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. Effect of this rule on State options for using alternative strategies in lieu of source by source BART 5 V. Statutory and Executive Order Reviews A. Executive Order 12866: Regulatory Planning and Review B. Paperwork Reduction Act 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, 6 ( 3) BART guidelines, contained in a new Appendix Y to 40 CFR part 51,

( 4) new and revised regulatory text, to be added to 40 CFR 51.308( e), regarding 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 1 See, e. g. CAA Section 169A( a)( 1).

7 submit implementation plans ( SIPs) to address regional haze visibility impairment in 156 Federally protected parks and 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. 8 The BART eligible sources are those sources which have the potential to emit 250 tons or more of a visibility impairing 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 a State determines " 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). 2 American Corn Growers et al. v. EPA, 291 F. 3d 1 ( 2002).

9 In the preamble to the regional haze rule, we committed to issuing further guidelines to clarify the requirements of the BART provision. The purpose of this rulemaking is to fulfill this commitment by providing guidelines to assist States as they identify which of their BART eligible sources should undergo a BART analysis ( i. e., which are " sources subject to BART"), and select 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. 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 EPA had prescribed for determining which eligible sources are subject to BART illegally constrained the authority Congress had conferred 12 on the States. Id. The court did not decide whether the general collective contribution approach to determining BART applicability was necessarily inconsistent with the CAA. Id.

at 9. Rather, the court stated that "[ i] f the [ regional haze rule] contained some kind of a mechanism by which a state could exempt a BART eligible source on the basis of an individualized contribution determination, then perhaps the plain meaning of the Act would not be violated. But the [ regional haze rule] contains no such mechanism." 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 appropriate techniques and methods 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, to address the holding of American Corn Growers by eliminating the previous constraint on State discretion, is 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, we have not included a portion of the proposed BART guidelines addressing alternative programs in 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 to revise the provisions of the regional haze rule 16 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. The relationship between BART and the Clean Air Interstate Rule ( CAIR) is discussed in section IV.

below.

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 17 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 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 5 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.

18 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.

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." 5 States certainly 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 6 CAA § 169A( b)( 2)( A).

7 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.

19 at 8. By the same rationale, we believe it would be an impermissible constraint of State authority for the EPA to force States to conduct individualized analysis in order to determine that a BART eligible source " emits any air pollutant which may reasonably be anticipated to cause or contribute to any impairment of visibility in any [ Class I]

area." 6 American Corn Growers did not decide whether 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 is consistent with the CAA and the findings of the D. C. Circuit.

We believe a State may conclude that all BART eligible sources within the State are subject to BART, without further analysis at that stage in the process. 7 Any potential for inequity towards sources could be addressed at the BART determination stage, which contains an 20 individualized consideration of a source's contribution in establishing BART emission limits.

States also have the option of performing an analysis to show that the full group of BART eligible sources in a State cumulatively may not be reasonably anticipated to 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 pose a 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. Either approach appears consistent with the D. C.

Circuit's statement that a collective contribution approach 21 may be appropriate so long as the States are allowed to exempt sources on the basis of an individualized contribution determination. 291 F. 3d at 8.

Today's Guidelines include different options States can use to assess whether source should be subject to BART.

States need to determine whether to make BART determinations for all of their BART eligible sources, or to consider exempting some of them from BART because they may not reasonably be anticipated to cause or contribute to any visibility impairment in a Class I area. 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, and a different process whereby States could exempt groups of sources with common characteristics based on representative model plant analyses.

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 22 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 permit States to take into account the degree of improvement in visibility that would result from imposition of BART on each individual source, when deciding on particular controls.

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 appropriate dispersion 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 24 hour 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. 23 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:

  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: 24 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 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. 25 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 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 26 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 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. 27 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 acknowledgethe State agency comments and the policy reasons in support consistency across States, we are 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 helpful 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 28 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 Step 2: Identify the start up dates of those emission 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 29 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 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 30 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 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). 31 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.

( 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) 32 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.

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. 33 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 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 34 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,

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. 35 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 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. 36 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.

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 8 See http:// www. epa. gov/ Region7/ programs/ artrd/ air/ nsr/ nsrmemos/ t urbines. pdf 37 have explained that combined cycle gas turbines do fall within the category of " fossil fuel fired steam electric plants." 8 ( 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 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, or viceversa We have added this clarification to the definition 38 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.

( Note that a boiler which is not integral, but is simply attached to a plant, should not be included.) For example,

Kraft pulp mills may have boilers that are not serving the energy infrastructure of the plant, but typically are serving a process directly by using the waste liquor from the process. Including such a 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.

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.

Step 2: Identify the start up dates of those emission units. 9 However, sources reconstructed after 1977, which reconstruction had gone through NSR/ PSD permitting, are not BART eligible.

39 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.

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. 9 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. 40 " 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.

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 41 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 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. 42 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 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. 43 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 ` 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 10 See CAA section 193.

44 1990 and implicitly endorsed by Congress in its 1990 amendments to the CAA. 10 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.

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. 45 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 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 46 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 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 47 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.

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. 48 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.

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 49 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.

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 50 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 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 51 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 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 52 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 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 11 See http:// wrapair. org/ forums/ ioc/ meetings/ 030728/ index. html ( specifically presentation by John Vimont, National Park Service).

12 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.

53 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 concern11, and 2003 direction to policy makers from the North American Research Strategy for Tropospheric Ozone ( NARSTO) 12 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 54 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 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. 13 See Fine particles: Overview of Atmospheric Chemistry, Sources of Emissions, and Ambient Monitoring Data, Memorandum to Docket OAR 2002 0076, April 1, 2005.

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

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

55 Final rule. PM10 as an indicator. While it is always necessary to assess PM2.5 impacts, 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 visibility impairment. 13 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. 14 We do recognize that coarse PM is likely to contribute more to regional haze in arid areas than humid areas. We believe that, as the Grand Canyon Visibility Transport Commission ( GCTVC) recognized, 15 States in the arid West, in particular, should take the coarse fraction of particulate matter into account in determining whether a source meets the threshold for BART applicability.

Because long range transport of fine particles is of particular concern in the formation of regional haze, we 16 Fine particles: Overview of Source Testing Approaches, Memorandum to Docket OAR 2002 0076, April 1, 2005.

56 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 quality modeling results will be more meaningful provide a more accurate prediction of a source's impact on visibility if the inputs account for the relative particle size of directly emitted particulate matter ( e. g. PM10 vs. PM2.5).

States shouldconsider whether their current test methods for measuring particulate matter emissions from stationary sources account for the condensible fraction of particulate matter, and consider revising any such stationary source test methods to 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. 16 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 location such that the most appropriate approach for States to take is a case by case approach. There are scientific data illustrating that ammonia in the atmosphere can be a precursor to the formation of particles such as ammonium 17 See Fine particles: Overview of Atmospheric Chemistry, Sources of Emissions, and Ambient Monitoring Data, Memorandum to Docket OAR 2002 0076, April 1, 2005.

57 sulfate and ammonium nitrate; 17 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 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 ammonia can contribute to visibility impairment, we believe the decision whether to consider ammonia as a visibility impairing pollutant in a specific case where a potential BART source actually emits more than 250 tons per year of ammonia is best left to the State. 18 Ibid.

58 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 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. 18 However, while progress has been made in understanding the role of VOCs in the formation of organic PM, this relationship remains complex, and issues such as the relative importance of biogenic versus anthropogenic emissions remain unresolved. 19 Ibid.

59 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 East19 suggest that there may be a greater contribution to particle formation in urban areas from VOCs as compared to rural areas, but we recognize that further research is needed to better determine the extent of the contribution of specific VOC compounds to organic PM mass. We do not agree, however,

with commenters who make the blanket assertion that rural VOCs are not a significant contributor to particle formation, as it is possible that in specific areas, such as 60 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.

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 61 250 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 account in determining any future rulemaking efforts to address the general definition of " potential to emit." For the time being, we believe that States may consider federally enforceable limits or emissions limitations in State permits, which are enforceable under State law, in determining a source's " potential to emit." 62 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.

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 63 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. The CAA requires BART at certain major stationary sources.

Accordingly we believe it could be appropriate, at the BART determination step, for States to allow sources to " average"

emissions across a set of BART eligible emission units within a fenceline, so long as the amount of emission reductions from each pollutant being controlled for BART would be at least equal to those reductions that would be obtained by simply controlling each unit. We have added language to the guidelines to this effect.

Step 4: Identify the emission units and pollutants that constitute the BART eligible source. 64 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 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. 65 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 cause or contribute to visibility impairment are required to go through a BART determination. 66 Final rule. We disagree with the comment that emissions of different visibility impairing pollutants must be added together to determine whether a source exceeds the 250 ton per year threshold. The CAA, in section 169A( g)( 7),

defines a " major stationary source" as one with the potential to emit 250 tons or more of " any pollutant."

We disagree with comments that the BART analysis is required only for those pollutants that individually exceed the 250 ton per year threshold. Section 169A( b)( 2)( A)

specifically requires States to submit SIPs that include a requirement that a major stationary source which, as determined by the State . . . emits any air pollutant which may reasonably be anticipated to cause or contribute to any impairment of visibility in any [ Class I area], shall procure,

install, and operate . . . the best available retrofit technology, as determined by the State .

. . for controlling emissions from such source for the purpose of eliminating or reducing any such impairment.

The regional haze regulations similarly require that the States submit a SIP that contains A determination of BART for each BART eligible source in the State that emits any air pollutant which may reasonably be anticipated to cause or 67 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 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 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 68 not necessarily the best reading of the BART provisions.

Section 169A( b)( 2)( A) of the Act can be read to require the States to make a determination as to the appropriate level of BART controls, if any, for emissions of any visibility impairing pollutant from a source. Given the overall context of this provision, however, and that the purpose of the BART provision is to eliminate or reduce visibility impairment, it is reasonable to read the statute as requiring a BART determination only for those emissions from a source which are first determined to contribute to visibility impairment in a Class I area.

The interpretation of the requirements of the regional haze program reflected in the discussion above does not necessitate costly and time consuming analyses. Consistent with the CAA and the implementing regulations, States can adopt a more streamlined approach to making BART determinations where appropriate. Although BART determinations are based on the totality of 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 69 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 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 70 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 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. 20 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).

21 Id.

71 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.'" 20 The ability to create de minimis exemptions from a statute is a tool to be used in implementing the legislative design. 21 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 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 72 these sources in the calculus of determining the appropriate level of BART.

We believe it would be permissible for States to create de minimis levels at a low 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 amending the regional haze rule to make clear that the States have this flexibility.

The de minimis levels discussed today apply on a plantwide 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 cost 73 effective 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. We believe States may, if they choose, 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 also believe 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 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 84 guidelines. Either approach is consistent with the regulation issued in this rule.

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

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

Cause or Contribute Background. Under section 169A( b)( 2)( A) of the Act,

each State must review its BART eligible sources and determine whether they emit " any air pollutant which may reasonably be anticipated to cause or contribute to any impairment of visibility in [ a Class I] area." If a source meets this threshold, the State must then determine what is BART for that source.

Proposed rule. In the reproposed guidelines, we identified three options for States to use in determining which BART eligible sources meet the test set forth in section 169A( b)( 2)( A) of the CAA. To determine whether a BART eligible source is " reasonably anticipated to cause or contribute to visibility impairment," the first proposed option was that a State could choose to consider the collective contribution of emissions from all BART eligible sources and conclude that all BART eligible sources within the State are " reasonably anticipated to cause or contribute" to some degree of visibility impairment in a 85 Class I area. The preamble to the 1999 regional haze rule explains at length why we believe that looking to the collective contribution of many sources over a broad area is a reasonable approach, and we explained in the 2004 reproposed guideline that we believed that a State's decision to use a cumulative analysis at this stage of the BART determination process would be consistent with the CAA and the findings of the D. C. Circuit in American Corn Growers.

The second proposed option was to allow a State to demonstrate, using a cumulative approach, that none of its BART eligible sources contribute to visibility impairment.

Specifically, we proposed to provide States with 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 visibility impairment in any Class I areas.

As a third option, we proposed that a State may choose to determine which sources are subject to BART based on an analysis of each BART eligible source's individual contribution. We labeled this option as an " Individualized Source Exemption Process," and proposed that States use an air quality model to determine an individual source's contribution to visibility impairment, calculated on a 24 hour basis, using allowable emissions, and compared to an established threshold. 86 Comments. Several commenters expressed the view that EPA was misinterpreting the American Corn Growers case to allow the States to apply a collective contribution test in determining whether BART eligible sources are subject to BART. These commenters took the position that, because this approach does not allow for a source to show that it does not individually cause or contribute to visibility impairment, it is incompatible with the language of section 169A( b)( 2)( A) of the Act. They argued that EPA should modify the provisions in the proposed rule to ensure that an individual source is afforded the opportunity to conduct an analysis to demonstrate that its emissions do not impair visibility in any Class I area. Conversely, several commenters indicated that the option to determine that all potential BART sources contribute to regional haze should be the starting point of determining BART eligibility.

Many industry commenters and some States supported the second proposed option which would allow a State to demonstrate through an analysis of the collective contribution of all its BART eligible sources that none of these sources contribute to visibility impairment. Several of these commenters added, however, that if this cumulative analysis were to show a contribution, then, consistent with the decision in American Corn Growers, the State must allow each individual source to demonstrate that its own emissions 87 do not, by themselves, contribute to the problem of visibility impairment. One commenter requested clarification on what visibility threshold a State should use in determining that no sources are reasonably anticipated to cause or contribute to any impairment in a Class I area.

A number of commenters supported the third option for determining BART applicability based on an analysis of source specific effects on visibility. However, many of the commenters stated that the CAA requires that the States either conduct such an analysis in determining those sources subject to BART, or allow an individual source to make a showing that it does not cause or contribute to visibility impairment. In addition, although supportive of the general notion of allowing for an exemption process for BARTeligible sources, several commenters stated that the third option contained burdensome modeling requirements, and that States need a more flexible, straightforward, and less costly method to make the " cause or contribute"

determination.

Several environmental groups commented that the proposed options potentially go too far in allowing sources to be exempted from the BART requirements. These commenters asserted that EPA should clarify that States may not allow a BART eligible source to avoid the BART requirements without an affirmative demonstration by the State, or by the source, 22 States choosing this approach should use the data being developed by the regional planning organizations, or on their own, as part of the regional haze SIP development process to make the showing that the State contributes to visibility impairment in one or more Class I areas.

88 showing that the source does not emit any air pollutant which may reasonably be anticipated to cause or contribute to any impairment of visibility in a Class I area. Absent such a demonstration, they argue, a State may not choose to waive the requirement to conduct a BART review of the source.

Final rule. The final BART guidelines adopt the general approach contained in the reproposal, providing the States with several options for identifying the sources subject to BART. The final BART guidelines describe the options contained in the reproposal as well as one new option. The discussion of options in the final guidelines are structured somewhat differently from the reproposal, and the options are explained in greater detail. The Guidelines reaffirm that a State may choose to consider all BART eligible sources to be subject to BART, and to make BART determinations for all its BART eligible sources. 22 For States that choose to consider exempting some or all of their BART eligible sources from review, the Guidelines then discuss three options that States may use to determine whether its sources are " reasonably anticipated to cause or contribute" to visibility impairment at a Class I area. 89 Options 1 and 3 are similar to options in the 2004 reproposal; under option 1, States may use an individual source attribution approach, while option 3 provides the States with an approach for demonstrating that no sources in a State should be subject to BART. Option 2 is new; it is an approach for using model plants to exempt individual sources with common characteristics.

Threshold for visibility impact One of the first steps in determining whether sources cause or contribute to visibility impairment for purposes of BART is to establish a threshold ( quantified in units called " deciviews") against which to measure the visibility impact of one or more sources. We believe that a single source that is responsible for a 1.0 deciview change or more should be considered to " cause" visibility impairment; a source that causes less than a 1.0 deciview change may still contribute to visibility impairment and thus be subject to BART.

The Guidelines note that because of varying circumstances affecting different Class I areas, the appropriate threshold for determining whether a source " contributes to any visibility impairment" for the purposes of BART may reasonably differ across States. Although the appropriate threshold may vary, the Guidelines state that the contribution threshold used for BART applicability 90 should not be higher than 0.5 deciviews. We discuss threshold issues in greater detail in the subsection immediately following this one, entitled Metric for Visibility Degradation.

Pollutants The Guidelines direct that States should look at SO2,

NOx, and direct particulate matter ( PM) emissions in determining whether sources cause or contribute to visibility impairment, including both PM10 and PM2.5.

Consistent with the approach for identifying BART eligible sources, States do not need to consider less than de minimis emissions of these pollutants from a source.

States may use their best judgement to determine whether VOC or ammonia emissions are likely to have an impact on visibility in an area. In addition, they may use PM10 or PM2.5 as an indicator for PM2.5 in determining whether a source is subject to BART. In determining whether a source contributes to visibility impairment, however, States should distinguish between the fine and coarse particle components of direct particulate emissions. Although both fine and coarse particulate matter contribute to visibility impairment, the long range transport of fine particles is of particular concern in the formation of regional haze. Air quality modeling results used in the BART determination will provide a more accurate prediction of a source's impact on 23 Grand Canyon Visibility Transport Commission, Recommendations for Improving Western Vistas, Report to the U. S. EPA, June 10, 1996.

91 visibility if the inputs into the model account for the relative particle size of any directly emitted particulate matter ( i. e. PM10 vs. PM2.5).

We believe that PM10 is likely to contribute more to regional haze in arid areas than humid areas. As the Grand Canyon Visibility Transport Commission ( GCTVC) recognized, 23 States in the arid West, in particular, will need to take the coarse fraction of particulate matter into account in determining whether a source meets the threshold for BART applicability.

Option 1 We agree with commenters supporting the use of an individual source analysis in determining if a BART eligible source causes or contributes to visibility impairment.

Consistent with American Corn Growers, this option provides a method for a State to evaluate the visibility impact from an individual source and show that the source is not reasonably anticipated to cause or contribute to visibility degradation in a Class I area and thus may be exempt from BART. ( Note also that an individual source analysis is used to inform the BART determination). In general, a dispersion model is used to assess the visibility impact from a single source, and that impact is compared to a threshold which is 92 determined by the State. The threshold ( quantified in deciviews) is the numerical metric that is used to define " cause or contribute"; if a source's impact is below the threshold, a State may exempt the source from BART;

otherwise the source would be subject to BART.

We discuss specific issues on the individualized source attribution process, including changes since proposal and issues raised by commenters, in the subsections immediately following this one: Metric for visibility degradation; Use of CALPUFF for visibility modeling; The use of natural conditions in determining visibility impacts for reasonable progress and comparison to threshold values; Modeling protocol; and Alternatives for determining visibility impacts from individual sources.

Option 2 In the final Guideline, we describe a modified approach, using model plants based on representative sources sharing certain characteristics, that the States may use to simplify the BART determination process, either to exempt ( individually or as a group) those small sources that are not reasonably anticipated to cause or contribute to visibility impairment, or to identify those large sources that clearly should be subject to BART review. States could use the CALPUFF model, for example, to estimate levels of visibility impairment associated with different combinations 24 Supplement to the CALPUFF Analysis in Support of the 2005 Changes to the Regional Haze Rule, U. S. Environmental Protection Agency, June 15, 2005, Docket No. OAR 2002 0076.

93 of emissions and distances to the nearest Class I area. In carrying out this approach, the State could then reflect groupings of specific types of sources with important common characteristics, such as emissions, stack heights and plume characteristics, and develop " composite model plants."

Based on CALPUFF analyses of these model plants, a State may find that certain types of sources are clearly reasonably anticipated to cause or contribute to visibility impairment.

Conversely, representative plant analyses may show that certain types of sources are not reasonably anticipated to cause or contribute to visibility impairment. Based on the modeling results, a State could exempt from BART all sources that emit less than a certain amount per year and that are located a certain distance from the nearest Class I area.

Our analyses of visibility impacts from model plants provide a useful example of the type of analyses that might be used to exempt categories of sources from BART. 24 Based on our model plant analysis, EPA believes that a State could reasonably choose to exempt sources that emit less than 500 tons per year of Nox or SO2 ( or combined NOx and SO2), as long as they are located more than 50 kilometers from any Class I area; and sources that emit less than 1000 tons per 94 year of combined Nox or SO2 ( or combined NOx and SO2) that are located more than 100 kilometers from any Class I area.

In our analysis, we developed two model plants ( a EGU and a non EGU), with representative plume and stack characteristics, for use in considering the visibility impact from emission sources of different sizes and compositions at distances of 50, 100 and 200 kilometers from two hypothetical Class I areas ( one in the East and one in the West). Because the plume and stack characteristics of these model plants were developed considering the broad range of sources within the EGU and non EGU categories, they do not necessarily represent any specific plant. However,

the results of these analyses may be instructive in the development of an exemption process for groups of BARTeligible sources, without modeling each of these sources individually.

States may want to conduct their own model plant analysis that take into account local, regional, and other relevant factors ( such as meteorology, sulfur dioxide,

nitrogen dioxide, and ammonia). If so, you may want to consult your EPA Regional Office to ensure that any relevant technical issues are resolved before you conduct your modeling.

In preparing our hypothetical examples, we have made a number of assumptions and exercised certain modeling choices; some of these have a tendency to lend conservatism 25 Reference modeling TSD 95 to the results, overstating the likely impacts, while others may understate the modeling results. On balance, when all of these factors are considered, we believe that our examples reflect realistic treatments of the situations being modeled. 25 A summary of the more significant elements and their implications is provided below.

Features of the modeling examples which may understate visibility impacts ° An annual emission rate was used for the example modeling ( e. g. 10,000 TPY divided by 365 days divided by 24 hours). " Real world" sources have variable emission rates, and in any 24 hour period may be operating well above the annual rate.

° The monthly average relative humidity was used, rather than the daily average humidity, and would contribute to lowering the peak values in daily model averages.

° A 24 hour average was calculated from modeled hourly visibility impacts, reducing the impact of any one particular hour that could be higher due to a number of meteorological effects.

Features of the modeling examples which may overstate visibility impacts ° We located receptors using a grid of concentric circles for distances of 50, 100 and 200 km. A receptor was 96 placed every 10 degrees around each circle, and highest impacts were reported regardless of direction from the source. In actuality, receptors would be located only in the Class I area, or in only one direction from the source.

° We used simplified chemistry ( i. e. for conversion of SO2 and NOx to fine particles) and disperson techniques which tend to overstate model impacts.

Special care should be used to ensure that the criteria used in the modeling are appropriate for a given State. Our modeling may not be appropriate for every region of the country, due to the unique characteristics of different Class I areas and varying meteorological and geographical conditions in different regions,

In addition, States may want to design their own model plants taking into account the types of sources at issue in their region.

Option 3 Under the BART Guidelines, a State may consider exempting all its BART eligible sources from BART by conducting analyses that show that all of the emissions from BART eligible sources in their State, taken together, are not reasonably anticipated to cause or contribute visibility impairment. To make such a showing, a State could use CALPUFF or another appropriate dispersion model to evaluate the impacts of individual sources on downwind Class I areas, aggregating those impacts to determine the collective contribution from all BART eligible sources in the 26 For 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.

97 State. A State with a sufficiently large number of BART eligible sources could also make such a showing using a photochemical grid model. 26 We agree with commenters who pointed out that the option of allowing a State to demonstrate that the full group of BARTeligible sources in the State do not contribute to visibility impairment would, by default, satisfy an individual source contribution assessment. Commenters have not shown any reason to believe that if the sum total of emissions from the BART eligible sources in a State do not " cause or contribute" to visibility impairment in any Class I area, that emissions from one such source will meet the threshold for BART applicability. A State following this approach accordingly need not undertake an affirmative demonstration based on a source by source analysis of visibility impacts to find that its sources are not subject to BART.

Metric for Visibility Degradation Background. The 2004 reproposed guidelines contained a proposed threshold for the States to use in determining whether 27 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.

28 In the proposal we noted that a 0.5 deciview change in visibility is linked to " perceptibility," or a just noticeable change in most landscapes. National Acid Precipitation Assessment Program ( NAPAP). Acid Deposition: State of Science and Technology Report 24, Visibility: Existing and Historical Conditions   Causes and Effects ( Washington, DC, 1991), Appendix D, p. 24 D2 (" changes in light extinction of 5% will evoke a just noticeable change in most landscapes"). Converting a 5% change in light extinction to a change in deciviews yields a change of approximately 0.5 deciviews.

98 an individual source could be considered to cause visibility impairment in a Class I area. We proposed a 0.5 deciview change ( delta deciview), relative to natural background conditions27, as a numerical threshold for making this determination. 28 We proposed the CALPUFF model as the preferred approach for predicting whether a single source caused visibility impairment if the modeled results showed impacts from the source that exceeded the threshold on any given day during a five year period. We also proposed that if a source had an estimated impact on visibility of less than 0.5 deciviews, a State could choose to exempt the source from further BART analysis.

Comments. We received numerous comments supporting the proposed threshold. A number of commenters stated that the 0.5 deciview threshold is appropriate given the low triggering 29 Ibid.

30 Henry, R. C. " Just Noticeable Differences in Atmospheric Haze", Journal of the Air & Waste Management Association, 52: 1238 1243, October 2002.

99 threshold for applicability established by Congress, and that the literature supports it as the minimum level of perceptibility.

Some commenters cited published documentation supporting their assertions that a minimum change in deciviews necessary for perceptibility is 0.5 deciviews. 29 Other commenters criticized the threshold as too low. They stated that a change of 0.5 deciviews is inconsistent with language in the regional haze rule pointing to 1.0 deciview as the appropriate perceptibility threshold, and they cited more recent literature justifying perceptibility as greater than a change of 1 deciview30.

One commenter said that we should allow States and regional planning organizations ( RPOs) the flexibility to determine appropriate visibility impact thresholds in light of current knowledge about a range of perceptibility thresholds. Another commenter said that we should explain our basis for establishing a threshold of a one time impact of greater than 0.5 deciviews, in light of the overall goal of the regional haze program. Yet another commenter said that the proposal would " change the regulatory role of the deciview metric by converting it into a regulatory 0.5 deciview standard ( versus a ` goal') for defining how States must exercise their authority and discretion in 100 determining whether an individual source ` causes or contributes'

to visibility impairment in a Class I area."

Several commenters said that the 0.5 deciview threshold is too high. A recurring comment was that the statutory BART applicability test from CAA Section 169A( b)( 2)( A) contains two separate elements: " causation" of any visibility impairment and " contribution" to any such impairment. Commenters pointed out that by setting a threshold of 0.5 deciviews, we had combined " cause or contribute" into a single test of causality, thus effectively eliminating the " contribution" element of the BART applicability test. The commenters asserted that a single BARTeligible source can " contribute" to visibility impairment with impacts much lower than 0.5 deciviews. They argued that we must set the minimum threshold for individual source contribution to visibility impairment at the lowest level detectable by modeling or other appropriate analysis, and that this minimum individual contribution level must in any event be set at no greater than a 0.1 deciview change relative to natural conditions, which is a clearly measurable level. One commenter suggested that a cause or contribute threshold be set at some percentage of the " just noticeable" change of 0.5 deciviews.

Another commenter said that in a case where multiple sources each have a visibility impact of less than a 0.5 deciview change,

but together result in a change of more than 0.5 deciview, each of these sources contributes to the resulting visibility impairment.

This commenter asserted that BART guidelines that result in 101 exemptions for these " contributing" sources would subvert the goals of the regional haze program.

Similarly, several commenters suggested that if any combination of BART eligible sources causes visibility impairment in a Class I area of more than 0.5 deciviews ( by CALPUFF modeling for any 24 hour period, for example), that State should determine that each individual source is subject to BART. Thus, the commenter added, the court's concern about the lack of " empirical evidence of a source's contribution to visibility impairment"

would be addressed.

Two commenters said that our requirement to use the maximum 24 hour value over the 5 year period of meteorological data in the modeling, as proposed, is too stringent, unreasonable,

inappropriate, and departs from the previous methodologies for the regional haze program. Additionally they said that the threshold is restrictive because the single highest 24 hour modeled impact over a three or five year period may be influenced by short term weather conditions, like high humidity, and the BART applicability determination should not be made based on a one time occurrence.

One commenter said that whatever the final threshold for a single source impact for BART sources, EPA should clarify that the purpose of this modeling assessment is to evaluate a source's anticipated contribution to uniform regional haze over the Class I area. EPA should state that the assumption of a uniform haze contribution based on CALPUFF modeling eliminates the need to assess issues related to the size of the Class I area, views 31 Moreover, the fact that the ultimate purpose of the visibility provisions is expressed as a " goal" does not mean that all aspects of the program are merely aspirational. CAA section 169A( a)( 4) requires EPA to establish regulations to ensure that reasonable progress is made toward the national visibility goal, and 169A( b)( 2) provides that EPA must require SIPs to contain emission limits, schedules of compliance, and other measures as may be necessary to make reasonable progress towards meeting the goal.

105 within a Class I area, and weather impact interactions. Finally,

one commenter said that thresholds should be established separately for the eastern and western regions of the United States, as natural visibility conditions are established separately for eastern and western regions in the guidance.

Final Rule. Today's guidelines advise States to use a deciview metric in defining " cause or contribute", as explained further below. The fact that the deciview is also used to track progress toward the goal of natural visibility does not in any way indicate that we are " converting" a " goal" into a requirement. 31 Use of the same metric in the " cause or contribute" context as used for establishing reasonable progress goals, tracking changes in visibility conditions, and defining baseline, current, and natural conditions simply provides for a consistent approach to quantifying visibility impairment.

In response to commenters who said we conflated the " cause or contribute" test, we are clarifying that for purposes of determining which sources are subject to BART, States should consider a 1.0 deciview change or more from an individual source 32 If " causing" visibility impairment means causing a humanly perceptible change in visibility in virtually all situations ( i. e. a 1.0 deciview change), then " contributing" to visibility impairment must mean having some lesser impact on the conditions affecting visibility that need not rise to the level of human perception.

106 to " cause" visibility impairment, and a change of 0.5 deciviews to " contribute" to impairment. 32 In a regulatory context, we believe that a State's decision as to an appropriate threshold for contribution could depend upon the number of sources affecting a class I area. To illustrate, if there were only one emissions source affecting visibility in a class I area, that source could have a deciview impact only slightly below the perceptibility threshold without contributing to noticeable impairment. However, if there were 100 sources each changing visibility by 0.1 deciviews, the total impact would be a 10 deciview change in visibility. In this hypothetical example,

all 100 sources would be contributing, in equal amounts, to substantial visibility impairment.