FEDERAL WATER POLLUTION CONTROL ADMINISTRATION
         NORTHWEST REGION PACIFIC NORTHWEST WATER LABORATORY

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          FEDERAL WATER POLLUTION CONTROL ADMINISTRATION

                NORTHWEST REGION, PORTLAND, OREGON

                 James L. Agee, Regional Director
                PACIFIC NORTHWEST WATER LABORATORY
                        CORVALLIS, OREGON
                     A. F.  Bartsch, Director
NATIONAL THERMAL
POLLUTION RESEARCH
Frank H. Rainwater
NATIONAL EUTROPHICATION
       RESEARCH
    A. F. Bartsch
NATIONAL COASTAL
POLLUTION RESEARCH
D. J. Baumgartner
BIOLOGICAL EFFECTS
Gerald R.  Bouck
TRAINING
Lyman J. Nielson
WASTE TREATMENT RESEARCH
AND TECHNOLOGY: Pulp,
Paper, Wood Products;
Food Processing;
Special Studies
James R. Boydston
CONSOLIDATED LABORATORY
       SERVICES
Daniel F. Krawczyk
POLLUTION SURVEILLANCE
Barry H. Reid
TECHNICAL ASSISTANCE
AND INVESTIGATIONS
Danforth G. Bodien
                    NATIONAL THERMAL POLLUTION
                          RESEARCH STAFF

                    Frank H. Rainwater, Chief
                    Bruce A. Tichenor
                    Alden G. Christiansen
                    Ronald R. Garton
                    Philip W. Schneider
                    Lawrence D. Winiarski

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           INDUSTRIAL WASTE GUIDE

                     ON

              THERMAL POLLUTION
                   Revised


           Revisions consist mainly

      of changes in the Example Problem,

                pages 93 - 104.
        U.S.  Department of the Interior
Federal  Water Pollution Control  Administration
               Northwest Region
      Pacific Northwest Water Laboratory
               Corvallis, Oregon
                September 1968

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                       FOREWORD

     Industry's accelerating emission of heated wastes to the en-
vironment poses hazards that have triggered an acute awareness and
concern on the part of the public, the policy makers and industry
itself.  Establishment of State-Federal water quality standards
brings the concern into sharp focus.  The waters of the nation can-
not accept heated wastewaters without quality degradation and human
sacrifice of beneficial uses.  Adding to the problem is the increas-
ing lead time required for delivery of heavy power generating equip-
ment and other industrial machinery, causing hurried management and
public policy decisions on plant siting, design and equipment that
will have long-range impact on the environment.
     This Industrial Waste Guide on Thermal Pollution seeks to as-
sist State, Federal and local regulatory personnel, community and
regional planners and industrialists in making sound decisions.
The literature contains much information on thermal pollution.  Yet,
the operating engineer is hard pressed for the time required to
search the widespread reference material in sufficient depth to ob-
tain a working understanding of the subject.  This Guide provides
such orientation and directs the investigator to sources of more
detailed information.

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 IV

     The principal  authors, Alden G.  Christiansen and Bruce A.

Tichenor, have drawn material  from many sources as well  as on their

own experiences for this document.  Nevertheless, the Guide is  less

than totally adequate.  Deficiencies  are recognized in today's  know-

ledge of heat sources and effects and of technology for water tem-

perature prediction and control.   Even as this treatise is published,

a revision is underway to include new facts and knowledge emitting

from governmental and privately sponsored research.

     We wish to express appreciation  to our numerous colleagues in

State pollution control agencies  who  cooperated in developing the

content of the Guide.  Such cooperation foretells a vigorous nation-

wide attack on thermal pollution  of our water resources.
                      Frank H. Rainwater, Chief
                      National Thermal  Pollution Research Program
                      Federal Water Pollution Control  Administration

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                      CONTENTS


                                                         Page

FOREWORD                                                 iii

GENERAL PROBLEM                                            1

INDUSTRIAL WASTE - HEAT LOADS                              5

   GENERAL                                                 5

   ELECTRIC POWER INDUSTRY                                 6

      Power Requirements and Sources                       6

      Plant Evaluation                                     7

   MANUFACTURING INDUSTRIES                               10

EFFECTS                                                   13

   PHYSICAL                                               13

   CHEMICAL                                               18

   BIOLOGICAL                                             21

      Water Temperature Criteria                          21

      General                                             26

      Fish Life                                           27

         General                                          28

            Metabolism                                    28
            Reproduction                                  29
            Development                                   29
            Distribution                                  29
            Synergistic Action                             30
            Dissolved Oxygen                              31
            Acclimation                                   32

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VI

                                                         Page

         Freshwater Fishes                                33

            Maximum Temperatures                          33
            Preferred Temperatures                        35

         Marine, Estuarine, and Anadromous Fishes         36

            Spawning                                      36
            Eggs                                          38
            Young Fish                                    38
            Adult Fish                                    41

      Shellfish                                           43

      Algae and Other Aquatic Plants                      45

      Benthos                                             46

      Bacteria                                            46

CONTROL                                                   51

   PROCESS CHANGES                                        51

      Increased Efficiencies                              51

      New Methods                                         56

   ENERGY UTILIZATION                                     58

   COOLING DEVICES                                        60

      Types                                               60

         Cooling Ponds                                    61

         Cooling Towers                                   62

            Natural  Draft Towers                          69
            Mechanical Draft Towers                       74

      Side Effects                                        77

      Costs                                               79

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                                                                vii
   TRANSPORT AND BEHAVIOR MANIPULATION                    81

      Dispersion and Dilution Techniques                  81

      Water Quality Management                            83

         Temperature Prediction                           83

            Micro Models                                  87
            Macro Models                                  88

         Thermal Regulation                               89

   EXAMPLE PROBLEM                                        90

REFERENCES                                               105

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                GENERAL   PROBLEM





     Waste heat is a pollutant equally as dangerous to our waters



as the more tangible forms of wastes which enter our nation's rivers,



lakes, and estuaries.  Thermal pollution has been defined as man-



caused deleterious changes in the normal temperature of water (75).



     Human activity can change the normal temperature of water in



many ways.  Temperature changes may be induced by altering the en-



vironment of a watercourse, e.g., through road building or logging,



by creating impoundments, or by diverting flows for irrigation.   Or,



water temperatures may be changed directly by adding or taking away



heat.



     Present and future demands indicate that industrial cooling



water, when viewed on the national scale, is a first-order source



of waste heat.  The electric power generating industry alone ac-



counts for about 80% of the cooling water used.  Therefore, the  best



single index of the thermal pollution potential lies in projecting



future electric power production (75).  Power generation has ap-



proximately doubled each 10 years during this century, and estimated



future demands indicate a shortening of the time span for similar



increases (60,74).  Waste heat output has not multiplied as fast as



power generation because of continued improvements in thermal plant



efficiency and development of hydropower.  However, fossil-fueled



plants are reaching a limit of efficiency because of metallurgical

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2




 restrictions, and nuclear plants, planned or built, necessarily



 waste an even higher proportion of heat than fossil-fueled plants.



 Waste heat increase can be expected to more closely parallel power



 production increase in the foreseeable future.



     With these considerations in mind, heat rejection from the



 predicted mixture of nuclear and fossil power plants is expected to



 increase almost ninefold by the year 2000 (44,60).  Waste heat out-



 put from the manufacturing industries will also increase.  However,



 the demand for electricity is expected to continue to increase at



 a more pronounced rate than the demand for manufactured goods (75).



 This indicates a somewhat smaller rate of increase in heat rejection



 from manufactur-ing as compared with the power industry.



     The problem is one of managing tremendous amounts of waste heat



 in a manner that will maintain, or enhance if necessary, the physi-



 cal, chemical, and biological nature of our water resources.  Water



 quality standards are being implemented to protect these resources,



 but thermal pollution control measures are costly and complicated.



 An estimate by the Federal Water Pollution Control Administration



 (FWPCA) places the cost of cooling facilities needed over the five



 years 1968 through 1972 at $1.8 billion (74).  By comparison, in



 one year alone (1965), $3 billion was spent on sport fishing (3).



 Thus, the potential effect of thermal pollution on this and other



 beneficial water uses must be considered.  We must develop a thorough



 understanding of the causes, effects, and control of thermal pollu-

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                                                                   3




tion in order to apply equitable,  reasonable,  and  effective  ap-



proaches toward its solution.

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    INDUSTRIAL   WASTE-HEAT   LOADS





                           GENERAL





     Tremendous amounts of water are used specifically for cooling



purposes.  Almost one-half of all  water used in the United States



is utilized for cooling and condensing by the power and manufactur-



ing industries (74).   In 1964 this amounted to about 50 trillion



gallons, nearly 90% of the intake water for these industries  (79).



Cooling water usage by industry is cited in Table 1.





                         TABLE 1 (73)



         USE OF COOLING WATER BY U.S. INDUSTRY, 1964
Cooling Water Intake
Industry (Billions of Gallons)
Electric Power 	
Primary Metal s 	
Chemical and Allied Products....
Petroleum and Coal Products 	
Paper and Allied Products 	
Food and Kindred Products 	
Machinery. ... 	
Rubber and Plastics 	
Transportation Equipment 	
All Other 	
TOTAL
40,680
3,387
3,120
1,212
607
392
164
128
102
273
50,065
% of Total
81.3
6.8
6.2
2.4
1.2
0.8
0.3
0.3
0.2
0.5
100.0

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                   ELECTRIC POWER INDUSTRY


                Power Requirements and Sources

     Power production has steadily increased throughout our nation's

history.  Table 2 indicates the amounts of electrical  power used in

certain past years as well as projected national  requirements through

1985.


                         TABLE 2 (4)

     U.S. ELECTRIC POWER -- PAST USE, FUTURE REQUIREMENTS


	    Year      	Billion KWH	

               1912                          11.6
               1960                         753
               1965                       1,060
               1970                       1,503
               1975                       2,022
               1980                       2,754
               1985                       3,639



     For almost a half-century power generation has increased at a

rate of 7.2% annually, virtually doubling every 10 years (74).   This

trend is expected to continue, and possibly accelerate, in future

years (60).

     Power is usually generated by hydro- or steam-electric plants,

with the latter process requiring cooling water for waste heat re-

moval.  The remaining sites which are suitable for hydroelectric

stations are limited, so the power industry must depend more and

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                                                                  7

more on thermal power generation to meet future needs.  As shown in

Table 2, total power consumption In 1960 was over 65 times that for

1912.  During this same period, power production from fossil-fueled,

steam-electric plants multiplied by a factor of 85-plus (47).  At

the present time thermal plants produce approximately 81% of the

electricity generated in the United States; predictions indicate

this figure may reach 92% by the year 2000, when two-thirds of the

plants may operate on nuclear fuel (44,60).  Thus, thermal plants

will continue to gain a larger portion of a steadily increasing

market for power.  Waste heat production will increase proportion-

ately, which in turn reflects the increase in waste heat disposal

that we must accomodate.


                       Plant Evaluation
     The overall thermal efficiency (ri )  of a steam-electric plant

is calculated as:

                   TVm - Electrical  Output   1nn
                    t(/o) ~ Th^^TTT^F    x 10°

For one kilowatt-hour:

                   ntm - 3413 BTU/KWH	
                    L{/°>   3413 BTU/KWH + Waste Heat (BTU/KWF)X

The denominator of the efficiency equation above represents the

"heat rate" of a plant, which is defined  as the average amount of

heat required to produce one kilowatt-hour of electricity.  This

measure is used throughout the power industry for comparisons.  It

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is actually a measure of thermal  efficiency due to the inverse pro-
portionality of the two.
     Thermal plant heat rates on  a national average basis have de-
creased continually as more efficient power production techniques
were employed (See Table 3).

                          TABLE 3 (30)
    STEAM-ELECTRIC PLANT STATISTICS—NATIONAL AVERAGE BASIS
Year
1930
1940
1950
1960
1962
1964
1966
Heat Rate
(BTU/KWH)
19,800
16,400
14,030
10,760
10,558
10,462
10,415
Thermal Efficiency
(%)
17.24
20.81
24.33
31.72
32.33
32.62
32.77
Waste Heat To
Cooling Water
(BTU/KWH)
13,420
10,530
8,510
5,730
5,560
5,480
5,440
     Sizable gains in efficiency, however, are a thing of the past.
The most efficient fossil-fueled plant presently operates at about
40% efficiency.  This figure is generally assumed to be a ceiling
which the national average for fossil-fueled plants may ultimately
approach (74).  Efficiency of nuclear plants of the pressurized or
boiling water reactor types now being built or planned to 1975 will
not exceed about 33% (72,74).
     Table 3 includes estimates of the amounts of heat wasted to
cooling water in BTU's per kilowatt-hour of electricity produced.

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                                                                  9
These values are less than those representing the "Waste Heat" por-
tion of the efficiency equation because of in-plant and stack losses,
Plant design and operating data indicate that 15% of the thermal  in-
put is a reasonable approximation of these losses for coal -fired
plants; for calculations on a kilowatt-hour basis this equals 15%
of the plant heat rate.  Therefore, the following equation  applies
to fossil-fueled plants:
     Heat to cooling water (BTU/KWH) = 0.85 x Heat Rate - 3413
The amount of heat rejected to cooling water from nuclear plants
may be computed in the same manner, except that heat losses up a
stack are not involved.  Typical in-plant losses are about  5% of
the heat rate, so that the resulting equation which applies to
nuclear-fueled plants is:
     Heat to cooling water (BTU/KWH) = 0.95 x Heat Rate - 3413
     As an example of the quantities of waste heat which can be ex-
pected in the future, the two types of plants are compared.  For  a
fossil-fueled plant at 40% efficiency:
     Heat Rate =  ~: — ^ —  =      -  = 8533 BTU/KWH
     Heat to cooling water = 0.85(8533) - 3413 - 3800 BTU/KWH
For a nuclear-fueled plant at 33% efficiency:
     heat Rate =  ^J  = 10,342 BTU/KWH
     Heat to cooling water = 0.95(10,342)  - 3413 = 6400 BTU/KWH

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10
     We may infer from these calculations that the advent of nuclear
power plants will not lessen, but rather will  increase,  by over 60%
(32), the amount of heat rejected to cooling water per KWH of elec-
tricity they produce.  This factor is taken into account in the es-
timated ninefold increase in heat rejection by the year  2000 as pre-
viously mentioned.
     A final observation is noteworthy in regard to waste heat re-
jection:  on a percentage basis,  the incremental decrease in waste
heat to cooling water per KWH is  much greater than the increase in
efficiency which is responsible.   For example, Table 3 indicates
that efficiency increased by about 15.5% from 1930 to 1966; the
amount of waste heat to cooling water decreased almost 60% in the
same period.  Hence, any gain in  efficiency is multiplied in terms
of decreased waste  heat rejection.

                   MANUFACTURING  INDUSTRIES

     As indicated in Table 1, about 80% of all industrial cooling
water is used by the power industry, and the remaining 20% by manu-
facturing industries.  Manufacturers' cooling facility needs are
expected to increase at a 4.5% annual rate, compared to  the 7.2%
annual increase expected by the power industry (74).
     To assess the  impact of an industry or an industrial complex
on the thermal properties of a stream, one must determine the quan-
tity of waste heat, i.e., total BTU's, discharged from each plant.

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                                                                 11
Specific values of heat wasted by various processes are generally
not applicable to individual plants, due to the wide range of pro-
duction processes, equipment combinations, and efficiencies employed.
Therefore, no attempt to formulate quantitative guidelines will  be
made here.  Rather, it is suggested that the situation be approached
through studying each manufacturing plant's discharge.  In this
manner, incorrect assumptions will not be used and a more valid  heat
load determination will be assured.

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                       EFFECTS





                          PHYSICAL



     Temoerature affects many physical  prooerties of water.   Of



these, the most significant to water quality are density, viscos-



ity, vapor pressure and solubility of dissolved gases.   Table 4



shows the effect of incremental changes in temperature  on these



properties for fresh water.





                           TABLE 4



                      WATER PROPERTIES
Temperature Density Abs. Viscosity
T°Cj (°F) (gm/OTH) (centi poises)
0
4
5
10
15
20
25
30
35
40
32
39.
41
50
59
68
77
86
95
104
0.99987
,2 1.00000
0.99999
0.99973
0.99913
0.99823
0.99707
0.99567
0.99406
0.99224
1.7921

1.5188
1.3077
1.1404
1.0050
0.8937
0.8007
0.7225
0.6560
Dissolved Oxygen
Pressure Saturation
(mm Hg) (nig/1 )
4.58

6.54
9.21
12.8
17.5
23.8
31.8
42.2
55.3
14.6

12.8
11.3
10.2
9.2
8.4
7.6
7.1
6.6
     Stokes'  law describes the velocity of settling particles in



a non-turbulent medium according to the following equation.

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14
                          _,?.
                              (PS-PW)
where  V = settling velocity, cm/sec
      ps = density of settling particle, gm/cm
      pw - density of water, gm/cm^
       y = viscosity of liquid, poises
       d = diameter of particle, cm
       g = acceleration of gravity = 980 cm/sec

     As indicated, settling velocity is inversely proportional  to

the water viscosity and density.  Thus, both properties  contribute

to increased settling rates at elevated temoeratures.   These in-

creased settling rates may promote better water treatment plant

operation, though probably to no measurable degree.   A difference

in settling velocities can have a significant effect on  the loca-

tion and amount of sediment and sludge deposition in sluggish

rivers, reservoirs and estuaries.  For a synopsis of the field  of

sedimentation, see the following publications:  Fluvial  Sedi-

ments, A Summary of Source, Transportation, Deposition,  and

Measurement of Sediment Discharge, Colby, B. R., 1963, U.S.

Geological Survey Bulletin 1181-A; Determination of Fluvial Sedi-

ment Discharge, Report No. 14, Water Resources Council,  Interagency

Subcommittee on Sedimentation, 1963.

     Very slight differences in density are sufficient to cause

thermal stratification in quiescent water bodies, but stratifica-

tion stability also depends on water movement and depth.  Stable

stratification is common in lakes and reservoirs where there is

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                                                                 15

a specific gravity difference of about .001  or .002 between

waters of the upper layer (epilimnion) and lower layer (hypo-

limnion) (22,80).  Such stratification inhibits vertical  mix-

ing and oxygen transfer to lower waters.

     In stratified reservoirs, cool, incoming waters may  travel

almost directly to the dam outlet in a density current at a depth

of compatible specific gravity.   This reservoir characteristic

is important in predetermining release temperatures and in select-

ing optimum discharge elevation.

     Evaporation rate increases  as water temperature rises elevate

water vapor pressure.  Evaporation is caused by the wind  and the

difference in water vapor pressure between the air and the water.

This is expressed mathematically as:

                      F - ^ (es-ea)


where  F = evaooration flux (Ib  ft"^
       L = latent heat of vaporization (BTU Ib  )

       C = empirical  evaporation coefficient

       W = wind speed (mph)

      es = water vapor pressure of saturated air at  the
           temoerature of the water surface (mm Hg)

      ea = water vapor pressure of overlying air (mm Hg)

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16
       The effect of changing water temperatures on evaporation
  rates can be shown by holding all terms constant except es:
       L = 1050 BTl) Ib"1
       C = 11.4 (Lake Hefner coefficient (27,p.35))
       W = 10 mph
      ea = 7.5 mm Hg (for an air temperature of 70°F with a
           relative humidity of 40%
       I              ,             W • I I I V* C   / • W /    rj	
                (1050)                   s        ft/ day
       Solving this equation for various water temperatures, i.e.,
  various es values, gives the following table:
Water Temperature
50
60
70
80
90
es
(mm Hg)
9.2
13.3
18.8
26.2
36.1
F
(Ib ff2 day-
0.19
0.64
1.24
2.06
3.15
1)





       The values shown for evaporation flux (F) are specific for
  the given values of L, C, W and ea.  However, similar relative
  changes in F with respect to water temperature will occur for
  other values of the independent variables.
       Most living organisms depend on oxygen in one form or
  another to maintain their life and reproductive processes; thus
  an adequate supply of oxygen must be available for any healthy

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                                                                 17



aquatic environment.  Hence, the relation of water temperature to



gas solubility is a very important aspect of thermal  pollution.



Oxygen does not react chemically with water.  Therefore, its solu-



bility is directly proportional to its partial pressure at any



given temperature under equilibrium conditions with the atmosphere.



The effect of temperature on the solubility of oxygen in fresh



water under one atmosphere of pressure is shown in Table 4.



     Temperature changes cause complicated adjustments in the



dynamic oxygen balance in waters and compound the difficulty of



relating dissolved oxygen and other factors to oxygen demand, atmo-



spheric reaeration, photosynthetic production, diffusion, mixing,



etc.  However, Phelps (57) states that "very few waters in nature



carry a full quota of dissolved oxygen."  Thus, general tempera-



ture rises, which decrease the oxygen holding capacity, may limit



oxygen quantities which are already less than optimum.



     Atmospheric nitrogen, with a solubility about one-half that



of oxygen, is usually not considered an important control para-



meter for water quality.  However, recent evidence on the Columbia



River indicates that fish may be seriously affected in waters



which have become supersaturated with nitrogen through raoid warm-



ing or pressure reduction after dam discharge.

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18



                          CHEMICAL



     Many factors affect chemical reactions, including the nature



and concentration of reacting substances, catalytic influence,



and temperature.  The last named is important because chemical



changes speed up as the temperature rises.   In general, the speed



of a chemical change is approximately doubled for each 10°C (18°F)



rise in temperature (42,71).



     In an irreversible reaction, higher temperatures will de-



crease the time required to produce the final products.  In a



reversible reaction, the process is complete when the reactants



reach a point of dynamic stability, i.e., when the rate of forward



reaction equals the rate of reverse reaction.  In this case,



temperature influences both the length of time required to reach



equilibrium and the proportion of reactants and products at



equilibrium conditions.



     Most of the chemical  effects on water quality, which are in-



fluenced by temperature, center around microbial  activity.  Any



chemical reaction or change that results from a life process is



properly termed a biochemical reaction.  The majority of chemical



reactions that organisms bring about occur through catalytic



action at far lower temperatures than would be needed in the



absence of catalysts.  Such catalysts are known as enzymes, and



are themselves temperature-sensitive.  The rate of microbial

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                                                                19



activity increases, to a point, with the rates of chemical  reac-



tions.  The majority of organisms affecting chemical  water



quality are in the mesophylic classification and thrive in a



temperature range of 10 to 40°C (18 to 104°F).  For this group,



activity usually reaches a maximum between 30 and 37°C (86 and



99°F), then falls off as enzymes become less active.



     Taste and odor problems induced by temperature-accelerated



chemical or biochemical action are accentuated when oxygen is



depleted.  Substances which may accumulate include hydrogen sul-



fide, sulfur dioxide, methane, partially oxidized organic matter,



iron compounds, carbonates, sulfates, and phenols, to list a few.



In addition to the greater amounts of such substances, tastes



and odors are usually more noticeable in warmer water due to



decreased solubility of gases.



     Biodegradable organic material entering water exerts a bio-



chemical oxygen demand (BOD) which must be satisfied before



assimilation of the material is completed.  When the temperature



of such a receiving water rises, the intensified action of micro-



organisms causes the BOD to be satisfied in a shorter distance



from the discharge than would be accomplished at a lower tempera-



ture.  Figure 1 depicts oxygen sag curves for a stream in which



all conditions, i.e., streamflow, wasteflow, BOD of the waste,



and initial percent DO saturation, were held constant, except



temperature.   It is apparent from the curves that the deoxygenation

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20



effect  caused by waste  assimilation  is exerted over a  shorter


stream  distance at higher temperatures; also that oxygen deple-


tion occurs to a greater extent, since the sag point is lower


at elevated temperature.  Hence, it  is possible that the dis-


charge  of an organic waste that previously had not caused


excessive oxygen depletion could pose problems at an elevated


temperature (26).
                         FIGURE  I (26)

    RELATION BETWEEN TEMPERATURE AND OXYGEN  PROFILE

                         (After  La Berge)
  10
\
o> 8
E

  7
UJ

^6
x

°s
IU
o
^  3
en  °
Q
  0
        WASTE OUTLET
                            40" C
       0            10            20           30

           Miles from Outlet Discharging Organic Waste

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                                                                 21



     Chemical effects of slightly increased temperatures may have



minor beneficial influences on water treatment.   Disinfectant



action is generally more rapid at higher temperatures.   For ex-



ample, for a given dose of free chlorine, the period required to



disinfect water at 46°F is more than nine times  greater than at



104°F (18).   Reports on coagulant dosages are contradictory,



although a report from the Commonwealth of Pennsylvania indicated



a savings of 30 to 50<£ per million gallons per each 10°F rise in



temperature  (56).  In any case, the potential beneficial effects



must be weighed against the undesirable effects  such as induced



slime or algae growth, taste and odor problems,  or unpalatable



drinking water temperatures (7,39).





                         BIOLOGICAL






                 Hater Temperature Criteria



     On April 1, 1968, the National Technical Advisory Committee



on Water Quality Criteria to the Federal Water Pollution Control



Administration published its Repart_p_n Water Quality Criteria (76).



Among the water quality parameters considered by this distinguished



panel was temperature.  The Committee produced recommendations



with regard to water temperature for both freshwater organisms



and marine and estuarine organisms.  These recommendations, based

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22



on the best available information, indicate the temperature



levels which will ensure the future growth and development of



aquatic organisms.  The Committee's recommendations are as



follow:





Fresh Water Organisms (76, pp.  42,43)



     "Recommendation for Warm Waters:  To maintain a well-



rounded population of warm-water fishes, the following restric-



tions on temperature extremes and temperature increases are



recommended:



     "(1)  During any month of the year, heat should not be added



to a stream in excess of the amount that will raise the tempera-



ture of the water (at the expected minimum daily flow for that



month) more than 5 F.  In lakes and reservoirs, the temperatures



of the epilimnion, in those areas where important organisms are



most likely to be adversely affected, should not be raised more



than 3 F above that which existed before the addition of heat of



artificial origin.  The increase should be based on the monthly



average of the maximum daily temperature.  Unless a special study



shows that a discharge of a heated effluent into the hypolimnion



or pumping water from the hypolimnion (for discharging back into



the same water body) will be desirable, such practice is not



recommended.

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                                                                 23




     "(2)  The normal  daily and seasonal  temperature variations



that were present before the addition of heat,  due to other than



natural causes, should be maintained.



     "(3)  The recommended maximum temperatures that are not to



be exceeded for various species of warm water fish are given in



table III-l.



     "Recommendations  for Cold Waters:   Because of the large num-



ber of trout and salmon waters which have been  destroyed, or made



marginal  or nonproductive, the remaining trout  and salmon waters



must be protected if this resource is to be preserved:



     "(1)  Inland trout streams, headwaters of  salmon streams,



trout and salmon lakes and reservoirs,  and the  hypolimnion of



lakes and reservoirs containing salmonids should not be warmed.



No heated effluents should be discharged in the vicinity of



spawning areas.



     "For other types  and reaches of cold-water streams, reser-



voirs, and lakes, the  following restrictions are recommended:



     "(2)  During any  month of the year,  heat should not be added



to a stream in excess  of the amount that will raise the tempera-



ture of the water more than 5 F (based  on the minimum expected



flow for that month).   In lakes and reservoirs, the temperature



of the epilimnion should not be raised  more than 3 F by the addi-



tion of heat of artificial origin.

-------
24

                         TABLE III-l


(Provisional maximum temperatures recommended as compatible with

the well-being of various species of fish and their associated

biota.)

     93 F:  Growth of catfish, gar, white or yellow bass,
            spotted bass, buffalo, carpsucker, threadfin
            shad, and gizzard shad.

     90 F:  Growth of largemouth bass, drum, bluegill,  and
            crappie.

     84 F:  Growth of pike, perch, walleye, smallmouth  bass,
            and sauger.

     80 F:  Spawning and egg development of catfish, buffalo,
            threadfin shad and gizzard shad.

     75 F:  Spawning and egg development of largemouth  bass,
            white, yellow, and spotted bass.

     68 F:  Growth or migration routes of salmonids and for
            egg development of perch and smallmouth bass.

     55 F:  Spawning and egg development of salmon and  trout
            (other than lake trout).

     48 F:  Spawning and egg development of lake trout, walleye,
            northern pike, sauger, and Atlantic salmon.
NOTE:  Recommended temperatures for other species, not listed

above, may be established if and when necessary information

becomes available.

-------
                                                                 25
     "(3)  The normal daily and seasonal temperature fluctuations
that existed before the addition of heat due to other than natural
causes should be maintained.
     "(4)  The recommended maximum temperatures that are not to
be exceeded for various species of cold-water fish are given in
table III-l.
     "NOTE:  For streams, total added heat (in BTU's) might be
specified as an allowable increase in temperature of the minimum
daily flow expected for the month or period in question.  This
would allow addition of a constant amount of heat throughout the
period.   Approached in this way for all periods of the year,
seasonal variation would be maintained.  For lakes the situation
is more complex and cannot be specified in simple terms.

Marine and Estuarine Organisms (76, pp. 69-70)
     "Recommendation:  In view of the requirements for the well-
being and production of marine organisms, it is concluded that the
discharge of any heated waste into any coastal or estuarine waters
should be closely managed.  Monthly means of the maximum daily
temperatures recorded at the site in question and before the addi-
tion of any heat of artificial origin should not be raised by
more than 4 F during the fall, winter, and spring (September
through May), or by more than 1.5 F during the summer (June
through August).  North of Long Island and in the waters of the

-------
26
Pacific Northwest (north of California), summer limits apply July
through September, and fall, winter, and spring limits apply
October through June.   The rate of temperature change should not
exceed 1 F per hour except when due to natural phenomena.
     "Suggested temperatures are to prevail  outside of established
mixing zones as discussed in the section on  zones of passage."

                           General
     Water temperature plays a major role in the ability of any
water-based ecological system to maintain optimum characteristics
throughout all biological stages.  Temperature effects on all
organisms in an aquatic community are important because of the
interdependence of species.  For example, temperatures which are
not lethal to fish or shellfish may affect metabolism, reproduc-
tion and growth, as well as reduce important food organisms,
thereby inducing a change in the balance of the entire system.
All natural biological systems are highly complex; hence it is
very difficult and potentially misleading to generalize on the
effect temperature changes have on the aquatic biota.  A more
realistic approach is to direct investigations to locally impor-
tant species.
     The scientific literature contains a large volume of informa-
tion on the effect of temperature on all levels of the aquatic
biota.  Data are given which indicate maximum temperatures,
optimum temperature ranges, maximum permissible temperature

-------
                                                                 27




changes, acclimation temperatures, etc., for a wide variety of



organisms.  These data are based upon both laboratory and field



investigations of various degrees of depth.  A report on



Temperature and Aquatic Life (71) by FWPCA's Technical Advisory



and Investigations Branch, Cincinnati, Ohio, covers the important



known effects which temperature has on aquatic biota.



     The information presented on the biological  effects of



thermal pollution is not complete.  Hopefully, however, it will be



useful in detecting potential biological problems associated with



water temperature changes.  Where such problems are anticipated,



a complete analysis of the situation, tailored to the specific



site and problem, is needed.





                          Fish Life



     The physiology of fishes is directly affected by temperature.



Fishes are classed as poikilothermic animals, i.e., their body



temperatures follow changes in environmental temperatures rapidly



and precisely.  In such animals, the factors favoring heat loss



tend to equal the factors producing body heat, and thus the body



approaches environmental temperature (59).  In a majority of fishes,



the body temperature differs by only 0.5 to 1.0°C (0.9 to 1.8°F)



from that of the surrounding water (52).  Therefore, a fundamental



requirement of fishes is that the external temperature be well



suited to internal tissue functionality (8).

-------
28
     The single most important point in analyzing or predicting
the effects of temperature change on a fishery is to look at the
individual species important to the specific water body under
study.  The following discussions are presented primarily to
give insight to how and why changes in thermal regimen affect
fish.  To analyze specific cases, the worker is referred to the
literature on specific species.

General
     Metabolism.--Rates of metabolism and activity increase with
increasing temperature.  For example, according to van't Hoff's
law, metabolic activity can double or even triple over a 10°C
(18°F) rise in temperature.  This increase in metabolic rate and
activity will  occur over most of the tolerated temperature range
and then often cease suddenly near the upper lethal  temperature.
The rates of increased activity vary with different species, meta-
bolic processes, and temperature ranges or levels.  The rates may
also be modified by salinity and oxygen factors (43).  Changes  in
metabolic rates caused by temperature changes may be signaling
factors for spawning or migration (52).  Chemical reactions within
the fish's body cells may be accelerated by temperature increases.
Temperature-induced changes in cell  chemistry are associated with
four possible death mechanisms:  1)  enzyme inactivity caused by
the acceleration of the enzyme reaction to such a state that the

-------
                                                                 29



enzyme is no longer effective, 2) coagulation of cell proteins,



3) melting of cell fats, and 4) reduction in the permeability of



cell membranes (58).   Cells may also be killed by the toxic



action of the products of metabolism (28).



     Reproduction.--The temperature range within which many fishes



reproduce is narrower than that required by the majority of func-



tions.  Fishes generally spawn when a certain temperature level



is reached.   Of course, this level varies from species to species.



Some fish spawn on a drop in temperature, while others respond to



a rise in temperature (36).  Even though the temperature require-



ments for breeding are narrow, fishes may populate a heated area



by continued migration from the outside (51).



     Development.--Temperature changes affect fish development in



several ways.  Abnormal temperatures can affect embryonic develop-



ment.  Low temperatures may slow down development, but in some



cases fish attain a larger final size because of their slow, long-



continued growth rather than the raoid growth experienced at



higher temperatures (43).



     Distribution.--Temperature is one of the more important factors



governing the occurrence and behavior of fish life; it affects the



general location of a given species and may also modify the species



composition of a community or an ecosystem (43,78,36).  Tropical



and subtropical fishes are more stenothermal (tolerant of a narrow

-------
30




temperature range) than fishes of higher latitudes, and marine



forms are more stenothermal  than those found in fresh water (52).



Some cold-water stenothermal  forms may be eliminated by heated



discharges, while the effect on some eurythermal  (tolerant of a



wide temperature range) species may be to increase the popula-



tion (51).  In tropical areas, species live close to their upper



thermal limits, thus the effect of a thermal discharge can be



quite severe.   However, in northern areas, species may live in



temperatures as much as 16°C (28.8°F) below their upper lethal



temperature and not be as severely affected.  Laboratory tests (8)



have shown that a slow rate of decrease in environmental tempera-



ture is more important for maintaining life than a slow rate of



increase.  Lethal cold can be more important than lethal heat as



a factor limiting the distribution of marine fish and as a hazard



to some in their native habitats (25).



     Synergistic Action.--Synergism is defined as the simultaneous



action of separate agents which, together, have a greater total



effect than the sum of their individual effects.   In reference to



water temperatures, synergistic action refers to the fact that



temperature rises increase the lethal effect of toxic substances



to fish and may also increase the susceptibility of the fish to



many diseases.  For example, a 10°C (18°F) rise in temperature



doubles the toxic effect of potassium cyanide, and an 8°C (14.4°F)

-------
                                                                 31



rise triples the toxic effect of 0-xylene (45).  It must be



realized, however, that since the temperature effect on toxicity



varies with each substance and with concentrations of any specific



material, no hard and quick rule may be formulated to determine



this temperature effect (45).  Since domestic and industrial wastes



are numerous in our nation's waters, the synergistic action between



temperature and toxicity is a relatively common occurrence.  Fish



kills have accompanied small temperature rises which might have



been relatively harmless in an unpolluted stream free of toxic



substances (45).  Thus, the concentration of a substance may be



harmless at one temperature, but may contribute to fish mortalities



when combined with the stress imposed by higher temperatures.  Also,



the virulence of fish pathogens may be increased by higher temoera-



tures.  For example, the myxobacteria Chondrococcus columnaris,



which can cause death through tissue destruction, becomes more



virulent as temperature is increased (68).



     Dissolved Oxygen.--Two factors associated with rising water



temperatures are decreases in available oxygen and increases in



metabolic rates.  These factors combine to render the aquatic



environment less compatible to fish life at high water temperatures.



At low water temperatures in the range of 0 to 4°C (32 to 39.2°F),



a dissolved oxygen level of one to two mg/1 is sufficient for



survival of many freshwater fish species.  When the temperature

-------
32




reaches 15 to 20°C (59 to 68°F),  less than three mg/1  of dis-



solved oxygen is often lethal.   At these temoeratures, oxygen



levels as high as five mg/1  are sometimes required to  support



minimum activity.  Safe or acceptable levels may be even higher



in order to support normal activity beyond that of merely



staying alive.



     Acclimation.--The temperature to which fish become adjusted



over an extended period of time,  i.e., the acclimation temperature,



is important because of its  influence on lethal temperature levels.



The capacity to acclimate depends on the genetic background, en-



vironmental history, physiological conditions, and age of the



organism involved (43).  For example, the resistance of animals



to cold is much more variable than resistance to heat, and resis-



tance to cold varies with size, smaller fish resisting best (36).



Acclimation to different temperatures may involve changes in



orientation, migration, and other behavioral aspects such as



territorialism and biological rhythms (43).  Gradual temperature



changes are tolerated much better than sharp changes.   Brief or



intermittent exposure to high temperature can result in markedly



increased resistance to heat which is not readily lost on subse-



quent exposure to low temperature (25).  However, it is the rapid



onset of low temperatures that probably causes death,  outstripping



the ability of fish to acclimate and resulting in greater mortal-



ities  (9).  Deaths resulting from the inability of fish to raoidly

-------
                                                                 33
acclimate to lowering temperatures have been reported (34,37).
Acclimation to low temperature usually tends to shift the lower
thermal limit downward, and acclimation to high temperatures
tends to shift the upper limts upward (43).   Thus, the ability
to acclimate affects the temperature range that a fish can
tolerate.  Fish acclimated to cold winter temperatures are often
subjected to lethal temperatures in the spring as warmer water
is encountered (71).

Freshwater Fishes
     Maximum Temperatures.--Maximum temperatures have been deter-
mined for numerous species of freshwater fish.  These temperatures
indicate the highest temperature at which a  fish can survive, but
they are often higher than the maximum temperature at which a
species can survive for long periods.  Thus, maintaining water
temperature at these maximums does not insure the maintenance of
a fish population.
     Table 5 shows maximum and minimum temperatures for various
species and acclimation temperatures (71,56).  Values shown are
LDgQ temperatures, i.e., temperatures survived by 50 percent of
the test animals.  These figures are based on specific test con-
ditions, so care must be taken in interpreting the data, since
temperature limits for a given species will  vary slightly depending
on the fish's rate of heating, size, and physiological condition.

-------
34













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                                                                 35



     A temperature need not kill a fish directly for it to be



lethal.  Brook trout were found to be comparatively slow in



catching food minnows at 17.2°C (63°F) and virtually incapable



of catching minnows at 21°C (70°F).  Thus, even though their



lethal limit is 23 to 25°C .(73.4 to 77°F) (Table 5), the fish



could not survive in this temperature due to a lack of food (56).



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indicating their "preferred temperature" (71,31).



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temperatures preferred.  In general, the difference between the



acclimation temperature and the preferred temperature decreases



as the acclimation temperature increases (31).



     Competition between species is also important to distribution



and survival since different species have different preferred



temperatures.  For example, temperatures higher than optimum may

-------
36

not kill trout, but they may produce environmental  conditions

favorable for the production of coarse fish and thus  reduce the

trout's food supply (70).


                           TABLE 6

     THE FINAL PREFERRED TEMPERATURE FOR VARIOUS SPECIES
       OF FISH AS DETERMINED BY LABORATORY EXPERIMENTS


Species
Bass, largemouth
Bass, smallmouth
Bluegill
Carp

Muskel lunge
Perch, yellow
n ii '

Trout, brook
Trout, brown
Trout, lake
Trout, rainbow
Marine, Estuarine
Fi
Preferred
°C
30.0-32.0
28.0
32.3
32.0

24.0
24.2
21.0

14.0-16.0
12.4-17.6
12.0
13.6
nal
Temperature
OF
86.0-89.6
82.4
90.1
89.6

75.2
75.6
69.8

57.2-60.8
54.3-63.7
53.6
56.5


Authority
Fry, 1950
Fry, 1950
Fry & Pearson, 1952
Pitt, Garside & Hepburn,
1956
Jackson & Price, 1949
Ferguson, 1958
McCracken & Starkma,
1948
Graham, 19-48
Tait, 1958
McCauley & Tait, 1956
Garside & Tait, 1958
, and Anadromous Fishes
     Spawning.--Limits of temperature requirements for spawning are

usually much more stringent than for adult fish survival.  For ex-

ample, the normal spawning temperature for sockeye salmon is between

7.2 and 12.8°C (45 and 55°F) (63); lower and upper lethal limits

are 0°C (32°F) and about 25°C (77°F), respectively.  Pink salmon

spawn best near  10°C  (50°F) (65).

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-------
38




     During migration salmon do not feed, so high water tempera-



tures which increase their metabolic rate may result in fuel



depletion before spawning can occur (33).  Fish migration is



hampered by unfavorable temperature conditions.  A thermal  block



of 21.1°C (70°F) at the mouth of the Okanogan River, Washington,



prevented migration into the stream from the Columbia River (46).



Generally for salmon, upstream migration and reproduction occur



best at temperatures between 7.2 and 15.6°C (45 and 60°F) (12).



     Eggs.--The incubation of eggs and development of fry generally



have more critical  temperature requirements than either fingerling



or adult fish.   Table 8 shows the minimum and maximum temperatures



reported for the successful hatching of various species of marine,



estuarine,  and anadromous fish eggs.  Care must be taken not  to



equate successful  hatching with fry survival; Chinook salmon  eggs



incubated at 16.1°C (61°F) hatched successfully, but suffered



severe mortality in the late fry stage (54).



     Young  Fish.--Table 9 shows the temperature limits for the



survival of various species of young marine, estuarine, and anad-



romous fishes at several acclimation temperatures.  This informa-



tion is based on laboratory tests which often produce data not



directly transferable to the natural environment.  For example,



laboratory  tests on striped bass fingerlings showed an upper  lethal

-------
                                                                             39
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                                                                 41




temperature of 35°C (95°F), but studies in the Atlantic Ocean



indicated striped bass fish kills occurring at temperatures of



25 to 27°C (77.0 to 80.6°F) (69).



     Fish in the estuarine environment are more susceptible to



temperature changes than those in fresh water.  However, wider



ranges of tolerance between species exists in estuarine waters.



Decreases in temperature seem to have more of an effect on



estuarine fishes than on freshwater fishes.  In studies of young



greenfish to determine the resistance and acclimation of marine



fishes to temperature changes, Doudoroff (24) found that heat



resistance was gained rapidly and lost slowly.  Acclimation to



decreasing temperatures was slower than acclimation to increasing



temperatures.  Transposed to the practical case, this fact implies



that the shutdown of a power generating plant may be more detri-



mental than its normal discharge of heat.



     Anadromous fingerlings have maximum growth in the temperature



range of 10 to 15.6°C (50 to 60°F) (12).  Research on the effects



of temperature on swimming speed indicates that for young sockeye



salmon optimum cruising speed occurred at 15°C (59°F), and for



young silver salmon at 20°C (68°F) (10); thus, the fish's mobility



for protection and feeding is affected by temperature changes.



     Adult Fish.--Table 10 shows the lethal temperature limits for



several species of adult marine, estuarine, and anadromous fishes.

-------
42





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                                                                 43
Adult fish are usually able to select their preferred temperatures,
unless trapped in shallow water or forced to migrate through
thermal blocks.  Adult anadromous fishes spend most of their life
cycle in the ocean and enter fresh water only to migrate up a
stream to spawn, where previously mentioned thermal conditions may
affect them.

                          Shellfish
     Most shellfish, such as clams, oysters, crabs and lobsters,
which are directly beneficial  to man as a food source, are marine,
stenothermal organisms.  Some  species are stenothermal for one
developmental stage and eurythermal for another.  Generally, how-
ever, breeding and spawning requirements are stenothermal.  The
time of mollusc, e.g., clams,  oysters, etc., spawning is tempera-
ture dependent.  Most molluscs with specific temperature-breeding
relationships spawn in the spring and summer, and many do not
spawn until a certain temperature is reached (1).  The American
oyster Crassostrea virginica spawns at temperatures between 15 and
34 C (59 and 93.2°F) depending on its condition, and spawning is
usually triggered by a rise in temperature (35).
     Many species tolerate temperatures in excess of those at which
breeding occurs.  For example, the shore crab Carcinus maenas
thrives, but does not breed, at temperatures of 14 to 28°C (57.2
to 82.4°F) (51).  In this case, temperature limits the population,
but migration of organisms can occur from outside the heated area.

-------
44
     Physiology, metabolism and development are all  affected by
temperature.  The American oyster C.  virginica ceases feeding at
temperatures below 7°C (44.6°F).   Above 32°C (89.6°F) ciliary
activity, which is responsible for water movement, is decreased,
and at 42.0°C (107.6°F) almost all body functions cease, or are
reduced to a minimum.  The European oyster Ostrea lurida tends to
close its shell as temperatures drop.   At 4 to 6°C (39.2 to 42.8°F)
the oyster's shell remains closed most of the time.   At 6 to 8°C
(42.8 to 46.4°F) the shell opens  for about six hours per day, and
at 15°C (59°F) the shell stays open for 23 hours a day (35).  Very
little is known about the prolonged effects of temperatures above
32 to 34°C  (90 to 94°F) on oysters; however, long exposure to such
temperatures may impede the oyster's normal rate of water circula-
tion.  When either low or high temperatures cause shells to close
or ciliary action to cease, oysters cannot feed and subsequently
lose weight.  Thus, temperature changes can produce an effect
similar to chronic toxicity.
     The distribution of benthic organisms is temperature dependent.
The American oyster C. virginica is present in Gulf Coast waters
that may vary between 4 and 34°C (39.2 and 93.2°F), but the European
oyster 0. edulis is restricted to water temperatures of 0 to 20°C
(32 to 68°F)  (36).  The opossum shrimp Neomysis americana is not
often found at temperatures above 31°C (87.8°F) in the Cheasapeake
estuary (49).

-------
                                                                  45



               Algae and Other Aquatic Plants



     Successive changes from continual temperature increase may



result in the elimination of desirable species along with the



establishment of undesirable or nuisance organisms.   Some species



of algae and other aquatic plants are nuisances because they are



unsightly or produce undesirable tastes and odors.  In addition,



the biological oxygen demand of the dead cells depletes dissolved



oxygen resources.   Blue-green algae are especially undesirable



from the standpoint of taste and odor problems in municipal water



supplies.



     There appear to be particular temperature ranges that are



tolerated by each algal species and by closely related species or



groups of species.  For example, in an unpolluted stream, diatoms



grow best at 18 to 20°C (64.4 to 68°F); green algae  at 30 to 35°C



(86 to 95°F); and blue-green algae at 35 to 40°C (95 to 104°F) (15).



If temperatures are increased from 10 to 38°C (50 to 100.4°F), the



predominant species groups change correspondingly from diatoms to



green algae to blue-green algae (77).  Some of the more high-



temperature-tolerant species belonging to algal groups other than



the blue-green may persist with the predominant blue-greens at



increased temperatures, and several less tolerant species of the



blue-green algae may succumb with the diatoms and green algae as



the temperature rises.

-------
46



                           Benthos



     Studies of particular species of benthic macro-invertebrates



have indicated that lethal temperatures vary considerably with the



type of organism.  Laboratory investigations on the freshwater



snail Lymnaea stagnalis showed a lethal temperature of 30.5°C



(89.6°F) (53), while the species Viviparus malleatus did not suc-



cumb until  the temperature reached 37.5°C (99.5°F) (40).



     Field work on rivers has indicated that benthic organisms



decrease in number when water temperature exceeds 30°C (86°F) (67).



The macro-invertebrate riffle fauna of the Delaware River has



decreased due to heated water discharges.  At 35°C (95°F) many



caddisfly,  Hydropsyche, were dead, and those which remained alive



were extremely sluggish.  This study suggests that there is an



upper tolerance level near 32.2°C (90°F) for a variety of different



benthic forms with extensive losses in numbers and diversity



accompanying a further increase in temperature (20).





                          Bacteria



     In discussing the effect of temperature changes on bacteria,



it is important to distinguish between rapid changes, which may



induce thermal shock, and slow, gradual changes.  Organisms can



adapt to gradual changes in the environment; however, such adapta-



tion may take several life cycles, i.e., each successive generation



is better adapted to its environment.  Since bacteria have very

-------
                                                                 47




short life cycles, many generations may occur within a relatively



short time.   If a gradual temperature increase occurs over



several life cycles, then each successive generation is subjected



to only a small portion of this total temperature increase.   Thus,



bacteria can adapt to slow temperature changes more easily than



higher forms such as fish.



     The relationships of temperature to microorganism growth and



survival are very complex.  Bacteria can be grouped according to



their temperature requirements for growth:



               <20°C (68°F) - psychrophiles



               20 to 55-65°C (68 to 131-149°F) - mesophiles



               >55-65°C (131-149°F) - thermophiles



The majority of bacteria are mesophilic.  Many found in natural



waters are saprophytes, i.e., organisms that live on preformed



organic matter, which have optimum temperatures of 22 to 28°C



(70 to 82°F).  Parasitic bacteria have optimum temperatures near



37°C (98.6°F) and include those microorganisms pathogenic to man.



Changes in temperature have a large effect on these organisms' rate



of activity.



     The effect of temperature on bacteria cannot always be con-



sidered separately from other environmental factors.  Some species



are more abundant in winter, while others abound in the summer



when different environmental conditions are encountered (13).

-------
48



     Rising stream temperatures can be favorable for those



bacteria which multiply in water by inducing the recurring cycles



of life and death more rapidly (61).  Higher temperatures in an



organically polluted stream generally result in increased bac-



terial numbers, and low temperatures are not conducive to rapid



growth.  Temperatures of 1 to 8°C (33.8 to 46.4°F) may suppress



growth and multiplication, but bacteria persist longer at these



cool temperatures.



     Increases in bacterial populations are not necessarily harm-



ful.  For example, those bacteria which play an active role in



stream self-purification do perform a useful function.  These



include the bacteria which aerobically oxidize organic material,



as well as those responsible for nitrification and anaerobic



decomposition of bottom sediments.  However, increases in patho-



genic bacteria should always be avoided.



     Bacterial slimes cause unsightly scums and foul fishing nets.



Rivers carrying a high organic load often develop such deleterious



slime growths at low temperatures.  A study on the Columbia River



indicated that Sphaerotilus slime grows best at 10 to 15°C (50 to



59°F).  Growth ceases below 4°C (39.2°F).  Infestation of



Sphaerotilus may occur below 10°C (50°F), given sufficient time  (2).



Beds of Sphaeroti1 us slime extend farther downstream from a waste

-------
                                                                 49



outfall during the winter than in the summer, because warmer



temperatures may inhibit the organism's food conversion effi-



ciency (23), or because of competition for food from other



microorganisms.



     A recent study on the survival of bacterial indicators of



pollution showed that, the lower the temperature, the longer the



survival  (17).  Table 11 shows the average time for 99% reduc-



tion in original titers of microorganisms from three sources (17).



     In summary, the temperature of natural  waters, even during



the summer, is usually below the optimum for pollution-associated



bacteria.  Increasing the water temperature  increases the bacterial



multiplication rate when the environment is  favorable and the food



supply is abundant.  Increasing temperature  within the growth range



causes a  more rapid die-off when the food supply is limited.

-------
50
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-------
                        CONTROL





                       PROCESS CHANGES





                    Increased Efficiencies



     The adage about prevention and cure applies as well  to waste



heat as to anything else.  Reduction of waste heat production is



desirable for two reasons:  1) less waste of expensive energy, and



2) fewer problems with or after disposal.  Upgrading the efficiency



of operations which produce heat as a by-product is, therefore, a



logical starting point when considering control of thermal  pollu-



tion.



     Efficiency gains in fossil-fueled, steam-electric stations



have reduced their waste heat discharge rate by approximately one-



half over the past 30 years (Table 3).  Such gains have been accom-



plished through a number of refinements in the plant itself and in



operating conditions.  Figure 2 presents a schematic diagram of the



basic components of a fossil-fueled steam-electric plant which may



be referred to for a better understanding of plant operation and



efficiency.



     The basic steam plant cycle is as follows:  the steam drum



furnace combination turns water into high-pressure steam, which



is carried to the turbines at a speed of about 200 miles per hour.



Within l/30th of a second the steam rushes through the turbines,

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                                                                 53
traveling through a series of stationary nozzles and revolving
buckets which spin the turbine rotor and connected generator shaft
at either 1800 or 3600 revolutions per minute.
     Drastic changes occur in the steam as it releases its energy
to the rotating buckets.  Steam may enter the turbines at tempera-
tures of over 1000°F and leave at less than 100°F.  It enters at a
pressure of 2000 or more psi, expands to a thousand times its en-
trance volume, and leaves at a pressure less than atmospheric.
     From the turbine exhaust the expanded, low-pressure steam goes
to the condenser, where it is cooled until it condenses to water.
The process reduces the volume of the steam by a factor of 27,000
in a near-perfect vacuum, thereby returning it to a state in which
it can be easily handled.  The water is returned to the boiler
through the feedwater heaters to be used over and over again as the
cycle continues endlessly.
     As the cycle repeats, it is necessary to continuously remove
from the condenser an amount of heat equal to that given up in
converting exhaust steam into water.  Plant and operational refine-
ments reduce the amount of heat entrained in exhaust steam which,
in effect, increases the overall plant thermal efficiency.  Reduc-
tion of exhaust heat is attained through several methods (44):
     1) Increasing steam pressure—Elevating the steam pressure at
the turbine entrance reduces exhaust heat by varying increments,
but in general a 100 psi pressure increase will reduce exhaust heat

-------
54




per unit of electricity by 0.4%.



     2) Superheating steam—Steam generated in the boiler is heat-



ed even more in a superheat section of the furnace.   Each 50°F ad-



ditional temperature rise reduces exhaust heat per unit of electri-



city by about 1.4%.



     3) Reheating steam--After the steam has passed  through the



high-pressure turbine section it  is returned to the  furnace reheat



section to absorb additional  heat energy.  Again,  each 50°F increase



here reduces exhaust heat per unit of electricity  by about 1.4%.



     4) Boiler feedwater heating--A portion of the steam is with-



drawn before it reaches the final turbine exhaust, thereby eliminat-



ing its passage through the condenser.  This steam is utilized to



increase the temperature of water entering the boiler.  Feedwater



heating can reduce exhaust heat up to 37% per unit of electricity,



depending on the number of heaters used.



     5) Reducing exhaust pressure—The pressure in the condenser is



transmitted to the turbine exhaust, i.e., turbine  backpressure.



This pressure influences heat rejection to the extent that each 1



psi reduction in pressure reduces exhaust heat per unit of electri-



city by 2.5%.



     Modern power plants are designed to make use  of these effi-



ciency refinements as much as possible.  Through such techniques,



new fossil-fueled plants attain efficiencies near  40%; nuclear-fueled



plants about 33%.

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                                                                 55
     Nuclear-fueled plants are inherently less efficient than
fossil-fueled plants even though they too utilize the basic steam
cycle to spin turbines and generate power.  The major factor in
the efficiency limitation is that imposed through reduced operat-
ing temperatures.  Technological difficulties make it impractical,
uneconomical, or unsafe to produce high-pressure, superheated steam
in a water-cooled reactor system.  Whereas modern fossil-fueled
plants utilize steam at temperatures near 1050 F and pressures over
3000 psi, nuclear-fueled reactors of the boiling water or pressur-
ized water types produce steam at about 600 F and about 1000 psi
or 2000 psi, respectively.
     Lower temperatures and pressures imply less energy content per
unit volume of steam.  Hence, nuclear-fueled plants, compared to
fossil-fueled plants, require larger turbines and condensers for a
given generating capacity in order to compensate for the lower
quality of steam used.
     The principal advantage of nuclear fuel is its tremendous energy
density.  One ton of uranium has the energy potential of three mil-
lion tons of coal.  Present-day reactors convert only about 0.5%
of this energy to usable heat, i.e., combustion efficiency is 0.5%.
Advanced reactor design, i.e., breeder types, will convert much
more energy into a useful form (66).  However, while advanced de-
signs will improve fuel consumption, they will not necessarily in-
crease the thermal efficiency to reduce waste heat in steam-electric

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56




plant operation.



     Reduction of waste heat output from nuclear plants will de-



pend on development of advanced converters which will allow higher



operating temperatures.  Such converters will employ a reactor



coolant other than water in the primary flow loop, which circulates



fluid through the reactor core for heat absorbtion.  The heat is



then transferred to steam through a heat exchange process in a steam



generator.  Systems of this type, still in developmental stages,



are using fluids such as helium, liquid sodium or liquid potassium



for coolants.  Reactor outlet temperatures of over 1000°F are pos-



sible.



     Because of the vast energy stores in nuclear fuel, its utili-



zation for power production is inevitable.  For the next 15 to 20



years, the number of plants in the 30% efficiency class will in-



crease rapidly, which indicates that more efficient systems will



surely lag behind our demands for power.  This being the case, our



immediate efforts must focus on waste heat utilization and dissi-



pation while technology is being developed for more efficient power



production methods.





                         N_ew_Methp_ds_






     Gas turbines offer a means of power production without cool-



ing water.  Air is taken from the atmosphere, compressed, and sub-



sequently burned with a liquid or gaseous fuel.  The resulting

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                                                                57



high-temperature, high-pressure gases expand through a power tur-



bine and then exit to the atmosphere.



     Today's gas turbine efficiencies of less than 25% are not



competitive for power production on a large scale, although some



relatively small turbines are being used for standby and peaking



operation.  Future development may achieve higher operating tem-



peratures and increased air flow, which in turn would increase



efficiency to a level near that of fossil-fueled steam plants.



     Heat exhausted from gas turbines might possibly be put to use



in a conventional steam-electric plant.  Such a combination would



reduce the waste heat discharge rate, although cooling water would



still be used.



     Other systems currently under development may offer promise



for future bulk power generation without the need for cooling water.



Two systems receiving much attention lately are fuel cells and



magnetohydrodynamics (MHD), which would convert heat energy directly



into electrical energy (38).



     Fuel cells are somewhat similar to conventional storage bat-



teries in that they consist of two electrodes separated by an



electrolyte.  The fuel  cell does not contain a store of energy; it



generates current as long as fuel and oxidant supply chemical energy



for conversion to electricity.



     Individual fuel cells produce very small quantities of power.



Hence, thousands of cells would have to be connected in groups

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58



to increase power output to a level which would permit large-



scale production.  Predicted eventual efficiencies of 50 to 85%



is a further attribute of the fuel cell system.  A prototype and



larger scale central station fuel cell plant are being developed



by Westinghouse under a contract from the Office of Coal Research,



Department of the Interior.  Target dates for construction of the



two plants are 1969 and 1973, respectively (38).



     MHD generators utilize the principle of passing a conductor



through a magnetic field to produce current.  In this system the



moving conductor is an ionized gas.  Very high temperatures and



gas velocities must be maintained, which at the present time pre-



sents some major technical difficulties.  In theory, the applica-



tion of a MHD generator can be visualized, possibly in combined



operation with a conventional steam plant, but major advances in



materials must be achieved before the future of MHD power generation



can be predicted (38).





                      ENERGY UTILIZATION





     The optimum solution to problems associated with waste heat



disposal would be the use of rejected heat for beneficial purposes.



When dealing with power plant discharges, however, one is con-



fronted with immense quantities of water which are of low quality



when considered as a heat source.  Utilization of waste heat in



this form  is therefore restricted to only a very few possible

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                                                                 59



applications.



     One potential for such utilization is aquiculture, the farm-



ing of plants or animals in fresh or salt water.  Aquiculture has



been successfully practiced in Japan and elsewhere.  Heated dis-



charges could be used to enhance the environment and increase pro-



duction of commercially valuable species such as pompano, catfish,



shrimp, oysters, and scallops.  Research, development, and pilot



studies are in progress to determine the feasibility of such cul-



tivation in American waters (50).



     Some nuclear plants could possibly be located to provide bene-



ficial use of heated discharges in keeping shipping lanes free from



ice for extended seasons.  A recent journal  article (5) contained



specific recommendations for such application to the St. Lawrence



Seaway, proposing extension of the shipping  season to the end of



December or even January.



     Heated discharges may have application  in irrigating and creat-



ing controlled environments for agricultural  crops.  In this manner,



growing seasons could be lengthened in certain areas for common



crops, and subtropical or tropical varieties  might be produced where



they are not normally adaptable.



     Cooling water may provide heat to warm  swimming areas.  Such



use should be guided by the National Technical Advisory Committee



on Water Quality Criteria (76) which recommends:  "In primary con-



tact recreation waters, except where caused  by natural conditions,

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60
maximum water temperature should not exceed 30°C (85°F)."
     Thermal discharges may also provide heat for desalination
or other processes, some of which might require higher temperature
water than that normally discharged from steam plants.  In such
cases, it may be possible to implement a "trade-off" whereby it
would be economical to alter the usual process for other benefits.
For example, steam from the final turbine exhaust may be 80°F and
0.5 psia.  If the steam were tapped off in front of the final tur-
bine stage it may be 250°F and at 10 psig, which might be worth more
for some use other than its final turbine passage.  Marketable
steam for use by other industries, for home heating, or for any
other purpose may warrant "trade-off" situations which would help
to reduce waste heat loads to streams and other water bodies.
     Creation and application of improved technology for electri-
cal energy conversion is an indirect, but effective, control mea-
sure.  The advent of the fluorescent light is a classic example of
getting more useful work from a watt of electricity.  Other fertile
areas are the heating, refrigeration, air-conditioning and motor
industries.

                       COOLING DEVICES

                            Types
     Waste heat rejection to the aquatic environment can be re-
duced through the  use of cooling ponds or cooling towers.  The most

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                                                                 61
popular devices now in use in this country are various types of
evaporative cooling towers.  In the future, large reservoirs used
as cooling ponds may find increased application in some areas.
     Any method that provides air-water contact for cooling removes
about 75% of the heat through evaporation and the remainder through
conduction-convection.  As water is vaporized, heat is consumed .at
the rate of about 1000 BTU per pound of water evaporated.   Almost
all of this heat is taken from the water that remains, thereby
lowering its temperature.

Cooling Ponds
     A cooling pond or reservoir is the simplest method of cooling
thermal discharges, although it is the least efficient in  terms of
air-water contact.   In a flow-through system, warm water is intro-
duced at one end of the pond, cooled through heat dissipation to
the atmosphere, and eventually withdrawn as cold water from the op-
posite end of the impoundment.  Since the natural cooling  process
is relatively slow without induced air and water movement, surface
area requirements may average about two acres per megawatt output,
depending on local  climatic conditions.
     Advantages of cooling ponds or reservoirs include:
     1.  Low construction cost.
     2.  Serves as  a large settling basin.
     3.  May be beneficial for other purposes, e.g., recreation.

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62




     Disadvantages are:



     1.  Low heat transfer rate, necessitating large land area.



     2.  Possible fogging, icing of nearby roads, etc.




     Cooling can be accelerated in a pond by introducing the warm



water through a spray system located 6 to 8 feet above  the water



surface.  Such a system may reduce the required pond surface area



by a factor of 20 through increased cooling efficiency.   This ad-



vantageous savings in land area may be negated through  spray system



cost, pumping costs, and increased water loss with its  associated



problems.





Cooling Towers



     There are many versions of cooling towers.  Terminology applied



to towers stems from basic differences in design or operation which



serve to categorize the types.



     A tower may be either "wet" or "dry," depending on whether



water is exposed directly to the air; "natural draft" or "mechani-



cal draft," depending on whether fans are employed for  air movement;



"cross-flow" or "counter-flow," depending on horizontal  or vertical



air flow through the heat transfer section of the tower.  In mechani-



cal draft towers, air flow can be either "forced," i.e., pushed



through by fan on bottom, or "induced," i.e., pulled through by fan



on top.  See Figures 3, 4, 5 and 6 for schematics (29,41) illustrat-



ing these types.

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                FIGURE 3

          NATURAL DRAFT TOWER
              DRIFT
 HOT WATER /ELIMINATOR
DISTRIBUTION
      COLD WATER
         BASIN
      WET (Evaporative) COUNTERFLOW

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               FIGURE 4

        NATURAL DRAFT  TOWER
HOT WATER
  BASIN
FILL   I
            DRIFT
         ELIMINATOR
                                SHROUD
                                      AIR
                                     INLET
        ^COLD WATER
           BASIN
      WET (Evaporative) CROSSFLOW

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                  FIGURE 5


         MECHANICAL DRAFT  TOWER
                   AIR OUT
 WATER IN
  \ ' /' ' ,

.'/ ','•', \'!/


!'.  0:/',^/V,
  VII, • Ml ' / "
  <•*,/ '"//
WATER OUT
                                   DRIFT

                                   ELIMINATOR
                                        AIR IN
                 FAN
     WET,(Evaporative) FORCED AIR FLOW

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                FIGURE 6
        MECHANICAL DRAFT TOWER
                        AIR OUT
          FAN
 WATER IN
WATER OUT
   AIR IN
                               -COOLER
                               SECTION
AIR IN
          DRY, INDUCED AIR FLOW

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                                                                 67


     Because it is important to understand the working "language


when discussing cooling towers, the following discussion of signi-


ficant terms is presented.


     Dry-Bulb Temperature:  (  F,  C)  Temperature of air read on


     an ordinary thermometer.

                             O   ""I
     Wet-Bulb Temperature:  (  F,  C)  Obtained by covering the


     bulb of an ordinary thermometer with wetted gauze and reading


     in moving air.  It depends on the dryness and initial tempera-


     ture of the air, but is lower than dry-bulb temperature because


     some water evaporates from the gauze, removing heat.   The wet-


     bulb temperature is the theoretical  limit to which water can


     be cooled through evaporation.


     Relative Humidity:  (%)  The ratio of the amount of water vapor


     actually present in the air to the greatest amount it could


     hold if saturated at that temperature and pressure.  When rela-


     tive humidity is 100%, wet-bulb temperature equals dry-bulb


     temperature; therefore, the lower the relative humidity, the


     greater the difference between wet-bulb and dry-bulb tempera-


     tures .


     Evaporation Rate:  The rate, e.g., gallons per minute, at which


     water is being evaporated to cool the circulating water.  It


     depends on the area of air-water surface contact, length of


     time of contact, and difference between wet-bulb temperature

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68




     of the air and water temperature.



     Cooling Range:  (  F,  C)   The temperature  difference  between



     hot water entering a tower and cold water  leaving.



     Approach:  (°F,  C)  The  temperature difference between cold



     water leaving a tower and wet-bulb temperature of the surround-



     ing air.



     Heat Load:  (BTU/hr, BTU/min)  The amount  of heat dissipated



     in a cooling  tower per unit time.   It equals water  circulation



     rate multiplied by cooling range,  i.e.,




                                             )  -  BTU/mln
     Drift,  Carry-Over,  or Windage Loss:   Water  carried  out  of a



     tower in mist or small  droplet form.   It is usually expressed



     as a percentage of  the circulating  water rate.   Caused  by high



     air velocities, it  can be almost entirely eliminated through



     good design and operation.



     t3as_i_n_:   The depressed bottom portion  of a tower used for col-



     lecting and storing cold water.



     Slowdown :   The continuous or intermittent discharge to  waste



     of a small  portion  of circulating water from the tower  basin.



     It is usually expressed as  a percentage of  the  circulating



     water rate.  It prevents build-up of  dissolved  solids left



     behind  during evaporation.



     Makeup:  (gpm,cfs)   Water required to replace normal system



     losses  from evaporation, drift,  blowdown, and small leaks.

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                                                                 69
     Packing or Fill:   Material  placed in a tower over which water
     flows.  It increases the air-water surface area and time of
     contact and maintains uniform air and water flow distribution.
     Packing design dictates the type of flow.   Counter-flow towers
     usually use film-type packing; cross-flow towers usually use
     splash- or droplet-type packing.
     Water Distribution System:   A network of pipes (usually-) which
     spreads incoming  hot water  uniformly over the packing in a
     tower.
     Drift Eliminators:  Baffles located above the water distribu-
     tion system in a  tower.  As air flows through the baffles in
     a curved path, water particles are thrown from the airstream
     by centrifugal force.

     Natural Draft Towers.--The  cooling tower finding frequent ap-
plication to large power plant discharges at the present time is
the wet, natural draft, hyperbolic type.  Over 20 of these towers
are now in various stages of operation or construction in this
country.
     Hyperbolic towers derive their name from the hyperbolic profile
of the reinforced concrete shell.   The largest are almost 450 feet
high and over 300 feet in diameter at the base.  The function of
the shell is that of a stack or  chimney in providing an enclosure
for air flowing through the packing which is located near the ground

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70




either inside or outside of the shell.   Air flow through a tower



is created by the difference in density between the internal  and



external  air.  Warm water passing through the packing heats the



air and saturates it with water vapor during evaporative heat trans-



fer.  Both processes decrease the air density and cause it to rise



up the tower.  More air is drawn in, resulting in the establishment



of a continuous air flow through the tower.  External winds moving



across the top of the tower also contribute somewhat to the air



flow by reducing the internal pressure, thereby creating a drawing



effect.  However, tower operation is not dependent on external  wind-



induced air movement.



     Internal packing is located in the bottom 10 to 20 feet of the



tower shell.  Warm water distributed above the packing flows down-



ward through it in thin layers, contacting air rising vertically



through the tower.  Such opposed flow denotes the counter-flow clas-



sification.  (See Figure 3)



     Packing may also be located on the outside periphery of a shell.



In this system the water is broken up into droplets by splash-type



packing and allowed to fall downward.  Incoming air flows horizon-



tally through the falling water and then travels upward through



the empty tower shell.  This case describes the cross-flow classi-



fication.  (See Figure 4)  Water loading over the packing is from



2 to 4 gpm per square foot of horizontal area (29).

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                                                                 71



     Advantages of the evaporative, natural  draft type of tower



are (48):



     1.  Does not have mechanical  or electrical  components, yet



         for a given load it has the same cooling capability as



         the mechanical draft type.



     2.  Low maintenance cost, ijoth in time  and  money.



     3.  Independent of wind velocity.



     4.  Large water loading capacity.



     5.  For counter-flow design,  air and water  flows are opposite



         in direction, with the driest air meeting the colder



         water first, ensuring maximum efficiency.



     Disadvantages are (48):



     1.  Internal resistance to air flow must be kept minimal.



     2.  Great shell heights are required to produce a draft.



     3.  Inlet hot water temperature must be hotter than air dry-



         bulb temperature to induce air movement.



     4.  Exact control of outlet water temperature is difficult



         to achieve.



     Evaporative loss of water through the system amounts to about



1.5% of the flow circulated.  Slowdown may require an additional



2 or 3%, depending on the quality  of the circulating and makeup



water.   Drift is negligible in a well designed tower, not exceed-



ing 0.2% of the circulating flow (41).

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72

     A fossil-fueled power plant in the 600 MW class or a nuclear-

fueled plant of about 400 MW would discharge about 2500 X 106 BTU's

per hour.  Typical design conditions for a hyperbolic, evaporative

tower to handle this heat load may be as follows (41):


         Waterflow	  450 cfs
         Hot Water Temperature	  115°F
         Cold Water Temperature	   90 F
         Design Wet-Bulb Temperature	   72°F
         Design Relative Humidity	   50%

Such conditions would require a tower about 400 feet high and 285

feet in diameter for counter-flow design, or about 370 feet high

and 380 feet in diameter for cross-flow design (41).

     Care must be exercised when comparing natural draft evaporative

tower requirements at different sites.  Each design is necessarily

based on specific conditions—temperature, humidity, etc.--for a

given geographical location.  Hence, the size and performance cited

for a tower at one plant site may not apply to another, even though

the plants to be served are quite similar.

     Other kinds of natural draft towers depend on air movement

without the use of a chimney or shell.

     Atmospheric spray-filled towers, which are really more like

narrow spray ponds, have nozzles located from 6 to 15 feet high

surrounded by a louvered fence which permits air passage but inhi-

bits water loss.  Air circulation is dependent mainly on wind velo-

city.  Such cooling systems are suited for small refrigeration and

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                                                                 73



engine-water jacket installations, where variations in a relative-



ly small cooling range will  not seriously hamper operations.   Where



locations permit prevailing  winds to flow unobstructed, the system



works fairly well with a minimum of maintenance.  Water loading



capacity may be up to 1.5 gpm per sq ft of active horizontal  area



with wind blowing at 5 mph (29).  Disadvantages may include clog-



ging nozzles, nigh pumping pressures required to atomize water, and



high windage losses.



     Atmospheric packed towers are similar to the spray-filled type



except that they are usually larger and contain packing for water



breakup and additional wetted surface exposure.  Such systems are



rarely built any more because of their high capital and pumping



costs, and of their dependence on wind for air circulation.  Small



mechanical draft towers which handle comparable loads at similar



costs are now preferred.



     A final consideration in the natural draft category is the



hyperbolic dry tower.  This  type also employs a shell for the draft



effect, but utilizes indirect heat transfer instead of evaporation



for cooling.  Completely closed cooler sections give up heat through



conduction-convection, hence there is no evaporative loss of heat



or water.  The indirect transfer of heat is much less efficient than



the evaporative process so that much larger volumes of air must be



circulated than in a wet tower.  Therefore, the shell size must be



larger, which adds to capital cost.

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74




     Dry towers are also at a disadvantage compared to wet types



because of the lower limit to which water may be cooled.  The theo-



retical lower limit in a dry process is the dry-bulb air tempera-



ture; the corresponding limit in a wet process is the wet-bulb



temperature, which is usually appreciably lower (64).



     Natural draft dry towers have not been generally used for



large-scale cooling because the capital cost is estimated to be



about three times as much as its wet counterpart (64).  However,



the elimination of water loss through the use of such systems may



prove to be a deciding factor in their acceptance in some loca-



tions in the future.



     Mechanical, Draft Towers.--Until 1963 when the first hyperbolic,



natural draft evaporative tower was built at the Big Sandy power



plant at Louisa, Kentucky, only mechanical draft towers had been



used in the United States.



     Advantages of evaporative, mechanical draft cooling towers



are (48):



     1.  Close control of cold water temperature.



     2.  Generally low pumping head.



     3.  Location is not critical.



     4.  More packing per unit volume of tower.



     5.  A smaller approach and greater cooling range are possible.



     6.  Small land area requirements.



     7.  Capital cost is less than for a natural draft chimney.

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                                                                 75



     Disadvantages include the following (48):



     1.   High operating costs, including power.



     2.   High maintenance costs,  both in time and money.



     3.   Subject to recirculation of hot,  humid  exhaust into



         the air intakes.



     4.   Climatic variation can affect performance because fans



         move a fixed volume of air regardless  of its density and



         related heat transfer properties.   Also, efficiency de-



         creases as wind speed increases,  up to  a critical  velocity;



         at velocities above the critical  value  the opposite is



         true because of less recirculation.



     Mechanical draft towers are used over a broad range of heat



loadings because they can be designed specifically for almost any



capacity.  Maximum fan sizes limit the capacity  of any single cell,



but additional cells may be built to form  a bank or unit capable



of meeting the total requirement.



     The two air flow designs commonly used in mechanical  draft



towers,  forced draft or induced draft, were referred to previously



and depicted schematically in Figures 5 and 6.



     Forced draft towers, with one or more fans  located in the air



intake,  are slightly more efficient than induced draft types because



some of  the pressure of air velocity is converted to static pres-



sure in  the tower and recovered in the form of  useful work.  Fan

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76




location close to solid foundation lessens vibration.  Also, locat-



ing fans at the air inlets reduces the possibility of moisture con-



densation on the equipment since most of the air moved is dry.



     Recirculation of hot air is common in forced draft towers be-



cause of the proximity of the exhaust to the low-pressure air-intake



region.  Hence, efficiency may vary and winter operation often causes



frost and ice formation on equipment or nearby buildings due to the



presence of moisture-laden air near ground level.



     Forced draft type fan diameters are limited to 12 feet or less,



compared to nearly 60 feet for the induced draft type, which neces-



sitates more cells for a given capacity (29).



     While forced draft towers employ only counter-flow air movement



through the packing, induced draft towers may use either counter-



flow or cross-flow design.  The basic differences in packing design



and arrangement, as described previously, apply here also.  For



either type of flow, recirculation is generally not a problem because



the top-mounted fan discharges heated air upward, directly away from



the air intake below.  Because hot, humid exhaust air moves through



the fan, corrosion of mechanical parts is more pronounced than in a



forced draft system.



     Operational pros and cons of cross-flow design versus counter-



flow design are fairly well balanced for operational characteristics.



Physically, cross-flow types can be built lower and provide easier



access to the water distribution system.

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                                                                 77



     Mechanical draft systems also may provide air movement in dry



towers, thereby fulfilling the purpose of the hyperbolic shell as



previously discussed.  As noted before, large volumes of air are



required because of less efficient heat transfer through conduction



and convection than through the wet evaporative process (64).



Therefore, large fans are required which continuously demand an



appreciable amount of power—about 3% of total electric power pro-



duction (6).   Economics related to mechanical draft dry systems



discourage large-scale application at this time.





                        Side Effects



     Concern  over possible side effects from cooling devices has



risen along with the projected use of such systems.  Primary con-



cern is with  potential fogging conditions caused by cooling towers



(14,62), but  other possible adverse side effects should be considered.



     Because  of the large amount of water vapor expelled from eva-



porative towers, extreme climatic conditions may cause condensation,



resulting in  ground level fog or drizzle.  However, such conditions



are not often encountered in practice (48).   A recent investigation



of fogging problems from natural and mechanical draft towers pres-



ently operating in the eastern U.S. supports this conclusion (11).



Reports indicate that natural draft towers did not produce ground-



level fog or  drizzle under any weather conditions.  Plumes rarely



dropped below the top of the tower for an extended distance, and

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78




 generally  dissipated within a few hundred feet of a tower.  Mechani-



 cal,  induced draft  towers reportedly produced substantial amounts



 of  ground  level  fog, especially during the winter.  The area affect-



 ed  by the  fog was very  small, however, extending a maximum of about



 one-fourth mile  from the towers.  Carry-over of some water droplets



 was also noted from the mechanical draft type.  Resulting precipita-



 tion  occurred in the immediate vicinity of the towers, causing some



 minor icing problems up to 300 feet away.



      In general, undesirable meteorologic effects from towers can



 be  prevented or  controlled to a large degree through modern design--



 effective  drift  eliminators, air-flow control, etc.  In situations



 where problems arise, the area affected is limited to that immediate



 to  the tower installation (16).



      Water circulating  through a condenser-cooling tower system may



 be  treated chemically to prevent corrosion and inhibit biological



 growth (21).  hence, water extracted for blowdown purposes may con-



 tain  constituents which would be detrimental to aquatic life in



 receiving  waters.   Such effects may be prevented by treating blow-



 down  waste separately or, more efficiently, by integrating blowdown



 disposal with other plant waste disposal facilities.

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                                                                 79
                            Cqst^s
     An article (41) discussing natural draft, evaporative cool-
ing towers states the following in regard to tower costs:
     "Single towers, regardless of design, will cost in the area
of $2.5 to $3.5 million each for the size of towers which have been
utilized to date in the United States.
     "The physical size and cost of a tower installation for a
given size generating unit, however, can vary widely with location,
fuel costs, load factors, and with individual practices regarding
capability penalties and capitalization rates.  It is possible that
the optimum cooling tower installations for two plants with identi-
cal rated outputs could differ in cost by a factor of two.  For this
reason, it is difficult and, indeed, dangerous to generalize when
discussing tower reouirements and costs.'1
     The following outlines cooling tower costs as related to each
other, to total plant or production costs, and to consumer costs.
     Natural draft evaporative tower capital costs in the eastern
U.S. have been at least 5% of the total capital cost of a power
plant.   For a given plant heat load, mechanical draft, evaporative
towers cost approximately two-thirds as much as natural draft;
either natural draft or mechanical draft dry types would probably
cost three to four times more than their wet counterparts.
     The indicated savings in initial cost for the mechanical draft,
wet tower is somewhat negated because of power costs for fans, which

-------
80




consume about 0.8% of the power generated by the unit served (44).



For the proposed 540 MW nuclear plant at Vernon, Vermont, the an-



nual cost for production of power to operate fans is estimated to



be about $130,000--about 2% of the initial capital tower cost of



$6 million.  Other maintenance costs for the mechanical draft tower



installation are estimated at $60,000 annually--l% of initial tower



costs.  For this plant, the initial cost for mechanical draft



towers amounts to 5.1% of the total plant cost of $118 million (19).



     In a detailed study for siting 1000 MW nuclear power plants in



the Pacific Northwest (55), natural draft cooling towers were recom-



mended at a number of locations.  At all sites the estimated initial



cost of such towers and related appurtenances was about $7.5 mil-



lion, or approximately 5.5% of a total plant capital cost of about



$140 million.  Induced draft towers were recommended in one case,



also at a capital cost of about 5.5% of the total plant cost.  The



cost of a 2600-acre pond at a location conducive to that type of



cooling system would be about 2.3% of the total plant cost.  It



should be noted, however, that the pond location was in an area of



relatively low land value.



     These examples indicate that evaporative cooling systems will



increase the capital cost of a power plant by about 5%.  An assess-



ment of all fixed and variable costs indicates that power produc-



tion costs are also increased by about 5% (19).   It should be noted,



however, that such increases are not carried over to consumer costs

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                                                                 81



in the same proportion because of intermediate fixed costs in-



curred through transmission and administration.   According to



Converse (19), production cost is only about one-fifth of consu-



mer cost.  In that case, the cost of electricity to the consumer,



because of the use of evaporative cooling towers, would increase



approximately 1%.





             TRANSPORT AND BEHAVIOR MANIPULATION





             Dispersion and Dilution Techniques



      The design of discharge outfalls is, at the present time,



more art than science.  Hydraulic model  studies, along with other



empirical information, are new the basis for design because theo-



retical equations of fluid motion have not yet reached the stage



of engineering aoplication.  Future developments in the area of



mathematical  models, hopefully, will place the design of outfall



structures more on a theoretical, rather than empirical, basis.



      The physical and hydraulic characteristics of the effluent



and receiving water largely determine the rate of dispersion and



areal  extent  of dilution.  Rate of dispersion is a function of the



existing turbulence of the receiving water, turbulence induced by



the kinetic energy of the effluent, and  the density gradient be-



tween  the effluent and receiving water.   The areal extent of dilu-



tion is a function of the dispersion rate plus the number and

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82




orientation of ports in the discharge manifold.   Outfalls should



be designed to accomplish specific objectives.



      If the objective is to minimize temperature gradients within



the water body, a diffuser designed to maximize  induced turbulence



and to distribute the discharge over a broad area is recommended.



The diffuser pipe could be placed in any of the  three spacial  dimen-



sions of the water body, but common practice is  to use a horizontal



diffuser pipe placed across the stream.



      A discharge technique which is quite common with TVA is  the



use of a discharge channel which floats  the warm water on the  sur-



face of the receiving stream or reservoir.  The  objective of this



method is to maximize dissipation of heat to the atmosphere and



minimize the water areas and volume affected by  the effluent;  mix-



ing is not desired.  By forming a warm water wedge over the cool



receiving water, rapid heat loss to the  atmosphere is encouraged



by increasing the energy transfer due to evaporation, convection,



and back radiation.  Thus, the warm water wedge  acts in much the



same manner as a cooling pond.  However, this technique results in



sharp temperature gradients near the surface and serious problems



can occur if temperature sensitive organisms are subjected to  such



gradients.  For example, this technique would not be desirable on



a stream inhabited by a cold-water fishery.



      A third alternative discharge technique is to develop a



thermal plume.  A single-point discharge below the surface of  the

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                                                                 83
receiving water will result in a plume extending in the direction



of the water flow and vertical density gradient.  Mixing is oro-



tnoted by both the energy of the receiving water's current and by



the kinetic energy of the discharge.  In some streams where plumes



originate near the bed, vertical mixing is rather rapid, but



lateral mixing is slower.  For example, plumes from AEC's nuclear



reactors at Hanford, Washington, on the Columbia River exhibit



such characteristics.



      A term which has recently been appearing in the literature



regarding thermal pollution is "thermal block."  A thermal block



occurs when a warm water mass interferes with fish migration (76,



p. 31).  Outfalls should be designed to prevent such a block from



occurring.



      A final point must be made concerning the control of heated



discharges by dispersion and dilution.  Such techniques cannot be



expected to solve the problems associated with the discharge of



large heat loads into moderate volumes of receiving water.  Any



heated discharge which will promote excessive temperature rises



will require the use of cooling devices.





                  Hater Quality Management





Temperature Prediction



      Mathematical  and physical  models of varying degrees of com-



plexity have been developed to determine the fate and persistence

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84



of heat in quiescent waters, flowing streams, estuaries,  and the



ocean.  The ability to predict water temperatures accurately is



necessary in order to determine the thermal  impact of:



     1.  Proposed waste heat discharges.



     2.  Changes in the hydraulic characteristics of a  water



         body or stream—for example, due to the construction



         of a dam with its resulting flow regulation.



     3.  Releases of water from stratified reservoirs with



         multilevel outlets.



     4.  Unusual meteorological conditions.



     The following discussion presents the basic approach which



is used to solve temperature prediction problems.  However, the



mathematical formulation of the physical  heat transfer  processes



which occur is not a simple matter.  The  scope of this  guide pre-



vents a presentation of the mathematical  derivations leading to



temperature prediction models for all situations.  However, a



simplified case is presented in the example problem of  the next



section.  For information on more sophisticated models, the reader



is urged to consult the technical literature.  An excellent basic



reference is the Edison Electric Institute's Publication  No. 65-902,



Heat Exchange in the Environment, by J. E. Ldinger and  J. C. Geyer,



Department of Sanitary Engineering and Water Resources, The Johns



Hopkins University, June 1, 1965 (27).

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                                                                 85



      It is necessary to consider heat transfer mechanisms in



water and between water and the atmosphere in order to describe



temperature regimes mathematically.  For localized problems,



e.g., outfalls or plumes, the mechanisms acting in the water



are most important; analysis of conditions throughout larger



systems (rivers, reservoirs, etc.) requires emphasis on the air-



water heat transfer mechanisms as well as those in water.   In



either case, specific predictions are desirable so that effec-



tive control or management techniques can be applied.



      There are two heat transport mechanisms which occur in



water--advection and dispersion or turbulent mixing.  Advection



is the transport of heat by the motion of a mass of water and is



accomplished through ordinary streamflow, utilization of a dis-



charge stream's kinetic energy, or water movement due to density



gradients.  Mathematical terms for advection express the rate of



heat energy transfer in terms of the water mass temperature and



velocity along longitudinal, lateral, and vertical axes.



      Turbulent mixing or dispersion cause heat interchange through



eddy diffusion or molecular diffusion.  Eddy diffusion occurs under



turbulent flow, which depends on fluid velocity and channel



characteristics.  Mixing results from the action of small  fluid



masses known as eddies, which are random both in size and orienta-



tion.  Molecular diffusion is that resulting from random motion



of molecules.   Its influence is much less than that from turbulent

-------
86
mixing.  Diffusion effects are combined in mathematical expres-
sions, and may be defined along longitudinal, lateral, and
vertical axes.
      Heat exchange which takes place between the water surface
and the atmosphere is made up of seven mechanisms.
      The mechanisms which are independent of water temperature
are (27):
      Qs = Incoming short-wave solar radiation (400 to 2800
           BTU/ft2/day).
      Q, = Incoming long-wave atmospheric radiation (2400 to
       a
           3200 BTU/ft2/day).
      Qsr  Qar = Portions of both short-wave and long-wave
                 radiation which are reflected or scattered by
                 the water surface (40 to 200 and 70 to 120
                 BTU/ft2/day, respectively).
      The mechanisms of heat transfer which are dependent on the
surface water temperature include the following (27):
      Qbr = Long-wave back radiation from the water to the
            atmosphere  (2400 to 3600 BTU/ft2/day).  It is pro-
            portional to the fourth power of the absolute water
            surface temperature (AT$), i.e., 0.^ <* (ATS)  .
      Qc  = Heat exchange due to conduction-convection (-300 to
            +400 BTU/ft2/day), which is proportional to the wind
            speed  (W) and the difference between water temperature

-------
                                                                87
            (T_) and air temoerature (T J, i.e., (1  cc W(TC-T ).
              b                        a          c      b  a
            A positive Qc indicates an energy loss.
      Qe  = Heat loss due to evaporation (2000 to 8000 BTU/ft2/
            day), which is proportional to the product of wind
            speed (W) and the difference between the water vapor
            pressure in saturated air at the water temperature
            (es) and the water vapor pressure in the overlying
            air (ea), i.e., Qe <* W(es - ea).  If ea > es, conden-
            sation takes place and the water body gains energy.
      The algebraic sum of these surface heat exchange parameters
is equal to the net rate of surface heat exchange.  Equilibrium
temperature is reached when this sum is zero.
      Micro Models.--In temperature prediction terminology, a micro
model is one which describes or predicts the distribution of heat
in the immediate vicinity of a thermal  discharge.  The micro models
available at the present time are based on many simplifying assump-
tions which render them less than totally adequate for predicting
local temperature distributions.  However, they are useful for
approximating heated discharge dilution rates by receiving waters.
Theoretical work is  progressing in areas such as mixing and dis-
persion and will aid in development of generalized micro models
for jets and plumes.
      Another factor which adds to difficulties with micro models
is the  unique character of many situations.   For example,  the nature

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88




of a stream channel at any location will influence mixing charac-



teristics.  Curvature or depth variation may direct discharges into



certain portions of a channel, thereby nullifying the theoretical



description of the length or degree of mixing.   Each situation will



therefore require careful description in terms  of discharge pumping



rate, river flow, and channel characteristics.



      Until generalized micro models can accurately predict local



temperature distributions under various hydraulic conditions, esti-



mates based on simplified models and past experience will be required.



      Macro Models.--Macro models are those which describe or pre-



dict temperature regimes in a complete river or river system, lake



or reservoir, estuary, or coastal area.  Such models combine heat



transfer mechanisms and water movement on a continual basis with



respect to time.  With the current state of the art, technology for



macro-prediction is more reliable than for micro-prediction.  This



is possible because of the compensating and averaging effects of



spacial differences in environmental variables.



      A macro model maintains an energy budget for the water body



under consideration, i.e., it maintains a heat balance of both the



internal heat exchange and the heat transfer at the water surface.



This heat budget may be expressed as follows:



       (Rate of Heat In) - (Rate of Heat Out) + (Rate of Heat



      Storage) + (Rate of Heat Exchange at Water Surface) - 0



The rate at which heat flows into and out of the water body is

-------
                                                                 89
determined from the flow rates and temperatures of inflowing and
outflowing water.  These rates require evaluation of the heat
transfer mechanisms in water to define the motion of heat entrained
water masses.  The rate of heat storage is determined from the
temperature and volume of the water body in consecutive time
periods.  The rate of heat exchange at the water surface is the
algebraic sum of all the water-atmosphere heat exchange rates.
      Macro models evaluate terms in the heat budget over specific
time periods, e.g., hourly, daily, weekly, etc.  The rate-time
evaluation results in quantitative values for each portion of the
heat budget for each period through the study time span.  By super-
imposing flow rates on the time scale, the location of a specific
water mass may be determined at any desired time.  For temperature
prediction, a model routes hypothetical masses of water along a de-
scribed course in order to simulate their movement and changes in
thermal properties; temperatures are thereby predicted at specific
locations and points in time.

Thermal Regulation
      The need to manage our environment has only recently been rec-
ognized, but we now realize that in order to continue the effective
use of our natural resources, environmental management is a neces-
sity.  In terms of thermal pollution control, we can perform water
temperature management through plant siting, coupled with effective
use of regulated river systems.  Effective water temperature predic-

-------
90
tion models will enable water resources managers to predict tempera-
tures which will result from combined dam releases and thermal in-
puts to a system.  Conditions can then be selected to minimize un-
desirable thermal effects.  Such temperature-discharge requirements
can be met through the use of multilevel dam outlets which permit
waters of various temperatures to be selectively released from
stratified reservoirs.

                       EXAMPLE PROBLEM
      This section presents a problem concerning temperature predic-
tion on a well-mixed stream and the sizing of flow-through cooling
ponds.  A complete explanation of the methodology is beyond the scope
of this guide, and the reader is urged to consult the literature for
an in-depth review of the many available computational techniques.
The problem solution uses basic methods, all of which can be found in
the publication by Edinger and Geyer (27).  As an aid in analyzing the
problem, references to appropriate pages in this reference are given.

                        The Situation
      A 1000 MW electrical output nuclear power plant of 33% effi-
ciency is to be located on a medium-sized river in the temperate
region of the nation.  Using applicable hydrologic and meteorologic
data, we wish to compute:
      A.  Downstream temperature, assuming once-through cooling
          and complete mixing in the river.
      B.  The area of a flow-through cooling pond necessary to
          prevent violation of water temperature standards.

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                                                                 91



Part A



     Compute the heat energy entering the cooling water as des-



     cribed in the "Plant Evaluation" section.
     1.  For 33% thermal  efficiency (r\.}:
                     •541-3

         Heat Rate = °  . 1An -  -    = 10,340 BTU/KWH
                     r).  v i uu    .00




     2.  Assuming a 5% in-plant heat loss:



         Heat to cooling water - (0.95 x Heat Rate - 3413)  BTU/KWH



         Heat to cooling water - [0.95(10,340) - 3413]  BTU/KWH



         Heat to cooling water = 6410 BTU/KWH



         Total heat to cooling water for the 1000 MW (106 KW)  plant



           106 KW x 6410 BTU/KWH = 6.41  x IP9 BTU/hr
     Compute the temperature rise in the stream, assuming once



     through cooling and complete mixing.




     Given a design flow in the stream of  3500 cfs,  which in terms



     of Ib/hr is:



          Q = (3500 cfs) (62.4 lb/ft3)  (3600 sec/hr)



          Q =  7.86 x 108 Ib/hr




     Since 1 BTU will raise the temperature of 1 Ib  of water 1°F,




          AT  = AT in river = <6'41  x 10'  BTU/h^	

            r                 (7.86  x 10B  Ib/hr) (1  BTU/lb °F)



          AT  = 8.2°F
            i

-------
92
     Equation for computing downstream temperatures.
     Downstream temperatures are computed by assuming exponential
     temperature decay.  This concept is presented mathematically
     as:

           ^= -K(T - E)                             (27, p. 43)

     where -rr = net rate of water surface heat exchange  (BTU ft   day   )

            K = energy exchange coefficient (BTU ft   day'  °F   )
            T = water surface temperature (°F)
            E = equilibrium temperature (°F)

     For a well-mixed stream, this equation can be written as:

         pCpyu|I = -K(Tx - E)                       (27, p. 129)
                                         _3
     where  p = water density (62.4 Ib ft  )
           C  = specific heat of water  (1 BTU Ib"1 °F"1)

            y = mean stream depth (ft)
            U = mean stream velocity (ft day  )

           TT~ = longitudinal temperature gradient  (°F ft" )

            x = downstream distance (ft)
     Define T  = temperature at x = o; then
                           -Kx  )
                          Pcpyu
            Tx = (T  - E)e
             /\     \J
                       Kx
     By defining a =  ^  y  ; then

            T  = (T  - E)ea + E
             x   v o

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                                                             93

Meteorologic Data

The following data are used in determining K and E:


Time Period
(6 hr intervals)
Midnight - 6 am
6 am - Noon
Noon - 6 pm
6 pm - Midnight
DAILY AVERAGE
For K
1 1
Wind ,u.
Speed w
(mph)
4.0
12.0
12.0
6.0
8.5

1
Net Radiation ,u ,
Input (tV
(BTU ft-* hr-1)
120
290
320
130
215
For E

Air (T ,
Temp 1V
(°F)
65
75
85
70
74


Relative
Humidity
{%}
40
30
20
35
--

Water Vapor '
Pressure of (e )
Ambient Air
(mm Hg)
6.3
6.7
6.2
6.6
6.5
Determination of K

The energy exchange coefficient is computed using a

variation of the equation given on page 48 (27):

     K = [15.7 + (0.26 + 3)(bW)]

where W = wind speed (mph)

      b = experimental evaporation coefficient  (a value of

          15 is used in this example)

      (3 = proportionality coefficient [See following table]

            Range of E              g
               (OF)(mm Hg op-I)

             50 to 60              0.405
             60 to 70              0.555
             70 to 80              0.744
             80 to 90              0.990

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94
     Thus, for an average daily value of K, using W = 8.5 mph:

          K = (15.7 + [0.26 + 3]  [(15) (8.5)])

     Using appropriate values of 3 for two ranges of E:


            i (°F)        K(BTU ft"2 day"1 °F"])

         60 to 70         120
         70 to 80         144

     Determination of E

     The equilibrium temperature is reached when the rate of change

     of energy at the water surface equals zero.  Edinger and Geyer

     (27) present a method for computing E (pp. 55-59). The method

     involves assuming a likely 10°F temperature range for E and by

     using the appropriate value for K and the given meteorological

     data, computing a value for E.  If the computed value of E falls

     within the assumed range, the process is complete. However, if

     the computed value of E falls outside the assumed range,

     another range must be assumed and the process repeated until E

     falls within the proper limits.  Thus, E is computed by a trial

     and error method.


     For the stated meteorological conditions and computed values

     of K, we can determine a daily average E by the following seven

     steps (27):

     Step 1.  Assumed range of E = 70 to 80°F

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                                                                95
Step 2.  Compute F(K) for use in step 6:
            K - 15.7
     F(K) =
               K
As computed for an E range of 70 to 80°F, K = 144 BTU ft"2 day"1 °F
     .'. F(K) -  ^ 144  - = °-891
Step 3.  Compute E-, for use in step 6:
          HD - 1801
     E  =
     -1       K
                                                        7    1
     From the meteorologic data table, HR =  215 BTU ft   hr

     or in terms of days, HR = 5160 BTU ft"2 day"1

      •     -  5160 - 1801  _
Step 4.  Compute E? for use in step 6:
          (0.26) (Ta)
     E2 ~ "(0.26 + 3)
     From the meteorologic data table, T  = 74°F, and from
                                        a
     the table of E range vs. 6, 3 = 0.744

      .  F  _ (0.26) (74)    _ ,q
     '  '  L2   (0.26 + 0.7447   Iy^
Step 5.  Compute E~ for use in step 6:
          e, - C(3)
           a
      3   (0.26 + 3)
     From the meteorologic data table, e  = 6.5 mm Hg.  C(3)
                                        a
     is related to ranges of E as follows:
           Range of E             C(3)
              (OF)   "            "(mm Hg)
            50 to 60              -11.22
            60 to 70              -20.15
            70 to 80              -33.30
            80 to 90              -53.33

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96
           Thus  for  an  E  range of  70 to  80°F, C(6) =  -33.3

           .   E   _ 6.5  - 1-33.3)   _ -q fi
          '  '  3   (0.26  +  0.744)   Jy'D

     Step  6.   Compute M for use in step  7:

          M =  E1  +  F(K) (E2 + E3)


          M =  23.3 + (0.891)  (19.2 + 39.6) = 75.7

     Step  7.   Compute E using the  following relationship:

          M=E+0.051E2
                     K

          Inserting M and  K and setting  up a quadratic equation  gives:


           2  °°

                       E - 75.7 - 0
          .'. 0.000354E2 +  E  - 75.7 - 0

          Solving  this equation using the quadratic formula gives:


          F  = -1 ± [1 -  (4)  (0.000354)  (-75.7)]1/2
          t        ~    2  (0.000354)


          F  = -1 ± (1.10719)172 =  -1 ±  (1.05223)
                   0.000708          0.000708
          Rejecting  the negative  value gives:

            =  n'nnrwna =  73.8°F   (This value  is  acceptable  because  it
                         	   falls within
                                 70  to 80°F.)
falls within the assumed range of
     Compute  Average  Stream  Velocity

          Q = 3500  cfs

     Given an average cross  section 800  feet wide  and  5  feet  deep:
          U  =             S  ft)  =  °'875  ft/sec = ZS^OO  ft/day

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                                                               97



Evaluation of a



          -Kx
     a =
         pCpyU
     For x'  in miles:  a = (      (1) (5) (75,600)
     a = -0.0322x'
Solve for T ,  for x1  = 10,  20,	50 miles
           X



     Assume unheated  river  temperature = 74 F



     .-.  TQ =  74°F +  ATR =  74°F + 8.2°F = 82.2°F




     TX,  = (TO - E)e-°-0322x'  + E



     For  x'  =  10 miles



     T ,  = (82.2-73.8)e-(°-0322>(10)+73.8
      X



     Tx,  = (8.4)e'°-322 + 73.8




     T ,  = (8.4) (0.725) +  73.8 = 79.9°F
      x
     For x'  =20 miles




     Use same value of a and replace T  by T ,  for x'  =  10  miles:
                                      0     X



     T ,  = (79.9 - 73.8) (0.725)  + 73.8 =  78.2°F
      A




     fojlA'  = 3°» 40'  50 miles



     Following  the same procedure:




     30 miles, T ,  - (78.2  - 73.8) (0.725) + 73.8 - 77.0°F
                X



     40 miles, T ,  - 76.1°F
                A



     50 miles, T ,  = 75.5°F
                X

-------
98

     These values represent the exponential temperature decay

which is graphically shown on the following plot:
Q  70
              Plant
  10         20        30
Distance Downstream from Plant
            (miles)
50
     This graph presents an idealized picture of the downstream

temperatures, since the computations were based on average daily

conditions, and thus no diurnal effect is evident.  It also assumes

that the weather data on which K and E are based are indicative

of conditions along the 50-mile stretch of the river.  In addition,

no tributary inflows or heated discharges are accounted for in the

50 miles.

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                                                                99



     The diurnal effect may be evaluated by using the six-hour



average meteorologic conditions given previously.  Following the



methods described, values of K and E were computed as:
Time Period
(6 hr intervals)
Midnight to 6 am
6 am to Noon
Noon to 6 pm
6 pm to Midnight
K
(BTU ft"2 day"1)
56
196
241
76
E
(°F)
53.8
79.2
84.0
58.1
0
(°F)
71
72
78
76
     The values of water temperature (T ) just upstream from the



plant reflect natural diurnal fluctuations.



     Using the exponential temperature decay relationship presented



previously and assuming slug flow in the stream, i.e., no longitudi-



nal mixing, the variation in temperature was computed for a parcel



of water which left the plant location at 6 pm.  The following



graph demonstrates the effect of diurnal variations in meteorological



conditions on the temperature of the water parcel for a distance of



50 miles downstream.  Note that the initial temperature of the



parcel is equal to the natural stream temperature (T ) plus the



temperature increase of 8.2°F caused by the plant discharge.

-------
100
                 TEMPERATURE OF A WATER PARCEL
    85
 Q)

 3

 O
 v_
 Q)
 a


 I


 E
 o
 «
 +-
 to
80
    75
             I
I
I
             10         2O         30        40

                Miles Downstream from  Plant
                                                          50
                          Time (Military)
0
o
00

o
o
^j-
CM
O
O
(Q
O
O
O
CM

O
O
5j-
CVI
O
O
CM
"™ *
O
o
^-
CM
6 '
o
CM

O
O

CM

-------
                                                           101
Part B
     Assuming a maximum allowable daily average stream temperature

of 80°F, what flow-through cooling pond area would be required at

the site?  The following sketch  describes the plant-river-pond lay-

out:
Q! = 1500 cfs

I, = 74° F
  RIVER
                             Q3 = 1500 cfs

                             T3 = 93°F
          COOLING
            POND
Q0=3500cfs^)
T0=74°F    '
,02= 2000 cfs
1T2 = 74°F
/Q4= 1500 cfs
 T4=   ?
   ;= 3500 cfs

-------
102



     Temperature Rise Through Plant



     Heat to cooling water = 6.41  x 109 BTU/hr



     Condenser flow = 1500 cfs = 3.37 x 108 Ib/hr
     AT  = AT through condenser =                   - = 19.QoF

       C                          (3.37 x 10b lb/hr)(l  BTU/lb °F)




       . T  = 74°F + 19°F = 93F
     Temperature Drop Through Pond



          A flow-through cooling pond is  assumed to be well  mixed



     in each cross section, but as in a stream,  there is a longitu-



     dinal temperature decay.  Thus,  the  equation for predicting the



     temperature drop through the pond is equivalent to the  exponen-



     tial  temperature decay equation  used on we'll -mixed streams.



          Using the temperature subscripts given on the sketch, the



     temperature from the pond can be computed by:




     T4 =  (T3 - E)e'a' + E                              (27, p. 113)




      ,      ,     KA
     where a  = ~r~nr~

                pCPQ3


                                  3    -1
          Q3 = plant discharge (ft  day  )


                            2

           A = pond area (ft )



          Using an experimental evaporation coefficient (b)  of 12, K =



     118 and E = 76.9 F.  These values are used  in the subsequent



     cooling pond calculations.

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                                                           103
Case I - Pond area required for discharge from pond =  80°F.




     .'.  T  = 80°F
     Solving the prediction equation for a'



     80 = (93 - 76.9)e"a'  + 76.9
     e~a= (80 - 76.9) / (93 - 76.9)
     e"a= 0.193
     .-. a'  - 1.65



     Solving the a'  equation for A:
     a< = T6274T7lTTi500jT24 hr/dayj73600 sec/hrj
     a1 = (1.46 x 10~°)A - 1.65




     .'.A = (1.65)7(1.46 x 10~8)  - 11.3 x 107 ft2
     In  acres: A =
                    (4.36 x 1(T ftVacre)
Ca,se__n_ - Pond area required for mixed river temperature  =  80  F.



     If a mixing zone is allowed in the stream such  that  the



mixed river temperature below this zone is equal  to  or less



than 80°F, a much smaller pond could be used.

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104

     Referring to the sketch:
     Solving for T. :


     T    T5Q5 - T2Q2 = (80)  (3500) - (74) (2000)
      4       Q4                  1500


     . M  = 88.0°F
     By using the same computational  techniques as for Case I

     a1 = 0.373

     .'.  A = (0.373)/(1.46 x 10"8) =  2.55 x 107 ft2


     in acres:  A = ^55 x 10' ft*> - = 585 acres
                   (4.36 x 10^ ft /acre)    -

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