Summary of Process to Identify the Appropriate Site-Specific Technology where Preapproved BTA is 

Infeasible

For the small number facilities where the preferred BTA is infeasible given site-specific factors,1EPA 

should establish a rigorous process for state environmental regulators and facilities to identify 

appropriate alternative technologies considering the expected impingement mortality reduction, 

including avoidance of impingement, and cost-benefit analyses. Appendix A highlights the types of 

plants that could have circumstances where the preapproved BTA will be infeasible because of site 

constraints or the preapproved BTA would have very substantial impediments to their effectiveness or 

could not be installed at existing cooling water intake structures at a reasonable cost.

The following outlines the process companies and permitting directors would undertake to identify the 

appropriate site-specific technology to ensure that the rule results in a significant national reduction in 

impingement mortality with important environmental and ecological benefits throughout the U.S.

Comparable Discussion for Impingement Mortality 

If the preapproved BTA2 is technically infeasible based on site-specific considerations, or if a company 

identifies that a more cost-effective technology will achieve comparable performance to preapproved 

BTA, the company, in coordination with the permitting director, should engage in a process to select the 

comparable BTA technology(ies) required for the site considering expected impingement mortality 

reduction, including avoidance of impingement, and considering social costs compared to social 

benefits. This analysis must reflect the Director’s determination of the maximum reduction in 

impingement mortality warranted after consideration of all factors relevant for determining BTA for the

facility.

For each site-specific BTA determination, the Director must provide a written explanation of the 

proposed BTA determination for the proposed permit. The written explanation must describe why the 

Director has rejected any impingement mortality control technologies or measures that are better-

 

1

As has been demonstrated during the public comment process, a small but important number of plants will have 

circumstances where the preapproved BTA will be infeasible because of site constraints or the preapproved BTA 

technology would have very substantial impediments to effectiveness or could not be installed at existing cooling 

water intake structures at a reasonable cost. As detailed in Appendix A, examples of these circumstances include: 

1) long return and unfavorable receiving water environment; 2) substantial debris-loading and NPDES prohibition 

on return of debris; 3) impacts due to cake and frazzle ice on screens, in trough, at point of return; 4) screen house 

and other infrastructure constraints on retrofit; and 5) redundancy with existing effective measures.

2

Pre-approved BTA includes: modified traveling screens, such as Ristroph screens or equivalent modified traveling 

screens, with a fish return system; approach velocity of 0.5 feet/second (fps), measured at the first point of entry 

to the cooling water intake system; pre-existing offshore velocity caps; or existing closed-cycle cooling, including 

cooling towers or cooling ponds that were not themselves considered to be waters of the U.S. at the time that they 

were built. As explained in our comments, EPA’s proposed definition of a “closed-cycle recirculating system” at 40 

CFR 125.92 is unnecessarily restrictive. The proposed definition indicates that closed-cycle cooling should not “rely 

upon continuous intake flows of water”. Our recommended revisions to the definition included in our comments 

intends to preclude one-time passage of water, but recognizes that it is common practice for cooling towers and 

cooling ponds to receive makeup water on a continuous or semi-continuous basis to offset evaporation, drift, and 

blowdown.
performing than the pre-approved BTA, and must reflect consideration of all reasonable attempts to 

mitigate any adverse impacts of otherwise available better performing impingement technologies. The 

Director may reject an otherwise available technology as BTA for impingement mortality if the social 

costs of compliance are not justified by the social benefits or if there are adverse impacts that cannot be 

mitigated and that the Director deems to be unacceptable. If all technologies considered have social 

costs not justified by the social benefits, or have unacceptable adverse impacts that cannot be 

mitigated, the Director may determine that no additional control requirements are necessary beyond 

what the facility is already doing. At a minimum, the proposed determination in the statement of basis 

must be based on consideration of the following factors: 

(1) Numbers and types of organisms impinged, considering technologies that reduce the number 

of fish impinged;

(2) Impingement mortality impacts on the waterbody, considering seasonal dynamics;

(3) Quantified and qualitative social benefits and social costs of available impingement 

technologies, including ecological benefits and benefits to any threatened or endangered 

species;

(4) Impacts on the reliability of energy delivery within the immediate area; 

(5) Impact of changes in particulate emissions or other pollutants associated with impingement 

technologies;

(6) Land and space availability inasmuch as it relates to the feasibility of impingement technology; 

(7) Impacts on water consumption;

(8) Location and design of current intake;

(9) Remaining useful plant life; and

(10) Facility size.

In identifying the site-specific BTA technology, the facility and permitting director should consider any 

applicable examples included in a database EPA should establish to illustrate the expected performance 

of BTA technologies at specific sites. These examples would be based on a robust data set and reflect 

different situations that will affect impingement and impingement mortality such as different water 

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

on both fish mortality and biomass, and account for actions that prevent fish impingement in the first 

place. This database and review will facilitate permitting authorities’ identification and assessment of 

alternatives to the preapproved BTA technologies. These examples would not establish a national 

precedent that would be applicable to all facilities.
Appendix A

Examples of Situations Where Preapproved BTA is Not Technically Feasible

A small but important number of plants will have circumstances where the preapproved BTA will be 

infeasible because the preapproved BTA technology would have very substantial impediments to their 

effectiveness or could not be installed at existing cooling water intake structures at a reasonable cost. 

Examples of these circumstances include:

1. Long return and unfavorable receiving water environment – Existing facilities are often located 

in industrial areas at some distance from the source of cooling water, and in many cases, cooling 

water canals have been constructed for both the intake and discharge flows to access the source 

and receiving waterbodies (which are not always the same). These features allow the plants to 

be constructed further away from the source waterbody, but the associated distances create a 

challenge to effective return of impinged organisms to their natural habitat. Often, the closest 

potential return location has substantially different characteristics (e.g., depth, currents, and 

water quality) such that returned organisms may be exposed to additional stress, predation, or 

other factors affecting their survival. Topographic extremes add to this issue, both in the case of 

flat terrain with long runs to the waterbody as well in more rugged terrain where straight runs 

to the waterbody may not be feasible. Such systems result in long residence times within the 

return system with increased potential for temperature and handling stresses. In many cases, 

nearby locations for fish return are affected by the thermal loading of the plant’s discharge, 

resulting in additional stress on the organisms once they are returned to the receiving water. In 

other cases, favorable locations for fish return are subject to heavy port activities and shipping 

traffic, precluding access to the waterbody by a fish return and likely adversely affecting the 

survival of returned fish. NextEra Energy’s Port Everglades plant exhibits all three of these 

potential concerns due to the length to the closest access to the source water (approximately 

one-half mile), which is used as a major harbor for commercial shipping and cruise ships.

Additionally, Constellation Energy’s Gould Street facility has traveling screens installed but no 

fish return system. A fish return system is not feasible given the location in a cove off of the 

Patapsco River. The facility is located between a Tyco cable-laying ship facility and a marina. 

Given the small size of the plant’s property and the surrounding uses in the area, there is no 

place to locate a fish return away from the intake and thereby avoid re-impingement. Because 

the waterbody has significant boat traffic, it is also not possible to install a fish return pipe 

extending beyond the cove. 

Another example of an ineffective and infeasible fish return is NextEra Energy’s Seabrook plant, 

which is located approximately 1.5 miles inland from a set of barrier islands and approximately 

one mile from the estuary. The plant receives its cooling water from a velocity cap located a 

further 1.3 miles offshore. Return of the (very small number of) impinged fish to the estuary will 

result in mortality due to the inappropriateness of this habitat compared with the deep offshore 

environment. Additionally, construction of a fish return to the ocean is precluded by the 

extremely long distance, which includes approximately one mile of wetlands, a half-mile of open 
water estuary, and the barrier islands. In fact, the existing subsea and underground tunnel for 

intake and cooling water was designed to avoid impacts to these sensitive environments and the 

near-shore sea bottom. The situation at NextEra Energy’s St. Lucie facility is very similar.

Finally, widely fluctuating water levels in rivers (either associated with locks and dams or normal 

hydrological variation) or tidal systems also complicate design of an effective fish return system. 

For example, at NextEra’s Wyman plant on the coast of Maine, the tidal variation is between 10 

and 12 feet. 

2. Substantial debris loading and NPDES prohibition on return of debris – Many of NextEra Energy’s 

regulated plants in Florida experience significant debris loading from floating macroalgae, 

uprooted seagrass, and jellyfish that result in substantial loading of naturally-occurring 

material/debris on the traveling screens. The discharge permits require that aquatic organisms 

be returned to their natural habitat but prohibits the return of any other material collected from 

the traveling screens to the receiving waters. We are also aware of similar prohibitions in other 

states and cases where the mass of man-made debris exceeds the mass of fish by approximately 

100-fold. We are concerned that these naturally-occurring events of seagrass and other 

material loading on the screens will result in compliance issues, primarily: 1) achieving the 

impingement mortality performance goals due to physical stress from the high debris loads on 

the organisms during impingement on the screens and during efforts to separate them from the 

debris; and 2) inability to comply with the prohibition on returning debris to the receiving water 

body due to the requirement to return aquatic organisms. Similarly, we are concerned that 

organisms that are attached or otherwise difficult to remove from the debris during these 

critical events would be included in the mortality losses, further contributing to potential noncompliance with the impingement mortality performance goals. Thus, the rule should include 

provisions for the impacts from these events similar to the Phase II rule’s recognition that the 

permitting director had the discretion to consider unique and exceptional events in evaluating 

compliance with that rule’s performance goals. 

3. Impacts due to cake and frazzle ice: on screens, in trough, at point of return – Many existing 

plants have operational measures to limit the impact of ice during cold weather. In some cases, 

warm water is circulated out to the front of the intake area to avoid ice buildup on bar racks and 

screens. While necessary to maintain normal plant operations, these measures will likely 

present additional obstacles for fish that are impinged and returned to the source water body at 

or near ambient temperatures. Under severe wintertime conditions, ice will form in the return 

troughs and at the point of return to the waterbody. Such conditions would be encountered at 

NextEra Energy’s Point Beach plant in Wisconsin as well as several other plants located in 

northern climates.

4. Screen house and other infrastructure constraints on retrofit – The intakes and traveling screens 

at many existing plants were designed primarily for the purpose of debris removal and were 

sized to preclude objects that would clog the condenser tubes. The majority of traditional 
traveling screens are housed in fiberglass enclosures installed to provide a safety enclosure to 

protect workers from the equipment as well as to protect the equipment from the elements. 

Facilities in more northerly climates have screen houses that shelter these enclosures. Many 

plants will face substantial space restrictions within the intake bays and the screen houses for 

retrofitting fish-friendly screens, additional pressure washes, fish return troughs, etc. Similarly, 

several existing plants are highly constrained by existing infrastructure both on the plant site 

and in the environs of the plant on the way to the source water. These have the potential to 

greatly complicate the construction of the return and increase the stress on the returned fish. 

Such is the case for NextEra Energy’s Port Everglades plant, which has a major thoroughfare 

between it and the closest location for a fish return. 

5. Redundancy with existing effective measures – A broad requirement for the installation of fishfriendly traveling screens and fish return systems provides an unnecessary level of redundancy 

with little additional benefit at some facilities. Examples include plants designed with offshore 

intakes that include velocity caps and acoustic deterrents (e.g., NextEra Energy’s St. Lucie, 

Seabrook, and Point Beach plants), where the combined benefits of offshore locations and use 

of velocity caps (St. Lucie and Seabrook) and the use of innovative offshore intake designs and 

deterrence systems (Point Beach) substantially reduce impingement rates. NextEra Energy’s 

Duane Arnold plant is already equipped with cooling towers that should be considered 

compliant with the proposed impingement mortality and entrainment mortality performance 

standards. Requirements for additional technologies are not cost-effective and do not provide a 

significant benefit to warrant their costs.