ML061420176

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Study of Winter Flounder Larval Transport in Coastal Cod Bay and Entrainment at PNPS, Ensr and Marine Research, Inc, February 2005
ML061420176
Person / Time
Site: Pilgrim
Issue date: 02/28/2005
From:
ENSR and Marine Research, ENSR International
To:
Entergy Nuclear Generation Co, Office of New Reactors
ALICIA WILLIAMSON 301-415-1878
Shared Package
ML061380814 List:
References
10658-001
Download: ML061420176 (27)
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Text

Entergy Nuclear Generation Company Plymouth, MA 4

oi ZAI Study of Winter Flounder Larval Transport in Coastal Cape Cod Bay and Entrainment at Pilgrim Nuclear Power Station Spring 2004 ENSR Corporation Marine Research, Inc.

February 2005 Document Number 10658-001

Entergy Nuclear Generation Company Plymouth, MA Study of Winter Flounder Larval Transport in Coastal Cape Cod Bay and Entrainment at Pilgrim Nuclear Power Station Spring 2004 Prearo By Reviewed By ENSR Corporation Marine Research, Inc.

February 2005 Document Number 10658-001

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1.0 INTRODUCTION

1-1 2.0 FIELD SAMPLING PROGRAM........................................

2-1 2.1 Sampling Program Design........................................

2-1 2.2 Winter Flounder Larvae Sampling........................................

2-1 2.3 Hydrodynamic Measurements........................................

2-3 2.4 Water Column Monitoring........................................

2-4 3.0 STUDY RESULTS.........................................

3-1 3.1 Winter Flounder Larvae Sampling Results........................................

3-1 3.2 Hydrodynamic Monitoring Results........................................

3-4 3.3 Water Column Monitoring Results........................................

3-6 4.0 DATA ANALYSIS AND ASSESSMENT........................................

4-1 4.1 Volumetric Water Flowrate Analysis........................................

4-1 4.2 Net Larval Transport and Entrainment Analysis........................................

4-3 4.3 Entrainment Analysis by Tidal Flushing........................................

4-5

5.0 CONCLUSION

S........................................

-1

6.0 REFERENCES

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MU IEM LIST OF TABLES Table 2-1 Long-Term Hydrodynamic Survey Deployment Description................................................. 2-5 Table 3-1 Larval Density and Proportion By Depth Strata.................................................................... 3-3 Table 3-2 Larval Stage Percentages of Total At Each Station Summarized For Each Survey............ 3-3 Table 4-1 Analysis of Net Volumetric Flowrate in Bay Study Area Compared to PNPS Withdrawal..4. -3 Table 4-2 Larval Flux and Entrainment Results Transect A-D.............................................................. 44 Table 4-3 Larval Flux and Entrainment Results by Tidal Flushing........................................................ 4-5 L

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LIST OF FIGURES Figure 2-1 Locations of Larvae Sampling and ADCP Deployment Stations......................................... 2-2 Figure 3-1 Total Larval Densities For Sampling Survey I....................................................

3-1 Figure 3-2 Total Larval Densities For Sampling Survey 2....................................................

3-2 Figure 3-3 Velocity Normal to Transect A-D: Flood Tide June 17, 2004.............................................. 3-5 Figure 3-4 Velocity Normal to Transect A-D: Ebb Tide June 17, 2004................................................. 3-5 Figure 3-5 Velocity Normal to Transect B-C: Flood Tide June 17, 2004..............................................

3-6 Figure 3-6 Velocity Normal to Transect B-C: Ebb Tide June 17, 2004................................................. 3-6 Figure 4-1 Water Velocities During Sampling Survey 1.........................................................................4-2 Figure 4-2 Water Velocities During Sampling Survey 2.2....................................................

42 Figure 4-3 Tidal Flushing Analysis Areas....................................................

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1.0 INTRODUCTION

Winter flounder (Pseudo pleuronectes amencanus) are commercially important in Cape Cod Bay and are a dominant species collected by the entrainment monitoring program at Pilgrim Nuclear Power Station (PNPS). The objective of this study was to evaluate the impact of winter flounder larvae entrainment at PNPS through direct field measurements. An approach was applied whereby field measurements were collected to determine the relative amount of net volumetric flow and winter flounder larvae entrained into the PNPS cooling water system compared to the net volumetric flow and amount of winter flounder larvae passing PNPS in offshore Cape Cod Bay waters.

This program was designed to update the similar studies completed in 2000 (ENSR and MRI, 2000) and 2002 (ENSR and MRI, 2003), based on the suggestions and comments of federal and state agency reviewers. The results of this study confirmed those of the prior studies in that:

PNPS withdraws a relatively small percentage of the available net volumetric flow of water-generally less than 0.1%.

The number of winter flounder larvae entrained by PNPS is a relatively small percentage of the net larval transport-conservatively estimated at less than one percent.

The field program was designed to collect sufficient measurements to determine the flux of winter flounder larvae moving along the Plymouth coast and the flux of winter flounder entering PNPS. To determine larvae flux, larvae concentration and volumetric flowrate of water were required. The field program featured determination of larval densities and water velocity measurements along the Plymouth coast in Cape Cod Bay and determination of larval densities in the PNPS cooling water system.

The field program was conducted between late May and late June and consisted of the following elements:

Winter flounder larvae sampling -

o in Cape Cod Bay at five offshore stations, and o

in the PNPS discharge canal (entrained in the cooling water flow).

Water velocity measurements -

O at four offshore stations in Cape Cod Bay, using bottom-mounted Acoustic Doppler Current Profiler (ADCP) units, and o

along transects using boat-based ADCPs.

Larvae and water velocity measurements were collected concurrently in late May and early June 2004 to support determination of larval flux. Larvae sampling was conducted along the Plymouth coast and at 1-1 J:\\WaterProjectFiles\\PIOO0\\10658_MRI\\10658001-PilgrimO4\\report\\LarvTransReportO4ftdoc February, 2005

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PNPS during two surveys, between May 26 and June 4, 2004. For each survey, larval samples were obtained four times, twice during the day, and twice during the night, during a one-day period. Water velocity measurements were collected continuously from fixed stations between May 20 to June 20, 2004 and from boat-based transects on June 17, 2004.

The ichthyoplankton data were cc.rnbined with the current measurements to determine the flux of larvae along the coast of Cape Cod Bay, for each of the two daily surveys. These values were then compared to the number of larvae entrained by the PNPS cooling system, as determined from the entrainment study, during the same two daily measurement periods.

Section 2 of this report describes the field sampling program. Section 3 provides the field study results.

Section 4 provides an analysis of the study results. Section 5 provides the study conclusion and an overall assessment of the entrainment by PNPS on winter flounder larvae from Cape Cod Bay.

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2.0 FIELD SAMPLING PROGRAM 2.1 Sampling Program Design The field program was designed in part based on the results of the similar studies performed in 2000 and 2002. In particular:

The sampling stations were deployed in a pattern that would provide the ability to capture currents flowing in any direction, as variable currents were observed during the 2002 study, as well as to perform an alternative analysis of tidal flushing (see Section 4.3).

Two larvae sampling surveys were performed, as this was deemed sufficient to capture the changes in larval densities observed as the season progressed.

2.2 Winter Flounder Larvae Sampling 2.2.1 Cape Cod Bay Larval winter flounder were collected at five stations in Cape Cod Bay (Figure 2-1). The stations were established in a diamond-shaped pattem. Three of the five stations (A, E, and D) were established along a single transect extending from just south of Rocky Point northeast into the 120' depth contour of Cape Cod Bay. The total transect length was approximately five nautical miles. Stations B and C were located approximately one nautical mile northwest and southeast, respectively, of Station E. The close proximity ol the larvae sampling stations to the hydrodynamic measurements facilitated correlation of the acquired hydrodynamic data with biological sample data to formulate an estimate of the population of winter flounder contained in Cape Cod Bay coastal waters flowing towards and past PNPS.

The five sampling stations were identified as Stations A through E. The approximate low-water depth at each station was as follows: Station A: 25'; Station B: 98'; Station C: 70'; Station D: 123'; Station E: 90'. As shown on Figure 2-1, the stations were positioned such that station E was centrally located between the other stations.

Two field surveys were completed during the spring of 2004: May 26 - 27, and June 3 - 4. Each survey was structured to capture the ebb and flood tides of two tidal cycles on each sampling day (4 sampling events per survey, 2 predominately during the day and 2 predominately during the night). Sampling was conducted at each station using 60-cm diameter "bongo" nets rigged with 0.202-mm and 0.333-mm nylon mesh plankton nets and with an epibenthic bottom sled rigged with a 0.333-mm nylon mesh net. The sled was constructed of PVC pipe identical to the one used for ichthyoplankton sampling near PNPS in 2002 (ENSR and MRI 2003). Tow duration for each sample was approximately six to eight minutes, which provided sample volumes ranging from 85 to 150 cubic meters and an overall average of 120 cubic meters.

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AiMA11Na RM3E"CK MC-d Q the entrainment section 3.3 of this document). Only the 0.202-mm mesh samples were analyzed; the 0.333-mm mesh samples were archived. Due to the abundance of zooplankton, 50% of the samples were T

split in half using a plankton splitter patterned after Motoda 1959 (see also Van Guelpin et al. 1982).

Counts were converted to larvae per 100 cubic meters of water (density) based on the flow-meter readings.

2.2.2 PNPS Discharge In conjunction with each offshore sampling series, ichthyoplankton samples were also taken from the PNPS cooling water discharge to assess the entrainment of winter flounder larvae. Sampling was conducted near the center of the discharge canal, approximately 30 meters downstream from the j

headwall, which is the same location used for the routine entrainment monitoring. Samples were collected using a 60-cm diameter plankton net constructed of 0.202-mm nylon mesh. On each survey, samples were scheduled to be taken every three hours for a total of eight samples per 24-hour sampling event. A backwash performed at the Station during the night of June 4 resulted in the collection of seven samples instead of eight. Each collection was made by streaming the net for 10 minutes. Exact filtration volumes were determined using a General Oceanics 2030R2 flowmeter mounted in the mouth of the net.

After sample collection, the net was rinsed from the outside using seawater to wash all plankton into the cod end of the net. The sample was then transferred into a 1-liter, wide mouth bottle and preserved using W

sufficient buffered Formalin to obtain a 10% solution. A waterproof tag listing the station, date, time of collection, and the flow-meter readings was placed into each sample container. Samples were returned to the laboratory and processed as described above for the offshore samples.

2.3 Hydrodynamic Measurements The hydrodynamic measurement component of the field program was designed to support determination of the total volumetric flowrate of water along the Plymouth coast. The long-term, fixed-base hydrodynamic monitoring program was scheduled to include the time of the two winter flounder larvae sampling surveys.

The hydrodynamic field program consisted of two components, a long-term survey and a synoptic survey.

The long-term and synoptic surveys successfully collected the data required to support the study and are described below.

2.3.1 Long-term Hydrodynamic Survey Hydrodynamic measurements were continuously collected at four locations (A, B, C, and D see Figure 2-1). At each hydrodynamic sampling location, the following measurements were collected for a period of one month.

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I1 m4 EKN2l Water velocity measurements were recorded throughout the water column using a Lm-.

based acoustic Doppler current profiler (ADCP). The ADCP measures the magnitude and direction of water movement through transmission of acoustic signals and interpretation of Doppler frequency shifts in acoustic retums. ADCP measurements were acquired at one-mete intervals throughout the full depth of the water column.

Sea surface elevation using a tide gauge (pressure transducer).

A description of long-term survey deployments, equipment, and data collection is provided in Table 2-1 fox each location.

The long-term hydrodynamic survey achieved the 100% data collection goal. Processing, analysis and application of the long-term hydrodyramic measurement data is described in Section 3.

2.3.2 Synoptic Hydrodynamic Survey Synoptic, boat-based water velocity measurements were collected using an ADCP instrument on 17 June 2004. The boat-based ADCP survey featured measurement of water velocities (direction and magnitude) at one-meter intervals throughout the water column. Two transits of Transect A-D and Transect B-C were performed, once each during an ebb and flood tide. The ADCP unit was rigidly mounted in a frame suspended over the side of the survey vessel. Published tidal information for this date at Gumet Point indicated low tide at 06:00, high tide at 12:11 and low tide at 18:02.The synoptic survey trans;'

'4ere performed at the times indicated below:

Flood tide: Transect B-C 08:55 to 09:41 and Transect A-D 10:03 to 11:18 Ebb tide: Transect A-D 14:04 to 15:19 and Transect B-C 15:42 to 16:20 The synoptic survey achieved the 100% data collection goal. Processing, analysis and application of synoptic hydrodynamic measurement data is described in Section 3.

2.4 Water Column Monitoring Measurements of water temperature (i 0.10 C), salinity (+/- 0.1 o/oo), and dissolved oxygen (+/- 0.1 ppm) were recorded at each station immediately preceding the surface ichthyoplankton tow using a Hydrolab Quanta multiparameter water quality instrument. Readings were recorded at surface, mid-depth and at a depth of within one meter of the bottom (Station A) or up to a maximum depth of 23 meters, the length of cable available. Bottom temperatures were also recorded by both the tide gauges and ADCPs. The water quality instrument failed during the first survey after the first samples were collected at Stations A and 8, for 10% data capture during the first survey. All water quality observabons were successfully made for the second survey.

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MAAD RSESAR 3.0 STUDY RESULTS 3.1 Winter Flounder Larvae Sampling Results Densities of larval flounder per 100 m3 of water by developmental stage for each sample appea Appendix A. Larval flounder were present on each sampling occasion (Figure 3-1 and Figure 3-2).

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00:00 03-Jun 06:00 03-Jun 12:00 03-Jun 18:00 04-Jun 00:00 04-Jun 06:00 04-Jun 12:00 Figure 3-2 Total Larval Densities For Sampling Survey 2 3,1.1 Cape Cod Bay The distribution of winter flounder larvae among developmental stage is shown in Table 3-1 pooled over both collection dates within sampling strata and including the PNPS discharge. All four developmental stages were found in the collections although stage 2 and 3 larvae accounted for 80 to 90% of the total within each strata. The low contribution of early stage I larvae likely reflected, at least in part, the late May, early June sampling dates, relatively late in the spawning season. The low numbers of stage 4 larvae probably reflected their lower numbers in general as a result of natural mortality and gear avoidance as a result of their benthic life style.

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Table 3-1 Larval Density and Proportion By Depth Strata UXe ppr Strata Lowe Strat Bottom~ Strata j' PNPSi Dischare7-tage-Density%

of Total Densit i cf Total Densty of Total Dlensity' of Total 71.4 14.8%

9.3 11.5%

8.4 2.0%

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2 31.2 61.9%

44.7 55.0%

183.0 43.3%

33.4 20.90%

3 11.7 23.2%

27.1 33.4%

231.3 54.7%

123.7 77.20/R 4

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0.1 0.1%

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1.2 0.80° Tt 50.4 81.2 423.1 160.2 I.

Overall, larval densities in Cape Cod Bay averaged higher near bottom. Densities in the upper half of the water column collected with the bongo net averaged 50.4 per 100 m3 of water compared with 81.2 per 100 m3 in the lower portion and 423.1 per 100 m3 near bottom as determined with the sled. Densities averaged 160.2 per 100 m3 in the PNPS discharge.

Summarized across stations and events for each survey, the percentages of each larval stage observed are given in Table 3-2. In general, larval densities in Cape Cod Bay were higher near shore and lower farther off shore and in deeper water, and larval densities in the PNPS discharge were within the range observed in the Bay. During the first survey, stage 2 larvae were most abundant in Cape Cod Bay, except at Station A, where like the PNPS discharge, stage 3 larvae were most abundant. In the second survey.

stage 2 and 3 larval densities in Cape Cod Bay were found in about equal proportion, except at Station D where stage 2 was most abundant and stage 1 was still significant. Stage 3 was fully three-quarters of the larvae observed in the PNPS discharge during the second survey.

Table 3-2 Larval Stage Percentages of Total At Each Station Summarized For Each Survey 16 42 54 0.1 431 1

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151 1 514 123 701 16 1108 3.1.2 PNPS Discharge 3

Mean densities of flounder larvae observed in the PNPS discharge were 149.8 and 172.0 per 100 m3 oft water for the May 26 and June 3 series, respectively.

The percentages of larval stages observed in the PNPS discharge are summarized above in Table 32 Stage 3 larvae were observed at a much higher percentage compared to the three other stages. Stage 1 J:%WateProjectFies\\P100\\1O658..MRfl10658001-Febnjary, 20065 PilgrimO4\\epo\\LarwvTmnsRepaitO4f.doc

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F7777TR.M larvae were approximately one percent of the total observed, suggesting that the spawning season ended earlier in May. Stage 4 larvae made up one percent or less of the total in both surveys.

3.2 Hydrodynamic Monitoring Results 3.2.1 Long-term Hydrodynamic Survey Hydrodynamic data from each of the three locations were inspected, processed, and exported for further analyses using RD Instruments WinADCP software. The conversion of the water velocity vectors (magnitude and direction) to velocity normal to a transect results in velocities and water flowrates being reported such that positive values are flowing North and/or West, and negative values are flowing South and/or East.

Over the duration of the ADCP deployment, the observed extremes of velocity averaged over the entire water column were, in meters per second:

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0.185

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-0.406 B

0.188

-0.282 0.118 -0.172 C

0.320

-0.356 0.140 -0.196 D

0.234

-0.302 0.121

- -0.157 Hydrodynamic data are provided in electronic form as Appendix C.

3.2.2 Synoptic Hydrodynamic Surveys Data from the four boat-based ADCP tows were inspected using RD Instruments WinRiver software, and exported for further analysis. The ADCP transect tows of June 17, 2004 are presented in Figure 3-3 to Figure 3-6. These figures show the velocity normalized perpendicular to the A-D and B-C transects, with positive values flowing northwest, and negative values flowing southeast. The results of the synoptic surveys show that the current profiles vary across the transect, however, the placement of the fixed ADCP stations should capture the major flow regimes. The synoptic survey also shows that the variation in currents is predominantly with depth rather than distance along the transect. As expected flow is mostly to the South (negative velocities across the transect in Figure 3-3) during flood tide and mostly to the North (positive velocities across the transect in Figure 3-4) during ebb fide.

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4737 Figure 3-6 Velocity Normal to Transect B-C: Ebb Tide June 17, 2004 3.3 Water Column Monitoring Results Water temperature, salinity, and dissolved oxygen data recorded at each station are tabulated in Appendix B. A malfunction with the Hydrolab equipment prevented the collection of hydrographic data on the May 26-27 survey for all collections except for 1-A and 1-B. The most significant variation observed during the 3-6 J:%Water1ProjectFiIesPt 00\\10658 MRI\\10658001-PilgrirO4\\report\\LarvTransRepoctO4f.doc February, 2005

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study was in temperature values. Bottom water temperature obtained from the ADCP instruments fu May survey ranged from 4.2° C at Station B to 10.60 C at Station A. Based on average readings for each station on the June survey, surface water temperatures ranged from 11.3° C at Station B to 15.00 C at Station A. Bottom readings ranged from 4.0° C at Station B to 11.40 C at Station A. Along the sampling transect both surface and bottom water averaged higher at inshore Station A than further offshore, the difference between locations being more pronounced in bottom water due to the increasing depth along the transect. Averaging all bottom temperatures for each survey, the May survey (6.2° C) was cooler than the June survey (6.8° C).

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4.0 DATA ANALYSIS AND ASSESSMENT The data discussed above were analyzed for (1) the percentage of net volumetric flow in nearby coastal Cape Cod Bay waters withdrawn by PNPS and (2) the percentage of winter flounder larvae in the net coastal flow entrained by PNPS. This allows an evaluation of the overall effect of winter flounder larvae entrainment at PNPS.

A separate calculation of the percentage of coastal flow withdrawn and larvae entrained by PNPS was performed for each of the two sampling surveys conducted. In addition, the volumetric flow analysis was performed over the entire monthly period that the hydrodynamic measurements were conducted. The larval analysis was performed for each of the four winter flounder larvae life stages and for total larvae.

Details of the analysis procedures and results are discussed below.

4.1 Volumetric Water Flowrate Analysis In order to correlate the four continuous-depth ADCP stations with the five discrete-depth larvae sampling stations, the ADCP water velocity data was processed in the following manner:

The flow across the transect A-D (from southwest to northeast) was analyzed. At each ADCP station, the water column was divided into three segments based on total depth at the time of the reading: the upper half, from half to three meters above the bottom, and the bottom three meters. The component of the ADCP velocity normal to the transect was averaged over each depth segment of the water column, for each 15-minute ensemble of data. Figure 4-1 and Figure 4-2 contain plots of water depth and the average velocities normal to the transect for ADCP stations A and D and for each depth interval during the two larvae sampling surveys.

For larvae sampling station E, velocities were estimated by taking the average of the transect normal velocities at the adjacent stations ie., E is average of B and C.

The flowrate of water across the transect was then calculated by multiplying each of the transect velocity series by the estimated cross-sectional area of the transect represented by that value. The cross-sectional areas were determined for each segment by multiplying the appropriate water depth interval at the station for that time by one-half of the combined distance to the two adjacent stations.

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In order to correlate the ADCP time series with the discrete larvae sampling events, the ADCP-based water flowrate data was averaged over the duration of each tidal phase. The tidal phase was defined as the time between the maximum and minimum tide heights at the station. The sum of the flowrates during the four tidal phases also was the basis for daily estimates of water flowrate across the study transect.

Table 4-1 compares the daily water flowrates during the sampling events with the average daily water flowrate during the study period. The percentage of the volumetric flow withdrawn by PNPS (with both pumps operating at the rated total maximum of 19.56 m3/s) ranges from 0.02% to 0.03% for the two larvae sampling days.

Table 4-1 Analysis of Net Volumetric Flowrate In Bay Study Area Compared to PNPS Withdrawal

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MayS7.T tu 3-4 72,587 86,141 0.03%

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4.2 Net Larval Transport and Entrainment Analysis 4.2.1 Larval Transport Analysis The flux or transport of winter flounder larvae flowing along the coast was determined for each of the two surveys using larvae density and hydrodynamic measurements. This approach integrated current velocity, water depth and larval stage density over the cross-sectional area of the transect during the time of each tidal phase.

The calculation was performed for each of the four winter flounder larval stages and the total winter flounder larval density at each of the four 6-hour tidal periods that constituted one 24-hour "day". The net larval flux over a given 6-hour tidal period was determined by multiplying the density of larvae (larvae/n 3) times the flowrate of water (m3/s) to yield larvae/second over the 6-hour period. The water column depth intervals were assigned corresponding larvae samples: surface by net, bottom by net, and sled. As noted in Section 2, the sled larvae sampling was incomplete for the first survey, so the bottom net samples were used for the deepest water column interval when sled data was missing. For each study day, the net larval flux was determined by taking the sum of the net larval flux over all the 6-hour tidal periods.

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EN RI 4.2.2 Larval Entrainment Analysis The number of winter flounder larvae entrained by PNPS during both surveys was determined from th station flow rate and the eight larval entrainment samples collected during the day specifically for thig study. The calculation was performed for each of the four winter flounder larval stages, by multiplying thk number of larvae for each stage entrained by the station by the station flow rate for the 6-hour tidal cycE over which the ambient flounder samples were collected. The sum of each of the 6-hour periods became the total entrainment per day.

The percentage of each larval stage entrained was determined by dividing the number of larvae entrainec during the day by the number of larvae carried past the station in the net longshore current (and ther multiplying by 100 to obtain a percentage). The larval entrainment results are presented in Table 4-2. fo the major transect in the study area, A-D.

In general, the results in Table 4-2 indicate that PNPS entrains a very small percentage of the winte flounder larvae in the coastal flow of Cape Cod Bay. These results are similar to those of the larvae transport studies performed in 2000 (ENSR and MRI, 2000) and 2002 (ENSR and MRI, 2003).

Table 4-2 Larval Flux and Entrainment Results Transect A-D

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i. P NPS lLar airi 31,042 37,634 Stage AY' LarvaeldYS 168,609,082 32,366,901

[nonrai ed 0.02 0.12 oNldS Uve da 492,234 705,010

$ae & BayLrvaehday 547,780,748 182,815,242 ntained $.1a0.09 0.39

.NPS Larvielday 2,106,405 2,270,584 Stage ay-L da y 115,972,069 93,189,196

% Entraine d

1.82 2.44 P:NS LavaefdayE 33,259 10,036 S

e w rvalday' 167,656 2,295,983 V lEntrat19.84 0.44 P

fx 2,654,071 3,018,245 t

Bay Wdralay 830,355,922 304,399,510

% Entrined;c 0.32 0.99 Based on this analysis, it is concluded that the percentage of winter flounder larvae transported in coastal Cape Cod Bay waters that is entrained by PNPS may be conservatively estimated at less than one percent. Though the results in Table 4-2 indicate higher entrainment percentages for Stages 3 and 4 larvae, it is likely that the actual entrainment rate for these larval Stages is similar to the total larvae entrainment rate of one percent or less. During Survey 1, the loss of the sled meant that two stations were 4-4 J:%WateraProjectFilesP1uO165MRI\\10658001-PilgrimO4Vrepor1LmNvTransReportO4f.doc February, 200!

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Since the sled samples routinely yielded the highest larvae counts, results for Survey 1 likely underestimate larval flux in the Bay. Also, for Stage 4, since the densities are so low, the change in count by one individual has a disproportionately high effect on densities, and thus on the percent entrained. For example, in Survey 1, 18 total Stage 4 individuals were counted in the PNPS samples, and two total Stage 4 individuals were counted in the net and sled samples in the Bay.

4.3 Entrainment Analysis by Tidal Flushing The spatial arrangement of sampling stations used for the 2004 study enabled an alternative method of calculating larval flux and entrainment. This method was used to determine the total amount of larvae transported by tidal currents into and out of an area defined by one tidal excursion near PNPS, thereby providing a measure of the tidally induced flushing of larvae in the region subject to entrainment by the station. The amount of larvae entrained by PNPS was then compared to this value to obtain an assessment of the entrainment rate compared to larval transport by tidal flushing.

The analysis was performed by the following method:

Determine total volume of water, entering the study area only (i.e., flowing in a southerly direction), across the B-D transect for each of the three depth segments over the two tide cycle P#

"day".

Apportion this total flow volume to each of the five stations according to the area it represents when Thiessen polygons (borders are equidistant from adjacent points) are constructed about the stations, as shown in Figure 4-3.

Multiply each station's fraction of the total flow by the larval density to get number of larvae flushed from the area during the day.

Results of this analysis are presented in Table 4-3 and generally are one to two orders of magnitude less than the transect method presented in Section 4.2.

Table 4-3 Larval Flux and Entrainment Results by Tidal Flushing

_O u r v o y S hou r v e'>,-t 11 y i2 '9S PNP$Larvailay S31,042 37,634 Stae By Lrvelay 5,370,497,708 1,563,085,127

% Entrain ed 0.001 0.002 i

Lrvae tda 492,234 705,010 Stge2.Ba Lrvelay 19,950,035,353 6,724,111,167

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'ay day 2,609,868 46,401,085

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~oal Ba'y a Vaelda 31,870,235,653 14,813,167,928 j

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5.0 CONCLUSION

S EIfCR.

12EMME This was the third larval transport study performed in Cape Cod Bay to examine the key conditions (net water flow and density of winter flounder larvae) affecting the entrainment of winter flounder larvae. These three studies-conducted adjacent to Pilgrim Station in 2000, 2002 and 2004 by ENSR and MRI-were designed to complement each other and were modified as needed, based on the suggestions and comments of federal and state agency reviewers.

They are intended to provide an empirical basis for the conclusion stated in the March 2000 316 Demonstration Report that "there have been no adverse impacts to the integrity of the winter flounder population due to the PNPS thermal discharge or CWIS." (ENSR, 2000)

The results of the 2004 study are similar to those of the previous studies performed in 2000 and 2002.

When viewed together, the significant conclusions are:

There is a consistent net flow of water and winter flounder larvae to the south along coastal Cape Cod Bay in the vicinity of PNPS.

A very small amount - less than 0.1% - of the net volumetric flow of water in Cape Cod Bay passes through PNPS.

The amount of winter flounder larvae in northwest Cape Cod Bay that is entrained by PNPS is conservatively estimated at less than 1 % of the net larval transport.

These findings are consistent with the 316 Demonstration Report, which stated that Pilgrim's potential entrainment impact to the winter flounder population is less than 5%. In fact, based on these results, the potential impact to the winter flounder population (less than one percent) is even smaller than the assessment provided in the 316 Demonstration Report. The clear conclusion is that entrainment at PNPS is minimal, and does not adversely impact the integrity of the winter flounder population.

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6.0 REFERENCES

ENSR and MRI, 2000. Study of Winter Flounder Transport in Coastal Cape Cod Bay and Entrainment at Pilgim NuclearPowerStation. Prepared for Entergy Nuclear Generation Company.

ENSR and MRI, 2002. Study of Winter Flounder Larval Transport in Coastal Cape Cod Bay and Entrainment at Pilgrim Nuclear Power Station. Prepared for Entergy Nuclear Generation Company.

Motoda, S., 1959. Devices of simple plankton apparatus. Memoirs of the Faculty of Fisheries, Hokkaido University 7: 73-94.

Marine Research, Inc., 1986. Winter Flounder early life history studies related to operation of Pilgrim Station-a review 1975-1984. Pilgrim Nuclear Power Station Marine Environmental Monitoring Program Report Series No.2. 111 pp. + appendix.

Van Guelpen, L., D.F. Markle, and D.J. Duggan, 1982. An evaluation of accuracy, precision, and speed of several zooplankton subsampling techniques. International Council for the Exploration of the Sea 40: 226-236.

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