Response to Comments 1 - 8: The EPA believes that the statistical method used to calculate the UPLs for Hg, PM, and HCl emissions from the existing units already accounts for fuel variability and no further adjustment factor is needed. The statistical analysis spreadsheets analyzing Hg, PM, and HCl emissions from the existing units utilize multiple emission test averages, per boiler (where available), in their UPL calculations. There are often twice as many data points as there are floor averages (Hg: 47 boilers in floor 90 total data averages, filterable PM: 130 boilers in floor 399 total data averages, HCl: 130 boilers in floor 185 total data averages). These large numbers of data points were unavailable in the IB MACT rule effort and account for variance in emissions over time and would therefore also account for fuel variability.
The EPA is mindful of the need to account for sources' variability in assessing sources' performance when developing technology-based standards. The EPA reviewed subcategory floor calculations in light of these comments and believes that the two-step MACT floor analysis process adequately addresses: (1) performance testing variability and (2) fuel analysis variability estimations. The EPA revised the MACT floor calculations in light of data submitted during and after the public comment period and also modified the approaches used at proposal for various aspects of the floor calculations.

The EPA first took fuel into consideration, to the extent it is reflected in differences in boiler design, when we divided the source category into subcategories. The EPA is aware that differences between given types of units, and fuel, can affect technical feasibility of applying emission control techniques, and has addressed this concern in the final rule. For a fuel based pollutant, such as PM, performance testing must be conducted under representative full load operating conditions, which, along with the parameter monitoring requirements, provides an assurance that the standards are being met at all times. For Hg and HCl, we modified the fuel based variability analysis in consideration of comments received on this approach. The first modification to the analysis was the introduction of a solid fuel subcategory, which includes any unit burning at least 10 percent, on an annual heat input basis, of any coal, fossil solid, biomass, or bio-based solid fuel. Given the wide variety in fuel types that compose the floor, the statistical analysis accounts for some of the inter-unit variability for different fuel types identified to be in the floor. The second modification was the development of a fuel variability factor (FVF). The FVF calculations were similar to the calculations used at proposal, but they were simplified to remove the control efficiency calculation and the method for identifying outliers in the data was also adjusted. The revised FVF analysis calculated a ratio for all fuel analysis data points for units in the top 12 percent for existing units and the top performing unit for new units in each subcategory. This ratio compared the reported fuel analysis data, converted to units of lb/MMBtu, to the emission test outlet data, converted to units of lb/MMBtu, during the stack tests. At proposal we conducted an outlier analysis of only the maximum ratios for each unit, but we revised the outlier analysis to consider all of the ratios from top performers within each subcategory. We then defined and identified outliers using the test of 3 times the standard deviation and 3 minus the standard deviation for all of the ratios in the subcategory. After removing outliers, the remaining maximum ratio for each subcategory was identified and multiplied by the 99 percent UPL.
For a discussion of how the EPA considered other non-fuel variability operations, such as boiler load, see response to the comments provided in section 4A07.
Comment 9: Commenter 17730 notes that the EPA provides no discussion in the proposed rule about how it may have considered the chemistry of the coal in determining the effectiveness of an emission control system, and its subsequent selection of a proposed emission limit. The mere fact that some units may achieve a low emission rate for a single constituent using a given emission control technology does not give due consideration to the fact that the base fuel may have had little to no concentration of the constituent in the fuel to begin with. The EPA's approach to setting the emission standards also does not take into consideration those fuels that may have had high initial base fuel constituent concentrations that are greatly reduced by a given emission control technology.
The commenter notes that the EPA aptly notes in the discussion of the proposed work practice standard for controlling the emissions of organic compounds; "a single component of the operating system; the burners and the burner components, play a great role in the combustion efficiency and the balance of carbon monoxide and oxides of nitrogen emissions that are created". The EPA should further consider these factors in establishing the emission standards for electric generating units.
Response to Comment 9: A review of the respective MACT floor spreadsheets reveals that a wide range of boiler, coal, and control types are represented in the respective MACT floor pools, indicating that such factors as noted by the commenter were included in the analyses.
Comment 10: Commenter 17725 states that their contractor also recommends that the EPA include percent reduction limits for fuel-related emissions (filterable PM, metals, HCl/HF) as an option in addition to the currently proposed lb/MMBtu or output standards. Commenter recommends using the following equation to establish the alternative percent reduction floor values each fuel-related pollutant:
%Rfloor = (1− Efloor/Efuel) x100
where:
%Rfloor = Percent reduction floor value for fuel related pollutant
Efloor = lb/MMBtu emission floor value for pollutant
Efuel = Average lb/MMBtu fuel concentration for pollutant based on all available
fuel emissions data reported by the sources in the emissions floor analysis

This approach assures that the alternative percent reduction value represents the average emission achieved by the best performing units as required by section 112 of the CAA.
Response to Comment 10: The EPA noted in the proposal preamble that it questioned whether a percent reduction format would comply with D.C. Circuit interpretations of CAA section 112, and we also stated that we did not have sufficient data to establish a percent reduction standard even if we believed we had such authority under CAA section 112. The agency believes the rule's emissions limitations and work practice standards are appropriate to meet the CAA's requirements.
Comment 11: Commenters 17807and 18024 state that the EPA's proposed rule severely constrains fuel supply reliability and operational flexibility due to overly broad HCI standards. TEC requests that the EPA publish the coal blends in the top 12% of each coal type category and develop specific nonmetal HAP and HCI permit limits based on chemical composition from each major coal region.
Response to Comment 11: The EPA addresses subcategorization issues elsewhere. This proposed subcategory approach suffers from the same flaws as others suggested by commenters and the commenter has not provided data to evaluate its suggested approach. The agency disagrees that the rule severely constrains fuel supply reliability and operational flexibility. On the contrary, the suite of choices available in the rule to owners or operators affords numerous ways of demonstrating compliance with HCl emissions limits, ranging from HCl CEMS to monthly emissions testing.
Comment 12: Commenter 17808 found, by examining the ICR database, that chloride and fluoride concentrations in oil can vary widely. In the MACT floor calculations the HCl reported was a much lower average chloride concentration during the test period, suggesting that the emission rates at these units could be higher with a different shipment of fuel. The wide variability in the chloride concentrations in fuel oil suggests that the EPA's variability adjustment may not result in a standard that would be achievable by the units that were included in the calculation of the MACT floor for liquid oil-fired EGUs.
Response to Comment 12: As mentioned elsewhere in this document, the agency believes its procedure used to establish floors and emissions limitations takes potential variability into account. The rule now offers liquid oil-fired EGUs the ability to demonstrate compliance with the acid gas emissions limits by documenting that their fuel moisture does not exceed one percent.
Comment 13: Commenter 17914 states that the emissions standard needs to consider the technical limitations of AQCS equipment operation and control in a real-world setting to achieve the proposed limits, as fuel composition changes within a single fuel category. The commenter recommends that the EPA set the standards at the levels that can be achieved "under the most adverse conditions which can reasonably be expected to occur," which is the appropriate legal standard 627 F.2d 416, 433 n. 46 (D.C. Cir. 1980).
Response to Comment 13: The EPA believes the approach for setting emission limits (as described in the proposal preamble) adequately accounts for fuel composition changes since the limits were set using data from a wide variety of facility configurations and coal types.
Comment 14: Several commenters (17813, 17925,17930,17975, 19114, 17254) state that the EPA's proposed rule does not adequately account for HAP variability in lignite or the variation in specific metals from sample to samples (e.g., arsenic). Hg content varies for lignite with no predictable pattern (even within the same mine). Since all lignite burning power plants are co-located with the mines that supply their lignite, this variability cannot be avoided. In order to account for this Hg variability in lignite seams, the averaging period needs to be extended to an annual averaging period and emissions limits should be raised to the MACT limit. Moreover, there are differences in constituents of coal grades such as subbituminous versus bituminous(because coal is not homogeneous), so different mercury emission limits for these two grades should be established and further subcategorization between the coal types should be applied so that more reasonable limits and treatment can be applied.
Comment 15: Commenter 17930 states that continuing with the proposed PM limits poses a dual problem for lignite units:
1. Lignite has a higher ash content than other types of coals
2. More lignite must be burned to generate the same level of energy produced as other types of coals.
The EPA states that :"[t]he boiler of a coal-fired EGU designed to bum [<8,300 coal] is bigger than a boiler designed to burn coals with higher heat values to account for the larger volume of coal that must be combusted to generate the desired level of electricity."
Comment 16: Commenter 17975 adds that the .03 lb/MMBtu standard that the EPA has proposed could result in emissions at levels well above the specific limits that the EPA has indicated are appropriate for arsenic and other non-Hg metals. The occasional sampling of metals that the EPA has proposed is inadequate due to the variation over numerous samples and at a minimum, they should be required to sample the metal content of coal, as it is burned on a daily basis.
Comment 17: Commenter 17254 believes that EPA should take into account coal sulfur content in setting the alternative acid gas SO2 standard and coal switching at scrubbed units should not be required.
Comment 18: Commenter 17904 states that the EPA's MACT analysis does not capture the variability inherent in lignite fuel and limited blending capability due to the "mine-mouth" nature of most lignite fired units. Lignite core samples show mercury concentrations from these mines range from a low average of about 20 lb/TBtu to a maximum of over 240 lb/TBtu. These units must be able to operate in compliance with any final MACT notwithstanding the high variability of mercury in any seam which supplies the facility. The EPA must develop additional data on variability, specifically including fuel variability, both in the coal from a single mine as well as variability at plants that burn coals from multiple sources.
Commenter 17904 further states that fuel concentrations are critical because the EPA's 1999 ICR confirmed the high degree of elemental Hg remaining in flue gases of low rank coal, showing concentrations that ranged from 56 percent to 96 percent of total Hg. Additionally, lignite typically has relatively high total Hg content (on a lb/TBtu basis).
Comment 19: Commenters 17807 and 17930 state that notwithstanding attempts to use statistical averaging methods and an averaging period of 30 days, the EPA's proposal does not properly take into account the extent of variability documented in lignite. Commenter 17930 states that lignite variability is not adequately accounted for in the ICR testing data. Depending on the seam being mined that day, Hg emissions data could vary significantly. The EPA tests (Sandow 5B and Oak Grove) were not conducted over a consistent and long enough period to reflect the potential lignite variability that could be experienced at these units.
Response to Comments 14-19: The EPA has recognized the differences in Hg emissions from units burning low rank, virgin coal by setting a separate emission limit. The EPA also knows that control technologies and monitoring techniques are available to allow operators to adjust to changes in Hg concentrations in the fuel. The EPA has also offered several options to show compliance for emission limitation of the non-Hg HAP metals. Operators have the option to meet limits for filterable PM, individual metals, or total metals. Although fuel switching is a legitimate compliance options, the EPA does not require any unit to switch fuel to comply with the emission limits in the rule. The EPA used all available data to establish the standards and commenters are incorrect to the extent they imply there is some flaw in the final rule because we did not collect additional data from low rank, virgin coal-fired EGUs.
Comment 20: Several commenters (19536, 19537, 19538) recommend that to better account for variability in the emissions of the top performing 12 percent of EGUs, the EPA should determined the 99[th] percentile UPL to the test data for the lowest emitting 40 EGUs. The EPA stated: "there are two fundamentally different approaches to incorporating variability into the proposed [MACT] rule: (1) including variability in the MACT floor calculation; or (2) including variability in the compliance method." Averaging over a month or year of data would provide opportunity for variations in the amount of a constituent in the fuel to be accommodated without exceeding the emission limitation. Use of a long-term average versus long-term testing evens out the ups and downs of variability in measured data. The EPA's approach to account for variability in emissions at the 12% best performing units results in a MACT floor determination that fails to reflect the average emissions of the best performing units. Specifically, the EPA determined the 99[th] percentile UPL Hg emission rate to be 1.1812 x 10-6 lb/MMBtu. This is over 55 times higher than the actual average emission rate (i.e., 2.1250 x 10-8 lb/MMBtu) of the EPA's data for the lowest emitting 40 EGUs. Of all the test results presented in the EPA's Hg MACT floor spreadsheet from the lowest emitting 40 EGUs, only two test results were over 1.1812 x 10-6 and the majority was at least an order of magnitude lower than 1.1812 x 10-6 lb/MMBtu. Further, in the entire 330 EGU Hg emissions dataset, more than half of the EGUs (153 units) had minimum Hg emission rates lower than the EPA's 99[th] percentile UPL.
Response to Comment 20: The EPA appreciates the suggested alternative approach for including variability in the emissions. However, the EPA is confident in the approach described in the proposal preamble and this final rule and we will continue to use that approach.
Comment 21: Commenter 17711 requests that the EPA re-examine the logic of establishing a MACT floor for a source subcategory for which emissions variability is the result of unmeasurable differences in fuel quality, and then setting MACT floor limits that can be consistently achieved only through use of a control technology that is not being used by any of the sources in the subcategory.
Response to Comment 21: The EPA did not base the MACT emission limits on fuel quality but, rather on measured stack emissions. We disagree with commenter that achievement of the MACT floor limits could only be accomplished by use of a control technology given the fact that the limits are based on emissions data from existing EGUs. However, we note that an alternate compliance method (1 percent moisture in the liquid oil) is included in the final rule.
Comment 22: Commenter 18963 states that coal refuse is created by the segregation of naturally occurring materials, and the specific characteristics of any individual coal refuse pile necessarily vary to some degree based upon geological and other considerations. Even to the extent that separate coal refuse piles were created from mining activity in the same general location, variability in coal refuse characteristics has been widely documented between, and even within, such piles. One of the reasons for this variability relates to the evolution of coal mining and processing activity over time. During the early history of coal mining and preparation, the relative value of the "virgin" coal did not justify significant effort to segregate all combustible material for sale or use as fuel. Therefore, material that had been segregated into piles and left at the mining or coal preparation site exhibits distinct characteristics relative to fuel parameters.
Over the course of time, separation techniques, and the economic return on the investment of effort, evolved to achieve different degrees of segregation, and different characteristics in coal refuse. Both the lack of precision in these mining and preparation activities, and the changes in practices and implementation of such activities, contributed to the variability in characteristics of coal refuse.
The variability in characteristics of coal refuse has been substantially documented and demonstrated through numerous sampling events. Analytical information from such sampling has been submitted to federal agencies, including FERC, in the context of routine filing. Such data clearly evidence the variability in coal refuse characteristics, relative to heat value, ash content and other relevant constituents, even among multiple samples collected from the same coal refuse piles.
Response to Comment 22: The EPA believes that variability associated with the composition of coal refuse was captured in the 2010 ICR data as there were several units tested that were using coal refuse as the primary fuel source.
4A07 - MACT Floor Methodology: Other
Commenters: 16513, 17265, 17385, 17402, 17620, 17621, 17627, 17637, 17718, 17725, 17758, 17776, 17796, 17803, 17808, 17812, 17848, 17867, 17904, 17914, 17975, 18018, 18034, 18421, 18444
1. Stringency/numerical limit recommendations.
Comment 1: Commenter 17620 states that as a result of the work of the 2001-2002 CAA Advisory Committee, they previously recommended the following limits: 1) 0.4 to 0.6 lb/TBtu for Hg, with an alternate 90 percent control requirement; 2) 0.015 lb/MMBtu for PM; 3) 95 percent reduction requirement for SO2 and HCl, based on the then-existing recorded BACT decisions; 4) 100 ppm CO as a surrogate for organic HAP; 5) a CO MACT limit, based on BACT levels, be established, and; 6) short-term CO limits be established to cover transient operating conditions. Commenter 17620 states that the most recent testing demonstrates that their earlier recommendations were readily attainable and recommends that the EPA incorporate higher control efficiencies for Hg and SO2 because of the advances in pollution control systems over the past decade and consider recent BACT determinations for PM and CO in setting MACT standards.
Response to Comment 1: The EPA has based the emission limits in the final rule on the newest control installations as commenter appears to be suggesting and believes that its approach complies with the statutory mandate and recent Court decisions. The EPA is constrained by the statute to establish MACT floors based on the emissions data of the best performing similar source or the existing sources in the category. The EPA also considered whether a beyond-the-floor standard was achievable for the final rule, but, except for one subcategory, we determined it was not achievable to establish beyond-the-floor standards primarily due to the costs of attaining additional HAP emission reductions.
Comment 2: Commenter 17848 states that except for the PM limits, the proposed EGU limits are substantially more stringent than those in the final boiler MACT. Commenter is concerned that issues of acceptability with the boiler MACT will be multiplied for sources subject to the EGU MACT. The states enabling legislation directs the commenter to consider technical practicability and economic reasonableness of regulations to reduce emissions. Commenter states that to the extent, if any, that the proposed limits are not technically practicable or economically reasonable, they request that the EPA revise the limits.
Comment 3: Commenter 17928 states that the final EGU MACT should be more consistent with the technical approaches used in the final ICI Boiler MACT.
Response to Comments 2 - 3: The EPA believes that the analytical approaches used on the final rule are appropriate for the source category and, where appropriate, consistent with those employed on other NESHAP rulemakings. The EPA has based its analyses on data obtained from EGUs and believes that the analyses comply with the statutory mandate and recent Court decisions. MACT standards must be at least as stringent as the emissions limitations achieved by the best controlled similar source for new source standards or the average emission control achieved by the best performing 12 percent of existing sources for the existing source standards (or best performing five sources for subcategories with less than 30 sources). This level of control is called the MACT floor and costs may not be considered when establishing the MACT floor. Further, we maintain that the standards are technically feasible to achieve for all EGUs.
Commenter 4: Commenter 18444 recommends that the EPA should require that the air pollution control systems needed to achieve these emission standards be operated in such a manner to reasonably minimize HAP emissions after construction.
Response to Comment 4: The EPA believes that the emission limits in the final rule are sufficient to ensure that emission controls are operated in a manner that will minimize HAP emissions.
Comment 5: Commenter 17718 argues that the total PM limit for existing sources is excessively stringent in that it requires compliance during startup and shutdown events without providing any margin for the higher emissions that unavoidably occur during those periods. Commenter requests that the EPA adopt separate work practice standards applicable during startup and shutdown events specific to the unit's boiler type and control equipment.
Response to Comment 5: The EPA is establishing work practice standards for periods of startup and shutdown in the final rule as discussed elsewhere in this document. We are not, as commenter seems to suggest, establishing different subcategories for startup and shutdown periods.
Comment 6: Commenter 18421 states that the ability for coal-fired units to meet strong standards is evidenced by the reductions achieved through existing state programs. Commenter adds that 17 states have a Hg emissions standard for EGUs, and the technology is available for all coal types and boiler configurations. The commenter goes on argue that state rules have stronger standards and timelines regarding regulation of Hg emissions.
Response to Comment 6: The EPA agrees that the standards in the final rule are consistent with the statute and we believe that all existing sources can meet the standards. We also note that states may establish more stringent standards than those contained in this final rule.
2. Variability.
Comment 7: Commeter 17621 states that there is no consistency in the equation used to calculate variability and the pooled mean in the MACT floor calculations. Examples given with discrepancies in the pooled mean are: the coal Hg >=8,300 Btu/lb, total PM for coal EGUs; calculations with discrepancies in the variability: Hg limit for existing coal >=8,300 Btu/lb and the total PM and metals in existing coal EGUs. Commenter recommends that the EPA standardize the equations used in the different datasets.
Response to Comment 7: The EPA has standardized the equations used in these different data sets. Also, the EPA is now finalizing a filterable PM surrogate standard for non-Hg metallic HAP limit rather than a total PM limit.
Comment 8: Commenter 17620 states that the Court decision that the EPA can calculate MACT floors considering the worst-case testing conditions that can reasonably be expected to recur does not mean the highest theoretically conceivable emissions. Rather, it should be understood to encompass the full use of installed pollution control devices, at those regularly used operating loads that maximize emissions and with the range of variation of fuels typically used by the facility.
Response to Comment 8: The EPA believes that the emission limits in the final rule satisfy the conditions noted by the commenter.
Comment 9: Commenter 17725 states that since neither the CEMS measurement variability or the plant operational variability, that will be an inherent part of the CEMS data, will be reflected in the reference method-based UPL, a separate multiplier should be applied to the UPL (or applied as an additional multiplier to the FVF adjusted floor average) to address for the CEMS/operating variability issue.
Response to Comment 9: The agency disagrees with the commenter's assertion that an additional multiplier related to CEMS variability should be applied to the UPL. As mentioned elsewhere, variability  -  including that attributed to load/operational variability, fuel variability, and other sources of variability  -  has been accounted for in the setting of the proposed and final emission limits. The method used to account for this variability was described in the preamble for the proposed rule. The method is consistent with methods used in other NESHAP rules that the EPA has promulgated. In general terms, the UPL procedure addresses variability from stack tests, while the 30-boiler operating day rolling average provides an additional allowance of variability for CEMS use and accounts for regular process and fuel variability over the averaging period.
Comment 10: Commenter 17821 adds there are a number of factors that may cause Hg, HCl, metals, particulate and other emissions to vary from power plant boilers and more importantly at the same boiler. These factors include variability in the fuel (i.e., variability in Hg content, chlorine content and heat content of coal, etc.), changes in operating conditions, measurement error, intermittent maintenance events, load variation, and unburned carbon in flyash.
 Response to Comment 10: As explained above, we believe that we have adequately accounted for variability in the final rule through application of the 99% UPL and inclusion of a 30-day rolling average for compliance.
3. Work practice standards.
Comment 11: Commenter 17620 states that EPRI's evaluation of the ICR dioxin/furan/PCB HAP emission tests (EPRI, 2010) confirms the EPA's finding that most congeners in this group were not detected. The commenter's own evaluation found that contamination of the samples from non-power plant sources biased emissions high in many samples. The chemicals in this HAP group are ubiquitous in the environment and the test method is so sensitive that it is very difficult to avoid contamination of the sample during sampling and analysis.
Response to Comment 11: The EPA proposed and is finalizing work practice standards for organic HAP emissions from EGUs because a significant majority of the organic-HAP emissions data was below the method detection limit, notwithstanding the fact that we required sources to test for certain organic HAP almost twice as long as normal, and we therefore conclude that it is not technologically and economically practicable to measure such emissions from EGUs.
4. Technical/data issues  -  MACT floor.
Comment 12: Commenter 17621 states that technical shortcomings and inconsistencies in the EPA's MACT floor calculation procedure should be resolved prior to issuance of a final rule.
Response to Comment 12: Although the commenter has not provided any specifics, partly based on comments received, the EPA has reevaluated its data base and we believe that we have resolved the identified inconsistencies prior to issuing the final rule.
5. Ability to/means of achieving compliance.
Comment 13: Commenter 17758 states that plants burning primarily eastern bituminous coal will have to install wet FGD for compliance because of the higher chlorine content, which will necessitate a more aggressive control technology to remove higher levels of HCl.
Response to Comment 13: The EPA acknowledges that different sources will have to employ different approaches to comply with the final standards. The EPA believes that all existing sources are able to comply with the final standards through the installation of control devices and/or other mechanisms that may reduce HAP emissions.
Comment 14: Commenter 17975 argues that in order to achieve PM capture consistently at all ranges, units need either baghouses or EPSs in combination with a scrubber. Commenter 17975 adds that PM emissions around the range of the proposed floor have much lower opacities than those seen in startup/shutdown/malfunction events, which means much greater PM emission and HAP metal emissions during such events.
Response to Comment 14: The EPA has established work practice standards for startup and shutdown periods in the final rule as discussed elsewhere in this document. We are retaining the affirmative defense for malfunction periods. The 30-day averaging period will provide sources the ability to comply with the standard by operating somewhat below the standard to accommodate intermittent periods of minor malfunctions. The use of CPMS will provide to sources the need to investigate and correct minor malfunctions. Sources will be able to use affirmative defense provisions for major malfunctions that occur in spite of reasonable attention to good operating and maintenance practices.
6. Data used to determine MACT floors and establish standards
Comment 15: Commenter 17796 states that the Department of Energy has investigated technologies to reduce Hg and other pollutants from EGUs and should be evaluated as part of the MACT floor evaluation for this rulemaking. The commenter noted that SCR reduces NOX and increases the proportion of oxidized Hg allowing it to be removed by traditional controls. The commenter also states that ACI using halogenated activated carbon is effective in removing Hg.
Response to Comment 15: To the extent that technologies noted by commenter are in use on existing EGUs and were in use during any testing used to provide data to the EPA through the 2010 ICR, the technologies' performance is included in the MACT floor analyses.
7. Miscellaneous.
Comment 16: Commenter 17637 discusses over 20 years of projects implemented to reduce emissions from fossil fuels, including SCR, supplemental precipitators and other control technologies and operation modifications to reduce NOX, SO2, CO2, Hg and PM emissions. Commenter requests that facilities that have self-initiated good controls not be disadvantaged compared to other competitors with fewer controls.
Commenter 17637 states that they have already implemented multiple projects including SCR, supplemental precipitators among other control technologies and modified its operations and fuel burned to reduce emissions of NOX, SO2, CO2, Hg and PM. The commenter requests that the EPA provide a level economic playing field by ensuring those facilities that have initiated such actions and have good controls in place are not disadvantaged relative to our competitors with less or no controls.
Response to Comment 16: The EPA does not understand the comment. All EGUs in a given subcategory must comply with the final standards so no EGUs are disadvantaged as compared with other sources. Sources that are well controlled may already comply with one or more of the final standards and poorly controlled EGUs will likely have to install controls to comply with the final standards.
Comment 17: Commenter 17265 states that it is not clear if or how the agency has taken into account the dramatic decline in EGU emissions over the last decade, citing that in their state EGU Hg emissions have declined over 80% since 1997.
Response to Comment 17: As required by CAA section 112, the EPA has based the emission limits in the final rule on emissions data obtained from existing EGUs. Historical emission trends do not play a role in the development of MACT limits under CAA section 112, except to the extent that data from the newer, better controlled sources will be used to establish the MACT floor standards.
Comment 18: Commenter 17385 supports the output-based limits for new and modified facilities because of their energy efficiency incentive.
Response to Comment 18: The EPA appreciates the support of the commenter.
Comment 19: Commenter 17385 asks if the EPA would consider for the NESHAP the benefit allowed in the NSPS for CHP units to account for avoided electric power transmission and distribution losses.
According to commenter 17385, the proposed NESHAP defines "gross output" in a way that credits useful thermal energy recovery from combined heat and power operations. However, in the proposed NESHAP, output-based limitations in Tables 1 and 2 of the rule are in units of mass of pollutant per electrical output. Table 10 of the preamble clarifies that output-based limitations are in unit of mass of pollutant per gross electrical output. The proposed NESHAP does not appear to allow any credit to CHP EGUs for thermal energy recovered. It is not clear if the NSPSs allow a thermal output credit for CHP. Commenter asks the EPA to clarify and consider a thermal output credit for applicable CHP EGUs.
Commenter 18439 encourages the EPA to consider allowing for a larger than five percent benefit for avoided transmission and distribution (T&D) losses. The commenter also encourages the EPA to consider an avoided T&D loss credit for CHP under the NESHAP rule as well. The commenter encourages the EPA to consider the comments from various members of commenter's organization recommending approaches for settling on a specific approach to settling line loss figures.
Commenter 18434 indicates that in the NSPS Rule, the EPA requests comment "on whether it is appropriate to recognize the environmental benefit of electricity generated by CHP units by accounting for the benefit of on-site generation which avoids losses from the transmission and distribution of the electricity." We agree that these avoided losses should be recognized. Indeed, such savings are one of the key benefits of distributed generation, and we commend the EPA for trying to find a way to account for this benefit in the NSPS rule. As an initial matter, we urge the EPA to account for avoided line losses in the NESHAP rule as well.
The commenter asserts that roughly two-thirds of energy inputs (68%) are simply emitted into the air with conventional generation, with a mere 32% actually delivered to customers. A sizeable portion of this loss can be attributed to transmission and distribution (1,596 TWh or 9% of net electricity production in the figure below). The unfortunate results are lost competitiveness and jobs, as well as increased emissions. By recognizing the transmission and distribution benefits of CHP and WHR, the EPA can help incentivize investments in these technologies.
The commenter believes, however, the suggested 5% multiplier for line losses is too low. According to EIA data, national, annual electricity transmission and distribution losses average about 7% (6.7%) of the electricity that is transmitted in the U.S., costing nearly $26-billion in foregone revenue in 2009 alone. These losses are even greater during peak hours. In fact, a recent report by the Regulatory Assistance Project finds that a grid segment or area with average line losses of 7% could have marginal line losses of 20% at the time of the system peak. Studies at Carnegie Mellon University and MIT have shown that one megawatt-hour (MWh) of local generation, like CHP, can displace up to 1.47 MWh of central generation, suggesting a 47% benefit for efficient CHP. Although 47% is clearly not a reasonable multiplier, these numbers nonetheless imply the CHP benefit should be well above 5%. Moreover, where facilities can credibly demonstrate higher local or regional line losses (which can be verified by a third party), a larger multiplier may be appropriate. In addition to being more efficient and less polluting, CHP and WHR projects significantly reduce line losses, free existing transmission, provide less expensive back-up electricity, and generate sustainable base-load power. The final rule should adopt a multiplier that fully credits the transmission and distribution savings of CHP and WHR and therefore incentivizes such investments.
Response to Comment 19: The EPA has clarified its terminology in the final rule.
8. Comments not requiring responses.
Comment 20: Commenter 17620 states that opportunities for improvement in the heat rate of existing EGUs are relatively small. In addition, many efficiency improvement options, such as soot removal, are not permanent and require ongoing maintenance to sustain improved performance. The EPA should develop a record in upcoming GHG regulations that would enable accurate measurement and determinations of sustainable efficiency improvements.
Response to Comment 20: The EPA is not establishing standard for GHGs in this rule, and, therefore, we need not respond to this comment.
Comment 21: Commenter 17812 states that the EPA's reasoning for applying numeric dioxin/furan limits to coal-fired ICI boilers is flawed. The EPA is splitting hairs to say that dioxin/furan emissions from ICI coal units are significantly different from EGUs from a testing feasibility perspective. Using the EPA data for both boiler and EGU regulations, the commenter compared average and total emission rates of dioxin/furan from the two sectors. Total dioxin/furan emissions estimated for the two sectors differs by only about 32 percent (2.5 grams for ICIs vs. 1.7 grams for EGUs). Average dioxin/furan emissions for ICI coal boilers is only 2.8 times higher than for EGUs, not 7 times higher as reported by the EPA (no documentation of the EPA's comparison has been found to date in the dockets). Commenter 17812 adds that because the EPA did not require eight hour test runs for the ICI boiler testing, it does not know what percentage of ICI boiler test runs would also be below the MDL with the extended test runs.
Response to Comment 21: The EPA is regulating EGUs in this final rule. This comment is out of scope and we are not responding to it.
Comment 22: Commenter 17867 argues that the EPA has a large degree of discretion in determining which HAP to included in the rule and requests that the EPA phase in standards for HAP based upon the EPA's expanding knowledge of HAP emissions from EGUs and their effects on human health and the environment. Commenter believes there is no reason for the EPA to allow limitations on Hg to be put at risk by including them in a rule with other HAP and Hg control devices have the potential to reduce other HAP emissions.
Response to Comment 22: Comments on the scope of this rulemaking are addressed in the proposed rule and in response to other comments in this RTC and the preamble to the final rule. We also note that we do not necessarily agree with commenter in its assertion that a phased approach is benefitial given it would create a level of regulatory uncertainty about potential future investments and also limit a sources ability to optimize control configurations when designing approaches to comply with the final standards.
Comment 23: Commenter 18018 argues that the EPA failed to prove any public health risk from non-Hg metal HAP and acid gases and that it is only appropriate to develop limits for Hg and nickel.
Response to Comment 23: Comments on the scope of this rulemaking are addressed in the proposed rule and in response to other comments in this RTC and the preamble to the final rule.
4A08 - MACT Floor Methodology: Mercury floor analysis
Commenters: 16469, 17409, 17620, 17621, 17623, 17689, 17712, 17716, 17718, 17725, 17728, 17732, 17739, 17740, 17758, 17761, 17775, 17776, 17795, 17796, 17800, 17816, 17820, 17821, 17869, 17871, 17878, 17881, 17885, 17886, 17904, 17909, 17931, 18014, 18015, 18021, 18033, 18034, 18038, 18428, 18443, 18444, 18445, 18449, 18498, 19114, 18023
1. MACT floor methodology.
Comment 1: Many commenters (16469, 17689, 17712, 177718, 17725, 17732, 17740, 17758, 17775, 17776, 17795, 17816, 17820, 17871, 17816, 17820, 17909, 17886, 17931, 18033, 18428, 18443, 18023) disagree with the EPA's methodology for establishing the Hg MACT for existing units. These commenters argue that the Hg standard must be recalculated because it was not established as the average of the best performing 12 percent of existing sources, but rather was based on an unrepresentative sample group (i.e., 40 units for subcategory 1, and 2 units for subcategory 2). Commenter 16469 states that by using only 40 units the EPA has omitted many units burning bituminous coals with wet scrubbers and SCRs, and notes that this combination of fuels and technologies is widely recognized as highly effective for Hg control. Commenter further states that virtually all of the top 131 units the EPA used to set the HCl and PM limits are equipped with controls that remove Hg, ranging from fuel pre-treatment to scrubbers and baghouses.
Comment 2: Multiple commenters (17689, 17712, 17732, 17775, 17740, 17820, 17885, 17909, 18033, 18443) believe that the EPA has developed a MACT standard that is more stringent than allowed under CAA section 112(d) of the CAA. Commenter 17740 believes that the EPA set artificially lower MACT standards by arbitrarily limiting the number of sources from which the MACT floor sources are to be selected and argues that this approach is not allowed by the CAA. Commenter 17776 argues that the CAA does not allow the EPA to artificially lower MACT standards by arbitrarily limiting the number of sources from which the MACT floor sources are to be selected.
Comment 3: Multiple commenters (17718, 17725, 17740, 17775, 17816, 17886, 18428, 18023) believe that the data the EPA used to determine the Hg standard were skewed toward potentially better performing units. These commenters note that the EPA's 2010 ICR request required stack testing of the best performing units. In the supporting statement that accompanied the EGU ICR, commenters note that the EPA described how it specifically selected sources for Hg testing with the "newest PM controls" that it believed to represent the best PM performers. As a result, the tested units included many sources with high efficiency fabric filter baghouses and included a number of sources with ACI, both of which tend to provide higher Hg removal characteristics. These new PM sources, they note, would also tend to have other new high efficiency NOX and SO2 controls that can also have an impact on Hg. The EPA supplemented the stack testing data from Part III of the 2010 ICR with additional historic test data from Part II of the 2010 ICR. Commenters assert that this approach resulted in the data for the top 12 percent of existing sources being skewed toward potentially better performing units. They argue that the EPA incorrectly treated the data used to set the standard as though it were randomly selected by using the top 12 percent of the data obtained in the floor analysis instead of assuming that the top 12 percent would be within the data collected as it did for all other pollutants.
Comment 4: Several commenters (17689, 17712, 17775, 17885, 17931, 18033) state that the EPA should not have proposed a rule if it lacked the necessary data to evaluate the top 12% of performing units. Commenter 17740 was obligated to collect information from additional sources so that the resulting standard would be based on the top performing 127 units in Subcategory 1 and top performing four units in Subcategory 2. Similarly, commenter 17776 believes the EPA should have collected information from additional sources.
Comment 5: Commenter 17775 believes that the EPA's use of 40 units to set the proposed Hg limits reneges on statements the EPA made to UARG and OMB about how it selected units to conduct Hg stack sampling when it sought approval of its EGU MACT ICR. According to the commenter, the EPA asserted in the preamble that the testing required for Hg did not target the best performers. Commenter states that the ICR to OMB states that the EPA believes it is testing the top performers for Hg.
According to commenter 18644 there is no rational basis for the proposed Hg emission floor. The commenter adds that the floors should simply be set at the simple average of the best performing 12% of emissions sampled from the test population.
Comment 6: Commenter 17739 states that the EPA is obligated to issue a new proposal to address the basis for, and number of units in, its Hg MACT floor for existing units. The CAA requires the EPA's proposed rules to contain a statement of basis that covers, among other things, the "factual data" and "methodology" underlying its proposal. Since the basis for the EPA's proposed 40 unit floor is factually incorrect based on the agency's own statements, the EPA needs to propose a new one, and it needs to establish a new methodology for selecting a floor. Commenter also believes the EPA's ICR assertions, as well as the data obtained, compel the EPA to propose for comment a 130 unit floor, and not a 40 unit floor.
Comment 7: Commenter 17620 agrees that the EPA has substantial latitude in determining the performance achieved by the best performing 12% of the units for which it has data and consider the results to be reasonable. They also believe that this approach provides the most useful data for the least cost and avoids problems associated with the use of statistical procedures and small data sets. However, the commenter is concerned that environmental groups will correctly argue that the floor should be based, not on all 131 test results, but on the top 12% of those results (i.e., the best 16 test results), although at the same time industry will correctly argue that to do so would result in the floor being based on "the top 12 percent of the top 12 percent."
Comment 8: Multiple commenters (17623, 17716, 17728, 17739, 17758, 17775, 17904) took issue with the pool of emissions data used to set the Hg MACT floor. Commenters state that although the EPA used emissions data from all sources in the EGU pool when setting HCl and PM emissions limits, the MACT floor for Hg in the coal-fired > 8300 Btu/lb subcategory contained only 40 units, or roughly 4% of the sources in that subcategory. Commenters state that the CAA requires the EPA to consider data from all sources for which it has data and not just those that performed mercury testing. Commenters state that the EPA requested testing of the best performing units and it only used Hg data from the Part II test data for emissions tests performed on or after 12/2007 through 12/2009, thus, the pool is not a random selection but instead the "best of the best." Commenters state that the EPA had 330 units with Hg data in the ICR data set and selected the top 12 percent from that portion of units rather than using data from all units that participated in the ICR. Commenters state that the EPA should consider all the available information at its disposal to set limits that accurately depict what the best performers in the source category achieve. Commenter 17904 states that because the EPA relies heavily on its 1999 for appropriate and necessary finding in proposing this rule, the Agency should better explain why it is deviating from its prior proposal or the agency would be establishing MACT on MACT.
Comment 9: Commenters 17878 and 18023 believe that had the EPA done the Hg MACT floor analysis correctly it would have concluded that the plants sampled during the Part III of the ICR were, in fact, the best performing units for Hg emissions.
Comment 10: Commenter 17716 states that the EPA selected sources with the newest controls, which represent about half of the Hg test sources in the EPA's database, but comprise the overwhelming majority of the lowest 128 Hg test results. Contrary to the statutory directive that the top 12% be selected from the all sources for which information is available, Commenter states that the EPA pre-selected sources with the newest controls for inclusion with knowledge that they were likely to, and did, produce the lowest test results. This not only contravenes the CAA, but also results in an average emissions limitation that underestimates the actual performance of the top 12 percent of all sources.
Comment 11: Commenter 17758 states that the Part III stack emissions testing, upon which the EPA bases the proposed non-Hg standards, included units with the lowest Hg emissions (they were equipped with ACI systems) contrary to the EPA's assertion that the ICR data did not represent the top 12% of sources for Hg. According to the commenter, 73% of the units with ACI (33/45) were required to conduct Part III Hg testing. This inordinately high percentage of ACI-equipped units required to conduct Part III testing is not random; rather, it demonstrates the EPA's intent to require Part III emissions testing at units that it believed had the lowest Hg emissions.
The commenter states that another indication that the ICR testing was improperly aimed at obtaining Hg emissions information from the lowest-emitting units is the large number of units equipped with baghouses that were required to test for Hg. Plants equipped with baghouses have long been known to have better than average Hg removal because as ash builds up on the filter bags, any unburned carbon in the ash acts like a carbon bed that adsorbs Hg from the gas stream. Of the 127 units with the lowest Hg emissions, 120 are equipped with fabric filters.
Comment 12: Commenters 17869 and 18021 believe the EPA needs to include emission values from more boilers with dedicated Hg reduction systems. Commenters point out that it makes sense to subcategorize CFBs separately from conventional coal-fired boilers, but since CFB boilers are heavily represented in the Part III ICR Hg testing, removing them from the dataset leaves few boilers on which to set a "best 12 percent" MACT floor. Commenters states that many or all of the boilers with Hg control systems such as ACI should be included in the sampled population since they will have the lowest Hg emissions. Commenter 17869 recognizes that subcategorizing CFBs will likely create very low floors, leading to measurement issues or compliance problems and suggests a CFB floor around 0.3 lb/TBtu, based on Hg measurement limitations.
Comment 13: Commenters 18014 and 18498 describe how the EPA selected units for testing that would tend to be among the best performers for Hg, although representing only half of the Hg test sources in the EPA's database, the EPA treated the data as if it were randomly selected by using the top 12% for floor analysis instead of assuming that the top 12% would be within the data collected.
Comment 14: Several commenters (17796, 17816, 17820, 17909) analyzed the types of unit design and control devices utilized by the best performing units. Commenter 17796 points out three units (Spruance unit Gen4, Spruance unit Gen1, Cherokee unit 4) that have high anomalous high data points, and their inclusion creates a great margin of variability an is merits from existing units that have already demonstrated significant Hg control. Commenter 17796 also states that the EPA has conducted a MACT floor determination using the 45 units reporting ACI usage, six of which were identified in the 12 percent. Commenter 17816 discusses that of the 40 units the EPA selected from the 2010 ICR data for the Hg MACT floor analysis for existing units designed to fire coal >8300 BTU/lb, 14 were fluidized bed units, but only six percent of the total industry population is made up of FBC units. Commenters 17820 and 17821 state there are several other reasons to conclude that the ICR Part III testing focused on units with the lowest Hg emissions. Commenters 17820 and 17821 cite that disproportionately high number (73 percent) of units tested were equipped with ACI, which is installed for the sole purpose of controlling Hg emissions. Commenters 17820 and17821 also note that that large number of units tested equipped with baghouses and fabric filters and a result the only appropriate action is for EPA to use 127 units to determine the MACT floor for Bituminous and Sub-bituminous Subcategory.
Comment 15: Commenter 17909 similarly states that the EPA cannot artificially lower Hg emission numeric standards by limiting the number of units used to set the floor. The EPA must revise its methodology to include all sources in its data set.
Comment 16: Commenter 17740 believes the EPA's approach to setting the Hg MACT floors for existing coal-fired units is an abuse of discretion because it allows the EPA to cherry pick from which sources to collect data and set a floor at whatever level it wants. Commenter argues that the EPA cannot arrogate to itself the authority to determine how stringent a MACT standard is by deciding not to acquire data from sources in a subcategory or only acquiring data from certain sources. Commenter states that Congress did not intend the EPA to have such unbridled discretion.
Comment 17: Commenters 17931 and 18033 disagree with the EPA's use of emissions data from only 40 units to calculate the MACT floor average for Hg, with variability accounted for by calibrating the UPL. The commenters point out that the UPL is larger than the MACT floor average and 154 units submitted Hg emissions data below the final UPL for Hg. Commenters question how many of the known units actually comply with all the proposed emission limits and estimates that only 3 percent of the total population are able to meet the proposed standards. Commenters are concerned that even this may be an overestimate, since achieving compliance once does not mean the unit is able to continuously achieve compliance. Because the EPA did not investigate a fundamental aspect of the proposed rulemaking by not basing the MACT floor on the top performing 12% of units, Commenters consider the rule arbitrary and capricious. Commenter 18033 calls on the EPA to reconsider the emissions standards to reflect the performance of actual operating units, as the HAP-by-HAP approach is not authorized by the CAA.
Comment 18: Commenter 17402 supports the EPA's calculation of the MACT floor pool for Hg. As the EPA did for acid gas and non-Hg metallic HAP, the EPA based its Hg MACT floor pool calculation on the top 12% of the total number of EGUs for which the EPA had Hg emissions information -- 330 sources. Thus, the MACT floor pool for Hg properly consists of 40 EGUs (12% of 330 sources).
Unlike the decades of emissions information that the EPA has for SO2 and PM, which formed the basis for the pool of units from which it calculated the best performing 12% of sources, the EPA does not have the equivalent data for Hg emissions. Although the EPA assumed that "ACI may be an effective control technology for controlling mercury emissions in coal-fired plants, . . The EPA has no direct stack test results showing how effectively these ACI-equipped plants reduce their mercury emissions." Thus, in selecting units for metallic HAP stack testing, the EPA chose a number of units with ACI installed. Thus, the EPA's MACT floor pool was properly calculated and the EPA's approach was entirely appropriate. Neither the statute nor case law interpreting it requires the EPA to collect additional emissions information before making the MACT floor determination. On the contrary, the Court in Cement Kiln Recycling Coalition, affirmed the EPA's "wide latitude in determining the extent of data-gathering necessary to solve a problem" and explained that courts "generally defer to an Agency's decision to proceed on the basis of imperfect scientific information, rather than to invest the resources to conduct the perfect study."
Comment 19: Several commenters (17715, 17757, 17681, 17871, 17877, 17904) believe the EPA's approach for setting the Hg limit was inconsistent with its approach for setting the limits for HCl and PM. Specifically, the EPA chose not to base the Hg limit on the top 12 percent of the 131 units that it required to test for Hg. Rather, the EPA chose to base the Hg limit on only 40 units, because it "did not believe those [other] units represented the top performing 12 percent of sources for Hg in the category at the time we issued the ICR and we made no assertions to that affect." A review of the Hg ICR data shows that the best performing units were indeed tested during the ICR and that the EPA should have used 131 units to set the MACT floor. That the EPA does not like the data obtained from these 131 units is not a sufficient reason not to use it, as required by CAA section 112(d)(3)(A). The fact that the EPA "did not believe" or "made no assertions" regarding the data is an insufficient basis to exclude the data. Accordingly, the EPA's decision to use a subset of the data, and the basis for that decision, is arbitrary, capricious and contrary to the CAA.
Commenter 17638 states, further, that the EPA's approach for setting the Hg limit was inconsistent with its approach for setting the limits for HCI and PM. Specifically, the EPA chose not to base the Hg limit on the top 12% of the 131 units that it required to test for Hg. Rather, the EPA chose to base the Hg limit on only 40 units, because it "did not believe those [other] units represented the top performing 12 percent of sources for Hg in the category at the time we issued the ICR and we made no assertions to that affect." A review of the Hg ICR data shows that the best performing units were indeed tested during the ICR and that the EPA should have used 131 units to set the MACT floor. That the EPA does not like the data obtained from these 131 units is not a sufficient reason not to use it, as required by CAA section 112(d)(3)(A). The fact that the EPA "did not believe" or "made no assertions" regarding the data is an insufficient basis to exclude the data. Accordingly, the EPA's decision to use a subset of the data, and the basis for that decision, is arbitrary, capricious and contrary to the CAA.
Commenter 17871 adds that the data set on which the EPA based the Hg MACT floor also contained errors that affected the determination of the MACT floor, which the EPA corrected without providing public notice and the opportunity to comment. The EPA's decision to quietly make corrections to the data set, which required revisions to the MACT Floor Memorandum and a change to the emission standard itself, prejudiced the public's ability to meaningfully comment and is inconsistent with the notice-and-comment provisions of the APA.
Response to Comments 1 - 19: The EPA selected for testing for non-Hg metallic HAP those 175 EGUs with the newest PM control devices installed, both ESPs and fabric filters. This selection was based on the premise that effective control of PM would also provide effective control of non-Hg metallic HAP and "...that these units represent those units having to comply with the most recent, and, therefore, likely most stringent, emission limits for PM" and that "...efforts by units to comply with stringent PM limits will likely represent the top performers with regard to non-Hg metallic HAP emissions." As we had selected the "best performing" 15% of units from among the entire coal-fired EGU population, the EPA used 12% of the entire population as the pool of units from which the MACT floor was derived.

However, the EPA stated in the proposed rule "[f]or Hg from coal-fired units, we used the top 12 percent of the data obtained because, even though we required Hg testing for the units testing for the non-Hg metallic HAP, we did not believe those units represented the top performing 12 percent of sources for Hg in the category at the time we issued the ICR and we made no assertions to that effect." (76 FR 25023.) This position is supported by statements made in the final Supporting Statement for the 2010 ICR where on pages 6-7 of Part B we stated:

      Emissions of certain non-mercury metallic HAP (i.e., antimony (Sb), beryllium (Be), cadmium (Cd), cobalt (Co), lead (Pb), manganese (Mn), and nickel (Ni)) have been assumed to be well controlled by particulate matter (PM) control devices. However, mercury (Hg) and other non-mercury metallic HAP (i.e., arsenic (As), chromium (Cr), and selenium (Se)), because of their presence in both particulate and vapor phases, have been reported, in some instances, to be not well controlled by PM control devices. There are very few recent emissions test data available showing the potential control of these metallic HAP from coal-fired utility boilers.

      The capture of Hg is dependent on several factors including the chloride content of thecoal, the amount of unburned carbon present in the fly ash, the flue gas temperature, and the speciation of the Hg. Based on available data, EPA believes that ACI may be an effective control technology for controlling Hg emissions in coal-fired plants. However, EPA has no direct stack test results showing how effectively these ACI-equipped plants reduce their Hg emissions.

      EPA has identified the 175 units with the newest PM controls installed. The EPA believesthat these units represent those units having to comply with the most recent, and, therefore, likely most stringent, emission limits for PM (Attachment 11). Even though PM may not ultimately be an adequate surrogate for some of the non-mercury metallic HAP, efforts by units to comply with stringent PM limits will likely represent the top performers with regard to non-mercury metallic HAP emissions. The units selected also include a number with ACI installed. As units have been identified as meeting the criterion of being a "top performing" unit, substitution of units will not be permitted. However, units selected for testing in this group that share a PM control system with another unit, testing after the PM control system will be allowed. (emphasis added)

As shown above, the EPA acknowledges that units using ACI were included among the units selected for non-Hg metallic HAP testing because they also were among the pool of units having the newest PM controls. However, the EPA also stated that "...EPA has no direct stack test results showing how effectively these ACI-equipped plants reduce their Hg emissions." We noted further that an unknown amount of Hg and several other non-Hg HAP (e.g., Se) vaporize in the EGUs and  may not be effectively captured by the PM control devices. With Se, we understand that it generally forms the acidic gas SeO2 in the post-combustion environment and, as discussed elsewhere, we believe that it is adequately addressed through a combination of PM and acid gas HAP controls.  Because of its unique chemical properties, we are unable to make similar conclusions about Hg. The EPA understands that there are a range of available technology options and strategies for controlling Hg emissions. Some plants choose to apply "mercury specific" control technology while others rely on co-benefit Hg control using existing air pollutant control equipment. Some facilities enhance the co-benefit control by addition of supplemental halogen (usually bromine) to the coal and others do not attempt to optimize the co-benefit control. Mercury oxidation and control can be affected by the age and activity of the SCR catalyst. Due to the complexity and unit specific nature of Hg control, the EPA did not believe that it could reasonably identify the top performing units.
For these reasons, the EPA did not select the units required to test for Hg and non-Hg metal HAP for testing based on a presumption that they would be among the "best performing" units for Hg and any statements made that imply that we could identify the best performing sources for Hg are not well founded. Our assumption was borne out by the data, , which included a considerable amount of Hg emissions data from not only the Part III testing but also from the Part II collection of available information. The EPA ranked all the Hg data and approximately 32 sources that were not selected as best performers for PM submitted Hg data that placed them among the best performing 126 units in the subcategory for Hg, and, of those, 10 were included among the best performing 47 units in the subcategory. In addition, none of the 11 low Btu, virgin coal units had data that placed them among the best performing 12% of sources for the entire subcategory. This fact confirms that the 175 best performing units for PM did not represent the best performing sources for Hg. In this situation, we could not reasonably state, as the commenters suggest, that the 175 units tested for PM were, in fact, the best performers for Hg. As such, we reasonably based the floor for Hg on 12% of the Hg data available to the Agency.
Finally, to the extent the commenters attack the EPA for failing to obtain additional emissions data, such assertions should be rejected. Neither the statute nor case law interpreting it requires the EPA to collect additional emissions information before making the MACT floor determination. On the contrary, the agency can base the floor on the emissions information available to the Administrator. In this case, the agency could not reasonably state that the sources tested were the best performing sources for Hg. It, therefore, used the top 12% of the data available to it (data from 339 units) in developing the proposed MACT floor for Hg.
Units selected as being potentially "best performing" units for non-Hg metallic HAP were required to test for Hg because the reference test and analytical methods employed obtained Hg results along with the non-Hg HAP metals. Thus, the EPA did not select "best performing" units for Hg as alleged by commenters. One commenter latches on to a statement in the November 5, 2009, Response to Comment on the proposed ICR. While that statement could be interpreted as suggesting that the EPA believed it had identified the best performing units for Hg, we also stated that "[e]ven though PM may not ultimately be an adequate surrogate for some of the non-mercury metallic HAP, efforts by units to comply with stringent PM limits will likely represent the top performers with regard to non-mercury metallic HAP emissions." See final Supporting Statement for the 2010 ICR (12-24-09) page 7 of Part B (emphasis added). In any case, we cannot reasonably interpret statements made in support of the ICR in a manner that is not consistent with our understanding of our ability to assess the best performing sources for Hg. Commenters also have failed to demonstrate that EGUs that are best performers for non-Hg metal HAP are also best performers for Hg. In fact, some of the commenters alleging that EPA has identified best performed because we included units with ACI, also claim that ACI may actually reduce PM control efficiency. Further, the EPA used all of the data provided to it in assessing the MACT floors. That is, data obtained through "Part II" of the 2010 ICR (the available data part) as well as data obtained through the required 2010 ICR testing ("Part III") were used in evaluating the best-performing units. In fact, the EPA had more "available data" for Hg than it did for any other HAP. As noted above, the EPA had no basis for claiming that it had selected the "best performing" units and, therefore, it used the top 12% of the data available to it (data from 339 units) in developing the proposed MACT floor for mercury.
Comment 20: Commenter 17758 states that the EPA should use data from the best-performing 12% of existing sources to determine the Hg standards. The Hg standard must be recalculated because it was not established as the average of the best-performing 12% of existing sources, but rather was based on an unrepresentative sample group. The EPA erred in establishing the Hg standard by using a data set different than the 127 units used to calculate the other MACT standards, particularly since the ICR stack emissions data that the EPA collected are adequate to calculate the Hg standard correctly.
Once this regulatory floor is established, the EPA could consider more stringent --beyond-the-floor options, only after taking into consideration cost, energy and environmental impacts, as the Agency did when establishing the Hg standard for lignite units in the proposed Utility MACT.
Response to Comment 20: The EPA disagrees and responds to this comment above.
Comment 21: Commenter 17740 notes that the MACT Floor Memo states that "30 sources are included in Subcategory 2" although the next paragraph states that Subcategory 2 "includes fewer than 30 sources." The commenter argues that the EPA should gather sufficient data to use at least four sources to set the MACT floor for this subcategory. They further believe that the EPA's decision to use less than four sources to set the MACT floor for Subcategory 2 is based on a very narrow interpretation of section 112(d)(3). Commenter believes that a review of the entire language of section 112(d)(3) "evidences Congress' true intent." Under CAA section 112(d)(3)(A) that MACT standards for existing sources may not be less stringent than "the average emission limitation achieved by the best performing 12 percent of the existing sources (for which the Administrator has emissions information)" for sources in categories or subcategories of 30 or more sources. For categories or subcategories with fewer than 30 sources, the commenter states that the EPA must set the standards at a level not less stringent than "the average emission limitation achieved by the best performing five sources (for which the Administrator has or could reasonably obtain emissions information)." (See CAA section 112(d)(3)(B)). Commenter asserts that the EPA is incorrectly using the parenthetical in section 112(d)(3)(A) to conclude that it can set the Hg MACT floor for Subcategory 2 based on only two units.
Response to Comment 21: There are 36 sources in the low rank, virgin coal EGU subcategory. Therefore, by the language of CAA section 112, the EPA is to use the top performing 12% of data, rather than data from five units, in calculating the MACT floor levels as would be required if the subcategory had less than 30 units. CAA section 112(d)(3)(B). The EPA does not agree that CAA section 112 (d)(3) mandates a minimum of five sources in all instances, and the literal language of the provision appears to compel a contrary result. The EPA recognizes that it indicated that there were less than 30 EGUs in the MACT standard memorandum for this subcategory, but that typographical error does not alter the fact that we have identified 36 units in the subcategory.
Comment 22: Commenter 17869 recommends that the EPA propose a Hg floor based on a simple geometric average of the top 12% and base compliance on long-term moving averages of emissions. The commenter argues that basing compliance on a long-term moving average, all "variability" (even from SSM periods) will be accounted for so UPL and FVF would be inappropriate. The commenter also states that Hg's health effects are unrelated to short-term spikes and Hg emissions are high at lower loads which would also be captured by long-term averaged measurements. The commenter also states that skewness analysis may be appropriate however, kurtosis evaluation or hurdle would be inappropriate.
Response to Comment 22: As noted elsewhere in this document, the EPA has used the geometric mean. However, we disagree that use of a longer-term moving average would be better than use of the 30-day rolling average that we are using. Our handling of the skewness and kurtosis analyses are discussed elsewhere.
Comment 23: Commenter 18038 points out that the proposed rule includes the addition of controls beyond those used to reduce Hg emissions, and which are not required under the CAA or the EPA's HAP study. Commenter requests that the EPA withdraw the rule and re-propose it in a way that addresses only methylmercury.
Response to Comment 23: Methylmercury is not emitted from stationary sources, including EGUs. Further, CAA section 112(b) does not list "methylmercury," but, rather, "mercury compounds" as the HAP that must be regulated. Neither the CAA nor the EPA's Utility Toxics Report to Congress requires the installation of any controls; sources are only required to comply with the final limits in any manner they choose. The final rule is based on the emission levels achieved in practice by EGUs with all types of emission controls installed.
2. Beyond-the-floor determination.
Comment 24: Commenter 19686 states that the EPA's proposed floors for MACT standards in the rule do not represent the best performing sources in the industry. The EPA's limits are well in excess of the average test emissions data of the best-performing sources, the sum effect of which is to establish standards that substantially diverge from the statutory standard. The commenter argues that:
   * The EPA uses inconsistent measures of plants' "actual" emissions to assess the floor. When selecting its best-performing sources, the EPA defines their emissions according to their lowest test, but when establishing the floor, the EPA defines plants' emissions as the variability-adjusted average of all of the EPA's data for that plant based on a ranking of all the available emissions data from lowest emissions to highest emissions. The EPA fails to provide any substantive analysis or rationale for using this variability-adjusted average for establishing the MACT floor, and why Hg controls operating under normal condition would experience extreme variations.
   * The EPA has failed to consistently apply the statutory - or any - standard by refusing to consider whether reductions beyond the statutory floor are achievable. For example, the EPA assumes that the top 12 percent of performers for non-lignite EGUs can do nothing further to reduce their Hg emissions although failing to conduct an analysis of the control technologies that these EGUs use and what further emission reductions are possible. The commenter notes that the EPA could and should have considered other control technologies, i.e., coal blending, coal cleaning and oxidation catalysts.
The commenter states that the EPA has violated the CAA by not setting a MACT standard that reflects the most stringent emission reductions achievable. The commenter recommends that the EPA set floors consistent with the statutory directive to reflect the actual performance of the best performers in this industry, and that the EPA conduct a beyond-the-floor analysis sufficient to ensure that the standards demand the maximum achievable reduction in hazardous pollutants.
Response to Comment 24: The EPA believes that its analyses comply with the statutory requirements of CAA section 112 and with the Court's interpretations of those requirements. The EPA is finalizing a beyond-the-floor emission limit for Hg from EGUs in the subcategory for units burning low rank, virgin coal. The basis for our determination is contained in elsewhere in the final rule record.
Comment 25: Commenter 18034 expresses concern that older units, even when retrofitted with ACI and fabric filters, will not be able to meet the beyond-the-floor emission limits based on a subset of emissions data from the two best-performing units. The commenter points out that the beyond-the-floor analysis is invalid because it is biased low and the EPA provides no justification for the technological feasibility of the beyond-the-floor emission limit beyond the preamble statement regarding the units in the floor analysis using ACI "to its fullest extent." The commenter also discusses the potential need for some facilities to switch fuels. The commenter believes the possibility that a facility would have to switch to a different fuel outside of its subcategory to comply with a beyond-the-floor emission limit, which the EPA acknowledges warrants separate categorization on establishing the emission limits, demonstrates the infeasibility of the beyond-the-floor limit. Fuel switching also contradicts the EPA's claim that lignite units only need to enhance the use of ACI to some unspecified extent in order to comply with the proposed beyond-the-floor Hg limit.
Response to Comment 25: The EPA disagrees with the commenter. The EPA established the beyond-the-floor Hg standard based on data from existing sources in the category and after considering the non-air quality health and environmental impacts as required in the statute. See CAA section 112(d)(2). We note that, based on the data available to the agency, there are currently five EGUs in the low rank, virgin coal subcategory that are meeting the beyond-the-floor standard in the final rule. In addition, the commenter has not identified any sources in the subcategory that will be unable to comply with the final standard and the EPA has also not identified any such sources. That sources may have to install additional controls and potentially maximize use of ACI or other Hg-specific controls does not render the final standard invalid as the commenter seems to imply. The EPA did not state that some units in this subcategory would have to switch fuels in order to comply with the beyond-the-floor Hg standard as the commenter suggests, but even that conclusion would not have made the beyond-the-floor standard invalid. Our analysis was based on the use of ACI in conjunction with other controls required under this final rule to reduce HAP emissions, and we determined the cost of going beyond the floor was reasonable as explained in the beyond-the-floor TSDs. As with all MACT standards, sources are required to comply with the emissions limits and the EPA does not dictate how compliance must be attained. Fuel switching is certainly among the available options for all EGUs subject to this final rule, including EGUs in the low rank, virgin coal subcategory. We disagree with the commenter that the beyond the floor standard assumes sources will have to switch fuels to comply and we have no data to suggest that is the case.
3. Variability.
Comment 26: Commenter 18449 questions if three short duration tests spread over 1 or 2 days can accurately capture the long-term emissions and whether the EPA's statistical techniques used to calculate the MACT limit are appropriate.
Comment 27: Commenter 19114 states that levels established for new and existing units are so low they do not accommodate the full range of operating conditions. The commenter requests that the EPA re-evaluate these sources for variability and recalculate the EGU-MACT limits.
Comment 28: Commenter 17621 states that there are different types of variability not available in the datasets used to calculate the MACT floors. Those types of variability are highly associated with the observed emissions. Measurement variability, the commenter states, includes both sampling variability (associated with obtaining a representative sample) and analytical variability (associated with precision of the method, accuracy with the matrix and potential interferences). Another source of variability is the process variable (associated with power plant process). All these sources need to be included in data analysis. Commenter notes how Hg emissions are affected by several factors.
Comment 29: Commenter 17796 has concerns with the EPA's Hg MACT analysis after finding upon review that 4 performance tests out of 20 are driving the variability and 3 of these units were not specifically controlled for Hg at the time of testing. Commenter also mentions that the fourth unit, BL England Unit 2 in New Jersey's, test results could not be reconciled with the commenter review of the facilities reported Hg results on file with NJ DEP.
Response to Comments 26 - 29: The EPA believes that it has adequately addressed variability in the final rule as explained elsewhere in the final rule record. We have addressed the UPL analysis and its inclusion of variability elsewhere in this document (including discussion of the tests noted by commenter). We would also note that the fact that, as commenter points out, some EGUs among the Hg MACT floor pool are not specifically controlled for mercury supports our position that we did not know how to determine the best performing EGUs for the purposes of mercury reduction.
4. Additional subcategorization.
Comment 30: Commenter 18015 argues that western EGU Hg emissions contribute very little to Hg deposition in western streams and lakes. The commenter adds that due to the low-chlorine content of western coal, western Hg emissions are mostly in elemental form and thus have lower deposition levels compared to the rest of the country. The commenter presents Hg deposition that to support this claim and argues regulating EGUs in the west will have little impact on reducing Hg deposition and limited health benefits.
Response to Comment 30: The EPA made no distinction between coals in its December 2000 regulatory finding or in the current Appropriate and Necessary Determination and, therefore, is not making any distinction in the final rule.
Comment 31: Commenter 17761 states that additional subcategorization is necessary to avoid establishing a performance standard for Hg that cannot be met by facilities that are already well controlled and employ specific Hg reduction controls.
Response to Comment 31: The EPA has provided discussion and responses elsewhere to comments related to additional subcategorization. The EPA believes the final limits are achievable by EGUs such as those noted by the commenter and that additional subcategories are not warranted.
5. Data used.
Comment 32: Commenter 17795 believes the EPA should not have used ICR Part II data in their floor analysis for Hg. The commenter argues that the EPA should not have included in its MACT floor analysis emission rates for sources that may not have been collected with the same methods or faced as strict quality assurance scrutiny as the ICR Part III data. The commenter notes that 8 of the 40 units included in the MACT floor for were from Part II data and that these 8 sources should be removed if the EPA decides to use only 40 units to set the MACT floor. The commenter states that the EPA used an emission rate of 5.33 E-09 lb/MMBtu for Hg from the Part II data for the Nucla facility. However, this same unit during Part III testing reported a Hg emission rate of 9.85 E-09 lb/MMBtu, which is 46% higher than the rate the EPA ultimately used as its NSPS for Hg.
Comment 33: Commenter 17623 states that the proposed Hg limits are based on data from only those plants that provided Hg testing information in Phase I of the ICR. In contrast, the emission limits for HCl and PM are based on data from all units submitting data under the ICR. According to the commenter, the CAA requires the agency to use the emissions information in its possession when developing MACT standards, which may not require the EPA to perform exhaustive testing and sampling but it does not excuse the EPA from not considering data already at their disposal, which would include all data collected from the information collection request and not just selective test data from one particular phase of the information collection request process.
Response to Comments 32 - 33: The EPA disagrees with the commenter that suggests we should not use all the available data even if it was provided in response to Part II of the ICR and we are confused by the commenter that suggests we did not use all the data from the ICR. The EPA believes that all quality assured data submitted in the proper format and obtained under current control configurations should be used in the analyses. The statute requires the EPA to establish standards based on data and information available to the agency. See CAA section 112(d)(3). In addition, absent use of all of the data, the EPA would have difficulty addressing variability. The EPA believes the two emission levels cited by commenter for the Nucla facility should be considered because the Part II test data was generated at a time the facility had the same control configuration currently in place and thus it is reasonable to consider that data when establishing the standards. In addition, the difference in Hg emissions is indicative of the level of variability that may be encountered at the facility for use in our variability analysis. The EPA does not understand commenter's statement that we used only Phase I data as no data were provided under that phase of the ICR. Should this be a typographical error and the commenter intended to mean either the Phase II or Phase III data, we did not rely on only one of these data sets for establishing the best performing 12% nor for determining the numerical emissions limit. Both data sets were used for both purposes.
Comment 34: Commenter 18499 questions the reliability of low level ICR data on which the MACT floor is based, stating that these measurements were conducted using Method 30B and occurred at or below the normal detection limit. The commenter adds that scientifically there is not a way to establish an emission limit with values at or below the detection limit and that QA/QC determine if the results are repeatable but not accurate. The commenter also performed a study demonstrating that CEMS was capable of measuring very low levels and could detect background levels reliably. The commenter concludes that routine monitoring of stack gas emissions of MACT limits that translate to 0.25 μg/m3 and higher is practical, but that the measurement of MACT limits that translate to stack concentration limits such as 0.02 μg/m3 would be far more problematical and accuracy would be questionable.
Response to Comment 34: We disagree with the commenter. Although sources with low Hg emissions may have measurement issues with Method 30B and short sample times, we did not find a significant number of with non-detects due to the use of sample times that were appropriate for the low Hg levels that we expected. In addition, we disagree that there is no way to establish an emissions limit with values at or below the detection limit and that provide repeatable and accurate results. The process which we are using to calculate the numerical standard achieves both. Although under the most extreme situation we may establish the numerical limit at a value that is three times the RDL, the process makes the best use of the available data and provides for a repeatable and accurate measurement of the pollutant.
Comment 35: Commenters 17775 and 17886 state that the existing source Hg limit is also unduly stringent because the EPA used minimum (instead of mean) values to calculate the average performance of the top 12 percent, employed a statistical method that does not account for all emissions variability of the best performing units, and failed to correct errors in its use of the ICR data. A proper MACT analysis produces an existing source Hg MACT limit of at least 1.42 lb/TBtu.
Response to Comment 35: The proposed Hg MACT floor was based on the average performance of the top 40 performers. Selection of the best performers was done by ranking the performance of each source using their 3-run emission averages, and selecting the 40 sources with the lowest emission average values. The statistical approach used to calculate the MACT floor has two main components; one is the average of the emissions of the best performers and the other is an estimate of the variability. The top 40 performers are the sources with minimum emissions, and the average is calculated using the emissions data from the best performers. The variance component in the statistical approach accounts for the variability of the best performing EGUs based on the data available. Calculations of this variance term incorporates the emissions values used to calculate the average and additional available data from the best performers to capture the within and between source variability. Based on data corrections and comments received, the number of data points in the Hg MACT floor pool is 47 for the final rule; the approach taken, however, remains the same as at proposal. The EPA believes it has adequately addressed variability in its development of the final rule based on the available data.
Comment 36: Commenter 18034 states that three Hg emissions data test runs from Sandow Unit 5B used for existing unit MACT floor analysis are not consistent with data used for the new unit MACT floor analysis for the same unit. The commenter adds that the new unit data used from the same unit is lower.
Response to Comment 36: Partly based on comments received, we have reassessed all of the MACT floor analyses and believe that the data are correct and consistent.
Comment 37: Several commenters (18444, 18445,17796) request that the EPA address the fact that test data used for BL England to calculate the Hg MACT appears to be incorrectly high. Commenter 18444 adds that quarterly tests used to calculate the MACT floor by the EPA at "EU_ICR_partl_and_partll" 3/16/11 database at http://www.epa.gov/ttnlatw/utilitv/utilitypg.htrnl are inconsistent with attached quarterly Hg test runs the commenter submitted. Commenter 17796 states that the test data cannot be reconciled with the test results on file with the NJ DEP and requests that the EPA review the data.
Comment 38: Commenter 17843 requests that the EPA review the variability among "complying units" for the MACT floor determination with ACI. The commenter concludes based on a review of the data that a unit from BL England that reported 2.4 lb/TBtu was an outlier and substituting this value with the maximum value otherwise reported results in a much lower MACT floor for ACI sources using the pooled variance statistical calculation accounting for 99% UPL.
Response to Comments 37 - 38: The company operating BL England was contacted and it was determined that the company's ICR submittal contained incorrect data for this test at the BL England facility. The data was corrected in the current Hg floor analysis.
Comment 39: Commenter 19114 states that it is inappropriate to derive the PM MACT from not equivalent methods and the EPA should conduct an analysis for the filterable PM MACT floor using either the Method 5 or the Method 29 data. The commenter argues that the EPA should recalculate a PM limit based on like-method comparison and use an average of the test series instead of the lower form the runs.
Response to Comment 39: As noted elsewhere in this document, the EPA is finalizing a filterable PM limit as a surrogate for the non-Hg metallic HAP.
Comment 40: Commenter 17677 is concerned that the EPA has set the Hg limit based off of a select few sources that do not represent a reasonable cross-section of coal-fired electric generation sources. The EPA did not use all the ICR sources to determine the mercury limitation, for some reason the EPA selected only 12 of the best performing sources and set the limit from those few sources.
Response to Comment 40: The commenter is incorrect in its assertion that the Hg limit in the proposed rule was based on 12 sources. As explained elsewhere in this document, the EPA based the Hg limit on 12% of the Hg emissions data available to the agency. See CAA section 112(d)(3)(A). We believe that the units in the Hg floor represent a broad range of EGUs of differing boiler types and sizes, burning varying ranks of coals from different regions, and using different combinations of controls.
6. Data corrections.
Comment 41: Commenter 17871 states that by failing to provide public notice of the changes to the corrections to the MACT standard, the EPA has acted contrary to the language of the CAA, rendering the MACT floor determination arbitrary and capricious under the APA. 42 U.S.C. section 112(d)(3)(A); 5 U.S.C. section 553(c). The commenter also disagrees with the EPA's decision not to re-propose the rule. The commenter argues that the EPA updated the data set and the MACT Floor Memorandum without any public notice of the change and that the docket does not indicate how correcting this significant error changed the MACT floor determination.
Comment 42: Commenter 17409 states that a statistical transcription error over estimated the removal efficiencies by a factor of 1,000, and although the EPA has contended this is an acceptable margin of error for variability, these errors and the cost of the proposal justify a comment period extension.
Comment 43: Multiple commenters (17761, 17800, 17821, 17878, 17881, 18449, 17931, 17871, 18014, 18023) have concerns regarding the conversion error that resulting in measurements for both existing and new source units being incorrect by a factor of 1,000. All commenters recognize that this error has been revised. Commenter 18449 adds that the although the errors were corrected, the proposed value is: unrealistic, impossible to achieve via Hg controls, based on suspect test results, and there are not NIST traceable calibration gases available for low level Hg measurements. Commenter 17931 argues that account for the error still does not provide persuasive evidence based on data that a coal-fired EGU can meet all the new source emissions standards. Commenter 17931 states 2007 EIA-860 report data from new coal-fired EGUs proves that on average, without considering variability, these units cannot meet the Hg limits. Commenter 17871 adds that the EPA said this error resulted in a "slight" increase in the Hg standard, when if fact it was not slight by a 20% increase. Commenter 18014 believes that, regardless of whether the conversion error was the genesis of the "top 40" approach used in the initial Hg floor analysis, it should be clear that using only the top 40 sources in the Hg floor analysis for existing coal-fired sources inappropriately biased the results.
Comment 44: Commenters 18034 and 17871 state that in violation of APA, the EPA did not adequately disclose critical errors and the effect of those errors on the standards to the public. Commenters add that the public must be given an opportunity to comment on how the revised MACT floor analysis will be applied.
Comment 45: Commenter 17800 states that the EPA needs to retract this rule and fix the errors before republishing and that if one substantial error has already been found it is indicative of possible other errors.
Response to Comment 41 - 45: The EPA corrected the error as soon as we were made aware of it and posted the revised spreadsheets both to the agency website and the docket. The fact that commenters were aware of this (through the docket) indicates that the public was aware of the change with sufficient notice to be able to provide comment. In addition, the EPA would have acted reasonably even if we had not made the correction and posted it to the docket at that time. The EPA often receives data corrections during the comment period and the agency is not required to re-propose standards when it revises emission limitations in the final rule based on those corrections. The EPA used the same methodology to establish the revised Hg standard after industry pointed out the conversion error. We could have waited until the close of the comment period to revise the standard based on the data correction, but we determined it was appropriate in that instance to immediately address the conversion error and provide the revised information for review.
The EPA addresses the remainder of these comments in response to other comments in this document and the preamble to the final rule.
Comment 46: Commenter 18034 states that in multiple parts of the preamble of the proposed NESHAP rule, the EPA mentions encouraging or achieving cleaner fuels for EGUs. By undertaking regulatory initiatives that the EPA admits result in a complete shift in new electrical power production capacity, the commenter believes that the EPA is setting energy policy for the country. The commenter believes that CAA section 112 may not be used as a mechanism for the EPA to drive national energy policy. In particular, CAA section 112(d)(3) specifies that the EPA must determine MACT limits based on the best controlled "similar" source. By establishing emission limits that are "fuel neutral," as the EPA describes, to encourage and achieve cleaner fuel-burning EGUs and thereby affect the fuel mix of the nation's electrical energy fleet, the EPA is ignoring this provision of CAA section 112(d)(3).
Response to Comment 46: The EPA is establishing CAA section 112(d) standards for EGUs consistent with statute and does not believe that this constitutes "setting energy policy for the country." Further, we disagree with the commenter's contention that we have established "fuel neutral" emission limits given that we have established limits for multiple subcategories of coal- and oil-fired EGUs based on data obtained from EGUs within those subcategories.4B01 - MACT Floor Results: Existing Coal (>8,300 Btu/lb) (Proposed)
Commenters: 16469, 16513, 17622, 17730, 17754, 17772, 17775, 17796, 17801, 17807, 17808, 17817, 17818, 17838, 17843, 17869, 17871, 17873, 17880, 17926, 17928, 17931, 17973, 17975, 18017, 18033, 18039, 18421, 18500, 18539, 18644, 18666, 18963, 19122, 19595, 19536/19537/19538, 18023
1. Opposition to proposed HCl limits.
Comment 1: Commenter 16469 states that many well-controlled plants equipped with flue gas scrubbers may not be able to meet the proposed HCl limits. Commenter illustrates this in referenced table - Well-controlled Units Not Meeting HCl Floor of 0.002 lb/MMbtu (see 16469-A1_table page 10. Commenter recommends that the EPA consider subcategorizing the HCl standard based on coal chemistry (e.g., chlorine or sulfur) to ensure that well-controlled units equipped with scrubbers and SCRs are able to meet the HCl standard.
Comment 2: Commenter 17754 states that coal refuse-fired facilities can't meet both HCl limits and Hg limits simultaneously. The relatively high levels of chlorine in the fuel promote the formation of oxidized Hg in the stack. By reducing the amount of HCl in the flue gas, the extent of oxidation of Hg in the stack would also be reduced, resulting in an overall reduction in Hg control efficiency. The use of different injection to control HCl from coal refuse-fired CFB units affects the quality of the ash residue. Such ash is currently used in the environmentally beneficial step of reclaiming lands and protecting and enhancing streams damaged by acid mine drainage. The HCl emission limit should be revisited with an appropriate health-based analysis for HCl.
Commenter 17838 states that although coal refuse fired CFB units achieve very low Hg emission rates and most would likely even satisfy the stringent applicable emission limits for Hg under the proposed rule, these clean-burning units generally could not simultaneously meet the proposed limits for HCl. In this respect, the proposed emission limitation for HCl is inappropriately stringent and inconsistent with statutory directives for establishing HAP emission standards.
Commenter 17838 states that the proposed HCl emission limit fails to reflect the relationship between the control of this pollutant and the simultaneous control of Hg emissions. Specifically, at facilities that combust coal refuse, the relatively high levels of chlorine in the fuel promote the formation of oxidized Hg in the stack, which can be readily controlled by a baghouse. By reducing the amount of HCl (and, therefore, chlorine) in the flue gas, as would be required in order to satisfy the stringent HCl standard under the proposed rule, the extent of oxidation of Hg in the stack (and, therefore, the efficiency of Hg control through the baghouse) would also be reduced, resulting in an overall reduction in Hg control efficiency. Accordingly, a proposed regulatory scheme that requires significant reductions in HCl emissions, but does not account for the direct relationship between the presence of chlorine and a facility's ability to control Hg, may have the unintended result of increasing Hg emissions as a consequence of reducing HCl emissions.
Response to Comments 1 - 2: Partly based on comments received, the EPA has reassessed the emission limits and believes that the emission limits in the final rule are consistent with the statutory mandate and achievable by all sources. The EPA addresses elsewhere in this document comments related to subcategorizing coal-fired EGUs by chlorine content of the coal and the health-based emission limits. The EPA disagrees with commenter's assertion that coal refuse-fired EGUs cannot achieve the HCl emission limit in the final rule as such units are in the MACT floor pool of sources from which the limit was derived. Further, based on data available to the Agency, there are at least two coal refuse fired CFBs unit that are meeting both the final Hg and HCl existing-source limits. In addition, there are at least 19 coal refuse-fired CFB EGUs that are meeting the final Hg existing-source limits. The EPA does understand the relationship between chlorine in the fuel and the oxidation of Hg. It is true that capturing HCl in a CFB may affect Hg oxidation. However, because subbituminous coal and lignites are faced with the same issue (unoxidized Hg), numerous technologies have been specifically developed and are available to capture mercury that is present in the combustion flue gas as elemental Hg vapor.
Comment 3: Commenter 17812 states that the proposed HCl emission limit fails to reflect the unique nature of coal refuse-fired EGUs utilizing CFB combustion technology in several ways. First, the commenter states that the incorrect proposed HCl emission limit identified in the proposed rule apparently results from the EPA's use of an improper methodology in developing the emission limits under the proposed rule. The commenter asserts that the proposed HCl emission limit fails to reflect the relationship between the control of this pollutant and the simultaneous control of Hg emissions. In developing the HCl emissions standard under the proposed rule, the EPA failed to consider any coal refuse-fired CFB units and, therefore, did not even evaluate any EGUs that employ CFB technology. The EPA clearly recognized the distinguishing characteristics of CFB technology in the context of developing the recently-promulgated MACT standards for industrial, commercial, and institutional boilers, by establishing a specific subcategory of existing coal-fired units for CFB boilers. See National Emission Standards for Hazardous Air Pollutants for Major Sources: Industrial, Commercial, and Institutional Boilers", 76 FR 15,689 (to be codified at 40 CFR pt. 63, subpart DDDDD) (the "Boiler MACT"). Second, there have been no commercially demonstrated applications of DSI for the control of HCl from coal refuse-fired CFB units.
Specifically, at facilities that combust coal refuse (e.g., waste coal plants), the relatively high levels of chlorine in the fuel promote the formation of oxidized Hg, which can be readily controlled by a baghouse. By reducing the amount of HCl (and, therefore, chlorine) in the flue gas, as would be required in order to satisfy the stringent HCl standard under the proposed rule, the extent of oxidation of Hg (and therefore the efficiency of Hg control through the baghouse) would also be reduced, resulting in an overall reduction in Hg control efficiency.
Accordingly, a proposed regulatory scheme that requires significant reductions in HCl emissions, but does not account for the direct relationship between the presence of chlorine and a facility's ability to control Hg, may have the unintended result of increasing Hg emissions as a consequence of reducing HCl emissions.
Accordingly, the [HCl] emission limits included in the Proposed Rule are based on an improper emission limit-setting methodology, and are unduly stringent and inappropriate for application to Northampton Generating Company coal refuse-fired CFB boiler. For these reasons, commenter 18963 requests that the EPA revise the proposed HCl emission limit in the Proposed Rule for existing coal-fired EGUs. As discussed more fully in section V.H., the EPA's analysis under the Proposed Rule demonstrates that the projected benefits from the Proposed Rule are primarily associated with reducing emissions of fine particles ("PM2.5"), rather than the other pollutants regulated under the Proposed Rule, including but not limited to, HCl. Therefore, the proposed emission limit for HCl under the Proposed Rule is unsupported by the associated projected health impacts for this pollutant. Accordingly, such emission limit should be revised consistent with an appropriate health-based analysis for HCl.
Comment 4: Commenter 17804 states that in addition to transforming waste coal piles into energy, coal refuse facilities produce a beneficially useful solid ash product which, with its alkaline quality and binding characteristics, is ideal for reclaiming abandoned mine lands because it binds with other reclamation materials and prevents migration of heavy metals and other pollutants that are the vestiges of historic mining activity. Therefore, the EPA's final Utility MACT rule should not establish HCl limits that would adversely impact the environmental beneficial use of waste coal.
The commenter is also concerned that the majority of the well-controlled CFB combustion units in Pennsylvania cannot meet the stringent HCl limits, 0.002 lb. HCI/MMBtu. Due to the uniqueness of the coal refuse, it is burned in CFB combustion units which do not employ the same type of control for acid gases that PC burning units employ (i.e., wet FGD units).
Commenter 17838 states that the proposed HCl emission limit fails to reflect the unique nature of coal refuse-fired EGUs utilizing CFB combustion technology in several ways. First, in developing the HCl emissions standard under the proposed rule, the EPA failed to consider any coal refuse-fired CFB units and, therefore, did not even evaluate any EGUs that employ the unique technology used by the commenter's plants. The EPA clearly recognized the distinguishing characteristics of CFB technology in the context of developing the recently-promulgated MACT standards for industrial, commercial, and institutional boilers, by establishing a specific subcategory of existing coal-fired units for CFB boilers.
Commenter 17838 states there have been no commercially demonstrated applications of DSI for the control of HCl from coal refuse-fired CFB units. Further, even to the extent that it is technologically feasible to use sorbent injection to control HCl from coal refuse-fired CFB units, the use of different sorbents for this purpose may affect the quality of the ash residue. Such ash is currently used in the environmentally-beneficial step of reclaiming lands and protecting and enhancing streams damaged by acid mine drainage.
Commenter 17838 states that the HCl emission limits included in the proposed rule are based on an improper emission limit-setting methodology, and are unduly stringent and inappropriate for application to the commenter's coal refuse-fired CFB boiler. The EPA's analysis under the proposed rule demonstrates that the projected benefits from the proposed rule are primarily associated with reducing emissions of fine particles (PM2.5) rather than the other pollutants regulated under the proposed rule, including but not limited to, HCl. Therefore, the proposed emission limit for HCl under the proposed rule is unsupported by the associated projected health impacts for this pollutant. Accordingly, such emission limit should be revised consistent with an appropriate health-based analysis for HCl. The commenter states that if the EPA does not revise the HCl limit to be consistent with a rate that prevents health impacts, they requests that the limit be revised to be consistent with the HCl limit under the Boiler MACT.
Comment 5: Commenter 17754 states that in establishing such limitations, the EPA must ensure that the MACT regulation does not establish applicable standards that cannot be reasonably achieved because of technology or fuel-specific considerations. The unique characteristics of CFB emission units must be considered in this context.
Response to Comments 3 - 5: We maintain that FBC/CFB units are able to meet all of the standards in the final rule and we explain that conclusion in response to other comments elsewhere in the final rule record. We also address comments related to the benefits of the final rule and health-based emission limits elsewhere in this document and in the preamble to the final rule. We have reassessed all of the analyses used in developing the MACT floor limits and believe that they are appropriate.
The EPA disagrees with the commenter that no FBC/CFB unit can meet, or is meeting, the final emission limit for HCl. As noted elsewhere in this document, there are a number of such units among those in the MACT floor pool for both Hg and HCl and, based on the data available, at least two coal refuse-fired CFB EGUs are meeting the final Hg and HCl limits (including variability). Further, the EPA is aware of a number of FBC/CFB units that have add-on "polishing" controls for acid gases (e.g., Seward, Foster Wheeler Mt. Carmel Cogen). We address the remaining assertions in this comment in response to other comments elsewhere in the final rule record.
The EPA disagrees with the commenter's assertion that it did not consider coal refuse-fired FBC units in setting the HCl emission limit. One of the very best performing units for HCl emission was a coal refuse-fired FBC EGU. Regarding the effect of HCl control on the oxidation and the subsequent control of Hg, the EPA understands that flue gas halogens will promote the oxidation of Hg which enhances its control. However, the EPA is also aware of several commercially available control options that have been specifically developed to control mercury that is present in the flue gas stream as elemental mercury vapor. Western subbituminous and many lignite coals have inherently low chlorine levels and tend to produce elemental Hg vapor in the post combustion flue gas. Facilities burning those fuels may also use those technologies (bromine injection, halogenated activated carbon, etc.).
2. Support for proposed HCl limits.
Comment 6: Commenter 17873 supports the EPA standard of 0.0020 lb/MMBtu for HCl to control acid gas emissions from low-chlorine coal-fired plants.
Comment 7: Commenter 17808 recommends that the EPA finalize the HCl emissions standard as proposed for existing coal EGUs; i.e., 0.0020 lb/MMBtu or 0.020 lb/MWh. Based on commenter's analysis of the 217 coal units that conducted stack emissions testing in 2010 as part of EPA's ICR emissions testing program, commenter found that more than 70% of all coal-fired generating units that submitted stack test data to the EPA are currently achieving the proposed HCl emissions standard. This translates to 158 units (out of a total of 217). The commenter also supports allowing existing sources the option to comply with the input or output-based standards, and recommends that the EPA maintain this flexibility in the final rule.
Response to Comments 6 - 7: The EPA appreciates the support of the commenters. The EPA has reassessed the HCl emission limit partly based on comments received and believes that the emission limits in the final rule are consistent with the statutory mandate.
3. Opposition to proposed SO2 limits.
Comment 8: Commenter 16469 states that the higher-sulfur coals supplied to scrubbed plants in the eastern U.S. may not be able to achieve the SO2 emission rate of 0.20 lb SO2/MMBtu even with an assumed 95% SO2 removal rate. The impacts on individual midwestern states (Ohio, Indiana and Illinois) could be particularly severe. The commenter recommends that the EPA consider subcategorizing the alternative SO2 standard to reflect sulfur content. For example, a higher standard could be set for units burning higher-sulfur coals with sulfur contents such as 2.0% and higher, with a lower standard set for units consuming lower-sulfur coal.
Comment 9: Commenter 17973 states that the SO2 limits for EGUs in western states without access to adequate water supply for wet scrubbers may need emission limits for acid gases more in line with that achievable through use of dry scrubbing techniques.
Comment 10: Commenter 18963 states that the proposed HCl emission limit for existing coal-fired EGUs should be revised consistent with an appropriate health-based analysis for this pollutant. Commenter further states that the proposed HCl emission limit for existing coal-fired EGUs is unduly stringent and inappropriate for application to coal refuse-fired CFB unit. Reducing the amount of HCl (and, therefore, chlorine) in the flue gas, as would be required in order to satisfy the stringent HCl standard under the proposed rule, would also reduce the extent of oxidation of Hg in the stack (and, therefore, the efficiency of Hg control through the baghouse), resulting in an overall reduction in Hg control efficiency. The EPA clearly recognized the distinguishing characteristics of CFB technology in the context of developing the recently-promulgated MACT standards for industrial, commercial, and institutional boilers, by establishing a specific subcategory of existing coal-fired units for CFB boilers. (See National Emission Standards for Hazardous Air Pollutants for Major Sources: Industrial, Commercial, and Institutional Boilers," 76 FR 15,689 (to be codified at 40 CFR Part. 63, subpart DDDDD) (the "Boiler MACT").) The commenter requests that the proposed emission limit for HCl be revised to be consistent with the EPA's rulemaking efforts for the same pollutant and similar source types. Specifically, the EPA could impose an HCl emission rate through the Utility MACT equivalent to the corresponding limit for HCl for existing coal-fired CFB boilers established in the EPA's Boiler MACT.
Response to Comments 8 - 10: The EPA addresses elsewhere in this document comments related to subcategorizing coal-fired EGUs by sulfur content of the coal and the health-based emission limits. The EPA disagrees with commenter's assertion that coal refuse-fired EGUs cannot achieve the HCl emission limit in the final rule as such units are in the MACT floor pool of sources from which the limit was derived. As noted elsewhere, based on the data available, there are at least two coal refuse-fired CFB EGUs meeting both the final Hg and HCl MACT floor limits (including variability). The EPA also disagrees with commenter's suggestion that EGUs should be subcategorized by wet- and dry-FGD use. Both types of FGD system are installed on EGUs in the MACT floor pool, indicating an ability to achieve the HCl emission limits in the final rule. In addition, we believe it is legally impermissible to subcategorize based on the type of air pollution control device. See Chemicals Manufacturers Association v. EPA, 870 F. 2d 177, 218 - 19 (5th Cir. 1989), modified on different grounds on rehearing, 884 F. 2d 253 (5th Cir. 1989) (rejecting subcategorization based on type of control device for purposes of the technology-based standards under the Clean Water Act, which are analogous to the CAA section 112 standards).
4. Support for proposed SO2 limits.
Comment 11: Commenter 17873 supports the use of an SO2 surrogate for compliance demonstration purposes. The use of surrogate allows facilities to demonstrate compliance with the HCI limit through periodic testing and continuous SO2 monitoring.
Response to Comment 11: The EPA appreciates the support of the commenter.
Comment 12: Commenter 17844 notes although the proposed SO2 surrogate standard (0.20 lb/MMBtu) is not as stringent as the New Jersey 2012 emission standard (0.15 lb/MMBtu 30-day average), it requires a good scrubber that should meet the MACT requirements. Recent data demonstrated that operation of spray dryer FGD at PSEG Fossil LLC's Mercer Generating Station Units I and 2 have achieved compliance with New Jersey's SO2 emission rate using 2 percent coal (see attached test data).
Response to Comment 12: The EPA established the emissions standards in the final rule consistent with the CAA. The EPA is not required to establish MACT standards that are at least as stringent as state standards applicable to HAP emissions or HAP surrogates, and states are authorized to establish HAP standards more stringent than those established pursuant to CAA section 112.
5. Establish lower MACT standard.
Comment 13: Commenter 16513 recommends the EPA establish a lower Hg NESHAP standard, as many northeastern states, particularly Connecticut coal-fired EGUs, comply with 0.6 lb/TBtu or an emissions rate equal to a 90% reduction of Hg from measured inlet concentrations.
Comment 14: Commenter 17926 recommends the EPA establish a lower Hg NESHAP standard of 0.6 lb/TBtu to 0.8 lb/TBtu to further reduce toxic emissions and improve public health. Montana maintains a standard of .9 lb/TBtu, and the industry has been able to comply.
Comment 15: Commenters 17926 and 18039 recommend that a lower MACT standard is both possible and appropriate. Commenter 18039 states that Massachusetts has already promulgated regulations limiting Hg emissions from the large coal-fired power plants.
Comment 16: Commenter 18421 states that many coal-fired units are already in compliance with the EPA's proposed emission standards for Hg, acid gases, and non-Hg metals and are meeting standards within a significant margin. In fact, nearly 60% of units that reported data to the 2010 ICR are in compliance with the EPA's proposed Hg standard for existing coal-fired units designed for coal >8,300 Btu.
Comment 17: Commenter 19595 states that the EPA should consider a lower standard for facilities other than lignite. This is both technologically and financially feasible, and would further protect public health and the environment.
Comment 18: Commenter 17844 notes that the EPA's proposed Hg emission limit of 1.2 lb/TBtu (equivalent to 5.45 mg/MWhr) is not as stringent as New Jersey Hg concentration limit of 3 mg/MWhr. If the MACT standard included an alternative limit of 90% control of Hg emissions, this would enable the concentration limit to be lower than the level proposed by the EPA and still allow high Hg coal to be burned with good air pollution control.
Response to Comments 13 - 18: The EPA established the emissions standards in the final rule consistent with the CAA. To the extent commenters are suggesting the EPA establish beyond-the-floor standards for Hg for units in the >8300 Btu subcategory based on, among other things, state Hg limits, we do not believe that we can justify such a standard based on the information currently available to the agency. The EPA is not required to establish MACT standards that are at least as stringent as state standards applicable to HAP emissions or HAP surrogates; however, states are authorized to establish HAP standards more stringent than those established pursuant to CAA section 112.
6. Support for Hg emission limits.
Comment 19: Commenters 17808 and 17926 support the Hg emissions standards as proposed for existing coal EGUs.
Comment 20: Several commenters (19536, 19537, 19538) supports the EPA for assuming the lowest emitting 12 percent of the EGUs for Hg emissions data.
Response to Comments 19 - 20: The EPA appreciates the support of commenters.
Comment 21: Commenter 17754 states that because of the clean-burning nature of the coal refuse-fired CFB facilities, it is anticipated that its member's plants could generally satisfy this stringent Hg standard under most operating conditions. However, the plants would be challenged in certain operating scenarios to consistently maintain this very low Hg emission rate, due in significant part to variability in fuel characteristics.
The commenter suggests that, at a minimum, due to the marked stringency of the 1.0 lb/TBtu emission limit, the agency must ensure that such standard would not be made even more stringent through the rulemaking process. It would likely be technologically and/or economically infeasible for affected units to demonstrate compliance with a Hg emission limit that is any more stringent than the current proposed 1.0 lb/TBtu standard.
Response to Comment 21: The existing source Hg standard has increased slightly since proposal based on data corrections and the inclusion of additional Hg emissions data.
Comment 22: Commenter 18039 states that the experience of Massachusetts in imposing stringent emissions limits for Hg and other pollutants clearly shows that the EPA's proposed limits are achievable and effective. For example, although the Massachusetts' Hg emission limits for existing coal-fired power plants are considerably more stringent than those proposed by the EPA, Massachusetts' facilities have been able to install control equipment with no impact on reliability of the electric power grid and have demonstrated consistent compliance with the limits. Moreover, ongoing monitoring efforts in Massachusetts and other states indicate that Hg levels in fish and other biota have fallen as the region's sources of Hg pollution have been addressed. This evidence indicates that Hg reduction requirements like those enacted in Massachusetts are effective at reducing environmental Hg levels, and are a worthwhile investment.
Response to Comment 22: The EPA agrees that the Hg standards in the final rule are consistent with the statute and achieveable by coal-fired EGUs. We note that the Hg standard for the EGUs in the >8300 Btu subcategory is a MACT floor level of control, which is the minimum stringency level under the statute. See CAA section 112(d)(3). The EPA's final standards will not affect EGUs responsibility to comply with the Massachusetts' Hg limit.
7. Opposition to Hg emission limits.
Comment 23: Commenter 17622 believes that the recalculated Hg emission limit of 1.2 lb/TBtu for existing coal-fired units >8,300 Btu/lb is achievable. However, the commenter states that the proposed MACT floor Hg emission limit for the subcategory of existing coal-fired units with a coal heating value of greater than 8,300 Btu/lb should be much tighter. The commenter adds that instead of the EPA's proposed value of 1.2 lb of Hg per trillion Btu, a review of the available data from the docket indicates that the appropriate MACT-floor emission limit should be 0.44 lb of Hg per trillion Btu (or 0.0042 lb per Gigawatt hour (GWh) based upon 32 percent efficiency).
Comment 24: Commenter 17730 states that the Hg emission control and monitoring equipment are still in limited use and the industry does not have substantial long term experience with use. Continuous Hg monitoring data as determined by certified Hg CEMS is not available or is only available in limited applications.
Comment 25: Several commenters (17754, 17838, 18963) state that the Hg emission limit of 1.0 lb/TBtu is four times more stringent than the already stringent limit for EGUs designed for coal < 8,300 Btu/lb subcategory. It would be technologically and/or economically infeasible for affected units to demonstrate compliance with a Hg emission limit that is more stringent than the current proposed 1.0 lb/TBtu standard.
Comment 26: Commenter 17801 states that the proposed IGCC Hg floor limit is not supported by the record and should be consistent with the minimum detection limits of monitoring technology. The commenter further states that IGCC plants do not have ability to reliably and accurately measure Hg at the proposed level of 0.0002 lb/GWhr (~2.28 x 10-8 lb/MMBtu at 39 percent HHV efficiency representative of new IGCC EGUs). The EPA's Method 30 B for the ICR and a qualifying test method for compliance testing in this proposed rule has a MDL of 8 x 10-8 lb/MMBtu  -  more than three times higher than the proposed limit. There is no commercially available CEMS that is capable of measuring at the required concentration levels. Monitoring by sorbent trap may also not be viable if required sampling times exceed a 30-day compliance period.
Comment 27: Commenters 17871 and 18644 state that the MACT floor for Hg represents emissions test data from 12% of the 330 sources that submitted emissions data pursuant to Part B of the ICR. These 40 sources are not representative of emissions of the top 12% of the subcategory as a whole, and the resulting Hg MACT standard for the subcategory is inappropriate.
Comment 28: Several commenters (19536, 19537, 19538) state that the EPA ignored the two lowest emitting units (Spruance Genco Units 2 and 3) in the >8,300 Btu/lb subcategory in the determination of the new source MACT floor for Hg. The Spruance units are comparable to other coal-fired EGUs, and can be controlled with the same Hg controls as other coal-fired EGUs. The EPA has not explained why smaller size affects a plant's ability to control Hg emissions. The EPA has not provided adequate justification for ignoring the lowest two emitting coal-fired EGUs in determining the new source MACT floor for Hg.