The discussion of " reconstruction" is based on the regulatory definition of the term which has been in place since 1980. We believe it makes sense for States to have the flexibility to consistently define " reconstruction" across programs, and that a major reconstruction should reasonably be considered as " new."

We also note that the statutory requirement for BART is still in effect, and nothing in the CAA allows EPA to disregard the requirements in section 169A because sources subject to it have aged considerably. We do not believe that any potential lack of records would pose a problem   sources can easily produce records to show when they were constructed. We believe that the statutory language of section 169A is clear enough on dates and that we cannot preemptorily change those dates.

In addition, many of these very old sources may still be uncontrolled and have considerable emissions of visibility impairing pollution; we believe they merit a BART review. States have the ability to judge, at the BART determination step, whether or not sources are adequately controlled.

2.2.5 Modified Units and BART Eligibility <IP_ADDRESS> Agree with EPA's Proposal to Address Modified Units Comment: 40 Nineteen commenters generally agreed with EPA's approach to modified units ( 28 244, 28 255, 28 256, 28 258, 28 263, 28 267, 28 273, 28 302, 28 335, 28 345, 28 349, 28 358, 28 362, 28 364, 28 388, 28 404, 28 748, 28 770, 28 779). Commenters ( 28 258, 28 267) specifically supported EPA's proposal to consider sources that began operation in the 1962 1977 window, but were modified after 1977 as BART eligible sources. Other commenters ( 28 273, 28 345, 28 349, 28 358, 28 364, 28 404, 28 779) also agreed that plants existing before 1962 that were later modified should be exempt from the BART requirements. Commenters ( 28 345, 28 349, 28 358, 28 364, 28 404, 28 748, 28 779) said this reading is consistent with the statute and avoids the difficulty of considering modifications that may have occurred up to 40 years ago.

Commenter 28 244 said making units subject to BART if they were modified during the 1962 1977 period would contradict the intent of Congress to exempt pre 1962 units from control. It would be very difficult if not impossible to determine whether modifications occurred during a period 38 to 24 years ago, at a time when no legal requirements concerning modifications were in place. Many sources may no longer have the relevant records. Commenters ( 28 255) agreed that modifications to emissions units should not change it's eligibility status. Commenter 28 256 said the best interpretation of modifications for the purposes of the visibility provisions is that modified units are still " existing." Other commenters ( 28 267, 28 362) said interpretation of " modification" in the BART guidelines should be consistent with the interpretation of that term in the PSD regulations, i. e., sources that propose to undergo a major modification are to be treated as new sources and must undergo NSR. Commenter 28 362 said these sources in operation prior to 1962 but modified within the 1962 1977 timeframe would be BART eligible.

Response:

We agree generally with the comments and are retaining the approach from proposal.

<IP_ADDRESS> Major Modifications Already Subject to RACT/ BACT/ LAER Should be Exempt Comment: Thirteen commenters said that major modifications that occurred after 1977 are already subject to RACT/ BACT/ LAER and should be considered new sources and, therefore, not BARTeligible ( 28 264, 28 273, 28 275, 28 304, 28 342, 28 343, 28 362, 28 363, 28 388, 28 403, 28 404, 28 779, 28 7003) for several reasons:

° These facilities controls would already meet BART requirements ( 28 273, 28 403) ° It would just be a paperwork exercise with little environmental benefit ( 28 264) ° State resources are better spent on focusing on greater sources of emission reduction ( 28 779) ° Any source that undergoes NSR is by definition a " new source" ( 28 275) 41 ° EPA should better integrate and coordinate BART control requirements with other controls required by the Act ( 28 304) ° The fact that the " BART requirements in the Act do not appear to provide any exemption for sources which were modified since 1977" does not ( even if correct) over ride the applicability of the PSD program and the policy behind the August 7, 1977 part of the age criterion ( 28 342).

Response:

We disagree that modifications after 1977 should change an emissions' unit date of construction for purposes of BART applicability. The commenter's suggestion that such sources already meet BART requirements may be accurate, but does not provide a basis for exempting the source from review. As we note in the guideline, the review process will take into account the controls already in place and the State may find that these controls are consistent with BART, or they may find that the source may or may not have been controlled to an adequate extent based on its contribution to regional haze.

2.3 Compare Potential Emissions to the 250 tpy Cutoff 2.3.1 List of Visibility Impairing Pollutants <IP_ADDRESS> Exclusion of Ammonia on the List of Visibility Impairing Pollutants Comment: Nineteen commenters agreed that ammonia should be excluded from the list of visibility impairing pollutants ( 0169, 0170, 0189, 0195, 0201, 0213, 0214, 0228, 0231, 0238, 0241, 0243, 0254, 0268, 0275, 0306, 0307, 0319, 0321, 28 304). Commenters gave several reasons:

° Ammonia has not been shown to be a significant threat to visibility in Class I areas ( 0169) ° EPA has provided no basis for its tentative determination that ammonia should be regulated as a visibility impairing pollutant ( 28 304) ° EPA has not provided any analysis of the indirect legal and regulatory implications of identifying ammonia as a visibility impairing pollutants such as becoming subject to PSD ( 28 304) ° Including ammonia would discourage use of SCR ( 28 304) ° Few if any point sources emit ammonia in amounts that exceed the proposed BART thresholds ( 0189, 0254, 0275) ° Ammonia's visibility impact is too complex and/ or not enough is known about its role in regional haze formation to justify an automatic BART requirement ( 0170, 0189, 0231, 0275, 0307, 0321) ° " Ammonia slip" is a necessary condition of the use of SCR for the control of NO x ( 0169, 0213, 0319) 42 ° More work is needed to determine whether ammonia emission reductions are cost effective in improving visibility in Class I areas ( 0231) ° Ammonia does not impair visibility directly and reductions in SO 2 and NO x emissions will tend to reduce the concentration of ammonia particles in the air ( 0243, 0321) ° The current inventory suffers from a tremendous amount of variability and uncertainty ( 0243, 0321) ° There would be limited visibility improvement relative to SO 2 controls ( 0254)

Commenter 0231 added that, a state would still be able to control a stationary source of ammonia as part of the reasonable progress requirement, if a technical analysis indicated such controls were needed to achieve reasonable progress goals.

If EPA nonetheless decides that ammonia should be subject to BART controls, one commenter ( 021) said sources with potential to emit less than 250 tpy of ammonia should be not required to conduct a BART analysis for ammonia. Given the uncertainty of the ammonia emissions inventory, the fact that ammonia does not impair visibility directly, and the fact that it could discourage the use of selective catalytic reduction to reduce NO x emissions, the commenter does not believe that BART analyses should be required for any BART eligible sources, let alone those that have the potential to emit less than 250 tpy.

Commenter ( 0254) said it is premature to require BART controls for those emissions until the visibility benefits of pending SO2, NO x and mercury controls have been observed as a result of CAIR, the Acid Rain Program, the NO x SIP Call, and the Mercury Rule. Conversely, controlling ammonia, VOC and PM from other, non EGU emission sources will lower PM levels and improve visibility. To finalize an effective rule and streamline the BART eligibility process for state environmental agencies, EPA should include a determination in the final rule that EGUs are excluded from eligibility for VOC, primary PM10 and primary PM2.5, in addition to ammonia.

Comment: Eight commenters argued that ammonia should be included on the list of pollutants ( 0179, 0186, 0200, 0218, 0219, 0232, 0259, 0302).

Commenter 0259 is confident that improvements are being made to both NH3 inventories and the understanding of ammonia in the haze formation process, which is complex and variable across western environments. Although EPA appears to be trying to strike a balance between the significance of ammonia and VOC emissions from BART eligible sources and the administrative burden of implementing BART for these emissions, the commenter is concerned about using current uncertainties and general trends in the state of science to make such broad relaxations when these pollutants are known to contribute to haze.

One commenter ( 0232) suggested that a de minimis threshold similar to those proposed for other visibility impairing pollutants may be appropriate for ammonia to address concerns that 43 certain large ammonia emission sources may have significant potential contributions to visibility degradation but would be exempt from installing control equipment if ammonia is not included.

Other commenters ( 0219, 0302) described the benefits and need for a comprehensive approach, especially in order to adequately reduce PM2.5. Commenter 0219 added that ammonia emissions are increasing, deposition of ammonia is increasing, and ecosystem damages due to excess nitrogen are already being identified. Continued increases in ammonia emissions will continue to exacerbate damages resulting from excess nitrogen deposition.

Commenters ( 0218, 0302) said a body of scientific evidence irrefutably demonstrates that ammonia is a known precursor to visibility impairing pollution. Commenter 0218 said EPA's proposed omission of ammonia directly contravenes Section 169A's mandate to regulate " any air pollutant which may reasonably be anticipated to cause or contribute to any impairment of visibility" and the Clean Air Act's expansive definition of " air pollutant" under section 302 of the statute. The commenter referenced the National Park Service scientist John Vimont's presentation at the July 28 29, 2003 WRAP meeting on NO x Issues in the West, available on line at http:// www. wrapair. org/ forums/ ioc/ meetings/ 030728/ index. html. The commenter disagreed with EPA's assertion that reduction of SO 2 and NO x through BART regulation reduces the two primary compounds with which ammonia combines to form visibility impairing aerosols. Instead, the BART regulations, even if vigorously implemented, will only reduce by a small fraction the total SO 2 and NO x concentrations in the atmosphere because BART only applies to a subset of major stationary sources constructed between 1962 and 1977, and 56 percent of NO x emissions are from transportation sources, which are not subject to the BART requirements. Therefore, significant amounts of SO 2 and NO x from other sources will remain and be available to form visibility impairing nitrate aerosols with ammonia.

Commenter 0179 said the concern about discouraging use of SCRs should be remedied by allowing the facility to make a determination showing that an increase in ammonia is due to decreasing NO x emissions, rather than excluding all sources of ammonia from BART eligibility Comment:. Commenters ( 0186, 0189, 0201, 0223, 0230, 0268, 0275, 0304, 0306, 0323) said EPA should encourage and/ or allow States to consider ammonia emissions in visibility protection plans and continue their efforts to characterize and understand the role of ammonia in their regions. Commenter 0186 said this is especially an issue in areas that are ammonia limited, and secondary aerosol formation may not be significantly reduced by traditional precursor emission reductions. In ammonia limited regions, ammonia reductions may be the most cost effective control strategy and may achieve greater visibility improvements than other precursor reductions.

One commenter ( 28 7008) urged EPA to limit ammonia to the BART guidelines at this time. If ammonia becomes a regulated pollutant under the title V program, permitting authorities may be required to evaluate operating permits for thousands of ammonia sources not previously 2 See Fine particles: Overview of Atmospheric Chemistry, Sources of Emissions, and Ambient Monitoring Data, Memorandum to Docket OAR 2002 0076, April 1, 2005.

44 included in the title V program, including animal feeding operations and wholesale/ retail fertilizer distribution facilities.

Response:

In regard to ammonia, we believe there is sufficient uncertainty about emission inventories and about the potential efficacy of control measures from location to location such that the most appropriate approach for States to take is a case by case approach. There are ample scientific data illustrating that ammonia in the atmosphere can be a precursor to the formation of particles such as ammonium sulfate and ammonium nitrate; 2 however, it is less clear whether a reduction in ammonia emissions in a given location would result in a reduction in particles in the atmosphere and a concomitant improvement in visibility. In other words, the question of whether ammonia does contribute to visibility impairment in a specific instance can be a difficult one.

It may be that States will not be faced often with the question of addressing ammonia in making BART determinations. As noted above, States are required to make BART determinations only for stationary sources that fall within certain industrial categories. The types of sources subject to the BART provisions are not typically significant emitters of ammonia. Because of this, it is unlikely that including ammonia on the list of visibility impairing pollutants in the BART guidelines would have much impact on the States' determinations of whether a source is BART eligible. Thus, while we believe ammonia can contribute to visibility impairment, the decision whether to consider ammonia as a visibility impairing pollutant in a specific case where a potential BART source actually emits more than 250 tons per year of ammonia will be left up to the State to make a reasoned determination.

<IP_ADDRESS> VOCs as Visibility Impairing Pollutants Comment: Five commenters said VOCs should not be treated differently in urban and rural areas ( 0179, 0221, 0227, 0231, 0304). Commenter 0231 said differentiation between urban and rural areas for VOC control purposes assumes there is more known about the chemistry than the current science supports. Commenter 0304 noted that while distance from a Class I area certainly factors into visibility impact, in general the impact a source has does not depend on whether it is located in an urban versus rural setting.

Commenter 0221 described the important role VOCs play in organic aerosol formation, which are a major constituent of visibility reducing aerosols. The commenter said EPA must include the contribution VOC emissions in implementing the BART requirement. Sources that are emitting more than one of the pollutants of concern ( i. e., SO 2, NO x, particulates, and VOC), 45 need to aggregate the emissions of all of these pollutants in determining BART eligibility since all of the pollutants are significant precursors to visibility degradation.

Instead of assuming that NO x are not present, EPA should require state agencies to demonstrate that there are not significant sources of NO x in these rural areas before allowing them to determine that BART would be no controls for VOCs ( 0179).

Comment: Nine commenters said more focus should be placed on controlling VOCs in urban rather than rural areas ( 0186, 0189, 0207, 0213, 0223, 0228, 0254, 0276, 0307). Commenters agreed with the approach in allowing states the discretion to handle VOC emissions in rural areas because anthropogenic VOC emissions are typically dwarfed by biogenic and/ or nonpoint VOC emissions ( 0189, 0207, 0213). Commenter 0186 said rural stationary sources subject to BART with VOC emissions of greater than 250 tons per year should undergo a BART determination. For smaller VOC sources, states should be allowed to determine that no BART controls are required.

Comment: Three commenters ( 0228, 0254, 0276) said that EPA should exclude VOCs for power plants because emissions are very low, reductions would be minimal and costly, and would provide insignificant visibility improvements. Commenter 0254 said that additional primary particulate matter reductions should also be excluded for the same reasons. Commenter 0276 said that the NO x SIP call, CAIR, and new EGU mercury controls will result in major SO 2 reductions by 2010, greatly reducing regional haze in Class I areas. Any remaining regional haze will likely be dominated by organic compounds. Therefore, these BART regulations should shift emphasis to the control of VOC emissions from major BART eligible manufacturing sources.

Comment: One commenter ( 0307) urged EPA to exclude VOCs from the required list of BART pollutants because automatic inclusion as BART pollutants is not justified based on current knowledge. States may include specific VOC species, or all VOCs, in their visibility protection plans if they believe such inclusion is justified. Other commenters ( 0223, 0230) said that, like ammonia, states should be encouraged to continue their investigations of these pollutants and where appropriate include controls on those pollutants in their regional haze SIPs.

Commenter 0302 said VOC should not be included as a pollutant to be controlled by BART. The state should be given the flexibility of determining the needs to meet health based standards first and subsequently determine if further controls are needed to meet regional haze regulations. If a control level is included, states should be given discretion in determining where and how to apply VOC controls regardless of the locale.

Comment: One commenter ( 0201) said EPA needs to further clarify the reasoning behind treatment of VOCs as either visibility impairing or not visibility impairing in urban or rural settings. To 3 Ibid.

4 Ibid.

46 assist states in completing BART analyses, EPA should describe the criteria to be used for determining whether a source is in a rural or urban area as it relates to BART ( 0201, 0304).

Response:

Organic compounds can be categorized according to their varying degrees of volatility: highly reactive, volatile compounds with six or fewer carbon atoms which indirectly contribute to PM formation through the formation of oxidizing compounds such as the hydroxyl radical and ozone; semivolatile compounds with between seven and 24 carbon atoms which can exist in particle form and can readily be oxidized to form other low volatility compounds; and high molecular weight organic compounds   those with 25 carbon atoms or more and low vapor pressure  which are emitted directly as primary organic particles and exist primarily in the condensed phase at ambient temperatures. The latter organic compounds are considered to be primary PM2.5 emissions and not VOCs for BART purposes. Current scientific and technical information clearly shows that carbonaceous material is a significant fraction of total PM 2.5 mass in most areas, and that certain aromatic VOC emissions such as toluene, xylene, and trimethyl benzene are precursors to the formation of secondary organic aerosol. 3 However, while significant progress has been made in understanding the role of VOCs in the formation of organic PM, this relationship remains complex, and issues such as the relative importance of biogenic versus anthropogenic emissions remain unresolved. Therefore we believe that the best approach for States to follow in considering whether VOC emissions are precursors to PM 2.5 formation is a case by case approach. States should consider, in particular, whether a source's VOC emissions are those higher carbon VOCs that are more likely to form secondary organic aerosols. In addition, given the variable contribution of a given amount of VOC emissions to PM 2.5 formation, States may also wish to exercise discetion in considering only relatively larger VOC sources to be BART eligible. After careful consideration of the comments, we agree with commenters who assert that EPA should not suggest a general distinction between the relative contributions of urban and rural VOC emissions to particle formation. The state of knowledge in this area is complex and rapidly evolving. Monitoring data in the East4 suggest that there may be a greater contribution to particle formation in urban areas from VOCs as compared to rural areas, but we recognize that further research is needed to better determine the extent of the contribution of specific VOC compounds to organic PM mass. We do not agree, however, with commenters who make the blanket assertion that rural VOCs are not a significant contributor to particle formation, as it is possible that in specific areas, such as where NOx emissions are high, rural anthropogenic VOCs could potentially play a significant role.

<IP_ADDRESS> PM as a Visibility Impairing Pollutant 5 See Fine particles: Overview of Atmospheric Chemistry, Sources of Emissions, and Ambient Monitoring Data, Memorandum to Docket OAR 2002 0076, April 1, 2005.

6 These methods are described at the following website: http:// vista. cira. colostate. edu/ improve/ Tools/ ReconBext/ reconBext. htm.

47 Comment: Two commenters ( 0199, 0254) said EPA should remove PM from the list of pollutants because additional reductions will not provide meaningful improvements in regional haze ( from power plants at least). Commenter 0254 said for power plants, additional primary particulate matter reductions and new VOC reductions likely will provide insignificant visibility benefits and their cost effectiveness in producing visibility benefits would be exceedingly low. Therefore, these emissions should not be considered under BART for EGUs. Moreover, it is premature to require BART controls for those emissions until the visibility benefits of pending SO 2, NO x and mercury controls have been observed as a result of CAIR, the Acid Rain Program, the NO x SIP Call, and the Mercury Rule. Conversely, controlling ammonia, VOC and PM from other, non EGU emission sources will lower PM levels and improve visibility. To finalize an effective rule and streamline the BART eligibility process for state environmental agencies, EPA should include a determination in the final rule that EGUs are excluded from eligibility for VOC, primary PM10 and primary PM2.5, in addition to ammonia.

One commenter ( 28 243) suggested that ground level or near ground level emission sources of PM10 could be excluded from a BART analysis.

Commenters ( 28 275, 28 333) said scientific data cited by EPA shows that PM coarse ( PM10  PM2.5) has fundamentally different visibility impacts than PM2.5, their interaction with light and other elements in the atmosphere is fundamentally different, and PM coarse has little impact on visibility and is not transported long distances. BART applicability should be based on emissions of PM2.5 only and PM10 emissions should be excluded.

Response:

The guideline continues to recommend that States use PM 10 as the indicator for particulate matter for the applicability step, i. e. in determining whether a source is BART eligible. We disagree with comments that the coarse fraction of PM does not contribute to visibility impairment; while we agree that the coarse fraction is less efficient at light scattering than fine particles, there is ample evidence that the coarse fraction does contribute to visibility impairment. 5 For example, standard methods for calculating reconstructed light extinction routinely include a calculation for the contribution to light extinction from the coarse fraction, an implicit recognition that these particles contribute measurably to visibility impairment. 6 Thus, we believe that States will need to take the coarse fraction of particulate matter into account in determining whether a source meets the threshold for BART applicability. 7 Fine particles: Overview of Source Testing Approaches, Memorandum to Docket OAR 2002 0076, April 1, 2005.

48 However, because long range transport of fine particles is of particular concern in the formation of regional haze, we also believe that it is very important to estimate the PM 2.5 fraction of direct particulate emissions as correctly as possible. In addition, we believe that air quality modeling results will be more meaningful if the inputs account for the relative particle size of directly emitted particulate matter ( e. g. PM 10 vs. PM 2.5).

The acceptability of existing stationary source test methods for regional haze SIPs depends upon what is measured under a State's current test methods for particulate matter. A State's current test methods for measuring particulate matter emissions from stationary sources may not be acceptable for regional haze SIP purposes if these methods ignore the condensible fraction of particulate matter. More specifically, for purposed of makig a BART determination, a test method that ignores a significant fraction of emissions may artificially limit the control measures considered in the BART analysis. Therefore we believe States should revise any such stationary source test methods to ensure that you account for the condensible fraction of particulate emissions. ( See the source testing technical support document ( TSD) in the docket for this rule, which discusses test methods for particulate matter in more detail. 7)

<IP_ADDRESS> General Comments on the List of Visibility Impairing Pollutants Comment: Three commenters said there is no explanation of scientific basis for list of pollutants and the presumption that reductions in NO x, VOC, PM, and ammonia will aid in visibility improvement ( 28 243, 28 266, 28 346). Commenters ( 28 243, 28 266) said further analysis is needed to determine the impacts of improving visibility. Commenter 28 346 said control levels for NO x, PM, VOCs and ammonia are not discussed, but the presumption that these controls are always beneficial to visibility in Class I areas is unsupported. Such controls would either provide no visibility benefits or their cost effectiveness would be low. Furthermore, it is premature to require BART controls for these pollutants before the impact of SO 2 is observed.

One commenter ( 28 390) said the BART analysis for steam electric plants should be limited to SO 2 controls. The emission reductions that result from the application of controls to BART eligible sources should be intended to provide the necessary reasonable progress in visibility improvement for the initial 10 year regional haze planning period. Thus, it seems reasonable that the SO 2 reductions associated with the implementation of BART should be sufficient to demonstrate reasonable progress for the first planning period. Consideration of additional emission reductions for ammonia, PM, NO x and VOCs from steam electric plant BART eligible sources should be postponed until the second 10 year planning period. 49 Another commenter ( 28 302) said nitrate may play a far more significant role in visibility impairment if SO 2 controls are successful at substantially reducing sulfate precursor species, leaving ammonia available to form ammonium nitrate. It is imperative that controls for SO 2 and NO x be implemented simultaneously. Commenter 28 358 said the problem of regional haze is caused primarily by sulfates, but other pollutants including nitrates, organics, light absorbing carbon and coarse particulate matter also play a significant role in visibility impairment. It was suggested during the public hearings on this BART proposal that controlling pollutants other than sulfates would provide little or no visibility improvements, or that these controls would not prove cost effective. This groundless claim is refuted by an overwhelming body of technical evidence. Two commenters ( 0221, 0235) said, with respect to the re proposed BART guidelines themselves, EPA must strengthen them to consider all visibility impairing contaminants.

Response:

The final BART guidelines and supporting information provide evidence that NOx, PM, VOC, and ammonia can impair visibility. See especially Fine particles: Overview of Atmospheric Chemistry, Sources of Emissions, and Ambient Monitoring Data, Memorandum to Docket OAR 2002 0076, April 1, 2005, as well as discussion of individual pollutants above and in the preamble. We also disagree that the available evidence supports a contention that BART control should focus solely on SO2 for steam electric plants. We agree with the commenter who noted that nitrates may be increasingly important to particle formation as sulfate emissions are reduced. This is discussed more fully in the memorandum to the docket cited above.

Comment: One commenter ( 0259) is concerned about any unintended consequences from such relaxations in the list, such as the possibility that the relaxations might limit the ability, if not authority, of states and tribes to address ammonia emissions through other regulatory provisions, such as reasonably attributable BART and reasonable progress from non BART sources. The commenter recommends that EPA consider an alternative approach to balancing administrative and compliance burdens against the likely significance of various pollutants ( including PM10) from BART eligible sources. Such an approach should be scientifically sound, consistent across all pollutants, and not create a poor precedent or exemption status which may limit state discretion as more is learned about the causes of haze and its control options. If the available science and technical analyses demonstrate that emissions of a particular pollutant from BARTeligible sources in a state or region may not be reasonably anticipated to cause or contribute to regional haze, then no further BART analysis for this pollutant would be necessary. Otherwise, the state or tribe would implement regional haze BART, an alternative program, or possibly an alternative program for another pollutant ( e. g., SO 2, NO x, or ammonia) which compensates for the " exemption" in an equitable way. Since BART eligible sources appear to emit ( possibly much) less than 5 percent of the anthropogenic PM10 inventory, the commenter would be interested in applying this approach to PM10 as well as ammonia and VOC. The commenter would also be willing to work with EPA to refine such an approach. 50 One commenter ( 28 266) asked if the list of visibility impairing pollutants is fixed or if states have the option to add other pollutants.

Response:

Given the current state of information on ammonia and VOC as discussed above, we believe we have fashioned a reasonable approach to regulating emissions of these pollutants for the BART program. States have considerable flexibility to take individual or regional circumstances into account in determining a level of focus on emissions of these pollutants whether these pollutants impair visibility in a region, and whether as a result BART limits or other measures addressing these pollutants are appropriate. For PM10, as discussed above, we believe our recommended approach will aid the States in determining how best to conduct the BART review, including assessment of visibility impacts from these pollutants. See also Fine particles: Overview of Source Testing Approaches, Memorandum to Docket OAR 2002 0076, April 1, 2005, and Fine particles: Overview of Atmospheric Chemistry, Sources of Emissions, and Ambient Monitoring Data, Memorandum to Docket OAR 2002 0076, April 1, 2005.

2.3.2 Defining " Stationary Source"

<IP_ADDRESS> Facilities Not Part of a BART Source Category are not BART eligible Comment: Five commenters agreed with EPA's proposed treatment of support facilities and conclusion that support facilities should not be included in the BART eligible source ( 0170, 0189, 0237, 0275, 0307). Commenter 0189 added that EPA's proposal is ambiguous because while the preamble correctly refers to " enforceable operational limitations", the draft guidelines refer, incorrectly, to " federally enforceable permit limits."

Commenter 28 748 said the " support facility concept" should not be included in the guidelines because Congress did not intend that BART applicability be determined by aggregation on an emissions unit by emissions unit basis. Second, the " support facility concept" appears nowhere in EPA's regulations but is instead merely a collection of informal interpretations that EPA has sought to engraft onto the PSD " source" definition. Third, even if the " support facility concept" were an appropriate part of the BART eligibility scheme, the proposal fails to state that the emissions from a support facility could be included only if the support facility itself was placed in operation between 1962 and 1977. Fourth, the support facility concept would be unworkable in practice. The problems involved in attempting to accurately allocate as of the time of construction of the unit to be " supported" the support facility's emissions among all the different emissions units being " supported" would likely be monumental or even impossible.

Commenter 28 349 added that the proposal fails to state that the emissions from a support facility could be included only if the support facility itself was placed in operation between 1962 and 1977. 51 Response:

We agree that emission units at a plant, even if they are a " support facility" for purposes of other programs, should not be considered for BART eligibility unless they are in one of the listed 26 source categories, and were themselves put into place within the 1962 1977 time period. We believe this represents the best reading of the statutory language in section 169A of the CAA.

<IP_ADDRESS> Grouping Individual Units Comment: Eight commenters said small emissions units under a support facility concept should not be included in the BART determination ( 28 242, 28 244, 28 345, 28 349, 28 355, 28 357, 28 364, 28 7007) for several reasons:

° It would be unnecessarily time consuming ( 28 243 ° Sources can't accept operating limits on back up units and it would be unreasonable to subject them to the same retrofit requirements as base load units ( 28 244) ° Congress did not intend the BART applicability be determined by aggregation on an emissions unit by emissions unit basis and/ or is unlawful ( 28 345, 28 349, 28 357, 28 364) ° The concept is unworkable in practice ( 28 349) ° BART analysis should only be conducted on the main electric generating boilers since these units usually make up more than 95% of the emissions from a power plant ( 28 7007).

Comment: Three commenters ( 0169, 0189, 0237) opposed aggregation as exceeding Clean Air Act requirements by extending BART from major stationary sources to emission units. Commenter 0237 described other regulatory precedents related to the definitions and boilers and concluded that EPA should narrow the scope of the BART eligibility criteria to equipment that began operation after 1962 in the distinct industrial source categories and withdraw step 4 of the BART guidelines that commands aggregation of emissions from different categories. The commenter added that the proposed guideline erroneously assumes that a boiler is part of one of the other 26 categories. If that were the case, there would have been no category for fossil fuel fired boilers. Equally true, the retrofit control for a boiler would be different than a BART control for the process with which it is associated. Therefore, EPA's rationale for aggregating different categories is not reasonably related to the purpose for applying BART controls to " major stationary sources" in the listed categories.

Response:

We do not believe there is a need for a blanket exemption for smaller emission units that would otherwise be considered part of the BART eligible source under the BART guidelines. We 52 see no need to prematurely exclude emission units from BART review, and that, as explained earlier in this document, in the BART determination the State has ample opportunity to make reasoned judgements about the level of control to require, if any, on particular emission units. We believe that the suggested approach in the BART guidelines represents the best reading of the CAA and the regulations. As explained above, a State may reasonably conclude that an industrial boiler smaller than 250 million Btu/ hour heat input that provides only heat and power to a facility is not integral to the process and should not be included in the BART eligible source. Where the industrial boiler is integral to the source, it is reasonable for the State to consider it as part of the BART eligible source. In such a situation, the State has ample opportunity to make reasoned judgements about the level of control to require, if any, on particular emission units.

2.3.3 Use of Potential Emissions Comment: Commenters ( 28 345, 28 349, 28 364, 28 748) said that PTE should be based on a realistic assessment of potential emissions when the source was put in operation, rather than an unrealistic approach based on today's air pollution regulatory system. The preamble does not explain why the " current" PTE is to be used rather than the PTE of the source when it was placed in operation. One commenter ( 0237) said EPA's proposal should address whether these defined types of facilities were major stationary sources in the period between 1962 and 1977. The commenter added that it may be more reasonable to reconstruct a source's potential to emit during that period by determining whether a source in one of the 26 categories " actually" has emissions of more than 250 tpy of a BART pollutant, than trying to determine from current data what a source's potential to emit was between 1962 and 1977. Commenter 0238 supported using a source's actual emissions. Most EGUs operate well below their allowable emissions, so an analysis of visibility impairment based on the allowable emissions rate inflates a source's actual emissions. One commenter ( 28 748) said the guidelines should provide that a source that constituted a " major stationary source" when placed in operation between 1962 and 1977 that is no longer a " major stationary source" for any " visibility impairing pollutant" is not subject to BART requirements. The source's PTE may be limited by emissions controls, permit limits, or other constraints that did not exist when the source was placed in operation. One commenter ( 0237) said for units such as boilers, other practical limitations on a source's potential to emit also must be considered, many of which are impossible to determine or if possible, certainly requiring an outlay of resources that would tax most plant operating budgets without any assurance of environmental benefit. This last set of difficulties apparently led EPA to rely on the current potential to emit of individual units that were put into operation between 1962 and 1977. This is equally in error, because there is no reasonable nexus between a piece of equipment's emissions in the BART eligibility time span and its emissions now, which are related to current plant production and limitations on throughput and upstream/ downstream equipment. EPA's failure to support its proposed current PTE as a surrogate for 1962 1977 PTE is arbitrary and capricious, and undermines the reasonableness of the re proposed guideline 53 Response:

CAA § 169A( g)( 7) defines a " major stationary source" as a source with the potential to emit 250 tons or more any pollutant. Based inter alia on that statutory definition, EPA's implementing regulations define BART eligible sources as those with the potential to emit 250 tons or more of any air pollutant. As these definitions clearly require consideration of a source's potential emissions, the guidelines state that a State should determine whether a source's potential emissions exceed the 250 ton threshold in determining whether the source is BART eligible.

The regional haze rule defines " potential to emit" to include "... any physical or operational limit on the capacity of the source to emit...", which includes any federally enforceable permit limits. We interpret this as requiring sources with a current potential to emit 250 tons per year as a major stationary source. We also agree that determining a source's potential to emit during 1962 to 1977 could be difficult. We also agree that a source's current potential emissions are more relevant to the question as to whether it is still a major stationary source. A source which no longer has the potential to emit 250 tons per year of a relevant pollutant need not be considered a major stationary source for purposes of BART.

Comment: Commenters ( 0184, 28 273) agreed that sources with federally enforceable emission limits can use the limit level as a cap for the purposes of calculating potential to emit. Another commenter ( 28 255) said EPA must expedite the rule making to determine whether only federally enforceable limits should be taken in to account in this as well as other programs. This issue must be settled as soon as possible. Commenter 28 385 said EPA should either go out with guidance that allows consideration of other kinds of enforceable limitations, such as those established by state programs, or at least remain neutral on the issue and expressly seek comment on the approach to be used. Also, EPA references the 1990 draft PSD manual for support, which has not been subjected to public review and comment. The manual has been in draft for longer than 10 years without being put in final. Thus, references to the manual should be removed. Nine commenters said EPA's definition of PTE limits that are federally enforceable rather than practicably enforceable is illegal because the courts have disapproved it ( 28 244, 28 304, 28 342, 28 344, 28 345, 28 349, 28 364, 28 393, 28 748 ). Five commenters said state enforceable limits should be considered as well as Federal limits ( 28 266, 28 278, 28 312, 28 404, 28 770)

Response:

As explained in the 2001 and 2004 proposed guidelines, the regional haze regulations define " potential to emit." The guidelines repeat that regulatory definition and provide an example illustrating its application. EPA did not propose to change the definition in 2001 or 2004, but merely highlighted the current definition in 40 CFR 51.301. Although we noted in the 2001 proposed guidelines that we expected to undertake a rulemaking to determine whether only federally enforceable limitations should be taken into account in the regional haze program 54 definition, we have not yet begun the process for such a rulemaking. However, we consider the comments criticizing EPA's definition of " potential to emit" as a request for reconsideration of the visibility regulations and will take these requests into account in determining any future rulemaking efforts to address the general definition of " potential to emit." As we have not yet undertaken such a rulemaking, the guidelines continue to refer to the existing regulatory definition of " potential to emit." For the time being, we believe that States may consider emissions limitations in State permits, which are enforceable under State law, in determining a source's " potential to emit."

Comment: One commenter ( 0189) noted that EPA's visibility rules provide for counting " fugitive" emissions toward the " major source" determination. However, any decision to actually impose controls on such emissions must be reasonable in terms of the Congressional factors for determining BART. There is no practicable control technique for many sources of " fugitive" emissions at forest products facilities, such as chip piles, log piles or material handling and conveyance systems. In addition, the emissions from such operations consist overwhelmingly of large particulates or naturally occurring VOCs with little or no impact on visibility. The commenter urged EPA to make clear that control of sources of fugitive emissions should be required only when it is technically feasible, cost effective, and produces visibility improvement benefits. Similarly, commenter 28 244 urged EPA to clarify that control of fugitive emissions from sources where there is no practicable control technique or whose fugitive emissions have no impact on visibility is not required. Commenters ( 28 266, 28 278, 28 312, 28 404) agreed that fugitive emissions should not count toward potential emissions, which is consistent with the PSD program.

Response:

The visibility regulations require the counting of fugitive emissions for purposes of determining whether a source is a " major stationary source." While fugitive emissions do count toward the " major source" definition, it is also true that when States conduct BART determinations they must take into account the five factors set out in the CAA, including, as the guidelines make clear, consideration of technical feasibility of controls, cost effectiveness, and expected visibility improvement.

2.4 Identify the Emission Units and Pollutants that Constitute the BART eligible Source 2.4.1 Requiring Analysis of All Pollutants When Only One Exceeds the 250 typ Threshold Comment: Ten commenters said the total amount of haze causing pollutants from all units at facility should be considered to meet the 250 ton criteria ( 0221, 28 247, 28 248, 28 260, 28 325, 28 55 334, 28 350, 28 358, 28 362, 28 399). Commenter 28 257 specified the aggregate approach should be taken for power plants..

One commenter ( 0221) said the relevant definitions in the Act, including the definition of a major stationary source as one that potentially emits 250 tpy of any pollutant or its precursors, and the fact the Administrator has identified NO x, SO 2, VOCs, and PM as either precursors to or part of the combination of agents which form visibility impairing particulate matter, requires the aggregation of those pollutants in determining whether a source potentially emits 250 tons or more of particulate matter or its precursors. The commenter provided an example showing why such aggregation is needed to avoid " absurd" outcomes.

Three other commenters agreed that a facility is subject to BART for all visibility impairing pollutants, even if a facility's potential to emit triggers the 250 tons per year threshold for only one pollutant ( 28 258, 28 266, 28 362). Commenter 28 262 added that it is appropriate that all visibility impairing pollutants be subject to BART once the PTE threshold has been crossed. It does not make sense, however, to conduct the PTE analysis on a pollutant bypollutant basis.

One commenter ( 0227) said EPA should aggregate all haze causing pollutants together when determining if a source exceeds the 250 ton per year threshold as part of the BART eligibility analysis.

Comment: Forty nine commenters said that a facility should be BART eligible only for each specified pollutant with emissions exceeding 250 tpy ( 0169, 0181, 0184, 0186, 0187, 0202, 0206, 0214, 0215, 0228, 0229, 0236, 0237, 0238, 0240, 0241, 0242, 0247, 0275, 0294, 28 259, 28 264, 28 273, 28 275, 28 304, 28 306, 28 332, 28 339, 28 341, 28 342, 28 344, 28 345, 28 347, 28 348, 28 349, 28 355, 28 360, 28 383, 28 385, 28 390, 28 392, 28 403, 28 404, 28 747, 28 778, 28 7001, 28 7007, 28 7008, 28 7013). Commenters ( 0181, 0215, 0228, 0238, 0240, 0241, 0242, 0247, 0294) said the BART Guidelines should say that the visibility impairment analysis must be done separately for each visibility impairing pollutant emitted by the source, and that only those pollutants that have been demonstrated, individually, to cause or contribute to visibility impairment from that source are required to go through a BART determination. Commenters ( 240, 28 273, 28 7008) said that this approach is consistent with the PSD regulations, one of the objectives of which is to protect visibility in National Parks. At a minimum, the rule should require that states adopt de minimis levels at or below PSD significance thresholds, as suggested on page 25193 of the preamble.

This proposal is inconsistent with the statute ( 0186, 0187, 0202, 0206, 0214, 0215, 0236, 0237, 0275, 28 304, 28 306, 28 342, 28 344, 28 345, 28 349, 28 355, 28 747). Commenter 0186 said the plain language of the statute says that only " major stationary sources" are subject to BART, and there is no suggestion that BART is intended to be applied to pollutants for which the 56 source would not be determined under section 169A to be a " major stationary source." Therefore, there is no policy or legal justification for the proposal, and EPA should limit BART determinations to pollutants that exceed 250 tons per year. Commenters ( 0187, 0206, 0215, 0236, 0237, 28 342, 28 349) added that the proposal contradicts Congressional intent. Commenters ( 0202, 0294, 28 345) said the " in for one, in for all" approach, especially on a cumulative basis for all affected sources, is not consistent with the individual facility assessment mandate in the Act. States should be required to assess available individual facility information before determining that all sources within the facility are BART eligible. Commenters ( 0187, 0215, 0236, 0238, 28 349) said the statutory language requires a pollutant specific visibility impairment analysis.

Commenter 28 348 said this requirement is inconsistent with other EPA air programs, which have threshold or " significant" emissions amounts for the " non triggering" pollutants below which assessment and controls are not necessary.

Commenter 28 7001 said this policy is unjustified and far too inclusive especially when one considers that the emission amount is calculated on a " potential to emit" basis which will always be greater than and often far greater than actual emissions. Once a sources is " subject to BART", further analysis should only apply to those EU's that trigger the 250 tpy applicability limit. Commenter 28 349 added that, at the very least, BART reviews should not be conducted unless the PTE of the pollutant in question exceeds a reasonable " significance" threshold Commenters ( 0206, 0214, 0187, 0236, 0238, 28 264, 28 339, 28 355, 28 383, 28 390, 28 392, 28 403, 28 747, 28 7007, 28 7013) said that applying BART to non major source pollutants would not produce a significant deterioration in visibility and control would not be cost effective.

Comment: Commenters ( 0241, 28 347, 28 778) said states would not be precluded from requiring controls to meet the regional haze SIP requirements for pollutants where the source's PTE is less than 250 tpy but would grant states the appropriate authority to choose whether to impose such controls. By requiring a BART evaluation for all visibility impairing pollutants over the PSD threshold levels, EPA is granting no deference to the states' decision making authority and would force states to evaluate BART even where there would be no clear environmental benefit. This would waste state resources and significantly impede the states' ability to complete the BART evaluation for all BART eligible sources in a timely fashion so as to meet the SIP submittal deadline. Commenter 28 385 added that said the requirements should allow states to focus their limited resources on completing BART reviews for pollutants that potentially impact visibility and regulated sources should not be saddled with unreasonable control and monitoring costs.

Response: 57 We disagree with the comment that emissions of different visibility impairing pollutants must added together to determine whether a source exceeds the 250 ton per year threshold. The CAA, in section 169A( g)( 7), defines a " major stationary source" as one with the potential to emit 250 tons or more of " any pollutant." We disagree with comments that the BART analysis is required only for those pollutants that individually exceed the 250 ton per year threshold. Section 169A( b)( 2)( A) specifically requires States to submit SIPs that include a requirement that a major stationary source which, as determined by the State . . . emits any air pollutant which may reasonably be anticipated to cause or contribute to any impairment of visibility in any [ Class I area], shall procure, install, and operate . . . the best available retrofit technology, as determined by the State . . . for controlling emissions from such source for the purpose of eliminating or reducing any such impairment. The regional haze regulations similarly require that the States submit a SIP that contains A determination of BART for each BART eligible source in the State that emits any air pollutant which may reasonably be anticipated to cause or contribute to any impairment of visibility in any mandatory Class I Federal area. 40 CFR 51.308( e)( 1)( ii). Nothing in these statutory or regulatory requirement suggests that the BART analysis is limited to those pollutants for which a source is considered major. At best, these provisions can be read as requiring a BART determination only for those emissions from a specific source which do, in fact, cause or contribute to visibility impairment in a particular Class I area, or at least which could reasonably be anticipated to do so. Commenters, however, have not presented any evidence that as a general matter emissions of less than 250 tons per year of PM 2.5, SO 2, or other visibility impairing pollutants from potential BART sources do not " cause of contribute to any impairment of visibility" in any of the Class I areas covered by the regional haze rule. As there is no such evidence currently before us, there is no basis to conclude that the States are required to make BART determinations only for those pollutants emitted in excess of 250 tons per year. At the same time, we agree with certain commenters that the CAA does not require a BART determination for any visibility impairing pollutant emitted by a source, regardless of the amount. After reviewing the language of the Act and the comments received, we have concluded that our interpretation of the relevant language in section 169A( b)( 2)( A) of the Act in the 2004 proposed guidelines is not necessarily the best reading of the BART provisions. Section 169A( b)( 2)( A) of the Act can be read to require the States to make a determination as to the appropriate level of BART controls, if any, for emissions of any visibility impairing pollutant from a source. Given the overall context of this provision, however, and that the purpose of the BART provision is to eliminate or reduce visibility impairment, it is reasonable to read the statute as requiring a BART determination only for those emissions from a source which are first determined to contribute to visibility impairment in a Class I area. The interpretation of the requirements of the regional haze program reflected in the discussion above does not necessitate costly and time consuming analyses. Consistent with the CAA and the implementing regulations, States can adopt a more streamlined approach to making BART determinations where appropriate. Although BART determinations should be based on the totality of circumstances in a given situation, such as the distance of the source from a Class I 58 area, the type and amount of pollutant at issue, and the availability and cost of controls, it is clear that in some situations, one or more factors will clearly suggest an outcome. Thus, for example, a State need not undertake an exhaustive analysis of a source's impact on visibility resulting from relatively minor emissions of a pollutant where it is clear that controls would be costly and any improvements in visibility resulting from reductions in emissions of that pollutant would be negligible. In a scenario, for example, where a source emits thousands of tons of SO2 but less than one hundred tons of NOx, the State could easily conclude that requiring expensive controls to reduce NOx would not be appropriate. In another situation, however, inexpensive NOx controls might be available and a State might reasonably conclude that NOx controls were justified as a means to improve visibility despite the fact that the source emits less than one hundred tons of the pollutant. Moreover, as discussed below, we are revising the regional haze regulations to allow the States to exempt de minimis emissions of SO 2, NO x, and PM 2.5 from the BART determination process which should help to address the concerns of certain commenters associated with the burden of a broad BART analysis.

2.4.2 De Minimis Emission Levels <IP_ADDRESS> Overall Support or Disapproval for the Concept Comment: Forty one commenters said there should be de minimis levels values for visibility impairing pollutants ( 0169, 0170, 0178, 0184, 0188, 0195, 0198, 0199, 0201, 0206, 0207, 0210, 0215, 0226, 0228, 0230, 0231, 0241, 0242, 0243, 0253, 0254, 0256, 0266, 0268, 0275, 0279, 0299, 0304, 0306, 0307, 28 244, 28 266, 28 267, 28 304, 28 332, 28 347, 28 391, 28 397, 28 403, 28 779) and that the states should have the flexibility to identify de minimis levels of pollutants ( 0178). Commenters provided several reasons for their support:

° BART eligibility for every visibility impairing pollutant, regardless of the magnitude of emissions, is costly and inefficient ( 0170, 0178, 0188, 0199, 0201, 0207, 0253, 0254, 0256, 0266, 0275, 0279, 0299, 0304, 0307) ° The magnitude of emissions at low levels will not cause or contribute to visibility impairment ( 0178, 0188,0199, 0206, 0207, 0210, 0266) ° Controlling such pollutants would not be likely to produce any perceptible visibility improvement ( 0188, 0207, 0210, 0230, 0253, 0256) ° Creating de minimus levels would avoid the enormous burden and costs associated with determining BART for countless low emitting units and establishing and tracking compliance with site specific permit terms and conditions for insignificant environmental benefits ( 28 304, 28 397, 28 779). ° Reduces resource demands on states ( 0210, 0230, 0231, 0256, 0266, 0279) ° Keeps the focus on relevant pollutants ( 0242, 0254, 0275) ° Similar to EPA's approach to consider only boilers emitting more than 250 tpy as eligible sources rather than aggregating all emissions units at these sources ( 0299) 8 EDF et al. v. EPA, 82 F. 3d 451, 466 ( D. C. Cir. 1996) citing Alabama Power v. Costle, 636 F. 2d 323 ( D. C. Cir. 1979).

9 Id.

59 Commenter 0199 specifically supported use of de minimis emission thresholds from auxiliary equipment at EUSGUs because there is no discernable improvement in Class I visibility impairment by retrofitting BART controls on these minor sources.

Comment: Three commenters opposed the use of de minimis exemptions ( 0179, 0200, 0221). Commenter 0179 said EPA is closing the wrong loophole. Instead of exempting sources that are clearly BART eligible, EPA should close the loophole that allows sources that emit a combined total of more than 250 TPY of haze forming pollutants to escape BART.

Commenter 0200 said the proposed rule makes clear that single pollutant de minimis exemptions are allowed. The commenter believes that all pollutants should be tested before an exemption is given.

Commenter 0221 gave an extensive discussion explaining why the proposed de minimis exemption contravenes the judicial limits on administrative exemptions established in Alabama Power Co. v. Costle, exceeds EPA's authority as evidenced by the language, structure, and purpose of section 169A of the Act, and is arbitrary and capricious in setting the de minimis ceilings equal to the PSD applicability levels. The EPA's proposed de minimis exemption provides no safeguards that would prevent a state from setting de minimis thresholds at levels which would eliminate or significantly reduce the benefits of applying the BART requirement to particular emissions at particular sources. When comparing the Administrator's exemption authority in section 169 to the expansive definition of what constitutes a major stationary source, it is clear that the BART applicability determination is a very low threshold which does not permit de minimis exemptions unless the operative statutory exemption requirements are satisfied.

Response:

As proposed in 2004, we believe that it is reasonable to give States the flexibility to establish de minimis levels so as to allow them to exempt from the BART determination process pollutants emitted at very low levels from BART eligible sources. As explained by the D. C. Circuit, " categorical exemptions from the requirements of a statute may be permissible ` as an exercise of agency power, inherent in most statutory schemes, to overlook circumstances that in context may fairly be considered de minimis.'" 8 The ability to create de minimis exemptions from a statute is a tool to be used in implementing the legislative design. 9 The intent of Congress in requiring controls on emissions from certain major stationary sources was to eliminate or reduce any anticipated contribution to visibility impairment from these sources. This, as section 169A( b)( 2)( A) states, is the " purpose" of BART. In making a 60 determination as to the appropriate level of controls, however, the States are required to take into account not only the visibility benefits resulting from imposing controls on these sources but also the costs of complying with the BART provision. The BART provision is accordingly designed to ensure that the States take into consideration all emissions of certain stationary sources in making a BART determination, but also to provide States with the flexibility to include the costs and benefits of controlling these sources in the calculus of determining the appropriate level of BART. Although as discussed above, it is not possible based on the information before us to assume that emissions of 250 tons per year of a visibility impairing pollutant do not cause or contribute to visibility impairment, we do believe it would be permissible for States to create de minimis levels at a much lower level. If a State were to undertake a BART analysis for emissions of less than 40 tons of SO 2 or NO x or 15 tons of PM 10 from a source, it is unlikely to result in anything but a trivial improvement in visibility. This is because reducing emissions at these levels would have little effect on regional emissions loadings or visibility impairment. We believe most States would be unlikely to find that the costs of controlling a few tons of emissions were justified. Because the overall benefits to visibility of requiring BART determinations for emissions of less than the de minimis levels would be trivial, we are amending the regional haze rule to allow the States this flexibility. The de minimis levels we provide for today apply on a plant wide basis. Applying de minimis levels on a unit by unit basis as suggested by certain commenters could exempt hundreds of tons of emissions of a visibility impairing pollutant from BART analysis. In at least some of the twenty six source categories covered by the BART provisions, a single control device can be used to control emissions from multiple units. Thus, it is possible that while emissions from each unit are relatively trivial, the costs of controlling emissions from multiple units might be costeffective in light of the BART eligible source's total emissions of the pollutant at issue. States should consider the control options in such situations and determine the appropriate approach for the specific source.

<IP_ADDRESS> PSD Significance Levels Comment: Two commenters opposed the use of the PSD levels because they are not protective enough. One commenter ( 0179) said the de minimis levels should be lower than the PSD significance levels. The regional haze rule is not intended to prevent significant deterioration of views; it is intended to restore views to their natural range. Therefore, PSD is, on its face, not appropriate for use in the BART rule. Because this provision does not appear to have any legal or scientific basis EPA should withdraw it from the final rule. Commenter 0221 said EPA has made no showing that the PSD applicability levels are an appropriate threshold to further the congressionally enunciated goal of visibility restoration in Class I areas. 61 Commenter 0306 said the PSD significance levels are a good starting point; however, the states should have flexibility to establish higher or lower emission rates based on state specific factors such as the distance to Class I areas.

Comment: Eighteen commenters supported setting the de minimis levels equal to the PSD significance levels ( 0178, 0181, 0195, 0210, 0213, 0214, 0223, 0228, 0229, 0230, 0231, 0238, 0259, 0266, 0268, 0271, 0304, 0314, 28 267, 28 304, 28 403). Commenter ( 28 304) said this approach would create consistency between the closely related PSD and Regional Haze programs, which would simplify and ease the implementation of regional haze requirements. Commenters ( 0181) said the application of such emission thresholds will limit BART applicability to pollutant emissions that have the greatest impact on visibility impairment in Federal Class I areas and result in the greatest air quality benefit in those areas. It is also important for flexibility in a state's ability to implement BART on a case by case basis ( 0229). Commenter 0304 said the de minimis levels used for BACT are familiar and have served the states well, so it is recommended that the same levels be used in the application of BART. The commenter prefers that these levels be set nationally so all states face the same de minimis thresholds and the program is equitably applied across state boundaries.

Commenters ( 0223, 0230, 0231, 0259, 0268, 0271) supported the de minimis concept, provided that the level could not be higher than the PSD applicability levels.

Comment: Commenters ( 0170, 0178) said that significant emission rates should be established for each pollutant ( similar in concept to PSD significant emission rates), below which BART would not be required for that pollutant. Commenter 28 391 suggested establishing the de minimus emission rates at 10 tpy. Commenters ( 0170, 28 779) said these thresholds could be established by considering the relative importance of each pollutant in the role of visibility impairment. This would allow the states to focus on the larger emitters.

Comment: Ten commenters said that de minimis levels should be higher than the PSD significance levels ( 0170, 0186, 0189, 0206, 0237, 0241, 0247, 0254, 0275, 0307) to reduce the burden on states and sources ( 0170, 0241), as justified by the statute and consistent with Congressional intent ( 0186, 0189, 206), and to avoid applying the BART review to sources that are unlikely to cause an impact in a Class I area and not be cost effective to control ( 0237, 0241, 0254). Commenters noted that while such de minimis sources would not be subject to BART, they would be included in the regional visibility plans ( 0186, 0189, 0275, 0307)

Commenters suggested alternative levels:

° 100 tpy, which defines a major source for title V and a large emitting source under compliance assurance monitoring regulations ( 0170) 62 ° 250 tpy, consistent with the statute and Congressional intent ( 0186, 0189, 206, 0237, 0275) and consistent with the PSD definition of " major" ( 0247).

Comment: Commenter 0285 asked EPA to clarify the significance of these levels to the overall BART determination process. For example, if the total potential emissions of a source for any BART pollutant are at or below the de minimis level, should the source be evaluated for BART control for that pollutant?

Response:

We are revising the regional haze rule to provide States with the ability to establish de minimis levels up to the levels proposed in 2004. States can accordingly exclude from the BART determination process potential emissions from a source of less than forty tons per year of SO 2 or NO x, or 15 tons per year for PM 10. In the guidelines, we include this as part of the BART determination in section IV of the guidelines. We believe that this approach is the clearest method for exempting trivial emissions from the BART determination process.

We are not requiring that States use these levels as de minimis levels. These emission levels represent the maximum allowable de minimis thresholds, because we believe that control of sources smaller than these levels is unlikely to result in anything but a trivial improvement in visibility. States retain their discretion to set the thresholds at lesser amounts of each pollutant, if they judge that lower levels are appropriate. Alternatively, States may find it useful to exclude de minimis emissions in identifying whether a source is subject to BART in section III of the guidelines. Either approach is consistent with the regulation issued in this rule.

<IP_ADDRESS> De Minimis Values for Ammonia Commenter 0259 said if EPA retains the classification of ammonia as a visibility impairing pollutant for BART purposes, then its de minimis level be given the same degree of technical, scientific, and administrative consideration as provided to other pollutants.

Response:

We have not provided a de minimis value for ammonia, as we have accorded States considerable discretion in determining whether ammonia is a visibility impairing pollutant in an area, and in assessing the predicted visibility impacts from ammonia emissions in areas where the ammonia is a problem.

<IP_ADDRESS> Guidance for Use of De Minimis Values 63 Sixteen commenters described the need for additional guidance on how the de minimis provisions would be implemented ( 0210, 0202, 0214, 0215, 0223, 0226, 0228, 0229, 0230, 0231, 0237, 0238, 0242, 0256, 0268, 0279).

Comment: Commenters ( 0201) said the final guidance should clarify where in the BART determination process de minimis levels may be used. Commenters ( 0201) noted the discussion of de minimis levels appears under step 4 of the eligibility determination in the preamble and under step 3 in the proposed guidance, leading to confusion over EPA's intent. Commenter 0202 said that the determination should be made at the eligibility level to reduce regulatory burdens on facilities. Otherwise, facilities may be required to submit visibility assessments, including CALPUFF modeling for de minimis levels of emissions. Commenter 0229 agreed that elimination of de minimis amounts of pollutants from BART determination should occur in the initial screening to avoid States expending unnecessary resources.

Other commenters ( 0214, 0215, 0223, 0226, 0228, 0230, 0238, 0268, 0279) agreed that the de minimis provisions should be contained in the BART determination stage. Commenters ( 0215, 0228, 0242, 0256) said the de minimis provision has no implication in the BART eligibility portion of the Guidance since these pollutants would be emitted in amounts less than the 250 tons per year pollutant specific BART eligibility threshold. Commenters ( 0214, 0215, 0223, 0226, 0228, 0238, 0242, 0256) said EPA should move these provisions to the BART determination section of the rule and specifically clarify that visibility impairing pollutants emitted in de minimis amounts would not be required to be examined in the BART determination. Commenter 0226 added that the BART determination process is technically involved and time intensive, and ultimately must consider visibility improvement. For units that emit less than the proposed de minimis amounts of a pollutant, even complete elimination of that pollutant will not likely produce a perceptible visibility improvement, therefore, controls could not be considered cost effective. It is important from a public policy perspective that States and sources be allowed to avoid BART determinations for these pollutants, as the result is a foregone conclusion.

Response:

We have retained use of de miminis in step 3 of the BART eligibility stage in the final guidelines but also allow for its use in step 4. We do not believe moving it to the BART determination step would have much practical significance, other than to include those minimal additional tons in the total tons of emissions counted when modeling to determine contribution to visibility impairment. In any case, the reduction in administrative burden on States would be virtually the same at either stage.

Comment: Commenter 0201 said other steps in the process that would benefit from the establishment of pollutant thresholds include 1) a unit level threshold for quantification of emissions in the eligibility determination, 2) a threshold for inclusion in modeling in determining which sources are 64 subject to BART and in step 5 of the engineering analysis, and 3) a source level threshold for inclusion in regional scale model demonstrations.

Commenters ( 0201) said it would be useful if de minimis levels would apply at the source and unit level to help determine which pollutants must be considered in an engineering analysis. EPA should clarify whether the proposed thresholds apply at the " source" or " unit" level. If the intent is to apply the thresholds at the source level, then EPA should allow states to also establish reasonable thresholds at the unit level. Commenter 0237 is concerned that EPA's intent is to continue with a flawed aggregation concept, which would result in conducting a BART analysis for many individual units tied to other non BART units, which Congress clearly did not intend to occur. Commenters ( 0214, 0237, 0238, 0256) said EPA should clarify that the de minimis provision applies on a unit basis. Commenter 0214 said these changes to the proposed rule would ensure that smaller units less able to economically equip with emissions controls would be able to logically forego the BART process. Commenters ( 0215, 0228, 0256) also agreed that a unit basis makes the most sense for steam electric plants.

Commenters ( 0214, 0215, 0238, 0256) also said EPA should state that a BART determination is required only for those visibility impairing pollutants that are emitted above de minimis levels from each individual emissions unit that is part of a BART eligible source.

Comment: Commenter 0231 said EPA should clarify whether actual or potential emissions should be compared to the de minimis levels.

Response:

The rule language makes clear that de minimis levels apply to the BART eligible source, not to each individual emission unit. If de minimis levels applied at the unit level, then emissions from a large number of units at a source could be excluded, while at the same time those emissions might constitute a considerable contribution to visibility impairment from the source. Further, we do not believe that applying de minimis levels at the " source" level would result in undue burden on the State. We believe that States retain enough discretion that they will be able to focus, at the BART determination stage, the greatest effort on the emissions units of greatest concern. We note that the pollutant for which sources most commonly have a multiplicity of emission units is VOCs, and the BART guidelines give States considerable flexibility in addressing VOCs. Finally, we have clarified that de minimis levels apply to a source's potential to emit each relevant pollutant.

2.5 States' Burden in Identifying the BART eligible Source Six commenters said the proposed process of identifying BART eligible sources is far too resource intensive for resource starved state agencies ( 28 264, 28 266, 28 272, 28 278, 28 312, 65 28 404). States lack the detailed inventories needed, including information on " in existence" and " in operation," as well as information on " reconstruction" activities and potential emissions ( 28 264, 28 266, 28 278, 28 312). Other commenters were concerned about the overall burden of the program on states as well ( 28 272, 28 278, 28 312).

Response:

As stated earlier, we have included additional provisions in the final guidelines aimed at reducing the burden on States ( such as discretion in covering VOC emissions). We believe that States will be able to identify the BART eligible sources and make reasoned BART determinations, and expect that they will be able to obtain needed information on emissions and construction and operation dates from sources.

2.6 General Comments Regarding Identifying the BART eligible Source Several commenters provided general comments regarding identifying the BART eligible source ( 0186, 0221, 0235, 0237, 0267, 0275, 0293, 0294, 28 340, 28 343, 28 343, 28 355, 28= 393).

Commenters ( 0186, 0237, 28 340, 28 343, 28 748) said EPA's approach for determining BART eligibility is not authorized by the Act and must be substantially rewritten to meet statutory intent. Commenter 0186 said the Act does not mention individual emission units, does not mention any type of aggregation over time, and does not mention aggregation involving parts of different types of major sources. In contrast, under the statutory scheme, if a new plant is one of the 26 listed ( e. g., petroleum refinery, chemical plant, etc.) and was placed in service between August 7, 1962 and August 7, 1977, then all a State needed to do was determine whether the plant's emissions exceeded the threshold emissions. This simple approach is strongly supported by the fact that Congress made it clear that federal guidelines were to only be established for large power plants. Other commenters ( 0237, 0275, 0294, 28 340, 28 343, 28 748) also discussed the complexity of the proposed process, its inherent infeasibility and impractibility, extensive costs, and inconsistency with the Act. Commenter 0237 added that in analyzing the cost of the proposal, EPA has failed to consider in its assessment whether such quantification procedures are either practical or feasible, and if so, at what cost per company. At the least, the Agency must carefully address the costs of determining BACT eligibility before finalizing this rule.

Commenters ( 28 342, 28 393) said the proposed guidelines exceed the scope intended by Congress by addressing BART applicability issues such as how source age, source heat input and source emission strength would affect BART eligibility, how the effect of a source's emissions on the visual air quality of a MCIF Area would affect BART eligibility and which emissions at affected sources would be subject to BART. The manner in which the states decide what sources and emissions are subject to BART is left to the discretion of the states as they apply the statutory factors. 66 Commenter 0267 was generally supportive of the guidelines. Commenter 0293 appreciated the additional flexibility provided in the revised BART guidelines. Maintaining flexibility in measures to achieve reasonable progress goals allows states to develop appropriate strategies according to the contributions to regional haze at each Class I area. The proposed rule and guidelines support state discretion in the process for determining BART eligible sources.

Commenter 28 255 said the extremely low threshold for BART eligibility cannot be justified given the limited emissions reductions required  in terms of geographic distribution, and type and amount of pollution reduced  to meet visibility goals. The rule's nationwide coverage cannot be justified given EPA's own conclusion that " virtually all" counties in the East, Midwest, Northeast and Southeastern parts of the U. S. with Class I areas will meet visibility goals as a result of emissions reductions due to other programs alone.

Commenters ( 0221, 0237) said with respect to the re proposed BART guidelines themselves, EPA must strengthen them to properly identify all BART eligible sources. Commenter 28 267 noted that ambiguity exists in the interpretation of exactly what constitutes a " BART eligible" source and EPA should clearly define this issue. When States begin the BART process there must be national consistency in the identification of sources to which that process applies, although the end result of a rigorous application of the process may appropriately define different strategies for different jurisdictions.

Response:

As explained earlier, we believe that States will be able to identify the BART eligible sources and make reasoned BART determinations, and we also believe that the BART guidelines as finalized are consistent the Congressional intent and should result in considerable reduction of regional haze.

3.0 Identify Sources Subject to BART 3.1 Methods of Determining Whether a Source is Subject to BART 3.1.1 States Assumes That All Sources are Subject to BART <IP_ADDRESS> States Should Have the Option Comment: Five commenters said that states should have the option to determine that all potential BART sources contribute to haze in a Class I area ( 0179, 0200, 0232, 0286, 0323). Commenters ( 0200, 0232) said this should be the starting point of source eligibility. Commenter 0179 added that under the proposed rule, facilities would still be allowed on a case by case basis to determine if they were not impacting a Class I area, and could therefore be exempt from BART. 67 Response:

As part of this rulemaking, States do have the option to determine that all of its BARTeligible sources collectively contribute to haze in a Class I area, and are thus subject to BART; but the State is not required to start at this point. The State may also determine that its BARTeligible sources collectively do not cause or contribute to any visibility impairment at a Class I area, or the State can use a source by source analysis to determine BART applicability. In no case is a State required to start at one or any of these steps.

<IP_ADDRESS> States Lack the Authority Comment: Sixteen commenters argued that the Act does not provide the authority to allow the aggregation of emissions ( 0185, 0186, 0188, 0215, 0223, 0226, 0228, 0229, 0230, 0242, 0253, 0254, 0256, 0279, 0319, 0321). Commenters said EPA's proposal has no legal support on under section 169A( b)( 2)( A) and was expressly rejected by the court. Commenter 0125 said, contrary to EPA's suggestion, the point of the statute and of Corn Growers is not simply to provide authority to the states irrespective of what the states choose to do with that authority. Rather, the point of the statute and the court decision is to provide authority to the states to determine  consistent with the source specific language of section 169A( b)( 2)( A)  whether the emissions from a particular source cause or contribute to a visibility impairment.

Commenter 0226 said use of EPA's proposed Option 1 for determining whether a source is subject to BART allows States to magically conclude that all BART eligible sources in that State " cause or contribute" to visibility impairment in Federal Class I area( s) without any analysis whatsoever. This effectively eliminates the second step and deems that all BART eligible sources automatically go through a BART determination. Commenter 0253 added that neither the language of Section 169A nor its legislative history suggest that BART may be triggered for any particular source by anything less than a technical analysis establishing that the source individually causes or contributes to visibility impairment.

Commenter 0186 noted that as a new alternative to continued use of the remanded " generic" finding approach, EPA would require States to make an individual finding of impairment ( or non impairment) through modeling of individual BART eligible sources. Such an extremely burdensome, costly and time consuming process will discourage resource limited States, already burdened by development of new State Implementation Plans for the 8 hour ozone and PM2.5 standard, from using this alternative approach. Instead, States would resort to the " generic" finding approach encouraged by EPA, which undoubtedly would lead to State lawsuits over an approach that has already been found to be inconsistent with statutory intent.

Response: 68 Given the low threshold for determining whether a source should be subject to BART, we do not believe that the CAA can be read as prohibiting States from adopting a cumulative approach to determining applicability. Congress provided an exemption process for sources that do not contribute significantly to impairment.

<IP_ADDRESS> States Must Use Source Specific Information Six commenters were concerned with the provisions of the proposed rule that suggest a state's ability to deny sources the opportunity to do a source specific analysis, and allows states to deny a source a BART exemption when a source demonstrates that its' impact on visibility is less than the established threshold ( 0185, 0188, 0215, 0254, 0256, 0279). Commenters said these provisions should be modified to ensure that individual sources are afforded the opportunity to conduct an analysis to demonstrate that its impact does not reasonably impair visibility in any Class I area. Commenter 0279 added that source assessments also must be made on a pollutantby pollutant basis.

Commenter 0254 said that EPA must reference the " 1999 study" referenced in the preamble ( 69 FR 25193 col. 2) as the basis for EPA allowing States to make a determination that all BART eligible sources are subject to BART and provide for proper stakeholder comment.

Response:

A sources has the opportunity to demonstrate to EPA ( and the relevant FLM) that it does not contribute to significant visibility impairment. In addition, in making BART determinations, the State considers the degree of visibility improvement likely to result from the installation of BART. Thus, a source has the opportunity to demonstrate to the State that it should not be required to install BART. As explained in the preamble, States that chose to determine that all BART eligible sources within the State are subject to BART will need to show that its emissions cause or contribute to visibility impairment in one or more Class I areas based on update emissions inventories. Stakeholders will have the opportunity to comment on that showing.

3.1.2 State Determines That No Sources are Subject to BART Using a Cumulative Approach <IP_ADDRESS> States Should Have the Option Comment: Nine commenters ( 0169, 0188, 0215, 0228, 0230, 0231, 0242, 0256, 0271) supported the second proposed option that allows States to use a cumulative approach to demonstrate that none of its BART eligible sources contribute to visibility impairment. Commenters ( 0188, 0228, 0256) added, if this cumulative analysis shows a contribution, the State must allow each individual source an opportunity to demonstrate that its own emissions do not by themselves contribute to visibility impairment in a Class I area. Commenters ( 0215, 0228, 0256) said this option creates no 69 conflict with the individual source focus of the statutory language and Corn Growers, because it is essentially a screening mechanism for individual sources.

Commenter 0231 suggested that EPA might want to provide more flexibility and expand this option to allow states to analyze smaller groups of sources ( less than the full universe of BART eligible sources) together to understand their cumulative impact. If the cumulative impact is below the threshold, then the conclusion would be that none of the individual sources contribute to visibility impairment.

Commenter 28 403 said EPA has identified individual states or multi state areas that do not possess any Class I areas as the only potential geographic areas that could conceivably demonstrate trivial contributions. This interpretation ignores the fact that states, particularly large Midwestern states, may be composed of many distinct and diverse geographical areas and related air sheds. EPA's interpretation would limit states and RPOs from making fundamental and wellreasoned decisions based upon actual source receptor relationships within these smaller geographic areas.

Response: The guidelines describe several approaches that States may use to determine whether its sources are reasonably anticipated to cause or contribute to any visibility impairment. States have the authority to adopt other, well reasoned approaches to this determination.

<IP_ADDRESS> Oppose the Option Comment: Three commenters ( 0179, 0181, 0275) opposed the option to justify a BART exemption by submitting an air quality modeling demonstration to EPA that shows that sources do not cause or contribute to any visibility impairment in a nearby Class I area. Commenter 0179 said, given the wide geographic dispersal of Class I areas it seems difficult to believe that any state could make a blanket declaration that NO facilities in their state could contribute to haze in a Class I area. The commenter was concerned that this provision would allow for " gaming" of the system and said it should be removed from the final rule. Commenter 0181 opposed a cumulative pollutant impact option because the " cause or contribute" test must be pollutant specific. Only those pollutants that contribute to visibility impairment in a Federal Class I area are required to undergo a BART engineering analysis. The commenter recommended that the final BART guidelines include an exemption provision that requires an air quality modeling demonstration to determine whether individual BART eligible sources " cause or contribute" to visibility impairment in a nearby Federal Class I area on a pollutant specific basis. Finally, commenter 0275 said the proposed test for determining whether a BART eligible source is subject to BART requirements conflicts with Congressional intent. In determining whether a source " may reasonably be anticipated to cause or contribute to any impairment of visibility in any such [ class I Federal] area" and therefore is subject to BART, the states are to consider the impact of the specific source in question, not the collective impact of all sources in a broad geographic area. 70 Response:

We concluded in the 1999 regional haze rule that all States contribute to regional haze, but it is possible that a State's may conclude that its subset of BART eligible sources by themselves are not reasonably anticipated to cause or contribute to visibility impairment in a Class I area. States may reach such a conclusion on a pollutant specific basis.

<IP_ADDRESS> Method of Determination Comment: Commenter 0323 said EPA needs to clarify option 2 that the 0.5 deciview, 24 hour maximum threshold applies to the cumulative contribution. Commenter 0231 recommended regional models such as CMAQ or CAMx be used for analyses of multiple source impacts.

Response:

The cumulative options in the guidelines will allow for a State to determine a threshold of comparison. CMAQ or CAMx may be used in the analyses contingent upon an acceptable modeling protocol.

3.1.3 State Makes a Source by Source Determination Using an Individualized Exemption Process <IP_ADDRESS> States Should Use a Source by Source Process Comment: Eighteen commenters supported the third option that is based on an individual exemption process ( 0181, 0184, 0188, 0195, 0202, 0214, 0215, 0224, 0228, 0230, 0238, 0241, 0254, 0268, 0277, 0304, 0314, 0321). Some commenters ( 0188, 0228, 0230, 0254, 0277, 0314) supported the idea that states and/ or sources should have access to this process. Commenters ( 0181, 0195, 0202, 0224, 0256) said that the BART identification process should be based on site specific air quality modeling demonstrations and that the Act requires individual facility evaluations. Commenters said this approach was reaffirmed by the 2002 Court decision.

Response:

The guidelines recommend an individual exemption process as one option that States may use. We do not agree that the CAA requires individual facility evaluations to show that a source is subject to BART.

Commenters also addressed the role that source driven assessments should play. Commenters ( 0184, 0197, 0214, 0215, 0228, 0238, 0241, 0254, 0268, 0321) said that without the right to perform source specific assessments, the proposal is in violation of American Corn 71 Growers Ass'n v. EPA. Instead, for legal and policy reasons, EPA should specifically direct the states in the guidelines to allow sources to conduct individualized source assessments in the sources' discretion. Further, states should have maximum flexibility in deciding whether to require individualized source assessments. EPA's proposal limits a state's discretion to identify which sources contribute to visibility impairment. Commenter 0241 added that EPA claims that any potential inequities resulting from its collective contribution test would be addressed during the BART determination process. However, sources should not be forced to expend resources to go through a full BART analysis to demonstrate they do not cause or contribute to visibility impairment in a Class I area. States should allow sources the opportunity early in the process to demonstrate that they should not be subject to BART. Commenters ( 0170,0171) noted that air quality modeling is important to allow individual sources to demonstrate they do not contribute to visibility impairment.

Response:

We agree that States have the right to perform source specific assessments and may allow sources to conduct these assessments. We do not agree that the guidelines limits the State's discretion in this area.

Commenter 0202 said facilities should be able to provide information on expected operations, control impacts and the costs to address BART eligibility. This factor is especially important for facilities that have curtailed operations, such as a number of primary aluminum facilities in the northwest United States. Commenter 304 said, in the end, most states will likely find that modeling of impacts from individual sources will need to be done to determine what sources must install BART.

Response:

We agree and the rule provides for this.

Comment: One commenter ( 0271) expressed concerns that States using a source by source determination of the visibility degradation effects of BART sources will not achieve the national goals of improving visibility in Class I areas.

Response:

A BART review allows for 5 factors to be considered for each source  visibility improvement is one factor and influences the BART decision to control a source. Source controls provide measurable improvement and is part of Reasonable Progress in State Implementation Plans toward the goal of natural conditions.

<IP_ADDRESS> Method of Determination 72 Comment: Three commenters discussed source specific modeling ( 0234, 0254, 0323). Commenter 0254 supported using air quality models such as CALPUFF or any other state approved model to show no contribution of visibility impairment in a given Class I area, and to make a determination whether a given source qualifies for an exemption.

Response:

EPA allows for the use of CALPUFF or other appropriated dispersion model. See 40 CFR Part 51, Appendix W in April 2003.

Commenter 0323 said that because source specific modeling is resource intensive, EPA should clarify that this option has two sub options: ( 1) states may analyze each BART eligible source in the state or, ( 2) states may chose to presume that all BART eligible sources within the state meet this applicability test, but provide( s) sources with the ability to demonstrate on a case by case basis that this is not the case.

Response: We agree; States are provided these options in the rule.

Commenter 0234 said for sources to be exempted, EPA should hold the showing of no contribution to a very high standard in order to protect the integrity of the regional haze program. Exempting BART eligible sources from controls should be a very high hurdle for both the owners and operators of sources and states.

3.1.4 Other Comments Regarding the Methods to Determine Whether a Source is Subject to BART Comment: Some commenters ( 0170, 0171, 0187, 0267, 0293) generally supported the three option approach proposed by EPA. Commenter 0293 added that maintaining flexibility in measures to achieve reasonable progress goals allows states to develop appropriate strategies according to the contributions to regional haze at each Class I area. The proposed rule and Guidelines support state discretion in evaluating whether BART is required. In contrast, commenter 0307 said EPA should not direct the states to use one specific method for comparison of alternatives, as this properly is within the latitude conferred upon the states by Congress in the Act for directing their visibility protection programs.

Response:

The guidelines provide the States with flexibility and do not direct the States to use one specific method for comparison of alternatives. 73 Commenters ( 0247, 0256, 0275) said EPA failed to provide source owners and operators with the necessary discretion to do source specific visibility impairment assessments as allowed by the Act. Commenter 0247 added that the opportunity for a source to demonstrate that it should not be subject to BART should be provided in all cases, independent of which option a state uses to identify affected sources.

Response:

We have provided a source by source visibility assessment methodology in this final rule for a State or a source to make a BART applicability assessment.

Commenters said that the statute requires a source by source review said the statute itself restricts BART to sources that " may reasonably be anticipated" to cause or contribute to visibility impairment ( 0189, 0197, 0208, 0237, 0275, 0308. 0321). Commenters ( 0189, 0275, 0294) added that the statute articulates a requirement for fact based state decisions on the reasons for visibility impairment before determining that a source is subject to BART. EPA's proposal violates that core requirement both by strongly endorsing an automatic finding that all BART eligible sources are subject to BART, and by requiring burdensome modeling for any attempt to show otherwise. Commenter 0208 said the first two options are therefore inconsistent with the statute. The guidelines in their current form recreate the " Group BART" approach dismissed by Corn Growers. Commenter 0237 said the Court's holding requires that if a source shows that its emissions are not reasonably anticipated to cause or contribute to a significant impairment of visibility in any mandatory Class I areas, EPA must exempt it from BART. The final rule must clarify that such an exemption is not permissive but mandatory.

Response:

Given the nature of regional haze, it is reasonable to conclude that a major source located in an area upwind of a Class I area contributes to visibility impairment. The regulations provide a process for EPA to exempt from BART a source that can show that its emissions are not reasonably anticipated to cause or contribute to a significant impairment of visibility.

Commenters ( 0200, 0232) said the variety of potential BART exemptions identified in the new rule could create a great disparity in the level of control applied. The success of a retrofit program is based on nationally consistent, stringent, application of controls to similar sources. Commenter 0232 said all potentially BART eligible sources should be considered subject to BART determinations. The commenter added that EPA should provide clear and uniform guidelines for how options " b" and " c" would be determined.

One commenter ( 0221) said EPA's proposed options go too far in allowing sources to be " exempted" from BART requirements. Initially, EPA needs to clarify that states may not permit a 74 BART eligible source to avoid BART requirements without an affirmative demonstration, either by the state or the source, that the source does not emit any air pollutant which may reasonably be anticipated to cause or contribute to any impairment of visibility in a Class I area. While it appears that EPA did not intend for sources to avoid BART in the absence of such a demonstration, the language of the proposal on this point must be made more clear so as to ensure meaningful implementation of the BART requirements of the Act. Otherwise, a state or a BART eligible source might attempt to avoid BART requirements simply by failing to conduct the proper analysis of visibility impairment contribution.

Response: We agree that the State must determine that a source is not reasonably anticipated to cause or contribute to visibility impairment in order to find that it is not subject to BART.

3.2 Source Exemption Process 3.2.1 Exemption Process for Sources More Than 50 km and Less Than 200 km from a Class I Area Comment: Commenter 0259 said for sources located more than 50 km from a Class I area, EPA's proposed guidelines would require the use of the CALPUFF model to exempt a BART eligible source from being subject to BART. It is the WRAP's position that EPA should allow states and tribes to choose an alternative to CALPUFF in such situations, providing they can demonstrate to EPA that it meets the same level of rigorous analysis as CALPUFF.

Response:

The rule allows for the use of alternate models to CALPUFF.

3.2.2 Exemption Process for Sources More Than 200 km from a Class I Area <IP_ADDRESS> Development of a Written Modeling Protocol Comment: Two commenters ( 0185, 0221) generally supported the use of modeling protocols. Commenter 0185 agreed with EPA that states or individual sources may perform assessments to determine whether a given source qualifies for an exemption. Commenter 0221 added that for source receptor distances substantially in excess of 200km, states must determine visibility impact using an EPA approved modeling protocol.

Response: 75 We agree. States should prepare or require their BART eligible sources to prepare a modeling protocol prior to conducting any modeling, regardless of the distance from the source and the Class I area. This is reflected in the rule.

Comment: Several commenters raised issued related to using CALPUFF for source receptor distances beyond 200 km ( 0183, 0230, 0245, 0319). One commenter ( 0319) said CALPUFF has not proven reliable over the extended distances that exist between Class I areas and power plants in rural areas and it is expensive to run. Developing alternative, more accurate modeling protocols will be complex and expensive. It will be difficult for states to justify such expenses, especially when the threshold limit is 0.5 deciviews and resulting improvements in haze may be imperceptible. The states are in a better position to determine which modeling protocol and model input values best reflect conditions in their states. Thus, the appropriate role for EPA is advisory to the states and tribes when states and tribes are approving CALPUFF and other modeling protocols and conducting assessments.

Response:

We agree that we should have only an advisory role in development of the protocol as the States better understand the BART eligible source configurations and the geophysical and meteorological data affecting their particular Class I area( s). We believe, however, that EPA should have final approval of State protocols so that the model, and the BART control decision which depends, in part, on the model results, is applied equitably across all regions. EPA approval will help ensure that vastly different modeling results are not produced for modeled BART eligible sources that have similar emission configurations and operate under comparable geophysical and meteorological conditions.

One commenter ( 0245) requested specific guidance regarding the use of CALPUFF in these situations: ° Guidance for providing input for nonhomogeneous ammonia emissions into CALPUFF ° Guidance for running CALPUFF over 300 to 1000 km from release or suggestions to offset biases observed by CAPTEX.

Response:

Emissions of ammonia are not considered in the CALPUFF model. Only a constant background concentration of ammonia is established by the model user. The majority of BARTeligible sources are within 500 km of a Class I area, and the modeling guideling provides suggestions for potentially improving the performance of CALPUFF beyond 200 km ( e. g. puff splitting). A modeling protocol for any visibility impact determination for the purposes of BART should be submitted to and approved by EPA prior to the modeling. Collaboration among interested parties is suggested as an appropriate means to assess how to run the model. 76 Comment: Three commenters discussed the need for additional guidance regarding modeling protocols ( 0185, 0188, 0201). Commenters 0188 and 0201 urged EPA to develop guidance on modeling protocols to address complex cases where the source is greater than 200 km away from the nearest Class I area, to help focus state resources on approvable protocols, and to provide flexibility. Commenter 0321 added that the purpose of the modeling is to determine whether a source passes or fails EPA's proposed exemption " threshold."

Response:

We have provided guidance as part of the final rule. Modeling can also be used to determine the degree of visibility improvement expected by potentially controlling a BARTeligible source.

<IP_ADDRESS> CALPUFF Limitations for Distances over 200 km or More Comment: One commenter ( 28 242) said EPA's December 1998 Interagency Workgroup on Air Quality Modeling recommends using CALPUFF for transport distances of 200 km or less. Oahu emission sources are more than 200 km from both Haleakala and Volcanoes parks. Thus, based on the most current EPA guidance for modeling long range transport, it would not be appropriate to model Oahu emissions impact on either Class I area using CALPUFF. The proposed rules should allow for BART exemptions for sources greater than 200 km from the Class I area.

Response:

The rule does allow for exemptions for distances beyond 200 km from a Class I area. We disagree that CALPUFF is inappropriate beyond 200 km. There are model options available which may improve the performance beyond this distance. A modeling protocol should be submitted prior to conducting any modeling analyses. The rule also allows for alternative methods to CALPUFF for determining BART exemptions.

3.2.3 Modeling Sources Less Than 50 km from a Class I Area Comment: Four commenters discussed the benefits of various models ( 0221, 0225, 0307, 0323 ). Commenter 0221 urged EPA to require either CALPUFF or some other air quality model approved by EPA for more local scale use such as PLUVUEII. Commenter 0225 said VISCREEN or PLUVEUII modeling results, for receptors less than 50 km from the BARTeligible source, should have equal priority to CALPUFF modeling results. Commenter 0307 added that EPA should also suggest to states that conventional dispersion models such as ISC3 and AERMOD may be useful in determining if a single source could contribute to visibility impairment where a satisfactory connection between concentration of pollutants and visibility 77 impairment thresholds can be demonstrated. For many BART eligible sources this type of conventional modeling may already have been done for purposes such as PSD or NAAQS demonstrations. Being able to capitalize on previous modeling work would save resources of both state agencies and source owners, thereby reducing the cost and complexity of the BART program. Commenter 0323 noted that plume impact models have traditionally been applied at distances less than 50 km and encouraged EPA to require such models be used. For such sources, a long range transport analysis may also be required to assess haze visibility impacts at Class I lands located beyond 50 km from the source.

Response: We agree and have provided for alternate models to be used in the analyses.

Comment: Commenter 0225 made specific recommendations regarding implementation of the various models:

° BART eligible sources should be exempt from having to evaluate or add controls when VISCREEN or PLUVEUII modeling results show the source will not cause a plume with any hourly estimates of delta E greater than or equal to 2.0, or the absolute value of contrast values (| C|) greater than or equal to 0.05. ° Due to its conservative nature, CALPUFF modeling for receptors less than 50 km from the BART eligible source located in complex terrain without a full CTDMPLUS meteorological data should be allowed a higher threshold, i. e., a threshold of a maximum 24 hr change of 1.0 deciview.

Response:

The final rule allows for alternative models and methodologies to be used for analyses. A modeling protocol should be submitted prior to conducting any modeling. Exemption decisions and thresholds are at State discretion.

3.2.4 Zero out Approach <IP_ADDRESS> Oppose Using Zero out Approach Comment: Four commenters said the zero out approach is invalid because it unrealistically excludes emissions from an entire region and ignores how those emissions would interact and change the conditions of the complex atmospheric reactions ( 28 405, 28 275, 28 333, 28 385). EPA must allow the States to exercise a much higher level of professional judgment and not rely on such simplistic analytical mechanisms to make these important determinations. Other commenters ( 28 348, 28 364, 28 387) said the approach only addresses Statewide or area wide emissions contributions ( not source by source contributions) to visibility impairment. 78 Commenter 28 385 said eliminating all man made emissions in zero out model runs will likely produce effects not contemplated by the model used. Hence, the results of zero out model runs are and should be viewed with suspicion. In addition, EPA states in 64 FR 35722 that " geographic ' regions' that can contribute to regional haze generally extend hundreds or thousands of kilometers." TVA's atmospheric modelers believe that making BART type determinations for distances of thousands of kilometers is beyond current modeling capabilities.

Response:

States have discretion in models and methodologies to use in making visibility impact determinations. Although most BART sources are within 300 km to 500 km from a Class I area, there are models available that are capable of reasonably estimating visibility impacts at much greater distances.

Comment: One commenter ( 28 358) noted that EPA hypothesizes that a state may demonstrate that it makes only a " trivial" contribution to visibility impairment in Class I areas. While the implications of a state asserting that it makes a trivial contribution are not expressly stated, from the context it appears that this would functionally operate as an exclusion to the BART requirement, either by exempting a state from the obligation to adopt a regional haze SIP as a threshold matter, or by exempting major stationary sources from the BART requirement through the implementation of a state's regional haze SIP. Neither of those outcomes is legally permissible: the statute does not admit of a de minimis exception for states from the BART requirements.

One commenter said EPA must revise the guidelines to require that states conduct a modeling demonstration of a non trivial contribution to visibility impairment prior to a source, or group of sources being subject to further BART analysis.

Response:

The guidelines provide an option for States to show that the emissions from its BARTeligible sources do not cause or contribute to visibility impairment. EPA determined in 1999 that all States must submit regional haze SIPs.

<IP_ADDRESS> Support Exempting Individual " Trivial Emissions" Sources Comment: Twelve commenters said sources should be allowed to demonstrate that they are individually " trivial" emissions sources ( 28 242, 28 272, 28 273, 28 311, 28 348, 28 357, 28 386, 28 392, 28 779, 28 7004, 28 7005, 28 7007). Commenter 28 242 described why this approach is relevant in Hawaii and some commenters ( 28 273, 28 779) provided other examples. Other commenters said a case by case exemption process is required by the Act ( 28 272, 28 79 357). Commenters stressed the states' role in determining sources subject to BART ( 28 311, 28 348, 28 386, 28 392, 28 7004, 28 7005). Commenters ( 28 386, 28 392) particularly objected to the requirement that states must prove the combined influence of all BART affected sources ( every power generator, industrial boiler etc. from each of the 26 source categories) is negligible for each of the 156 Class I areas. Commenter 28 7004 stressed that an engineering analysis should not be required of any sources with trivial contributions to visibility impairment in Class I areas.

Response:

The guidelines provide the States with considerable discretion to adopt reasonable approaches for making BART determinations.

Commenter 28 7005 said additional language should be included that would allow states with large discrepancies in the distances between sources and the nearest Class I area to provide for an exemption for non culpable sources. Modeling showing the culpability of sources and/ or subgroups of sources within a state or region is likely to show that the implementation of BART, or any other types of controls in areas great distances from Class I areas will have a trivial effect on the visibility in those areas. Commenter 28 7007 agreed that relative contributions based on emissions and the distance of the plant from the Class I area should be taken into consideration.

Response:

In this final rule, States may conduct an individual exemption analysis for BART eligible sources.

<IP_ADDRESS> Need Guidance and Definitions to Use Zero out Approach Comment: Five commenters said EPA does not address the smallest acceptable geographic area to be " zeroed out" or the amount of difference between the base rule and " zero out" run that is considered to be " trivial" ( 28 266, 28 273, 28 312, 28 357, 28 7008). Commenter 28 273 added that while it might be challenging to establish a bright line threshold beyond which contribution is no longer trivial, the rule should at least attempt to face this challenge, or at least provide some factors or other guidelines to assist the states in making this determination. Commenter 28 7008 added that EPA must also further delineate the process and requirements that must be followed in making a demonstration that emissions only constitute a " trivial contribution to visibility impairment."

Response:

This rule establishes that States can develop a " cause or contribute" visibility threshold and that modeling demonstrations can be made for comparison to such threshold and if impacts 80 are below this threshold, a source or group of BART eligible sources may be exempt from a BART analysis.

Commenter 28 357 said there is only one possible definition that would be consistent with 169A: EPA should remind the states that they may exempt geographic areas as " trivial" contributors to visibility impairment if the BART eligible sources within a geographic region do not by themselves cause humanly perceptible impairment of visibility in a Class I area. If it does not choose such a definition, EPA is not only reading the statutorily required cost/ benefit analysis out of the BART process, it is robbing the word " visibility," the heart of the entire program, of any meaning.

Response:

A source or group of sources need not cause perceptible impairment of visibility in order to " contribute" to visibility impairment. As explained in the rule, the number of sources contributing to visibility impairment is one factor to consider in establishing an appropriate threshold.

3.2.5 General Comments Regarding the Source Exemption Process <IP_ADDRESS> Flexibility Over the Choice of Models Comment: Eight commenters discussed the limitations or other technical issues associated with using CALPUFF ( 0189, 0198, 0217, 0230, 0257, 0302, 0309, 0314).

Commenter 0189 cited recent experience showing that appropriate consideration of meteorological events such as precipitation should be allowed in the refined BART assessment using CALPUFF. Enhancements to the CALPUFF code soon may be available that could greatly facilitate the incorporation of meteorological interference issues in regional haze modeling.

Response:

Any revisions to the CALPUFF code, including adjustments for meteorological influences, that have been approved for use by EPA are allowed for BART assessments. The final rule also allows for alternative models and methodologies to be used for analyses.

Commenters pointed out several limitations to the CALPUFF model in this application ( 0198, 0217, 0230, 0275, 0302). Commenters ( 0198, 0230, 0275) supports the use of the CALPUFF model as a screening tool only. Limitations described include: ° CALPUFF simplifies many atmospheric processes that are important for estimating visibility impairment at Class I areas due to emissions from potential BART eligible sources. 81 ° CALPUFF sulfate ( SO4) and nitrate ( NO3) formation chemistry modules have many limitations: a) They were developed for conditions not representative of those that occur in the locales of many potential BART eligible sources during large portions of the year, b) They are inaccurate compared to current state of science chemistry modules, and c) They are out of date having been developed over two decades ago. ° SO4 and NO3 estimates from CALPUFF are likely to be inaccurate and generally overestimated. ° The CALPUFF model has not been approved for visibility evaluations. ° CALPUFF has not been adequately tested or evaluated for Class I type air quality analyses. ° There is very little information regarding CALPUFF's performance over large distances and complex terrain. ° There has been no testing of the accuracy of the CALPUFF chemistry models. ° CALPUFF is time consuming and data intensive.

Response:

As discussed in the preamble to the rule, we understand the concerns of commenters that the chemistry modules of the CALPUFF model are less advanced than some of the more recent atmospheric chemistry simulations. To date, no other modeling applications with updated chemistry have been approved by EPA to estimate single source pollutant concentrations from long range transport. In its next review of the Guideline on Air Quality Models, EPA will evaluate these and other newer approaches and determine whether they are sufficiently documented, technically valid, and reliable to approve for general use. In the meantime, as the Guideline makes clear, States are free to make individualized showings that these or other alternative approaches are valid and appropriate for their intended applications. Theoretically, the CALPUFF chemistry simulations, in total, may lead to model predictions that are generally overestimated at distances downwind of 200 km. Again, States can make judgements concerning the conservativeness or overestimation, if any, of the results. The use of other models and techniques to estimate if a source causes or contributes to visibility impairment may be considered by the State, and the BART guidelines preserve a State's ability to use other models.

One commenter ( 0309) had serious concerns about the CALPUFF model used by the EPA to assess the impact of the proposed BART rule on Indian country. The model fails to independently incorporate tribal lands because horizontal grid sizes are primarily based on county boundaries which ignore overlapping tribal and state jurisdictions. Such modeling therefore has absent from it the necessary input from tribal lands that insures an effective analysis of air dispersion from individual sources, and the ultimate effect of such source emissions on Class I areas. According to the commenter, a CALPUFF assessment of an individual source cannot be used as the preferred approach for determining whether a BART eligible source may be exempt from BART until air dispersion over tribal lands is properly modeled, taking into account the unique and vast terrains that exist on such lands. 82 Response:

We disagree. For purposes of modeling, a BART eligible source is independent of grid size and can be located anywhere in the model domain which may include tribal lands and the meteorological and terrain effects in those geographic areas. Air quality impacts predicted by dispersion models is not geographically specific.

Comment: Ten commenters said EPA should clarify that models other than CALPUFF may be used subject to approval by the state agency ( 0188, 0214, 0217, 0228, 0231, 0238, 0256, 0268, 0270, 0302). Some commenters noted that the inconsistencies in the preamble compared to the rules needs to be clarified to make this point. Commenter 0256 added that EPA should revise the guidelines to remove the references to CALPUFF, other than an introductory statement that indicates that CALPUFF is one air quality model that may be used and that other models may be used subject to approval by the state air agency.

Response:

We agree and the rule provides for the use of alternative models. However, a modeling protocol, including a proposal to use alternative models to CALPUFF, should be submitted prior to conducting any modeling. This will ensure consistency of model use across states and regions.

Commenter 0270 said prior to mandating that any modeling for BART eligible sources located at least 50 km from a Class I area be performed using CALPUFF, EPA must explain why the use of CALPUFF is discretionary under Part 51 and mandatory under Part 308 and, in turn, must solicit comment on the propriety of specifying CALPUFF as the sole modeling technique for such sources. Until EPA solicits such comment, it is unable to require a state or sources within the state and located at least 50 km from a Class I area to use only the CALPUFF model when trying to demonstrate no reasonably attributable haze impairment to a Class I area.

Response:

The rule does not mandate the use of CALPUFF and provides States the flexibility to use other models to conduct visibility impact assessments.

Commenter 0237 objected to the unreasonable modeling regime laid out in the proposed BART guidelines for proving a " negative determination. For all practical purposes, CALPUFF modeling will always demonstrate some sort of impact on a Class I area, even at great distances from Class I areas. Further if exemption is predicated on this type of modeling alone   to the exclusion of other simpler methodologies   the cost of the modeling will discourage most states from choosing to allow sources to try to show the impact, even if this could be done successfully. If this is the only method EPA allows in the final rule, it would be tantamount to not allowing a 83 showing at all, and the BART guideline clearly would fail to satisfy the Court's decision in American Corn Growers Association v. EPA.

Response:

We disagree. The rule allows State discretion in determining an appropriate " cause or contribute" threshold for BART applicability. Also, States may develop their own methodologies, including non modeling techniques for assessing BART applicability, or they have the flexibility to use models other than CALPUFF.

Comment: Commenters discussed alternatives to CALPUFF ( 0183, 0201, 0210, 0245). Speaking generally, commenters ( 0201, 0210) said all parties will acknowledge that CALPUFF has limits and encouraged EPA to include language in the final guidance that allows the use of other analysis tools that may better represent actual conditions, including grid models ( 0210). Commenter 0245 instead encouraged EPA to use the CAIR program as the more appropriate first step to achieve visibility goals. This will allow sufficient time for EPA to focus its resources on the refinement and development of additional tools with a higher degree of confidence in the results than those problematic tools relied upon in this proposal. Commenters 0198 and 0230 described the important role that photochemical grid models can play and that their use should be allowed. Commenter 0183 was concerned about the differences in the chemistry mechanisms in CALPUFF compared to photochemical models. Use of photochemical models by regional planning organizations may produce results inconsistent with results obtained from using CALPUFF to model single sources.

Response:

As discussed in the preamble to the rule, we understand the concerns of commenters that the chemistry modules of the CALPUFF model are less advanced than some of the more recent atmospheric chemistry simulations. To date, no other modeling applications with updated chemistry have been approved by EPA to estimate single source pollutant concentrations from long range transport. In its next review of the Guideline on Air Quality Models, EPA will evaluate these and other newer approaches and determine whether they are sufficiently documented, technically valid, and reliable to approve for general use. In the meantime, as the Guideline makes clear, States are free to make individualized showings that these or other alternative approaches, including grid models, are valid and appropriate for their intended applications. With regard to the CAIR program, affected states have the option to use the CAIR provisions to meet the BART requirements for BART eligible EGUs or other source types covered by CAIR.

Commenter 0202 noted that research is progressing on developing dilution tunnel methods to assess aerosol formation from stack gas testing, relying on air chamber analysis for atmospheric aerosol formation. Those alternatives may become a viable measurement method for many 84 operations. Commenter 0217 said an example of other models that could be used would include the EPRI plume chemistry model, SCICHEM ( which is technically far superior to CALPUFF). Commenter 0275 said that additional consideration should be given to the " weight of evidence" approach ( as adopted in ozone demonstrations) in appropriate circumstances.

Response:

We agree. States have the option to use alternatives to CALPUFF in making visibility assessments for BART.

Comment: Four commenters said that the choice of models should be at the states' ( or RPOs) discretion ( 0217, 0223, 0226, 0242). Three commenters said that states and sources should both be allowed this flexibility ( 0228, 0230, 0230). Commenter 0230 added that increasing the flexibility in the potential modeling approaches and requiring the development of a Modeling Protocol to allow EPA and others to review the proposed modeling approaches would alleviate the current inconsistencies and contradictions between the Proposed BART Rule and EPA's air quality modeling guidelines and draft fine particulate and regional haze modeling guidance.

Response: