temperature
u          mean wind speed
u          mean wind speed at stack exit
           root mean square of wind speed fluctuations
WQ         stack gas exhaust speed
x          distance downwind from plant
y          distance perpendicular to wind direction
z          distance above local terrain surface
z          aerodynamic roughness length
AZ         increment of distance in the vertical
p          density
P.         density of ambient air
 a
PO         density of stack gas
o          standard deviation of lateral spread of plume
a,         standard deviation of vertical spread of plume
SUBSCRIPTS
(
(
(
(
(
>1
>2
)f
>m
>.
Stack 1
Stack 2
full-scale
model scale
free stream value

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                            ACKNOWLEDGEMENTS

     The author is grateful  for the assistance of the entire  staff  of the
Fluid Modeling Facility and  to Mr.  Len Marsh,  in  particular,  who  spent many
hours collecting the wind-tunnel  data.  The cooperation of Geomet,  Inc.
employees who were contacted was  greatly appreciated.  Mr.  David  Bearden
is to be commended for an excellent job of typing the final draft.
                                   XI

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                                SECTION 1
                              INTRODUCTION
     The effects of complex terrain on the transport and dispersion of
pollutants released from point sources within such areas are not well
understood.  Adequate design (height and diameter) of smokestacks for
power plants and factories located in hilly or mountainous regions must
include an analysis of these effects.  A 16-month field measurement program
of dispersion from the Clinch River Power Plant was recently completed
by Geomet, Inc. under contract 68-02-2260 with EPA.  Data analysis and
numerical modeling of the results are currently underway.  This report
describes an effort to complement and extend the data base of the field
study by wind-tunnel modeling, makes direct comparisons of wind-tunnel
and field measurements, and attempts to explain the physics and some of
the anomalies of the flow over complex terrain.
     A 1:1920 scale model of the terrain surrounding the power plant was
constructed and installed in the EPA Meteorological Wind Tunnel.  Dispersion
of sulfur dioxide ($02) from the two stacks at the plant was studied for
neutral atmospheric conditions.  Wind speeds and pollutant concentrations
were measured at various positions over the model.  When possible, values
measured in the model were compared with field measurements.  Visualization
of the plume was achieved through release of an oil fog from the model
stacks.  The emissions from the two stacks merged close tc the plant to
form one plume, hereafter referred to as "the plume."

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     Wind speed and concentration measurements at positions corresponding
to fixed sampling sites of the field study compared favorably with the
field measurements.  The standard deviations of vertical  and lateral plume
spread were determined as a function of downwind distance.
     The most significant influence of the complex terrain  was a large
initial spread of the plume near the power plant.  A large  hill upwind
of the plant and extending above the stacks produced a highly turbulent
flow that resulted in frequent downwashing of the plume.  The local terrain
then deflected the plume substantially from the mean flow direction until
the plume rose above the terrain.

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                                SECTION 2
                               CONCLUSIONS
     A wind-tunnel study of dispersion of SC2 from the stacks of a coal-
fired power plant located in complex terrain was performed.   A terraced
model was constructed at a scale of 1:1920 and placed in the test section
downwind of boundary-layer generation devices.  Neutral  atmospheric conditions
with high wind speeds were modeled corresponding to two 1-hour periods
for which field data were available.  The conclusions of the study can
be divided into three categories:  comparisons of laboratory data and
field data, remarks on dispersion over complex terrain, and  general conclusions,
     (1)  Comparisons of the wind-tunnel measurements with field data were
          good.  In specific:
          (a)  The wind fields matched quite well.  Vertical profiles of wind
          speed determined from double theodolite-tracked gas-filled pilot
          balloons (pibals) released from a site near the plant were the goal
          for achievement of the boundary layer in the wind tunnel.  A
          comparable profile was obtained over the pibal site in the model.
          Other available field data were wind speeds at 10 m for some of the
          fixed sampling sites.  Agreement between these measurements in the
          wind tunnel and in the field was good.
          (b)  Qualitative smoke visualization of the plume near the stack
          showed terrain-induced downwash of the plume.  Photographs of
          the actual plume were available and were quite similar to those
          of the model study.

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(c)  Ground-level concentrations compared quite well.   For the
July 24, 1000-1100 EST conditions, the Tower site S02  field
concentration and wind-tunnel  value were both 73 ppb.   The Nash
Ford site had 0 ppb in the field while the wind tunnel  indicated a
concentration below the field  threshold of 1 ppb.  For April  28,
1800-1900 EST, a Tower concentration of 4 ppb in the field compared
to 95 ppb measured in the wind tunnel.  However, the following
hour, the field concentration  was 21 ppb.
(d)  The mobile sampling van was parked at two different sites on
July 24.  At one location, the van was positioned in the plume
from the coal preparation plant and measured 15 ppb of SO^.  This
source was not included in the wind-tunnel model and the power
plant plume did not reach this location, resulting in a concentration
of 0 ppb in the wind tunnel.  At the other van location, the
wind-tunnel concentration was  10 ppb while the van measured 35 ppb.
(e)  Direct comparison of the  "instantaneous" helicopter
values with time-averaged values of the wind tunnel were not
appropriate   At a distance of 2.3 km from the plant,  two
helicopter traverses indicated a plume roughly 1/3 as wide and
with higher peak concentrations than the corresponding wind-tunnel
traverses.  At a distance of 8.2 km from the plant, the available
helicopter data were much more difficult to interpret and compare
with model data.   (At this time, field data have not been
completely reduced or validated by Geomet and should be considered
in that light.)

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(2)   The complex terrain influenced dispersion  both  initially at the
     release from the stacks  and as the plume traveled downwind.
     (a)  The Clinch River Power Plant  is  located  on  an oxbow of the
     river.   For the wind direction considered  in  this study, a  ridge
     extended around this oxbow upwind  of  the plant.   There  was  a hill
     just downwind of the plant.  The ridge  and hill  were  slightly
     higher  than the power plant stacks.   Neutral  flow over  the  ridge
     produced a turbulent wake that resulted in frequent downwashing
     of the  plume and greatly enhanced  the initial plume spread.   The
     plume was forced to follow a path  up  the valley  at about 30° to
     the mean freestream wind direction.   This  resulted in a lateral
     offset  of the plume of about 500 m at downwind distances of
     greater than 2 km.
     (b)  The rough surface of the complex terrain region  resulted in
     more rapid vertical  plume spread than would be obtained over flat
     terrain.  Gaussian  curve fits resulted  in  values for  vertical
     standard deviation  of concentration  (o  ) that were between
     Pasquill-Gifford values  for B and  C  stability (Turner,  1970).
     The horizontal profiles  were also  fit to Gaussian formulas,  and
     values  for lateral  standard deviation of concentration  (o )  were
     compared to Pasquill-Gifford values.   Near the source,  a resembled
     that of C stability; at  a distance of 10 km,  it  resembled that
     of D stability.
     (c)  Given the actual plume path (Conclusion  2a), the maximum
     ground-level concentration under the  plume center!ine agreed

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     surprisingly  well  with  predictions  using  a  flat  terrain  Gaussian
     model  for Pasquill-Gifford  C  stability.   The  effective stack
     height,  a function of the wind  speed  (which could  not be determined
     a priori), was  found  to be  less than  the  true stack  height  for
     both periods  modeled.
(3)   Some general  conclusions and  observations concerning wind-
     tunnel modeling of such sources in  complex  terrain in wind
     tunnels  can be  stated.
     (a)   Modeling buoyant plumes  at such  reduced  scales  requires
     very low wind-tunnel  airspeeds.  Generating a suitable boundary
     layer in the test section of  a  wind tunnel  can be  done with
     vortex generators, a  trip,  and  surface roughness.   But much
     effort and care must  be spent in obtaining  a  laterally
     homogeneous approach  flow at  these  low speeds.
     (b)   Exaggeration of  the stack  diameter to  allow higher  wind-
     tunnel  speeds than strict geometric modeling  would dictate
     was  found to be a practical and workable technique,  based on
     plume visualization experiments.

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                                SECTION 3
                  EXPERIMENTAL DETAILS AND PROCEDURES
3.1  Field Study
     The Clinch River Power Plant is located in Carbo, Virginia,  about
200 km west of Roanoke.  The area surrounding the plant is quite  rugged,
with closely-spaced hills typically extending 180 m above the river.
The river valley is bounded by ridges of mountains 300 to 400 m high  oriented
along a NE-SW direction.  The valley is roughly 15 km wide.  The  power
plant has two stacks 138 m in height with diameters of 4.75 and 3.81  m.
The plant has three boilers, two of which exhaust to the larger stack
(hereafter referred to as Stack 1).  The 712 MW plant is operated by  the
Appalachian Power Company and burns local low-sulfur coal.  There is  only
one other source of pollution, a coal preparation plant, producing signi-
ficant SOp concentrations within the area of the study.  This plant is
located about 3,5 km northeast of the power plant and less than 1 km northwest
of the nearest fixed monitoring station.  With northwesterly winds, relatively
high concentrations of SO,, at this station were easily distinguished  as
coming from the coal preparation plant.
     The field study monitored emission conditions at the power plant,
local meteorology, and concentrations of pollutants at eight fixed stations
and at additional locations with a helicopter and two mobile vans.  The
temperature and volumetric flow from each boiler were recorded on an  hourly
basis.  The emitted concentrations of S0? were calculated for each of
the boilers based upon sulfur content and emission factors for the coal
being burned.  For comparison, measurement of SO  jn the exhaust  of one
                                     7

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boiler was made on an hourly basis.   Of the eight fixed sites, two recorded
wind speed and direction at two levels each (10 and 30 m); the rest measured
wind speed and direction at 10 m only.  Sulfur dioxide was monitored at
all eight sites.  Nitrogen oxide and oxides of nitrogen were monitored
at six stations; particulates were monitored for sulfate analysis at five.
Averaging time for the fixed stations was 1 hour.  The mobile vans measured
sulfur dioxide, nitrogen oxide, nitrogen dioxide, oxides of nitrogen,
and ozone.  To determine the wind speeds and directions aloft, pibals
were released regularly from an open field near the plant.  Many had T-
sondes (temperature sounders) attached to provide information on the local
temperature gradient or atmospheric stability.  The field study is described
in detail by Koch et al. (1979).
3.2  Selection of Model Scale and Orientation
     A model scale on the order of 1:2000 was necessary to include field
sampling sites in the area to be modeled.  At this scale, an area of about
8 km by 20 km could be fit into the test section of the Meteorological
Wind Tunnel (Figure 1).  The field sampling site nearest to the power
plant was Tower, at a distance of 3.2 km.  An exact scale of 1:1920 was
chosen to facilitate construction of a terraced model using standard materials
and maps as to be described in Section 3.5.
     A wind direction of 238° was selected for two reasons:  (1) This
direction is along the river valley and aligns the large mountain ridges
that bound the river valley with the wind-tunnel walls.  These ridges
would be beyond the area modeled for most wind directions, and choosing
a direction other than 238° would have made it difficult to include the
                                     8

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effects of these ridges in the wind-tunnel  flow.   (2) For this direction,
there were two fixed sampling sites nearly  directly downwind of the plant.
Two other sites were also included in the modeled area.
3.3  Selection of Periods to Model
     Periods of the field study that exhibited neutral  conditions with fairly
high wind speeds (10 m/s or greater) and an upper-level  wind direction of
"238° needed to be selected from the field  data.   The selections were
based upon data from pibals with T-sondes attached that were released
within a few hours of the periods considered for modeling.   In addition,
the sampling and monitoring equipment had to be operational  during the
period.  It was also desirable to have a mobile van sampling and the helicop-
ter flying through the plume to provide data on concentrations at additional
locations.
     During a 2-week intensive measurement  program, most of  the above
conditions were satisfied.  July 24, 1977,  1000 to 1100 EST  was chosen
as the 1-hour period to model.  Table 1 lists the meteorological conditions,
plant operating conditions, and measured concentrations.  A  period with
a higher wind speed - April 28, 1977, 1900  to 2000 EST - was also modeled,
but there were no helicopter or mobile van  data for that period (see
Table 2).  Figures 2 through 4 illustrate the pibal velocity and temperature
profiles for these periods.  For April 28,  the pibal was taken much earlier
in the day than the study hour.  However, wind records at Hockey and Tower
show that the winds were of about the same  speed and direction throughout
the day.  Therefore, the pibal was considered to be representative of
the study period.

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TABLE 1.   SUMMARY OF FIELD CONDITIONS FOR THE CLINCH RIVER POWER PLANT

AND FIELD SAMPLING SITES, JULY 24, 1977, 1000-1100 EST
 Unit
Number
Temperature
    (K)
  Plant Data

Aicflow
(m3/s)
Calculated S02
Emission (g/s;
   Meas. S0«
Emission (g/s)
  1              389        175 (254)*        248              	

  2          —Unit 2 down for repaii	            	

  3              386        182 (275)*        253             233.0 (353)*



                           Sampling Site Data

 Site       Wind Speed  Wind Dir.   Wind Speed  Wind Dir.   S09 Cone.
                At      At 10 m         At      At 30 m        (ppb)
            10 m (m/s)              30 m (m/s)

Tower1"      -	-	-	Missing data	        73

Munsey         1.6        231°           -          -             0

Nash Ford      2.6        227°           -          -             0

Lambert     	Site not operational	

Hockey         5.;        197°          6.6        232°           0
*  Numbers in parentheses are values adjusted by Geomet, Inc. after
completion of this wind-tunnel study.

t  Ambient temperature = 301 K at Tower site.  S0? concentration at
Tower site for 0900-1000 EST = 38 ppb and for 1100-1200 EST = 21 ppb.
                                    10

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TABLE 2.  SUMMARY OF FIELD CONDITIONS FOR THE CLINCH RIVER POWER PLANT

AND FIELD SAMPLING SITES, APRIL 28, 1977, 1800-1900 EST

Plant Data
Unit
Number
1
2
3
Temperature
(K)
397
407
395
Airflow
(m3/s)
225 (327)*
232 (358)*
230 (350)*
Calculated S02
Emission (g/sf
376
392
388
Meas. S02
Emission (g/s)


Missing
                           Sampling Site Data

 Site       Wind Speed  Wind Dir.    Wind Speed  Wind Dir.    SG~  Cone.
                At      At 10 m         At      At 30 m        (ppb)
            10 m (m/s)              30 m (m/s)
Tower1^
Munsey
Nash Ford
Hockey
Lambert
6.45
1.06
3.38
8.15
2.67
256° 7.94 244°
278° 	 	
243°
215° 9.31 234°
261°

4
0
0
0
0

*  Numbers in parentheses are values adjusted by Geomet,  Inc.  after
completion of this wind-tunnel  study.

t  Ambient temperature = 290 K at Tower site.  S0? concentration  at
Tower site for 1700-1800 EST = 4 ppb and for 1900-2000 EST =  21 ppb.
                                    11

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     The wind speed profiles of Figure 2 show the wind speed approaching a
constant value at approximately z = 800 m.   Figure 4b indicates the wind
direction at this height to be within a few degrees of 238° for each of the
pibals.  By extending the logarithmic wind speed profiles of Figures 2
and 3 to u = 0, an aerodynamic roughness length for this terrain is seen to be
on the order of 20 m.  Points below z = 100 m should be ignored, since they fall
below the typical nearby mountain height.  Thompson (1978) found values on
the order of 30 m in an earlier analysis of pibal data from this site for
this wind direction.  Thus, an 800-m-high logarithmic boundary layer with a
ZQ of 20 m and freestream wind direction of 238° was selected to approximate
the field conditions for the study periods considered.
3,4  The Meteorological Wind Tunnel and Modifications
     The EPA Meteorological Wind Tunnel (Figure 1) has a test section that is
3.7 m wide, 2.1 m high, and 18.3 m long and is an open-circuit tunnel suitable
for modeling neutral atmospheric flows.  The fan and a diffuser are located
downstream of the test section in a sound-attenuating enclosure.  At the
entrance of the wind tunnel, a honeycomb and four screens straighten the
flow and remove th° large-scale turbulence.  A contraction joins the entrance
section to the test section.  A more complete description of the tunnel may be
found in Thompson and Snyder (1976),or Snyder (1979).
     The wind tunnel was designed to operate at a maximum speed of 10 m/s.
At the beginning of this study, operating the tunnel at speeds of 1 m/s or
less resulted in unsteady flow patterns.  The boundary-layer depth and velocity
profile changed from run to run and sometimes during a given run.  The

                                    12

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following arrangement of devices upstream of the test section produced
a steady boundary-layer flow over the model:   A settling chamber was construc-
ted to shroud the entrance of the wind tunnel  (Figure 5).  The chamber,
left open at the top, was 6.1 m wide, 3.66 m high, and 2.44 m deep (20 ft
by 12 ft by 8 ft); that is, as wide as the wind-tunnel entrance and 85%
as high.  The chamber was installed to serve two purposes:   (1) Air was
drawn into the chamber from a given level in the room to avoid enhancement
of the vertical room temperature stratification through the contraction.
(2) Influence from air currents in the laboratory was minimized.
     A section of Verticel (paper triangular cell honeycomb; cell length
= 0.15 m and hydraulic diameter = 0.01 m) was installed at  the exit of
the contraction; that is, at the upstream end of the test section.  The
flow through the lower section of the honeycomb was found to vary slightly
across the width of the test section.  The variations were  minimized by
blocking the regions of high velocity with strips of paper  tape.  Two
fiberglass screens (16 x 18 mesh) separated by 0.1 m were placed just
downstream of this honeycomb to produce an additional pressure drop and
help smooth any remaining velocity variations.
     Figure 5 shows the arrangement of vortex-generating fins, sawtooth
trip, and roughness blocks that was found to produce the desired boundary-
layer velocity profile.  As suggested by Counihan (1969), vortex-generating
fins were used to initiate the boundary layer flow.  The fins were 0.61 m
high, 0.30 m in the flow direction, and 0.07 m wide at the  rear of their
base.  They were spaced on 0.30 m centers across the span of the test
section.  A 0.14-m-high sawtooth trip with 0.04-m-high teeth cut on a
                                    13

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45° angle placed downwind of the vortex-generating fins was found to
produce a more laterally homogeneous flow than the castellated barrier
placed upwind used by Counihan.  Staggered rows, 0.16 m on center, of
0.04-m x 0.04-m x 0.24-m blocks separated by 0.24 m within rows served
as roughness elements over the next 5 m of the test section.  To avoid
an abrupt change at the upwind edge of the model, the height was increased
for a few blocks just upwind of the portions of the model with larger
mountains,
3.5  Model Cpn_sjbructj_ojT_
     A terraced model was constructed from 0.0064-m (1/4-in) plywood sheets;
each thickness of plywood corresponding to the 12,2-m elevation intervals
of U.S. Geologic Survey (USGS) topographic maps to give a model scale
of 1:1920.  At this scale, a model of a 7-km x 21-km area of the Clinch
River Valley was constructed to occupy a 3.66-m-wide by 11-in-long portion
of the Meteorological Wind Tunnel test section.  The terrain model was
constructed by Model Display Studio, Inc. of Raleigh, N.C. using a technique
developed by the Calspan Corporation (Ludwig and Skinner, 1976).  As shown
in Figure 6, the modeled area  included the power plant and four of the
field sampling sites.  The area was laid out on a composite map using
the USGS maps (1:24000 scale,  divided into sections representing 1.22-
m  (4-ft) squares of the model).  Each section was photographed and two
1,22-m-square prints were made of each section.  These prints were glued
to 1,22-m-square sheets of 0.0064-m-thick plywood.  For each pair of sheets
corresponding to a given area, every other contour line on one sheet was
cut with a saber saw; the same was done to the other sheet for the inter-
                                    14

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mediate contour lines.  These pieces were then stacked (by alternating
pieces from the two sheets) and glued and nailed together to form the
sections of the terraced model (Figure 7).   Each section was mounted on
a firm base of 0.0127-m (1/2-in) plywood and built up to the proper level
to match the neighboring sections in elevation.  The squares were painted
with a light coat of green paint without covering the printing on the
maps.  The sections of the model were fastened to the floor of the wind-
tunnel test section with wood screws in each corner. All joints were filled
with architectural putty.
3.6  Similarity Criteria and Constraints
     In modeling dispersion from stacks, the momentum and buoyancy of
the plume must be properly scaled.  It is also desirable to maintain the
highest possible Reynolds number value based on stack diameter and exit
velocity.  If the Reynolds number is too low, the plume will be laminar
and the entrainment mechanism of the model  will not resemble that in the
field.
     Exaggeration of the diameter of the model stacks (that is, making
them larger in the model than the geometric scale dictates) helps to increase
the Reynolds numbers of the stacks and also increases the operating speed
of the tunnel (Liu and Lin 1976).  Too severe of an exaggeration, however,
reduces the effluent-speed-to-wind-speed ratio to a point where stack-
induced downwash of the plume occurs.  An exaggeration of about 2.9 was
used for the stacks in this study.  The exaggeration factor was determined
by selecting sizes of available tubing that would provide both stacks
with nearly the same exaggeration while keeping the ratios of exit velocity
                                    15

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to crosswind speed greater than 1.0.   The 4.75-m-diameter stack  was  modeled
with a 0.0072-m-diameter stack, and the 3.81-m-diameter stack was modeled
with a 0.0056-m-diameter stack.  To help ensure turbulence of the plume
at the stack exit, a trip in the form of an orifice was installed in each
stack (Liu and Lin 1976).  For each stack, the diameter of the opening
in the orifice was one-half the inside diameter of the stack  and the orifice
was placed 10 stack diameters from the stack exit.
     For the model effluent, a buoyant gas that could serve as a tracer
and be measured by the flame ionization detector was needed.  Using  a
single gas provided more accurate control of the effluent rate than  mixing
gases to balance densities and tracer concentrations.  Thus,  pure methane
(p/p. = 0.57) was selected as the model effluent.  For flow visualization
    a
experiments, air and helium were mixed to obtain an effluent  with the
same density as methane.
     Proper modeling of the buoyant release using an exaggerated stack
diameter was accomplished by adjusting the effluent conditions to scale
the buoyancy length and momentum length of the plume according to the
geometric length scale of the model (1:1920).  Briggs (1975)  defines these
characteristic lengths as:
                                            g  (To-Ta) WQ  D*
                         buoyancy length =  —
                                            4     To
                                                          n  D
                                             1
                     LM = momentum length = -w-(T,/T,J   u,
                      n                      c.    a  o     5
                                   16

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If we use the subscripts f for field and m for wind tunnel,  the scaling
criteria is stated as:

                     LBm  ' LBf  / 19?0

                     Ll*  = LMf  / 192°
     Also, where gases  of different density are used to model  field temperature
differences, we substitute (p - p^)/pa for (T  - T_)/T  and  (P^/P.) for
                             aoa       oflo       Oa
(T /T ) in the above formulas (prt and pa are the effluent and  ambient
  a  o                          o      a
gas densities).
     Inserting known values of the parameters from the field and model
enables solving for each stack's effluent rate and for the wind-tunnel
speed.  Since a field measurement of the wind speed at the top of the
stacks was not made, the wind-tunnel value is used to estimate the wind
speed at the stack exit in the field.  As discussed in Section 4, wind-
tunnel velocity measurements indicated the mean wind speed at  the stack
exits to be about 0.47  times the freestream tunnel speed. The mean speed
aloft was 9 m/s for the July 24, 1977 study period.  Therefore,
(u$)f = 0.47 x 9 m/s =  4.2 m/s.
     For Stack 1 (the larger-diameter stack), the exit velocity is computed
from the data in Table  1 to be (wQ)f = 9.88 m/s.  Substituting these known
values into the momentum length scaling requirement results  in

                         m /  m /(us>3m = 15'9  s2/^
                                     17

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Solving these two equations for (w0)m and (us)m yields

                         (w0)m = 0.23 m/s
                         (us)m = 0.24 m/s
Performing the same calculations for Stack 2 results in
                         (wQ)m =0.38 m/s
                         (us)m = 0.24 m/s
The freestream wind speed for the wind tunnel is then computed to be
                         (u )m = (0.24 m/s)/0.47 = 0.5 m/s
                           CO
and effluent rates for the two stacks are

                         (CMm = (wolJB(ir Dl/4) = 58° cm3/min
                         (Q2)m = (wo2)m(ir D*/4) = 560 cm3/min
     Computations for the April 28, 1977 study period result in the
following conditions:
                         (On, = }'Q m/s
                         (wol)n- 0.49 m/s
                         (wo2}m * °'42 m/s
                         (Q^ = 1260 cm3/min
                         (Q2)m = 630 cm3/min
     After this wind-tunnel study was completed using stack airflow rates
from quarterly reports of the field study, Geomet, Inc. revised their
method of computation, resulting in adjusted airflow rates of about 40
                                     18

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to 50 percent higher.  The airflow rates enter the plume scaling calculations
as a linear effect on both Lg and LM; thus, these values should have been
40 to 50 percent larger in the wind-tunnel  study for exact modeling.
However, the highly turbulent flow in the vicinity of the stacks produced
a strong terrain-induced downwash that resulted in a large initial  spreading
of the plume.  A 50 percent increase in LB and LM would probably not
produce an observable difference in the plume shape or a significant
difference in concentration.
     For multiple sources with exaggerated stack diameters and stack exit
Velocities, the proportion of tracer gas that should be released from
each of the stacks to enable simple relation of the wind-tunnel measurements
to the fullscale values is not immediately obvious.  It is shown below
that the ratio of mass fluxes of tracer for the model stacks must be the
same as for the pollutant mass fluxes for the fullscale stacks.

     The concentration (in mass per unit volume) of a pollutant c at a
position in the plume is proportional to the effluent rate (in mass per
unit time) of the source Q and inversely proportional to the mean wind
speed u and the plume cross-sectional area A.  That is, c <* Q/uA.  Consider,
both for the fullscale and for the model, a position downwind of two stacks
where concentrations from each are present:
              Fullscale Stack 1:         cf^ Qf,/ufiA,r-|
              Model Stack 1:              cml- Qml/umlAml
              Full scale Stack 2:         Cf2a Qf2/uf2Af2
                                   19

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              Model Stack 2:              Cm2a Qm2/um2Am2
or
              cfl =
              c« - Qf2UmAm2
What we desire is a relation between the fullscale concentration,
cf = cfl + cf2» and the model  concentration,  cm = c^  + cm2-   Assuming
the same plume shape and spread in the model  and field,
                                             2
                        Aml/Afl = Am2/Af2 = L
where L is the geometric length scale of the model.
                        r  - r   +r   . Qfl  Um Aml .    A Qf2 um Am2 .
                        C^ ~ C^i "" Cfn '
if we set Qf|/Qmi = Qf2/^m2 = ^f/^m'   That is' lf the ratio of the mass
flux of the tracer for the model stacks is equal  to the ratio of the fluxes
of the pollutants for the fullscale stacks, the model concentrations can
be used to calculate fullscale values according to:

                        cf =  (l2) Sn '

     Since there were only two stacks that were emitting roughly the same
concentrations of S02 and the model diameters were scaled at nearly the
same exaggeration, emitting pure methane as the tracer from both stacks
                                   20

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resulted in the correct proportion of tracer in each stack.  Because of
this, concentrations measured in the model were easily converted to field
values.  Thus, for the July 24, 1977 study period:
        (501 g S02/s) (0.5 m/s) © (] x 10"6 ^ SQ2  }
                                       2.93 x 10"3 g S09
   cf ~ 	£	c
                (1.14 x 10~3 m3 CH4/min) (9 m/s) (1920)2     m

or cf = 1.36 x 10"  c , where concentrations are now expressed on a volume/
volume basis.  Similarly, for the April  28, 1977 period, c^ = 1.7 x 10   c .
     Correct modeling of atmospheric flow and dispersion in wind tunnels
requires satisfying many other similarity criteria.  Standard procedures
were followed for meeting the imposed conditions.

3.7  Visualization and Measurement Techniques
     Flow visualization cf the plume was performed using a paraffin-oil
smoke-generation apparatus.  Air and helium were mixed in the proper ratio
to produce the desired density of effluent and correct total flow rate
for both stacks.  The flow rates of air and helium were monitored with Meriam
Laminar Flow Elements.  Paraffin oil was vaporized in an in-line canister
by pumping the air-helium mixture from the canister and returning it through
an aspirating nozzle that drew oil  from the bottom of the canister and
sprayed it onto the tip of a hot soldering iron.  Valves on the  lines to
the stacks were adjusted to divide the flow between the stacks in the
correct proportion.  The flow rate to each stack was checked with a bubble
meter and stopwatch.  Photographs of the smoke patterns were taken with
a 35-mm camera using black and white ASA 400 film.  A shutter speed of
1/30 s and an aperture of f/16 were used.
                                     21

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     Velocity and turbulence intensity measurements were made with a
Thermo-Systems hot-film anemometer.   The anemometer (Model  1053B)  and
Model 1057 signal conditioner controlled a Model  1212 single cylindrical
probe.  The analog output of this system was digitized,  processed, and
stored on disk by a Digital Equipment Corporation PDP-11/40 minicomputer.
For routine velocity measurements, a 120-s sampling period  and a rate
of 250 samples/s were used.  When raw data were to be stored for later
spectral analysis, sampling rates ranged as high as 1000 samples/s for
120 s.  Calibration was achieved by positioning the probe in the freestream
flow above the model.  Stroke puffs were released into the flow and timed
over a fixed distance to determine airspeed at low speeds;  at high speeds,
a pitot tube and manometer were used to obtain six calibration speeds.
     A tank of 99% pure methane served as the supply of tracer gas for
concentration measurements.  This tank fed two lines, one to each stack,
each with a metering valve and a Model 50MK10-2 Meriam Laminar Flow Element
to control the desired efflux rate for each stack.
     Mean methane concentrations were measured at selected points over
the model by use of a Beckman 400 Hydrocarbon Analyzer.   A small pump
drew a continuous sample through a 0.002-m-diameter probe and fed it
directly to the analyzer.  The minicomputer was again used to process
and store the data.  Since the response of the hydrocarbon analyzer is
only 0.5 s and (therefore) only mean concentrations can be obtained, a
sampling rate of 50 samples/s for 120 s was used.
                                     22

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                                SECTION 4
                  EXPERIMENTAL RESULTS AND DISCUSSION
     With the exception cf the discussion of the approach boundary layer,
all results are presented in field units.  That is, concentrations are
in parts per billion S02 that would be observed in the field,  distances
are full scale, etc.  The coordinate system has its origin at the power
plant, x is measured directly downwind (azimuth = 58°), y is to the WNW
(azimuth = 328°), and z is the vertical distance from the local surface.
"Elevations" are from mean sea level.
4.1  Wind-Tunnel Boundary Layer
     The desired characteristics of the boundary layer over the model
were based on the field pibal measurements.  The pibal was released near
the plant with the terrain upwind of the release site typical  of the modeled
area. That is, there were no extremely large hills or regions  of relatively
smooth terrain just upwind of the field pibal site.  Roughness elements
placed upwind of the terrain model were selected to produce a  scaled ZQ
of 1/1920th of the field value.  The wind-tunnel measurements  of the wind
speed profile at the pibal site are shown in Figures 2 and 3 for comparison
with the field data.  Figures 8 and 9 illustrate variations in the mean
wind profile alcng the model for the two study periods.  Good  lateral
homogeneity was achieved in the approach boundary layer (Figure 10) using
the arrangement of devices described earlier.
4.2  Hind Speed Measurements
     Mean velocities and turbulence intensities for July 24, 1000-1100
EST are presented in Figures 11 and 12.  Figures 13 and 14 present these
                                    23

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parameters for April  28, 1800-1900 EST.   The mean  velocity at the height
of the stacks (138 m) over the plant site was 4.6  m/s  for July 24 (Figure 11)
and 9.3 m/s for April 28 (Figure 13).   The ratios  of these values to freestream
speed are 4.6/9.0 = 0.51 and 9.3/20 = 0.47.   The value of 0.47 was available
at the time of emission conditions design and was  used in the analysis
presented in Section 3.6.
     With the exception of Munsey and Lambert (Figure  12a), mean velocity
profiles were quite similar for all sites.  Munsey and Lambert exhibited
higher velocities than the other locations for July 24 conditions.  These
sites were near the wind-tunnel wall.  The boundary layer on the wall
at the low wind-tunnel speed (0.5 m/s) could have produced a small region
of higher velocity above these sites to compensate for the velocity deficit
of the wall boundary layer.
     Available field measurements of wind speed are also shown in Figures
12 and 13.  All measurements were made at a height of  10 m, which is near
the surface where the speed increases quite rapidly with height.  However,
the field measurements agreed quite well with the wind-tunnel values.
4.3  Plume Visualization
     During the  ... tensive field measurement portion of the Geomet, Inc.
study, photographs of the power plant plume were fortunately made possible
through reduction of the electrostatic precipitators for one stack.  Figures
15 and 16 present two series of photographs taken at 2-min intervals.
The erratic nature of the plume path is noteworthy.  In Figure 15b, the
plume is rising nearly vertically; in Figures 15a and  15d, 2 min before
and 4 min after, the plume is leaving the stack nearly horizontally.

                                     24

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The extent of the downwash can be seen in Figure 16a where the plume is
nearly touching the ground at the base of the stack.  Similar plume
patterns were observed in the smoke visualization experiments of the wind-
tunnel study (Figure 17).  Notice the downwash in Figure 17a and the
similarity to Figure 16a.
     The power plant is located just downwind of a large hill extending
120-150 m above the valley that wraps around the plant from west to
north (see Figure 6).   There is also a large hill extending 160 m above
the valley downwind of the plant.  This forms a channel  that deflects
the plume toward the north for the wind direction studied.  Figure 17d
is a top-view photograph of the wind-tunnel  plume that demonstrates the
amount of plume deflection.  Concentration measurements  to be presented
later confirm this plume path.
4.4  Concentrati on Measurements
     Tracer concentrations were measured at  various positions on the ground
and aloft.  Attempts were made to reproduce  field measurements when possible;
thus, more measurements were made for the July 24 period than for the
April 28 period.
     In spite of frequent downwashing of the plume, ground-level concen-
trations measured near the base of the stack for July 24 conditions were
negligible.  Measurements on the face of the hill just downwind of the
stack (see Figure 6) were quite low, with a  value of 13  ppb occurring
en the hill top (Figure 18).  This was due primarily to  deflection of
the plume around this hill to the north.  A  lateral ground-level traverse
(Figure 19) across the plume over this hill  top, x = 0.64 km, shows a
maximum concentration of 122 ppb offset a distance of y = 360 m.  That
                                    25

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is, the maximum ground-level  concentration occurred 30° from the freestream
wind direction.  At a distance of x = 3.2 km,  the maximum ground-level
concentration was 82 ppb and the offset was ~500 m (Figure 20).
     Lateral traverses at constant elevation were made at downwind distances
of x = 1.2, 2.3, 4.8, and 8.2 km (Figures 21-24, respectively) for July 24,
                                                         p
1000-1100 EST.  Curves of the form c = c   exp(-0.5(y/o ) ) were fit
                                        l'lCLs\            V
to each traverse to determine the standard deviation, a , of the lateral
plume spread.  The lateral shift of the plume centerline increased to
500 m at a distance of x = 2.3 km and remained at that approximate value
for farther downwind distances.
     Helicopter field data were available for x = 2.3 km and 8.2 km and are
shown for comparison in Figures 22 and 24.  The helicopter data were raw
data from a magnetic tape supplied by Geomet, Inc.  Geomet had not completed
analysis and validity-checking of this data.
     Direct comparison of the wind-tunnel and helicopter data was difficult
partly because of the difference in sampling times.  The helicopter data
were nearly instantaneous, since it took only about 2 minutes to fly through
the plume; the wind-tunnel results, in contrast, were time-averaged values.
Also, the helicopter data for x = 8.2 km were obtained for a later period
in the day; emission rates and meteorological conditions were quite similar
to those for the modeled period, however.
     The helicopter profile at x = 2.3 km and elevation of 1158 m showed a
high background level.  This was most likely due to a problem with the
sampling equipment; since only raw data were available, however, the values
were plotted uncorrected  (Figure 22).  A background level of 45 ppb was
                                   26

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removed from this profile for comparison with the wind-tunnel  data.  At
an elevation of 1158 m, the peak field S02 concentration minus background
was 50 ppb and the peak wind-tunnel concentration was 10 ppb.   At an elevation
of 975 m, the peak field concentration was 65 ppb and the peak wind-tunnel
concentration was 50 ppb.  The helicopter sampled a plume about one-third
as wide as the wind-tunnel plume and with a sorrewhat higher maximum concentra-
tion.
     At a downwind distance of x = 8.2 km (Figure 24), the helicopter data
were more difficult to compare with the wind-tunnel data.  The helicopter
profiles showed multiple peaks, and at the higher elevations the lateral
profiles were much wider than those in the wind tunnel.  The maximum
concentration for each elevation measured by helicopter was about double
the concentration measured in the wind tunnel.
     As a check on the lateral concentration profiles at this downwind
distance, a conservation of mass calculation can be made for the wind-
tunnel data.  The mass continuity requirement is stated as
                            OO      CO
                       Q =   \     i   u c dy dz
That is, the rate of mass leaving the source is equal  to the rate of mass
crossing a plane downwind of the source.  A Gaussian distribution, with
0  = a constant independent of z, is assumed to give
 */
                             c = Wz)
                                   27

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This is integrated to give
                           Q =
cmax M u (2> dz
which is approximated by
This calculation was performed for the July 24, x = 8.2 km wind-tunnel
data using N = 6 layers in the vertical.  A calculated Q of 470 g/s SO,,
was obtained for comparison with the actual source rate of 501 g/s SIX,.
Thus, the wind-tunnel data satisfied the mass conservation requirement
to within ~6% using this rough approximation technique.  The helicopter
data, which showed much higher concentrations and a wider plume (and hence
more SQ^ passing this plane) can be questioned.
     Ground-level concentrations were measured under the plunge centerline
as determined from the lateral ground-level and elevated traverses (Figure
6).  Figure 25 shows measurements for both modeled periods and the terrain
elevation.  For the first 1.4 km, the plume followed the local valley
(elevation = 460 m); then the path went up over Sinkhole Valley
(elevation - 600 m).  For both July 24 and April 28, the maximum ground-
level concentration occurred on the local  river valley before the plume
encountered the valley wall.  This suggests that the plume rose to accom-
modate the increasing terrain height rather than colliding with the terrain,
These data are plotted on logarithmic axes in Figure 26.  Also plotted.
are ground-level concentrations to be expected over flat terrain with
                                   28

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a uniform wind field.  As described by Turner (1970), the Gaussian model
                                                  p
for this case is c = (Q/iro  oz u)exp(-0.5(Heff/az) .   The freestream wind
speed, u, was used with a  and o^ for Pasquill-Gifford atmospheric stability
C (slightly unstable).  Had Pasquill-Gifford a  and oz for B or D stability
been used, the distance to the maximum ground-level concentration would
not match the wind-tunnel result.  Previous wind-tunnel experiments (Huber
et al. 1979) have shown boundary layers in the EPA Meteorological Wind
Tunnel to exhibit plume spreads characteristic of C stability in the vertical
and D stability in the lateral directions.  For July 24 conditions (Figure
26a), an effective stack height of ~100 m resulted in a good fit to the
data.  For April 28 (Figure 26b), the effective height was found to be
75 m.  As a result of downwashing of the plume, concentrations near the
plant were much higher than the Gaussian model estimates.  It should be
emphasized that state of the art techniques do not provide for a priori
estimation of H -^ or the plume path for this complex terrain situation.
The comparison here was made primarily to examine the nature of the reduction
of ground-level concentration with distance from the source for the wind-
tunnel study, and not to suggest that Gaussian plume theory is necessarily
a good predictive tool.
     On July 24, the mobile van sampled S02 at two locations.  From 0919
to 1030 EST, the van was located on a bearing of 25°  at a distance of
4 km from the plant.  During that time, S02 concentrations were 13-16 ppb.
On the model, this position corresponds to x = 3.2 km, y = 2.0 km, just
beyond the lateral extent of the lateral wind-tunnel  profile measured
at x = 3.2 km (Figure 20).  Therefore, the comparable wind-tunnel concen-
                                   29

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tration was C ppb.  One possible reason for the higher level  observed
in the field could be that this sampling position was  0.76  km directly
downwind of the coal preparation plant mentioned (the  only  other  significant
source in the area).
     From 1249 to 1348 EST, the van was located on a tearing  of 57°  at
a distance of 11.2 km from the plant.   SOp levels of 33-37  ppb were  measured.
This position was near the plume center!ine, for which Figures 25 and
26a show concentrations.  Concentrations in the wind tunnel were  measured
out to a distance of 8 km.  Extrapolating to a distance of  11.2 krr yielded
a concentration of ~10 ppb.
     Vertical traverses were made at field sampling sites,  at downwind
distances of lateral profiles, and at some intermediate positions.
Figures 27-31 are for July 24, 1000-1100 EST conditions for downwind distances
of x = 1.65, 3.2, 4.8, and 10.2 km, respectively.  Figures  32-34  are for
April 28, 1800-1900 EST conditions and distances of x  = 1.2,  2.3, and
3.2 km.  To determine a parameter describing the vertical spread  of  the
plume, a reflected Gaussian plume shape was assumed:
        c = cmax[exp(-0.5((z-Heff)/oz)2) + exp(-0.5((z+Heff)/oz)2)]

(see Turner 1970).  Effective stack heights of 100 tr and 75 m were used
for July 24 and April 28, respectively.  A best fit routine was used to
compute the standard deviation, a .  Field data for the fixed sampling
sites are included on Figures 28, 31, and 34.  Good agreement was obtained
for Tower site on July 24 (Figure 28). For the 1000-1100 EST  period  modeled,
the wind-tunnel concentration was 73 ppb, exactly the  value recorded in
                                    30

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the field.  For the preceding and following 1-hour periods, the field
concentrations were somewhat less, at 38 and 21 ppb.  For this same period,
wind-tunnel values at the Nash Ford site (Figure 31) were below the field
threshold value of 1 ppb.  The field concentrations were below threshold
for the preceding and following periods as well.  There was less agreement
between field and wind-tunnel values for the April 28 conditions (Figure 34).
In the wind tunnel, a value of 95 ppb was observed; in the field, only
4 ppb was detected for the modeled period and preceding hour and 21 ppb
was measured for the following hour.  The meteorological conditions were
not as well defined for the April 28 model period as for July 24.  The
April 28 pibal was released much earlier in the day than the period modeled.
An error in plume direction could have caused the wind-tunnel concentration
to fall below the field value.
4.5  Plume Spread
     The standard deviation of lateral plume spread (o ) and vertical plume
spread (o ) as determined above can be compared directly with those of
Pasquill-Gifford (Turner 1970) for flat terrain.  The a  values for
the July 24 period are shown in Figure 35.  Near the source, o  was larger
than for C stability; beyond x = 3 km, a  was less than for C stability.
The downwind distance was measured from the stack; no virtual source position
was attempted to compensate for the initial plume spread produced by the
turbulent wake of the ridge just upwind of the stacks.  The a  values
determined for both of the modeled periods were larger than for Pasquill-
Gifford C stability values.  It is interesting to note that oz remains
essentially constant at x = 1.65 and 3.2 km for July 24 and at 1.2 and
                                   31

-------
2.3 km for April 28.  This was approximately where the plume had to
climb above the river valley wall  and the local  surface elevation increased
by about 140 m.  This increase in  terrain height produced a converging
flow.  Thus the vertical spread of the plume was severely limited to the
extent that the increase in terrain height just offset any vertical
growth of the plume.
                                    32

-------
                               REFERENCES
Briggs, G.A., 1975:   Plume Rise Predictions,  ATDL No.  75/15,  Environmental
Research Laboratory, National  Oceanic and Atmospheric  Administration,
Oak Ridge, TN. 46 pp.

Counihan, 0., 1969:   An Improved Method of Simulating  an Atmospheric
Boundary Layer in a  Wind Tunnel, Atmospheric  Environment, 3,  197-214.

Huber, A.M., W.H. Snyder, R.S. Thompson and R.E.  Lawson, 1979 (in  press),
The Effects of a Squat Building on Short Stack Effluents, Environmental
Monitoring Series Report, U.S. Environmental  Protection Agency,  Research
Triangle Park, NC.

Koch, R.C., W.G. Biggs, D. Cover, H.  Rector,  P.P. Stenberg,  and  K.E.  Pickering,
1979:  Power Plant Stack Plumes in Complex Terrain - Description of an
Aerometric Field Study, EPA-600/7-79-010a, U.S. Environmental Protection
Agency, Research Triangle Park, NC.

Liu, H.T. and J.T. Lin, 1976:   Plume  Dispersion in Stably Stratified  Flows
over Complex Terrain; Phase 2, EPA-600/4-76-022,  U.S.  Environmental Protection
Agency, Research Triangle Park, NC.

Ludwig, G.R. and G.T. Skinner, 1976:   Wind Tunnel Modeling Study of the
Dispersion of Sulfur Dioxide in Southern Allegheny County, Pennsylvania,
EPA 903/9-75-019, U.S. Environmental  Protection Agency, Philadelphia,  PA.

Snyder, W.H., 1972:   Similarity Criteria for  the  Application  of  Fluid  Models
to the Study of Air  Pollution  Meteorology, Boundary Layer Meteorology,
3, 113-134.

Snyder, W.H., 1979:   The EPA Meteorological Wind  Tunnel - Its Design,
Construction and Operating Characteristics, U.S.  Environmental Protection
Agency, Research Triangle Park, NC, (cleared  for  publication  as  EPA report).

Thompson, R.S. and W.H. Snyder, 1976:  EPA Fluid  Modeling Facility, in
EPA 600/9-76-016, Proceedings  of the  Conference on Environmental Modeling
and Simulation, U.S. Environmental Protection Agency,  Washington,  DC.

Thompson, R.S., 1978:  Note on the Aerodynamic Roughness Length  for Complex
Terrain, J. Appl. Meteor., 17, 1402-1403.

Turner, D.B., 1970:   Workbook  of Atmospheric  Dispersion Estimates,  AP-26,
Office of Air Programs, U.S. Environmental Protection  Agency, Research
Triangle Park, NC.


                                     33

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                                   TECHNICAL REPORT DATA
                            (Please read Instructions on the reverse before completing}
 1 REPORT NO.
   EPA-600/4-79-052
4 TITLE AND SUBTITLE
 DISPERSION OF  SULFUR DIOXIDE FROM THE CLINCH RIVER
 POWER PLANT
 A Wind-Tunnel  Study
                                                           5 REPORT DATE
               6. PERFORMING ORGANIZATION CODE
                                                           3. RECIPIENT'S ACCESSION-NO.
                 September  1979
7. AUTHOR(S)

 Roger S. Thompson
               8. PERFORMING ORGANIZATION REPORT NO.

                Fluid Modeling  Report No. 7
9. PERFORMING ORGANIZATION NAME AND ADDRESS
 Environmental  Sciences Research Laboratory
 Office of  Research  and Development
 U.S. Environmental  Protection Agency
 Research Triangle Park, NC  27711
               10. PROGRAM ELEMENT NO.
                1AA603 AB-20  (FY-78)
               11. CONTRACT/GRANT NO.
 12. SPONSORING AGENCY NAME AND ADDRESS
 Environmental  Sciences Research Laboratory — RTF,  NC
 Office of Research  and Development
 U.S. Environmental  Protection Agency
 Research Triangle Park, NC  27711
               13. TYPE OF REPORT AND PERIOD COVERED
               in-house   6/77  -  12/78
               14. SPONSORING AGENCY CODE
                 EPA/600/09
 15. SUPPLEMENTARY NOTES
 16. ABSTRACT
      A wind-tunnel  study of the transport and dispersion  of sulfur dioxide from the
 Clinch River Power  Plant in Virginia was performed  for  periods of neutral atmospheric
 conditions corresponding to two 1-hour periods for  which  field data were available.
 A 7-km x 21-km  area of the quite rugged complex terrain surrounding the power plant
 was modeled at  a  scale of 1:1920 using a terraced construction.   Exaggerated stack
 diameters were  used in modeling the buoyant emissions from the plant's two stacks.
      The most significant influences of terrain on  the  plume were found to be frequent
 downwashing and an  angle of ~30° to the mean wind direction for the plume's initial
 direction.  These phenomena were produced by the hills  just upwind and downwind of the
 stacks.  Ground-level  concentrations measured at positions corresponding to field
 sampling sites  compared well with field measured values.   Comparisons of concentration
 measured above  the  model surface with helicopter field  measurements were not good,
 but the wind-tunnel measurements were shown to satisfy  a  conservation of mass require-
 ment.  The standard deviations of plume spread in the vertical  and horizontal
 directions were measured for various downwind distances and compared to Pasquill-
 Gifford values  for  flat terrain.  Ground-level concentrations under the plume center-
 line were compared  to  Gaussian plume model estimates, given the plume path and
 effective stack height determined experimentally.
 7.
                               KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
                                             b.IDENTIFIERS/OPEN ENDED TERMS
                            c.  COSATl Field/Group
 * Air pollution
 * Sulfur dioxide
 * Meteorology
 * Atmospheric diffusion
   Electric power  plants
 * Wind tunnels
   Terrain models
                              13B
                              07B
                              04B
                              04A
                              10B
                              14B
 8. DISTRIBUTION STATEMENT


   RELEASE TO  PUBLIC
  19. SECURITY CLASS (This Report)
   UNCLASSIFIED
                                                                        21. NO. OF PAGES
75
                                             20 SECURITY CLASS (Thispage)
                                              UNCLASSIFIED
                                                                        22. PRICE
EPA Form 2220-1 (9-73)
63

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