ML13196A189

Email from B. Balsam, NRR to J. Crocker, NOAA Pilgrim: NRC Complete Responses to 4-9-12 Nmfs Questions

ML13196A189
Person / Time
Site:	Pilgrim
Issue date:	04/12/2012
From:	Balsam B A Office of Nuclear Reactor Regulation
To:	Crocker J G US Dept of Commerce, National Oceanographic and Atmospheric Administration
References
FOIA/PA-2013-0135
Download: ML13196A189 (84)

Text

Craver, PattiFrom: Balsam, BrianaSent: Thursday, April 12, 2012 1:01 PMTo: Julie Crocker

Subject:

RE: Pilgrim:

NRC's complete responses to 4-9-12 NMFS questions Attachments:

Normandeau 1977.zipReference 3 of 4.From: Balsam, BrianaSent: Thursday, April 12, 2012 12:56 PMTo: 'Julie Crocker'Cc: Logan, Dennis; Susco, Jeremy; Smith, Maxwell;

'jeganl@entergy.com'

Subject:

Pilgrim:

NRC's complete responses to 4-9-12 NMFS questions Julie,I attached the NRC's completed responses to the questions on Pilgrim that you sent in your April 9email to follow-up on our partial response dated April 10.I will also be forwarding several zip files containing the documents referenced in the responses insubsequent emails. I tried to send them all as one zip folder, but it seems as if my agency's emailattachment size limit is a bit higher than yours-the last email I was able to send, but it came backundeliverable.

All of the references should also be publically available in our ADAMS system also,and I have included the accession number for each in the attached responses, so that would beanother way for you to access those documents if email doesn't work.BrianaBriana A. BalsamBiologist Division of License RenewalOffice of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission 301-415-1042 briana.balsamanrc.pgov

THERMAL SURVEYS OFBACKWASHING OPERATIONS AT PILGRIM STATIONDURING JULY 1977Conducted for.BOSTON EDISON COMPANY800 Boylston StreetBoston, Massachusetts 02199underPurchase Order No. 60107byNORMANDEAU ASSOCIATES, INC.Bedford, New Hampshire 03102August 1977 TABLE OF CONTENTSPAGE1.02.02.12.23.03.13.1.13.1.23.1.33.1.43.1.53.24.04.14.1.14.1.24.1.34.1.3.14.1.3.24.1.3.34.1.3.44.1.3.5ABSTRACT

............

.............

INTRODUCTION

..................STUDY AREA AND STATION CHARACTERISTICS

..THERMAL SURVEYS ............METHODS OF STUDY ..... ...........

...FIELD SURVEYS .........................

TEMPERATURE PROFILING.

.............

CURRENT PROFILING

..................

CONTINUOUS TEMPERATURE MONITORING

.......TIDE OBSERVATIONS

...............

WIND AND AIR TEMPERATURE OBSERVATIONS

.....PLANT OPERATIONS

...............

RESULTS .......................

JULY 9 AND 10 LOW-WATER BACKWASH SURVEY. ....PLANT OPERATION

......................

AMBIENT TEMPERATURE

..................

THERMAL SURVEYS.

.................

Late Ebb (Prebackwash)

-2140 to 0038 EST ....Early Flood (Backwash West Pump)-0039 to 0203 ESTMid Flood (Backwash East Pump)-0204 to 0309 ESTLate Flood (Post Backwash)-0310 to 0415 ESTLate Flood (Survey Complete)-0416 to 0430 EST..e ....IO ....2245* .....52* .....12* .....9.... .11.... ..12... .12... .12.... .14* .....1414.***14......19....26......19.... ..29......314.1.3.6 Summary ..........................

31i PAGE4.1.44.1.54.1.64.1.74.24.2.14.2.24.2.34.2.3.14.2.3.24.2.3.34.2.3.44.2.3.5CURRENTS.

..................AIR TEMPERATURE

........ .... .......WIND CONDITIONS

......... ..............

.TIDES ........ ...............

...JULY. 16 AND 17 HIGH-WATER BACKWASH SURVEY ...PLANT OPERATION

................AMBIENT TEMPERATURE

..............THERMAL SURVEYS ................Late Flood (Prebackwash)

-2302 to 0002 EST.Early Ebb (Backwash West Pump)-0003 to 0139 ESTMid Ebb (Backwash East Pump)-0140 to 0349 ESTLate Ebb (Post Backwash)-0350 to 0517 EST ..Low Water (Survey Complete)-0518 to 0538 EST. *Summary ....................CURRENTS.

...................AIR TEMPERATURE

...........*. ...WIND CONDITIONS

................TIDES ... ...................DISCUSSION.

................. ..PLUME DYNAMICS.

................TEMPERATURE RISES ..........

.............

EFFECT OF WIND ON PLUME MOVEMENT

.... .AMBIENT VARIABILITY

............SUMMlARY AND CONCLUSIONSi

..........REFERENCES.

..................353538383838424242455155576161636363666666'ro96970734.2.3.64.2.44.2.54.2.64.2.75.05.15.25.35.46.07.0ii

... -.... ..- -., .-'. M ., .., -.ý , .ý '- ---.., __ .-., , .ý , '_ _ ___ ...-I C - -...1 --, --.. .... ...... 4 -... ...LIST OF FIGURESPAGE2.1-1. Location map showing Pilgrim Nuclear Power StationUnit 1 and Unit 2 (Proposed) and adjacent coastal.waters.

Pilgrim Station Backwashing

Studies, 1977...9 .03.1-1. Location map showing approximate sampling stationsand in-eitu instrumentation for the backwash surveyof July 9 and 10, 1977. Pilgrim Station Backwash-ing Studies, 1977.. q.. ..........................

3.1-2. Location map showing approximate sampling stationsand in-eitu instrumentation for the backwash surveyof July 16 and 17, 1977. Pilgrim Station Backwash-ing Studies, 1977 ....... ...........3.1-3. Flow chart for processing thermal survey data.Pilgrim Station Backwashing.Studies, 1977 .. .....36710164.1-1* Temperature monitor data from the west pumpwaterbox, the discharge canal and the ambientin-aitu unit at Station 28 during backwashing operations on July 9 and 10, 1977. PilgrimStation Backwashing

Studies, 1977. ..............

4.1-2. Contour maps of observed temperature rises (AT)in degrees F above ambient during late ebb (pre-backwash) at surface and 3.3 ft (1.0 m) on July9 and 10, 1977. Pilgrim Station Backwashing

Studies, 1977 ........184.1-3. Contour maps of observed temperature rises (AT)in degrees at 9.8 ft (3.0 m) and bottom on July9 and 10, 1977. Pilgrim Station Backwashing

Studies, 1977. ........................204.1-4. Temperature data from an anchored survey boat atStation 6 on July 9 and 10, 1977 showing actualtemperatures and corresponding Wt's aboveambient in degrees F. Pilgrim Station Back-washing Studies, 1977. 214.1-5. Temperature data from an anchored survey boat atStation 15 on July 9 and 10, 1977 showing actualtemperatures and corresponding AT above ambientin degrees F. Pilgrim Station Backwashing

Studies, 1977. ...... .....9 .a ........224.1-6. Contour maps of observed temperature rises (AT)tindegrees F above ambient during early flood (backwash westpump) at surface and 3.3 ft (1.0 m) on July 10, 1977.Pilgrim Station Backwashing

Studies, 1977 .........24iii 4.1-7. Contour maps of observed temperature rises (AT) indegrees F above ambient during early flood (back-wash west pump) at 9.8 ft (3.0 m) and bottom onJuly 10, 1977. PIlgrim Station Backwashing

Studies, 1977 ...............

...............

254.1-8. Contour maps of observed temperature rises (AT) indegrees F above ambient during mid flood (back-wash east pump) at surface and 3.3 ft (1.0 m) onJuly 10, 1977. Pilgrm Station Backwashing

Studies, 1977 ....................

..... 274.1-9. Contour maps of observed temperature rises (AT) indegrees F above ambient during mid flood (back-wash east pump) at 9.8 ft (3.0 m) and bottom onJuly 10, 1077. Pilgrim Station Backwashing

Studies, 1977 ..... * .................

..9 ... 284.1-10. Contour maps of observed temperature r~ses (AT)in degrees F above ambient during late flood (post-backwash) at surface and 3.3 ft (1.0 m) on July10, 1977. Pilgrim Station Backwashing Studies,1977...........

.... ... ............................

304.1-11 Contour maps of observed temperature rises (iT)in degrees F above ambient during late flood(postbackwash) at 9.8 ft (3.0 m) and bottom onJuly 10, 1977. Pilgrim Station Backwashing

Studies, 1977. ........... ..... ...................

324.1-12. Contour maps of observed temperature rises (AT)in degrees F above ambient during late flood(survey complete) at surface and 3.3 ft (1.0 m)on July 10, 1977. Pilgrim Station Backwashing

Studies, 1977. ......... ... ....... ...................

334.1-13. Contour maps of observed temperature rises (AT)in degrees F above ambient during late flood(survey complete) at 9.8 ft (3.0 m) and bottomon July 10, 1977. Pilgrim Station Backwashing

Studies, 1977. .....* * * .... .. .. .344.1-14. Vector plots of current measurements in degreestrue (referenced toward which currents wereflowing) and kn from Station 1 (upper) andStation 6 (lower) on July 9 and 10, 1977 ... ... .364.1-15. Air temperature and wind vector plots in degreestrue (referenced from which wind was blowing)and mph from the 3'-t (10 m) level of the BostonEdison Company meteorological tower on July 9 and10, 1977. PIlgrim Station Backwashing

Studies, 1977 .... 37iv 04.1-16. Plot of NOAA-NOS predicted tide elevations for thePilgrim Station area along with NAI tide observations for July 9 to 10, 1977. Pilgrim Station Backwashing

Studies, 1977 * ............

394.2-1. Temperature monitor data from the west pump waterbox, the discharge canal and the ambient Station 28 duringbackwashing operations on July 16 and 17, 1977.Pilgrim Station Backwashing

Studies, 1977. ........414.2-2. Contour maps of observed temperature rises (AT) indegrees F above ambient during late flood (preback-wash) at surface and 3.3 ft (1.0 m) on July 16 and 17,1977. Pilgrim Station Backwashing

Studies, 1977 ..... .434.2-3. Contour maps of observed temperature rises (AT) indegrees F above ambient during late flood (preback-wash) at 9.8 ft (3.0 m) and bottom on July 16 and17, 1977. Pilgrim Station Backwashing

Studies, 1977 ..- .444.2-4. Temperature data from an anchored survey boat atStation 6 on July 16 and 17, 1977 showing actualtemperatures and corresponding AT above ambientin degrees F. Pilgrim Station Backbashing

Studies, 1977. .......................464.2-5. Temperature data from an anchored survey boat atStation 15 on July 16 and 17, 1977 showing actualtemperatures and corresponding AT's above ambientin degrees F. Pilgrim Station Backwashing

Studies, 1977. ......................

474.2-6. Contour maps of observed temperature rises (AT) indegrees F above ambient during early ebb (backwash west pump) at surface and 3.3 ft (1.0 m) on July17, 1977. Pilgrim Station Backwashing

Studies, 1977 .... 484.2-7. Contour maps of observed temperature rises (AT). indegrees F above ambient during early ebb (backwash west pump) at 9.8 ft (3.0 m) and bottom on July17, 1977. Pilgrim Station Backwashing

Studies, 1977....

504.2-8. Temperature profiles from Station 1 during the startof backwashing of the east circulating water pump onJuly 17, 1977. Pilgrim Station Backwashing Studies,1977' ..* 524.2-9. Contour maps of observed temperature rises (AT) indegrees F above ambient during mid ebb (backwash east pump) at surface and 3.3 ft (1.0 m) on July17, 1977. Pilgrim Station Backwashing

Studies, 1977. *

• 53V 4.2-10. Contour maps of observed temperature rises (AT) indegrees F above ambient during mid ebb (backwash eastpump) at 9.8 ft (3.0 m) and bottom on July 17, 1977.PIlgrim Station Backwashing

Studies, 1977. .........

544.2-1l. Contour maps of observed temperature rises UT) indegrees F above ambient during late ebb (postbackwash) at surface and 3.3 ft (1.0 m) on July 17, 1977.Pilgrim Station Backwashing

Studies, 1977. .........564.2-12. Contour maps of observed temperature rises (AT) indegrees F above ambient during late ebb (post-backwash

) at 9.8 ft (3.0 m) and bottom on July 17,1977. Pilgrim Station Backwashlng

Studies, 1977. * .... 584.2-13. Contour maps of observed temperature rises'.(AT)in degrees F above ambient during low water (surveycomplete) at surface and 3.3 ft (1.0 m) on July17, 1977. Pilgrim Station Backwashing

Studies, 1977. 594.2-14. Contour maps of observed temperature rises (AT) indegrees F above ambient during low water (surveycomplete) at 9.8 ft (3.0 m) and bottom on July 17,1977. PIlgrim Station Backwashing

Studies, 1977. ......604.2-15. Vector plots of current measurements in degrees true(referenced toward which currents were flowing) andkn from StatToin--(upper) and Station 6 (lower) onJuly 16 and 17, 1977. Pilgrim Station Backwashing

Studies, 1977. ..... ... ..... .. ........ 624.2-16. Air temperature and wind vector plots in degrees true(referenced from which wind was blowing) and mph fromthe 33 ft (l1ii" level of the Boston Edison Companymeteorological tower on July 16 and 17, 1977.PIlgrim Station Backwashlng

Studies, 1977. ......... 644.2-17. Plots of NOAA-NOS predicted tide elevations for thePilgrim Station area along withNAI tide observations for July 16 to 17, 1977. Pilgrim Station Backwashing

Studies, 1977 ....... .........

..........655.1-1. Photographs of the western portion of the study areain front of the Pilgrim Station intake at high water(upper) and low water (lower).

Pilgrim StationBackwashing

Studies, 1977. .. .............

..67vi ILIST OF TABLESPAGE3.1-1. SPECIFICATIONS FOR INSTRUMENTATION UTILIZED IN THENAI THERMAL SURVEYS AT PILGRIM STATION.

PILGRIMSTATION BACKWASHING

STUDIES, 1977 ...........

.84.1-1. SAMPLING RUNS AND AMBIENT BASE TEMPERATURES FROMSTATION 28 FOR THE JULY 9 AND 10, 1977 LOW-WATER BACKWASH SURVEY. PILGRIM STATION BACKWASHING

STUDIES, 1977.. .......... ............154.2-1. SAMPLING RUNS AND AMBIENT BASE TEMPERATURE FROMSTATION 28 FOR THE JULY 16 AND 17, 1977 HIGH-WATER BACKWASH SURVEY. PILGRIM STATION BACK-WASHING STUDIES, 1977. .................

40vii IPILGRIM STATIONTHERMAL SURVEYS1.0 ABSTRACTTwo weekend surveys of actual backwashing operations at PilgrimNuclear Power Station under varying tidal conditions were conducted byNormandeau Associates, Inc., during July 1977. These surveys documented the spatial extent of the thermal backwash plume within the intake areaand out into Cape Cod Bay. For the first survey on July 9 and 10, 1977,backwashing began at low water and continued into early flood tide. Forthe second survey dated July 16 and 17, 1977, backwashing began at highwater and continued into early ebb tide.Backwashing formed a thermal plume about 5- to 6-ft thick (1.5to 1.8 m) in front of the intake screenwall.

Here, maximum surfacetemperatures of 100.9 F (38.3 C) were observed, representing a &T of43.4 F (24.1 C) above ambient.

The distal edge or frontal zone of theplume spread slowly seaward at about 0.2 kn; where it became thinner andrapidly lost heat by convection to the surrounding waters, dilution andultimate release to the atmosphere.

Along the intake shoreline theplume was often less than 1 ft (0.3 m) thick. Most of the hot water wasdissipated within several hundred feet of the intake with AT's of 10 to15 F (5.6 to 8.3 C) above ambient.

Under the influence of strongsouthwesterly winds during the second survey, some hot water was apparently carried beyond the outer breakwaters into Cape Cod Bay. In summary,the backwashing operation caused a relatively thin thermal plume whichspread rapidly across the western portion of the study area and alongthe outer breakwater.

Within a few hours, it had completely dissipated.

The funding for this study was provided by Boston EdisonCcmpany.

Technical and logistical support was provided by the Environ-mental Sciences Group of the Nuclear Engineering Department and thestaff of the Security and Operations Departments at Pilgrim Station.I

2.0 INTRODUCTION

2.1 STUDY AREA AND STATION CHARACTERISTICS The Pilgrim Nuclear Power Station is located on the shore ofCape Cod Bay in Plymouth, Massachusetts, about 5.5 mi (8.9 km) east-southeast of the Town Center. The site, which is owned and operated bythe Boston Edison Company, now contains a 655 mw light water moderated, boiling water nuclear reactor (Unit 1) with a once-through condenser cooling system. Water used for cooling the condenser is removed fromCape Cod Bay through a shoreline intake (Figure 2.1-1). It enters theintake between two breakwaters via a dredged channel which is about 18to 24 ft deep (5.5 to 7.3 m) at mean low water (IML).Under normal operating conditions, the water is drawn intothe intake by two pumps, circulated through the condenser system anddischarged to a surface canal at a rate of about 510 million gallons/day and a AT (difference between the discharge and intake temperatures) averaging 30.0 F (16.7 C). Unit 1 has a circulating water flow of 690ft 3/sec (cfs) at a maximum temperature rise of 30.0 F (16.7 C) and a.service water flow of 23 cfs at a maximum temperature rise of 15 F or8.3 C (Stone and Webster, 1975). The Unit 1 screenwell contains twocirculating water pumps whose water supply passes under the skimmerwall. Its bottom is about 7.5 ft (2.3 m) below MLW at the front of theintake structure.

Condenser tubes on Unit I can be cleaned by backwashing on a 1-to 2-week interval, depending upon biofouling severity.

Generally 45 to 60 min is required to treat each of the two circulating waterpumps, with elevated temperatures averaging around 100 F (37.8 C).Occasionally the temperatires peak at from 110 F (43.3 C) to 120 F (48.9C) depending upon the amount of heat treating necessary.

Because plantload must be reduced during. backwashing, the operation is generally conducted during off-peak hours late Saturday night and early Sundaymorning.

Figure 2.1-1. Location map showing Pilgrim Nuclear Power StationUnit I and Unit 2 (Proposed) and adjacent coastalwaters, Pilgrim Station Backwashing

Studies, 1977.

ii2.2 THERMAL SURVEYSNormandeau Associates, Inc. (NMAI) was contracted by BostonEdison Company to conduct two thermal surveys of actual backwashing operations during mid suwmmer when ambient water temperatures were ator approximately their annual peaks (NAI, 1977). The purpose of thesurveys.

was to determine the spatial extent in the waters between thetwo breakwaters and out into Cape Cod Bay of the resulting backwashplume under varying tidal conditions.

It was desired to avoid periodsof spring tides when tide ranges are higher than average and periods ofneap tides when tide ranges are lower than average.

In addition, thesurveys were to avoid stormy weather when waves, currents and windscould upset normal backwashing plume dissipative processes

( a con-servative approach).

Two separate thermal surveys were conducted.

The first wasJuly 9 and 10, 1977, during which the backwashing operation began at lowwater. One week later on July 16 and 17, 1977, the second survey wasconducted with backwashing beginning at high water. During both surveys,emphasis was placed on examining the time history of plume build-up anddissipation.

3.0 METHODS OF STUDY3.1 FIELD SURVEYSThermal surveys of actual plant backwashing operations wereconducted overnight during July 9 and 10, 1977 (low-water backwash) aswell as July 16 and 17, 1977 (high-water backwash).

The surveys con-sisted of the following:

3.1.1 TEMPERATURE PROFILING During both nights a series of four basic thermal surveys wereconducted throughout the entire study area. Approximate sampling locations for July 9 to 10, 1977 are shown in Figure 3.1-1. Sampling locations for July 16 to 17, 1977 are shown in Figure 3.1-2. Actual samplingstations for specific surveys are indicated in the respective figures inSection 4.0. Each survey was conducted as rapidly as possible to providequasisynoptic temperature distributions in the study area.At each given station depth-temperature profiles were obtainedwith an NAI Model 3100-TD profiling system. Data were directly recordedon a Houston Instruments Model 2000 X-Y recorder.

The rapid responsetime of the system allowed complete profiles to be obtained from surfaceto bottom at each station over a 30-to 45- sec period. Instrumentation specifications are given in Table 3.1-1. Actual plots were field anno-tated as to station number, time (Eastern Standard was used throughout) and range distances to navigational transponders.

Precision locationdata for each station were obtained with a Motorola Mini-Ranger III andonboard printer using two transponders placed on shore. One transponder was located at the east end of a footbridge over the discharge canal,the other was located on top of the seawall near the old barge landingsite (Figures 3.1-1 and'3.1-2).

Supplemental temperature profiles were obtained each nightfrom small boats anchored along the axis of the dredged intake channel Figure 3,1.1.Location map showing approximate sampling stationsand in-situ Instrumentation for the backwash surveyof July 9 and 10, 1977. Pilgrim Station Backwash.

ing Studies, 1977.

E5(6 IE6000Figure 3Ml-2,Location map showing approximate sampling stationsand Instrumentation for the backwash surveyof July 16 and 17, 1977, Pilgrim Station Backwash-ing Studies, 1977.

TABLE 3.1.1M SPECIFICATIONS FOR INSTRUMENTATION UTILIZEO IN THE HAI THERMAL SURVEYSAT PILGRIM STATION.

PILGRIM STATION BAC(WASHING STUrIES9 1977.No) WMN bpti1k11 0.Od4 %a to Iku I w1 0s.01 W )Idi. Wtait dw M4.y. *od-of holak 061291remt low iinwua To vim pwtwit~~rc f III I"1 man 16 4"i WtiMNlift kw ALh1 A W 3mdyita wI ww-Rk -N --wo5mmM1 RO bpt~nbw*

0 /1 17/i *ZNC/III N4m Hca2ima "AmuIroflut" ilatm li f dtuul 0A 0 to 40C i 0.09 K"I~ 1001110Up I lowPAh~ 0 atoaN t s ,I It 1-1 V/A clacilus ba IwN,alA1 oil 1) lptvmti M "am O4l3RuwU~~01 bidq ~itjqlo III townE hoflwerrin PIR/t W" Wo 402 0 CtasAllIfitil pisii tatt 9(Figures 3.1-1 and 3.1-2). Observers in each boat used NAI Model 631digital thermometers to obtain profiles from surface to bottom every 10min. in general, sampling depths were surface, 1.6 ft (0.5 m), 3.3 ft(1.0 m), and thereafter every 3.3 ft (1.0 m) to bottom. Data wererecorded on HAI Form PS-121, Physical Sciences Hydrographic Data Sheet,in accord with NAI Physical Sciences Data Processing Technical Pro-cedures Manual 5.0 (NAI, 1976a).During mobilization prior to the surveys and demobilization following the surveys, all of the instruments were calibrated as appro-priate in accord with HAI Technical Procedures Manual 3.0 (NlA, 1976b)Supplemental reference checks were made for each temperature instrument in the field prior to the surveys using a large barrel of sea water andprecision grade mercury thermometers.

All calibration data and supporting paperwork were reviewed and audited independently by N1h's QualityAssurance Director in accord with Company procedures and Technical Procedures Manuals (NAI, 1976c).Data were processed as shown in Figure 3.1-3. once field datawere keypunched, listed, edited and verified, observed temperatures weretransformed to true temperatures by means of appropriate regression equations from calibration data for each respective field instrument.

Finally using measurements from ambient near-bottom waters at Station 28(mid channel between the two breakwaters as in Figures 3.1-1 and 3.1-2),a delta-T or approximate temperature rise above ambient was calculated for each temperature measurement.

For ease in report preparation, thecomputer converted all depth data to both ft and m and temperature datato both F and C, regardless of which units were originally input.3.1.2 CURRENT PROFILING At selected stations during both surveys (Figures 3.1-1 and3.1-2) current profiles were obtained from near surface to near bottomusing Bendix Model Q-2S ducted impeller current meters and Model 270recorders.

During mobilization prior to the surveys and demobilization 10Figure 3.1-3.Flow chart for processing thermal survey data.Pilgrim Station Backwashtng

Studies, 1977.

following the surveys, all of the instruments were calibrated as appro-priate in accord with NAI Technical Procedures Manual 3.0 (NAX, 1976 b).Supplemental reference checks were made in the field prior to the surveys.Complete instrumentation specifications are given in Table 3.1-1.Data were recorded on strip charts and annotated as appropriate along with visual observations of ambient wind conditions and flowpatterns.

The primary survey vessel collected data from a number ofmid-channel stations.

The small boat anchored closest to the intakenear Station 6 collected data from various depths at a single location.

The strip charts were manually time based and reduced.

Directional datawere converted to degrees true (referenced toward which the current wasflowing) and depicted vectorially.

3.1.3 CONTINUOUS TEMPERATURE MONITORING During each overnight survey an In-situ NAI temperature monitorwas deployed about 3.3 ft (1.0 m) above the bottom at Station 28. Itspurpose was to obtain continuous ambient temperature data from waterswhich would be unaffected by backwashing operations.

A second MA temperature monitor was deployed at the plant.One thermistor was positioned about 3.3 ft (1.0 m) below a styrofoam float inside the waterbox of the west circulating water prop. It wasset for a range of 70 to 120 F (21.1 to 48.9 C) to document actual timesand temperatures of backwashing.

The other thermistor was attached toconcrete blocks and submerged in the discharge canal. It was set for arange of 50 to 120 F (10.0 to 37.8 C) to document normal plant discharge temperatures in real time. Both channels of data were input to aRustrak Model 2133 DC strip-chart recorder with a time sharing featurefor maximum data resolution.

Actual deployment locations for these temperature monitors areshown in Figures 3.1-1 and 3.1-2. Instrumentation specifications aregiven in Table 3.1-1. During mobilization prior to the surveys and de-12mobilization following the surveys, all of the instruments were cali-brated as appropriate in accord with NAT Technical Procedures Manual3.0 (NAI, 1976b).Data were recorded on strip charts. The strip charts weremanually time based using start times, 3-hr timer marks, and end times.Data were manually reduced to obtain readings every 10 min.3.1.4 TIDE OBSERVATIONS During both surveys visual observations of tide elevation atthe intake screen wall were made using the large tide staff locatedbeside the plant access ladder (Figures 3.1-1 and 3.1-2). In general,readings were made each time station 1 was occupied.

Resulting datawere plotted to the same scale as the National Oceanic and Atmospheric Administration

-National Ocean Survey tide predictions (NOAA-NOS, 1977).3.1.5 WIND AND AIR TEMPERATURE OBSERVATIONS During both surveys visual observations of wind conditions andperiodic readings of air temperature were made from the main surveyvessel. Hourly average measurements of wind speed, wind direction andair temperature from the 33-ft (10-m) level at the 160 ft (48.8 m) me-teorological tower east of Pilgrim Station (Figure 2.1-1) were obtainedfrom Boston Edison Compeny.3.2 PLANT OPERATIONS The plant backwashing operation was scheduled to begin ateither low water (July 9 and 10) or at high water (July 16 and 17).Backwashing is accomplished by operating a single circulating waterpump, completely closing the discharge valves at each outlet water box,and operating the crossover valve connecting the discharge water boxes.

I--, I-I.- -I-.----.-.---

Circulating water will flow naturally through one side of the condenser, cross over, and flow in the reverse direction through the other side,discharging back to the intake structure through the idle circulating water pump. Generally, 45 to 60 min is required to treat each sideof the condenser.

Plant temperature measurements and operational datafrom the backwashing were obtained from Boston Edison Company..rpIIir j 144.0 RESULTS4,1 JULY 9 AND 10 LOW-WATER BACKWASH SURVEY4.1.1 PLANT OPERATION This backwash survey consisted of five sampling runs keyed toactual plant operations (Table 4.1-1 and Figure 4,1-1). First, plantload was gradually brought down, resulting in temperatures in the dis-charge canal decreasing from 87 F (30.6 C) to 74.6 F (23.6 C). Next,Pump B (west) associated with water boxes 1-2 and 1-4, was backwashed from about 0030 to 0119 EST. The in-situ temperature monitors recordeda sudden sharp rise in discharge temperature to about 83 F (28.3 C) thena sharp drop to about 65.3 F (18.5 C). Simultaneously, water box temp-eratures rose sharply to about 104 F (40.0 C) and were sustained formuch of the backwashing period. As backwashing of Pump B neared completion, discharge temperatures rose again to 83.2 F (28.4 C) and water boxtemperatures dropped back down to below 70 F (21.1 C). From about 0150to 0227 EST Pump A (east) associated with water boxes 1-1 and 1-3 wasbackwashed in a similar manner with backwash temperatures about the samefor both pumps. During this backwashing, discharge temperatures droppedto about 70.6 F (21.4 C), then rose to 87 F (30.6 C) for a short time,dropped back down to about 75 F (23.9 C), and then gradually started torise back toward normal operational levels (Figure 4.1-1).4.1.2 AMBIENT TEMPERATURE In any study of power plant thermal effects, "many different approaches can be taken to define what "ambient" temperature (temperature of surrounding waters that are essentially unaffected by the plant) actuallyis. For example, one could use seasonal mean temperatures, monthly meantemperatures, weekly mean temperatures, daily mean temperatures, or evenhourly mean temperatures from whatever location and depth deemed appropriate.

The rationale for determining ambient temperature for this and the subsequent TABLE 4.1-1. SAMPLING RUNS AND AMBIENT BASE TEMPERATURES FROM STATION 28 FOR THE JULY 9 AND 10, 1977LOW-WATER BACKWASH SURVEY.AMBIENT BASE AMBIENT TEMPERATURE RANGETEMPERATURE MAXIUM MINIMSAMPLING SAMPLINGRUN TIDE STAGE (PLANT STATUS) INTERVAL; EST F C F C F C1 Late ebb (Pre-bacvash) 2140 to 0038 52.0 11.1 58.0 14.3 49.0 9.42 Early flood (Backwash West Pump) 0039 to 0203 57.2 14.0 57.9 14.4 56.0 13.33 Kid flood (Backwash East Pump) 0204 to 0309 57.6 14.2 59.0 15.0 57.0 13.94 Late flood (Post backwash) 0310 to 0415 60.3 15.7 60.5 15.8 59.6 15.35 Late flood (Survey complete) 0416 to 0430 60.3 15.7 60.4 15.7 60.2 15.6 110-100-90-I ~I II II II I-40-73-30LL.w80-70-U-25~w.2 iu'I/60-AHBIENTSTATION 28BACKWASHING 10-5WESTPUMPEASTPUMP40-iJULY 9TIME, ESTI I I I I'34JULY 10Figure 4.1-1.Temperature monitor data from the west pump waterbox, the discharge canaland the ambient in-.itu unit at Station 28 during backwashing operations on July 9 and 10, 1977. Pilgrim Station Backwashing

Studies, 1977, 17July 16 and 17 survey was as followss First an area which was well awayfrom the intake but close enough to still be source water for the powerplant intake was selected.

It had to be an area which presumably wouldnot be influenced by either backwashing or the discharge plume. Accord-ingly Station 28 in the middle of the dredged channel between the endsof the breakwaters was selected (Figure 3.1-1). Here an in-situ tempera-ture monitor was deployed at about 3 ft (0.9 m) above the bottom inorder to obtain a continuous temperature record throughout the survey.Data taken for the duration of each run were averaged to obtain anambient base temperature for that run (Table 4.1-1). This ambient basetemperature was used as an input to the computer and the resulting ATabove or below ambient at each sampling point was calculated.

For this survey the ambient temperature started around 49 to50 F (9.4 to 10. C). The ambient temperatures increased to about 58 F(14.4 C) around low water at 0030 EST (Figure 4.1-1). Throughout therest of the night, ambient temperatures continued to rise slowly,reaching about 60 F (15.6 C) by the end of the survey. This rise may re-present some recirculation of the discharge plume toward the intake areain response to local winds and coastal currents.

4.1.3 THERMAL SURVEYS4.1.3.1 Late Ebb (Prebackwash)

-2140 to 0038 ESTThe prebackwash survey during late-ebb was conducted from 2140EST on July 9 through 0038 EST on July 10, 1977. Once all stations hadbeen sampled, the survey boat returned to Station 1 at the intake andawaited start of backwashing.

Surface temperatures showed rises (AT)above ambient (52.0 F or 11.1 C) ranging from 9.1 F (4.1 C) near thedischarge to 4.9 F (2.7 C) at Station 3 (Figure 4.1-2). Apparently themain part of the discharge plume missed Station 30. Note that this figure(and all subsequent ones like it) shows the configuration of the shoreline in front of the plant, the breakwaters which form the intake area and theapproximate limits of water at each of the various sampling depths.

g 16J PILGRIM STATION THERMAL SURVEYDATE: 7-9.10-77 TIM[I 2140-0038 TRUEDEPTH: SURFACE TIDE: LATE ENH.9.1- O '/*8~ \3?OI1Ni*0'49*N1~o-LIMIT OWATER DEPTH .4 UM LrMIT OF WATER DEPTHNI' "a SCALE, FT.IS e IEl PILGRIM 000* NIT'I S'TATION 6 "c£ 5 0 00- 3 ..C6 L _ M .0 0ESOOPiLGRIM STATION THERMAL SURVEYDATE: 7.9.10-77 TIME: 2140-0038 TRU1OEPTH-.3,3(lm)

TIDE. LATE EBB PLANT* NORTH"/ */4 OI 9"9.6 .~~7.3/ '".9 & /"84NI11000-/

LIMITOFNIT WATER DEPTH.- , 5 .LIMIT OF WATER DEPTHUNI'I r.3 SCALE FT.ISCHAROE N1 l t PILGRIM "0 6Figure 4.1-2. Contour maps of observed temperature rises (aT)in degrees F above ambient during late ebb (pre-backwash) at surface and 3.3 ft (1.0 m) on July9 and 10, 1977. Pilgrim Station Backwashlng

Studies, 1977.

19Slightly deeper at 3.3 ft (1.0 M), AT's ranged from 9.6 F (5.3 C) nearthe discharge to 3.7 F (2.1 C) at Station 6 (Figure 4.1-2). At 9.8 ft(3.0 m) AT's were 6.8 and 7.5 F (3.8 and 14.2 C) due to drawdown at theintakei AT's ranged from 0.5 to 5.3 F (0.3 to 2.9 C) along the dredgedchannel, and ranged from 5.9 to 8.4 F (3.3 to 4.7 C) outside the break-waters (Figure 4.1-3). At the bottom, *tepeeature AT's were 3.4 to 4.6F (1.9 to 2.6 C) at the intake, but were 0Qornegative along the channel.Note that 0 or negative AT's are always shown with a dot pattern.

Out-side the breakwaters they ranged from 1.0 to 6.1 F (0.6 to 3.4 C)..Consistent with the survey vessel data, measurements at Station6 (Figure 3.1-1) showed the surface AT's of 9.3 F (5.2 C) gradually droppingto 7.5 F (4.2 C). These AT's corresponded to actual temperatures of61.2 F (16.2 C) and 59.5 F (15.3 C) respectively (Figure 4.1-4). Near-bottom temperatures started with a AT of 2.7 F (1.5 C) and then becamenegative, corresponding to actual temperatures of 54.6 F (12.6 C) downto 51.8 F (11.0 C).Further away from the intake at Station 15 (Figure 3.1-1) asimilar pattern was observed (Figure 4.1-5). Surface AT's went from 8.5to 6.4 F (4.7 to 3.6 C), corresponding to actual temperatures of 60.5 to58.7 F (15.8 to 14.8 C). Along the bottom the AT's were all negative(down to 2.0 F or 1.1 C), corresponding to actual temperatures of 49.8to 53.0 F (9.9 to 11.7 C).4.1.3.2 Early Flood (Backwash West Pump)-0039 to 0203.ESTAt about 0030 EST backwashing started on the west circulating water pump. The first visible evidence was a sudden rush of hot, turbulent water whose presence was marked by foam and a steamy vapor right in frontof the intake. As the backwashing progressed, the hot water formed asurface layer about 5 ft (1.5 m ) thick in front of the intake screenwall, reaching temperatures as high as 100 F (37.8 C). This layer formed adistinct frontal zone with ambient Cape Cod Bay waters. The frontal zonemoved slowly as a concentric ring northward (or seaward) away from the 20Figure 4.1-3.Contour maps of observed temperature rises (AT) indegrees F above ambient during late ebb (preback-wash) at 9.8 ft (3.0 m) and bottom on July 9 and10, 1977. Pilgrim Station Backwashing

Studies, 1977.

21BACKWASHING 6WSWILuU-,<,0-TIME, ESTU)cc-5-6-701L2-5-6ý-70 6 1TIME, ESTJULY 9JULY 10Figure 4.1-4.Temperature data from an anchored survey boat atStation 6 on July 9 and 10, 1977 showIng actualtemperatures and corresponding

&T 's aboveambient in degrees F. Pilgrim Station Back-washing Studies, 1977.

22BACKWASHJ N1WEST ES05'WLJIU)W~I-WLu'CALULaU5I!TIME, EST-O0-5-.-1K 2F10-I-UJIL.-3 ULi15-2021-6ý-7.TIMTIME, EST4%JULT VJULY 10Figure 4.1-5.Temperature data from an anchored survey boat atStation 15 on July 9 and 10, 1977 showing actualtemperatures and corresponding OT's above ambientin degrees F. Pilgrim Station Backwashing

Studies, 1977.

23intake, bulging in the middle and slightly restrained along shore due tofrictional effects.

The water temperatures in the near-surface thermalplume gradually decreased with distance away from intake and time, dueto evaporative heat loss and dilution (mixing with ambient waters).At the surface,#AT's of 42.1 F (23.4 C) in front of the westpump and 24.8 F (13.8 C) in front of the east pump were observed (Figure4.1-6). Within less than 100 ft (30.5 m), the AT from the western puwpwas 28 F (18.6 C) or less. High AT water hugged the outer breakwater, apparently as a possible consequence of the southwesterly winds whichwere blowing at the time (refer ahead to Figure 4.1-15).

Surface AT'sof 10 F (5.6 C) and greater were confined to the western third of thearea between the breakwaters.

The remainder of the area experienced AT'S equal to or colder than observed prior to backwashing (Figure 4.1-2). At the 3.3 ft (1.0 m) depth AT's were 23.4 to 24.3F(13.0 to 13.5 C)in front of the intake. Within less than 200 ft (61 m) they were downto 18.2 F (10.1 C)l beyond that distance they were 14.8 to 6.7 F (8.2 to3.7 C). Near the outer end of the breakwaters AT's were 2.4 to 3.3 F(1.3 to 1.8 C).At 9.8 ft (3.0 m), AT's were 4.6 F (2.6 C) or less in front ofthe intake and 1.2 to 2.1 F (0.7 to 1.2 C) along the dredged channel(Figure 4.1-7). Along the bottom all of the AT's were negative, orcolder than conditions at the outer end of the breakwaters.

maxiizm-values were -4.4 F (-2.4 C) at Station 6.The continuous profiles at Station 6 showed that the back-washing from the western pump formed a distinct slug or pulse of hotwater along the surface and extended down to about 7 ft (2.1 m). Theheated effluent apparently took about 15 min to reach and about 75 minto pass the anchored boat (Figure 4.1-4) as it progressed seaward.Maximum observed AT at the surface was 22.6 F (12.5 C) which represented an actual temperature of 79.0 F (26.1 C). Near-bottom temperatures were53.4 to 56.2 F (11.9 to 13.4 C) which represented negative AT's of upto -4.7 P (-2.6 C).

24Figure 4.1-6.Contour maps of observed temperature rises (AT) indegrees F above ambient during early flood (backwash westpump) at surface and 3.3 ft (1.0 m) on July 10, 1977.Pilgrim Station Backwashing

Studies, 1977.

I25diFigure 4.1-7.Contour maps of observed temperature rises (AT) indegrees F above ambient during early flood (back-wash west pump) at 9.8 ft (3.0 m) and bottom onJuly 10, 1977. Pilgrim Station Backwashing 26Further away at Station 15 a similar slug of backwash waterwas observed (Figure 4.1-5). It was slightly colder than what wasObserved at Station 6 (maximum temperature 77.0 F or 25.0 C representing a 19.8 F or 11.0 C AT). In addition this plume was thinner (only about3.3 ft or 1.0 m). It took about 30 min from the start of backwashing toreach the anchored boat and about 45 min to pass. Near-bottom temperatures remained cold (49.8 to 55.0 F or 9.9 to 12.8 C), showing negative AT'sas low as -7.4 F or -4.1 C.By about 0119 EST backwashing of the west pump was complete.

4.1.3.3 Mid Flood (Backwash East Pump)-0204 to 0309 ESTAt about 0150 EST backwashing of the east circulating waterpump started.

As before, there was a sudden surge of hot, turbulent andsteam water at the surface; within minutes a thin thermal plume and adistinct frontal zone was observed to be moving seaward.At the surfaceeAT's of 43.4 F (24.1 C) and 23.9 F (13.3 C)occurred in front of the east and west pumps respectively (Figure 4.1-8). This was essentially the same as during backwashing of the west pump(Figure 4.1-6). Surface AT's were generally 20 F (11.1 C) and more acrossthe western third of the study area; the middle third was 10 to 20 F (5.6 to11.1 C)l and the eastern third 5 to 10 F (2.8 to 5.6 C). As before, thehighest temperatures were along the outer breakwater.

At 3.3 ft (1.0 m)AT's were 15.5 to 23.4 F (8.6 to 13.0 C) next to the intake and gradually decreased seaward to 1.9 F or 1.0 C at Station 27.At 9.8 ft (3.0 m) there was no evidence of the backwash plume(Figure 4.1-9). Observed AT's ranged from 1.2 to 3.3 F (0.7 to 1.8 C).Along the bottom AT's remained negative and actually increased in thenegative sense from earlier in the evening (down to -4.9 F or -2.7 C).At Station 6 the second backwash manifested itself as anotherpulse of hot water, warmer than before (up to 81.1 F or 27.3 C), butslightly thinner and not lasting as long (Figure 4.1-4). This plume wasrepresented by AT's of up to 23.5 F (13.1 C) at the surface.

Apparently 27Figure 4.1-8.Contour maps ofdegrees F abovewash east pump)July 10, 1977.C4.,A4...E Ifl7observed temperature rises (AT) inambient during mid flood (back-at surface and 3.3 ft (1.0 m) onPilgrm Station Backwashing IiIi28PILGRIM nTAnOt THERMAL SURVEIDATE: 7-10-77 TIM& 0204-0309 DEPTha 9.O'(MTIDE; HI0 FLOODFigure 4.1-9.Contour maps ofdegrees F abovewash east pump)July 10, 1077.Studies, 1977.observed temperature rises (aT) Inambient during mid flood (back-at 9.8 ft (3.0 m) and bottom onPilgrim Station Backwashing 29it took about 10 to 15 min for this second plume to reach the anchoredboat, but its effects were only seen for about 60 min. By the time theplume had passed, it was only about 1 to 2 ft (0.3 to 0.6 m) thick.Near-bottom temperatures showed little change, ranging from 54.1 to 56.2F (12.3 to 13.4 C) and representing negative AT's (down to -3.4 F or -1.9 C).At Station 15 a second pulse of hot water from backwashing theeast pump was observed.

As before, it took about 30 min for the thermalplume to reach this location.

It was colder than the first pulse (maximumtemperature of 75.8 F or 24.3 C), thinner (only about 2 to 3 ft or 0.6to 0.9 m) and persisted for about 45 min. Near-bottom temperature dis-tribution remained unchanged.

By about 0227 EST backwashing of the east pump was complete.

4.1.3.4 Late Flood (Post Backwash)-0310 to 0415 ESTBy the time this survey began, all backwashing had been completed for the night. The intake was again drawing water in from Cape Cod Bayand the thermal effluent was being discharged via the canal. Surfacetemperatures dropped dramatically from those of the previous hour,reflecting the rapid dissipation of backwash heat (Figure 4.1-10).

Thehighest AT's were 11.4 F (6.3 C) at Station 1 and 9.6 F (5.3 C) atStation 2, both adjacent to the-intake.

At Stations 3,4, 6 and 7, inthe western portion of the study area, AT's were actually negative

(-1.0 F or-0.6 C). Elsewhere#AT's ranged from 1.5 to 5.3 F (0.8 to 2.9 C)with no residual pockets of hot water. Slightly deeper at 3.3 ft (1.0m), the general temperature distribution was essentially the same as atthe surface.

It should be noted that by this t3ime, strong winds fromthe northwest made offshore waters very rough (refer ahead to Figure4.1-15).At the 9.8 ft (3.0 m) level AT's were negative throughout thewestern half of the study area (up to -1.5 F or-0.8 C at Station 4) and0 to 1.3 F (0 to 0.7 C) out to and beyond the breakwaters (Figure 4.1-LI30tFigure 4.1-10.Contour maps of obse'rved temperature rises (aT)in degrees F above ambient during late flood (post-backwash) at surface and 3.3 ft (1.0 m) on July10, 1977. Pilgrim Station Backwashlng Studies,1977.

3111). Along the bottom AT'S were even lower, ranging from -2.2 to-4.4 F (-1.2 to -2.4C) and essentially 0 at the outer end of the channel.These temperatures were quite similar to bottom conditions earlier in thenight from 0204 to 0309 EST (Figure 4.1-9).Once backwashing had been completed,water at Station 6 cooledIV off quickly (Figure 4.1-4). Surface temperatures dropped about 10F (5.6 C) to 60.9 F (16.1C) in less than an hour; whereas, bottomtemperatures held between 55.0 and 57.0 F (12.8 and 13.9 C), represent-ing AT's of down to -4.6 F (-2.6 C).At Station 15, the water temperature also dropped quickly,reaching ambient levels or colder around 0330 EST (Figure 4.1-5).Thereafter, both surface and bottom temperatures gradually rose a fewdegrees, 63.3 F (17.4 C) and 56.2 F (13.4 C) respectively.

4.1.3.5 Late Flood (Survey Complete)-0416 to 0430 ESTBy this time normal plant operations had resumed and alltraces of hot water from backwashing were gone. At the surface, AT'swere 1.0 to 2.6 F (0.6 to 1.4 C) in front of the intake and 0.6 and 3.1F (0.3 to 1.7 C) further out at Stations 6 and 15 respectively (Figure4.1-12).

At 3.3 ft (1.0 m) AT'S were 0.6 to 1.7 F (0.3 to 0.9 C).Deeper down at 9.8 ft (3.0 m) ATWe were all negative, ranging from -0.6to -1.5 F or -0.3 to -0.8 C (Figure 4.1-13).

Finally along the bottomeven greater negative AT's of -4.0 F (2.2 C) were observed.

4.1.3.6 SummaryThe elevated surface temperatures from the backwashing operation persisted for about 2 to 2.5 hrs in the western portion of the studyarea and even less in the eastern portion, before being completely dissipated.

32Figure 4.1-11Contour maps of observed temperature rises (AT)in degrees F above ambient during late flood(postbackwash) at 9.8 ft (3.0 m) and bottom onJuly 109 1977. Pilgrim Station Beckwashing

Studies, 1977.

33Figure 4.1-12.Contour maps of observed temperature rises (&T)in degrees F above ambient during late flood(survey complete) at surface and 3.3 ft (1.0 m)on July 10, 1977. Pilgrim Station Backwashtng

Studies, 1977.

34Figure 4.1-13.Contour maps of observed temperature rises (AT)in degrees F above ambient during late flood(survey complete) at 9.8 ft (3.0 m) and bottomon July 10, 1977. Pilgrim Station Backwashlng.

Studies, 1977.

354.1.4 CURRENTSFlow patterns in the study area during the course of the July9 and 10, 1977 survey were dominated by plant operation (Figure 4.1-14).In this figure, current vectors have been plotted relative to the in-stantaneous water surface, showing the direction toward which currentswere flowing.

At Station 1 adjacent to the intake and at Station 6about 200 ft away, flows were southwestward or into the plant at 0.1 to0.25 kn during the study period, except for during actual backwashing.

Backwashing caused a shearing in the water column, with near-bottom currents continuing to flow toward the intake and near-surface currentsof up to 0.3 kn flowing seaward.

Once the backwash plume was established, continued pumping carried it away from the plant.Current-meter data from other locations further seaward alongthe dredged channel showed near-surface flows in toward the plant through-out the night except during actual backwashing.

The backwashing operation formed a seaward flowing near-surface layer which gradually spread awayfrom the plant, entraining ambient waters and leasing out progressively

thinner, the further it was carried.

Near-bottom flows remained intoward the plant throughout the night.4.1.5 AIR TEMPERATURE Air temperature measurements at the 33-ft (-i-m) level onBoston Edison Company's 160 ft (48.8 m) meteorological tower (Figure2.1-1) showed a gradual late afternoon warming trend to a peak of 73 F(22.7 C) around 1800 EST (Figure 4.1-15).

Then temperatures cooledslightly to 70 F (21.1 C) before a rapid drop from midnight to 0400 ESTwith a leveling off to about 63 F (17.2 C).

S. .-. '...~.......

36I-WLL0)Lu=WUwULCCr-tn3CLUa.JULY 9 JULY 100-5-15-N, TRUE-0-1-a."3Q)-5-6-7$40 ý -" ýAl0 .i t3 Knt t LI ---I0JULY 9 TIME, ESTIJULY 10Figure 4.1-14.Vector plots of current measurements in degrees true(referenced toward where currents were flowing andkn from Stattffn"(upper) and Station 6 (lower) onJuly 9 and 10, 1977. Pilgrim Station Backwashlng

Studies, 1977.

a ft --*AIR EV1EfATyRE U..1'-IJJ,0..IJJI.-205WI.5J-11K/N, TRUE(DIRECTION FROM)0 5 .10MPH12 14 16 18 20 22 24 4 6 8 10 2TIMJULI IL aIij 0JULY 1.0Figure 4.1-15,Air temperature and wind vector plots In degreestrue (referenced f which wind was blowing)and mph from the 33 ft (10 m) level of the BostonEdison Company meteorological tower on July 9 and10, 1917. Pilgrim Station Backwashing

Studies, 1977.w'.4 38I4.1.6 WIND CONDITIONS.

Wind speed and direction measurements at the 33-ft (10-m) levelon Boston Edison Company's 160 ft (48.8 m) meteorological tower showed apronounced change during the night (Figure 4.1-15).

During the late after-noon and evening of July 9, 1977, winds were from the southwest at 8 to10 miles per hour (mph). From midnight to 0200 EST they swung around tonorthwest, then started blowing stronger at 11 to 14 mph. As the night pro-gressed, the winds became more northerly and seas outside the breakwater became very choppy. Wind stress may have helped force the backwash plumealong the outer breakwater during the early flood survey (Figure 4.1-6)l butduring the rest of the survey, the outer breakwater apparently providedsufficient shelter to negate any effects of the onshore winds.4.1.7 TIDESThe tide observations showed good agreement with NOAA-NOS tidepredictions (Figure 4.1-16).4.2 JULY 16 AND 17 HIGH-WATER BACKWASH SURVEY4.2.1. PLANT OPERATION One week after the first survey, a second survey under different tidal conditions was conducted.

As before, this backwash survey consisted of five sampling runs keyed to actual plant operation (Table 4.2.1 andFigure 4.2-1). Plant load was gradually brought down, resulting in alowering of temperatures in the discharge canal from about 84 F (28.9 C)to about 74 F (23.3 C). The western pump (B) was backwashed from about2350 to 0113 EST. The In-situ temperature monitor in the discharge canal showed a gradual lowering of discharge temperature to about 73 F(22.8 C), then a sudden short peak at the end of backwashing to 80 F(26.7 C; Figure 4.2-1). simultaneously, the waterbox temperature rosesharply to about 97 F (36.1 C). Toward the end of the 73-min backwash 3910-6-4-0NOAA-NOS PREDICTED TIDE ELEVATION 2C-,-1-0NAI,OBSERVATIONS MLWU. UII II I16 isTIME,4E2EST4JL6 8JULY 10HI II l!JULY 9JFigure 4.1-16.Plot of NOAA-NOS predicted tide elevations for thePilgrim Station area along with NAI tide observations for July 9 and 10. 1977. Pilgrim Station Backwashing

Studies, 1977.

TABLE 4.2-1. SAMPLING RUNS AND AMBIENT BASE TEMPERATURES FROM STATIO-N 28 FOR THE JULY 16 AND 17, 1977HIGH-WATER SURVEY,AMBIENT BASE AMBIENT TEMPERATURE RANGETEMPERATURE MAXIBM MINIMUMSAMPLING SAMPLINGRUN TIDE STAGE (PLANT STATUS) INTERVAL; EST F C F C F C1 Late flood (Pre backwash) 2302 to 0002 53.6 12.02 Early ebb (Backwash West PwV) 0003 to 0139 54.7 12.63 Mid ebb (Backwash East Pump) 0140 to 0349 51.6 10,9 No Data Available 4 Late ebb (Post backwash) 0350 to 0517 52.5 11.45 Low water (Survey complete) 0518 to 0538 52.5 11.40 110"100-90-fiNTAVIAI'S "A!-40-35U-25*1IU-w80-70-60-5AMIENTSTATION 28IBACKWASHING II IIWEST EASTPH~ PH,-15I II I i22 23 24JULY 161TIME, EST12334415JULY 17Figure. 4,2.1,Temperature monitor data from the west pump waterbox, the discharge canaland the ambient Station 28 during backwashing operations on July 16 and 17,1977. Pilgrim Station Backwashlng

Studies, 1977.

42cycle, temperatures peaked at 107 F (41.7 C). The jump in discharge temperature is attributed to the short period of normal pumping beforebackwashing began on the east pump (A) at about 0159 EST. After about68 min of backvashing on this pump, the plant resumed normal operations (around 0307 EST) and discharge temperatures increased to around 80 F(26.7 C). Backwash temperatures were about the same for both pumpsIhowever, this series of. backwashes lasted 20 to 25 min longer than res-pective ones the week before. The time extension of the backwash periodis attributed to increased fouling of the condenser tubes,4.2.2 AMBIENT TEMPERATURES The rationale for determining ambient temperature was the same asfor the July 9 and 10 survey (see Section 4.1.2). Temperature data fromthe near-bottom ambient reference location (Station

28) showed relatively little change overnight (Figure 4.2-1). The In-sltu monitor worked foronly a short period of time before becoming inoperative; therefore, theprofile data from the survey boat had to be used to determine the ambientbase temperature for each sampling run (Table 4.2-1).4.2.3 THERMAL SURVEYS4.2.3.1 Late Flood (Prebackwash)-2302 to 0002 ESTThe prebackwash survey during late flood tide was conducted from 2302 EST on July 16 through 0002 EST on July 17. Surface AT's showedtemperature rises of 3.7 to 6.4 F (2.1 to 3.6 C) inside the breakwaters (based on ambient of 53.6 F or 12.0 C and 21.6 F or 12.0 C near the endof the discharge canal (Figure 4.2-2). At the 3.3 ft (1.0 m) depth AT'swere somewhat lower, ranging from 1.9 to 4.6 F (1.1 to 2.6 C) in thestudy area and 8.5 F (4.7 C ) at the discharge.

Data from 9.8 ft (3.0m) showed AT's of 0.7 to 3.0 F (0.4 to 1.7 C); whereas, at the bottomthe AT'S showed temperatures very close to ambient (range from 1.2 to -0.2 F or 0.7 to -0.1 C; Figure 4.2-3).

43Figure 4.2-2.Contour maps of observed temperature rises (AT) Indegrees F above ambient during late flood (preback-wash) at surface and 3.3 ft (1.0 m) on July 16 and 17,1977. Pilgrim Station Backwashing

Studies, 1977.

44Figure 4.2-3.Contour maps of observed temperature rises (AT) indegrees F above ambient during late flood (preback-wash) at 9.8 ft (3.0 m) and bottom on July 16 and17, 1977. Pilgrim Station Backwashing

Studies, 1977.

45Measurements from the anchored boat at Station 6 (Figure 4.2-4),were consistent with the survey vessel data showing surface AT's of 4.2 F(2.3 C) which corresponded to an actual temperature of 57.8 F (14.3 C).Bottom temperatures were as low as 52.9 F (11.6 C)r representing a ATof -0.7 F (-0.4 C).Further along the dredged channel at Station 15 (Figure 3.1-2),temperatures were slightly warmer (Figure 4.2-5). The surface temperature was 58.6 F (14.8 C) or AT of 5.5 F (3.1 C) above ambient.4.2.3.2 Early Ebb (Backwash West Pump)-0003 to 0139 ESTAt about 2354 EST backwashing started on the west pump. Thistime, in sharp contrast to the low-water backwashing, the surface appear-ance of the backwash waters was much less dramatic.

The thermal plumewas somewhat turbulent and steamy, but the thermal front along theinterface with Cape Cod Bay waters was much less distinct that it hadbeen the week before. That is, this backwashing thermal plume lacked asharp interface which could be readily discerned with the naked eye,probably because more dilution or "receiving" water was available at highwater than during the low-water backwash the week before.The surface AT's were 28.2 F (15.7 C) in front of the westpump and 17.1 F (9.5 C) in front of the east pump (Figure 4.2-6).Warmest temperatures were along the west side of the study area withAT's from 28.0 F down to about 14.8 F (15.6 to 8.2 C).Across the middle portion of the study area, AT's ranged from15 to 10 F (18.3 to 15.6 C) with most of the hot water apparently beingblown against the outer breakwater by the strong southwesterly windswhich persisted throughout the survey (refer ahead to Figure 4.2-16).Much lower AT's were seen along the shore in front of the power plant(6.1 to 9.1 F or 3.4 to 5.1 C). In the eastern portion of the studyarea, some warm water was observed along the outer breakwater (8.7 to11.8 F or 4.8 to 6.6 C); but, close to shore at Stations 23 and 24, 46BAC KWASH INGEAST I WEST001615.VWU-U)cc4.1TIME, EST0--5-6-751.5-0"1Ca,-4-6P-1-10-15-20-mwJULY 16TIME, EST ,,, v 17%DUI,.I I IFigure 4.2-4.Temperature data from an anchored survey boat atStation 6 on July 16 and 17, 1977 showing actualtemperatures and corresponding AT's above ambientin degrees F. Pilgrim Station Backwashing

Studies, 1977;

-r.- -~-r-.'~-'"..................-

-. ......-.II47BACKWASHING EAST WESTILaILOli54.155.4 63.0 M34CCiuiL-.IL.JULY 16 TIME, EST JULY 17Figure 4.2-5.Temperature data from an anchored survey boat atStation 15 on July 16 and 17, 1977 showing actualtemperatures and corresponding OT's above ambientin degrees F. Pilgrim Station Backwashing

Studies, 1977.

48IiFigure 4.2-6.Contour maps of observed temperature rises (AT) indegrees F above ambient during early ebb (backwash west pump) at surface and 3.3 ft (1.0 m) on July17, 1977. Pilgrim Station Backwashtng

Studies, 1977.

49prebackwash conditions were observed (AT's of 3.0 to 3.2 F or 1.7 to 1.8C). At the discharge the temperature rise was 14.6 F (8.2 C). At the3.3 ft (1.0 m) level AT'S were lower than at the surface, but the generaldistribution of the backwash plume was about the same (Figure 4.2-6).These ranged from 13.8 and 16.0 F (7.7 and 8.9 C) in front of the intake,to 5.0 F (2.8 C) and less out at the end of the breakwaters.

At thedischarge the AT was 9.4 F (5.2 C).At 9.8 ft (3.0 m) AT's were small, ranging from near 0 at theintake to 0.1 to 1.9 F (0.06 to 1.1 C) at the end of the discharge canal. All near-bottom AT's were negative (down to -1.3 F or -0.7C),apparently due to cold water being entrained by the backwash plume(Figure 4.2-7).Temperature measurements from the boat anchored at Station 6showed that the west pump's backwash plume arrived within 5 to 10 min ofthe start of backwashing (Figure 4.2-4). The AT's rose sharply to 14.4F (8.0 C) or an actual temperature of 69.1 F (20.6 C). The resulting thermal plume seemed to be about 2 to 3 ft (0.6 to 0.9 m) thick andpersisted for almost 90 min, with highest temperatures of 70.7 F (21.7C) or 17.0 F (9.4 C) AT occurring around 0140 EST after backwashing hadbeen completed.

Throughout this time the lower two-thirds of the watercolumn had negative AT's down to -2.1 F (-1.2 C) or actual temperatures of 52.5 F (11.4 C) which serves to demonstrate where dilution water wascoming from.Data from Station 15 were less complete due to sampling omissionby the vessel observer, but the plume apparently passed between 0030 and0200 EST (Figure 4.2-5). Along the bottom, AT's were negative as atStation 6 (Figure 4.2-4).Actual backwashing of the west pump was completed around 0113EST.

50Figure 4.2-7.Contour maps of observed temperature rises (AT) Indegrees F above ambient during early ebb (backwash west pump) at 9.8 ft (3.0 m) and bottom on July17, 1977. Pilgrim Station Backwashlng

Studies, 1977.

514.2.3.3 Mid Ebb (Backwash East Pump)-0140 to 0349 ESTAt about 0159 EST of the east pump started.

Actual4temperature profiles in front of the intake at Station 1 depicts how thebackwashing progressed (Figure 4.2-8). Prebackwashing observations at0147 EST showed warm water near the surface and as a residual effectfrom the first backwashing.

At 0159 EST backwashing started as a suddensurge of hot water which flowed out of the intake. About 13 min laterthe backwashing was well along, and near-field thermal plume about 3- to4-ft thick (0.9 to 1.2 m) had been established.

Surface AT's were 43.2 F (24.0 C) in front of the east pumpand 25.2 P (14.0 C) in front of the west pump (Figure 4.2-9). Elsewhere AT's were generally higher than during the previous sampling run (Figure4.2-6). Temperature rises of 20 F (11.1 C) and more were found acrossthe channel to the outer breakwater.

As before the elevated AT's wereobserved along the outer breakwater (AT's of 15 to 20 F or 8.3 to 11.1C), possibly due to continuing influence of the wind (refer ahead toFigure 4.2-16)1

however, temperature rises along shore were much higherthan before (12.8 to 13.7 F or 7.1 to 7.6 C). Some warm water was ob-served in the edge of Cape Cod Bay beyond Station 28 due to the transient meteorological conditions at this time of the survey. The exact amountis unknown, but it is estimated that this transient phenomenon was onlya small percentage of the backwash thermal plume. At this time the ATat the discharge was 15.9 F (8.8 C).slightly deeper at 3.3 ft (1.0 m) the temperature distribution was about the same as at the surface (Figure 4.2-9). At most stationsactual temperatures or AT's were about 3 F (1.7 C) lower, indicating that this was close to the base of the surface plume.Conditions at 9.8 ft (3.0 m) were much warmer than earlier inthe evening with AT's ranging from 3.7 and 4.8 F (2.1 and 2.7 C) at theintake to 0.7 F (0.4 C) at Station 28 (Figure 4.2-10).

Backwash AT'swere around 9..1 F (5.1 C). Bottom AT's showed a sharp rise too. Con-ditions ranged from 3.6 F (2.0 C) at Station 2 down to 0.0 at Station28.

52TEMPERATURE (F)wLI-V)InzIJJ0U-TEMPERATURE (C)Figure 4.2-8.Temperature profiles from Station 1 during the startof backwashingof the east circulating water pump onJuly 17, 1977. Pilgrim Station Backwashing Studies,1977.

Figure 4.2-9.Contour maps of observed temperature rises (AT) Indegrees F above ambient during mid ebb (backwash east pump) at surface and 3,3 ft (1.0 m) on July17, 1977. Pilgrim Station Backwashing

Studies, 1977.

54Figure 4.2-10. Contour maps ofdegrees F abovepump) at 9.8 ftPilgrim Stationobserved temperature rises (AT) inambient during mid ebb (backwash east(3.0 m) and bottom on July 17, 1977.Backwashing

Studies, 1977.

55At Station 6, the passage of the east puMP therLmal plume wasvery evident (Figure 4.2-4). It took less than 10 min for the backwashwater to arrive and, as before, it persisted for about 90 main. Thetemperatures were slightly higher this time, with the greatest riseoccurring at 0320 EST after backwashing was complete (74.4 F or 23.6 Crepresenting a AT of 22.9 or 12.7 C). Temperatures at depth also rose,but bottom temperatures became sharply positive.

At Station 15, the second backwash plume was also evidenced but actual temperature rises near the surface are uncertain because ofsampling omission by the vessel observer.

At depth AT's rose considera-bly up to 5.3 F (2.9 C) at 0220 EST.At about 0307 EST backwashing of the east pump was completed and the plant started to return to normal operation.

4.2.3.4 Late Ebb (Post Backwash)-0350 to 0517 ESTBy the time this survey run began, all backwashing for theevening had been completed.

Surface AT's provide evidence of residualwarm water in front of the intakes (16.8 and 20.9 F or 9.3 to 11.6 C)and out along the western portion of the study area, with AT's of 10 to15 F or 5.6 to 8.3 C (Figure 4.2-11).Conditions were 8 to 10 F (4.4 to 5.6 C) in front of the plantand 3 to 6 F (1.7 to 3.3 C) out to the outer breakwaters.

Some residualwarm water apparently from the second backwashing was observed along thebreakwater from Stations 13 to 20, forced there by the southwest winds(AT's of 12.5 to 16.6 F or 6.9 to 9.2 C). At this time the plant wasback in normal operation with AT's of 23.4 F (13.0 C) at the discharge.

At 3.3 (1.0 m) AT's were 11.8 F (6.6 C) at Station 1 and 8.6 F(4.8 C) at Station 2 in front of the intake (Figure 4.2-11).

Warm waterwas seen along shore at Station 3 (9.6 F or 5.3 C) and up at Station 20 56N!Figure 4.2-11.Contour maps of observed temperature rises (AT) indegrees F above ambient during late ebb (postbackwash) at surface and 3.3 ft (1.0 m) on July 17, 1977.Pilgrim Station Backwashing

Studies, 1977.

57(16.1 F or 8.9 C). Elsewhere AT's ranged from 0.3 to 6.4 F (0.2 to 3.6C) with coldest conditions along shore. At the discharge the AT was20.9 F (11.6 C).At 9.8 ft (3.0 m) AT's in front of the intake were 2.8 and 3.7F (1.6 and 2.1 Ci Figure 4.2-12).

About halfway along the channel theywere 1.0 to 2.0 F (0.6 to 1.1 C). Further from the intake AT's were 1.0F (0.6 C) or less. On the bottom they were still slightly warm in frontof the intake (1.4 F or 0.8 C), but elsewhere they were close to 0 orslightly negative.

At Station 6 temperature conditions had again stabilized afterthe backwashing.

Surface temperatures were 55.7 to 56.6 F (13.2 to 13.7C) representing AT's of 3.2 to 4.1 F (1.8 to 2.3 C). Bottom tmperatures were 51.5 to 53.1 F (10.8 to 11.7 C) or negative AT's of up to -1.4 F (-0.8 C).Further from the intake at Station 15, the temperatures re-mained slightly warmer with AT's of 4.0 to 8.0 F (2.2 to 4.4 C) in theupper part of the water column and near 0.0 along the bottom (Figure4.2-5).4.2.3.5 Low Water (Survey Coinplete)-0518 to 0538 ESTAt this time the plant had resumed normal operations and alltraces of hot backwash water were gone. Surface AT's were 4.3 F (2.4 C)at Station 1 and 1.2 F (0.7 C) at Station 2 (Figure 4.2-13).

At Stations6 and 15 AT's were around 3.2 F (1.8 C). Slightly deeper at 3.3 ft (1.0m) AT's were 1.0 to 2.1 F (0.6 to 1.2 C) near the intake and 0.6 to 3.7F (0.3 to 2.1 C) at Stations 6 and 15. At 9.8 ft (3.0 m) the AT'sranged from -0.1 to 1.2 F (-.06 to 0.7 C1 Figure 4.2-14).

ii58IFigure 4.2-12.Contour maps of observed temperature rises (AT) indegrees F above ambient during late ebb (post-backwash

) at 9.8 ft (3.0 m) and bottom on July 17,1977. Pilgrim Station Backwashing

Studies, 1977.

IiI59/Figure 4.2-13.Contour maps of observed temperature rises (aT) indegrees F above ambient during low water (surveycomplete) at surface and 3.3 ft (1.0 m) on July17. 1977. Pilgrim Station Backwashing

Studies, 1977.

60Figure 4.2-14.Contour maps of observed temperature rises (aT) indegrees F above ambient during low water (surveycomplete) at 9.8 ft (3.0 m) and bottom on July 17,1977. Pilgrim Station Backwashing

Studies, 1977.

61Finally along the bottom, temperatures ranged from -1.0 F (-0.6 C) atStation 6 to 0.5 F (0.3 C) at Stations 2 and 15. As noted previously; temperature conditions had stabilized at Stations 6 and 15 (Figures4.2 -4 and 4.2-5).4.2.3.6 SumaryThe elevated surface temperatures and thermal backwashing plumes persisted for almost 4 hrs in the western portion of the studyarea and somewhat less in the eastern portion, before dissipating.

Windseemed to play a role in .forcing the hot water along the outer breakwater and keeping it away from the shore in front of Unit 1.4.2.4 CURRENTSFlow patterns in the study area were again dominated by plantoperation, as they were during the July 9 and 10, 1977 survey (Figure4.2-15).

Currents at both Stations 1 and 6 were southward or into theplant at 0.1 to 0.37 kn throughout the survey,,

except for during actualbackwashing.

As before, backwashing caused a shearing in the watercolumn, with near-bottom currents continuing to flow toward the intake,vertical flow near the screenwall and near-surface currents (up to 0.2kn) flowing seaward.

Once the hot backwash plume was established at thesurface, continued pumping carried it out toward Cape Cod Bay. Flows atstations further from the plant were still dominated by drawing of theintake system, but wind stress from the strong southwest winds helpedforce the hot water seaward during much of the night.

620 N, TRUE-0-1-2r-5U,ZEC310-15-20-25-/-6-7/of.35371352I jj--- -- j b A k v 4I IJULY 16JULY 17O.5- N. TRUE-o-1-2,d-~-I.10-15-go-11 ,Z.3KO-6-7-4JULY 16TIME,ESTJULY 17IFigure 4.2-15. Vector plots of current measurements in degrees true(referenced toward which currents were flowing) andkn from StatTonT-1(upper) and Station 6 (lower) onJuly 16 and 17, 1977. Pilgrim Station Backwashing

Studies, 1977.

634.2.5 AIR TEMPERATURE Air temperature measurements at the 33-ft (10-m) level onBoston Edison Company's 160 ft (48.8 m) meteorological tower (Figure2.1-1) showed a gradual warming during the day to about 83 F (28.3 C) at1800 EST (Figure 4.2-16).

During the night temperatures dropped gradually to a low of about 73 F (22.7 C) but humidity remained very high. Start-ing at dawn temperatures rose sharply to 89.5 F (31.9 C) by noontime.

4.2.6 WINID COHDITIONS Wind speed and direction measurements at the 33-ft (10-m)level on Boston Edison Company's 160 ft (48.8 m) meteorological towerindicated the presence of light winds from the southeast until earlyevening (Figure 4.2-16).

At about 1800 EST, the wind shifted to south-westerly and intensified.

Wind speed was steady at 12 to 15 mph allnight. These winds may have helped carry the backwash plume out alongthe outer breakwater and forced some hot water into Cape Cod Bay.4.2.7 TIDESTide observations generally showed good agreement with NOAA-NOS tide predictions (Figure 4.2-17).

Although data were incomplete, itappears that the early morning low tide was slightly lower than predicted.

AIR TEMPERATURE U.'wU(LI-lI.-N, TRUE(IND(DIRECTION FROM)I I I I I I I I 1 1 I, I I I 1I I I I I I12 14 16 18 20 22 24 2 4 6 6 1 0 12,,,v Vic TIME, EST ,,, 7iJUI .i UJULl .LIFigure 4,2.16,Air temperature and wind vector plots in degrees true (referenced toward which wind was blowing) and mph from the 33 ft (10 m) levelFit Boston Edison Company meteorological tower on July 16 and17,1977.

Pilgrim Station Backwashing

Studies, 1977.

65NOAA-NOS PREDICTED TIDE ELEVATION U.P=,1 18JULY2616TIME, ESTAJULY617Figure 4.2-17.Plot of NOAA-NOS predicted tide elevations for thePilgrim Station area along with NAI tide observations for July 16 and 17, 1977. Pilgrim Station Backwashlng

Studies, 1977.

665.0 DISCUSSION 5.1 PLUME DYNAMICSIn general the dynamics of the backwash plume were quitesimilar during each of the survey weekends.

Backwashing was firstevidenced by a pulse of hot water at depth from the intake (Figure 4.2-8). As the pumping continued, the buoyant hot water rose to the surface.Within a few minutes it formed a highly stratified thermal plume averag-ing 3 to 5 ft (0.9 to 1.5 m) in thickness.

During the first weekendsurvey, the thermal plume formed a distinct frontal zone of foam andturbulent, steaming water which could be easily tracked by eye. Underthe influence of the reverse intake flows, the initial jet mmentum, theplume buoyancy effect and the localized hydrostatic head in front of thescreenwall, the frontal zone moved slowly across the study area. Alongshore and in shallow water, frictional effects slowed the frontal zone,causing the plume to take on a bulge in the center. The hot waterpropagated toward the western portion of the study area and the outerbreakwater; but relatively little hot water contacted the shoreline areain front of Unit 1 during both of the surveys.

During the second surveythe frontal zone behaved in a similar manner; but was much less distinct, possibly because of the increased volume of receiving water (high watercondition).

The difference between high water and low water in front ofthe intake can be readily seen from the photographs in Figure 5.1-1.5.2 TEMPERATURE RISESDuring the first weekend, backwashing was coincident with low-water and early flood conditions when receiving water volumes wereminimal.

Each actual backwashing lasted from 37 to 49 min. Maximumsurface temperatures of 100.9 F (38.3 C) were observed in front of theintake, representing a AT of 43.4 F or 24.1 C.

G7Figure 5.1-1.Photographs of the western portion of the study areain front of the Pilgrim Station intake at high water(upper) and low water (lower).

Pilgrim StationBackwashlng

Studies, 1977.

68At Station 6, two distinct pulses of hot water from eachbackwashing were observed, with maximum surface temperatures of 79.0 F(26.1 C) and 81.1 F (27.3 C), respectively (Figure 4.1-4). Thus,temperatures had dropped substantially within less than 200 ft (61 m) ofthe intake. Based on arrival times, it appears that the front moved outat about 0.2 kn, which was consistent with current-meter measurements, Further seaward at Station 15, similar pulses were observed about 30 to40 min after backwashing started.

Actual surface temperatures were evenlower than at Station 6 (77.0 F or 25.0 C and 75.8 F or 24.3 C for eachbackwash, respectivelyi Figure 4.1-5). During the first weekend the hotwater required about 2 to 2.5 hrs. to dissipate.

During the second weekend when backwashing was coincident withhigh water and early ebb, receiving water volumes were close to maximum.Each of these backwashes lasted longer than before (58 to 73 miin) butthe plant backwash operational temperature remained about the same.Apparently, due to the increased volume of available diluting or re-ceiving water, maximum observed surface temperatures in front of theintake were only 94.9 F (34.9 C), representing a AT of 43.2 F or 24.0 C.The frontal zone moved out at about 0.2 kn, as it had the preceding weekend.At Station 6, two pulses of hot water from backwashing wereobserved.

The first reached 70.7 F (21.5 C) whereas the second was upto 74.4 F (23.6 C). Similar pulses were observed at Station 15 butmaximum surface temperatures attained are unknown due to samplingomission.

During the second weekend it took much longer for the hotwater to dissipate than the first weekend (nearly 4 hrs), probablybecause each backwash lasted longer (Figure 4.2-1).

i5.3 EFFECT OF WIND ON PLUME MOVEMENTBecause of the relative thinness of the thermal plume and thepronounced stratification it created, it appeared to be highly- sus-ceptible to wind shear effects.

During both weekend surveys, south-westerly winds forced much of the plume against the outer breakwater, leaving the shoreline area much less affected'.

During the second week-end some hot water was apparently forced out into Cape Cod Bay beyondthe outer breakwater by transient wind effects (estimated to be only asmall percentage of the surface backwash thermal plume)..

In general,the eastern portion of the study area remained relatively unaffected by the hot water during both studies.

Where the thermal plume impingedthe shoreline, such as along the breakwaters, it was generally less than2 ft (0.6 m) thick.5.4 AMBIENT VARIABILITY The observed near-bottom ambient temperature variations atthe reference Station 28 agree with historical data from these waters(Stone and Webster, 1975). The warming trend observed at this locationon July 9 and 10 suggests that some water from the discharge can re-circulate into the intake area.

706.0 SUMMARY AND CONCLUSIONS Based on the two weekend surveys of actual backwash operations at Pilgrim Station under varying tidal conditions, the following con-clusions have been reached:1. During a typical backwashing operation, plant water boxtemperatures are generally held at 90 to 98 F (32.2 to35.7 C) for 45 to 60 sin depending upon how fouled thecondenser tubes are. Toward the end of the cycle evenhigher temperatures of up to about 120 F (48.9 C) mayoccur for 10 to 15 sin. Backwash temperatures on thewest pump sometimes are run slightly higher than on theeast pump because fouling there tends to be greater andmore heat treatment is required.

2. Backwashing was first evidenced by a pulse of hot waterissuing from the intake at depth. As the pumping con-tinued, the buoyant hot water rose to the surface.Within a few minutes of inception, it formed a highlystratified thermal plume averaging 3 to 5 ft (0.9 to 1.5m) in thickness.

During the first weekend the thermalplume formed a distinct frontal zone of foam and turbulent, steaming water which could be easLly. tracked by eye.Under the influence of the reverse intake flows and thelocalized hydrostatic head in front of the screenwall, the frontal zone moved slowly across the study area.During the second survey the frontal zone behaved in asimilar manner but was much less distinct, possiblybecause of increased volume of receiving water at hightide.3. During the first weekendbackwashing was keyed to low-water and early flood conditions when receiving watervolumes were minimal.

Each actual backwashing lastedfrom 37 to 49 min. ftaximum surface temperatures of 100.9F (38.3 C) were observed in front of the intake, 71representing a AT of 43.4 F or 24.1 C. During the secondweekend when backwashing was keyed to high water andearly ebb, receiving water volumes were close to maximum.Each of these backwashes lasted longer than before (50to 73 min) but the plant backwash operational temperature remained about the same. Apparently due to the increased volume of available diluting or receiving water, maximumobserved surface temperatures in front of the intakewere only 94.9 F (34.9 C), representing a AT of 43.2 For 24.0 C.4. Profile data from anchored boats at Stations 6 and 15showed distinct pulses of hot water from each backwashing.

Generally the frontal zone arrived at Station 6 within5 to 10 min and at Station 15 within 30 to 40 min.Based on arrival times, it appears that the front movedout at about 0*2 kn,which was consistent with near-surface current-meter measurements.

5. Along shore and in shallow water, frictional effectsslowed the frontal zone ,causing a bulge in the center.During both surveys, the hot water propagated towardsthe western portion of the study area and the outerbreakwatery but relatively little hot water was seen toaffect the shoreline area in front of Unit 1 and thecoast toward the east. Heat was lost very rapidly asthe thermal plume moved seaward, as evidenced by temp-erature drops at Stations 6 and 15 which were progressively further from the intake. During the first weekend thehot water required about 2 to 2.5 hrs to dissipate.

During the second weekend when backwashing lasted alittle longer, it required nearly 4 hre for the hotwater to dissipate.

6. The thermal plume was thickest close to the intakescreen wall (5 to 6 ft or 1.5 to 1.8 m at times)l but,along its distal edges it thinned rapidly, often to 1 ft(0.3 m) or less right along shore.

727. Because of the relative thinness of the thermal plumeand the pronounced stratification it created, it appearedto be highly susceptible to wind-shear effects.

Duringboth weekend surveys, southwesterly winds forced much ofthe plume against the outer breakwater, leaving the shore-line area much less affected.

The second weekend somehot water was apparently forced out into Cape Cod Baybeyond the outer breakwater by the wind (estimated to beno more than 5% of the maximum near-surface backwashthermal plume). In general, the eastern portion of thestudy area remained relatively unaffected by the hotwater during both studies.8. In summary the backwashing operation caused a relatively thin thermal plume which spread rapidly across the westernportion of the study area and along the outer breakwater.

Within a few hours it was completely dissipated.

7

37.0 REFERENCES

National Oceanic and Atmospheric Administration National Ocean Survey1977. Tide Tables for East Coast of North and South America.

U.S.Dept. Comm., Washington, D.C. 290pp.Normandeau Associates, Inc. 1976a. Physical Sciences Data Processing Technical Procedures Manual 5.0._ 1976b. Physical Sciences Equipment and Instrumentation Technical Procedures Manual 3.0._ 1976c. Quality Assurance Manual.* 1977. Proposal to conduct hydrothermal surveys of backwashing operations at Pilgrim Station for Boston Edison Company.Stone and Webster Engineering Corporation.

1975. 316 Demonstration PilgrimNuclear Power Station Units 1 and 2 Boston Edison Company.

Craver, PattiFrom: Balsam, BrianaSent: *Thursday, April 12, 2012 1:01 PMTo: Julie Crocker

Subject:

RE: Pilgrim:

NRC's complete responses to 4-9-12 NMFS questions Attachments:

ENSR 2000 316 Demonstrationzip Reference 4 of 4.From: Balsam, BrianaSent: Thursday, April 12, 2012 12:56 PMTo: 'Julie Crocker'Cc: Logan, Dennis; Susco, Jeremy; Smith, Maxwell;

'jeganl@entergy.com'

Subject:

Pilgrim:

NRC's complete responses to 4-9-12 NMFS questions Julie,I attached the NRC's completed responses to the questions on Pilgrim that you sent in your April 9email to follow-up on our partial response dated April 10.I will also be forwarding several zip files containing the documents referenced in the responses insubsequent emails. I tried to send them all as one zip folder, but it seems as if my agency's emailattachment size limit is a bit higher than yours-the last email I was able to send, but it came backundeliverable.

All of the references should also be publically available in our ADAMS system also,and I have included the accession number for each in the attached responses, so that would beanother way for you to access those documents if email doesn,'t work.BrianaBriana A. BalsamBiologist Division of License RenewalOffice of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission 301-415-1042 briana.balsam@nrc.gov