* I



# .

FINAL REPORT BIOLOGICAL EVALUATION OF A MODIFIED TRAVELING SCREEN 

### MYSTIC STATION 

# - UNIT NO. 

### 7

Prepared 

### for BOSTON EDISON COMPANY

AUGUST 1981



### BY STONE E 

### WEBSTER ENGTNEERING CORPORATION

# . SUMMARY


### On the basis of concerns raised by the 

### U.S. Environmental ProtectionAgency 

### (EPA), Boston Edison Company has conducted a study to determine the effectiveness of a modified, traveling screen in reducing mortality of fish at Mystic Station

# - Unit 

### No. 7. 

### Modifications included the attachment of fish lifting buckets to each debris tray on 

### one Unit 

### 7 screen and the installation of a low-pressure spraywash to gently wash fish from the screen into a fish trough. 

### A new transmission on the screenmotor allowed the screen to be rotated at test speeds of approximately 3.3, 7.5, 

### 10, and 15 ft/min. Impingement survival studies were conducted 

### on four separate occassions between October 1980 and June 1981; these studies encompassed the fall, winter, and spring seasons and the period of peak fish impingement. The studies were concentrated 

### on obtaining survival data for four species of concern to 

### EPA: winter flounder, rainbow smelt, alewife, and blueback herring. Sampling consisted of collecting.andidentifying all fish removed from the modified screen and categorizing them as live, dead, or stunned. Live and stunned fish were placed 

### in holding pools and monitored for 96 

### hours. .Overallsurvival was then calculated by combining initial and latent mortality values. Results indicate that reasonable survival can be achieved among the key test species at Mystic Station

### by modifying traveling screen design and operation. Survival of winter flounder was high under all operating conditions and exceeded 

### 96 percent during the peak abundanceperiod. Rainbow smelt, alewife, and blueback herring exhibited lower survival rates, ranging from 

### 23 to 

### 67 percent depending on 

### screen rotation speed and species,with the exception of adult herring which showed low survival.under all conditions. 

### On the basis of these results, it would appear that a modified traveling screen offers an effective means of alleviating fish mortality at Mystic Station

# - Unit 

### 7. Further, since the majority of fish impingement occurs over a period of 3 

### to 

### 4months, continuous screen operation only during these months should afford a high level of protection 

### on a yearly basis. Finally, 

### on the basis of cost-benefit considerations, it 

### is recommended that the modified screens be operated at intermediate travel speeds on the order of 8 

### ftlsec.

### FINAL 

### REPORT BIOLOGICAL EVALUATION OF 

### A MODIFIED TRAVELING SCREEN MYSTIC STATION

# - UNIT NO. 

### 7 BOSTON 

### EDISON COMPANY
INTRODUCTION

One of the two traveling water screens atMystic Station

# - Unit No. 

### 7 has been modified topermit a test of the effectiveness 

### of the screen, equipped with liftbuckets and low-pressure sprays, inreducing fishmortality. 

### On the basis of discussions with the Environmental Protection Agency, four species 

### were selected as being of primary concern atMystic: winter flounder (Pseudopleuronectes americanus), rainbow 

### smelt 

### (Osmerus mordax), alewife (Alosa pseudoharengus), and blueback herring (Alosa aestivalis). The latter two species are difficult to distinguish from each other; therefore, 

### inthis report, they are grouped as Alosa spp.

Previous studies atMystic Station (Stone & Webster, 1978) had shown that flounder are capable of withstanding impingement and removal from the existing, unmodified screens with relatively high survival. 

### It was probable that the modified 

### screen would enhance survival of this species further. Smelt and Alosa spp. had not been evaluated atthis site, but available data indicated that adequate survival might be obtained under certain conditions of continuous screen rotation. Therefore, in order to determine the survival of the four species of concern atMystic, an experimental screen system was installed 

### inthe fallof 1980.

1

# -

' r
1



# . One 

### Unit 

### No. 7 traveling 

### water screen was modified 

### in an effort 'to enhance fish survival. The existing

### Unit No. 7 screenwell 

### is 

### shown on Figure 1. Modifications included:



### 1. the attachment 

### of fishliftingbuckets toeach of the existing debris trays

### ;



### 2. installation of a low pressure spray header with nozzles 

### to gently wash fishoff of the screen after passing over the head shaft;



### 3. installation of a fish trough to collect fish removed from the
screen;



### 4. incorporation of a fish collection area from which the fish can be gently removed and transferred to holding tanks for latent survival studies;



### 5. movement of the existing high pressure debris spray header from the ascending to the descending run of the screen; and



### 6. installation of a new debris trough (located directly under the fishtrough) to carry debris around the screen to the existing Unit 

### No. 7 debris trough.

These modifications are shown on Figure 2. In addition to these modifications, the screen was equipped with a two-speed motor and a four-speed transmission. The transmission and motor permitted approximate

2PLAN C.W. PUW GATESLOTn '

### LDEBRIS TROUGHI 

# 5 TRAVELING WATER SCREEN

3MSILL 

### I


### SECTION A-A

SCALE-FEET 

### FIGURE 1 

### CIRCULATING WATER INTAKE MYSTIC STATION 

## - WIT 7 BOSTON 

### EDISON CWANY STONE & WEBSTER 

### ENGINEERING CORPORATION

### ---



### -- LOW PRESSURE SPRAY WASH

SHEET 

### PILING- (BELOW FISHTROU3-l)

DEBRIS TROUGH

# -

L= c 

# -

CONC BLOCK WALL FISH COLLECTION AEA 

## 5SCREEN LOW PRESSURE SPRAY WASH SCFZEEN HOUSING FIBERGLASS FISH TROUGH DEBRIS TROUGH
MAX H.W. EL. 15.78' 

# #
k-0 

# - :4., 

### . :!b 4 . M.H.W. EL. 10.45'



### - I_ I_ EXTREME L.W. EL. (-)2.72' 

## =
\-HIGH PRESSWE EL. (-)7'-0" 1' ; SPRAY WASH
FLOW 

# -Li

FIGURE 2 EL (

## -127' -3"3 

# \I/

BOSTON EDISON COWANY STONE E. WEBSTER ENGINEERING COWORATIC

### screen travel speeds of 

### 2.5, 3.3, 

### 5, 7.5, 10, 

### 15, and 

### 30 ft/min tobe selected. Finally, water supply and 

### return systems 

### were installed in the Unit 

### Nos. 1 and 

### 2 screenhouse to 

### service the fishholding facilitylocated inthis area.

METHODS

The biological evaluationof the modified screen began on October 

### 6, 1980. Two types of sampling were conducted: 1) total impingement collections, and 2) impingement survival testing. Total impingement sampling consisted of counting and identifying all fishcollected on both Unit 7 traveling water
screens throughout the study period. To accomplish this, the contents of all screen washings for both screens were picked and sorted for fish several 

### times per week. 

### Allfishwere identified to species and recorded. The primary purpose of this sampling effort was tomonitor impingement patterns inorder to 

### select periods of fishabundance for impingement survival sampling and thus ensure meaningful sample sizes. Total impingement sampling was suspended on April 27, 1981due to a unit outage and subsequent shutdown of the circulatingwater pumps. 

### An abundance of jellyfish, present after the lateMay restart of the unit and the circulatingwater pumps, prevented all further total impingement sampling.
Impingement survival sampling, which was the primary purpose of the study,
was intended to determine survival rates of fish collected by the modified
screen. Prior to the startof each test, the traveling screen was rotated for a period of time atthe appropriate test speed and allpreviously impinged debris and fishwere removed from the screen and a specially3constructed collection area (Figure 

### 2). Each 

### test began after 

### several


### screen rotations. As fish

### were washed from the buckets and screens into the collection area, they 

### were categorized as live, dead, or stunned and 

### were transported in a water-filled bucket toholding pools. The pools 

### were supplied with water 

### on a flow-through basis from a submersible pump located off the southeast corner of the intake building.
Testing was primarily concerned with determining the screen speed which would maximize the survival of a species. Since screen speed is directly related to impingement duration and, therefore, stress, it is reasonable to
assume that higher speeds would result inlower mortality. However, it is important to clearly define the nature of this speed/mortality relationship, since higher speeds result inincreased maintenance and reduced reliability of the screen. While faster rotation may produce higher survival, at some point the incremental increase in survival may be negligible. Therefore, the intent of this study was todetermine the optimal screen speed which would yield adequate fish survival while not jeopardizing 

### screen reliability.

The method used to determine the optimal screen speed for each species involved a sequential sampling strategy inwhich two or three speeds were evaluated during each sampling period. Testing in each period lasting no longer than one month. During alltest periods, fish were collected at
screen speeds of 3.3 and 15 ft/min, which represented the longest and shortest impingement durations tested. During fall testing, an intermediate speed of 

### 7.5 ft/min was tested. During winter testing, an intermediate

4

### speed of 

### 10 ft/min was tested. 

### In the spring, an intermediate speed was not evaluated.

As stated previously, all 

### fish collected from the modified screenwere identified, categorized as live, dead, or stunned,and recorded. These numberswere used to calculate initial survivalvalues. All live and stunned fish were held in holding pools for up to 96 

### hr to determine latent survival. Moribund fish were removed from tanks at time intervals of 

### 1, 24, 

### 48, 72, 

### and 96 

### hours from time of sampling. 

### All test fish were measured and weighed at time 

### of death or 

### at 

### 96 hours if alive. The overall survival following impingementand removal from the modified screen system was calculated by combining initial and latentmortality values.



### In addition to recording mortality over time, all fish collected were weighed and measured and their condition recorded to determine whether differences 

### in size or conditionaffect survival. Examinationof length data from past studies indicated that both young-of-the-yearand adults of the genus Alosa are abundant at Mystic. Therefore, collection of length data for Alosa spp. also allowed for differentiationof survival 

### by lifestage.



### In the fall season, samples were collected on 9 

### days in October and 12 

### days in November. Winter impingementsurvival testing was conducted on 

### 6days in January. Also in January, a continuous 38-hour sample was collected in order to obtainmaximum numbers of smelt and flounder. These species were found to be impinged in greater numbers at night. Spring sampling was conducted from April 13 to April 15, and again on April 23 

### and June 1 

### and 2.



### 5

# --
Samplingwas not conducted at high and low tides to account for possible tidal effects 

### on mortality, as had been planned. The low and variable numbers of fishwhich occur at Mystic Station, combined

### with the short sampling durations required in the original samplingplan, would not have yielded sufficient numbers of test organisms to permit comparisons of tidal effects. 

### In retrospect,qualitative observations of proportions 

### of fish initially live, dead, or stunned at high and low tides indicate that tidal differences in impingement survival are probably small compared to 

### differences resulting from varying screen travel speed.

Data for comparison of screen speeds were binomial. That is, each organism collected at a particular screen speed was classified as live or dead. These data were collected in a period when other environmentalvariables, such as water temperature and salinity,did not 

### vary to a great extent.

Data of this type can be appropriatelyanalyzed by contingency table or Chi-square analysis. These analyses test the hypothesis that the mortality is the same for each pair of screen speeds being compared. For 

### details on the computationalprocedure and an example of a Chi-square analysis, see Steel and Torrie 

### (1960, p. 346-351).



### RESULTS

Results contained in this report represent sampling efforts through spring 1981. Table 1 lists numbers of 

### fish impinged by week for all species collected from October 7, 1980 

### throughApril 27, 1981. 

### In 

### this time period,
a 

### total of 103,384 fish were impinged on 

### both traveling water screens of

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### 15 ft/min screen speed. 

### Results of 

### tests at 

### 15 ft/min show nearly 

### 50 percent 

### survival (initial 

### and latent combined) 

### 96 hours after impingement. 

### In general, impingement survival increased with screen travel speed. The large Alosa showed high initial survival, but latent survival
was low atallscreen speeds.

Results of falltesting with winter flounder are also separated by size since a plot of number tested versus length revealed a bimodal pattern separated at 

### 11.5 cm (see Fig. 

### 4). Data from Scott and Crossman 

### (1953, pg. 

### 281) indicate the smaller fish are 

### intheir first year of life. In Table 2, these firstyear winter flounder are listed as "winter flounder small." From Table 

### 2, 

### we see that over 

### 50 percent of both large and small flounder survived impingement even atthe 

### 3.3 ft/min screen travel speed.

Results for falltesting with smelt are only marginally quantitative. Smelt
were not greatly abundant inthe fallperiod and were impinged 

### less frequently during the day (when impingement survival testing was conducted) than during night hours. Results indicate about 3 to

### 4 percent 

### of the 

### smelt impinged atthis season survive.

Results for other species are qualitative since test organisms 

### were few in number. However, in general, it appears mummichogs and cunner have good survivalpotential inthe fall, while butterfish, mackerel, pollock, and white perch appear to have a poorer survivalpotential.

Results of winter testing arepresented inTable 3. During this period, only 

### 16 Alosa were captured due to their low abundance atthis time. Data

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### was 

### no better than that for large Alosa 

### collected during 

### fall testing.

Flounder tested during winter showed 

### very high survival atall screen travel speeds, as shown inTable 3.

Results for 

### smelt are separated by size since a plot of number tested versus length revealed a bimodal pattern separated at 14 

### cm (see Fig. 

### 5). Data from Scott and Crossman (1953, pg. 

### 138) and 

### Liem and Scott (1966, pg. 121) indicate that smaller 

### smelt comprising the 

### 9 cm to 

### 14 cm mode were 

### too large tobe firstyear fish. Therefore, it 

### seems more probable that the two modes represented, respectively, age 

### I1 fish and age 

### I11 fish. Initial survival for large and small 

### smelt was high for all speeds tested. Latent survival
was significantly lower atthe 

### 3.3 ftjmin speed than atthe 10 or 15 ft/min
screen speed forboth the large and small 

### smelt. The 15.0 

### ft/min screen speed yielded the greatest survival for both the large and small 

### smelt, however, it was not significantly different than the 10 ft/min speed. Interestingly, the smaller size 

### smelt had greater survival than the larger test specimens ata given speed.

Results for other species tested 

### inthe 

### winter aremore qualitative. Sculpin survivalwas very high as was that of Atlantic tomcod and threespined stickleback. Pollock of all sizes appear to have better survival 

### in the winter season ata screen speed of 15 ft/min than 

### in fall. The few white perch collected alldied.

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### The results of spring impingement

### survival testing are limited due to the very low abundance of 

### fish at times when samples could be taken. Tests conducted in the April 13 

### to April 

### 15 period were terminated prior to the normal 

### 96 hour holding period due to operationalproblems with the fish holding facility water supply. These shorter term (24 

### hour) holding results indicated good survival of flounder and poor survival of smelt (Table 4). 

### Later impingement survival testing resulted in a limited collectionof 

### test specimens,especially in June. Fish impingementon 

### the Unit 7 

### screens was extremely low at this time. Latent survival results show good survival of sticklebacks,flounder,pipefish, and eels and poor survivalof 

### smelt (Table 5).

SUMMARY 

### OF TEST RESULTS

Previous studies of winter flounder survival after impingement on 

### the unmodified Unit 

### No. 7 

### traveling water screens showed 

### 85 percent survival with continuously rotated screens and 

### 55 percent survivalwith 2-hour screen wash intervals. The data from the present study show 

### an improved survival of winter flounder impinged 

### on the modified screen, and a 

### virtual eliminationof mortality when the screens are continuously rotated at all speeds during the period of 

### peak abundance in the winter.

Survival of Alosa and smeltwas lower than that of winter flounder. These species are difficult to maintain under laboratory conditions and overall survival would probably exceed observed values 

### if these fish were to be returned directly to the river. 

### In addition,differences in 

### survival due to


### screen speed for Alosa and smelt are not as dramatic as those for winter

10

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### flounder. Regardless, smallAlosa 

### and smelt 

### of all sizes displayed moderate survivalat screen speeds of 

### 15.0 ft/min in fall and winter.

Less abundant species such as tomcod, stickleback,sculpin,mackerel, mummichogs, and cunner appear to have good survivalpotential at any screen speed.



### An interesting and very positive general conclusion is that species show high survivalwhen they are abundant.



### DISCUSSION

Itwould appear from the results of this study that a 

### modified, traveling
screen system offers an effective means of alleviating fishmortality at Mystic Station

# - Unit 7. 

### Should such a system be incorporated as a permanent solution to impingement losses, the engineering implications of 

### continuous operationduring periods of 

### fish impingement should be considered:
1) 

### Continuous screen operation reduces the life of screen components,
2) 

### Increasing speed of screen rotation under a continuous operating mode increases the rate of wear of screen components.

Since these factors have a major impact on maintenance requirements and operating costs and can jeopardize unit reliability, every attempt should 

### be made to 

### minimize the duration and speed of 

### continuous screen operation.

11

c1'

Based 

### on the seasonal patterns 

### of impingement noted 

### inthis study 

### (refer to Table l),as

### well as those observed 

### inpast impingement monitoring studies at

### Mystic Station, it appears that 

### a major portion of the fish impinged could be protected by operating modified screens atUnit 7 on a continuous basis for only severalmonths each year. While impingement sampling was not conducted from April 27 toJune 1, it was evident from observations atUnit 

### 6 during this period that numbers of fishimpinged remained atthe low level observed for theprior 

### ten weeks. Historically, the number of fish impinged atMystic Station from June through September 

### is very low, while jelly fish (Aurelia aurita) are inabundance. Therefore, 

### it is believed that the impingement numbers presented inTable 1 represent the majority of the fish impinged at

### Unit 7 on a yearly basis. Using these numbers, it is clear that two peaks in impingement of the four species of concern occurred. The periods of high abundance 

### were short induration, while the remainder of the year numbers were low. As shown inTable 

### 6, atleast 

### 80 percent of each species occurred during the two seven week periods of October 21 toDecember 8 and December 30 to February 16. Therefore, if modified screens had been
run continuously during fourteen weeks of the year, protection would have been afforded to a largepercentage of the fish collected during the entire year.

While the periods of peak fish abundance atUnit 

### 7 vary in time from year to year, impingement data gathered over a number of years show that definite peaks occur each year. Therefore, should modified screens be utilized at Unit 

### 7, it is recommended that they only be run continuously during periods of peak abundance. Such an operationalmode would provide a high degree of fishprotection ina cost-effective manner while limiting the potential for

12

### TABLE 

### 6

Species Rainbow smelt Alosa spp. 

### Winter flounder

Species Rainbow smelt
Alosa spp. 

### Winter flounder Percent of Total No. Collected During Period of PeakAbundance the 

### Two Peak Periods December 30

# - February 16 

### 90 October 21 

# - December 

### 8 

### 93 December 30

# - February 16 80



### TABLE 7



### Size 

## - Large Small Large Sma

### 11 All Mean Percent Survival During Period 

### of PeakAbundance 

### by Screen Speed Low Medium High 11.0 31.3 40.0 22.5 58.3 66.7

0.8 0 6.7 23.4 48.1 96.8 100 98.6 0.5problems associatedwith operation?maintenance? and general reliability. Since the peak periods of fishabundance atMystic Station are distinguishable from periods of lower abundance, the decision tooperate continuously could be made 

### on the basis of periodic observations during intermittent operation.

A final consideration inemploying modified screens atUnit 

### 7 would be the speed atwhich to rotate the 

### screen during 

### times of continuous operation. As shown on Table 7, higher survivalwas obtained atthe highest speed than atthe lower speeds. 

### It would appear that the lowest speed would achieve a high level 

### of survival with flounder only. On the other hand, the intermediate and high speeds both resulted ingood survival �or most species tested. The final decision to 

### run at a specific speed must take into consideration engineering reliability and cost considerations, as well as survival.

The engineering implications of operating athigher speeds involve greater
wear of the rotating parts of the screens: the rollers, bushings, and pins of the chains; the foot shaft and headshaft bearings and bushings; and the tooth-inserts on the sprockets. Wear of these components increases exponentially with screen speed. Wear of the rotating components results in slack inthe chains and the interference of the baskets with the bottom boot plate where the baskets rotate around the foot shaft and sprockets. This
can result inbreaking away of the basket, jamming of the traveling screens, breakdown of the tooth-inserts, and breaking of the chains (Mussalli et al. 1977).

13Wear 

### of the screens can lead, therefore, to increased maintenance costs and jeopardize 

### unit reliability. The estimated incremental maintenance cost for high speed versus medium speed operation of two modified screens atMystic Station

# - Unit 

### 7 would be 

### $5,000.00 annually based on 

### 14 weeks of continuous operation. This cost includes materials and labor to replace the footshaft and headshaft bushings and bearings and the chains approximately every five years. Potentially more important than routine maintenance costs would be the major costs associated with a unit outage resulting from equipment

- failure due to high screen speed operation.

The specific drawbacks of operating a modified screening system atMystic Station

# - Unit 

### 7 at

### a high travel speed rather than medium speed can be summarized as follows:

1. Wear of screen components would be four times greater atthe higher speed,

2. Annual maintenance costs would.be higher,

3. The reliability of Unit 7 would be placed ingreaterjeopardy, and additional costs could be incurred due to unit outage as a result of equipment failure,



### 4. Flounder, the most valuable commercial species, are afforded equal protection atall operating speeds.

14 IFor these reasons, 

### it is recommended thatmodified 

### screens be operated at intermediate travel speeds should theybe required at

### Mystic Station

# - Unit 

### 7. Considering the relatively low commercial value 

### of Alosa and 

### smelt, the costs and potentially high reliability risks of high-speed operation would not be warranted.
During periods when flounder are the only abundant species even intermittent (Stone & Webster 

### 1978) screen operation would afford an adequate level of protection.



### LITERATURE CITED

Steel and Torrie. 

### 1960. Principles and Procedures of Statistics. McGraw-Hill, 

### New York. 

### 481 pages.

Stone & Webster Engineering Corporation 

# . 1978. Fish Impingement Monitoring, Mystic Station

# - Unit No. 

### 7. July 

### 1978. 54 pages.
Mussalli, Y. G., Taft, 

### E. P. 

### 111, and Hofmann, 

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