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Environ Effects of Midland Plant Cooling Pond Summary Rept.
	ML19329F070
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Site:	Midland
Issue date:	04/28/1972
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t THE ENVIRONMENTAL EFFECTS OF THE MIDLAND PLANT COOLING POND 1

SUMMARY

REPORT FOR CONSUMERS POWER COMPANY s Jackson, Michigan BECHTEL COMPANY JOB 7220 APRIL 28, 1972

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O TABLE OF CONTENTS Page CONCLUSIONS 1 INTRODUCTION 3 BACKGROUND 3 OBJECTIVES 5 GENERAL PLAN 6 DEFINITIONS AND NOMENCLATURE 7 THE MIDLAND PLANT COOLING POND 9 SITE DESCRIPTION 9 CLIMATOLOGY 9 COOLING POND THERMAL DESCRIPTION 10 SERVICE WATER COOLING SYSTEM DESCRIPTION 10 BLOWDOWN COOLING SYSTEM DESCRIPTION 10 STUDY PONDS 12

, COFFEEN PLANT 12 s 4-CORNERS PLANT 12 COOLING PONDS

SUMMARY

13 FIELD PROGRAM 15 PRELIMINARY PROGRAM 15 RECENT PROGRAM 16 FOG STUDY DATA BASES 17

a. Pond Temperature Studies 17

b. Steam Fog Data 17

c. Comparisons of Fog Data 24

d. Fog Index Number 25 EXTENT OF FOG PLUMES STUDY 27

a. Steam Fog Plume Extent Data 27

b. Fog Droplet Size Data 31

c. Plume Extent Calculations and Comparisons 34

! ICE DEPOSITION 39

a. Observations 39

b. Calculations 40 EXTENSION TO THE MIDLAND PLANT COOLING POND 43 FREQUENCY OF COOLING POND FOG 43

a. Natural Fog 43

b. Pond Fog or Stratus With Natural Fog 43

c. Pond Fog or Stratus Without

( Natural Fog 46 l

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I O Page

[ EXTENT OF FOG PLUME

a. Calculational Method 53 53

b. Statistical Analogue to Midland Plant 54

c. Direct Analogue to Midland Plant 55

d. Summary, Extent Estimates for Midland Winters 56 EFFECTS OF ICING 58

a. Review of Data 58

b. General Icing Effects at the Midland '

Plant 58 STEAM FOG DOWNWIND LOCATIONG 62

a. General Downwind Remarks 62

b. Specific Downwind Locations 62

c. Road Icing in the Environs 65

d. Airports 66

e. Winds from the Southeast 66 SNOW 67 EFFECTS OF COOLING TOWERS 68 SERVICE WATER COOLING SYSTEM 68 BLOWDOWN COOLING SYSTEM 68 ACKNOWLEDGEMENTS 69 REFERENCES 70 t

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t TABLES No. Page

1. Conclusions 2

2. Cooling Pond Comparisons 14

3. Fog Test Data 18

4. Extent of Plume Data 28

5. Liquid Water Concentration and Droplet Density 33

6. Fog-Stratus Extent and Liquid Water Data -

Measurements.and Calculations 37

7. Summary of Ice Accretion Data 41

8. Comparison of Ice Accretion Data to Sweep-Out Calculations 42

9. Frequency of Natural Fog, Tri City Airport 43

10. Percent Frequency of Fog Index Number During Hours when Natural Fog Occurs 45

11. Occurrence of Pond Fog With, Natural Fog 44

12. Percent Frequency of Fog Index Number With-out Natural Fog, Winter 47

13. Percent Frequency of Fog Index Number With-out Natural Fog, Spring 48

14. Percent Frequency of Fog Index Number With-out Natural Fog, Summer 49

15. Percent Frequency of Fog Index Number With-out Natural Fog, Autumn 50

16. Percent Frequency of Fog Index Number With-out Natural Fog, Annual 51

17. Occurrence of Pond Fog or Stratus Without Natural Fog Present 52

18. Calculated Downwind Extent on the Average Winter Morning 53

19. Calculated Downwind Extent on the Extreme Winter Morning 54

20. Summary, Extent of Plume, Midland Plant Pond 57 l 21. Icing Effects at Midland Plant, Comparison

! of Interim Report With Summary Report Results 59 t 22. Hours of Occurrence of Sub-Zero Temperature, Midland Area 61 l

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t FIGURES

1. Plot Plan of the Midland Plant

2. River Intake, Plant Flow and Discharge

3. Mean Surface Temperature, Cooling Pond

4. January surface Isotherms of Cooling Pond

5. Plot Plan of the Coffeen Plant Pond

6. Plot Plan of the 4-Corners Power Plant Pond

7. Schedule of Unit Operation, 4-Corners Plant

8. Surface Temperature Study, 4-Corners Cooling Pond

9. Mean Surface Temperature Vs Date, 4-Corners Pond

10. Smoothed Surface Temperature Vs Date, 4-Corners Pond

11. Fog Teste, diT Vs Wind Speed

12. Fog Tests, diT Vs Stability Category

13. Fog Tests, lit Vs Ew-Es

14. Fog Tests, lit Vs Es-Ea

15. Stratus and Fog Frequency Vs Fog Index Number

16. Photographs of Fog, Fog-Stratus, and Stratus from Cooling Pend

17. Wind Sectors, Steward Rd., 1.4 mi from Pond 17a. Wind Sectors, Stewart Rd., 1.4 mi from Pond, due East Wind i

18. Wind Sectors, Stewart Rd., 0.4 mi from Pond

19. Wind Sectors, Stewart Rd., 0.2 mi from Pond

20. Wind Sectors, Bullock Creek Elementary School

21. Wind Sectors, Mapleton

22. Wind Sectors, Gordonville Road l

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THE ENVIRONMENTAL EFFECTS OF THE MIDLAND PLANT COOLING POND -

SUMMARY

REPORT CONCLUSIONS This Summary Report describes the program to characterize steam fog and ice from the Midland Plant cooling pond. A field test program, the data obtained and the analysis are given. From this, the expected effects of the Midland Plant cooling pond are predicted. All the data of a previous re-port, the Interim Report of June 1971, are incorporated in this Summary Report.

From the analysis of the field data, the concept of a fog in-dex number is developed. This number is At/(e s-e a), F/mbs.

A relationship is dereloped for frequency of occurrence or steam fog, fog-stratus and stratus as a function of the fog index number. For fog index numbers of 90+, fog or stratus always coeurs. The fog index number concept is considered generally applicable for cooling ponds at all geographical locations and for all seasons of the year.

For the Midland area, natural fog occurs in the winter (Dacember, s January, February) 16.4 percent of the time. Its annual occur-ence is 10.8 percent. The frequency of fog index number cate-gories coincident with natural fog is calculated. This is multiplied by the probability of occurrence of fog as a function of fog index number. This yields an estimate, for the Midland Plant cooling pond, of steam fog or stratus, with natural fog present, of 14.8 percent of the time in winter and, for the year, of 8.4 percent. These steam fog statistics carry little wind direction significance due to the simultaneous occurrence of natural fog.

It is estimated for cooling pond steam fog or stratus, with-out natural fog present, for winter, for all directions, a total frequency of 43.5 percent and a maximum frequency of 6.2 percent with west southwest winds. Yearly, the comparable frequencies are 25.0 percent and 3.3 percent maximum with west southwest winds.

For an average Midland winter morning, called Scenario A, it is estimated that the steam fog plume t'ill extend along the ground about 600 feet and then lift to form a stratus layer whose extent, from the pond, will be about 3 miles. For the ex-treme low temperature Midland winter morning, called Scenario B, the steam fog plume will extend along the' ground 1600-5000 feet and/or extend aloft as stratus for about 12 miles. The aver-age duration of Scenario A is 10 hours1.157407e-4 days 0.00278 hours 1.653439e-5 weeks 3.805e-6 months and of Scenario B is 8.6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months . The average occurrence of Scenario A is most winter mornings and of Scenario B is about 2 mornings per winter month.

New information on the particle size distribution of the liquid ,

water droplets in the steam fog has been obtained. The data '

shows that the droplets are largely 10 microns in diameter.

This indicates that the sweepout or deposition process will re-sult in a frost or rime ice rather than glaze. Such frost or rime ice is estimated to amount to 0.002 inches in 10 hours1.157407e-4 days 0.00278 hours 1.653439e-5 weeks 3.805e-6 months on roadways and 0.4 inches in 10 hours1.157407e-4 days 0.00278 hours 1.653439e-5 weeks 3.805e-6 months on poles or wires. Its de-position pattern will follow that of the ground plume extents given for Scenarios A and E. The duration of ice deposition during Scenario B events is particularly dependent on the wind direction. Any deposited frost or rime ice is light-weight and friable with little strength to support its own weight. Thus large ice burdens are very improbable. The new data and its interpretation are significantly different from those presented in the Interim Report and the environmental consequences are certtinly less severe.

An analysis was made to estimate the frequency of fog with no natural fog present at selected locations in the environs. The results are shown in Figures 17 to 22 inclusive. For the An-alysis, all the noncoincident steam fog frequencies for all the wind sectors bearing on the location were summed and the plume extent data added. The results are summarized in Table 1.

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TABLE 1 FREQUENCY 0F NON-COINCIDENT GROUND FCG AT SELECTED LOCATIONS IN WINTER Average Extreme Days /Mo.* Hrs /Mo.

i Stewart Rd, 1.4 mi West of Pond None 1 Stewart Rd, 0.4 Mi West of Pond None 1 Stewart Rd, 0.2 Mi West of Pond None 1 Bullock Creek Elementary School None 1 to 2 Mapleton None None Gordonville Road 15 11

An average day has a 10-hour duration of fog The Tri City Airport would experience stratus from the cooling pond for about 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months per winter month. The Midland (Barstow)

Airport would experience stratus from the cooling pond less than 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months a winter month.

During the winter months , light snow would be expected from the steam fog plume up to 16 percent of the time.

The operation of the cooling towers for the Service Water Cooling System or the Blowdown Cooling System will have no significance on the above results within the accuracy of these estimates.

INTRODUCTION The design of the Midland Plant of Consumers Power Company include? a recirculating cooling pond for rejection of heat from the turbine condenser to the atmosphere. The main potential effect upon the environment beyond the Plant pro-perty is from the evaporation of large amounts of water from this pond and the subsequent potential for formation of fog and/or stratus which could extend off-site. During sub freezing temperatures there is also the potential for ice deposition. In addition,to the cooling pond there will be water added to the atmosphere from the service water cooling towers and blow down cooling towers. This concern for the effects of the cooling pond is accentuated by the close proxi-mity of the City of Midland, neighboring residential areas and industrial plants.

The purpose of this report is to summarize cooling pond fog data from two other power plants, to present the method of analysis of these data and calculational methods developed therefrom, and lastly to apply the resulting methods and models

. to the Midland Plant pond design using local Midland area climatology to estimate the frequency and extent of the steam fog and/or stratus and the icing potential from this cooling pond.

This report was prepared with the guidance of Dr. J. B. Knox and Dr. T. V. Crawford, Meteorological Consultants, and their analyses and opinions are an integral part of the results which follow. Dr. Crawford participated in the on-site' i

meteorological investigations at Midland, Michigan,and at the 4-Corners Power Plant near Fruitland, New Mexico.

l BACKGROUND The phenomena of fog or " steam fog" occurring over bodies of water which are warm relative to the adjacent air is a f amiliar one to those living in northern regions in the winter. Thus, it is expected that "stcam fog" will occur over the Midland Plant's 880-acre heated pond during the cold months of the year.

From this, several questions are asked including (1) How often will pond-induced steam fog or stratus occur? (2) With what wind direction will it be associated? (3) How far from the cool-and (4) Will there be an icing ing pond's edge will it extend?

problem during the winter months? To answer these cuestions, and others, it is necessary to develop a steam fog occurrence l

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criteria and methods of estimating the steam fog extent and icing, which can then be applied to the Midland cooling pond

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design and climatological data for the Midland area.

Church (1945) reviewed some steam fog observations for Lake Michigan and pointed out several general characteristics discussed by earlier writers. For example (1) steam fog could form if the saturated vapor pressure immediately above the water surface was grecter than that in the air, (2) the presence of light wind and strong temperature inversion were favorable for steam fog formation, and (3) extreme tempera-ture differences between air and the water surface are necessary. However, these descrii;ive characteristics, or factors were not quantified criteria. Church then proposed a criteria of 5 mb vapor pressure difference between air and water surface as being necessary for steam fog to be present.

This was based on data he obtained on boat trips across Lake Michigan.

Miller (1946) in commenting upon Church's paper pointed out the importance of the large variations in the moisture gradients and 3. the vertical exchange coefficients.

Jacabs (1946) suggested the use of the vapor pressure of the wat;. surface, ew, less the vapor pressure at saturation of the air, e g. He showed that the density of the fog increased with greater values of ew-es and with greater values of tw-ta j i ( At) . With values of e w-e s of 5 mb or greater and with tw-ta i

greater than 13C (23F) to 14C (250, his analysis showed dense fog. However, it is not possible to develop criteria from these data which can be used for the Midland Plant pond because the air properties above the pond are not known now and Church's observations were taken from a boat in or above the fog.

Willet (1928) reported that air temperatures had to be less than -60C (21F) for steam fog to form, and yet Saunders (1964) found that freezing temperatures were not a prerequisite to steam fog formation. Saunders (1964) quite thoroughly reviewed the steam fog literature, and to quote his summary "They are found to occur with air temperatures between SC (9F) and 40C (72F) lower than the water temperature, in winds from calm to gale; they have liquid water contents in the range 0.01-0.5 g/m3, extend in height from 1 to 1500 m and commonly exhibit either a columnar or banded structure." Sanders solved the advec-tion diffusion equation for heat and moisture for the case of cold air flowing over warm water. From these results and the use of the curve of saturation mixing ratio versus temper-ature,he was able to derive a nomogram (his Fig. 3) describing

the necessary properties for the onset of steam fog (water 4 temperature, difference between water temperature and air

( temperature, and relative humidity). For the Midland Plant cooling pond in the winter with pond temperature ab9ut 15C (59F) and a relative humidity, in the morning, ofiacout 80%,

Sanders' nomogram indicates that the air temperature should be about 8C (14F) colder than the water temperature as a neces-sary condition for fog to occur. Comparison with observations (his Fig. 7) indicate that actual conditions of steam fog have air temperature SC (9F) to 8C (14F) colder than given by his necessary condition. The application of this result to Midland indicates a tw-ta of 13C (23F) to 16C (29F) as being necessary for the occurrence of steam fog on the aver-age winter morning.

Since this fog study commenced, Decker (1970) has published on the meteorological effects of cooling ponds. Decker visited many locations in Europe during the summer of 1969 for the purpose of obtaining information on the use of lakes, ponds, and slack water for the rejection of waste heat. He recorded several miscellaneous comments relevant to pond-induced steam fog. They are; (1) "the water was 170C (30F) or 18 C (32F) warmer than the air during a case of sea smoke,"

(2) "the wisps of fog seem to go up to some clouds at 500 to 1000 ft above the lake," (3) "with water some 50 C (90F) warmer being discharged into a 300 to 400 meter square pond i to 2 m deep,the breezes carried a fog plume downwind 500 to 1000 meters," (4) " low fog tends to develop over the hot water sheet N which flows down the outlet channel, but this fog does not ex-tend more than a few hundred feet beyond the actual water sur-face."

One could probably find other isolated comments or fragmentary evidence on steam fog from heated or natural ponds. But not enough competent quantitative information was available with which to make competent estimates of either the occurrence or the extent of the potential steam fog from the Midland Plant cooling pond. There was no systematic observations of any large heated pond, at least in the United States, nor in 1969, could a pond be found of similar size, thermal heat load or meteorological setting similar to that being designed for Midland. And yet the large size, thermal. loading, the cold winter climate location, and the proximity of the town of Midland all indicated that a solid technical study be performed of cooling pond fog.

OBJECTIVES The objectives of this present study are:

1. To develop technical criteria for determining the frequency of occurrence of steam fog.

2. To develop methods for estimating the extent of steam fog downwind of the pond edge and for estimating ice deposition.

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3. 'To prepare estimates of the local enhancement of fog fre-quency and the off-site extent thereof at the Midland Plant Site.

4. To assess the potential for frosting or icing of roadways, wires, and structures and the~ potential for snow in the im-mediate environs of the Midland Plant cooling pond.

GENERAL PLAN In view of the objectives and the fragmentary nature of pre-viously available data on steam fog, it was believed that fre-quency criteria could best be developed by direct observation of steam fogs from cooling ponds with size, heat load, and meteorological conditions as close to those of the Midland Plant, as possible. The observational program would also be broad enough to include extent and icing data so that methods of ad-dressing these problems could be developed and verified before application to Midland. The method of data analysis would be general enough to account for pond and meteorological differences between the study ponds'and the Midland Pond.

The Coffeen and the 4-Corners cooling ponds, described later, were selected for study. Two visits were made to the Coffeen Plant during cold weather with a high steam fog potential. The

, Coffeen Plant pond temperature is. generally lower than the Mid-land Plant pond design. For this reason it was not as good an.

experimental analogue to the Midland Plant pond as desired. How-ever, the data from Coffeen was retained in order to develop a fog prediction criteria from a larger data sample and for more than one pond. With the addition of more units at the 4-Corners plant, that cooling pond was approaching or equalling the temper-ature planned for the Midland Plant cond. By mid-1971, the pond thermal loading at 4-Corners approximate that planned for l the Midland pond if all units were operating. Also, the mean winter minimum temperatures are about the same at 4-Corners as at Midland, although it is a little drier at 4-Corners. Thus, the 4-Corners pond became a reasonably close analog to that planned for the Midland Plant.

l Consequently, the study shifted to the 4-Corners ponds Each l survey was during cold weather and was of two days duration.

l The data from the above surveys provided a data base for the

Interim Report of June, 1971. During October, November, and

[ December, 1971, daily observations were taken at 4-Corners in l

order to develop a statistical basis for steam fog occurrence criteria and to broaden the data base on fog extent and icing.

In the sections that follow,the Midland Plant, Coffeen Plant i and 4-Corners Plant cooling ponds are described. The data collected at the two study ponds are presented,and steam fog ,

occurrence criteria are developed. Fog plume extent data are l also described, as is icing data, and compared to calculations. l The results from the cooling pond study are then applied to the Midland Plant pond design conditions and the Midland area ,

climatological data in order to quantitatively assess the !

potential of steam fog on the environment in the vicinity of the Midland Plant pond.

DEFINITIONS AND NOMENCLATURE To aid in understanding the subsequent sections, the-follow-ing definitions and nomenclature are presented.

Fog from a cooling pond, also referred to as steam fog, is said to occur when visibility across the pond is impaired to the extent that the far bank of the pond cannot be seen due l

to the suspension of water particles in the air, the water-particle suspension extends upwards from the surface of the pond at least five feet, and the water-particle suspension flows downwind over an adjacent land surface.

Slight fog, or slight steam fog, occurs when water-particle suspension in the air above the pond is so dilute that the

. far shore can be seen, and most of the water surface itself can also be seen. This case represents a transition stage between the occurrence or non-occurrence of fog.

No fog is said to occur whenever no suspended water-particles can be seen in the air over the pond, or at most, can be seen covering less than ten percent of the pond area adjacent to the discharge canal.

Stratus is a layer-type cloud that forms at low altitudes and

. whose base is at least fifty feet above ground level surface.

I The following definitions are used by weather observers in recording hourly occurrence of fog, ground fog or ice fog.

Fog is any restriction to horizontal visibility of 6 miles or less and of sufficient depth so that sky conditions can not be seen from ground level. The restriction may be due to a combination of fog with haze, smoke or other factors or combinations of factors.

Ground fog is similar to fog except that sky conditions can be seen by a ground level observer.

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Ice fog is similar to fog except that ice crystals are ob-served instead of liquid water droplets.

The atmosphere is termed " stable" when the ambient condi-tions are suitable for suppressing vertical motions, and hence, suppressing vertical mixing. The atmosphere is con-sidered to be " unstable" when ambient conditions are such as to enhance vertical motions and vertical mixing. Stability is related to the atmospheric wind and the vertical tempera-ture structure.

observational experience with atmospheric diffusion and turbulence has been classified into a simple scheme of sta-bility classes which are related to the ambient wind and the temperature structure. These stability or diffusion categories range from Category A (large dispersive power and unstable) to Category F (poor dispersive power and stable).

Winter season includes the months of December, January and February.

Average Midland winter morning is typified by winds of 6 mph (3m/s), mean minimum air temperature of 18.4F (-7.6C), rela-tive humidity of 82 percent, and atmospheric stability category nf E.

( Extreme Midland winter morning is typified by winds of 4 mph (2m/s), air temperature of 0F (-17.8C), relative humidity of 82 percent, and atmospheric stability category of F.

Scenario A is an average Midland winter morning.

Scenario B is an extreme Midland winter morning.

1

THE MIDLAND PLANT COOLING POND s SITE DESCRIPTION The Midland Plant utilizes an 880 acre pond as the primary means of rejecting heat from the condenser recirculating cooling water system. The principal modes of heat dissipation from the pond are evaporation, conduction and radiation.

In addition to the cooling pond, the Midland Plant also incor-porates a Service Water Cooling System, SWCS, and a Blow Down Cooling System, BDCS. The SWCS is used to provide an extra means of cooling the service water system. The BDCS is required for final cooling of pond water blowdown before discharge into the Tittabawasee River.

The plan of the Midland Plant site is shown in Figure 1. This shows the location of the power plant and the cooling pond.

The cooling pond dike will extent about 5 feet above the normal water level. The dike will vary in height above the surrounding, i. e., outside of the pond, natural grade by about 2 feet at the Southwest corner to about 31 feet at the Northwest corner. The plan of the SWCS and BDCS cooling towers is shown on Figure 2.

CLIMATOLOGY

( Weather data for the Midland area show that the mean temperature for the winter months is 26F and for summer is 70.3F. The mean daily maximum and minimum temperatures for January are 31.9F and 17.3F and for July are 84.lF and 60.4F. Temperatures reach the 100-degree mark in about one summer out of six and days with 90 degrees or above average 14 per summer. At the other extreme, temperatures fall to zero or lower on an average of six times during the winter season.

The mean daily maximum and minimum relative humidities for January are 82% and 72% respectively.

Average annual rainfall amounts to 29.8 inches. Precipitation is heaviest during the crop season and averages 58 percent of the annual total during the six months of April through September. The heaviest rainfall is in June with an average of 3.15 inches.

Snowfall totals 33.3 inches during an average winter at Midland.

However, there has been considerable variation in seasonal totals with amounts ranging from as little as 11.8 inches in the 1932-33 season to as much as 72.4 inches in the 1951-52 season. Measurable amounts of snow have occurred on eight of the twelve months but there are usually only five or six months in which measurable amounts are recorded.

Cloudiness is greatest in the late fall and early winter, a condition accentuated in Michigan's Lower Peninsula by the

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presence of Lake Michigan on the west and, to some extent, Lake Huron on the east. Prevailing wind direction in the area is southwest and average hourly speed is greatest in the early spring and lowest in late summer and early fall.

COOLING POND THERMAL DESCRIPTION Under maximum guaranteed loaC on both units, the cooling pond will be rejecting 7.69 x 109 Btu /hr of heat, The mean surface temperatures for the months of the year are shown in Figure

3. The maximum temperature is 97F and occurs in July. The minimum temperature is 62F and occurs in January. These values were derived from hydraulic and thermal model tests (Ferron, 1970) and calculations related to the power plant design and the climatology of the Midland Plant area. Isotherms for January of the cooling pond surface temperature are shown in Figure

4. The mean flow path of the water is about 3 miJes between the outlet and inlet.

SERVICE WATER COOLING SYSTEM DESCRIPTICN This description is based on preliminary studies. A three-cell mechanical draft cooling tower standing 48 feet wide, 90 feet long and about 60 feet overall height is envisaged.

The total heat duty is 200 x 106 Btu /hr. During the summer months the cooling system will be operating and would pro-duce about 170,000 lb/hr of water vapor eritted into the air.

During other seasons, the cooling pond will perform the cooling function of the SWCS.

BLOWDOWN COOLING SYSTEM DESCRIPTION This description is also based on preliminary studies. The design indicates a 7-cell structure 48 feet wide,'210 feet long and about 60 feet high. The following listing indicates l the approximate average water vapor emission from the cooling tower.

I l January April July October Water Evap., 103 lb/hr 163 360 None 315 In operation, the flow is adjusted to maintain the required 1 degree Fahrenheit temperature difference between the river water and blowdown water.

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5 Both the SWCS and the BDCS cooling towers are located in Figure 2. This figure, itself, is preliminary in nature and shows more cooling cells than described above. The above description represents the best estimate to date, and Figure 2 shows the location of the cooling towers.

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STUDY PONDS

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An experimental program was conducted to develop data bearing on criteria for frequency of occurrence of steam fog, its extent downwind and any icing effects from~1arge operating cooling ponds. The two cooling ponds studied are described below.

COFFEEN PLANT The first series of tests were made at the Coffeen Plant of Central Illinois Public Service Company at Coffeen, Illinois.

Figure 5 shows the general plan of the power plant and the cooling pond. The cooling pond is formed by a dam across the junction of two small streams. The pond is 1100 acres in area, with irregular and wooded shorelines, set in small natural valleys. At the time of the fog tests, one power unit of 365 Mwe capacity was operating, but the power load was variable.

The climatology of the Ccffeen Plant is similar to that of Hillsboro, Illinois, the closest reporting weather station.

At Hillsboro, the mean temperature for the winter months is 32.2F and for summer is 75.6F. The mean daily maximum and minimum temperatures for January are 39.4F and 21,6F and for July are 89.9F and 65.3F respectively._ The mean daily

( maximum and minimum relative humidities in' January are 85%

and 73% respectively. Annual rainfall is 38.3 inches, of l

which 59 percent falls during the months of April through September. No snowfall records are kept at Hillsboro but at l nearby Vandalia an average of 13.4 inches per year is reported.

The cooling pond heat load, with Unit No. 1, varied from 0.5 to 1.0 x 109 Btu /hr depending on the percent of capacity operational mode being followed. The pond heat load, con-sequently, varied between 0.45 to 0.9 x 106 Btu /hr/ acre.

The mean flow path from the flume outlet to the intake structure is about four miles, somewhat longer than the mean flow path length of 3 miles for the Midland Plant or the 4-Corners Plant ponds. The mean winter pond water tempera-ture sampled varied from 41-69F. The temperature of the water diminishes rapidly downstream of the discharge canal outlet with only one unit operating.

4-CORNERS PLANT The 4-Corners Power Plant is operated by Arizona Public Service Company (APS) and is located near Fruitland, New Mexico. All fog tests subsequent to those taken at the Coffeen Plant.were conducted on the 4-Corners Plant cooling pond. Figure 6 shows a plan of the plant, pond and locations of the major fog test and ice test stations. The cooling pond was formed l

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by placing an earth dam across a valley. The pond is supplied

(~ with make-up water from the San Juan River, about 3 miles away. The area is of high messa formations interspersed by washes and broad valleys. Rock and sandy surfaces covered by low brush predominate. The cooling pond area is 1200 acres with no dominant shoreline up-slopes. To the west, beyond the dam, the land is generally lower than pond surface by about 100 feet and broadly extends many miles westward at this lower elevation.

At Fruitland, the mean temperature for the winter months is 31.7F and for summer 72.5. The mean daily maximum and minimum temperature for January are 42.7F and 16.6F and for July are 92.7F and 57.2F respectively. The mean daily maximum and minimum relative humidities for January are about 70% and 46%

respectively. Annual rainfall is 7.0 inches of which 53 per-cent falls within the months of April through September. No snowfall records are kept at Fruitland but at nearby Aztec Ruins National Monument an average snowfall of 21.6 inches per year is reported.

There are five power units now operating at the 4-Corners Plant. The Unit No. and its capacity in megawatts are as follows. No. 1-175, No. 2-175, No. 3-225, No. 4-750 and No. 5-750. During the January 1970 tests, only Unit Nos.

1, 2 and 3 were operating. Before December 1970, Unit No. 4 was operating and before the last extended series of tests starting in October, 1971, Unit No. 5 was operating. All units are not always operating at the same time due to load demand or maintenance requirements, and if they are operating, they may not be at full capacity. For this reason, the heat rejection to the cooling pond varies. However, thermographs show that the surface water temperature changes very slowly

-on a time scale of days- and are as responsive to weather changes as to heat load changes.

If Units 1, 2, 3 and 4 only are operating at full capacity during winter conditions, the heat load rejected to the pond is about 6.5 x 109 Btu /hr or 5.4 x 10 6 Btu /hr/ acre. If all units are operating, similarly, the heat load is about 10 x 109 Btu /hr or 8.4 x 10 6 Btu /hr/ acre. The mean flow path of the pond water is about 3 miles from outlet to inlet.

i COOLING PONDS

SUMMARY

A summary of the cooling pond characteristics for the Midland Plant, Coffeen Plant and the 4-Corners Plant are shown in l Table 2. The mean water temperature range given for the Midland Plant are taken from Figure 3. The corresponding values for the test ponds were the highest and lowest tempera-tures sampled and used subsequently to form the data base for the fog occurrence criteria. The heat load data for the Midland Plant is for maximum guaranteed load on both units.

i l

1 The heat load data given for the other plants should not 1

imply that all indicated units were on or at full power all the time when the fog tests were being made.

TABLE 2 COOLING POND COMPARISONS Midland Coffeen 4-Corners Plant Plant Plant Units 1-4 Units 1-5 Location Midland,Mich. Coffeen,Ill. Fruitland, N.M.

Pond Area, acres 880 1100 1200 1200 Heat Load, 109 Btu /hr 7.69 1.0 6.5 10 HeagLoad, 5.4 10 Btu /hr/ac 8.75 0.91 8.4 Mean Winter Water Temp., F 61-68 41-69 53-68 56-80 i

_._ _ - . _ _ _ . , , -- _ _ _ ._ _ ~ _ _. _ _ _ _

FIELD PROGRAM

( !

The field program to obtain data on cooling pond fog and ice '

may be considered to fall into two general categories, depend-ing on when the investigations were made and the reporting period. The two field programs are described below.

PRELIMINARY PROGRAM The first fog studies were made in the months of February and March, 1969, at the Coffeen Plant cooling pond. This was followed by studies made at the 4-Corners Plant cooling pond during January and December, 1970 and January and April, 1971.

The results of this work, anc analyses, were reported as

" Interim Report, The Environmental Effects of the Midland Plant Cooling Pond' dated June, 1971. The purpose of the Interim Report was to present the data and its application to the Midland Plant on the basis of the information then available.

All of the results of the preliminary program, and the Interim Report, updated, are incorporated in this present summary report of all tests.

During periods of optimum fog conditions, defined below, the area about the pond was traversed in a predetermined pattern to collect temperature, moisture and wind data. Supplementary data were obtained from the power plant and the nearest first

( order weather station.

~

A period of " optimal fog condition" was characterized by light winds, clear skies, inversion conditions, and sub-freezing weather to maximize air-water temperature difference and to reduce the water vapor holding capacity of the air.

In the fog and ambient air, observations were made of dry and wet bulb air temperatures, surface wind speed and direction, total water content of the air. Downwind of the cooling pond, the thickness of ice accumulated on upright objects of 1 cm and 5 cm diameters, and on power poles and flat horizontal surfaces were documented.

Plant data included condenser intake and discharge flow and temperature, and water temperatures along flow path. Weather station data included synoptic hourly surface wind speed and direction, cloud cover and ceiling, air temperature and dew point temperature.

The conclusions of the Interim Report showed the criteria for the occurrence of steam fog is a water-air temperature differ-ence equal to or greater than 33F, winds equal to or greater than 3 knots, and stability category c, D, E or F. Stratus

(

9

~

would occur under similar conditions except the surface wind

- speed is less than 3 knots. When applied to the Midland Plant

( pond, the results indicated maximum pond fog in any single 22.5 sector, with no natural fcg present, occurrence for the year of 5.7 percent of the hours with west southwest winds. For all directions, pond-induced steam fog was estimated to occur 44 percent of the time annually. Natural fog occurred 10.8 percent of the annual hours. Depending on the deposition process, the plume in winter would normally extend 1/2 to 3 miles downwind of the pond in the winter. The frost or ice and snow deposition from the fog plume was discussed.

RECENT PROGRAM From October 6, 1971, through December 21, 1971, a semi-continuous study of steam fog occurrence and measurement of meteorological variables in the fog and ambient air were made at the 4-Corners Plant cooling pond. This intensive study was undertaken to provide a larger base of data from which to develop more re]iable steam fog occurrence criteria than hithertofore possible. With this expanded data base, the possibility would exist for a statistical treatment of the results instead of the categorical "yes" or "no" occurrence frequency criteria previously developed.

In addition, the recent study program expanded the data base in regard to the extent of the fog and/or stratus, and frost or icing effects on vertical and horizontal surfaces.

During the recent program, records were kept of the operational condition of the five power units et the plant. This record was made upon first arrival of the observer at the pond and usually coincided with sunrise. Figure 7 shows the record of results. This record does not indicate level of power opera-tion when the unit is on, or when the unit came on before the observation or at what time thereafter it went off, if this

! occurred. For special' tests, plant data were taken including condenser intake and discharge flow and temperature. These

. were used to calculate heat loading of the pond.

The observational procedure for the recent program was similar to that previously used, but expanded in detail and scope. A special ice test station was built to obtain data on accretion i of ice at elevations of 1, 10 and 20 feet above the ground surface. Special fog droplet size measurements, discussed later, were made by MRI, Inc. Two pond surface temperature traverses by boat were made. Records of pond surface temper-ature stations kept by Arizona Public Service were analyzed.

The pond was regularly sampled on all four sides for surface water temperature.

L

FOG STUDY DATA BASES 4

a. Pond Temperature Studies During the most recent study of the 4-Corners pond, the observer made routine measurements of surface water temper-ature from the shore at test stations 1-4 inc, see Figure 6.

However, during the period of study, the lake level varied enough to make questionable the validity of the surface.

temperature data. As lake level rose or fell, the shallowness near the banks increased or decreased, especially at Station 2 and 4. Another effect on temperature data was the inflow from the flume of cold make-up water and the changing patterns of the surface isotherms due to changing wind speed and direction.

To obtain a better definition of surface water temperature distribution, two surveys were made by the APS boat on the pond surface. These were conducted on October 21-22, 1971.

An example of the results for the first test are shown in Figure 8. The results of the 2nd test are similar. An analy-sis of the results in terms of mean pond surface temperature and a comparison of the shore-side temperature results for the same days showed that the most representative shore-side values were obtained by taking the average of Station 1 and 2 and adding 50F. This new mean surface water temperature is called the " calculated" water temperature.

i Subsequently, long-term surface water temperature data recorded by APS at their mid-lake recorder No. 4, see Figure 6, became available. Figure 9 shows a comparison of the calculated mean surface temperature data and the recorded data. The scatter of the calculated data, and the question of its original valid-ity, suggested that it be smoothed to correspond to the APS recorded data. This was done. After November 21, 1971, no additional APS data was collected, so from that period on, a smooth line through the calculated data was generated. The results are shown in Figure 10, and are the average water temperature values used in the most recent program study.

From the information developed in the most recent program, the water temperature results reported in the preliminary program for 4-Corners were reviewed and calculated data used in their

[ place.

b. Steam Fog Data A listing of all the significant fog test data is ;iven in Table 3. Table 3 summarizes all the obse'rvati'n o obtained in the program of fog, fog-stratus, stratus, slight fog or no fog together with their ambient air conditions and mean pond N

! , - . .- - _~ ., - - - . - . . - . -.

- ,~ ,-

TABLE 3 FOG TEST DATA A t, I" **/

Ambient Air Conditions Water t -t At Test Stah. Wind Tgmp. RII Tgmp. e -e e -e e -e No. Date Time Fog

Cat. mph F % F F Mbss gbsa s a Coffecn Plant Cooling Pond i 1 2-13-69 0130 SLF F 4 21 88 56 35 ,11.6 0.4 87.5 g 2 2-13-69 0145 NO F 4 21 88 48 27 7.7 0.4 67.5 8 3 2-13-69 1000 NO B 2 25 65 54 - 29 9.8 1.5 19.3 4 2-13-69 2315 FOG F 1 24 87 69 45 20.1 0.5 90.0 5 2-14-69 0050 SLF E 5 25 73 59 34 12.6 1.2 28.3 6 2-14-69 0640 SLF E 3 23 77 62 39 15.0 0.9 43.3 7 2-14-69 0800 NO D 10 25 78 55 30 10.4 1.0 30.0 l 8 3-11-69 0115 SLF F 3 18 78 61 43 15.1 0.7 61.4 1

9 3-11-69 0230 NO F 3 18 78 50 32 9.1 0.7 45.7 10 3-11-69 2215 FOG F 0.5 17 83 64 47 17.4 0.5 94.0 11 3-11-69 2325 FOG F 0.5 17 83 68 51 20.4 0.5 102 12 3-11-69 2335 FOG F 0.5 17 83 66 49 18.8 0.5 98.0 13 3-11-69 2355 FOG F 0.5 17 83 64 47 17.4 0.5 94.0 14 3-12-69 0015 FOG F 0.5 19 80 64 45 17.1 0.7 64.3 15 3-12-69 0035 NO F 0.5 19 80 54 35 10.9 0.7 50.0 16 3-12-69 0040 NO F 0.5 19 80 52 33 9.9 0.7 47.1 17 3-12-69 0110 NO F 0.5 19 80 41 22 5.4 0.7 31.4 18 3-12-69 0630 ST F 0 14 93 63 49 17.0 0.2 245

c .a ,-

I atj Indexf Ambient Air Conditions Water t -t At Test Stab. Wind RH " " -e Tgmp. Tgmp. e -e e -e No. Date Time Fog

Cat. mph '

F F F e$bss mbs a s a 4-Corners Plant Cooling Pond 19 l-30-70 0620 FOG' F 2 14 65 55 41 12.2 0.9 45.6 20 1-31-70 0010 NO E 5 34 23 56 22 8.7 5.1 4.3 21 12-16-70 0710 FOG E 7 21 84 68 47 19.7 0.6 78.3 22 12-16-70 0805 FOG E 9 24 59 68 44 19.2 1.7 25.9 23 12-16-70 0920 FOG D 11 30 54 68 38 17.8 2.6 14.6 24 12-16-70 1800 NO C 6 36 48 68 32 16.2 3.7 8.6 25 12-17-70 0750 NO D 13 29 67 63 34 14.3 1.7 20.0 26 1- 6-71 0715 FOG D 4 -12 ^- 4 5 56 68 14.6 0.4 170

, 27 1- 7-71 0700 Sr F 3 -14 ~ 50 53 67 13.1 0.3 223

' e 28 4- 2-71 0630 SLF F 0.5 26 39 67 41 17.9 2.8 14.6

? 29 10- 6-71 1625 NO B 0 74.0 24 80.0 6.0 6.4 21.7 0.3 30 0- 7-71 0720 SLF F -3 43.6 76 80.0 36.4 25.4 2.3 15.8 31 .0- 7-71 0900 NO C 5 53.5 55 80.0 26.5 21.1 6.3 4.2 32 10- 8-71 0730 SLF C 2 47.8 73 80.0 32.2 23.6 3.1 10.4 33 10- 8-71 0830 NO C 5 55.0 55 80.0 25.0 20.2 6.7 3.7 34 10- 9-71 0730 SLF D 4 45.3 71 80.0 34.7 24.6 3.0 11.6 35 10- 9-71 0858 NO C 4 55.2 52 80.0 24.8 20.1 7.2 3.4 36 10-10-71 0715 SLF F 0 45.0 76 80.0 35.0 24.8 2.4 14.6 37 10-10-71 0850 NO C 4 52.8 61 80.0 27.2 21.3 5.3 5.1 38 10-11-71 0725 SLF F 3 44.2 67 80.0 35.8 25.1 3.3 10.8 39 10-11-71 0826 NO C 3 52.5 56 80.0 27.5 21.5 5.9 4.7 40 10-12-71 0722 SLF F 0.5 41.0 67 80.0 39.0 26.3 2.9 13.4 41 10-12-71 0900 NO B 2 51.5 50 80.0 28.5 22.0 6.5 4.4 42 10-13-71 0725 SLF F 4 43.2 59 80.0 36.8 25.5 3.9 9.4 43 10-13-71 0751 NO D 17 54.5 70 80.0 25.5 10.5 4.5 5.7 44 10-14-71 0730 SLF D 4 42.0 64 80.0 38.0 25.9 3.3 11.5 45 10-14-71 0910 NO C 5 53.0 49 80.0 27.0 21.3 7.0 3.9 46 10-15-71 0728 SLF F 4 45.5 60 79.8 34.3 24.5 4.1 8.4

3 Index, Ambient Air Conditions Water t -t At Test Stab. Wind " ^

Tgmp. RH Tgmp. e -e e -e e -e No. Date Time Fog

Cat. mph F U s s a

%_ P P Mbs Ebsa 47 10-15-71 0910 NO D 12 53.0 49 79.8 26.8 21.1 7.0 3.8 48 10-18-71 0809 FOG E 4 35.5 86 83.0 47.5 31.4 1.0 47.5 49 10-19-71 0726 FOG-ST F 1 28.0 77 77.2 49.2 26.8 1.2 41.0 50 10-19-71 1300 SLF B 3 45.5 61 77.2 31.7 21.6 4.0 7.9 51 10-20-71 0737 FOG-ST C 3 32.5 82 76.8 44.3 25.3 1.1 40.3 52 10-20-71 1000 SLF B 2 45.5 61 76.8 31.3 21.2 4.0 7.8 53 10-20-71 1152 NO A 0 52.0 50 76.8 24.8 18.3 6.6 3.8 54 10-21-71 0730 SLP E 5 41.0 65 76.2 35.2 22.0 3.0 11.7 55 10-21-71 1223 NO D 4 57.0 24 76.2 19.2 14.8 12.1 1.6 56 10-22-71 0745 SLF D 4 39.5 82 75.9 36.4 22.2 1.5 24.3 57 10-22-71 1100 NO A 1 49.5 56 75.9 26.4 18.4 5.3 5.0 58 10-23-71 0732 SLF D 6 36.5 71 75.6 39.1 22.9 2.1 18.6 b 59 10-23-71 1115 NO C 8 59.5 43 75.6 16.1 12.8 9.9 1.6

? 60 10-24-71 0730 NO D 11 52.0 58 75.3 23.3 16.8 5.5 4.2 61 10-25-71 0732 SLP P 1 41.0 92 74.7 33.7 20.6 0.7 48.1 62 10-25-71 1000 NO C 4 54.5 75 74.7 20.2 14.8 3.6 5.6 63 10-26-71 0720 SLF F 2 40.0 86 73.9 33.9 20.2 1.2 28.3 64 10-27-71 0732 SLF C 1 35.0 91 73.0 38.0 20 8 0.6 63.3 65 10-27-71 1200 NO B 6 56.5 57 73.0 16.5 12.1 6.7 2.5 66 10-28-71 0716 NO D 12 45.0 52 72.0 27.0 16 6 4.9 5.5 67 10-29-71 0728 NO D 11 48.0 63 71.0 23.0 14.6 4.2 5.5 68 11- 2-71 0711 ST C 0 25.5 97 68.0 42.5 18.9 0.1 425.0 69 11- 2-71 1010 NO C 4 42.2 52 68.0 25.8 14.2 4.4 5.9 70 11- 3-71 0628 FOG-ST F 1 28.0 89 67.5 39.5 17.8 0.6 65.8 71 11- 3-71 0915 NO B 1 40.0 50 67.5 27.5 14.5 4.2 6.5 72 11- 4-71 0640 FOG F 3 28.0 74 67.0 39.0 17.4 1.3 30.0 73 11- 4-71 0850 NO B 2 41.5 51 67.0 25.5 13.6 4.4 5.8 74 11- 5-71 0650 SLF D 5 33.5 69 66.8 33.3 15.9 2.0 16.7 75 11- 5-71 0805 NO C 3 40.0 47 66.8 26.8 14.0 4.5 6.0 76 11- 6-71 0655 SLF C 1 29.0 69 66.7 37.7 16.9 1.6 23.6 77 11- 6-71 0907 NO B 2 43.0 47 66.7 23.7 12.8 5.0 4.7 4 -

~

A t, " **'

Ambient Air Conditions Water t,-t a At Test Stab. Wind Tgmp. RH Tgmp. e -e e -e e -e No. Date Time Fog

Cat. mph F F F Mbss Ebsa s a i

} 78 11- 8-71 0656 SLP F 0 31.0 71 66.5 35.5 16.3 1.7 20.9 79 11- 8-71 0900 NO C 4 43.0 58 66.5 23.5 12.7 3.9 6.0 i 80 11- 9-71 0655 SLF F 4 30.0 70 66.5 36.5 16.5 1.7 21.5 j 81 11- 9-71 0845 NO C 7 43.0 50 66.5 23.5 12.7 4.7 5.0 82 11-10-71 0703 SLF C 0 28.0 69 66.5 38.5 17.0 1.6 24.1 83 11-10-71 0808 NO C .3 39.0 50 66.5 27.5 14.0 4.0 6.9

. 84 11-12-71 0707 NO C 1 38.5 52 66.5 28.0 14.2 3.8 7.4 4

85 11-15-71 0716 FOG-ST D 6 38.5 93 67.3 28.5 14.9 0.6 47.9 86 11-15-71 1008 NO D 0 45.0 84 65.5 20.5 11.2 1.6 12.8 87 11-16-71 0715 FOG C 1 35.5 92 65.0 29.5 13.9 0.6 49.2 88 11-16-71 0907 NO B 0 39.5 80 65.0 25.5 12.8 1.6 15.9 89 11-17-71 0700 FOG D 24 32.0 91 66.2 34.2 15.9 0.5 68.4 L 90 11-17-71 1045 NO D 34 38.0 67 64.5 26.5 13.1 2.5 10.6 H' 91 11-18-71 0755 SLF D 15 28.0 64 65.5 37.5 16.3 1.8 20.8 92 11-18-71 0952 NO D 17 33.0 55 6'.8 30.8 13.8 2.9 10.6 93 11-19-71 0714 FOG C 2 20.5 85 63.7 43.2 16.5 0.5 86.4 94 11-19-71 1040 NO B 1 34.0 62 63.7 29.7 13.5 2.5 11.9

! 95 11-20-71 0720 ST C 0 23.0 81 63.6 40.6 16.1 0.8 50.8 5

96 11-20-71 0900 NO B 0 34.5 54 63.6 29.1 13.3 3.1 9.4 .

97 11-21-71 0725 SLF D' 2 28.5 85 63.5 35.0 14.8 0.8 43.8

! 98 11-21-71 1100 FOG D 11 42.0 69 63.5 21.5 10.9 2.8 7.7 l 99 11-22-71 0718 FOG D 3 30.0 94 65.2 35.2 15.6 0.3 11.7 j 100 11-22-71 1100 SLF D 18 36.5 83 63.5 27.0 12.7 1.2 22.5

101 11-23-71 0711 ST C 0 26.0 88 63.5 37.5 15.4 0.6 62.5 I 102 11-23-71 0742 ST C 0.5 27.0 95 63.5 36.5 15.2 0.2 183 103 11-23-71 1045 NO B 0 41.0 75 63.5 22.5 11.3 2.2 10.2 104 11-24-71 0716 FOG-ST D 7 29.0 90 63.5 34.5 14.7 0.5 69.0

! 105 11-30-71 0725 FOG D 5 27.0 84 63.5 36.5 15.2 0.8 45.6 j 106 11-30-71 1115 NO B 0 39.0 74 63.5 24.5 11.9 2.1 11.7 107 12- 1 0730 SLF C 3 32.0 62 63.5 31.5 13.9 2.3 13.7 j 108 12- 1-71 0930 NO D 10 36.0 56 63.5 27.5 12.8 3.2 8.6

, e' s l

l l

l Index, A t, Ambient Air Conditions Water t -t w a At Test Stab. Wind Temp. RH Tgmp. e -e e -e e -e Mbss s a l No. Date Time Fog

Cat. mph F %_ F F Mbsa 109 12- 2-71 0726 SLF D 5 30.5 81 63.4 32.9 14.2 1.1 29.9 110 12- 2-71 1200 SLF D 5 36.0 86 63.4 27.4 12.7 1.0 27.4 111 12- 3-71 0905 NO D 0 35.5 78 63.2 27.7 12.7 1.5 18.5 112 12- 4-71 0755 FOG D 6 21.0 80 63.0 42.0 15.9 0.7 60.0 113 12- 4-71 1245 SLF B 2 32.0 76 63.0 31.0 13.5 1.5 20.7 114 12- 5-71 0726 FOG-ST C 1 19.0 85 62.5 43.5 16.1 0.5 87.0 115 12- 5-71 1310 SLF B 1 31.0 67 62.5 31.5 13.6 1.9 16.6 116 12- 6-71 0750 FOG D 11 21.5 86 62.1 40.6 15.4 0.5 81.2 117 12- 6-71 1237 NO D 11 35.0 68 62.1 27.1 12.2 2.2 12.3 118 12- 7-71 0806 FOG C 2 29.5 84 61.7 32.2 13.4 0.9 35.8 119 12- 7-71 0910 NO C 0 39.5 58 61.7 22.2 10.6 3.4 6.5

120 12- 8-71 0826 FOG D 10 24.5 95 63.0 38.5 15.3 0.2 193 121 12- 8-71 1210 FOG D 9 31.0 80 63.0 32.0 13.8 0.8 40.0

. 0 122 12- 9-71 0822 ST C 2 15.5 83 60.8 45.3 15.4 0.5 90.6 y 123 12- 9-71 1230 SLF B 1 27.0 68 60.8 33.8 13.4 1.5 - 22.5 124 12-10-71 0750 FOG-ST D 8 19.0 85 60.0 41.0 14.4 0.5 82.0 125 12-10-71 1230 NO D 11 36.0 43 60.0 24.0 10.5 4.1 5.9 126 12-11-71 0806 SLF C 2 25.5 82 59.5 34.0 12.9 0.8 42.5 127 12-11-71 0933 NO B 3 39.5 47 59.5 20.0 9.2 4.3 4.7 128 12-12-71 0752 FOG D 11 16.0 68 58.7 42.7 13.9 0.9 47.4 129 12-12-71 1145 NO- C 6 30.5 71 58.7 28.2 11.1 1.7 16.6 130 12-13-71 0815 FOG D 7 29.0 94 58.0 29.0 11.1 0.3 96.7 131 12-13-71 1230 NO D 1 34.5 88 58.0 23.5 9.6 0.8 29.4 132 12-14-71 0830 FOG D 29 18.5 71 58.8 40.3 13.7 0.9 44.8 133 12-14-71 1212 FOG D 25 27.5 52 58.8 31.3 11.9 2.4 13.0 134 12-15-71 0803 FOG C 2 20.0 72 56.9 36.9 12.3 1.0 36.9 135 12-15-71 1140 NO C 4 28.0 69 56.9 28.9 10.7 1.6 18.1 136 12-16-71 0812 FOG D 20 18.5 92 58.0 39.5 13.2 0.3 132 137 12-16-71 1200 FOG D 17 23.0 81 58.0 35.0 12.5 0.8 43.8 138 12-17-71 0805 FOG-ST C 3 12.0 72 56.5 44.5 13.2 0.7 63.6 139 12-17-71 1230 SLF B 1 23.5 58 56.5 33.0 11.5 1.7 19.4 140 12-18-71 0812 ST C 1 11.5 90 56.3 44.8 13.2 0.2 224

I c- ry 1

A t, Index, Test Ambient Air Conditions Stab. Wind Tgmp. RH Water Tgmp.

t"-t " e -e e -e At e -e r No. Date Time Fog

Cat. mph F O s s a

% F F _$bs Ebsa 141 12-18-71 1234 SLF D 5 22.5 69 56.3 33.8 11.6 1.2 28.2 142 12-19-71 0815 ST C 2 21.0 73 56.3 35.3 11.8 1.0 35.3 143 12-19-71 1200 NO B 0 30.0 65 56.3 26.3 9.9 2.0 13.2 144 12-20-71 0810 FOG C 2 15.0 91 56.3 41.3 12.8 0.2 207 145 12-20-71 1200 NO B 0 30.0 70 56.3 26.3 9.9 1.7 15.5 1

146 12-21-71 0710 FOG C 1 12.5 90 56.3 43.8 13.1 0.2 219

,l

< l fo Y

i

)

FOG is fog, SLF is slight fog, ST is stratus, NO is no Fog, SLF, or ST, FOG-ST is fog turning into stratus, j

i,

l I

water temperatures. The ambient air data was measured upwind e of the pond. The water-air temperature difference, t v-t a, is .

k listed for each case.

The table also shows, for each case, the values in millibars, mbs, of the vapor pressure difference between the water, e w, and the ambient air if saturated, e; s the values in mbs of the vapor pressure difference, i.e. the saturation deficit, between es and the ambient air at its humidity value, e; a and finally a fog index number, At/(e -e s )

a . The fog index number, de-veloped in this study, is a fog predictor. This is discussed below.

c. Comparisons of Fog Data Figure 11 shows the data cases when At, water-air, is arrayed as a function of wind speed. This shows that pond fog has been observed in winds up to 28 mph and at At's down to 21.5F, although most fog or stratus cases are concentrated in the higher at regioru. Slight fog was not found at a at higher than 43F or lower than 25F; it was found from wind speeds from calm to 18 mph. Most slight fogs occupy the mid ranges of the at values, at the lower wind speeds, between the no-fog and fog cases. No-fog cases occur at the lower values of at and range from values of 6 up to 35. No-fog wind speeds range from calm up to 34 mph, the highest wind speed observed during the tests. The single fog criteria of at = 33F used in the

( Interim Report is consistent with these data,although the present larger body of data shows significant scatter about the At = 33F criteria.

l Figure 12 shows occurrence of fog, slight fog or no fog when l

At is compared to atmospheric stability category. The stabil-ity categorization was made by the method proposed by D. Bruce Turner (1964). No pond fogs or stratus were observed in cate-gories A and B. Many are found in all the other categories, particularly in the higher values of At. The slight fogs, as in Figure 11, occupy the middle ranges of at values, regardless i

of stability category. The no-fog cases dominate the lower at I values in all stabilities. These data fit qualitative expecta-l tions as one does not expect pond fog under good diffusion conditions in the mid-day periods when Categories A and B are normally found. The presence of fog cases at only the higher At values for Categories E and F is probably only a reflection that, with the lower wind speeds associated with these categories, j the at has to increase in order to transport sufficient sensible, radiant, and latent heat away from the pond.

l Figure 13 shows the relationship between at and vapor pressure difference of water-saturated ambient air, i.e., ew-e s. The

(

strong influence of at is again observed, as previously dis-J cussed. Fog cases are seen ranging from ew-e s values of 10.9

\ mbs up to 31.4 mbs. Fog cases, as expected, can occur with lower At's and lower ew -es's due to the inability of the air to hold the quantity of evaporated moisture. As seen previously in Figure 11, the lower At's contain mostly no-fog cases, regardless of e w-es. The slight fog cases occur mostly between the fog and no-fog cases.

Figure 14 displays the fog test data with at arrayed by the ambient air saturation deficit, e s-e a. This figure again re-veals the strong dependence on at for pond fog to occur. Also shown is the strong dependence on es -ea,which is a measure of the water vapor holding capacity of the air. Although a few cases of pond fog occur with es -e, values between 2.0 and 3.0, by far the greater numbers of fog cases occur with e -e s a values frul 0.1 up to 1.0. Most of these latter fog cases are also found in the at range from 34F upward. The occurrence of fog or stratus, slight fog or no-fog is more is more clearly defined in Figure 14 than in Figures 11-13.

d. Fog Index Number The concept of the teg index number was developed to provide a method for statistical analysis of all the fog, fog-stratus, stratus, slight fog and no-fog cases listed in Table 3. The O F/ (e -e ) , mbs. The basis for fog index number is simply ot, a

(

the relationship is shown in Figure $4, wherein is seen the greater the At and the smaller the saturation deficit, i.e., the smaller the e s -e a, the more prevalent the occurrence of pond fog or stratus. Thus pond fog is directly proportional to et and inversely proportional to e s-e a-l The objective of this analysis is to provide a statistical state-ment of the probability of occurrence of pond fog, fog-stratus, or stratus as a function of the fog index number.

As a first step, a listing was prepared, in ascending fog index numbers from 1 to equal or greater than 90, of all the Table 3 data cases. This listing was with respect to 1) combined fog, fog-stratus or stratus, 2) slight fog and 3) no fog. This listing was then divided into convenient class intervals for collection of data cases. In each class interval, the percent occurrence and mean fog index number of each of the three components above, was calculated. At fog index numbers 2 90, only fog, fog-stratus or stratus occurred.

The next step was to plot the percentage frequency of the fog /

stratus occurrence versus fog index number on a log probability i

graph. From this plot, mean fog / stratus occurrence frequency values were obtained for classes of fog index number of 0-9, x

i

10-19, 20-29, etc. to 90+. Finally, the midpoint values of the classes of fog index number, e.g., 5, 15, 25, etc. to k' 90+ were plotted against the percentage frequency of occurrence of fog stratus.

The results of the analysis are shown on Figure 15. The figure may be read as follows: Assuming a fog index number of, e.g.,

55, the probability of occurrence of fog, fog-stratus or stratus would be 69 percent. This probability analysis will be used later to provide the estimate of hours of occurrence -

of fog from the Midland Plant cooling pond..

I l

I

EXTENT OF FOG PLUMES STUDY k a. Steam Fog Plume Extenc Data Church (1945) reports that he has never seen steam fog flow inland more than 200 meters from the water's edge before dis-appearing. Decker (1970) reports of a plume extending 500 to 1000 meters downwind from a small hot pond. The Bechtel In-terim Report of June 1971 presented some steam fog extent data from the Coffeen and 4-Corners cooling ponds. Table 4 includes these data as well as the 4-Corners data acquired in the fall and winter of 1971. The data in this table shows plume extents ranging from a few tens of feet in fog to several miles in a stratus plume.

The fog extent data reported in this table are the distances along the ground that the fog remained in contact with the ground surface. In some cases, with relatively light winds, the steam fog flowing along the ground slowly lifted and formed a plume above the ground that then extended downwind for several miles as stratus. The dates of 10/19/71, 10/20/71, 11/15/71, 11/24/71, 12/5/71 and 12/10/71 are examples of this. If the winds were strong within the fog layer, this transition to stratus did not occur. The data are not unambiguous on this point because systematic efforts to independently (from the fog) estimate stratus extent were not made. However, the data suggest that 1/6/71, 12/4/71, 12/6/71, 12/20/71 and 12/21/71 might be examples of this situation. On the other hand there

( are some cases where no fog extent is reported,because there was no extent on the surface past the pond edge,but there was stratus. These were under almost calm winds where the steam fog rose almost vertically above the pond, and formed a stratus layer that slowly drifted downwind. The data of 3/12/69, 1/7/71, 11/3/71, 11/20/71, 11/23/71, 12/17/71, 12/18/71 and 12/19/71 are examples of this. In fact, the observer noted on 12/18/71 that there was a tendency for the light surface wind direction all around the lake to be toward the lake; i.e., the indraft to feed the rising column of steam stratus.

In examining Table 4 in detail,there are several thoughts which should be emphasized. These are:

1. The heat being dissipated by the pond is a function of the number of units running, their power rating (see earlier description of the rating of each unit), and the percent of rated capacity being used. The observer only noted which units were running. For approximately one-third of the fog cases reported, power plant heat discharge data was used to calculate pond heat loading as discussed later in this section. '

2. Fog moving onto the west shore at 4-Corners passes over a mile wide dam whose top is about 100 fu above the down-wind ground surface. One might believe that the downwind fog

\

l

? <-

y

/

TABIX 4 EXTENT OF PLUME DATA D01rfvIND 700 DOWNWIND EX'ITNT WIND POWut 700 DTME%Sa1NS FMM POND 72)CE P114E AMBIE W AIR SPEED UNITS INDEX At HEIGHT WIDIN lt)G, SIRAWS, CIr!O TD1P. BH, Inentes Dm T, ar SPEED, IN 70G, Tag cw.m . _ No. _ n. n. n. _xitzS saE 1, wa MPu mms Citt;en 02/13/69 2315 1 90.0 45.0 No Data No Data 120-180 None West 24.0 er 1 2 Coffsen 02/14/69 06k0 1 43 3 39 0 No Data No Data 120 100 None West Carrien 102.0 23 0 77 3 9 a 03/11/69 2325 1 $1.0 Nc,Cata No Data 150 450 None K.E. 17 0 Cofften 03/12/69 245 0 83 05 05 0630 1 49 0 N.A. N.A. N.A. n,300 ft. N.A. 14.0 93 0 0 b,e,4 h Corners 01/3c/70 0620 1,2,3,4 45.6 41.0 No Data 5,280 300 None West 14.0 65 2 19 4 Ctroero 12/16/70 M10 1,2,3,4 78 3 47 0 30 5,280 100 None West 21.0 84 4 Corners 1,2,3,4 7 19 12/16/70 0805 25 9 44.o No Data 5,28o 60 120 None West 24.0 59 21 4 Corners 01/c6/71 1,2,4,5 68.o 5,280 9 0T15 170.0 300 10,500 None West -12.0 45 4 12 -

4 Cornere 01/07/71 0700 1,2,4,5 223 0 67 0 N.A. N.A. N.A. 11+ West -14.0 50 4 4 Corners. 10/18/71 1,2,3,4 3 b,4 0809 47 5 47 5 1,320 30 7G None North 35 5 86 4 go 4 Corners 10/19/71 1,2,3,4 41.0 9 e UT55 49.2 500 5,280 3c 1/4 wet 28.o 77 1 7 3 4 Corners 10/2C/71 00C3 1,2,3,4 44 3 300 5,200 Poo f

4 Cornere 31/03/71 1,2,3,4 ko.} 10+ West 32 5 82 3 15 s C652 65. 39.5 50 2,640 50 1 West 23.0 89 1 1 4 Cornere 11/A/71 0705 1,2,3,4 30.0 39 0 10 5,280 60 4 C rners # None wat 28.0 74 3 13 1 L 9/71 0T13 1,2,4 21.5 36.5 10 5,280 100 None West 4 Cornera r.,15/71 0r16 1,2,3,4 30.0 70 4 13 a 31.2 18 7 600 5,280 $00 3 East 38.5 93 6 e 4 Corners 11/16/71 1,2,3,4 49.2 7 0735 29 5 30 5,280 300 Iwe weet 35 5 4 Corners 11/17/71 0700 1,2,3,4 68.4 34.2 200 3,700 92 1 9 1,000 None East 32.0 91 24 15 e 4 Cerners 11/18/71 0718 1,2,3,4 20.8 37 5 10 100 4 C:,rners 300 hoan East 28.0 64 15 15 a,e 11/19/71 0737 1,2,3,4 86.4 43 2 15 5,280 100 None wet 20.5 2 4 C:rrars 11/20/1 1,2,4 85 8 7 OT20 $0.8 40.6 N.A. N.A. None No Data N.A. 23 0 81 0 0 4 Carners 11/21/71 1100 1,2,3,4 b 77 21 5 20 5,280 500 None West 42.0 0 11 20 h 4 Corners 11/22/71 UT18 1,2,3,4 117 0 35 2 100 3,700 400 None East 30.o 94 3 15 4 C;rners 11/23/71 0711 1,2,3,4 62.5 37 5 N.J.. N.A. None N.A. 26.o 88 4 Carners 11/23/71 0742 1,2,3,4 5+ o o i 183 0 36.5 N.A. N.A. None 5+ N.A. 27.o 0.5 4 Cornere 11/24/71 0716 (2,3,4 69 0 34.5 600 5,200 95 0.5 6 490 3+ West 29.o 7 9 4 C*rners 11/10/71 0745 1,2,3,4,5 45.6 36.5 100 5,280 20 4 Carnere 500 Mone West 27 0 <* 5 21 12/ % /71 0815 1,2,3,5 60.o 42.0 300 5,2% 5,280 None West 21.0 80 6 4 C rners 12/05/71 1,2,3,5 26 OT51 87 0 43 5 ~600 5,280 5,280 10+ West 19.0 85 1 4 4 Corners 12/06/71 0812 2,3,5 81.2 ko.6 200 5,28o 5,280 None West 21.5 86 11 25 b Corners 12/or/71 0806 2,3,5 35.8 32.2 10 5,280 Comment None West 29 5 84 2 0 4 CIrners 12/08/71 0758 2,3,5 193 0 38.5 300 5,280 J 4 Corners 500 None East 24.5 95 10 6 e,k 12/C8/71 1210 2,3,5 40.0 32.0 150 5,28o 100 . r,e s.E. 80 4 Crrners 12/09/71 0822 2,3,5 31.0 9 9 e,k 90.6 45 3 N.A. N.A. Mone No Data N.A. 15 5 83 2 2 b 4 Corraers 12/10/71 0815- 2,3,5 82.0 41.0 300 10,500 1,320 4 C m.ere 12/12/71 0818 3+ N.t. -19.0 85 8 9 .

2,3,5 47 4 42 7 100 5,200 4fr) None West 16.0 68 11 26 4 Corners 12/13/71 0815 1,2,5 96.7 29 0 200 5,280 4 Corners 15o None West 29 0 94 7 20 1 12/lb 71 0808 1,2,3,5 44.8 40 3 30 4,000 500 None 8.E.

4 Corners 12/lb 71 1200 1,2,3,5 18.5 71 29 28 e 13 0 31 3 20 4,000 300 None S.E. 27 5 52 25 24 4 Cornero 12/1571 1,2,5 e 0830 36 9 36 9 10 5,280 100 None West 20.0 2 10 72

__J

,e 1-s TAB 12 4 (Continued) 22 TENT OF PLUME DATA DOWifW7YJ F00 DOWNWIND EK'IENT POWER FOO DDFE.SION3 VIND FROM 70MD 111CE P:ANE AMBIENT AIN

!!NI'IS INDEX At , HEIGHT WIDTN FOG, SPEED TACATION DATE _TTW OPER. NO. O F M.

S11tARIS, Offf0 tutP. Mf, SPEED, IN F00, M. FT. MIIFS Entre OF 1 _WW WN IBOITS 4 Corners 12/16/71 7155 1,2,5 132.C 4 Corners 39 5 No Data No Data 100 None ,S.E.

12/16/71 1200 1,2,5 43.8 35.0 18.5 92 20 12 e,t 4 Corr.cre 300 5,260 500 None S.g.

12/17/71 0823 1,2,3,5 63 6 4. 5 500 5,280 23 0 81 17 20 h Corners No Dat e 10 west 12.0 12/18/71 0812 1,3,5 224.0 M.$ N.A. N.# . N.A.

72 3 13 b Corners 12/19/71 0615 1,5 No Data N.A. 11.5 90 35 3 35 3 N.A. N.A. N.A. No Data 1 1 b 4 Corners 12/20/71 0825 1,5 2er.0 N.A. 21.0 73 2 2 b b Ccrners 41 3 100 5,200 300 None west 15.0 12/21/71 &I35 1,5 219 0 43 8 20 5,280 200 91 2 13 None West 12 5 90 i 1 16 FJ W

I NOTES:

a. Slight fog conditions with wisps onto shore.

b. Condition is stratus.

5

c. Extent data is for height of plume.

d. N.A. means not applicable.

e. Mean water temperature adjusted for locati:n of pluss over land.

f. Pitme rose ocenatonally 600 feet high over the pond.

g. Plume extent interprated frca photostraph.

h. Fog and weather conditions were changeable.

J. Light fog in 20-m11e area west of pond -- the e was not evident.

k.

Natural fog in vietaity of pond, steam fog pine dimensicas uncerta'in.

1. Natural snow falling.

4

l extent might be less, due to mixing in the cavity in the lee

- of the dam, than would be the case with flat land downwind.

( However, only on 1/6/71 and on 12/5/71 was the fog noted to decrease in elevation after passing over the dam. In the case of 12/5/71 the plume was noted to dip slightly downwind of the dam and then slowly rise without any apparent increase in diffusion rate. The observer from October to December, 1971, at the 4-Corners pond was quite explicit about this only happening once during this time.

3. The observer was not present every day during October, November, and December, 1971, so there are a few days missing in the raw data.

4. The times associated with the plume extent data in Table 4 may not coincide exactly with the times given in Table 3 for fog frequency,because the ambient weather measurements were made at slightly different times than the fog dimension estimates.

5. At 4-Corners, fog that went onto the north, east, and south shores was usually generated from the eastern part of the pond. This is the hottest part of the pond, as can be seen from Figure 8. Therefore, the pond water temperature used to compute the at and the fog index in Table 3 was chosen to be representative of the eastern half of the pond under these circumstances-instead of a temperature representing the i average of the whole pond.

6. Judgment was exercised by the authors in entering "none" in the stratus extent column of Table 4 because explicit

observations were not regularly made. However, the observer i believes that fog depths of greater than 100 ft had to occur l

in order for stratus to form. This " rule" and the obvious' correlation of stratus with wind speed in Table 4 was useful in the data interpretation.

Summarizing the 4-Corners data, it is seen that if fog occurs, its extent on the ground is 2t 100 ft 88 percent of the time, 2t500 ft 35 percent of the time, a 1000 f t 18 percent of the time, and 2* 5000 f t 12 percent of the time.

l If stratus occurs, its extent above the ground is 2h 1 mile 91 percent of the time,Et 5 miles 55 percent of the time, and 2: 10 miles 36 percent of the time. This is a purely statis-tical result from the information presented about 4-Corners in Table 4.

l 1

1

The general features of three types of steam fog do emerge from these data. They are:

{

1. Fog. This is fog which extends along the ground and

~

eventually dissipates with increasing distance but does not lift off the ground. This is the most frequent situation found in the data of Table 4. It is characterized by fog index num-bers of 20 to 200, winds of 10 to 25 mph, and extends 100 ft to 1 or 2 miles. For extents greater than 1000 ft the fog index numbers are 60 or greater,but the converse is not always true.

2. Fog which changes to stratus. This is fog which starts out along the ground and then lif ts with increasing distance to form stratus. It is usually characterized by fog index numbers of 30 to 90, winds of 5 to 10 mph, and extents of 200 to 5000 ft along the ground and 1 to 10 miles as stratus.

This changing of fog to stratus with distance is also consistent with the calculations of Tsai and De Harpporte (1971). They report average winter extents from a cooling pond of about 200 to 800 ft along the ground and under extreme conditions up to 2500 ft along the ground. Unfortunately, the pond character-istics and geographical location are not included in their report.

3. Stratus. This is stratus which forms over the pond and

(. then moves slowly downwind scarcely touching the ground at the downwind edge of the pond. It is usually characterized by fog index numbers of 60 to over 200, winds of calm to 3 or 4 mph and extents of 1 to 10 miles downwind from the pond.

Examples of these three types of cooling pond fog are shown in the photographs in Figure 16.

b. Fog Droplet Size Data An understanding of pond fog droplet size is necessary since deposition velocity and thus the downwind extent of the fog plume are partially dependent on it. The type of ice deposition also depends on the liquid particle size. The following is a discussion of this subject.

Kocmond (1966) found that in seven cases of study of natural fog, over half of all droplets were of less than 21/(diameter.

Using treated slides he found that the average minimum and maximum drop diameters were 6;( and 63/A respectively in four advection fogs and 4/A.and 52/ a diameters in three frontal fogs in the Buffalo, N. Y., area. It is noted that due to the sampling method used, the observed values probably indicated average droplet diameters too large.

(

l l i

Kunkel (1971), using a hologram camera on July 15, 1965, at f Otis AFB, Falmouth, Mass., measured droplet concentrations

( in advection fog. The fog formed over the water south of Otis AFB, and moved inland during the night. The peak number concentration in one test sequence ranged from 15 - 30.sc diameter, and many bimodal and trimodal distributions were observed. Mean diameters varied from 17 - 283 (. The liquid-water contents varied from 0.02-0.15 gm/m3, Aufm Kampe et al (1952) show an approximate relationship between liquid water content (LWC) and fog droplet size and concentra-tion. For typical agvection from 0.1 to 0.2 gm/m .

and radiation fogs, the LWC ranges Droplet sizes were between 8 - 30s u diameter.

Meteorology Research, Inc. (MRI), under subcontrqct to Bechtel, measured the liquid droplet size of fog particles from the 4-Corners cooling pond. No similar information had been found in the literature. MRI personnel visited the 4-Corners cooling pond on January 19-20, 1970, to make the measurements.

The technique used is the special Formvar plastic film on glass plates. The plates are swept on a metal wand through the fog.

Liquid fog droplets are impacted on the wet plastic solution and encapsulated. The droplets form replicas which can be examined and sized at a later date.

( At the MRI laboratory, the slides were examined, using a Leitz s Dialux microscope. After initial calibration of the microscope, each slide was analyzed to determine the number of droplets in each of six size categories. The number of fog droplets reported '

in each size category represents the number of droplets counted in ten randomly chosen grid areas on the slide.

The results of the study are shown in Table 5. This table shows the sampling station where the measurements were made, the range of droplet size classes, the average total density of droplets counted and calculated as number per cubic centimeter, and the average total liquid water content (LWC) as calculated in grams /

cubic meter.

The results show generally that the steam fog droplet sizes predominate in the 7.5 to 10j( diameter size with a preference for the 7.5/A diameter value at the dam, station 1, and 8 - 10/ s diameter elsewhere. Likewise, the liquid water content was highest at the dam; this was particularly notgceable on the test of January 20, 1972, when a value of 0.20 g/m was recorded. At the time of this test, winds were from the east at 1 mph, and the condition generally was slight fog. On the previous day, the condition was fog with winds from the east at 4 mph.

TABLE 5 i,

LIQUID WATER CONCENTRATION AND DROPLET DENSITY Fog Test Droplet Size Avg Total Density Avg Total LUC Date , Station Dia. ja e/cc g/m3 1-19-72 1 7.5 222.1 0.0537 G-10 5.87 10.1-11 0.52 12-15 0.64 2A 7.5 0 8-10 83.3 0.0470 10.1-11 3.85 12-15 0.45 3 7.5 0 0.0105 8-10 20.2 10.1-11 0 12-15 0 4 7.5 0 0.0547 8-10 94.2

, 10.1-11 5.39 12-15 0.89 1-20-72 1 7.5 875.0 0.2007 8-10 14.29 10.1-11 0 -

12-15 0 2A 7.5 0 0.0576 8-10 110.95 10.1-11 0 12-15 0 '

4A 7.5 0 0.0331 8-10 54.36 10.1-11 3.48 12-15 0.80 Note: 1. Station 2A is approx. 500 ft. northerly of Station 2.

2. Station 4A is on access road to Island, approx.

1-1/16 miles west of Station 4.

\

According to Johnson (1960), for spheres of water falling in air, Stokes' law behavior is followed for droplets with a radius:s 40 microns.

To calculate the falling velocities of fog droplets, the fol-lowing equation is used.

V = 2Dgr 279 j where V is the velocity, cm/sec D is the density of the droplet, g/cm 3 r is the droplet radius, em

,AL is the viscosity of air, poise For OC air, the fog droplets described in Table 5 exhibit the following velocities:

Mean Droplet Velocity, Dia, microns am/sec 7.5 0.18 9 0.26 10.5 0.35 13.5 0.58

c. Plume Extent Calculations and Comparisons

( In the Interim Report of June 1971 &nd in this report attempts have been made to calculate the extent of the visible steam fog plume. These calculations have been compared to data in order to test the applicability of the methodology to the Midland Plant pond. The calculational model was particularly important in the Interim Report,because of the sparaity of data at that time,which was directly analogous to the Midland Plant situation. Although this type of calculation is of less importance now, due to the large body of data from the 4-Corners Plant, some extent calculations have been performed, but to a limited degree, in this present report.

The basic diffusion equation used in these calculations is the Gaussian plume diffusion equation for a ground-based continuous source. This is:

X/Q = 1/Wap0z" where X is the centerline concentration g/m 3 Q is the source strength, g/sec is the standard deviation of the lateral diffusion, m gY is the standard deviation of the vertical diffusion, m g5 is wind speed, m/see and 0 , are given as a function of The standardstability atmospheric deviation, cat c~Egory a5d distance dcwnwind by Slade

(1968). For ponds without large dikes or obstructions at the downwind edge, which might result in cavitational effects, this

( equation was used af ter finding the distance upwind of the

" virtual" point source for the. stability category involved by setting 0y to 0.35 times the cross-wind width of the pond.

For flow over a downwind obstacle, i.e., a dike or the dam at 4-Corners when there was evidence of cavitational effects the equation used was X/Q = 1/ (W c*ycz + cA) u where cA accounts for dilution in the wake of an obstacle.

"A" is the cross-sectional area normal to the wind of the ob-struction and "c" expresses the relationship of "A" to the size of observed wakes. Vales of "c" range from 0.5 to 2.; a value of 1.0 was used in this report. This equation was used to describe the cavitational effects noted at 4-Corners on the visits of 1/30/70 and 12/16/70. On two other occasions, 1/6/71 and 12/5/71 the plume was noted to dip down slightly downwind of the dam at 4-Corners but without any significant increase in dilution. No cavitation was assumed in the calculations for these latter two occasions.

During cases where the cross-wind dimension is large, the virtual point can be a long distance upwind. This makes it difficult to obtain accurate changes of e y and 52 with distance

, from the pond edge from the available graphs. Because the ex-( tent data obtained in October, November, and December, 1971, at 4-Corners included fog depth and width data at the downwind pond edge of the pond, the above equation was used with these late 1971 data and with "A" being defined as the cross-sectional area of the steam fog at the downwind edge of the pond. The atmospheric stability category was determined at the time of extent observation using Turner's (1964) method.

In order to calculate the downwind extent of the steam fog plume, it is necessary to calculate the downwind diffusion of sensible heat and of water. First, the sensible heat flux (cal /sec) and the water evaporation rate (g/sec) from the pond must be determined. To a good approximation, the total heat dissipated by these two processes during the times of day when steam fog is a potential problem, can be obtained by subtracting the heat lost due to long wave radiation to the sky from the total heat loading on the pond from the power station. Then ambient measurements of air tempera'ture, and dew point as well as pond water temperature can be used to calculate a Bowen ratio. This is the ratio of sensible heat flux to evaporativa heat flux. With this information, the total heat load being dissipated can be partitioned into these two processes. Finally, by using the heat of vaporization of water, the evaporative heat s

l l

flux (cal'/sec) is converted to evaporation rate (g/sec). l r

\ The diffusion of sensible heat is used to calculate a teropera-ture excess in the plume as a function of distance. This is i added to the ambient temperature to give the actual temperature in the plume. The water holding capacity (g/m3) of the air at saturation at this temperature is found. From this value ig l subtracted the actual water content of the ambient air (g/m )

to give excess water vapor holding capacity of the air.

i l Thediffusionog)theevaporatedwatergivestotalwatercon-centration (g/m as a function of distance. This is corrected 4 by deposition as a function of distance, stability category, I and wind speed. If this water concentration of the plume is

greater than the excess water holding capacity, in vapor form, a visible plume is assumed to exist. The distance at which this water plume concentration just equals the excess water holding capacity of the plume is the theoretical downwind ex-tent where the visible plume vanishes. One of the objectives of the experimental program at-Coffeen and at 4-Corners has been to obtain data to check this calculational scheme.

Several of the fog occurrences with extent data presented in Table 4 have been used to check the calculational scheme.

These data are summarized in Table 6.

In the case of Coffeen, the majority of the heat ' load is assumed

( to be dissipated to the atmosphere in the first arm of the '

cooling pond. Water temperature measurements from a boat, dur-1 ing the tests in March, 1969, justify this assumption.

In the case of 4-Corners when the flow was to the west, it was assumed that the'whole pond was envolved in providing sensible heat and evaporation to be carried off past the pond edge; this is reflected in the pond temperatures presented earlier in this

, report. For flow towards the north, east, or south it was as-sumed that the warmer easterly half of the pond was the principle source of heat and water to the atmosphere.

The data of 1/7/71 and earlier in Table 6 was presented in the Interim Report. The December 1971 data represents a few new interesting days for which calculations were done. It was intended that this comparison be illustrative rather than com-prehensive so no attempt was made to calculate all of the cases for which there is extent data. In several cases calculations were done for two wind speeds, the ambient wind upwind of the pond and the wind in the fog on the downwind edge. The latter 4 ,

e ,.

m TABLE 6 FOG-STRATUS EXTENT AND LIQUID WATER DATA - MEASUREMENTS AND CALCULATIONS

, Evapo- Fog-Stratus Mind Speed Heat Load ration Extent Calculated Used in LWC Calculated in Pond Rate Downwind Extent Calc. in Fog LWC Loc. Date Time Btu /hr g/sec m m m/sec g/m3 g/m3 C 2/13/69 2315 9.1x108 6.2x104 40 to 60 50 0.9 No data 0@ 50m C 2/14/69 0640 8,8x108 5.3x104 40 to 60 euSO 4.0 No data 0 0 50m C 3/11/69 2325- 9.5x108 6.1x104 50 to 150 ev50 0.22 No data 0 0 50m C 3/12/69 0630 8.4x10 8 4.4x104 50 to 150a 0 to 100 0.22 No data 0.2 9 50m 9 5 4C 1/30/70 0620 8.5x10 3.8x10 50 to 150 0 9.0 1.4 @ dam 0.6 @ dam 4C 12/16/70 0710 5.9x109 3.0x105 20 to 40 0 9.0 1.6 @ dam 0.6 @ dam

, 4C 12/16/70 0805 5.9x10 9 3.3x10 5 20 to 40 0 10.0 0.5 9 dam 0 9 dam d 4C 1/ 6/71 0715 4.7x109 1.6x105 3,000 to 3,000 to 1.8 0.4 to 0.9 0.4 @ 50m 8

3,400 4,000 0 damb in plume 9

4C 1/ 7/71 0700 4.7x10 1.5x105 14,000 to 20,000 to 1.4 No data 1.0 0 50m i

18,0003 40,000 in plume 4C 12/ 4/71 0815 9.1x10 9 5.4x105 >1600 0 11.6 No data 0 2-3000 2.7 0.1 @ 100m 4C 12/ 5/71 0751 5.6x109 2.9x105 16,000a 0 1,. 8 No data 0 6-10,000 0.45 0.6 @ 100m 4C 12/ 6/71 0812 8.2x109 4.7x105 >1600 0 11.2 No data 0 3-4,000 4.9 0.2 @ 100m 9 5 4C 12/10/71 0813 8.2x10 4.6x10 3200 to 3000 to 3.8c No data 0.2 @ 100m 8000a 4000 4C 12/20/71 0825 5.9x10 9 2.8x10 5 100 1-2,000 5.8d No data 0.3 @ 100m 4C 12/21/71 0735 5.9x10 9 2.8x10 5 60 1-2,000 7.2d No data 1.5 @ 100m

a. Fog turning into stratus.

b. Not in main plume, which was calculated.

c. Ambient wind speed was 3.6 m/sec, speed over the dam was 4.0 m/sec, average used in calculation.

d. Since fog depth was shallow, wind speed in fog was used.

l i

is the higher speed in this table. It is seen that the fog extent is sensitive to the speed used. In the crses

\ of 12/4,5,6/71, the fog was deep and extended a considerable distance downwind so that the ambient winds are probably the most representative ones to use for the entire extent of the plume.

The cases of 12/20,21/71 are somewhat of an enigma as the con-ditions were severe and yet the extent was minimal. Perhaps there was some cavitational effects downwind of the dam which the observer did not notice.

In summary the calculations in Table 6 show reasonable con-sistency with the observations. Although greater precision would, of course, be desirable, it is probably not possible without a much better physical description of the environment around the pond than was within the scope of this study. The Table indicates the sensitivity of the calculations to wind speed (which should be representative of that which the steam fog plume experiences over its length) and the calculations are also quite sensitive to the initial cross-wind dimensions of the plume at the downwind edge.

(

ICE DEPOSITION 7 a. Observations

('

At Coffeen and at 4-Corners Plants, qualitative observations were made of ice occurrence and extent. In addition, ice build-up rates were determined by measuring the diameter of wooden rods, placed vertically near the downwind edge of the pond, as a function of time. The rods were cleared of ice after each measurement.

During the fall and winter 1971 observation program at 4-Corners, regular ice measurements were made on vertically oriented rods at 1, 10, and 20 feet above the ground at the location indicated on Figure 6. This location was selected for operational reasons and not by being an optimal downwind edge location. With easterly winds it would tend to be in the steam fog from the warmest;part of the pond, and the con-verse would be true for uesterly winds. Prior to the fall s of 1971, ice deposition rate measurements were made on vertically oriented rods located in the fog at the downwind edge of the pond at a location selected by the observer after arrival at the pond.

The qualitative picture that emerges from a review of the tests at Coffeen and 4-Corners is one of ice being observed, occa-sionally, for a few tens of feet downwind from the pond edge.

The deposition is primarily on bushes and vertical objects; it is not usually on flat surfaces unless in the form of k

snow. The density of the ice was not measured. Keeping in mind that glaze ice has a specific gravity of about 0.9, rime ice about 0.3 to 0.8, and hoar frost less than 0.6 (see Hackay -

1969),'it is useful to discuss a few specific cases. These follow:

1. At Coffeen, late on the night of February 13, 1969 frost, which could be easily scraped off, was on some steel and wood signs near the canal weir outlet. By 0640 the following morning,these same signs were covered by hard ice about 0.002 inches thick. This is the only observation of hard ice at Cof-feen. The place of the observation is only a few feet from the flume and canal. Se'nsible heat from the canal warming the air probably~ permitted the ice to freeze slowly with the resulting glaze of hard ice. This is not expected to be the case at off-site distances from the Midland Plant cond.

2. At Coffeen, on March 11, 1969 it was observed that all of the reeds within about 10 feet of the water edge were loaded with 1/2 inch long needle crystals of ice. The crystals all faced into the wind only and were very fragile. They-also only existed at heights below one foot on the reeds; the higher parts of the reeds were bare except for scattered droplets of ice. The measurement of ice deposition rate on this day was of the growth of these ice crystals on a reed.

3. At 4-Corners, on January 6, 1971 it was noted that all around the lake on the immediate shoreline the bushes were covered with hoar (needle-like crystals). Alongside the lake

the crystals were up to 3/4 inch long and at about 20 feet from e the lake they were up to 1/4 inch long. The road along the

( crest of the dam was covered with about 3/4 inch of snow. Sim-ilar snow coverage extended up to ten miles or more downwind of the pond. No similar snow existed in the general area. The snow is attributed to an accumulation from several days of ex-tremely cold weather and consequent steam fog.

4. At 4-Corners, on January 7, 1971 snow was lightly falling from the steam fog plume onto the dam. On the access road to the east of the pond there were several patches of ice.

The mine road further to the east (100 feet from the pond) has smaller patches of ice. As the winds were of low speed from east to west, it is not clear that these patches of ice can be attributed to the pond.

5. At 4-Corners, during the fall of 1971, no ice was observed on roads,but some was seen on bushes in the vicinity cf the pond. Occasionally, frost on bushes disappeared when the steam fog waa blown into that particular area. In these circum-stances, it indicates that the steam fog was not supercooled.

Yet air temperatures in the fog, often 5 to 7 F warmer than ambient, were in the 20's on many of the steam fog occasions in December 1971. The temperatures at the ice measuring station during the Fall 1971 were probably even warmer due to its prox-imity to the warmest part of the pond; most of the in-fog temper-ature measurements were made on the dam which is further from the hot part of the pond than is the ice measuring st,ation.

3 A

Although not explicitly stated in the test data, it is believed that there is a tendency for rime ice to form instead of glaze ice. This is most likely a result of the small droplet size in the steam fog; in the case of glaze ice associated with freezing rain or drizzle, the droplet sizes are at least an order of magnitude larger than observed in the steam fog. In the latter circumstances, the water spreads upon impaction before freezing.

The quantitative ice build-up measurements made with the verti-cally oriented wooden rods are presented in Table 7. Typical build-up rates are of the crder of one mm/hr for ambient temperatures of about 20F or less. No significant variation in these build-up rates with elevation was observed. For sub-zero temperatures, the build-up rates are an order of magnitude higher. The measurement on January 7, 1971,was made below the main steam fog plume.

b.

Calculations l A limited number of calculations of ice. deposition due to sweepout have been made using the calculated liquid water contents from Table 6. In the case of the December 1971 data, E ambient wind speeds were used because the location of the ice I

TABLE 7

(

SUMMARY

OF ICE ACCRETION DATA Ambient Ambient Height Ice Build-up Air Temp Wind Speed Above Rate Date Time O mph Location F Water ft in/hr mm/hr Coffeen 3/11/69 2325 17 0.5 1 0.079 2 4-Corners 1/6/71 0715 -12 4 1 0.51 13 4-Corners 1/7/71 0700 -14 3 1 0.018 0.45 4-Corners 11/19/71 0737 20.5 2 1 0.0089 0.23 4-Corners 12/4/71 0755 21 6 1 0.0625 1.6 10 20 :

4-Corners 12/5/71 0726 19 1 1 0.0312 0.80 10 20 4-Corners 12/6/71 0750 21.S 11 1 0.0166 0.42 10 0.0166 0.42 20 0.0098 0.25 4-Corners 12/12/71 0752 16 11 1 0.0365 0.93 10 0.0365 0.93 20 0.0365 0.93 4-Corners 12/17/71 0805 12 3 1 0.0468 1.2 10 0.081 2.1 20 0.081 2.1 4-Corners 12/20/71 0810 15 2 1 0.0418 1.1 10 0.0528 1.3 20 0.0468 1.2

e deposition measuring station probably did not experience as

( high a wind as was measured at the dam. These calculations are presented in Table 8.

TABLE 8 COMPARISON OF ICE ACCRETION DATA TO SWEEP-OUT CALCULATIONS (assumes density of ice is 1.0)

Rate of Growth, mm/hr

. Location Date Measured Calculated Coffeen 3-11-69 2.0 0 4-Corners 1- 6-71 13.0 2.6 4-Corners 1- 7-71 0.45 2.3 4-Corners 12- 9-71 1.6 1.0 4-Corners 12- 5-71 0.8 1.0 4-Corners 12- 6-71 0.4 3.5 4-Corners 12-20-71 1.2 1.0 In some cases there is reasonable agreement,and in others there are large differences. These could only be understood, if the study program had been sufficiently broad to have in-cluded liquid water measurements and wind speeds at the ice measuring station during the time of build-up of ice. As a point of departure in these sweep-out calculations, it is useful to note that 0.1 g of liquid water per cubic meter of l air and a wind speed of 1 m/sec results in a sweep-out ac-cumulation rate of 0.36 mm/hr.

Independent of the results in Table 8, it was previously noted fromtheliteraturethatgiquidwatercontentsofnaturalfogs range from 0.1 to 0.2 g/m . This is consistent with the liquid water contents measured by MRI in cooling pond fog at i

4-Corners. With these typical values of liquid water content and winds of a few m/sec, the calculated deposition rates are consistent with those observed in Tchle 7.

i l

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l l

EXTENSION TO THE MIDLAND PLANT COOLING POND r

k This section draws on the experimental data from the prelimin-ary and recent field programs, the special tests, and the analytical treatment of the results to provide a prediction of the occurrence and extent of pond induced steam fog from the Midland Plant cooling pond. In addition, estimates are made for deposition of ice and snow from the fog.

FREQUENCY OF COOLING POND FOG

a. Natural Fog To place incidence of pond steam fog in perspective, the in-cidence of natural fog, of coincident natural fog with cooling pond steam fog and steam fog without natural fog present is discussed. If natural fog is already oresent in the environs, whether or not the pond is also fogging only contributes to the density and not to the hours of occurrence.

To obtain information on incidence of natural fog in the Mid-land environs, six years of hcurly weather data from Tri City Airport, Michigan, were examined. All recorded events of fog, ground fog and ice fog were analyzed. The results are shown in Table 9.

k TABLE 9 FREQUENCY OF NATURAL FOG, TRI CITY AIRPORT Winter Spring Summer Autumn Annual Ave Occurrences, Hr 360 204 147 238 949

% of Possible 16.4 9.3 6.7 10.9 10.8 Table 9 shows the average number of occurrences of natural fog in the environs. For the year natural fog occurs 10.8 percent of the time. In winter when most natural fog occurs, the hourly frequency is 16.4 percent. In summer when least fog occurs, the frequency is 6.7 percent. When natural fog occurs, it covers a large area; therefore, the perception of it by an ob-server is independent of wind direction or bearing from the cooling pond. That is to say, an observer will generally see the natural fog, if such exists, regardless of the direction of the wind.

b. Pond Fog or Stratus With Natural Fog The earlier section on Fog Stud Data Cases introduces the fog index number. This number is T/(e s -*a). Figure 15 has been

described and shows the stratus and fog occurrence frequency related to the fog index number. From Figure 15, for a given

( fog index number, the probability of occurrence of fog is given. How this is used to obtain hours of pond fog is now described.

From the same data source used to determine the hours of natural fog, the Bechtel WEATHER-8 Computer Program was used to deter-mine, for each hour of the 6 years, the fog index number. For this determination, mean pond surface temperatures were taken from Figure 3. For this particular analysis, hourly index numbers were calculated only for hours when natural fog was observed. To permit the calculation when 100 percent relative humidity obtains, i.e., when the saturation deficit is zero, the index number for that hour is arbitrarily assigned as 100.

Since the probability of fog occurrence is 1.0 for fog index numbers of 90+, this arbitrariness will have no effect on the resulting fog frequency prediction.

The results of the fog index number calculation are shcwn in Table 10. This shows the seasonal and annual frequency of oc-currence for various classes of fog index number during natural fog.

To calculate the hours of cooling pond fog with coincident natural fog; multiply the occurrence probability of an index number from Table 10 times the probability of pond fog in Figure 15 for index numbers corresponding to the fog index number in the suitable k

column heading of Table 10 times the number of hours of natural fog and then sum. The pond fog probabilities are also shown in Table 10.

The results of the calculation are shown in Table 11. This table shows that for winter there are 319 hours0.00369 days 0.0886 hours 5.274471e-4 weeks 1.213795e-4 months when pond fog occurs with natural fog. This is 14.8 percent of all possible winter hours and 88.7 percent of the natural fog hours. In summer, the comparable values are 83 hours9.606481e-4 days 0.0231 hours 1.372354e-4 weeks 3.15815e-5 months , 3.8 percent and 56.4 percent. Annually, the comparable hours are 735, and these exist for 8.4 percent of the year and include 77.5 percent of the natural fog hours. As discussed in the case of natural fog, no directionality is attached to these hours of pond fog coin-cident with natural fog, although the fog would be somewhat thicker immediately downwind of the pond due to the contribution of the steam fog to the natural fog.

TABLE 11 OCCURRENCE OF POND FOG WITH NATURAL FOG Winter Spring Summer Autumn Annual Ave Occurrence, Hours 319 165 83 168 735

% of Possible Hours 14.8 7.5 3.8 7.7 8.4

% of Natural Fog Hours 88.7 80.8 56.4 70.6 77.5

- ,~ ,

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TABLE 10 PERCENT FREQtIENCY OF FOG INDEX NO. DURING HOURS WHEN NATURAL FOG OCCURS Hourly Fog Index Number Mean s(10 10-19 20-29 30-39 40-49 50-59 60-69 70-79 80-89 90+ Hours Winter 0.74 1.02 2.45 3.56 4.12 6.57 3.70 2.69 2.73 72.41 360 Spring 0.82 3.11 6.38 5.07 5.48 5.23 6.38 5.56 2.70 59.28 204 Summer 6.80 14.61 10.99 14.16 8.27 6.68 3.74 1.47 1.36 31.94 147 2

Autumn 1.61 7.07 10.71 7.70 7.35 5.11 4.90 3.78 2.45 49.34 238 Annual 1.91 5.09 6.69 6.57 5.86 5.94 4.58 3.39 2.44 57.53 949 i

yi Probability of Pond Fog 0.04 0.075 0.17 0.44 0.63 0.69 0.73 0.76 0.93 1.00 1

Note: Probability of pond fog is read from Figure 15.

I i

f .

c. Pond Fog or Stratus Without Natural Fog b -

The method used in estimating the frequency of pond fog or stratus without natural fog present is the same as described in the previous section for pond fog or stratus with natural fog present.

Tables 12-16 inclusive show the percent frequency of fog index number without natural fog for each direction and calm. In contrast to Table 10, where a large number of the cases oc-curred in the large fog index number categories, these tables indicate that without natural fog present, the fog index num-bers are considerably less. This is to be expected, since, in the case of natural fog, with high relative humidity, e s-e a is small and the fog index number is large.

The fractional frequencies of Tables 12-16 are multiplied, as before, by the probabilities of fog or stratus and the number of hours of index occurrence. These products are summed for each direction.

The final result of the calculations is shown in Table 17. These data are presented as a function of wind direction, because areas outside of the cooling pond will experience this pond fog only if they are downwind of the pond. The data in Table 17 show that on an annual basis the peak occurrence of pond fog or stratus without natural fog present (non-coincident) is 3.3 i percent with winds from the west southwest. The least annual occurrence is 0.5 percent from east winds. The winter season contains the most non-coincident pond fogs or stratus and shows peak incidence of 6.2 percent with west southwest winds. This contrasts with the 8.2 percent developed in the Interim Report from the simple criteria of At = 33F. Consideration of the excess water vapor holding capacity of the air in the use of the fog index number caused this difference. This effect shows in all the directions and in the sum of 43.5 percent for all directions in winter from Table 17 as compared to the value of 57.2 percent given in the Interim Report.

Other seasonal and yearly values show similar reductions, but the effect is particularly marked in the summer where the higher ambient air temperatures permit higher excess water vapor holding capacity.

The fog index number probability statements were derived from data gathered near Coffeen in Central Illinois and near Fruitland in Northwestern New Mexico. The samoling period extended from '

late winter through early spring near Coffeen and for periods from mid-fall through mid-spring near Fruitland. Since the fog index number accounts for both water-air temperature differences and for vapor pressure saturation deficits, it is the belief of the investigators that application of the method to include analy-( sis of summertime data is valid. Similarly, such application is generally valid. Similarly, such application is generally valid for all geographical locations.

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HOURtI_EOG_INEEX NUMBEe a F93He (10 10-19 20-29 30-39 40-49 50-59 60-69 70-79 80-89 90-99 >99

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_ . N3IIS L_1. E*$ED_0N f._ YEARS 0f_RECQRDa 901nt-54_1931

2. P Ct.UDES 52584 0F 52560 POSSIBLE OBSERVATIONS 3_. O t S LRhI.1D P11.81 aS F n og_1-HOURLY _REcDHD.1 N G S

d. AJERACE HOURS OF FOG INDEX OCCURED 2059 TIMES

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....".,.. 4 PERCENT FREQUENCY OF FOG INDEX NO. WITHOUT NATURAL' F03 VERSUS DIRECTION SECTOR SURFACE WINDS.TRI CITY AIRPORTe SAGINAWe MICHIGAN

_ ___ H I N S ___ .__ - N00RtY FOG _INDEX NUMBEn =

FR31* cic 10 19 20 29 30-39 40 49 50-59 60 69 70 79 80 89 90 99 *>99 eTOTAL

__e ..... ..... ..... .;... .. .. .1. =; ..... ..... ..... ..... .... e

" .*5 9.48 a:<A 9:3' er?A n_2A n,Jn Atf n DO A Lg4 n 3 Q. 1 69 NtE 1 74 0.86 0.55 0 37 0 27 0.23 0 19 0 11 0 08 0 05 0.44 4.89

_ _ - -t E. 2.31 0.87 a.4^ a:3d a.23 0.'17 0 09 .).DA a.04 a.OA 0.39 9.08 EVE 1.87 0.64 0.42 0.26 0.19 0.*16 0.09 J.08 0.06 0.05 0.25 4.05

.E n.e5 0.34 n.21 a:la 0 10 0:09 a . 0 &_-- a.04 a.03 a.01 0 14 1 91 EIE 1.

4 0.63 0.52 0.33 0 22 0 19 0 10 0 09 0 08 0 03 0 29 4.03

s e.74 n_A7 n_is n_to n.an -0.05 n.32 n.in 0.is n .D 7 n .n 7 3.89 SIE 7.62 0.90 0.49 0.26 0.20 0.13 0.10 0.07 C.04 0.05 0.24 5.11

.1 :.91 n.7n n,qn n 21 n-17 n.15 n.00 a.os n.01 0.03 0.19 3.97 S3w 4.36 1.30 0.76 0 49 0 25 0.16 0 16 0 09 0.09 0.07 0.J1 8.05

_lw 5.25 1.11 1.19 n.10 n.51 0214 n.28 a.2a 0.14 0.13 0.64 11.38 usw 5.97 2.12 1.66 1.00 0.82 0.57 0.40 0.25 0.17 0.15 0.88 14.01 y 2.31 s_1n 1.no n.8i n.sn n.38 n ,3 7 n.22 n,16 n.13 n 19 n .j s WNw 7.6' 1.29 1.05 0.75 0.57 0.42 0.34 0.22 0.15 0.12 0.66 8.21

_sw !. t 0.99 0.87 0.5n n jt 0.28 n .18 0.16 n.09 0.08 n.42 5.57 i 'l iw 1. f. ! 1.01 0.88 0.59 0.40 0.*31 0.24 0.18 0.08 0.11 0.63 6.11

._ut _I4.8 . <2 01J 0 0.15 0115 a 12 di D8 Q,06 n.no o,34 a.02 0.26 1.45 w

__I T n T D_ 31 JJ 16.38 91.s7 7.44 s.dn 4217 7.98 s oga 1.44 f.?? 7.36 1en NOIES_1_1._ EASED _CN A VEARs nE._ RECORD._49alaid4192'

2. I N D.b D E S 52584 0F 52560 POSSlHLE OBSERVATIONS 3._geSEEyaTrans nasFn nu t.nounty RFcnnntNns 4 ALE 9 AGE HOURS OF FOG INDEX OCCURED 7807 TIMES f._!a?_RERCEH1_HudlntfY nccuRFn AN AYERAGF or 113 YtMrs d

h

-e TABLE 16

~*

TABLE 17 OCCURRENCE OF POND FOG OR STRATUS Without Natural Fog Present Wind Winter Spring Summer Autumn Annual From Hours % 1:ours % Hours % _ Hours % Hours %

N 44 2.0 28 1.3 17 0.8 30 1.4 119 1.4 NNE 48 2.2 39 1.8 12 0.5 19 0.9 118 1.3 NE 41 1.9 33 1.5 10 0.5 14 0.6 98 1.1 ENE 35 1.6 27 1.2 8 0.4 10 0.5 80 0.9 E 17 0.8 17 0.8 3 0.1 6 0.3 43 0.5 ESE 46 2.1 24 1.1 6 0.3 14 0.6 90 1.0 SE 38 1.8 18 0.8 7 0.3 16 0.7 79 0.9 SSE 41 1.9 16 0.7 6 0.4 16 0.7 81 0.9

(

S 30 1.4 10 0.5 7 0.3 20 0.9 67 0.8 SSW 51 2.4 17 0.8 16 0.7 36 1.6 120 1.4 SW 104 4.8 31 1.4 22 1.0 59 2.7 216 2.5 WSW 134 6.2 61 2.7 26 1.2 66 3.1 288 3.3 W 92 4.3 51 2.3 20 0.9 36 2.6 219 2.5 WNW 92 4.3 58 2.6 18 0.8 42 1.9 210 2.4 NW 57 2.6 43 1.9 16 0.7 26 1.2 142 1.6 NNW 59 2.7 44 2.0 20 0.9 45 2.1 168 1.9 l

CALM 10 0.5 7 0.3 14 0.6 20 0.9 51 0.6 Total S39 43.5 524 23.7 230 10.4 496 22.7 2189 25'.0 Notes: 1. Based on 6 years of Tri City, MI, Airport data.

( 2. Includes 52542 of 52584 possible observation

3. Observations based on 1-hourly recordings

4. Percent is based on the total seasonal or annual hours

, _ , -_ v--. , , , . . _ _ _ . --

EXTENT OF FOG PLUME The discussion of the extent of the steam fog plume from the Midland Plant pond emphasizes the winter season. This season contains about twice the frequency of occurrence of steam fog as the fall and spring seasons and about four times the summer steam fog frequency. Winter is also the season when the plume extents would be expected to be the largest.

Three different methods will be used to estimate the steam fog plume extent for the average winter morning at Midland. These '

are: (1) Calculational, (2) Statistical analogue to the 4-Corners data, and (3) Direct experimental analogue to one or more days at 4-Corners. All three methods will be used here to examine the consistency of the results and enhance the confidence level in the conclusions to be drawn with regard to the extent of steam fog plumes from the Midland Plant pond.

a. Calculational Method In the Interim Report of June 1971 this approach was used; no other approach was possible at that time due to the sparsity of plume extent data. Applying the calculational approach outlined earlier in this report to the Midlaad Plant pond using suitable pond and ambient meteorological conditions (wind speed of 3 m/sec, mean minimum temperature in winter of 18.4F, relative humidity of 82 percent, and stability category E) leads to the estimated

( downwind extents for the average winter morning given in Table 18.

TABLE 18 -

CALCULATED DOWNWlPD EXTENT ON THE AVERAGE, WINTER MORNING Deposition Velocity, em/sec

! 0 0.25 0.50 1.0 Extent, ground based plume, km 7 3 1 0.1 Extent, plume axis at 10m height, km 7 5 3 1.5 l

l Table 18, taken from the Interim Report, shows extents which are dependent on the height of the plume axis and deposition ,

velocity. These are total extents; i.e. fog plus stratus.

The data obtained since the June, 1971, report suggest that, l for winds of 3 m/sec, the average winter morning condition will be one of fog changing to stratus downwind of the pond.

As turbulent deposition processes near the earth's surface are i most usually characterized by deposition velocities of about l

1 cm/sec, this suggested that the plume would extend about

(. 100 meters (300 feet) downwind along the ground. Once lift-ing, the deposition process is most likely to be dominated by the gravitational falling of the liquid water drops. As pointed out earlier in this report, a typical drop size is about 10 microns in diameter with a Stoke's Law falling speed of about 0.3 cm/sec. From Table 18, this suggests a total extent of the stratus of about 5000 meters (15,000 feet). The stratus would be actually higher than 10 meters but the fall velocity is a little greater than 0.25 cm/sec. Thus, the additional data has provided a better basis than was possible in the Interim Report for deciding which values for deposition velocity in Table 18 were applicable to the Midland Plant pond situation.

On winter mt 7ings which are very stable (wind speed equal to 2 m/sec, air temperature of 0F, relative humidity of 82 percent, and a stability category of F) the calculated downwind extents are given in Table 19. These conditions could occur about twice a month in winter (or have a probability of occurrence of about 7 percent) .

TABLE 19 CALCULATED COWNWIND EXTENT ON THE EXTREME WINTER MORNING k Deposition Velocity, cm/sec 0 0.25 0.50 1.00 Extent, ground based plume, km 45 15 3 0.5 Extent, plume axis at 10m height, km 45 20 15 10 Table 19 was also given in the June 1971 report. Applying the interpretation used above for Table 18 based on the 4-Corners data, it appears that on these extreme winter mornings the steam fog plume would extend along the ground about 500 meters (1500 feet). The stratus total extent would be about 20 kilo-meter (12 miles). With these light winds it is possible that the fog might be lifted off the ground prior to reaching 1500 feet downwind. The calculational model used is not sophisti-cated enough to have included buoyancy effects so that a calculational assessment of this lifting action was not made,

b. Statistical Analog to Midland Plant

In order to apply directly to the Midland Plant the stetistical data on plume extents, when steam fog occurred as shown in

(

Table 4, there should be similar pond loading characteristics

(' (there is for the 4-Corners Plant data) and similar meteoro-logical conditions to those expected on the average winter morning at Midland. A review of the ambient meteorological conditions in Table 4 indicates that typically fog extents were measured with temperatures in the 15 to 30F range and with relative humidities of 70 to 90 percent in the ambient air. Accepting for the moment that this is a good analogue to Midland, it implies that when fog occurs at Midland during the winter its average extent along the ground will be between 100 and 500 feet with a stratus extent of about 5 miles.

For the infrequent extreme conditions, with a similar occurrence probability of two days per month, discussed above, the statis-tical use of the 4-Corners data suggest extents along the ground greater than 5000 ft 12 percent of the time when fog occurs. Multiplying this times the probability of fog occur-rence - noncoincident with natural fog - gives a total prob-ability of about 5 percent. Another statistic that can be obtained from the data is that txtents of greater than 1000 ft along the ground are associated with fog index numbers of 60 or greater. As Tables 12 and 17 indicate, this occurs with a total probability of about 13 percent during the winter season.

For stratus, the plume extent at these probability levels is 10 miles or greater.

, It is not likely that these maximum fog and stratus extents, i at these probability levels, will occur simultaneously. The maximum stratus extents at 4-Corners were associated with light wind speeds so that the plume lifted off the ground relatively close to the pond edge. If one says that these maximum stratus extents will only occur with winds of 3 mph or less and that the winter wind speed statistics have the same speed distribu-tion as the annual,then one obtains the eatimate of 3.4 percent, as the frequency of occurrence of the lor.g-stratus extents.

This is the percent of time winds of less than 3 mph occur times the probability of non-coincident fog in the winter.

c. Direct Analogue to Midland Plant Examination of the data in Table 4 indicates that the best single day analogue to the average winter morning at Midland is Decem-ber 10, 1971. The ambient temperature was 19.0F which compares with the average winter morning minimum of 18.4F at Midland.

The relative humidity was 85 percent versus the average winter morning value of 82 percent at Midland. The winds were 8 to 9 mph compared to the Midland average winter wind wind speed of l 11.6 mph. Independently, an estimate of 3 m/sec (7 mph) has l been used as typical for the average winter morning at Midland.

I On December 10, 1971, the plume flow was also onto the north shore of the 4-Corners pond so that no complications due to

(

the presence of the dam are envolved. On this day, the fog

- extended 1320 feet along the ground before lif ting to form a I stratus layer which extended at least 3 miles from the pond edge.

d. Summary, Extent Estimates for Midland Winters Table 20 summarizes the extent estimates for the average winter day for the Midland Plant cooling pond from the above three approaches. These estimates indicate that on the typical winter morning, the steam fog will extend along the ground from 300 to 1300 feet before lifting into a stratus layer whose total extent from the pond will be about 3 to 5 miles.

Table 20 also summarizes the fog extents that might occur at Midland during the winter about two mornings per month on the average. These estimates indicate extents along the ground of 1600 to 5000 feet and stratus extents of the order of 12 miles.

It is not likely that these extreme strctus extents would occur on the same mornings as the extreme ground fog extents.

\

>- - u. __

TABLE 20

(

"UMMARY, EXTENT OF PLUME, MIDLAND PLANT POND Statistical Direct calculational Analogue to Anklogue to.

Average Winter Morning Method Midland Plant Midland Plant Fog on the ground, m/ft 100/3001 0: 100/300 400/1300 Stratus, km/ miles 5/32 2 8/5 5/3 Extreme Winter Morning Fog on the ground, m/ft 500/1G00 3 1500/5000 4 -

Stratus, km/ miles 20/12 3 > 16/104 -

NOTES: 1. A turbulent deposition velocity of 1.0 cm/sec i was used.

2. A water droplet deposition velocity of 0.25 cm/sec

( was used.

3. Used days with 00F minimum temperature. These occur with about a 7 percent probability.

4. Used days which were equalled or exceeded about 12 percent of the time when fog occurred. This yield a total wintertime probability of about 5 percent.

l 6

(

1 1

. - . . _ _ , - . _ _ . . - . - . - . _ - - = .

EFFECTS OF ICING

a. Review of Data The added data acquired in the recent program at 4-Corners has contributed significant new information bearing on icing from steam fog. The salient features of this data include the following:

1. The observation that the fog plumes generally lift in the downwind direction such that the extent of the surface fog can be much shorter than the total extent of the plume.

Table 20 shows a summary of the extent of. plume analysis.

2. From Table 20, fog scenarios or descriptions are fitted into the folleving categories:

Scenario A. Average Midland winter morning. Fog extends along the ground an average of about 200 meters (600 feet) and then lifts into a stratus layer whose total extent will be about 5,000 meters (3 miles).

Scenario B. Extreme Midland winter morning. Fog extends along the ground 500-1500 meters (1600-5000 feet) or stratus forms with a length of about 20,000 meters (12 miles). See discussion of

( Statistical Analogue to Midland Plant.

3. Furthermore, direct measurements of the mass-particle size distribution in the steam fog are also new information.

These data indicate that the steam fog droplets are largely 10 microns in diameter. This small particle size suggests that the sweep-out or deposition of this type of droplet should be a frost or rime ice rather than glaze. This is confirmed by the recent field data from the 4-Corners Plant.

It also indicates that water droplet deposition velocities of l

l the order of 0.2 to 0.3 cm/sec are appropriate for the part of the fog-stratus plume which is above the ground surface.

j At the ground Lurface, the deposition of these small drop.* ;t-will be determined by turbulent processes which are charaores-ized by a deposition velocity of 1 cm/sec.

b. General Icing Effects at the Midland Plant With the analysis of the new data and its interpretation, it is now possible to prepare better estimates of the extent, or range, and type of icing effects around the Midland Plant pond in winter and estimates of their probability of occurrence.

Table 21 is a summary and a comparison of the factors affect-l ing the deposition of ice as evaluated in the Interim Report l in June 1971 and in this present Summary Study.

(

r TABLE 21

(

ICING EFFECTS AT MIDLAND PLANT Comparison of Interim Report with Summary Report Results Factor Interim Repcrt Summary Report

1. Predomininant Not measured 10 micron in diameter steam fcg drcplet size

2. Deposition 1 cm/sec 1 cm/sec velocity by turbulent pro-cesses

3. Extent of plume 0.5 to 3 mi typical Scenario A. 3 mi most or stratus down- during the 57% of winter mornings wind the winter mornings Scenario B. 12 mi a with non-coincident few mornings por fog 2-9 miles a few month mornings per month

4. Extent of fog Assumed to be the Scenario A. About.600 ft along the ground same as above most winter mornings

. surface Scenario B. 1600-5000 ft a few mornings

(- per month

5. Average dura- 10 hours1.157407e-4 days 0.00278 hours 1.653439e-5 weeks 3.805e-6 months Scenario A. 10 hours1.157407e-4 days 0.00278 hours 1.653439e-5 weeks 3.805e-6 months tion of steam Scenario B. 8.6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months fog

6. Liquid water 0.1 g/m3 0.1 g/m3 content

7. Rate of deposi- 0.05 mm/10 hr 0.05 mm/10 hr, or i tion on flat 0.002 in./10 hr surfaces, 500m

8. Ice rate on 1 cm/10 hr. Some 1 cm or 0.4 in. per vertical ice out to 3 mi; 10 hr. Ice not expected surfaces near form of ice not beyond 5000 ft. Ice ground, 500m discussed expected to be frosty or rime and only then a few times /mo. Most icing effects to be within about 600 ft of the pond on a typical

( winter morning.

l

! (

l t

1 . . _ _ . _ _ . - . -,

The salient features of this table are as follows:

( l. Extent: On most winter mornings the extent of the surface fog is now estimated to be about 600 feet. Any icing effects on non-coincident steam fog mornings would be confined to this range.

On a few winter mornings a month, surface fog is now esti-mated to extend along the ground to 1600 to 5000 feet. If the winds are light, the along grounds extent will be sig-nificantly less, but the associated stratus will extend to about 12 miles. Any significant icing of horizontal surfaces on such mornings would be within the range of 1600 to 5000 feet.

2. Duration: The duration of the potential non-coincident steam fog at Midland for Scenario A, the typical winter morn-

! ing, can be estimated from Table 17. This table shows that

! steam fog or stratus occurs an estimated 43.5 percent of-l the 2160 hours0.025 days 0.6 hours 0.00357 weeks 8.2188e-4 months in the three winter months, or 940 hours0.0109 days 0.261 hours 0.00155 weeks 3.5767e-4 months . This, divided by 90, the number of mornings, gives 9.4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months aver-age duration. Therefore, it is assumed that an average duration for Scenario A is 10 hours1.157407e-4 days 0.00278 hours 1.653439e-5 weeks 3.805e-6 months .

The duration of Scenario B is estimated from Table 22. This is the summary of sub-zero temperature weather at Tri City Airport, Michigan, for the years 1962-66, five winters. The

( Scenario B duration is about 8.6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months .

3. Type of Ice: All evidence of the type of ice observed at 4-Corners, from ice sticks, vegetation, rocks, poles, signs, etc. , suggests that the " sweep-out" deposited ice is rime or frost-like, and friable with little strength to support weight.

This noted characteristic is certainly a favorable one in that large ice burdens are very improbable under these conditions.

l The rime or frost-like nature of the deposition is attributed to the small particle size of the steam fog droplets which appear to freeze on impact before spreading or flowing into a solid layer.

!!ence, with the new data, its interpretation, and reasonable extension to the Midland site, one finds that the present description of icing effects as summarized above, are significantly different than presented in the Interim Report and the environmental consequences are certainly less severe.

t 8

i l l :

f

- TABLE 22

(.

HOURS OF OCCURRENCE OF SUB-ZERO TEMPERATURE Midland, Michigan, Area Wind Ave Hours % Hours of From Per Year _ Yearly Total N 6.8 0.08 NNE 2.6 0.03 NE 2.4 0.03 ENE 0.2 +

E 2.4 0.03 ESE O O SE 1.2 0.01 SSE 0.4 +

S 0.6 0.01 SSW 4.4 0.05 SW 20.6 0.23 WSW 18.0 0.21 W 22.4 0.25 WNW 8.4 0.10 NW 6.0 0.07 NNW 5.4 0.06 CALM 1.0 0.01

(

TOTAL 102.8 1.17 Total 5-year hours of occurrence--------------------514 Total 5-year no. of occurrences--------------------- 60 Average duration, hours-----------------------------8.6 Note: 1. This table is based on occurrence of tempera-tures _4_ OF

2. Data from Tri City Airport, 1962-1966

(

STEAM FOG DOWNWIND LOCATIONS

( a. General Downwind Remarks The above discussion has been presented without referenca ,

to any directionality effects or features of the pond that l might alter the above assessment. In this regard some l comments should be made.

In both Table 17, The Occurrence of Pond Fog or Stratus Without Natural Pog P esent, and in Table 22, Hours of Occurrence of Sub-Zero Temperature, directionality is given for the frequency of occurrence in winter. Both tables have a minimum of occurrence for wind blowing from the east, and a maximum for winds. blowing from southwest through west. These data comparisons indicate that about 1/3 of all winter steam fogs will be towards the northeast from the pond, and about 1/2 of the most severe steam fog-Scenario B, or 2 mornings /per winter month, will also be towards the northeast.

Figure 4 shows the average January surface isotherms for the Midland Plant pond. It is noted that the warmest part of the pond, near the inflow, is in the northwest portion.

The coolest is on the southeast and eastern side. The field program at 4-Corners has provided some insight,

, however qualitative in nature, into the effect of gradia-

\

tions in the pond surface water temperatures on the intensity and width of the steam fog. Observations suggest that the steam fog is more intense over the warm parts of the pond; that cool parts of the pond can sometimes be relatively t

clear of steam fog while the warm part of the pond is a fog source; that the width of the fog can be halved by a favorable orientation of the wind with respect to the pond surface water temperature distribution.

The foregoing observations imply that on winter mornings with east southeast through south southeast winds, the l steam fog can be more intense and extend somewhat further l

on-shore than noted in the Scenarios A or B because of proximity to the warmest part of the pond. Also, on winter mornings when the wind is from the northwest quadrant there will be a tendancy for the cool part of the pond to be a buffer for the area to the southeast. Detailed discussion of the directional effects is not possible at this time from the present body of information; however, it can be noted that some of the directional effects appear to be favorable; for instance, in the example just given, the hottest part of the pond is 'bnffered from. the Mapleton area.

b. Specific Downwind Locations

( Certain receptor areas in the Midland Plant area are selected for more detailed consideration in regard to the meteorological

~

i l

I I

effects of the cooling pond. These recepter areas are dis-e cussed below.

(

The locations were selected in that they represent major roadways adjacent to the cooling pond, a nearby school at a distance of about 2500 feet, and the community of Maple-ton. The discussion for these recepter areas which follows will be given only for the winter season.

1. Stewart Road, 1.4 Miles West Of The Cooling Pond Figure 17 shows the roadway network and specific centers of interest in the immediate vicinity of the Midland Plant cooling pond. The wind sector affecting the recepter area of Stewart Road at a range of 1.4 miles from the nearest edge.of the cooling pond is shown. Superimposed on the map is shown the outline of the surface fog extent for Scenarios A and B, and the outlina of the edge of lifted stratus as they would exist when the wind would carry fog towards this receptor. The frequency of fog being transported towards this portion of Stewart Road in winter is 0.8 percent or 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months per month in winter.

Since sub-zero temperatures occur only in the winter months, Table 22 shows about 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months per motth of Scenario a occur-rence for this location. Therefore, the other 5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months are Scenario A occurrences. In both of these types of steam

( fog, a resident at this range would be outside of the sur-face fog. There would be stratus overhead fcr short periods.

The frequency of occurrence of fog in the sector towards Stewart Road for seasons other than winter are also shown in Figure 17. Spring is probably fairly similar to winter. In summer and fall,one would expect Scenario A to dominate almost completely. This comment is generally applicable to all the receptor areas discussed in this section.

Figure 17a shows the edge of the stratus and the extent of the surface fog under Scenarios A and B respectively for the situation of a due east wind.

The additional areas of fog in Figure 17 as compared to Figure 17a come about from consideration of the cooling pond as being an area source for steam fog. Thus, sector averaged experience will differ from that of a specific wind direction.

2. Stewart Road, 0.4 Miles From the Pond The description of the graphics on Figure 18 parallels that of Figure 17 and will not be repeated. It should be noted that the receptor in question, Stewart Road at a range of 0.4 miles is in the zone of surface fog for Scenario B in k

winter, and outside of the surface fog zone for Scenario A.

c A resident or observer in this location would, during winter,

( experience about 3 mornings a month, or 32 hrs / month, in which the steam fog would be blown towards him. The Table 22 data implies about 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months per month when surface fog would reach this location, during a Scenario B event. For the Scenario B event which reaches this location, the data in Table 21 indicates an ice deposition on vertical structures,

, oi about 0.04 inches. As previously noted, icing from the steam fog would be of a rime or frost-like type whose lack of strength would limit its accumulation. The pond icing and surface fogging experience at this range and location would not be significant when compared to the winter average of 16.4 percent for the natural occurrence of fog in the area.

3. Stewart Road, 0.2 Miles West of the Pond The description of the graphics of Figure 19 parallels that of riguie 17 and will not be repeated here. The principle change in the fog and icing expected as one comes closer to the edge of the pond is that the recepter gradually has the ,

number of days on which the steam fog surrounds him increase from very low frequency of occurrence of much less than one day per month to about 45 hours5.208333e-4 days 0.0125 hours 7.440476e-5 weeks 1.71225e-5 months per month or about 5 mornings per month. At a range of 0.2 miles, the observer would,on those 45 hours5.208333e-4 days 0.0125 hours 7.440476e-5 weeks 1.71225e-5 months per month, mostly see a wall of dissipating steam fog immediately to the east or some stratus overhead.

Table 22 indicates that for about 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months a month, during the

( winter, this resident or observer would experience a Scenario B steam fog. As before, icing would amount to about 0.04 inches on vertical structures.

4. Bullock Creek Elementary School The description of the graphics of Figure 20 parallels that of Figure 17 and will not be repeated. The Bullock Creek School is located about 1/2 mile from the pond. This loca-tion is of a sufficient distance frcm the cooling pond so that the typical steam fog, Scenario A, places the school beyond the surface fog by almost two thousand feet. The wind will be blowing from the pond towards the school 4.7%

of the time during the winter, (34 hours3.935185e-4 days 0.00944 hours 5.621693e-5 weeks 1.2937e-5 months per month). This is about 3 days per month. Attendees at the school these few mornings will see the steam fog dissipating to the east southeast or some overhead stratus. Infrequently, e.g.,

1 to 2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months per winter month, Scenario B can occur. In this case, the school would be in the surface fog. Table 21 indicates ice deposition of 0.04 to 0.08 inches. The. ice should be friable, easily brushed off of poles, equipment, etc., and would not constitute any real or apparent hazard to the school environs, or its operation.

4 k l

1 1

5. Mapleton, 1.6 Miles Easterly From Pond -

l

The description of the graphics of Figure 21 is parallel to that of Figure 17 and is not repeated here. It should be noted that the community of Mapleton is the receptor area from the cooling pond whenever the wind is from the west northwest or west, for a total frequency of 8.6 percent in winter. This is about 62 hours7.175926e-4 days 0.0172 hours 1.025132e-4 weeks 2.3591e-5 months per winter month or about 6 days per month. Also some portions of Saginaw Road lie in this sector. Mapleton and Saginaw Road lie outside of the range of the surface fog of Scenario A. Therefore, on the winter mornings when Scenario A applies and the wind is directed toward Mapleton, the residents looking to the northwest would see the dissipating steam fog and occasion-ally stratus overhead. Table 22 indicates about 10 hours1.157407e-4 days 0.00278 hours 1.653439e-5 weeks 3.805e-6 months per month that Saginaw Road would be in surface fog corres-ponding to Scenario B.

a As previously stated, Mapleton residents using Saginaw Road in the winter would encounter surface fog from the pond about 10 hours a month in winter. Any icing effects would be equal or less than as described in Table 21.

6. Gordonville Road, Along the South Edge of the Pond Figure 22 shows the location of Gordonville Road along the south edge of the cooling pond. It is seen that all wind

( sectors from west northwest to east northeast will transport steam fog over the roadway during Scenario A events. The total frequency of occurrence of steam fog in this receptor area is 17.3 percent of the time. If the average duration of the steam fog is 10 hours1.157407e-4 days 0.00278 hours 1.653439e-5 weeks 3.805e-6 months , then steam fog would prevail on Gordonville Road about one half of the winter mornings.

Table 22 indicates that Scenario B would occur about 11 hours1.273148e-4 days 0.00306 hours 1.818783e-5 weeks 4.1855e-6 months per month. Travelers on this road would have to exer-cise caution appropriate for driving in fogs on these occa-sions. Icing deposi. tion will be similar to that described in Table 21.

c. Road Icing in the Environs A special study of road icing in the environs of the Midland Plant cooling pond was made. The study is reported in Con-sumers Power Company Applicants Supplemental Environmental Report, pages 5.1 - 22, and will not be repeated here. The results of the study showed an estimated frequency of road icing of 49 days from steam fog with no natural fog present.

This is consistent with about half of the days during the winter months having fog on Gordonville Road as discussed above.

4

P In view of the results of this present summary report, the following additional comments are made,

{

a) of the 49 days of icing given above, approximately 43 would occur on the average winter day and extend down-wind from about 600 feet, and b) About 6 days of icing would occur during the extremely low temperature days and extend about 1600 to 5000 feet from the edge of the pond.

It is noted from the ASER, p. 5.1.-30 that during a recent year, the Midland County Road Commission had their winter road-clearing equipment in operation for 88 days.

d. Airports The Tri City airport is located about 7 miles southeast of the cooling pond. The airport would receive a stratus plume from the pond only during Scenario 3 and if the winds were from the west northwest. Table 22 shows a mean annual oc-currence of 8.4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months , or about 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months per winter month when stratus could extend to the Tri City Airport.

The Midland (Barstow) Airport is located about 5 miles north northwest of the cooling pond. This airport would thus receive a stratus plume from the pond only during Scenario B

t. conditions and only if the winds were from the south southeast.

Table 22 shows a mean annual occurrence of 0.4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months or a small fraction of an hour on a winter month basis when this could occur.

e. Winds from the southwest Tables 17 and 22 indicate that the frequency of occurrence of non-coincident steam fog and that the severity of it are most often associated with winds from the routhwest. In particular, Table 22 indicates that 59% of the sub-zero temperatures are dissociated with winds from only 3 direc-l tions, SW, WSW and W. Examination of Figures 1 and 4 also l indicate that winds from these 3 directions will come over the hottest part of the pond and then carry the steam fog into the plant area. This would be the region of greatest potential icing on-site. It should also be noted that the Scenario B fog would extend into the offsite industrial area east through northeast of the pond.

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SNOW Enow has been observed falling from the fog from 4-Corners cooling pond. This was during the visit of January 6-7, 1971, when extremely low air temperatures occurred. During the time snow fell, the highest air temperature recorded was -8F. The ambient relative humidity was not recorded but the relative humidity of the air throughout the region was approximately 80 percent. On the other hand, the lowest air temperature recorded with no snow observed from a cooling pond was 14F with 65 percent relative humidity.

This was during the Coffeen Plant tests. Furthermore, as reported in Monthly Weather Review, May 1965, snow fell from a cooling tower plume in Oak Ridge, Tennessee. This was during ambient conditions of 7F with 78 percent relative humidity. At Oak Ridge, no snow fell later in the day when the air temperature rose to 17F with 70 percent relative humidity.

In view of these data, it is believed possible to experience some snowfall from cooling pond fog when the ambient air temperature is 10F or less and the relative humidity is about 70 percent or greater. This presumes the availability of nuclei in the atmosphere for nucleation.

The Tri City, Michigan Airport data for the years 1963 and 1964 were analyzed for hours of occurrence of snow-f, producing temperatures and humidities. It was found that on the average, the winter months each contained 116 such hours or 16 percent of the time. March had 5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months , the other months had none. Most frequently, these hours are from midnight to 6:00 a.m. Based on the observation of snowfall from steam fog at 4-Corners, it is expected that any snowfall from the Midland Plant Cooling Pond will be light.

/

\

EFFECTS OF COOLING TOWERS SERVICE WATER COOLING SYSTEM (SWC6)

The SWCS was described in the Midland Plhnt Cooling Pond sec-tion. The preliminary designBtu of /hr the and cooling tower indicates a operates only during heat load of about 200 x 10 the summer season. .

The heat load of the SWCS is about 2-1/2 percent of the cooling pond. This source of water vapor to the atmosphere is so small compared to that from the cooling pond that the estimates in this report of fog frequency and extent of plume are not really affected by either its inclusion or exclusion. To explicitly include the SWCS data and revise the present results could possibly create the impression that the study results are valid to within 2 percent.

BLOWDOWN COOLING SYSTEM (BDCS)

The BDCS has been described. The preliminary design indicates that 163,000 lb/hr of water vapor will be added to the air in January, the month of greatest fog concern. This system will not be required in summer, when the SWCS cooling towers are operating. Thus, the moisture effects in the atmosphere of the two systems are not additive.

The water vapor added to the atmosphere by the BDCS in winter is about 5 percent that of the cooling pond. This increcse in water vapor content will have no effect that alters the results previously given. When the winds are northerly or southerly, the plume from the cooling towers will mix with the air to or from the cooling pond and no qualitative differentia-tion can be made within the accuracy of the present results.

l l With winds easterly or westerly, during atmospheric condi-I tions conducive to cooling tower fogging, a separate visible plume will be seen from the cooling tower. This may 1) merge with the steam fog f ron. the cooling pond, 2} merge with steam stratus from the pond, or 3) continue until extinc-tion as either separate ground fog or separate stratus. These choices depend on the exact wind direction and speed and whether the cooling tower and/or the cooling pond plumes are ground fog, ground fog lifting into ctratus, or stratus. If the two plumes merge, the results will not be different than the general results previously given in this study. If the cooling tower plume does not merge, it will extend a few hundred feet downwind until it dissipates.

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a ACKNOWLEDGEMENTS

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This report was prepared as an account of work sponsored by Consumers Power Company. Both Arizona Public Service Company and the other Four Corners Project members of the Western Energy Supply and Transmission Associates (WEST) and the Cen-tral Illinois Public Service Company cooperated in the field tests by opening their facilities, supplying plant information, counsel and material support.

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REFERENCES Aufm Kampe, H. J. and Traberts Formula and the Determination Weickman, H. K., of the Water Content in Clouds, J. Meteor., 9, 167-171, 1952 Church, P. E., Steam-Fog Over Lake Michigan in Winter, Trans, Ame Geoph Union, Dec, 1945 Decker, F. W., Background Study for Pond Cooling for Industry, Oregon State Uni, Corvallis, Ore., Report RLO-2218-1, March, 1970 Ferron, Albert G. Model Study Midland Cooling Pota?

Consumers Pcver Co. for Bechtel Corp.

Power and Industrial Division; Alden Research Laboratory, Worcester Poly-technic Institute, Jan., 1970 Jacobs, W. C., Discussion of Church's Paper, Trans, Ame Geoph Union, Aug, 1946 Johnson, J. C., Physical Meteorology, published jointly i

by the Technical Press of M.I.T. and John Wiley & Sons, Inc., N. Y., 1960, p 223 Kockmond, W. C. and Investigation of Warm Fog Properties

! Pilie, R. J., and Fog Modification Concepts, NASA l

CR-368, Cornell Aero. Lab., p 48 by Kocmond, W. C., 1966 Kunkel, B. A., Fog Drop - Size Distribution Measured With a Laser Hologram Camera, J. Appl.

Meteor., June, 1971 McKay, G. A. and Estimating the Hazard of Ice Accretion Thompson, H. A., in Canada from Climatological Data, J. Appl. Meteor., Dec, 1969 Miller, D. H., Discussion of Church's Paper, Trans, Ame Geoph Union, Aug, 1946 i

f-

Saunders, P. M., Sea Smoke and Steam Fog, Quarterly

( J. Royal Meteor. Soc., 90, 156-165, 1964 Slade, D. H., et al, Meteorology and Atomic Energy, 1968, TID-24190, Air Resources Lab, Res.

Labs, ESSA, Commerce, July, 1968 Tsai, Y. J. and Unpublished paper, Stone & Webster DeHarpporte, D. R., Engineering Corp., Boston, Mass, 1971 Turner, D. B., A Diffusion Model for an Urban Area, J. Appl. Meteor., 3, Feb, 1964 Willett, H. C., Fog and Haze, the Causes, Distribution and Forcasting, Monthly Weather Review, 56, 435-568, 1928 s _ . . _ . , _ _ _ _ . _

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. BULLOCK CREE K b 6 ,

I E LE,ME NTAR,Y . SCHOOL

'I MILLER RD li/hc. I

_ ,wg SALZBURG RD

$ [' !

W [ p' .

i m STEWAR T ,RD3 ! . E MsLNER RD

. Cootga poNo GOR DONVIL.L(RD . j

__m____,___,_,____

MAPLET 'N

~

h, ,'!,k

+ , '. . . EXTENT OF SURFACE FOG SCENARIO A SURFACE FOG ,

SCENARIO B SCALE or rEEr

( o- isoo- 3200- 4aoo-OCCURRENCE OF POND FOG OR STRATUS Without Natural Fog Present

% FREQUENCY FROM AFFECTED SECTOR (S)

FROM SECTOR WINTER l SPRING SUMMER FALL ANNUAL E 0.8 0.8 0.1 0.3 0.5 WING SECTOR AFFECTING STEWART RD.

1.4 MILES WEST OF THE POND

(

Figure 17 SITE ENVIRON S - MIDLAND PLANT

v e

} \

/

O I.

k E

e 2 3

! a 8 =f 5 ?

$ BULLOCK CREEK I h.

a ELEMENTARY SCHOOL MILLER RD .

SALZBuRG RD L ,::E' f

M S.' .'

STEWART RD!:i w E MILNER RD

'NUNG POND

'REA

__ GORDONDiN'did*i W. p

\ RANGE OF SURFACE FOG NNYN EXTENT OF SURFACE FOG SCENARIO A SCENARIO B SCALE OF FEET

(

o- tsoo- saco- 4soo-OCCURRENCE OF POND FOG OR STRATUS Without Natural fog Present

% FREQUENCY FROM AFFECTED SECTOR (S)

FROM SECTOR WINTER SPRING SUMMER FALL ANNUAL E 0.8 0.8 0.1 0.3 0.5 WIND SECTOR AFFECTING STEWART RD.1.4 MILES WEST OF THE POND WITH A DUE EAST WIND 1

I l (

Figure 17a SITE ENVIRONS - MIDLAND PLANT 1

l _ _

O

\ n

.~ Yf $ a

[ E E

- 8, O

I -

i \

.::h' ..!!kkhhkbkh.N$kK 6 !!!$: .f.4.@;$.@9.Y.SC,HOO C .

MILLER RD - .u N[ SALZ8URG RD g',. ; 7

/'

nB

, p $Qgfb STEWARiidii gxTEN AgtO A ""'""

~ E 3><==~

GORDONUl[L'd'RU!:

gicig - -

w.) nyuuccccccccccccccc.cci,. . MAPLETO a * ++

.,.,.... .:.:.:s

8.ii:.:8.:8.yy

~

ESE RANGE OF Ch SURFACE FOG SCALE OF FEET

( SCENARIO B o' '800- noo' 4800' OCCURRENCE OF POND FOG OR STRATUS Without Natural Fog Present

% FREQUENCY FROM AFFECTED SECTOR (S)

FROM SECTOR WINTER SPRING SUMMER FALL ANNUAL ENE 1.6 1.2 0.4 0.5 0.9 E 0.8 0.8 0.1 0.3 0.5 ESE 2.1 1.1 0.3 0.6 1.0 TOTAL 4.5 3.1 0.8 1.4 2.4 STEWART ROAD - 0.4 MILES WEST OF POND

(

Figure 18 SITE ENVIRON S - MIDLAND PLANT

4 A

i

E O s I i g

e 33m i

5 5

.. ENE

...!!:.WUubs. Mini: ii!Q-f "E .sleutmnsCeiOO +-.

MILLER HD . / ,/j^ #

SAL 7 BURG RD 4..

EXTENT OF STEWART.RD::: SURFACE FOG ""'""

E h , COOLING POND-- SCENARIO A l AREA N GORDON'VibE'Nb!!! ,

, MAPLETON

. /

ESE N N. N ,

RANGE OF ' ' "t SURFACE FOG @

SCENARIO B SE SCALE OF FEE 1 t .

o- isoo- 3200- 4eoo-OCCURRENCE OF POND FOG OR STRATUS WithOut NOtural fog Present

% FREQUENCY FROM AFFECTED SECTOR (S)

FROM SECTOR WINTER SPRING SUMMER FALL ANNUAL ENE 1.6 1.2 0.4 0.5 0.9 E 0.8 0.8 0.1 0.3 0.5 l ESE 2.1 1.1 0.3 0.6 1.0 SE 1.8 0.8 0.3 0.7 0.9 TOTAL 6.3 3.9 1.1 2.1 3.3 l

1 STEWART ROAD - 0.2 MILES WEST OF POND

(

l ,

Figure 19 SITE ENVIRON S - MIDLAND PLANT

J h .

8 d 5 E-!

C :i * - : ' 96GB6isselR)i...::s ..

f iik.! .

3iEM%tnQN.Mti46N'N

' 2'I ^

MILLER ROff: __

_ SALZBuRG RD

[ EXTENT OF %

SURFACE FOG d= SCENARIO A E

STEWARNdi! MILNER RD

. 6. COOLING PONO

. >j AREA GoRooNVjifQb!!! '

!:-g ,

i$N' ESE d' "

RANGE OF U F SURFACE FOG FOG SCENARIO B IO B SCALEo H EET SE 3 '2"_ i L OCCURRENCE OF POND FOG OR STRATUS Without Natural Fog Present

% FREQUENCY FROM AFFECTED SECTOR (S)

FROM SECTOR WINTER SPRING SUMMER FALL ANNUAL E 0.8 0.8 0.1 0.3 0.5 ESE 2.1 1.1 0.3 0.6 1.0 '

SE 1.8 0.8 0.3 0.7 0

,.9 TOTAL 4.7 2.7 0.7 1.6 2.4 BULLOCK CREEK ELEMENTARY SCHOOL Figure 20 SITE ENVIRON S - MIDLAND PLANT

ML19329F070

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