DocketOW-2002-0049 DCN#: 6-5046F Jirxk S. N.Decker, W. Dey, J. Young, and 0.Dirorx, ASAAnalvJiJ and EPRI A Review-of ImpingementSurvivalStudies at SteamElectric Power Stations 

### A 

### REVIEW 

### OF' IMPINGEMENT SURVIVAL

### STUDIES 

### AT 

### STEAM-ELECTRIC POWER STATIONS

Steven 

### M. Jinks', Nancy Decker', William Dey', John Young', Douglas Dixon2

1ASA Analysis & Communication, Inc. 291 County Route 

### 62 New Hampton,

### NY 10958
2EPFU 34 

### 12Hillview Avenue Palo Alto, 

### CA 94304

Abstract.-EPA has recently proposed draft $3 16(b)regulations for existingpower producing facilitiesthat containperformance requirementsbased, in part, on reducing fish and shellfishimpingementmortality at the cooling water intake structureby 80% to 95% relative to 

### a baseline consistingof a shoreline intake with
no impingement controls. Analyses of the potential for focal speciesto surviveimpingement for both existingand alternativeintake design and operation will be important for demonstrating compliancewith this requirement. Recognizingthis fact, 

### EPRI has recently sponsored a review 

### ofthe historical studies on impingement survival. The majority of impingement survival studieswere conductedbetween the mid1970s and mid-1980s, aspart ofthe initial surge of activity in response 

### to the requirements 

### of $3

### 16(b) ofthe Federal Water Pollution Control Act Amendments of 1972. The review included studies at 31 steamelectricplants located in 15 states 

### and the province of Ontario, covering all four 

### ofthe major waterbody types for which USEPA has proposed 93 16(b)performance requirements. Variousbiological, CWIS, and water body factorshave been shown to influenceimpingement survivalrates, but 

### no generally applicable mechanistic models for predicting impingement survival have been developed. Results ofthe review indicatethat over half ofthe taxonomic familiesof fish and shellfish studied to date have the potential for impingement survivalrates of 70-80% or higher with adequate screen design and operation. Reported data also indicatethat modifying screenwashoperation to a continuousmode is one of the most effective means for enhancing impingement survival. Uses and limitations of the historical studies and available summaries and a database ofkey information from the historical studies are discussed.

### Introduction

In April 2002, USEPA proposed CWA $3 16(b)regulations for existingutility and non-utility power producing facilities with cooling water flows greater than 50 million gallons per day. Theseproposed regulations would establish national performance standards for BTA based, in part, on reducing fish and shellfish impingementmortality at the cooling water intake structureby 80% to 95% relative to a baseline consisting of a shoreline intake with no impingement controls. These required reductions could be achieved through a combination of intake system design and operational controls, implementedin whole or in part to reduce impingementmortality, or through environmental enhancements or restoration. However, a facility may also qualify for a site-specific determinationofBTA if it can demonstratethat the costs to the specific facility are significantly greater than consideredby USEPA in establishing the standard or if the costs to the facilityof complying with the standard are significantlygreater than the associated environmentalbenefits. Impingementmortality is a functionboth ofthe number of organisms impinged and their rate ofmortality from exposure to the impingementprocess (Text Box 1). Estimates of impingement mortality rates for the primary species impinged at existing facilities will, therefore,be an important input for assessing compliancewith the new regulations, whether that assessment is focused on demonstratingcompliancewith the performance requirements for reducing impingement mortality or 

### on balancing risk reductionbenefits
versus costs of alternative fish protection measures. The probability of death from impingement, or impingementmortalityrate, has been studied at a number of existing steam-electric stations since the mid-1970’s in response to the requirements of §316(b)

### of the Federal Water Pollution Control Act Amendments of 1972. Thepurpose ofthese studies was generallyto: 1) documentthe actual impingementmortality rate at an existing intake so that estimates of impingement losses, and associatedpotential for adverse environmental impact 

### (AEI), could be more accurately assessed; and/or 2) evaluate the reduction in impingement mortalityrate, and impingementmortality, achieved by changes in screen design and operation’. Typically,these studies used the proportion of organisms surviving as the measure of organismresponse to the impingement stress2,and are therefore generally referred to as “impingement survival’’ studies. Recognizingthat existinginformation on impingementmortality would provide valuablebackground for planning and conducting future studies and assessmentsto address the new regulatoryrequirements, EPRI sponsored a review ofprior impingement survival studies to serve as an informationresource for 

### a diversity of users involved in the regulatoryprocess, including scientists, engineers, managers, and lawyers working for the utility industry, regulatory and resource management agencies, academic and private consultants, and environmental advocates. The specificpurposes ofthis review were to:

0 Identify and summarize impingement survival studies conducted to date; Facilitate access to impingement survival studyreports; Identify factors potentially influencingimpingement survival; and Discuss important considerations for using impingement survival data in BTA assessments. Impingement survival study reports available for this review were identified and accessed from several
sources including: 1)the EPRI Intake Systems Database maintained by Alden Research Laboratories; 2) the library ofASA Analysis & Communication;3)a search ofthe open literatureusing the DIALOG system; 4)

The latter studies were often part of SPDES permitting agreementsto test alternative intake screen technology. I 2 The impingementmortality rate is simply equal to (1-proportion surviving).questionnaires soliciting impingement survival information that were sent by EPRI to its members; and 5) direct requests to severalpower companies thought to have completed impingement survival studies. The results of the review of these impingement survivalreports arebeing published in full in Evaluating the Effects ofPower Plant Operations: Summary ofImpingement Survival Studies, EPRI Report 1007821 (EPRI 2003). This paper provides an overview ofthat report and summarizes some ofthe results ofthe review.

TextBox 1. Definitions ofKev Terms

Impingement Mortality Rate-A measure ofthe sensitivity ofthe organisms to impingement exposure fix., probability ofdying as a result ofimpingement). Typicallymeasured in site studies as the proportion of organismssurviving impingement, or impingementsurvival rate fix., ImpingementMortality Rate = (I
- ImpingementSurvival Rate). Impingement Mortality-Impingement loss, or the numberoforganisms ofeach species killed by impingement. Impingement loss is a function ofboth the exposure (numbers impinged)and sensitivity (mortalityrate as a result ofimpingement)ofthe organisms. Sensitivity-An organism’s tolerance or ability,when exposed to a stress, to resistejrects or to maintain its physiologicalstate within normal homeostatic bounds.



### Summary 

### of the Impingement Survival Studies Sixty-five impingement survival source documents were obtained for the review. The majority of these
source documents are reports on studies funded or conductedby electric generating companies at steamelectric facilities. The review summarized the general methodologyused in the impingement survival studies, the species, waterbodies, and screen designs coveredby the studies, and the survivalrate estimates obtained from the studies. 

### GeneralMethodology Usedin Prior Studies Debris and organisms in the cooling water withdrawn into steam-electricpower plant intakes are usual�y filtered, first with fixedbar racks (typically about 8-10 cm spacing) and then with rotating traveling screens (typically 0.95 cm, but at some facilities as small as 0.5 

### mm spacing). A screen-wash spray system washes organisms 

### and debris that impinge on the traveling screens into a sluiceway,which discharges the wash water to the source waterbody. Impingement survival studies monitor the post-impingement survivalrate of fish and macroinvertebrates that are washed from the intake traveling screens. The detailed methods that have been used to conduct this monitoringvary somewhat among facilities and, sometimes, among years at a given facility. Variations in methods over time generallyreflect attempts to refine and improve impingement survival estimatesby reducing handling and holding stresses, or to accommodate testing of alternative intake screen technology (Muessig et al. 1988). Nevertheless, the large majority of studieshave used similarmethods that allow description of a general approach for monitoringimpingement survival, which isprovided below.
Data Collection For impingement survival study, impinged organisms generallywere collected s;om the screenwashwater using a dip-net or a basket type of device containing a mesh opening equal to, or slightlysmallerthan, thatofthe traveling screenpanels. The collection location was either at a point along the sluiceway (often at a debris collectionpit designed to allow removal of largepieces of debris before dischargeto the waterbody)
or at the point where the sluice water discharges to the waterbody (Figure 1). At some sites, modifications
were made to the sluiceway system itselfto bypass impinged organismsto collectionpools or tanks for use in the impingement survival studies (ECSI and 

### LMS 1996,Davis et al. 1988). Sampling gear consisted of metal mesh baskets, with or without net liners, floating live-pens, or angled screen flumes. Brief sampling intervals (e.g., 15-30minutes) or continuous dip-netting from the sluiceway or collection devicewere often used to minimize damage from the collectionprocess (e.g., Tatham et al. 1977;

### NUSC 1986). Most studies either focused sampling on peak periods of impingementor sampled seasonallyto obtain data representative ofthe majority of impingement at the facility. Immediatelyfollowing collection, impinged organisms are categorized as live or dead, or as live, stunned;
or dead. Data on length or age classification is often also taken at the time of sample collection. These initial survival datahave typically been taken on all fish species collectedin the samples, as well as on important shellfish species. Most impingement survival studies have also collected data on delayed, or latent, mortality from impingementby transferring organisms initially alive to 

### a holding facility and monitoringmortality (number dead) at pre-established intervals over an extendedperiod of time. Typically, mortality observations are made at least once during each 24-hour period ofthe extended survival studyto avoid data loss through decay, scavenging, etc. To optimize the use ofholding facilities and monitoring efforts, these “extended” survival studies have often been limited to focal species that are frequently impinged and/or of commercial, recreational, or other importance in the waterbody. Holding facilitiesused for the extended survival studieshave consisted eitherof land based flow-through tanks suppliedwith water by pumping from the sourcewaterbody or floatinglive pens maintained in the source waterbody near the cooling water intake. Extended survival observationshave typically ranged from less than 24 hours up to 108hours, although at least one study monitored mortality of impinged fish for 

### up to 204 hours 

### (EA 1979a).
To distinguishimpingement effects from the effects of sampling and holding, some studies have conducted survival tests on several fish species using controls collectedby seining or box trapping in the source waterbody (Serven and Barbour 1981;Muessig et al. 1988;EA 1983). Field-collected fish were generally held for a day or more to allow recovery from collection stressprior to their use as controls, after which they
were introducedto the collection device (collection controls) 

### andordirectly into the holding facility (holding controls).
Data Analysis The majority of studies conducted to date have used the proportion of impinged organismsremaining alive
as the principal statisticfor survival analysis and the binomial distribution as the basis for calculating variance about the measured proportion surviving. The alternative approach has been to use failure analysis methods such as the Kaplan-Meier survivorship function (ECSI and LMS 1996). The definitions and formulae used to calculate impingement survivalproportions and associated standard errors are reported in Muessig et al. (1988). Initial survival is calculated for each species and age group studied by dividing the counts of living organisms (“alive” = “live” plus “stunned”)by the total numbers collected. The “stunned” category used in many studies has generally had two purposes. First, it provided a basis for representatively sub-sampling

3 In some studies, a “damaged”or “stressed” category was used instead. The distinctionbetween these categories is apparently based on whetherbehavioral observation (e.g. non-equilibrium, struggling movements) or visual inspection for injuries was used to classify fish. The text uses the term “stunned”to mean any of these categories.

3both undamaged and damaged fish for use in extended survival studies when too many organismswere collectedto allow them all to be transferred to the holding facilities. Second,ifno extended survival studies
were conducted, it provided an indicator ofthe potential for delayedmortality. In effect, initial survival estimates calculated using counts of “live”, rather than the “live” plus “stunned”, in the numerator adjust survival for delayed mortality by assumingthat all stunned organismswill die from damage caused by impingement. Extended survivalis the conditionalprobability of survivingboth initially and during the extended-survival monitoring period, calculatedby multiplyingthe initial survivalproportionby the proportion of initially living organismsthat survive to each extended observationinterval (Table 2-1). While some of the prior impingement survival studies reported extended survival estimates for each observation interval used in the study, many chose not to report extended survival for intermediateobservation intervals, and instead presented estimatesof initial survival and extended survival determined at the last observation interval (e.g., 96-hr extended survival). The observed survival resulting from impingement, collection, and holding can be adjusted for control survival (reflectingthe effects of collection and holding) to obtain estimates of survivalresulting 

### from the effects ofimpingementalone. Control-adjustedimpingement survival estimates are calculatedby dividing the initial or extended survivalproportion by the corresponding proportion of controls surviving. However, control-adjusted impingement survival estimates are available 

### in relatively few studies and for only a few species, largely as a result ofthe difficulty of obtaining suitable control fish. Therefore, unadjusted extended survivalis typically used as the best available estimate of impingement survival. To the extent that such estimatesinclude mortality from collection and holding stresses, which they probably often do, they overestimate the mortality rate fiom impingement. 

### Coverage

### ofthe Studies The majority of the impingement survival studies were performedbetween the mid-1970s and mid-l980s,
as part ofthe initial surge of activity 

### in responseto the requirementsof 53 16(b) ofthe Federal Water Pollution Control Act Amendments of 1972. State Pollution DischargeElimination System (SPDES)permit conditions that required testing of intake system alternatives for reducing impingementmortalityprovided the impetus for many ofthe studies, particularly during the 1980s and 1990s. The source documents reported impingement survival studies at 3 1power plants located near the Atlantic, Pacific, and Gulf coasts ofthe U.S., on the Great Lakes, and on the upper Mississippi and Columbia River basins. More than half of the studieshave been at plants located in the mid-Atlantic and southernNew England states (Figure 2). Altogether, impingement survivalhas been studied for at least 31 steam-electric plants located in 15 states and the province of Ontario. The faciliti’es at which studies were conducted are located on 22 different waterbodies covering all four of the major waterbody types for which 

### USEPA has proposed $3 16(b)performance requirements (USEPA 2002), as follows:

0 Freshwater streams and rivers4 facilitieslocated on 3 waterbodies; Great Lakes-5 facilities located on 2 waterbohes; Tidal rivers and estuaries-1 6 facilities located on 13waterbodies; and Oceans4facilities located ora 4 waterbodies. Impingement survival data is available for three basic types of vertical traveling screens: angled, dual-flow, and through-flow, as follows: Angled screens-5 reports covering studies at 4 facilities;Dual-flow screens-6 reports covering studies at 

### 5 facilities; and Through-flow screens-55 reports covering studies at 23 facilities Three facilities, Danskammer Point, Oswego, and Roseton, have studied survival using single-flow and either dual-flow or angled screens. The majority of studieshave tested some form of modificationto screen design and/or operation intended to enhance impingement survival. The historical studiesreport data for over 300 different taxa, most identified to 

### &e species level. Grouped by waterbody type there are 55 taxa represented fiom facilities on fieshwater streams and rivers, 39 from facilities on the Great Lakes, 184 from facilities on tidal rivers and estuaries, and 85 from facilities located at coastal ocean sites, of course with some overlap oftaxa among waterbody types. The majority of species
were collected in relatively low numbers in these studies, mostly because only a portion ofthe resident species are highly susceptibleto impingement at any given facility. 

### For comparison,there were about 180 taxa where 10or more organisms were collected in 

### an individual study.


### In

formation Summaries Sourcedocumentswere reviewed for selectedtypes of information, which, if available,was compiled in a hierarchical database (Figure 3). 

### EPRI (2003) provides tables listingthe facilities and dates of studies, waterbodies, screen designs, and taxa that are covered inprevious impingement survival studies. The 

### EPRI report also contains tables of impingement survivalrate estimatesby species and by screen design and operation. To provide the broadest reasonable amount of survival information, impingement survivalrate estimates available in the source documentswere included in the database, if those estimates were based on ten or more organisms collected. The database contains several types of survival rate estimates, including the initialproportion surviving (&=(live

### + stunned)/totalcollected), initial proportion surviving assuming stunned are dead (Sidd=live/totalcollected), and extended survival 

### (S,) at the end of the latent effects holding period. 

### Factors Influencing Impingement Survival
The survival of impinged organisms depends on the nature and magnitude of stresses imposed on them during impingement and on the tolerance ofthe organismsto those stresses. Theoretically,the magnitude of the various potential stressesof impingement, such as physical impact and abrasion, acidosis and neurological shock, suffocation, desiccation and thermal shock, depend 

### on CWIS design and operation; while the sensitivities of impinged organisms vary depending on biological and waterbody characteristics. The impingement survival source documents were reviewed for information that would assist in characterizingthe influenceoftheoretically importantbiological, CWIS, and waterbody factors on impingement survival rates. Examples ofthe information available from prior studies are provided below, and discussed more fully in EPRI (2003). 

### Biological Characteristics The biological variables that could affect impingement survival include speciestype, developmental stage and size, and physiological condition. Studies at operatingpower plants have shown that impingement survival is strongly influenced by the inherent sensitivityof species to impingement stresses. The morphological, physiological and behavioral characteristicsof each species affect its sensitivityto impingement stress, although the relationshipsbetween these characteristics and impingement survival have not been quantitatively defined. In general, species types that are found to be hardy in terms of their resistance to collection and handling stress (e.g., crabs, killifish, catfish) are also tolerant of impingementstresses,while those that are difficult to collect and keep alive (e.g.,herrings, anchovies, smelts) tend to be sensitive to impingement.
It may be helphl to qualitativelyconsider species characteristicsin the context of each ofthe sources of impingement stress discussed above when evaluatingthe potential for species to survive impingement at a CWIS (e.g., for planning site studies). For example, speciespossessing heavier skeletal structure, thick scales or bony scutes, thick protective slimes, or hard exoskeletonswould be more likelyto resist physical injury and desiccation than would speciesthat have light skeletons, and thin scales that shed easily. Similarly, species that are better adaptedto low oxygen conditions or are able to extract some oxygen directly from the air are less likely to experience suffocation. Behavioral characteristics ofthe speciesmay also have important influences on impingement survival. Some species may be responsive to local hydraulic conditions and, 

### in the case ofpelagic species, may tend to maintain a position up in the water column in the intake flow upstream ofthe screens. Such prolonged swimmingmay lead to systemic stress from oxygen debt and acidosis (Powers 1977), and increasedmortality when the fish become exhausted and
are impinged. Prior studies provide little information on the specific relationship between various species characteristics and impingement survival. However, studiesconducted at the Millstone Nuclear Power Station examined the aggregate effects ofbody type and habitat preference on impingement survival (NUSC 1986, 1987). Crustaceans and demersal fish species generally showed much higher impingement survival in these studiesthan either pelagic fish species or squid. The variation in extended impingement survival rates among taxonomic familiesthat has been observed in prior studies is illustrated 

### in Figure 4, which shows the mean and standard deviation of extended survival rate estimates reported for 36 taxonomic families under continuous screenwash condhons. The mean and standard deviation of the survival rate estimates reported for each taxonomic family for all screenwash conditions are presented in Table 1. Within family and screenwash frequency groups, survivalrate estimates vary due to differences among facilities, and among other study conditions such as length ofthe extended survival observation and season. However, the survival rate estimates appearto reflect the relative species tolerances to impingement that would be expectedbased on the nature of the impingement stresses and the biological characteristicsofthe species. For example, families with relatively high survivalrates consist mostly ofmacroinvertebrates with hard exoskeletons, fish generally inhabiting shallow, turbid waters and known to be easily held in captivity such as killifish and minnows, demersal species and species tolerant of low dissolved oxygen levels such as flounders, catfishes and sunfishes, and species that are heavily scaled or armored, such as pipefishes and sculpins. Families with low survival rates are mostly characterized by soft-bodied pelagic forage species such as anchovies, herrings and smelts. Survivalrate estimates for about two-thirds ofthe taxonomic families exceed 50 percent when screenwashis continuous. Twenty-eight out of the forty-sevenfamilies for which data have been reported, or about 60 percent, appear to have the potential, given adequate screenwash frequency, for impingement survival rates greater than about 70 to 80percent. Within species, changes in sensitivityto the physical stresses of impingement should be most evident during distinct developmentaltransitions that significantly alterphysical characteristics and/orphysiological mechanisms (e.g., osmoregulation). The source documents contained several examples ofthe potential influence of such transitions on impingement survival rate. For example, studies of impingement survival
on fine-mesh intake screens show that the survivalrate of fish increased sharply as larvae transitionto the juvenile stage, possibly reflecting the additionalprotection afforded by scale and skeletal development at this stage (EA 1979b). Likewise, the absence of a hard exoskeleton during molting increased the sensitivity of decapod crustaceansto impingement, resulting in more moderate survival rates of juveniles and adults

6 

# 7during the molting season than at other times of the year (NtJSC 1987;CP&L 1985;Tatham et al. 1978; Serven and Barbow 1981). On the other hand, no consistent relationshipbetween size or age of juvenile and older fish and impingement survival is apparent in the prior studies. Extended impingement survivalrates have in some cases tended to increase (CP&L 1985; ECSI and LMS 1996)or decrease (ECSI and LMS 1996)with size of the fish. Other studies have found little consistenttrend in extended impingement survivalrates among size classes (Serven and Barbow 1981) or among age groups (Muessig et al. 1988) of several species. The ability to observe consistent trends in survival due solely to size or age may be confounded by other factors influencing survival, including seasonal differences in debris loadings or cooling system operation (e.g., cooling water flow rates), size-related differences in handling and holding mortality, and environmental variables influencingthe physiological state of the organism prior to impingement. Environmentalfactors that affect the organism’s physiology and condition are also likelyto influence its sensitivityto impingement stresses. Nutrition, disease, and reproductive state (Con Ed 1986) may influence impingement survival rate, but relativelylittle information is available from prior studies regardingthese factors. 

### C

### WIS Characteristics The impingement survival realized by each species and life stage may be greatly influenced by intake screen design and operating conditions. Physical stressespresent during impingement are influencedby screenwashfrequency, screenrotation speed, and screen modifications intended to reduce stress associated with fish separation and handling. 

### A review of the biological effectiveness, engineeringpracticability, and costs of fishprotection systems, including active screening systems,has been presented in detail in three EPRI reports (EPRI 1986,1994,1999a).
For vertical traveling screens there is generally a substantialincrease in organism survival associatedwith decreased time between screen washes, with continuous screen rotation providing the highest survival (Kmg et al. 1978; Tatham et al. 1978). When screens are stationary for long periods oftime, impinged organisms may become moribund in repeated attempts to free themselves and may suffocate against the screen. 

### Inthe studies that contained data for various screenwash frequencies, extended impingement survivalrate for most species decreased, often very substantially, as time between screen washes increased (Figure 5). However, the survival rate for several hardier species (e.g., tessellated darter,three-spine stickleback,hogchoker) was very high, regardless of the length of interval between screen washes. The duration of organism impingement on the traveling screens is also directlyrelated to rotation time ofthe screen, or the in other words, the time oftravel required before impinged fish reach the screenwashheaders. This travel tive is determinedboth by the speed of screen rotation and the elevation or height of the screen. Faster rotation and/or khorter screenswould be expected to decrease stress. Screen elevation above the intake decking may also affect the length ofthe drop that fish experience from the screen to the screenwash sluiceway, which could potentiallyalso impact impingement suwival. Several studieshave examined the relationship between the speed of screen rotation and impingement survival. Studies at the Dunkirk, Mystic, and Brunswick generating stations indicated faster screenrotation speeds generally resulted in higher impingement survival rates (Table 2) (Beak 1988; SWEC 1981; CP&L 1985). Studies on Ristroph-modified dual-flow traveling screens at the Roseton generating station at screen speeds of 9.8 ft/min and 19.7 Wmin found no definitive trend in survivalbetween the two screen speeds

7(Normandeau 1995). 

### Six of ten fish species with 20 or more organismscollected had higher survival at the faster screen speeds, while 3 fish species and blue crab had higher survival at the slower screen speed. A number ofphysical modificationsto screen systemshave been developed specificallyto protect fish and other aquatic organisms. Screen systems employingfish buckets4(or troughs), continuous operation, and low pressure washes with fish returns to the waterbody are typicallyreferred to as Ristroph screens, after the original developer ofthe modified screen. Because fish protectionmeasures evolved or were added over the years, later versions ofthe modified screens are sometimesreferred to as modified Ristroph screens. One of the last modifications to the Ristroph design was to add a recurved lip to the screen fish buckets. Fletcher (1990) showed in laboratory studies that, in selected species, strugglingbehavior resulted in a downward movement along the screen mesh that directed them to the fish-liftingbucket attached to each of his experimental screenpanels, Redesigning the bucket with a recurved edge creates a calm zone, where fish
were found to seek shelter and remained in the bucket as the screen’srotation carried them upward to the water surface and spraywash fish removal system. The effectiveness ofmodified screen systems in reducing impingement mortality compared to conventional
screenshas been evaluated at the Oyster Creek, Salem, Arthur Kill, and Roseton generating stations. Both modified and unmodified screens were single-flow (or through-flow) at the first two stations, and dual-flow at the Arthur Kill station.The study at Roseton compared survival on dual-flowmodified screensto that on single-flow conventional screens. At the Oyster Creek’, Arthur Kill, and Roseton stations, impingement survivalrates measured on modified screens were compared to those from unmodified, conventional
screens. Studies at the Salem station, evaluated the benefits ofprogressive improvements in the fish protection measures incorporatedinto existingRistroph screens. Overall, the comparisons indicate that the Ristroph modifications are effective in improving the survival rates, especially of species that are sensitive 

### or moderatelytolerant of impingement stresses (Table 3). However, the incremental fish protection benefits ofRistroph modifications, versus continuously operated conventional screens, may vary widely among species and power plant sites, Other CWIS factors, such as screen approach velocity, intake configuration, and the proximity ofthe screenwash discharge and fish return to the cooling water intake may influence impingement survivalrates. However, the potential affect ofthese factors on survivalrate has not been examined in any detail in the studiesreviewed. Screen approachvelocity and intake configurationcould affect the behavior and energy expenditures of fish prior to encounteringthe screen surface, as well as the damage incurred during impingement. Theproximity ofthe fish return to the cooling water intake, together with the hydrodynamics of the waterbodyin the vicinity of the station, influences the magnitude of dish reimpingement after return to the waterbody. Multiple impingement exposures may tend to reduce survival as 

### a result of cumulative stress and injury.


### WaterBody 

### Characteristics Many ofthe impingement survival studies report survivalrates separately for various timeperiods or seasons during the year, though only a portion ofthose studies have attempted to explicitly address the relationship of survival to season or to seasonal changes in environmentalconditions (Tatham et al. 1978;

“Buckets” are essentially troughs mounted along the bottom edge of each screenpanel that hold a few inches ofwater. Their purpose is to reduce escape and reimpingementof impinged fish and keep them immersed as they are lifted from the waterbody. 5 The unmodified screens at Oyster Creek were operated intermittently(up to 2 hoursbetween screenwashes).Unmodified
screens at Arthur Kill and Roseton were apparently operated continuously,as were the Rstroph screens at all these plants.

8Muessig et al. 1988; Con Ed 1986;Beak 1988; 

### NUSC 1987;ECSI and LMS 1996;LMS 1991;

### EA 1986; Normandeau 1995;Reider 1984). A variety of water body characteristics that vary seasonallyor over shortertime periods in response to weather conditionscould potentially affect the mortality of impinged organisms. Such factors include: loadings of debris and other organisms that may damage fish; water temperature; dissolved oxygen and turbidity; and, in the case of estuarine sites, salinity. Intake screen loadings of debris and organismswith hard exoskeletons (e.g., crabs) appear to cause an increase in"injuryand death, reducing survival of impinged fish (Landry and Strawn 1974). Occurrence of debris and its blockage of intake screens is a highly site-specific factor. Someresearchers have noted lower survival of impinged fish specieswhen large masses ofjellyfish are present (NUSC 1987)or when the numbers and activity of crabs on the intake screens is high (Tatham et al. 1978). The potential for injury fromphysical contact with plant materials and man-made debris dwing impingementunderlies the design of
screensthat include separate fish and debris spraywash removal troughs. A number of studies have examinedthe relationshipbetween impingement survival and ambient water temperatures. Seasonalwater temperatures near the upper or lower temperaturetolerance limit ofthe species may increase their sensitivityto the subsequent stress of impingement,thereby lowering impingement survivalrelativeto that observed at other times of the year. The elevation ofmetabolic rate as temperaturesincrease to their summermaximums may exacerbatethe physiological stresses of impingement, including increasing the rate of oxygen starvation oftissues and suffocation. Very low temperatureshave been observed to increase mortality due to handling and rearing stress as a result of increased osmoregulatorydysfunction (Wedemeyer 1972;Miles et al. 1974). 

### In temperate zones, many species are unable to fully adaptphysiologicallyto the wide changes in water temperaturesthat occur seasonally. Although many ofthese species adapt behaviorallyby seasonal migration to habitats with more favorabletemperatures, some portion oftheir populations often reside in waters quite close to the limits of their thermal tolerance. As a result, these organismsmay be more susceptibleto impingementmortality or may evenbe susceptibleto natural seasonalmortality, especiallyin particularly cold winters or hot
summers. For example, Lankford (1997) has shownthat Atlantic croaker, which uses bays and estuaries during summer and fall months, can become highly stressed and more susceptibleto impingement when water temperatures are lowest. Lajeone and Monzingo (2000) reported that the vast majority of fish (gizzard shad and freshwater 

### drum) were either dead or moribund prior to their arrival on the Quad Cities generating station screens. One may expect that the affect ofwater temperatures on impingement survival will vary among ecosystems and species, depending on the adaptations of species to their thermal environments, Variation in temperaturerelationships observed in field studies can also result from covarying factors that may affect survival, such as increasingfish size during the growth season and, in the case of estuaries, salinity. It is therefore not surprising that reported temperaturerelationships vary considerably among the impingement survival studies. However, the general pattern of affect on fish that emergeswhen these data are examined collectively is one ofhighest impingement survival over some intermediate ambient temperature range, with the potential, depending upon species, for decreasing survival at temperatures above and below this range6 (Muessig et al. 1988;EA 1986;LMS 1991;NUSC 1987;Normandeau 1995). The limited data available suggest that this intermediatetemperaturerange maybe relatively narrow for pelagic species more sensitiveto impingement and relatively broad for demersal or littoral species more

I tolerant of impingement (EA 1986;NUSC 1987;Normandeau 1995;LMS 1991). For example, at the

6 It shouldbe noted that those studiesthat have explored the relationshipbetween impingementsurvival and temperaturehave not found such a relationship for all species. This may be due to variation among species andorto limitations ofthe data.

9Roseton station, impingement survival ofblueback herring, bay anchovy, and alewife steadily declined as temperature increased above about 

### 16°C; fromthe 20 to 40 percent range below 16°Cto near zero percent at 22 to 28°C (Normandeau 1995;LMS 1991). 

### In contrast, impingement survival ofbrown bullhead decreased only slightly at temperaturesup to 28°C. Most ofthe observations ofreduced impingement survival at low water temperatures (lessthan about 4.5 to 

### 7" C) suggestthat the effect maybe confinedto temperaturesnear the low temperature tolerance limits ofthe species, with the increased impingement mortality caused by the thermally stressed condition ofthe organisms at the time of impingement. Some impingement survival studies have not explicitlyexamined survivalrelationships to temperature,but have observed differences in extended impingement survival at various times of year (Tatham et al. 1978; Reider 1984;Beak 1988). Those observationsthat spanwarm and cold seasons, summarizedbelow, are not inconsistentwith the typical seasonal cycles of ambient water temperature in temperate zones of the U.S. and the temperaturepatterns discussed above. In general, impingement survival rates observed in these studies for a given species have been lowest in 

### summer and highest in spring and fall,with intermediate survival rates in winter. The reduced impingement survivalrate at higher summerwater temperatures that has been observed for
some species may, in part, reflect the influence of seasonal changes in dissolved oxygen levels. The concentration of dissolved oxygen in water is determined by the interaction of severalbiological and physical processes, which typicallyresults in a seasonal pattern ofhighest dissolved oxygen concentrations in the winter and lowest during the summer. The correlation of increasing water temperatureswith decreasing djssolved oxygen levels makes it difficultto distinguishmgthe independent effects of dissolved oxygen on impingement survival rate. One studyused discriminant analysis to examine the importance of temperature, dissolved oxygen, and other factors on impingement survival (Normandeau 1995). Dissolved oxygen was identified as a primary factor influencingthe impingement survival ofblueback herring and a secondary factor influencingthe survival of alewife. For both ofthese species, impingement survivalrate was significantlyhigher at dissolved oxygen concentrations of 100 12mg/l than it was at 7-8 mg/l.
Water salinitymay be an important factor influencing impingement survival in the brackish water regions of estuaries, where salinity vaxies seasonallyin responseto changes in fieshwaterdischarge and tidal height. Low to moderate levels of salinity reduce the energy input required for osmoregulation, and thereby act as a general stress ameliorator (Bowser and Buttner 1991; Kane et al. 1990;Palawski et al. 1985). Impingement survival studiesinbrackish water regions of the Hudson River suggestthat the stressreducing effects of salt result in higher impingement survival of some species when brackish water 

### is present than during freshwaterperiods (ORU 1977). For example, at the Bowline Point generating station, extended survival of whiteperch and stripedbass increased in proportion to the logarithm of conductivity (Muessig et al. 1988). In studies at the Indian Point station, extended impingement survival of striped bass, white perch, weakfish, bay anchovy, and blueback herring was higher in August and Septemberwhen water salinity was 6 to 8ppt than it was later in the year, when salinity decreased to less than 1ppt (Con Ed 1986). 

### Impingement Survival and §316(b) 

### Compliance Compliancewith the $3 16(b) regulations soon to be established for existingpower plants will likely require 

### NPDES permit applicantsto assess the level of fish and shellfishprotection provided by existing and alternative intake technologies and operationalmeasures, and in some cases may also compel applicants to assess the ecological significance of entrainment and impingement at their generating facilities as part of a cost-benefit analysis. These assessments will typically require quantitative estimation of fish losses from impingement, and impingementmortality rates will be needed as one ofthe inputs for calculatingthose

10losses. Adequate characterization of impingement mortalityrates 

### for focal species impinged at the existing and alternative intakes is obviouslyimportant for the demonstratingcompliance since the historical impingement survival data show that mortality rates are strongly influencedby biological and 

### CWIS characteristics,but can be very low for many species, given adequate screen design and operation. Estimates of impingement mortalityrates for use in the compliancedemonstration may be obtained from site-specific studies conducted at the facilityconcerned or from published reports on impingement survival studiespreviously conducted elsewhere. Existing impingement survival data may be useful in a variety of ways in the BTA determination, including: Screening ofintake alternatives-as part of 

### this screening, existing impingement survival studies can be used to identify intake alternativesthat would have potential for reducing impingement losses and prioritize them for more detailed evaluation. Selection of focal (criticalor representative) species-ane criterion for selection is susceptibilityto effects ofthe intake. Existing impingement survival data can be used 

### to help assurethat the focal species selected for assessment adequatelyrepresent a range of species’ sensitivitiesto impingement. Detailed evaluations of fish protection benefits from intake alternatives-prospective analysis of potential benefits prior to selectionand installation of alternatives,which necessarilyrequires impingementmortality rate estimates derived from prior survival studies at other facilities, is required to assure that economically justifiable and environmentallybeneficial actions are taken. Detailed evaluations of fish protection benefits from the existingintake-evaluations of impingement losses for the existing intake using survival estimates appropriately selected from studies at other sites may help to identifyfacilities or specieswith low potential for impact and to evaluatewhether feasible alternatives are likelyto provide appreciable additional fishprotection benefits? Defining additional data needs-the prior studies provide background informationthat is valuable for selecting impingementmortalityrate estimates appropriate for the species, 

### CWIS and waterbody characteristicspresent at a facility and help to identify additional information needed for adequately demonstratingcompliancewith the 

### BTA requirements. During the planning stage ofthe 

### 53 16@) compliance assessment, available impingement survival information shouldbe compiled and evaluated as part ofthe development of an analysisplan. 

### This process may identifjr additional data needed for the assessment, and should result in an analysisplan that includes approaches for addressinguncertainties identified. Impingementmortality rate estimatesused in the assessment shouldbe based on survival datathat is representative of the sensitivity ofthe impinged species, the design and operation ofthe existing CWIS and any alternativesunder consideration, and the waterbody conditions during primary periods of impingement. 

### Relevance of 

### MortalityRate Estimates 

### toSite Conditions Sincethe inherent stress tolerance of different species types is one ofthe greatest influenceson impingement survivalrate, impingementmortality rates for the specific focal species at issue should be used, when available. However, the level ofuncertainty associated with using mortality rate estimates for congeneric species, or in some cases even species of the same taxonomic family, may be acceptablewhen species-specificdata are unavailable.

7 Later verification of the assumptionsused in the evaluations,including impingement mortality rates, can stillbe required.

11Mortality rate estimates shouldbe consistent with the screenwashfrequencynormally used at the existing facility, and with that planned for alternative technologies and operations, since screenwash frequencyis
one ofthe most important 

### CWIS factors affecting impingement survival. Screen travel time may be an additional considerationfor evaluatingmortality of sensitive and moderately tolerant species during continuous screenwash, particularlywhen screen speed is relatively slow (e.g., 2 or 3 ft/min). Ristroph modifications appear to increase impingement survival rates for sensitiveand moderately tolerant species. However, in comparing Ristroph screensto conventional screen alternatives, assessors should take care to use mortality rates that reasonably represent the incremental improvement of each alternative. For example, the incremental benefit of Ristroph screens over conventional screens operated intermittently at very slow rotation speeds ougbt to be greaterthan their incrementalbenefit over conventional screensoperated continuously and at relatively high rotation speeds. Many ofthe impingement survival studies report variations in survival at different times ofyear. The most substantial changes seem to be associated with high summer ambient temperatures, or very cold winter temperatures, whchresult in higher mortality rates. In estuaries, survivalrates appear to be substantially higher when water is brackish than when it is fresh. Sinceprevailing environmentalconditions may vary from year to year, inter-annual variation in survivalrate may also be expected. No generally applicable mechanistic models have been developed for predictingchanges in impingement survival rate based on environmental conditions. Therefore, assessors must select or collect data that are reasonably representative of conditions that occur during the primary periods of impingement of the focal species. For many species quantifylngvariationsin impingement survival rates during all seasons or over all environmentalconditions may be impracticaland unnecessary, since the largemajority 

### of impingement occurs during only a portion ofthe year. 

### Uncertainty in Impingement Survival Study Methods The methods used to collect impingement survival data and calculatemortality rates may introduce uncertainties in the assessmentof impingement losses. Some of these uncertainties reflect inherentpractical limitations that are not easily addressedby study design, and may either overestimate or underestimate actual impingementmortality rates, including:
No correctionfor collectionholding mortality-relatively few studies have conducted control tests on the mortality due to stress of collection, handling, and holding for latent effects. As opposed to laboratorybioassays where standard test organisms are readily available for use in testing, obtaining control organisms from the wild for testing is difficult and often impractical for many species. For many species, the holding stresses alone are sufficient to cause mortality, even when holdingprotocols conform

### to standardbioassay practice. Mortality rate estimatesthat are unadjusted for controlmortality may overestimate the actual mortality rate from impingement. No interaction ofhandlingholding and impingement stresses-studies that adjust mortality rate estimates for control survival assume that the probability of mortality from impingement and collectionholding are independent stxessesthat do not interact. To the extent that these stresses are interactive, this assumption overestimates the impingement mortality rate. No accounting for fish mortality from stressesprior to impingement-impingement survival studies generally assume that all dead fish that are collected have been killed by impingement. To the extent that some portion ofthe impinged fish may have died from natural causes or other anthropogenic stresses, this assumption overestimatesthe impingement mortality rate. Such overestimation could be substantial in cases where large fish kills have occurred, such as fkom low winter temperaturesor

12 00 disease outbreaks. 

### In such cases, the majority of impinged fish may be dead or moribund prior to their arrival on the power station screens (LaJeone and Monzingo 2000). Distinguishing other sources of mortalityby recording the physical condition of dead impinged fish (e.g., eye opacity and decomposition) and documenting local or regional fish kills may be an important considerationfor design of future studies. Screenwash efficiency- impingement survival studies should assure that all fish are being representatively sampled. Impingement mortality may be underestimated to the extent that fish are carried over the screen or are trapped within the return system. Proper design and maintenance ofthe screenwash system and monitoring ofthe fish transportpathways can minimize biases from low screenwash and collection efficiency. Potential for predation-increased susceptibilityto predation is a potential source of impingement mortality that has not been measured by impingement survival studies. To the extent that predation effects occur, impingementmortality rates would be underestimatedby these studies. The potential for predation may depend on screenwash system design factors that affect attraction 

### and immediate access ofpredators, such as fish and birds (eg., enclosed fish sluice, location and depth ofreturn). Other factors to consider in the assessment are theseasonalpatterns in abundance and feeding rates of predators in relation to the primary impingement season(s).

13

### REFERENCES

Beak Consultants,Inc. 1988. Dunkirk Station Biological Studies,Final Report, January-December 1987. Prepared for Niagara-Mohawk Corporation. Lancaster,

### NY. Bowser, P.R. and 

### J.K. Buttner. 1991. General Fish Health Management. 

### NRAC Bull.No. 111-1992. NortheasternRegional Aquaculture Center,University of Massachusetts,N. Dartmouth, 

### MA.
CarolinaPower & Light Company

- Biology Unit (CP&L). 1985. Bmnswick Steam Electric Plant 1984 Biological Monitoring Report. New Hill, NC.
ConsolidatedEdison CompanyofNew York, Inc. (Con Ed). 1985. Biological Evaluation of a Ristroph Screen at InhanPoint Unit 2. ConsolidatedEdison CompanyofNew York, hc. New York, 

### NY.
Con Ed. 1986. Survival ofFish Impinged on a Ristroph-type Traveling Screen at the Indian Point Generating Station, Summer and Fall, 1985. New York,

### NY. Davis, R.W., 

### J.A. Matuousek, 

### M.J. Skelly, and 

### M.R. Anderson. 1988. Biological Evaluation ofBrayton Point Station Unit 4 Angled Screen Intake. In: Proceedings:Fish Protection at Steam and Hydroelectric Power Plants, Electric Power Research Institute, Palo Alto, CA. EPRI CS/EA/AP-5663-SR. Ecological Analysts, Inc. (EA). 1979a. Bowline Point Impingement Survival Studies 1975-1978Overview Report. Prepared for Orange & Rockland Utilities, Inc., Pearl River,

### NY.
EA. 1979b. Evaluation ofthe Effectiveness of a ContinuouslyOperating Fine Mesh Traveling Screenfor Reducing Ichthyoplankton Entrainment at the Indian Point Generating Station. Prepared for Central Hudson Gas & Electric Corp., ConsolidatedEdison Company ofNewYork, Inc., Orange and Rockland Utilities, Inc., Power Authority ofthe State ofNew York. Middletown,

### NY.
EA. 1983. Moss Landing Power Plant CoolingWater Intake Structures 316(b) Demonstration. Prepared for Pacific Gas & Electric Company, San Francisco, CA.
EA. 1986. Entrainment and Impingement Studies at Oyster Creek Nuclear Generating Station. Prepared for 

### GPU Nuclear Corporation. Sparks,

### MD.
Electric Power Research Institute (EPRI). 1986. Assessment of DownstreamMigfantFish Protection Technologies for HydroelectricApplication. EPRI Report No. AP-4711. Palo Alto, CA. EPRI, 1994. Research Update on Fish Protection Technologiesfor Water Intakes. EPRI Report No. TR104122,Project No. 2694-01. Palo Alto, CA.
EPRI. 1999a. Fish Protection at CoolingWater Intakes. EPRI Report No. TR-114013. Pa10 Alto, CA.
EPRI. 2003. Evaluating the Effects ofPower Plant Operations: Summary of Impingement Survival Studies. EPRI. Palo Alto, CA. Report 1007821

1Environmental Consulting Services,Inc and Lawler, Matusky, and Skelly, Inc. (ECSIC and LMS). 1996. 1995 Supplemental Impingement Studies with an Assessment of Intake-Related Losses at Salem Generating Station. Prepared for Public Service Electric and Gas Company, HancocksBridge, NJ. Fletcher, I.R. 1990. Flow Dynamics and Fish Recovery Experiments: Water Intake Systems. Trans. Am. Fish. SOC.119: 393-415. Kane, A.S., R.O. Bennett, and E.B. May. 1990. Effect ofhardness and salinityon survival of striped bass larvae. 

### N. Amer. J. Fish. Management 10:67-71. King, L.R., J.B. Hutchison, and T.G. Huggins. 1978. Impingement survival studies on white perch, striped bass, and Atlantic tomcod at three Hudson River power plants. 

### In: Fourth National Workshop on Entrainment and Impingement (L. Jensen, ed.), EcologicalAnalysts, Inc., Melville,

### NY. Bp. 21’7-233. LaJeone, L.J. and R.G. Monzingo. 2000. 3 16(b)and Quad Cities Station, CommonwealthEdison Company. Envir. Sci. Policy 3(Suppl. l), S322. Landry, A.M. and 

### K. Strawn. 1974. Number of individuals and injury rates of fishes caught on revolving
screens at the P.H. Robinson Generating Station. In: Proceedings of the SecondEntrainment and Intake ScreeningWorkshop (L. Jensen, ed.), Electric Power Research Institute, Palo Alto, CA. Pp. 263-271. Lankford, T.E., Jr. 1997. Estuarine recruitmentprocesses and stock structure in Atlantic croaker, Micropogonias undulatus (Linnaeus). Ph.D. dissertation. University ofDelaware. Lawler, Matusky, and SkellyEngineers (LMS). 1991. Roseton Generating Station Intake Debris Screen Post-Impingement Survival Evaluation Study. Prepared for Central Hudson Gas and Electric Corporation, Poughkeepsie,

### NY. Miles, H.M., S.M. Loehner, D.T. Michaud, and S.L. Salivar. 1974. Physiological responses ofhatchery reared muskellunge (Esox masquinongy)to handling. Trans. 

### Am. Fish. SOC. 103:336-342. Muessig, 

### P.H., J.B. Hutchison, Jr., L.R. King, R.J. Ligotino, and M Daley. 1988. Survival of fishes after impingementontraveling screens at Hudson River power plants. 

### In: Science,Law, and Hudson River Power Plants: A Case Study in Environmental Impact Assessment. American Fisheries Society Monograph4.
Normandeau Associates, Inc. (NA). 1995. Roseton Generating Station 1994Evaluation ofPost Impingement Survival and ImpingementAbundance. Prepared for Central Hudson Gas and Electric Corporation, Poughkeepsie,

### NY.
Northeast Utilities Service Company (NUSC). 1986. The Effectiveness ofthe Millstone Unit 1 Sluiceway in Returning Impinged Organisms to Long Island Sound. Waterford, CT.
WSC. 1987. The Effectiveness ofthe Millstone Unit 3 Fish Return System. Waterford, CT Orange and Rockland Utilities, Inc. (ORU). 1977. Bowline Point Generating Station Near-Field Effects of Once-Through Cooling System Operation on Hudson EverBiota, Pearl River,

### NY.

2Palawski, D., J.B. 

### Hunn, and F.J. Dwyer. 1985. Sensitivityof young striped bass to organic and inorganic contaminants in fresh and salinewaters. Trans. 

### Am. Fish. SOC. 114:748-753. Powers, D.A. 1977. Physiology of fish impingement:role of hemoglobin and its environmentalmodifiers. 

### In: Third National Workshop on Entrainment and Impingement (L. Jensen, ed.), EcologicalAnalysts, Inc., Melville,

### NY. Pp. 241-254. Reider, R.H. 1984. Alternative Screen Wash Suwival Study at the Monroe Power Plant April-September, 1983. Semen, J.T. and M.T. Barbour. 1981. C.P. Crane Power Plant: ImpingementAbundance and Viability Studies,Final Report January


### - December 1980. Prepared for Baltimore Gas and Electric Company, Baltimore, 

### MD.
Stone & Webster Engineering Corporation (SWEC). 1981. Final Report, Biological Evaluation of a Modified Traveling Screen, Mystic Station

- Unit No. 7. Prepared for Boston Edison Company. Tathm, T.R., D.L. Thomas, and G.J. Miller. 1978. Survival of fishes and macroinvertebratesimpinged at Oyster Creek Generating Station. 

### In: Fourth National Workshop on Entrainment and Impingement 

### (La Jensen, ed.), Ecological Analysts, Inc., Melville,

### NY. Pp. 235-243.
USEPA. 2002. National Pollutant Discharge Administration-Proposed Regulations to Establish Requirements for Cooling Water Intake Structuresat Phase 

### II ExistingFacilities; Proposed Rule. 67 Fed. Reg. 17,122 (Apr. 9,2002). Washington,D.C. Wedemeyer, G. 1972. Somephysiological consequences ofhandling stress in thejuvenile coho salmon (Onchorhynchuskisutch) and steelhead trout (Salmo gairdneri). J. Fish. Res. Board Can. 29: 1780-1783.

3AIternative impingement survivaI Screen-wash sampling locations Screen-wash jceway Traveling screens trash pit Waterbody

~ ~ ,.-,.. 

# I ,!,

# 5,

, 

# \ 

# ,,

Figure 4 Typical impingementsurvival study collection locations along the screenwash sluiceway system.

4Figure 2 Locations of Impingement Survival Studies (numerals indicate number of facilities studied in each statelprovince).

5C 

# I Ic 0 m a 

# - b

oc! (9 

### T c\! Q 0 0 00 r 

# FL

w 

# t0 0 

## 8 8 ?3 E 03
00 0 

### 8

00 md. -!% 

### 88
00

ON W 

### 95 7 0 

### F2g

00

bcD CO 0 mc? 00 

### 2 

### 8

r m 03 I7 9 "? 7 0 0 0 0

0 0 v! 2 $ 

### 2 0 00

m 03 .i- 0 m 

## 8 8 

### 8 8 8

7 0 

### 2 

### 8

0 0 om* 777 

### 8 8 000

m I- 0 "? rc 0 0

Ln 

### 2

N CO .i­ 

## 2 0

W2m wNooWaI-.i- mm0m I-N om @ 

### 802 -9-!77*7-! mmhlm 

# *-! 22 ; 00000000 0000 00 

### 20 

## 8

0 9 0

0 0 

### 88

00 0 

### gg 2

fo m 

## z 8 8 0

0 00 Ob b co 

## 8 88 qcs, rc ': 00 0 0

0 

### 8

moo 999 000

0 

### 8

(D m b 

### 8 0 ': 

## 8

0 mb 

# - d 9 9 

### 8 00 

### 2 

### 8

lcmm cvhl9 000

@l N 

### 0 2 .r I- 

# - 0 

### 8 0

03 

### 8

N O T- a6-V ( v c 

### 8 8 7 r:Ln 0 00 

### 2:Table 2 Extended Survival of Fish by Screen Speed at the Dunkirk, Mystic, and Brunswick Power Plants

Mean Percent Survival (96 hr) During Period of Peak Abundance Power Plant (screen speeds) Species SizelStage Low Medium High Dunkirk (1 8, 54 ft/min) Emerald shiner Juvenile 89 96 

## II 

# I Mystic (2.5, 7.5-10, 15 fffmin) Rainbow smelt Rainbow smelt Adult Large 39 11.0 31.3 59 40.0 Small 22.5 58.3 66.7 Alosa spp. Large 0.8 0 0.5 Small 6.7 23.4 47.1 Winter flounder All 96.8 100 98.6 Brunswick (2.5, 6.5-10 ft/min) Atlantic croaker c25 mm 9.6 28.9 >25 mm 35.6 36.0 spot c25 mm 7.6 31 .O Bay anchovy 0 0

11Table 3 Summary of Mean Extended Impingement Survival Observed in Studies Comparing Conventional and ModifiedScreens

Extended Survival (Proportion) Conventional Ristroph ModifiedSpecies Screens Screens Ristroph Screens Station Oyster Creek

Salem

Arthur Kill

Roseton Bay anchovy Atlantic silverside Winter flounder Sand shrimp Weakfish White perch Bay anchovy Atlantic croaker spot Alosa sp. Alewife Atlantic herring Atlantic silverside Bay anchovy Blueback herring Butterfish Menhaden Mummichog Northern searobin Seahorse Striped killifish Three-spine stickleback Weakfish White perch Winter flounder Alewife American shad Atlantic tomcod Bay anchovy Blue crab Bluegill Brown bullhead Gizzard shad Hogchoker Pumpkinseed Spottail shiner Striped bass White catfish White perch .06 .I9 .77 .80 1 

### .o .93 .92 .95 .61 .82 .87 .95 .29 .45 .51 .85 .81 .93 .40 .80 .05 .95-.99’ 

### .oo -22-.40 .51 .98-.99 

### .oo .41-.52 .I

5 .79-.96 .I8 .72-.76 .05 .71-.76 .95 .80-.92 .82 .90-.97 1 

### .o 1 

### .o-I .o .91 .87-.96 .99 I.o-1 

### .o .42 .92-.97 .63 .85-.90 .4 1 .97-.97 

### .oo .oo .oo .01 .08 .20 

### .oo 

### .oo .96 .96 .83 .98 .65 .84 .05 .I 0 .92 .97 .73 .94 .49 .68 .24 .43 .75 .84 .28 .46

1 Range for the two modified screens tested.