Data Requirements Rule for the 1-Hour Sulfur Dioxide (SO2, 27445-27472 [2014-09458]

Agencies

• ENVIRONMENTAL PROTECTION AGENCY

[Federal Register Volume 79, Number 92 (Tuesday, May 13, 2014)]
[Proposed Rules]
[Pages 27445-27472]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2014-09458]



[[Page 27445]]

Vol. 79

Tuesday,

No. 92

May 13, 2014

Part IV





 Environmental Protection Agency





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40 CFR Part 51





 Data Requirements Rule for the 1-Hour Sulfur Dioxide (SO2) 
Primary National Ambient Air Quality Standard (NAAQS); Proposed Rule

Federal Register / Vol. 79 , No. 92 / Tuesday, May 13, 2014 / 
Proposed Rules

[[Page 27446]]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 51

[EPA-HQ-OAR-2013-0711; FRL-9903-61-OAR]
RIN 2060-AR19


Data Requirements Rule for the 1-Hour Sulfur Dioxide 
(SO2) Primary National Ambient Air Quality Standard (NAAQS)

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing a rule 
directing state and tribal air agencies (air agencies) to provide data 
to characterize current air quality in areas with large sources of 
sulfur dioxide (SO2) emissions if such areas do not have 
sufficient air quality monitoring in place to identify maximum 1-hour 
SO2 concentrations. The proposed rule describes criteria for 
identifying the sources around which air agencies would need to 
characterize SO2 air quality. It also describes a process 
and timetables by which air agencies would characterize air quality 
around sources through ambient monitoring and/or air quality modeling 
techniques and submit such data to the EPA. The EPA has issued separate 
non-binding draft technical assistance documents on how air agencies 
can conduct such monitoring or modeling. The air quality data developed 
by the states in accordance with this rulemaking would be used by the 
EPA in future rounds of area designations for the 1-hour SO2 
National Ambient Air Quality Standards (NAAQS).

DATES: 
    Comments. Comments must be received on or before July 14, 2014.
    Information Collection Request. Under the Paperwork Reduction Act, 
comments on the information collection provisions must be received by 
the Office of Management and Budget (OMB) on or before July 14, 2014.
    Public Hearings. If anyone contacts the EPA requesting the 
opportunity to speak at a public hearing concerning the proposed 
regulation by May 23, 2014, the EPA will hold a public hearing 
approximately 30 days after publication of this proposed regulation in 
the Federal Register. Additional information about the hearing would be 
published in a subsequent Federal Register notice.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-HQ-
OAR-2013-0711, by one of the following methods:
     www.regulations.gov: Follow the on-line instructions for 
submitting comments.
     Email: a-and-r-docket@epa.gov.
     Mail: Attention Docket ID No. EPA-HQ-OAR-2013-0711, U.S. 
Environmental Protection Agency, 1301 Constitution Ave. NW., 
Washington, DC 20460. Mail Code: 2822T. Please include two copies if 
possible. In addition, please mail a copy of your comments on the 
information collection provisions to the Office of Information and 
Regulatory Affairs, Office of Management and Budget (OMB), Attn: Desk 
Officer for the EPA, 725 17th St. NW., Washington, DC 20503.
     Hand Delivery: U.S. Environmental Protection Agency, EPA 
West (Air Docket), William Jefferson Clinton West Building, 1301 
Constitution Avenue Northwest, Room 3334, Washington, DC 20004, 
Attention Docket ID No. EPA-HQ-OAR-2013-0711, EPA Headquarters Library, 
The EPA/DC Public Reading Room is open from 8:30 a.m. to 4:30 p.m. 
Eastern Standard Time (EST), Monday through Friday, Air and Radiation 
Docket and Information Center.
    Instructions. Direct your comments to Docket ID No. EPA-HQ-OAR-
2013-0711. The EPA's policy is that all comments received will be 
included in the public docket without change and may be made available 
on-line at 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 www.regulations.gov 
or email. The www.regulations.gov Web site is an ``anonymous access'' 
system, which means the EPA will not know your identity or contact 
information unless you provide it in the body of your comment. If you 
send an email comment directly to the EPA without going through 
www.regulations.gov, your email 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, the EPA recommends that you include your name and other 
contact information in the body of your comment and with any CD you 
submit. If the EPA cannot read your comment due to technical 
difficulties and cannot contact you for clarification, the 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 the 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 the SUPPLEMENTARY INFORMATION section of this document.
    Docket. All documents in the docket are listed in 
www.regulations.gov. 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 www.regulations.gov or in hard copy 
at the Air and Radiation Docket and Information Center in the EPA 
Headquarters Library, Room Number 3334 in the William Jefferson Clinton 
West Building, located at 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.

FOR FURTHER INFORMATION CONTACT: For further general information on 
this rulemaking, contact Mr. Rich Damberg, Office of Air Quality 
Planning and Standards, U.S. Environmental Protection Agency, by phone 
at (919) 54l-5592, or by email at damberg.rich@epa.gov; or Ms. Rhonda 
Wright, Office of Air Quality Planning and Standards, U.S. 
Environmental Protection Agency, by phone at (919) 54l-1087, or by 
email at wright.rhonda@epa.gov. To request a public hearing or 
information pertaining to a public hearing on this document, contact 
Ms. Pamela Long, Air Quality Policy Division, Office of Air Quality 
Planning and Standards (C504-01), Environmental Protection Agency, 
Research Triangle Park, North Carolina 27711; telephone number (919) 
541-0641; fax number (919) 541-5509; email address: long.pam@epa.gov.

SUPPLEMENTARY INFORMATION: 

I. General Information

A. Does this action apply to me?

    Entities potentially affected directly by this proposal include 
state, local and tribal governments. Entities potentially affected 
indirectly by this proposal include owners and operators of sources of 
SO2 emissions (such as coal-fired power plants, refineries, 
smelters, pulp and paper related facilities, chemical

[[Page 27447]]

manufacturing and facilities with industrial boilers for power 
generation) that contribute to ambient SO2 concentrations, 
as well as people whose air quality is affected by these facilities.

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

    1. Submitting CBI. Do not submit this information to the EPA 
through www.regulations.gov or email. Clearly mark the part or all of 
the information that you claim to be CBI. For CBI information on a disk 
or CD-ROM that you mail to the 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 to be 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:
     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 Code of 
Federal Regulations (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 notice will be posted at https://www.epa.gov/air/sulfurdioxide/implement.html.

D. What information should I know about possible public hearings?

    To request a public hearing or information pertaining to a public 
hearing on this document, contact Ms. Pamela Long, Air Quality Policy 
Division, Office of Air Quality Planning and Standards (C504-03), 
Environmental Protection Agency, Research Triangle Park, North Carolina 
27711; telephone number (919) 541-0641; fax number (919) 541-5509; 
email address: long.pam@epa.gov.

E. How is this document organized?

    The information presented in this document 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 the EPA?
    C. Where can I get a copy of this document and other related 
information?
    D. What information should I know about possible public 
hearings?
    E. How is this document organized?
II. Background for Proposal
    A. The 2010 SO2 NAAQS
    B. The Area Designations Process
    C. History of Designations for the SO2 NAAQS
    D. Use of Air Quality Modeling Information in Area Designations 
for the SO2 NAAQS
    E. SO2 NAAQS Preamble: Suggested Implementation 
Approach
    F. The EPA White Paper and Stakeholder Input
    G. The EPA's February 2013 SO2 Implementation 
Strategy Paper
III. Source Coverage and Emission Threshold Options
    A. Background
    B. Proposed Source Emission Threshold Options
IV. Data Requirements and Program Implementation Timeline
    A. From Promulgation of This Rulemaking to January 15, 2016: Air 
Agency and the EPA Regional Office Consult on List of SO2 
Sources; Air Agency is Required To Submit its List of Sources Along 
With Its Election of Monitoring or Modeling for Characterizing Air 
Quality to the EPA Regional Administrator
    B. January 15, 2016: Air Agency Is Required To Submit Modeling 
Protocols for Sources That Will Be Characterized With Modeling
    C. July 2016: Annual Monitoring Network Plans Due to the EPA 
Regional Administrator Should Include SO2 Monitoring 
Network Modifications Intended To Satisfy the Data Requirements Rule
    D. January 1, 2017: SO2 Monitors Intended To Satisfy 
the Data Requirements Rule Are Required To Be Operational
    E. January 13, 2017: States Electing To Model Are Required To 
Provide Modeling Analyses to the EPA Regional Administrators
    F. By August 2017: Expected Date by Which the EPA Would Notify 
States of Intended Designations
    G. December 2017: Intended Date by Which the EPA Would Issue 
Final Designations for a Majority of the Country
    H. August 2019: Anticipated Due Date for State Attainment Plans 
for Areas Designated Nonattainment in 2017
    I. May 2020: Required Certification of 2019 Monitoring Data; 
States Have the Opportunity To Provide Updated State Recommendations 
to the EPA Regional Administrators
    J. August 2020: Expected Date by Which the EPA Would Notify 
States of Intended Designations for the Remainder of the Country Not 
Yet Designated
    K. December 2020: Intended Date by Which the EPA Would Issue 
Final Designations for the Remainder of the Country
    L. August 2022: Anticipated Due Date for State Attainment Plans 
for Areas Designated Nonattainment in 2020
V. Technical Considerations
    A. Monitoring
    B. Modeling
VI. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review and 
Executive Order 13563: Improving Regulation and Regulatory Review
    B. Paperwork Reduction Act
    C. Regulatory Flexibility Act
    D. Unfunded Mandates Reform Act
    E. Executive Order 13132: Federalism
    F. Executive Order 13175: Consultation and Coordination With 
Indian Tribal Governments
    G. Executive Order 13045: Protection of Children From 
Environmental Health and Safety Risks
    H. Executive Order 13211: Actions Concerning Regulations That 
Significantly Affect Energy Supply, Distribution, or Use
    I. National Technology Transfer and Advancement Act
    J. Executive Order 12898: Federal Actions To Address 
Environmental Justice in Minority Populations and Low-Income 
Populations
Statutory Authority
List of Subjects

II. Background for Proposal

A. The 2010 SO2 NAAQS

    On June 2, 2010, the EPA Administrator signed a final rule that 
revised the primary SO2 NAAQS under section 109 of the Clean 
Air Act (CAA or Act) to provide requisite protection of public health 
with an adequate margin of safety (75 FR 35520, June 22, 2010). 
Specifically, the EPA promulgated a new 1-hour daily maximum primary 
SO2 standard at a level of 75 parts per billion, based on 
the 3-year average of the annual 99th percentile of 1-hour

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daily maximum concentrations.\1\ The revised SO2 NAAQS will 
improve public health protection, especially for children, the elderly 
and people with asthma. These individuals are more susceptible to the 
health problems associated with breathing SO2 than 
individuals from the general population.
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    \1\ The standard is defined in 40 CFR 50.17(a)-(b). The 3-year 
average of the annual 99th percentile of 1-hour daily maximum 
concentrations is referred to as the ``design value.'' The design 
value is compared to the level of the standard to determine whether 
air quality at that location meets the standard.
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    The reaction of SO2 with other pollutants in the 
atmosphere and the resulting long-range contribution of SO2 
to regional air pollution problems such as fine particle formation and 
acidic deposition are well-understood effects of SO2 
emissions. However, SO2 as a directly emitted pollutant can 
also cause relatively localized health impacts. For example, in 
previous guidance, the EPA has indicated a general guideline that the 
distance between a source and the maximum ground level concentration of 
SO2 is generally 10 times the stack height in flat 
terrain.\2\ This means that maximum concentrations can be expected to 
be observed within 1-2 miles of some large power plants and other 
facilities. It is important to recognize, however, that conditions such 
as unique terrain features and associated meteorological conditions can 
impact the location and magnitudes of significant concentration 
gradients.
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    \2\ See March 1, 2011, memorandum from Tyler Fox, EPA Office of 
Air Quality Planning and Standards, ``Additional Clarification 
Regarding the Application of Appendix W Modeling Guidance for the 1-
hr NO2 NAAQS.'' Research Triangle Park, North Carolina 
27711. This memo is available at: https://www.epa.gov/ttn/scram/Additional_Clarifications_AppendixW_Hourly-NO 2 
2- NAAQS--FINAL--03-01-2011.pdf. See also the December 
2013 ``Draft SO2 NAAQS Designations Modeling Technical 
Assistance Document,'' issued by EPA Office of Air Quality Planning 
and Standards, available at https://www.epa.gov/airquality/sulfurdioxide/pdfs/SO2 ModelingTAD.pdf.
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    The SO2 standard was established with a 1-hour averaging 
time particularly to protect sensitive individuals from respiratory 
effects associated with short-term exposures to SO2. Thus, 
from an air quality management perspective, the SO2 NAAQS 
can be considered to be a largely ``source-oriented'' NAAQS rather than 
a ``regional'' one (i.e., more similar to the lead NAAQS than to the 
ozone NAAQS). Strategies to attain the SO2 NAAQS are 
expected to be focused on key point sources. The largest sources of 
SO2 include coal-fired electric utilities, industrial 
boilers, refineries, pulp and paper-related industries and chemical 
manufacturing.

B. The Area Designations Process

    When a NAAQS is revised, CAA provisions trigger various actions and 
implementation responsibilities for air agencies \3\ and the EPA. Two 
important milestones are: (1) The area designations process under CAA 
section 107 and subsequent nonattainment area plan development under 
CAA sections 172 and 191-192, and (2) submittal of ``infrastructure'' 
plans by air agencies within 3 years of NAAQS promulgation under 
section 110(a)(1)-(2) of the CAA.
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    \3\ ``Air agency'' refers to the air quality management agency 
of the relevant state government or tribal nation.
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    The area designations process typically relies on air quality 
concentrations characterized by ambient monitoring data collected by 
the air agency to identify areas that are either meeting or violating 
the relevant standard. Air agencies are required to provide the EPA 
with area recommendations and supporting technical information within 1 
year after a standard is revised. The EPA considers this information 
and commonly sends a letter to the air agency (at least 120 days prior 
to finalizing the designation) that describes its intended designation 
and boundaries of the nonattainment areas and other areas in the state.
    During this 120-day period, the air agency has the opportunity to 
demonstrate why an EPA-intended modification to its recommendation 
would be inappropriate. The EPA then finalizes the area designations 
process by sending letters to each governor and publishing the NAAQS 
designations for each state (and tribal area, as appropriate) in the 
Federal Register. The final designations are listed in 40 CFR part 81.
    Once an area is designated as nonattainment for the SO2 
NAAQS, CAA section 191 directs the air agency to submit to the EPA 
within 18 months of designation a NAAQS attainment plan that 
demonstrates, typically through air quality dispersion modeling, how 
the area would attain the standard as expeditiously as practicable, but 
no later than 5 years after designation as provided by section 192. CAA 
section 172 lists additional elements that NAAQS attainment plans are 
to contain. The air quality modeling for an attainment demonstration 
needs to ensure that the area would attain even if all contributing 
sources emitted at ``permitted allowable'' levels. The specifications 
of attainment demonstration modeling techniques are described in 40 CFR 
part 50, Appendix W.

C. History of Designations for the SO2 NAAQS

    The original SO2 NAAQS \4\ were established in 1971, and 
the EPA originally designated nonattainment areas for the prior 
SO2 NAAQS in March 1978.\5\ The Federal Register final rule 
for this action noted that certain areas were designated on the basis 
of modeling data: ``In the absence of sufficient monitored air quality 
data, other evaluation methods were used, including air quality 
dispersion modeling.'' In a September 11, 1978, supplement to the March 
3, 1978, final rule, the EPA responded to commenters and upheld certain 
designations based on modeling information.\6\ A second supplement to 
the March 1978 designations notice affirmed the use of modeling for 
SO2 designations and determining air quality status, stating 
that, ``the EPA's policy related to designations for SO2 
permit the use of either modeling or monitoring to determine attainment 
status.'' \7\
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    \4\ See 36 FR 8186 (April 30, 1971).
    \5\ See 43 FR 8962 (March 3, 1978).
    \6\ See 43 FR 40416 (September 11, 1978).
    \7\ See 43 FR 40502 (September 12, 1978).
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    Five years later, in 1983, the EPA conducted a review of all 
section 107 NAAQS designations made to date. A related EPA memo, 
``Section 107 Designation Policy Summary,'' identified the importance 
of modeling information for source-oriented pollutants in cases where 
existing monitors did not adequately characterize peak concentrations: 
``In general, all available information relative to the attainment 
status of the area should be reviewed. These data should include the 
most recent eight consecutive quarters of quality-assured, 
representative ambient air quality data plus evidence of an implemented 
control strategy that the EPA had fully approved. Supplemental 
information, including air quality modeling, emissions data, etc., 
should be used to determine if the monitoring data accurately 
characterize the worst case air quality in the area.'' \8\
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    \8\ Memorandum From Sheldon Myers, Director, EPA Office of Air 
Quality Planning and Standards, to Regional Office Air Division 
Directors. ``Section 107 Designation Policy Summary.'' April 21, 
1983.
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D. Use of Air Quality Modeling Information in Area Designations for the 
SO2 NAAQS

    Past area designations processes for most NAAQS (such as for ozone) 
having violations caused and contributed to by multiple sources over a 
broad region have relied primarily on air quality monitoring data to 
identify areas that

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violate the standard. However, it is important to note, as the EPA 
explained in the final 2010 SO2 NAAQS preamble, that there 
is a long history of also using dispersion modeling information to 
inform area designations for the SO2 NAAQS. See, e.g., 75 FR 
at 35551-3. The EPA and the air quality management community have 
recognized over many years that peak concentrations of SO2 
are commonly caused by one or a few major point sources in an area and 
peak concentrations are typically observed relatively close to the 
source. Many factors influence the observed SO2 
concentrations around emissions sources, including the sulfur content 
of fuel that is combusted, the sulfur content of material being heated 
as part of an industrial process, the rate of SO2 emissions 
per hour, stack height, topography, meteorology, monitor location and 
source operating schedule. But because ambient SO2 
concentrations are not the result of complex chemical reactions (unlike 
ozone or PM2.5), they can be modeled accurately using well-
understood air quality modeling tools, especially in areas where one or 
only a few sources exist. In the 1970's, when the original 
SO2 NAAQS were established, there were significantly more 
SO2 monitors in operation nationally than today. Even then, 
the EPA and air agencies acknowledged the utility of modeling in order 
to inform area designations under the SO2 NAAQS. See e.g., 
43 FR 45993, 45994-46002 (Oct. 5, 1978).
    Over time, air agencies have operated monitoring networks to 
characterize SO2 concentrations as effectively as possible. 
However, the ambient SO2 monitoring network has declined in 
number since its peak of approximately 1,500 monitors in 1980 to its 
current size of approximately 450 monitors (as of June 2013), due to 
improving air quality and, more recently, due to increasingly limited 
resources at the local, state and federal levels. As part of the 2010 
SO2 NAAQS review, the EPA conducted an analysis of the 
existing monitoring network to inform potential updates to 
SO2 minimum monitoring requirements that might accompany a 
revised NAAQS. The study concluded that only up to a third of the 
SO2 monitors in operation at the time were sited to 
characterize peak 1-hour ambient SO2 concentrations. The EPA 
acknowledged this in the SO2 NAAQS final preamble: ``In 
preparation for the SO2 NAAQS proposal, the EPA conducted an 
analysis of the approximately 488 SO2 monitoring sites 
operating during calendar year 2008 (Watkins and Thompson, 2009). This 
analysis indicated that approximately 35 percent of the sites in the 
monitoring network were addressing locations of maximum (highest) 
concentrations, likely linked to a specific source or group of sources. 
Meanwhile, just under half (~46 percent) of the sites were reported to 
be for the assessment of concentrations for general population 
exposure. These data led the EPA to conclude that the network was not 
properly focused to support the revised NAAQS, given the EPA's belief 
at the time that source-oriented monitoring data would be a primary 
tool for assessing compliance with the NAAQS.'' \9\ While the current 
ambient SO2 monitoring network does serve multiple 
monitoring objectives (which includes some source-oriented monitoring), 
on the whole, the network is not appropriately positioned or of 
adequate size for purposes of the 2010 SO2 standard to 
characterize the air quality around many of the nation's larger 
SO2 sources in operation today.
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    \9\ See 75 FR 35557 (June 22, 2010). See also Watkins and 
Thompson. (2009). SO2 Network Review and Background; 
OAQPS; Office of Air Quality Planning and Standards, U.S. 
Environmental Protection Agency, Research Triangle Park, NC. Sulfur 
Dioxide NAAQS Review Docket (OAR-2007-0352-0037). Available at 
https://www.regulations.gov.
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    In implementation of the prior SO2 NAAQS, the EPA thus 
relied upon both modeling and monitoring to inform decisions regarding 
whether areas were violating the NAAQS. See e.g., 67 FR 22168, 22170-71 
(May 2, 2002). This historical use of modeling along with monitoring 
has been affirmed as technically valid and lawful under the CAA by 
reviewing courts. See e.g., Montana Sulphur & Chemical Co. v. the EPA, 
666 F.3d 1174, 1185 (9th Cir. 2012); PPG Industries, Inc. v. Costle, 
630 F.2d 462, 467 (6th Cir. 1980). Because of the inherent challenges 
in characterizing peak SO2 ambient air quality strictly 
through monitoring techniques, past EPA SO2-related 
designations actions, state implementation plan (SIP) approval and 
disapproval rulemakings, federal implementation plan rulemakings and 
non-binding guidance have recognized that air quality modeling can be 
appropriately used to identify areas that are meeting or violating the 
SO2 NAAQS, and can be used to confirm air quality monitoring 
data when an area is seeking redesignation to attainment.
    The EPA believes that existing air quality modeling tools are 
technically sound and historically have been used when monitoring data 
were not available; therefore, the EPA considers these modeling tools 
appropriate for use in combination with ambient monitoring data for 
assessing air quality impacts from SO2 emissions. The EPA 
has recently issued a draft modeling technical assistance document 
(TAD) \10\ suggesting an approach that could be used by states to 
characterize SO2 concentrations around SO2 
sources using the AERMOD \11\ model with actual emissions data, actual 
meteorological data and actual stack height information. More details 
on the EPA's modeling TAD are provided in section V, Technical 
Considerations.
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    \10\ The Draft SO2 NAAQS Designations Modeling 
Technical Assistance Document can be found at https://www.epa.gov/airquality/sulfurdioxide/pdfs/SO2ModelingTAD.pdf.
    \11\ ``AERMOD'' stands for the American Meteorological Society/
EPA Regulatory Model.
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E. SO2 NAAQS Preamble: Suggested Implementation Approach

    The preamble to the final SO2 NAAQS issued in 2010 noted 
that although the current SO2 ambient monitoring network 
included 400+ monitors nationwide, the scope of the network had certain 
limitations and approximately two-thirds of the monitors were not 
located to characterize maximum concentration, source-oriented impacts. 
In order to address potential public health impacts in areas without 
adequate monitoring that could be experiencing SO2 
concentrations that violate the NAAQS, in the June 2010 SO2 
NAAQS preamble the EPA recommended, but did not require, that air 
agencies characterize air quality in these areas with limited 
monitoring through the use of air quality modeling, and adopt 
substantive emission limitations to ensure attainment of the 
SO2 NAAQS where the modeling indicated a violation. The 
preamble stated that the EPA expected that such analyses and emission 
limitations would be submitted as part of the section 110(a)(1) 
infrastructure plans due in June 2013 in order to demonstrate how areas 
with sources emitting over 100 tons of SO2 per year would 
attain and maintain the NAAQS in the future. The EPA subsequently 
issued draft implementation guidance in September 2011, which further 
described this suggested approach and requested comments from the 
public.\12\
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    \12\ The draft guidance for 1-Hour SO2 NAAQS SIP 
Submissions can be found at https://www.epa.gov/oaqps001/sulfurdioxide/pdfs/DraftSO2Guidance--9-22-11.pdf.
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    A number of commenters on the draft guidance expressed concern with 
the suggested implementation approach and some challenged this approach 
in court

[[Page 27450]]

as part of the final SO2 NAAQS rule.\13\ Many commenters 
maintained that areas should be designated as nonattainment first, 
before they are expected to provide technical analyses and adopt 
enforceable emission limitations demonstrating attainment. They claimed 
that the recommended approach in effect bypassed the designation 
process for areas without adequate monitoring, frustrating the 
preferred sequence in implementing NAAQS under the CAA. A number of 
commenters were concerned about the level of effort and resources 
needed to develop plans that essentially required modeling for all 
sources with annual SO2 emissions exceeding 100 tons. (There 
were more than 1,680 sources across the country exceeding 100 tons of 
actual emissions based on 2008 national emissions inventory data. Based 
on data from the 2011 National Emissions Inventory, there are about 
1500 sources exceeding 100 tons of annual SO2 emissions.) It 
was also pointed out that the statutory due date of June 2013 for the 
section 110 infrastructure plans (which would have included control 
requirements based primarily on modeling information under the EPA's 
then-suggested approach) would come well before the attainment plan 
submittal due date for areas to be designated as nonattainment. (At the 
time the draft guidance was issued in September 2011, the EPA was 
planning to issue final designations in June 2012, meaning that 
nonattainment area plans would have been due 18 months from the 
effective date of designations, or approximately in February 2014.) 
\14\
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    \13\ On July 20, 2012, the D.C. Circuit Court of Appeals issued 
a decision upholding the 2010 SO2 NAAQS. See National 
Environmental Development Association's Clean Air Project v. EPA, 
No. 10-1252 (D.C. Cir. July 20, 2012). The U.S. Supreme Court 
declined to hear an appeal of this decision.
    \14\ Note that on July 27, 2012, the EPA announced that it was 
extending the deadline for the initial round of SO2 NAAQS 
area designations by an additional year, to June 3, 2013, which thus 
compounded this timing discrepancy in many commenters' views.
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F. The EPA White Paper and Stakeholder Input

1. Background
    In response to the comments received on the draft implementation 
guidance issued in September 2011, the EPA Assistant Administrator for 
Air and Radiation, Gina McCarthy, sent letters to state Environmental 
Commissioners on April 12, 2012, indicating that the EPA wanted to 
further consult with stakeholders regarding how to best implement this 
standard and protect public health in an effective manner. The letters 
also stated that the EPA would not expect air agencies to submit 
substantive attainment demonstrations and emission limitations by June 
2013 (as part of section 110(a) infrastructure plans) for areas not 
designated as ``nonattainment,'' but would expect those submittals to 
resemble more traditional infrastructure SIPs.
    The EPA then issued a May 2012 paper titled, ``Implementation of 
the 2010 Primary 1-Hour SO2 NAAQS: Draft White Paper for 
Discussion'' (White Paper) on possible alternative approaches for 
implementing the SO2 standard.\15\ The EPA convened 3 
stakeholder meetings to discuss the White Paper in May and June of 2012 
with, respectively, environmental group representatives; state, local 
and tribal air agency representatives; and industry representatives. 
The EPA also accepted written comments on the White Paper from 
interested parties through the end of June.
---------------------------------------------------------------------------

    \15\ The May 2012 White Paper and high-level summaries of 
stakeholder meetings are available at: https://www.epa.gov/oaqps001/sulfurdioxide/implement.html. These documents and written comments 
received from stakeholders are also included in the docket for this 
rulemaking.
---------------------------------------------------------------------------

    In the White Paper and during the stakeholder meetings, the EPA 
framed the basic challenge of how to more broadly characterize 1-hour 
SO2 concentrations in priority locations across the country 
such that these data could inform future area designations for the 
SO2 NAAQS, while taking into consideration limited EPA and 
air agency resources. The paper noted that peak 1-hour concentrations 
of SO2 are most commonly observed in relatively close 
proximity to emission sources, yet many monitors in the current 
SO2 ambient monitoring network are not sited in appropriate 
locations to document these peak concentrations. Thus, many existing 
monitors are in effect ``under-reporting'' peak 1-hour concentrations.
    The White Paper indicated that there are more than 20,000 
SO2 sources nationally and to add a significant number of 
ambient monitors to the national network to adequately characterize 
peak concentrations would take significant resources. The EPA estimates 
that the capital costs of siting a new monitor can be on the order of 
$50,000 to $100,000. Routine operations and maintenance costs would be 
in addition to those up-front capital costs.
    Given this background, the White Paper described two monitoring-
focused approaches and one modeling-focused approach for characterizing 
peak 1-hour SO2 concentrations, and it outlined a range of 
policy, technical, and implementation issues and questions associated 
with each approach. The issues and questions highlighted in the White 
Paper were discussed in depth during the stakeholder meetings. The 
White Paper and high-level summaries of each meeting are available on 
the EPA's SO2 implementation Web site.\16\
---------------------------------------------------------------------------

    \16\ See https://www.epa.gov/airquality/sulfurdioxide/implement.html.
---------------------------------------------------------------------------

2. Monitoring and Modeling Approaches Described in White Paper
    Two possible monitoring-focused approaches were described in the 
White Paper. The White Paper indicated that about 440 SO2 
monitors were operational as of April 2012, but only about a third of 
those monitors might be considered to be in ``source-oriented'' 
locations. Thus, if air agencies were to implement a monitoring-only 
approach without supplemental data from modeling, a number of monitors 
would either need to be moved within the existing network and/or a 
number of new monitoring sites would need to be established.
    The first monitoring-based approach described in the White Paper 
would involve air agencies reallocating the monitors that are not 
source-oriented and otherwise not required to be in their current 
locations to be moved to source-oriented locations, and then adding 
additional monitors as necessary to address all areas warranting 
further characterization of air quality. For example, such a network 
might be designed to characterize air quality for about 550 sources 
with annual emissions greater than 2,000 tons, which in total would 
account for about 93 percent of nationwide SO2 emissions 
(based on 2008 national emission inventory data). This option would 
identify source areas for monitoring based on a single emissions 
threshold. It would focus on providing air quality characterization 
around the largest sources and would not provide additional emphasis on 
sources located in highly populated areas.
    The second monitoring-focused option presented in the White Paper 
was an extension of the Population Weighted Emissions Index (PWEI) 
concept that was included in the 2010 SO2 NAAQS ambient 
monitoring requirements. The PWEI was established to define monitoring 
requirements for Core Based Statistical Areas (CBSAs) based on 
calculations using the total SO2 emissions and total 
population in the area. This suggested option in the White Paper would 
require approximately 400 sources located in areas with a high PWEI and 
having SO2

[[Page 27451]]

emissions over 750 tons per year (tpy) to have source-oriented 
monitoring; and an estimated 170 additional sources located outside 
those PWEI areas having emissions over 5,000 tpy to have source-
oriented monitoring. This option also would account for more than 90 
percent of nationwide SO2 emissions (based on 2008 national 
emission inventory data).
    Thus, both monitoring-only approaches, using the example cutoffs 
identified in the White Paper, were estimated to provide for the 
characterization of air quality for at least 500 sources that accounted 
for at least 90 percent of national emissions (based on 2008 emissions 
data).\17\ One key difference between the 2 options was that the second 
option provided some additional emphasis on ensuring the 
characterization of air quality in areas with relatively higher 
populations.
---------------------------------------------------------------------------

    \17\ Based on 2008 emissions data, about 480 sources with actual 
emissions exceeding 2,800 tons per year accounted for 90 percent of 
national SO2 emissions.
---------------------------------------------------------------------------

    The White Paper also included discussion of a modeling-based 
approach, in which air quality dispersion modeling with AERMOD would be 
used to characterize air quality for areas in which the largest 
SO2 sources are located. The EPA presented this potential 
approach because air quality modeling has been used for SO2 
designations in the past, and conducting air quality modeling analyses 
for SO2 would likely be less resource intensive than the 
full-scale expansion and operation of the ambient monitoring network 
described in the Paper. Under this approach, modeling would be required 
to characterize air quality in areas in which sources exceeding a 
specified emissions threshold are located.
3. Comments on Monitoring-Based Approaches
    In the May-June 2012 stakeholder meetings and written comments 
received thereafter, a number of stakeholders, including several state 
and local air agency representatives, expressed a preference for the 
use of ambient monitoring alone to characterize air quality 
SO2 concentrations. They indicated that, since the 1970s, 
ambient monitoring has been the traditional approach for characterizing 
air quality to assess compliance with all other NAAQS. They claimed 
that the expanded use of air quality modeling to characterize 
SO2 concentrations, as described in the draft September 2011 
guidance, would not be appropriate because they believed that modeling 
techniques inherently over-predict SO2 concentrations by 
assuming a constant rate of peak emissions and worst-case 
meteorological conditions.
    Commenters from some of the states with the greatest number of 
large SO2 sources (such as Ohio, Indiana and Pennsylvania) 
indicated that for each source, as many as 3 monitors or more might be 
needed to adequately characterize 1-hour SO2 concentrations 
around the source, in order to avoid monitoring that underestimates 
maximum SO2 concentrations.\18\ Some also recommended the 
addition of an onsite meteorological station near each source to aid 
monitoring data analysis.
---------------------------------------------------------------------------

    \18\ See, for example, comments from Ohio EPA, docket number 
EPA-HQ-OAR-2010-1059-0123.
---------------------------------------------------------------------------

    Representatives from environmental organizations did not favor 
monitoring-based approaches. They emphasized the importance of 
characterizing air quality in priority areas expeditiously in order for 
such data to be used in the area designations process and monitoring 
approaches would take several years to site new monitors and collect 3 
years of data. They pointed out that high 1-hour concentrations can 
occur in any direction around a source and that state air agencies 
would not have the resources to provide for multiple monitors around 
priority sources.
    While some air agencies nevertheless maintained a preference for 
ambient monitoring, a number of them also expressed the concern that it 
would be difficult to expand their SO2 networks with 
additional air quality monitors as needed because state budget 
resources are very limited today. Some commented that from a practical 
standpoint, if an expanded SO2 monitoring network was to be 
established, it would need to be funded by the federal government, or 
by the source owners themselves. In contrast, a number of commenters 
representing sources of SO2 emissions or industry 
associations maintained that ambient air quality monitoring to protect 
public health should be a governmental responsibility, rather than the 
responsibility of the emissions sources themselves. Some industry 
representatives indicated that they operate their own monitoring 
networks and could explore with corresponding air agencies the 
possibility of using data from such monitors under a monitor-based 
approach. Such monitors would need to meet the EPA's quality-assurance 
requirements, the data would need to be made publicly available and an 
agreement for long-term operation and funding would need to be 
considered.
    Thus, while ambient monitoring appeared to be the favored 
methodology by a number of stakeholders, there were very pragmatic 
concerns expressed about the cost of expanding current networks 
sufficiently to ensure proper coverage and uncertainty about how many 
new monitors could be established in actuality. Some air agency 
representatives remarked that if modeling is also recognized as an 
acceptable approach for characterizing air quality, then they would be 
open to both approaches, as long as the state has the flexibility to 
use the analytical method that would make the most sense for each 
identified source area, considering the coverage of the state's 
existing monitoring network, various resource and staffing 
considerations, and other factors.
4. Comments on Modeling Approach
    Environmental group representatives generally favored the use of 
modeling, citing the EPA's prior policy and various regulatory 
precedents in which modeling has been used to characterize 
SO2 air quality. They emphasized that modeling can be done 
more quickly, with less expense and for more locations (including 
locations where physically siting a monitor would be very difficult) 
than monitoring. They indicated that the cost of modeling assessments 
for certain source areas could be done for less than $10,000.
    Many air agency and industry commenters asserted that if the 
September 2011 draft modeling guidance for attainment plans (which, 
consistent with longstanding guidance and practice in SO2 
attainment planning, recommended the use of allowable, not actual, 
emissions rates) is maintained as the guidance for characterizing 
current air quality and is used for designations purposes, it would 
lead to significant over-predictions of 1-hour SO2 
concentrations. Some commenters opposed the use of modeling at all for 
this reason, without suggesting ways to correct this asserted over-
prediction. Some commenters also cited specific technical issues with 
the AERMOD model (such as the treatment of low wind speed conditions 
and the treatment of building ``downwash'' conditions) which they 
believe contribute to the over-prediction of air quality 
concentrations.
    A number of commenters did not oppose modeling outright, but 
suggested that if modeling is part of the EPA's overall approach, the 
EPA should allow air agencies to conduct modeling based on actual 
emissions, since modeling in this context in effect would serve as a 
surrogate to comprehensive ambient

[[Page 27452]]

monitoring, while overcoming the current monitoring network's relative 
lack of coverage. For example, the Florida Department of Environmental 
Protection provided an example analysis in their comments which showed 
modeled air quality results using actual emissions inputs in close 
agreement with monitored air quality values near a large emission 
source in Florida.\19\
---------------------------------------------------------------------------

    \19\ See Docket item the EPA-HQ-OAR-2010-1059-0172, June 29, 
2012, letter from Florida Department of Environmental Protection 
with comments on the EPA's April 2012 SO2 White Paper.
---------------------------------------------------------------------------

    The EPA notes that the reason the draft modeling guidance issued in 
September 2011 recommended the use of the source's allowable emissions 
rate in the modeling analysis is because it was developed for 
predictive situations, such as when an air agency would be 
demonstrating attainment for the future, where use of allowable 
emissions rates is common for providing assurance that the prediction 
includes a full range of potential emissions scenarios. However, the 
EPA acknowledges that for the purpose of characterizing current \20\ 
air quality, it is reasonable for modeling presumptively to use actual 
emissions data and/or actual 1-hour emission rates as an input in order 
to most closely represent ambient monitoring results. The EPA has 
concluded that using actual emissions data and meteorological data as 
inputs to AERMOD modeling can adequately characterize peak 
concentrations in multiple directions around a source. Note also that 
after considering the White Paper comments, the EPA developed the draft 
SO2 NAAQS Designations Modeling TAD that recommends using 
AERMOD to estimate air quality concentrations near a large 
SO2 source by using actual emissions data (such as 1-hour 
emissions rates from continuous emission monitors) and meteorological 
data from appropriate proximate nearby locations.\21\
---------------------------------------------------------------------------

    \20\ ``Current'' air quality in this context refers to the air 
quality indicator that may be used by the EPA for various regulatory 
decisions in a future designations process (e.g., the most recent 3 
years of monitoring data).
    \21\ While the use of actual emissions data is recommended in 
the draft modeling TAD, there may be situations where the use of 
allowable emissions rates to characterize current air quality may be 
beneficial for the air agency or source to show that even with this 
type of conservative assumption, the source area would be expected 
to attain the standard. One benefit of an analysis demonstrating 
attainment of the 1-hour standard based on allowable emission rates 
is that it would avert the need for recurring review to determine 
whether emission increases have created new potential for NAAQS 
violations.
---------------------------------------------------------------------------

    In light of the practical concerns about the cost of adding new 
ambient monitors, the uncertainty (at the time of the stakeholder 
meetings) about whether actual emissions would be able to be used for 
air quality modeling for this purpose, and how accurate the predictive 
results of such modeling would be, many commenters suggested that air 
agencies should be provided the flexibility to choose whichever 
approach makes the most sense on a case-by-case basis for 
characterizing air quality around each priority source in the state. In 
addition, based on comments received on the White Paper regarding state 
resource concerns, it appears that some air agencies likely will need 
to rely primarily on air quality modeling techniques.
5. Comments on Emissions Threshold
    While there was not consensus with respect to using a single 
approach for characterizing air quality from SO2 sources, 
one issue that all parties involved in the stakeholder discussions 
generally agreed upon was the concept of having a ``threshold'' of some 
sort to identify the largest sources around which ambient air quality 
would need to be characterized to inform future rounds of area 
designations. A number of stakeholders commented that, given current 
budgetary and other constraints on resources for characterizing air 
quality through either monitoring or modeling, focusing on the largest 
sources of emissions would be a reasonable approach for prioritizing 
sources to be evaluated for purposes of assessing attainment with the 
1-hour SO2 NAAQS. Many stakeholders found the basic policy 
approach expressed in the White Paper (where air agencies would 
characterize air quality for sources accounting for 90 percent of 
national SO2 emissions for use in future designations) to be 
reasonable and preferable to the approach in the September 2011 
guidance (where air agencies were expected to demonstrate attainment 
around all sources in the state emitting more than 100 tons of 
SO2 per year).
    Some commenters offered recommendations for specific SO2 
thresholds based on annual emissions or other factors that would define 
which sources air agencies would be expected to characterize through 
monitoring or modeling in the future. Some commenters suggested single 
threshold levels ranging from 100 to 5,000 tons of SO2 
emissions per year. A few commenters suggested a phased approach, in 
which larger sources (e.g., 2,000 tpy and larger) would be addressed in 
an initial phase and smaller sources (e.g., 500-2,000 tpy) would be 
addressed in a second phase 2 or more years later.\22\ Several 
commenters observed that because the SO2 NAAQS is a 1-hour 
standard, a potentially more appropriate metric for a threshold would 
be one based on hourly emissions rates rather than tpy. Others 
recognized, however, that 1-hour emissions data are not readily 
available for many types of emissions sources other than electric 
generating units (EGUs) (which commonly operate continuous emissions 
monitors (CEMs)).
---------------------------------------------------------------------------

    \22\ Comments on the EPA White Paper from the Georgia Department 
of Natural Resources, EPA Docket ID No. EPA-HQ-OAR-2010-1059-0136, 
June 29, 2012.
---------------------------------------------------------------------------

    Some commenters stated that because protection of public health is 
the principal objective of the SO2 NAAQS, a program to 
direct air agencies to characterize SO2 concentrations 
around large SO2 sources should include some specific 
emphasis on sources located in areas with higher populations. Some 
suggested that other factors such as the height of emissions stacks, 
proximity to sensitive receptors (i.e., schools, hospitals, nursing 
homes), or source compliance record should also be considered in 
establishing a threshold-based approach.
6. Comments on Program Implementation
    A number of stakeholders provided comments on the timing of 
implementation for any program requiring air agencies to further 
characterize peak 1-hour SO2 concentrations. Many commenters 
stated that any new modeling or monitoring requirements should be 
established through a notice-and-comment rulemaking process. In 
addition, a number of air agency representatives indicated that the 
program needs to be structured in such a way that allows for sufficient 
time to conduct the necessary monitoring or modeling, citing the large 
number of sources to be addressed (even with a threshold), limited 
resources and the stringency of the 1-hour standard. The proposed 
timeline for implementation is discussed in more detail in section IV 
of this preamble.
    The input received from stakeholders during these meetings and in 
written comments was invaluable to informing the EPA's refinement of 
its SO2 implementation strategy, which was released in 
February 2013 and is discussed in the next section. Input from the 
stakeholder meetings and comments on the White Paper also informed the 
recent TADs on

[[Page 27453]]

monitoring \23\ and modeling for designations.
---------------------------------------------------------------------------

    \23\ The Draft SO2 NAAQS Designations Source-Oriented 
Monitoring Technical Assistance Document can be found at https://www.epa.gov/airquality/sulfurdioxide/pdfs/SO2MonitoringTAD.pdf.
---------------------------------------------------------------------------

G. The EPA's February 2013 SO2 Implementation Strategy Paper

    On February 13, 2013, as part of the initial area designations 
process, the EPA notified air agencies that we intended to designate 30 
areas as nonattainment, based on monitored violations of the 
SO2 NAAQS.\24\ We also notified air agencies that the EPA 
was not yet prepared to propose designations for other areas without 
violating monitors. On the same day, the EPA also issued an 
implementation strategy paper titled, ``Next Steps for Area 
Designations and Implementation of the SO2 NAAQS.'' \25\ 
This Strategy Paper described the agency's plan for addressing public 
health concerns in areas other than the areas identified in initial 
designation. The Strategy Paper recognizes the need to further 
characterize current air quality across the country to address 
important public health impacts, noting that ``the current monitoring 
network provides relatively limited geographic coverage, and many 
monitors in the existing network are not sited with the objective of 
characterizing source-oriented maximum concentrations.'' The Paper also 
supports the long-standing approach in the CAA for the EPA to designate 
nonattainment areas through an orderly exchange of recommendations and 
technical information between state governments and the EPA.
---------------------------------------------------------------------------

    \24\ The EPA finalized nonattainment designations for 29 of 
those 30 areas August 5, 2013 (78 FR 47191, 47205). The EPA took no 
designation-related action on the rest of the country. Estimated 
total stationary source SO2 emissions (calendar year 
2011) in these areas ranged from 562 tons (lowest area) to 144,267 
tons (highest area) per year.
    \25\ The February 2013 SO2 NAAQS implementation 
strategy paper can be found at: https://www.epa.gov/oaqps001/sulfurdioxide/implement.html.
---------------------------------------------------------------------------

    The main elements of the implementation strategy include the 
following:
     The EPA would develop a rulemaking directing air agencies 
to characterize air quality in priority source areas through either air 
quality monitoring or air quality modeling and submit such data to the 
EPA. The present proposal is a key step in fulfilling this aspect of 
the strategy.
     The rule would identify priority sources as those sources 
exceeding specific thresholds based wholly or in part upon annual 
emissions. Some threshold options may be ``2-pronged,'' meaning they 
could include a lower threshold for sources located in metropolitan 
areas larger than a certain size and a higher threshold for sources 
located outside such metropolitan areas.
     Prior to proposal of the rulemaking, the EPA would issue 
draft TADs on siting ambient, on source-oriented SO2 
monitors at locations of expected maximum concentration and on the use 
of air quality modeling to characterize ``current'' air quality around 
an emission source for purposes of designations recommendations.
     To fulfill their requirements to characterize air quality, 
states would have flexibility to choose whether to use monitoring or 
modeling to characterize air quality around or in proximity to 
identified sources. Air agencies would follow the timeline provided in 
the rule, which would specify the dates by which they need to identify 
the method to be used to characterize air quality and the date for 
submitting these data to the EPA along with relevant designation 
recommendations.
     The EPA and air agencies would use these data to complete 
two additional rounds of area designations as soon as feasible after 
the data become available.
     The Strategy Paper noted that this approach provides an 
incentive for states and other air agencies to work with their sources 
to achieve early reductions to improve public health and potentially 
avoid a nonattainment designation for as many priority source areas as 
possible.
    With regard to identifying priority sources through source 
threshold options, the Strategy Paper first discussed appropriate 
monitoring objectives for a NAAQS pollutant that can have localized 
impacts, such as SO2 or lead. It indicated that important 
monitoring objectives should include (1) characterization of peak air 
quality concentrations in the area around the source (e.g., source-
oriented and maximum concentration monitoring); and (2) 
characterization of air quality in populated areas, intended to 
represent ambient concentrations to which people in the area are 
exposed.
    To meet these two objectives, the EPA suggested the establishment 
of a ``2-pronged'' emissions threshold for identifying sources for 
which the air agency would need to further characterize air quality. 
The paper states: ``Under such an approach, a lower threshold (e.g., 
2,000-3,000 tpy) would apply to sources located in more heavily 
populated areas (e.g., CBSAs having 1,000,000 or more persons); and a 
higher threshold (e.g., 5,000-10,000 tpy) would apply to sources 
located in less populated areas outside of such CBSAs. To illustrate 
potential coverage of possible options, a 2-pronged threshold including 
3,000+ ton sources located in CBSA's with a population of 1,000,000 and 
10,000+ ton sources outside of these CBSA's, would cover 202 sources 
and 66 percent of national emissions. A 2-pronged threshold including 
2,000+ ton sources located in CBSA's with a population of 1,000,000 and 
5,000+ ton sources outside of these CBSA's, would cover 341 sources and 
81 percent of national emissions.''
    The Strategy Paper goes on to say, ``In a future rulemaking, 
factors to consider in selecting appropriate thresholds could include 
the comprehensiveness of the total emissions represented; the 
comparability of source coverage under this approach with typical 
source coverage of an ambient monitoring network; emission levels for 
sources in areas with monitored violations; and emission levels 
associated with `well-controlled' sources. Upon analysis of such 
factors, the EPA would expect to propose a range of threshold options 
for a minimum level of coverage (preliminary estimates suggest that 
this range could cover sources accounting for 66 percent to 90 percent 
of national SO2 emissions). In addition, the basis for the 
emissions that would be compared to the threshold (e.g., highest of the 
most recent 3 years of data) would need to be defined in the 
rulemaking.''

III. Source Coverage and Emission Threshold Options

A. Background

    This section discusses the proposed ``threshold'' options for 
identifying source areas for future air quality characterization and 
the factors that the EPA considered in developing them. The EPA 
believes the key objective to be achieved by using SO2 
source emission thresholds would be to focus the limited available 
resources at the local, state and federal levels toward characterizing 
air quality in areas having the largest SO2 emitting sources 
(and greater potential for relatively higher SO2 
concentrations) but may be lacking sufficient air quality data. In 
proposing source threshold options, the EPA seeks to collect additional 
air quality data intended to achieve protection of public health on a 
widespread basis from the adverse health effects of short-term exposure 
to high SO2 concentrations. However, the EPA recognizes that 
for SO2 and all other NAAQS, characterizing air quality in 
areas around all sources nationally is not feasible. Thus, just as 
NAAQS ambient monitoring networks are designed to

[[Page 27454]]

measure air quality in areas where the public is likely to be exposed 
and violations may be likely, these SO2 threshold options 
are designed to meet a similar objective. These options also provide 
for the characterization of air quality in a substantial number of 
source areas that account for a high percentage of the national 
SO2 emissions inventory in a manner that provides 
flexibility to air agencies, given existing funding and resource 
constraints.

B. Proposed Source Emission Threshold Options

    The purpose of establishing emission thresholds by rule will be to 
identify those SO2 emissions sources for which air agencies 
will be directed to either: (1) Characterize air quality through either 
ambient monitoring or air quality modeling; or (2) demonstrate that 
there are adequate enforceable emission limits in place for the area's 
sources by January 2017 that will ensure attainment with the 1-hour 
SO2 standard. We note that some commenters suggested that a 
number of sources are planning to shut down during the next few years 
and should not be subject to this rule. If sources have indeed shut 
down by January 2017, a demonstration to that effect would also be 
sufficient.
    We note that air agencies may have other factors or reasons that 
lead them to evaluate 1-hour air quality concentrations for 
SO2 source areas other than those that may be required to be 
characterized pursuant to this proposed rule. This proposed rule only 
presents a minimum set of sources for which surrounding ambient air 
quality would need to be characterized. As discussed in more detail in 
section IV, the air agency or the EPA Regional Administrator \26\ may 
identify other sources that should be characterized beyond the minimum 
requirements of this proposed rule.
---------------------------------------------------------------------------

    \26\ Throughout this proposed rule the ``EPA Regional 
Administrator'' refers to the Regional Administrator or a delegated 
representative.
---------------------------------------------------------------------------

    In developing the proposed source emission threshold options, the 
EPA considered two important preliminary questions: (1) What is an 
appropriate metric for defining a source threshold? and (2) should 
population centers be addressed by source threshold options? The EPA 
considers each of these questions first before discussing the three 
proposed source threshold options.
1. What are the appropriate emissions metrics for use in a threshold 
approach?
    The EPA's 2012 White Paper and the 2013 Strategy Paper discuss 
appropriate metrics to use in establishing a threshold-based approach 
to characterize ambient air quality surrounding a subset of priority 
SO2 sources. In these papers, the EPA described the source 
emission threshold concept in terms of the metric of annual tons of 
SO2 emissions. Because the standard is expressed in terms of 
a 1-hour form, a potentially more appropriate metric to use for 
establishing a source threshold concept to identify priority sources 
may be the 1-hour emission rate. Many EGUs are already required to 
track and report 1-hour emission rates in accordance with existing 
requirements to operate CEMs for compliance with existing programs. 
However, most facilities in non-EGU sectors (e.g., pulp and paper 
facilities, Portland cement plants, petroleum refineries, etc.) do not 
currently operate CEMs nor do they collect emissions data on an hourly 
basis.
    Commenters on the White Paper also identified some other factors 
that potentially could be used or incorporated into an approach to 
identify sources for air quality characterization. These factors 
include stack height, proximity to sensitive populations (e.g., 
schools, hospitals, nursing homes) and topography, among others. Some 
commenters suggested that the EPA develop a complex matrix of multiple 
factors for identifying sources.
    The EPA recognizes that any source emission threshold approach 
needs to strike a reasonable balance between the robustness of the 
technical approach and the feasibility of implementing it. The EPA 
believes that inclusion of factors other than emissions data in a 
source threshold approach will be difficult for implementation because 
current databases do not provide comprehensive data for other factors 
for all SO2 candidate sources nationally. In addition, we do 
not anticipate that the introduction of these multiple other potential 
factors would improve the source identification approach by such a 
degree that it would justify the complexity and additional 
administrative burden introduced by the inclusion of such factors.
    The EPA therefore is proposing that the emissions-based component 
in the threshold options presented in this rulemaking be expressed in 
terms of annual emissions of SO2. Annual emissions data are 
available for all SO2 emissions sources over 100 tpy, 
whether EGU or non-EGU, and thus providing a stable and common metric 
for large sources. Requirements for the submittal of such data already 
are found in existing regulations for large SO2 sources, 
whereas submittal of 1-hour emissions data is not currently required 
for all large sources of SO2. Thus, an annual emissions-
based approach would not impose substantial new reporting burdens on 
states and sources. This metric will also allow for program 
implementation based on a common and complete dataset; and importantly, 
many stakeholders in past meetings have expressed support for the use 
of annual emissions.
    The EPA requests comment on the use of annual emissions (i.e., tons 
of SO2 per year) as the metric to be used for an emissions 
and population-based threshold approach, or, alternatively, for a 
solely emissions-based threshold approach, to identify SO2 
sources for further ambient air quality characterization with respect 
to the 1-hour SO2 NAAQS. The EPA also requests comment on 
any potential alternative factors that should be considered for 
defining emissions thresholds, along with any information about the 
availability of data related to this factor for all SO2 
sources nationally, the time and resources needed to develop a database 
for this additional factor, any associated technical analysis and 
rationale for using these other factors in defining source thresholds.
2. Should a tighter threshold apply in more populated areas?
    In the 2012 White Paper, the EPA presented the issue of whether 
population exposure could have a role in the process of identifying 
where limited resources should be focused in creating new air quality 
data, as it historically has in designing ambient air quality networks. 
In feedback received during meetings with stakeholders, commenters 
varied in their opinions regarding whether there should be a 
population-based aspect to the source threshold concept or not. Some 
stakeholders supported a threshold based strictly on SO2 
emissions, while others supported an option with both a source-oriented 
component and a population-based component.
    After considering these comments, the EPA in its February 2013 
SO2 Strategy Paper presented example options for 
establishing ``2-pronged'' source thresholds that would include a lower 
emissions threshold for sources located in areas with higher population 
and a higher emissions threshold for sources outside those higher 
population areas. One advantage of a 2-pronged option is that it 
directly addresses source-

[[Page 27455]]

oriented emissions and includes an element of population exposure. A 
lower threshold for urban sources can help increase public health 
protection because there are more people in an area that could be 
impacted by relatively smaller sources. At the same time, the higher 
threshold outside the populated areas allows resources spent on 
characterizing air quality around smaller sources to be more 
efficiently focused on the more populated areas.
    Consistent with the February 2013 Strategy Paper, the EPA believes 
it would be most prudent to design this data requirements rule to 
include specific priority for characterizing air quality around sources 
located in areas of higher population and therefore the potential for 
greater population exposure to unsafe 1-hour SO2 
concentrations. The air quality data to be developed by air agencies 
will be used in protecting public health in these areas through the 
area designations process. The inclusion of population exposure as an 
objective in this program also would be generally consistent with the 
rationale behind the PWEI concept used in the monitoring requirements 
promulgated in the 2010 SO2 NAAQS final rule.
    The EPA believes that in defining the population exposure component 
of a source threshold approach, it is preferable to link the threshold 
to population data for CBSAs. As a precedent, the EPA has recently used 
the population threshold of CBSAs having 1,000,000 or more persons for 
certain minimum monitoring requirements for nitrogen dioxide 
(NO2), carbon monoxide and particulate matter. Further, the 
recent 2013 Revision to Ambient Nitrogen Dioxide Monitoring 
Requirements rule modified the dates by which required near-road 
NO2 monitors are to be operational, with the first phase of 
these monitors focused in CBSAs having 1,000,000 or more persons.
    Based upon 2012 population estimates from the U.S. Census Bureau, 
areas meeting the 1,000,000 person CBSA threshold represent 
approximately 55 percent of the total U.S. population. The EPA believes 
this threshold is a reasonable metric to use when there is a need to 
more explicitly consider issues of concern in the nation's more 
urbanized areas. Due to the recent use of this particular population 
threshold, we again propose to use it as a means of demarking how a 
source threshold approach might be applied in the more populated areas 
of the country. The EPA requests comment on its proposed use of the 1 
million person CBSA population threshold for representing the 
population exposure component of the source threshold options in this 
rule. The EPA also requests comment on whether to include a population 
exposure-based threshold at all, and on whether alternative or 
additional criteria would be appropriate to further focus resources on 
characterizing air quality in areas with a higher likelihood of 
population exposure. The EPA also recommends that commenters provide 
appropriate supplementary information to support their comments.
3. What are the proposed options for source emission and population 
thresholds?
    The EPA is proposing a preferred source emission and population 
threshold option and we are requesting comment on two other alternative 
options. These options are summarized in Table 1 below. Data from the 
emissions year of 2011 were used to calculate the number of sources 
covered and the percent of national SO2 emissions covered by 
each option. Total SO2 emissions in 2011 were 5.8 million 
tons.
    All of these options are in the form of a ``2-pronged'' approach 
using both source emissions and population data. Each has a lower 
annual SO2 emissions tonnage threshold for sources located 
in urbanized areas (e.g., CBSAs) with a population greater than 
1,000,000, and a higher annual emissions tonnage threshold for sources 
located outside of such areas. These options have been developed after 
taking into account comments from a number of stakeholders during 
previous discussions in 2012 as discussed in section II above.
    The intent of the following proposed options is to identify a 
minimum set of sources meeting a common set of criteria for which 
additional monitoring or modeling would be conducted to characterize 
current ambient air quality in priority areas with the greatest 
potential for exposure to violations of the SO2 NAAQS (such 
as may be used to inform future designations under the SO2 
NAAQS). However, we note that, while a state that meets these minimum 
requirements would satisfy the rule, there may still be a need to 
characterize air quality for other sources below the thresholds in this 
rule that the air agency or the EPA Regional Administrator deems may 
have the potential to violate the NAAQS. For any such source areas, the 
air agency could choose whether to characterize air quality through 
monitoring or modeling. In a modeling analysis, a source below the 
threshold could be accounted for directly as one of the sources 
included in the modeling assessment, or in some cases it could be 
sufficient to account for smaller stationary and area sources of 
SO2 in how background emissions are characterized in the 
analysis.
    The EPA is proposing Option 1, which would require ambient air 
quality characterization around sources with emissions greater than 
1,000 tpy which are located within any CBSA having 1,000,000 or more 
persons, and around sources with emissions greater than 2,000 tpy 
located outside CBSAs having 1,000,000 or more persons. Based upon 2011 
emissions data and 2012 census estimates, Option 1 would identify 443 
sources which account for 75 percent of the total SO2 
emissions inventory located in areas currently not designated. In 
addition to those sources, Table 1 also indicates that 53 sources 
exceeding these thresholds were included in areas designated 
nonattainment in 2013,\27\ and, according to 2011 emissions data, they 
accounted for over 900,000 tons of SO2. Thus, the total 
coverage of this option, including sources above the thresholds and 
sources included in designated nonattainment areas, would be 496 
sources and 90 percent of national SO2 emissions in 2011.
---------------------------------------------------------------------------

    \27\ See EPA memorandum to the docket that identifies 
SO2 emissions sources that would be covered by each 
proposed source emissions threshold option, and sources located in 
designated nonattainment areas.
---------------------------------------------------------------------------

    The EPA notes that the ``90 percent threshold'' concept embodied in 
the preferred Option 1 was first described in the May 2012 White Paper 
and discussed in the May-June 2012 stakeholder meetings. A number of 
stakeholders expressed general support for a threshold at this level 
because, while still addressing 90 percent of the inventory, it 
efficiently focused program requirements on a limited subset of the 
20,000+ SO2 sources nationally, and substantially fewer 
sources than the almost 1,700 100-ton sources targeted by the original 
strategy discussed in the final SO2 NAAQS preamble and 
September 2011 draft and the EPA guidance. Under Option 1, it is 
estimated that no more than 32 sources from any one state would meet 
the minimum source threshold criteria. Option 1 also is generally 
consistent with the monitoring coverage provided by the lead NAAQS, 
which is a standard designed primarily to address source-oriented 
emissions impacts, similar to the SO2 NAAQS.
    Option 2 would require ambient air quality characterization around 
sources with emissions greater than 2,000 tpy that are located within 
any CBSA

[[Page 27456]]

having 1,000,000 or more persons, and around sources with emissions 
greater than 5,000 tpy located outside CBSAs having 1,000,000 or more 
persons. Based upon 2011 emission year data and 2012 census estimates, 
Option 2 would identify for characterization 270 sources that account 
for 66 percent of the total SO2 emissions inventory located 
in areas currently not designated.\28\ Therefore, the total coverage of 
this option, including sources above the thresholds and sources 
included in designated nonattainment areas, would be 323 sources and 82 
percent of national SO2 emissions in 2011.
---------------------------------------------------------------------------

    \28\ Options 2 and 3 were provided as examples in the February 
2013 SO2 implementation strategy paper and have been 
discussed with various stakeholders since that time.
---------------------------------------------------------------------------

    Option 3 would require ambient air quality characterization around 
sources with emissions greater than 3,000 tpy that are located within 
any CBSA having 1,000,000 or more persons, and around sources with 
emissions greater than 10,000 tpy located outside CBSAs having 
1,000,000 or more persons. Based upon 2011 emission year data and 2012 
census data, Option 3 would identify for characterization 158 sources 
that account for 54 percent of the total SO2 emissions 
inventory located in areas currently not designated. Thus, the total 
coverage of this option, including sources above the thresholds and 
sources included in designated nonattainment areas, would be 211 
sources and 69 percent of national SO2 emissions in 2011.
    The preferred Option 1 and the other two options are summarized in 
Table 1 below with regard to emission thresholds, population 
thresholds, number of sources identified for characterization and 
percent of national inventory (before and after subtracting sources 
already in areas designated nonattainment).

                                                     Table 1--Summary of Source Threshold Options a
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                           Threshold for sources                            Percent of     Plus sources
                                 ----------------------------------------    Number of       national     in 2013 desig.   Total source        Total
             Option                  Inside CBSAs        Outside CBSAs      sources **       emissions     nonatt. areas     coverage        emissions
                                    greater than 1M     greater than 1M                    [dagger] (%)      [Dagger]                      coverage (%)
--------------------------------------------------------------------------------------------------------------------------------------------------------
 1*.............................  1,000 TPY.........  2,000 TPY.........             443              75              53             496              90
2...............................  2,000 TPY.........  5,000 TPY.........             270              66              53             323              82
3...............................  3,000 TPY.........  10,000 TPY........             158              54              53             211              69
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ The emissions in this table are based on the 2011 National Emissions Inventory (NEI) and differ from the information in the February 2013 Strategy
  Paper, which was based on the 2008 NEI and preliminary 2011 data. These numbers are also based on the 2013 CBSA definitions.
* Preferred option.
** These do not include sources located in nonattainment areas designated in 2013.
[dagger] Total SO2 emissions in 2011 were 5.8 million tons.
[Dagger] There are 53 sources with annual emissions greater than 1,000 tpy in nonattainment areas designated in 2013.

    The EPA proposes that states be required to characterize air 
quality around SO2 emission sources identified by the 
thresholds presented in Option 1. The agency requests comment on the 
proposed option, and the other options described and presented here. 
Specifically, comment is requested on the emission threshold values (in 
tpy), the 1 million CBSA population thresholds, their combination as a 
means of determining how SO2 sources would be identified and 
on any possible alternatives that might be appropriate for 
consideration. The EPA requests comment on the scope of sources for 
which we are requiring data through this proposed rulemaking. The EPA 
is also interested in commenters' preferences and clear explanation of 
the rationales for their positions. The EPA also requests any 
information identifying sources that would be included by these options 
but that have confirmed documentation to show that they will shut down 
in the next several years. A number of sources included in the source 
counts included in Table 1 have indicated their intent to shut down or 
repower, meaning that the number of sources around which air agencies 
would be directed to characterize air quality under this program is 
likely overestimated for all options in Table 1. An updated and more 
complete picture of which SO2 sources are scheduled for 
modification or shutdown would be useful for refining the estimates in 
Table 1 of the number of sources that would be covered under each 
option.

IV. Data Requirements and Program Implementation Timeline

    This section discusses the deadlines for air agency actions that 
would be required under this proposed rule. It also discusses, for 
informational purposes, additional anticipated implementation 
milestones that are important in the SO2 designations and 
implementation process. These deadlines and milestones were initially 
suggested in the February 2013 SO2 Strategy Paper. In the 
February 2013 SO2 Strategy Paper, the EPA also indicated its 
intent to use these data (and any updated recommendations from the air 
agency) to inform future designations in a timely manner. The EPA 
believes that the implementation timeline proposed below is responsive 
to concerns raised in comments on the May 2012 White Paper requesting 
that air agencies have the flexibility and sufficient time to pursue 
either the monitoring or modeling pathway for identified sources within 
their jurisdiction. We also believe that this timeline represents a 
practical but expeditious schedule for developing information needed to 
determine SO2 air quality data for purposes of designations. 
This schedule allows air agencies to account for SO2 
reductions that will occur over the next several years as a result of 
trends in industry and implementation of national and state level 
programs. EPA solicits comments on the feasibility of the proposed 
implementation timeline below.

------------------------------------------------------------------------
               Date                                Action
------------------------------------------------------------------------
From promulgation of this           From promulgation of this rulemaking
 rulemaking to January 15, 2016.     to January 15, 2016: Air agency and
                                     the EPA Regional Office consult on
                                     list of SO2 sources; air agency is
                                     required to submit its list of
                                     sources along with its election of
                                     monitoring or modeling for
                                     characterizing air quality to the
                                     EPA Regional Administrator.

[[Page 27457]]

 
January 15, 2016..................  Air agency is required to submit
                                     modeling protocols for sources that
                                     will be characterized with
                                     modeling.
July 2016.........................  Annual Monitoring Network Plans due
                                     to the EPA Regional Administrator
                                     should include SO2 monitoring
                                     network modifications intended to
                                     satisfy the Data Requirements Rule.
January 1, 2017...................  SO2 monitors intended to satisfy the
                                     Data Requirements Rule are required
                                     to be operational.
January 13, 2017..................  States electing to model are
                                     required to provide modeling
                                     analyses to the EPA Regional
                                     Administrators.
August 2017.......................  Expected date by which the EPA would
                                     notify states of intended
                                     designations.
December 2017.....................  Intended date by which the EPA would
                                     issue final designations for a
                                     majority of the country.
August 2019.......................  Anticipated due date for state
                                     attainment plans for areas
                                     designated nonattainment in 2017.
May 2020..........................  Required certification of 2019
                                     monitoring data; states have the
                                     opportunity to provide updated
                                     state recommendations to the EPA
                                     Regional Administrators.
August 2020.......................  Expected date by which the EPA would
                                     notify states of intended
                                     designations for the remainder of
                                     the country not yet designated.
December 2020.....................  Intended date by which the EPA would
                                     issue final designations for the
                                     remainder of the country.
August 2022.......................  Anticipated due date for state
                                     attainment plans for areas
                                     designated nonattainment in 2020.
------------------------------------------------------------------------

A. From Promulgation of This Rulemaking to January 15, 2016: Air Agency 
and the EPA Regional Office Consult on List of SO2 Sources; 
Air Agency Is Required To Submit Its List of Sources Along With Its 
Election of Monitoring or Modeling for Characterizing Air Quality to 
the EPA Regional Administrator

    The EPA strongly encourages each air agency to consult with its EPA 
Regional Office to identify sources exceeding the emission thresholds 
in the final rule (as described in section III) and any other areas 
near sources that do not exceed the emission thresholds but which would 
be appropriate for air quality characterization as well. It will be 
important for the air agency and the EPA to carry out this consultation 
process as soon as possible and to reach agreement on the list of 
sources quickly and efficiently.
    As a starting point, the EPA has included in the docket to this 
proposed rule a preliminary list of sources that appear to meet the 
criteria described in the EPA's proposed source threshold approach.\29\ 
This list was developed based on the most recent publicly available 
information found in national EPA databases, including the 2011 NEI as 
well as the most recent data submitted in accordance with the EPA Acid 
Rain Program and the Air Emissions Reporting Requirements (AERR) 
rule.\30\ The EPA requests that air agencies provide in their comments 
on this proposed rule any relevant updated information that would 
support the addition or removal of a source area from this preliminary 
list, along with relevant rationale and supporting information.
---------------------------------------------------------------------------

    \29\ See EPA memorandum to the docket that identifies 
SO2 emissions sources that would be covered by each 
proposed source emissions threshold option, and sources located in 
designated nonattainment areas.
    \30\ Information on continuous emissions monitoring under the 
Acid Rain Program can be found at: https://www.epa.gov/airmarkets/emissions/continuous-factsheet.html. Information on the AERR can be 
found at: https://www.epa.gov/ttnchie1/aerr/.
---------------------------------------------------------------------------

    Based on relevant information received during the comment period, 
the EPA will update this preliminary list of source areas identified 
for air quality characterization as warranted and issue a revised 
version of the list at the time this rulemaking is finalized (currently 
scheduled for late 2014). The EPA will also post the list on the EPA 
SO2 designations Web site. We expect that in developing this 
revised version of the list, data for calendar year 2013 would be the 
most recently available information for EGU's subject to the Acid Rain 
Trading Program. Emissions for these sources are recorded with CEMs and 
the data for a particular calendar year are certified and publicly 
available early in the following year.\31\ For non-EGUs, many of which 
do not operate CEMs, SO2 emissions data for calendar year 
2012 would be the most recently available data in late 2014.
---------------------------------------------------------------------------

    \31\ See acid rain program emissions reporting requirements at 
40 CFR part 75.
---------------------------------------------------------------------------

    Section 51.1203(a) of this rulemaking, as proposed, would then 
require each air agency to submit to its EPA Regional Administrator 
\32\ by January 15, 2016, a final list identifying the specific sources 
in the state around which SO2 air quality is to be 
characterized, and whether the air agency commits to conduct monitoring 
or modeling to characterize air quality around the source according to 
the process defined in this rulemaking. We note that, while a state may 
not have any sources that exceed the minimum source threshold 
requirements, there may still be a separate need (such as may arise in 
making future designations recommendations) for the air agency to 
characterize air quality for any other sources below the thresholds in 
this proposed rule that the air agency or the EPA Regional 
Administrator deems may have the potential to violate the NAAQS. For 
example, the air agency or the EPA Administrator may determine that the 
air quality should be characterized around multiple sources located in 
close proximity that individually are below the threshold but whose 
combined emissions may violate the NAAQS.
---------------------------------------------------------------------------

    \32\ As stated previously, the term ``EPA Regional 
Administrator'' refers to the Regional Administrator or a delegated 
representative.
---------------------------------------------------------------------------

    We expect that meeting this submittal requirement could be 
satisfied through a letter submitted to the EPA Regional Administrator. 
By January 15, 2016, the EPA would expect that 2014 data would be 
available for EGU sources and 2013 data would be available for non-EGU 
sources. By considering the most recent emissions data, the air agency 
and the EPA will be able to take into account any recent emissions 
increases or decreases that would cause a source to be subject to the 
requirements in this proposed rule or not.
    The EPA believes that this proposed requirement for the air agency 
to submit a list of source areas identified for further air quality 
characterization, and the other data submittal requirements found in 
sections 51.1203 of the proposed rule, are appropriate steps needed to 
understand SO2 air quality throughout the country prior to 
designations, and are consistent with section 110(a)(2)(B), section 
110(a)(2)(K) and section 301(a)(1) of the CAA. Section 110(a)(2)(B) 
indicates that state SIPs are to ``provide for establishment and 
operation of appropriate devices, methods, systems, and procedures 
necessary to (i) monitor, compile and analyze data on ambient air 
quality and (ii) upon request, make such data available to the 
Administrator.'' Section 110(a)(2)(K) states that SIPs shall ``provide 
for (i) the performance of such air quality modeling as the 
Administrator may prescribe for the purpose of predicting the effect on 
ambient air quality of any emissions of

[[Page 27458]]

any air pollutant for which the Administrator has established a NAAQS 
and (ii) the submission, upon request, of data related to such air 
quality modeling to the Administrator.'' In this proposed rule, the EPA 
is requiring air agencies to submit such SO2 monitoring and 
modeling data, as requested. Lastly, section 301(a)(1) provides the EPA 
with general authority to establish regulations as necessary to carry 
out the agency's functions, which in this case includes ensuring the 
attainment of the SO2 NAAQS throughout each state. This 
section states that ``The Administrator is authorized to prescribe such 
regulations as are necessary to carry out his functions under this 
chapter. The Administrator may delegate to any officer or employee of 
the EPA such of his powers and duties under this chapter, except the 
making of regulations subject to section 7607(d) of this title, as he 
may deem necessary or expedient.''
    Since the process proposed in this rulemaking will lead to the 
collection of additional air quality data to be used in the area 
designations process, the EPA intends to make publicly available on the 
EPA SO2 designations Web site the air agency submittals 
required pursuant to this rule, any updated designation recommendations 
from the air agency and any designation-related correspondence from the 
EPA. Making this information readily available on the agency's Web site 
would be consistent with what has been done for other NAAQS 
designations processes.
    We also are aware that due to a number of factors, there may be 
sources in the power industry and other sectors that are in operation 
as of January 15, 2016, but may be scheduled to shut down (e.g., due a 
consent decree or other legal agreement) prior to January 2017 (when 
the air agency should have ambient monitors operational and air quality 
modeling completed). The EPA would expect that any applicable source 
that intends to shut down but is still in operation on January 15, 
2016, should be included on the air agency's list for SO2 
air quality characterization. However, if by January 1, 2017, the air 
agency can provide the EPA with a legal agreement or other detailed 
information confirming that the source has permanently shut down, then 
the air agency will have no further obligation regarding air quality 
characterization for this source pursuant to this rulemaking.

B. January 15, 2016: Air Agency Is Required To Submit Modeling 
Protocols for Sources That Will Be Characterized With Modeling

    For source areas that the air agency identifies would be evaluated 
through air quality modeling, the EPA proposes that an air agency must 
also provide a modeling protocol to the EPA Regional Administrator by 
January 15, 2016. The modeling protocol would include information about 
such issues as the emissions input data, modeling domain, receptor 
grid, meteorological data and how to account for background 
concentrations. More details on the specific elements recommended to be 
included in the modeling protocol can be found in section V.B.2 of this 
proposed rule and in the draft modeling TAD,\33\ but air agencies also 
have the option to use alternative elements on a case-by-case basis as 
appropriate. The EPA Regional Office staff would be available to 
consult with air agency officials to refine and agree upon the modeling 
protocol for each relevant source. The EPA Regional Offices would 
review the submitted information and follow-up with the states as 
expeditiously as practicable, either approving the submitted 
information in a similar manner to approval of annual monitoring plan 
updates, or following-up with the states if adjustments to modeling 
protocols are warranted.
---------------------------------------------------------------------------

    \33\ The Draft SO2 NAAQS Designations Modeling 
Technical Assistance Document can be found at https://www.epa.gov/airquality/sulfurdioxide/pdfs/SO2ModelingTAD.pdf.
---------------------------------------------------------------------------

C. July 2016: Annual Monitoring Network Plans Due to the EPA Regional 
Administrator Should Include SO2 Monitoring Network Modifications 
Intended To Satisfy the Data Requirements Rule

    Under this proposed rule, air agencies may elect to characterize 
air quality around some or all sources through ambient SO2 
monitoring, using existing and new monitoring sites. The EPA proposes 
that air agencies be required to submit relevant information about 
these monitoring sites to the EPA Regional Administrator by July 1, 
2016, as part of their annual monitoring network plan, in accordance 
with the EPA's monitoring requirements specified in 40 CFR part 58. The 
EPA anticipates that states electing to monitor to satisfy this 
proposed rule will need to take explicit actions to identify, relocate 
and/or install new ambient SO2 monitors that would 
characterize peak, 1-hour SO2 concentrations in areas around 
or impacted by identified SO2 sources. The EPA encourages 
states to work with the EPA Regional Offices in the development of an 
appropriate network plan to satisfy the intent of this rulemaking. In 
the annual monitoring network plan, the EPA encourages states to 
provide details on the adequacy of the SO2 network, 
including rationale for why the proposed number of sites and their 
individual locations are appropriate. Considerations for siting these 
monitors are discussed in the draft monitoring TAD.\34\
---------------------------------------------------------------------------

    \34\ The Draft SO2 NAAQS Designations Source-Oriented 
Monitoring Technical Assistance Document can be found at https://www.epa.gov/airquality/sulfurdioxide/pdfs/SO2MonitoringTAD.pdf.
---------------------------------------------------------------------------

D. January 1, 2017: SO2 Monitors Intended To Satisfy the 
Data Requirements Rule Are Required To Be Operational

    The EPA proposes that air agencies that have chosen to characterize 
air quality for certain SO2 sources through ambient 
monitoring must have any relocated and/or new monitors operational by 
January 1, 2017. Under this approach, it is anticipated that the first 
3 years of data would be collected from 2017 through 2019, allowing the 
first design value for each monitor to be calculated by May 2020. These 
new monitoring data could then inform the air agency's designation 
recommendation for the final round of designations (primarily for areas 
for which air quality is characterized through ambient monitoring).

E. January 13, 2017: States Electing To Model Are Required To Provide 
Modeling Analyses to the EPA Regional Administrators

    The EPA proposes that air agencies choosing modeling to 
characterize ambient air quality around identified SO2 
sources be required to submit modeling analyses to the EPA Regional 
Office by January 13, 2017, for all source areas they had previously 
declared would be characterized through air quality modeling. These 
modeling analyses should be conducted in accordance with the 
recommendations in the EPA's modeling TAD or as otherwise approved on a 
case-by-case basis. (Section V provides more information on the 
technical details of these analyses.) The EPA believes that 2 years 
from promulgation of the final rule is a reasonable amount of time for 
air agencies to prepare the necessary data inputs and conduct such 
modeling for all subject sources.
    The EPA intends to conduct a second phase of designations during 
2017, relying on modeling analyses and other related information and to 
notify the

[[Page 27459]]

states of intended designations by August 2017. The EPA therefore 
encourages states to submit with their modeling analyses updated 
designation recommendations. In developing any updated designation 
recommendations, the air agency should follow the EPA's most recent 
SO2 designation guidance.\35\ We recommend that any such 
updates to designation recommendations be submitted to the EPA Regional 
Office at the same time the modeling analysis is due, by January 13, 
2017.
---------------------------------------------------------------------------

    \35\ The EPA issued guidance on the SO2 area 
designations process on March 24, 2011. See: https://www.epa.gov/air/sulfurdioxide/pdfs/20110411so2designationsguidance.pdf. However, the 
EPA may provide updated SO2 designations guidance, as 
appropriate, in advance of the January 2017 submittal date.
---------------------------------------------------------------------------

    The EPA Regional Office and the air agency should engage actively 
in consultation to understand the inputs, assumptions and findings 
associated with each air quality modeling analysis. The air agency 
should submit thorough documentation of its modeling analysis and 
should provide the EPA with supplemental information about the analysis 
upon request, as the analysis will provide the basic technical 
supporting information used by the EPA in developing the designation 
for the area.
    The EPA received a number of comments on the White Paper and in 
subsequent policy discussions with stakeholders requesting that in the 
next round of SO2 designations in 2017, the EPA should 
designate areas as unclassifiable/attainment if it can be demonstrated 
that such areas do not violate the SO2 NAAQS. Some 
commenters provided examples of states having large areas with very few 
SO2 sources, or no SO2 sources at all and 
indicated that such areas would be candidates for an unclassifiable/
attainment designation.
    The EPA finds merit in such examples and suggests that for this 
next round of SO2 designations, the air agencies should 
consider providing the EPA with any recommended boundaries and 
supporting information for parts of their states for which they 
recommend an ``unclassifiable/attainment'' designation (e.g., an area 
without SO2 sources or that is not impacted by sources in 
other areas). If the air agency recommends such a designation, the 
boundary of the area would need to be developed carefully, keeping in 
mind the fact that an additional set of source areas may be designated 
3 years later based on monitoring data. Since the EPA expects to 
designate the majority of the country in 2017, the only areas the EPA 
would not be ready to take action on in 2017 are the areas for which 
states have elected to install new monitors. The EPA's initial thinking 
is that the state should not recommend a designation for any county 
that includes a source area with new monitoring under way. The EPA 
could designate as unclassifiable/attainment any area for which the 
state has submitted sufficient appropriate modeling or monitoring data 
to support such designation. The EPA may consider providing additional 
designation boundary guidance, including guidance for areas without 
sources, for this round of boundary recommendations at a later date.
    In January 2017, there also may be undesignated areas with existing 
ambient air quality monitors that have data for the most recent 3 years 
(e.g., 2013-2015) that indicate a violation of the standard. The EPA 
intends to designate any area that has newly monitored violations as 
nonattainment in this next round of designations.
    In other cases, air agencies may demonstrate that the existing 
monitoring network suffices to evaluate the air quality status of 
particular areas, such that monitoring data available by January 2017 
are sufficient to justify designating the areas as attainment. For such 
areas, the governors may wish to update their designation 
recommendations and provide suggested boundaries for the areas, based 
on their analysis of sources and source regions contributing to air 
quality at the applicable monitor(s). Submittal of such recommendations 
should be supplemented with a thorough network analysis as described in 
the monitoring section of this rule, demonstrating that the network is 
sufficient to assess peak concentrations in the area.

F. By August 2017: Expected Date by Which the EPA Would Notify States 
of Intended Designations

    Under CAA section 107(d)(1)(B)(ii), the EPA is authorized to 
promulgate designations that differ from the designations recommended 
by the state, but the EPA must notify the state of any such 
modifications at least 120 days before promulgating modified 
designations, providing the state an opportunity to provide further 
input on the designations and boundaries for the affected areas. For 
any areas being addressed in this round of designations, the EPA 
intends to notify the states of intended designations by August 2017. 
As with the previous SO2 designation process completed in 
2013, these letters would indicate the EPA's intended designation and 
boundary information for these areas and the states would have an 
opportunity to provide comments and suggest modifications as 
appropriate.

G. December 2017: Intended date by Which the EPA Would Issue Final 
Designations for a Majority of the Country

    Under the anticipated schedule, the EPA expects to finalize 
designations by the end of 2017 for the following areas: (1) Those with 
modeled violations, (2) any previously undesignated area with ambient 
monitoring data from 2014-2016 indicating a violation, and (3) any 
unclassifiable/attainment areas as appropriate. EPA anticipates that 
this round of designations would address many areas across the country. 
Areas that would not be designated at this time would include (but not 
necessarily be limited to) those areas conducting new monitoring. For 
purposes of further outlining the timeline for submitting attainment 
plans and demonstrations, we will assume there will be a 60-day period 
between publication of the final designations in the Federal Register 
and the effective date of the designations, meaning that new 
nonattainment designations are anticipated to become effective in 
February 2018.

H. August 2019: Anticipated Due Date for State Attainment Plans for 
Areas Designated Nonattainment in 2017

    Areas that are newly designated as nonattainment would have a new 
SIP obligation due 18 months from the effective date of the 
designation.\36\ Thus, areas with an effective date of designation in 
February 2018 would have attainment SIPs due in August 2019. These 
plans would need to demonstrate how the area would attain the standard 
as expeditiously as practicable, but no later than 5 years from the 
effective date of the designation, or by February 2023.\37\
---------------------------------------------------------------------------

    \36\ SO2 SIPs are due within 18 months, per CAA 
section 191(a).
    \37\ The attainment date for SO2 nonattainment areas 
is as expeditiously as practicable, but not later than 5 years from 
the date of designation, per CAA section 192(a). The SO2 
implementation guidance can be found at: https://www.epa.gov/oaqps001/sulfurdioxide/implement.html.
---------------------------------------------------------------------------

I. May 2020: Required Certification of 2019 Monitoring Data; States 
Have the Opportunity To Provide Updated State Recommendations to the 
EPA Regional Administrators

    As noted in paragraph D above, air agencies electing to use 
monitoring to satisfy this data requirements rule will be required to 
have relocated and/or new monitors operational by January 1, 2017. In 
early 2020, the air agency

[[Page 27460]]

would be able to certify data collected during 2019, thereby providing 
a complete, quality-assured data set for 2017-2019 for each ambient 
monitor.
    In this scenario, in the event that the new monitoring data result 
in changes to designation recommendations previously submitted, the 
state would also have the opportunity to submit revised designation and 
boundary recommendations to the EPA by May 1, 2020, for all parts of 
the state that have not yet been designated. The EPA expects that the 
state would recommend nonattainment boundaries that include any nearby 
contributing sources, in the same manner as discussed in the EPA's 
SO2 designations guidance. Presumably, at the completion of 
this round of the designations process, any areas not designated as 
nonattainment would be designated as unclassifiable/attainment.

J. August 2020: Expected Date by Which the EPA Would Notify States of 
Intended Designations for the Remainder of the Country Not Yet 
Designated

    As noted above, CAA section 107(d)(1)(B)(ii) authorizes the EPA to 
promulgate designations that differ from the designations recommended 
by the state but requires the EPA to notify the state of any such 
modifications at least 120 days before promulgating modified 
designations. For the areas identified in paragraph I above, the EPA 
expects to notify the states of intended designations in August 2020. 
The letters would include the EPA's intended designation and boundary 
information for these areas and the states would have the opportunity 
to provide comments and suggest modifications as appropriate.

K. December 2020: Intended Date by Which the EPA Would Issue Final 
Designations for the Remainder of the Country

    Under its anticipated designations schedule, the EPA would finalize 
designations for the remaining undesignated areas in each state in the 
December 2020 time frame. The timeline below for submitting attainment 
plans and demonstrations assumes there will be a 60-day period between 
publication of the final designations in the Federal Register and the 
effective date of the designations, meaning that any new nonattainment 
designations are anticipated to become effective in February 2021.

L. August 2022: Anticipated Due Date for State Attainment Plans for 
Areas Designated Nonattainment in 2020

    Areas that are newly designated as nonattainment would have a new 
SIP obligation due 18 months from the effective date of the 
designation.\38\ Thus, nonattainment areas with an effective date in 
February 2021 would have attainment SIPs due in August 2022. These 
plans would need to demonstrate how the area would attain the standard 
as expeditiously as practicable, but not later than 5 years from the 
effective date of the designation, or by February 2026.\39\
---------------------------------------------------------------------------

    \38\ SO2 SIPs are due within 18 months of area 
designation per CAA section 191(a).
    \39\ The attainment date for SO2 nonattainment areas 
is as expeditiously as practicable, but not later than 5 years from 
the date of designation, per CAA section 192(a).
---------------------------------------------------------------------------

V. Technical Considerations

    Section III of this preamble presents detailed discussion of the 
threshold-based air quality characterization approach that will focus 
limited resources most efficiently to implement the SO2 
NAAQS in areas that contain sources with larger SO2 
emissions and higher numbers of people, in order to address areas where 
there may be higher potential for NAAQS violations that adversely 
affect public health. This section discusses the different 
opportunities air agencies may use to provide the necessary air quality 
information to the EPA for areas around those identified sources. Based 
on this information, the EPA proposes taking an approach that allows 
for the use of air quality monitoring or modeling information, or a 
combination of both, for designations.
    An approach using monitoring or modeling for designations actions 
would be consistent with the EPA's historic practices for 
SO2 NAAQS implementation, where both monitoring and modeling 
have been used as appropriate in the designations process. Air agencies 
would have the flexibility to assess whether their SO2 
sources above the thresholds are violating the SO2 NAAQS by 
employing either ambient air quality monitoring or air quality 
modeling. An air agency would not be limited to employ only one method 
within its jurisdiction.
    When considering whether monitoring or modeling may be most 
appropriate for the area around each identified source, air agencies 
are encouraged to consider a number of factors. One key factor is 
whether or not the location or characteristics of an identified source 
or facility are conducive to modeling. The EPA strongly encourages air 
agencies to consider using monitoring to characterize air quality near 
those sources that are not easily characterized through dispersion 
modeling. Sources that may not be easily characterized through 
dispersion modeling include a source situated in an area of complex 
terrain and/or situated in a complex meteorological regime and areas 
that have multiple, relatively small sources with overlapping plumes.
    States would need to consider each area around a source on a case-
by-case basis to determine whether the modeling or monitoring pathway 
is most appropriate for characterizing air quality around that source. 
For areas with multiple sources that a state could recommend be 
included in a common area, the EPA suggests that a common analytical 
approach for assessing air quality be followed for all of the sources 
in the common area. For situations where multiple sources are located 
in proximity across state boundaries, the EPA recommends that the 
relevant air agencies work together to determine a common analytical 
approach for assessing air quality in that area. In these types of 
situations, it would not be appropriate to choose monitoring for some 
sources and modeling for others, since under this proposed rule areas 
with sources using these pathways would be designated on different time 
frames. In general, however, the determination of whether to use 
monitoring or modeling to characterize air quality around a source 
should be done on a case-by-case basis.
    To assist states in the implementation of this rulemaking, the EPA 
has produced draft, non-binding technical assistance documents that 
discuss options and suggested approaches, and methods on how monitoring 
or modeling efforts to characterize air quality around an identified 
source might be conducted. The monitoring TAD provides potential 
options and recommendations on different approaches that can be used to 
site source-oriented SO2 monitors in locations of expected 
maximum 1-hour concentrations. Modeling is generally a less costly and 
less resource intensive option for providing reliable information for 
use in designations. In addition, refined dispersion models are able to 
characterize SO2 air quality impacts from the modeled 
sources across the domain of interest on an hourly basis with a high 
degree of spatial resolution. The modeling TAD provides recommendations 
for states planning to model source areas in their state.

[[Page 27461]]

A. Monitoring

    States that identify monitoring as the pathway to assess air 
quality around a particular SO2 source would have the option 
to identify, relocate and/or install new monitors around the source by 
January 1, 2017, to provide data for use in designations in 2020. These 
monitors are expected to be source-oriented and sited to characterize 
location(s) of expected maximum 1-hour concentrations.
    The monitoring TAD provides different approaches describing how 
source-oriented monitoring networks might be designed or augmented. The 
TAD discusses information that would be most useful to collect at the 
outset of formulating or evaluating a source-oriented network design, 
with an eye toward identifying sites at which maximum 1-hour 
concentrations can be expected. Examples include considering data about 
the source itself (emissions rate info, CEM data, stack height, stack 
temperature, permit requirements, control technology, etc.); similar 
information about any nearby SO2 sources; existing air 
quality data from any nearby ambient monitors; any existing modeling 
data for the source, such as from past prevention of significant 
deterioration permits revision; meteorological data; and information 
about the local geographic setting of the source and surrounding area. 
The TAD presents options on using this information to feed into one or 
more siting approaches, including modeling, exploratory monitoring, or 
other analysis, such as a ``weight of evidence'' approach, to inform an 
appropriate monitoring network design to characterize the air quality 
around an identified SO2 source.
    As noted above, the EPA estimates that up to a third of the 
existing SO2 monitoring network (as of 2013) may be 
considered to be source-oriented and/or characterizing maximum 
concentrations. The agency recognizes that using and leveraging 
existing infrastructure is a logical consideration in developing a 
network design and, in some cases, there may be a limited number of 
existing monitors appropriately situated in a way that might satisfy 
this rule. Air agencies that choose to identify, relocate, or install 
new monitors in an effort to satisfy this rule may use these monitors 
to satisfy the existing PWEI minimum monitoring requirements 
(promulgated in the 2010 SO2 NAAQS revision [40 CFR part 58, 
Appendix D, Section 4.4.2]), if applicable to an area. However, those 
existing monitors currently in use to satisfy the PWEI-induced minimum 
monitoring requirements are not automatically eligible to satisfy the 
data requirements rule, as they may not be appropriately sited (e.g., 
they might not be source-oriented, maximum concentration sites). The 
EPA notes that PWEI monitors and other existing monitors (both 
regulatory and non-regulatory) may be helpful in providing information 
to help states determine appropriate locations for relocated or new 
monitors.
    As discussed in section IV, this rulemaking proposes that in 
January 2016, states will submit to their EPA Regional Administrator 
the list of sources for which they will collect additional information 
for initial designations. This list would include all the sources that 
are above the annual emissions threshold that is ultimately finalized, 
as well as those sources that either the state or the EPA Regional 
Administrator has also identified as needing additional information on 
local air quality. As discussed above, the state would also commit at 
that time to the particular pathway (monitoring or modeling) it would 
employ to characterize air quality around each source. The EPA believes 
that the proposed requirement for the air agency to submit a list of 
sources identified for further air quality characterization, and the 
other associated data submittal requirements found in sections 51.1203 
of the proposed rule, are appropriate steps needed to characterize 
SO2 air quality throughout the country prior to 
designations, and are consistent with section 110(a)(2)(B) and section 
110(a)(2)(K) of the CAA.
    This rulemaking also proposes that in their annual monitoring 
network plans submitted in July 2016, air agencies must identify the 
new monitoring sites they have elected to deploy to assess air quality 
around selected sources to satisfy this data requirements rule. The EPA 
expects that states would provide analyses supporting the network 
design approach to characterize air quality around each relevant source 
(i.e., number of monitors for each SO2 source, information 
demonstrating that the monitors would be placed in the area/areas of 
maximum concentrations, etc.). The EPA proposes that any relocated or 
new monitors must be installed and operational by January 1, 2017, and, 
thus, allowing for data collection during the 2017-2019 timeframe and 
for use of these data for designations expected in 2020. The EPA also 
proposes to require that any relocated or new monitors be operated in a 
manner equivalent to those monitors operated elsewhere in the State and 
Local Air Monitoring Stations (SLAMS) network; they do not, however, 
have to be designated as SLAMS. Specifically, the monitors should use 
Federal Reference Methods (FRMs) or Federal Equivalent Methods and meet 
the requirements of 40 CFR part 58 Appendices A, C and E. Further, the 
resulting data should be reported to the Air Quality System (AQS) and 
would be subject to annual data reporting and certification 
requirements listed in 40 CFR parts 58.15 and 58.16. When the data are 
reported to AQS, the data will be available to the public through this 
system.
    The EPA recognizes that in some cases the deployment of a 
monitoring site might be delayed for a short period of time due to 
certain factors not directly under the air agency's control (e.g., 
obtaining permits or access to power for the site) and could cause the 
air agency to miss the January 1, 2017 deadline. In the event that a 
state has chosen the monitoring pathway for air quality assessment for 
a particular source and it does not have the monitor(s) installed and 
operational by the January 1, 2017, deadline such that the monitor 
would not have complete data for the first quarter, this would be a 
reason for concern for the EPA because the state would not be in a 
position to collect 3 complete calendar years of monitoring data (2017-
19) as would be required for all other new monitoring sites established 
by other states pursuant to this rulemaking.\40\ In those situations 
where it is evident that sufficient and appropriate monitoring will not 
be conducted in a timely manner, the EPA proposes that the source would 
be ``moved'' to the modeling pathway and would be included in the 
designations process intended to be conducted in 2017, based on 
appropriate information the EPA has obtained at that time. In this 
situation, if the state fails to provide modeling information for the 
source, the EPA would make decisions for designations based on the 
modeling and monitoring information available to the EPA at the time of 
designations. Therefore, the EPA strongly encourages states to only 
choose the monitoring option for a source if the state is confident in 
its ability to install and begin operation of any new monitors in a 
timely manner and to follow through with continued operation of the 
monitoring network as required by this rulemaking. The EPA requests 
comment on the approach proposed above. The EPA also requests

[[Page 27462]]

comments on any alternative approaches that could most effectively 
address a situation where an air agency is acting in good faith to 
deploy monitors on time but experiences a delay outside of its control.
---------------------------------------------------------------------------

    \40\ Data completeness requirements for the 1-hour 
SO2 NAAQS are described in 40 CFR part 50, Appendix T. A 
quarter is considered to have complete data when at least 75 percent 
of the sampling days have complete data.
---------------------------------------------------------------------------

    The potential use of third party SO2 monitors was raised 
in past stakeholder discussions. In some cases, there may be industrial 
or other stakeholder monitoring sites in operation in an area around a 
source that a state chooses to monitor. If one or more of those sites 
is determined to be in an appropriate location to characterize peak 1-
hour concentrations around the identified source, there is potential 
for such monitors to be leveraged to satisfy the requirements in this 
rule.\41\ The use of such monitors, including details on how the 
monitors and monitoring data would be ensured to meet quality assurance 
and other criteria in 40 CFR part 58 Appendices A, C and E, would need 
to be documented and included in the annual monitoring network plan 
submitted to the EPA in July 2016. The EPA encourages air agencies to 
engage other stakeholders to pursue ambient monitoring partnerships 
wherever possible to use existing infrastructure, increase 
communication among parties and use available resources as efficiently 
as possible.
---------------------------------------------------------------------------

    \41\ Monitors operated by third parties have been used for 
certain regulatory purposes in the past, provided they met certain 
quality assurance and oversight requirements.
---------------------------------------------------------------------------

    In other cases, air agencies may have limited budgets which would 
not allow for the funding of additional monitors, but affected sources 
may wish to fund the deployment of additional monitors as indicated in 
comments previously received on the White Paper. Any new monitoring 
sites funded by the regulated community also would need to be operated 
in manner equivalent to SLAMS, meeting quality assurance and other 
criteria in 40 CFR part 58 Appendices A, C and E, subject to data 
reporting and certification requirements, and there would need to meet 
applicable requirements for continued operation into the future if 
ambient concentrations exceed NAAQS levels. These sites would need to 
be documented and included in the annual monitoring network plan 
submitted to the EPA in July 2016.
    In comments on the 2012 White Paper and on the 2013 draft 
monitoring TAD, the EPA received feedback from states and industry to 
consider a pathway to allow the shut-down of monitors operated to 
satisfy this proposed rule if no NAAQS violations are discovered. 
Specifically, due to current state and local resource constraints and 
in consideration of the potential collaboration that could occur 
between states and industry to operate some source-oriented 
SO2 monitoring sites, commenters suggested that monitoring 
operations should be allowed to cease if no NAAQS violations are found.
    As proposed, states electing to monitor around identified 
SO2 facilities would be expected to have SO2 
monitors that are intended to satisfy this proposed rule to be 
operational by January 1, 2017. In a majority of those cases, the EPA 
believes that states will have to install new monitors, relocate 
existing monitors and/or work with industry to install new monitors or 
leverage existing industrially operated SO2 monitors to 
satisfy the data requirements rule. In any case, the monitors operated 
to satisfy this proposed rule would be expected to have 3 years of 
complete data (spanning 2017 through 2019) available for design value 
calculations in early 2020.
    In consideration of recent feedback received on this issue in 
comments on the monitoring TAD and SO2 White Paper, the EPA 
is proposing that a monitor that has been deployed pursuant to this 
rule and is located in an area that is designated attainment in the 
anticipated third round of initial designations in 2020 may be eligible 
for shutdown provided the monitor meets certain criteria. Any 
SO2 monitor identified in an approved state annual 
monitoring network plan to satisfy this proposed data requirements rule 
may be eligible for shut-down in 2021 or later if the following 
criteria are met: (1) The monitor is not also satisfying other minimum 
SO2 monitoring requirements listed in 40 CFR part 58 
Appendix D; (2) the monitor is not otherwise required to meet 
requirements in a SIP or permit; and (3) the monitor has recorded a 3-
year design value that is no greater than 50 percent of the 1-hour 
SO2 NAAQS. The EPA also proposes that any SO2 
monitor eligible for shutting down would need to be approved by the EPA 
Regional Administrator before monitoring operations could cease. This 
policy is similar to the provision allowing the EPA Regional 
Administrators to waive Lead NAAQS monitoring requirements if data 
indicate that the design value of the lead monitor has not exceeded 50 
percent of the Lead NAAQS, as listed in 40 CFR part 58 Appendix D, 
Section 4.5(ii). The EPA proposes the 50 percent criterion for 
SO2 monitors because such a precedent was established in the 
lead monitoring regulations and because SO2 is a ``source-
oriented'' pollutant similar to lead. As an alternative, the EPA is 
also proposing an option in which the same criteria noted above would 
need to be met, except that the monitor would be eligible to cease 
operations if it recorded a design value in 2018-2020 or a later 3-year 
period that is no greater than 80 percent of the 1-hour SO2 
NAAQS. This 80 percent criterion is indirectly derived from existing 
language in 40 CFR part 58.14(c)(1) describing one of several pathways 
to for states to shutdown existing SLAMS monitors, and it was also a 
criterion suggested by a state air agency in comments on the monitoring 
TAD. The EPA requests comment on the two proposed options for design 
value criteria for SO2 monitor shutdowns, as well as other 
values within the 50-80 percent range. EPA requests that commenters 
provide specific technical rationale supporting any approach they 
recommend.
    The EPA proposes these options to cease monitor operations in 
response to stakeholder concerns, but also believes it is important for 
air agencies to assess whether, even after monitoring data indicate low 
ambient SO2 concentrations, the areas around these sources 
that are required to be characterized under this rulemaking continue to 
attain the standard in the future. To address this need, the EPA 
proposes that the air agency be required to assess SO2 
emissions changes annually, beginning in the year after the monitor 
ceases operation. Emissions data for large SO2 sources would 
be available from annual reporting required for various emissions 
trading programs, the AERR rule, and other regulations. The AERR rule 
requires states to report SO2 emissions data annually for 
large SO2 sources. Every 3 years states must report data on 
SO2 sources with potential to emit more than 100 tons per 
year. In other years, the AERR rule requires states to report data on 
SO2 sources with potential to emit more than 2,500 tons per 
year. In addition, under the Acid Rain Program and other emission 
trading programs, many large combustion sources of SO2 are 
required to continuously measure and record emissions of 
SO2. These sources report hourly emissions data to the EPA 
on a quarterly basis. These requirements would be expected to cover the 
vast majority of sources subject to the SO2 data 
requirements rule. States would need to work with any other source not 
subject to an annual SO2 emissions reporting requirement 
under existing regulations to ensure that annual SO2 
emissions can be reported for the source under this data requirements 
rule. For areas around these sources in which total SO2 
emissions increase over the

[[Page 27463]]

emissions for the previous year, the air agency would be required to 
submit to the EPA an assessment of the cause of the increase and 
provide an initial determination of whether or not the air quality 
around that source should be further re-assessed. The air agency could 
choose to reinstate the operation of the air monitor or complete air 
quality modeling for the source area to verify that the area continues 
to attain the standard. Factors that the air agency should consider in 
making this determination include: The magnitude of the emissions 
increase and information about changes in the emissions profile, hourly 
emission rate, or operating schedule of the source.
    The EPA proposes two options for how the air agency would submit 
this report and how the EPA would review and act on it. Under the first 
procedural option, we propose that the air agency would submit a report 
to the EPA annually as an appendix to the air agency's annual 
monitoring plan. The annual monitoring plan is required to be submitted 
to the EPA Regional Administrator by July 1 each year. A primary 
objective of this approach would be to enable the air agency to save 
time and resources by providing a single process for the public review 
and opportunity for comment on the annual monitoring plan and annual 
reports to demonstrate ongoing attainment of previously monitored 
areas.
    The inclusion of this verification report as an appendix to the 
annual monitoring plan would ensure that the report would be subject to 
the same opportunities for public review and comment that are to be 
provided for the monitoring plan pursuant to regulations at 40 CFR part 
58.10. Those regulations specify that if the air agency modifies the 
monitoring plan from the previous year, then prior to taking final 
action to approve or disapprove the plan, the EPA would be required to 
provide an opportunity for public comment on its proposed action. The 
public would have the opportunity to comment on any plan by the state 
to cease operation of an existing monitor or to add any new monitor to 
the network. In addition, the public would also have the opportunity to 
comment on the state's annual report of emissions data for sources for 
which the state ceased the operation of nearby monitors. The 
regulations also indicate that if the state has already provided a 
public comment opportunity in developing its revised monitoring plan 
and has made no further changes to the plan after reviewing public 
comments that were received, then it could submit the public comments 
along with the revised plan to the EPA and the Regional Administrator 
would not need to provide a separate opportunity for comment before 
approving or disapproving the plan.
    Under the second procedural option, the annual report of emissions 
data for sources for which the state ceased the operation of nearby 
monitors would not be submitted to the EPA as an appendix to the annual 
monitoring network plan. Instead, it would take the form of a separate, 
independent annual submittal from the state to the EPA Regional 
Administrator. However, we propose that this report would be due by the 
same July 1 date each year. This independent submittal would follow the 
general guidelines set forth in 40 CFR 58.10 regarding opportunities 
for public review and comment as described in Option 1 above, but the 
report would only include the annual assessments associated with 
sources in areas that were designated unclassifiable/attainment and for 
which the EPA granted approval to cease monitoring. The public would 
have the opportunity to comment on each report when it is submitted 
annually.
    The EPA believes that the main advantage of the first option is 
that from a procedural standpoint, it would leverage the time and 
resources that are already devoted to the existing annual monitoring 
plan development and public review process. In contrast, the second 
option would require additional state and the EPA resources to provide 
for public review opportunities in parallel with the monitoring plan 
process. Regardless of which procedural approach is included in the 
final rule, we believe that it will be important for the EPA to 
communicate to each state the reasoning behind any action or decision 
the EPA makes with regard to the submitted ongoing verification of 
attainment report. This information should be provided in writing in a 
letter or Federal Register document, as appropriate.
    The EPA solicits comments on the merits of the proposed monitor 
shutdown policy and the use of 50-80 percent of the NAAQS as a 
criterion for shut-down eligibility. The EPA also solicits comments on 
preferences regarding the approach for ongoing assessment of air 
quality after a monitor is shutdown either as an appendix to the annual 
monitoring network plan or as a separate document, as the means by 
which air agencies provide information to the EPA Regional Office. The 
EPA requests any suggested alternatives to these procedural options.

B. Modeling

    This section explains how modeling should be conducted and 
submitted to the EPA for those sources for which a state chooses to 
characterize ambient SO2 air quality conditions using air 
quality modeling. While the basic modeling tools to be used to assess 
air quality around these sources are the same tools often used for 
other modeling exercises, such as attainment demonstrations or 
permitting of new/modified sources, this rule and the associated 
modeling TAD describe significant differences in the way these modeling 
tools should be used that are unique to the area designations 
process.\42\ When modeling to assess SO2 air quality for the 
area designations process, it is appropriate to characterize actual air 
quality and it is not necessary to project potential air quality. 
Modeling conducted for the purposes of designations in effect is used 
as a surrogate for ambient monitoring of current actual air quality. 
Therefore, when modeling is used for SO2 designations, the 
inputs to the models may be designed to more accurately represent 
actual air quality.
---------------------------------------------------------------------------

    \42\ Air quality modeling that is conducted to demonstrate 
attainment for a nonattainment area or to project potential air 
quality impacts for the permitting of a new or modified source 
commonly uses allowable or permitted emissions levels rather than 
actual emissions levels.
---------------------------------------------------------------------------

    The EPA anticipates that states would use AERMOD to conduct this 
designations modeling, as AERMOD is the EPA's preferred near-field 
dispersion model and has been demonstrated to be a reliable predictor 
of SO2 air quality given appropriate input data. As part of 
its development, AERMOD was evaluated using 17 field studies, several 
of which involved short-term measurements of SO2, robust 
site-specific meteorology and accurate measurements of emissions. The 
EPA is confident that AERMOD can provide accurate predictions of actual 
SO2 concentrations, given representative meteorology and 
accurate emissions inputs.
1. Inputs for Designations Modeling
    There are 3 air quality modeling inputs used for designations 
modeling that would differ from the permit and implementation plan 
modeling requirements set forth in Appendix W of 40 CFR part 51. As 
noted above, the objective of this designations modeling approach is to 
assess actual, current air quality. The 3 modeling inputs that are 
required to reflect actual air quality are: emissions data, stack 
height and years of meteorological data.

[[Page 27464]]

(a) Emissions--General Issues
    Dispersion modeling has typically been used to estimate the ambient 
impact of a source's allowable emissions for use in attainment 
demonstrations or in setting emission limits. In these situations, it 
is important to consider the full potential a source has to emit the 
relevant pollutant(s). In contrast, for the designations process it is 
important to understand what a source is actually emitting, or has 
actually emitted in the recent past. Traditionally, to characterize air 
quality for the designations process for other NAAQS pollutants, the 
EPA has exclusively used data from air quality monitoring networks. 
However, as noted above, due to the fact that SO2 
concentrations can vary substantially with distance and direction away 
from the source, given the limitations in the existing monitoring 
network in identifying peak SO2 concentrations and given 
that modeling data has already been employed for past designations for 
the SO2 NAAQS, the EPA believes that dispersion modeling is 
an appropriate option for representing current (or recent) 
SO2 air quality.
    Traditionally, when modeling is used for estimating future air 
quality, a source's allowable emission limits are used in the modeling 
application to assess whether the potential emissions from the source 
might cause violations. For designations, the EPA believes it is 
appropriate to use current actual emissions to obtain estimates of 
current actual air quality. Specifically, the EPA recommends that the 
air agency should use a source's most recent 3 years of actual 
emissions in the modeling analysis to estimate air quality for that 3-
year period. There are a range of recommended options for determining 
these actual emissions which are discussed in the modeling TAD. While 
actual emissions would be the preferred choice to use for emissions 
inputs, states have the option of using a more conservative approach by 
inputting a source's most recent 3 years of allowable, or ``potential 
to emit,'' emissions. Further discussion below describes situations in 
which states may prefer to use allowable emissions in this analysis. 
Additional information and recommendations on this approach are 
discussed in the modeling TAD.
    In addition to considering actual emissions from the principal 
source or sources in an area, the modeling analysis needs to take into 
consideration the relevant SO2 ``background'' concentration 
for the area. When modeling is intended to assess current air quality 
(such as modeling for the designations process), the modeling also 
needs to consider the background concentrations of SO2. The 
inclusion of ambient background concentrations to the model results is 
important in determining the modeled cumulative impacts of all nearby 
sources. In an area with an air quality monitor, the SO2 
concentrations recorded by the monitor might reflect the combination of 
local source impacts and any other ``background'' contribution to 
SO2 concentrations from other sources. The inclusion of 
ambient background concentrations to the model results is important in 
determining the modeled cumulative impacts of all nearby sources. Thus, 
ambient background concentrations are determined on a case-by-case 
basis, depending on factors such as the proximity of other 
SO2 sources to the source being modeled, and the distance 
and location of the closest ambient monitor to the source or sources 
being modeled. Please see the modeling TAD for additional suggestions 
on identifying background concentrations to be incorporated into this 
modeling.\43\
---------------------------------------------------------------------------

    \43\ The Draft SO2 NAAQS Designations Modeling 
Technical Assistance Document can be found at https://www.epa.gov/airquality/sulfurdioxide/pdfs/SO2ModelingTAD.pdf.
---------------------------------------------------------------------------

(b) Emissions--Accounting for Recent Emission Reductions in Modeling 
Analyses
    The EPA seeks to provide an incentive to states to work with 
sources to install controls and reduce emissions prior to final 
designation in 2017. The EPA expects that in some cases, air quality 
modeling conducted well in advance of January 2017 may indicate a 
violation of the 1-hour SO2 standard in some areas. To 
address such situations and potentially avoid a nonattainment 
designation, the air agency may wish to consult with the source and 
conduct additional analyses with the source to identify a control 
measure or an emission limit that would ensure attainment with the 1-
hour SO2 standard for the area around the source. The air 
agency could then take action to adopt enforceable emissions 
limitations as necessary prior to January 2017 and conduct modeling 
analyses based on these new emissions limits as explained below.
    The EPA expects that a number of emissions sources may be 
candidates for this optional approach. Many EGUs will need to meet 
compliance deadlines for the Mercury and Air Toxics Standards (MATS) in 
2015-2016 and EPA expects that many will become subject to Title V 
permits that require compliance with MATS SO2 emission 
limits as the means of demonstrating compliance with the MATS 
requirements related to acid gas emissions. These EGUs may be able to 
adopt control technologies and enforceable emission limits to reduce 
emissions of SO2 as well as mercury. Similarly, industrial 
boiler operators will have the incentive to adopt SO2 
emission limits as part of their strategy for complying with the 
Industrial Boiler Maximum Achievable Control Technology Standard.
    As long as these controls are implemented and enforceable as of 
January 2017, the EPA believes it would be appropriate for the new 
lower allowable emission limit to be used in a modeling analysis in 
place of the old, higher, actual data from the last 3 years. The air 
quality impacts from such a source would, at worst, be characterized by 
the new enforceable allowable limit and could be used as a basis for 
future designations. Thus, for the purposes of meeting the data 
requirements rule where a source has adopted new enforceable emission 
limits, the state may use these new allowable emission limits when 
completing their modeling analyses due in January 2017. Instead of 
using the most recent 3 years of actual emissions data or previously 
allowable emissions limits, the air agency could use the new emissions 
information as the inputs for all 3 years of their designations 
modeling.
    This approach allows additional time in 2015 and 2016 for the 
sources to reduce their emissions and if the state is able to 
demonstrate attainment with the new controls or emission limits, the 
governor of the state has the opportunity to modify its designation 
recommendation accordingly. The EPA notes that this option to model 
recently adopted emissions limits to avoid a nonattainment designation 
provides an incentive for the air agency and facility to achieve 
emissions reductions that will result in health benefits sooner in the 
communities located near these sources (since local air quality would 
improve sooner than if the area were designated nonattainment in 2017 
and attainment were required by no later than 2022).
(c) Stack Height
    Air quality modeling that is used for projecting future air quality 
when setting emission limits must use ``good engineering practice'' 
(GEP)\44\ stack height in order to not allow inappropriate credit in 
SIPs and federal implementation plans for techniques

[[Page 27465]]

that disperse rather than reduce or eliminate emissions, as required by 
CAA section 123 and the EPA's stack height rules.\45\ This approach 
helps ensure the attainment of the NAAQS with the use of these emission 
limits.
---------------------------------------------------------------------------

    \44\ For a complete definition of GEP stack height, see 40 CFR 
51.100(ii).
    \45\ See stack height regulations at 40 CFR 51.100(ff)-(kk); and 
40 CFR 51.118.
---------------------------------------------------------------------------

    As noted previously, the modeling approach described in this 
proposed rule for initial area designations is to be used for assessing 
actual air quality rather than for the development of future emissions 
limitations. Accordingly, it is more appropriate to use actual stack 
height in conjunction with actual emissions when using a modeling 
approach to characterize current air quality. The concern about giving 
inappropriate credit for dispersion techniques is not relevant in this 
situation as section 123 applies only to emission limitation controls. 
This situation is unique for these initial SO2 designations 
because states would be assessing actual air quality and this is 
different from the situations subject to section 123 requirements, 
where GEP stack height is traditionally used to determine what emission 
limits are needed to ensure future attainment of a NAAQS. The 
combination of actual stack height with actual emissions would more 
effectively characterize the current air quality around a source.
    As discussed in the previous section, there may be certain sources 
that states wish to model using allowable emissions. If a state chooses 
to use allowable emissions, then it should also use GEP stack height 
when the actual stack height exceeds the GEP height. In situations 
where the actual stack height exceeds the GEP height, the GEP stack 
height is more appropriate because the GEP height is used when 
calculating the allowable emission rates and using actual stack height 
in such a case would not reflect the true allowable emissions for the 
source. Stacks with actual stack heights below the GEP height would use 
the actual stack height because GEP stack height would not have been a 
relevant factor in determining the source's prior emissions limit, and 
use of GEP stack height in this case would not accurately reflect 
actual ambient impacts. Additional recommendations on the use of actual 
stack height can be found in the modeling TAD.
(d) Meteorological Data
    In accordance with 40 CFR part 51, Appendix W, air agencies and 
sources conducting SO2 modeling for permitting or SIP 
attainment demonstrations generally use either 5 years of National 
Weather Service meteorological data, or 1 year of on-site 
meteorological data. These data need to be representative of the area's 
meteorology, but do not necessarily need to be from the most recent 
years of data. In contrast, the modeling approach discussed in this 
proposed rule uses alternate meteorological inputs to characterize 
current air quality. For purposes of conducting modeling that better 
simulates what might be expected to be measured by an ambient monitor, 
this rule proposes the use of 3 years of meteorological data. Ideally, 
air agencies would use the most recent 3 years of meteorological data 
and the same 3 years of actual emissions data when modeling for 
designations. The modeling TAD has additional suggestions on these 
meteorological inputs.
2. Modeling Protocols and Analyses
    As discussed previously, this rulemaking proposes that each state 
submit to its EPA Regional Administrator by January 15, 2016, a list 
identifying the sources for which it will characterize nearby air 
quality and the analytical approach (monitoring or modeling) to be used 
for each source. This list should include all sources in the state that 
are above the relevant emissions thresholds and those additional 
sources that either the state or the EPA Regional Administrator has 
also identified as needing additional information on local air quality.
    In preparation for conducting modeling, the state would need to 
develop a modeling protocol for all the sources the state plans to 
model. This protocol can be source specific, or in some cases, the 
state may propose a standard protocol for all the sources in its state. 
Details on the suggested protocol elements and the recommended standard 
format of this protocol can be found in the modeling TAD. The state 
would submit this protocol to the Regional Administrator for review at 
the same time it submits its list of sources outlining its monitoring 
and modeling choices. The state is encouraged to work with its EPA 
Regional Office throughout 2015 while developing its modeling 
protocols.
3. State Recommendations for 2017
    Under this rule, air agencies would be required to submit modeling 
analyses for selected source areas by January 13, 2017, and at the same 
time air agencies could submit revised designation and boundary 
recommendations for these areas based on these new modeling data. These 
recommendations could include modeling demonstrating that the source 
area is either attaining or violating the current SO2 
standard.
    States could also assess recent data from their existing 
SO2 monitoring networks and provide designations 
recommendations based on these data as well. If they have properly 
sited source-oriented monitors that are attaining the current 
SO2 NAAQS with 3 years of quality assured data, they could 
submit a demonstration showing that those monitors are properly sited 
(following the suggested guidelines in the monitoring TAD), along with 
a recommendation for a designation of unclassifiable/attainment for the 
associated area. Likewise, if the state has an existing monitor that is 
violating the standard and the area has not yet been designated 
nonattainment, it should provide a nonattainment area boundary 
recommendation for the associated area at this time. Lastly, the state 
may wish to submit revised boundary recommendations for areas with low 
emissions that do not contain any sources above the threshold, or for 
areas with additional sources identified by the state or Regional 
Administrators for further characterization.
    Thus, since the EPA expects to designate the majority of the 
country in 2017, the only areas the EPA would not be ready to take 
action on in 2017 are the areas for which states have elected to 
install new monitors. The EPA's initial thinking is that the state 
should not recommend a designation for any county that includes a 
source area with new monitoring under way. The EPA may consider 
providing additional designation boundary guidance for this round of 
boundary recommendations at a later date.
4. Ongoing Air Quality Characterization Requirements for Areas 
Designated Attainment Based on Modeling
    Typically, in situations where ambient monitoring data alone are 
used to assess air quality to determine whether an area is attaining 
the NAAQS, these monitoring data continue to be collected by the air 
agency, made publicly available and used for a variety of regulatory 
and non-regulatory purposes. Ambient monitoring is commonly continued 
to verify ongoing maintenance of the standard, both for areas that were 
designated nonattainment and for areas that were designated 
unclassifiable/attainment alike.
(a) Options for Ongoing Verification
    The use of modeling to characterize SO2 NAAQS-related 
air quality and serve as a surrogate for monitoring raises the issue of 
how a state will

[[Page 27466]]

continue to have data to assure ongoing attainment of the NAAQS. A 
monitoring network provides data on a continuous basis, but any 
modeling conducted pursuant to this rule to assess attainment of the 
SO2 NAAQS for designations purposes would represent a 
discrete 3-year period (similar to determining a 3-year design value 
based on ambient monitoring data). A one-time modeling analysis using 
actual emissions information would not provide for ongoing verification 
of continued attainment.
    For this reason, the EPA is proposing 3 policy options for how 
states that satisfy the requirements of this rulemaking by using the 
modeling option in a given area will need to conduct additional 
emissions and/or modeling analyses to demonstrate continued attainment 
for an area around a source. The EPA expects that such additional 
analyses will be needed for areas that are designated as 
``unclassifiable/attainment'' based on modeling information and would 
be intended for the purpose of verifying that such areas continue to 
meet the standard, just as monitors do now in many areas. The EPA also 
presents 2 procedural options describing the process by which states 
would provide an opportunity for public review and comment and submit 
their report to the EPA and for the EPA to take action on the reports.
    Before introducing the options for ongoing verification of 
attainment, we note that source areas would not be subject to these 
ongoing verification requirements if: (1) Modeling for the source was 
conducted using allowable emissions; or (2) the modeling for the source 
was conducted using actual emissions and the relevant sources then 
adopted enforceable emission limits consistent with the actual 
emissions rates used in the modeling. First, if an allowable emissions 
rate were used in the modeling, then an enforceable emission limit 
would already be in place to limit the source's emissions in the 
future, so emissions would not be expected to exceed what was modeled. 
Therefore, compliance with the emissions limit for areas associated 
with these sources should be sufficient to ensure air quality meets the 
standard and the EPA is not proposing additional means of verification 
for such areas. Indeed, since use of actual emissions requires 
recurring review to judge whether air quality may have worsened and 
compliance with allowable emissions can demonstrate that no such review 
would be necessary, states would have the incentive to use allowable 
emissions limits in their modeling if it would demonstrate that 
emissions at allowable levels would not cause violations of the NAAQS.
    Second, for an area that was modeled as attaining the standard 
based on actual source emissions, the state always has the option to 
adopt for the source(s) in the area federally-enforceable emission 
limits at levels that are consistent with the actual emissions used in 
the modeling and that ensure attainment with the standard. These 
emission limits would ensure that the source's emissions would not 
increase in the future. Assuming the limits are adopted, enforceable 
and being met by the time designations are completed, this approach 
would require no additional submittal by the air agency after initial 
designations beyond the usual ongoing source compliance demonstrations. 
Under this approach, it would be assumed, subject to compliance 
monitoring, that the source would remain in compliance with its 
emission limits and the area would continue to attain the standard. If 
a state does not take either of the approaches described above, 
however, some mechanism for confirming that air quality continues to 
meet the standard must be in place. Descriptions of the 3 proposed 
options on which we request comment are presented below.
(1) Ongoing Verification Option 1
    The first option would require the air agency to assess 
SO2 emissions annually for sources that are located in areas 
designated unclassifiable/attainment based on modeling using actual 
emissions, and to conduct updated air quality modeling every 3 years. 
On an annual basis, beginning the year after designations are 
effective, the air agency will be required to provide an assessment of 
the most recent emissions data for each source and whether it has 
increased in emissions or changed its emissions profile (e.g., change 
in operating schedule). Emissions data for large SO2 sources 
would be made available by the state from annual reporting required for 
the acid rain program, the air emissions reporting rule, or other 
regulations. For each source, the air agency also will be required to 
make a determination as to whether it finds that additional modeling is 
needed to assess if the area around the source(s) is still attaining 
the SO2 NAAQS. Factors the air agency should consider in 
making this determination include: The estimated design value from the 
original modeling analysis and how close that value was from exceeding 
the standard; the magnitude of the emissions increase; and information 
about changes in the emissions profile (e.g., operating schedule of the 
source) or hourly emission rate. The EPA Regional Administrator will 
assess the information provided by the air agency and determine on a 
case-by-case basis if additional modeling will be requested from the 
state to assess potential changes in air quality. If the air agency 
determines that additional modeling is necessary, the EPA expects the 
air agency to conduct such modeling and provide the results of that 
assessment in a timely fashion.
    In the third year after designations are effective and continuing 
every 3 years after that, the air agency would also be required to 
submit a modeling analysis assessing the air quality around each 
source(s) using actual annual emissions and meteorological data from 
the most recent 3 years. Based on this analysis, the air agency will 
need to determine whether the area is still attaining the 
SO2 NAAQS. If any new modeling by the air agency indicates 
that an area is not attaining the SO2 NAAQS, the EPA may 
take appropriate action, including, but not limited to, requiring 
adoption of enforceable emission limits to ensure continued attainment 
of the SO2 NAAQS, redesignation to nonattainment, or 
issuance of a SIP Call. Air agencies may request that the EPA Regional 
Administrator approve a suspension of the triennial modeling 
requirement for an area if their most recent modeling design value is 
less than 50 percent of the NAAQS and if that modeling is not also 
required as part of a SIP or permit. Note that for such areas, the air 
agency will still be required to provide an annual assessment of the 
most recent emissions data for each source and whether it has increased 
in emissions or changed its emissions profile (e.g., change in 
operating schedule).
    The EPA believes that this approach is appropriate for assessing 
ongoing attainment of the SO2 NAAQS, as it follows a similar 
approach to what states would be required to do if there was a monitor 
near a source. The EPA believes that this approach would be a 
reasonable way to provide for an ongoing assessment of key sources. 
Recognizing state resource limitations, this approach does not require 
air agencies to conduct modeling for each source every year, and, in 
the years when modeling is required, much of the information from prior 
modeling will likely continue to be applicable (e.g., stack parameters, 
terrain). Thus, compared to a situation in which the air agency would 
be required to operate and maintain an ambient monitor to ensure 
ongoing attainment, this

[[Page 27467]]

requirement to track emissions annually and conduct updated modeling 
every 3 years provides appropriate ongoing characterization of air 
quality while being less burdensome than monitoring for the air agency. 
The EPA is also proposing two alternative options for comment below.
(2) Ongoing Verification Option 2
    The second option would also require the air agency to provide the 
EPA with an assessment of SO2 emissions changes for each 
source annually, beginning in the year after the area is designated 
unclassifiable/attainment. This annual review of emissions would be 
similar to the requirement discussed in the first option. As noted 
above, emissions data for large SO2 sources would be 
available from annual reporting required for the acid rain program, the 
air emissions reporting rule, or other regulations. However, instead of 
modeling every 3 years, EPA would require that, for each source in 
which total SO2 emissions increase over the emissions for 
the previous year, the air agency would be required to submit to the 
EPA an assessment of the cause of the increase and provide an initial 
determination of whether or not air quality modeling would be needed to 
verify that the area around the source continues to attain the 
standard. Factors the air agency should consider in making this 
determination include: The estimated design value from the original 
modeling analysis and how close that value was from exceeding the 
standard; the magnitude of the emissions increase; and information 
about changes in the emissions profile or hourly emission rate.
    For example, if the previous modeling of actual emissions in the 
area estimated the design value to be just below the level of the 
standard and 5 years later the area emissions increased by 15 percent, 
then this likely would be a sufficient reason for the air agency to 
conduct an updated modeling analysis.\46\ On the other hand, if the 
initial modeling using actual emissions for the area indicated that the 
design value would be less than half the level of the standard and in a 
subsequent year indicated the area emissions increased by 5 percent, 
then this might be a sufficient reason for the air agency to recommend 
that it does not need to conduct an updated modeling analysis.
---------------------------------------------------------------------------

    \46\ Moreover, the prevention of significant deterioration 
program would likely require such an analysis if the emissions 
increase originated from a major modification to an existing source.
---------------------------------------------------------------------------

    The Regional Administrator would consider the air agency 
recommendation for each area around a source on a case-by-case basis 
and may direct the air agency to conduct an updated modeling analysis 
using the SO2 emissions from the most recent 3 years and to 
submit the results of such analysis to the EPA Regional Office by a 
specific date. If the air agency determines that additional modeling is 
necessary, the EPA expects the air agency to conduct such modeling and 
provide the results of that assessment in a timely fashion--within 12 
months. The EPA will consider the results of any updated modeling 
analysis in order to determine whether the area continues to attain.
    The EPA believes that this option strikes a balance between 
analytical burden and air quality protection because it provides a 
simple, easy-to-track benchmark for requiring further investigation of 
an emissions increase by the air agency, and it allows the Regional 
Administrator to first consider the air agency's analysis of each 
particular case before determining whether a more resource-intensive 
modeling analysis would be required. The EPA believes that this option 
would be a reasonable alternative to option 1 for requiring some 
further assessment of source areas, but a key difference is that it 
would not require modeling every 3 years. Because modeling likely would 
be required less frequently under this option, it would be less 
resource intensive than option 1, but the verification of ongoing 
attainment would not reflect the same degree of certainty as option 1.
(3) Ongoing Verification Option 3
    Under the third option, the state would be required to perform 
periodic screening modeling every 3 years for all source areas that had 
been previously modeled and determined to be attaining the standard, 
and submit such modeling for review to the EPA. Screening modeling 
typically uses conservative assumptions to determine whether an area 
around a source(s) would still be expected to attain the standard, and 
it requires less work by the air agency in preparing model inputs as 
compared to preparing for a full-scale modeling analysis. The companion 
screening model for AERMOD is the AERSCREEN model. A complete, full-
scale modeling analysis with updated emissions and meteorological 
inputs would only be required if the state performs screening modeling 
that indicates a potential violation.
    If this new full-scale modeling by the air agency indicates that an 
area is not attaining the SO2 NAAQS, the EPA may take 
appropriate action, including, but not limited to, requiring adoption 
of enforceable emission limits to ensure continued attainment of the 
SO2 NAAQS, redesignation to nonattainment, or issuance of a 
SIP Call. The basic rationale behind this option is that since these 
areas were designated as unclassifiable/attainment based on modeling, 
then it would be appropriate to require periodic updated modeling to 
continue to verify attainment. Because the states will have already 
gone through the process of modeling these sources, it is expected that 
it will be less resource intensive to conduct this periodic screening 
modeling in subsequent years.
(b) Procedural Options for Ongoing Verification
    As with the prior section regarding ongoing verification following 
removal of a monitor, the EPA also proposes two options regarding the 
procedure by which air agencies would submit ongoing verification 
reports to the EPA when a state elects to use the modeling option and 
the procedure by which the EPA would review and act on them. The 
contents of the verification report will depend on which of the above 
policy options is ultimately finalized.
(1) Procedural Option 1
    Under the first procedural option, we propose that in order to 
demonstrate ongoing verification of attainment for sources that have 
been designated unclassifiable/attainment based on modeling analyses, 
the air agency would submit a report to the EPA annually as an appendix 
to its annual monitoring plan. The annual monitoring plan is required 
to be submitted to the EPA Regional Administrator by July 1 each year. 
This annual process for verifying ongoing attainment for areas 
designated attainment based on modeling in effect would be a surrogate 
for ongoing ambient monitoring (which would provide a new 3-year design 
value with each new year of air quality data). A primary objective of 
this approach would be to enable the air agency to save time and 
resources by providing a single process for the public review and 
comment on the annual monitoring plan and annual reports to demonstrate 
ongoing attainment of previously modeled areas.
    The inclusion of this verification report as an appendix to the 
annual monitoring plan would ensure that the report would be subject to 
the same opportunities for public review and comment that are to be 
provided for the monitoring plan pursuant to regulations at 40 CFR Part 
58.10. Those regulations specify that if the air agency modifies the 
monitoring plan from the previous

[[Page 27468]]

year, then prior to taking final action to approve or disapprove the 
plan, the EPA would be required to provide an opportunity for public 
comment on its proposed action. The regulations also indicate that if 
the state has already provided a public comment opportunity in 
developing its revised monitoring plan and has made no further changes 
to the plan after reviewing public comments that were received, then it 
could submit the public comments along with the revised plan to the 
EPA, and the Regional Administrator would not need to provide a 
separate opportunity for comment before approving or disapproving the 
plan.
(2) Procedural Option 2
    Under the second procedural option, the ongoing verification of 
emissions report would not be submitted to the EPA as an appendix to 
the annual monitoring network plan. Instead, it would take the form of 
a separate, independent submittal from the state to the EPA Regional 
Administrator. However, we propose that this report would be due by the 
same July 1 date each year. This independent submittal would follow the 
general guidelines set forth in 40 CFR 58.10 regarding opportunities 
for public review as described in option 1 above, but the report would 
only include the annual assessments associated with sources in areas 
that were designated unclassifiable/attainment based on modeling of 
actual emissions.
    The EPA believes that the main advantage of the first procedural 
option is that from a procedural standpoint, it would leverage the time 
and resources that are already devoted to the existing annual 
monitoring plan development and review process. In contrast, the second 
option would require additional state and the EPA resources to provide 
for public review opportunities in parallel with the monitoring plan 
process. The main advantage of the second option is that it would keep 
the information submitted to verify ongoing attainment for modeled 
areas separate from the annual monitoring plan. It may be considered 
advantageous from the perspective of managing workflow in an air 
quality management organization to not have the modeling verification 
reports be combined with the annual modeling plans.
    Regardless of which procedural approach is included in the final 
rule, the EPA would communicate to each state the reasoning behind any 
action or decision the EPA makes with regard to the submitted ongoing 
verification of attainment report. For example, the EPA should describe 
the supporting rationale for a decision to require additional 
monitoring from the state, or for a decision to allow the state to 
suspend the periodic modeling requirement for a source because the 
latest modeled design value is below 50 percent of the NAAQS. This 
information should be provided in writing in a letter or Federal 
Register document, as appropriate. The EPA seeks to adopt an effective 
approach for verifying ongoing attainment for modeled source areas that 
can serve as a reasonable surrogate to ongoing ambient monitoring 
without creating undue burden for states.
    The EPA requests comment on the 3 policy options presented above, 
and requests that each commenter provide a clear rationale for their 
position. The EPA also requests comments on the two procedural options 
presented above. For both sets of options, the EPA would be interested 
in any alternative ideas suggested by commenters. For any such 
recommendations, the EPA requests the commenter provide a detailed 
rationale and estimate of any associated costs.

VI. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review and Executive 
Order 13563: Improving Regulation and Regulatory Review

    Under Executive Order 12866 (58 FR 51735, October 4, 1993), this 
action is a ``significant regulatory action'' because it raises novel 
policy issues. Accordingly, the EPA submitted this action to OMB for 
review under Executive Orders 12866 and 13563 (76 FR 3821, January 21, 
2011) and any changes made in response to OMB recommendations have been 
documented in the docket for this action.

B. Paperwork Reduction Act

    The information collection requirements in this proposed rule have 
been submitted for approval to the OMB under the Paperwork Reduction 
Act, 44 U.S.C. 3501 et seq. The Information Collection Request (ICR) 
document prepared by the EPA has been assigned the EPA ICR number 
2495.01.
    The EPA is proposing this SO2 Data Requirements rule to 
require air agencies to more extensively characterize ambient 
SO2 air quality concentrations, pursuant to section 
110(a)(2)(B) and 110(a)(2)(K) of the CAA, to inform the area 
designations process for the 2010 SO2 NAAQS. For purposes of 
analysis of the estimated paperwork burden, the EPA assumed that 47 
states and tribes would take actions to characterize air quality 
through either air quality modeling or ambient monitoring in 443 areas 
across the country and such states would submit the results of these 
analyses to the EPA. Under this rule, the air agency will have the 
ability to choose, on an area-by-area basis, the analytical approach to 
follow for characterizing air quality around each qualifying source. 
For this reason, there is no way of determining exactly how many areas 
may be characterized through ambient monitoring versus air quality 
modeling approaches. Therefore, this section presents two sets of 
estimated costs, one that assumes all sources would be characterized 
through ambient monitoring, and the other that assumes that all sources 
would be characterized through air quality modeling.
    Potential ambient air monitoring costs are estimated based on the 
assumption that air quality for each of the 443 SO2 sources 
exceeding the Option 1 threshold would be characterized through a 
single newly deployed air monitor. (Note, however, that the Monitoring 
TAD discusses situations where more than one monitor may be appropriate 
or necessary to properly characterize peak 1-hour SO2 
concentrations in certain areas.) Estimates are provided for a 3 year 
period and include a calculation for equipment amortization over seven 
years (as is typically done in monitoring-related ICRs). For the period 
of 2016, 2017, and 2018 (the SO2 requirement begins in 
2016), the total approximate average annual monitoring cost, including 
a calculation for equipment amortization is $9,308,824 (total capital, 
and labor and non-labor operation and maintenance) with a total burden 
of 110,543 hours. The annual labor costs associated with these hours is 
$7,608,287. Included in the $9,308,824 total are other annual costs of 
non-labor operations and maintenance of $760,011 and equipment and 
contract costs of $940,526. For reference purposes, an estimate for 
initial establishment of a new SO2 monitoring station is 
$92,614 (does not include equipment amortization). In addition to the 
costs that would be incurred by the state and local air agencies, there 
would be an estimated burden to the EPA of a total of 52,717 hours and 
$776,005. Burden is defined at 5 CFR 1320.3(b).
    Potential air quality modeling costs are estimated based on the 
assumption that air quality for each of the 443 SO2 sources 
exceeding the Option 1 threshold would be characterized through air 
quality modeling analyses. Based on market research, stakeholder 
feedback, and assumptions about the

[[Page 27469]]

procedures to follow when conducting modeling for designations 
purposes,\47\ an estimate of modeling costs for a single modeling run 
centered on an identified source would be approximately $30,000. If 
states choose to characterize air quality through modeling analyses 
around all 443 sources identified under source threshold Option 1, then 
total national costs for modeling analyses would be estimated at 
$13,300,000. If these costs were incurred over the course of three 
years, then the approximate annual cost for each year over that period 
would be $4,433,333.
---------------------------------------------------------------------------

    \47\ The Draft SO2 NAAQS Designations Modeling 
Technical Assistance Document can be found at https://www.epa.gov/airquality/sulfurdioxide/pdfs/SO2ModelingTAD.pdf.
---------------------------------------------------------------------------

    An agency may not conduct or sponsor, and a person is not required 
to respond to, a collection of information unless it displays a 
currently valid OMB control number. The OMB control numbers for the 
EPA's regulations in 40 CFR are listed in 40 CFR part 9.
    To comment on the agency's need for this information, the accuracy 
of the provided burden estimates and any suggested methods for 
minimizing respondent burden, the EPA has established a public docket 
for this rulemaking, which includes this ICR, under Docket ID number 
EPA-HQ-OAR-2013-0711. Commenters should submit any comments related to 
the ICR to both the EPA and OMB. See the ADDRESSES section at the 
beginning of this notice for where to submit comments to the EPA. Send 
comments to OMB at the Office of Information and Regulatory Affairs, 
Office of Management and Budget, 725 17th Street NW., Washington, DC 
20503, Attention: Desk Office for the EPA. Since OMB is required to 
make a decision concerning the ICR between 30 and 60 days after May 13, 
2014, a comment to OMB is best assured of having its full effect if OMB 
receives it by June 12, 2014. The final rule will respond to any OMB or 
public comments on the information collection requirements contained in 
this proposal.

C. Regulatory Flexibility Act

    The Regulatory Flexibility Act (RFA) generally requires an agency 
to prepare a regulatory flexibility analysis of any regulation subject 
to notice and comment rulemaking requirements under the Administrative 
Procedures Act or any other statute unless the agency certifies the 
rule will not have a significant economic impact on a substantial 
number of small entities. Small entities include small businesses, 
small organizations and small governmental jurisdictions.
    For purposes of assessing the impacts of this proposed rule on 
small entities, small entity is defined as: (1) A small business as 
defined in the Small Business Administration's (SBA) regulations at 13 
CFR 121.201;) (2) a small governmental jurisdiction that is a 
government of a city, county, town, school district or special district 
with a population of less than 50,000; and (3) a small organization 
that is any not-for-profit enterprise which is independently owned and 
operated and is not dominant in its field.
    After considering the economic impacts of this proposed rule on 
small entities, I certify that this action will not have a significant 
economic impact on a substantial number of small entities. This 
proposed rule will not impose any requirements directly on small 
entities. Entities potentially affected directly by this proposal 
include state, local and tribal governments and none of these 
governments are small governments. Other types of small entities are 
not directly subject to the requirements of this rulemaking. We 
continue to be interested in the potential impacts of the proposed rule 
on small entities and welcome comments on issues related to such 
impacts.

D. Unfunded Mandates Reform Act

    This action contains no federal mandate under the provisions of 
title II of the Unfunded Mandates Reform Act of 1995 (UMRA), 2 U.S.C. 
1531-1538 for state, local and tribal governments, in the aggregate, or 
the private sector. This action imposes no enforceable duty on any 
state, local or tribal governments or the private sector. Therefore, 
this action is not subject to the requirements of section 202 and 205 
of the UMRA.
    This action is also not subject to the requirements of section 203 
of the UMRA because it contains no regulatory requirements that might 
significantly or uniquely affect small governments. The CAA imposes the 
obligation for states to submit information to the EPA to characterize 
air quality in order for such data to inform the area designations 
process following the revision of a NAAQS. This rule interprets the 
requirements in section 110(a)(2)(B) and 110(a)(2)(K) in order for air 
agencies to more broadly characterize ambient SO2 
concentrations for the SO2 NAAQS designations process.

E. Executive Order 13132: Federalism

    This action does not have federalism implications. It will not have 
substantial direct effects on the states, on the relationship between 
the national government and the states, or on the distribution of power 
and responsibilities among the various levels of government, as 
specified in Executive Order 13132. The requirement to characterize air 
quality to inform the area designation process for a revised NAAQS is 
imposed by the CAA. This proposed rule, if made final, would interpret 
those requirements as they apply to the 2010 SO2 NAAQS. 
Thus, Executive Order 13132 does not apply to these proposed 
regulations.
    In the spirit of Executive Order 13132 and consistent with the EPA 
policy to promote communications between the EPA and state and local 
governments, the EPA specifically solicits comments on this proposed 
action from state and local officials. In addition, the EPA intends to 
meet with organizations representing state and local officials during 
the comment period for this action.

F. Executive Order 13175: Consultation and Coordination With Indian 
Tribal Governments

    This proposed action does not have tribal implications, as 
specified in Executive Order 13175 (65 FR 67249, November 9, 2000). It 
would not have a substantial direct effect on one or more Indian 
tribes. Furthermore, these proposed regulation revisions do not affect 
the relationship or distribution of power and responsibilities between 
the federal government and Indian tribes. The CAA and the Tribal Air 
Rule establish the relationship of the federal government and tribes in 
characterizing air quality and developing plans to attain the NAAQS, 
and these revisions to the regulations do nothing to modify that 
relationship. Thus, Executive Order 13175 does not apply to this 
action.
    Although Executive Order 13175 does not apply to this action, the 
EPA held several meetings with tribal environmental professionals to 
discuss issues associated with this rule, including discussions at the 
National Tribal Forum on May 1, 2013, and on National Tribal Air 
Association policy calls. These meetings discussed the SO2 
implementation White Paper. The EPA also provided an opportunity for 
tribes and stakeholders to provide written comments on the concepts 
discussed in the White Paper. Summaries of these meetings are included 
in the docket for this proposed rule. The EPA specifically solicits 
additional comment on this proposed action from tribal officials. The 
EPA also intends to offer to consult with any tribal government to 
discuss this proposal.

[[Page 27470]]

G. Executive Order 13045: Protection of Children From Environmental 
Health and Safety Risks

    The EPA interprets E.O. 13045 (62 FR 19885, April 23, 1997) as 
applying only to those regulatory actions that concern health or safety 
risks, such that the analysis required under section 5-501 of the E.O. 
has the potential to influence the regulation. This action is not 
subject to E.O. 13045 because it does not establish an environmental 
standard intended to mitigate health or safety risks. These proposed 
regulatory provisions are designed to help implement the already-
established SO2 NAAQS, which was promulgated in 2010 to 
protect the health and welfare of individuals, including children, who 
are susceptible to the adverse effects of exposure to unhealthy levels 
of ambient SO2.

H. Executive Order 13211: Actions Concerning Regulations That 
Significantly Affect Energy Supply, Distribution, or Use

    This action is not a ``significant energy action'' as defined in 
Executive Order 13211 (66 FR 28355 (May 22, 2001)), because it is not 
likely to have a significant adverse effect on the supply, 
distribution, or use of energy.

I. National Technology Transfer and Advancement Act

    Section 12(d) of the National Technology Transfer and Advancement 
Act of 1995 (NTTAA), Public Law 104-113, section 12(d) (15 U.S.C. 272 
note) directs the EPA to use voluntary consensus standards in its 
regulatory activities unless to do so would be inconsistent with 
applicable law or otherwise impractical. Voluntary consensus standards 
are technical standards (e.g., materials specifications, test methods, 
sampling procedures and business practices) that are developed or 
adopted by voluntary consensus standards bodies. NTTAA directs the EPA 
to provide Congress, through OMB, explanations when the agency decides 
not to use available and applicable voluntary consensus standards.
    This proposed rulemaking does not involve technical standards. 
Therefore, the EPA is not considering the use of any voluntary 
consensus standards.

J. Executive Order 12898: Federal Actions To Address Environmental 
Justice in Minority Populations and Low-Income Populations

    Executive Order (E.O.) 12898 (59 FR 7629 (Feb. 16, 1994)) 
establishes federal executive policy on environmental justice. Its main 
provision directs federal agencies, to the greatest extent practicable 
and permitted by law, to make environmental justice part of their 
mission by identifying and addressing, as appropriate, 
disproportionately high and adverse human health or environmental 
effects of their programs, policies and activities on minority 
populations and low-income populations in the United States.
    The EPA has determined that this proposed rule will not have 
disproportionately high and adverse human health or environmental 
effects on minority or low-income populations because it does not 
affect the level of protection provided to human health or the 
environment. The proposed regulations would, if promulgated, require 
air agencies to characterize ambient SO2 air quality levels 
more extensively throughout the country, particularly in areas near 
large emissions sources. The EPA has designed options in this proposed 
rule that would require air agencies to characterize air quality around 
smaller emissions sources, if such sources are located in more highly 
urbanized areas, because such areas would have the potential for a 
greater number of people to be exposed to adverse effects of ambient 
SO2 concentrations. This aspect of the proposed rule can 
help to ultimately provide additional protection for minority, low 
income and other populations located in these urbanized areas. As such, 
the EPA finds that this proposed rule would not adversely affect the 
health or safety of minority or low-income populations, and that it is 
designed to protect and enhance the health and safety of these and 
other populations.

Statutory Authority

    The statutory authority for this action is provided by 42 U.S.C. 
7403, 7407, 7410 and 7601.

List of Subjects in 40 CFR Part 51

    Environmental protection, Air pollution control, Intergovernmental 
relations, Sulfur oxides.

    Dated: April 17, 2014.
Gina McCarthy,
Administrator.

    For the reasons stated in the preamble, title 40, chapter I, part 
51 of the Code of Federal Regulations are proposed to be amended as 
follows:

PART 51--REQUIREMENTS FOR PREPARATION, ADOPTION AND SUBMITTAL OF 
IMPLEMENTATION PLANS

0
1. The authority citation for Part 51 continues to read as follows:

    Authority:  23 U.S.C. 101; 42 U.S.C. 7401-7671q.

0
2. Add Subpart BB to read as follows:
Subpart BB--Data Requirements for Characterizing Air Quality for the 
Primary SO2 NAAQS
Sec.
51.1200 Definitions.
51.1201 Purpose.
51.1202 Applicability.
51.1203 Air agency requirements.
51.1204 Enforceable emission limits.
51.1205 Assuring continued attainment.

Subpart BB--Data Requirements for Characterizing Air Quality for 
the Primary SO2 NAAQS


Sec.  51.1200  Definitions.

    The following definitions apply for the purposes of this subpart. 
All terms not defined herein will have the meaning given them in 
section 51.100 of this part or in the CAA. 2010 SO2 NAAQS means the 
primary NAAQS for SO2 as codified at 40 CFR 50.17, as 
promulgated on June 2, 2010.
    Air agency means the agency or organization responsible for air 
quality management within a state, local governmental jurisdiction, 
territory or area subject to tribal government.
    Annual SO2 emissions data means the quality-assured annual 
SO2 emissions data for a stationary source as reported to 
the EPA in accordance with any existing regulatory requirement (such as 
the National Emissions Inventory, the Acid Rain Program database, or 
the Clean Air Interstate Rule database).
    Applicable source means a stationary source that has annual 
SO2 emissions of 2000 tons or more; has annual 
SO2 emissions of 1000 tons or more and is located within a 
CBSA with a population equal to or greater than 1 million persons; or 
has been identified by the air agency or by the EPA Regional 
Administrator as requiring further air quality characterization.
    CBSA means core based statistical area, as defined and maintained 
by the Office of Management and Budget (OMB) pursuant to OMB Bulletin 
13-01 (February 28, 2013). The most recent revision to CBSA definitions 
were developed in accordance with OMB's ``Standards for Delineating 
Metropolitan and Micropolitan Statistical Areas,'' 75 FR 37246 (June 
28, 2010).


Sec.  51.1201  Purpose.

    The purpose of this subpart is to require air agencies to take 
actions to develop air quality data characterizing maximum 1-hour 
ambient concentrations of SO2 more extensively across the 
United States through either additional ambient air quality

[[Page 27471]]

monitoring or air quality modeling analyses at the air agency's 
election. Such additional monitoring and modeling data may be used in 
future initial area designations by the EPA, or for other actions 
designed to ensure attainment of the 2010 SO2 NAAQS and 
provide protection of the public from the short-term health effects 
associated with exposure to SO2 concentrations that exceed 
the NAAQS.


Sec.  51.1202  Applicability.

    This subpart applies to any air agency in whose jurisdiction is 
located one or more applicable sources of SO2 emissions that 
has annual SO2 emissions of 2,000 tons or more; has annual 
SO2 emissions of 1,000 tons or more and is located within a 
CBSA with a population equal to or greater than 1 million persons; or 
has been identified by the air agency or by the EPA Regional 
Administrator as requiring further air quality characterization. The 
subject air agency shall identify applicable sources of SO2 
based on the most recent publicly available annual SO2 
emissions data for such sources.


Sec.  51.1203  Air agency requirements.

    (a) The air agency shall submit a list of applicable sources 
located in its jurisdiction to the EPA by January 15, 2016. This list 
may be revised by the Regional Administrator after review based on 
available SO2 emissions data.
    (b) For each area containing an applicable source, the air agency 
shall state by January 15, 2016, whether it will characterize air 
quality through ambient air quality monitoring or through air quality 
modeling techniques. For any area with multiple applicable sources, the 
air agency (or air agencies if a multi-state area) shall use the same 
technique (monitoring or modeling) to characterize air quality for all 
sources in the area.
    (c) Monitoring. For any area for which air quality will be 
characterized through ambient monitoring, the monitors shall be sited 
and operated in a manner equivalent to SLAMS, including, but not 
limited to being subject to reporting data to AQS, data certification 
and satisfying criteria in 40 CFR part 58 Appendices A, C and E. The 
air agency shall include relevant information about monitors used to 
characterize air quality in areas with applicable sources in the air 
agency's annual monitoring network plan required by 40 CFR 58.10. The 
air agency shall consult with the appropriate the EPA Regional Office 
in the development of plans to install, supplement, or maintain an 
appropriate ambient SO2 monitoring network pursuant to the 
requirements of 40 CFR part 58 and this proposed rule. The air agency's 
annual monitoring network plan due on July 1, 2016 shall reflect such 
monitoring and ensure that such monitors will be operational by January 
1, 2017.
    (1) All existing, new or relocated ambient monitors intended to 
satisfy section 51.1203(b) must be operational by January 1, 2017.
    (2) By no later than May 1, 2020, the air agency shall determine 
whether any new ambient monitoring sites deployed pursuant to this 
subpart indicate a violation of the 2010 SO2 NAAQS based on 
ambient monitoring data from the most recent 3 calendar years.
    (3) Any SO2 monitor identified by an air agency in its 
approved Annual Monitoring Network Plan as having the purpose of 
satisfying section 51.1203(b) of this proposed rule and which is not in 
an SO2 nonattainment area, and is not also being used to 
satisfy other ambient SO2 minimum monitoring requirements 
listed in 40 CFR part 58 Appendix D, section 4.4, or which may 
otherwise be required as part of a SIP or permit, and that produces a 
design value of no greater than fifty percent of the 1-hour 
SO2 NAAQS, may be eligible for shut-down. The air agency 
must receive the EPA Regional Administrator approval prior to the shut-
down of any qualifying monitor.
    (d) Modeling. For each area for which air quality will be 
characterized through air quality modeling, the air agency shall submit 
by January 15, 2016, a technical protocol for conducting such modeling 
to the Regional Administrator for review. The air agency shall consult 
with the appropriate the EPA Regional Office in developing these 
modeling protocols.
    (1) The modeling protocol shall include information about the 
modeling approach to be followed, including but not limited to the 
model to be used, modeling domain, receptor grid, emissions dataset, 
meteorological dataset and how the state will account for background 
SO2 concentrations.
    (2) Modeling analyses shall characterize air quality based on 
either actual 1-hour SO2 emissions from the most recent 3 
years, or federally enforceable allowable emissions. If the air agency 
intends to use allowable emissions limits for this analysis, it may 
submit such allowable emissions limits for the EPA's approval at the 
time the modeling protocol is submitted.
    (3) The air agency shall conduct the modeling analysis for any 
applicable source identified by the air agency pursuant to section 
51.1203(a), and for its associated area and any nearby area, as 
applicable, and submit the modeling analysis to the EPA Regional Office 
by January 13, 2017.


Sec.  51.1204  Enforceable emission limits.

    At any time prior to January 13, 2017, for any area that does not 
have an initial area designation conducted pursuant to section 107(d) 
of the CAA, the air agency may submit to the EPA for an applicable 
source a currently applicable and federally enforceable SO2 
emissions limit or limits, associated air quality modeling, and other 
analyses that demonstrate the area, and any nearby area, as applicable, 
does not violate the 2010 SO2 NAAQS, and that the source 
emissions limit will ensure continued attainment. The EPA will consider 
such enforceable emissions limits and modeling demonstrations in the 
initial designations process for these areas.


Sec.  51.1205  Assuring continued attainment.

    (a) For any area in which one or more applicable sources is located 
and which has been initially designated attainment pursuant to this 
proposed rule based on ambient monitoring data or based on a modeling 
analysis using recent actual emissions, the air agency shall ensure 
that the area continues to attain the 2010 SO2 NAAQS in 
subsequent years.
    (b) Modeled areas. For any area initially designated attainment 
where modeling of actual emissions was conducted to characterize air 
quality to satisfy the requirements listed in 51.1203 of this part, the 
air agency shall submit a report to the EPA Regional Administrator as 
an appendix to its annual monitoring plan (due on July 1 each year per 
40 CFR 58.10) documenting the annual SO2 emissions of each 
applicable source in each such area and providing an assessment of the 
cause of any emissions increase. The first report for each such area is 
due by July 1 of the year after the effective date of the area's 
initial designation.
    (1) Along with the annual emissions report, the air agency shall 
provide a recommendation regarding whether additional modeling is 
needed to characterize air quality in any area to determine whether it 
continues to attain the 2010 SO2 NAAQS. The EPA Regional 
Administrator will consider the emissions report and air agency 
recommendation, and may require that the air agency conduct updated air 
quality modeling for the area and submit it to the EPA by a specified 
date.
    (2) For any area initially designated attainment where modeling of 
actual emissions was conducted to characterize air quality, the air 
agency also shall submit to the EPA an updated air quality modeling 
analysis by July 1 of the third year after the designation for

[[Page 27472]]

the area is effective every 3 years thereafter.
    (3)(i) The air agency may request that the EPA Regional 
Administrator approve ceasing continued triennial modeling of the area 
as required by paragraph (b)(2) of this section if the following 
criteria are met:
    (A) the modeling is not otherwise required to meet any requirement 
in a SIP or permit; and
    (B) the most recent modeling for the area resulted in a modeled 
design value that is no greater than fifty percent of the 1-hour 
SO2 NAAQS.
    (4) The EPA will act upon such a request to cease triennial 
modeling as part of its action on the annual monitoring plan under 40 
CFR 58.10. For areas where the EPA has approved the air agency's 
request to cease continued modeling of the area, the air agency will be 
required to continue to meet the requirements of paragraphs (b) and 
(b)(1) of this section.
    (c) Monitored areas. For any area initially designated attainment 
where SO2 monitoring was conducted to characterize air 
quality to satisfy the requirements listed in section 51.1203 of this 
part, the air agency shall continue to operate the monitor(s) used to 
satisfy those requirements and report ambient data pursuant to existing 
ambient monitoring regulations.
    (1)(i) The air agency may request that the EPA Regional 
Administrator approve the shut-down of any monitor in operation to 
satisfy the requirements of section 51.1203 of this part if the 
following criteria are met:
    (A) the monitor is not also satisfying other minimum SO2 
monitoring requirements listed in 40 CFR part 58 Appendix D;
    (B) the monitor is not otherwise required to meet any requirement 
in a SIP or permit; and
    (C) the monitor recorded a design value in the most recent 3-year 
period that is no greater than fifty percent of the 1-hour 
SO2 NAAQS.
    (ii) The EPA will act upon any request to cease operation of a 
monitor as part of its action on the annual monitoring plan under 40 
CFR 58.10.
    (2) For any area for which the EPA has approved the air agency's 
request for an SO2 monitor to cease operations, the air 
agency shall submit a report to the EPA Regional Administrator as an 
appendix to its annual monitoring plan (due on July 1 each year per 40 
CFR 58.10) documenting the annual SO2 emissions of each 
applicable source in each such area and providing an assessment of the 
cause of any emissions increase. The first report for each such area is 
due by July 1 of the year after the monitor operations were terminated.
    (3) Along with the annual emissions report, the air agency shall 
provide a recommendation regarding whether additional air quality 
characterization is needed to determine whether the area continues to 
attain the 2010 SO2 NAAQS. The EPA Regional Administrator 
will consider the emissions report and air agency recommendation, and 
may require that the air agency reinstate ambient monitoring or conduct 
additional modeling and submit relevant data to the EPA by a specified 
date.
    (d) If modeling or monitoring information required to be submitted 
by the air agency to the EPA pursuant to section 51.1205 of this part 
indicates that an area is not attaining the 2010 SO2 NAAQS, 
the EPA may take appropriate action, including but not limited to, 
disapproving the monitoring plan, requiring adoption of enforceable 
emission limits to ensure continued attainment of the 2010 
SO2 NAAQS, redesignation of the area to nonattainment, or 
issuance of a SIP Call.

[FR Doc. 2014-09458 Filed 5-12-14; 8:45 a.m.]
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