Document ID: EPA-HQ-OW-2008-0667-3632
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2014-08-15T04:00Z

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 18, 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 installations 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.

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 specific sources for performance data) are presented in Attachment A.

Technology Performance

The overall performance of existing offshore intakes with velocity caps 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 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 rule Technical Development Document, locating submerged intakes in the deeper regions of 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 CWISs 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 600 feet (ft.) out in the water (ONR 2013). In addition, 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 reduce 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.  As discussed in Section 6.13 of the proposed rule Technical Development Document, wedgewire screens can be very effective in reducing impingement.  Nearly 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 between 800 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 reduce 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.

The available impingement reduction performance data includes estimates of reductions based on three components/combinations: 1) location alone; 2) velocity cap alone; and 3) a combination of both location and velocity cap. Table 1 presents a summary of impingement reduction data for each. Note that this data typically 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. There was a very limited amount of data available due 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 only for 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 studies (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 Type
                                    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 calculated for the site visit report and where 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. Such data was available for two intakes. One was for intakes located 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 by 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 how this data relates 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. 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 intakes located in the same general area. The summary data in Table 1 indicate that velocity caps alone can reduce impingement by 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 velocity 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 by simply summing the reductions.  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 estimate of the combined performance of velocity cap and location was also available for the intake at Seabrook. Here, the estimated 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 supports an assumption that existing intakes with the combination of 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
                                   Waterbody
                                     Depth
                               Distance Offshore
                                 Velocity Data
                               Performance Data
                            % Impingement Reduction
                         Technology 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
Approach 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.
Ambient fish sampling; number fish/sq ft net.
Data used in Table 1. Offshore 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 fish/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, Ormond 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 combined 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, WI
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 <2% of value for Units 3&4.
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)
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 recreationally important species and excluded forage and non-use species.
Data used in Table 1.
Clean Water 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 data identified
n/a
We Energies
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
Water 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%
Combination
Impingement for Seabrook Velocity Cap compared to Pilgrim Shoreline Intake located about 65 miles away.
Age 1 equivalent losses 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 rely on 2006-2008 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%
Combination
Impingement for Seabrook Velocity Cap compared to Pilgrim Shoreline Intake located about 65 miles away.
Number fish impinged /MG
Data used in Table 1. 76% value is from 2006 PIC Basis 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 used
Off-shore, Mid Depth Velocity Caps as Best Technology Available for Impingement Control (DCN 11-6501L)

2006 PIC reports 81% reduction (from baseline) when recirculation flow averaging 47 MGD is factored in.
81%
Combination plus flow reduction
Impingement for Seabrook velocity cap compared to Pilgrim shoreline intake located about 65 miles away plus flow reduction.
Number fish impinged /MG.
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
Water 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 average 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 study.
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 not included in impingement reduction calculations.
Off-shore, Mid Depth Velocity Caps as Best Technology Available for Impingement Control (DCN 11-6501L)
City of Los Angeles
Scattergood Units 1-3
Los Angeles, CA
Santa Monica Bay
Water 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 temporarily).
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 Water Act Section 316(b) Velocity Cap Effectiveness Study (DCN 12-6809)

95/97% IM reduction based on biomass metric/abundance 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 data, 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 Water 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)
Constellation
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; Minimum 6 ft above bottom
621 m
0.5 fps (0.15 m/sec)

No detailed performance data identified
n/a
Constellation
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; Intake 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)
Ontario Power
Nanticoke Thermal Generating Station
Ontario, Canada
Lake Erie
West intake in 12 m deep water
West 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)