Air Quality Implementation Plans; Montana; Attainment Plan for Libby, MT PM2.5, 55713-55725 [2010-22848]

Agencies

• ENVIRONMENTAL PROTECTION AGENCY

[Federal Register Volume 75, Number 177 (Tuesday, September 14, 2010)]
[Proposed Rules]
[Pages 55713-55725]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2010-22848]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R08-OAR-2006-0952; FRL-9200-9]


Air Quality Implementation Plans; Montana; Attainment Plan for 
Libby, MT PM2.5 Nonattainment Area and PM10 State Implementation Plan 
Revisions

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: EPA is proposing to approve the State Implementation Plan 
(SIP) revision submitted by the State of Montana on March 26, 2008. 
Montana submitted this SIP revision to meet Clean Air Act requirements 
for attaining the 15.0 micrograms per cubic meter ([mu]g/m3) 
annual fine Particulate Matter (PM2.5) national ambient air 
quality standard (NAAQS) for the Libby nonattainment area. The plan, 
herein called an ``attainment plan,'' includes an attainment 
demonstration, an analysis of Reasonably Available Control Technology 
and Reasonably Available Control Measures (RACT/RACM), base-year and 
projection year emission inventories, and contingency measures. The 
requirement for a Reasonable Further Progress (RFP) plan is satisfied 
because Montana projects that attainment with the 1997 PM2.5 
NAAQS will occur in the Libby nonattainment area by April 2010. In 
addition, we are proposing to approve the PM10 SIP revisions 
to the Lincoln County Air Pollution Control Program submitted by 
Montana on June 26, 2006 for inclusion into Libby's attainment plan. 
This submittal contains provisions, including contingency measures, for 
controlling both PM10 and PM2.5 emissions from 
woodstoves, road dust, and outdoor burning. Finally, EPA is proposing 
to find on-road directly emitted PM2.5 and oxides of 
nitrogen (NOX) in the Libby, Montana nonattainment area 
insignificant for regional transportation conformity purposes. If this 
insignificance finding is finalized as proposed, the Libby, Montana 
nonattainment area will not have to perform a regional emissions 
analysis for either direct PM2.5 or NOX as part 
of future conformity determinations for the annual 1997 
PM2.5 NAAQS.

DATES: Written comments must be received on or before October 14, 2010.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R08-
OAR-2006-0952, by one of the following methods:
     https://www.regulations.gov. Follow the on-line 
instructions for submitting comments.
     E-mail: freeman.crystal@epa.gov.
     Fax: (303) 312-6064 (please alert the individual listed in 
FOR FURTHER INFORMATION CONTACT if you are faxing comments).
     Mail: Callie Videtich, Director, Air Program, 
Environmental Protection Agency (EPA), Region 8, Mailcode 8P-AR, 1595 
Wynkoop St., Denver, Colorado 80202-1129.
     Hand Delivery: Callie Videtich, Director, Air Program, 
Environmental Protection Agency (EPA), Region 8, Mail Code 8P-AR, 1595 
Wynkoop St., Denver, Colorado 80202-1129. Such deliveries are only 
accepted Monday through Friday, 8 a.m. to 4:30 p.m., excluding Federal 
holidays. Special arrangements should be made for deliveries of boxed 
information.
    Instructions: Direct your comments to Docket ID No. EPA-R08-OAR-
2006-0952. 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 information about EPA's public 
docket, visit the EPA Docket Center homepage at https://www.epa.gov/epahome/dockets.htm. For additional instructions on submitting 
comments, go to Section I, ``General Information,'' 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, e.g., CBI or other information 
whose disclosure is restricted by statute. Certain other material, such 
as copyrighted material, will be publicly available only in hard copy. 
Publicly available docket materials are available either electronically 
in https://www.regulations.gov or in hard copy at the Air Program, 
Environmental Protection Agency (EPA), Region 8, 1595 Wynkoop St., 
Denver, Colorado 80202-1129. EPA requests that, if at all possible, you 
contact the individual listed in FOR FURTHER INFORMATION CONTACT to 
view the hard copy of the docket. You may view the hard copy of the 
docket Monday through Friday, 8 a.m. to 4 p.m., excluding Federal 
holidays.

FOR FURTHER INFORMATION CONTACT: Crystal Freeman, Air Program, 
Environmental Protection Agency (EPA), Region 8, Mailcode 8P-AR, 1595 
Wynkoop Street, Denver, Colorado 80202-1129, Phone: (303) 312-6602, 
Fax: (303) 312-6064, freeman.crystal@epa.gov.

SUPPLEMENTARY INFORMATION: 

Definitions

    For the purpose of this document, we are giving meaning to certain 
words or initials as follows:
    (i) The words or initials Act or CAA mean or refer to the Clean Air 
Act, unless the context indicates otherwise.
    (ii) The words EPA, we, us or our mean or refer to the United 
States Environmental Protection Agency.
    (iii) The initials SIP mean or refer to State Implementation Plan.
    (iv) The initials PM2.5 mean or refer to particulate 
matter with an aerodynamic diameter of less than 2.5 micrometers.
    (v) The initials PM10 mean or refer to particulate 
matter with an aerodynamic diameter of less than 10 micrometers.
    (vi) The word State or Montana refers to the State of Montana 
unless the context indicates otherwise.
    (vii) The initials NAAQS mean or refer to National Ambient Air 
Quality Standards.

[[Page 55714]]

Table of Contents

I. General Information
II. What Action Is EPA Proposing?
III. What Is the Background for EPA's Proposed Action?
    A. Designation History
    B. Clean Air Fine Particle Implementation Rule
IV. What Is Included in Montana's Submittal?
    A. Background
    B. PM10 SIP Revisions to the Lincoln County Air 
Pollution Control Program
    C. Libby and Vicinity PM2.5 Control Plan
V. EPA's Analysis of Montana's Submittal
    A. PM10 SIP Revisions to Lincoln County Air Pollution 
Control Program
    B. Attainment Demonstration
    C. Analysis of Montana's Submittal
    1. Pollutants Addressed and Attainment Date
    2. Monitoring Data
    3. Emission Inventory
    4. Modeling
    5. RACT/RACM
    6. Contingency Measures
    7. Transportation Conformity Requirements
VI. Proposed Action
VII. Statutory and Executive Order Reviews

I. General Information

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

    1. Submitting CBI. Do not submit this 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 that is claimed as CBI. In addition to one 
complete version of the comment that includes 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 CFR part 2.
    2. Tips for Preparing Your Comments. When submitting comments, 
remember to:
    a. Identify the rulemaking by docket number and other identifying 
information (subject heading, Federal Register date and page number).
    b. Follow directions--The agency may ask you to respond to specific 
questions or organize comments by referencing a Code of Federal 
Regulations (CFR) part or section number.
    c. Explain why you agree or disagree; suggest alternatives and 
substitute language for your requested changes.
    d. Describe any assumptions and provide any technical information 
and/or data that you used.
    e. If you estimate potential costs or burdens, explain how you 
arrived at your estimate in sufficient detail to allow for it to be 
reproduced.
    f. Provide specific examples to illustrate your concerns, and 
suggest alternatives.
    g. Explain your views as clearly as possible, avoiding the use of 
profanity or personal threats.
    h. Make sure to submit your comments by the comment period deadline 
identified.

II. What action is EPA proposing?

    EPA is proposing to approve two Montana SIP submittals for the 
Libby nonattainment area: (1) PM10 SIP revisions to the 
Lincoln County Air Pollution Control Program submitted by Montana on 
June 26, 2006; and (2) the Libby PM2.5 attainment plan 
submitted by Montana on March 26, 2008. EPA has determined that the 
PM10 SIP revisions and the PM2.5 attainment plan 
meet applicable requirements of the Clean Air Act, including the Clean 
Air Fine Particle Implementation Rule (herein referred to as the 
implementation rule) issued by EPA on April 25, 2007 (72 FR 20586). 
Furthermore, EPA has determined that Montana's PM2.5 SIP 
submittal for the Libby area includes an attainment demonstration, an 
analysis of RACT/RACM, base-year and projection-year emission 
inventories and contingency measures. The attainment plan supports a 
determination that the Libby PM2.5 nonattainment area will 
attain the 1997 PM2.5 NAAQS by the April 2010 deadline for 
attainment. Finally, EPA is proposing to find on-road directly emitted 
PM2.5 and NOX in the Libby, Montana nonattainment 
area insignificant for regional transportation conformity purposes.
    EPA's analysis and findings are discussed in this proposed 
rulemaking. Additional technical support documents are available at 
https://www.regulations.gov, Docket No. EPA-R08-OAR-2006-0952.

III. What is the background for EPA's proposed action?

A. Designation History

    On July 18, 1997 (62 FR 38652), EPA established PM2.5 
NAAQS, including an annual standard of 15.0 [mu]g/m3 based 
on a 3-year average of annual mean PM2.5 concentrations, and 
a 24-hour (or daily) standard of 65 [mu]g/m3 based on a 3-
year average of the 98th percentile of 24-hour concentrations. EPA 
established the standards based on significant evidence and numerous 
health studies demonstrating that serious health effects are associated 
with exposures to PM2.5.
    Following promulgation of a new or revised NAAQS, EPA is required 
by the CAA to designate areas throughout the United States as attaining 
or not attaining the NAAQS; this designation process is described in 
section 107(d)(1) of the CAA. In 1999, EPA and state air quality 
agencies initiated the monitoring process for the 1997 PM2.5 
NAAQS, and, by January 2001, established a complete set of air quality 
monitors. On January 5, 2005, EPA published initial air quality 
designations for the 1997 PM2.5 NAAQS (70 FR 944), based on 
air quality monitoring data for calendar years 2001-2003. On April 14, 
2005, EPA published a final supplemental rule amending the agency's 
initial designations (70 FR 19844). EPA did not consider modifications 
made in this rule to be ``re-designations'' because the changes were 
made before April 5, 2005, the effective date of the initial 
designations. As a result of the final supplemental rule, 
PM2.5 nonattainment designations are in effect for 39 areas, 
comprising 208 counties within 20 states (and the District of Columbia) 
nationwide, with a combined population of about 88 million people. The 
Libby nonattainment area which is the subject of this rulemaking is 
included in the list of areas not attaining the 1997 PM2.5 
NAAQS.
    On October 17, 2006, EPA strengthened the 24-hour PM2.5 
NAAQS to 35 [mu]g/m3 and retained the level of the annual 
PM2.5 standard at 15.0 [mu]g/m3 (71 FR 61144). On 
November 13, 2009 EPA designated areas as either attainment/
unclassified or nonattainment with respect to the revised 24-hour NAAQS 
(74 FR 58688). In the November 2009 designation action, EPA established 
a deadline of December 14, 2012 for states to submit attainment plans 
for areas designated as nonattainment for the revised 24-hour 
PM2.5 NAAQS.
    Of relevance to the proposed rulemaking herein, the notice for the 
November 2009 action clarified designations for the 1997 
PM2.5 NAAQS by relabeling the existing designation tables to 
identify designations for the annual NAAQS, and by providing a separate 
table identifying designations for the 1997 24-hour NAAQS (i.e., 65 
[mu]lg/m3). In that table, the Libby nonattainment area is 
designated as attaining the 1997 24-hour PM2.5 NAAQS.

[[Page 55715]]

B. Clean Air Fine Particle Implementation Rule

    On April 25, 2007, EPA issued the Clean Air Fine Particle 
Implementation Rule for the 1997 PM2.5 NAAQS (72 FR 20586). 
The implementation rule describes the CAA framework and requirements 
for developing state PM2.5 attainment plans. An attainment 
plan must include a demonstration that a nonattainment area will meet 
applicable NAAQS within the timeframe provided in the statute. This 
demonstration must include modeling (40 CFR 51.1007) that is performed 
in accordance with EPA modeling guidance (EPA-454/B-07-002, April 
2007). It must also include supporting technical analyses and 
descriptions of all relevant adopted federal, state, and local 
regulations and control measures that have been implemented by the 
proposed attainment date.
    For the 1997 PM2.5 NAAQS, an attainment plan must show 
that a nonattainment area will attain the standard by 2010. 
Alternatively, if the area is not expected to meet the NAAQS by 2010, a 
state may propose an attainment-date extension for up to five years 
based on the severity of the nonattainment problem and on the 
availability and feasibility of pollution control measures (CAA section 
172(a)(2)).
    For each nonattainment area, the state must demonstrate that it has 
adopted all RACT/RACM needed to show that the area will attain the 
PM2.5 standards ``as expeditiously as practicable.'' The 
implementation rule provided guidance for making these RACM and RACT 
determinations (72 FR 20616-21). Any measures that are necessary to 
meet these requirements which are not already either federally 
promulgated or part of the state's SIP must be submitted in enforceable 
form as part of a state's attainment plan.
    The implementation rule also included policies on pollutants that 
comprise total PM2.5. Five main types of pollutants 
contribute to fine particle concentrations: direct PM2.5, 
sulfur dioxide (SO2), nitrogen oxides (NOX), 
ammonia, and volatile organic compounds (VOCs). All but direct 
PM2.5 is considered to be ``precursors'' to PM2.5 
formation. The effect of reducing emissions of each of these five types 
of pollutants varies by area, depending on PM2.5 
composition, emission levels, and other area-specific factors. For this 
reason, the implementation rule established policies regarding what 
states should include in their PM2.5 attainment plans for 
evaluating these pollutants.
    Under these policies, sources of direct PM2.5 emissions 
(including organic particles, elemental carbon and inorganic particles) 
and SO2 must be evaluated for emission reduction measures in 
all PM2.5 nonattainment areas. Sources of NOX 
must be evaluated for emission reduction measures in each area unless 
the state and EPA demonstrate that NOX is not a significant 
contributor to PM2.5 concentrations in a specific area. 
Neither VOC nor ammonia sources are required to be evaluated for 
emission reduction measures in an area unless the state or EPA 
demonstrates that either of these pollutant types significantly 
contributes to PM2.5 concentrations. To reverse any of the 
presumptive precursor policies, the implementation rule provided 
guidance on the types of analyses that may be included in a technical 
demonstration.
    The implementation rule also provided guidance on other elements of 
a state's attainment plan, including but not limited to, consideration 
of emission inventories, contingency measures, and motor vehicle 
emissions budgets used for transportation conformity purposes.

IV. What is included in Montana's submittal?

A. Background

    Libby, Montana, a small rural community, is located in Lincoln 
County in the northwestern part of the State. Libby sits in the narrow, 
triangular Kootenai valley at an elevation of 2,100 feet. The 
nonattainment area is dominated by three major mountain ranges that 
limit the air-shed: (1) The Rocky Mountain and Flathead Ranges on the 
eastern boundary; (2) the Purcell Range, which roughly bisects the area 
from north to south; and (3) the Selkirk and Cabinet Ranges on the 
western boundary. The vast majority of the area surrounding Libby is 
National Forest managed by the U.S. Forest Service. Based on the 2000 
census and a growth rate through 2005 of 3.71%, Libby's population is 
estimated at 2,674.
    The highest PM2.5 concentrations in Libby generally 
occur during the winter months of November through February. The winter 
concentrations are related to stagnant weather conditions dominated by 
light winds and strong temperature inversions. These meteorological 
conditions can trap emissions within the valley for many days or weeks.
    Air quality data recorded during 2001-2003 at the PM2.5 
monitor at the Libby Courthouse Annex showed violations of the annual 
PM2.5 standard. Libby was designated nonattainment for 
PM2.5 under section 107(d)(3) of the CAA, on April 5, 2005 
(40 CFR part 81). The air quality planning requirements for 
PM2.5 nonattainment areas are set out in Title I subpart 1 
of the Act.\1\
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    \1\ Subpart 1 applies to nonattainment areas generally.
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    Historically, Libby was designated nonattainment for 
PM10 by operation of law on November 15, 1990 (56 FR 56694, 
56794, November 6, 1991), under CAA section 107(d)(4)(B) and was 
classified as ``Moderate.'' The PM10 attainment plan was 
approved by EPA on August 30, 1994 (59 FR 44627). Montana has submitted 
revisions to the Lincoln County Air Pollution Control Program (herein 
referred to as the Program) and the Libby and Vicinity PM2.5 
Control Plan (herein referred to as the Libby attainment plan) for the 
purpose of demonstrating attainment of the annual PM2.5 
NAAQS. After public notice, public hearings regarding these two 
submittals were held on February 27, 2006 for the Lincoln County Air 
Pollution Control Program and on March 25, 2008 for the Libby and 
Vicinity PM2.5 Control Plan. The Montana Board of 
Environmental Review approved the revised Lincoln County Air Pollution 
Control Program on March 23, 2006 and the Libby attainment plan on 
March 25, 2008. Montana has met the requirements of Section 110(a)(2) 
for reasonable notice and public hearings.

B. PM10 SIP Revisions to the Lincoln County Air Pollution Control 
Program

    Montana submitted revisions to the PM10 SIP for the 
Lincoln County Air Pollution Control Program for the Libby 
nonattainment area to improve and strengthen the PM10 
attainment plan. The revisions include several provisions to regulate 
solid fuel burning devices and require owners and operators to obtain 
operating permits. Operating permits may only be issued for EPA-
certified woodstoves or for pellet stoves. Furthermore, only specified 
materials can be burned in these devices, and visible emissions of 
greater than 20% opacity from them are prohibited. Additionally, these 
provisions allow for air pollution alerts if PM10 or 
PM2.5 concentrations averaged over a 4-hour period exceed a 
level 20 percent below any federal or state particulate matter 
standard. Provisions are also included for penalties for non-compliance 
and contingency measures.
    Additionally, revisions were made for open and outdoor burning 
regarding prohibited materials, major open burning and management 
burning, minor open burning or residential open

[[Page 55716]]

burning, and special burning. These revisions generally included 
significant limits on the time periods for open burning activities as 
compared to the existing PM10 SIP. Further restrictions also 
include prohibitions on burning from November 1 to March 31, which is 
the winter-time period when exceedances of PM2.5 typically 
occur. Lincoln County's Program prohibits burning the same materials as 
the State but is more restrictive because the burning of trade waste, 
Christmas tree waste, leaves, grass clippings and stumps is prohibited 
within the Air Pollution Control District \2\ (herein referred to as 
the District). The June 26, 2006 submittal also included a stringency 
analysis for the Program showing that the revisions are more stringent 
than comparable State law.
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    \2\ The boundaries of the District are identical to those for 
the nonattainment area.
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C. Libby and Vicinity PM2.5 Control Plan

    The Libby attainment plan provides a demonstration that the annual 
PM2.5 NAAQS will be met by April 2010 through the 
implementation of the Lincoln County Program described in section B 
above. The Libby attainment plan includes an emissions inventory (EI), 
a woodstove air pollution control calculation, and a technical analysis 
showing that the emissions of PM2.5 will be reduced 
sufficiently to meet the NAAQS. The key components of the Libby 
attainment plan are described as follows:
    1. Ambient air quality monitoring in the Libby area began in 1999 
and is conducted using Federal Reference Method (FRM) PM2.5 
samplers at the Courthouse Annex site in downtown Libby. Based on 
monitoring data from the years 2001 to 2003, the 3-year annual design 
value was 15.9 [micro]g/m\3\, which is a violation of the annual 
PM2.5 NAAQS. In February 2002, speciation monitoring was 
conducted to determine possible PM2.5 emission sources. The 
results identified organic carbon as the main component of wintertime 
PM2.5 emissions. Further ambient monitoring was conducted 
from November 2003 to February 2004 to determine the geographic 
distribution of PM2.5 concentrations. After additional 
monitoring from various locations beyond Libby city limits and 
meteorological data from Libby Courthouse Annex site, it was determined 
that the Libby Courthouse Annex site represented the worst-case ambient 
PM2.5 levels in the area.
    2. A chemical mass balance study (CMB) was conducted during the 
winter of 2003-2004 by the University of Montana, Center for 
Environmental Health Sciences (UM-CEHS). The goal of the CMB study was 
to identify those emission sources in the Libby area that contributed 
to elevated PM2.5 concentrations. The CMB model runs 
indicated that emissions from residential wood combustion were the 
major source of the fine particles on the PM2.5 filters, 
averaging 82% during the CMB study period (i.e., winter months). Other 
contributing PM2.5 sources identified by the CMB model were 
automobile exhaust (7%), ammonium nitrate (5%), diesel exhaust (4%), 
and sulfate (2%).\3\
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    \3\ Ward, T.J., Rinehart, L.R., Lange, T. The 2003/2004 Libby, 
Montana PM2.5 Source Apportionment Research Study. 
Aerosol Science and Technology. Vol. 40:166-177. 2006.
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    3. Carbon 14 (\14\C) analysis, as a part of the CMB study completed 
by UM-CEHS, was conducted by the University of Arizona's Accelerator 
Mass Spectrometry Laboratory Facility to provide further evidence that 
wood combustion was the major source of PM2.5 emissions in 
Libby.\4\
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    \4\ Ibid.
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    4. The Libby base year PM2.5 EI included a 
quantification of actual PM2.5 emissions and apportioned the 
emissions on a seasonal and annual basis for point and area sources. 
The State used calendar year 2005 as the base year for the development 
of an EI for the Libby area. The EI was used to support a proportional 
rollback model for the emission control plan. The State developed 
information for 2005 that allowed for the calculation of residential 
wood combustion and commercial fuel use.
    5. The Libby PM10 SIP as revised also serves as the 
control plan for emissions of PM2.5. Controls exist for 
reducing emissions from re-entrained road dust through aggressive 
street sweeping and flushing, and traction sand durability 
requirements. Emissions of organic carbon are controlled through 
residential woodstove regulations and outdoor burning restrictions.
    6. A significant part of the PM2.5 control strategies 
has been the completion of a woodstove changeout program. Approximately 
1,130 uncertified woodstoves were replaced with EPA-certified 
woodstoves or pellet fuel burning devices. After the changeout, 
PM2.5 emissions have been reduced from approximately 138.78 
tons/year to 57.21 tons/year, a decrease of 59%.
    PM2.5 control strategies are primarily focused on 
residential wood combustion. The control strategies also include: air 
pollution alerts may be declared during the winter months; solid fuel 
burning devices must have an operating permit; only EPA-certified 
woodstoves and pellet fuel burning devices can obtain permits; and only 
permitted pellet fuel devices can operate during air pollution alerts. 
Other control strategies for PM2.5 have included an expanded 
area for the prescribed burning control program and the continuing 
federal tailpipe standards.
    7. Analysis for RACT/RACM was conducted for the Libby area. EPA's 
RACT/RACM guidance covers three general source categories: stationary, 
mobile and area (79 FR 20586). The Libby PM2.5 CMB study did 
not identify any emissions from local stationary sources, only a minor 
amount from mobile sources, and a significant amount from an area 
source category--residential wood combustion. EPA's area source RACM 
guidance covers four source categories: (1) Reduced solvent usage or 
solvent substitution; (2) controls on charbroiling or other commercial 
cooking operations; (3) controls on woodstoves and fireplaces; and (4) 
new or improved regulations on open burning (79 FR 20586 and 20621). 
The Libby attainment plan concluded that wood combustion control 
strategies and more stringent rules on open burning constituted RACM 
for area sources. The analysis further noted that the other two 
categories of area sources, commercial users of solvent and commercial 
cooking, were infrequent in the Libby area. The analysis also 
considered mobile sources, but determined that in light of their small 
contribution to PM2.5 nonattainment, existing federal 
tailpipe standards and natural turnover rates of the local vehicle 
fleet made additional measures for mobile sources unnecessary.
    8. The Lincoln County Air Pollution Control Program is legally 
enforceable by Lincoln County, and by the State should Lincoln County 
fail to administer the program. The Libby attainment plan also provides 
for contingency measures if the NAAQS are exceeded after 
implementation. There is one contingency measure for wood burning for 
space heating purposes if it is determined that wood burning emissions 
contribute to an exceedance of the PM2.5 NAAQS, then only 
biomass pellet fuel burners may operate within the District. Other 
contingency measures are included for re-entrained dust and industrial 
facilities. There is also a review process to consider permanent 
adoption of a contingency measure.

[[Page 55717]]

V. EPA's Analysis of Montana's Submittal

A. PM10 SIP Revisions to Lincoln County Air Pollution Control Program

    EPA's summary of the PM10 SIP revisions is addressed in 
detail under section IV.B. These revisions were made for two purposes: 
(1) To address PM2.5 attainment plan requirements; and (2) 
to improve and strengthen requirements for continued attainment of 
PM10. The revisions are a significant improvement to a plan 
that was approved by EPA 16 years ago. The Libby area has not had an 
exceedance of the PM10 NAAQS since 1993. Furthermore, 
clarifications were made to the language to better explain to the 
public the requirements of the air quality program. The revisions 
removed exemptions and replaced them with requirements for obtaining 
permits for wood burning appliances. These revisions also added 
enforcement provisions where previously none had existed.
    Section 110(l) of the Clean Air Act states that a SIP revision 
cannot be approved if the revision would interfere with any applicable 
requirement concerning attainment and reasonable further progress 
toward attainment of the NAAQS or any other applicable requirement of 
the Act. The Libby area is currently meeting the NAAQS for all criteria 
pollutants and has not had any violations of the PM10 
standard for over a decade. Furthermore, the revisions do not relax the 
stringency of any SIP provision; in fact, the revisions generally 
strengthen the SIP. As a result, the PM10 SIP revisions do 
not interfere with attainment of the NAAQS or any other applicable 
requirement of the Act. Therefore, section 110(l) requirements are 
satisfied.

B. Attainment Demonstration

    In accordance with section 172(c) of the CAA and the implementation 
rule, the attainment plan submitted by Montana for the Libby area 
included: (1) Emission inventories for the plan's base year (2005) and 
projection year (2009); and (2) an attainment demonstration consisting 
of: (a) Technical analyses that locate, identify, and quantify sources 
of emissions contributing to violations of the annual PM2.5 
NAAQS; (b) analyses of future-year emission reductions and air quality 
improvements expected to result from national and local programs, and 
from new measures to meet RACT/RACM requirements; (c) adopted emission 
reduction measures; and (d) contingency measures.

C. Analysis of Montana's Submittals

1. Pollutants Addressed and Attainment Date
    In accordance with policies described in the implementation rule, 
Montana's PM2.5 attainment plan evaluates emissions of 
direct PM2.5, SO2 and NOX in the Libby 
area. Montana provided documentation of expeditious attainment of the 
annual PM2.5 NAAQS in the Libby area by April 2010. Areas 
that demonstrate attainment by 2010 are considered to have satisfied 
the requirement to show reasonable further progress toward attainment 
and need not submit a separate RFP plan. For similar reasons such areas 
are also not subject to a requirement for a mid-course review.
    Montana's evaluation of emissions is based on the work conducted by 
UM-CEHS for the CMB model runs indicating that emissions from 
residential wood combustion were the major source (82%) of the fine 
particles on the PM2.5 filters. Other PM2.5 
sources identified by the CMB model were automobile exhaust (7%), 
ammonium nitrate (5%), diesel exhaust (4%), and sulfate (2%). In 
addition, a Carbon 14 analysis confirmed that wood combustion is the 
major source of PM2.5 emissions in the Libby area and that 
emissions of both SO2 and NOX are very minor 
compared to PM2.5 emissions from residential wood 
combustion. As described in the emissions inventory, the sources of 
SO2 are from home heating oil and sources of NOX 
are from on-road and off-road mobile sources (see further discussion in 
section V.C.7. on NOX emissions from mobile sources).
2. Monitoring Data
    As shown in the table below, the annual weighted average for 2009 
shows that the Libby area has met the April 2010 deadline for the 1997 
PM2.5 NAAQS. The trend in annual average concentrations is 
downward and coincides with the implementation of the woodstove 
changeout program. This is based on quality-controlled and quality-
assured monitoring data from 2005-2009 that is available in the EPA Air 
Quality System (AQS).

                               Table V.2-1
------------------------------------------------------------------------
                                              Annual weighted average
                   Year                             ([mu]g/m\3\)
------------------------------------------------------------------------
2005.....................................                          15.8
2006.....................................                          15.2
2007.....................................                          13.0
2008.....................................                          12.9
2009.....................................                          10.7
------------------------------------------------------------------------

3. Emission Inventory
    CAA section 172(c)(3) states that for nonattainment areas, the 
State shall prepare a statewide emission inventory no later than three 
years after designation. The baseline emission inventory for calendar 
year 2005 or another suitable year shall be used for attainment 
planning (40 CFR 51.1008(b)). EPA promulgated the Air Emissions 
Reporting Rule (AERR) (40 CFR part 51, subpart A) in order to 
consolidate the various reporting requirements that already exist, 
including those requirements outlined in the PM2.5 
implementation rule. The AERR requires states to report state-wide 
emissions every three years. Montana prepared a statewide emission 
inventory for 2005. This inventory included annual totals of emissions 
of criteria pollutants and their precursors. The State used data from 
this statewide inventory to create an emission inventory specific to 
the Libby area.
    Monitoring data for 2005 showed an exceedance of the 
PM2.5 annual standard. The year 2005 is a suitable year for 
attainment planning because an emission inventory for this year is 
representative of ambient emission levels that led to the exceedance of 
the annual standard. The 2005 emission inventory showed that 
residential wood burning comprised 82% of the direct PM2.5 
emissions during the winter. The next largest direct source, road dust, 
was 11%, followed by locomotive emissions at 3.4%. The remaining 
criteria pollutant emissions were very minor, including the precursors 
of PM2.5 (i.e., NOX and SO2). 
Background values of PM2.5 were accounted for by the State 
using monitored data collected at remote stations far away from 
emissions sources in the Libby area. EPA notes that the State used a 
conservative emission inventory approach for projecting future growth 
for the 2010 attainment year which involved increasing the vehicle 
emissions by 2.1% (the population growth rate) from the 2005 base year 
inventory, and not taking any credit for potential emission reductions 
that may have been available from fleet turnover and the Federal 
tailpipe standards for vehicles. Condensable particulate matter was not 
considered in the emission inventory because of a lack of sources in 
the Libby area.
4. Modeling
    CAA Section 172(c) requires states with nonattainment areas to 
submit an attainment demonstration. A PM2.5 attainment 
demonstration consists of (1) analyses which estimate whether

[[Page 55718]]

selected emissions reductions will result in ambient concentrations 
that meet the NAAQS and (2) a set of control measures which will result 
in the required emissions reductions.
    Montana's analysis of future-year emissions reductions and air 
quality improvements was based on a proportional rollback model for 
showing attainment of the standard and a roll forward model 
demonstrating attainment in the future. The proportional models were 
applied in conjunction with the findings from chemical mass balance and 
Carbon 14 studies conducted by the University of Montana.
    In the particular case of Libby, a proportional model is more 
appropriate than dispersion models. The great majority of periods with 
elevated PM2.5 concentrations in Libby occur during 
wintertime stagnation conditions. Furthermore, dispersion in Libby is 
constrained by steep terrain. The most suitable approach for stagnation 
conditions should be determined on a case-by-case basis, (see sections 
7.2.8 and 8.3.4.2(b) of the Guideline on Air Quality Models, 40 CFR 
part 51, appendix W), and an alternative model should be selected by 
the EPA Regional Office when a preferred model is less appropriate (see 
section 3.2.2 of the Guideline).
    The proportional model used the emission inventory for 2005 when 
there was an exceedance of the standard. The decrease in 
PM2.5 emissions for the Libby area resulting from the 
woodstove changeout program was calculated based on the amount of wood 
burned by the EPA-certified woodstoves and then compared to the amount 
of emissions resulting from burning the same amount of wood from the 
uncertified woodstoves that were still in use. The decrease in 
emissions would be an indication of the effectiveness of the control 
strategy. Montana estimated that PM2.5 emissions would be 
reduced by 81.57 tons as a result of the new EPA-certified woodstoves 
installed in Libby households.
    The State projected future annual average PM2.5 
concentrations for Libby at 9.5 [mu]g/m\3\. This projection was based 
on the installation of the new stoves and a 100 percent compliance with 
the wood burning restrictions for Libby. EPA's guidance is based on 
emission sources complying with state and local restrictions on 
emission sources (Emissions Inventory Guidance for Implementation of 
Ozone and Particulate Matter National Ambient Air Quality Standards 
(NAAQS) and Regional Haze Regulations, appendix B, EPA-454/R-05-001, 
August 2005.) The guidance defines rule effectiveness (RE) as a method 
to account for the reality that not all emission sources are in 
compliance 100% of the time.
    The guidance provides a listing of the factors that are most likely 
to affect RE. EPA used a conservative 70% RE instead of a 100 percent 
compliance to determine if Libby would still reach attainment of the 
PM2.5 standard. EPA estimated that using the more 
conservative compliance percentage for wood burning restrictions, the 
future value for Libby would still be below the PM2.5 
standard of 15 [mu]g/m\3\. As stated above in Table V.2.-1 the Libby 
area 2009 annual average is currently 10.7 [mu]g/m\3\.
5. RACT/RACM
    Determination of RACT/RACM is a three-step process: (1) Identifying 
potential measures that are reasonable; (2) modeling to identify the 
attainment date that is as expeditious as practicable; and (3) 
selecting RACT/RACM. Identification of potential measures should 
ordinarily be supported by an inventory of emissions of directly 
emitted PM2.5 and of precursors from the relevant sources 
and source categories; the technologically feasible control measures 
for each source or source category; and, for each measure, the control 
efficiency, possible emission reductions by pollutant, estimated cost 
per ton, and the date by which the measure was or could be implemented; 
and other relevant information.
    For the first step, identification of potential measures that are 
reasonable, Montana supported its RACT/RACM analysis with the emissions 
inventory and the CMB study. The RACT/RACM analysis first noted that 
there are no major stationary sources of PM2.5 in the Libby 
area. It also noted that minor stationary sources are currently 
regulated under Montana's minor source program, which requires permits 
and a Best Available Control Technology (BACT) review. As discussed in 
the implementation rule, if state or federal rules already regulate a 
given sector, it is reasonable for a state to look to unregulated 
sectors for RACT/RACM measures. Furthermore, the implementation rule 
permits the state to use reason in the extent of its effort to identify 
potential control measures. For example, the rigor of the analysis may 
depend on the relative contribution of a particular pollutant to the 
PM2.5 nonattainment problem (72 FR 20613). As shown by the 
CMB study, stationary sources are a very minor contributor to 
PM2.5 nonattainment in Libby. Similarly, the RACT/RACM 
analysis reasoned that mobile sources are currently regulated, make 
only a minor contribution to the nonattainment problem, and the overall 
emissions will continue to be reduced through fleet turnover. Thus, the 
first step focused on measures for area sources.
    The analysis further noted that two types of area sources 
(commercial users of solvents and commercial charbroilers or other 
commercial cooking operations) were infrequent in the Libby area. The 
analysis also discussed re-entrained road dust, which the CMB study did 
not identify as a contributor to PM2.5 nonattainment, and 
noted that there were existing SIP provisions to control road dust. As 
to home heating oil, a source of SO2, the CMB study found 
only a 2% contribution to PM2.5 nonattainment for all 
sulfates combined. Thus, the RACM analyses focused on the remaining 
area sources of wood burning devices and open burning and identified 
several control measures to be included in the attainment plan.
    For the second step, as discussed in more detail in section V.C.4, 
Montana modeled attainment by 2010 based on adoption of these 
reasonable control measures. Finally, for the third step, based on the 
analysis, Montana selected and adopted RACM for wood burning devices 
and open burning. For wood burning devices, the State developed and 
implemented a woodstove changeout control strategy. The woodstove 
changeout permanently removed 1,130 old, uncertified woodstoves and 
replaced them with EPA-certified woodstoves or pellet stoves. 
Additionally, the State adopted measures that require permits for solid 
fuel burning devices (including woodstoves) and restrict installation 
and operation of these devices to three categories: pellet stoves, 
devices with a catalytic emissions control system, and devices with a 
non-catalytic emissions control system. For the latter two, emission 
limits are imposed.
    RACM measures were also included for major open burning, management 
burning, residential burning, and special burning. The PM2.5 
attainment plan includes BACT and permits for an expanded area, which 
is the entire Air Pollution Control District, for all of these 
different types of burning activities. Additionally, these burning 
activities were restricted to shorter time periods.
    In summary, the State evaluated, by source category, sources of 
direct PM2.5, SO2 and NOX for RACT/
RACM control measures. The State's evaluation of sources of 
SO2 and NOX resulted in their decision that no 
additional controls are necessary to attain the

[[Page 55719]]

NAAQS based on the absence of major sources or area sources that can be 
cost effectively or reasonably controlled. The State therefore adopted 
RACM for direct PM2.5. In accordance with Section 172(c) of 
the CAA, Montana has adopted all RACT/RACM needed to attain the 
standards as expeditiously as practicable. EPA has reviewed Montana's 
RACT/RACM analysis and has determined that the state reasonably 
identified potential control measures, modeled the attainment date that 
is as expeditious as practicable and reasonably selected RACT/RACM for 
the Libby area.
6. Contingency Measures
    In conformance with Section 172(c)(9) of the CAA, the 
implementation rule requires that PM2.5 attainment area 
plans include contingency measures. These measures must be fully 
adopted or otherwise ready for quick implementation, should contain 
trigger mechanisms and an implementation schedule, should be measures 
not included in the SIP control strategy, and should provide the 
equivalent of one year of RFP. Once triggered, a contingency measure 
should take effect without further action by the State or EPA.
    The Libby SIP contains contingency measures for residential wood 
burning, re-entrained dust, and industrial facilities. If it is 
determined that residential wood burning contributes to an exceedance 
of the PM2.5 NAAQS, then only biomass pellet fuel burners 
may operate within the District. If re-entrained dust contributes to 
noncompliance, then the existing regulations (which currently only 
apply in a limited area) are made applicable to the entire Air 
Pollution Control District. Finally, if an industrial facility 
contributes to noncompliance, the Montana Department of Environmental 
Quality (MTDEQ) will initiate contingency measures to reduce emissions. 
Once a contingency measure is initiated, it must remain active until 
the Libby SIP demonstration is revised and resubmitted to EPA for 
approval.
    The contingency measures for residential wood burning and re-
entrained dust meet the requirements of the implementation rule. The 
contingency measure for major point sources would require further 
action by MTDEQ to determine whether additional controls are necessary. 
However, the contingency measures for residential wood burning and re-
entrained dust are sufficient to meet the requirements of the CAA, 
including equivalence to one year of RFP.
7. Transportation Conformity Requirements
    Transportation conformity is required under CAA section 176(c) (42 
U.S.C. 7506(c)) to ensure that transportation plans, transportation 
improvement programs (TIPs) and federally supported highway and transit 
projects are consistent with (``conform to'') the state air quality 
implementation plan. Transportation conformity applies to areas that 
are designated nonattainment, and to those areas redesignated to 
attainment after 1990 with a CAA section 175A maintenance plan 
(``maintenance areas''), for transportation-related criteria 
pollutants: carbon monoxide (CO), NOX and particulate matter 
(PM2.5 and PM10).
    EPA's transportation conformity rule (40 CFR parts 51 and 93) 
establishes the criteria and procedures for determining whether 
transportation activities conform to the SIP. One requirement of the 
rule is that transportation plans, TIPs, and projects must satisfy a 
regional emissions analysis for the relevant pollutants and precursors 
(40 CFR 93.118, 119). However, section 93.109(m) of this rule states 
that an area is not required to satisfy a regional emissions analysis 
for a pollutant or precursor if the SIP demonstrates that motor vehicle 
emissions of that pollutant or precursor are an insignificant 
contributor to the area's air quality problem. In today's notice, EPA 
is proposing to find that motor vehicle emissions of PM2.5 
and NOX are insignificant contributors to Libby's 
PM2.5 nonattainment problem. If this proposal is finalized, 
PM2.5 and NOX motor vehicle emissions budgets 
(MVEB) would not be established and a regional emissions analysis would 
not be required for either PM2.5 or NOX in any 
future conformity determination in Libby. Please note, however, that 
this proposed action would not apply to PM2.5 hot-spot 
analyses for individual projects, if such an analysis is required in 
the future for transportation conformity purposes.
    There are specific transportation conformity provisions that EPA 
proposes to determine as applicable to the Libby PM2.5 
nonattainment area. As provided in more detail in 40 CFR 93.109(m), 
these specific conformity provisions are addressed when EPA finds that 
emissions from motor vehicles in the Libby PM2.5 
nonattainment area are an insignificant contributor to the areas' 
nonattainment problem for a relevant NAAQS and/or precursor.
    To consider making such an insignificant finding, EPA evaluated the 
provisions of 40 CFR 93.109(m) against the relevant information 
contained in the SIP attainment plan, the SIP revision's associated 
technical support document (TSD), and additional information as 
developed by EPA. We evaluated the following factors in determining 
whether on-road direct PM2.5 and NOX emissions 
are insignificant contributors to the area's PM2.5 air 
quality problem; (1) the percentage of motor vehicle emissions in the 
context of the total SIP inventory; (2) the current state of air 
quality as determined by monitoring data for that NAAQS; (3) the 
absence of SIP motor vehicle control measures; and (4) historical 
trends and future projections of the growth of motor vehicle emissions. 
Our evaluation and conclusions are as follows:
a. The Percentage of PM2.5 Motor Vehicle Emissions in the 
Context of the Total SIP Inventory
    This factor, with regard to PM2.5 emissions, is 
addressed in two areas of the SIP revision documentation. Table 
27.12.11.4B (``PM2.5 Annual Demonstration of Compliance'') 
of the Libby attainment plan provides relevant information with regard 
to 2003-2004 CMB percentages by source category, percent reduction in 
emissions due to control strategies, estimated growth in emissions over 
the 2005 to 2010 time period, and 2010 compliance year contributions. 
The dominant CMB source was residential woodstoves at 82% with motor 
vehicle tailpipe emissions at 7% of total PM2.5 mass and 
diesel exhaust at 4% of the total PM2.5 mass.
    The contribution of motor vehicle PM2.5 emissions is 
also documented in Table 5.1A (``Seasonal PM 2.5 Emissions in Libby by 
Source Category'') of the SIP's TSD. Table 5.1A presents estimated 
emissions based on metric tons and percentage of the inventory for 
2005, by season; we have provided these motor vehicle tailpipe 
PM2.5 emissions, as percent of total PM2.5 
emissions, in Table V.7-1 below. We note that in Table 5.1A of the 
SIP's TSD, the inventory is dominated by woodstove emissions in all 
four seasons.

[[Page 55720]]



                Table V.7--1 Motor Vehicle PM2.5 Emissions Percentage of Total Inventory for 2005
                                        (All figures are in metric tons)
----------------------------------------------------------------------------------------------------------------
                                                                                                  Motor vehicle
                          Season                              Motor vehicle    Total inventory   emissions % of
                                                             PM2.5 emissions   PM2.5 emissions        total
----------------------------------------------------------------------------------------------------------------
Winter....................................................              0.48             80.63              0.59
Spring....................................................              0.55             46.43              1.18
Summer....................................................              0.66             13.66              4.83
Fall......................................................              0.51             97.67              0.52
    Total Year............................................               2.2            238.38              0.92
----------------------------------------------------------------------------------------------------------------

    As shown in Table V.7.-1 above, motor vehicle tailpipe 
PM2.5 emissions represent an annual average of only 0.92% of 
the total PM2.5 inventory. That is, motor vehicle emissions 
are less than one percent of the inventory over the course of a year. 
During the summer, motor vehicle emissions make up close to five 
percent of the inventory, but motor vehicle emissions are only slightly 
higher during the summer than during other seasons. The motor vehicle 
emissions percentage is much greater during the summer compared with 
other seasons primarily because total PM2.5 emissions are 
significantly reduced during the summer compared to other seasons; 
summer is the season with the fewest emissions from woodstoves. The 
information provided in the State's submittal supports a conclusion 
that regional PM2.5 on-road mobile source emissions are a 
minimal percentage in the context of the total PM2.5 
emissions inventory. Therefore, this factor supports the proposed 
finding that on-road PM2.5 emissions are insignificant for 
the Libby PM2.5 nonattainment area.
b. The Current State of Air Quality as Determined by Monitoring Data 
for the PM2.5 NAAQS
    This factor is addressed as shown in the table below. From the 
State's SIP revision and section V.B.2 above, from 2007 to 2009 the 
Libby area continues to demonstrate attainment of the 1997 annual 
PM2.5 NAAQS. Furthermore, the trend in annual average 
concentrations is downward and coincides with the implementation of the 
woodstove changeout program. This data is based on quality-controlled 
and quality-assured monitoring data from 2005-2009 that are available 
in the EPA AQS. This factor supports the proposed finding that on-road 
PM2.5 emissions are insignificant for the Libby 
PM2.5 nonattainment area.

                              Table V.2.-1
------------------------------------------------------------------------
                                           PM2.5 annual weighted average
                   Year                              ([mu]g/m3)
------------------------------------------------------------------------
2005.....................................                          15.8
2006.....................................                          15.2
2007.....................................                          13.0
2008.....................................                          12.9
2009.....................................                          10.7
------------------------------------------------------------------------

c. The Absence of SIP Motor Vehicle Control Measures for 
PM2.5
    The Libby PM2.5 attainment plan relies on a 59% 
reduction in residential woodstove emissions to reach attainment of the 
annual PM2.5 NAAQS and took no credit for any emission 
reductions in the motor vehicle tailpipe and diesel exhaust categories 
(e.g. Federal tailpipe emission standards and fleet turnover). The 
State further described these assumptions in sections 27.12.7.3 
(``Federal Tailpipe Standards Control Program'') and 27.12.11.4 
(``PM2.5 2010 Demonstration of Compliance'') of the Libby 
attainment plan. EPA also notes there is no State or local mandated 
motor vehicle emission control requirements (e.g., inspection and 
maintenance program, fuels, or transportation control measures) for the 
Libby PM2.5 nonattainment area. Therefore, this factor 
supports the proposed finding that on-road PM2.5 emissions 
are insignificant for the Libby PM2.5 nonattainment area.
d. Historical Trends and Future Projections of the Growth of Motor 
Vehicle PM2.5 Emissions
    Libby's annual PM2.5 2001-2003 design value was 15.9 
[mu]g/m\3\. In November 2003 through February 2004 air quality data was 
collected in Libby to support CMB modeling. This CMB modeling showed 
that residential wood smoke was the primary source of PM2.5 
in Libby. Table 27.12.11.4B in the Libby attainment plan shows that, 
when the results of the CMB modeling are applied to the air quality 
data from 2001-2003, residential wood smoke contributed 13.0 [mu]g/m\3\ 
(82%) of the 2001-2003 annual PM2.5 design value, motor 
vehicle tailpipe emissions contributed 1.1 [mu]g/m\3\ (7%), and diesel 
exhaust emissions contributed 0.7 [mu]g/m\3\ [mu]g/m\3\ (4%). Based on 
the results of this modeling Montana based its attainment strategy for 
the area on a woodstove change-out program.
    The SIP assumes that the woodstove change-out program will reduce 
those emissions by 59% in 2010. The SIP also assumes that motor vehicle 
tailpipe emissions and diesel exhaust emissions would grow by 2.1% 
between 2005 and 2010, which is equal to the expected population growth 
rate during that period. The SIP does not account for any reductions in 
motor vehicle emissions or diesel exhaust that would occur due to fleet 
turnover to new lower emission motor vehicles, on-road diesel vehicles 
or off-road equipment. Table 27.12.11.4B in the Libby attainment plan 
shows that in 2010 the predicted annual average PM2.5 
concentration would be 8.37 [mu]g/m\3\. The table also shows that 
residential wood smoke is expected to contribute 5.44 [mu]g/m\3\ (65%) 
in 2010, motor vehicle tailpipe emissions would contribute 1.12 [mu]g/
m\3\ (13%), and diesel exhaust emissions would contribute 0.71 [mu]g/
m\3\ (8%). As can be seen, on a percentage basis the contribution of 
motor vehicle emissions and diesel exhaust increases; however, overall 
PM2.5 concentrations are expected to decrease by 53% to 8.37 
[mu]g/m\3\, the contribution of wood smoke emissions is expected to 
decrease by 59%, and the total contribution of emissions from motor 
vehicles and diesel exhaust to PM2.5 mass in 2010 is 
expected to increase by only 0.03 [mu]g/m\3\ between 2005 and 2010. 
This increase in mass is due to the assumptions that emissions from 
these sources increase at the same rate as population growth and that 
no emissions reductions from fleet turnover are included in the 
calculations. Both of these are conservative assumptions.
    EPA notes that the contribution of motor vehicle emissions of 13% 
to PM2.5 mass in 2010 represents the projected chemical mass 
balance of PM2.5 and not an emission inventory projection. 
The

[[Page 55721]]

SIP includes a base year PM2.5 inventory (Table 5.1A) for 
2005. That inventory shows that motor vehicle emissions of 
PM2.5 are 2.20 tpy and that total PM2.5 emissions 
in the base year are 238.39 tpy. Therefore, the motor vehicle emissions 
in the base year are slightly less than 1% of the total direct 
PM2.5 emissions. On the surface this may seem to be in 
conflict with the results of the CMB modeling, which shows that motor 
vehicle exhaust contributed about 7% of the PM2.5 mass in 
the base year. However, it should be noted that the chemical mass 
balance data and the PM2.5 data collected at the Libby 
Courthouse Annex represents only one receptor within the City of Libby, 
and only for the period of late 2003 through early 2004. While this 
location is believed to be representative of Libby's air quality, 
numerous factors influence the local particulate matter concentrations 
and air quality. Local scale meteorology (wind speed, wind direction, 
temperature, relative humidity, barometric pressure, and solar 
radiation at a minimum), traffic patterns, and precipitation are a few 
examples of these factors which vary throughout the city. Accepting 
that variable conditions exist throughout Libby, as well as the 
inherent uncertainty associated with ambient air monitoring, the 
difference that exists between PM2.5 monitoring data at one 
receptor and a city-wide emission inventory appears to be plausible.
    We also note that the actual location of the monitor may have 
exposed it to additional influence from motor vehicle emissions. We 
have not performed an in-depth analysis, but we do note that the 
monitor is located directly adjacent to U.S. Highway 2, the main north/
south highway through Libby. Although motor vehicle PM2.5 
emissions are shown to be minimal in the State's emissions inventory 
(ref. Table 5.1A: ``Seasonal PM2.5 Emissions in Libby by 
Source Category'' and Table V.7.-1 above), motor vehicle emissions may 
have shown a greater than anticipated contribution on the chemical mass 
balance analysis due to the monitor's close proximity to Highway 2.
    Overall, this factor supports the proposed finding that on-road 
PM2.5 emissions are insignificant for the Libby 
PM2.5 nonattainment area. In summary, all four factors 
support the proposed finding. After weighing these four factors 
described in 40 CFR 93.109(m) and evaluated above, EPA proposes to find 
that on-road PM2.5 emissions are insignificant for the Libby 
PM2.5 nonattainment area. We turn to applying the four 
factors to on-road NOX emissions.
e. The Percentage of NOX Motor Vehicle Emissions in the 
Context of the Total SIP Inventory
    The Libby attainment plan focuses on directly emitted 
PM2.5 and controls of PM2.5 emissions from 
woodstoves and does not address any motor vehicle NOX 
emissions other than to indicate in Table 27.12.11.4B 
``PM2.5 Annual Demonstration of Compliance'' that the CMB 
data show that ammonium nitrate was only 5% of the mass found on the 
filters. EPA, therefore, drew upon other relevant, available data to 
evaluate whether NOX motor vehicle emissions in the Libby 
PM2.5 nonattainment area are significant and require that a 
NOX motor vehicle emissions budget be established for 
transportation conformity purposes or whether on-road NOX 
emissions could be found insignificant based on the criteria in 40 CFR 
93.109(m).
    EPA revie