Prevention of Significant Deterioration New Source Review: Refinement of Increment Modeling Procedures, 31372-31399 [E7-10459]

Agencies

• ENVIRONMENTAL PROTECTION AGENCY

[Federal Register Volume 72, Number 108 (Wednesday, June 6, 2007)]
[Proposed Rules]
[Pages 31372-31399]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E7-10459]



[[Page 31371]]

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Part II





Environmental Protection Agency





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40 CFR Parts 51 and 52



 Prevention of Significant Deterioration New Source Review: Refinement 
of Increment Modeling Procedures; Proposed Rule

Federal Register / Vol. 72, No. 108 / Wednesday, June 6, 2007 / 
Proposed Rules

[[Page 31372]]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 51 and 52

[EPA-HQ-OAR-2006-0888; FRL-8320-7]
RIN 2060-AO02


Prevention of Significant Deterioration New Source Review: 
Refinement of Increment Modeling Procedures

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: Under the requirements of the Clean Air Act (Act), the New 
Source Review (NSR) program includes Prevention of Significant 
Deterioration (PSD) measures, which protect air quality in areas that 
currently have clean air. For some pollutants, the PSD program protects 
clean air through a system of ``increments.'' These increments specify 
the maximum extent to which the ambient concentration of these 
pollutants may be allowed to increase above the legally defined 
baseline concentration in an area with clean air. In this rulemaking, 
we propose to refine several aspects of the method that may be used to 
calculate an increase in concentration for increment purposes. These 
refinements are intended to clarify how States and regulated sources 
may calculate increases in concentrations for the purposes of 
determining compliance with the PSD increments.

DATES: Comments. Written comments must be received on or before August 
6, 2007.
    Public Hearing. If anyone contacts EPA requesting to speak at a 
public hearing by June 26, 2007, we will hold a public hearing 
approximately 30 days after publication in the Federal Register. 
Additional information about the hearing would be published in a 
subsequent Federal Register notice.

ADDRESSES: Comments. Submit your comments, identified by Docket ID No. 
EPA-HQ-OAR-2006-0888, by one of the following methods:
     https://www.regulations.gov: Follow the online instructions 
for submitting comments.
     E-mail: a-and-r-docket@epa.gov.
     Fax: (202) 566-1741.
     Mail: Environmental Protection Agency, EPA Docket Center 
(EPA/DC), Air and Radiation Docket, Mail Code 6102T, 1200 Pennsylvania 
Avenue, NW., Washington, DC 20460. Please include 2 copies.
     Hand Delivery: EPA Docket Center, (Air Docket), EPA/DC, 
EPA West, Room 3334, 1301 Constitution Ave., NW., Washington, DC. Such 
deliveries are only accepted during the Docket's normal hours of 
operation, and special arrangements should be made for deliveries of 
boxed information.
    Instructions. Direct your comments to Docket ID No. EPA-HQ-OAR-
2006-0888. EPA's policy is that all comments received will be included 
in the public docket without change and may be made available online at 
https://www.regulations.gov, including any personal information 
provided, unless the comment includes information claimed to be 
Confidential Business Information (CBI) or other information whose 
disclosure is restricted by statute. Do not submit information that you 
consider to be CBI or otherwise protected through https://
www.regulations.gov or e-mail. The https://www.regulations.gov Web site 
is an ``anonymous access'' system, which means EPA will not know your 
identity or contact information unless you provide it in the body of 
your comment. If you send an e-mail comment directly to EPA without 
going through https://www.regulations.gov, your e-mail address will be 
automatically captured and included as part of the comment that is 
placed in the public docket and made available on the Internet. If you 
submit an electronic comment, EPA recommends that you include your name 
and other contact information in the body of your comment and with any 
disk or CD-ROM you submit. If EPA cannot read your comment due to 
technical difficulties and cannot contact you for clarification, EPA 
may not be able to consider your comment. Electronic files should avoid 
the use of special characters, any form of encryption, and be free of 
any defects or viruses. For additional instructions on submitting 
comments, go to section I.B of the SUPPLEMENTARY INFORMATION section of 
this document.
    Docket. All documents in the docket are listed in the https://
www.regulations.gov index. 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 https://
www.regulations.gov or in hard copy at the Air Docket, EPA/DC, EPA 
West, Room 3334, 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 Air 
Docket is (202) 566-1742.

FOR FURTHER INFORMATION CONTACT: Ms. Jessica Montanez, New Source 
Review Group, Air Quality Policy Division (C504-03), U.S. Environmental 
Protection Agency, Research Triangle Park, NC 27711, telephone number: 
(919) 541-3407; fax number: (919) 541-5509, or electronic mail e-mail 
address: montanez.jessica@epa.gov.

SUPPLEMENTARY INFORMATION: The information presented in this preamble 
is organized as follows:

I. General Information
    A. Does this action apply to me?
    B. What should I consider as I prepare my comments for EPA?
    C. Where can I get a copy of this document and other related 
information?
    D. How can I find information about a possible hearing?
II. Background
    A. What is the PSD program?
    B. What are PSD increment analyses?
    C. Why do we need to clarify the method for analyzing increment 
consumption?
    D. What are the Clean Air Act requirements related to 
increments?
III. Summary of This Proposed Action
IV. Proposed Clarifications Regarding the Effect of the Draft New 
Source Review Workshop Manual
V. Proposed Clarifications and Changes to Increment Modeling 
Procedures
    A. What kind of emissions consume or expand the PSD increment?
    B. How are emissions estimated for sources that consume 
increment?
    C. What meteorological models and data should be used in 
increment consumption modeling?
    D. What are my documentation and data and software availability 
requirements?
VI. Implementation Issues
    A. Is there a need for States to make revisions to their SIPs?
    B. When would these policies be put into effect?
VII. Statutory and Executive Order Reviews
    A. Executive Order 12866--Regulatory Planning and Review
    B. Paperwork Reduction Act
    C. Regulatory Flexibility Analysis
    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 and Safety Risks
    H. Executive Order 13211--Actions That Significantly Affect 
Energy Supply, Distribution, or Use
    I. Executive Order 12898--Federal Actions To Address 
Environmental Justice in Minority Populations and Low-Income 
Populations
    J. National Technology Transfer and Advancement Act
VIII. Statutory Authority

[[Page 31373]]

I. General Information

A. Does this action apply to me?

    Entities potentially affected by this proposed action include 
owners and operators of emission sources in all industry groups, as 
well as the EPA and State, local, and tribal governments that are 
delegated authority to implement these regulations. The majority of 
sources potentially affected are expected to be in the following 
groups:

------------------------------------------------------------------------
          Category                  NAICS\a\           Industry group
------------------------------------------------------------------------
Industry....................  221111, 221112,       Electric services.
                               221113, 221119,
                               221121, 221122.
                              32411...............  Petroleum refining.
                              325181, 32512,        Industrial inorganic
                               325131, 325182,       chemicals.
                               211112, 325998,
                               331311, 325188.
                              32511, 325132,        Industrial organic
                               325192, 325188,       chemicals.
                               325193, 32512,
                               325199.
                              32552, 32592, 32591,  Miscellaneous
                               325182, 32551.        chemical products.
                              211112..............  Natural gas liquids.
                              48621, 22121........  Natural gas
                                                     transport.
                              32211, 322121,        Pulp and paper
                               322122, 32213.        mills.
                              322121, 322122......  Paper mills.
                              336111, 336112,       Automobile
                               336712, 336211,       manufacturing.
                               336992, 336322,
                               336312, 33633,
                               33634, 33635,
                               336399, 336212,
                               336213.
                              325411, 325412,       Pharmaceuticals.
                               325413, 325414.
Federal government..........  924110..............  Administration of
                                                     Air and Water
                                                     Resources and Solid
                                                     Waste Management
                                                     Programs.
State/local/tribal            924110..............  Administration of
 Government.                                         Air and Water
                                                     Resources and Solid
                                                     Waste Management
                                                     Programs.
------------------------------------------------------------------------
\a\ North American Industry Classification System.

    This table is not intended to be exhaustive, but rather provides a 
guide for readers regarding entities likely to be affected by this 
action. If you have any questions regarding the applicability of this 
action to a particular entity, contact the person listed in the 
preceding FOR FURTHER INFORMATION CONTACT section.

B. What should I consider as I prepare my comments for EPA?

1. Submitting Confidential Business Information (CBI)
    Do not submit Confidential Business Information to EPA through 
https://www.regulations.gov or e-mail. Clearly mark the part or all of 
the information that you claim to be CBI. For CBI information in a disk 
or CD ROM that you mail to EPA, mark the outside of the disk or CD ROM 
as CBI and then identify electronically within the disk or CD ROM the 
specific information claimed as CBI, a copy of the comment that does 
not contain the information claimed as CBI must be submitted for 
inclusion in the public docket. Information so marked will not be 
disclosed except in accordance with procedures set forth in 40 Code of 
Federal Regulations (CFR) part 2.
2. Suggestions for Preparing Your Comments
    When submitting comments, remember to:
     Identify the rulemaking by docket number and other 
identifying information (subject heading, Federal Register date and 
page number).
     Follow directions. The agency may ask you to respond to 
specific questions or organize comments by referencing a CFR part or 
section number.
     Explain why you agree or disagree; suggest alternatives 
and substitute language for your requested changes.
     Describe any assumptions and provide any technical 
information and/or data that you used.
     If you estimate potential costs or burdens, explain how 
you arrived at your estimate in sufficient detail to allow for it to be 
reproduced.
     Provide specific examples to illustrate your concerns, and 
suggest alternatives.
     Explain your views as clearly as possible, avoiding the 
use of profanity or personal threats.
     Make sure to submit your comments by the comment period 
deadline identified.

C. Where can I get a copy of this document and other related 
information?

    In addition to being available in the docket, an electronic copy of 
this proposal will also be available on the World Wide Web. Following 
signature by the EPA Administrator, a copy of this notice will be 
posted in the regulations and standards section of our NSR (New Source 
Review) home page located at https://www.epa.gov/nsr.

D. How can I find information about a possible hearing?

    Persons interested in presenting oral testimony should contact Ms. 
Pam Long, New Source Review Group, Air Quality Policy Division (C504-
03), U.S. EPA, Research Triangle Park, NC 27711, telephone number (919) 
541-0641 or e-mail long.pam@epa.gov at least 2 days in advance of the 
public hearing. Persons interested in attending the public hearing 
should also contact Ms. Long to verify the time, date, and location of 
the hearing. The public hearing will provide interested parties the 
opportunity to present data, views, or arguments concerning this 
action.

II. Background

A. What is the PSD program?

    Part C of title I of the Act contains the requirements for a 
component of the major NSR program known as the PSD program. This 
program sets forth procedures for the preconstruction review and 
permitting of new and modified major stationary sources of air 
pollution locating in areas meeting the National Ambient Air Quality 
Standards or ``NAAQS'' (``attainment'' areas) and areas for which there 
is insufficient information to classify an area as either attainment or 
nonattainment (``unclassifiable'' areas).
    The NSR provisions of the Act are a combination of air quality 
planning and air pollution control technology program requirements for 
new and modified stationary sources of air

[[Page 31374]]

pollution. In brief, section 109 of the Act requires us to promulgate 
primary NAAQS to protect public health and secondary NAAQS to protect 
public welfare. Once we have set these standards, States must develop, 
adopt, and submit to us for approval a State Implementation Plan (SIP) 
that contains emission limitations and other control measures to attain 
and maintain the NAAQS and to meet the requirements of section 110(a) 
of the Act. Each SIP is required to contain a preconstruction review 
program for the construction and modification of any stationary source 
of air pollution to assure that the NAAQS are achieved and maintained; 
to protect areas of clean air; to protect Air Quality Related Values 
(including visibility) in certain national parks, wilderness areas, and 
other natural areas of special concern; to assure that appropriate 
emissions controls are applied; to maximize opportunities for economic 
development consistent with the preservation of clean air resources; 
and to ensure that any decision to increase air pollution is made only 
after full public consideration of all the consequences of such a 
decision. Most States have SIP-approved major NSR programs; however 
there are some States that instead implement the Federal PSD program at 
40 CFR 52.21 through delegation.\1\
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    \1\ Where a State does not have a SIP-approved program and 
chooses not to accept delegation of the Federal PSD program, EPA 
implements the PSD requirements as the reviewing authority within 
that jurisdiction. In addition, we implement the PSD program in 
Indian country until such time as a Tribe elects to adopt, and we 
approve, a Tribal Implementation Plan (TIP) that contains a PSD 
program that meets the requirements of the Act.
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    The applicability of the PSD program to a particular source must be 
determined in advance of construction and is pollutant specific. Once a 
source is determined to be subject to PSD, among other requirements, it 
must undertake a series of analyses to demonstrate that it will use the 
best available control technology (BACT) and will not cause or 
contribute to a violation of any NAAQS or any maximum allowable ambient 
pollutant concentration increase (increment). In cases where the 
source's emissions may adversely affect an area classified as Class I, 
additional review is conducted to protect the increments and special 
attributes of such an area defined as ``air quality related values'' 
(AQRVs).
    When the reviewing authority reaches a preliminary decision to 
authorize construction of a proposed new major source or major 
modification, it must provide notice of the preliminary decision and an 
opportunity for comment by the general public, industry, and other 
persons that may be affected by the major source or major modification. 
After considering and responding to the comments, the reviewing 
authority may issue a final determination on the construction permit in 
accordance with the PSD regulations.

B. What are PSD increment analyses?

1. Framework for Increment Analyses
    Under section 165(a)(3) of the Act, a PSD permit applicant must 
demonstrate that emissions from the proposed construction and operation 
of a facility ``will not cause, or contribute to, air pollution in 
excess of any * * * maximum allowable increase or maximum allowable 
concentration for any pollutant* * *.'' The ``maximum allowable 
increase'' of an air pollutant that is allowed to occur above the 
applicable baseline concentration for that pollutant is known as the 
PSD increment. The maximum allowable concentration is the ceiling 
established by adding the PSD increment to the baseline concentration. 
By establishing the maximum allowable increase in a particular area, an 
increment defines ``significant deterioration.''
    Increments have been established for three pollutants--Sulfur 
Dioxide (SO2), Particulate Matter (PM), and Nitrogen Dioxide 
(NO2)--and for a variety of averaging periods, which 
correspond to the averaging periods for the NAAQS for those pollutants. 
In addition, all attainment and unclassifiable areas are classified as 
Class I, Class II, or Class III, and different increment levels apply 
in each type of area. Class I areas include certain national parks, 
wilderness areas, and other natural areas of special concern; the 
smallest increments are specified for these areas. Nearly all other 
areas in the United States are currently classified as Class II, where 
higher increments are specified. States and Tribes have the authority 
to redesignate Class II areas to Class III (with still higher 
increments) to promote development, but, to date, none have chosen to 
do so. States and Tribes also may redesignate Class II areas to Class I 
to provide additional protection; some Tribes have done so. The 
increments are codified at 40 CFR 51.166(c) and 52.21(c). The current 
increment values are shown below in Table 1.

                    Table 1. Current Increment Values
------------------------------------------------------------------------
                                                              Maximum
                                                             allowable
                                                             increase
                        Pollutant                           (micrograms
                                                             per cubic
                                                              meter)
------------------------------------------------------------------------
                                 Class I
------------------------------------------------------------------------
Particulate matter:
    PM-10, annual arithmetic mean.......................               4
    PM-10, 24-hr. maximum...............................               8
Sulfur dioxide:
    Annual arithmetic mean..............................               2
    24-hr. maximum......................................               5
    3-hr. maximum.......................................              25
Nitrogen dioxide:
    Annual arithmetic mean..............................             2.5
------------------------------------------------------------------------
                                Class II
------------------------------------------------------------------------
Particulate matter:
    PM-10, annual arithmetic mean.......................              17
    PM-10, 24-hr. maximum...............................              30

[[Page 31375]]

 
Sulfur dioxide:
    Annual arithmetic mean..............................              20
    24-hr. maximum......................................              91
    3-hr. maximum.......................................             512
Nitrogen dioxide:
    Annual arithmetic mean..............................              25
------------------------------------------------------------------------
                                Class III
------------------------------------------------------------------------
Particulate matter:
    PM-10, annual arithmetic mean.......................              34
    PM-10, 24-hr. maximum...............................              60
Sulfur dioxide:
    Annual arithmetic mean..............................              40
    24-hr. maximum......................................             182
    3-hr. maximum.......................................             700
Nitrogen dioxide:
    Annual arithmetic mean..............................              50
------------------------------------------------------------------------

    For PSD baseline purposes, a baseline area for a particular 
pollutant emitted from a source includes the attainment or 
unclassifiable area in which the source is located as well as any other 
attainment or unclassifiable area in which the source's emissions of 
that pollutant are projected (by air quality modeling) to result in an 
ambient concentration increase of at least 1 [mu]g/m3 
(annual average). See, e.g., 40 CFR 52.21(b)(15)(i). Once the baseline 
area is established, subsequent major sources undergoing PSD review in 
that area must address the fact that a portion of the available 
increment may already have been consumed by previous emissions 
increases.
    Three dates related to the PSD baseline concept are important in 
calculating the amount of increment consumed by pollutant emissions 
from the major source undergoing PSD review and other applicable 
emissions increases and decreases in a particular baseline area. In 
general, the submittal date of the first complete PSD permit 
application in a particular area is the operative ``baseline date.'' 
\2\ On or before the date of the first complete PSD application, most 
emissions are considered to be part of the baseline concentration. Most 
emissions increases that occur after the baseline date will be counted 
toward the amount of increment consumed. Similarly, emissions decreases 
after the baseline date expand the amount of increment that is 
available.
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    \2\ Baseline dates are pollutant specific. That is, a complete 
PSD application establishes the baseline date only for those 
regulated NSR pollutants that are projected to be emitted in 
significant amounts (as defined in the regulations) by the 
applicant's new source or modification. Thus, an area may have 
different baseline dates for different pollutants.
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    In actuality, there are two baseline dates that are related to the 
determination of how much increment is being consumed in a particular 
baseline area. These two dates, described below, are necessary to 
properly account for the emissions that are to be counted toward 
increment consumed in accordance with the statutory definition of 
``baseline concentration'' in section 169(4) of the Act. The statutory 
definition provides that the baseline concentration of a pollutant for 
a particular baseline area is generally the air quality at the time of 
the first application for a PSD permit in the area. Consequently, any 
increases in actual emissions occurring after that date (with some 
possible exceptions that we will discuss later) would be considered to 
consume the applicable PSD increment. However, the statutory definition 
also provides that ``[E]missions * * * from any major emitting facility 
on which construction commenced after January 6, 1975 shall not be 
included in the baseline and shall be counted in pollutant 
concentrations established under this part.''
    To make this distinction between the date when emissions changes in 
general (i.e., from both major and minor sources) count in the 
increment and the date when emissions resulting from the construction 
at a major stationary source count in the increment, we established the 
terms ``minor source baseline date'' and ``major source baseline 
date,'' respectively. See 40 CFR 51.166(b)(14) and 52.21(b)(14). 
Accordingly, the ``minor source baseline date'' is the date on which 
the first complete application for a PSD permit is filed in a 
particular area. Any change in actual emissions after that date counts 
in the PSD increment for that area. The ``major source baseline date'' 
is thus named because it is the date after which actual emissions 
associated with construction at a major stationary source affect the 
available PSD increment. In accordance with the statutory definition of 
``baseline concentration,'' the PSD regulations define a fixed date to 
represent the major source baseline date for each pollutant for which 
an increment exists. Congress defined the major source baseline date 
for the statutory increments for PM and SO2 as January 6, 
1975. For the NO2 increments, which we promulgated in 1988 
under our authority to establish an increment system under section 
166(a) of the Act, the major source baseline date was selected as 
February 8, 1988--the date on which we proposed increments for 
NO2.
    Finally, the PSD regulations set out the third date that is 
relevant to the PSD baseline concept. These regulations provide that 
the earliest date on which the minor source baseline date can be 
established is the date immediately following the ``trigger date'' for 
the pollutant-specific increment. See, e.g., 40 CFR 52.21(b)(14)(ii). 
For PM and SO2, Congress defined the applicable trigger date 
as August 7, 1977--the date of the 1977 amendments to the Act

[[Page 31376]]

when the original statutory increments were established by Congress. 
For NO2, we selected the trigger date as February 8, 1988--
the date on which we proposed increments for NO2. See 53 FR 
40656, 40658; October 17, 1988.
    Under this approach, the baseline concentration is not actually 
established for a PSD baseline area until after the ``minor source 
baseline date'' is established by the submission of the first PSD 
permit application for a source whose emissions would affect a given 
baseline area. Although major source emissions may consume increment 
prior to this date, they are not factored into the calculation until 
the minor source baseline date is triggered.
    Once the minor source baseline date associated with the first 
proposed new major stationary source or major modification in an area 
is established, the new emissions from that source consume a portion of 
the increment in that area, as do any subsequent emissions increases 
that occur from any source in the area. When the maximum pollutant 
concentration increase defined by the increment has been reached, 
additional PSD permits cannot be issued until sufficient amounts of the 
increment are ``freed up'' via emissions reductions that may occur 
voluntarily, e.g., via source shutdowns, or via control requirements 
imposed by the reviewing authority. Moreover, the air quality in a 
region cannot deteriorate to a level in excess of the applicable NAAQS, 
even if all the increment has not been consumed. Therefore, new or 
modified sources located in areas where the air pollutant concentration 
is near the level allowed by the NAAQS may not have full use of the 
amount of pollutant concentration increase allowed by the increment.
2. General Approach to Increment Analyses
    The EPA and the States have generally used an emissions inventory 
and modeling approach to identify the degree to which an increment has 
been consumed or will be consumed by major source construction. Ambient 
monitoring has not been used to establish baseline concentrations or to 
evaluate increment consumption because ambient measurements reflect 
emissions from all sources, including those that should be excluded 
from the measurements. We have not necessarily required the 
identification of a specific baseline concentration but rather have 
focused on measuring the change in concentration from the legally 
established baseline date to the time of the analysis. For example, in 
the preamble to the 1978 PSD regulation (43 FR 26388, 26400; June 19, 
1978), we stated the following:

    The regulations promulgated today no longer suggest that the 
baseline concentration be formally established. The Administrator 
feels that increment consumption can be best tracked by tallying 
changes in emissions levels of sources contributing to the baseline 
concentration and increases in emissions due to new sources. Data to 
establish baseline air quality in an absolute sense would be needed 
only if increment consumption were to be tracked using ambient 
measurements. Thus, to implement the air quality increment approach, 
the reviewing authority needs to verify that all changes from 
baseline emissions rates (decreases or increases as appropriate) in 
conjunction with the increased emissions associated with approved 
new source construction will not violate an applicable increment * * 
*.

This method has made it easier to comply with the statutory provisions 
(discussed below in section II.D of this preamble) excluding certain 
increases in emissions at major sources from the baseline concentration 
and allowing other emissions to be excluded from increment consumption.
    Even with that said, we believe that it would also be acceptable 
and consistent with the Act for a State to use an approach of 
establishing an actual baseline concentration using an initial baseline 
emissions inventory. The State could then calculate the consumed 
increment by revising the inventory to include the relevant emissions 
increases and decreases as discussed above.
3. Agency Guidance and Specific Approaches Used in Practice
    Over time, the Agency developed some recommended approaches that 
reviewing authorities could use to determine whether changes in 
emissions rates and increases in emission associated with new 
construction since the baseline date have or have not increased 
concentrations above the increments. Our recommendations have generally 
been described in modeling guidelines and guidance documents, while the 
PSD regulations in 40 CFR 51.166 and 52.21 contained only a few basic 
requirements for the increment analysis.
    Some of our recommendations for the increment analysis have been 
included in the ``Guideline on Air Quality Models,'' which is located 
in appendix W to 40 CFR part 51. Appendix W provides modeling 
guidelines for sources and reviewing authorities under a variety of 
Clean Air Act programs. The PSD regulations cite appendix W and state 
that all PSD air quality modeling should be based on the ``applicable 
models, data bases, and other requirements'' specified there. See 40 
CFR 51.166(l) and 52.21(l). Although appendix W is incorporated by 
reference in the PSD regulations, we have continued to refer to this as 
a ``guideline'' and used language in the guideline to indicate that it 
does not mandate specific procedures in all cases. See, In re: Prairie 
State Generating Company, PSD Permit Appeal No. 05-05, slip. op. at 132 
(EAB August 24, 2006) (``Appendix W is replete with references to 
`recommendations,' `guidelines,' and reviewing authority discretion.'') 
It is also important to keep in mind that appendix W provides 
guidelines for other types of regulatory applications, not just PSD 
increment analyses. As a result, not all the recommendations included 
in appendix W are applicable to an analysis of increment consumption 
under the PSD program. Care must be taken to evaluate whether certain 
recommendations are appropriate for the particular circumstances of 
each increment analysis.
    We also included some suggestions for the increment analysis in the 
1990 draft ``New Source Review Workshop Manual'' (draft NSR Manual).\3\ 
This draft document addressed many aspects of PSD permitting, including 
the increment analyses. However, we made clear on the very first page 
that this manual was not intended to establish binding regulatory 
requirements. Draft NSR Manual at 1 (Preface). In addition, we never 
finalized the 1990 draft of the NSR Manual and accordingly never 
intended for the manual itself to establish final EPA policies or 
interpretations of our NSR regulations. Nevertheless, many people have 
looked to this document for guidance and have sometimes improperly 
construed the draft NSR Manual to contain requirements that must be 
followed.
---------------------------------------------------------------------------

    \3\ This document is often referred to as the ``Puzzle Book'' 
due to the depiction of jigsaw puzzle pieces on its cover.
---------------------------------------------------------------------------

    The EPA's Environmental Appeals Board (``Board'') has sometimes 
referenced the draft NSR Manual as a reflection of our thinking on 
certain PSD issues, but the Board has been clear that the draft NSR 
Manual is not a binding Agency regulation. See, In re: Indeck-Elwood, 
LLC, PSD Permit Appeal No. 03-04, slip. op. at 10 n. 13 (EAB Sept. 27, 
2006); In re: Prairie State Generating Company, PSD Permit Appeal No. 
05-05, slip. op. at 7 n. 7 (EAB Aug 24, 2006). In these and other 
cases, the Board also considered briefs filed on behalf of the Office 
of Air and Radiation that provided more current information on the 
thinking of the EPA headquarters program office on specific PSD issues

[[Page 31377]]

arising in particular cases. Thus, the Board has looked to the draft 
NSR Manual as one resource to consider in developing Agency positions 
through case-by-case adjudications, while recognizing that the draft 
NSR Manual does not itself contain binding requirements.
    Other non-binding EPA guidance letters or memoranda that have 
addressed increment consumption analyses are discussed in more detail 
below in the context of discussion on specific issues.
    Based largely on prior EPA guidance, the approach that has 
generally been used in States and EPA Regional Offices for increment 
analyses has involved the following four steps:
    1. Determine the 1 [mu]g/m3 ``significant impact area'' 
for the particular pollutant for which the new major source or major 
modification is undergoing PSD review. (If the source is subject to an 
increment analysis for more than one pollutant, each analysis is 
carried out independently).
    2. Identify the other sources in the vicinity of the new or 
modified source whose emissions affect the significant impact area.
    3. Estimate the emissions from those sources that consume 
increment.
    4. Model the change in emissions to get a concentration change, and 
compare that concentration change to the applicable increment.

    The actual increment analysis that a proposed new or modified 
source undergoing PSD review must complete will depend on the area 
impacted by the source's new emissions.
    We have provided approved air quality models and guidelines for 
sources to use to project the air quality impact of each pollutant 
(over each averaging period) for which an increment analysis must be 
done. In addition, we established significant impact levels for each 
pollutant under the nonattainment major NSR program that have also been 
used under the PSD program to identify levels below which the source's 
modeled impact is regarded as de minimis. See 40 CFR 51.165(b) and part 
51, appendix S, section III.A.\4\ In the event that a source's modeled 
impacts of a particular pollutant are below the applicable significant 
impact level at all ambient air locations modeled, i.e., de minimis 
everywhere, EPA policy provides that no further modeling analysis is 
required for that pollutant. Our policy has been that when a 
preliminary screening analysis based on the significant impact level is 
sufficient to demonstrate that the source's emissions will not cause or 
contribute to a violation of the increment, there is no need for a full 
impacts analysis involving a cumulative evaluation of the emissions 
from the proposed source and other sources affecting the area.
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    \4\ The cited regulations actually apply to sources located in a 
PSD area, which must demonstrate that they will not cause or 
contribute to a violation of the NAAQS in an adjacent nonattainment 
area. This demonstration may be made by showing that the emissions 
from the PSD source alone are below the significant impact levels 
set forth in 40 CFR 51.165(b)(2). Based on EPA interpretations and 
guidance, these significant impact levels have also been widely used 
in the PSD program to define the extent of the impact area where an 
increment analysis must be performed. We proposed to codify these 
significant impact levels for use in the PSD program in 1996 as part 
of a comprehensive proposal to revise the major NSR regulations. See 
61 FR 38250, 38325, July 23, 1996. We have not yet taken final 
action on this proposal.
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    Within the impact area of a source that does have a significant 
impact, increment consumption is calculated using the source's proposed 
emissions increase, along with other emissions increases or decreases 
of the particular pollutant from other sources that would consume 
increment and which have occurred since the minor source baseline date 
established for that area. (For major sources, emissions increases or 
decreases resulting from construction as defined at 40 CFR 51.166(b)(8) 
and 40 CFR 52.21(b)(8) that have occurred since the major source 
baseline date consume or expand increment). Thus, an emissions 
inventory of sources whose emissions consume or expand the available 
increment in the area must be compiled. The inventory includes not only 
sources located directly in the impact area, but sources outside the 
impact area that affect the air quality within the impact area. Section 
IV.A.1 of this preamble discusses the types of sources that are to be 
included in the emissions inventory for increment analyses.
    The inventory of emissions includes emissions from increment-
affecting sources at two separate time periods--the baseline date and 
the current period of time. For each source that was in existence on 
the relevant baseline date (major source or minor source), the 
inventory includes the source's actual emissions on the baseline date 
and its current actual emissions. The change in emissions over these 
time periods represents the emissions that consume increment (or, if 
emissions have gone down, expand the available increment). For sources 
constructed since the relevant baseline date, all their current actual 
emissions consume increment and are included in the inventory.
    An emissions inventory must be prepared for each averaging period 
for which an increment has been specified for the pollutant under 
review. In many cases, direct emissions data are not available for some 
or all averaging periods, and actual emissions must be estimated. This 
can be particularly challenging for existing sources where the baseline 
emissions must be determined and the baseline date is well in the past. 
The approach generally used per EPA guidance has been to base the 
annual emissions inventory on the actual measured emissions or actual 
hours of operation, fuel usage, raw materials used, etc., while basing 
the emissions inventory for shorter averaging periods on the maximum 
emissions over each averaging period as determined from available data 
(again, emission measurements, operating hours, fuel or materials 
consumption, etc.).
    When the inventory of emissions has been compiled, computer 
modeling is used to determine the change in ambient concentration that 
will result from these emissions when combined with the proposed 
emissions increase from the new major source or major modification that 
is undergoing PSD review. The modeling has generally been guided by the 
``Guideline on Air Quality Models'' (40 CFR part 51, appendix W), which 
includes provisions on air quality models and the meteorological data 
input into these models.
    Two possible approaches have been used to predict the change in air 
pollutant concentration using models. One approach is to make a single 
model run after calculating the difference in emissions from the 
baseline date to the current period of time. An alternative approach is 
to make two model runs (one based on an inventory of baseline emissions 
and the second based on an inventory of current actual emissions) and 
calculate the difference between them.
    The model output (expressed as a change in concentration) for each 
relevant averaging period is then compared to the corresponding 
allowable PSD increment. If the model results indicate that the 
increment(s) will not be exceeded, the reviewing authority may issue a 
PSD permit to the source. Except as discussed below, if the modeling 
shows that the source would cause or contribute to a violation of a PSD 
increment,\5\ the reviewing authority

[[Page 31378]]

may not issue the permit. The source may revise its permit application 
to reduce its proposed emissions, or it may mitigate the impact of its 
emissions through obtaining offsetting emission reductions from other 
sources in the emissions inventory.
---------------------------------------------------------------------------

    \5\ The proposed source is deemed to ``cause or contribute to'' 
an increment violation if the modeling shows that the impact 
attributable to the source at the time and place of the violation is 
greater than the relevant significant impact level.
---------------------------------------------------------------------------

    If the modeling shows only an increment violation in a Class I 
area, the source has the opportunity to apply for a ``variance'' from 
the Federal Land Manager (FLM) that has responsibility for that Class I 
area. If the source successfully demonstrates to the FLM that emissions 
from the source will not have an adverse effect on the AQRVs of the 
Class I area, and to the reviewing authority that the emissions will 
not violate a set of higher increment levels specified in the Act 
(generally equal to the Class II increments), the reviewing authority 
may issue a PSD permit to the source. The source may further appeal to 
the Governor and the President in certain situations. These variances 
are discussed in greater detail in section IV.A.2 of this preamble.

C. Why do we need to refine the method for analyzing increment 
consumption?

    We have never adopted detailed regulations establishing a specific 
methodology that sources and reviewing authorities must use to 
calculate an increase in concentrations for purposes of determining 
compliance with the PSD increments. Instead, increment analyses have 
been conducted by States and EPA Regional Offices based on the 
guidelines and guidance discussed in the previous section. In the 
absence of definitive requirements, sources and reviewing authorities 
have attempted to apply the available guidance to a wide range of 
situations. Differing interpretations and approaches have resulted, 
along with controversy over how binding the guidelines and guidance are 
on reviewing authorities and who (EPA or the reviewing authorities) has 
the ultimate discretion to determine which approaches are reasonable 
for a specific increment analysis. With this proposal, we intend to 
provide greater clarity on several issues.
    One push for greater clarity has come from the Western States Air 
Resources Council (WESTAR) PSD Reform Workgroup, with participants from 
Western States, the U.S. National Park Service, U.S. Fish and Wildlife 
Service, U.S. Forest Service, and the U.S. Bureau of Land Management 
and consultation by EPA. The workgroup was formed in early 2004 to 
develop recommendations to improve the effectiveness of the PSD 
program. The goal of the WESTAR effort was to propose changes to the 
PSD program that would result in a more practical program, 
significantly reducing constraints in the current program that they 
viewed as limiting State and local agencies' abilities to address 
cumulative incremental consumption and Class I AQRV analysis and 
protection, some of which were identified in a letter to EPA.\6\ While 
the purpose of today's notice is focused on refining increment analysis 
procedures, we are considering broader changes to the program as a 
separate rulemaking to address additional concerns that WESTAR and 
others have raised.\7\
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    \6\ ``Recommendations for Improving the Prevention of 
Significant Deterioration Program.'' Stuart A. Clark, President, 
Western States Air Resources Council, May 19, 2005.
    \7\ In addition to WESTAR's recommendations, we received 
comments from the Northeast States for Coordinated Air Use 
Management (NESCAUM) on the WESTAR recommendations in a letter and 
attachment from Arthur N. Marin, Executive Director of NESCAUM, 
October 18, 2005.
---------------------------------------------------------------------------

    A major point raised by WESTAR is that States need to consult early 
and often in order to agree in advance on modeling protocols to enable 
consistency between the States in performing the analyses and to ensure 
equity in application of the analysis. WESTAR further recommended that 
we take steps to ensure that EPA Regional Offices, in partnership with 
States and FLMs, operate consistently among themselves in inter-
jurisdictional contexts and develop data and methods that will better 
enable inter-jurisdictional analysis. WESTAR stressed that a balance is 
needed between providing States with case-by-case, cross-jurisdictional 
PSD increment analysis flexibility and providing the national or 
regional standardization necessary to ensure equity among States, 
simplify cross-jurisdictional analysis, and facilitate coordination 
with FLMs. The WESTAR report also noted a lack of clarity and sometimes 
narrow interpretations of the definition of actual emissions used for 
purposes of calculating point source emissions for inclusion in 
emissions inventories for PSD analyses. All of the WESTAR workgroup 
representatives agreed that it is desirable to bring greater clarity 
and consistency to approaches for conducting refined analyses, 
particularly related to approaches for calculating point source 
emissions. Today's notice is a step toward achieving that balance 
between case-by-case flexibility and inter-jurisdictional consistency.

D. What are the Clean Air Act requirements related to increments?

    The PSD increments are established under sections 163 and 166 of 
the Act. In section 163 of the Act, Congress adopted specific numerical 
increments for particulate matter and sulfur dioxide in each of the 
three classes of PSD baseline areas (i.e., Class I, II, and III, as 
described above in section II.B.1). In 1990, Congress created section 
166(f) of the Act which authorized us to substitute increments based on 
the PM10 indicator for the original particulate matter 
increments contained in section 163. Consistent with this provision, we 
substituted PM10 increments for the increments based on 
total suspended particulate matter in a 1993 rulemaking (58 FR 51622, 
June 3, 1993). In section 166(a) of the Act, Congress directed and 
authorized EPA to promulgate additional increments for nitrogen oxides 
and other pollutants. We promulgated increments for NO2 in 
1988 and reaffirmed those increments in a 2005 rulemaking (53 FR 40656, 
Oct. 17, 1988; 70 FR 59582, Oct. 12, 2005).
    The Act does not directly specify how to determine an increase in 
concentrations for purposes of determining compliance with the PSD 
increments. Section 163(b) of the Act provides that ``the maximum 
allowable increase in concentrations of sulfur dioxide and particulate 
matter over baseline concentration of such pollutants shall not 
exceed'' specified amounts for each pollutant. See CAA sections 
163(b)(1)-(3). The Act does not define an ``increase in 
concentrations'' for purposes of section 163. Likewise, section 
165(a)(3) prohibits permitting a source that causes or contributes to 
``air pollution in excess of any maximum allowable increase or maximum 
allowable concentrations,'' but does not specify how EPA is to 
determine that air pollution would exceed the allowable increase or 
concentration. Section 166 of the Act directs EPA to promulgate 
pollutant-specific PSD regulations which contain ``specific numerical 
measures against which permit applications may be evaluated'' and 
indicates that such measures ``may contain air quality increments.'' 
See CAA sections 166(a), (c), (d). However, there is no further 
guidance in section 166 concerning the method to be used to measure an 
increase in air pollutant concentrations for purposes of evaluation 
against the PSD increments.
    We have found some guidance in the Act in the definition of 
``baseline concentration,'' which we interpret to support our view that 
an increase in concentration for increment purposes

[[Page 31379]]

should be determined on the basis of actual emissions. Section 169(4) 
of the Act defines ``baseline concentration'' as ``the ambient 
concentration levels which exist at the time of the permit 
application.'' The opinion of the United States Court of Appeals for 
the District of Columbia Circuit in Alabama Power v. Costle interpreted 
section 169(4) in a manner that supports establishing the PSD baseline 
concentration using actual emissions. 636 F.2d 323, 375-381 (D.C. Cir. 
1980). Since emissions that consume increment are not included in the 
baseline, we have long recognized that an increase in concentration 
(the consumption of increment) is directly related to baseline 
concentration (45 FR 52676, 52718, Aug. 7, 1980). In light of these 
considerations, we reached the following conclusion:

    Since the Alabama Power decision and the statute both provide 
that actual air quality be used to determine baseline 
concentrations, but provide no guidance on increment consumption 
calculations, EPA has concluded that the most reasonable approach, 
consistent with the statute, is to use actual source emissions, to 
the extent possible, to calculate increment consumption or 
expansion.

See 45 FR 52676, 52718 (Aug. 7, 1980). We expressly incorporated the 
definition of ``actual emissions'' into the regulatory definition of 
``baseline concentration'' (40 CFR 51.166(b)(13) and 52.21(b)(13)). In 
this definition of ``baseline concentration,'' the term ``actual 
emissions'' is referenced both in the provision describing how to 
determine the baseline concentration and in the provision identifying 
emissions that affect the maximum allowable increases (the increment). 
See, e.g., 40 CFR 51.166(b)(13)(ii). The term ``actual emissions'' is 
itself defined in 40 CFR 51.166(b)(21) and 52.21(b)(21).
    The Act also provides some direction concerning the increment 
consumption analysis by identifying particular sources whose emissions 
are counted against the maximum allowable increases and listing 
categories of sources whose emissions may be excluded from the 
increment consumption analysis. In the statutory definition of 
``baseline concentration,'' section 169(4) of the Act specifies that 
``[e]missions of sulfur oxides and particulate matter from any major 
emitting facility on which construction commenced after January 6, 
1975, shall not be included in the baseline and shall be counted 
against the maximum allowable increases in pollutant concentrations 
established under this part.'' This provision makes clear that 
emissions of these pollutants from new or modified major sources that 
commence construction between 1975 and the baseline date for a given 
area shall be counted against the increments and thus are considered to 
``consume'' increment. In addition, section 163(c) authorizes States to 
exclude certain pollution concentrations from the increment consumption 
analysis. This provision authorizes States to ``promulgate rules 
providing that for purposes of determining compliance with the maximum 
allowable increases in ambient concentrations of an air pollutant, the 
following concentrations of such pollutants shall not be taken into 
account.'' The concentrations identified are those attributable to (1) 
fuel switches required under other laws (15 U.S.C. 792 or 16 U.S.C. 
791a); (2) construction or other temporary emission-related activities; 
and (3) new sources outside the United States. The PSD regulations 
reflect these provisions of sections 163(c) and 169(4) of the Act.
    The existing PSD regulations reflect these specific requirements of 
the Act. As discussed earlier, we implemented the last sentence of 
section 169(4) by establishing two separate baseline dates--the major 
source baseline date and the minor source baseline date. See 40 CFR 
51.166(b)(14) and 52.21(b)(14). We implemented section 163(c) of the 
Act by promulgating 40 CFR 51.166(f), which is discussed further below.
    Within the boundaries described above, we read the Act to provide 
EPA with fairly broad discretion to establish regulations concerning 
the approach to be used to measure an increase in concentration for 
purposes of assessing consumption of PSD increments. Since the Act does 
not define ``increase in concentration'' for increment purposes, we 
interpret the Act to grant EPA discretion to develop a method for 
measuring this increase, so long as that method is reasonable and 
consistent with the limited requirements described above. The absence 
of specific direction in the Act concerning how to calculate an 
increase in concentration for increment purposes is similar to the gap 
in the Act concerning how to calculate an increase in emissions for 
purposes of identifying a major modification. With respect to the 
latter issue, the DC Circuit has recently observed that ``In enacting 
the NSR program, Congress did not specify how to calculate `increases' 
in emission, leaving EPA to fill that gap while balancing the economic 
and environmental goals of the statute.'' New York v. EPA, 413 F.3d 3, 
27 (Jan. 25, 2005). We believe Congress intended a similar result with 
respect to ``increases'' in concentration under the increment 
provisions of the PSD side of the NSR program. As observed by the court 
in Alabama Power, ``Congress expected EPA to use `administrative good 
sense' in establishing the baseline and calculating exceedances.'' See 
Alabama Power, 636 F.2d at 380. In this rulemaking, we propose to 
exercise our rulemaking discretion on this topic and provide additional 
guidance to States and regulated sources on how to calculate increases 
in concentrations for purposes of determining compliance with the PSD 
increments.

III. Summary of This Proposed Action

    This action proposes clarifications in eight areas related to 
increment analyses. They are summarized below:
     Effect of the 1990 draft ``New Source Review Workshop 
Manual.'' Discussed in detail in section IV; no regulatory revisions.
     Treatment of sources that have previously received a Class 
I area FLM variance in subsequent increment consumption modeling. 
Discussed in detail in section V.A; regulatory revisions in 40 CFR 
51.166(f)(2) and 52.21(f)(2).
     Data used to estimate emissions. Discussed in detail in 
section V.B.1; regulatory revisions in 40 CFR 51.166(f)(1) and 
52.21(f)(1).
     Time period of emissions used to model pollutant 
concentrations. Discussed in detail in section V.B.2; regulatory 
revisions in 40 CFR 51.166(f)(1) and 52.21(f)(1).
     Actual emissions rates used to model short-term increment 
compliance. Discussed in detail in section V.B.3; regulatory revisions 
in 40 CFR 51.166(f)(1) and 52.21(f)(1).
     Meteorological data and processing. Discussed in detail in 
section V.C.1; no regulatory revisions.
     Years of meteorological data. Discussed in detail in 
section V.C.2; no regulatory revisions.
     Documentation and data and software availability. 
Discussed in detail in section V.D; no regulatory revisions.

IV. Proposed Clarifications Regarding the Effect of the Draft New 
Source Review Workshop Manual

    To avoid future misunderstandings concerning the effect of the 
draft 1990 New Source Review Workshop Manual (draft NSR Manual), we 
propose in this action to make clear that the draft NSR Manual is not a 
binding regulation and does not by itself establish final EPA policy or 
authoritative interpretations of EPA regulations under the New Source 
Review Program. As discussed above, because this document was never 
finalized, we never intended for the manual to establish final agency 
policy

[[Page 31380]]

or authoritative interpretations of EPA's NSR regulations. Furthermore, 
in many areas the positions reflected in the document have become 
outdated and superseded by statutory amendments, rulemakings, 
additional guidance memoranda, and adjudications by the Administrator 
and the EPA Environmental Appeals Board.
    Notwithstanding this proposed clarification concerning the effect 
of the draft NSR Manual, we recognize that some of the views expressed 
in the draft NSR Manual may have been promulgated in EPA regulations or 
adopted by the Agency as final policy statements or interpretations in 
other actions taken before or after the release of the draft NSR Manual 
in 1990. On some topics, the draft NSR Manual compiled pre-existing EPA 
policy and interpretations, but on other matters the document expressed 
proposed policies or interpretations that were never finalized by the 
Agency. To the extent EPA subsequently or previously adopted a view 
expressed in the draft NSR Manual through other action that was clearly 
final, those positions may have achieved the status of final policies 
or interpretations, but positions that are only expressed in the draft 
NSR Manual should not be considered to be a final EPA policy or 
interpretation.
    With respect to the increment analysis that is the subject of this 
rulemaking action, we are proposing to establish regulations that 
supersede many of the recommended approaches for conducting the 
increments analysis set forth in the draft NSR Manual and other EPA 
guidance documents, as discussed in more detail below. However, we are 
not proposing in this action to supersede or change specific policies 
or interpretations not discussed in this notice that EPA may have 
adopted in final form prior to or after the development of the draft 
NSR Manual.
    With respect to the draft NSR Manual as a whole, we are only 
proposing to clarify that the 1990 draft of the NSR Manual does not by 
itself establish final policies or interpretations of the EPA. To the 
extent such policies or interpretations are reflected in other action 
or documents that were issued in a final form (such as rulemakings, 
guidance memorandum, or adjudications by the Administrator or the 
Environmental Appeals Board), EPA will continue to follow them unless 
the Agency has otherwise indicated that it no longer adheres to such 
policies or interpretations. For example, it remains EPA's policy to 
use the five-step, top-down process to satisfy the Best Available 
Control Technology (``BACT'') requirements when PSD permits are issued 
by EPA and delegated permitting authorities, and we continue to 
interpret the BACT requirement in the Clean Air Act and EPA regulations 
to be satisfied when BACT is established using this process, as it has 
been described in decisions of the Environmental Appeals Board. 
However, notwithstanding this policy and the interpretations of the 
BACT requirement reflected in EPA adjudications, EPA has not 
established the top-down BACT process as a binding requirement through 
regulation.
    We request comment on this proposal to clarify that the draft NSR 
Manual is not a binding regulation and does not independently reflect 
or establish a final statement of EPA policy or an authoritative 
interpretation of EPA regulations.

V. Proposed Refinements to Increment Modeling Procedures

A. What kind of emissions consume or expand the PSD increment?

1. What types of sources are included in increment consumption 
modeling?
    In defining ``baseline concentration,'' the PSD regulations also 
spell out the emissions sources that must be included in an increment 
analysis. Specifically, in 40 CFR 51.166(b)(13)(ii) and 
52.21(b)(13)(ii), the regulations indicate that the following emissions 
are not included in the baseline concentration, but instead affect the 
available increment:
     Actual emissions from any major stationary source on which 
construction commenced after the major source baseline date.
     Actual emissions increases and decreases at any stationary 
source occurring after the minor source baseline date.

Thus, the sources that affect available increment, and therefore must 
be included in an increment analysis are: (1) Major sources that have 
increased or decreased actual emissions after the major source baseline 
date as a result of construction of a new source, a physical or 
operational change to an existing source, or shutdown of an existing 
source; and (2) any source that has had an increase or decrease in 
actual emissions since the minor source baseline date. The latter 
includes major sources, minor sources, and area sources that have been 
constructed since the minor source baseline date (i.e., new sources) or 
have experienced a change in actual emissions since the minor source 
baseline date (i.e., existing sources that have been modified or have 
changed their capacity utilization or hours of operation).
    For many years, we have interpreted the PSD regulations to require 
increases and decreases in mobile source emissions to be included in 
the increment consumption analysis. See, e.g., 53 FR 40656, 40662 
(October 17, 1988). However, we understand that many States have not 
consistently accounted for mobile source emissions in their increment 
analyses. To make clear that mobile source emissions need to be 
included in an analysis of increment consumption, we are proposing to 
amend the refe