Impingement mortality can be reduced greatly by reducing the through-screen velocity in any screen. Reducing the rate of flow of cooling water through the screen (through-screen velocity) to 0.5 fps or less reduces impingement of most fish because it allows them to escape the intake current. (See 66 FR 65274 [December 18, 2001] and DCN 2-028A, EPRI's "Technical Evaluation of the Utility of Intake Approach Velocity as an Indicator of Potential Adverse Environmental Impact Under Clean Water Act 316(b).") As a result, some facilities have designed and operate their modified traveling screens or wedgewire screens so as not to exceed a through-screen velocity of 0.5 fps. Swim speed studies demonstrate that for most facilities, an intake velocity of 0.5 fps or less will result in 96 percent or better reductions in impingement mortality for most species. EPA notes that preliminary results from recent studies of fine mesh screens suggest that at even lower intake velocities such as 0.25 fps, some hydrodynamic influences may reduce entrainment mortality even more, because flow dynamics are nonlinear. It is unclear as to whether such observations hold true when cooling water withdrawals (water volumes) are large. While higher intake velocities are sufficiently protective for some species of fish, the higher intake velocities are not necessarily protective of all life-stages. For example, younger fish may not be strong swimmers or may have not a developed avoidance response. Therefore higher intake velocities are not a high performing technology. As noted previously, low intake velocity has limited application, and is therefore not available as a candidate BTA technology. However, the technology is a demonstrated high performing technology, and is therefore included as a compliance alternative for those facilities where the technology is available.
D.	Technology Basis for Today's Final Rule
As described above, EPA examined the full range of technologies that reduce impingement or entrainment or both. From an assessment of all factors, EPA identified one technology that is best technology available for minimizing the adverse impacts of impingement mortality at existing facilities: modified traveling screens with a fish-friendly fish return. EPA identified no single best technology that is available for minimizing entrainment at existing facilities for today's final rule. For new units at existing facilities, EPA identified mechanical draft wet cooling systems as BTA for both impingement and entrainment.
EPA did not identify any single technology or group of technology controls as the basis for establishing the national BTA standard for entrainment for existing units. Instead, EPA has established a national BTA standard for entrainment for existing units that requires determination of BTA entrainment requirements on a site-specific basis in a structured permitting setting. The framework for determining entrainment requirements provides for the consideration at a minimum of certain specified factors that must be considered in the Director's determination of the BTA controls.
   1. 	Alternative Impingement Mortality Standards for Existing Units
After considering all factors identified above, EPA has concluded that modified traveling screens, such as modified Ristroph screens and equivalent modified traveling screens with fish-friendly fish returns, are a best technology available for minimizing impingement mortality. These screens use 3/8 inch, or similar, mesh with collection buckets designed to minimize turbulence, a fish guard rail/barrier to prevent fish from escaping the collection bucket; "fish-friendly," smooth, woven or synthetic mesh; and a low-pressure wash to remove fish before any high-pressure spray to remove debris. The fish removal spray must be of lower pressure, and the fish return must be fish friendly, provide sufficient water and minimize turbulence. Modified traveling screens generally must be rotated continually to minimize aquatic exposure to impingement or to the air and thus obtain the highest reductions in impingement mortality.
      Under the seventh option for complying with the BTA impingement mortality standard in today's final rule, a facility may rely on any technology it chooses so long as it demonstrates through biological compliance monitoring that it achieves the required 12 month impingement mortality performance standard that EPA calculated based on the performance of the BTA technology  -  modified traveling screens with fish return. As discussed in the TDD (see, for example, TDD Exhibits 11-1 and 11-3), EPA based the 12 month percent mortality performance at § 125.94(c)(7) on data from facilities with traveling screens modified with features to improve the post-impingement survival of organisms such as smooth mesh, continuous or near-continuous rotation of the screens, buckets with guard rails, low pressure sprays for collecting fish, and fish return systems. The statistical basis for the 12 month impingement mortality performance standard includes 26 sets of 12 month survival percentages across 17 facilities demonstrating average impingement mortality rates ranging from 1.6 to 48.8 percent under conditions of 18 to 96 hour holding times. EPA established the 12 month percent mortality as 24 percent which is the arithmetic average of the impingement mortality rates from the 17 facilities. (This is consistent with EPA's proposed rule use of expected value of the beta distribution which can be calculated as the arithmetic average.) Note: The 12 month impingement mortality performance standard means that no more than 24 percent of the impinged fish may die or alternatively at least 76 percent of the impinged fish must survive. EPA has occasionally used average annual limitations in the effluent guidelines program, most recently for the pulp and paper industry category (40 CFR 430, promulgated in 1998). In these instances, such as the technology-based BAT, EPA has defined the annual average limitations to be the average level demonstrated by the technology. Thus, EPA's approach to calculating the 12 month percent survival performance standard is consistent with past practice.
EPA recognizes that variability in the technology performance occurs due to changes in seasons, differing intake locations, higher mortality of certain species, and speciation found in different water bodies. By using a full 12 months of data, EPA has ensured that the resulting performance standard reflects the widest range of potential conditions present in EPA's database. EPA has further incorporated variability into the 12 month impingement mortality performance standard by basing it on data from 17 facilities which collectively performed more than 1,500 sampling events beginning as early as 1977. EPA notes that seven facilities had mortality rates less than 10 percent which provides evidence that facilities can, and have, maintained and operated their systems in a manner consistent with the performance standard. Another four facilities demonstrated impingement mortality rates significantly greater than the performance standard of 24 percent, however, EPA notes these facilities were not required to optimize their technology performance as part of their study, and data collection was not required to achieve a certain level of performance. In each study, EPA has identified elements of the technology operation that a facility could modify to achieve the 12 month percent impingement mortality performance standard. By using the 12 month percent impingement mortality performance standard, EPA has ensured that the resulting performance standard reflects the widest range of potential conditions present in EPA's database. In addition to those studies meeting the criteria for use in the 12 month percent survival performance standard calculations, there are further studies in EPA's record that provide additional performance data showing facilities can, and have, maintained and operated their systems in a manner consistent with the performance standard. EPA's record includes approximately 250 total studies related to impingement (see TDD Exhibit 11A-1).

Despite the overwhelming evidence that the 12 month percent survival performance standard of 24 percent was consistent with demonstrated performance for the best technology, EPA considered other alternatives that might incorporate more variability into a performance standard. EPA concluded that none of the alternatives were consistent with the need for facilities to demonstrate ongoing maintenance and operations over a long period of time, such as a year. Any alternative would be less stringent and would allow facilities to target long-term performance at a level that would be less than the optimal performance demonstrated by facilities with the technology in place. Further, the 12-month average impingement mortality performance standard will require a facility to actively evaluate performance during the 12 month period enabling the facility to optimize the technology to improve performance to counterbalance a result above the standard by one below the standard. If EPA had included a monthly average standard, it would have similarly needed to incorporate allowances for exceedances. Allowing for exceedances would have provided no incentive for improving operations for such exceedances. Therefore, EPA determined that the 12 month impingement mortality performance standard is sufficient to ensure performance consistent with best technology available. For this reason, EPA is not promulgating the monthly average that was included in the proposal. EPA's decision also is consistent with effluent guidelines where compliance with the monthly average limitation is not required for facilities subject to a longer term limitations such as an annual average limitation (e.g., pulp and paper 40 CFR 430 Subpart B AOX limitation).
EPA did not include in the final rule a number of requirements it had considered at proposal. The proposed rule would have required the seasonal deployment of barrier nets on estuaries and oceans as one element of the best technology available for minimizing the impingement mortality of shellfish (crustaceans). EPA has opted not to include any specific requirements for shellfish in the final rule, because EPA's review of the impingement data it used to develop today's final rule impingement performance standard includes data that incorporate shellfish survival as part of the performance standard. Further, as previously explained, the final rule provides for the Director to establish additional requirements where necessary.
EPA expects facilities complying with § 125.94(c) of today's rule by compliance option (7) to track their compliance with the 12 month percent impingement mortality performance standard on an ongoing basis and to proactively modify their technology or operations when a trend in the sampling suggests that they might be in danger of exceeding the 12 month percent impingement mortality performance standard in the future. The 12 month percent impingement mortality performance standard requires that impingement mortality not exceed 24 percent, calculated as the sum total number of fish that were impinged and died within the holding time divided by the sum total number of fish impinged for a 12-month period. EPA expects the ratio will be calculated based either on direct sampling counts, or based on both counts being extrapolated to represent annual counts. Because comments provided data that expanding the proposed 24 to 48 hour holding time requirement would generally not affect the observation of mortality due to impingement, the regulation allows for holding times from 18 to 96 hours.
As explained in more detail in Section VI.E and G below, the BTA technology for impingement does not minimize adverse environmental impacts associated with entrainment.
2.	Entrainment Standards for Existing Units
As discussed below, EPA is not basing BTA for entrainment at existing units (that is, excluding new units at existing facilities) on closed-cycle recirculating cooling systems, a highly effective technology, because this technology is not available nationally and therefore does not represent BTA. EPA also has not identified any other effective, available and demonstrated candidate technology (or combinations of technologies) for entrainment reduction at existing units that is available nationally. For other entrainment technologies that might be available on a site-specific basis, see Section VI.E.2 below and Chapter 6 of the TDD. EPA did not select the other flow-reduction technologies (such as variable-speed drives and seasonal flow reductions) as the technology basis for entrainment control measures because these technologies are not uniformly best and are not broadly available for most facilities. Further, EPA has not identified a basis for subcategorizing existing units at which flow reduction technologies are feasible. The effectiveness, availability, and utility to a given facility of flow reduction or other entrainment reduction methods depends on site-specific geographical and biological conditions as well as operations of the facility. For example, this is the reason that EPA did not select relocation of a shoreline intake to far offshore as a technology basis for the BTA entrainment standard because this technology is not widely available for most facilities.
3.	Impingement and Entrainment Standards for New Units at Existing Facilities
In contrast to existing units, installing a closed-cycle cooling system at a new unit is far less complex. The technology is also highly effective, generally achieving greater than 95 percent reductions in IM and E (mechanical draft (wet) cooling towers achieve flow reductions of 97.5 percent for freshwater and 94.9 percent for saltwater sources, or by operating the towers at a minimum of 3.0 and 1.5 cycles-of-concentration, respectively). These reductions in flow and the concurrent reductions in impingement and entrainment impacts are among the highest reductions in adverse environmental impact possible at an intake structure.
As described below, EPA has concluded that new units, in contrast to existing units, have much greater flexibility in terms of cooling system design, construction scheduling, and other factors that help minimize many of the negative aspects associated with closed-cycle cooling. For a more detailed discussion of this rationale, see below.
Under the final rule, a new unit at an existing facility, where the facility that withdraws or will withdraw more than 2 mgd when the new unit begins operating will have requirements similar to the requirements of a new facility in Phase I. Under the rule, a new unit (as defined at § 125.92(u) and described above) is required to have a flow limited to that which is commensurate with a closed-cycle recirculating system as it would be applied to the new unit. Today's final rule also includes an alternative approach (similar to Track II in Phase I), in which a facility could comply with the new unit standards by demonstrating that the technologies and operational measures employed will reduce the level of adverse environmental impact from any cooling water intake structure used to supply cooling water to the new unit to a comparable level to that achievable by implementing a closed-cycle recirculating system as defined at § 125.92(c)(1).
As discussed above, today's final rule defines a "new unit" at an existing facility as a stand-alone unit the construction of which commences after the effective date of today's final rule. New unit includes stand-alone units that are added to a facility for purposes of the same general industrial operation as the existing facility. This is in contrast to the definition of new facility, where a new facility does not include new units that are added to a facility for purposes of the same general industrial activity (40 CFR 125.83). The provision "for purposes of the same general industrial operation" is explicitly included in today's final rule definition of new unit at an existing facility for clarity. A new unit may have its own dedicated cooling water intake structure, or the new unit may use an existing or modified cooling water intake structure. Any unit at an existing facility that does not meet the new unit definition in today's rule is subject to the existing unit provisions.
EPA is adopting more stringent requirements for new units at existing facilities because such new units can be designed and constructed without many of the additional expenses and operational disadvantages associated with retrofitting an existing unit to closed-cycle cooling. For example, the incremental downtime that can be associated with retrofitting to closed-cycle cooling is avoided altogether at a new unit. In addition, when new units are added, the condensers can be configured for closed-cycle, reducing energy requirements (by substantially reducing the turbine backpressure energy penalty) and associated air emissions.
   The three factors that led EPA to reject closed-cycle cooling as BTA (described below in Section E) are far less relevant for new units at existing facilities than for retrofitting existing units. This section discusses why EPA concluded that each factor is not a significant concern for new units, and why the record supports EPA's conclusion that closed-cycle cooling is an available and feasible technology for new units at existing facilities.
   * Land Availability: In contrast to retrofitting the entire existing facility, the amount of space dedicated to closed-cycle for the new unit will be limited to the new unit rather than the entire facility. As a result, space constraints will be much less of an issue. New units also present the opportunity to design an optimized closed-cycle recirculating system for the new unit. Retrofitting an existing facility for the full intake flow of the facility would require a facility to identify (or possibly obtain) enough space to accommodate the cooling towers and associated equipment. Furthermore, new units and their corresponding cooling system can be built in stages rather than as a facility-wide retrofit, and since the new unit has not yet been built, there is no energy reliability concern (discussed further below).
   * Air Emissions: EPA expects that emissions are significantly less of a concern at new units. The condensers will be optimized for closed-cycle, reducing energy requirements, and high-efficiency cooling towers can be incorporated into the design of the new unit, potentially allowing for smaller cooling towers to be installed. Turbine backpressure and the associated energy penalty can be substantially reduced in a new unit, but EPA acknowledges new units will still have auxiliary power consumption for fans. Therefore energy penalties and air emissions for tower operations can be minimized (though not eliminated). The emissions effects of requiring closed-cycle cooling at new units at existing facilities is similar to the effects of this requirement at new facilities and will not pose an unacceptable impact. For more information, see Chapters 6, 8, and 10 of the TDD. Further, the new unit is likely to be more efficient and emit less pollution than existing units, therefore net emissions are expected to decrease as new units replace older, less efficient units.
   *  Remaining Useful Plant Life: This is clearly not an issue for new units. A new unit has its full useful life remaining and thus would experience the maximum possible reductions in adverse environmental impacts throughout that useful life.

 EPA does not expect that the requirements for new units at existing facilities will be a disincentive for facilities to repower existing units. The requirements only apply to stand-alone units. Requirements for entrainment at repowered units will thus be determined by the Director.  EPA notes, however, for facilities that do choose to repower an existing unit, the costs of employing a closed-cycle cooling system are not a barrier, as described above. In fact, some facilities may find closed-cycle cooling to be less costly over the long-term. For example, in locations with limited water resources such that once-through cooling of an additional unit is not possible, overall reliability will be increased by using closed-cycle cooling systems.
 EPA also recognizes that installing closed-cycle cooling systems at new units is a prevailing trend in industry, regardless of the regulatory requirements imposed by today's final rule. For example, see DCN 12-6672 in the record for today's rule, and DCNs 2-009 and 4-4023C (from the Phase I and Phase II dockets, respectively). These documents show that, on the basis of responses from facilities to the 316(b) industry questionnaire, facilities constructed in recent years are significantly more likely to employ closed-cycle cooling.
EPA recognizes that at some point in the future, every unit will be rebuilt, replaced or repowered (or retired). EPA projects that approximately 227 MW in new generating capacity per year, will be subject to the new unit provision, reflecting the general industry trend towards more efficient units. EPA's analysis projects an equivalent number of new units at manufacturing facilities will be constructed each year. See the Phase I rule for more information regarding the affordability and barrier to entry analysis for new construction.
EPA notes that the new unit provision is an important element of the final rule, given the generally long lifespan of equipment at industrial facilities. For example, generating units at a power plant are often projected to have a 50-year lifespan. As a result, these facilities have a slow rate of "evolution" in adopting newer technologies. By requiring closed-cycle cooling in new units, EPA is ensuring (along with the Phase I rule) that no new once-through cooling units or facilities will be built.

E. 	Option Selection
After considering all factors identified above, EPA has concluded that it should base the BTA impingement mortality standard for existing units on the performance of traveling screens (e.g., modified Ristroph screens and equivalent modified traveling screens with fish-friendly fish returns)  -  the "best technology available" for minimizing impingement mortality.  While there are a number of technologies that may perform as well as or better than traveling screens, these technologies were not feasible or available on a nationwide basis and thus were not the "best technology available" for standard setting purposes.  Moreover, the impingement mortality standard for existing units provides a number of alternatives, including some of these other technologies, for compliance with the standard. EPA based the BTA impingement mortality standard for existing units on the performance of traveling screens because EPA concluded that this technology is effective, widely available, feasible, and does not lead to unacceptable non-water quality impacts.
      As explained above, EPA has not identified a technology or combinations of technologies that EPA concluded is "best technology available" for minimizing entrainment at existing units.  EPA did not identify a technology for reducing entrainment that is effective, widely available, feasible, and does not lead to unacceptable non-water quality impacts. As such, EPA is unable to identify a nationally applicable BTA technology on which to base the BTA entrainment standard.
      While EPA concluded that closed-cycle recirculating systems reduce entrainment (and impingement mortality) to the greatest extent and are the most effective performing technology, after careful consideration of multiple factors, EPA concluded that a closed-cycle recirculating system is not the "best technology available" for existing units within the meaning of the statute.  It is not the best technology available on a national basis for minimizing adverse environmental impact and should not form the sole basis for the BTA standard for entrainment for the reasons explained below.
      EPA also determined that there were no other "available" technologies for entrainment whose performance came close to that of closed-cycle recirculating systems.  Further, while reduced intake velocity was a very effective control for impingement and may also reduce entrainment of some life stages of fish and shellfish, it does not significantly reduce entrainment of eggs and non-motile stages of larvae, and it is not physically available in many locations.
      EPA has broad discretion in what factors it should consider when it determines the best technology available for minimizing the adverse environmental impacts of cooling water intake structures.  As both the U.S. Supreme Court and the Second Circuit Court of Appeals have underscored, section 316(b) is "sui generis," in a class by itself, unencumbered by "specified statutory factors,"  Entergy Corp. v. Riverkeeper, Inc, 556 U.S. 208, 222 (2009); Riverkeeper, Inc. v. EPA, 358 F, 3d 174,187 (2d Cir. 2004).   The Second Circuit explicitly rejected the argument that, because section 316(b) does not mention costs or other factors, EPA cannot give costs or other factors "any" weight in deciding what is the best technology. Riverkeeper, Inc., 358 F.3d at 195.  Furthermore, the Second Circuit recognized that EPA may base its decision on factors other than the effectiveness of a given technology in reducing impingement and entrainment and that EPA is entitled to deference in deciding what weight to give to the factors it considers in its BTA determination.  Riverkeeper, Inc., 358 F.3d at 196.
      As noted, costs are one factor EPA may consider in its BTA determination.  Here, while EPA did consider costs, costs were not a dispositive factor in the decision to reject closed-cycle cooling as the basis for a uniform national BTA entrainment standard.  EPA did not reject closed-cycle cooling here either because it was not economically achievable or because the costs of closed-cycle would exceed its benefits.  Instead, EPA rejected closed-cycle cooling as the technology basis for a uniform national BTA entrainment standard based on three factors: land availability, air emissions, and remaining useful plant life as explained below.
      Central to EPA's evaluation of the availability of closed-cycle as BTA was EPA's new understanding of the limitations of technologies other than closed-cycle in reducing entrainment.  This presented EPA with a sharper choice than it had in the Phase II rule.  For today's rulemaking, EPA took a second look at the data it had relied on in the Phase II rule, particularly in light of new data received since the Phase II rule.  As a result, EPA learned that entrainment exclusion does not necessarily equate to entrainment survival (76 FR 22185), a key underpinning to EPA's BTA standards for entrainment in the remanded Phase II rule.
      For the remanded Phase II rule, EPA had established national BTA performance standards for entrainment (and impingement) and included a number of different alternative means to achieve the standards.  First, if a facility demonstrated that it could achieve reductions in flow associated with closed-cycle cooling, the facility met the BTA performance standards.  Alternatively, a facility could demonstrate that it met the entrainment performance standards by a combination of installed technology and operational or other measures (including restoration measures).  See 69 FR 41590 for a description of the final Phase II rule.  Critical to EPA's decision to provide an array of choices for achieving the national BTA entrainment performance standards was a key factual conclusion.  That conclusion was that a number of technologies would achieve performance reducing entrainment that was "comparable" to that of closed-cycle cooling.  Consequently, for the Phase II rule, EPA established an entrainment performance standard of 60 to 90 percent based on data it reviewed for the Phase II rulemaking.  See 69 FR 41598 for information on EPA's rationale for establishing compliance alternatives as part of the final rule.
      In the Phase II rule, while EPA looked to the performance of closed-cycle as the benchmark against which it evaluated technologies for the BTA standards, EPA did not mandate the achievement of flow reductions that were in all cases equivalent to closed-cycle.  Given that the available data supported the view that there were other much less expensive technologies that obtained significant reductions in entrainment, EPA was comfortable with a BTA standard that required achievement of a level of performance that was generally comparable though not equivalent to closed-cycle.
      Since the Phase II rulemaking, EPA has received new data and learned that its understanding of entrainment technology performance was incomplete.  Following the remand of the Phase II rule, EPA reexamined the data as well as new information on the performance of various entrainment control technologies it had previously reviewed.  As a result, EPA determined that its conclusion regarding the capability of these other technologies  -  a conclusion on which the Agency had based the Phase II BTA performance standards  -  was no longer supported by the data EPA had before it.
      There is a second additional consideration that further required EPA to focus renewed attention on how widely available closed-cycle cooling in fact was nationally.  The Second Circuit decision in the Phase II rule removed restoration as a compliance option that EPA could consider.  The decision underscored that restoration measures  -  one compliance option included in the Phase II rule  -  were not an available tool for complying with any 316(b) standard.  However, at the time of the Phase II promulgation, EPA expected some facilities would use restoration in lieu of closed-cycle cooling, thus making closed-cycle or reductions commensurate with closed-cycle feasible (76 FR 41609). With the court decisions that restoration was not an available tool for compliance, compliance with a standard based on closed-cycle cooling alone is less feasible than EPA had expected at the time of the Phase II promulgation.
	The changed landscape has narrowed markedly EPA's range of options with respect to the technology basis for today's BTA standards.  The gap between the performance of the most effective entrainment reduction technologies (closed-cycle) and other less expensive technologies has widened significantly. EPA's narrowed range of compliance technology choices required EPA to look even more closely at the feasibility of closed-cycle cooling and reduced flow.  As the Second Circuit has noted, EPA is clearly entitled to make its choice among alternative BTA technologies based on more factors other than just a technology's effectiveness in reducing impingement and entrainment.  Riverkeeper, Inc., 358 F.3d at 196.  EPA identified three factors as significant in its decision to reject closed-cycle cooling as the sole technology basis for a national BTA entrainment standard.  The three factors that collectively support rejecting closed-cycle cooling systems as a uniformly applicable BTA for existing facilities (except new units) are land availability, increased air emissions and remaining useful life.
1.	Land Availability and Geographical Constraints Could Be a Factor on a Local Basis
While EPA's record indicated that the majority of facilities have adequate available land to retrofit to closed-cycle cooling, some facilities have land constraints. While EPA originally estimated as many as 23 percent of facilities would not have enough space, it observed on site visits that some facilities with a small parcel of land could still install closed-cycle cooling by using creative engineering solutions. On the other hand, EPA found that some facilities with large acreage could not feasibly install cooling towers because of local zoning or other local concerns. Thus, existing physical space at the facility was not the only factor contributing to uncertainty about land availability.  Further review has shown that setback distances to mitigate noise and plume abatement (based on GPS mapping of residential areas) act as an additional constraint on land available for retrofitting to closed-cycle, and the cost of acquiring new land may be prohibitive for some facilities. Consequently, EPA estimates that 25 percent or more of facilities might have one or more constraints on land availability that would limit the ability to retrofit for cooling towers for the entire facility. EPA lacks adequate support to indicate that land constraints can be accommodated at existing facilities.
EPA also attempted to determine criteria based on the data in its record that would enable it to define a threshold for determining land availability on a nationwide basis, but was unsuccessful.  For example, one analysis explored a threshold of approximately 160 acres per GW (gigawatt) below which a facility could not feasibly install cooling towers.  Based on acres and the footprint of the facility and its surroundings (primarily those sites for which EPA conducted site visits), EPA found such an approach did not accurately identify which facilities could feasibly install closed-cycle.
2.	Increased Air Emissions Could Be a Factor on a Local Basis
As previously discussed, retrofitting closed-cycle cooling (without also repowering) would result in increased air emissions of various pollutants, including particulates, sulfur dioxide, nitrogen oxides, mercury, and greenhouse gases, among others. As a result of installing closed-cycle cooling structures, fossil-fueled facilities would need to burn additional fuel, thereby emitting additional PM, CO2, SO2, NOX, and Hg. Two factors are responsible: (1) the need to compensate for energy required for operating cooling towers, and (2) slightly lower generating efficiency attributed to higher turbine backpressure when the condenser is not replaced with one optimized for closed-cycle operation when retrofitting existing units (also referred to as the energy penalty). While both of these factors contribute to increased air emissions, the larger contributor to projected increased air emissions is by far the energy penalty.
The impact of the increased emissions varies according to the local circumstances. The increased emissions could consist of stack emissions from increased fuel usage, cooling tower emissions, and plumes of water vapor. EPA's analysis suggested that the most significant impacts would be increased PM2.5 emissions, which are associated directly with an increase in human health effects. EPA notes that cooling plume abatement and drift elimination technologies exist to address cooling tower emissions (and EPA included costs for such technologies in its analysis of Proposal Options 2 and 3).  Further, EPA expects most effects of the particulates from cooling tower emissions would be limited to the immediate vicinity, confined wholly to the facility property. (See DCN 10-6954.) Therefore, EPA's primary concern is increased air emissions associated with additional fuel usage due to the energy penalty when retrofitting to cooling towers.  EPA's review of emissions data from E-GRID (year 2005) suggests that impacts from these pollutant discharges could be significant. These include the human health and welfare and global climate change effects  -  all associated with a variety of pollutants that are emitted from fossil fuel combustion. EPA is not able to quantify the frequency with which facilities could experience these local impacts, and therefore has concluded that the proper forum to address such local impacts fully is in a site-specific setting.
3.	Remaining Useful Plant Life Could Be a Factor on a Facility Basis
A number of facilities are nearing the end of their useful life. Considering the long lead time to plan, design, and construct closed-cycle cooling systems, EPA determined that the Director should have the latitude to consider the remaining useful plant life in establishing entrainment mortality requirements for a facility. The remaining useful plant life, along with other site-specific information, will affect the entrainment reduction of closed-cycle cooling at a facility. For example, retrofitting to a closed-cycle system at a facility that is scheduled to close in three years will result in little entrainment reduction as compared to retrofitting to closed-cycle at a facility that will continue to operate for a significantly longer period.
The Decision to Establish a National BTA Standard Requiring Site-Specific Determination of BTA Entrainment Controls
      Once EPA determined that a "one-size-fits-all" approach for entrainment for existing units is not generally feasible, it is appropriate to assess the required controls on a site-specific basis.  Therefore, for existing units, EPA decided to adopt as the BTA entrainment standard an overarching regulatory framework under which the Director will establish BTA entrainment requirements on a site-specific basis following prescribed procedures and applying specified factors for decision-making prescribed in the regulation and as described below.
EPA concluded that site-specific proceedings are the appropriate forum for weighing all relevant considerations in establishing BTA entrainment requirements. Closed-cycle cooling is indisputably the most effective technology at reducing entrainment. Closed-cycle reduces flows by 95 percent and entrainment is similarly highly reduced. But given that EPA estimates that 25 percent of existing facilities may face some geographical constraints on retrofitting closed-cycle cooling and concerns about air emissions and the remaining useful life of a facility, EPA rejected the option of requiring uniform entrainment controls based on closed-cycle cooling. Instead, EPA elected to adopt as the entrainment standard a more flexible process in which, following consideration of a host of factors, the Director will prescribe 316(b) entrainment conditions appropriate at a particular site. For additional discussion on how a site-specific consideration of entrainment control requirements will be implemented, see Section VIII below.
EPA has several reasons for adopting the framework approach as the BTA standard for entrainment. As explained, the record shows that though closed-cycle cooling is effective, it is neither widely available nor feasible, and has significant unacceptable non-water quality impacts. While EPA cannot identify with precision the extent of these limitations on installing closed-cycle cooling systems nationwide, the record indicates that the circumstances are neither isolated nor insignificant. In light of this, EPA decided not to establish closed-cycle cooling as a presumptive BTA entrainment standard, pending a site-specific demonstration of the limitations. Instead, entrainment control requirements will be determined in a site-specific setting where the opportunity for local input in decision-making process will be maximized.
With regard to new units at existing facilities, based on the performance of properly operated cooling tower operation and the availability, feasibility and affordability of closed-cycle cooling at new units, EPA selected closed-cycle recirculating systems based on wet cooling towers as BTA. For a discussion of how the three factors (availability, feasibility and affordability) relate to new units, see Section VI.D.3. Consistent with the Phase I rule for new facilities, EPA has also included a compliance alternative allowing a facility to show performance comparable to that of a closed-cycle recirculating system. The new unit provisions in today's final rule are essentially the same as the requirements for new facilities under the Phase I rule.

F.	Other Options Considered for Today's Final Regulation
EPA considered several other options for the BTA standards in developing today's rule, but ultimately rejected them. This section includes a discussion of these options, as well as some technologies that EPA considered, but did not include as compliance alternatives to the impingement mortality standards.
1.	Proposal Option 4 -- Flexible Impingement Mortality Controls Similar to Final Rule at Existing Facilities with DIF of 50 mgd or more; BPJ Permits for Impingement Mortality and Entrainment at Existing Facilities with Design Intake Flow between 2 mgd and 50 mgd; Site-specific Entrainment Standard for Existing Facilities with DIF of 50 mgd or more; and Uniform Impingement Mortality and Entrainment Controls for All New Units at Existing Facilities Similar to Final Rule
At proposal, EPA's preferred option was Option 1, which was the option closest to today's final rule, and the starting point for the description of the changes to the rule in Section V above.  At proposal, EPA also considered a variant of Option 1, called Option 4, which changed the impingement mortality requirements for facilities under 50 mgd from the performance standard in Option 1 to BTA as determined by best professional judgment. In the case of an existing facility below 50 mgd that added a new unit, the flow associated with the new unit would have been subject to the uniform entrainment requirements based on closed-cycle cooling. Finally, all existing facilities withdrawing more than 2 mgd of DIF would have been subject to entrainment requirements established on a site-specific basis, with the exception noted above for new units.	  The option analyzed here, called Proposal Option 4, is likewise similar to the final rule, but for the impingement standard based on BPJ for facilities between 2 and 50 mgd.
EPA ultimately rejected Proposal Option 4 because EPA found that the technologies on which the impingement mortality performance standard of today's final rule is based are available, feasible, demonstrated, and affordable for all regulated facilities on a national basis. Moreover, EPA's analysis showed that the difference in the total costs for the two options was nominal. Additionally, EPA notes that many facilities with a DIF under 50 mgd already use closed-cycle cooling and would have minimal burden under the final rule. These facilities would have no difficulty complying with the requirements EPA is establishing in today's final rule. Proposal Option 4, by not distinguishing between those facilities under 50 mgd that have already minimized adverse environmental impacts from those that have not, masks the actions that would have to be taken by the latter group to comply with today's final rule. In addition, the flexibilities introduced in the June 11, 2012 NODA and included in today's final rule applied to all facilities, rather than taking the Option 4 approach at proposal of providing for more Director discretion for only the smaller withdrawing facilities. EPA also concluded that the data collection activities required under the final rule will be more protective of threatened and endangered species because they provide information on a larger number of facilities than Proposal Option 4 for consideration by the Director in permitting decisions. Lastly, EPA acknowledges that Proposal Option 4 is more burdensome to permitting authorities than is the final rule, as it requires more case-by-case decision making.
2.	Proposal Option 2 -- Flexible Impingement Mortality Controls Similar to Final Rule at All Existing Facilities that Withdraw over 2 mgd DIF; Site-specific Entrainment Standard for Existing Facilities with DIF at or below 125 mgd; Require Flow Reduction Commensurate with Closed-cycle Cooling by Facilities greater than 125 mgd DIF; and Uniform Impingement Mortality and Entrainment Controls for All New Units at Existing Facilities

As previously explained, EPA assessed a number of different technologies that reduce impingement mortality and entrainment as the possible basis for section 316(b) requirements. EPA concluded that closed-cycle recirculating systems (based on wet cooling towers) are the most effective technology for reducing impingement mortality and entrainment. Notwithstanding that conclusion, EPA has decided not to establish a performance standard for impingement and entrainment based on closed-cycle recirculating systems for existing facilities.  Furthermore, EPA found that there are no other effective technologies for entrainment that are available nationally. As described previously, each of the three factors for rejecting closed-cycle cooling as BTA for entrainment would also apply in the case of Proposal Option 2, despite the smaller number of facilities that would be subject to a requirement to retrofit.  The technology basis for entrainment mortality controls for facilities greater than 125 mgd DIF under this option would have been wet cooling systems. The constraints discussed above that are associated with retrofitting a large portion of the universe of affected facilities, led EPA to conclude that requiring closed-cycle cooling on a uniform basis scale was not appropriate for a national regulation.
EPA notes that it proposed multiple options that included closed-cycle, and solicited comment on all aspects of closed-cycle cooling. After fully considering all comments and data, EPA still finds closed-cycle cooling is not the "best technology available for minimizing adverse environmental impact" required by section 316(b). Because of a combination of concerns over feasibility/availability, air emissions, and remaining useful life of the facility, EPA has rejected closed-cycle recirculating systems as the basis for national impingement and/or entrainment controls. Nor is EPA able to identify a subcategory for which these concerns no longer apply. Moreover, the complex interaction of all of these factors at individual sites does not lend itself to other regulatory options that would require closed-cycle recirculating systems with an "off ramp" if any of the factors were shown to result in unacceptable impacts because this would create a presumption for closed-cycle cooling rather than an equal balancing of all relevant factors. EPA decided not to establish any presumptive BTA entrainment outcome.  EPA finds the entrainment standards framework in today's final rule will provide a
EPA concluded that site-specific proceedings are the appropriate forum for weighing all relevant considerations in establishing BTA entrainment requirements. Closed-cycle cooling is indisputably the most effective technology at reducing entrainmentconsistent, more
efficient, and more effective approach  While EPA cannot identify with precision the extent of these limitations on installing closed-cycle cooling systems nationwide, the record indicates that the circumstances are neither isolated nor insignificant.  Instead, entrainment control requirements will be determined in a site-specific setting where the opportunity for local input in decision-making process will be maximized.

On the other hand, EPA found that some facilities with large acreage could not feasibly install cooling towers because of local zoning or other local concerns.

 As a result of installing closed-cycle cooling structures, fossil-fueled facilities would need to burn additional fuel, thereby emitting additional PM, CO2, SO2, NOX, and Hg.
The impact of the increased emissions varies according to the local circumstances. The increased emissions could consist of stack emissions from increased fuel usage, cooling tower emissions, and plumes of water vapor. EPA's analysis suggested that the most significant impacts would be increased PM2.5 emissions, which are associated than standards with an  EPA expects most effects of the particulates from cooling tower emissions would be limited to the immediate vicinity, confined wholly to the facility property. (See DCN 10-6954.)  all associated with a variety of pollutants that are emitted from fossil fuel combustion. EPA is not able to quantify the frequency with which facilities could experience these local impacts, and therefore has concluded that the proper forum to address such local impacts fully is in a site-specific setting.
.	Remaining Useful Plant Life Could Be a Factor on a Facility Basis
A number of facilities are nearing the end of their useful life.

	"off ramp."
3.	Proposal Option 3 -- Flexible Impingement Mortality Controls at All Existing Facilities that Withdraw over 2 mgd DIF; Require Flow Reduction Commensurate with Closed-Cycle Cooling at All Existing Facilities over 2 mgd DIF
Proposal Option 3 was, in many ways, the same as requiring closed-cycle cooling at all existing facilities. As described above, each of the three factors for rejecting closed-cycle cooling as BTA for entrainment would apply with equal force for Proposal Option 3. As a result, EPA has concluded Proposal Option 3, similarly, is not appropriate as BTA for entrainment.

4.	Proposal Option 4 Variant
EPA also considered a variant of Proposal Option 4.  As compared to Proposal Option 4, this variant did not include flexible alternatives for complying with the BTA impingement mortality standards (including pre-approved and streamlined alternatives), but did adopt the 50 mgd threshold to determine those facilities for which the Director has more discretion in determining BTA via BPJ.  EPA analyzed this option to directly compare the effects of introducing flexible IM compliance alternatives at all facilities (as the final rule does) to the effects of introducing greater Director discretion for a subset of facilities, via BPJ permitting (as the Proposal Option 4 variant does).  The preferred option at proposal, Option 1, was estimated to be more costly than Option 4 (Option 1 was estimated to cost $384 annually as compared with $327 million annually for Option 4).  Under the analysis supporting the final rule the EPA is adopting today, however, today's final rule is estimated to cost $275 million annually in comparison with an estimated cost of $284 million annually for the Proposal Option 4 variant. Thus, EPA has concluded that providing flexible alternatives for compliance with the BTA IM standard at all facilities is both more effective at reducing costs to society and more readily justified as best technology available as compared to the approach of introducing greater Director discretion for only a subset of facilities (below 50 mgd).  Hence, EPA rejected the Proposal Option 4 variant, and the approach of introducing greater Director discretion for only a subset of facilities (below 50 mgd).
The technology basis for entrainment mortality controls for facilities greater than 125 mgd DIF under this option would have been wet cooling systems.

 In the case of an existing facility below 50 mgd that added a new unit, the flow associated with the new unit would have been subject to the uniform entrainment requirements based on closed-cycle cooling. Finally, all existing facilities withdrawing more than 2 mgd of DIF would have been subject to entrainment requirements established on a site-specific basis, with the exception noted above for new units.
 Moreover, EPA's analysis showed that the difference in the total costs for the two options was nominal. Additionally, EPA notes that many facilities with a DIF under 50 mgd already use closed-cycle cooling and would have minimal burden under
5.	Proposal Option 2 Variant
EPA also considered a variation of Proposal Option 2 that would have used 125 mgd AIF rather than 125 mgd DIF as the threshold. However, as described above, EPA rejected Proposal Option 2 and, for the same reasons, rejected this variant of Option 2.
6.	Site-Specific Approach to Addressing Impingement
Many commenters (primarily from manufacturing facilities) commented that EPA should adopt a site-specific approach to addressing impingement mortality, similar to that employed for entrainment. As a result, EPA also considered an approach that would have established both impingement mortality and entrainment requirements fully on a site-specific basis taking into account for the particular facility, among other factors, those previously described as pertinent to EPA's 316(b) BTA determination. EPA rejected a fully site-specific approach for impingement controls principally because low-cost technologies for impingement mortality are available, feasible, demonstrated, and affordable for facilities nationally. Because technologies are available, a fully site-specific approach would place an unnecessary additional burden on state permitting resources. Moreover, the final impingement mortality standard includes several alternatives that allow site-specific demonstration that a particular technology performs at a level representing the best technology available for the site. EPA is instead promulgating a modified version of the proposed rule, adding several elements of flexibility (i.e., compliance alternatives), and thus directly addressing many of the concerns raised by these commenters.
7.

	Pre-approved Technologies
Many commenters requested that EPA pre-approve technologies that, once installed, would obviate the need for further regulatory conditions such as periodic monitoring. This is similar to the approach taken for cylindrical wedgewire screens in the remanded 2004 Phase II rule (see 69 FR 41693). EPA has adopted, in significant measure, commenters' suggestion in the BTA impingement mortality standard in today's rule by including several pre-approved and several streamlined compliance alternatives in the form of technologies that may be approved following a demonstration of required performance, so long as the facility shows that its alternative technology is operating in a manner that minimizes adverse environmental impacts. As an option for achieving the impingement mortality standards, a facility may install and operate specified impingement controls whose performance is comparable to or better than the technology EPA concluded was the "best technology available" for impingement mortality reductions:
    *       Closed-cycle recirculating systems, defined at § 125.92(c)
    *       Existing offshore velocity caps, defined at § 125.92(v)
    *       Technologies that result in a design intake velocity less than or equal to 0.5 fps, including most modern cylindrical wedgewire screens
    *
Although this rule leaves the BTA entrainment determination to the Director, with the possible BTA decisions ranging from no additional controls to closed-cycle recirculating systems plus additional controls as warranted, EPA expects that the Director, in the site-specific permitting proceeding, will determine that facilities with properly operated closed-cycle recirculating systems do not require additional entrainment reduction control measures. Refer to Section E.1 for the EPA's rationale for selecting these controls.

G.	Final Rule BTA Performance Standards
The rule establishes the following BTA standards for Impingement Mortality and Entrainment: Impingement Mortality Standards at All Existing Units at Existing Facilities that withdraw greater than 2 mgd DIF; an Entrainment Standard that requires site-specific entrainment controls determined by the Director for Existing Units at Existing Facilities that withdraw over 2 mgd DIF; BTA standards for impingement mortality and entrainment for new units at existing facilities. The previous section described the other options that EPA considered but ultimately rejected, and the basis for those decisions.
1.	Impingement Mortality Controls for Existing Units at Existing Facilities for the Final Rule.
Today's final rule provides a facility a number of alternatives for complying with the BTA impingement mortality standard. As discussed more below, EPA's BTA impingement mortality standard is based on EPA's conclusion that, on a national basis, modified traveling screens with fish-friendly return systems are the best performing technology available for impingement mortality reduction. But EPA is not requiring compliance with the BTA impingement mortality standards only through monitoring data that demonstrates achievement of the numeric reduction in mortality levels that EPA has determined well-operated modified traveling screen will achieve. Rather, the final rule allows facilities to comply by employing any of seven alternatives, including monitored compliance with a numeric impingement mortality performance standard.
Based on its review of available data and information submitted by commenters, EPA identified a number of other technologies and operational measures that could achieve equivalent, or better, performance to the impingement mortality reductions achieved with modified traveling screens that may be available for some sites. Thus, the final rule provides seven alternatives for complying with the BTA impingement mortality standards. These include three compliance paths based on pre-approved technologies, and three compliance paths that offer a streamlined approach to compliance. EPA expects the majority of facilities will use one of these six options to comply with the BTA impingement mortality standards (see Exhibit VIII-1 for more information).
The following pre-approved technologies will comply with today's rule and are associated with minimal monitoring and reporting of operational and/or design parameters. These technologies are (the numbering reflects the numbering in § 125.94(c)): operating (1) a closed-cycle recirculating system; (2) a cooling water intake structure that EPA or the State NPDES permitting authority determines has a design maximum through-screen intake velocity of 0.5 feet per second; or (4) an existing offshore velocity cap. The general intent behind a compliance path based on a pre-approved technology is to provide a level of certainty to the regulated entity that they would be deemed compliant with the relevant rule requirements by designing, installing, and operating the technology as specified in the regulation. The three pre-approved compliance alternatives are each based on a particular technology approach. The permit for each compliance alternative will necessarily include criteria, design standards, and operational conditions specific to the pre-approved technology. The compliance paths based on pre-approved technologies in today's final rule include simplified permit application requirements (such as reduced or minimal study), documentation, or reduced monitoring, and will therefore result in greatly simplified implementation. In today's final rule, there are no biological compliance monitoring requirements for any of the three compliance paths based on pre-approved technologies.
Under the streamlined alternatives, a facility must demonstrate to the Director that traveling screens or some combination of technology controls or operational measures represent BTA performance under the conditions at the site. The three streamlined compliance alternatives are (the numbering reflects the numbering in § 125.94(c)) operating (3) a cooling water intake structure that EPA or the State NPDES permitting authority determines has an actual maximum through-screen intake velocity of 0.5 feet per second; (5) modified traveling screens whose demonstrated performance represents the best technology available for impingement reduction at the site; or (6) a system or combination of technologies or operational measures whose demonstrated performance is the best technology available for impingement reduction at the site. In order to demonstrate BTA performance, a facility will need to conduct a two-year site-specific study at the same time it conducts its source water characterization and Entrainment Characterization Study.  This study must demonstrate that its modified traveling screens, or combination of technology controls and operational measures, have been adjusted and optimized so as to minimize impingement mortality. If the Director concludes that the facility has demonstrated optimized performance for its controls, the facility will have no subsequent biological monitoring and reporting requirements as compared to a facility that complies using the impingement mortality performance standard.  If the screens or other measures are not already installed, the Director may approve postponing the two-year study to be conducted after the entrainment determination has been made.  These three streamlined compliance alternatives are based on a technology or suite of technologies and practices with more variable performance, and as such necessitate some degree of study, in order to optimize technology performance for the site-specific conditions encountered by a facility. A streamlined compliance alternative may require some level of monitoring, but once the optimal performance of the technology has been identified, conditions included in the permit specifying optimal operation ensure that the streamlined alternative is similar to or better than the impingement mortality performance standard. For example, the streamlined compliance alternatives also do not require biological compliance monitoring.
The seventh alternative (at § 125.94(c)(7)) for complying with the BTA impingement mortality standards requires the owner or operator to demonstrate compliance with the numeric impingement mortality performance standard through biological monitoring. Under this alternative, the owner or operator has the flexibility to choose any technology, including a new or innovative technology, provided the compliance monitoring demonstrates the performance standard is achieved.
Each of these seven alternatives is further described below.  In addition, further discussion of how each of these alternatives will be implemented may be found in Section VIII.
a.	Closed-Cycle Recirculating Systems
As described above, in Chapter 6 of the TDD, and in prior rulemakings, EPA has long recognized the benefits of flow reduction from closed-cycle recirculating systems for reducing impingement (as well as entrainment). A facility employing a closed-cycle recirculating system will typically reduce impingement by more than 95 percent. As a result, a facility may choose to comply with the BTA impingement mortality standards in today's final rule by demonstrating that it uses a properly operated and maintained closed-cycle recirculating system.
EPA estimates that approximately 18 percent of intake structures (i.e., those that already have an existing closed-cycle recirculating system, plus facilities located in California and New York, whose State regulations are at least as stringent as the final rule) will choose this alternative.
EPA does not have the data to determine precisely which impoundments are serving as part of a closed-cycle recirculating system as defined at 40 CFR 125.92(c)(2).   However, EPA is aware that some facilities have created their impoundments in a water of the U.S as part of their cooling system.  EPA does not intend to eliminate the use of such lawfully created impoundments for their intended purpose, as doing so could result in a large number of stranded assets.  If the cooling system with the impoundment minimizes the withdrawal of make-up water for cooling purposes, the Director may determine the cooling system meets the definition of a closed-cycle recirculating system.
b.	Reduced Intake Velocity
EPA has long recognized the relationship between impingement and intake velocity. EPA conducted an analysis of fish swim speeds in the Phase I rule (see 66 FR 65274, December 18, 2001) and concluded that a design through-screen velocity of 0.5 fps is protective of 96 percent of motile organisms. However, EPA did not select intake velocity as the technology basis for the BTA impingement mortality standards. Although the performance of 0.5 fps intake velocity achieves greater reduction in impingement mortality than the technology on which the BTA impingement mortality standards are based, reducing a facility's intake velocity is not widely available or feasible for all existing facilities (see Chapter 6 of the TDD).
EPA is including reductions in intake velocity as an alternative for complying with the BTA impingement mortality standards through reduced intake velocity.  A facility choosing this alternative must demonstrate that (1) the through-screen design velocity could not exceed 0.5 fps or (2) the actual intake velocity does not exceed 0.5 fps.
EPA estimates that approximately 34 percent of intake structures will choose this alternative. This estimate includes facilities that have an existing intake velocity of 0.5 fps or less, plus those facilities that are projected to install a technology that would reduce their intake velocity (larger intake, wedgewire screens, or variable speed pumps).
i.	Design Intake Flow Basis
Consistent with EPA's determination in its earlier 316(b) regulatory efforts, the final rule allows a facility to comply with the BTA impingement mortality standards by demonstrating that its intake has a maximum through-screen design velocity of 0.5 fps. EPA concluded that facility's operating at this through-screen design velocity will protect the vast majority of impingeable aquatic organisms. Facilities choosing to comply with the BTA impingement mortality standards may not average velocity across multiple intakes at a facility.
ii.	Actual Intake Flow Basis
EPA is also adopting a provision to allow facilities to demonstrate that the through-screen intake velocity at an intake structure does not exceed 0.5 fps on the basis of the intake's actual flow. (Again, note that facilities choosing this compliance alternative may not average intake velocity across multiple intakes.) In contrast to design flow above, a facility with an intake having a design through-screen intake velocity greater than 0.5 fps may be operated at a reduced capacity and therefore may withdraw cooling water at a velocity less than 0.5 fps. As long as the actual intake flow is such that the velocity remains at or below 0.5 fps, the reductions in impingement (and subsequently, impingement mortality) remain the same as a facility with a maximum design through-screen intake velocity of 0.5 fps. As described below, a facility will be required to monitor its intake flow and report this data to the Director to verify that intake flows do not exceed 0.5 fps. This approach also permits the Director to allow brief periods where the intake velocity will exceed 0.5 fps under extreme conditions.
c.	Existing Offshore Velocity Caps
A number of commenters stated that EPA should consider existing offshore intakes fitted with velocity caps to be pre-approved and complying with the BTA impingement mortality standards. Locating submerged intakes in the deeper regions of larger waterbodies (particularly outside the littoral zone) has the potential to reduce both impingement and entrainment (I&E), due to the lower densities of aquatic organisms as compared to a shoreline-based intake. EPA has identified 11 facilities with offshore velocity caps, and reviewed a number of studies documenting the performance of these facilities. These studies show that the impingement reduction performance of intakes submerged far offshore with velocity caps is dependent on site-specific conditions. The data show that solely locating an intake far offshore (i.e., without also employing a velocity cap) achieves a 60 to 73 percent reduction in impingement, and therefore does not achieve impingement mortality reduction comparable to that of well-operated modified traveling screens. Similarly, the data also show that velocity caps alone achieve a 50 to 97 percent reduction in impingement, and therefore could result in compliance performance comparable to or better than modified traveling screens in some, but not in all cases. However, the combination of an existing intake located far offshore (i.e., approximately 850 feet, as identified in the data for Nine Mile Unit 1 and Oswego Unit 5) in combination with use of a velocity cap will result in performance that exceeds the 12-month average impingement mortality performance standard (alternative seven described above).[,] Because there is some amount of uncertainty in measuring distances from a shoreline, including but not limited to due to variations in water levels, storm swells, or tidal excursions, EPA has set the minimum distance offshore at 800 feet. As a result, the final rule at § 122.95(c)(4) allows a facility to comply with the BTA impingement mortality standards with an existing offshore intake with an existing velocity cap located at least 800 feet offshore, based on the performance data from the 11 identified facilities.
As noted above, the record shows all existing facilities with a velocity cap located at least 800 feet offshore will meet or exceed the 12-month average mortality performance standard of 125.94(c)(7). EPA does not have data showing velocity caps located at lesser distances offshore will consistently achieve the impingement mortality performance standards, but is aware that some facilities may be able to achieve the impingement mortality standards through a combination of technologies that includes an offshore location. For example, the Office of Naval Research states that the littoral zone in ocean environments generally extends from the shore to 600 ft out in the water (ONR 2013). SEAMAP data in EPA's record shows installing the intake to depths where there is a lower concentration of living organisms (i.e., at least 65 feet) is also expected to decrease environmental impacts associated with intake operations. Therefore, the final rule allows facilities with intake structures at significant distances offshore to demonstrate the performance of their technology under § 122.95(c)(6), as further discussed below.
In addition facilities may opt to construct an offshore velocity cap at new locations. In those circumstances, the facility will need to demonstrate that theperformance of its velocity caps is the best technology available for impingement reduction under the alternative found at § 122.95(c)(6). For more information, see DCN 12-6601.
EPA estimates that approximately 1 percent of intake structures (i.e., those with an existing velocity cap meeting the definition at § 125.92(v) will choose this alternative.
d.	Install Modified Traveling Screens
In the June 11, 2012 NODA, EPA discussed a streamlined compliance option that would provide facilities with a less burdensome alternative than the proposed rule. In the final rule, EPA has included an option at §125.95(c)(5) for facilities that install traveling screens  -  the technology that forms the basis for the numeric IM performance standards. Under this option, the facility must demonstrate to the Director that it will install and operate modified traveling screens as defined at 125.92(s) that are or will be optimized to minimize IM mortality at the site. The facility will also be required to submit an impingement technology performance optimization study (§ 122.21(r)(6)) which will include a 2-year optimization study for the intake technology. The facility will conduct 2 years of monthly impingement data collection, during which the facility will seek to optimize the technology performance to minimize impingement mortality. This study is intended to determine the optimal configuration and operating conditions of modified traveling screens and the fish handling and return systems for that intake to be consistently protective of aquatic organisms. During the course of the study, EPA expects that a facility will evaluate the interim results and make changes to the technology or operating conditions as needed to identify the most appropriate set of operational characteristics to ensure long-term success. For example, a facility could adjust the spray wash pressure, adjust the rotating speed of the screens, rotate the screens more frequently, re-angle the fish sluicing sprays, ensure adequate water in the return flume, design the fish return to avoid avian and animal predation on the aquatic organisms, and locate the fish return in such a way to avoid predation. Once a facility has optimized its technology performance, the study will identify operational measures that will serve as observable and enforceable permit conditions. As evidenced by the data used in determining the performance standard, by requiring facilities to study the conditions for optimized performance, many facilities will achieve impingement mortality reductions much greater than the 12-month average impingement mortality performance standard without significant additional investment. Biological data collection beyond this two-year study will not be required. The facility will simply be required to ensure that it is operating its technology under the identified conditions for optimized performance. If the Director concludes that the screens will achieve optimized performance, the Director will also incorporate operating conditions to ensure optimized performance as terms of the facility's NPDES permit.
As discussed in the NODA and Chapter 4 of TDD, EPA's data indicate that most facilities employ traveling screens. EPA anticipates that, as a result, many facilities will view the streamlined screen-based compliance route as a logical choice for complying with the final rule. The streamlined option provides an opportunity for a large number of the affected facilities (i.e., those that do not meet the criteria for the other compliance technologies) to demonstrate that their intakes are effectively reducing impingement mortality while significantly reducing the burden on both facilities and regulatory agencies. EPA estimates that approximately 30 percent of intake structures will choose this alternative.

EPA is aware that some facilities have no technologies installed and will choose to install modified traveling screens, and further that some facilities with traveling screens will choose to either retrofit to modified traveling screens with fish handling and returns. Obviously, the impingement technology performance optimization study cannot be undertaken until the technology is first installed. In this case the NPDES permit would be issued before the completion of the optimization study. EPA expects a permit will be issued that includes a schedule for both the technology installation and the required optimization study. As discussed earlier, the Director can establish interim measures as appropriate (40 CFR 125.94(b)).
e.	System of Technologies as the BTA for Impingement Mortality
EPA recognizes that cooling water intake structures have a variety of configurations and facilities may choose to comply with the final rule by using more than one of the compliance approaches outlined above. In the June 11, 2012, NODA, EPA described an approach where facilities would be able to demonstrate "credit" toward meeting the impingement mortality requirements by reducing the total number of organisms impinged. EPA also intended for facilities to have the flexibility to employ any system of technologies or combination of operational measures to address impingement mortality so long as the performance of the selected impingement reduction measures represented the best technology available for the site. The final rule includes an alternative reflecting these objectives.
In the broadest sense, facilities have a number of options for reducing impingement mortality. Some may choose to comply using an approach where a single technology achieves the level of compliance necessary. Others may choose an approach of employing multiple technologies or operational measures, including reducing the number of organisms that are impinged or susceptible to being impinged. The following are examples of approaches for which a facility might be able to take credit for impingement reduction under this alternative:
   * Partial closed-cycle cooling
   * Variable speed pumps
   * Seasonal outages (including standard maintenance outages that are specifically scheduled to avoid a biologically sensitive period)
   * Certain impingement technologies that reduce the number of organisms exposed to the intake structure (e.g., diversions, louvers, barrier nets)
   * Intake location
   * Behavioral technologies (e.g., light or sound barriers)
In each case, the technology employed reduces the number of organisms that potentially are impinged, resulting in a reduction in the number of organisms actually impinged (i.e., a reduction in the rate of impingement). By virtue of reducing the actual impingement, mortality caused by impingement is no longer a consideration -- an organism that is never impinged cannot be killed by the intake structure. Some technologies work to reduce the intake flow, thereby reducing the potential organisms exposed to the intake. Others work to divert organisms away from the screens, either through a physical exclusion or by being placed in a less biologically productive area. EPA concluded that it is appropriate to recognize these reductions in impingement as a step in achieving a BTA impingement mortality reduction performance at a particular site. As a result, EPA expects the reduction in impingement will be treated as an equivalent reduction in impingement mortality, and will therefore be considered by EPA or the State NPDES permitting authority in evaluating whether the chosen technologies and operational measures represent BTA performance under the site's conditions. For example, an intake that operates infrequently due to the infrequent operation of the electric generating unit(s) it serves (such as a peaking unit) may use a relatively small amount of water on an annual basis when compared to the design capacity of the intake structure. This facility may choose to comply with the impingement mortality standard at (c)(6) by demonstrating to the Director that the facility operates at an annual intake flow that is less than or equal to 24 percent of its design intake flow on an annual basis. This level of flow reduction could achieve a level of performance equivalent to or better than the impingement mortality performance standard in (c)(7), and therefore could be considered to be compliant with the requirements of today's final rule. This demonstration may include design data, several years of past operating data, and dispatch modeling. These operating conditions would then be incorporated into the NPDES permit.
A facility complying under this part, must submit a impingement technology performance optimization study, which must include the calculated percent impingement mortality reflecting optimized operation of the system of technologies, operational measures, and best management practices and all supporting calculations. Total system performance is the combination of impingement mortality performance reflected in all of the following which apply:
         * Rate of impingement  -  The estimated reductions in rate of impingement must be based on a comparison of the system to a once-through cooling system with a traveling screen whose point of withdrawal from the surface water source is located at the shoreline of the source waterbody.  For impoundments that include waters of the United States, the facility's rate of impingement must be measured at a location within the cooling water intake system that the Director deems appropriate.
         * Impingement mortality  -  If the demonstration relies in part on a credit for reductions in impingement mortality already obtained at the facility, two years of biological data collection must be provided, demonstrating the level of impingement mortality the system is capable of achieving.
         * Flow reduction  -  If the demonstration relies in part on flow reduction to reduce impingement, the data must include two years of intake flows, measured daily, as part of the demonstration. This must include documentation of how the flow reduction results in reduced impingement.
The permitting authorities would consider this information shown in the two-year impingement technology performance optimization study that must be submitted under this alternative. For example, at facilities choosing to comply by demonstrating that they are operating below 24 percent of their intake capacity, or that they are peaking units, the Director should use this study to establish operating conditions that ensure that the intake continues to operate below 24 percent of its intake capacity or continues to serve only peaking units and that these units are not later used as intermediate or baseload units.  The operating conditions and parameters identified in the study will then be incorporated in the facility's permit conditions. EPA estimates that approximately 17 percent of intake structures will choose this alternative.
f.	Comply with the Numeric Impingement Mortality Performance Standard
Facilities complying with the BTA impingement mortality standard by achieving the numeric performance standard at § 125.94(c)(7) will perform monthly compliance monitoring to verify that the 12 month percent impingement mortality resulting from operation of its intake is below the standard established in today's final rule. (For more details on complying with the impingement requirements, see Section VIII.) EPA expects that, save for future technologies or innovations, few facilities will avail themselves of this option.
2.	Entrainment Controls for Existing Units at Existing Facilities
The BTA entrainment standard for the final rule establishes a framework under which EPA or the State NPDES permitting authority must establish site-specific BTA entrainment requirements for each facility in the scope of today's rule. EPA considered promulgating no further controls to address entrainment mortality, and to rely instead only on the BTA impingement mortality controls, which would achieve up to a 34 percent reduction in total AEI. EPA did not select this option as the basis for national BTA because, in EPA's view, some facilities either are having a significant impact as a result of entrainment or might be able to do more to control entrainment at costs that are low relative to benefits. In addition, EPA's data on entrainment at facilities are not sufficient to allow the Agency to categorize facilities requiring no additional controls for entrainment. Thus, the final rule by requiring prescribed information in the permit application will provide the Director with adequate information for decision making.  Requiring a structured site-specific analysis of candidate BTA technologies for entrainment control will allow the Director to determine where it is appropriate to require such controls. One outcome of the site-specific analysis could be that the Director would determine that no other technologies beyond impingement controls are required for BTA entrainment reductions, either because they are not feasible or because the social costs of additional control measures are not justified by the social benefits.
In the case of site-specific entrainment controls for facilities withdrawing greater than 125 mgd AIF, the final rule requires facilities to also develop and submit an Entrainment Characterization Study and related supporting information, as described in § 122.21(r)(9)-(13) of today's rule, for use by the Director in establishing site-specific BTA. For facilities above 125 mgd AIF that also meet the definition of closed-cycle recirculating systems at § 125.92(c), the Director may reduce or waive some or all of this information.
 EPA considered simply requiring this information of all facilities above 125 mgd AIF without authorizing Directors to reduce or waive this information. However, EPA also recognizes that, in some instances, these same facilities have already minimized adverse environmental impacts significantly. In such cases, there may be limited value to the Director requiring a full benefit-cost analysis, or even obtaining the Entrainment Characterization Study at (r)(9).
EPA also considered not requiring this information of any facilities above 125 mgd AIF meeting the definition at § 125.92(c).  First, EPA noted that even though these facilities meet the definition of a closed-cycle recirculating system, they may still withdraw at least 125 mgd, and in some instances withdraw considerably more than 125 mgd. This is not an insubstantial volume of water withdrawn for cooling, and in the case of inland waters this withdrawal may comprise a large proportion of that source waterbody. In addition to withdrawing large volumes of water, EPA recognizes that some facilities, particularly those meeting the definition at § 125.92(c)(2), potentially withdraw water at a rate similar to a once-through facility not withdrawing from an impoundment, with the potential to cause adverse environmental impacts similar to those of once-through cooling. The Director may find the information in § 122.21(r)(9)-(13) to be useful in determining whether additional controls are warranted. In these instances, the Director may decide to require the Entrainment Characterization Study at (r)(9) first, in order to determine if other studies in (r)(10) to (13) are also warranted.
Facilities at or under the 125 mgd AIF threshold must still provide certain information under the permit application requirements at § 122.21(r). The Director may require additional information from these facilities including some or all of the studies at § 122.21(r)(9)-(13) if there is reasonable concern regarding entrainment impacts at the facility. Where an owner or operator of a facility intends to comply with the BTA standards for entrainment using a closed-cycle recirculating system as defined in § 125.92(c), the Director may reduce or waive some or all of this information.
	Facilities with a closed-cycle recirculating system as defined at § 125.92(c)(2) would still submit the studies at § 122.21(r)(9)-(13) if they withdraw greater than 125 mgd AIF, and if the Director has not waived the requirements.  These facilities have cooling systems that include impoundments of waters of the U.S. where the impoundment(s) was constructed prior to [INSERT effective date of the final rule] and lawfully created for the purpose of serving as part of the cooling water system. This purpose must be documented to the Director's satisfaction in the project purpose statement of any required Clean Water Act section 404 permit obtained to construct the impoundment. In the case of an impoundment whose construction pre-dated the CWA requirement to obtain a section 404 permit, where alternative permitting documents were required, the facility must document the project's purposes to the satisfaction of the Director by some other license or permit obtained to lawfully construct the impoundment for the purposes of a cooling water system.  EPA notes that for impoundments constructed in uplands or not in waters of the United States, no documentation of a section 404 or other permit is required.  EPA received comments that such impoundments should be treated as closed-cycle cooling and has agreed to make this change.  The Director would still make the determination that make-up water withdraws have been minimized. Further, EPA's data shows that many facilities that utilize impoundments as part of their cooling water systems may actually use a combination of cooling water systems (for example, detailed survey responses showed eight facilities with an impoundment in addition to other IM technologies). The requirement that these facilities provide the Director with certain information will help ensure that the Director has adequate information upon which to base a decision for these impoundments as to whether these facilities have adequate controls already or should be taking additional measures to protect the relevant waterbody.
    The Entrainment Characterization Study will include information already collected to meet existing § 122.21(r)(4) requirements. In addition, under the permit application requirements being added today at § 122.21(r)(5) to (13), the facility will submit certain additional site-specific information. This will include an engineering study of the technical feasibility and incremental costs of candidate entrainment mortality control technologies. The facility will also study, evaluate, and document the technical feasibility of technologies, at a minimum, including closed-cycle cooling, fine mesh screens with a mesh size of 2 mm or smaller, and water reuse or alternate sources; engineering cost estimates of all technologies considered; any outages, downtime, or other effects on revenue along with a discussion of all reasonable attempts to mitigate these cost factors; and a discussion of the magnitude of water quality and other benefits, both monetized and nonmonetized, of the candidate entrainment mortality reduction technologies evaluated. Finally, the information must include a discussion of the changes in non-water quality environmental impacts attributed to technologies and/or operational measures considered. The factors include, for example, increases and decreases in the following: energy consumption, and air pollutant emissions including particulates and associated human health and global climate change impacts, water consumption, noise, safety (e.g., visibility of cooling tower plumes, icing), grid reliability, and facility reliability. For a thorough discussion of these study requirements, see Section VIII. The final rule also requires peer review of the Comprehensive Technical Feasibility and Cost Evaluation Study, Benefits Valuation Study, and Non-Water Quality and Other Impacts Assessment. Peer review of the Entrainment Characterization Study is not required.  Note that the peer reviewed studies will rely on data gathered in the Entrainment Characterization Study.  Peer reviewers will be selected in consultation with the Director, who can also consult with EPA and Federal, State, and Tribal fish and wildlife management agencies with responsibility for fish and wildlife potentially affected by the cooling water intake structure(s).
Under the final rule, EPA expects that the Director will review the candidate technologies for entrainment mortality control that, at a minimum, includes closed-cycle recirculating systems, fine-mesh screens with a mesh size of 2 mm or smaller, and water reuse or alternate sources. In the decision about what additional entrainment controls (if any) to require, the Director will consider all the facility-specific factors in § 125.98(f)(2) and described above. At a minimum, the Director must provide a discussion explaining how issues concerning air emissions or land availability, insofar as they relate to the feasibility of adoption of an entrainment technology, and remaining useful plant life, were addressed in the site-specific determination. Under the final rule, the Director must issue a written explanation for the basis of the BTA entrainment determination for each facility. The Director's decision must include a written explanation that, at a minimum, includes consideration of the following factors: (i) numbers and types of organisms entrained; (ii) impact of changes in particulate emissions or other pollutants associated with entrainment technologies; (iii) land availability inasmuch as it relates to the feasibility of entrainment technology; (iv) remaining useful plant life; and (v) social costs and benefits, which may include qualitative, quantified and monetized categories. The Director may also base the proposed determination on several other factors, including thermal effects and water consumption.
In addition to the information required for development of impingement controls discussed above, the regulation also requires, in the case of facilities withdrawing greater than 125 mgd AIF, submission of certain other information for use in the site-specific entrainment determination of BTA. The final rule also adds the permit application requirements at § 122.21(r) (9)-(13) to require the facility to prepare several studies, including an Entrainment Characterization Study, that will fully characterize the extent of entrainment at the facility. (For more details about the study, see above). In addition, under the final rule, the facility will provide detailed information on the other factors relevant to the Director's site-specific BTA determination. These will include information concerning the technologies available for control of such entrainment, the costs of controls, the non-water quality environmental impacts of such controls, the monetized and nonmonetized benefits of such controls, and the presence of any threatened and endangered species. The final rule does not limit the Director's discretion to consider non-water quality impacts in determining whether further entrainment measures are justified. EPA encourages, and the CWA requires, the public to have a role in the permitting process. Interested members of the public may submit written comments on a draft permit during the 30 day public notice and comment period and request a public hearing on a draft permit. For permits that are issued by EPA instead of a state, additional opportunities for public involvement include comment, and in some cases, a public hearing on a permittee's State Water Quality Certification under section 401 of the CWA. (See 40 CFR 124.10, 124.11, 124.12(a) and 124.17(a).)  Therefore, the final rule clearly affords the public a meaningful opportunity for participation in the site-specific decision making to help ensure the soundness of both the information and subsequent determinations.

H.	Economic and Benefit Analysis for the Final Rule
For example, the incremental downtime that can be associated with retrofitting to closed-cycle cooling is avoided altogether at a new unit. In addition, when new units are added, the condensers can be configured for closed-cycle, reducing energy requirements
    This section discusses why EPA concluded that each factor is not a significant concern for new units, and why the record supports EPA's conclusion that closed-cycle cooling is an available and feasible technology for new units at existing facilities.
   * As a result, space constraints will be much less of an issue. New units also present the opportunity to design an optimized closed-cycle recirculating system for the new unit.
   * Therefore energy penalties and air emissions for tower operations can be minimized (though not eliminated).  effects of requiring closed-cycle cooling at new units at existing facilities is similar to the effects of this requirement at new facilities and will not pose an unacceptable impact. For more information, see Chapters 6, 8, and 10 of the TDD.
   *

In fact, some facilities may find closed-cycle cooling to be less costly over the long-term.
 in the record for today's rule, and DCNs 2-009 and 4-4023C (from the Phase I and Phase II dockets, respectively). These documents show that, on the basis of responses from facilities to the 316(b) industry questionnaire, facilities constructed in recent years are significantly more likely to employ closed-cycle cooling.
EPA recognizes that at some point in the future, every unit will be rebuilt, replaced or repowered
EPA notes that the new unit provision is an important element of the final rule, given the generally long lifespan of equipment at industrial facilities. For example, generating units at a power plant are often projected to have a 50-year lifespan. As a result, these facilities have a slow rate of "evolution" in adopting newer technologies.

1.	Economic Justification for the Final Rule
Pursuant to the principles in E.O. 12866 and E.O. 13563, EPA has assessed costs and benefits for the final rule and has reasonably determined that the benefits of the rule justify the costs. EPA has estimated the social cost of this rule to be $275 million annually. For more information on EPA's analysis of the rule's costs, see Section IX.
As described in more detail below in Section X, significant benefits are associated with the rule. These benefits include the annual reduction in impingement mortality of 652 million age-one equivalents for existing units. There are, in addition, other important benefits, many of which EPA cannot quantify. These benefits include effects on many shellfish species and nonuse values associated with the vast majority of fish and shellfish. The rule also requires establishing site-specific entrainment controls through a process in which specific environmental conditions and the localized benefits of entrainment reductions will be assessed along with the costs of controls. The information generated in the required studies will enhance the transparency of decision making and provide an opportunity for meaningful public participation, ensuring that decision making is based on the best available data. Overall, these requirements and subsequent Director actions under this rule will foster protection and restoration of healthy aquatic ecosystems that have important commercial, recreational, aesthetic and cultural values to their surrounding communities. Many of the benefits that will result from the rule are not monetized or quantified, and as a result the Agency's monetized benefits analysis underestimates the totality of the rule's benefits. On the basis of the record, EPA has determined that the impingement mortality and entrainment controls will result in benefits that justify the costs of the rule.
EPA also notes that it was able to generate only a partial estimate of benefits for today's rule. In particular, EPA's analysis does not fully quantify or monetize certain potentially important categories of benefits, such as existence values for threatened and endangered species, secondary and tertiary ecosystem impacts, benthic community impacts, shellfish impacts and the impacts arising from reductions in thermal discharges that would be associated with closed-cycle cooling. Changes in fish assemblages due to impingement, entrainment and thermal effects are also not fully valued. These categories of benefits which are not fully valued are often referred to as nonuse benefits  -  i.e., benefits that people derive apart from using an affected resource, such as fishing. For example, nonuse benefits would include the value that individuals place on knowing that an aquatic ecosystem is healthy.  EPA conducted a nonuse benefits transfer was based on a species that represents less than one percent of adverse environmental impacts. EPA developed and implemented an original stated preference survey to estimate total values (use plus nonuse values) for aquatic resource improvements under 316(b) regulatory options.   EPA decided not to employ the survey results for purposes of decision-making and EPA has not accounted for values estimated from the survey in the quantitative comparison of costs and benefits.  It is also important to note that EPA's stated preference survey was designed to estimate respondents' willingness to pay for changes in the health of fish populations and aquatic ecosystems and to be statistically representative at large (regional and national) scales; the results were not specifically designed to be statistically representative at the facility level for the assessment of benefits for individual site-level permitting decisions.
As noted at the outset, it is not always the case that private decision making regarding withdrawals of cooling water takes into account society's preferences for fish protection, nor are there market transaction opportunities for individuals to express their willing to pay for fish protection. Thus, despite the limited information on monetized social benefits, EPA has concluded that the benefits of today's rule justify the costs of today's rule.
2.	Comparison of the Other Options
As discussed above, EPA considered three other primary options before selecting today's rule. See Section VI.F Other Options Considered for more detailed explanation of each option. Exhibit VI-1 illustrates a comparison of the total annualized social costs and benefits.
Exhibit VI-1. Comparison of the primary options for 316(b) ($2011 millions at 2013, 3% discount rate)
                                    Option
                         Total Annualized Social Cost
                              Monetized Benefits
      Proposal Option 4
                                                                         $251.8
                                                                          $31.0
       Final Rule
                                                                         $274.9
                                                                          $32.8
       Proposal Option 2
                                                                        $3643.2
                                                                       -$1542.6

I.	Site-Specific Consideration of Entrainment Controls
As described above, EPA is not promulgating uniform national requirements for entrainment for existing facilities. Instead, EPA is setting standards for entrainment that include a framework by which a facility will be subject to a site-specific determination by EPA or a State NPDES permitting authority of appropriate BTA requirements for entrainment. This section describes the process for determining section 316(b) requirements for an individual facility under the national BTA standard for entrainment. It describes the elements that the Director must consider in the permitting decision and how costs and benefits may be considered in such an evaluation.
1.	Implementation of a Site-Specific Evaluation of Entrainment for Existing Facilities
The final rule requires a site-specific determination of BTA entrainment conditions in individual permits and prescribes the requirements for that permitting proceeding. The final rule includes permit application requirements for facilities with a cooling water intake structure. These requirements are designed to elicit the information the Director needs to determine the best technology for reducing entrainment for a particular facility, including information pertinent to an assessment of whether the benefits justify the costs of any particular control measures under consideration.
Today's final rule is a modification of the proposed approach of a site-specific BTA entrainment determination. It will result in one of two outcomes at any facility:
      1.       Determination that the facility must install additional control measures that reduce entrainment beyond that achieved by the currently installed equipment. These may include closed-cycle cooling and/or other technologies.
      2.       Determination that the facility's current, existing technology for entrainment achieves the entrainment BTA requirements under the national BTA standard.
Thus, EPA expects that, under this approach, there will be additional entrainment controls for some facilities and none for others. Even where the Director's determination requires no additional control measures, the Director may conclude the permit should include conditions that specify proper operation and maintenance of the installed technology.
EPA notes that in a number of areas of the country (California, Delaware, New York, and New England; see, for example, DCNs 10-6963 and 10-6841, and EPA Region I's Brayton Point), permitting authorities have already required or are considering requiring existing facilities to install or retrofit to closed-cycle cooling systems. These facilities are still subject to today's rule but the existing requirements have been taken into account in costing..
For facilities that withdraw more than 125 mgd, the rule generally requires that the facility conduct an entrainment study as part of its permit application. The study will indicate, at a minimum, the specific entrainment data collection methods, taxonomic identification to the lowest taxon possible, latent mortality identification, documentation of all methods, and quality assurance/quality control procedures for sampling and data analysis appropriate for a quantitative survey. Peer reviewers must be selected in consultation with the Director, who may consult with EPA and Federal, State, and Tribal fish and wildlife management agencies with responsibility for fish and wildlife potentially affected by the cooling water intake structure. Data from the entrainment study is important to provide corroboration of any through-facility entrainment survival study results in § 122.21(r)(7) or from any other studies conducted.
The final rule also requires the permit application to include the following information as part of the entrainment study (which refers to the requirements at § 122.21(r)(9) through (13), as opposed to the Entrainment Characterization Study at (r)(9)). For a thorough discussion of these study requirements, see Section VIII:
   * An engineering study of the technical feasibility and estimated costs of all candidate entrainment control technologies, including closed-cycle cooling, fine-mesh screens with a mesh size of 2 mm or smaller, and water reuse or alternative sources;
   * A discussion of any outages, downtime, or other effects on revenue along with a discussion of all reasonable attempts to mitigate these cost factors
   * A discussion of the magnitude of water quality benefits, whether qualitative, quantitative or  monetized, of the candidate entrainment reduction technologies evaluated; thermal discharges; and
   * A discussion of the changes in non-water quality environmental impacts and other factors attributed to technologies and/or operational measures considered, including, for example, increases and decreases in the following: energy consumption; air pollutant emissions including particulates and their health and environmental impacts; noise; safety (e.g., visibility of cooling tower plumes, icing); electric grid reliability, and facility reliability.
The permit application will provide the Director with information about options for entrainment reductions at the site and other possible avenues for addressing any adverse effects from entrainment. The purpose of the entrainment study and other permit application materials is to assist the Director in better understanding the effect of entrainment on species in the waterbody from which cooling water is withdrawn. More specifically, the entrainment study will identify species that might be entrained, and estimate their baseline entrainment rates given current entrainment controls. Moreover, the entrainment study will include information about the aquatic ecosystem effects of entrainment of species, and any threatened and endangered species whose range of habitat includes waters where the facility's intake is located. An understanding of the potential ecosystem consequences of entrainment for species will help inform Director decisions about additional information required in the permit application, or permit requirements for any possible additional technologies and management practices. EPA will endeavor to identify high-quality examples of entrainment studies as they are completed, and post them to its website for this rule as a resource for study preparation.
EPA's benefits estimates were based on an extrapolation of available literature on impingement and entrainment studies; the specific Entrainment Characterization Study prepared by a facility could lead to a different estimate of impingement and entrainment for that facility relative to its share of EPA's estimate in the analysis supporting this rule and in the record.
Following the Director's review of this information, the Director must determine what BTA entrainment requirement to propose and explain in writing the basis for the draft permit. The draft permit will then be available for comment from the interested public under the Director's normal permitting process.
2.	Site-Specific Consideration of Cost and Benefits
In establishing requirements under section 316(b) of the CWA, the Supreme Court in Entergy made clear that one factor that EPA may, but is not required, to consider is the costs and benefits associated with various control options. That is, in setting standards, EPA may consider the benefits derived from reductions in the adverse environmental impacts associated with cooling water intake structures and the costs of achieving the reductions. As previously explained, following E.O. 13563, EPA has determined that the benefits of the final rule justify its costs. In addition, EPA has explained (in Section II.C above) why consideration of quantitative and qualitative social costs and benefits may be appropriate in the site-specific determinations when establishing entrainment controls.
In the site-specific proceeding, the Director must consider, among other factors, monetized, quantified and qualitative social benefits and social costs of available entrainment controls, including ecological benefits and benefits to any threatened or endangered species. The Director may be able to reject otherwise available entrainment controls if the costs of the controls are not justified by their associated benefits (taking into account monetized, quantified, and qualitative benefits), and the other factors discussed in the final rule.
In making the site-specific entrainment BTA requirements determination, the final rule requires that the Director consider the information submitted under § 122.21(r) with the section 316(b) permit application. Further, in the case of the larger withdrawing cooling water intake structures (125 mgd AIF or greater), the rule requires submission of additional information including, studies on entrainment at the facility, the costs and feasibility of control options, and information on the benefits of entrainment controls. In evaluating benefits, the Director should not ignore benefits that cannot be monetized or quantified or consider only the impingement and entrainment reductions that can be counted. To result in appropriate decisions from society's standpoint, the assessment of benefits must take into account all benefits, including categories such as recreational, commercial, and other use benefits; benefits associated with reduced thermal discharges; reduced losses to threatened and endangered species; altered food webs; benefits accruing nonlocally due to migration of fish; nutrient cycling effects; and other nonuse benefits. Merely because it is difficult to put a price tag on those benefits does not mean that they are not valuable and should not be included at least qualitatively in any assessment.  The rule does not require the Director to require a facility owner or operator to conduct or submit a willingness-to-pay survey to assess benefits. Further, the rule does not limit the Director's discretion to consider non-water quality impacts in determining whether further entrainment measures are justified. When some benefits are not monetized, the requirement to consider costs and benefits in today's rule does not mean the Director should base decisions solely on the monetized benefits and costs, ignoring the non-monetized benefits.  Instead, the Director should consider the costs and what the magnitude of the non-monetized benefits would have to be in order to justify the costs.
An aggregate evaluation of benefits (even if accurate) would not account for the variations in benefits from location to location. On the basis of available information, EPA's analysis of benefits relied on extrapolating data from existing impingement and entrainment characterization studies to all facilities in the same region on a flow-weighted basis. Differences in species, life stages, and biological abundance across intake locations (even within a region) could lead to very different results for a site-specific analysis of a facility as compared to that facility's share of national costs and benefits, even if the national results are, on average, accurate. A national assessment tends to mask variations in benefits and costs from different geographical locations for different water bodies. For example:
   * Some fish species at coastal facilities have biological spawning attributes that differ from those at other locations.
   * The proportion of the receiving water withdrawn for cooling could also vary among sites.
   * The values that communities place on their resources could vary from site to site.
   * One ecological environment might experience large masses of hardier eggs and larvae subject to potential entrainment; another will have fewer but less hardy eggs and larvae susceptible to entrainment. Without detailed study information, it's difficult to ascertain which ecological environment faces the greater adverse environmental impact from a similar cooling water intake.
The resulting differences in the value of reduced entrainment -- which could be dramatic for some sites -- necessarily disappear in a national aggregation of results. The Agency has decided that this masking of variation in benefits further supports EPA's decision to require consideration of the site-specific benefits of entrainment control technologies in the site-specific process to establish entrainment controls.
The Director must then explain the basis for rejecting an available technology not selected for entrainment control in light of the submissions after consideration of the three factors that supported EPA's determination not to establish a uniform national entrainment standard based on closed-cycle cooling. The Director also must base the determination about BTA controls on the number and types of organisms entrained, including Federally-listed, threatened and endangered species and designated critical habitat (e.g., prey base) as well as consideration of the site-specific social costs and benefits (monetized and nonmonetized) of the various control technologies considered for the facilities.
As noted, the Director may reject an otherwise available entrainment technology as the BTA requirement (or not require any additional BTA controls) if the social costs of the controls are not justified by the social benefits (monetized and nonmonetized). EPA decided to adopt this approach in determining site-specific entrainment controls because it is permissible under Entergy, under E.O. 13563, and consistent with the more than 30-year history of section 316(b) permitting decisions.
This history illustrates the role that cost/benefit considerations have played. As early as 1977, EPA in a permitting decision and a General Counsel opinion explained that, while section 316(b) does not require a formal cost-benefit analysis, the relationship of costs and benefits may be considered in 316(b) decision making. In re Pub. Serv. Co. of N.H. (Seabrook Station, Units 1 and 2), No. 76-7, 1977 WL 22370 (June 10, 1977), remanded on other grounds, 572 F.2d 872 (1st Cir. 1978); accord In re Central Hudson Gas & Elec. Corp., Op. EPA Gen. Counsel, NPDES No. 63, 1977 WL 28250, at *8 (July 29, 1977). In the more than 30 years since, EPA and State permitting authorities have considered the relationship between costs and benefits to some extent in making individual permitting decisions. See, for example, In re Pub. Serv. Co. of N.H. (Seabrook Station, Units 1 and 2), No. 76-7, 1978 WL 21140 (E.P.A. Aug. 4, 1978), aff'd, Seacoast Anti-Pollution League v. Costle, 597 F.3d 306, 311 (1st Cir. 1979).
Because E.O. 13563 directs agencies to propose and adopt rules only upon a reasoned determination that the benefits justify the costs, EPA is allowing this consideration to be applied at the permit level. This approach is consistent with the historical application of section 316(b) requirements and will allow for a full assessment in permit decisions of both qualitative and quantitative benefits and costs. As designed, EPA's requirement for the establishment of site-specific BTA entrainment requirements strikes an appropriate balance between environmental improvements and costs, allowing the Director to consider all the relevant factors on a site-specific basis and determine BTA on the basis of those factors.
After considering the factors relevant to a site, the Director must establish appropriate entrainment controls at those facilities. The Director must review available control technology and may reject otherwise available entrainment controls as BTA if the social costs of the controls are not justified by their social benefits (taking into account both quantified and non-quantified benefits) or if the Director concludes that there are other unacceptably adverse factors that cannot be mitigated. As designed, EPA's national BTA standard for establishing site-specific BTA entrainment requirements strikes an appropriate balance between environmental improvements and costs by selectively requiring closed-cycle cooling or other entrainment technologies at some facilities, without requiring the same technologies at all facilities.
3.	Potential Cost for Site-Specific Entrainment Controls
For the proposed rule, EPA analyzed possible additional costs associated with reductions in entrainment mortality that might result from the Directors' determinations of site-specific BTA requirements. Because this process will play out over a number of years as Directors consider waterbody-specific data, local impacts, and public comment, and weigh land availability, air quality impacts, and remaining useful life, those estimates of the costs of site-specific determinations are highly speculative. EPA is not presenting specific cost estimates today for prospective entrainment requirements because we do not have in hand the robust data that will be generated for individual site-specific settings as required under the national BTA standard for entrainment. Without that refined information on a site-specific basis, EPA has no ability to predict Director decision-making and therefore, the Agency is not estimating costs associated with the ultimate entrainment requirements. Similarly and for the same reasons, EPA did not estimate costs associated with requirements at § 125.94(g), 125.94(c)(8) or 125.94(c)(9).
EPA estimates that the most effective technology for reducing entrainment, closed-cycle cooling, is not available to at least one quarter of all facilities because of geographic constraints, air permitting restrictions in a nonattainment area and remaining useful life of the facility. EPA has limited information on which facilities these are, despite the certainty that these availability concerns are real and significant. In addition, EPA does not have in hand the site-specific data that will be generated as a result of today's rule. If EPA had this data, it would be possible to estimate the costs and benefits ultimately associated with the Directors' site-specific determinations under the national BTA standard for entrainment. The hypothetical costs generated at proposal were reported in an attempt to signal that EPA neither expects that zero facilities would be subject to closed-cycle cooling as a result of the site-specific BTA process for entrainment, nor that all facilities at which these technologies are feasible would be subject to closed-cycle cooling requirements. Without the site-specific information, there is significant uncertainty around any estimates EPA could generate of these costs (including those reported at proposal) and benefits.

VII.	Response to Major Comments on the Proposed Rule and Notices of Data Availability (NODAs)
Over 1,100 organizations and individuals submitted comments on a range of issues in the proposed rule, including over an additional 62,000 letters from individuals associated with mass letter writing campaigns. An additional nearly 250 comments were received on the two NODAs. Responses to all comments, including those summarized here, are in the Response to Comments document in the official public docket (see DCN 12-0004). To facilitate a more comprehensive response and to simplify the task of discussing EPA's rationale for promulgating the final rule, EPA is responding to these public comments in essay form. Each topic area discussed in the comment letters has been addressed in one of the comprehensive essay responses. The major comments received and EPA's responses are summarized in this section.
A.	Scope and Applicability
1.	Source of Water  -  Impoundments
Many commenters expressed concern that the proposed rules do not adequately address the unique water bodies resulting from the many man-made reservoirs specifically designed and constructed as cooling water impoundments (referred to as cooling ponds in the proposed rule). Commenters expressed confusion regarding the applicability of the proposed regulations because impoundments have both intakes from the impoundments and intakes that supply water to the impoundment. Many requested that EPA clarify that man-made impoundments, built to supply water for power plants, do not constitute water of the United States for purposes of implementing the rule or that they should be classified as meeting the definition of closed-cycle cooling.
Response:  As discussed in Section I, facilities that withdraw cooling water from impoundments that are waters of the United States and that otherwise meet the criteria for coverage (including the requirement that the facility has or will be required to obtain an NPDES permit) are subject to today's rule.  Revisions to the definition of waters of the U.S. are outside the scope of this rulemaking. However, today's regulatory definition of closed-cycle recirculating systems specifies that such a system may include impoundments of waters of the U.S. where the impoundment was constructed prior to today's final rule. To meet the rule definition for closed-cycle recirculating system, this impoundment must have been lawfully created for the purpose of serving as part of the cooling water system as documented in the project purpose statement for the Clean Water Act section 404 permit obtained to construct the impoundment. In the case of an impoundment whose construction pre-dates the CWA requirement to obtain a section 404 permit, EPA expects documentation of the project's purpose to be demonstrated to the satisfaction of the Director.  This documentation could be some other license or permit obtained to lawfully construct the impoundment for the purposes of a cooling water system, or other such evidence as the Director finds necessary.
The definition of closed-cycle recirculating system at § 125.92(c)(1) of  today's rule also specifies that impoundments that are not waters of the United States but withdraw make-up water from waters of the U.S. meet the definition of a closed-cycle recirculating system, if make-up withdrawals have been minimized.  These impoundments are constructed in uplands, and are not required to obtain a 404 permit.  Thus, these impoundments do not need to provide documentation of the project's purpose.
2.	New Units
In the proposal, EPA defined new units as newly built units added to increase capacity at the facility. The definition did not include any rebuilt, repowered or replacement unit, including any units where the generation capacity of the new unit is equal to or greater than the unit it replaces. Many industry stakeholders agreed that the definition of new units should not include repowered existing units. Others thought that new units should be treated similarly to existing units with entrainment standards applied on a site-specific basis and that the nine proposed factors should also be applied to entrainment decisions for new units. Environmental organizations argued that EPA should set a deadline by which all existing facilities must comply with the new unit standards and that EPA's exclusion of repowered/rebuilt facilities created a loophole through which existing facilities could perpetually operate as an existing unit, even after replacing all of the generating equipment. Many of the comments had several elements in common:
       Requirements should be flexible enough to address sites where meeting the requirements is not technically feasible (e.g., limited land availability).
       EPA needs to provide greater clarity regarding how new unit standards apply to manufacturing facilities.
       The DIF is a more appropriate parameter for determining compliance because AIF cannot be determined until after the system is built, and baseline AIF would require assumptions about as-yet undetermined operational factors.
       It is unclear how the new unit requirements will be applied to manufacturing units, and the requirements do not appear to consider the circumstance where a new unit is constructed at an existing manufacturing facility where construction of the new unit does not require any modifications to the existing intake structure.
       Some commenters have noted that the new unit provisions are a departure from previous determinations and are unclear. They argue that they have not had adequate opportunity to comment on this issue and request EPA re-propose new unit requirements if it wants to continue with this initiative.
Response: EPA's definition of a "new unit" for the final rule can be found at § 125.92(u). New units includes the addition of a stand-alone unit that is constructed at an existing facility. The rule definition makes it clear that the new unit may be for the same general industrial activity as the existing facility. Because the requirements are much like the Phase I requirements for new facilities the costs for installing controls at new units are similar to the costs imposed on new facilities. The cooling water withdraws made by the rest of the existing facility are subject to the requirements at 40 CFR 125.94(c) and (d).
With respect to impingement mortality and entrainment, the final rule requires, at § 125.94(e)(1), that new units achieve flows commensurate with that of a closed-cycle recirculating system. As with the new facility Phase I rule, the new unit may choose to meet an alternative requirement at 40 CFR 125.94 (e)(2) and demonstrate to the Director that the technologies and operational measures employed will reduce the level of adverse environmental impact from any cooling water intake structure used to supply cooling water to the new unit to a comparable level to that which would be achieved upon implementing closed-cycle recirculating for that new unit. This includes a demonstration showing that the entrainment reduction is equivalent to 90 percent or greater of the reduction that could be achieved through implementing a closed-cycle recirculating system. This demonstration must also include a showing that the impacts to fish and shellfish, including important forage and predator species, within the watershed will be comparable to those which would result if the facility were to implement a closed-cycle recirculating system.
Facilities may choose to install a closed-cycle recirculating system, and EPA has observed that many new units are selecting closed-cycle recirculating systems on their own, particularly for combined cycle and natural gas for reasons unrelated to 316(b) (such as water availability). In these cases, benefits related to reductions in IM&E would be expected to occur.