Docket OW-2002-0049 DCN#: 6-50460 

Young, J., W.Dey, S. Jiizks, N. Decker, M. Daley, and 

J. Camriglit, ASA Analysis and Dynegy 

Evaluation of Variable Pumping Rates as a N&f Reduce Entrainment Mortalities 

EVALUATION OF VARIABLE PUMPING RATES AS A MEANS TQ REDUCE 

ENTRAINMENT MORTALITIES 

John Young 

William Dey 

Steven Jinks 

Nancy Decker 

ASA Analysis & Communication, hc. 

Washmgtonville, NY 

Martin Daley 

John Camright 

Dynegy Northeast Generation 

Newburgh, NY 

Abstract 

We evaluated the potential of a load-based flow strategy (vary flows with generating load to use minimum 

flow sufficient to meet specified thermal characteristics) to meet the USEPA proposed entrainment 

reduction targets (60% to 90%) for the Roseton Generating Station. Actual generatingloads from 1999­

2001 were used as the operation schedule. Operating rules that would minimize flows while keeping 

discharge temperatures below a maximum of 20” to 40” C and AT below 15”to 3Q” C were used to predict 

cooling water use. These strategies would have reduced cooling water use by 63% to 70% from the full 

withdrawal capacity of the station. Striped bass entrainment numbers would be reduced fkom 71% to 75% 

from a hll-flow full-operation baseline condition. When expected entrainment survival at the Roseton 

Station was factored into the analysis, potential reductions of striped bass losses increased to 89% to 91%. 

For facilities that vary the generating loads to meet peak loads, a load-based flow strategy appears to be a 

viable option to approach or meet the reduction targets of the proposed new regulations. The achievable 

reductions were not highly sensitive to the thermal design criteria, which should allow plant operators to 

find a set of thermal criteria that reduce entrainment and still allow efficient operation of the facility. The 

ultimate utility of load-based flow strategies to achieve compliancewith entrainment reduction targets will 

depend on the final definition of “baseline” conditions. If baseline is defined as the full capacity of a station 

to entrain fish (hll flow and full generation) then a load-based flow strategy can be an important component 

to achieving compliance. However, if baseline becomes defined by past operating levels and practices, then 

it is unlikely that a load-based flow strategy could achieve the additional reductions required, especially for 

facilities that already operate at reduced flows as a matter of practice. Stations in this situation would be left 

to choose between closed cycle systems, or application for site-specific conditions. 
Introduction 

The new regulations that the United States Environmental Protection Agency OJSEPA) has proposed for 

9316(b) of the Clean Water Act will pose distinct challenges to operators of electric generating facilities to 

meet criteria for reducing entrainment and impingement mortality. A number of technologies are currently 

available that can either reduce the numbers of fish that are impinged, by keeping them away from the 

screens through physical exclusion or behavioral means, and/or to improve the survival rates of fish that are 

impinged. However, for entrainment mortality, there are far fewer options. Physical exclusion systems, 

such as the Marine Life Exclusion System, are currently being tested, but even if exclusion systems are 

successfbl in some locations be applicability may not be universal. Behavioral exclusion is not effective 

because most entrainable stages do not have swimming capabilities or a behavioral repertoire sufficient to 

escape the flow into a power plant intake. Thus, reducing the coolingwater flow is the primary means for 

reducing entrainment. We explored the potential of variable speed pumping as a means to meet entrainment 

reduction goals at an existing power station on a tidal river. ’ 

The Roseton Generating Station is situated on the west shore of the Hudson River, 105 kmupstream from 

the Battery, a setting that, according to the proposed Phase I1 regulations, would require a reduction of 

entrainment between 60% and 90% of baseline levels. The station, which began commercial operation in 

1974, has two 600-MW oil/gas-fired generating units that use Hudson River water for condenser cooling. 

The single intake structure contains four circulating water pumps that draw through 8 intake bays. Six of 

the bays are fitted with conventional 9-mm mesh traveling screens, and two have dual-flow screens. The 

four pumps feed cooling water into a single inlet conduit that serves both units. Depending upon generating 

loads and river water temperatures, the plant may be operated with 2 pumps (1,584 m3/min), 3 pumps 

(2,124 m3/min), or 4 pumps (2,424 m3/min). Under full generation and full flow, the design AT for the 

station is 9.8”C. 

Although the Roseton Generating Stationwas originally constructed as a base-load facility, its recent use 

has been to follow the daily and seasonal demand patterns. In this mode its generating loads can vary 

substantially between peak and off-peak periods. If cooling water use could be matched closely to the 

generating load, then entrainment numbers could be reduced. Because a substantial base of entrainment 

abundance information exists for the Roseton Station, it is possible to quantitatively assess the potential of a 

variable flow strategy to approach or achieve the USEPA’s target reduction levels. In addition, the Roseton 

Station also has a large amount of data on entrainment survival rates for key taxa, therefore it is possible to 

assess the contribution entrainment survival provides towards meeting USEPA’s target reduction levels. 

Availability of site specific entrainment abundance and survival data provides a reasonable and defensible 

basis for the design of prudent operating rules that would guarantee that flow reductions do not actually 

exacerbate entrainment mortality. 

Methods 

The Roseton Generating Station is an excellent site for evaluation of variable pumping rates due to the 

amount of infomation available. Although an evaluation could be conducted on a theoretical basis using 

hypothetical abundance patterns and entrainment survival rates, the Roseton Station possess a large base of 

empirical information which makes the evaluation process highly relevant and establishes the groundwork 

for additional evaluation that could ultimately lead to renewed dischargepermits. The available data 

included: 

2 
Seasonal and daily operatingpattern 

In the post-deregulation electric generating industry, it is very difficult to predict future operating patterns. 

Plant operations are no longer determined by demand patterns within a utility's service territory, which are 

relatively predictable in the short term, but are now determined by the market. Rather than attempt to 

predict future operations of the Roseton Station, we used the 1999-2001 actual operation patterns as 

examples of how the station operates, and might be expected to operate in the future. The Roseton Station 

varies its generation to match seasonal and daily load changes, thus hourly information on the intake 

temperature, cooling water flows, and generating load for each unit were used to establish the operating 

pattern for evaluation (Figure 1). 

Density of entrainable life stages 

Entrainment densities were sampled from May through July from 1983-1987 using a net-in-barrel pumped 

sampling system with a 0.5 mm mesh net at a rate of approximately 1m3/min.(Figure 2). Sampling location 

was in the discharge seal well just prior to the point where the conduit entered the river. Sampling was 

conducted on a variable frequency, from 1 to 7 days per week. On each sampling event, 24 l-hour samples 

were collected and analyzed. During laboratory analysis, ichthyoplantkonwere identified to species where 

possible, and subsamples of key taxa were measured to the nearest 0.1 mm. The data were used to estimate 

the density (number of organisms per m3) of each 1-mm length interval during each hour of each day 

sampled. The densities on bunsampled days were interpolated between sampled days on an hour and length 

interval basis. The final expected density pattern was then developed from the average density over the 

1983-1987 annual patterns (Figure 3). For this evaluation, only data on striped bass were used, but the 

results would be similar for other taxa whose temporal pattern is similar to striped bass. 

Mortality of entrained organisms 

Entrainment mortality studies were conducted from 1976-1980. Sampling was conducted with pumped 

larval flumes, and rear-draw and pumpless systems (EPRI 2000). Samples were collected from the intake to 

establish the level of sampling mortality, and simultaneously from the discharge. 

Initial survival in samples was used to estimate a logistic regression equation (Sokal and Rohlf 1995) to 

predict survival as a function of length of organism and discharge temperature range. For this evaluation, 

only the data for 1980 were used because the most advanced sampling techniques were used in that year and 

the sample size was relatively large (1252 individuals). The predicted logistic regression curves for 

discharge samples collected at temperatures < 30°C, and the intake samples (Figure 4) were used to estimate 

the mechanical component of entrainment mortality according to Abbott's formula: 

Mechanical mortality = 1 -(Survival in discharge samples) / (Survival in intake samples) 

Because few larvae were collected under higher dischargetemperatures, laboratory thermal tolerance data 

were used to estimate the thermal mortality component based on lower and upper temperature thresholds. If 

the predicted exposure temperature was below the lower threshold (TL)then thermal mortalitywas 0. 

Temperatures above the upper threshold (TU)were assumed to result in 100%mortality. Between TLand 

3 
TU ~ mortality rate was linearly related to temperature. The TLand TUvalues were estimated as functions of 

ambient temperature, exposure temperature, and transit time (Central Hudson et a1 1999). 

The mechanical and thermal components of mortality were assumed to be independent: 

Entrainment Mortality = 1-(1 -Mechanical Mortality)(1 -Thermal Mortality) 

Evaluation Process 

There are five distinct steps in the evaluation process; 

Set hourly generating load and inlet temperatures. The actual 1999-2001 data were used to establish 

these values. Use of past operating data essentially makes the evaluation an analysis of the theoretical 

entrainment levels in these years if the flow reduction strategy had been followed. The calculation 

baseline for comparison was 365-day per year operation at full flow (2,424 m3/mh),with an assumed 

100% mortality of entrained organisms. 

Use operating rules to establish cooling water flow and discharge temperatures. The basic 

procedure of the load-based flow strategy is to use the minimum cooling water flow required to maintain 

discharge temperature and AT within specified bounds. We examined a range of maximum hscharge 

temperatures from 20" to 40" C in increments of 5"C, and AT from 15" to 30°C in increments of 5°C. 

The analysis was conducted as if the station operators would, on at least anhourly basis, adjust cooling 

water flows to match the current generation load. The AT for a given generating load, and transit time 

through the cooling system, are inversely proportional to cooling water flow. Analysis was conducted 

for fill-flow full-generation, and for actual flows and generation 

Estimate numbers of organisms entrained. Entrainment numbers were estimated as the product of 

the estimated hourly densities and the hourly cooling water flows. The goal to reduce entrainment was 

aided, for some later life stages, by the offset in daily generation load and entrainment density (Figure 5) 

in whch highest entrainment densities occurred at night when generating load and cooling water flow 

were lowest. 

Calculate mortality component. The numbers dying in each hourly interval was calculated by 

adjusting the total number entrained by the hourly projected mortality rate. The mortality rate is the 

combined effect of mechanical and thermal mortality calculated for each length interval. 

Estimate percentage reduction from baseline. The hourly estimates of numbers entrained and 

number killed were summed for each year. The totals from the load-based flow strategy were compared 

to the full-flow full-generation baseline. Estimates based on actual flows were also calculated for 

comparison. Percent reductions were calculated as: 

% Reduction = 100 x (Baseline Number Killed -StrategyNumber Killed) / Baseline Number Killed 

For the baseline number killed, 100% entrainment mortality was assumed. For the strategy number killed, 

both the empirically-based estimates, and a 100% mortality assumption were used. 

Results 

The load-based flow strategy, if implemented during 1999-2001,had the potential to reduce flows 

substantially fiom baseline levels (Figure 6). Over all sets of operating rules, flows would have been 

4 
reduced from 63% to 70%, with higher reductions occurring at higher ATs and lower maximurn discharge 

temperatures. 

For striped bass, a load-based flow strategy would have resulted in substantial reductions in entrainment and 

entrainment mortality at the Roseton Generating Station. For numbers entrained, the average annual 

reduction was on the order of 75% from the full-flow full-generation baseline (Figure 7). This reduction was 

higher than the reduction in flows due to the additional protection resulting fiom the diel pattern in 

entrainment. Striped bass densities in the vicinity of the intake are at their lowest at the time when 

generation, and need for cooling water, is highest. The percentage reduction was relatively insensitive to 

the maximum discharge temperature or maximum AT. The range of reduction in entrainment was 

approximately 71% to 75% under all combinations of maximum discharge temperature and maximum AT. 

Reductions were near the high end of the range at the highest ATs and extreme values of maximum 

discharge temperature (20" or 40°C). The wide range of conditions that produced relatively similar 

reductions in entrainment provides considerable latitude in finding plant operation schemes that will allow 

reasonably efficient operation and also decrease entrainment. 

When entrainment survival estimates for striped bass were factored into the analysis, the reduction from 

baseline levels of entrainment mortality (which are based on an assumption of no survival) reached 

approximately 90% (Figure 8). As with numbers entrained, the percent reduction was relatively insensitive 

to the operating rules, ranging fiom about 89% to 91% across all combinations of maximum discharge 

temperature and maximum AT. In contrast to the pattern for numbers entrained, the percent reductions of 

numbers llled was highest at intermediate values of maximum discharge temperature. 

Discussion 

The analysis shows that, for plants such as Roseton that have highly variable operations, a load-based flow 

strategy could approach or achieve the reductions of entrainment required under the USEPA's proposed 

regulations. The actual reductions achieved for any taxon would depend upon the timing of the presence of 

entrainable life stages relative to the generating demand on a seasonal, and perhaps daily, basis. Particularly 

for taxa whose peak densities occur outside the seasonal generating peaks, load-based flows could be 

sufficient to achieve compliance. 

For taxa that could be expected to exhibit moderate to high levels of entrainment survival, such as striped 

bass, a strong base of entrainment survival information would provide a safety margin for potential 

compliance, or could bring the reduction levels closer to or within the required levels for compliance. Thus 

stations that entrain relatively hardy taxa, but have no site-specific information on survival, might consider 

conducting carefully designed and executed entrainment survival studies in order to be able to include 

survival in the assessment process. 

This evaluation was only of the biological potential for load-based flows to reduce entrainment, i.e. does 

entrainment occur at a time when flow could be reduced below maximum levels, and could flow be reduced 

enough to achieve compliance with the reduction targets. The results were encouraging in that a wide range 

of operating rules (use minimum flow to stay below a maximum discharge temperature and maximum AT) 

would meet the target levels of entrainmentreduction. However, significant additional evaluation is 

necessary before a load-based flow strategy could be considered for implementation. The operating rules 

must still be evaluated for operational feasibility and economic implications on a site-specificbasis. To the 

5 
extent that these rules would cause departures from a facility’s design operating state, there may be reduced 

generating efficiency, or additional risks of equipment failure. Existing pumps, or pump control equipment 

may need to be replaced, and the facility’s compliance with $316(a) standards or thermal water quality 

criteria also must be considered. 

USEPA’s final definition of “baseline” conditions will be crucial to determining whether a load-based flow 

strategywill be a viable means to achieve the required percent reductions of entrainment. If, as suggested in 

USEPA’s original proposal (USEPA 2002), ‘‘baseline” is interpreted as the full potential of a power station 

to entrain and kill fish, then a load-based flow strategy may allow many non-baseload stations to achieve 

compliance, even without considering the issue of entrainment survival. However, if baseline is interpreted 

as past operatingpractices, as has been recently suggested by USEPA (USEPA 2003) and advocated by 

some parties (Super 2003), then a load-based flow strategy will likely not be sufficient to achieve 

compliance at stations that already operate at reduced flows on a seasonal basis. This interpretation would 

essentially penalize stations like Roseton by requiring them to reduce entrainment 60% to 90% below their 

already-reduced levels, while stations that historically operate at full flow year-round, regardless of 

generating load, would have their full entrainment potential as the yardstick for measuring percent 

reductions. One way USEPA can apply its reduction criteria fairly and equitably to all stations would be to 

establish full-flow, full-generation, 100%mortality as the baseline for all facilities. Then any design 

features, operating practices, or technology innovations that reduce the numbers entrained and/or 

demonstrably increase their survival rates would be part of the overall compliance package for the facility. 

If USEPA takes a load-based flow strategy out of the compliance options by improperly defining the 

calculation baseline, then the only options available to many stations will be either closed-cycle cooling or a 

site-specific determination of Best Technology Available. Given only these two choices, existing facilities 

that operate well below maximum capacity are likely to seek a site-specific determination far more often 

than USEPA may have anticipated. 

Literature Cited 

EA Engineering, Science & Technology (EA). 1984. Roseton and Danskammer Point Generating Stations 

Entrainment Abundance StucZles 1983 Report. Prepared for Central Hudson Gas & Electric Corporation, 

Poughkeepsie, NY. 

Electric Power Research Institute (EPRI). 2000. Review of Entrainment Survival Studies: 1970-2000. 

Palo Alto, CA. 

Central Hudson Gas & Electric Corporation, Consolidated Edison Company of New York, Inc., New York 

Power Authority, and Orange & Rockland Utilities, Inc. 1999. Draft Environmental Impact Statement for 

the Renewal of State Pollutant Discharge Elimination System Permits for Bowline Point 1 & 2, Indian Point 

2 & 3, and Roseton 1 & 2 Steam Electric Generating Stations. Poughkeepsie, NY. 

Sokal, R.R. and F.J. Rohlf. 1995. Biometry. Third Edition. W. H. Freeman and Company. New York. 

887 p.. 

Super, R. 2003. An Overview of Flow Reduction Technologies for Reducing Aquatic Impacts at Cooling 

Water Intake Structures. Presentation at “A Symposium on Cooling Water Intake Technologiesto Protect 

Aquatic Organisms.” May 6-7,2003. Arlington, VA. 

6 
United States Environmental Protection Agnecy (USEPA). 2002. National Pollutant Discharge Elimination 

System--ProposedRegulations to Establish Requirements for Cooling Water Intake Structures at Phase I1 

Existing Facilities. Federal Register April 9,2002 (Volume 67, Number 68), pp 17121-17170. 

USEPA. 2003. National Pollutant Discharge Elimination System--Proposed Regulations To Establish 

Requirements for Cooling Water Intake Structures at Phase I1 Existing Facilities; Notice of Data 

Availability. Federal Register: March 19,2003 (Volume 68, Number 53), pp 13521-13587. 
s 

700 

600 

n 

-

I 500 

C 

.-0 

.c, 

g 400 

S 

8 

L 300 

3 

0

I

5 200 

9 

I00 

0 1 1 1 1 1 1 1 1 1 1 1 1 1 l I I I I I I l I 

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Hour 

Figure I Typical diel generating load at the Roseton Generating Station during May-July. 

8 

I 
--- I-=­

1 

w 

Figure 2 Net-in-barrelcollection system used for entrainment abundance sampling. (From EA 1984) 

9 
4 .E+OI 

I.E+OO 

e9

E 1.E-01 -

Q)

Q 

5 

Q

,E21.E-02 -

S 

Q

i! 

I.E-03 . 

1.E-04 - , , 8 I I I I I I I 1 I I 

Figure 3 Seasonal pattern of entrainment density (# per m3)of striped bass, white perch, American shad, and river 

herring (all life stages combined) at the Roseton Generating Station based on 1983-1987 data. 
1.oo 

0.90 

0.80 

a0.70 

.-S

-E0.60 

3 

0.50 

S 

.-0 

0.40 

! 

LL 0.30 

0.20 

0.10 

0.00 

0 5 10 15 

+intake n = 514 

Dischargec 30 n = 655 c 

Discharge 30-33 n = 97 

0 Discharge> 33 n = 6 

20 25 30 35 40 

Length (mm) 

Figure 4 Initial survival as a function of length from entrainment samples collected at the intake, and at the discharge 

sampling locations at temperatures 30°C,30°-33"C,and > 33°Cat the Roseton Generating Station, 1980. 
Q) 

.- 

2 

Yolk-sac Larvae 

I.5 

-

3 

3 

E 

(II 

S I 0 

rc1 

$ 

.c, 

-(II 

B 

0.5 

0 

I 2 3 4 5 6 7 8 9 IO I1 12 13 14 15 16 17 18 19 20 21 22 23 24 

Hour 

Figure 5 Daily variation in density of entrainable striped bass life stages and generation load at the Roseton 

GeneratingStation. (Relative density values above 2 were cut off in order to improve resolution in 0-2 range.) 

12 
Re!ductionfrom 

Full Flow 

Baseline 

urn 

Discihai 

Target 

Figure 6 Percent reductionfrom full-flow baseline of total cooling water flow under 1999-2001 operations at the 

Roseton Generating Station due to a load-based flow strategy. Maximum discharge temperatures range from 20" to 

40°C and maximumATfrom 5"to 15°C. 

13 
Re!ductionfrom 

Full Flow 

Baseline 

30 

Maximum 

AT Discharge T'emperature Target 20 

Figure 7 Percent reduction from full-flow baseline of numbers entrained under 1999-2001operations at the Roseton 

Generating Station due to a load-basedflow strategy. Maximum discharge temperatures range from 20" to 40°Cand 

maximum AT from 5"to 15°C. 

44 
Reductionfrom 

Full Flow 

Baseline 

Maximum AT 

DischargeTemperature Target 

:igure8 Percent reduction from full-flow baseline of numbers killed under 1999-2001 operations at the Roseton 

Generating Station due to a load-based flow strategy. Maximum discharge temperatures range from 20"to 40°C and 

maximum AT from 5"to 15°C. 

15