Intake modi®cations to reduce entrainment and impingement atCarolina Power & Light Company's Brunswick Steam Electric

Plant, Southport, North Carolina

Thomas Thompson*

Carolina Power & Light Company, Harris Energy and Environmental Center, Route 1, Box 327, New Hill, NC 27562, USA

Abstract

The Brunswick Steam Electric Plant (BSEP) is a two-unit nuclear station located in the lower Cape Fear River Estuary (CFE)

near Southport, NC. Once-through cooling water is withdrawn from the CFE and discharged to the Atlantic Ocean. Estuarine-dependent ®sh and shell®sh species are potentially subject to entrainment and impingement during cooling-water withdrawal.Mitigation technologies include a ®sh diversion structure (9.4-mm mesh screens) at the mouth of the intake canal to reduce

impingement of large organisms, 1-mm ®ne-mesh traveling screens to reduce entrainment of larvae, a ®sh return system toreturn impinged organisms alive back to the estuary, and ¯ow minimization. Installation of the ®sh diversion structure resultedin a 40% reduction in number and 70% reduction in the weight of larger organisms impinged. Use of ®ne-mesh screenssuccessfully reduced the number of organisms entrained by as much as 80% depending upon species present. Survival of

organisms returned to the CFE ranged from <1% to approximately 92% depending upon species and size class. In addition tomonitoring the e�ectiveness of the intake modi®cations, over 20 years of extensive environmental studies in the estuary indicatethat operation of the BSEP has had no measurable adverse e�ect on the ®sheries of the CFE. The species composition,

seasonality, and abundance of organisms using the CFE have not changed as a result of operation of the BSEP. 7 2000Elsevier Science Ltd. All rights reserved.

Keywords: Entrainment; Estuary; Fish return system; Impingement; Diversion structure

1. Introduction

Use of water for condenser cooling purposes resultsin the potential for entrainment and impingement oforganisms. Entrained organisms are small and typi-cally the larval forms of aquatic organisms that aredrawn into a power plant's cooling water system alongwith the cooling water. Impinged organisms includethe juvenile and adult life stages of aquatic organismsthat are forced onto the intake screens by the incomingcooling water. Section 316(b) of the clean water actrequires that adverse environmental e�ects of entrain-ment and impingement be minimized. The purpose of

this paper is to summarize over 20 years of 316(b)related studies and describe the intake modi®-cations used to minimize the potential adverse e�ectsof entrainment and impingement at the BrunswickSteam Electric Plant (BSEP). Data regarding the e�ec-tiveness of these modi®cations are included in thispaper.

The BSEP is a two-unit nuclear station located ap-proximately 9.2 km upstream from the mouth of theCape Fear River Estuary (Fig. 1). Unit 2 began oper-ation in 1975 and Unit 1 began operation in 1977. TheCape Fear River Estuary (CFE) extends about 45.1 kmfrom the mouth of the river to the general location ofthe salt water boundary near Wilmington, NC. TheCFE is an elongated shallow bay with a narrow 12.1-m deep ship's channel dredged to Wilmington. Above

Environmental Science & Policy 3 (2000) S417±S424

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* Tel.: +1-919-362-3270; fax: +1-919-362-3391.

the narrow constriction at Sunny Point, the CFE ishighly strati®ed with salt water intrusion along thebottom and freshwater ¯ow out along the surface.Below Sunny Point the CFE is well mixed and charac-terized by a large ocean exchange rate of about 80%of the water over a 12-h period (Carpenter and Yonts1979). It is from this lower reach of the CFE that cool-

ing water is withdrawn from the surface layer via a4.8-km long intake canal.

The intake structure for each unit consists of fourintake bays and pumps. Originally, vertical travelingscreens installed in each bay were ®tted with 9.4-mmmesh screening. Currently, three of the four travelingscreens for each unit are ®tted with 1-mm ®ne-mesh

Fig. 1. Location of the Brunswick Steam Electric Plant and the Cape Fear River, NC.

T. Thompson / Environmental Science & Policy 3 (2000) S417±S424S418

screens. Intake structure technologies also include a®sh return system, a ®sh diversion structure, and a sea-sonally based ¯ow minimization regime (Fig. 2). Cool-ing water ¯ow is reduced from 31.1 cm/unit duringApril±November to 26.1 cm/unit during December±March. Normally, all ¯ow is through traveling screens®tted with ®ne mesh. The cooling water ¯ow for oneunit only may be increased to 34.8 cm during July,August, and September by using a forth intake pumpwith 9.4-mm mesh screens. The diversion structure,completed in 1982, is located approximately 3.5 kmfrom the plant intake bays near the con¯uence of theintake canal and Walden Creek. Copper-nickel screenpanels (9.4-mm mesh) are set between reinforced con-crete pilings. Installation of two ®ne-mesh screens perunit and the ®sh return system was completed in 1983.The third ®ne-mesh screen per unit was installed in1987. Impinged organisms are washed o� the screensinto a 1.4-km long ®berglass ¯ume and transported toa constructed return basin opening to a tributary ofWalden Creek.

Organisms of interest were the larvae, juveniles, andadults of the dominant or commercially and recrea-tionally important ®sh and shell®sh species found inthe CFE (Table 1). Most of these species are transientocean-spawned species potentially subject to entrain-ment during recruitment to the estuary and impinge-ment during movement back to the ocean. In additionto the bay anchovy, other dominant noncommercial

taxa included gobies (Gobiosoma spp. and Gobionellusspp.) and silversides (Atherinidae).

Studies of the CFE and the populations of organ-isms using this estuary were conducted as early as1968, 7 years prior to commercial operation of theBSEP. Entrainment and impingement studies began in1974 when the ®rst intake pumps began operation andcontinue today, although much reduced in scope com-pared to previous years. Before 1976, ®eld investi-gations were largely baseline studies designed to collectpreliminary biological and environment data prior tosimultaneous operation of both units during 1977.

Using the results of baseline studies, intensive ®eldstudies were designed in conjunction with plantentrainment and impingement studies (CP&L, 1980).Conducted from 1976±1978, the objectives of thesestudies were to fully characterize the CFE with respectto its physical and hydrological nature, the popu-lations of dominant organisms utilizing the CFE, andPlant impact. Several ®eld studies were conducted toexamine the populations of dominant larval, juvenile,and adult ®sh and shell®sh (CP&L, 1980). Variables ofparticular interest with respect to each life stage ofthese organisms were species composition, seasonaldistribution, abundance, size distribution, and spatialdistribution. Larval ®sh studies using surface and bot-tom, replicate plankton nets were conducted in thenear shore ocean and along the main axis of the estu-ary (Copeland et al., 1979). These studies along with a

Fig. 2. Location of the diversion structure and ®sh return system at the Brunswick Steam River Plant.

T. Thompson / Environmental Science & Policy 3 (2000) S417±S424 S419

larval retention study (Weinstein, 1979b) examined therecruitment and retention dynamics of ocean-spawnedlarval ®sh. Seine and rotenone sampling were con-ducted to examine the use of tidal creeks and shallowmarsh nursery areas by the postlarvae and juveniles ofthese ocean-spawned species (Weinstein, 1979a). Anekton study using gill net and trawl sampling pro-vided an assessment of use of the open water areas ofthe CFE by juvenile and adult ®sh and shell®sh(Schwartz et al., 1979a,b). In addition to the majorbiological studies, several special studies were con-ducted to evaluate sampling methods. These includedgear e�ciency and gear comparison studies, ¯owmetercalibration, sample replication studies and subsamplingstudies. Integration of the various components of thesestudies allowed for the formulation of a Fish Popu-lation Model (FPM) that provided a simulation ofspot and croaker recruitment and a quantitative esti-mate of ®sh population impacts (CP&L, 1980; Lawleret al. 1980a,b, 1988). Losses of spot and croaker aspredicted by the FPM ranged from 2.4 to 21.7% in1977 and 1978 depending upon Plant ¯ow conditionsand assumptions of gear e�ciency.

A key issue was the potential for plant operation toadversely a�ect recruitment of larvae to Walden Creek(adjacent to the Plant intake canal) and to theupstream nursery areas of the CFE. Thus, sampling lo-cations for the major biological studies ranged fromthe lower CFE to near Wilmington, NC, with intensivesampling in the vicinity of the intake canal and Wal-den Creek. Intensive biological monitoring of the CFEthrough 1978 allowed researchers to show that speciescomposition and seasonality of the dominant organ-isms using the CFE remained unchanged and were notadversely a�ected by Plant operation. There was a sea-sonal movement into and residence of ocean-spawnedspecies and the dominant species entrained re¯ected

that of river larval ®sh (CP&L, 1980, Copeland et al.,1979). Di�erences in spatial distribution from year toyear were related to environmental conditions, primar-ily changing freshwater ¯ow and salinity (Copeland etal., 1979; CP&L, 1980; Weinstein, 1979a; Weinstein etal., 1980). Copeland et al. (1979) successfully predictedmovement of postlarval spot and croaker to the upperestuary by using a quadratic model based upon tem-perature, freshwater ¯ow, and the interaction of thesetwo parameters. Thus, the abundance of both of thesetwo species adjacent to and upriver of the Plant wereas expected based upon yearly variation in freshwater¯ow and water temperature.

In 1979, a long-term monitoring program was in-itiated by CP&L with the objective of providing a con-tinuing assessment of the operation of the BSEP onthe CFE and an assessment of the success of the intakemodi®cations in reducing entrainment and impinge-ment. Although reduced in scope and frequency, thelong-term monitoring program consisted of some ofthe components of the original sampling programincluding river larval ®sh, nekton, entrainment andimpingement (CP&L, 1982). The marsh study wasresumed in 1981 with the addition of trawl samplingwhich allowed for direct comparison to juvenile ®shsampling conducted by the North Carolina Division ofMarine Fisheries. Results of long-term ®eld studies didnot indicate signi®cant decreases in the abundance oforganisms over time; this implies that the e�ects ofentrainment and impingement were minimal. Forexample the annual density of total larval organisms inWalden Creek, adjacent to the Plant intake canal,remained stable over 14 years of Plant operation from1979 through 1993 (Fig. 3). Nursery areas adjacent toand upriver of the Plant intake were being used to ca-pacity by ®sh and shell®sh species and movement tothese nurseries was not limited by Plant operation. For

Table 1

Representative dominant or commercially and recreationally important taxa collected by various sampling programs during studies associated

with the Brunswick Steam Electric Plant, 1971±1998

Sampling Programa

Taxa Common name LF M N E I S

Brevoortia tyrannus Atlantic menhaden X X X X X X

Anchoa mitchilli Bay anchovy X X X X X X

Mugil spp. Striped and white mullet X X X X X X

Leiostomus xanthurus Spot X X X X X X

Micropogonias undulatus Atlantic croaker X X X X X X

Cynoscion spp. Weak®sh, spotted sea trout X X X X X X

Gobidae Gobiosoma spp., Gobionellus spp. X X X X X X

Paralichthys spp. Southern and summer ¯ounder X X X X X X

Penaeus spp. White, pink, and brown shrimp X X X X X X

Callinectes sapidus Blue crab X X X X X X

Portunidae Portunid crab megalops X X X X

a Sampling program designations Ð LF: larval ®sh; M: marsh; N: nekton; E: entrainment; I: impingement; S: survival studies.

T. Thompson / Environmental Science & Policy 3 (2000) S417±S424S420

example, marsh study data from 1993, indicated abun-dances of selected species to be higher in the marshesadjacent to and/or upstream of the Plant intake canalcompared to nursery area below the Plant intake canal(Table 2).

2. Assessment of intake modi®cations

Entrainment and impingement studies along withseveral special studies addressed the e�ectiveness ofintake modi®cations in reducing entrainment andimpingement of ®sh and shell®sh. Prior to installationof ®ne-mesh screens, all entrained larvae were dis-charged to the ocean rather than back to the estuary,therefore they were considered losses to the estuary. In1984, a larval impingement study was added to assessimpingement of larvae on the ®ne-mesh travelingscreens and the resulting reduction in entrainment(CP&L, 1985a,b). Survival studies were also initiated

to determine the e�ectiveness of the ®sh return systemin transporting impinged larval, juvenile, and adultorganisms alive back to the CFE (CP&L, 1985a,b).

Initial assessments of ®ne-mesh screen e�ectivenessincluded comparisons of entrainment densities betweenthe two units (one with ®ne-mesh screens and onewithout ®ne-mesh screens) and back-to-back 24-h com-parisons of entrainment densities from the same unitoperating with and without ®ne-mesh screens. Hogarthand Nichols (1981) projected reductions in entrainmentof 44±70% as a result of two ®ne-mesh screens perunit and ¯ow minimization. Results of studies con-ducted from November 1984 to January 1985 indicateda reduction of 82% in the density of total organismsentrained for that time period (CP&L, 1985a,b). Time-series analysis of entrainment density for selectedspecies also indicated signi®cant decreases in the den-sity of organisms entrained (CP&L, 1986).

In 1990 an approach was used in which the numberof larvae entrained during a 24-h sampling period was

Fig. 3. Time-series analysis of river larval ®sh data showing densities of total larval organisms collected in Walden Creek, 1979±1993.

Table 2

Annual catch-per-unit-e�ort by creek system for nine selected species collected in the Brunswick Steam Electric Plant Marsh Study during 1993a

Species Bald Head Creek Walden Creek Mott's Bay Alligator Creek

Atlantic menhaden 12 103 500 3

Bay anchovy 2 12 180 8

Spot 241 498 257 15

Croaker < 1 5 96 16

Southern ¯ounder < 1 7 5 41

Brown shrimp 5 65 11 3

Pink shrimp < 1 3 15 1

White shrimp < 1 4 2 22

Blue crab 5 7 5 3

a Results represent trawl data collected from marsh nursery areas below the Plant intake canal (Bald Head Creek), adjacent to the Plant intake

canal (Walden Creek), and upstream of the Plant intake canal (Mott's Bay and Alligator Creek).

T. Thompson / Environmental Science & Policy 3 (2000) S417±S424 S421

compared to the number of larvae impinged on the®ne-mesh screens during that same sampling period(CP&L, 1991). This was driven by a reduction insampling frequency from weekly to once per monthand the desire to still be able to obtain some indicationof ®ne-mesh screen e�ectiveness. E�ectiveness wasobtained by dividing estimates of the total number oflarvae impinged during the sampling period by thesum of the total number of larvae entrained plus thetotal number of larvae impinged. Fine-mesh screene�ectiveness by month for total organisms rangedfrom 14 to 81% depending on species present andwhether or not a coarse-mesh screen was operating(Table 3).

Success of the diversion structure in reducing theimpingement of larger organisms was measured bychanges in the numbers, weights, and sizes of organ-isms impinged before and after the diversion structurewas installed. In addition, data from the nekton moni-toring study and several special studies using multiple

gear types (trawls, gill nets) compared catches atsampling stations located inside and outside the diver-sion structure. The mean density of total organismsimpinged after installation of the diversion structure(1981±1985) was 43% less than the mean densityimpinged prior to the installation of the diversionstructure (Table 4). The mean weight of organismsimpinged was reduced by 72%. After completion ofthe diversion structure, bay anchovy replaced Atlanticmenhaden as the numerically dominant species oforganism impinged. Examination of cumulative length-frequency distributions documented a shift to theimpingement of smaller individuals since larger indi-viduals were excluded from the intake canal (CP&L,1985a,b). This was considered important since largerindividuals have a greater chance of surviving longenough to reproduce. Results of trawl and gill netsampling in the intake canal also documented areduction in the abundance of larger organisms atlocations inside the diversion structure relative to

Table 3

Percent e�ectiveness of ®ne-mesh screens in reducing the number of selected species entrained per sampling day at the Brunswick Steam Electric

Plant during 1990a

Month Gobiosoma spp. Portunid megalops Penaeus spp. Anchoa spp. Spot Croaker Atlantic menhaden Total organisms

Jan NC NC NC 100 24 51 100 46

Feb NC 100 100 100 42 65 100 60

Mar NC 79 62 55 24 22 76 27

Apr 100 67 65 29 53 18 100 28

May 7 4 75 26 100 100 NC 22

Jun 11 73 76 65 NC NC NC 44

Jul 56 94 95 70 NC NC NC 78

Aug 3 19 21 25 NC NC NC 14

Sep 30 59 38 26 NC NC NC 37

Oct NC 81 81 100 NC NC NC 81

Nov 22 91 85 100 NC 59 NC 80

Dec 100 64 100 80 NC 47 NC 59

a E�ectiveness=[total number larvae impinged/(total number larvae entrained+total number larvae impinged)] � 100. NC indicates none col-

lected.

Table 4

Mean density (number/million m3) and mean weight density of selected (kg/million m3) species impinged at the Brunswick Steam Electric Plant,

1977±1985a

Density Weight

Taxa 1977±1981 1982±1985 Percent change 1977±1981 1982±1985 Percent change

Atlantic menhaden 5481 395 ÿ93 38.8 3.4 ÿ91Blue crab 351 251 ÿ29 4.5 3.6 ÿ20Spot 362 103 ÿ72 3.7 1.0 ÿ73Bay anchovy 1788 4261 +138 2.5 3.7 +48

Croaker 199 127 ÿ36 1.0 0.7 ÿ30Total organisms 10538 5971 ÿ43 60.6 17.3 ÿ72

a Data from 1983 is not included since impingement was not sampled the entire year due to installation of the ®sh return system. Units are

based on million m3 of water pumped by the Plant.

T. Thompson / Environmental Science & Policy 3 (2000) S417±S424S422

locations outside the diversion structure (CP&L, 1984,1985a,b, 1987, 1991).

Survival studies, conducted from 1984±1987, docu-mented survival of organisms returned to the CFE viathe ®sh return system (CP&L, 1988). Organisms werecollected and held for 96 h so that latent mortalitycould be measured as well as initial mortality. Meanpercent survival depended on species, size class, andscreen-rotation speed (Table 5). The highest survivalrates (75±96%) occurred for the larvae, juveniles, andadults of the most valuable commercial species, shrimpand blue crab. Survival for spot and croaker was inter-mediate ranging between 9 and 60% with the larger ju-veniles and adults exhibiting the best survival. Thepoorest survival was exhibited by the bay anchovy(<1±5%).

3. Summary

Some form of biological monitoring associated withthe Brunswick Steam Electric Plant and the Cape FearRiver Estuary has been conducted for over two dec-ades. Entrainment and impingement monitoring beganwhen the intake pumps ®rst began withdrawing cool-ing water in 1975 and continue today, although muchreduced in scope and frequency. In addition to entrain-ment and impingement monitoring, ®eld studies wereconducted to fully assess the potential impact on thepopulations of ®sh and shell®sh in the Cape FearEstuary.

Results indicated that operation of the Plant had nosigni®cant adverse e�ect on the species composition,seasonality, abundance, and spatial distributions of®sh and shell®sh inhabiting the Cape Fear RiverEstuary. Short-term changes in the distribution andabundance of species was related to changing

environmental conditions, primarily freshwater ¯owand salinity. Further, recruitment of ®sh and shell®shlarvae to the nursery areas adjacent to and upriver ofthe Brunswick Steam Electric Plant was not limited byPlant operation. Although reduced in scope, monitor-ing studies from 1979 through 1993 continued to sup-port conclusions reached from results of the intensivesampling conducted from 1976 through 1978. In ad-dition, monitoring study results were su�cient to pro-vide an indication of how e�ective the intakemodi®cations were in reducing the entrainment andimpingement of organisms. Installation of the diver-sion structure reduced the density of larger organismsimpinged approximately 43%. The biomass of organ-isms impinged was reduced approximately 72%. Re-ductions in the number of larvae entrained ranged upto approximately 80% due to ®ne-mesh screens. Survi-val rates of the most valuable commercial species,penaeid shrimp and blue crabs, ranged up to 96%.

Maintenance associated with the diversion structurecan be labor intensive during portions of the year.Daily cleaning of the ®xed vertical screens by a three-person crew is required during the summer months toremove debris accumulation and prevent damaged di-version screens. Although the intake traveling screensare rotated and washed continuously, ®ne-mesh travel-ing screen clogging events and subsequent circulatingwater pump trips have occurred. Occasionally, theseclogging events were a result of high densities of mar-ine life such as hydromedusae, caprellid amphpipods,and Gracilaria spp. and were unpredictable. Usually,clogging events were a result of detritus and mud ac-cumulation on the traveling screens during low to midincoming tides. More frequent periodic dredging of theintake canal (every 2 years) lessens the likelihood of®ne-mesh screen clogging events due to detritus andmud.

Table 5

Survival of selected taxa impinged at the Brunswick Steam Electric Plant during 1987a

Larvae Juvenile and adult

Taxa Slow screen rotation speed Fast screen rotation speed Slow screen rotation speed Fast screen rotation speed

Atlantic menhaden 0 3 ND 16

Bay anchovy < 1 1 1 5

Mugil spp. 7 70 ND 92

Spot 9 29 57 60

Atlantic croaker 14 34 53 45

Cynoscion spp. ND 13 ND 35

Gobionellus spp. ND 15 ND ND

Paralichthys spp. ND 93 ND 71

Penaeus spp. 75 96 87 94

Blue crab 86 87 92 96

a Slow screen rotation speed was 75 cm/min and fast screen rotation speed was 200 cm/min. ND indicates that no survival data was collected

for that taxa, life stage, and screen rotation speed.

T. Thompson / Environmental Science & Policy 3 (2000) S417±S424 S423

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Thomas Thompson possesses 20 years of experience in the area of en-

vironmental assessment with special strength in ®sheries assessment

in marine, estuarine, and freshwater ecosystems. He possesses a BS

degree in zoology from North Carolina State University, Raleigh,

NC (1976) and a MS degree in marine science from the University of

North Carolina-Wilmington, Wilmington, NC (1989). Mr Thompson

has considerable experience with entrainment and impingement stu-

dies and ®sheries population assessment. In addition, Mr Thompson

has extensive experience with biofouling surveillance and control

techniques of raw water intake systems. Additional experience

includes water quality monitoring, toxicity testing, laboratory bioas-

says, groundwater monitoring and environmental radiological moni-

toring. A bioassay project Mr Thompson recently directed resulted

in the establishment of selenium tissue concentrations associated

with reporductive impairment in largemouth bass. Mr Thompson is

a member of the American Fisheries Society and the Estuarine

Rsearch Society. He has authored or co-authored technical publi-

cations dealing with marine and estuarine ®sheries and biofouling

control.

T. Thompson / Environmental Science & Policy 3 (2000) S417±S424S424