unesco aquatic effects of water pollution

8/3/2019 UNESCO aquatic effects of water pollution

1/170


2/170

Technical papers in hydrology 20


3/170

In thisseries1 Perennial ice a n d s n o w m a s s e s . A guide for compilation a n d a s s e m b l a g e

of data for a w o r l d inventory.2 Seasonal s n o w cover. A guide for m e a s u r e m e n t , compilation and

a s s e m b l a g e of data.3 Variations of existing glaciers. A guide to international practices for

their m e a s u r e m e n t .4 Antarctic glaciology in the International Hydrological D e c a d e .5 C o m b i n e d heat, ice and water balances at selected glacier basins. A

guide for compilation and assemblage of data for glacier m a s s balancem e a s u r e m e n t s .

6 T e x b o o k s on hydrologyanalyses and synoptic tables of contents ofselected textbooks.

7 Scientific f r a m e w o r k of wo rl d water balance.8 Flood studiesan international guide for collection and processing of

data.9 G u i d e to wo rl d inventory of sea, lake, and river ice.

10 Curricula and syllabi in hydrology.11 T e a c h i n g aids in hydrology.12 Ecology of water w e e d s in the neotropics.1 3 Th e teaching of hydrology.14 L e g e n d s for g e o h y d r o c h e m i c a l m a p s .15 Re se a rch on u r b a n hydrology, vol. 1.16 Re se a rch on u r b a n hydrology, vol. 2.17 Hydrological p r o b l e m s arising f rom the d e v e l o p m e n t of energy.18 U r b a n hydrological modelling and c a t c h m e n t research, international

s u m m a r y .19 R e m o t e sensing of s n o w and ice.2 0 Predicting effects of p o w e r plant once-through cooling on aquatic

systems.


4/170

A contribution to theInternational Hydrological Programme

Predicting effects ofp o w e r plant o n c e - t h r o u g hcooling o n aquatic systems

A state-of-the-art reportof IHP Working Group 6.2on the effectsof thermal discharges

Chief editors:W . Majewski andD . C. Miller

yiesoo


5/170

T h e designations e m p l o y e d a n d t h e presentation of the material d o notimpl y the expression o f a n y o p i n i o n w h a t s o e v e r o n t h e p a rt o f U n e s c o c o n cerning the legal status o f a n y country or territory, or of its authorities, o rconcerning the frontierso f a n y c o u n t ry o r territory.

Published in 19 79 by theU n i t e d N a t i o n s E d u c a t i o n a l , Scientific a n d C u lt ur a lOrganization7 , place d e F o n t e n o y , 7 5 7 0 0 ParisPrinted by Etienne Julien, ParisI S B N 9 2 - 3 - 1 0 1 7 0 4 - 7 U n e s c o 1 9 7 9Pr imed in France


6/170

Preface

T h e "Technical Papers in H y d r o l o g y " series, like the related collection of "Studies and Reports in H y d r o logy", w a s started in 1965 w h e n the International Hydrological D e c a d e w a s launched by the G e n e ra l C o n f e rence of U n e s c o at its thirteenth session. T h e aim of this undertaking w a s to p r o m o t e hydrological sciencethrough the d e v e l o p m e n t of international co-operation and the training of specialists and technicians.

Population g r o w t h and industrial and agricultural development are leading to constantly increasingd e m a n d s for w a t e r , hence all countriesare e n d e a v o u r i n g to i m p r o v e the evaluations of theirwater resourcesa n d to m a k e m o r e rational use of t h e m . T h e I H D w a s instrumental in p r o m o t i n g thisgeneral effort. W h e nthe D e c a d e e n d e d in 1974, I H D National C o m m i t t e e s hadbeen f o r m e d in 1 0 7 of U n e s c o ' s 1 3 5 M e m b e r States to carry out national activities a n d participatein regional a n d international activitieswithin the I H D p r o g r a m m e .

U n e s c o w a s conscious of the need to continue the efforts initiated during the International Hydrological D e c a d e and, following the r e c o m m e n d a t i o n s of M e m b e r States, the Organization decided at its seventeenth session to launch a new long-term intergovernmental p r o g r a m m e , the International HydrologicalP r o g r a m m e ( I H P ) , to follow the d e c a d e . T h e basic objectivesof the I H P w e r e defined as follows: (a) to p r o vide a scientific f r a m e w o r k for the general d e v e l o p m e n t of hydrological activities; (b) to i m p r o v e the studyof the hydrological cycle and the scientific m e t h o d o l o g y for the assessment of water resources throughoutthe w o r l d , thus contributing to their rational use; (c) to evaluate the influence of m a n ' s activities on thew a t e r cycle, considered in relation to environmental conditions as a w h o l e ; (d) to p r o m o t e education andtraining in hydrology; (f) to assist M e m b e r States in the organization and d e v e l o p m e n t of their nationalhydrological activities.

T h e International Hydrological P r o g r a m m e b e c a m e operational on 1J a n u a r y 1976 and is to be executed t h ro u gh successive phases of six years' duration. I H P activities are co-ordinated at the international levelb y an intergovernmental council c o m p o s e d of thirty M e m b e r States. T h e m e m b e r s are periodically electedb y the G e n e r a l Conference and their representatives are chosen by national committees.

T h e "Technical Papers in H y d r o l o g y " series is intended to provide a m e a n s for the e x c h a n g e of inform a t i o n on hydrological techniques a n d for the co-ordination of research a n d data collection. In order to coordinate scientific projects, h o w e v e r , it is essential that data acquisition, transmission and processing beconceived in such a w a y as to permit the c o m p a r i s o n of results. In particular, the e x c h a n g e of informationo n data collected throughout the world requires standard instruments, techniques, units of m e a s u r e m e n ta n d terminology.

It is believed that the guides on data collection and compilation in various specific areas of hydrologyw h i c h h a v e been published in the "Technical Papers in H y d r o l o g y " series h a v e already helped hydrologiststo standardize theirrecords of observations a n d thus h a v e facilitated the study of h y d r o lo g y on a w o r l d - w i d ebasis.

M u c h stillremains to be d o n e in this field, h o w e v e r , even as regards the simple m e a s u r e m e n t of basicelements such as precipitation, s n o w cover, soil humidity, run-off, sediment transport and g r o u n d - w a t e rp h e n o m e n a .

U n e s c o therefore intends to continue the publication of "Technical Papers in H y d r o l o g y " as an indispensable m e a n s of bringing together and m a k i n g k n o w n the experience accumulated by hydrologiststh r o u g h o u t the w o r l d .

5


7/170

Contents

FOREWORD

I. INTRODUCTION1113

1.5

II.SUMMARYII.II .II .II.II.II.II.II.II,II,IT,II.II,II,

III.SUMMARYIII.III.III.

The Need, Objective and Scope of the ManualPlace of Environmental Impact Assessment in Planning New Electrical

Generating PlantsPredictive Environmental Impact AssessmentSteam Electric Plant Cooling Water RequirementsPlant Siting and Cooling System Design Options to Meet CoolingRequirementsPOTENTIAL AND OBSERVED ECOLOGICAL EFFECTS OF ONCE-THROUGHCOOLING SYSTEMS

Sources of Potential Ecological ChangesPotential for Adverse Physical/Chemical ChangesPhysical effects on waterChemical effects on waterAtmospheric effectsPotential and Observed Biological Changes From Once-Through CoolingChanges due to physical alterations: Construction of intakesand dischargesChanges from entrapment and impingement at intakes

Change due to entrainment of small organisms with pumped cooling waterChanges from exposure to the cooling system discharge: Near fieldthermal and physical effectsChanges from small temperature elevations over wide areasChanges from power plant chemicalsChanges from total combined stressesPotential Changes Due to Cooling Towers From Entrainment in CoolingTower Makeup WaterA CONCEPTUAL FORMAT FOR COOLING SYSTEM ENVIRONMENTAL IMPACTASSESSMENT PROJECTS

20

S3

III.3

IntroductionThe conceptual assessment formatProbability of Hydraulic Involvement of the Biota: SiteHydrographie Modelling and Preliminary Field StudiesProbability of Direct Biological Damage

Description,


8/170

IV. P H Y S I C A L A S P E CT S O F I NTA K E A N D D I S C H A R G E O F C O O L I N G W AT E R 68S U M M A R YIV ,IV ,IV ,IV ,IV ,IV ,IVIVIVIVIVIVIVIVIVIVIVIV

V .S U M M A R Y

I n t r o d u c t i o nI n t a k e a n d D i s c h a r g e O u t l e t o f C o o l i n g W a t e rW a t e r B o d i e s u s e d f o r O n c e -T h r o u g h C o o l i n gR i v e r sL a k e sR e s e r v o i r sE s t u a r i e sC o a s t a l w a t e r sC o o l i n g W a t e r I n t a k eS o m e i n t a k e d e s i g n r e q u i r e m e n t sE x a m p l e s o f i n t a k e s t r u c t u r eV e l o c i t y a n d t e m p e r a t u r e ' f i e l d s n e a r t h e i n t a k e S t u d i e s o f s e l e c t i v e w i t h d r a w a l D i s c h a r g e o f H e a t e d W a t e rB u o y a n t s u r f a c e d i s c h a r g e sS u b m e r g e d d i s c h a r g e sS t r a t i f i e d f l o wM e t h o d s o f i n v e s t i g a t i o nH E AT E X C H A N G E B ET W E E N W AT E R A N D ATMO S P H E R E . A N D W AT E R L O S S B Y E V A P O R ATI O N 8 7 C o m p o n e n t s o f S u r f a c e H e a t E x c h a n g eN e t s o l a r r a d i a t i o n ( R s n = R s - R s r )N e t a t m o s p h e r i c r a d i a t i o n ( R a n = R a - R a r ) L o n g - w a v e r a d i a t i o n e m i t t e d f r o m t h e w a t e r b o d y , L bE v a p o r a t i v e h e a t f l u x H eC o n d u c t i v e ( s e n s i b l e h e a t f l u x H c )H e a t E x c h a n g e C o e f f i c i e n t a n d E q u i l i b r i u m Te m p e r a t u r eE v a p o r a t i v e L o s s e sF o g F o r m a t i o nR e c o m m e n d a t i o n s f o r P r a c t i c e

V I .S U M M A R YV IV IV IV IV IV IV iV Iviv V IV IV IV IV IV I . 7

P R E D I CTI O N A N D M O N ITO R I N G O F W AT E R V E L O C ITY A N D TE M P E R AT U R E F I E L D SI n t r o d u c t i o nP r e d i c t i v e T e c h n i q u e sM a t h e m a t i c a l m o d e l sP h y s i c a l m o d e l sC r i t e r i a f o r t h e C h o i c e o f P r e d i c t i v e Te c h n i q u eP h y s i c a l B a s i s f o r H y d r o t h e r m a l A n a l y s i s M a t h e m a t i c a l M o d e l sG o v e r n i n g e q u a t i o n sA p p l i c a t i o n o f m a t h e m a t i c a l m o d e l s t o d i f f e r e n t w a t e r b o d i e sP h y s i c a l M o d e l sS c a l e r e q u i r e m e n t sM o d e l c o n s t r u c t i o n a n d e q u i p m e n tR e c o m m e n d a t i o n sM o n i t o r i n g o f W a t e r V e l o c i t y a n d Te m p e r a t u r eP r e o p e r a t i o n a l m o n i t o r i n g a nd s u r v e y sP o s t - c o m m i s s i o n i n g m e a s u r e m e n t s

104


9/170

VII.SUMMARY

PREOPERATIONAL COOLING SYSTEM IMPACT ASSESSMEN T:BIOLOGICAL INFORMATION REQUIREMENTS PHYSICAL AND 118 VII.VII.VII.VII.VII.VII.VII.VII.VII.VII.VII.VII.

IntroductionSite and Receiving Water Description and Preliminary Power PlantDesign InformationSite location and layout (proposed)Hydrodynamic and meteorological informationSediment transportPlant operation data (proposed)1 Intake structures2 Pumps3 Heat exchangers4 Biofouling control5 Entrainment thermal experience6 Other relevant data on cooling water circulation system, intakeand receiving waterVII.2.5.7 Outfa ll configurati on and operationVII.3 Hydrological and Meteorological Information to Assess Cooling System IiipactVIP.3.1 Intake structure and pumped entrainment consideration sVIT.3.2 Cooling water discharge considerationsVII.4 Preliminary Biological InformationVII.4.1 Information neededVII.4.2 Identification of topics for detailed site-specific studiesVIT.4.3 Identifying low-risk biota VIT. 5 Detailed Preoperative Ecological StudiesVIT.5.1 Selection of representative and important species potentiallyreceiving significant impactVII.5.2 Laboratory studies to predict direct biological damagesVIT.5.3 Detaile d field studies VIT.6' Summary and Interpretation of Preoperational Impact Assessment DataVIT.6.1 Data reduction and analysisVIT.6.2 Predictive biological modelsVITT.SUMMARYVIII.VIII.VIII.VIII.VIII.VIII.VIII.VIII.VIII.

OPERATIONAL MONITORING OF COOLING SYSTEM IMPACTS

IntroductionThe Question of Significance of Observed ImpactsApproaches for Biological MonitoringThe holistic approachReference stationsMonitoring direct effectsEvaluating popu lation consequences of cooling system dama ge Monitoring community and ecosystem impactReference Material on Methods for Power Plant Impact Montioring

137

IXSUMMARYIXIXIXIXIXIXIX,

BENEFICIAL USES OF DISCHARGE HEATPotential Uses for Low-Grade HeatAquacultureOpen-Field Agriculture Greenhouse Agriculture Animal SheltersSpace HeatingIndustrial Process Heat

14 6


10/170

X CONCLUSIONS AND RESEARCH NEEDS 156X.l ConclusionsX.2 Research Needs APPENDIX I Abbreviations used 163APPEND IX II Glossary of symbols used in Chapters IV, V, and VI 164 APP END IX III. SI SystemConversion TableAPPENDIX IV Main properties of water 171


11/170

Foreword

The hydrological aspects of water pollution were identified as priority study topicsby the Intergovernmental Council of the International Hydrological Programme (IHP) at its firstsession in 1975. The Council agreed that studies should be made of the consequences of increaseduse of natural water bodies for industrial processes or waste discha rge, including the mannerthat waste products are dispersed, accumulated or destroyed in different receiving environme nts.The Council thus established a project Entitled "Hydrological and Ecological Aspects of WaterPollution". These studies are intended to contribute scientific information for pollutionabatement measures and environmental protection. The project is being carried out in closecooperation with relevant UN agencies, especially the Unesco "Man and Biosphere" Progr amme:"The Ecological Effect of Human Activities on the Value and Resources of La kes , Mars hes, andRivers, Del tas , Estuar ies and C oastal Zones1.'The IHP pr oject, "Ecological and Hydrological Aspects of Water Po llution," is comprisedof three sub-projects. The present report is the product of one of these , "Investigations ofthe Effects of Thermal Discharge s". The study draws on the experience of industrialized co untries to examine the environmental problems associated with cooling water use by electric gene rating plants. This sub-project has focused primarily on the tools available for forecasting(prima facie) and monitoring (post facto ) the consequences of power plant cooling water usein the various aquatic environments, as well as reviewing some of the hydrological, atmosphericand ecological effects observed to date at operating p ower plant s.The IHP working group on the effects of thermal discharges was comprised of D r. M.L.Heitmann, Research Institute of Hydrometerology, B erlin, German Democratic R epublic; Mr. J.Jacquet, Electricit de France, Paris, France; Dr. W. Majewski, Polish Academy of Sciences,Gdansk, Poland; Dr. D.C. Miller, U.S. Environmental Protection Agency, Narragansett, R .I., U.S.A.Also , Dr. C.C, Cotant, Oak Ridge National Laboratory, Oak R idge, TN, U.S.A., participated asa representative of Unesco/MAB. Mr . J.A. da Co sta, Unes co, served as Technical Secretary ofthe Group through December, 1977, followed by Mr . W.H. Gilbrich, Unesco. Dr . Majewski chairedthe Working Group.The first meeting of the Working Group was held in Paris in March 1976. Papers onpotential environmental problems and physical aspects of cooling water use were presented byC.C. Cotant and Mr . J.F. Janin (WMO, France). The Working Group agreed to review informationon environmental impact assessment for hydrologists , ecologists and engineers concerned withpower plant cooling system problems. To this end, the manual discusses physical processesat intakes and discharges and identifies the potential for direct biological damage for theentire cooling ciTcuit. The manual should also serve as a source book, as primary methods arecrted for predicting and monitoring physical and ecological changes potentially occurring wit hcooling water use. The primary aim of this report is to enable those charged with the prepa ration of environmental impact assessments to develop an ecologically sound study to evaluatepower plant siting and cooling system design options.The scope, format and general topics to be included in the manual were worked out duringthe first meeting of the Working Group. Chapter assignments were also agreed on. Meetings weresubsequently held in April 1977 in Paris and in January 1978 in Oak Ridge to jointly reviewchapter drafts. The co-editors, Drs . Majewski and Mill er, met in Paris in August 1978 for thefinal review. The chapters of the manual were contributed as follows: Chapter I, Majewski ,Mill er and Cotant; Chapter II, Miller and C otant; Chapter III, Cotant; Chapter IV, Majewski;Chapter V, Heitmann ; Chapter VI , Majewski; Chapter VII and VIII, Miller and Cotant; Chapter IXCotant; Chapter X, Majewski and Miller.

11


12/170

I . Introduct ion

I.i The Need , Objective and Scope of che Manu alCurrently, many countries of the world are planning construction of new electricitygenerating facilities to accomodate population growth and increased industrial and domesticdemand for electric energy. There is now a general tendency to shift from fossil-fuel to nuclearpower plants because of possible future shortage of conventional fueis (oil, coal). These newpower plants are usually large, comprised of one to four unit s, each reaching up to 1000 MW( e)in capacity. Increases in the size of production units and the concentration of several largeunits on a single site results from decreasing capital costs and increasing efficiency of largeunits in comparison with small o n e s. Present nuclear power plants have smaller overall effi

ciencies (30-33 per cen t) than fossil-fue l (40-42 per cent). This results in a greater coolingwater requirement by nuclear power plants.Included with engineering and economic considerations of these large power plants isa concern to minimize deleterious environme ntal effects of their construction and operation.One important environmental problem pertains to the power plant cooling system which requiresvast quantities of water and rejects waste h eat created in process of converting thermal energyto mechanical and finally to electric al. Of many cooling water systems (dry and wet coolingtowers, cooling pond s, and once-through s y s t e m s ), the best efficiencies and the lowest capitaland operational costs of cooling systems are achieved with once-through cooling with the powerplant sited on large natural water bodi es. As these power plants withdraw and pump coolingwater through the condense rs, there is the potential for the entrainment of large numbers oflarval fish and invertebrates. There may also be the problem of entrapment of larger fish andother organisms at water intake structure s. The potential for environmental damage due tothermal addition at the discharge is dependant on the capacity of the receiving water body todilute and eventually dissipate waste heat to the atmosphere.It is the purpose of this manual to introduce some basic procedures to predict ecolo gical impact of once-through cooling for proposed electricity generating plants on aquatic environments. The manual is intended to serve as a source book for the working ecologist and engineerresponsible for designing, implementing or evaluating results of cooling system impact asse ssment studies. Potential environmental problem s, impact assessment approa ches, and physical andbiological information needs are discussed in a general manner . Publications which provide moredetailed information are cited. A chapter on beneficial uses of thermal discharges ic includedto encourage consideration of heat use options as an integral aspect of power plant plannin g.This manual focuses primarily on once-through cooling systems. Assuming adequatewater availability, this represents the first cooling option due to its low initial cost andpotentially higher efficiency. Some environmental problems and limitations of closed-cyclecooling systems are included but not addressed in detail for impact assessment.1.2 Place of Environmental Impact Assessment In Planning NewElectrical Generating Plants

The potential for adverse environmental impact of power plant cooling systems can beminimized by early involvement of specialists in ecology, hydraulics , hydrolo gy, meteorologyand related fields in site selection considerations and proposed cooling system design. Studiesof natural resources and ecological systems should be looked to as important input to these

13


13/170

decisions, and not undertaken post facto to justify choice of power plant site or cooling systemdesigns. Environmentally unsuitable locations for a power plant can be identified early in theplanning cycle; detailed studies will identify site-specific problems which can possibly bemitigated by careful engineering of the cooling systems. Many environmental problems encounteredat power plants today are the direct consequence of poor siting or cooling system designs whichfailed to consider the biological aspects of interfacing with the natural water body. Closed-cycle cooling systems have been looked to as one recourse to reduce impact of power plants onaquatic syste ms. While this may be practical in some situations, closed-cycle cooling is notwithou t its own set of environmental problems which potentially impact not only aquatic, butalso atmospheric and terrestrial environments as well.In some countries , laws require that major projects be reviewed for their environmentalcompatibility before construction. Such a law is the National Environmental Policy Act (NEPA)in the U S A ; other countries are developing similar requir ements. In the USA, NEPA mandates useof a systematic, interdisciplinary planning process involving both the natural and social sciencesfor all major projects under the jurisdiction of Federal agencies . The preparation of environmental impact statements to evaluate the potential for significant environmental effects is oneelement of this process. A thorough evaluation of project alternatives is also required. UnderNEPA , the environmental impact statement is not intended to be a document to support or denypredetermined objectives or decisio ns. Rath er, it is to permit administrative planners toinclude environmental consideratons in their decision maki ng.

1.3 Predictive Environmental Impact AssessmentThe task of predicting the potential impact of an engineering project on the environment is a difficult one. In the case of power plant s, for example, we cannot predict with precision the specific stresses that a given cooling system design will impose on the biota ofwaterway. And we have a very limited understandi ng of the extent that populations of wholeecosystems can compensate for environmental change or direct loss of organisms. The difficultyof impact prediction is also compounded since assessments usually must be completed within ashort time period. Rarely are more than a few years available in a planning programme beforethe major decisions must be made on an activity. As a consequence, it is usually not possibleto undertake ail the ecological studies which one might l ike. Als o, it will not be possible toadequately measure natural ecosystem variations over time. As a consequence, it may not bepossible to determine with certainty whether the data of short-term field studies are indeedtypical for a given sit e, or to predict the extent of natural variation which may occur there

over a period of yea rs. These limitations recognized, an impact assessment team can none theless make a useful appraisal of potential environmental prob lems by drawing on existing ecological principle s, on tne first hand knowledge of experienced fieid biologists and on existinginformation of impacts which have occurred at similar facilities in the past .The field of environmental assessment is a young one , with the preferable studyapproaches and methods still being developed, in addition to looking to ecological and planningconcepts to improve,impact assessment technique s, we can also draw some lessons from the problemsand deficiencies of past studies. Many early environmental impact projects suffered from bothinadequate procedura l guidelines and poor scientific design (Andrews et a l., 1977). Officialguidelines have frequently been too broad and general to provide f ocus, define scope or clearlyindicate the environmental components and relationships which should be considered in an asse ssmen t study. Clarification of such questions is important to the design and conduct of goodassessment wor k.The scientific design of ecological assessment projects can be improved by giving

careful attention to dficiences identified in early impact studies (Andrews et ai., 1977).The3e include:absence of a clear statement of the objective of the evaluation;- failure to ask specific ecological questions or to frame hypotheses and conductstudies to test them;- species lists only tabulate the potential biota or the rare and endangered species;community descriptions primarily qualitative, with little quantitative data onbiomass, spatial heterogeneity or temporal variability;little or no real consideration of community functional as pects , impact vulnerabilityand assimilative cap acitie s, or linkages within and between the various ecolo -

14


14/170

gicai compartm ents, including man ;- reliance on a single index (e.g. a species diversity index or a productivitymeasurement) to describe the health or condition of a community. (Multiplecommunity indices should be used.)Three approaches to ecological impact assessment can be distinguished at present.There are the studies which are primarily des criptive, with impact prediction highly subjective;those which also involve detailed quantitative and experimental assessment for a limited numberof important ecosystem c omponents, usually populati ons; and holistic studie s, which focus on thefunction of the ecosystem as a who le.One common descriptive approach involves listing all potentially relevant aspects ofthe environment, then subjectively evaluating the liklihood of impact by the proposed activityfor each environmental component. The conclusions are often summarized in tabular form (e.g.a Leopold matrix), with the degree of importance of the ecological parameter and the liklihoodof impact rated on a scale of 1 to 1 (Fisher and Davie s, 1973). Other methods of ranking andweighting potential impacts are discussed by Bi sset (19/8).The second type of study also employs an initial descriptive phase to ascertain thenature and makeup of the ecological system in the locality of the proposed pro ject, but thenselects important species and/or community components for detailed invest igations. This wouldinclude experimental studies to measure vulnerability to the proposed activity. This is theapproach pursued in this manual . Selection of the principal study species and species assemblages is typically based on their perceived importance to the ecological system or tneireconomic or aesthetic value to man. Potential susceptibility to impact is also considered inthe selection. If the studies indicate a high potential for appreciable loss of an importantbiotic component, a population model may also be developed to evaluate the long term consequencesof this impact.The holis tic, or ecosystem approach seeks to assess impact potential by studyingproperties and requirements of the total system. As the major functional components of thesystem and their interdependence are identified through energy and materials flow studies andperturbation experiments, it may be possible to discern the consequences of an environmentalchange or of direct loss of biota resulting from an engineering project (Andrews et al. , 1977).Today, elements of eacn of the above three approaches are being incorporated intothe design of predictive impact assessment projects. The studies usually have a preliminarydescriptive phase to ascertain the types of communities and dominant populations present. Withthis informatio n, the scope of the project is defined, based on the subjective judgment bybiologists and engineers of the maximum plausible impact of an activity. If several populationsare selected for intensive study, they are chosen in part because of their interrelationshipswith the larger ecosystem. Few predictive assessment studies have been purely holistic, atleast for aquatic sy stems, although this has been long proposed by professional ecologists(Odum, 19/2). To date , most workers consider the information needs simply too great to developan aquatic ecosystem model which could reliably predict tne consequences of an engineeringproject. Nonthele ss, many holistic concepts and certain ecosystem study techniques have beenshown to be valuable in developing impact assessment projects (Gilliland and Ri sser, 1977). Andthe holistic approach can be quite profitably employed in monitoring for ecological change atoperating power plants (McKeliar, 1977).1.4 Steam Electric Plant Cooling Water Requirements

The production of electric energy in fossil-fuel or nuclear power plants require s theconversion of thermal energy into mechanical energy and finally into electric energy. All energyconversion processes operate at efficiencies less than 100%. The efficiency of steam electricpower production is governed by thermodynamics of the heat cycle. The ideal or Carnot efficiencyis determined by the temperature of the heat source (boiier or nuclear reactor) and the heatsink, which is the surrounding air or water.The ideal efficiency is given by:

usabl e energ y prod uced / -sinkenergy consumed y T xlOOsource

where sink and source temperatures are measured on an absolute scal e. Thus, by decreasing sinktemperature or increasing source temperature increased etficiency may be achieved. There are,

15


15/170

OCDOC

oac"oocI

-ca

1oinninQinmocaC

toicul_Zaeua01amcQoCoo1h< ceuoeu.ai_QJCcoQ.I0

ooinfN

oooCN

ooin^

oCO

OOm

9M

as)UdeM

O

\

aso

cmc

rrF1i-

i

-as

Eac

ccccTco(_

c

a

T

ir=

-C

sinO2mc

COc1JCCBcM3Vc11MCIC366CHUcMcCC6HauocBcXUecMcCco

c

o

^

a

o

c

m

>

Cp36

1


16/170

however, limitations which restrict source temperature to certain values because of technological or protective requirements. Further, sink temperature is dependent on natural meteorological and hydrological conditions. In all mechanical and thermodynamic processes, the working or overall efficiency is much less than the ideal efficiency because of certain additionalinplant and stack losses. At present, the overall efficiency for modern thermal plants isabout 40-42 per cent and for nuclear power plants it.ranges from 30-33 per cent. Thus, in anuclear power plant, for every kilowat-hour (kWh) of produced electric energy, the equivalentof 2 kWh of energy is rejected to surrounding water or atmosphere. For the remainder of thiscentury, it is expected that electric energy will continue to be produced by liquid-vapourcycles using fossil or fission fuels and the power plants overall efficiency will remain inthe 30-40 per cent range. Further, it is necessary to expect that because of economical reasons the power plants will grow in size and lead to greater*concentration of cooling waterconsumption and thermal discharges in one place.

A general scheme of a thermal power plant is shown in Fig. 1.1. Cooling water withdrawn at the intake from the water body is pumped through the condenser. Waste heat derivedfrom low pressure steam leaving the turbine is transferred to the cooling water in condensertubes. Here the cooling water increases its temperature by the value AT and returns to theoriginal water body through the outlet. The rate of heat transfer from the power plant to thecooling water is given byH = Q x p x C p x A T

where: H - rate of waste heat transfer J s--*- or kcal s~lQ - cooling water discharge m3 s~lp - water density kg m~3Cp- specific heat capacity of J kg-^ K~l or kcal kg-^ K -1AT- temperature rise across condensers C

Condenser designs normally produce a temperature rise of cooling water in the range 6-16C.When the temperature rise (i.e. the AT) is low, cooling water use is high. Typical coolingwater requirements for fossil and nuclear power plants, based on current technology arepresented in Fig. 1.2 (US Environmental Protection Agency, 1973).1.5 Plant Siting and Cooling System Design Options to Meet Cooling Requirements

Siting decisions for power plants are generally made primarily for reasons of loaddemand, availability of electricity transmission corridors and fuel transport (coal and oil).Water availability for cooling is also one of the important considerations; in arid lands itmay be the most important. Choice sites for power plants, have included large rivers, naturallakes, existing reservoirs, estuaries and coastal waters.Where a large natural water body is not available, artificial, cooling reservoirs canbe built, provided sufficient amount of. water and land is available. These reservoirs mayrange iti size from 9mall cooling ponds to large artificial lakes. All of these sites can usethe once-through system, although the smaller cooling ponds, are, in fact, closed-cycles. Thedistinction between cooling reservoirs and cooling ponds is not very precise. Cooling pondsusually have high thermal load, small surface area and volume.It is possible for waste heat to be transferred more directly to the atmosphere byusing closed-cycle cooling, like cooling ponds, cooling canals, spray canals or cooling towers(natural draft and mechanical draft.) In these systems, evaporation is a predominant processof heat transfer. These evaporative systems require water to make up for evaporation l o s s , andto remove accumulated salts (blow-down).. Such consumptive water use can be considerable inclosed-cycle cooling. Direct transfer of waste heat from the coolant to air can be accomplishedusing dry cooling towers, where consumptive water use is negligible. Although very expensiveto operate, dry cooling towers are used in arid areas.Once-through cooling systems (including cooling reservoirs) have certain advantagesover closed-cycle cooling. These advantages may be summarized in the following points: lowercapital costs; lower consumptive use of water; lower consumption of energy for pumping of c o o l ing water; dissipation of waste heat to the atmosphere over large area; greater thermal inertia.Disadvantages of once-through cooling are related to the possible damage to aquaticlife as large volumes of water are pumped through the power plant and by subsequent discharge ofheat.

17


17/170

Precise economical comparisons between various cooling systems are rather difficultbecause each power plant site is different. Closed-cycle cooling usually involves higher capitalc o s t s, whether for construction' cooling towers or to acquire land tor cooling pon ds. Consumptivewater use in closed-cycle cooling is usually less than 10 per cent of that used in once-throughcooling systems. Yet this quantity ot water can stiil be considerable and in some cases specialreservoirs may be necessary to provide the required cooling water.. In closed-cycle coolingsystems, additional consumption of electric energy is usually incurred. In wet cooling towers,cooling water- must be pumped to the top of the tower. Forced draft cooling towers requireextra energy consumption for fan operation.Harleman (1976) presents data of overall efficiency reduction for a simulated performanc e of a 100 MW(e ) nuclear steam electric plant located in the temperate zone using differentcooling systems. The power plant has the overall efficiency 33 per cent. Table 1.1, illustratesthe reduction of electric power output due to increased intake water temperature if closed-cycle cooling is employed. Once-through system is taken as the basis for comparison.Large water bodies are well suited for once-through cooling systems . They have greatthermal inertia which means that they do not react rapidly to changing meteorologica l conditionsor varying rates of waste heat discharge from power plants due to load changes . Changes inintake water temperature for once-through systems on large water bodies are of the order ofseveral days while in closed-cycle cooiing sy stems, changes can occur within few hour s. Rapidincrease in intake water temperature results in lower overall efficiency of the power plant.For ecological rea sons, power plant sites are preferable that have low biologicalvalue - that is, they are not located on important migratory route s, spawning or nursery areas,unique habitats , etc. Carerul cooling system design can minimize specific ecological problems(e.gby^ considering type and length of intake or discharge co nduits, configuration of discharge ports ,orientation and location of intake structures and screens). Knowledge of important physical andbiological processes occuring at potential sites can provide the necessary information forselecting the most appropriate designs.One important design decision is the relationship between A T and volume of coolingwater (Fig. 1.2) . The amount of heat to be dissipated remains constant bu t, within ce rtainlimits, A T and water volume can be varied. The more water pumped, the lower the AT will be. Alarge A T often results in greater thermal impacts while large volumes of cooling water can causelarge losses of entrained organisms through physical damages at intakes and during passage through

H E A T E X C H A N G E A N D E V A P O R A T I O N B EN EF IC IA L U S E S O F(CHAPTER 5) D I S C H AR G E D H E A T(CHA PTER 9)

Figure 1.3 Heat exchange

18


18/170

the cooling system. The type of biota to be protected will determine which alternative isselected. For example, if there is a major plankton componen t, yet physical en tr ap me nt damagescannot be controlled, present thinking suggests that the highest A T that is feasible forengineering reasons is the most desirable.TABLE 1.1

REDUCTION OF EL ECTRIC POWER O UTPUT FORDIFFERENT COOLING SYSTEMS

Cooling system

Once-throughCooling pondWet cooling towerDry cooling tower

Yearly average reductionper cent Maximum summer dailyreduction (per cent)02.13.14.9

03.A6.87.8

REFERENCES CITEDAndrews, R.N.L.; Cro mwe ll, P; En k, G.A.; Farn wort h, E.G.; Hibbs-, J.R.; Sha rp, V.L . 1977 .Substantive guidance for environmental impact assessment : An exploratory study. The institute of Ecology. Holcomb Re s. Inst., Butler Universi ty, Indianapolis, Indiana.Bisset, R. 1978. Quantification, decision-making and environmental impact assessment in the

United Kingdom. J. Environ. Manag. Vol. 7. p. 43-58.Clark, B.D.; Bisset , R.; Wathern, P. 1979. Environmental impact analysis: A bibliographywith abstracts. Mansell Information/Publishing Ltd., London ( in press).Fisher, D.W.; Davi es, G.S. 1973. An approach to assessing environmental impacts. J. Environ .Manag. Vol . 1. p. 207-227.Harleman, D.R.F. 1976. Waste heat management and ecological effects. International advancedcourse-heat disposal from power generation. Dubrovnik, Yugoslavi a.Gilliland, M.W.; Risse r, P.G. 1977. The use of systems diagrams for environmental impactassessment: Procedures and an application, E c o l. Modelling,. Vol.3, p. 183-209.McKellar, H.N., Jr. 1977. Metabolism and model of an estuarine bay ecosystem affected by acoastal power plant . Ecol. Modelling. Vol.3, p . 85-118.Odum, H.T. 1972. Use of energy diagrams for environmental impact statements. In: Tools forCoastal Management. Proc. 1972 Conference , Marine Technology S o c , Washington, D.C.,p . 197-213US Environmental Protection Agency. 1973. Reviewing environmental impact statements - power plantcooling systems engineering aspects. Environ, Protection Techn. Series., EPA-600/2-73-016Washingto n, D.C. p. 93.

19


19/170

I L Potential a n d observed ecological effects o fo nce- thro ugh cooling systems

SUMMARYThis chapter surveys the sources of potential ecological damage for power plant coolingsystems, with emphasis on once-through cooling. Heated discharges are only one of severalsources of potential adverse ecological chang es, others being physical damages of entrapment andimpingement at intak es, physi cal, chemical as well as thermal stresses of entrainment throughthe cooling ci rcuit, discharge chlorination toxicity, and hydrological and habitat changes withthe construction- new intake and discharge structures. Observed evidence for these changes aredetailed to illustrate that many of the impacts can be r e a l, and not merely hypothesized.

II. 1 Sources of Potential Ecological ChangesThe heated discharge of a power station is only one of several sources of potentialecological change from the cooling system operations. In addition, researchers also now reco gnize the potential for ecological effects associated with power plant intakes and processesassociated with passage of water through the power plant. Large fish and invertebrates are oftenimpinged and killed on intake screens which are designed to keep debris out of the condensertubes; small organisms, particularly larval stages of fis h, can be mutilated or thermallykilled during their transit (entrainment) through pumps , heat exchange condensers and piping.Whether screened out or entrained wit h the cooling wate r, organisms entrained in the water atthe intake may fare worse than organisms which only encounter the discharge plume.The shift in attention to include intake entrainment problems as well as dischargestresses occurred with utility industry development of estuarine sites for steam electric stations. Small, freshwater rivers generally have only limited amounts of planktonic organisms

that would be susceptible to entrainment. Estuar ies, howeve r, are important spawning groundsand nursery areas for large numbers of aquatic species. Her e, recirculating hydraulic patternsof fresh and salt water have encouraged evolution of drifting larvae. These drifting larvaegenerally do not distinguish between the patterns of water flow that provide recirculation andnourishment for them within the estuary and those that draw them into power station intakes. Aspower stations grow both in size of individual units and in numbers of units on a given estuary,and cooling water use increa ses, the probability increases that a larval fish will be entrainedin a power station cooling system before it leaves the estuary (see for exampl e, US NuclearRegulatory Commission, 1975).The principal engineering alternative to the traditional "once-through" cooling systemis the cooling tower. Yet we now recognize that this alternative has its own potential to adversely influence the environment, with impact on the terrestrial as well as the aquatic system.These impacts are briefly addressed in this chapter to indicate some of the potential environmental problems of this alternative.The sources of potential ecological change from once-through (open cycle) power station cooling systems are currently recognized to include the following (Fig. 11.1).

1. Change in the physical (structural) features of the intake and discharge areas bydredging, filling, change of substrate (such as placing rock jetties on sand andgravel b e a c h e s ) , or construction of inlet and outlet works (such as intake pumphouses

20


20/170

or discharge pipes);2. Changed current patterns near the intake and discharge which may extend to areas farremoved from the power station and result in altered patterns of such factors asestuarine salinity, lake thermal (and biochemical) stratification or movement of n u t rient and plankton concentrations;3. Entrapment and impingement of larger organisms, principally fish, on intake screens ;4. Entrainment of phytoplankton, Zooplankton, and larvae and juveniles of fish andinvertebrates with the pumped cooling water during which these organisms are exposedto :(a) physical damage from mechanical contacts with pumps and piping, and physicaleffects of pressure changes and shear;(b) temperature shock in the condenser tubes followed by a period of exposure tothat elevated temperature until the discharge reaches cooler receiving waters;(c) chemical expos ures, principally to chlorine which is added periodically to thecirculating water as a biocide to prevent accumulations of fouling materials onheat exchange surfaces and other parts of the piping system, but also includingin some plants such varied materials as laundry wastes or radionuclides; ,5. Plume entrainment of organisms in the discharge area through dilution of the effluentwhere organisms receive thermal and chemical exposures which vary according to theirlocation in the mixing zone (physical damages may also result if pumps are used toaugment effluent m i x i n g );6. Temperature elevation for resident and thermally attracted org anism s, which is g r e a test in the vicinity of the discharge and is less at mere remote locations, and mayinfluence to some degree the whole of small water bodies;7. Unnatural temperature change s, often rapid, which may occur in the vicinity of thedischarge due to plant operations (e.g. sudden shutdown or start-ups) or due toenvironmental changes which affect rates of mixing and dispersion of the effluent;,8. Chemical (biocides and condenser metals) exposure for plume biota;9. Changes in dissolved gas concentrations in the intake and effluent areas due toincreased biochemical oxygen demand of warmed waters , to pumping of oxygen-poorhypolimnetic waters , or to gas supersatuation of discharge waters in winter;10. Increase in nutrients in the effluent area due to kill of plant-entrained plankton;11. Combinations of the above, which may cause effects greater than the sum of individualeffects (synergism).Cooling towers have several sources of potential ecological chan ge, some of w h i c hare unique while sone are similar to, but of lesser magn itud e, than those for once-through

systems. They include:1. Impingement and entrainment of aquatic organisms at the intake where makeup water isadded to the cooling loop to compensate for evaporation and dilution ("blow-down")flows;2. Chemicals released to water bodies as the "blow-down" or dilution flow released fromthe "closed-cycle" loop to prevent build-up of dissolved s olids , which containsmaterials added to the cooling loop to prevent corrosion (e.g. chromtes, zinc,organophosphorous complexes) or to eliminate biological fouling (e.g. c h l o r i n e );3. Chemical "drift" in the form of small droplets and aerosols which emerge to theterrestrial environment from the top of the tower and contain, in addition to w a t e r ,chemicals used in the circulatory water system;4. Temperature elevations or other changes due to heat in the "blow-down" relea ses;5. Meteorological effe cts, including fogging, which affect the terrestrial environment,including man;6. Combinations of the above (synergism).II.2 Potential for Adverse Physical/Chemical Changes

Pollution has often been defined as a change in water or air quality that adverselyaffects other uses. Power plant cooling can change the physical and chemical characteristicsof water and air so that other direct uses are impaired. Accelerating trends in many countriestoward closed-cycle cooling, especially cooling tow ers, has encouraged broadened considerationof impacts on air as well as water.

21


21/170

II.2.1 Physical effects on waterTemperature changes are known to affect every physical property of concern in waterquality management, including water density, state, viscosity, vapour pressure, surface tensiongas solubility and diffusion (Appendix I V ) . Some of these changes are of importance in theirsubsequent effects on aquatic life. For example, temperature-induced gas solubility changesaffect dissolved gas content and can create supersaturated gas conditions that cause gas bubbledisease in aquatic orgniamss (Uolke et al., 1975). (This phenomenon is discusssed further in

Section II.3e.4 on biological effects.)Vapour pressure changes can influence rates of evaporation and thus water consumption.In many regions the quantity of water which is transferred through evaporation by various typesof cooling systems is becoming a major factor in the siting and design of large steam-electricpower generating facilities. The amounts of water evaporated depends on.the specific environmental and plant condition involved. For example, for open water surfaces such as lakes, ponds,r i v e r s, reservoirs and estuaries, about half of the heat is dissipated by evaporation, whereaswith wet cooling towers over 75% of the heat is transferred by evaporation during the summer.The magnitude of the potential water consumption problem for large power plant facilities canbe considerable. Approximately 2000 nr/h of water are transferred to the atmosphere throughevaporation in a wet cooling tower for a 1000 MW(e) nuclear power plant (IAEA, 1974). A powerstation can, therefore, be in direct competition for water resources with other uses such asagricultural irrigation and drinking water supplies.Increased temperature and the resulting decreased viscosity may also result in increased

sedimentation in water bodies. This could lead to potential sludge problems, changed sedimentcarrying capacity of rivers or changes in riverbed.Temperature-induced density stratification of lakes is a principal regulator of chemicalwater quality in deep hypolimnetic waters. Changes in thermal structure by power stations canalter the normal annual cyclic pattern. Municipal or industrial water works could be affectedby such changes. Problems of a similar nature can arise in stratified estuaries where theecosystem depends upon the complex stratification and mixing patterns of saline and freshwater.Temperature increases in winter can reduce ice-cover. This may prolong navigation inrivers and affect biota, such as attracting overwintering waterfowl. Dingman et al., (1968)estimated that a 600 M (e) nuclear power station could keep 18-25 km of the St. Lawrence River(Canada) ice free.

TL.2.2 Chemical effects on waterPower stations can influence the chemistry of natural waters by changing reaction ratesthrough temperature changes and by direct addition of chemicals to the cooling water. Alteredchemical reaction rates affect the assimilation of other wastes in water bodies, the efficacyof water treatment systems, corrosion of materials, and biological processes.Certain chemicals are added in the operation or power plant cooling systems for protection against corrosion, scale and biogenic slime build-up on heat transfer surfaces, andbiofouling of the cooling water piping or other surfaces. Chlorination of once-through coolingwater is the accepted practice at most power stations, either as periodic slugs or as continuous,low-level additions. The discharge of chemical-laden "blow-down" water from cooling towers y s t e m s, used to avoid excessive concentrations of dissolved solids within the cooling system,is an essential part of plant operation. The use of oxidizing biocides such as chlorine is alsoperiodically required in a recirculating cooling system to minimize the growth of algae.Chlorination has recently been questioned because recent studies show formation ofchlorinated organics in both polluted and natural waters (Jolley, 1975). These chlorinated

organic materials can remain toxic for aquatic life for long periods, as well as being of concern to municipal water users (Gehrs et al., 1974). Chlorinated organic compounds have recentlybeen identified from several municipal water supplies in the USA (Morris and McKay, 1975). Theseare believed to derived from chlorinated waste effluents.II.2.3 Atmospheric effects

Large cooling towers, either mechanical or natural draft, and large arrays of coolingponds represent much more rapid means of releasing heat and moisture to the atmosphere than thedischarge through large natural water bodies. Accordingly, cooling towers and cooling ponds,

22


22/170

hold the greatest potential atmospheric effects. These include:(a) ground level fog and icing;(b) clouds and precipitati on;(c) severe weather effects ;(d) plume length and shadowing; (and)(e) drift.(Peterso n, 1973; IAEA, 1974; Hann a and P e l l , 1975).More attention has been given to fog and ice associated with plumes from evaporative cooling towers than to any other effects. Many cooling tower reports from the United Statescontain statements that mechanical and natural draft cooling towers have the 'potential' tocause or increase the frequency of ground level fog or icing. Theoretical analyses (e.g. McVe hil,1970; EG & G; Inc., 1971) all predict tower-induced ground level fog for various periods oftime with a greater fog persistence existing in cold weather. In these theoretical studiesmaximum fog frequencies would result from mechanical draft cooling towers. Available physicalobservations near towers and extensive European observations indicate that the plumes usually donot cause surface fog (e.g. Decke r, 1969; Aynsl ey, 1970; IAEA, 1974; Hanna and P e l l , 1975).In these field observations the warm, moist plume enters the atmosphere at heights of 100 metresor more and evaporates before it reaches ground le vel. These observations indicate that theoretical models may be too pessimistic in their assumptions.In the operation of cooling lakes or ponds local climatological changes are to beexpected, such as changes in the intensity, frequency, and inland penetration of induced fog ,including the creation of freezing fog near the water's edge . Observations at cooling pondsindicate that the fog over the pond is usually thin, wisp y, and does not penetr ate inland mo rethan 100 to 300 metr es. Because the water vapour is released slowly over large are as, ponds arenot a major source of fog despite the release at ground level (IAEA, 1974). However, in weathersituations producing natural fog over large areas , ponds would act to intensify and prolong fogconditions. Cooling pond site selection is important in order to assure that induced fogs (andfreezing fogs) do not affect roads and bridg es. Spray units, with which the effective evapor ation area is greatly increased by spraying the heated water over the pond or through a can al,will also increase the frequency and intensity of dew, fog, frost, and icing conditions along thebanks or downwind of the pond or canal.Quantitative data on the effects of moist plumes from cooling towers on clouds andprecipitation are very limited. Occasional observations of light drizzle or snow have beenreported in the vicinity of towers (e.g. Culkow ski, 1962; Federal Water Pollution ControlAdministration, 1968). Additional heat and/or moisture fed into a developing storm cloud mightconceivably produce an imbalance that would result in intensifi cation into, a severe weatherstate. In view of the paucity of data availahle in this area, any effects are only conjecturet this time. The psychological aspects of the shadowing effect of atmospheric plumes fromcooling towers have been considered in nuclear power plant studies in Western Europ e. Calc ulations performed in Switzerland for two natural draft cooling towers (Broehl, 1868) indicatesthat even if visible .cooling tower plumes are assumed to be fully o paqu e, the reduction of sunlight in nerby areas would be insignificant (the average reduction was one minu te per daycorresponding to 0.35% of sunshine.) The shadowing effect of nechanical draft towers is smallerthan from natural draft towers because the vapour pl ume, through the several ejection poi nts ,obtains a more rapid atmospheric dilution.A problem in the operation of wet cooling towers involves a small portion of thetotal water circulated in the tower which enters the atmosphere without being evaporated. Thisphysical water loss is due to droplets entrained in the air leaving the tower and is oftenreferred to as 'drift'. Drift fall-out which occurs near the tower may cause problems such ashighway icing in the winter and transmission line flash-over. Drift contains all the salts andimpurities in the intake cooling water . When deposited in the area surrounding the plant sit e, the drift droplets evaporate and leave a solid or salt residue behind. This residue can causevegetation to accumulate chemicals present in drift (Taylor et al., 1975; Hanna and P e l l , 1975).Of particular concern is long-term build-up of potential toxicants such as chromium.Published test data indicate drift loss rates of 0.005 to 0.0076% for mechani caldraft towers and Q.0Q12 to 0.0025% for natural d raft towers (Ehm et al ., 1971). Additionaloperating test data are needed to validate the drift loss rates in this study . Tower equipmentcompanies now guarantee drift rates to be limited between 0.002 and 0.005% of the circulatingWa te r flow. For a 100 MW(e) power plant, water loss due to drift can be less than one litreper. second.

23


23/170

Up to the present time, wet cooling towers at power stations have been limited to non-saline make-up water. Evaporative towers are, however, now being installed in estuarine orcoastal locations of power plants. The first hyperbolic natural draft cooling tower in theUnited States using brackish water is installed in conjunction with a 630 MW(e ) oil-fired powerplant at Chalk Point, Maryland (Pell, 1975). A comprehensive soil and vegetati on research programme is planned for this sit e, in order to determine the potential effects that brackishwater cooling towers may have on the surrounding veget ation. Additional field studies of thistype will be required as salt or brackish water cooling towers are introduced into common powerplant use ih other regions.In addition to the meteorological e ffec ts, cooling towers may impact the environmentin other ways. For e xample, the synergistic effects of cooling tower plumes mixing with industrial stack effluents which contain oxides of sulphur and nitrogen require further study andevaluatio n. In some inst ances , acid rains may result due to the mixing of the cooling towerplumes with fossil-fueled power plant stack effluen ts. The environmental impact of noise andthe aesthetic ef fects of large cooling tower arrays also deserve consideration.-II.3 Potential and Observed Biological Changes From Once-Through Cooling

It would be imposs ible for this section to comprehensively report the biological dataand observations from laboratory and field studies that bear on cooling system damages to organisms and ecological sys tems. The scientific literature is simply too va st , and the particularlocations and species too divers e. Emphasis has been placed on once-through cooling systems,as these biological problems are better documented. For each source of potential biologicaldamage, knowledge of the circumstances and probability of dama ge, especially as indicated byoperational power pl ant s, is useful for estimating damages or their lack at a given site. Thissection will emphasize this type of information and indicate where additional information canbe obtained. This section also provides an update of an early review on effects of thermaldischarges (US Senate Committee on Public Work s, 1973) plus the additional consideracin of thebroader, non-thermal effects of cooling water use.

II.3.1 Change due to physical alteration s: Cons truction of intakes and dischargesConstruction activities required to build intake and discharge structures may* involvedredgin g, cutting or tunnelling. Normall y, these impacts are of a temporary natur e. Increasedsiltati on, for example, may act only as a temporary stress through reducing oxygen content ofa water body segment or reducing food uptake by filter feeding invertebrates. Yet heavy orcontinued siltati on (e.g. from scouring by high velocity dischar ge) can lead to long term lossof benthic communities where suspension feeders dominate, such as oyster bars or coral reefs.Construction which cuts across a barrier dune system of an open beach could also result in long-term ecological alterati on. If dune revegetation is not quickly accomplished, storms canbreach the beach at,this poi nt, resulting in a new ocean inlet which may persist for some time.In inter-tidal are as, slumping of dredged canal banks will result if side slope design exceedsone on fifteen. In cut and fill operations across marsh la nds, top soil will be required toachieve revegetation, as the pH of marsh soil drops greatly upon exposure to the atmosphere.These effects are not unique to power plant construction.Submerged cooling system structures will be colonized by sessile org anisms , to whichfish and other motil e organisms will be attracted to feed. These mobile forms will be exposedto potential intake impingement or entrapment, or at the discharg e, possible entrainment inthe effluent . Attracti on of fish to submerged intake structures has been found to be greaterat some off-shore locations e.g. off the California coast) than within large estuarine channels.New patterns of water circulation, will develop around any cooling system structurewhich extends into a waterway. These may also serve to attract motile organisms. When intakesare indented into the original shore-li ne, currents develop which reta in fish within intakeb a y s; if protrud ing, end bay sections may experience greater impingement due to eddy currentswhich develop (e.g. Lake Norman in the USA, Edwards et al., 1976). Intake structures builtflush with the shore-line can minimize these probl ems. Circulation will also be altered uponoperation of the cooling system. Benthic scouring immediate to the intake and discharge iscommon. This can cause additional benthic loss downstream due to increased sedimentation(Merriman, 1976).

24


24/170

P O W E R P L A N T

T R A V E L I N G S C R E E NINTAKE ( P U M P E D ) E N T R A P M E N T

(a) M E C H A N I C A L D A M A G E(b) T H E R M A L S H O C K

PHYTOPLANKTONZOOPLANKTON. r t - V - " - : . ' - : . V . : : : - : . : - . 0 - > , L A R V A Ltegiv^a^^V. . FISH

Figure II.1 Sources of potential ecological changes at apower plant cooling system

SHORELINE

f>

*rW A T E RpJ M O V E M E N T

r

T O W A T E RP U M P S

P^\o\ FSH\ % A \ MOVEMENT

^i^ \

f ^f

S

x r>$sFigure II.2 Fish passage

25


25/170

In estuarine a reas, problems can arise if cooling water use creates new circulationpatterns which appreciably alter the local salinity regime. At the mini mum, a shift in theindigenous community would occu r, with a loss of intolerant species and the addition of others.Establishm ent of intake and discharge structures in small marsh creeks at the Oyster Creek(N.J.) Nuclear P lant resulted in movement of more saline bay water into the marsh system.Wood-bori ng mari ne shipworms moved into the creek, which resulted in loss of a local economicand recreational resource, as pilings, docks and boats at several marinas were destroyed(Turner, 1973). Knowledge of the salinity tolerance of potential deleterious species shouldmake predictable.Concern has been expressed whe ther jet discharges might affect free movement of animals past a power plant. While the thermal component of discharges may cause problems forsome species, discharge currents per se have not been found to block movement of animals (Leg-g e t t , 1970; Maryland Power Plant Siting Programme, 1977).II.3.2 Changes from entrapment and impingement at intakes

Field experience at operating power station intakes has shown clearly that largenumber s of fish and invertebrates can be killed on the screens (USEPA, 1976a). The underlyingcauses of entrapment and impingement remain little understood and predictability is thereforepoor. Reasonably quantitative laboratory data on fish swim speeds have been obtained (e.g.Blax ter, 1969) with the initial assumption that physical stamina could be compared directlywith water flow rates through screens to determine likelihood of impingnient. This has notproved reliable. Current thinking relates susceptibility to impingement to:(1) behaviour patterns of fi sh, many completely un known, in the vicinity ofvelocity accelerations and intake structures;(2) physical characteristics of the intake area which many or may not allowroutes for easy return to open water following withdrawal to an intake channel;(3) environmental factors such as low water temperature, Griffith and Tomljanovich,(1975); Griff ith, (1978) and high turbidity which influence normal behavioursuch that an organism cannot (or does not) escape;(and) (A) attrac tants, such as recirculating warm water (often for ice control) in wint er,lights, shade, or presence of food organisms.It seems that some spec ies, particularly in the family Clupeida e, are especially susceptibleto impingement.Reports of chronic intake impingement probl ems experienced at operating plants can beuseful to evaluating site-specific aspects contributing to the problems as well as to identifysusceptible species and environmental correlates with impingement. In the USA, this information is available for nuclear plants in reports made to the Nuclear Regulatory Commissionand Environmental Protection Agency, (see, for example, the Millstone Nuclear Power Station,316b report;(Northeast Utilities Service Co.,' 1976 ); and reviews by L oar et a l., 1977 andUziel, 1978). At some power plants a direct correlation is apparent between species impingedand the abundance and seasonality of fishes present in the water body segment (Maryland PowerPlant Siting Programme, 1977; Landry and Strawn, 1974; Benda and Guluas, 1976). In thesecases, the power plant intake represents a non-discriminate stress on the nekton community.The same can also apply to pelagic marine macro-in verteb rates, such as squid and swimmingcrabs. Yet scavenger s, such as blue cra bs, may be differentially attracted to intake bays insuch abundance as to achieve nuisance proportion s. Impingement susceptibility can also bespecies dependent and not representative of the local icthyio-fauna at large, as seen byEdwards et al., 1976, at four freshwater sites in North Carolina, USA. Thread-fin shad wasthe major species impa cted, especially during the late fall and wint er, when this species istypically highly stressed or killed by low temperatures. With this specie s, there was norelationship between intake velocity and impingement, nor was a skimmer wall effective inreducing impingement. A survey of freshwater power plants in the sourtheast of the USA (Loare t al. , 1977), pinpointed the cold sensitivity of threadfin shad as the major cause of impingement in this large region. Additional correlates between impingement and season, river flow,and water level are cited by Grimes (1975 and Mathur et al . (1977).

The numbers of animals lost due to impingement is difficult to assess . (At US nuclearplants, counts of dead animals are summarized and reported to the US Nuclear Regulatory Commis sion).. Some impinged fish are returned alive to the waterway although the chances of theirultimate survival is questionable. For certain fragile fishes, such as the family Clupeidae,

26


26/170

there is little probability of survival once the screens are impacted. For other speci es, survival estimates should be made conservatively. The ability of impinged fish to withstand d i s ease following loss of surface mucus or scales, or to withstand normal predator pressure fo l- 'lowing impingement stress is doubtless markedly reduced following impinge ment. Benda and Gulvas(1976) report signs of physical damage in over 50 % of the impinged fish at a Lake Michigan powerplant. They rate the chances of survival of these fish as mini mal. Field or laboratory asses sment of injury rate and survival suggest post-impingement survival to be better during coldwinter mont hs, with loss increasing proportionally with seasonal temperature increase (MarylandPower Plant Siting Progra mme, 1977; Landry and Strawn, 1974; Northeast Utilities Service Co .,1976). Relative sensitivity of eight estuarine fish species to impingement stress is reportedby Burton Maryland Power Plant Siting Programm e, 1977).The significance of fish mortalities at intake structures can be placed in some per spective by distinguishing between repeated chronic kill and the very conspicu ous, but infr equent major kills . Heavy fish kills due to entrapment or impingement are dramatic in natur e andare always a serious problem for the power plan t, possibly resulting in plant shutdown as thescreens become clogged. Yet if major kills occur only infrequently, their ecological signi ficance may be mini mal. For example, loss of 50 million juvenile menhaden and blueback herring atMillst one, Conn., (Northeast Utilities Service C o., 1976) occured as atmospheric cooling be ganin late summer, 1971, and the fish were leaving the estuarine nursery grounds to move sou th inthe fall. Such an event has not reoccurred. In contrast, impingement of winter flounder occurschronically at the same plan t, with this species comprising 23% of all fish impinged over a fouryear period. The number of flounder impinged represented 0.3, 0.7 and 0.9% of the estimatedlocal population during three of these years . If none of the impinged flounder survive d, whichis probably unlikely for this species, it is projected that the local population would be reduced by 12% after 35 years operation of three generating uni ts, assuming present impingementexperience continued. Fish troughs will be added to the screens at this plant in an attemptto minimize impingement mortalities in this species.State-of-the-art intake technology to minimize impingement is summarized by Ray etal., 1976, and USEPA, 1976a. These reports address intake orientation (off-shore condui t,shore-line or banksi de, and intake approach c h a n n e l ), behavioral and physical intake barriersand fish removal systems. Also discussed are potential approaches to minimize entrainment oflarval fish. An extensive bibliography on fish protection at intake structures , with abst ract s,has been compiled by Huber (1974). Impingement problems and intake design have also been thetopics of several workshops (Jensen, 1974, 1976, 1978). At prese nt, it is difficult to general ize on best technologies for intake structures w hich minimize environmental impact due to thesite specific nature of the problem. For exam ple, the louver bypass system described bySchler and Larson (1975), was a site specific design and may not be the best technology else where (Schler, personal com munic ation ). At prese nt, there is considerable research underwayto develop better phsyical barriers and to perfect fish removal syst ems. Until new designsare proven in field te sts, modifications of the standard rotating vertical screen barrier citedby Ray et a l., 1976, should be explored to mitigate impingement loss. These modificationsinclude provision for escape routes inside the intake suction pit or screen w e l l , equippingthe screens with fish troughs and continuously rotating the screens to minimi ze impingementtime for a fish. It is usually recommended that intake velocities not exceed 0.15 m sec--'- atthe trash rack to permit fish to escape the screen wall (Boreman, 1977).II.3.3 Change due to entrainment of small organisms with pumped cooling water

All small aquatic organisms capable of passing through the intake screens (usually1 cm openings) are entrainable and potentially subject to passage through power plant coolingsystems. This would include planktonic and weakly swimming pelagic organisms ranging frommicroalgae to copepods and eggs and larvae of fish and invertebrates. Organisms entrainedthrough the cooling system experience a combination of thermal and mechanic al stress , plusexposure to a chemical biocide during periods of application. Survival of entrained organis msfollowing plant passage is problematic and will depend- on cooling system desi gn, plant ope rating characteristics as well as overall tolerance of the species and life stages entrained.The larger copepods and fish eggs and larvae tend to be the more se nsitive, with entrainmentlosses reported as ranging from 70 to 100% at several plant s. More typical losses averageabout 30% over an annual cycle (Lawler et a l., in p r e s s ) . Of primary environmental concern isentrainment loss of meroplankton (i.e. the eggs or larvae of fish and macroinvertebrate s) si nce

27


27/170

these species can have generation times on the order of one to several yea rs. In contra st,phytoplankton or copepods can produce replacement generations in a matter of hours to days, respectively, during favourable seasons.The significance of meroplankton entrainment loss for the adult populations can beevaluated by biological models , such as developed for the winter flounder by Hess et al. (1975).(For additional deta ils, see also Northeast Utilities Services Co ., 1976; Van Wi nkle, 1977.)Similar modelling efforts are currently being conducted in the USA for the striped bass in theHudso n (discussed in chapter III), and Potomac Riv ers . Enright (1977) has proposed a simplefirst order ap proach to assess maxim um probable impact of larval entrainment -mortalities uponthe adult populations.Our present understanding of the pumped entrainment problem is summarized in a volumeedited by Schubel and Marcy (1978). Some early papers which document aspects of pumped entrainment stress include Cotant (1970, 1971) and Hoss et al . (1974) (thermal shock); Ma rc y, (1973)and Carpenter et al., (l974b) (mechanical); and Hamilto n et a l. (1970) (chemical). Ma rc y, (1975)has written a succinct overview of the interaction of these three entrainment stress es, parti cularly as they pertain to fishes. Additional articles can be found in a review by Car rier, (1978)and in the proceedings of several entrainment workshops (Jensen, 1974, 1976, 1978).The magnitud e and the nature of pumped entra inment damage is plant specific, dependingon the entrainable biota and hydrodynamic c haracteristics of the site, cooling system designand operating conditio ns. Beck et al . (1978) have tabulated, by species, reports of entrainmentdamage at 14 power plants with once- through cooling systems in the USA. Some of these studiesalso evaluated the relative influence of single stressor s. They suggest that physical stresscan be a major contributor of larval and juvenile fish mortal ity, accounting for 80-100% ofobserved losses in almost every study where cause of mortality has been partitioned. Thermalstress often contributes to mortalities during the summer, when water temperature is naturallyh i g h . Chemical bioc ides, most frequently used during spring and summer, can dominate as a stressduring any period of applicatio n, and more so during periods of maximum thermal elevation(Hoss et al ., 1977). Zooplankton appear to be more affected by chlorine than are fish larvae.Yet it must be emphasized that the above conclusions are tenuous at best , as the datafrom operating power plants are s parse, and often of limited use due to sampling probl ems,variatio n in study techniques between wor ker s, and potentially unique differences in power plantcooling syst ems. Illogical results such as greater numbers of live organisms in the dischargethan in the intake or opposite results from day to day or year to year at a single plant emphasize the inadequacy of many of the study methods used.Problems of sampling entrained plankto n have been discussed by Heinle (1976a, 1976b)and Copeland et a l. (1976) (estuarine), Jude (1976) (large lake , Kind and Mancini (1976) (river)and Bowles et al . (1978) (ichthy oplankt on). Numbers of larvae or Zooplankton captured tend tobe highly variable due to their patchy distributi on (both horizontally and vertically ) in thewater column, diel variation in activ ity, possible day-time avoidance of n e t s, watermass changesat the intake due to tidal (in estuaries) and/or weather changes (especially in large lakes),plus unknown changes in distribution of plankton in the forebay of the intake. At the dischargesampling is usually complicated by high water velocities and changes in organism buoyancy andswimming behaviour due to the hea t, which affect vertical distribution . Another problem centresaround ability to detect entrainment damage. Problems of net collection, including the potentialfor net dama ge, hav e been addressed by some worker s by use of a pump for sampling.' Vitalstains have been used to distinguish living from dead animals when it is not practical to makecounts immediately following collection (Heinle, 1976a). The potential for latent ef fect s, suchas reduced ecological fitness and subsequent loss from the system due to differential prdation,for example, has been little considered to date. Studies which simply tally mortalities immediately following discharge from the power plant are probably describing only a portion of theultimate loss.

It is also difficult to directly document the consequences of through-plant entrainmentdamage s on populations on the whole ecosystem in water bodies used for cooling. Many\examplesexist of field sampling programmes at power stations where no decreases of plankton have beenseen that can be attributed to the inplant l osse s, (e.g. Carpenter et a l., 1974 a ) . "Natural"variability of plankton is typically so great that only very large impacts would be directlydiscernable if they did exist.Components of Plant Entrainment Stress : Phys ical . Physical damage to entrained biota can

28


28/170

result from four stresses operating in power plant cooling systems: pressu re; accelerationforces, shear and abrasion or collision ( Ulanowitz, 1975; Schubel and Mar cy, 1978). At thepumps, organisms are exposed tosudden fluctuations in pressure and velocity shear force s,physical buffeting and abrasion. Once in the pump , there is rapid positive and negative chargesin hydrostatic pres sure, ranging from 0.29 to 1.6 atm. There is potential for contact withimpeller blades (2-5%) or pump walls and pump shear stresses can b e up to 10 times that e x i s ting near the walls of the condenser tubes. Accordin gly, the pump is considered the mostlikely site of physical damage within an open cooling system. In the condenser water box,physical stress takes the form of negative pressures and high flow rat es, which are maximum atthis poin t. Negative pressure is considered particularly- damaging to entrained fish. In thecondenser tubes, shear and pressure changes also occur, but may pose a minima l physical stressat this point (Marcy et al. , 1978).The consequences for entrained biota of the combined physical forces of a power pla ntcooling system can be most realistically studied at an operating power plant . Plants pumpingwater through a cooling system without any thermal load have provided this opportunity at afew sites (e.g. Marc y, 1973). Pressure is one force that can be studied separately (Beck etal., 1975). However it is difficult at present to relate the findings of such studies to anoperating power plant , where the magnitude of any one stress is hard to define and its consequences problematical due to interaction with multiple additional stress es. A scaled totalcooling system simulator constructed at Oak Ridge National Laboratory (US) may permit detailedcause and effects experimental studies of the whole compliment of cooling system physicalstresses which to date have not been possible at operating powe r plants (Cotant, personalcommunication).Studies to date suggest great differences exist betwee n power plants with regards tophysical enfcrainment damage . The primary variables regarding physical da mage to entrainedbiota fall into two categories. Those which are a function of cooling system design andoperation, and those which are dependent on the specific biota entrained. Location and designof the intake has the potential to enhance or minimize entrainment of planktonic organ isms, aswill volume of water pumped. Pump design and the efficiency of their operation (inefficientoperation results in excessive cavitation and high biological damage) is another variable . Thepractice of augmentation pumping to reduce discharge water temperature, for examp le, is nowrecognized as clearly counterproductive and not a wise approach to mitigate discharge t emperatures, as it increases the number of planktonic organisms e^nosed to damag e. Indeed, thedesign option of a higher operating At to reduce the volume of cooling water required might beconsidered, should plant entrainment of meroplankt on pose a potentially serious environment.-'!problem. The biological variables influencing the probability of physical entrainment damagefocus on the relative fragility of the entrained specie s, which is often a function of s ize andlifestage. Fish eggs and larvae appear to be more se nsitive, among which the most fragile arelarvae of the clupeids, menhad en, Atlantic silversi de, sea rob in, tautog, cunner and anch ovy,(Marcy et al ., 1978). Species with the larger respiratory apparatus have also b een reportedas highly susceptible to physical entrainment stres s, possibly since the head area in fish isespecially vulnerable to damage (Nawrocki, 1977). For other species, the yolk and post-yolksac embryonic stages have been seen to be highly sensitive. There has also been a good correlation, for both ichythoplankton (Marcy, 1973) and inv ertebrat es, of increasing physical damagewith organism size. Marcy et al. (1978) have proposed a generalized model which relates percent mortality to size of the entrained b iota. For some fishes however there is an upper sizelimit for this generalization, with the largest entrainable individuals of some species sho wingincreased tolerance to physical stress (Teleki, 1976; Nawr ocki , 1977).Thermal. The contribution of high temperature per ^e_ as a dominant entrainment stress hasbeen best illustrated at operating plants by increased loss during the summ er, the period thatnature water temperature is at its maximum. If the discharge canal is long, considerable killdue to temperature will occur. (For further discussion of this topic, see Sec. 3.4 ). Butotherwis e, good estimates of the specific contribution of temperature alone to observed ent rain ment damage are difficult to mak e. This would require a good assessment be first made of theextent of damage from mechanical forces alone (i.e. damage without any heat load not chloreadded). Only a few workers, such as Marcy (1973), Carpenter et al (1974b), Alden et al . (1976)and Lauer et al. (1974) have had such an opportunity. Reviewing this literature, Schubel etal. (1978), conclude that high temperature can be the dominant entrainment stress at plantswhere mechanical stress is minimal and biocides are used only infrequently or no t at all .

29


29/170

Laboratory studies can be useful in identifying entrainable organisms which clearly cannot tolerate the thermal regime of a given power plant. Yet organisms surviving a laboratorysimulation of the entrainment thermal experience will not necessarily survive cooling system p a s sage where mechanical and possibly chemical stresses are also present and probably will act in asynergistic fashio n. A laboratory thermal stress simulation typically uses entrainable organismscommon to the site in question and acclimation temperatures typical of the site during theseasons of occurrence of the test organism. The thermal dose (i.e. duration and magnitude ofheating) should be comparable to that expected in the power plant, including the manner the elevation is exper ience d, i.e. as an initial instantaneous heat shock. Cooling may occur as a gradualdecay if there is a surface discharge (Schubel, 1975), or a sudden drop in the case of a jet discharge (Hoss et al., 1974).Schubel et al. (1978) suggests that fish eggs and larvae are usually significantly moresensitive to simulated thermal plant entrainm ent stress than are Zooplankton or macroinvertebrat es.Early fish embryos (i.e. early cleara ge to blastopore clo sure) are more sensitive than laterembryonic stages. Mortality is usually complete with a 20 A t , while hatching success may bereduced at a 15 A t , depending on species. Larval deformities can also result when the eggs arethermally stressed ( A t = 10and 1 5), markedly affecting their ability to swim normally anddoubtless reducing their ability to avoid prdation or feed (Koo and Johns on, 1978).Working w ith larval fish , Hoss et al . (1974) found entrainment simulated temperatureshock to be potentially very damaging in itself, especially the second (cooling) shock. Thelarvae exhibit marked initial deviations in beha viou r, including complete immobilization. Thosewhic h might survive the direct effects of heat are clearly rendered more susceptible to prdationat the time of discharge. Species differences in larval thermal resistance times and thermalshock effects should be considered when evaluating the potential for thermal entrainment damageat a given site. Hoss et al. (1974) observed a range in thermal tolerance among the six larvalspecies he tested, with the flounders the more tolerant and menhaden the least. Striped basslarvae appear to have a relatively high thermal tolerance (Laurer et al ., 1974).Juvenile fish may have greater thermal tolerances than either the larval or adultstages (Otto, 1976; Brett , 1956). (The same phenomenon is frequently seen among invertebratesas w e l l ) . Accor dingl y, Schuble et al . (1978) suggest that any damage experienced by entrainedjuvenile fish is probably more due to physical forces than from temperature alone.Many of the generalizations of thermal entrainment stress made above for larval fishhave also been observed with Zooplankton and macroinvertebrates at operating power plants or inlaboratory simulat ion studie s. Schubel et al . (1978) cite several papers showing temperaturecan be the dominant entrainment stress in the summer at plants w ith a larjje At (e.g. in excessof 13-15), or when the excess temperature exposure is prolonged by discharge into a long canalor if plume dispersi on is slow. (Fig. II.3)Chemical Biocide Stress. Biocides, such as chlorine, are employed for the purpose of killingbacteria and algae which can build up on condenser wa lls, and to prevent settlement of growthof fouling invertebrates, such as mussels or barnacles. Accordingly, it is to be expected thatmany other entrained organisms will be

unesco aquatic effects of water pollution

Documents