Tetra Tech, Inc.

10306 Eaton Place, Suite 340

Fairfax, VA 22030

phone 703-385-6000

fax 703-385-6007

DATE: November 1, 2011

TO: Paul Shriner and Lisa Biddle, USEPA

FROM: John Sunda and Kelly Meadows, Tetra Tech

SUBJECT: Analysis of Intake Through

System Intakes

As a companion to other analyses on intake velocity, Tetra Tech was tasked with 

intake velocities at facilities utilizing closed

Table 1 provides a summary of the distribution of the 

the detailed questionnaire (DQ) for

cost analysis and were classified as closed

similar data for all intakes reported in both the DQ and short technical questionnaire (STQ) but is 

limited only to facilities where the entire plant was classified as recirculating (i.e., does not 

include facilities classified as combination, other

velocity distributions.

Distribution of Through

Power Generation Intakes Used in Costing

Through

Velocity

>0.5 

>1.0 

>1.5 

Includes both retrofits and original CCRS

MEMORANDUM

November 1, 2011

Paul Shriner and Lisa Biddle, USEPA

John Sunda and Kelly Meadows, Tetra Tech

of Intake Through-screen Velocity at Existing Closed Cycle Cooling 

As a companion to other analyses on intake velocity, Tetra Tech was tasked with 

intake velocities at facilities utilizing closed-cycle cooling systems.

the distribution of the through-screen velocity data reported in 

) for power generation facility intakes that were included in the 

cost analysis and were classified as closed-cycle systems with cooling towers. Table 2 provides 

similar data for all intakes reported in both the DQ and short technical questionnaire (STQ) but is 

limited only to facilities where the entire plant was classified as recirculating (i.e., does not 

ied as combination, other, etc.). Both data sets result in similar screen 

Table 1

of Through-screen Velocity for Closed Cycle

Power Generation Intakes Used in Costing

Through-screen 

Velocity (fps)

Number

of Intakes

Percent of 

Total

≤0.5 25 42%

>0.5 - ≤1.0 11 18%

>1.0 - ≤1.5 9 15%

>1.5 - ≤2.0 3 5%

>2.0 12 20%

Total 60 100%

Includes both retrofits and original CCRS

screen Velocity at Existing Closed Cycle Cooling 

As a companion to other analyses on intake velocity, Tetra Tech was tasked with analyzing the 

velocity data reported in 

power generation facility intakes that were included in the 

Table 2 provides 

similar data for all intakes reported in both the DQ and short technical questionnaire (STQ) but is 

limited only to facilities where the entire plant was classified as recirculating (i.e., does not 

etc.). Both data sets result in similar screen 
Table 2

Distribution of Through-screen Velocity for Closed Cycle

Power Generation Intakes for Both STQ and DQ Intakes

Through-screen 

Velocity (fps)

Number

of Intakes

Percent of 

Total

≤0.5 47 45%

>0.5 - 1.0 23 22%

>1.0 - 1.5 8 8%

>1.5 - 2.0 7 7%

>2.0 20 19%

Total 105 100%

Includes both retrofits and original CCRS

For comparison, Table 3 shows the distribution for all power generation intakes as reported in 

the TDD.

Table 3

Distribution of Design Through-Screen Velocities 

For All Power Generation Facilities

Through-screen 

Velocity (fps)

Estimated 

Number of 

CWISs1

Percent of 

Total

≤0.5 148 17%

>0.5 – 1.0 200 22%

>1.0 - 2.0 316 35%

>2.0 162 26%

Total 893 100%

1 Weighted estimates

Source: Exhibit 4-17 of TDD

A comparison of Tables 1 and 2 to Table 3 indicates that a much larger portion of the subset of 

closed-cycle intakes would be able to meet a 0.5 fps velocity standard. The reduced intake flow 

volume of a closed-cycle system is likely to be a contributing factor to this trend.

The intakes in Tables 1, 2, and 3 include both cooling water systems originally built as closed 

cycle plus those that have been converted from once-through to closed-cycle cooling (i.e., 

retrofits). To determine if there is any difference in the intake velocity distribution between 

those two groups, a review of readily available information of facilities with retrofits was 

performed. Currently, EPA has identified 10 facilities where closed-cycle retrofits have

occurred. Post retrofit intake through-screen velocity data was available from the technical 

surveys for those retrofits that occurred prior to the year 2000 and from site visit data for several 

of the more recent retrofits. Table 4 identifies the retrofit plants, retrofit dates, and availability of 

screen velocity data. The Jeffries plant reported data for two intakes.
Table 4

Summary of Known Plants that have 

Performed a Closed Cycle Retrofit

Plant State Retrofit 

Year

Post Retrofit 

Velocity Data 

Available

Wateree SC 2006 No

Nearman Creek KS 2006 No

Brayton Point MA Ongoing No

Linden NJ 2002-2005 NA1

Yates GA 2004 Yes2

McDonough GA 2008 Yes2

Canadys SC 1972&1975 Yes

Jefferies SC 1985 Yes

Jefferies SC 1985 Yes

Pittsburg Unit 7 CA 1976 Yes

Palisades MI 1974 Yes

1 Uses gray water as makeup source and no longer has an intake

2

Installed 0.5 fps wedgewire screens.

Table 5 summarizes the distribution of the through-screen velocities for the seven intakes at 

facilities where closed-cycle retrofits have occurred.1 A comparison of the distributions in Table 

5 to Tables 1 and 2 shows a similar proportion of intakes with through-screen velocities ≤0.5. 

The most noticeable difference is that no intakes in the known retrofit sample had through-screen 

velocities >1.0 fps compared to 40% and 33% in the larger samples in Tables 1 and 2 that 

include both retrofits and original CCRS systems. 

Table 5

Distribution of Through-screen Velocity at Intakes Where 

Closed Cycle Retrofits are Known to Have Occurred

Through-screen 

Velocity

Number 

of Intakes

Percent 

of Total

≤0.5 3 43%

>0.5 - ≤1.0 4 57%

>1.0 - ≤1.5 0 0%

>1.5 0 0%

Total 7 100%

 

1

The “intake” for the Linden facility theoretically has a velocity of “0” since it no longer uses its intake, but was not 

included since reuse of gray water is not available to most facilities.
Possible Followup Analysis

As seen in Table 5, two of the retrofit intakes were installed fairly recently and it’s possible the 

design requirements imposed may have been influenced by recent 316(b) regulatory

developments. To help confirm these differences, it would be useful to attempt to identify

additional intakes associated with closed-cycle retrofits. The DQ survey includes questions 

regarding cooling towers that ask for the “Calendar Year Cooling Tower(s) Installed” on a per 

Cooling Water System (CWS) basis. It should be possible to identify other “pre-year 2000” 

closed-cycle retrofits where through-screen velocity data is available by combining this “year 

installed” data with EIA data regarding the year(s) generating units came online for those plants 

with closed cycle systems. While there may be some difficulty identifying which towers (or 

CWSs) are associated with each generating unit, for those where the generating units clearly predate the cooling towers, the likelihood that a retrofit occurred will be high.