ALTERNATIVE INTAKE DESIGNS FOR REDUCING FISH LOSSES MYSTIC STATION - UNIT BOSTON EDI SON COMPANY JULY 1979 , f'

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I hereby certi fy that thi report and plans were prepared under my direct supervision and that I am a duly registered professional engineer under the laws of the State of Massachusetts

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t ~ STONE & WEBSTER ENGINEERING CORPORATION BOSTON, MASSACHUSETTSSection 3. 1 4. 1

TABLE OF CONTENTS Ti tIe Page SUMMARY AND CONCLUSIONS INTRODUCTION . 1-1 PRESENT INTAKE DESIGN AND OPERATION . 2-1 SUMMARY OF FISH IMPINGEMENT EXPERIENCE.

.. . . 3-1 INTRODUCTION. . . 3-1 RESULTS OF IMPINGEMENT MONITORING STUDIES . 3-1 CONCLUSIONS

.. . . 3-1 EVALUATION OF ALTERNATIVE INTAKE DESIGNS FOR THE MYSTIC STATION - UNIT

.. . .. . . 4-1 INTRODUCTION. .

.. . . 4-1 Assessment of Fish Impingement Losses on the Population

.. . . 4-1 Divers ion Devices . 4-2 Behavioral Barriers

.. . . 4-2 Fish Collection Systems . 4-3 Physical Barriers

.. . . 4-3

Summa ry . 4 - 4 VELOCITY REDUCTION . 4-4 Biological Evaluation . 4-4 Engineering Description of Alternatives for Reducing Velocities. . 4- Removing the Bottom Sill at Certain Times of the Year

.. . .. . .. . . 4-4 Utilizing the Units 1-3 Intake Bays for Supplemental Cooling Water for Unit 7. . 4-5 Reducing Unit 7 Operation to One Circulating Water Pump

.. . .. . .. . .. . . 4-7 Installing Variable Speed Control on Circulating Water Pumps to Discharge Temperature

.. . . 4-8 Installing the Screens Flush with the Front of the Intake Bays

.. . . 4-10

Constructing Additional Intake Bays . 4-11 Deepening the Area Immediately in Front of the Existing Intake Bays . 4-13 PHYSICAL BARRIERS - BARRIER NET IN FRONT OF THE EXISTING INTAKE BAYS. .

.. . . 4-14

111TABLE OF CONTENTS (Cant) Section Ti tle Page FISH COLLECTION AND REMOVAL SCHEME - MODIFIED TRAVELING SCREENS . 4-14 Biological Evaluation . 4-14 Engineering Description . 4-18 Evaluation af the Modified Screen Alternative . 4-19

ESTIMATED COSTS AND CONSTRUCTION SCHEDULE . 5-1 REFERENCES. . . R-1LIST OF TABLES Table Ti tle

After Page 3-1 Mortality of Winter Flounder at Several Screenwash Intervals with 95 Percent Confidence Intervals. . 3-3 3-2 Summary of an Analysis of Variance of Differences Observed in the Mortality of Winter Flounder at Several Screenwash Intervals and During the 96-Hr Holding Period. . 3-3 4. 4-1 96-Hr Impingement Survival Results Pulliam Power Plant , 1977. . 4-17 5-1 Estimated Costs.

.. . .. . 5-1 5-2 Total Proj ect and Capitalized Costs (in $1 000). . 5-1 5-3 Construction Periods

.. . .. 5-2LIST OF FIGURES Figure Ti tle 2-1 Plot Plan

.. . 2-2 Circulating Water Intake. 2-1 Flow Transport From Units 1 , 2 & 3 - Plan View 2-2 Flow Transport From Units 1 , 2 & 3 Section View. 2-3 Plan - Flush-Mounted Screens 2-4 Section A-A - Flush-Mounted Screens. . 2-5 Additional TWS Scheme - Plan below Operating Deck. 2-6 Additional TWS Scheme - Plan above EI. 17 ft 6 in. 2-7 Additonal TWS Scheme - Scheme Views. 2-8 Proposed Dredging and Flounder Sill. 4-1 Screen Detail - Modified Through - Flow Screens -

Front Wash

. . . . 4-2 Screen Detail - Modified Through - Flow Screens - Back Wash

After Page 2-1 2-2 4-5 4-6 4-10 4-10 4-11 4-11 4-11 4-13 4-15 4-18SUMMARY AND CONCLUSION Fish impingement monitoring studies have been ongoing at Boston Edison Company s Mystic Station since 1971. On the basis of a review of the study resul ts , the U. S. Environmental Protection Agency (EPA) and the Massachusetts Division of Marine Fisheries requested that a feasibility study of alternative intake designs be conducted even though Boston Edison Company has taken a number of measures to reduce fish impingement at the station. At the request of EPA , Boston Edison Company investigated the feasibility of utilizing various intake modifications which would minimize the numbers and/or mortality of fish at Mystic Station. This effort consisted of (1) reviewing the existing intake design at Mystic and the impingement losses associated with its present operation , (2) evaluating available fish protection systems that might be applied at this site , and (3) developing engineering designs and costs for those systems which appeared to be feasible , cost- effective , and to offer potentially effective methods for minimizing fish entrapment at Mystic. The alternative designs evaluated can be grouped into four categories depending on their mode of operation: diversion devices , behavioral barriers , collection systems , and physical barriers. Available fish protection systems in each of these categories were reviewed relative to their potential biological effectiveness , engineering practicability, and operational reliability as applied to the Mystic Station. A number of these alternative designs and/or modified operating schemes were specifically suggested by EPA. On the basis of this review , nine al ternati ve intake designs or operating schemes were selected for detailed evaluation and conceptual design as described briefly below. Estimated costs were developed for those designs which appeared feasible. 1 . Removing the Bottom Sill at Certain Times of the Year Impingement studies at Mystic have shown that a bottom sill located in the Unit 7 screenwell reduces flounder impingement but may cause an increase in the numbers of pelagic species collected , presumably due to the increase in velocities caused by the sill. If benthic and pelagic species were present at different periods of the year , the sill could be installed only during the period of flounder impingement. At other times of the year , there would be no sill , thus reducing

veloci ties and , consequently, the impingement potential of pelagic species. Unfortunately, both types of species fish generally occur simultaneously and removal of the sill would be of little or no benefit. Utilizing the Units 1-3 Intake Bays for SuEPlemental Cooling Water

for Unit 7 Another potential method of reducing impingement losses would involve reducing the flow , and therefore velocity, into Unit 7 by utilizing the Units 1-3 intakes to supplement the existing Unit 7 intake flow.The scheme would consist of modifying the Units 1-3 pump bays , replacing the existing pumps with vertical axial flow pumps , and manifolding the pump discharge pipes into a supply pipe that would traverse the front of the bays and would discharge into the Unit 7 intake. The Unit 7 screens would be relocated farther upstream toward the front of the bays. A new wharf with protective dolphins would also be required as an unloading facility for oil barges. The total capitalized cost of this scheme is $6 674 000. While this action would reduce velocities at Unit 7 , data are not available to quantify the possible degree of fish protection which would be achieved. In fact , studies on the Hudson River indicated that reducing approach velocities to 0. 5 fps at a power plant did not significantly reduce impingement. Considering the costs associated with this scheme , and the uncertain influence of velocity reductions on fish impingement , it is not believed that this concept is the most

cost- effective option for reducing fish losses. Reducing Unit 7 Operation to One Circulating Water Pump The feasibility of reducing velocities at Unit 7 by operating one circulating water pump was also investigated. The results , however indicated that operating Unit 7 with one circulating water pump would result in loss of plant generating capacity, violation of thermal rise and discharge temperature limitations , reductions in condenser reliability and pump life , and an increase in velocity in the operating screen

bay. Because of the operational problems of this option and because the operation of one pump only would actually increase velocity in the operating bay, it is believed that this alternative is impractical. Installing Variable Speed Control on Circulating Water Pumps Another option for reducing velocities at Unit 7 would be to incorporate variable speed control on the circulating water pumps to permit flow reductions during periods of low demand. Unfortunately, the use of variable speed control would not reduce the velocity in the Unit screenwell substantially due to loss of pump discharge pressure and would create reliability problems. Operating problems which would affect reliability include lower pump discharge pressures , condenser tube fouling, increased pump motor maintenance , and potential violation

of thermal discharge limits. Therefore , this scheme is not considered viable at Mystic Station. Installing the Screens Flush With the Front of the Intake Bays Moving the traveling screens forward in the existing screenwells such that they would be flush with the front of the intake bays would create a more uniform velocity distribution through the screens and would eliminate embayment areas that might entrap fish. However al though these improvements would probably reduce impingement to someextent , velocities would still be rela ti vely high. Therefore , the potential biological effectiveness of this design is uncertain.

The total capitalized cost of this scheme is $1 168 000. Since velocities would not be reduced appreciably and potential biological effectiveness is unknown , it is believed that pursuing this

alternative at this time is unwarranted. Constructing Additional Intake Bays Another method for reducing velocities at Unit 7 would consist of constructing two additional intake bays west of the existing intake. A new screenhouse would contain four new screens and two low-head supplemental pumps that would feed water into the existing Unit 7 bays. The existing traveling screens would be moved to the front of the Unit 7 bays to be flush with the piers. Lateral fish passageways would also be provided. The total capitalized cost of this scheme is $7 383 000. Because of the uncertainty of velocity reductions on biological effectiveness and the high cost , it is not believed that such a major modification offers significant benefits over other more cost- effective alternati ves .

7 . Deepening the Area Immediately in Front of the Existing Intake Bays Deepening the area in front of the Unit 7 intake through dredging would create a new bottom sill consisting of the vertical foundation wall of the screenhouse , thereby allowing removal of the existing bottom sill. This action could maintain the reduced level of flounder impingement achieved by the existing sill and potentially reduce impingement of pelagic species because of lower intake velocities throughout the water column. However , actual reductions in impingement cannot be quantified. Dredging would be confined to the immediate area in front of Unit 7 to maintain structural integrity of the screenhouse. Since the dredged

area would fill with sediment , maintenance dredging would have to be carried out periodically. This would require obtaining permits for dredging and spoil disposal on a periodic basis. The total capitalized cost of this scheme is $393 000. Because of the limited areal extent of dredging possible , the necessity to periodically dredge , and the unknown benefits of this scheme , it is believed that this alternative provides only limited potential advantages.

Barrier Net In Front of the Existing Intake Bays Physical barriers , such as barrier nets , have been evaluated as a method for preventing fish impingement at power plant intakes; results have been variableBarrier nets have been at least partially effective in reducing fish losses at several power plants. However , a net would be difficult to maintain at Mystic because of strong tidal currents and heavy debris loading, particularly with jellyfish and mussels. For these reasons this scheme is believed to be impractical as a long-term solution at Mystic StatioQ. Modified Traveling Screens Fish collection and removal systems , specifically various types of traveling screens , have been used at several power plants with good results. Recently, modifications to conventional traveling screens have been developed which have greatly improved the survival potential of impinged fish. Modifications include the addition of fish lifting buckets , a low pressure spray wash for gently removing fish , and the capability for continuous operation. Such modifications could be made at Mystic at a total capitalized cost of $596 000. Available data indicate that modified screens could act to reduce losses of fish occurring at this site. Of the alternatives investigated , it is believed that the modified traveling screen concept presently represents the most cost- effective system for

further reducing fish mortality. If additional measures for protecting fish are required at Mystic Station Unit 7, it is proposed that a study be conducted which would be designed to quantify survival rates of selected , important species and to identify optimal survival conditions for each species on a modified screen. A preliminary study plan for such an acti vi ty is presented in this report.SECTION INTRODUCTION Impingement monitoring studies were conducted at Boston Edison Company Mystic Station from August 1971 to December 1977. The purpose of the studies was to determine the level of fish losses occurring at Units 1-6 (1971 to 1975) and at Units 1-7 (1975 to December 1977). Initially, review of the earlier studies by the U. S. Environmental Protection Agency (EPA) and the Massachusetts Division of Marine Fisheries indicated that the level of winter flounder impingement was relatively high at Unit 6 and that measures should therefore be undertaken to reduce impingement of this species at Unit 6 and Unit 7. In response to this concern , Boston Edison Company initiated several design modifications (i. , bottom sills reduced curtain walls , etc) for incorporation into Units 6 and 7. As a result of these modifications , flounder impingement was reduced dramatically (approximately 50 percent). Upon subsequent review of the later monitoring study reports by EPA and other agencies , concern was expressed that , although flounder impingement was reduced , total numbers of fish impinged were high.

At the request of the EPA , Boston Edison Company initiated a study to investigate the feasibility of utilizing various intake modifications which would minimize the numbers and/or mortality of fish presently being impinged at the station. The EPA suggested specific options to be investigated. The engineering options included (1) modification of existing screens for continuous operation during times of the year when impingement is most serious , (2) reduction of intake velocities by modifying the existing intake structure or adding new structures to reduce flows , and (3) removing the bottom sill and dredging the area immediately in front of the intake. In addition , the EPA requested information regarding the feasibility of determining the population levels of key species within the Mystic River Boston Harbor estuarine complex for the purpose of assessing station losses on the selected species population. It was also suggested that a program be described to evaluate survivability of fish impinged on modified screens during continuous operation. The EPA also requested any additional information on other alternatives which may be practical for reducing fish impingement or mortality. This report evaluates the status of existing intake technologies for minimizing fish losses and determines the engineering feasibility, potential biological effectiveness , and order- of- magni tude costs of the options presented by EPA. In addition , information is provided on other potentially cost- effective means for reducing fish losses at Mystic Station. 1-1SECTION 2 PRESENT INTAKE DESIGN AND OPERATION General Mystic Station Unit 7, owned and operated by Boston Edison Company, is located on the north bank of the Mystic River. Most of the 42- acre site is in Everett , Massachusetts. A small portion along the western edge is in Boston. The station is in an area zoned for industrial development. The site is bounded by a refinery on the northeast , a tank farm on the east the Mystic River on the south , Alford Street on the west , and a playground and residential area on the north.

At this location , the Mystic River is approximately 1 100 ft wide and its depths vary from 0 ft to 30 ft measured from mean low water. Amelia Earhart Lock and Dam is about 0. 5 mi upstream of the site. This dam effectively bounds the salt water portion of the river. Relatively small amounts of

fresh water pass the dam , making tidal exchange the only important natural

flow at the station. Mean tidal flow is approximately 1 000 cfs. The highest known tide was at el 15. 78 ft. The lowest tide level was el -2. 72 ft. Mean high water is at el 10. 45 ft , mean water level is el 5. 65 ft , and mean

low water is el O. 78 ft. Tide levels are referenced to Boston City Base

(eI O). The Mystic corner has refineries bank. The 12. 5 ft in

River is used for commercial shipping. Everett' s southwest docking facilities for oil tankers and cargo ships. Two sugar are located southeast of the station on the river s southern

United States Pier and Bulkhead Line is located approximately

front of the existing screenwells. Mystic Station has four operating and three retired units. Units 1 , 2 , and 3, now retired , each had a capacity of 50 MW. Units 4 , 5 , and 6 each have a capacity of approximately 150 MW. Unit 7 is rated at 600 MW. The six older units were built between 1943 and 1961 and were originally coal-fired. They were converted to oil-fired units by May 1966. Unit 7 was constructed as an oil-fired station and started commercial operation in 1975. All units have once-through circulating water systems. They draw water through individual screenwells located in the southwest corner of the site and have a common discharge east of the intakes. The discharge was designed as a surface jet to provide improved mixing of the effluent with the cooler river water. Discharge velocities vary from 4. 5 fps at high tide to 7. 0 fps at low tide. Velocity decreases rapidly as river water is entrained. At 200 ft from the outfall , velocities are 2. 9 and 2. 3 fps for low and high

tide , respectively. The general site plan for the station is shown in Figure 2-1. Units 1 , 2 , and 3 at Mystic Station utilized four circulating water pumps each in its own bay. Normally, three pumps operated and one was used as a

spare. All four bays are 10 ft wide at the entrances and have a bottom elevation of -27 ft - 3 in. The curtain walls are at el -13 ft - 3 in. 2-1FUEL 01STORAG ETANK S. --..hOUTFALL STRUCTUREUNITS4-7,--- .'-,)I'--v, J~--1- ,-.,-----,- '-L AUX1!./lYUNIT UNIT UNITUNITSUN IT 7I 6I, 2e. 3I .-1....3 4 5 K V.. '..-.-..J.. .. 'l - -- - - -- - ---- - ---"SWITCHYA. .._.~.--. -wI 1-- .i agE iEXISTING Lk---'-~ ARDt=:~==~,-L-=::;-~--:::::.-= I. ": ~~: H Y. fL----! -.--,..---"L-')I-..,..FENC~.----.--.--- ~1Nf'S,L--,-.-.~----,.PROPERTYUN IT 7STACK"('\'X\c:.':J;)PRECIP (TYP)EXISTING UNIT 1- 6OUTFALL(ABANDONED)('1UNITS 1-~'(S C R E EN WELL SUN IT 7SCREENWELLFIGURE 2-1PLOT PLANALTERNATIVE INTAKE STUDYMYSTIC STATION - UNIT 7BOSTON ED ISON COMPANYSTONE & WEBSTER ENGI NEER I NG CORPORAT IEach bay is Uni ts 1 and screen bay. resul ting gross area.

equipped with trash racks located in front of the curtain wall. 2 have 6- ft- wide screen bays; Unit 3 has a 6 ft-8 in. - wide When operating, each unit used 91 cfs of circulating water a mean velocity at the curtain wall of 0. 65 fps , based on the

Units 4 and 5 each have one 10-ft- wide screenwell. The curtain walls are at el -13 ft - 3 in. and the floors are at el -27 ft - 3 in. These screenbays have trash racks in front of their curtain walls and 9 ft - 0 in. screens behind the walls. Each unit uses 169 cfs of circulating water resul ting in a gross area mean velocity of 1. 21 fps under the curtain wall. Unit 6 uses a single 9-ft- wide bay. A curtain wall extends to el -7. 25 ft

and the floor is at el -27 ft - 3 in. The trash rack and screen arrangement are similar to those of the other five units. With its circulating water flow rate of 169 cfs , the gross area mean velocity under the curtain wall

is 2. 35 fps. Intake Design The circulating water system for Mystic Station Unit 7 pumps 646 cfs at a total dynamic head of 21. 6 ft when the river is at mean sea level. The circulating water system was designed to remove 2. 77 x 109 Btu/hr from the main station condensers with a maximum temperature rise of 19. 9 F. After the Unit 7 discharge is combined with the discharge from the other units the resulting temperature rise is approximately 19 The main features of the Unit 7 screenwell , shown in Figure 2-2 , are trash racks , curtain walls , traveling water screens , and circulating water pumps. There are two screenbays; each is 9 ft wide with a bottom elevation of -27 ft - 3 in. Curtain walls extend to el -7 ft - 3 in. and are located 11. 5 ft behind the entrance to the screenbays. Trash racks consisting of sloping steel bars are located upstream of the curtain walls. The racks are manually raked to remove debris. An 8-ft-high bottom sill is installed at the entrance of each screenwell to exclude flounder and other bottom dwelling organisms. The upstream faces of the traveling water screens are 25. 5 ft behind the

entrances of the screenbays. Screen panels are made from 3/8-in. wire mesh. The screens are equipped with low- pressure (30 psi) and high- pressure (90 psi) spray headers. The purpose of the low- pressure spray is to wash fish from the face of the screen and the trash lips. The high- pressure spray, located above the low- pressure header , removes debris from the

screens. Fish and debris are washed into a common 16-in. semicircular trough and are sluiced back to the Mystic River. I The Unit 6 screen also washes into the Unit 7 trough. A minimum water depth of 6 in. is maintained in the trough when the screens are operating. Approximate flows from each screen are 16 gpm for the low- pressure wash and 234 gpm for the

high- pressure wash , for a total of 250 gpm. Behind the traveling water screens are two vertical mixed flow pumps. Each is rated at 323 cfs. A specially designed suction elbow conducts water from the screenwell to the pump impellers. Calculated velocities at mean low water el +0. 78 ft in the screenwell are 2. 6 fps over the sill , 2. 9 fps 2-2- 6 W. PUMPS TRAVELING WATER r SCR EEN

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... SECTION A-A 10 SCALE - FEET FIGURE 2-2 CIRCULATING WATER INTAKE ALTERNATIVE INTAKE STUDY MYSTIC STATION - UNIT 7 BOSTON ED I SON COMPANY STONE & WEBSTER ENG I NEER I NG CORPORA T IONunder the curtain wall , and 3. 2 fps approaching the screen based on flow streamlines. Mystic River water quality is poor but improving. Trash loading of the screens can be high at some times during the year. Also , jelly fish are periodically impinged on the screens in large numbers creating operating problems. Normally the screens are rotated once per 8-hr shift. 2-3SECTION 3 SUMMARY OF FISH IMPINGEMENT EXPERIENCE 3. 1 INTRODUCTION Impingement monitoring studies were conducted at Boston Edison Company I s Mystic Generating Station from August 1971 to November 1977. The studies consisted of (1) an impingement monitoring program for Units 1-5 combined and Unit 6 from 1971 to 1975 , including a bottom sill evaluation for Unit (2) an impingement monitoring program for Units 4 , 5 , 6 , and 7 from 1975 to August 1976; and 3) an impingement monitoring program for Units 6 , 71, and 72 from December 1976 through December 1977 , including a fish recirculation and reimpingement study, a bottom sill evaluation for Unit 71, and a winter flounder mortality study. A summary of these studies is presented below. RESULTS OF IMPINGEMENT MONITORING STUDIES Fish impingement monitoring began at Mystic Station in August 1971 and was centered around Units 1-5 and Unit 6. Field data indicated that flounder Atlantic herring, Alosa spp. (alewife and blueback herring), and rainbow smelt were the most frequently impinged species. From 1971 through 1973 Unit 6 consistently impinged more fish (two to three times as many) than Units 1-5. The higher rate of impingement at Unit 6 was believed to be attributable to a higher intake velocity (Stone & Webster Engineering Corporation (S&W), 1976). In December 1973, at the request of the U. Environmental Protection Agency (EPA) and the Massachusetts Division of

Marine Fisheries , a bottom sill , consisting of an 8-ft stop log gate , was installed in the Unit 6 intake bay in an attempt to reduce flounder impingement. In addition , 12 ft - 2 in of the curtain wall were removed , raising it from el- 19 ft - 5 in. to el - 7 ft - 3 in. and thereby reducing the velocity in this area. During the 1974 monitoring program , the bottom sill successfully reduced flounder impingement by 53 percent and reduced impingement of all other species by 27 percent (S&W , 1976).

In 1975 , with the addition of Unit 7 to the Mystic Station , total impingement of fish increased. Unit 7 accounted for approximately 87 percent of the fish impinged that year. The higher impingement rate for Unit 7 was tentatively attributed to the higher flow rate and intake velocitiesDuring the 1976 monitoring program , Units 6 and 7 , operating individually or together , accounted for 96 percent of all fish impinged. Herring and flounder were the two most abundant species impinged. Flounder was more abundant in the spring and fall collections than in the winter. Fish length data indicated that the majority of flounder , herring, and alewives impinged were juveniles. Impinged smelt appeared to be adults , at least 2 yr old. Since the impingement of fish at Unit 6 had been effectively reduced by reduction of the curtain wall and the installation of a bottom sill , it was recommended that a similar sill be installed in one of the two forebays of Unit 71 and that impingement rates of Unit 71 (with the sill) and Unit 72 3-1(without a sill) be compared. At the request of the EPA and the Massachusetts Water Resources Commission , a 52- week impingement monitoring program was conducted from December 1976 through November 1977 at Units 6 , 71, and

72, The purpose of the program was to determine the effectiveness of the bottom sill in reducing flounder impingement at Unit 7 and to examine several additional aspects relating to impingement , including recirculation reimpingement , and flounder mortality, as discussed later. With respect to winter flounder , the results of the bottom sill evaluation in 1974 were consistent with the results obtained for Unit 6. Impingement of flounder in Unit 71 was reduced by 53 percent. However , impingement of pelagic species was variable and species-dependent. An increase in the impingement of Atlantic herring, rainbow smelt , and other species was observed in Unit 71 when compared to Unit 72' Al though the da ta collected indicated an increase in the impingement of pelagic species , the reduction in flounder impingement resulted in the recommendation that bottom sills be installed in Unit 72 as a deterrent to flounder. A bottom sill was subsequently installed in Unit 72 in November 1977.Based on the rate of impingement calculated during the impingement monitoring program from December 1976 to November 1977 , it was estimated that 000 flounder , 16 000 Atlantic herring, and 43 000 Alosa spp. would be lost annually. This conservatively assumes 100 percent mortality of fish which have been impinged. As discussed later , mean survival of flounder under existing operating conditions approaches 50 percent. Therefore , the estimated loss of this species due to impingement is conservatively high. These numbers represented O. 14 , 0. , and O. 16 percent of the average 1970-1977 Massachusetts annual commercial catch for these species , respectively (S&W 1978). In terms of the dollar value of the fish impinged at the Mystic Station (assuming 100 percent mortality), approximately $1 747

of flounder , $161 of herring, and $22 of Alosa spp. would be lost annually. Based on the results obtained during impingement monitoring studies from 1971 to 1976 , it became evident that the mortality associated with impingement at Mystic was not 100 percent , and that , for some species , survival may actually be relatively high. Accordingly, various studies began in late 1976 to investigate the survival potential of fish and to determine whether certain design and operational features of the screenwell might be contributing to mortality. Specifically, these studies were designed to (1) determine the physical condition of fish being impinged on the Units 6 and 7 screens , (2) determine whether fish returned to the Mystic River via the sluiceway are subject to recirculation , (3) establish whether fish tend

to fall off of the screen s lifting lips during screenwashing and are thereby subj ect to reimpingement , and (4) evaluate the effect of reducing the time interval between screenwashings on flounder survival. The physical condition of impinged fish was investigated from December 1976 to May 1977. Sampling consisted of collecting all fish impinged on the Units 6 and 7 screens over 9-hr periods , determining initial survival , and checking the fish for screen markings , scale loss , and other damage. The data indicated that the majority of the impinged fish were dead (88 percent)

and consisted primarily of the fragile clupeids and smelt. Winter flounder

3-2cunner , and threespine stickback survival was higher (36 percent for all three species). Mummichog exhibited the highest survival (40 percent) of all species collected. Considering that these fish were impinged for up to 9 hr prior to removal , it would appear that higher survival could be achieved if the screens were washed more frequently. This conclusion is substantiated by results of the flounder mortality study discussed later.

The recirculation , reimpingement , and winter flounder mortality studies were conducted between October and December 1977. During the recirculation study, marked live and dead fish were released from the screenwash sluiceway servicing Units 6 and 7 on the high and ebbing tide (maximum potential for recirculation) Following release , the traveling screens of all operating units were monitored daily for 72 hr. In four releases of 259 fish (total), only 11 fish were recirculated in 72 hr , most of which had been dead when released. Therefore , recirculation of live fish is not considered a problem

at Mystic. During the flounder reimpingement study, live and dead flounder were tagged and released in the Unit 71 screenwell between the curtain wall and traveling screen. The screens were then operated continuously for 8 hr and the time of recapture was noted for each fish. The results of this study indicated that flounder reimpingement does occur , particularly among live fish. Of the dead test fish recaptured , all but one were collected within the first 15 minutes of the screenwashing (one screen revolution). three tests , a maximum of 40 percent of the live fish were recaptured during the same period. Recapture of live fish continued at a low level throughout the 8-hr collections. It was noted that , although all fish removed from the screens were still alive even after 8 hr , the condition of those fish recaptured toward the end of the period was poorer than those recaptured during the first hour. Therefore , it appears that live fish are flipping off the screen lips as the screen clears the water surface and are dropping back into the screenwell. This process certainly contributes to mortality and probably accounts for the fact that survival of flounder observed during the impingement mortality study (discussed below) was lower than expected for such a hardy species. The flounder mortality study involved the collection of fish from the Units 71 and 72 screens under the following operating modes: continuous 2-hr , 4-hr , and 8-hr washes. Fish were collected over an 8-hr period which encompassed low tide (when impinged fish would experience higher intake velocities). Initial mortality was recorded and the fish were then held

for 96 hr. Mortality was recorded daily. In general , results of this study showed a trend of increasing mortality with an increase in impingement duration. Initial mortality (Table 3-1) of impinged flounder for the continuous , 2-hr , 4-hr , and 8-hr screenwash

intervals ranged from 2. 6 percent (continuous) to 41. 4 percent (4-hr interval). Analysis of variance CANOVA) demonstrated that the differences in initial mortality between screenwash intervals were not statistically significant at the p ( 0. 05 level (Table 3-2). However , flounder mortality after 96 hr

ranged fr 10. 3 percent (continuous) to 58. 2 percent (4-hr interval), and ANOVA and least- squares differences demonstrated that survival under the continuous wash was significantly higher than at the 4-hr screenwash interval. Other wash intervals were not significantly different. 3-3TABLE 3-1MORTALITY OF WINTER FLOUNDER AT SEVERAL SCREENWASH INTERVALSWITH 95 PERCENT CONFIDENCE INTERVALSPercent Mortali tyInitial96-HrTotalScreenwash IntervalContinuous6 (05_16.10.3 (0.4-30.14.6 (1.0-39.22.3 (5.6-45.29.3 (9.3-54.44.2 (17.9- 72.41.4 (18.6-66.58.2 (32.4-81.66.2 (37.6-89.35.6 (14.2-60.38.6 (15.7-64.54.4 (26.3-81.2-Hr4-Hr8-HrNOTES:1 .Calculated from arcsine transformation.Percentage of flounder found dead onscreens.Percentage of flounder which died during the 96-hr testperiod.Number dead on screen plus number died during 96-hr test perioddivided by total number of floundercollected.Confidence interval less thanzero.Source:Stone & Webster Engineering Corporation, July 1978TABLE 3-2SUMMARY OF AN ANALYSIS OF VARIANCE OF DIFFERENCES OBSERVED IN THE MORTALITY OF WINTER FLOUNDERAT SEVERAL SCREENWASH INTERVALS AND DURING THE 96-HOUR HOLDING PERIODInitialMortali tyF-Ratio96-hourMortali tyTotalMortali tySource of VariationDegrees ofFreedomScreenwash Interval1(A)2945. 741;~196;96-hourTest Period2(B)N/A289;N/AA x BN/A430N/ALeast Square Differences(significantly differentscreenwash intervalsat p05 level)Cont. vs. 4-hourCont. vs. 4-hourNOTES:1 .Continuous, 2-hour, 4-hour, and 8-hour screenwashes.Four 24-hour periods within 96-hour testperiod.*Significant at p05 level.Source:Stone & Webster Engineering CorporationJuly 1978Total mortality (initial plus 96-hr) ranged from 14. 6 percent (continuous wash) to 66. 2 percent (4-hr screenwash interval). Again , least- squares differences demonstrated that the continuous wash survival was significantly different only from the 4-hr screenwash. Mortali ty among flounder held as controls was low , averaging 2. 5 percent for the four 96-hr monitoring periods and indicating that mortality among the test fish was most likely the result of impingement. CONCLUSIONS On the basis of studies conducted at Mystic to date , several conclusions can be drawn: 1 . The bottom sill is effective in reducing flounder impingement; however , it may increase the impingement of pelagic species. Survival of pelagic species under the present operating conditions (8-hr wash cycle) is relatively low. On the average , survival of flounder is relatively high and tends to be highest under a continuous screenwash operating mode. Reimpingement of flounder , particularly live individuals , is occurring; survival might be enhanced if reimpingement were eliminated. Recirculation of fish from the screenwash sluiceway to the intake screens does not appear to be a problem. These results indicate that modifications to the existing traveling screens which would reduce impingement time and eliminate reimpingement might greatly enhance survival of flounder as well as pelagic species. An alternative scheme incorporating such modifications is presented in Section 3-4SECTION 4 EVALUATION OF ALTERNATIVE INTAKE DESIGNS FOR THE MYSTIC STATION - UNIT 4. 1 INTRODUCTION As discussed in Section 1 , there are two basic approaches to resolving the question of impacts related to fish impingement losses at power plants. One approach is to gather biological field data in the area of plant influence and develop an impact assessment based on data analyses. For the reasons discussed below , this approach is not deemed cost- effective for the Mystic Station. The second approach is to modify an existing intake design or alter operating conditions , such that the number of fish impinged is actually minimized. This approach is preferred for the Mystic Station , and descriptions of various alternative designs or operational modifications are presented in this section. Assessment of Fish Impingement Losses on the Population Fish impingement represents a loss of individuals to their respective populations and can therefore be characterized as an additional source of exploitation to species populations. Considerable experience has been gained in the assessment of exploitation effects on a population , primarily in the area of fisheries management. Therefore , one useful method of

evaluating impingement effects is the analysis of this exploitation on the persistence of the species population. This type of assessment has been applied at many power plant sites with varying degrees of sophistication. The type of information available on the size and dynamics of the population of the exploited species is the primary limiting factor in the level of sophistication of the analysis. Basic population dynamics information on length of life , age of sexual maturity, sex ratio , fecundity, and survivorship can frequently be obtained from scientific literature. Information on the local population is usually more difficult to obtain and , if not presently available , is quite expensive

to gather. If , however , the population is presently being exploited for a commercial fishery, this type of information can usually be developed from reported landings. The information of interest for the local population is its geographic distribution and its size by age. Such information is not available for the local populations of fish found in the Mystic River. Without this

information , the only assessment that can be made is the static loss due to impingement. This static loss is helpful , as can be seen in the comparison discussed in Section 3 of this report. In summary, proceeding from the present level of analysis to a dynamic assessment of the effect of impingement on the respective species ' populations would require extensive information on the local populations of these species. The information would need to focus on the size and distribution of the population with attention to secondary characteristics such as age

structure. Due to the location of Mystic Station and the nature of the 4-1species involved , primarily herring, alewife , flounder , and smelt , a considerable field effort over several seasons throughout the harbor and possibly adj acent areas would be required to study these populations. Such an effort is not believed to be practical since alternate design modifications exist to minimize impingement losses. Diversion Devices Diversion devices are not considered to represent primary alternatives for minimizing impingement losses at Mystic Station for a number of reasons. Inclined plane screens are not commercially available at present. Large revolving drum screens require more costly support structures than vertical traveling screen structures and have not been evaluated biologically (U. S. EPA , 1976); thus , they are not considered to offer an advantage over the existing screen structures at Mystic. The horizontal traveling screen has been shown to be an effective device for guiding juvenile and adult fish; however , application of this screen system at power plant intakes is presently impractical since the screen can only be used when water depth does not exceed 10 ft and is relatively constant (Rexnord , 1973). Furthermore , the horizontal traveling screen is not commercially availabl~. Although louver systems have been shown to have high guidance efficiencies with respect to juvenile and adult fish (Taft and Mussalli , 1978), stationary louvers at Mystic could create reliability problems due to their potential for clogging. Traveling louver systems minimize clogging problems but are costly and would require maj or structural modifications. In addition since louvers have wide spacings (1 in. or greater), backup screens are required to collect unscreened debris and fish. Thus , the overall cost of a louver system is relatively high. Therefore , louvers are not considered to offer an operationally reliable or cost- effective means of reducing fish losses at Mystic. Angled traveling screens operate on the same guidance principle as louvers.

However , since the screens utilize 3/8-in. mesh , they act as both a diversion device and a screening medium (Taft and Mussalli , 1978). Installation of angled traveling screens at Mystic would require maj or modifications to the existing intake which are not warranted at this time considering the availability of other less costly and effective systems as presented later in this section. Behavioral Barriers A number of devices have been developed which are designed to alter , or take advantage of , the natural behavioral patterns of fish so that they

will avoid , or be deterred , from an intake flow. These devices include electrical screens , air bubble curtains , hanging chains , lights , sound water jet curtains , and chemicals. However , the potential effectiveness of any of these devices at Mystic Station is questionable , based on experience at other power plants and hydroelectric facilities (U. S. EPA , 1976). Therefore , behavioral barriers are not considered to offer a viable al ternative for minimizing fish impingement at the Mystic Station.

4-2Fish Collection Systems Collection systems are devices which are designed to actively collect organisms entrapped within a screenwell. These include fish pumps , netting devices , and various types of traveling water screens. Fish pump systems are generally used where velocities are relatively low and uniformly distributed. They operate on the principle that fish entering a screenwell will congregate in low velocity areas at the surface and therefore , will be susceptible to the suction of the pump (Eisele and Malaric , 1978). However , bottom-dwelling fish , such as flounder , would probably not be successfully collected. Thus , the fish pump systems are not considered to offer a viable means of collecting and removing fish from the Mystic screenwells. Similarly, fish netting systems , although they have been shown to be effective interim measures for reducing fish losses at several power plant intakes (Detroit Edison Co. , 1975), are not considered to offer an effective long-term solution to impingement losses. The center-flow vertical traveling screen is also not considered viable for Mystic , since use of this system in the existing screen bays would result in unacceptably high intake velocities (throat velocities ranging from 4. to 9. 9 fps , corresponding to locating the screen at the front of the bay or at the present location) and would adversely affect pump performance due to uneven flow distribution downstream of the screens. Modified , through-flow traveling water screens are presently considered to offer a potentially effective and practical means of reducing fish losses at Mystic. The modified through-flow screens incorporate a low pressure spraywash system , with fish lifting buckets and frequent or continuous operation. This system is discussed in detail in Section 4. Physical Barriers The concept of using low screen velocities for reducing fish losses at power plants has been considered for many years and has been recently incorporated into the design of various new intake structures. By reducing velocities at the traveling screens , fish are better able to avoid impingement , and the screen , therefore , acts as a physical barrier (U. S. EPA 1976). The EPA has generally recommended velocities of 0. 5 fps or less for reducing impingement losses at new intakes. However , the actual reduction in impingement which can be achieved through low velocities has not been quantified. At Mystic Station , there are a number of structural or operational modifications which could be considered for achieving lower intake velocities than presently occurring. These modifications are discussed in

detail in Section 4. Physical barriers , such as infiltration intakes (radial wells or artificial filter beds), are not feasible at Mystic since they require an adequate aquifer and other geological conditions not found at Mystic. Barrier nets

however , have been shown to be effective under certain conditions and have been considered for application at Mystic Station. Such nets are described in detail in Section 4. 4-3Summary On the basis of the available information , it is believed that three alternative fish protection concepts offer the potential for reducing fish losses at Mystic Station and therefore warrant further consideration: velocity reduction , barrier nets , and modified traveling screens. Accordingly, various methods of implementing these concepts at Mystic are presented in detail in Sections 4. , 4. , and 4. , respectively. Total costs for each engineering design are given individually; a complete breakdown of these costs is presented in Section VELOCITY REDUCTION Biological Evaluation The concept of designing intake structures to incorporate low velocities at the traveling screens has recently received much attention as a method for minimizing fish impingement. In fact , the use of velocities of 0. 5 fps (or less), coupled with mounting the screens flush with the shoreline (no embayments) and creating lateral fish passageways , has currently been accepted as best available technology at some power plant sites. Unfortunately, since few intakes of this design are in operation , few studies have been conducted to quantify the level of protection which can be expected. Resul ts of one study conducted at a Hudson River power plant indicated that reducing approach velocities from 1. 0 to 0. 5 fps did not significantly reduce the impingement of fish (Texas Instruments , 1974). Until further research has been conducted at power plants with low intake velocities , it will not be possible to draw general conclusions regarding acceptable velocities at specific sites. It is likely that velocity effects are species- specific , age-dependent , and influenced by seasonal variations in water quality and other environment~l parameters (particularly temperature), since all of these factors influence the swimming speed of fish. Thus while various design modifications for reducing velocities are possible at Mystic (as discussed below), it is not possible to estimate quantitatively the potential reductions in impingement which might be achieved through their implementation. It is reasonable to assume that reducing the approach velocities at Mystic would not have a negative effect , and , in some cases may reduce impingement. However , considering the cost (Section 5) of implementing most of the alternative designs and the uncertainty regarding their potential effectiveness , it is not believed that the concept of reducing velocities is the most cost- effective option for reducing fish losses. This general discussion applies to all of the alternatives described below. However , each design modification has additional biological advantages and/or disadvantages which are addressed further in the following discussions. Engineering Descriptions of Alternatives for Reducing Velocities Removing the Bottom Sill at Certain Times of the Year As discussed in Section 3 , a bottom sill placed in the Unit 6 intake bay at Mystic Station was successful in reducing flounder impingement by 53 percent. 4-4Impingement of all other species was reduced by 27 percent. A similar bottom sill , installed in one of the two forebays of Unit 7 , also reduced flounder impingement by 53 percent; however , impingement of other species increased , presumably due to the increased velocities created by the presence of the sill. It has been suggested that removing the bottom sill at Unit 7 during certain times of the year might reduce impingement of pelagic species. This suggestion was based on the idea that there may be differences between the seasonal abundance of pelagic species and demersal species. If this were the case the sill could be installed only during the period of flounder impingement while during the remainder of the year the sill would be removed , thereby eliminating the potential for increased impingement of pelagic species. Although seasonal variations are observed in the total numbers of fish impinged at Unit 7 , (generally fish are more abundant in the spring and/or fall than during the winter , except for of Atlantic herring, which was more abundant during the winter and spring), data indicate that the seasonal pattern of impingement of flounder is similar to the pattern for other species. Therefore , periodic removal of the bottom sill in Unit 7 would probably not reduce impingement of pelagic species and might cause an increase in total flounder impingement. Utilizing the Units 1-3 Intake Bays for Supplemental Cooling Water for Unit Another concept for reducing velocities of Unit 7 would involve the use of the decommissioned Units 1-3 screenwells and pump houses to supply additional screening area for the Unit 7 flow. Of the total 646 cfs required for Unit 7 , 320 cfs would be pumped from the Unit I , 2 , and 3 screenwells conveyed by a new pipe network , and discharged into each of the two bays at Unit 7. The existing Unit 7 screens would be relocated farther upstream in the bays to provide sufficient space for the 320- cfs flow to be discharged downstream of the screens. The remaining 326 cfs required would pass through the Unit 7 screens. The approach velocity at the face of the screen mesh for Unit 7 would be 0. 87 fps at mean low water el 0. 78 ft. As shown in Figure 4. 2-1 , the forebays of Units I , 2 , and 3 are each 10 ft wide at the entrance where the trash racks are located. The bays then transition down to a 6-ft width at the face of the traveling screens. Prior to decommissioning, Units 1 , 2 , and 3 had a normal rated flow of 000 gpm (80 cfs) at mean low water (el 0. 78 ft). This flow is based on three pumps operating, with one pump idle as a spare. At this flow , the approach velocity at the face of the screen mesh is 1. 57 fps. The 36 000- gpm flow rate per bay was selected as the quantity to be pumped to Unit while maintaining the previous maximum appproach velocity of 1. 57 fps. It would be necessary to replace the four existing vertical volute dry pi pumps at Units 1 , 2 , and 3 with vertical column axial flow pumps (Figure 4. 2-2) each rated at 36 000 gpm at approximately 5 ft of head. The pump suction bells would be connected directly to the existing suction tubes located at pump pit floor level. A hydraulic model study would be required to determine if any modifications of the suction tubes would be needed to provide suitable flow patterns for the axial flow pumps , since such pumps are more sensitive 4-5EXISTING 5'11PIPES TO UNITS~---L ~-RELOCATEEXISTING VALVE CONTROLPANELAND PENETRATE SUPERSTRUCTURE.21TS4 - 6'- - I, -JALTERNATIVE ROUTEBURIED ALONGFRONT OF SCREENHOUSE IFUTI LlTYCONFLICT ISNOT EXTENSIVE.C. W. PUMPS-+- --t--- t :: II'--PI PESPENETRA TESUPERSTRUCTUREINSTALL BAFFLE INEXISTING SCREENGU I DESLOTBRACING( TYP)PI PESPENETDECKSLOPE PIPE TOSUITSITE CONDITIONSINSTALLREMOVABLE ITRASH RACKSBFVCZJPI L E S fASTEEL FRAMEPIPE SUPPORTSTRUCTURERELOCATED!TR V.WATERSCREENSTRASHRACKSrr --SlOPI~FACE tTYP)I I....-1,-El.EL.. J II IEXISTINq STOP lOGSLOT...-TO UNIT---~-I I..., ;S. HARBOR LlNEPLAN ABOVE DECKUNIT 7SCALE-FEETPLAN ABOVEDECKUNITS 1-2fAFIGURE 4. 2- 1FLOW TRANSPORT FROMUNITS 1,PLAN VIEWALTERNATIVE INTAKE STUDYMYSTIC STATION - UNIT 7BOSTON ED ISON COMPANYSTONE & WEBSTER ENGI NEER I NG CORPORAT IONto inlet flow conditions than the existing volute pumps. The four new pumps would have an additional installed power requirement of 373 kW. The screens at Units 1 , 2 , and 3 would require additional installed power of

45 kW. The additional annual energy required for this scheme would be 294 MWh. The four pump discharge pipes would be located above the operating deck level and would manifold into one 7. 5-ft-dia pipe. This pipe would be supported on a pile and steel frame structure constructed along the eastern side of the Unit 1 screenwell and then along the southern (harbor) side of the screenwells of Units I through 7. The pipe would then bifurcate into two 5-ft-dia pipes on the western side of Unit 7. These pipes would penetrate the Unit 7 screenwell superstructure , and one pipe would penetrate the deck above each of the two Unit 7 bays. Each pipe would be equipped with a butterfly valve for use in flow balancing or shutoff in the event that one of the associated Unit 7 pumps were shut down. A detailed hydraulic model study would be required to assure uniform flow patterns approaching the Unit 7 pumps. Pending results of such a study, it might be necessary to include diffusers at the discharge of each pipe to spread the flow in the screen bays and a vertical baffle array between the diffusers and the pump inlet conduits to straighten the flow (Figure 4. 2-2). Baffles may also be required between the relocated traveling water screens and the diffusers to assure that flow from the diffusers does not disturb the flow patterns at the screen faces. A reduction in flow through the Unit 7 pumps may result if the baffles required have significant head loss. Based on an estimated 1-ft head loss , the flow would be reduced about

3 percent. New trash racks would be installed in the existing Unit 7 stop log slots upstream of the screens. The rack structure would be designed such that stop gates could be placed over the rack face for dewatering. Most of the new pipe network would be operated under siphon. Therefore , a vacuum priming system would be installed to fill the pipes and then maintain the siphon by continuous air removal. The existing traveling water screens at Units I , 2 , and 3 would be replaced the screen wash systems would be rebuilt , and the trash racks would be repaired , if necessary. A bearing lubrication and seal water system would be required for the new pumps. Electrical systems would be rebuilt as necessary to meet current codes and system needs , and new control systems would be installed for all operating equipment. The screenwells and pump

house would be renovated , as required. The existing Units 1 , 2 , and 3 screenwells are presently used as a dock and unloading facility for oil barges. These barges have a 22-ft draft and would obstruct or distort flow patterns at the screen bay entrances if used as a supplemental intake. Therefore , it would be necessary to construct a new wharf east of the screenwell with protective dolphins and an access ramp to shore to avoid this problem. The total capitalized cost of implementing this design for reducing intake velocities would be $6 674 000. 4-6RELOCATED TRAVELINGWAT ER SCREENEL,17-6INSTALLBAFFLEII (WALLNSTALL10-TR~SHRACKS, I'-1./. ~:!t. to...~-~.4~,;t-SECTION A-AAX.15.MEAN H. W.MEAN L. W.EXT. L.(-) 2.SCALE-FEETINSTALL REMOVAB LECURTAIN WALL TO EL .(-)3_!"~....J~,~ .FLOWDIFFUSER9 '- 0....,,6;~....: ..~.;..~)9 '- 0EL.(-)27!.3~:.. ,4MIt."&.SECTION B-B......~----" ":It'--:, .....~. ,(\-,..-." .,iI~~ ...;1.-. ". Pt'REMOV EEXISTING PUMPMOTOR ,VALVESAND PIPINGI \: 1: I: IIINSTALL NEW VERTICALPUMP: I0 ,d..- --=I 'I "I \\ I j,1 \,., , I, I~ do~ - - ,L ~"-I " ,-- ~----., \:;\I II \II ,'I1/ / \, IINSTALL BLINDFLANGEI ~- j-.: --=-:;l.LliL - -1!ltil ~ --I '-----tll ~~_o -~- -/I:r - -'I-)-. = 1~-tU- -BOLT SUCTION BELL TOEX ISTING FLOOR TH IMBLESECT ION C-CSCALE -FEETFIGURE 4.2-2FLOW TRANSPORT FROMUNITS 1,SECTION VIEWALTERNATIVE INTAKE STUDYMYSTIC STATION - UNIT 7BOSTON EDISON COMPANYSTONE & WEBSTER ENGI NEER I NG CORPORAT I ONReducing Unit 7 Operation to One Circulating Water Pump Another method of reducing intake velocities at Unit 7 would involve reducing the flow of circulating water to the plant at selected times by shutting down one of the two circulating water pumps. Unfortunately, this mode of operation can have serious impact on plant load and heat rate. The use of a single circulating water pump would not be feasible , even at low demands , for several reasons. Reducing the flow may result in increased bio-fouling of interior tube surfaces since velocities would be substantially reduced (6 fps to 3. 6 fps). It would be possible to limit biofouling by isolation of condenser sections; however , the ability of Unit 7 to respond to sudden system demands would be seriously impaired. As a result of reduced flow , system pressures would drop, which may cause increased corrosion of tube surfaces since tube surfaces would be exposed at low tidal conditions. Loss of system pressure would also necessitate throttling of the condenser outlet valves to maintain sufficient flow in the cooling water heat exchangers. This would cause a further loss of cooling efficiency. With a two- pump parallel system , shutting down one pump will cause the second pump to run out to 60 percent of the two- pump flow. This would reduce pump efficiency from 84 to below 40 percent , with a corresponding increase in motor load and subsequent shortening of pump motor life. Since the operating pump will actually pick up 60 percent of the two- pump flow veloci ty into the operating bay will increase by 20 percent. If single- pump operation was implemented during peak load periods several addi tional problems would occur. In order to go from two- pump to one- pump operation , load would have to be decreased gradually to avoid unnecessary stresses to plant equipment and subsequent reduction of equipment life. Flow reduction and subsequent loss in pressure would reduce plant output by as much as 280 MWe at an equivalent cost of $10 750/hr for replacement

power. Thermal criteria would also be violated at high load conditions. A temperature condenser rise of up to 35 o f could occur with one- pump opera tion; consequently, during times of the year when ambient water temperatures are high (above 60 F), maximum allowable outfall temperatures of 93 F would be exceeded. In summary, reducing the circulating water system flow by operating with one of two circulating pumps would have the following results: Condenser tube fouling due to tube water velocity reduction from 0 fps to 3. 6 fps; A severe loss of plant generating capacity, approaching 280 MW/hr during peak demand periods; Violation of thermal rise and/ or discharge temperature limitations will occur at loads low enough to allow operation of the 4-7condenser below turbine back pressure limits (5 in. ) and above the plant load necessary to violate the temperature limitations; A reduction in pump life; A reduction in condenser reliability and availability due to increased corrosion problems; and A 20 percent increase in approach velocity to the operating screen. Accordingly, although one- pump operation would limit impingement to one of the two Unit 7 screens , increased velocities could actually increase impingement on the operating screen. Such operation would also create serious reliabili ty problems which could jeopardize plant output. Therefore , it is not believed that potential environmental benefits of this operational mode justify the risks and costs. Installing Variable Speed Control On Circulating Water Pumps to Control Discharge Temperature Another method for reducing the flows and velocities at the Mystic Unit intake structure would involve installing variable speed capability on the circulating water pumps to control flow based on discharge temperature. Theoretically, by reducing the speed of the pump, a reduction in flow rate directly proportional to the speed could be realized. However , as the speed is reduced , the pump discharge pressure would fall off in proportion to the square of the speed reduction. This would be done in order to maintain the discharge channel temperature at below 93 F and to prevent the thermal rise from intake structure to outfall channel from exceeding 2s The required speed reduction at a 60 F inlet water temperature with only Unit 7 operating would be approximately 33 rpm , which represents a 13 percent

reduction. This would result in a decrease in velocity approaching the intake screens to approximately 2. 8 fps , at mean low water el. 0. 78 ft. During the warmer months when river temperatures are high , flow reductions would not be allowable at all. In order to achieve this reduction in

veloci ty by pump speed reduction , the following options are available: 1 . Two- speed Motor Drives - By analyzing the discharge flow rate tidal level , intake water temperature , and Units 4 through operating loads , it might be possible to find a single lower speed which would provide some reduction in flow rate at constant second speed. A two- speed motor drive arrangement would be the least expensive and least complex speed control method available. The key factor in applying two- speed motors is in the coincidence of the circulating pump system operating point with an available second speed on the motor. Two- speed , single- winding motors are

limi ted to a 2-to-l speed ratio. Since the second operating point at Mystic is not one-half of normal speed , these motors

were not considered. Two- speed , two- winding motors , not limi ted to 2-to-1 speed ratios , may have a second speed at any synchronous subset of base speed; for example , 1 200/900 rpm , 1 200/720 rpm 900/720 rpm , etc. 4-8Finding a second speed which would be matched to the entire plant circulating water system and the motor is a complex procedure which would be unlikely to provide significant flow reductions at Mystic. Also , operating the circulating water pumps with two- speed motors would require timed load reductions which would further complicate the operating process. Dc Motor Drive - Direct current motors (with electronic ac to adjustable voltage Dc power) have become a most common means of providing adjustability in speed and torque. A limiting factor in dc motor application is the fact that energy is supplied to the motor rotor through a series of copper bars around the periphery of the rotor , called the commutator. Large amounts of driving power must pass from the dc line to the rotor through stationary carbon brushes rubbing against rotating commutator bars. This energy transfer may reduce the practical base speed of a high horsepower dc motor drive to a point below the speed required for the circulating water pumps. Constant maintenance requirements of the commutator and brushes also discourages the application of dc drives in this case. Electronic ac Motor Drives - There are two types of electronics drive systems available. The first of these ac power systems utilizes wound rotor motors to drive the pumps. Simply stated the speed of a wound rotor motor can be adjusted by changing the power flow through its rotor circuit. This system is referred to as the wound rotor slip recovery drive. The second of these ac power electronic drives is known as the synchronous motor adjustable frequency system. This system works on the principle that the synchronous speed of the motor directly proportional to the frequency applied to the motor terminals and inversely proportional to the number of its field poles. This system is about 2 percent more efficient than the wound rotor slip recovery system , making it the most efficient electrical system available over wide speed ranges. Utilizing brushless excitation to supply rotor field current , the system has no commutator or slip ring with their attendant maintenance problems. Other benefits of this system are equal acceleration and shutdown times and low electrical line power draw. The cost of the most flexible variable speed conversion , including motors and controls , is approximately $925, 000. The practical benefits of a variable speed conversion are minimal. Screen approach velocity would be reduced from 3. 2 fps to approximately 8 fps (mlw) or lower (depending on the various uni t loads). However , operating problems would result , including lower pump discharge pressures , tube fouling, increased pump motor maintenance and potential thermal violations , since the speed changes necessary to avoid thermal limitations are limited by time versus load pickup restraints. Changes in thermal discharge temperatures could occur quickly during unit trips , necessi tating increased flow to the remaining condensers in operation. 4-9In view of the minimal reduction in velocity which could be achieved with a variable speed control on the circulating water pumps , the operational problems which would result , and the cost of implementation , this scheme for reducing velocities is not considered viable at Mystic Station. Installing the Screens Flush with the Front of the Intake Bays As discussed previously, the flush mounting of screens , combined with lateral fish passageways and low velocities , has been suggested as a possible means of reducing fish losses at power plants. There are , however , no data which would indicate the degree of reduction in impingement which might be expected to occur at different sites. Installing screens flush with the front of the intake at Mystic would result in a more uniform velocity distribution through the screens than presently exists due to the increased distance between the circulating water pumps and the screens. In addition , the existing screenwell embayment , which may act to entrap fish would be eliminated. However , although these improvements would probably reduce impingement to some extent , the total flow through the screens would not change and the velocities would still be relatively high (approximately 7 fps at mlw). Therefore , the potential biological effectiveness of this

design is uncertain. This scheme would consist of installing the traveling screens flush with the piers at the front of the Unit 7 intake bays , as shown in Figures 4. 2-3

and 4. 2-4. The existing traveling screens , curtain walls , and racks would be removed. New screens , with either a back- wash or front- wash system (as discussed in Section 4. 2), would be installed flush with the front of the intake bays. The screens would be designed for continuous operation , if required. However , the additional annual energy requirements of 4 MWh are based on intermittent operation. New vertical racks and curtain wall would be located in front of the existing structures. The racks and piers and the curtain wall would be separated from the screen by 5 ft to provide a lateral fish passageway. The curtain wall would extend down to el -3. 0 to exclude cold air in winter and to block large floating debris. The trash racks would be cleaned by hoist- operated mechanical rakes traveling in guides down the sides of the racks. Each traveling screen could be isolated by stop logs and dewatered for repair. A superstructure for the screenwell addi tion would enclose all equipment. During scheduled downtime , the area in front of the Unit 7 screenwell could

be excavated , piles driven , and a tremie concrete mat poured supported on the piles. During normal operation , the piers and curtain walls of the rack structure would be fabricated as a unit from steel plate on shore and partially filled with concrete as ballast. This unit would then be floated into position at the face of the Unit 7 screenwell and anchored into place. All joints would be grouted to provide an effective seal and the remainder of the steel plate unit would be filled with concrete. After the rack structure was completed , the area surrounding each new screen would be graded to allow installation on the screen in the dry. This would require partial decrease in generation due to one pump shut-down during screen installation. 4-10.-,-r t-. \\.- ....' 1-- - ~EX ISTINGPROPOSEDRACK STRUCTURERELOCATEDTRAV. WATER SCREENS._--TR ASH-1BAS!(ET ,'"TRASH RACK(TYP)FLOWDIRECTION- -._.T -r Tt-- +.LI__t. C.W. LINEFISH TROUGH ABOVE/DEBRIS TROUGHBELOW--1- -I-l-,--.-,L..-.rTOEXISTINGRETUR N SYSTEMH ARBORLINELATERAL FISHPASSAGEWAYPLANSCALE- FEETFIGURE 4. 2- 3PLANFLUSH MOUNTED SCREENSALTERNATIVE INTAKE STUDYMYSTIC STATION - UNIT 7BOSTON ED ISON COMPANYSTONE & WEBSTER ENGI NEER I NG CORPORAT I ONEl,- - -JlI '...- --'j-... 'a ... -..0 0'::-:. .1.-- ~~ ,""'r--=- ... .".,~...... "-:\ ",,-:. t~'"" ~'EXISTING TRAVELINGWATERSCREEN(REMOVED)(-.'r-..,I ~,I t-- --..1::' t ~r--;I '-II '~ -L - - - ~ - -- ,- --....#o.::.0 .. ", , ).-, t.... ". :;..' .;' :-- ... -SECTION A-ABU IlD ING ADDITIONTRAVELINGWATER SCREENMONORAIF ISH TROUGHDEBRISTROUGHEXISTINGWAll(REMOVED)l- j~ .TRASHRACK( .'or!FLOWDIRECT IONE l . - 27- 3- --' -" ...'" .." "- ..' '. -- :.~. ~':.. -, . :"" "' ,,,- ),~ ... 6. '. '"~-...EXI STING STRUCTUREPROPOSED EXTENSION'1 MAX. H .W. El. 15.~MEAN H.W. El.IO,-=-=MEAN loW.El. 0.!. EXTREME l.W. El.-2.BOTTOM El. -3STOP lOG SLOTSCALE - FEETS.HARBOR LINElATERAL FISHPASSAGEWAYFIGURE 4.2-4SECTION AFLUSH MOUNTED SCREENSAL TERNA T I VEI NT AKESTUDYMYSTIC STATION - UNIT 7BOSTON EDISON COMPANYSTONE & WEBSTER ENGI NEER I NG CORPORAT IONThe total capitalized cost for this alternative intake design will be 168 000. Considering the cost associated with moving the screens , the fact that velocity reductions are minimal and that the potential biological effectiveness is unknown , it is not believed that such modification is warranted. Constructing Additional Intake Bays The purpose of this concept would be to provide flush- mounted traveling screens while achieving a maximum velocity at the screen mesh of 0. 5 fps (at mean low water el O. 78 ft). This concept would also provide a lateral fish passageway along the face of the screens. The flow approaching the existing Unit 7 screens would have to be reduced in order to lower the velocity. The design flow of Unit 7 is 646 cfs. The maximum allowable flow through the Unit 7 screens to meet a 0. 5 fps criterion

would be 180 cfs. Therefore , the flow through the existing screens would have to be reduced by 466 cfs. This would be achieved by constructing two additional intake bays containing two supplemental pumps ' and associated screening equipment. The additional screenwell would be constructed on the western side of the Unit 7 screenwell and would be connected to the screenwell wall (Figure 4. 2-5). Each pump would discharge into a separate s-ft-dia pipe which would traverse above the operating deck and penetrate the Unit 7 screenwell superstructure wall. Each pipe would then penetrate the deck above a screenbay and discharge downstream of the flush- mounted Unit 7 screens. The screenwell addition would have two pump bays , each served by two 10-ftwide traveling screens mounted in Il. 2s-ft- wide bays and oriented flush

with the front of the structure. The screenwell addition , as shown in

Figures 4. 2-5 , 4. 2-6 , and 4. 2-7 , has been conceptually designed to meet Hydraulic Institute Standards. However , model testing would be required to finalize the bay configuration to ensure satisfactory pump performance. Vertical trash racks would be located along the face of the new screenwell structure. The racks and piers would be separated from the screens and screen bay piers by 5 ft to provide a lateral fish passageway. Curtain walls upstream of the trash racks would extend down to el -3. 0 ft (extreme low water elevation = -2. 72 ft) to exclude cold air in winter and to block large floating debris. The trash rack and curtain wall structure would also extend across the face of the existing Unit 7 screenwell. In addition , trash racks and curtain walls would be installed at the ends of the lateral fish passageways. The trash racks would be cleaned by a hoist- operated mechanical rake traveling

in guides along the sides of the racks. Each traveling screen could be isolated by stop logs and dewatered for repair. The superstructure for the screenwell addition and for Unit 7 would enclose all equipment.

As with the screenwell addition , a hydraulic model study would be required to ensure uniform flow patterns approaching the existing Unit 7 pumps. Diffusers might be required at the outlets of the 5-ft-dia pipes to distribute the flow in the screen bays. A vertical baffle across the screen bay might 4-11EXISTING UNITSPROPOSED UNIT 7ADDITION62-rt)S. HARe-OR LINEUN I T7 'SUP PLEMENTALP UMP(TYP OF 2)I ,TRAVELINGWATERSCREENS (TY P)V=0_5FPSUN I T No.UNIT 7PUMP(TY POF 2)PIP ING ABOVE \i(g) EL . 2 2 . 5..." --------:--- - -L-:=------- -v= 0.5 FPS~FISHPASSAGE~V= 0.4FPVERTICAL TRASH RACKS--- --tPLAN BELOWOPERATING DECK(ELEVATION + 15CURTAIN WALL TOELEV. -78 EAM TOELEV, 14- 6BAFFLE ORSTOP LOGSLOT(TY0 2 46 810 12.. .SCALE- FEETCURTAIN WALLTO ELEV- -3FIGURE 4.2-5ADD ITIaNAL TWS SCHEMEAL TERNA T I VEI NT AKESTUDYMYSTIC STATION - UNIT 7BOSTON ED ISON COMPANYSTONE & WEBSTER ENGINEERING CORPORATIONFISHRETURNPI PE~ STOP L, SLOTS(TYP)UNIT No.CIRCULATORSCf.BAFFL E SLOTSFI SHTROUGH---------------- - -- - - - --- -_. - -- - - _.U NIT No."---STOP LOGSLOTSBAFFLE OR STOPLOGSLOT(TYP)MONORA I LABOVE FORTRASH RAKET. W.SCREENHOUSING( TY P )----------- ---:- - - --, ---------------------------TRASHTROUGHP LANA B 0 V EEL- 17- 6 II2 46 810 12. fSCALE- FEETFIGURE 4.2-6ADD ITIONAL TWS SCHEMEALTERNATIVE INTAKE STUDYMYSTIC STATION - UNIT 7BOSTON ED ISON COMPANYSTONE & WEBSTER ENGINEERING CORPORATIONDECKEL .SUPPLEMENTARYCOOLING WATER PUMPFI SH TROUGHDEBRIS TROUGHI...... "IEL.\ +FLUSHMOUNTEDTRAVELING WATERSCREEN- 3FISH PASSAGESECTION A-AMAX .EL.15.MEAN H.EL.IO_MEAN loW.EL. 0EXT.L.W.EL .-2.TRASHRACKFLOWDIFFUSERSSECTIONB-BUNITNO- 64 610SCALE -FEETSLAB EL_-27FIGURE 4. 2- 7ADD I T I ONALTWS SCHEMEAL TERNA T I VEI NT AKESTUDYMYSTIC STATION - UNIT 7BOSTON EDISON COMPANYSTONE & WEBSTER ENGINEERING CORPORATIONalso be required downstream of the discharge pipes. In addition , baffles might be required between the flush- mounted traveling screens and the discharge pipes to ensure that the flow approaching the screens is not disturbed by backflow from the discharge pipes. One or both supplemental pumps could be shut down without affecting the existing Unit 7 pumps. In this case , the total flow would be drawn through the existing Unit 7 screens. The upper part of the supplemental pump columns and most of the discharge piping would operate under siphon. Therefore , a vacuum priming system would be installed to fill the system and to maintain the siphon during operation by continuous air removal. The two supplemental pumps would require additional installed power of 448 kW. The screens and screenwash system in the new screenwell would require additional installed power of 158 kW. The additional annual energy required for this scheme is 3 945 MWh. The screenwell addition would be constructed in a braced sheet pile cofferdam. Sheet piling would form the perimeter walls except for the east wall , which is common to Unit 7. The sheeting would be braced , mud would be removed and the cofferdam would then be dewatered in a manner similar to that used in construction of the existing screenwells. The screenwell addition would be constructed inside the cofferdam to the point where it was watertight. The sheet piling at the flow entry openings below the curtain walls would then be removed. The new screenwell would become operational prior to initiation of work on the existing Unit 7 screenwell to minimize downtime. One existing Unit 7 pump bay would be kept in operation during construction in the other bay. The non- operating bay would be dewatered , the traveling screen removed , baffles installed , and the discharge pipe and diffuser installed. The other bay would then be modified in the same manner. The rack structure for Unit 7 would be constructed in a manner different from that used for the new screenwell addition in order to minimize Unit downtime. During scheduled downtime , the area in front of the Unit 7 screenwell could be excavated , piles driven , and a tremie concrete mat poured supported by the piles. During normal operation , the piers and curtain walls of the rack structure would be fabricated onshore as a unit from steel plate and partially filled wi th concrete as ballast. This unit would then be floated into position at the face of the Unit 7 screenwell and anchored into place. All joints would be grouted to provide an effective seal and the remainder of the steel plate unit would be filled with concrete. Stop logs would be installed in the rack structure and upstream of the discharge pipe in one bay such that the new screen area could be dewatered and the screen installed in the dry. The affected Unit 7 circulating water pump would remain operational at a reduced flow rate by utilizing the respective supplemental pump. The remaining screen would be installed in similar manner. Upon removal of the stop logs , the scheme would become opera tional. The total capitalized cost for this alternative intake design would be $ 7 , 383, 000. 4-12Since this alternative incorporates all of the suggested features for reducing impingement (low velocity, flush- mounted screens , and lateral fish passageways), it would probably have the best potential for biological effectiveness at Mystic. However , as previously discussed , there is no assurance that it would reduce impingement to a level which would be considered acceptable. Considering the cost of backfitting additional intake bays (Section 5) and the uncertainties regarding potential biological effectiveness it is not believed that such a major modification is warranted. Deepening the Area Immediately in Front of the Existing Intake Bays The concept of removing the existing bottom sill at certain times of the year was discussed in Section 4. 2. 1 and was eliminated as a viable option for reducing impingement. An alternative to this option would be to create a new bottom sill by excavating the area upstream of the Unit 7 screenhouse to a depth of 8 ft and thereby exposing the vertical support wall of the screenhouse to act as a new bottom sill. This action would then allow removal of the existing sill without eliminating the barrier concept for blocking the movement of flounder into the screenwells. . Biologically, this would appear to be a viable al ternati ve , assuming that removal of the existing sill would actually reduce the impingement of pelagic species. There is some question as to whether this reduction would actually occur since data from two different studies yielded conflicting evidence.

Figure 4. 2-8 shows the proposed dredging plan. The area immediately in front of the Unit 7 intake bays would be dredged to el -35 to provide an 8-ft-high bottom sill. Existing sheet piling at the entrance to the intake bays will prevent structure undermining. The dredging to el -35 would extend about SO ft from the bays in conformance with the existing sill/ bottom topography relationship. Dredging slopes are shallow to provide a smooth transition from the existing topography. Existing rip rap would be retained with the proposed dredging scheme , with the addition of a small rip rap area to provide stability in an area of steeper dredging slopes. Entrance velocity to the structure would be reduced to 1. 64 fps while screen approach velocity would be 2. 83 fps at mlw. Dredging would be confined to the immediate area in front of Unit 7 in order to protect the structural integrity of the screenhouse. The anticipated volume of dredged material would be 3 400 cu yd , and some existing rip rap might have to be stockpiled temporarily. It is anticipated that all existing rip rap would be utilized in the proposed dredging scheme. The total capitalized cost of this scheme is $393, 000. Silt deposition near the intakes in the dredged area would gradually reduce the effectiveness of the sill. Therefore , periodic dredging would be required to maintain an adequate sill height. Permits for dredging and

spoil disposal would be required. For estimating purposes , it is assumed that maintenance dredging would be performed once every 2 yr.

4-13-- --=:,/(10) (5)(-15)- ..--20). ."--'-.........:'.......... I.1- -'1 -_.(- 27)::: /SCREENWELLUNfTSlfA2SCREENWELLU NIT S 34 fA 5SCREEN WELLUNITS 6Xt.(0)-5)S. PIER &BULKH EAD LINE25SCA LE -FEETPLA N(- 25)Q::.......Q::'--CI))...(- '25)LEGEND:---------,-,--- --- - ---P'/////-25)-35EXIST.BOTTOM Sill(TO BE REMOVED)'\ZUN ITINTAKE BAY(TYP): fEXIST. RIP RAP: 1- -- --- I' '" I I8 IEL.-35EL.-27.9':" .~ .;-...." .EXISTINGSH EETPiliNG-----,--' -SECT IONAPPROX.EXIST, RIVERBOTTOMPROFILE1'\/ -.- ~-- -.....-...- -0 EXISTING El.PROPOSED DREDGE LI NEA-AEXISTINGTOPOGRAPHYEXISTING DREDGEDAREAEXISTING RIP RAPBOUNDARYPROPOSED DREDGED AREAPROPOSED EXTENDED RIPRAP AREAEXISTING BOTTOM ELEVATIONPROPOSED BOTTOMELEVATIONNOTES:DREDGING SLOPES 1:4 TO1:5RIP RAP 2!..6:t: ON EXIST. SOILNO NEED TO PLACE RIP RAPIN FRONT OFSCREENWELLWITHIN PROPOS EDDREDGING AREA, USE RIP RAPDREDGED FROM TH IS AREAWITHIN PROPOSEDEXTENDED RIP RAP AREAAS NEEDED.SCALE-FEETFIGURE 4.2-8~ROPOSED DREDGINGFLOUNDER SILLALTERNATIVEINTAKE STUDYMYSTIC STATION - UNIT 7BOSTON EDISON COMPANYSTONE & WEBSTER ENGI NEER I NG CORPORAT I ONPHYSICAL BARRIERS - BARRIER NET IN FRONT OF THE EXISTING INTAKE BAYS Barrier nets have been installed at several power plants and results have varied. At Detroit Edison I s Monroe Plant on Lake Erie , a net was placed across the intake canal in an effort to exclude fish , primarily yellow perch and gizzard shad. Unfortunately, because of high intake velocities

() 1. 3 fps), the net clogged wi th fish and collapsed. At Orange & Rockland Utilities ' Bowline Point Generating Station on the Hudson River , good results have been obtained with a barrier net placed in

a V- arrangement around the intake structure (Lawler , Matusky, and Skelly, 1978). At this site , it was possible to achieve velocities which are generally well below 0. 5 fps. Also , because the intake is situated in a relatively stagnant pond , it is not subjected to the current forces of the

river. Nylon mesh nets with 0. 95- and 1. 27- 2 openings have been under investigation since the spring of 1976. Impingement monitoring and tagging studies have indicated that the nets effectively reduce impingement of whi te perch and striped bass , the two species evaluated. Al though the

plant is on a major river , clogging of the net by debris or detritus has

not been a problem. Similar results have been obtained at Carolina Power and Light Company Brunswick Nuclear Power Station. The intake structure at this station located at the end of a long canal and has , in the past , impinged relatively large numbers of fish (primarily menhaden). In January 1979, a barrier screen (1. 27 cm mesh) was placed in a V- shape in front of the intake similar to the arrangement at Bowline Point. As of March 1979 , the barrier was still in place and has substantially reduced impingement at the intake

during the entire period. Debris has not created any problems to date;

however , the periods of heavy debris loading and biofouling have not yet occurred. Although extensive information on barrier nets is not yet available , it appears that under the proper conditions , such a design can be effective in reducing impingement at power plants. The most important factors in effectiveness appear to be velocity and debris. At Mystic , such a net would be difficult , if not impossible , to maintain due to strong tidal currents and heavy debris loading, particularly with mussels , jelly fish , and other aquatic organisms which have created operational problems in the past. The influx of such debris has been so great in the past that even the traveling screens have experienced difficulty in operation. Should a barrier net clog in a similar fashion , it would restrict plant flow and might actually be drawn into the intake , possibly resul ting in shutdown. It is believed , therefore , that this alternative is not practical as a long-term solution for reducing fish losses at Unit

FISH COLLECTION AND REMOVAL SCHEME - MODIFIED TRAVELING SCREENS

Biological Evaluation Many types of traveling water screens are commercially available for power plant application. Most power plants in the United States presently utilize through-flow traveling screens similar to those at Mystic , as described in 4-14Section 2. However , with attention being focused on fish protection , new screen types and modifications to old screens are being developed. stated in Section 4. , the modified through-flow screen is considered to offer the most potentially effective and practical means of reducing fish losses at Mystic. Information supporting this design concept is presented in the following discussion. Conventional traveling screens can injure fish because of the multiple sources of stress to which they are exposed. First , where screen rotation

is intermittent , fish may be subj ect to suffocation while impinged. Second as fish are lifted free of the water surface , they are no longer held

against the screen cloth and can , therefore , fall back into the water and reimpinge. As discussed in Section 3 , it appears that reimpingement is occurring at Mystic to some extent. Third , conventional screenwash systems operate at high pressure (80 to 100 psi). The high velocity jets which clean the screens of debris can cause injury. Finally, where attempts have been made at power plants to return live fish to their natural environment after impingement and removal , the discharge point is frequently close to the intake structure , a situation which can result in recirculation and consequently, reimpingement. However , studies at Mystic ' indicate that recirculation is not a problem. Modified screen and spray- wash systems have been recently developed which eliminate some of the problems inherent in conventional screen designs (Figure 4. 4-1). Since these modified systems can be backfitted to existing

screens , they have obvious advantages over systems that require construction of new structures. However , because the modified screens rely on the impingement of fish , such systems can be employed only after it has been determined that the species of concern can withstand this type of handling. The following briefly describes the operating experience of modified traveling screens relative to their biological effectiveness. There is only one presently operating power plant with a modified traveling screen and spraywash system which has been biologically evaluated (White

and Brehmer , 1975). The Surry Power Station is situated on the James River and withdraws 3 740 cfs of water for condenser cooling. Prior to installation of the modified screens , unscreened water was pumped from the river to a canal in which it flowed by gravity to the plant. Early operating experience showed that fish were being pumped into the canal and were ultimately impinged on the traveling screens located at the plant. To remedy this

situation , eight modified screens were installed at the river to collect fish upstream from the pumps. Screen modification involved bolting steel " fish lifting buckets " on the trash lips of each conventional screen basket. The troughs extend approximately 5 in. from the screen face and are capable of maintaining a minimum water depth of 2 in. during screen rotation. This arrangement prevents fish from flipping off the screen and becoming reimpinged and also ensures that the fish are in water as they are lifted to the point of release. Collected fish are carried over the headshaft sprocket and either fall into a collection trough or are gently washed into the trough with a low pressure jet (15-20 psi) on the back side of the screen. The low pressure wash feature of the modified screen prevents the damage caused by conventional spray- wash systems. 4-15RETURN TROUGH

""- I I U '

: ~. ~ . ~ . " , 0

.. ,

- .- . ~ 0

~ . . AVERAGE WATER ELEVATION WATER FLOW

'- \ ~ - - \\ ~~ ./ """/ - - " - ' . "::~ FIGURE 4. 4-1

co .

: , , . SCREEN DETA I L MOD I F I ED THROUGH- F LOW SCREENS - FRONT WASH ALTERNATIVE INTAKE STUDY MYSTIC STATION - UNIT 7 BOSTON EDISON COMPANY STONE & WEBSTER ENGINEERING CORPORATIONTo ensure maximum survival of impinged fish , the modified screens are operated continuously at a speed of 10 fpm. Consequently, fish are not impinged on the screen mesh for more than 2 minutes. Results of an 18- month evaluation demonstrated that the modified screens can achieve a high degree of success in collecting fish while maintaining low mortality (White and Brehmer , 1975). Short-term holding studies (approximately 15 minutes) showed that , on the average , survival of 58 fish species was 93. 3 percent. Average survival of 13 Atlantic and 26 Atlantic-freshwater species (American Fisheries Society designation) was 94. 3 and 92. 3 percent , respectively. A number of species collected at Surry also occur at Mystic , as listed below:

Common Name American eel Blueback herring Alewife Atlantic menhaden Carp Mummichog Striped killifish Atlantic silverside Threespine stickleback Whi te perch Bluefish Weakfish

Scientific Name Percent Survival Anguilla rostrata Alosa aestivalis Alosa pseudoharengus Brevoortia tyrannus Cyrinus carpio Fundulus heterocli tus Fundulus majalis Menidia menidia Gasterosteus aculeatus Morone americana Pomotomus saltatrix Cynoscion regalis

98. 90. 90. 94. 92. 100. 100. 94. 100. 99. 85. 59. Seven species of the family Clupeidae (which includes blueback herring, Atlantic menhaden , and alewife), representing 58. 1 percent of the 18- month collection total , showed a percent survival range from 82. 3 to 94. 3 with an average survival of 93. 3 percent. These initial survival values are encouraging considering the fragile nature of these species. On the basis of these short-term survival data , it appears that the modified traveling screens have provided an effective means for minimizing fish impingement mortality at Virginia Electric Power Company s Surry site. Various utilities (among them Public Service Electric & Gas , Northeast Utili ties Service Company, Long Island Lighting Company, and Wisconsin Power and Light Company) are presently modifying existing screens or incorporating modified screens into the design of new power plants. Due to this interest and the apparent potential for effective operation , several screen manufacturers now offer modified screens and spray- wash systems as standard items for new and existing stations. Although modified screens appear to have good potential for alleviating impingement mortality, it should be pointed out that short-term mortality studies alone may not adequately reflect possible longer term mortality which may result from injury incurred during the impingement and removal process , particularly among less hardy species. On the basis of impingement survival data collected at a power plant located on the Hudson River it has been suggested that immediate survival may be a poor indication of impingement mortality for some species and that consideration of latent mortality is required for adequate assessment of impingement damage (Ecological Analysts , Inc. , 1976). For example , at the Bowline Point Generating 4-16Station , initial survival of young- of-the- year white perch and striped bass impinged on continuously operated screens was high , ranging from 81-98 percent for white perch and 89-98 percent for striped bass. Mortality increased however , during the holding period , with survival after 96 hr ranging from 55-56 percent for white perch and 52-81 percent for striped bass. Similar trends were noted at the Roseton and Danskammer Point Generating Stations (King, Hutchison , and Huggins , 1978). There are several reasons why the Hudson River data should not be considered contradictory to the results obtained at the Surry Power Station. First , the Hudson River studies were conducted at plants which do not incorporate modified screens (i. e. , lifting buckets). Therefore , there was a good chance that fish could drop off the flat debris lip as it cleared the water surface and be reimpinged one or more times , as occurred at Mystic (Section 3). Second , those fish which were retained by the lip were out of water for a period of time and , in some cases , were exposed to relatively high pressure sprays. Finally, standard shallow , rough concrete sluiceways which can cause injury by abrasion were generally used to convey fish to a collection area. All these factors may have biased the results toward higher mortality than would be expected with a modified screen system. Therefore , it is probable that modification of the traveling screens (incorporation of fish lifting buckets , low pressure sprays , and a return system) and a more extensive evaluation would show substantially higher survival rates. Survival potential also appears to be species- specific. For certain species initial survival may be a valid indication of impingement damage. For example , 96-hr impingement mortality studies with yellow perch were conducted at Wisconsin Public Service Corporation s (WPSC) J. P. Pulliam Power Plant during 1977 (WPSC , 1978). Initial survival of yellow perch was high under the two test conditions evaluated: (1) impingement only and (2) impingement plus high pressure screenwashing. The screens at Pulliam are conventional with no modifications for fish protection. During the study, impinged fish were handpicked off the screens and placed in holding tanks. Initial survival was high , ranging from 84 to 100 percent. Survival after 96 hr did not drop appreciably. The lowest survival rate (79. 2 percent) was believed to be the result of overcrowding in the holding tank and warm water temperatures (77 F) rather than impingement stress. Mean 96-hr survival (total of four tests) was 82. 1 percent (WPSC , 1978)

(Table 4. 4-1). During the impingement- screenwash study, the use of the high pressure wash (70 psi) did not increase mortality. Survival rates of impinged fish after 96 hr ranged from 73. 3 to 100 percent (Table 4. 4-1) with a mean of 87. 8 percent (WPSC , 1978). Thus , it is apparent that , although latent survival is probably the best indication of impingement damage for fragile species such as clupeids initial survival may be an appropriate measure of impingement impact for some of the hardier species. As discussed in Section 3, mean initial survival of flounder at Mystic was 97. 4 percent under the continuous screen4-17TABLE 4. 4-1 96-HR IMPINGEMENT SURVIVAL RESULTS PULLIAM POWER PLANT , 1977 No. Fish No. Fish Alive Percent Test No. Placed in Tank After 96 Hr Survival Phase I - Impingement only 100. 100. 743 589 79. 352 305 86.

Total 123 922 82. Phase II - Impingement - Screenwash 100. 87. 89. 96. 78. 73. Total Source:

329 289 87. Wisconsin Public Service Corporation , 1978wash cycle. Total survival at 96 hr (85. 4 percent) was only 12 percent lower than the initial value. Initial mortality generally increased with an increase in screenwash interval. However , total mortality (96 hr) was never more than 25 percent greater than initial mortality. It should be noted that , even though the Mys tic survival studies were conducted with conventional traveling water screens , winter flounder survival rates were relatively high. It would appear that modifying the existing screens with lifting buckets and low pressure spraywashes would further enhance survival of flounder. Results of survival studies at Surry further indicate that the potential exists for collecting other , more fragile , species at Mystic with relatively high survival. However , it is not possible to predict the actual effectiveness of such a system without additional studies at the plant. Therefore , since this scheme is believed to offer a cost- effective means for minimizing fish losses at Mystic , a study program to evaluate

this system has been developed , as presented in Section 4. Engineering Description Two types of modified traveling screens with fish lifting buckets are commercially available for collecting fish and debris: ' one with a frontwash spray system and one with a back- wash spray system. The back- wash system , similar to that installed at Surry (shown in Figure 4. 4-2), consists of screens equipped with lifting buckets that hold 2 in. of water. The fish and debris are washed on the back side of the screen into separate troughs. An overhead , 2- psi external spray washes fish into the fish trough while a second high pressure spray (80 psi) internal spray washes debris into the debris trough. At Mystic , this system would require raising the screen head assembly about 2 to 4 ft above that of the existing installation to provide space for the second collection trough. Front- wash spray systems are being installed at power plants on Long Island Sound and are being evaluated in Florida and on the Hudson River for possible application. This system consists of screens equipped with lifting buckets that can hold 1. 75 in. of water. At Mystic , the fish and debris would be washed from the front of the screen into a common trough. An external spray with a 10- psi pressure would wash fish from the lifting buckets , and a second high pressure (80 psi) spray (located above the low pressure spray) would remove debris. Lateral sprays would also be incorporated to wash remaining debris from the lifting buckets , thereby preventing carry- over. Utilization of this system at Mystic would not require raising of the head assembly. Collected fish would be returned to the Mystic River in a trough carrying approximately 6 in. of water at a velocity of about 3 fps. Augmentation flow would be provided in the return trough to achieve these velocities and water levels. An additional low head pump would be required to provide this flow as well as the low pressure spray- wash flow. Smooth-top, oblong (1/8 by 1 in. ) screen mesh material could be incorporated which might enhance fish survival. In addition , a debris deflector could be added to the back of the screen to seal the opening between the screen and the concrete deck. A second high pressure debris spray could be added 4-18l"USE 'i"".i~"f'~'

TRO UGH ~~v

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--../ LOW PRESSURE FISH WASHING SYSTEM v8\J FISH BUCKET CONVENTIONAL HIGH PRESSURE SPRAY

---' .., SIDE ELEVATION FISH SCREEN \ FLOW FIGURE 4. 4-2 SCREEN DETAIL MOD I F I ED THROUGH- F LOW SCREENS - BAC K WASH AL TERNA T I VE I NT AKE STUDY MYSTIC STATION - UNIT 7 BOSTON EDISON COMPANY STONE & WERBSTER ENGINEERING CORPORATIONto ensure the removal of debris , and a filter could be installed in the spray nozzle supply lines to prevent nozzle clogging. As discussed in Section 4. , the modified screens might have to operate continuously during the period of greatest fish impingement. Such operation would require upgrading of the screen components , including the use of heavy duty chains , head shaft roller bearings , foot shaft stoody bushings and liners , and proper slack tensioning. Based on continuous operation of the screens , the additional annual energy required for this scheme is 463 MWh. This scheme lends itself to a phased approach to evaluating its biological effectiveness prior to complete installation at Mystic Unit 7. First , one screen could be backfitted with a front- wash spray system and fish buckets only. This design would require minimum modifications. A study plan for conducting a biological evaluation of such a system is described in Section 4. If the system were found to be acceptable , the other screen would be modified and both screens would be upgraded for continuous operation. It is possible that the condition of the existing screens could be such that the installation of new screens would be more practical. Construction of the modified screens would be carried out by isolating one screen bay at a time to allow upgrading of the existing screens or removal of the screens and installation of new screens. Alternatively, this activity could be scheduled to occur during a plant maintenance shutdown to minimize downtime. The total capitalized cost for modifying the screens at Unit 7 is $596 000. Evaluation of the Modified Screen Alternative As previously discussed , results of studies at Mystic Station and other power plants indicate that traveling water screens can successfully and safely collect and remove fish given certain design and operational modifications. Additional studies could be conducted at Mystic to determine the actual effectiveness of modified traveling screens in returning important species at this site to their natural environment in a viable condition. The following is a brief description of the type of study that could be conducted to achieve this obj ecti ve. On the basis of discussions with EPA , it would appear that winter flounder rainbow smelt , and Alosa spp. (herring and alewife) are the primary species of concern at Mystic Station. It has already been shown that flounder are capable of withstanding impingement and removal from the existing traveling screens with good survival (Section 3). It is probable that a modified screen would enhance survival of this species further. Smelt and Alosa spp. have not been evaluated at this site , but available data indicate that adequate survival may be achieved under certain conditions. Therefore , the intent of a modified screen survival study would be to examine fish mortality at different operating modes to identify those conditions which yield the greatest efficiency. For the purpose of this study, one traveling screen at Unit 7 would be modified to incorporate fish lifting buckets (on all screen panels) and a 4-19low pressure spray wash system. Provisions for continuous long-term operation would not be included at this time. The screenwash sluiceway and collection area would be modified , as necessary, to allow for the removal

of fish without additional injury. The test program would consist of collecting fish from the modified screen under different operational and environmental conditions and , subsequently, holding them for up to 96 hr for observation of latent mortality. Prior to each test , the traveling screen would be rotated and cleared of all fish and debris. The screen would then be maintained in a stationary position for the specific length of time under investigation. Subsequently, the screen would be rotated and washed , and all fish would be collected and

transferred to a holding pool. While in the pool , all fish would be identified and recorded as initially alive or dead. Live individuals of those species selected for detailed study would then be placed in holding tanks for 96 hr; all other species would be returned to the river. The primary operational variable of interest would be the frequency of screenwashing. Since the purpose of the study would be to determine the screenwash interval which yields the highest survival of fish , appropriate test conditions cannot be firmly established at this time. However , initial impingement durations would range from those resulting from continuous screen rotation up to an 8-hr interval. Pending early results , intervals would be shortened or lengthened , as appropriate. To gather survival data with all species of concern , it is likely that studies would be conducted periodically in the summer , fall , and winter

months. Since environmental parameters (particularly water temperature) vary widely over this period , correlations between these parameters and survival would be possible. Therefore , all pertinent environmental parameters would be recorded during each study period. Plant operational conditions which would influence the hydraulic characteristics of the screenwell containing the modified screen , and would therefore influence

fish survival , would also be recorded. At the completion of the study, it would be possible to identify optimal screenwash modes for maximizing survival of each species and to evaluate whether survival potential varies as a result of environmental and/ or plant operational factors. The results would then serve as a basis for determining the practicability of modifying the other screen at Mystic Unit 7 and confirming optimal operational conditions. It is expected that all data required to achieve the objectives of this proposed study program could be gathered over a maximum period of 1 yr with actual sampling occurring seasonally over several 2-to-4 week periods. Should this option be selected as the most feasible and found necessary to implement , a detailed study plan would be developed. 4-20SECTION 5 ESTIMATED COSTS AND CONSTRUCTION SCHEDULE Order- of- magnitude costs were developed for each of the proposed alternative intakes for the Mystic Station - Unit 7. The order- of- magnitude cost is defined as the cost that requires the minimum amount of time and has the minimum degree of accuracy in its results. It is usually based on historical data from other proj ects and is adjusted for identifiable differences and size on a case-by- case basis. These costs allow a valid comparison of the cost difference between alternatives as a reasonable estimate of the probable cost of any scheme. The estimated costs , listed in Tables 5-1 and 5-2 , are based on the follow1ng: Present-day prices and fully contracted labor rates as of July 1979 Forty-hour work week , single- shift operation Allowance for indeterminates to cover uncertainties in design and construction at this preliminary stage of work All construction performed on a fully contracted basis Allowance for overhead to cover distributable construction cost indirect costs , and general and administrative costs Allowances for escalation , allowance for funds used during construction , taxes , contingency, and other owner costs. The total evaluated costs for the various schemes are presented in Table 5-1. Also included in this table are the estimated additional power and energy requirements and the 1979 maintenance costs for each scheme. The energy requirements are based on continuous operation of the screens for Scheme intermittent operation of the screens for Schemes 1 , 2 , and 3, and operating the supplemental pumps continuously for Schemes 1 and 3. The maintenance costs for the continuously operating traveling screens (Scheme 5) are based on experience with similar installations. The maintenance costs for the screenwash pumps are based on 5 percent of the capital cost of the pumps and for the supplementary flow pumps on 1. 5 percent of the capital costs. The maintenance cost for deepening the area immediately in front of the existing screens is based on dredging every 2 yr.

Total project costs , capitalized costs , and levelized annual costs for the various schemes are listed in Table 5-2. The total project costs consist of the 1979 direct , distributables , and engineering costs , escalation to proj ect completion , contingencies , and allowance for funds used during construction. A common project completion date for all schemes has been taken for the purpose of comparison. 5-1TABLE5-1ESTIMATED COSTSSchemeAdditional1979InstalledAdditionalAdditionalDirect CostPower RequiredAnnual EnergyMaintenance(in $1000)MWhCosts (in $1000:4285422941 .Utilizing Intake Bay ofUni ts1-3 for SupplementalCooling Water for Unit 7(Not including new wharf)Installing Screens Flush withfront of Intake Bays701Constructing Additional IntakeBays, 752610945Deepening Area Immediatelyin Front of Existing IntakeBaysModified Traveling Screens259463Modifying1 ScreenTABLE 5-2TOTAL PROJECT AND CAPITALIZED COSTS*(IN $1000)ItemScheme 1Utilizing IntakeBays of Units 1-3for SupplementalCooling Water forUni t 7Direct CostDistributablesEngineering428285Subtotal805EscalationContingenciesAllowance for FundsUsed During Construction331470108Subtotal714Add Cost of New Wharf472186Total Project CostCapitalized Performance Penalties289Capitalized Operationand Maintenance Cost199Total Capitalized Cost674Levelized Annual Cost422NOTES:Q979 based data~kRepresents equivalent capital andincludes:Replacement energyReplacement capacityHeat rate charge. Scheme 2InstallingScreens Flushwi thFront ofthe IntakeBaysScheme 3ConstructingAdditionalIntake Bays701129752168308901228110116431699290, 1556481556485262091687 ,383249573Scheme 4DeepeningArea ImmediatelyIn Front ofExisting IntakeBaysScheme 5Modified TravelingScreens259304397397153303393596127The capitalized costs are calculated by multiplying each year s cost by the appropriate present- worth factor , summing the present- worth values , multiplying the result by the capital recovery factor , and dividing by the fixed charge rate. The total capitalized costs consist of the total proj ect cost , the capitalized performance and auxiliary power penalty, and the capitalized operation and maintenance costs. The levelized annual costs are calculated by multiplying the capitalized costs by the fixed charge rate. The construction periods required for each scheme are presented in Table 5-3. These periods do not include engineering and design, equipment procurement or permits. 5-2TABLE 5..,3 CONSTRUCTION PERIODS Scheme Mon ths 1 . Utilizing Units 1-3 Intake Bays for Supplemental Cooling Water for Unit Installing Screens Flush with Front of Intake Bays Constructing Additional Intake Bays 16. Deepening Area Immediately in Front of Existing Intake Bays Modified Existing Screens Modifying 1 ScreenREFERENCES CITED Ecological Analysts , Inc. 1976. Bowline Point Generating Station Impingement Recirculation and Survival Studies , November 1975 - April

1976. Prepared for Orange & Rockland Utilities , Inc. Eisele , P. J. , and Malaric , J. F. 1978. Summary Report on the Prototype Fish Pumping Studies at the Monroe Power Plant. The Detroit Edison Company, Technical Report. King, L. R. ; Hutchinson , J. B.; and Huggins , T. G. 1978. Impingement Survival Studies on White Perch , Striped Bass , and Atlantic Tomcod at

Three Hudson River Power Plants.

Lawler , Matusky, and Skelly Engineers , 1978. 1977 Hudson River Aquatic Ecology Studies at the Bowline Point Generating Station. Prepared for Orange & Rockland Utili ties , Inc.

Rexnord Company. 1973. Traveling Screens to Protect Fish in Water Intake Systems. Envirex , Inc. Bulletin , 316-300. Stone & Webster Engineering Corporation (S&W) , 1976. NPDES Permit MAOO04740 , Fish Impingement Monitoring Program , Mystic Station - Unit No. , Boston Edison Company (October). 1978. Fish Impingement Monitoring, Mystic Station -

No. , Boston Edison Company (July).

Unit Taft , E. P. , and Mussalli , Y. G. 1978. Angled Screens and Louvers for Diverting Fish at Power Plants. Proceedings of the American Society of

Civil Engineers , Journal of the Hydraulics Division

Vol. 104 , No. HYs (May). Texas Instruments , Inc. 1974. Indian Point Impingement Study Report for the Period June 15 , 1972 through December 31 , 1973. Prepared for Consolidated Edison Company of New York , Inc. White , J. C. , and Brehmer , M. L. 1976. Eighteen-Month Evaluation of the Ristroph Traveling Fish Screens. In: Jensen , L. D. (Editor), Proceedings of the Third National Workshop on Entrainment and Impingement New York City, February 24 , 1976. Wisconsin Public Service Corporation (WPSC). 1978. J. P. Pulliam Power

Plant , Fish Impingement , April 1977-December 1977 (March). U. S. Environmental Protection Agency (EPA). 1976. Development Document for Best Technology Available for the Location , Design , Construction and Capacity of Cooling Water Intake Structures for Minimizing Adverse Environmental Impacts. R-1