1 6560 50 P ENVIRONMENTAL PROTECTION AGENCY 40 CFR Part 51 [ FRL xxxx x]

RIN: 2060 xxxxx Regional Haze Regulations and Guidelines for Best Available Retrofit Technology ( BART) Determinations AGENCY: Environmental Protection Agency ( EPA).

ACTION: Final Rule.

SUMMARY: On July 1, 1999, EPA promulgated regulations to address regional haze ( 64 FR 35714). These regulations were challenged, and on May 24, 2002, the U. S. Court of Appeals for the District of Columbia Circuit issued a ruling vacating the regional haze rule in part and sustaining it in part. American Corn Growers Ass'n v. EPA, 291 F. 3d 1 ( D. C.

Cir. 2002). Today's rule addresses the court's ruling in that case.

In addition, prior to the court's decision, EPA had proposed guidelines for implementation of the best available retrofit technology ( BART) requirements under the regional haze rule, ( 66 FR 38108; July 20, 2001). The proposed guidelines were intended to clarify the requirements of the regional haze rule's BART provisions. We proposed to add the guidelines and also proposed to add regulatory text 2 requiring that these guidelines be used for addressing BART determinations under the regional haze rule. In addition,

we proposed one revision to guidelines issued in 1980 for facilities contributing to " reasonably attributable"

visibility impairment.

In the American Corn Growers case, the court vacated and remanded the BART provisions of the regional haze rule.

In response to the court's ruling, on May 5, 2004 we proposed new BART provisions and reproposed the BART guidelines. The American Corn Growers court also remanded to the Agency its decision to extend the deadline for the submittal of regional haze plans. Subsequently, Congress amended the deadlines for regional haze plans ( Consolidated Appropriations Act for Fiscal Year 2004, Public Law 108 199,

January 23, 2004). The May 5, 2004 proposed rule also contained an amendment to the regional haze rule to conform to the new statutory deadlines.

We received numerous comments on both the July 20, 2001 proposal and the May 5, 2004 reproposal. Today's final rule reflects our review of the public comments.

DATES: The regulatory amendments announced herein take effect on [ insert date 60 days after publication in the Federal Register]. 3 ADDRESSES: Docket. All documents in the docket are listed in the EDOCKET index at http:// www. epa. gov/ edocket. Although listed in the index, some information is not publicly available, i. e., CBI or other information whose disclosure is restricted by statute. Certain other material, such as copyrighted material, is not placed on the Internet and will be publicly available only in hard copy form. Publicly available docket materials are available either electronically in EDOCKET or in hard copy at the OAR Docket,

EPA/ DC, EPA West, Room B102, 1301 Constitution Ave., NW.,

Washington, DC. The Public Reading Room is open from 8: 30 a. m. to 4: 30 p. m., Monday through Friday, excluding legal holidays. The telephone number for the Public Reading Room is ( 202) 566 1744, and the telephone number for the OAR Docket is ( 202) 566 1742.

FOR FURTHER INFORMATION CONTACT: Kathy Kaufman at 919 541

0102 or by e mail at Kaufman. Kathy@ epa. gov or Todd Hawes at 919 541 5591 or by e mail Hawes. Todd@ epa. gov.

SUPPLEMENTARY INFORMATION:

Regulated Entities. This final rule will affect the following: State and local permitting authorities and Indian Tribes containing major stationary sources of pollution affecting visibility in federally protected scenic areas. 4 This list is not intended to be exhaustive, but rather provides a guide for readers regarding entities likely to be regulated by this action. This list gives examples of the types of entities EPA is now aware could potentially be regulated by this action. Other types of entities not listed could also be affected. To determine whether your facility, company, business, organization, etc., is regulated by this action, you should examine the applicability criteria in Part II of this preamble. If you have any questions regarding the applicability of this action to a particular entity, consult the people listed in the preceding section.

Outline. The contents of today's preamble are listed in the following outline.

I. Overview of Today's Proposed Actions II. Background A. Regional Haze Rule B. Partial Remand of the Regional Haze Rule in American Corn Growers C. Changes to the Visibility Regulations D. Changes to the BART Guidelines III. Detailed Discussion of the BART Guidelines A. Introduction B. Scope of the Rule  Whether to Require States to Follow the Guidelines for All BART Sources C. How to Identify BART eligible Sources D. How to Determine Which BART eligible Sources are Subject to BART E. The BART Determination Process IV. Statutory and Executive Order Reviews A. Executive Order 12866: Regulatory Planning and Review B. Paperwork Reduction Act 5 C. Regulatory Flexibility Act D. Unfunded Mandates Reform Act E. Executive Order 13132: Federalism F. Executive Order 13175: Consultation and Coordination with Indian Tribal Governments G. Executive Order 13045: Protection of Children from Environmental Health Risks and Safety Risks H. Executive Order 13211: Actions That Significantly Affect Energy Supply, Distribution, or Use. I. National Technology Transfer Advancement Act J. Executive Order 12898: Federal Actions to Address Environmental Justice in Minority Populations and Low Income Populations I. Overview of Today's Actions Today's rulemaking provides the following changes to the regional haze regulations:

( 1) revised regulatory text in response to the American Corn Growers court's remand, to require that the BART determination include an analysis of the degree of visibility improvement resulting from the use of control technology at each source subject to BART,

( 2) revised regulatory text in 40 CFR 51.308( b) and deletion of 40 CFR 51.308( c) Options for regional planning in response to Congressional legislation amending the deadlines for submittal of regional haze implementation plans. This provision had provided for an alternative process for States to submit regional haze implementation plans in attainment areas,

( 3) BART guidelines, contained in a new Appendix Y to 40 CFR part 51, 6 ( 4) new and revised regulatory text, to be added to 40 CFR 51.308( e), to require the use of Appendix Y in establishing BART emission limits, and ( 5) revised regulatory language at 51.302 to clarify the relationship between New Source Performance Standards ( NSPS) and BART for reasonably attributable visibility impairment.

How This Preamble Is Structured. Section II provides background on the Clean Air Act ( CAA) BART requirements as codified in the regional haze rule, on the D. C. Circuit Court decision which remanded parts of the rule, and on the April 2004 reproposal responding to the remand. Section III discusses specific issues in the BART guidelines in more detail, including background on each issue, major comments we received on the July 2001 proposal and May 2004 reproposal, and our responses to those comments. Section IV provides a discussion of how this rulemaking complies with the requirements of Statutory and Executive Order Reviews.

II. Background The Regional Haze Rule In 1999, we published a final rule to address a type of visibility impairment known as regional haze ( 64 FR 35714;

July 1, 1999). The regional haze rule requires States to submit implementation plans ( SIPs) to address regional haze visibility impairment in 156 Federally protected parks and 1 See, e. g. CAA Section 169A( a)( 1).

7 wilderness areas. These 156 scenic areas are called " mandatory Class I Federal areas" in the Clean Air Act ( CAA), 1 but are referred to simply as " Class I areas" in today's rulemaking. The 1999 rule was issued to fulfill a long standing EPA commitment to address regional haze under the authority and requirements of sections 169A and 169B of the CAA.

As required by the CAA, we included in the final regional haze rule a requirement for BART for certain large stationary sources that were put in place between 1962 and 1977. We discussed these requirements in detail in the preamble to the final rule ( 64 FR 35737 35743). The regulatory requirements for BART were codified at 40 CFR 51.308( e), and in definitions that appear in 40 CFR 51.301.

The CAA, in sections 169A( b)( 2)( A) and in 169A( g)( 7),

uses the term " major stationary source" to describe those sources that are the focus of the BART requirement. To avoid confusion with other CAA requirements which also use the term " major stationary source" to refer to a somewhat different population of sources, the regional haze rule uses the term " BART eligible source" to describe these sources.

The BART eligible sources are those sources which have the potential to emit 250 tons or more of a visibility impairing 8 air pollutant, were put in place between August 7, 1962 and August 7, 1977, and whose operations fall within one or more of 26 specifically listed source categories. Under the CAA,

BART is required for any BART eligible source which " emits any air pollutant which may reasonably be anticipated to cause or contribute to any impairment of visibility in any such area." Accordingly, for stationary sources meeting these criteria, States must address the BART requirement when they develop their regional haze SIPs.

Section 169A( g)( 7) of the CAA requires that States must consider the following factors in making BART determinations:

( 1) the costs of compliance,

( 2) the energy and nonair quality environmental impacts of compliance,

( 3) any existing pollution control technology in use at the source,

( 4) the remaining useful life of the source, and ( 5) the degree of improvement in visibility which may reasonably be anticipated to result from the use of such technology.

These statutory factors for BART were codified at 40 CFR 51.308( e)( 1)( ii).

In the preamble to the regional haze rule, we committed to issuing further guidelines to clarify the requirements of 2 American Corn Growers et al. v. EPA, 291 F. 3d 1 ( 2002).

9 the BART provision. The purpose of this rulemaking is to fulfill this commitment by providing guidelines for States to use in identifying their BART eligible sources, in identifying which of those sources must undergo a detailed BART analysis ( i. e., which are " sources subject to BART"),

and in conducting the technical analyses of possible controls in light of the statutory factors listed above (" the BART determination").

American Corn Growers v. EPA In response to challenges to the regional haze rule by various petitioners, the D. C. Circuit in American Corn Growers2, issued a ruling striking down the regional haze rule in part, and upholding it in part. This section discusses the court's opinion in that case, as background for the discussion of specific changes to the regional haze rule and the BART guidelines presented in the next two sections, respectively.

We explained in the preamble to the 1999 regional haze rule that the BART requirements in section 169A( b)( 2)( A) of the CAA demonstrate Congress' intent to focus attention directly on the problem of pollution from a specific set of existing sources ( 64 FR 35737). The CAA requires that any of these existing sources " which, as determined by the 3 CAA Sections 169A( b)( 2) & ( g)( 7).

10 State, emits any air pollutant which may reasonably be anticipated to cause or contribute to any impairment of visibility [ in a Class I area]," shall install the best available retrofit technology for controlling emissions. 3 In determining BART, the CAA requires the State to consider several factors that are set forth in section 169( g)( 2) of the CAA, including the degree of improvement in visibility which may reasonably result from the use of such technology.

The regional haze rule addresses visibility impairment resulting from emissions from a multitude of sources located across a wide geographic area. Because the problem of regional haze is caused in large part by the long range transport of emissions from multiple sources, and for certain technical and other reasons explained in that rulemaking, we had adopted an approach that required States to look at the contribution of all BART sources to the problem of regional haze in determining both applicability and the appropriate level of control. Specifically, we had concluded that if a source potentially subject to BART is located within an upwind area from which pollutants may be transported downwind to a Class I area, that source " may reasonably be anticipated to cause or contribute" to visibility impairment in the Class I area. Similarly, we 4 See 66 FR 35737 35743 for a discussion of the rationale for the BART requirements in the 1999 regional haze rule.

11 had also concluded that in weighing the factors set forth in the statute for determining BART, the States should consider the collective impact of BART sources on visibility. In particular, in considering the degree of visibility improvement that could reasonably be anticipated to result from the use of such technology, we stated that the State should consider the degree of improvement in visibility that would result from the cumulative impact of applying controls to all sources subject to BART. We had concluded that the States should use this analysis to determine the appropriate BART emission limitations for specific sources. 4 In American Corn Growers v. EPA, industry petitioners challenged EPA's interpretation of both these aspects of the BART determination process and raised other challenges to the rule. While rejecting industry's other challenges, the court in American Corn Growers concluded that the BART provisions in the 1999 regional haze rule were inconsistent with the provisions in the CAA " giving the states broad authority over BART determinations." 291 F. 3d at 8. Specifically, with respect to the test for determining whether a source is subject to BART, the court held that the method that we had prescribed for determining which eligible sources are subject to BART illegally 12 constrained the authority Congress had conferred on the States. Id. However, the court expressly declined to hold that the general collective contribution approach to determining BART applicability was necessarily inconsistent with the CAA, were it not for the infringement on State authority. Id. at 9. Rather, the court stated that the collective contribution approach may have been acceptable if EPA had allowed for a State exemption process based on an individualized contribution determination. Id. at 12.

The court in American Corn Growers also found that our interpretation of the CAA requiring the States to consider the degree of improvement in visibility that would result from the cumulative impact of applying controls in determining BART was inconsistent with the language of the Act. 291 F. 3d at 8. Based on its review of the statute,

the court concluded that the five statutory factors in section 169A( g)( 2) " were meant to be considered together by the states." Id. at 6.

Changes in Response to American Corn Growers Today's rule responds to the American Corn Growers court's decision on the BART provisions by including changes to the regional haze rule at 40 CFR 51.308, and by finalizing changes to the BART guidelines. This section outlines the changes to the regional haze rule due to the court's remand. It also explains the minor change we are 13 making to the section of the regulation governing the use of the 1980 BART guidelines when conducting BART analyses for certain power plants for reasonably attributable ( i. e.,

localized) visibility impairment.

1. Determination of Which Sources are Subject to BART Today's action addresses the American Corn Growers court's vacature of the requirement in the regional haze rule requiring States to assess visibility impacts on a cumulative basis in determining which sources are subject to BART. Because this requirement was found only in the preamble to the 1999 regional haze rule ( see 291 F. 3rd at 6,

citing 64 FR 35741), no changes to the regulations are required. Instead, this issue is addressed in the BART guidelines, which provide States with processes for determining which BART eligible sources " may reasonably be anticipated to cause or contribute to any impairment of visibility in any mandatory Class I Federal area." These processes has been designed to address the holding of American Corn Growers by eliminating the previous constraint on State discretion, as explained in further detail in sections II. D. and III below.

2. Consideration of Anticipated Visibility Improvements in BART Determinations Pursuant to the remand in American Corn Growers, we are amending the regional haze rule to require the States to 14 consider the degree of visibility improvement resulting from a source's installation and operation of retrofit technology, along with the other statutory factors set out in CAA section 169A( g)( 2), when making a BART determination.

This would be accomplished by listing the visibility improvement factor with the other statutory BART determination factors in section 308( e)( 1)( A), so that States will be required to consider all five factors,

including visibility impacts, on an individual source basis when making each individual source BART determination.

Center for Energy and Economic Development v. EPA After the May 2004 reproposal of the BART guidelines,

the D. C. Circuit decided another case where BART provisions were at issue, Center for Energy and Economic Development v.

EPA, No. 03 1222,( D. C. Cir. Feb. 18, 2005)(" CEED"). In this case, the court granted a petition challenging provisions of the regional haze rule governing the optional emissions trading program for certain western States and Tribes ( the " WRAP Annex Rule").

The court in CEED affirmed our interpretation of CAA 169A( b)( 2) as allowing for non BART alternatives where those alternatives are demonstrated to make greater progress than BART. ( CEED, slip. op. at 13). The court, however, took issue with provisions of the regional haze rule governing 15 the methodology of that demonstration. Specifically, 40 CFR 51.308( e)( 2) required that visibility improvements under source specific BART   the benchmark for comparison to the alternative program   must be estimated based on the application of BART controls to all sources subject to BART.

( This section was incorporated into the WRAP Annex rule by reference at 40 CFR 51.309( f)). The court held that we could not require this type of group BART approach   vacated in American Corn Growers in a source specific BART context   even in a program in which State participation was wholly optional.

The BART Guidelines as proposed in May 2004 contained a section offering guidance to States choosing to address their BART eligible sources under the alternative strategy provided for in 40 CFR 51.308( e)( 2). This guidance included criteria for demonstrating that the alternative program achieves greater progress towards eliminating visibility impairment than would BART.

In light of the D. C. Circuit's decision in CEED, and the consequent need to revise § 308( e)( 2), we are removing the section of the BART guidelines addressing alternative programs from today's rulemaking. We remain committed to providing States with the flexibility to address BART through alternative means   and we note again that our authority to do so was upheld in CEED. Therefore we intend 5 http:// www. epa. gov/ cair/ pdfs/ cair_ final_ preamble. pdf.

6 " Demonstration that CAIR Satisfies the ' Better than BART' Test As proposed in the Guidelines for Making BART Determinations," at http:// www. epa. gov/ cair/ pdfs/ finaltech04. pdf.

16 to revise the provisions of the regional haze rule governing such alternatives, and provide any additional guidance needed, in a subsequent rulemaking conducted as expeditiously as practicable.

Relationship between BART and the Clean Air Interstate Rule ( CAIR)

On March 10, 2005, EPA issued the Clean Air Interstate Rule ( CAIR), requiring reductions in emissions of SO2 and NOx in 28 eastern States and the District of Columbia. When fully implemented, CAIR will reduce SO2 emissions in these states by over 70 percent and NOx emissions by over 60 percent from 2003 levels. The CAIR imposes specified emissions reduction requirements on each affected State, and establishes an EPA administered cap and trade program for EGUs in which States may participate as a means to meet these requirements. This section gives a brief overview of the relationship between BART and the CAIR, in those States to which the CAIR applies. For a more thorough discussion,

see section IX. C of the CAIR preamble5 and the associated Technical Support Document. 6 17 In the CAIR Notice of Proposed Rulemaking ( SNPR), we proposed that States which adopt the CAIR cap and trade program for SO2 and NOx would be allowed to treat the participation of EGUs in this program as a substitute for the application of BART controls for these pollutants to affected EGUs. ( See 69 FR 32684, 32702 707, June 10, 2004).

We presented emissions and air quality modeling results which demonstrated that the CAIR would achieve greater emission reductions and greater visibility improvement than would BART. The emissions modeling was based on the application of the 2004 proposed presumptive BART control levels to BART eligible EGUs. Using this modeling, we applied the proposed test ( also contained in the 2004 proposed BART Guidelines) for determining whether a trading program or other alternative method achieves greater reasonable progress than BART and can therefore be used in lieu of BART. ( This is referred to in shorthand as the " better than BART" test. In brief, the test requires that the alternative program does not result in visibility degradation at any Class I area, and achieves a greater overall improvement in visibility, on average, at all affected Class I areas).

We noted that, based on this preliminary analysis, it appeared that CAIR would pass this " better than BART" test and therefore be an acceptable alternative to BART for SO2 7 Specifically, in the SNPR analysis, controls were " required" ( i. e., assumed by the model) for BART eligible EGUs greater than 250 MW capacity, for both NOx and SO2. In the NFR, BART controls were assumed for SO2 for all BARTeligible EGU units greater than 100 MW, and NOx controls for all BART eligible EGU units greater than 25 MW.

18 and NOx at EGUs in affected States. However, we also noted that because the emissions scenarios available at that time were developed for other purposes, they did not precisely match the geographic scope of CAIR reductions as proposed,

and did not account for the fact that BART would continue to be in effect outside of the CAIR region. We therefore committed to refining the analysis for the final rule.

In the CAIR Notice of Final Rulemaking ( NFR), we presented and discussed that refined analysis. The analysis was improved from the SNPR version by: correcting the geographic distribution of Nox and SO2 emission reduction requirements to reflect those contained in the proposal;

increasing the number of Class I areas represented from 44 to 116; adding a scenario consisting of CAIR reductions in the CAIR affected States plus BART reductions in the remaining States ( excluding Alaska and Hawaii); and improving the BART control assumptions by increasing the number of BART eligible units included. 7 As in the SNPR,

the analysis examined projected improvements on both the 20%

worst ( most impaired) days and the 20% best ( least impaired)

days. 19 This updated visibility analysis reaffirmed that under the proposed two pronged test, CAIR controls are " better than BART" for EGUs. The modeling predicts that the CAIR cap and trade program will not result in degradation of visibility at any of the 116 Class I areas considered. With respect to the proposed requirement for greater

averageimprovement the modeling indicated that the CAIR emissions reductions in the east produce significantly greater visibility improvements than source specific BART.

Specifically, for the 29 eastern Class I areas analyzed, the average visibility improvement, on the 20 percent worst days, expected solely as a result of the CAIR applied in the East and BART applied in the West is 1.6 dv, as compared to the average degree of improvement predicted for nationwide source specific BART of 0.7 dv.

Similarly, on a national basis, the visibility modeling showed that for all 116 Class I areas evaluated, the average visibility improvement, on the 20 percent worst days, in 2015 was 0.5 dv under the CAIR cap and trade program in the east and BART in the west, but only 0.2 deciviews under the nationwide source specific BART approach.

The modeling showed similar results for the 20 percent best visibility days, although there is less visibility improvement on the best days compared to the worst days.

For the 29 eastern Class I areas analyzed, the average 20 visibility improvement, on the 20 percent best days,

expected solely as result of the CAIR applied in the east and BART applied in the west is 0.4 dv, as compared to the average degree of improvement predicted for nationwide source specific BART of 0.2 dv. On a national basis, the visibility modeling showed that for all 116 class I areas evaluated, the average visibility improvement, on the 20 percent best days, in 2015 was 0.1 dv under both the CAIR cap and trade program in the east and BART in the west, and under the nationwide source specific BART approach.

Despite this demonstration, we concluded that it was premature to make a final determination regarding the sufficiency of the CAIR as a BART alternative, primarily because ( 1) the guidelines for source specific BART determinations in response to American Corn Growers had not been finalized, and ( 2) there was now a need to revise the Regional Haze Rule and the guidelines for BART alternative programs in response to the recently decided case of CEED v.

EPA. We noted that the source specific BART guidelines would be finalized on or before April 15, 2005, and that further rule changes controlling BART alternative programs would be proposed soon thereafter, in order to revise the portions of the regional haze rule invalidated by CEED v.

EPA. 21 Today's action finalizes the source specific BART guidelines under regional haze rule section 308( e)( 1). We remain committed to conducting a separate rule making in the near future to revise section 308( e)( 2) and establish criteria for determining whether alternative programs may substitute for BART, in accordance with the decision in CEED v. EPA. As we also noted in the CAIR, we can foresee no circumstances under which BART for EGUs could produce greater visibility improvement than the CAIR, but we must continue to defer a final determination until an analysis can be conducted under the provisions established by this subsequent rule making.

Overview of The BART Process The process of establishing BART emission limitations can be logically broken down into three steps: First,

States identify those sources which meet the definition of " BART eligible source" set forth in 40 CFR 51.301. Second,

States determine whether such sources " emit[] any air pollutant which may reasonably be anticipated to cause or contribute to any impairment of visibility [ in a Class I area.]" A source which fits this description is " subject to BART." Third, for each source subject to BART, States then identify the appropriate type and the level of control for reducing emissions.

Identifying BART eligible sources 22 The CAA defines BART eligible sources as those sources which fall within one of 26 specific source categories, were built during the 15 year window of time from 1962 to 1977,

and have potential emissions greater than 250 tons per year.

The remand did not address the step of identifying BARTeligible sources, which is conceptually the simplest of the three steps.

Sources reasonably anticipated to cause or contribute to visibility impairment ( sources subject to BART)

As we noted in the preamble to the 1999 regional haze rule, defining the individual contributions of specific sources of the problem of regional haze can be timeconsuming and expensive. Moreover, Congress established a very low threshold in the CAA for determining whether a source is subject to BART. We are accordingly finalizing several approaches for States for making the determination of whether a source " emits any pollutants which may reasonably be anticipated to cause or contribute to any visibility impairment." The first two of these approaches would allow States to avoid undertaking unnecessary and costly studies of an individual source's contribution to haze by allowing States to adopt more streamlined processes for determining whether, or which, BART eligible sources are subject to BART. 8 64 FR 335740, July 1, 1999. The regional haze rule discusses at length why we believe that States should draw this conclusion. 64 FR 35739 40.

23 In 1999, we adopted an applicability test that looked to the collective contribution of emissions from an area.

In particular, we stated that if " a State should find that a BART eligible source is ` reasonably anticipated to cause or contribute' to regional haze if it can be shown that the source emits pollutants within a geographic area from which pollutants can be emitted and transported downwind to a Class I area." 8 States have the discretion to consider that all BART eligible sources within the State are " reasonably anticipated to cause or contribute" to some degree of visibility impairment in a Class I area.

This option is consistent with the American Corn Growers court's decision. As previously noted, the court's concern with our original approach governing BART applicability determinations was that it would have " tie[ d]

the states' hands and force[ d] them to require BART controls at sources without any empirical evidence of the particular source's contribution to visibility impairment." 291 F. 3d at 8. By the same rationale, we believe it would be an impermissible constraint of State authority to force States to conduct individualized analysis in order to determine that a BART eligible source " emits any air pollutant which 9 CAA § 169A( b)( 2)( A).

10 See 64 FR 35714, 35721. See also July 29, 1997 memorandum to the regional haze docket A 95 38, " Supporting Information for Proposed Applicability of Regional Haze Regulations," by Richard Damberg, EPA, Office of Air Quality Planning and Standards.

24 may reasonably be anticipated to cause or contribute to any impairment of visibility in any [ Class I] area." 9 In this respect, we believe that it is important to note that the court in American Corn Growers expressly declined to hold that consideration of visibility impact on a cumulative basis would be invalid in all circumstances. 291 F. 3d at 9.

Given the court's emphasis on the importance of the role of the States in making BART determinations, we believe that a State's decision to use a cumulative analysis at the eligibility stage would be consistent with the CAA and the findings of the D. C. Circuit.

We believe there is ample technical evidence supporting a finding by a State that all BART eligible sources within the State are subject to BART, without further analysis at that stage in the process. 10 Any potential for inequity towards sources would be addressed at the BART determination stage, which contains an individualized consideration of a source's contribution in establishing BART emission limits. 25 States also have the option of performing an analysis to show that the full group of BART eligible sources in a State cumulatively do not cause or contribute to any visibility impairment in Class I areas. We anticipate that in most, if not all States, the BART eligible sources are likely to cause or contribute to some visibility impairment in Class I areas. However, it is possible that using a cumulative approach, a State could show that its BART sources do not collectively pose a measurable problem.

Finally, States may consider the individualized contribution of a BART eligible source to determine whether a specific source is subject to BART. Specifically, States may choose to undertake an analysis of each BART eligible source in the State in considering whether each such source meets the test set forth in the CAA of " emit[ ting] any air pollutant which may reasonably be anticipated to cause or contribute to any impairment of visibility in any [ Class I]

area." Alternatively, States may choose to presume that all BART eligible sources within the State meet this applicability test, but provide sources with the ability to demonstrate on a case by case basis that this is not the case. This approach is consistent with the D. C. Circuit's statement that a collective contribution approach may be appropriate so long as the States are allowed to exempt 26 sources on the basis of an individualized contribution determination. 291 F. 3d at 8.

For assessing the impact of BART eligible sources on nearby Class I areas, we are including a process whereby the States would use an air quality model able to estimate a single source's contribution to visibility impairment.

States may also choose to use other, less resource intensive methods of assessing a source's individualized contribution to regional haze visibility impairment.

The BART determination The State must determine the appropriate level of BART control for each source subject to BART. Section 169A( g)( 7)

of the CAA requires States to consider the following factors in making BART determinations: ( 1) the costs of compliance,

( 2) the energy and nonair quality environmental impacts of compliance, ( 3) any existing pollution control technology in use at the source, ( 4) the remaining useful life of the source, and ( 5) the degree of improvement in visibility which may reasonably be anticipated to result from the use of such technology. The remand did not address the first four steps of the BART determination. The remand did address the final step, mandating that we must provide a way for States to take into account the degree of improvement in visibility that would result from imposition of BART on each individual source. 27 The first four factors are somewhat similar to the engineering analysis in the original BART guidelines proposed in 2001 and reproposed in 2004. The BART guidelines also contains a detailed discussion of available and cost effective controls for reducing SO2 and nitrogen oxides ( NOx) emissions from large coal fired electric generating units ( EGUs).

For assessing the fifth factor, the degree of improvement in visibility from various BART control options,

the States may run CALPUFF or another EPA approved model to predict visibility impacts. Scenarios would be run for the pre controlled and post controlled emission rates for each of the BART control options under review. The maximum hourly emission rates would be modeled for a period of three or five years of meteorological data. States have the flexibility to develop their own methods to evaluate model results.

III. Detailed Discussion of the Final BART Guidelines A. Introduction In this section of the preamble, we discuss changes or clarifications to the reproposed BART guidelines. Where relevant, we also respond to comments received during the comment period on the 2001 proposal. For each provision of the guidelines that we are changing or clarifying, we provide discussion of, as appropriate: 28   background information,

  how the provision was addressed in the May 2004 reproposal ( and in the 2001 proposal, if different from the reproposal),

 a summary of comments received on the provision,

either from the May 2004 reproposal, from the July 2001 proposal, or from both, and  the changes or clarifications that we are finalizing and the reasons for these changes or clarifications.

B. Scope of the Rule   Whether to Require States to follow the Guidelines for All BART Sources Background. Section 169A( b)( 1) of the CAA requires EPA to issue regulations to provide guidelines to States on the implementation of the visibility program. In addition, the last sentence of section 169A( b) states:

In the case of a fossil fuel fired generating powerplant having a capacity in excess of 750 megawatts, the emission limitations required under this paragraph shall be determined pursuant to guidelines, promulgated by the Administrator under paragraph ( 1).

This statutory requirement clearly requires us to promulgate BART guidelines that the States must follow in establishing BART emission limitations for power plants with a total capacity exceeding the 750 megawatt cutoff. The 29 statute is less clear regarding the import of the guidelines for sources other than 750 megawatt power plants.

Proposed rules. Both the 2001 proposal and the 2004 reproposal included a requirement for States to follow the procedures set out in the guidelines in determining BART for sources in all of the 26 listed BART categories. The 2001 proposal requested comment on whether the regional haze rule should: ( 1) require the use of the guidelines only for 750 megawatt utilities, with the guidelines applying as guidance for the remaining categories, or ( 2) require the use of the guidelines for all of the affected source categories.

Comments. We received comments on this issue in both 2001 and 2004. Comments varied widely on whether we can or should require the use of the guidelines for all of the affected source categories.

Comments from State, local and tribal air quality agencies generally supported our proposal to require the use of the guidelines for all of the source categories. These comments cited a need for national consistency in the application of the BART requirement across the source categories, and from State to State. One State agency commenter questioned our legal authority to require the use of the guidelines for all source categories; and several State agency commenters, while supporting the proposal,

requested that we provide clarification of the legal 30 authority for requiring the States to use the guidelines in establishing BART emission limitations for all categories.

Comments from the utility industry, from various manufacturing trade groups, and from individual companies were critical of the proposal to require States to follow the guidelines generally. Many commenters also argued that EPA lacked the authority to issue guidelines for any industrial category other than 750 megawatt powerplants,

whether the use of such guidelines were mandatory or not.

Other commenters stated that the language in the CAA clearly restricts the scope of mandatory guidelines to larger powerplants. The commenters cited the legislative history of the 1977 Clean Air Act amendments in support of this position, and frequently claimed that requiring the guidelines for all 26 categories of sources would deprive States of flexibility in implementing the program.

Comments from environmental organizations and the general public supported the approach in the proposed rule and stated that EPA is obligated to establish regional haze BART guidelines by rulemaking for all 26 categories of stationary sources. Environmental organization comments noted that while Congress expressed a particular concern for 750 MW powerplants, this added emphasis on one sector does not change requirements in the Act for all BART eligible sources. Accordingly, these commenters believed that we 31 should not construe a special emphasis on powerplants as a restriction on our authority to require use of the guidelines for all categories.

Final rule. The CAA and the relevant legislative history make clear that EPA has the authority and obligation to publish mandatory guidelines for powerplants exceeding 750 megawatts. As previously noted, Congress in section 169A( b) of the CAA expressly provided that emission limitations for powerplants larger than 750 megawatts " shall be determined pursuant to guidelines promulgated by the Administrator." ( Emphasis added). This unambiguous language leaves little room to dispute that the guidelines EPA is required to promulgate must be used by States when making BART determinations for this class of sources.

Having carefully considered the comments and further reviewed the CAA and the legislative history, we have concluded that it would not be appropriate for EPA to require States to use the guidelines in making BART determinations for other categories of sources. The better reading of the Act indicates that Congress intended the guidelines to be mandatory only with respect to 750 megawatt powerplants. Thus, while we agree with the State agency comments noting the strong policy reasons in support of covering all categories in order to establish consistency across States in how BART determinations are made, we are 32 not requiring States to use the BART guideline for these other categories. In response to State concerns about equitable application of the BART requirement to source owners with similar sources in different states, we do encourage States to follow the guidelines for all source categories but are not requiring States to do so. States should view the guidelines as guidance for these other categories.

We disagree with comments that the CAA and the legislative history prohibit us from issuing guidance for other source categories. As the guidelines make clear,

States are not required to follow the approach in the guidelines for sources other than 750 megawatt powerplants.

As such, although we believe that the guidelines provide useful advice in implementing the BART provisions of the regional haze rule, we do not believe that they hamper State discretion in making BART determinations.

C. How to Identify BART eligible Sources Section II of the BART guidelines contains a step

bystep process for identifying stiationary sources that are " BART eligible" under the definitions in the regional haze rule. The four basic steps are:

Step 1: Identify the emission units in the BART categories 33 Step 2: Identify the start up dates of those emissin units Step 3: Compare the potential emissions from units identified in Steps 1 and 2 to the 250 ton/ year cutoff Step 4: Identify the emission units and pollutants that constitute the BART eligible source.

In this section of the preamble, we discuss some of the comments we received on the steps in this process, and any changes we are making in light of those comments.

Step 1: Identify the emission units in the BART categories The BART guidelines list the 26 source categories that the CAA uses to describe the types of stationary sources that are BART eligible. Both proposals clarified the descriptions of particular source categories.

Comments. The final rule addresses comments on the following source categories. Some comments discussed below were submitted in response to the 2001 propoosal and were not addressed in the reproposal; other comments were submitted in response to the reproposal in 2004.

( 1) " Charcoal production facilities." We received comments in 2001 from two industry trade groups requesting that the final guidelines explicitly exclude " low emission"

charcoal production facilities from BART. These comments cited a 1975 study considered by Congress in development of the BART category list in the 1977 CAA amendments. This 34 1975 study noted that some charcoal production facilities have much higher emissions factors ( i. e., 352 pounds of PM per ton of charcoal produced versus 20 to 25 pounds of PM per ton of charcoal produced). Accordingly, the comments asserted that the intent of Congress in the 1977 CAA amendments was to provide incentives for higher emitting facilities to reduce their emissions, rather than to make the entire category BART eligible.

( 2) " Chemical process plants." In 2001 a trade group representing the pharmaceutical industry requested that we determine in the guidelines that the term " chemical process plants" does not include pharmaceutical plants.

( 3) " Primary aluminum ore reduction." Comments from the aluminum industry in 2001 noted that not all emissions units at these facilities are necessarily involved in " primary ore reduction." Thus, the comments recommended that we clarify that contiguous sources that are not related to primary aluminum ore reduction, such as fabricating facilities and ingot operations, are not BART eligible.

Further, the comments recommended that we use definitions in the NSPS for primary aluminum plants to describe the BARTeligible emissions units.

( 4) " Fossil fuel fired steam electric plants of more than 250 million Btu/ hour heat input." The 2004 reproposal contained the clarification, requested by commenters, that 35 this source category refers only to those fossil fuel fired steam electric plants that generate electricity for sale.

One commenter objected to this clarification on the basis that emissions from co generators would be excluded; many other commenters supported the clarification. Another commenter requested that we also clarify that this category includes only those steam electric plants that burn greater than 50 percent fossil fuel, in order to be consistent with the definition of fossil fuel boilers proposed in the guidelines. Other commenters requested that we clarify whether the definition includes units which are located at a steam electric plant, but which themselves are not in any of the 26 BART source categories, such as simple cycle turbines, emergency diesel engines, and reciprocating internal combustion engines ( RICE).

Several commenters opined that the category should exclude combined cycle units with heat recovery steam generators that lack auxiliary firing, arguing that these units should count as simple cycle turbines. These commenters pointed to other EPA regulatory programs that treat combined cycle units with supplemental firing differently from combined cycle units without supplemental firing. They argued that we should only consider a combined cycle unit to be a " steam electric plant" if it has supplemental firing. 36 ( 5) " Fossil fuel boilers of more than 250 million Btu/ hour heat input." The 2004 reproposal clarified that this category should be read as including only those boilers individually greater than 250 million Btu/ hour heat input.

We received many comments on this interpretation, both in favor and opposed. Those favoring this interpretation ( generally industry commenters) cited the implementation burden that including smaller boilers would pose, the high cost effectiveness of controlling smaller boilers, and the relatively smaller impact on regional haze that smaller boilers would pose. They also noted that this interpretation is most consistent with definitions in the NOx SIP call and new source performance standards ( NSPS).

Commenters opposing this interpretation ( environmental groups, one state, and one regional planning organization)

noted that regarding all boilers, irrespective of size, as BART eligible so long as the aggregate heat input exceeds 250 million Btu/ hour is more consistent with the definition of stationary source under the Prevention of Significant Deterioration ( PSD) program. These commenters noted that under the CAA, BART and PSD are complementary programs aimed at regulating the same source categories; either one or the other applies depending upon when the source was constructed. 37 The 2004 reproposal also clarified that if a boiler smaller than 250 million Btu/ hour heat input is an integral part of an industrial process in a BART source category other than electric utilities, then the boiler should be considered part of the BART eligible source in that category. Under these circumstances, the boiler, as part of the BART eligible source, should be considered for emission control. Some commenters opposed this interpretation,

asserting that it would result in an " arbitrary and capricious" inconsistency, in that some smaller boilers would be BART eligible, and others would not. These commenters also noted that these boilers could be included in regional haze SIPs as necessary for making " reasonable progress" toward CAA visibility goals, even if they are not considered to be BART eligible.

Final rule. After considering the comments, we have made the following determinations on the definitions of the following source categories:

( 1) " Charcoal production facilities." We believe that in using the term " charcoal production facilities" Congress intended to encompass all types of charcoal production facilities. We do not agree with comments that any inferences can necessarily be made regarding the presence of different PM emission factors for different types of charcoal production facilities in the 1975 report. For 38 example, if Congress only intended to regulate a subset of the charcoal production industry, the we believe Congress could have easily indicated this in the source category title, as was done for " kraft pulp mills" and for " coal cleaning plants ( thermal dryers)." We also note that it is more likely that plants in the charcoal production industry with lower emission factors have emissions that are less than the 250 tons per year cutoff for BART eligibility.

( 2) " Chemical process plants." We believe that there is a clear precedent to include pharmaceutical manufacturing operations as " chemical process plants." In the standard industrial classification ( SIC) system, pharmaceutical operations are generally in SIC codes 2833 and 2834, which are a subset of 2 digit category 28 " Chemical and Allied products." Similarly, in the new North American Industrial Classification Codes ( NAICS), pharmaceutical manufacturing is codes 32541 and 32542, which is a subset of the " chemical manufacturing subsector" which is code 325. Accordingly,

in the PSD program, pharmaceutical plants have been treated as " chemical process plants." The commenter is correct in noting that EPA has consistently distinguished between chemical manufacturing and pharmaceutical manufacturing.

Examples where different standards or guidelines are established included control technique guideline ( CTG)

documents, NSPS standards under section 111 of the CAA, and, 39 most recently, maximum achievable control technology ( MACT)

standards under section 112 of the CAA. We do not agree that these differentiations for emissions standards necessarily require differentiation for purposes of determining BART eligibility. Therefore we believe pharmaceuticals should not be excluded from BART. However,

we expect that because of the MACT standards, there is a very low probability that BART determinations will lead to further control requirements from chemical production processes at pharmaceutical plants.

( 3) " Primary aluminum ore reduction." We agree with commenters that BART eligible units in this source category should be defined consistently with the NSPS definition for primary aluminum ore reduction. Therefore we have added a clarification to that effect in the final BART guidelines.

We note that this definition is also consistent with the definition at 40 CFR 63.840, which establishes applicability for this source category for the MACT program.

( 4) " Fossil fuel fired steam electric plants of more than 250 million Btu/ hour heat input." We have retained the clarification that this source category refers only to those fossil fuel fired steam electric plants that generate electricity for sale. We believe that this clarification helps to distinguish those plants that are electric utilities from plants in other industrial categories. We 40 also believe that while large co generators would be excluded from the fossil fuel fired steam electric plant source category, most large co generators will be BARTeligible under the fossil fuel fired boilers source category.

We do not believe it makes sense for this category to include only those steam electric plants that burn greater than 50 percent fossil fuel. We do not believe that a boiler should be excluded from BART review simply because it is located at a plant which burns less than 50 percent fossil fuel. Emissions from any such boiler could be a significant contributor to regional haze, and as such, we believe that each fossil fuel fired boiler merits a BART review.

We do wish to clarify that units which are located at a steam electric plant, but which themselves are not in any of the 26 BART source categories, should not be considered to be BART eligible units. We believe that Congress intended that BART review be focused on units in the source categories it delineated. This interepretation is most consistent with the definition of BART eligible source as we have explained it elsewhere in this preamble in reference to whether entire plants are included if only some units at the plant meet the statutory criteria. 11 See http:// www. epa. gov/ Region7/ programs/ artrd/ air/ nsr/ nsrmemos/ t urbines. pdf 41 Finally, we believe that all combined cycle units are included in the definition of fossil fuel fired steam electric plant, regardless of whether the combined cycle unit's heat recovery steam generator lacks auxilliary firing. Commenters are correct that some EPA programs have treated combined cycle units with supplemental firing differently from combined cycle units without supplemental firing. However, while some EPA programs do not consider a unit to be a combined cycle unit unless it contains supplemental firing, the definition at issue here is the definition of fossil fuel fired steam electric plant, not fossil fuel fired unit. The CAA defines both " stationary source" ( for visibility purposes) and " major emitting facility" ( for PSD purposes) to include " fossil fuel fired steam electric plants." In previous guidance for PSD, we have explained that combined cycle gas turbines do fall within the category of " fossil fuel fired steam electric plants." 11 ( 5) " Fossil fuel boilers of more than 250 million Btu/ hour heat input." We have decided to retain the interpretation that this category should be read as including only those boilers individually greater than 250 million Btu/ hour heat input. We agree with commenters who 42 noted that including smaller boilers would pose considerable implementation burden. As noted in the 2004 reproposal notice, we do not believe that this interpretation is likely to have a substantial impact. Because smaller boilers are generally less cost effective to control, we believe that BART review would be unlikely to result in a significant amount of control on these boilers.

We are also retaining the clarification that if a boiler smaller than 250 million Btu/ hour heat input is an integral part of an industrial process in a BART source category other than electric utilities, then the boiler should be considered part of the BART eligible source in that category. ( By " integral to the process", we mean that the process uses any by product of the boiler. We have added this clarification to the definition in the BART guidelines.) We believe that if a State is already considering a BART eligible industrial process for control,

and a boiler is integrated into that process, it makes common sense not to prematurely rule out control options any of the emissions from that process as a whole. Including the boiler in consideration of control options for the process adds minimal additional burden while leaving maximum discretion to the State in determining BART for the process as a whole. 43 We are also clarifying today that we have determined that this category should include all individual boilers of greater than 250 million Btu/ hour heat input burning any amount of fossil fuel, as opposed to only those boilers that burn greater than 50 percent fossil fuel. We believe that it is quite possible that boilers of this size could contribute to regional haze in a Class I area, even if they burn less than 50 percent fossil fuel. Therefore we believe that each fossil fuel fired boiler merits a BART review and should not be prematurely ruled out.

Step 2: Identify the start up dates of those emission units.

Background. BART applies only to a major stationary source which " was in existence on August 7, 1977 but which has not been in operation for more than fifteen years as of such date." The visibility regulations define " in existence" and " in operation" in 40 CFR 51.301. Under these regulations, promulgated in 1980, " in existence" means that the owner or operator has obtained all necessary preconstruction approvals or permits . . . and either has ( 1) begun, or caused to begin, a continuous program of physical on site construction of the facility or ( 2)

entered into binding agreements or contractual obligations. 12 However, sources reconstructed after 1977, which reconstruction had gone through NSR/ PSD permitting, would not be BART eligible.

44 The term " in operation" means engaged in activity related to the primary design function of the source.

Step 2 also addresses the treatment of " reconstructions" and " modifications." Under the definition of BART eligible facility, sources which were in operation before 1962 but reconstructed during the 1962 to 1977 time period are treated as new sources as of the time of reconstruction. 12 The same policies and procedures for identifying reconstructed " affected facilities" under the NSPS are used to determine whether a source has been reconstructed for purposes of the BART requirements.

" Modifications" under the CAA refers to physical change or change in the method of operation at a source which has led to an increase in emissions. In the proposed BART guidelines, we stated that the best interpretation of the visibility provisions is that a modification to a source does not change an emission's unit construction date for purposes of BART applicability. We requested comment on an alternative interpretation that we believed would be more difficult to implement. Under this approach, sources built before 1962 but modified during the 1962 to 1977 time frame would be considered " new" at the time of modification. 45 Comments. We received comments in 2001 and 2004 on the discussion in the guideline of the term " in existence."

These comments were critical of our statement in the guidelines that sources which had " commenced construction,"

that is, those which had entered into binding contracts,

would be considered to be in existence, even if actual operations did not begin until after the August 7, 1977 cutoff date. These commenters asserted that Congress did not intend to treat a source as " existing" in 1977 if it was not yet built.

Other commenters interpreted the proposed guidelines as expanding the definition of BART eligible sources by requiring States to find that all emission units at a facility are BART eligible if one part of the facility was built within the 1962 1977 time period. Other comments did not suggest that we had already expanded the definition in the proposed guidelines, but did suggest that we should expand the definition in that way in the final guidelines.

Some commenters noted that there was a degree of confusion in the regulated community on whether the proposed guidelines were requiring BART for all units at a power plant, including those that were in operation before August 7, 1962, if these units are co located with one or more units that were put in place within the 1962 1977 time 46 period. These commenters requested that we clarify that such pre 1962 units would not be BART eligible.

Some commenters asserted that our proposed approach is unworkable, because the approach requires States to identify all emissions units put in place between the 1962 and 1977.

Some of these commenters asserted that Congress intended that BART would apply only if entire plants satisfy the statutory criteria. These comments suggested that BART should apply only if an entire plant that is one of the 26 listed source category types had been placed in operation at a discrete point within the 15 year time period for BART eligibility. These commenters asserted that our proposed guidelines, which involved the identification and aggregation of individual emission units within the 1962

1977 time period, were inconsistent with Congress' intent.

Other comments suggested that EPA could improve implementation of the program by covering discrete projects rather than individual emissions units. A few commenters suggested that for purposes of identifying such discrete projects, we consider using the term " process or production unit" that we used in hazardous air pollutant regulations under CAA section 112( g).

One commenter requested that the guidelines clarify that emissions from " linked" emission units should not be considered in determining BART eligibility. That is, even 47 if changes in emissions from one unit could affect the emissions from a " linked" unit that was not put in place within the 1962 1977 time period, that would not affect whether the " linked" unit was BART eligible. Another commenter suggested that the approach set forth in the guidelines for identifying BART eligible sources is inappropriate because the particular set of units identified as BART eligible will not necessarily " provide a reasonable and logical platform for the installation of controls."

Other commenters stated that facilities that had been modified after 1977 should not be included in the pool of sources subject to BART. Such facilities, it was argued,

already meet the BART requirements because of the controls installed to meet the requirements of PSD, NSR, or the NSPS.

Final rule. We disagree with the comments recommending that we interpret the term " in existence" to refer to sources that are in actual operation. The discussion of this term in Step 2 is based on the regulatory definition which has been in place since 1980. The guidelines reiterate this definition and provide examples of its application. Interpreting the term " in existence" as suggested by commenters would not be consistent with the plain language of the regulations.

In the 2001 and 2004 proposed guidelines, we noted that " the term ` in existence' means the same thing as the term 13 See CAA section 193.

48 ` commence construction' as that term is used in the PSD regulations." Commenters were critical of this statement,

claiming that EPA was unlawfully reinterpreting section 169A in the guidelines. The statement in Step 2 of guidelines,

however, is not a reinterpretation of the term " in existence," but merely a statement noting that the definitions used in the visibility regulations and the PSD regulations are essentially identical.

To the extent that commenters are claiming that the existing regulatory definition of " in existence" is unlawful, EPA's interpretation of this term in promulgating the 1980 regulations was a reasonable one. First, it is worth noting that the regulations adopting this interpretation of the term " in existence" were in effect in 1990 and implicitly endorsed by Congress in its 1990 amendments to the CAA. 13 Moreover, the definition at issue accurately reflects Congress' intent that the BART provision apply to sources which had been " grandfathered" from the new source review permit requirements in parts C and D of title I of the CAA. For all the above reasons, we are neither revising the regional haze regulations to change the definition of " in existence," nor adopting a strained interpretation of the regulation in the guidelines. 49 We agree with commenters that the definition of "

BARTeligible source" does not require States to find that all emission units at a facility are subject to the requirement of the BART provisions if only one part of the facility was built within the 1962 1977 time period. We received comments on this issue in 2001 and clarified in 2004 that the BART guidelines do not direct States to find that all boilers at a facility are BART eligible if one or more boilers at the facility were put in place during the relevant time period. Under Step 2 of the process for identifying BART eligible sources set out in the guidelines,

States are required to identify only those boilers that were put in place between 1962 and 1977. As explained in the preamble to the 2004 reproposed guidelines, only these boilers are potentially subject to BART.

We do not agree with those commenters claiming that Congress clearly intended to apply BART only if an " entire plant" was put into place between 1962 and 1977. Most of the BART source categories are broad descriptions types of industrial facilities such as " kraft pulp mills," " petroleum refineries" or " primary copper smelters." For such source categories, the implication of commenters' argument would that if any portion of the plant was in operation before August 7, 1962, then Congress intended to exempt the entire plant from BART. Such an interpretation is problematic and 50 inequitable. For example, under this approach BART would not apply if a company chose to expand its production by building a second production line at an existing line in 1965, but would apply if the same company chose to build the same equipment at a greenfield site. Under the approach set forth in the guidelines, such a production line would be treated similarly under either set of facts. We do not believe that either the plain language of the statute or the relevant legislative history indicate that Congress intended for major emitting sources of visibility impairing pollutants to be exempted from the BART requirements because a plant contains some emission units that began operation before 1962.

Also, we disagree with the comment 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.

We agree with the comments related to " linked" emission units. The comment appears to address whether emissions from the " linked" units are considered in determining BART eligibility. In the guidelines, we are focusing on only the 51 emissions units that were put in place during the 1962 to 1977 dates and the emissions from those units. We agree that even if changes in emissions from one unit could affect the emissions from a " linked" unit that was not put in place within the 1962 1977 time period, this would not affect whether the " linked" unit was BART eligible.

We disagree with commenters that the approach set forth in the guidelines for identifying BART eligible sources is inappropriate because the particular set of units identified as BART eligible will not necessarily " provide a reasonable and logical platform for the installation of controls." We do not agree that this factor is relevant to the identification of those emissions units which meet the definition of BART eligible source. Such factors are important in the States' consideration of control strategies and options but do not clearly relate to the first step of identifying those sources which fall within one of 26 source categories, were built during the 15 year window of time from 1962 to 1977, and have potential emissions of greater than 250 tons per year. We do thus agree generally with the commenter's recommendation of allowing States to consider the particular history and control potential of units in determining BART, but do not agree that it is relevant to the predicate question of identifying the BART eligible source. 52 Finally, the approach to identifying a " BART eligible source" in the guidelines is based on the definitions in the regional haze rule of the relevant terms. For 750 MW power plants, States are required to apply the definitions as set forth in the guidelines; for other sources, States may adopt a different approach to the task of identifying BARTeligible sources, so long as that approach is consistent with the Act and the implementing regulations. In other words, while the guidelines adopt an approach for large power plants which involves the aggregation of all emissions units put into place between 1962 and 1977, States have the flexibility to consider other reasonable approaches to the question of identifying BART eligible sources for other source categories.

For 750 MW power plants, many of the issues identified by commenters with the approach of looking at a facility on an emission unit by emission unit basis do not exist.

Unlike many types of industrial processes, power plants consist generally of a discrete number of very large emission units. For other types of facilities such as kraft pulp mills or chemical process plants which may have many small emission units that have undergone numerous changes,

the guidelines do not limit the ability of the States to approach the question of identifying BART eligible sources in ways which make sense for the particular sources given their design and history. 53 Step 3: Compare the potential emissions to the 250 ton/ yr cutoff.

Background. Step 3 of the guidelines addresses the question of whether the units identified in Steps 1 and 2 have emissions in excess of the threshold for major sources set forth in section 169A( g)( 7) of the CAA. The guidelines pose the following questions to help the States in determining whether the relevant emissions units have the potential to emit in excess of the 250 tons per year threshold of any single visibility impairing pollutant:

( 1) What pollutants should I address?

The 2001 proposed guidelines included the following list of visibility impairing pollutants: sulfur dioxide ( SO2), nitrogen oxides ( NOX), particulate matter, volatile organic compounds ( VOCs), and ammonia. We proposed in 2001 and again in 2004 that States use PM10 as the indicator for particulate matter. As explained in the guidelines, there is no need to have separate 250 ton thresholds for PM10 and PM2.5 because emissions of PM10 include the components of PM2.5 as a subset. In addition, because of various uncertainties associated with regulating VOCs and ammonia, we requested comment in 2004 on the level of discretion States should exercise in making BART determinations for VOCs and took ammonia off the list of visibility impairing pollutants. 54 In both proposals, we clarified that the 250 tons per year cutoff applies to emissions on a pollutant by pollutant basis. In other words, a source is subject to BART only if it emits at least 250 tons per year of an individual visibility impairing pollutant.

( 2) What does the term " potential" emissions mean?

The proposed guidelines in 2001 and the reproposed guidelines in 2004 excerpt the definition of " potential to emit" from the regulations at 40 CFR 51.301. As the definition makes clear, the potential to emit of a source is calculated based on its capacity to emit a pollutant taking into account its physical and operational design. Under this definition, federally enforceable emission limits may be taken into account in calculating a source's potential emissions; however, emission limitations which are enforceable only by state and local agencies, but not by EPA and citizens in Federal court, cannot be used to limit a source's potential to emit for purposes of the regional haze program.

( 3) What is a " stationary source?"

As explained above, States are required to make a BART determination only for " stationary sources" of a certain size that fall within one of 26 types of industrial categories listed in the statute and that were built within a certain time frame. The regional haze rule ( 64 FR 3714,

July 1, 1999) contains definitions that are relevant to the 55 determination of the emissions units that comprise a " stationary source." First, the regulations define " stationary source" as " any building, structure, facility,

or installation which emits or may emit any air pollutant."

Second, the terms " building, structure, or facility" are defined in part based on grouping pollutant emitting activities by industrial category:

Building, structure, or facility means all of the pollutant emitting activities which belong to the same industrial grouping, are located on one or more contiguous or adjacent properties, and are under the control of the same person ( or persons under common control). Pollutant emitting activities must be considered as part of the same industrial grouping if they belong to the same Major Group ( i. e., which have the same two digit code) as described in the Standard Industrial Classification Manual, 1972 as amended by the 1977 Supplement ( U. S. Government Printing Office stock numbers 4101 0066 and 003 005 00176 0 respectively).

In the 2001 proposed guideline, we noted that support facilities, i. e. facilities used to convey, store, or otherwise assist in the production of the principal product,

are considered to fall within the same industrial grouping 56 as the primary facility. To clarify this, in 2004 we proposed to add language to the guideline noting that emission units at a plant, even if they are a " support facility" for purposes of other programs, would not be subject to BART unless they were within one of the 26 listed source categories and were built within the 1962 to 1977 time frame.

Discussion of " what pollutants should I address?"

Comments. PM10 as an indicator. Some comments questioned the use of PM10 ( which includes both coarse and fine particulate matter) as the indicator for particulate matter. Commenters noted that the coarse fraction, that is particulate matter between 10 and 2.5 micrograms in diameter, fundamentally differs compared to the fine mass in how it interacts with light. Commenters suggested that only the fine mass ( PM2.5) component of particulate matter is likely to contribute to visibility impairment.

Accordingly, these commenters recommended that the 250 ton cutoff for particulate matter should be based upon emissions of PM2.5.

Ammonia. Many commenters addressed the exclusion of ammonia from the list of visibility impairing pollutants. A number of commenters, primarily from industry but also from one state and one regional planning organization, supported the exclusion of ammonia. These commenters generally cited 14 See http:// wrapair. org/ forums/ ioc/ meetings/ 030728/ index. html ( specifically presentation by John Vimont, National Park Service).

57 the complexity and variability of ammonia's role in the formation of PM2.5 in the atmosphere, the relative greater benefits of controlling NOx and SO2, the uncertainties in the inventory of ammonia emissions, and the inherent complexities of gauging the contribution of potential ammonia reductions to improving visibility in Class I areas.

In addition, commenters noted that few, if any, point sources emit ammonia in amounts that exceed the 250 ton per year threshold.

Other commenters, including a number of environmental groups and several states, regional planning organizations,

and industry commenters, argued that ammonia should be included in the list of visibility impairing pollutants in the guidelines. In support of this view, commenters cited evidence that ammonia is a known precursor to PM2.5. One commenter noted that improvements are being made to ammonia inventories and to the understanding of ammonia's role in the formation of haze. Other commenters pointed to a National Park Service ( NPS) analysis of monitoring data that indicates that visibility impairment due to nitrate aerosol formation ( to which ammonia contributes) is of significant concern14, and 2003 direction to policy makers from the North American Research Strategy for Tropospheric Ozone 15 NARSTO ( 2004) Particulate Matter Assessment for Policy Makers: A NARSTO Assessment. P. McMurry, M. Shepherd, and J. Vickery, eds. Cambridge University Press, Cambridge, England. ISBN 0 52 184287 5.

58 ( NARSTO) 15 indicating that consideration of control strategies needs to include ammonia in combination with other precursors to particle formation. Many commenters also argued that EPA should encourage or allow the States to consider ammonia in their visibility protection plans, and noted that ammonia reductions could be a cost effective way to improve visibility under certain conditions.

Volatile Organic Compounds ( VOCs). Several commenters responded to our request for comments on whether States should treat VOCs in urban areas differently from VOCs in rural areas. Environmental groups and a few States argued that the current state of scientific knowledge does not support a differentiation between urban and rural sources of VOCs. One environmental commenter cited evidence that organic aerosols are a major constituent of visibilityreducing aerosols and that VOCs are important precursors to the formation of secondary organic aerosols. One commenter also stated that VOCs may play a particularly significant role in particle formation in those rural areas with significant nearby sources of NOx. Commenters also cited evidence that the contribution of VOC to particle formation likely varies widely in different areas of the country, and 59 argued that States should retain flexibility to address local VOC sources if they determine that those sources are contributors of concern.

Several industry commenters stated that more focus should be placed on controlling VOCs in urban rather than rural areas. A few commenters from industry argued that VOCs in rural areas have not been shown to be a significant contributor to particle formation, and should be excluded from the list of pollutants to be addressed in the BART process. One argued that VOCs should be excluded from BART entirely based upon uncertainties in the current state of knowledge, and a few argued that VOCs from both power plants and rural sources should be excluded from BART, based on low emissions and the cost of controls. One regional planning organization requested that EPA clarify the definitions of " urban" and " rural" areas.

Final rule. PM10 as an indicator. The guideline continues to recommend that States use PM10 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; wWhile we agree with commenters who stated that the coarse fraction is less efficient at light scattering than fine particles, there is ample evidence that the coarse fraction does contribute to 16 See Fine particles: Overview of Atmospheric Chemistry, Sources of Emissions, and Ambient Monitoring Data, Memorandum to Docket OAR 2002 0076, April 1, 2005.

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

18 Grand Canyon Visibility Transport Commission, Recommendations for Improving Western Vistas, Report to the U. S. EPA, June 10, 1996.

60 visibility impairment. 16 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. 17 We do recognize that coarse PM is likely to contribute more to regional haze in arid areas than humid areas. Thus, wWe believe that, as the Grand Canyon Visibility Transport Commission ( GCTVC) recognized, 18 States in the arid West, in particular, shouldwill need to take the coarse fraction of particulate matter into account in determining whether a source meets the threshold for BART applicability. More humid Eastern states may not need to account for the coarse fraction for purposes of regional haze.

However, bBecause 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 PM2.5 fraction of direct particulate emissions as correctly as possible. In addition, we believe that air 19 Fine particles: Overview of Source Testing Approaches, Memorandum to Docket OAR 2002 0076, April 1, 2005.

61 quality modeling results will be more meaningful if the inputs account for the relative particle size of directly emitted particulate matter ( e. g. PM10 vs. PM2.5).

The acceptability of existing stationary source test methods for regional haze SIPs depends upon what is measured under your current test methods for particulate matter.

YourStates will need to take care to consider whether their current test methods for measuring particulate matter emissions from stationary sources may not be acceptable for regional haze SIP purposes if these methods ignore account for the condensible fraction of particulate matter, and consider revising. 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 you 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. 19 Ammonia. In regard to ammonia, we believe there is sufficient uncertainty about emission inventories and about the potential efficacy of control measures from location to 20 See Fine particles: Overview of Atmospheric Chemistry, Sources of Emissions, and Ambient Monitoring Data, Memorandum to Docket OAR 2002 0076, April 1, 2005.

62 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; 20 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 BARTeligible Thus, while we believe ammonia can contribute to visibility impairment, the decision whether to consider 21 Ibid.

63 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.

VOCs. 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 PM2.5 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. 21 However, while significant progress has been 22 Ibid.

64 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 PM2.5 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 PM2.5 formation, States may also wish to exercise discretion 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 East22 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 65 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.

Discussion of the term " potential" emissions.

Comments. A number of commenters were critical of the restriction in the regional haze rule that allows States to credit federally enforceable limitations on emissions but not limitations that are enforceable only by States and local agencies. These commenters believed that this restriction had been rejected by the D. C. circuit court for a number of other EPA regulations and noted that EPA has developed policies that currently credit state enforceable limits. The comments recommended that EPA issue guidance consistent with what commenters claimed were current policies for other regulations. In addition, we received comments arguing that in determining whether a source is a major stationary source, the States should consider a source's actual  rather than potential  emissions. These commenters stated that using a source's potential emissions overstates a source's actual emissions and impacts on visibility. 66 Final rule. 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 BARTeligible

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 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 67 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."

Discussion of what emissions units should be considered part of a " stationary source".

Comments. A number of comments in 2001 expressed concern with our statement that a " support facility" should be grouped with a primary facility in determining which emissions units belong to the same industrial grouping.

These comments generally coincided with comments discussed above that EPA should determine BART on a plantwide basis,

rather than by aggregating emissions units. Commenters on the 2004 reproposal noted with approval the clarification that " support facilities" should only be considered BARTeligible if these units themselves were both constructed within the 1962 1977 time frame and fell within one of the listed source categories.

Two commenters felt that we should more clearly define the BART eligible source, either by identifying emission units within source categories, or by somehow accounting for the specific set of emission units, within the fenceline, to which controls would logically apply. 68 Final rule. The guidelines continue to note that the definition of " building, structure or facility" in the regional haze rule is based upon aggregating emissions units within the same industrial grouping. This discussion in the guidelines is consistent with the language in the definition of " building, structure or facility" in the regional haze rule which contains a specific reference to the 2 digit SIC classifications. The BART guidelines refer to this definition and explain how 2 digit SIC codes are used in determining the scope of BART for a given plantsite. ( In the rare situation where industrial groupings in separate 2

digit SIC codes exist at a single plant site, then there would be more than one separate " stationary source" present.

In that situation, each " stationary source" should be looked at individually for purposes of determining BARTeligibility

We agree that more clarity is needed to account for situations where a specific set of units constitute the logical set to which BART controls would apply. We have added language to the guidelines, at the BART determination step, encouraging States to allow sources to " average"

emissions across a set of BART eligible emission units within a fenceline, so long as the emission reductions from each pollutant being controlled for BART would be greater 69 than those reductions that would be obtained by simply controlling each unit.

Step 4: Identify the emission units and pollutants that constitute the BART eligible source.

Background. The final step in identifying a "

BARTeligible source" is to use the information from the previous three steps to identify the universe of equipment that makes up the BART eligible source. The 2001 and 2004 proposed BART guidelines stated that if the emissions from the list of emissions units at a stationary source exceed a potential to emit of 250 tons per year for any individual visibilityimpairing pollutant, then that collection of emissions units is a BART eligible source. The guidelines also stated that a BART analysis would be required for each visibilityimpairing pollutant emitted from this collection of emissions units.

In the 2004 reproposed BART guidelines, we noted that we believed that section 169A( b)( 2)( A) of the CAA requires a State to undertake a BART analysis for " any"

visibilityimpairing pollutant emitted by a BART eligible source,

regardless of the amount emitted. We proposed, however, to provide the States with the flexibility to identify de minimis levels for pollutants at BART eligible sources, but limited that flexibility so that any such de minimis levels could not be higher than those used in the PSD program: 40 70 tons per year for SO2, NOx, and VOC, and 15 tons per year from PM10. We requested comment on this provision and on the use of de minimis values.

Discussion of whether to include all emitted visibility impairing pollutants in the BART analysis Comments. A number of commenters supported the concept of including all pollutants in the BART analysis once an individual pollutant triggers the BART review. Other commenters, although supportive of the concept generally,

recommended that we should add the pollutants together before the comparison with the threshold.

A number of commenters disagreed with EPA's conclusion that the CAA requires States to make a BART determination for any visibility impairing air pollutant emitted by a BART eligible source. These commenters stated that undertaking a BART analysis for all pollutants emitted by a major stationary source is an unnecessary administrative burden with minimal environmental benefit. Commenters argued that Congress intended for BART to apply only to those pollutants for which a source is major. Commenters accordingly recommended that the 250 ton per year threshold apply to each pollutant emitted by a source and that BART apply only to those pollutants which meet this threshold. A number of these commenters argued alternatively that only those pollutants from a source demonstrated, individually, to 71 cause or contribute to visibility impairment are required to go through a BART determination.

Final rule. 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 72 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 PM2.5,

SO2, 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 73 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 distinction between these two interpretations of this provision is unlikely to be significant in practice, however, as one of the factors to be taken into account in making a BART determination is the degree of visibility improvement resulting from the use of controls.

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 74 circumstances in a given situation, such as the distance of the source from a Class I 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 SO2, NOx, and PM2.5 from the BART determination process which should help to address the concerns of certain commenters associated with the burden of a broad BART analysis.

De minimis levels 75 Comments. Many commenters agreed that we should establish de minimis levels for individual pollutants in order to allow States and sources to avoid BART determinations for pollutants emitted in relatively trivial amounts. Many commenters suggested that States would be unlikely to impose emission limits for pollutants emitted at the proposed de minimis levels because it would not be costeffective to do so and such emission reductions could not be expected to produce any perceptible improvements in visibility. Several commenters agreed that the pollutant coverage requirements for BART eligibility should be consistent with those for the PSD program, but others argued that BART should be required only for pollutants emitted in amounts greater than 250 tons per year. Commenters also noted that the guidelines were not clear as to whether the de minimis provision would apply on a plant wide or unit by unit basis. A few commenters also noted that the final guidelines should clarify where in the BART determination process de minimis levels may be used.

Other commenters opposed the use of de minimis exemptions. These commenters argued that it would be unreasonable to rule categorically that a certain level of emissions had a trivial impact on visibility without assessing the impacts of these emissions in particular circumstances. These commenters argued that States should 23 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).

24 Id.

76 consider the emissions of all visibility impairing pollutants in a BART determination regardless and that,

consequently, there should be no de minimis levels.

Final rule. 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.'" 23 The ability to create de minimis exemptions from a statute is a tool to be used in implementing the legislative design. 24 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 determination as to the appropriate level of controls,

however, the States are required to take into account not 77 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 SO2 or NOx or 15 tons of PM10 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 78 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.

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 SO2 or NOx, or 15 tons per year for PM10. ( Note also that for sources that are BART eligible for one pollutant, we are suggesting that States could allow those sources to model the visibility impacts of pollutants at levels between de minimis and 250 tons in order to show that the impact is negligible and 79 should be disregarded. See section D below). In the guidelines, we include this as part of the BART determination in section IV of the guidelines. ( We note that these emission levels represent the maximum allowable de minimis thresholds   States retain their discretion to set the thresholds at lesser amounts of each pollutant, or to not provide any pre determined de mininis levels.) We believe that this approach is the clearest method for exempting trivial emissions from the BART determination process. 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.

How to Determine Which BART eligible Sources are " Subject to BART"

[ PLACEHOLDER FOR DISCUSSION OF " CAUSE OR CONTRIBUTE"]

Use of CALPUFF for Visibility Modeling Background. In providing the States with the option of making a determination as to which sources are subject to BART based on a consideration of each source's individual contribution to visibility impairment, we proposed that States use an air quality model such as CALPUFF. We also 25 H. R. Rep. No. 95 294 at 204 ( 1077).

80 proposed that States use a CALPUFF or other EPA approved model in the BART analysis itself. The CALPUFF system, as explained in the 2004 reproposed guideline, consists of a diagnostic meteorological model, a gaussian puff dispersion model with algorithms for chemical transformation and complex terrain, and a post processor for calculating concentration fields and visibility impacts.

The regional haze rule addresses visibility impairment caused by emissions of fine particles and their precursors.

As fine particle precursors, such as SO2 or NOx, are dispersed, they react in the atmosphere with other pollutants to form visibility impairing pollutants. In fact, Congress implicitly recognized in 1977 the role of chemical transformation in creating visibility impairment,

when it stated that the " visibility problem is caused primarily by emissions of SO2, [ NOx], and particulate matter." 25 In most cases, to predict the impacts of a source's specific contribution to visibility impairment, a State will need a tool that takes into account not only the transport and diffusion of directly emitted PM2.5 but also one that can address chemical transformation.

Because the air quality model CALPUFF is currently the best application available to predict the impacts of a single source on visibility in a Class I area, we proposed 26 To determine whether a BART eligible source " may reasonably be anticipated to cause or contribute to any visibility impairment in any Class I area," it may not always be sufficient for the State to predict the impacts of a BART eligible source only on the nearest Class I area ( or on the nearest receptor in the nearest Class I area). The particular meteorological and topographical conditions, for example, could mean that a source's greatest impacts occurred at a Class I area other than the nearest one.

81 that a CALPUFF assessment be used as the preferred approach first, for determining whether an individual source is subject to BART, and second, in the BART determination process. The CALPUFF assessment is specific to each source,

taking into account the individual source's emission characteristics, location, and the particular meteorological, topographical, and climatological conditions of the area in which the source is located, any of which may have an impact on the transport of PM2.5 and its precursors.

CALPUFF can be used to estimate not only the effects of directly emitted PM2.5 emissions from a source, but also to predict the visibility impacts from the transport and chemical transformation of fine particle precursors.

The CALPUFF model is generally intended for use on scales from 50 km to several hundred kilometers from a source. As a general matter, States will typically need to assess the impacts of potential BART sources on Class I areas located more than 50 km from the source. 26 However,

in situations where the State is assessing visibility impacts for source receptor distances less than 50 km, we 27 PLUVUEII is a model used for estimating visual range reduction and atmospheric discoloration caused by plumes resulting from the emissions of particles, nitrogen oxides, and sulfur oxides from a single source. The model predicts the transport, dispersion, chemical reactions, optical effects and surface deposition of point or area source emissions. It is available at http:// www. epa. gov/ scram001/ tt22. htm# pluvue.

82 proposed that States use their discretion in determining visibility impacts, giving consideration to both CALPUFF and other EPA approved methods. As an example, we suggested that States could use an appropriate local scale plume impact model, such as PLUVUEII27, to determine whether a source's emissions are below a level that would be reasonably anticipated to cause or contribute to visibility impairment in any Class I area.

Comments. A number of States, environmental groups,

and some industry commenters strongly supported the use of CALPUFF as proposed. Many commenters supported the use of CALPUFF but indicated that States must have the flexibility to use additional tools for their individual source analyses. Some suggested options for the " cause or contribute" determination were the use of photochemical grid models, or more simplified, non modeling approaches.

Commenters claimed that States must have the option to incorporate advances in science and technologies into models or other applications that may produce more accurate simulations of meteorology, chemistry, and visibility 83 impairment. Other industry groups and States argued that CALPUFF has significant limitations, especially simulating complex atmospheric chemistry, and that EPA's recommendation of CALPUFF as the preferred approach is therefore inappropriate.

Another issue raised by commenters was the use of CALPUFF for estimating secondary particulate matter formation. Commenters recognized that CALPUFF was incorporated into the " Guideline on Air Quality Models" at 40 CFR Part 51, Appendix W in April 2003 as the preferred model for Prevention of Significant Deterioration ( PSD)

increment and National Ambient Air Quality Standards ( NAAQS)

compliance assessments of long range transport of primary emissions of SO2 and PM2.5. However, commenters stated that CALPUFF has not been incorporated into the Guideline on Air Quality Models for predicting the secondary formation of PM.

The commenters remarked that EPA guidance indicates that photochemical grid models be used to simulate secondary PM formation and concluded on this basis that the application of CALPUFF as we proposed is in conflict with our guidance.

Final rule. We believe that CALPUFF is an appropriate application for States to use for the particular purposes of this rule, to determine if an individual source is reasonably anticipated to cause or contribute to impairment of visibility in Class I areas, and to predict the degree of 28 The model code and its documentation are available at no cost for download from the model developers' Internet Web site: http:// www. src. com/ calpuff/ calpuff1. htm.

84 visibility improvement which could reasonably be anticipated to result from the use of retrofit technology at an individual source. We encourage States to use it for these purposes28.

CALPUFF is the best modeling application available for predicting a single source's contribution to visibility impairment. It is the only EPA approved model for use in estimating single source pollutant concentrations resulting from the long range transport of primary pollutants. In addition, it can also be used for some purposes, such as the visibility assessments addressed in today's rule, to account for the chemical transformation of SO2 and NOx. As explained above, simulating the effect of precursor pollutant emissions on PM2.5 concentrations requires air quality modeling that not only addresses transport and diffusion, but also chemical transformations. CALPUFF incorporates algorithms for predicting both. At a minimum,

CALPUFF can be used to estimate the relative impacts of BART eligible sources. We are confident that CALPUFF distinguishes, comparatively, the relative contributions from sources such that the differences in source configurations, sizes, emission rates, and visibility impacts are well reflected in the model results. States can 85 make judgements concerning the conservativeness or overestimation, if any, of the results. In fact, although we focused on the use of CALPUFF for primary pollutants in revising the Guideline of Air Quality Modeling, section 7.2.1. e. of the Guideline states:

e. CALPUFF ( Section A. 3) may be applied when assessment is needed of reasonably attributable haze impairment or atmospheric deposition due to one or a small group of sources. This situation may involve more sources and larger modeling domains than that to which VISCREEN ideally may be applied. The procedures and analyses should be determined in consultation with the appropriate reviewing authority ( paragraph 3.0( b) and the affected FLM( s).

We believe that our proposed use of CALPUFF is thus fully in keeping with the Guideline on Air Quality Models, especially in light of the low triggering threshold for determining whether a source is reasonably anticipated to cause or contribute to visibility impairment in a Class I area, and the fact that the modeling results are used as only one of five statutory criteria evaluated to determine BART emission limits.

Even so, as commenters point out, CALPUFF has not yet been fully evaluated for secondary pollutant formation. For the specific purposes of the regional haze rule's BART 29 Under CAA section 165( a), a major emitting facility may not be constructed unless the owner or operator of the facility demonstrates that the emissions from the facility will not cause or contribute air pollution in excess of an increment or NAAQS.

86 provisions, however, we have concluded that CALPUFF is sufficiently reliable to inform the decision making process.

EPA revised the Guideline on Air Quality Models in 2003 ( 40 CFR Part 51, Appendix W, April 2003), in part, to add CALPUFF to the list of approved models for particular uses.

At that time, we considered comments that CALPUFF should be approved for use in predicting the impact of secondary emissions on particulate matter concentrations. As we stated in the revision, CALPUFF represents a substantial improvement in methods for assessing long range transport of air pollutants. However, as explained in the response to comments for that rulemaking, the modeling results in the context of a PSD review may be used as the sole determining factor in denying a source a permit to construct. 29 Although its use in simulating long range transport is beneficial, given the significance of the modeling results in assessing increment consumption due to a single source's impacts, we made a determination that it would not be appropriate in the rulemaking revising Appendix W to approve CALPUFF for use in modeling secondary emissions.

In contrast to the significance of the modeling results in the PSD context, the use of CALPUFF in the context of the 30 CALPUFF Analysis in Support of the Regional Haze Rule, U. S. Environmental Protection Agency, April 15, 2005, Docket No. OAR 2002 0076.

31 Ibid.

87 regional haze rule is not determinative of a source's ability to construct or operate. A State may use CALPUFF to determine whether a source can reasonably be anticipated to cause or contribute to visibility impairment and so should be subject to additional review to determine if the source should be subject to control.

Based on our analysis of the power plants covered by the guidelines, we believe that all but a handful of these plants have impacts of greater than 1.0 deciview on one or more Class I areas. 30 In fact, we anticipate that most of these plants are predicted to have much higher maximum impacts. 31 Because of the scale of the predicted impacts from these sources, CALPUFF is an appropriate or a reasonable application to determine whether such a facility can reasonably be anticipated to cause or contribute to any impairment of visibility. In other words, to find that a source with a predicted maximum impact greater than 2 or 3 deciviews meets the low triggering threshold in the Act does not require the degree of certainty in the results of the model that might be required for other regulatory purposes.

In the unlikely case that a State were to find that a 750 MW power plant's predicted contribution to visibility 88 impairment is within a very narrow range between exemption from or being subject to BART, the State can work with EPA and the FLM to evaluate the CALPUFF results in combination with information derived from other appropriate techniques for estimating visibility impacts to inform the BART applicability determination. Similarly for other types of BART eligible sources, States can work with the EPA and FLM to determine appropriate methods for assessing a single source's impacts on visibility.

As discussed in in section E. below we also recommend that the States use CALPUFF as a screening application in estimating the degree of visibility improvement that may reasonably be expected from controlling a single source in order to inform the BART determination. As we noted in 2004, this estimate of visibility improvement does not by itself dictate the level of control a State would impose on a source; " the degree of improvement in visibility which may reasonably be anticipated to result from the use of [ BART],"

is only one of five criteria that the State must consider together in making a BART determination. The State makes a BART determination based on the best estimates available for each criterion, and as the CAA does not specify how the State should take these factors into account, the States are free to determine the weight and significance to be assigned to each factor. American Corn Growers v. EPA [ cite to 89 dissent, fn. 10]. CALPUFF accordingly is an appropriate application for use in combination with an analysis of the other statutory factors, to inform decisions related to BART.

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 32For regional haze applications, regional scale modeling typically involves use of a photochemical grid model that is capable of simulating aerosol chemistry, transport, and deposition of airborne pollutants, including particulate matter and ozone. Regional scale air quality models are generally applied for geographic scales ranging from a multi state to the continental scale. Because of the design and intended applications of grid models, they may not be appropriate for BART assessments, so States should consult with the appropriate EPA Regional Office prior to carrying out any such modeling.

90 considered by the State, and the BART guidelines preserve a State's ability to use other models. Regional scale photochemical grid models may have merit, but such models have been designed to assess cumulative impacts, not impacts from individual sources. Such models are very resource intensive and time consuming relative to CALPUFF, but States may consider their use for SIP development in the future as they are adapted and demonstrated to be appropriate for single source applications and such use has been approved by the appropriate EPA regional offices. However, to date,

regional models have not been evaluated for single source applications. Their use may be more appropriate in Options 1 and 2 discussed above32. In evaluating visibility improvement as one of the five factors to consider in setting BART controls, other models, used in combination with CALPUFF, may be helpful in providing a relative sense of the source's visibility impact and can aid in informing the BART decision. A discussion of the use of alternative models is given in the Guideline in Appendix W, section 3.2. 33 Guidance for Estimating Natural Visibility Conditions Under the Regional Haze Rule ( U. S. EPA. September 2003). http:// www. epa. gov/ ttncaaa1/ t1/ memoranda/ rh_ envcurhr_ gd. pdf Natural background conditions, expressed in deciviews, are defined for each Class I area. EPA has issued guidance for estimating natural background conditions which has estimates of default conditions as well as measures to develop refined estimates of natural conditions.

91 [ PLACEHOLDER FOR Metric for Visibility Degradation ]

The Use of Natural Conditions in Determining Visibility Impacts for Reasonable Progress and Comparison to Threshold values Background. As set out in section 169A( a) of the CAA and stated in the 1999 Regional Haze Rule, a return to natural visibility conditions, or the visibility conditions that would be experienced in the absence of human caused impairment, is the ultimate goal of the regional haze program. To implement the CAA goal, the regional haze rule requires that a comparison with natural conditions for the 20 percent best and worst days to calculate " reasonable progress" determinations. Default values for natural visibility conditions are provided in EPA guidance. 33 In the 2004 reproposal of the BART guidelines, we proposed that changes in visibility, expressed in deciviews, should be determined by comparing the impact from a single source to natural visibility conditions. That impact should then be 92 compared to a threshold impact, also expressed in deciviews,

to assess if a BART eligible source should be subject to a BART review.

Comments. Opposing commenters said that a return to natural conditions is unattainable as it would require the elimination of every manmade source, and that changes should be compared against currently existing conditions. They added that true " natural conditions" cannot be verified, do not account for manmade emissions from other countries, and are not a realistic target for improvement. Further, they argued that natural conditions are a " goal" representing a benchmark that is relevant to the States' determination,

under the regional haze program, of the level of " reasonable progress" to achieve; however they stated that there is no legal requirement ( and there could not be a legal requirement) that the natural conditions goal ultimately must be achieved. Several commenters added that current visibility conditions make more sense as a baseline because sources that are subject to BART today will likely not be in operation in the 2064 time frame. A commenter added that using current visibility conditions for the analysis will give a more realistic, real world prediction of whether controlling the source pursuant to BART will actually improve visibility. The commenter said that Congress did not intend for sources to have to consider retrofitting controls under the BART provision if those sources currently 93 are not impacting real world visibility. Other utility groups stated that in addition to international emissions,

the estimated natural visibility conditions failed to account for natural phenomena such as sea salt, wildfires,

and natural organics. One commenter noted that natural visibility estimates will be revised and refined over time and it would be unwise to compare impacts and improvements to a moving baseline.

On the other hand, numerous commenters supported the use of natural visibility conditions as a baseline for measuring visibility improvements. Several environmental groups said that any increase in the baseline beyond natural visibility conditions will unlawfully distort and weaken the BART requirement by effectively raising the applicability threshold in less protected, highly polluted areas, which would be illogical. Further, they pointed out that these BART eligible sources clearly are contributing to the very manmade visibility impairment that the Act is explicitly designed to remedy by a return to natural conditions. They added that measuring natural conditions as opposed to some other baseline condition is a more appropriate approach,

given that the planning goal is to achieve natural visibility by the end of the program. They also added that a baseline other than natural conditions would never assure " reasonable progress". 34 See also our explanation of the CAA goal provided in the regional haze rule at 64 FR 126.

94 Finally, two commenters asked for clarification on the values for natural conditions to be used for estimating changes in visibility. The commenters appeared to assume that we intended for the comparison to be done for natural visibility conditions on the 20% best days.

Final Rule. We disagree with commenters saying that the use of natural conditions as the baseline for making visibility impact determinations is inappropriate. The visibility goal of the CAA is both the remedying of existing impairment, and prevention of future impairment. The court,