# MEMORANDUM

**Tetra Tech, Inc. 10306 Eaton Place, Suite 340**  **Fairfax, VA 22030 Phone**  **703**

**- 385** 

**- 6000**  **Fax 703** 

**- 385** 

**- 6007** 

TO : Lisa Biddle, EPA FROM : John Sunda, Tetra Tech DATE: December 1 8 , 2012 (updated May 13 , 2014)

SUBJECT: Velocity Cap Performance Data

This memo provides a summary of available design and performance data concerning known existing velocity

cap instal l ations in the US and worldwide

. As discussed below, existing velocity caps combine the advantageous characteristics of an offshore location and a well

performing technology ; this combination is sufficiently protective of impingeable organisms to be deemed equivalent to meeting the impingement mortality (IM) requirements for the Existing Facility rule. 1



# Data Sources

The data was obtained from a review of available documents including previous Technical Development Documents, survey data, EPRI’s 2007 compendium, other technology documents, site visit reports, and information from various Tetra Tech support documents for 316(b) implementation. A complete list of known velocity cap installations and summary data (including the sp ecific sources for performance data) are presented in Attachment A

.
**Technology Performance**

The overall performance of existing offshore intakes with velocity cap s with respect to impingement reduction is the result of the combination of two components; the intake location and the velocity cap

.

Intake Location

Intakes may

be located offshore for several reasons including: 1) to take advantage of a cooler source of water ; 2 ) to prevent recirculation of the heated discharge ; 3 ) to take advantage of lower

1 

## Note that this analysis assumes that the impingement mortality performance standard is 7 4 %.

# density

of biological organisms, and/or 4 ) limitations regarding the availability of a suitable shoreline location. Often

, a combination of these factors is considered when selecting the location of a submerged intake. As discussed in Section 6.18.4 of the proposed r ule Technical Development Document

, locating submerged intakes in the deeper regions o f larger waterbodies (particularly outside the littoral zone) has the potential to reduce impingement and entrainment (I&E)

, due to the lower densities of aquatic organisms as compared to a shoreline

-based intake. In Entrainment of Fish Larvae and Eggs on the Great Lakes, with Special Reference to the D.C. Cook Nuclear Plant, Southeastern Lake Michigan (1976), researchers noted that larval abundance is greatest within the area from the 12.2

-m (40

- ft) contour to shore in Lake Michigan and that the abundance of larvae tends to decrease as one proceeds deeper and farther offshore. This finding led to the suggestion of locating CWIS s in deep waters. For 316(b) Phase I, EPA considered relocating intakes 125 meters (410 feet) outside of the littoral zone to be a good engineering practice aimed at reduced impingement and entrainment

. The Office of Naval Research states that the littoral zone in ocean environments extends from the shore to 60 0 feet ( ft .) out in the water ( ONR 2013). Inaddition, installing the intake to depths where there is a lower concentration of living organisms (i.e., at least 20 meters) is also expected to decrease environmental impacts associated with intake operations. The reduction in I&E is highly site

specific ; the data in Attachment A suggests that

, by itself

, while often effective in reducing I&E, simply being located offshore does not sufficiently reduc e I&E to merit any designation of compliance on a national scale.

Velocity Caps

Intakes at a submerged offshore location can utilize various inlet designs including open pipe, perforated pipe, cribs, wedgewire screens, velocity caps, etc. Of these, only velocity caps and wedgewire screens are designed to reduce impingement. 2 

# As discussed in Section 6. 13 of the
proposed r

ul e Technical Development Document

, wedgewire screens can be very effective in reducing impingement. 3 

# Nearl y all of the velocity caps identified for this memo were located in the Pacific Ocean, the Atlantic Ocean or one of the Great Lakes and were located b etween 8 0 0 ft. and 7,000 ft. offshore. As above, the data in Attachment A suggests that

, by itself

, while often effective in reducing I& E, simply utilizing a velocity

cap does not sufficiently reduc e I&E to merit any designation of compliance on a national scale.

Analysis of Data

Depending on the design and location, the combination of submerged offshore location with a velocity cap can potentially

serve as an effective impingement reduction technology when compared to shoreline intakes without impingement reduction technologies. This analysis focuses on submerged intakes with velocity caps. Other types of intakes are not included

, except as they provide baseline data regarding the effect of the velocity cap alone.

2 

## A deep offshore location can be effective in reducing the density of organisms subject to entrainment. However, this memo focuses only on the performance of velocity caps with respect to im pingement mortality.
3 

## Fine mesh wedgewire screens may also reduce entrainment; however, this memo focuses solely on compliance with impingement requirements.

# The available impingement red uction performance data includes estimates of reductions based

on three component s/combinations : 1) location alone ; 2) velocity cap alone ; and 3) a combination of both location and velocity cap

. 4 

# Table 1 presents a summary of impingement reduction data for each

. Note that this data ty pically refers to a percent reduction in the number of impinged fish or biomass and does not necessarily reflect survival in cases where fish impinged on shore

-based screens are returned to the source water. 5 

# There was a very l imited amount of data available d ue to the small number of intakes with the velocity cap technology

and performance data. As a result

, EPA included all available data in the summary data shown in Table 1 regardless of whether the performance metric is based on number of fish or biomass and in a few instances the basis of the metric was unclear. In Table 1, the few data points for “Location” (two) and “Combination” (one) are based on number of fish data only. Biomass data

was available onl y f

or the “Velocity

Cap” technology group and there was only one study that

was clearly based on number of fish and that study reported the highest reduction ( 97%)

, The other six studie s (four biomass and two unclear) were also included because these studies present a much wider range of performance ( 50% to 94.5%) than the single study based on number of fish.

**Table 1**

**Summary of Velocity Cap Impingement Percent Reduction Data** Performance Ty

pe Average Median Minimum Maximum Count Location 66 % 66 % 60% 73 % 2 Velocity Cap 78% 82% 50% 97% 7 Combination 76% 76% 76% 76% 1

Note: See Attachment A for a full list of the data sources, all of which are included in EPA’s record for the rule. The following performance data presented in the attachment are not included in Table 1:

 Data for the San Onofre intake is an estimate of the survival of fish returned by the fish elevator system and does not reflect velocity cap performance.

 Data for Seabrook where it is unclear how values were c alculated for the site visit report and w here flow reduction was considered.

 Data for Edgewater unit 5 is for a velocity cap with 3/8 inch break away screens. These screens break away when they become plugged and it was not clear whether these screens were in

-place during sampling.



# Estimates of impingement reduction associated with location alone were identified for only two locations . Impingement reductions associated with location alone are difficult to establish because they

require either the presence of both a shoreline intake and a submerged offshore intake without a velocity

cap at the same facility

or the collection of impingeable fish densities data at separate locations. S uch data was available for two intakes . One was for intakes loc ated 850 ft. offshore in 22 ft. deep water in Lake Ontario and the other was located 1,200 ft. offshore in the Atlantic Ocean in 24 ft. deep water

. Two estimates are provided for the second location. The average of these two is used in the summary data. In both instances

, the impingement reduction estimates are developed b y comparing fish density data from gill net sampling conducted close to shore and close to the submerged intake. These limited data suggest that location alone can account for 60% to 73 % reduction in impingement

. However, it is not clear

4 

## Different data sources used different analytical approaches and study methods, proving a wide variety of data for comparison.
5 

## For this analysis, this type of data is acceptable; a fish “not impinged” can be considered towards complying with the impingement requirements.

# how this data relate s to other waterbodies. These data suggest that impingement reductions

associated with a submerged offshore location alone may not be sufficient to meet impingement standards

. Estimates of the performance of the velocity cap alone involve comparing the performance of separate intakes located in the same general area or comparing the performance of the same intake with and without the velocity cap. Seven sets of impingement performance data for the velocity cap alone were available

. 6 

# For three of the intakes located in the Pacific Ocean in California

, performance was evaluated by reversing the flow between the intake and the heated water discharge pipes

, which are also located submerged far offshore and are open pipes (i.e., have no screening technology) . For two intakes

, data were collected before and after velocity caps were installed or replaced . For two intakes

, data were collected for separate intake s located in the same general area. The summary data in Table 1 indicate that velocity caps alone can reduce impingement b y 50% to 97% with an average of 78% and median of 82%. This data suggests that in more than half of the velocity caps evaluated the ve locity caps alone may provide sufficient impingement reduction to meet the impingement performance standard ; however, for some intakes, the velocity cap alone may

not be sufficient.

Theoretically

, the reductions for the combination of the location and velocity cap could be calculated b y simply summing the reductions

. 7 

# This is a valid approach for data from the same facility since the starting point for data on a “velocity cap alone ” is based on the fish available at the offshore location. However, the combination of data from different facility locations has drawbacks

, especially

since the “ location alone ” reductions are very site

- specific. Regardless, based on the available data, the worst

- case combination of the minimum “ location alone ” reduction of 60% and the “velocity cap alone ” reduction of 50% results in an estimated combined reduction of 80%. An actual e stimate of the combined performance of velocity cap and location was also available for the intake at S eabrook

. Here, the estimate d impingement reduction was 76% and was calculated by comparing performance with a shoreline intake at a similar facility

located 65 miles away

. While there is some uncertainty regarding the validity of the estimate since it is from two facilities so far apart, the estimate suggests that the technology performance is compliant with the impingement standard . The reduction of 76% is also consistent with the estimated combined reduction of 80% derived by combining the minimum location and velocity cap only reduction.

**Conclusion**

The impingement reduction performance of intakes submerged far offshore with velocity caps is dependent on site

- specific conditions . The available data suggests that locating an intake far offshore alone may

not result in compliance with the impingement performance standard

. The available data also suggests that velocity caps alone may

result in compliance but not in all cases

. However, the data strongly su pports an assumption that existing intakes with the combination of

6 

## An additional intake with a higher impingement reduction than the others (98%) included 3/8 in screens at the inlet that break away as they become plugged ; since it was not clear whether these screens were in

-place during data collection

, this data is not included in Table 1 summary.
7 

## For example, if the location reduced impingeable fish by 60%, and the velocity cap reduced the remaining 40% by 50%, the combined reduction would be 80% (60% + (100

- 60)*50%).

# an intake located far offshore (e.g., at a minimum distance of 800 feet from the shoreline) and the

use of a velocity cap will result in performance comparable to, and in some cases better than, the impingement performance standard

.

# References

ONR

- Office of Naval Research. Ocean Regions: Littoral Zone

– Characteristics

. Webpage accessed on April 19, 2013 at: http://www.onr.navy .mil/focus/ocean/regions/littoralzone1.htm

# Attachment A **Summary of Velocity Cap Installations and Performance Data**

**Owner Facility** 

**Name Location**  **Waterbod y**  **Depth Distanc** 

**e Offshor** 

**e Velocity** 

**Data Performance** 

**Data %** 

**Impingemen t**  **Reduction Technolog** 

**y Aspect**  **Evaluated Basis of** 

**Comparison Metric**  **Notes Performance**  **Data Source** NRG Oswego Harbor Power, LLC Oswego

Harbor Units 5 & 6 Oswego,

NY Lake

Ontario Unit 5

–

22 ft; Unit 6

– 22 ft Unit 5

850 ft; Unit 6 950 ft Approac

h velocity 1.0 fps at max flow Offshore fish

density near intake was 60% lower than shoreline fish density based on gill net sampling (1.57 fish/sq ft net near shore and 0.63 fish/sq ft net offshore)

. 60% Location Gill net sampling near shore

versus near intake

. A mbient fish

sampling; number fish/sq ft net

. **Data used in**

**Table 1**

. Offs hore net size was twice nearshore so fish/sq ft metric was used. Unit 5 & Unit 6 each have similar offshore intakes with velocity caps. Unit 6 has an onshore diversion/bypass system

- comparative impingement data for diversion system is available. Total

fi sh/species collected by gill nets near

- shore and adjacent to Oswego Steam Station offshore intake (DCN 10

- 6511D)

Southern California Edison Co San Onofre

Nuclear Units 2 & 3 San

Clemente, CA Pacific

Ocean 32 ft 3,200 ft 1.5 fps Data cited for impingement reduction is based on four other southern California facilities. Value cited in 2008 Comprehensive Demonstration study (CDS) was 88.2% Velocity Cap Value

reported was from four other Southern California plants (El Segundo, Huntington Beach. Scattergood, O rmond Beach)

. **No useful data.** Due to design of discharge diffuser system evaluation of velocity cap not possible. Value reported was from other plants included in this table. Site Visit Report

for San Onofre (SONGS) (DCN 10

- 6548)

Effectiveness of fish elevator and return is 72% for a total c ombined estimated reduction of 97%. 72% Fish Return System Survival Entrapped

fish survival versus 100% mortality

. Impingement

mortality of entrapped fish

. **Data not used**

.

This value represents fish return efficacy only and not performance of velocity cap

. Separate data is available for fish and invertebrates; performance cited is for fish only. San Onofre

(SONGS) Comprehensive Demonstration Study (DCN10

- 6548C)

Alliant Energy Edgewater

Unit 5 Sheboygan

, W I Lake

Michigan Depth

below surface 10 ft 1,500 ft Cap has 3/8 in grills with through

screen velocity of 0.4 fps 2007 IMEC Study

reports IM for two intakes of similar distance offshore and similar design flow but Units 3&4 intake does not have a velocity cap

. Estimated annual IM for Unit 5 was 98% Velocity Cap with inlet screen Impingement

for two similar intakes with and without Velocity Cap

. Estimated

Annual Impingement for each intake

. **Data not used.**

Could not determine if reduction was due to velocity cap or screens

. Velocity Cap has 3/8 in mesh inlet screens that may or may not have been intact

. Section 316(b)

Impingement Mortality and Entrainment Characterization Study for the Edgewater Generating Station (DCN 11

- 5402)**Owner Facility**  **Name Location**  **Waterbod y**  **Depth Distanc** 

**e Offshor** 

**e Velocity** 

**Data Performance** 

**Data %** 

**Impingemen t**  **Reduction Technolog** 

**y Aspect**  **Evaluated Basis of** 

**Comparison Metric**  **Notes Performance**  **Data Source** <2% of value for Units 3&4. NRG Energy El Segundo

Units 3 & 4 El

Segundo, CA Santa

Monica Bay 29 ft

deep; 15 ft below MLLW 2,600 ft 2.4 fps at cap 94.5% IM

reduction in initial 1958 study of before and after velocity cap installation. 94.5% Velocity Cap Before and

after installation of velocity cap

on submerged intake in 1958

. Biomass:

focused on impingement of commercially and recreationall y important species and excluded forage and

non

- use species

. **Data used in**

**Table 1.** Clean W ater Act

Section 316(b) Velocity Cap Effectiveness Study (DCN 12

- 6809)

AES Redondo

Beach Units 5

- 8 Redondo

Beach, CA Units 1

- 6

King Harbor; Units 7

- 8 Pacific Ocean Units 1

- 6

30 ft deep 20 ft top to surface; Units 7&8 45 ft deep 30 ft top to surface Units

5&6 1,000 ft; Units 7&8 950 ft; Both approx. 3,000 ft from facility **No detailed**  **performance d**  **ata identified**  n/a

WeEnergies Presque

Isle Marquette,

MI Lake

Superior 27 ft

deep 8 ft top to surface 900 ft **No detailed**  **performance data**  **identified** n/a

Florida Power & Light Seabrook Seabrook, NH Atlantic

Ocean Wa ter is

60 ft deep; 18 ft from bottom, 42 ft from surface 7,000 ft DIF velocity is 0.5 fps at face Seabrook age 1

equivalent average annual impingement loss was 68% lower than at Pilgrim (calculated by EPA in Phase II Case Study)

. 68% Combinatio

n Impingement

for Seabrook Velocity Cap compared to Pilgrim Shoreline Intake located about 65 miles away. Age 1

equivalent l osses due to impingement

- it is not clear whether the difference in intake flow Seabrook (593 MGD) and Pilgrim (448 MGD)

was accounted for

. **Data not used.**

Differences in calculating annual impingement for each location may have affected calculated reduction. Pilgrim used design flow

- Seabrook used average flow also Seabrook did not sample at night

- suggest rel y on 2006

- 200 8 data reported by facility

. Case Study

Analysis for the Proposed Section 316(b) Phase II Existing Facilities Rule (DCN 4

- 0003)

83% (Next Era 2008) based on comparable data from nearby Pilgrim Plant. 2006 PIC reports a 76% reduction based on number fish/MG

. 76% Combinatio

n Impingement

for Seabrook Velocity Cap compared to Pilgrim Shoreline Intake located about 65 miles away. Number fish

impinged /M G **Data used in**

**Table 1**

. 76% value is from 2006 PIC B asis of 83% value could not be confirmed ( it is possible that this includes flow reduction since it is similar to 81% value reported in 2006 PIC)

. Only 76% value is Off

- shore, Mid Depth Velocity Caps as Best Technology Available for Impingement Control (DCN 11

- 6501L)**Owner Facility**  **Name Location**  **Waterbod y**  **Depth Distanc** 

**e Offshor** 

**e Velocity** 

**Data Performance** 

**Data %** 

**Impingemen t**  **Reduction Technolog** 

**y Aspect**  **Evaluated Basis of** 

**Comparison Metric**  **Notes Performance**  **Data Source** used 2006 PIC reports 81% reduction (from baseline) when recirculation flow averaging 47 MGD is factored in. 81% Combinatio n plus flow reduction Impingement

for Seabrook

v elocity cap compared to Pilgrim shoreline i ntake located about 65 miles away plus flow reduction

. Number fish

impinged /M G

. **Data not used**

.

Since submerged offshore intake withdraws cooler water plant is able to recirculate an average of 47 mgd

- 81% value includes consideration of flow reduction when compared to average intake pump flow. Does not reflect velocity cap performance alone

. Seabrook

Nuclear Power Station Proposal for Information Collection (DCN10

- 6514D)

Florida Power & Light St Lucie

Nuclear 1&2 Hutchinson

Island, FL Atlantic

Ocean Wa ter is

24 ft deep; 7 ft from bottom and 5 ft from intake top to surface at low tide 1,200 ft Emergency shoreline intake is on Indian River estuary. Gill net sampling near ocean shore shows impingeable density of 2.5 fish/100 m3 dropping to 0.8 fish/100 m3 beyond the caps (68% reduction)

. 68% Location Gill net sampling near shore

versus beyond the intake

. Number Fish

impinged /100 m3

. **Data used in**

**Table 1** as
a verage of the two location performance studies Site Visit Report

for St. Lucie (DCN 10

- 6515)

First year (2006) result of recent study shows impingement reduction of 71.6% for fish, 98.5% for shell fish and 77.1% overall comparing estuary to ocean

. 77% Location No details provided Fish and

shell fish combined

. **Data used in**

**Table 1** as average of the two location performance studies

. Partial results of 2006 study. Few details provided

. Site Visit Report

for St. Lucie (DCN 10

- 6515)

Average of two studies identified 73% Location **Data used in Table 1** 

. Average of two above studies including both fish & shellfish in second s tudy

. Site Visit Report

for St. Lucie (DCN 10

- 6515)

AES Huntington

Beach Units 1

-4 Huntington

Beach, CA Pacific

Ocean 18 ft

from surface and 5 ft above riser 1,500 ft 2.8 fps at cap 82% overall

reduction in impingement during 1978

- 79 study in which intake and discharge were switched (see TDD)

. 82% Velocity Cap Capped

versus un

- capped offshore intake by reversing intake and discharge

. Biomass of

impinged fish excluding silversides. **Data used in**

**Table 1**

**.** Results are conservative (effectiveness otherwise greater) as silversides, which were only present during

reverse operations, were Off

- shore, Mid Depth Velocity Caps as Best Technology Available for Impin gement Control (DCN 11

- 6501L)**Owner Facility**  **Name Location**  **Waterbod y**  **Depth Distanc** 

**e Offshor** 

**e Velocity** 

**Data Performance** 

**Data %** 

**Impingemen t**  **Reduction Technolog** 

**y Aspect**  **Evaluated Basis of** 

**Comparison Metric**  **Notes Performance**  **Data Source** not included in impingement reduction calculations. City of Los Angeles Scattergoo

d Units 1

- 3 Los

Angeles, CA Santa

Monica Bay Wa ter is

29 ft deep, 13 ft from bottom 1,600 ft 1.5 fps at velocity cap opening 83% reduction in

impingement during early 1970s study in which damaged cap was left off for a period. 83% Velocity Cap Capped

versus un

- capped offshore intake (damaged cap removed temporaril y)

. Biomass **Data used in Table 1** 

**.** Comparisons between periods were confounded by variations in plant operations and cooling water flows due to power demand and outages

. Clean W ater Act

Section 316(b) Velocity Cap Effectiveness Study (DCN 12

- 6809)

95/97% IM reduction based on biomass metric/abundanc e in a 2006 study where intake and discharge were reversed

. 97% Velocity Cap Capped

versus un

- capped offshore intake

- reversed intake and discharge flow direction

. Number of

impinged fish **Data used in**

**Table 1**

**.** No significant differences in fish densities were detected between the intake and discharge structures from the hydroacoustic dat a, indicating that differences in impingement between normal and reverse flow regimes were attributable to the presence or absence of the velocity cap and not the fish densities in the vicinity of the two structures

. Clean W ater Act

Section 316(b) Velocity Cap Effectiveness Study (DCN 12

- 6809)

Reliant Ormond

Beach Oxnard, CA Pacific Ocean 35 ft 1,950 ft Overall reduction in entrapment of 61% at night and 87% during the day (Next Era 2011)

. 74% Velocity Cap Capped

versus un

- capped offshore intake by reversing intake and discharge

. Impinged

fish excluding mackerel. Likely reported as biomass

- Scattergood report summary does not specify biomass but data is from report of a 4 plant study and biomass is specified for other plants. **Data used in**

**Table 1**

**.** Averaged night and day values but would be better if this was a weighted average. Mackerel were removed from analysis because of unusually high relative abundance of mackerel schools in the study area. Off

- shore, Mid Depth Velocity Caps as Best Technology Available for Impingement Control (DCN 11

- 6501L)**Owner Facility**  **Name Location**  **Waterbod y**  **Depth Distanc** 

**e Offshor** 

**e Velocity** 

**Data Performance** 

**Data %** 

**Impingemen t**  **Reduction Technolog** 

**y Aspect**  **Evaluated Basis of** 

**Comparison Metric**  **Notes Performance**  **Data Source** Constellatio

n Nine Mile

Point Scriba, NY Lake Ontario 6 ft from

bottom; 14 ft from surface Unit 1

850 ft; Unit 2 1,000 ft Unit 1

- 2

fps; Unit 2

- 0.5 fps Site visit Report

refers to gill net sampling being conducted near shore and near intake but data was not available at time of visit. **No detailed**  **performance data**  **identified** n/a

AES Kintigh

(Somerset) Somerset,

NY Lake

Ontario Depth

below surface 16 ft; Minimu m 6 ft above bottom 621 m 0.5 fps (0.15 m/sec) **No detailed**  **performance data**  **identified** n/a

Constellatio

n Ginna Ontario, NY Lake Ontario 11 ft

from bottom 15 ft below surface 3,100 ft 0.6 fps **No useful data**

. Gill net sampling was performed near shore and near intake but data was only compared to impingement data and not between net locations. Comprehensive

Impingement Mortality and Entrainment Characterization Report for RE Ginna Nuclear Power Plant (DCN 12

- 6810)

EDF Energy Sizewell

Power Station (Intake B) England Intake A 300 m; I ntake B 600 m Two intakes with and without caps. Impingement at intake B is about 50% below intake A 50% Velocity Cap Unclear if data is number of fish or biomass **Data used in**

**Table 1**

**.** Technical

Development Document for the Proposed Section 316(b) Existing Facilities Rule (DCN 10

- 0004)

Dungeness Power Station (Intake B) England Two intakes with and without caps. Impingement at intake B is about 62% below intake A 62% Velocity Cap Unclear if data is number of fish or biomass **Data used in**

**Table 1** 

**.** Technical

Development Document for the Proposed Section 316(b) Existing Facilities Rule (DCN 10

- 0004)**Owner Facility**  **Name Location**  **Waterbod y**  **Depth Distanc** 

**e Offshor** 

**e Velocity** 

**Data Performance** 

**Data %** 

**Impingemen t**  **Reduction Technolog** 

**y Aspect**  **Evaluated Basis of** 

**Comparison Metric**  **Notes Performance**  **Data Source** Ontario Power Nanticoke

Thermal Generating Station Ontario,

Canada Lake Erie We st intake in 12 m deep water We st

Intake 475 m; East Intake 525 m **No data.** Mentioned in Phase II TDD Technical

Development Document for the Proposed Section 316(b) Existing Facilities Rule (DCN 10

- 0004)