Impingement Mortality Decision Tree for BTA Technology Requirem

Either1 (1) install preapproved

BTA (i.e., modified travelling screens such as If preapproved BTA i

De Minimis Exception : Does ( , g Ristroph screens with post‐Fletcher modifications

or maximum intake velocity (i.e., approach

velocity)) and operate such BTA technology

consistent with best management practices or (2)

operate pre existing offshore velocity caps or

closed cycle cooling2 consistent with best

management practices

If preapproved BTA i

based on site specifi

company demonstrates 

technology(ies) will 

performance to preapp

technology(ies), in coor

director, through 

the facility’s impingement

mortality meet one of the de

minimis exceptions (e.g.,

actual vs. design flow, numeric

impingement level, or

operating characteristics)?

If not No

Technology Optiopotentially availa

Operate intake

consistent with best

management

Yes

management practices.

Select BTA (or combination of technologies) and

install and operate consistent with best

management practices and manufacturer’s

p y combination of te

considering techninstalled, that miimpingement mo

• Advanced scree

systems;

practices.

management practices and manufacturer s

recommendations. Verify effectiveness during

required permitting review considering expected

effectiveness identified in ranking process.

• Intake Velocity (

screen velocity);• Offshore velocit

• Diversion techn• Wedgewire scre• Other technolospecific factors

Justification

preapproved BT

Impingement Analysis: Rank

remaining technologies based on

Cost Benefit Analysis with

Permitting Authority: In

coordination with permitting

director, evaluate remaining

technologies and identify most

effective control based on cost preapproved T

infeasible at site 

other infeasible 

on site specif

remaining technologies based on

expected impingement mortality

reduction including avoidance of

impingement.

effective control based on cost

benefit analysis4 (e.g., reduction in

impingement mortality, avoided

impingement, and other social

costs and benefits) and document

results.
Impingement Mortality Decision Tree for BTA Technology Requir

This decision structure provides a logical and consistent mechanism to make a BTA determination for a facility. 

preapproved option and obligation to operate that technology consistent with best management practices, we 

vast majority of facilities will install the preapproved BTA technology For the small subset of facilities where ad1. Preapproved BTA include modified travelling screens such as Ristroph screens with post‐Fletcher modific

intake velocity (i.e., approach velocity). Pre‐existing offshore velocity caps or closed cycle cooling (includ

vast majority of facilities will install the preapproved BTA technology. For the small subset of facilities where ad

minimal intake velocity is not technically practical, this decision process ensures BTA is installed at the facility ba

considerations. Notes

or cooling ponds that are not determined to be the waters of the U.S.) would be deemed compliant with mortality standards under section 316(b). Thus, units that have pre‐existing offshore velocity caps or clohave or install modified travelling screens such as Ristroph screens with post‐Fletcher modifications; or t

maximum intake velocity (i.e., approach velocity) would be required to operate those technologies cons

management practices.

2. The proposed definition of closed cycle cooling should be refined to eliminate the requirement of a min

cycles of concentration.

3. In identifying all BTA technologies, the facility and permitting director should consider any applicable exa

database EPA establishes to illustrate the expected performance of BTA technologies at specific sites. Th

be based on a robust data set and reflect different situations that will affect impingement such as differe

fragile species, facility sizes, and seasonal dynamics. The expected performance should be based on bo

biomass and account for actions that prevent fish impingement. This database would facilitate permittiidentification and assessment of alternatives to the preapproved BTA technologies. These examples wo

national national standard standard that wo ld u be applicable applicable to all facilities facilities.

4. Cost Benefit Analysis Criteria – In the cost benefit analysis, the facility and permitting director should ev

and environmental impacts associated with each option remaining under consideration. The “top” rank

combination of technologies should be considered BTA unless the facility demonstrates, and the permitt

th t a the economic and envi tl ronmental i t mpac s j tif us y a concl i us on th t a the th l ec no ogy is not f ibl eas e or 

justified at that facility. In this evaluation, the facility and permitting director should consider comparab

database noted above, applicable literature, and any available site or comparable site studies. This cost 

would be consistent with the analysis for entrainment.