[Federal Register Volume 80, Number 162 (Friday, August 21, 2015)]
[Rules and Regulations]
[Pages 51051-51088]
[FR Doc No: 2015-20367]

Vol. 80

Friday,

No. 162

August 21, 2015

Part V

 Environmental Protection Agency

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40 CFR Part 51

 Data Requirements Rule for the 2010 1-Hour Sulfur Dioxide
(SO2) Primary National Ambient Air Quality Standard (NAAQS);
Final Rule

Federal Register / Vol. 80 , No. 162 / Friday, August 21, 2015 /
Rules and Regulations

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 51

[EPA-HQ-OAR-2013-0711; FRL-9928-18-OAR]
RIN 2060-AR19

Data Requirements Rule for the 2010 1-Hour Sulfur Dioxide
(SO2) Primary National Ambient Air Quality Standard (NAAQS)

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: The Environmental Protection Agency (EPA) is promulgating 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 to identify maximum 1-hour
SO2 concentrations in ambient air. The final rule
establishes minimum criteria for identifying the emissions sources and
associated areas for which air agencies are required to characterize
SO2 air quality. Air agencies remain free to also
characterize air quality in additional areas beyond those required to
be characterized under the rule. The final rule also sets forth a
process and timetables by which air agencies must characterize air
quality 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 recommending how air
agencies should conduct such monitoring or modeling. The air quality
data developed by air agencies pursuant to this rule may be used by the
EPA in future actions to evaluate areas' air quality under the 2010 1-
hour SO2 National Ambient Air Quality Standard (NAAQS),
including area designations and redesignations, as appropriate.

DATES: This final rule is effective on September 21, 2015.

ADDRESSES: The EPA has established a docket for this action under
Docket ID No. EPA-HQ-OAR-2013-0711. All documents in the docket are
listed on the http://www.regulations.gov Web site. Although listed in
the index, some information is not publicly available, i.e.,
confidential business information or other information whose disclosure
is restricted by statute. Certain other material, such as copyrighted
material, will be publicly available only in hard copy. Publicly
available docket materials are available either electronically in
http://www.regulations.gov or in hard copy at the Docket ID No. EPA-HQ-
OAR-2013-0711, EPA/DC, William Jefferson Clinton West Building, Room
3334, 1301 Constitution Avenue 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<PHONE_NUMBER> and the telephone number for the Air and
Radiation Docket Information Center is<PHONE_NUMBER>. For additional
information about the EPA's public docket, visit the EPA Docket Center
homepage at: http://www.epa.gov/epahome/dockets.htm.

FOR FURTHER INFORMATION CONTACT: For further general information on
this rulemaking, contact Dr. Larry D. Wallace, Office of Air Quality
Planning and Standards, U.S. Environmental Protection Agency, by phone
at<PHONE_NUMBER>, or by email at<EMAIL_ADDRESS>or Mr. Rich
Damberg, Office of Air Quality Planning and Standards, U.S.
Environmental Protection Agency, by phone at<PHONE_NUMBER>, or by
email at<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION:

I. General Information

A. Does this action apply to me?

    Entities potentially affected directly by this final rulemaking
include state, local and tribal governments. Entities potentially
affected indirectly by this final rulemaking, depending on how state,
local and tribal agencies choose to regulate such entities in the
future, include owners and operators of sources of SO2
emissions (such as coal-fired power plants, refineries, smelters, pulp
and paper related facilities, waste incinerators, chemical
manufacturers 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. 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 document will be posted at: http://www.epa.gov/air/sulfurdioxide/implement.html. Upon its publication in the Federal Register, only the
published version may be considered the final official version of the
notice, and will govern in the case of any discrepancies between the
Federal Register published version and any other version.

C. 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. Where can I get a copy of this document and other related
information?
    C. How is this document organized?
II. Background for Final Rulemaking
III. Summary of the Final Rule Requirements
IV. Responses to Significant Comments on the Proposed Rule
    A. The Use of Monitoring and/or Modeling Data
    B. Source Coverage and Emission Threshold Options
    C. Data Requirements and Program Implementation Timeline
    D. Technical Issues Relating to Modeling and Monitoring
    E. Other Key Issues and Comments
V. Environmental Justice Considerations
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 (PRA)
    C. Regulatory Flexibility Act (RFA)
    D. Unfunded Mandates Reform Act (UMRA)
    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
    K. Congressional Review Act (CRA)
    L. Judicial Review
Statutory Authority

II. Background for Final Rulemaking

    On May 13, 2014, the EPA proposed the Data Requirements Rule (DRR)
for the 2010 1-hour SO2 Primary NAAQS. The preamble to the
proposal provided a discussion of the events that led to the EPA's
proposal of a new regulation to direct state, tribal and local agencies
\1\ to better characterize ambient air SO2 concentrations
near large polluting sources. See 79 FR 27447, May 13, 2014. This
discussion addressed the adoption of the 2010 SO2 NAAQS and
the suggested implementation approach described in the preamble of that
rulemaking; the area designations process under section 107 of the
Clean Air Act (CAA); the history of

designations for prior SO2 NAAQS, including the use of air
quality modeling information; the Agency's subsequent issuance of an
implementation white paper in May 2012 and input received from
stakeholder groups; and the EPA's February 2013 SO2 NAAQS
implementation and designations strategy paper, developed in response
to feedback received through this outreach process.\2\ This final
rulemaking notice does not repeat all of that discussion, but refers
interested readers to the preamble of the proposed rule for this
informative background.
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    \1\ The final rule applies to air agencies in all states. The
definition of ``state'' in section 302(d) of the Clean Air Act (CAA
or Act) means a state, the District of Columbia, the Commonwealth of
Puerto Rico, the Virgin Islands, Guam, and American Samoa and
includes the Commonwealth of the Northern Mariana Islands.
    \2\ The May 2012 White Paper and high-level summaries of
stakeholder meetings are available at: http://www.epa.gov/oaqps001/sulfurdioxide/implement.html. These documents and written comments
received from stakeholders are also included in the docket for this
rulemaking.
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    The proposed rule noted that although the current SO2
ambient monitoring network included more than 400 monitors nationwide,
the scope of the network had certain limitations, and approximately
two-thirds of the monitors are not located to characterize maximum 1-
hour SO2 concentration impacts from emissions sources. To
more effectively assess potential public health impacts from exposure
to high SO2 concentrations, the proposed rule presented
options for requiring air agencies to characterize air quality in the
vicinity of large sources of SO2 emissions that exceed
specified annual emissions thresholds. The EPA's proposed preferred
emissions threshold option specified that air agencies would be
required to characterize air quality in the vicinity of sources that
emit over 1,000 tons of SO2 per year and are located in more
highly populated areas (i.e., Core-Based Statistical Areas (CBSA) with
population of at least 1 million), and in the vicinity of sources that
emit over 2,000 tons of SO2 per year and are located outside
metropolitan areas of at least 1 million population. The EPA also
identified two other emission threshold options and requested public
comment on these potential emission thresholds values, a CBSA
population threshold of 1 million, the combination of emissions and
population thresholds as a means of determining how SO2
sources would be identified, and on any possible alternatives. Under
the proposed approach, air agencies, or the EPA, also could require air
quality characterization around other sources, if warranted. See 79 FR
27453, May 13, 2014.
    Under the proposed rule, air agencies would determine for each
emissions source exceeding the threshold whether air quality
characterization for that source would be done either through air
quality modeling analysis or by conducting ambient monitoring. Apart
from the proposed rule, the EPA issued two draft technical assistance
documents (TADs) on modeling and monitoring to assist air agencies with
this analytical work. The proposed rule also described a process and
timetable by which air agencies would be required to identify sources
to be characterized, conduct the relevant analyses and submit such data
to the EPA. See 79 FR 27456, May 13, 2014.
    Specific technical considerations regarding air quality monitoring
and modeling were also discussed in the proposed rule, along with
options for ongoing verification of the air quality characterization in
areas that are not otherwise designated as nonattainment. See 79 FR
27460, May 13, 2014. The proposal also discussed incentives for air
agencies and sources to work together to establish federally
enforceable limits on emissions expeditiously in order to avoid
requirements for air quality characterization altogether. We refer
readers to the proposed rule for the technical, policy and legal
rationale that were presented in support of the proposal, and for a
complete discussion of the issues for which the EPA requested public
comment. Several supporting memoranda, analyses and data were included
in the docket for the proposed action.
    The 60-day public comment period for the proposed rule closed on
July 14, 2014. In section IV of this preamble, we summarize each key
issue from the proposal, briefly summarize major comments received and
provide a response, and describe the final policy in the rule,
including any changes made to the approaches presented in the proposal.
A more detailed response to comments document can be found in the
docket for this rulemaking.

III. Summary of the Final Rule Requirements

    This section provides a brief summary of the requirements of the
final rule. Further discussion of the basis for these requirements and
responses to significant comments are provided in the next section. The
EPA believes that the approach set forth in this rule directing air
agencies to gather additional data to characterize ambient air in the
vicinity of larger SO2 sources is uniquely suited for
implementation of the 1-hour SO2 NAAQS, and the Agency does
not anticipate it to be used for other NAAQS pollutants. The final rule
establishes minimum requirements for air agencies to characterize 1-
hour SO2 air quality concentrations across the country, with
an emphasis on doing so in the vicinity of sources that have the
largest annual SO2 emissions. Note that there are already
minimum SO2 ambient monitoring requirements in place that
were established when the 1-hour SO2 NAAQS was adopted. See
75 FR 35520, June 22, 2010. The requirements in the present rule
supplement those monitoring requirements, which remain in place. As
discussed in more detail in the next section, these requirements are
intended to establish a flexible yet effective program for
characterizing SO2 air quality in priority areas across the
country, given existing funding and resource constraints, and given the
particular characteristics of SO2 air pollution in the
affected areas. This final rule also reflects the fact that numerous
larger sources of SO2 across the country have in recent
years installed, and are expected to install in the near future,
additional control measures that may substantially reduce
SO2 emissions in some cases.
    Under this rule, each air agency is required to submit a list to
the EPA by January 15, 2016, that identifies all sources within its
jurisdiction that have SO2 emissions that exceeded the 2,000
tons per year (tpy) annual threshold during the most recent year for
which emissions data for that source are available, plus any additional
sources and their associated areas identified by the air agency or by
the EPA as also warranting air quality characterization. (The list is a
permanent list of prioritized sources that excludes sources in areas
designated as nonattainment before January 2016 and is not altered by
designations after January 2016.) The rule requires air quality
characterization of the area associated with each listed source, and
provides two options for this characterization, namely the use of
monitoring or modeling. The final rule also provides a third option,
under which air agencies would establish a limit requiring emissions
from a listed source to be below the 2,000 tpy threshold, which, with
the concurrence of the EPA Regional Administrator, would result in that
source and its associated area not being subject to requirements for
air quality characterization. The EPA anticipates discussions with air
agencies early in 2016 to resolve any questions as to what areas
warrant air quality characterization. These discussions are intended to
address whether any additional areas (e.g., areas with clusters of
sources) warrant air quality

characterization, whether existing monitoring networks might serve to
address air quality characterization requirements, and whether any new
limits intended by the air agencies negate the need for air quality
characterization.
    For each source on the list, the air agency will be required to
indicate by July 1, 2016, whether it will characterize air quality
through ambient monitoring or through air quality modeling or,
alternatively, whether it will be subjecting the pertinent source or
sources to emission limit(s) that will keep the source(s) below this
rule's 2,000 tpy threshold. The option identified by the air agency for
each source and its associated area will determine the submittal and
timing requirements for the air agency to provide the required
information.
    If the air agency chooses the first option, ambient monitoring for
a source, the air agency must include information about the planned new
monitor(s) in the annual monitoring plan that the air agency must
submit to the EPA by July 1, 2016; and the air agency must also ensure
that the new monitor(s) are operational by January 1, 2017. The
required monitors shall be sited and operated either as State and Local
Air Monitoring Stations \3\ (SLAMS) or in a manner equivalent to SLAMS.
In either case, monitors shall be subject to reporting and data
certification requirements as prescribed in 40 CFR 58.15 and 58.16
(e.g., quarterly reporting of monitoring data to the Air Quality
System, and the annual certification of data by May 1 of the following
year), and must satisfy applicable criteria in 40 CFR part 58,
appendices A, C, and E.
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    \3\ The SLAMS network is an air quality surveillance system that
consists of a network of monitoring stations designated as SLAMS
which measure ambient concentrations of those pollutants for which
standards have been established in 40 CFR part 50.
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    If the air agency chooses the second option, air quality modeling
for a source, it must submit a modeling protocol for each such source
to the EPA by July 1, 2016, for review and consultation with the EPA
Regional Office. The modeling analyses must then be submitted to the
EPA by January 13, 2017.
    If the air agency chooses the third option, to provide federally
enforceable emissions limitations that limit emissions of an applicable
source to less than 2,000 tpy, or to provide documentation that the
applicable source has permanently shut down, the air agency must notify
the EPA of its decision by July 1, 2016, and provide a description of
the planned emission limitation, including identification of the level
of the limitation being planned. Especially in areas with multiple
sources, the limit(s) should be sufficiently low as to avert the need
for air quality characterization that applies for other listed sources.
Therefore, the rule requires the concurrence of the EPA as to whether
the limit that the air agency intends will suffice in lieu of
conducting air quality characterization. By January 13, 2017, the air
agency must provide EPA with documentation demonstrating that the
emission limits are federally enforceable, adopted, and require
compliance by January 13, 2017, in order for areas containing such
sources to avoid the need to characterize ambient SO2
emissions under the rule. If EPA approval is required to make a limit
federally enforceable, the submittal must be sent to the EPA early
enough such that the EPA has enough time to complete a rulemaking to
make the limit federally enforceable by the January 13, 2017, date.
    Section IV.D of this preamble provides a discussion of selected
technical considerations related to characterizing air quality, but the
rule does not prescribe how an ambient monitoring network around an
identified SO2 source is to be designed, or how air quality
modeling must be specifically done to meet the objectives of this rule.
As stated in the proposal, the EPA has developed TADs that provide
approaches on ambient monitoring and air quality modeling when planning
and executing air quality characterization activities, and recommends
that air agencies refer to these documents to support their efforts.
For example, the TAD for ambient monitoring suggests potential options
and recommendations on different analyses and approaches that could be
considered to help the air agency site source-oriented SO2
monitors in locations of expected maximum 1-hour concentrations. The
TAD for air quality modeling explains that 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. It suggests that in order to
characterize recent air quality levels around a source, it would be
acceptable to use actual hourly emissions data, actual meteorological
data and actual stack height information as technical inputs to the
modeling analysis. However, it is important to note that, except to
require that monitoring be sited and operated in a manner equivalent to
SLAMS and to provide that modeling may be based on actual or allowable
emissions, this rule does not promulgate any specific requirements with
regard to these analytical approaches, and air agencies are expected to
use their best professional judgment, consulting as appropriate with
the EPA, in conducting these analyses. Air agencies should also contact
their respective EPA Regional Offices regarding any additional issues
beyond those addressed in the TADs.
    The final rule also includes provisions specifying how
characterization requirements for listed sources continue into the
future (i.e., ongoing data requirements). For areas where air quality
is to be characterized through ambient monitoring, the rule requires
the monitoring to be conducted for the calendar years of 2017 through
2019, in order to calculate a valid design value for each area. The
rule requires that air agencies (or other parties conducting the
monitoring) continue the operation of all existing and new monitors
used to meet the requirements of this rule. However, it also provides
for the possibility that an air agency may obtain EPA approval to
terminate operation of a monitor that was established to meet the
requirements of this rule if the air quality values at the monitor are
low enough to meet specific criteria. Following commencement of
operation of a new monitor, the air agency may seek EPA approval to
terminate operation of the monitor pursuant to Sec.  51.1203(c)(3) of
this rule, if the monitored design value for the first 3-year period or
second 3-year period is no greater than 50 percent of the 1-hour
SO2 NAAQS. After the fourth year following commencement of
operation of a new monitor, the air agency may be able to seek approval
to shut down the monitor if it meets the criteria specified in existing
regulations at 40 CFR 58.14.
    For areas that were characterized using air quality modeling, the
ongoing data requirement applies only where the modeling was based on
actual emissions and where the area has not subsequently received a
nonattainment designation. In such cases, the air agency will be
required to submit an annual report to the EPA providing updated
emissions information and recommending to the EPA whether further
modeling is warranted to assess any expected changes in recent air
quality. For example, it may be appropriate for the air agency to
conduct updated modeling for an area if there have been increases in
short term emissions rates, an increase in annual emissions, or changes
in facility operations. Where warranted, the air agency shall conduct

updated modeling to characterize air quality in light of the identified
emissions changes and present the results in its annual report to the
EPA. Analogous to the monitor shutdown provisions noted earlier, the
requirement for the annual emissions assessments for an area originally
characterized by modeling may be terminated if the air agency provides
a modeling analysis demonstrating that actual emissions in the previous
year for SO2 sources in the area results in a modeled design
value that does not exceed 50 percent of the NAAQS at any receptor
within the modeling domain. While the annual assessment requirement
under this rule would be terminated in such cases, any other EPA
requirements to provide data (e.g., for the Air Emission Reporting Rule
(AERR)) would not be affected.
    The EPA received more than 80 comments on the proposed rule. Taking
into consideration the range of comments received, the EPA made a
number of revisions that are reflected in the final rule, including the
following:
     The source emissions threshold approach was changed to a
single 2,000 ton annual SO2 emissions level, so the final
rule does not include thresholds that vary depending on the population
of the area.
     Air agencies still need to identify in January 2016 a list
of sources in their jurisdiction for which air quality is to be
characterized, but they now have until July 2016 to indicate whether,
for each source, they plan to use modeling or monitoring to
characterize air quality, or to adopt an enforceable emissions limit.
(The rule clarifies that this list would not include any source located
in an area already designated as nonattainment for the 2010
SO2 NAAQS.) The approach in the proposal would have required
the air agency to indicate its planned approach for each source in
January 2016.
     The final rule also includes a set of monitor shutdown
provisions that is a hybrid of the options included in the proposed
rule and the existing monitor shutdown provisions in 40 CFR part 58. A
monitor required under this rule would be eligible for shutdown if it
has a design value less than 50 percent of the SO2 standard
during one of the first two 3-year periods of operation. After this
point in time, any potential shutdown would need to meet the basic
shutdown provisions that apply for SLAMS monitors as described in 40
CFR 58.14.
     The proposal took comment on three potential approaches
for ongoing requirements for air agencies to provide modeling or
emissions data for areas that were originally characterized with
modeling based on actual emissions data. As noted earlier, the approach
in the final rule requires the air agency to provide emissions data to
the EPA annually for all sources not designated as nonattainment, and
to recommend to the EPA whether an emissions change was substantial
enough to warrant updated air quality modeling.
     A number of commenters suggested that an air agency should
be able to avoid the air quality characterization requirement for a
source if it adopted a federally enforceable requirement limiting
annual emissions at the source to less than 2,000 tpy. The final rule
now includes such a provision. This type of limit would need to be
adopted and in effect by January 2017.

IV. Responses to Significant Comments on the Proposed Rule

A. The Use of Monitoring and/or Modeling Data

1. Legal Authority To Require States To Submit Data Pursuant to This
Rule
a. Summary of Proposal
    In the proposed rule, the EPA explained that the requirements for
the air agency to submit the SO2 monitoring and modeling
data described in Sec.  51.1203 of the proposed rule are appropriate
steps needed to understand SO2 air quality throughout the
country, and are consistent with section 110(a)(2)(B), section
110(a)(2)(K) and section 301(a)(1) of the CAA. See 79 FR 27457, May 13,
2014.
b. Brief Summary of Comments
    Some state commenters asserted that the DRR modifies the CAA and
imposes new monitoring and modeling obligations on air agencies. One
commenter suggested that requiring states to develop monitoring or
modeling data in accordance with this proposal modifies the statutory
mandate to designate all areas by June 2013 because the EPA intends to
use these data for designations. One industry commenter stated it is
not appropriate to replace the CAA's statutory directive for
designations with extra-statutory provisions like those proposed in the
DRR.
    Several state and industry commenters stated that the proposed
requirements and schedules conflict with requirements that apply to the
EPA to timely complete designations under section 107 of the CAA. These
commenters stated that the CAA required the EPA to make area
designations under the new SO2 standard no later than June
3, 2013, and that the EPA failed to comply with that mandatory
obligation. Therefore, the commenters claimed, the DRR proposal's
discussion of a schedule for issuing designations by December 2020 is
beyond the EPA's authority. One state commenter cited EME Homer City
Generation LP v. Envt'l Prot. Agency, 696 F. 3d 7, 27 (D.C. Cir. 2012)
and stated that the DRR cannot stand as proposed because it fails to
follow the mandatory timelines for promulgating area designations, and,
therefore, exceeds the EPA's statutory authority.
c. EPA Response
    The comments that assert that the EPA has not designated areas
under the 2010 SO2 NAAQS in a timely manner are beyond the
scope of this rulemaking, and are not germane to the issue of the EPA's
statutory authority to direct air agencies to conduct monitoring or
modeling to further characterize ambient air concentrations of
SO2. Through this rulemaking, the EPA is not establishing or
modifying any area designation requirements provided for in section 107
of the CAA, nor does any aspect of this final rule conflict with any
provision of section 107 that directs states and the EPA to take timely
action to issue designations. The purpose and effect of this rulemaking
is to require air agencies to characterize air quality in priority
areas throughout the country where existing ambient monitors may not be
adequately characterizing peak 1-hour SO2 ambient air
concentrations. The air quality data obtained as a result of this
rulemaking then may be used in future analytical actions by the EPA,
including designations of any undesignated areas or redesignations of
already designated areas. It is true that in the proposed rule preamble
we discussed how the timing of the implementation of this rule would
fit with our intended schedule for completing area designations, but
the proposal did not itself purport to establish a binding schedule for
completing designations.
    The EPA notes that litigation was filed against the EPA to compel
the Agency to complete designations under CAA section 107, and on March
2, 2015, the court in one of those cases issued a ruling that places
the EPA on a binding schedule to complete area designations for the
2010 1-hour SO2 NAAQS. See, Sierra Club, et al. v. McCarthy,
Case No. 13-cv-03953-SI (N.D. Cal., March 2, 2015) (Order Granting
Joint Motion To Approve And Enter Consent Decree And Denying Other
Motions As Moot; and Consent Decree). Copies of the court's order and
the March 2015 consent decree setting forth the EPA's schedule

for completing designations have been placed in the docket for this
rulemaking. Under the schedule ordered by the court, the EPA is
required to complete the designations in no more than three future
rounds.
    First, by July 2, 2016 (16 months from the date of the court's
order), the EPA must sign a notice for publication in the Federal
Register that promulgates designations for remaining undesignated areas
that: (a) Based on air quality monitoring in the three full calendar
years preceding that date have monitored violations of the NAAQS; or
(b) contain any stationary source that has not by March 2, 2015, been
``announced for retirement'' and that, according to data in the EPA's
Air Markets Database, either (1) emitted more than 16,000 tons of
SO2 in 2012, or (2) emitted more than 2,600 tons of
SO2 and had an annual average emission rate of 0.45 lbs.
SO2/Mmbtu or higher in 2012. (The March 2015 consent decree
defines ``announced for retirement'' as meaning ``any stationary source
in the United States with a coal-fired unit that as of January 1, 2010,
had a capacity of over five (5) megawatts (MW) and that has announced
it will cease burning coal at that unit through a company public
announcement, public utilities commission filing, consent decree,
public legal settlement, final state or federal permit filing, or other
similar means of communication.'')
    Second, by December 31, 2017, the EPA must sign such a notice
promulgating designations for remaining undesignated areas in which, by
January 1, 2017, states have not installed and begun operating a new
SO2 monitoring network meeting EPA's specifications
referenced in this rulemaking. Finally, by December 31, 2020, the EPA
must sign a notice promulgating designations for all remaining
undesignated areas.
    The EPA notes that the schedule imposed by the court will allow at
least the latter two stages of designations to be informed and
benefited by the additional information that is timely obtained
pursuant to this final rule, as appropriate. However, we also note that
the round of designations that is required to be completed by July 2,
2016, will likely be conducted before state air agencies and the EPA
will have been able to implement this final rule, and will instead rely
upon data and information that is separately developed or obtained
during the designations process. Nevertheless, as explained later in
this document, depending on how those areas become designated in 2016,
the rule may still result in additional information that could inform
future assessments of attainment status for such areas.
    The EPA continues to believe that the requirements of this rule for
air agencies to submit a list of sources where further air quality
characterization is needed, and the other data submittal requirements
found in Sec.  51.1203 of this rule, are appropriate steps needed to
better understand SO2 air quality throughout the country,
and are consistent with section 110(a)(2)(B), section 110(a)(2)(K), and
section 301(a)(1) of the CAA. The commenters did not challenge this
view. Section 110(a)(2)(B) indicates that State Implementation Plans
(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 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.'' 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 EPA often establishes and revises monitoring requirements for
implementing NAAQS. Those requirements will not necessarily always
generate new information in time to inform timely area designations
under CAA section 107. See, e.g., 75 FR 81126, 81130, December 27,
2010. The validity of such rules does not depend upon whether
information generated pursuant to those requirements will be gathered
in time to support designations that are timely under section 107.
Here, the commenters have raised no objection to the central premise of
the rule, which is that additional information that better
characterizes air quality near larger sources of SO2 is
warranted and is authorized to be required under sections 110 and 301
of the Act. Irrespective of when the EPA uses this information--for
example, irrespective of whether the EPA promulgates initial
designations of ``unclassifiable'' (and then uses the information
collected pursuant to this data requirements rule in later
redesignations), or whether the EPA promulgates the remaining
designations after the information required here becomes available--the
EPA believes that this rule is authorized and is warranted. Therefore,
in this final rulemaking, the commenters have provided no basis for the
EPA to not require air agencies to submit such SO2
monitoring and modeling data to the EPA, as proposed. The final rule is
fully consistent with the Agency's broad authority under section 110
and 301, as well as with the EPA's authority under CAA section
114(a)(1) to direct any person to provide information as is reasonably
required to improve characterization of ambient air quality near larger
sources of SO2.
2. Legal Authority To Base Air Quality Evaluations on Modeling Data
a. Summary of Proposal
    In the proposal, the EPA stated that existing air quality modeling
tools are technically sound and historically have been used to
characterize SO2 air quality when monitoring data were not
available; therefore, the EPA considers these modeling tools
appropriate for assessing air quality impacts from SO2
emissions. The EPA stated that historical use of modeling to
characterize SO2 air quality concentrations has been
affirmed as technically valid and lawful under the CAA by reviewing
courts. See 79 FR 27448, May 13, 2014.
b. Brief Summary of Comments
    Some industry group commenters stated that the DRR provisions
allowing for modeling to characterize ambient SO2
concentrations go beyond what is necessary to comply with the CAA,
arguing that 40 CFR 50.17 provides that monitoring is the sole basis
for determining attainment. Commenters stated that the precise wording
of 40 CFR 50.17 establishes ambient air monitoring as the only basis
for determining if the SO2 NAAQS is being met because it
specifies that:
    (a) The level of the national primary 1-hour annual ambient air
quality standard for oxides of sulfur is 75 parts per billion (ppb,
which is 1 part in 1,000,000,000), measured in the ambient air as
SO2.
    (b) The 1-hour primary standard is met at an ambient air quality
monitoring site when the 3-year average of the annual (99th percentile)
of the daily maximum 1-hour average

concentrations is less than or equal to 75 ppb, as determined in
accordance with appendix T of this part.
    (c) The level of the standard shall be measured by a reference
method based on appendix A or A-1 of this part, or by a Federal
Equivalent Method (FEM) designated in accordance with part 53 of this
chapter.
    One public interest group commented that the provisions in the
proposed DRR for conducting modeling are consistent with the EPA's
historic use of air dispersion modeling for multiple NAAQS
implementation purposes. This public interest group stated that
dispersion modeling has a lengthy history as an appropriate tool for
use in SO2 designations and other actions, and provided
several references to the EPA's documents and to court rulings to
demonstrate that historic use.
    In contrast, without disputing the fact that the EPA has often
relied upon modeling to inform decisions implementing the
SO2 NAAQS, several state and industry commenters stated that
monitoring, not modeling, has historically been used for designation of
areas as attainment or nonattainment under this and other NAAQS.
Several industry commenters supported the EPA's use of notice-and-
comment rulemaking through the DRR to address certain major issues,
including the use of monitoring and/or modeling to characterize air
quality and make remaining area designations.
c. EPA Response
    This final rule does not make any decisions or determinations
regarding whether any area is in fact meeting or not meeting the NAAQS
based on either monitoring or modeling information. Those decisions
will be made in separate future actions, or have already been made for
some areas in prior actions. See e.g., 78 FR 47191, August 5, 2013.
Therefore, this final rule does not take final action on the issue of
whether it is permissible to implement the commenter's previous quoted
provisions of 40 CFR 50.17(a)-(c) based on a combination of both
monitoring and modeling information where both are available, or
exclusively on modeling information where appropriate modeling
information is available and monitoring is not. The commenters'
objections appear to focus on how future-gathered information resulting
from the rule may or can be used in subsequent NAAQS implementation
actions, but the focus of this rule is on the initial gathering of the
information itself. In future designation, redesignation, or other
implementation actions, commenters may raise their objections to the
validity of information that the EPA relies upon in those specific
actions, but such objections are beyond the scope of this final rule.
    The commenters appear to be raising objections that were also
raised after the EPA's promulgation of the 2010 SO2 NAAQS,
in response to the EPA's final rule preamble discussion explaining the
Agency's then-intended implementation approach under the NAAQS. In
their petitions for judicial review of the NAAQS, several states
claimed that the EPA's discussion of the intended use of modeling in
NAAQS implementation contravened the regulatory text of Sec.  50.17.
However, noting that the petitioners' claims addressed potential final
implementation actions that had not yet in fact occurred, the U.S.
Court of Appeals for the D.C. Circuit dismissed the petitioners' claims
without addressing their merits, or lack thereof. See National
Environmental Development Association's Clean Air Project v. EPA, 686
F.3d 803 (D.C. Cir. 2012). Likewise here, the EPA is not yet taking any
action to apply modeling regarding any decision of whether an area is
or is not meeting the NAAQS.
    In any event, we note that although 40 CFR 50.17(a)-(c) very
clearly sets forth the criteria for determining whether the NAAQS is
met at a monitoring site, it does not by its terms restrict how such
decisions may be made more broadly in areas impacted by SO2
sources, including areas where there are no monitoring sites or where
monitors are not sited at the point of maximum ambient concentration.
Indeed, it is the relative scarcity of such monitors that has caused
the EPA to undertake this rulemaking to enable states and the Agency to
better understand just what the ambient air impacts are from larger
sources of SO2, which may not be captured by the current
limited monitoring network. It is true that 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 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 35551, June
22, 2010.
    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 that 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 atmospheric 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, October 5, 1978.
3. The Use of Monitoring and/or Modeling for Making Decisions About Air
Quality
a. Summary of Proposal
    In the proposed rule, the EPA explained that the current ambient
SO2 monitoring network, on the whole, 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. The EPA
stated that, 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. However, the EPA noted that some areas may not be
conducive to modeling, and for such areas the EPA encouraged air
agencies to consider using enhanced monitoring to characterize air
quality. See 79 FR 27448, May 13, 2014.
b. Brief Summary of Comments
    Several state and industry commenters supported the provision in
the proposed rule allowing air agencies to have the option to use
modeling and/or monitoring to characterize SO2 ambient air
concentrations, as it provides appropriate flexibility for both the
states and affected sources. Several commenters supported the EPA's
observation that modeling may not be appropriate for all SO2
evaluation scenarios, and supported the ability of

states to choose to evaluate NAAQS attainment through either dispersion
modeling or ambient monitoring. However, several state and industry
commenters cautioned that monitoring data should be the primary basis
for such decisions, especially designating nonattainment areas. Several
commenters claimed that, as modeling is frequently affected by factors
such as emissions inputs, meteorological data and local geography, it
is not as accurate or reliable as real-time, multiple-year monitoring.
Other commenters claimed that modeling is advantageous because it
characterizes air quality in all directions around a source with
appropriate accuracy and can be done with less expense than ambient
monitoring, which only characterizes air quality at a single location.
Some industry commenters suggested the text of proposed Sec.  51.1201
be revised to state that monitoring is the EPA's preferred analytical
approach under the rule.
c. EPA Response
    The EPA agrees with commenters who stressed the need to give air
agencies the option to characterize SO2 ambient air quality
through either enhanced monitoring or modeling, and the EPA is
maintaining that approach in this final rule. The EPA believes that the
commenters have not presented any persuasive reasons for changing the
basic positions previously discussed in the preamble to the final rule
of the 2010 SO2 NAAQS rulemaking, the February 2013 Strategy
Paper, or in the proposed rule for why both air quality modeling and
ambient monitoring are appropriate tools for characterizing ambient air
quality for purposes of informing future decisions to implement the
SO2 NAAQS. However, as explained earlier, in this final rule
the EPA is not taking final action to make any determinations regarding
any area's status with respect to attaining or not attaining the NAAQS,
but is only prescribing criteria and a process for how and when air
agencies are to gather and provide to the EPA additional needed
information. How the information is used in subsequent actions
evaluating the attainment status of specific areas will depend upon the
information that air agencies collect in the future and what it shows
about areas' ambient air quality.

B. Source Coverage and Emission Threshold Options

1. Summary of Proposal
    In the proposal, the EPA recognized that the characterization of
air quality in areas around more than 20,000 SO2 sources
nationally would not be feasible. The proposal stated that the key
objective to be achieved by using SO2 source emission
thresholds would be to focus the limited available resources at the
state, tribal, local and federal levels toward characterizing air
quality in areas having the largest SO2 emitting sources due
to the fact that larger sources can be expected to be the most likely
potential contributors to violations of the SO2 NAAQS. The
EPA stated in the proposed rule that, just as NAAQS ambient monitoring
networks are designed to measure air quality in areas meeting specific
criteria where the public is likely to be exposed and violations may be
likely to occur, the SO2 annual emission threshold options
in the rule are designed to meet a similar objective. See 79 FR 27453,
May 13, 2014.
    In considering how to develop effective options for identifying the
minimum set of sources around which states would be required to
characterize ambient air quality, we considered three important issues
and requested comment on each:

--What would be an appropriate emissions metric for identifying
sources?
--Should the threshold options require characterization of smaller
sources in areas with higher populations?
--What would be an appropriate threshold for identifying sources near
which air quality is to be characterized?

    The notice of proposed rulemaking also addressed a number of
additional elements of the implementation of these thresholds. In the
discussion below, the EPA summarizes these additional proposed
features, summarizes comments on these proposed features, and describes
the EPA's responses. Note that this section is structured so that all
the issues related to emissions thresholds are presented together
before proceeding to the comment summaries on these issues, and then to
the EPA's responses and final decision.
a. Emissions Metric: What would be an appropriate emissions metric for
identifying sources?
    The proposal presented a discussion about what emissions-related
metric would be most appropriate for this rule. The proposal noted that
for the 1-hour SO2 NAAQS, the ideal metric for identifying
sources near which air quality is to be characterized would be a 1-hour
SO2 emissions rate. However, the EPA observed that while 1-
hour SO2 emission rate data are available for most
electricity generating units (EGUs) because they operate continuous
emission monitors, many non-EGUs do not operate continuous emission
monitors on all emission points and produce 1-hour data. For this
reason, the proposal stated that the emissions threshold options
presented in this rulemaking should be expressed in terms of annual
emissions of SO2 because annual emissions information is
readily available for all large SO2 sources.
    The EPA requested 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 around which further ambient air quality
characterization with respect to the 1-hour SO2 NAAQS might
be required. The EPA also requested 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 any alternative factor for all SO2 sources
nationally, the time and resources needed to develop a database for
this alternative factor, any associated technical analysis and
rationale for using these other factors in defining source thresholds.
See 79 FR 27454, May 13, 2014.
b. Should the threshold options require air quality characterization
near smaller sources in areas with higher populations?
    In the proposed rule, the proposed emissions threshold option and
the other two options on which the EPA requested comment each had a
``two-pronged'' form. Each potential option was expressed with a higher
emissions threshold for identifying sources located outside of CBSAs
with a population equal to or greater than 1 million persons, and a
lower emissions threshold for identifying sources located within such
CBSAs. The reasoning given for this proposed approach was that a lower
threshold for urban sources could help increase public health
protection because there are more people in an area that could be
impacted by relatively smaller sources. The EPA requested 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 requested 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. See 79 FR
27455, May 13, 2014.
c. What is an appropriate threshold level or levels for identifying
sources near which air quality is to be characterized?
    The EPA proposed one preferred option and took comments on two
additional options. Option 1 (proposed preferred option) would require
ambient air quality characterization around any source with annual
emissions greater than 1,000 tpy and which is located within a 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. Option 2 would require ambient air quality characterization
around sources with emissions greater than 2,000 tpy that are located
within any CBSA 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. 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.
    The EPA requested comment on the preferred option and the other two
options described in the proposal. The EPA also requested comment on
any possible alternatives that might be appropriate for consideration.
The EPA requested comment on the scope of sources for which we would
require data. In addition, the EPA also requested any information
identifying sources that would be identified by these options but that
have confirmed documentation to show that they will shut down in the
next several years.
d. Discretion for Air Agencies and the EPA To Address Additional
Sources
    The EPA noted in the proposed rule that, in addition to meeting the
requirements to provide information regarding areas with sources over
the future promulgated thresholds, there may still be situations where
an air agency would need to characterize air quality for other sources
below the thresholds; specifically, where the air agency, or the EPA
Regional Administrator, determines that they may have the potential to
violate the NAAQS. Application of air quality characterization
requirements was noted to be possibly warranted, for example, where
multiple smaller sources located in close proximity may collectively
exceed the emissions thresholds and/or cause or contribute to NAAQS
exceedances. See 79 FR 27455, May 13, 2014.
2. Summary of Comments
    This section provides a brief summary of comments received on each
of the four source threshold issues identified previously, as well as
additional features of the EPA's proposed implementation of thresholds.
a. Comments on an Appropriate Emissions Metric
    Most commenters that addressed the emissions metric issue supported
using annual SO2 emissions (in tpy) as the appropriate
metric for defining source thresholds. Several commenters stated that
it is most appropriate to evaluate annual emissions since these data
are widely reported to the EPA and are readily available. Some industry
commenters stated that using an annual emissions based threshold
approach for identifying areas to be evaluated would serve to make more
manageable the demands on state, tribal, local and federal resources.
Several other commenters stated that the use of additional factors such
as stack height, 1-hour SO2 emission rate, proximity to
sensitive populations, and topography would make the source
identification process unnecessarily difficult and time consuming. On
the other hand, a few regulatory agency commenters urged the
establishment of supplemental criteria based on short-term spikes in
emissions.
b. Comments on Whether the Options Should Require Characterization Near
Smaller Sources in Areas With Higher Populations
    A number of state and industry commenters supported the application
of a lower emission threshold in urban areas. Some commenters stated
that population centers represent locations of higher potential public
exposure and, therefore, characterization of air quality in these areas
would be more representative of the public's SO2 exposure
risk. Several state and industry commenters stated that a threshold
approach based purely on emissions could inappropriately focus limited
resources on areas with limited to no public exposure. Some state
commenters noted that, as a precedent, a population threshold has been
used to establish the minimum monitoring requirements for the
SO2 NAAQS as well as the NAAQS for nitrogen dioxide, carbon
monoxide, and particulate matter.
    Some commenters stated that many sources located within an existing
CBSA are located on the edge of the boundary in less populated areas
and urged the EPA to consider more refined census data based on
population density. One industry commenter suggested, for example, that
the EPA could use population density data around the affected
facilities out to a radius of 10 kilometers (km) and, if average
population density from the 2010 census in this area exceeds a certain
threshold (e.g., 100 persons/square km), then the lower emissions
criteria would be used. Some tribal commenters, some environmental
group commenters, and some state commenters recommended against
applying different thresholds in less populated areas, in order to
assure that all areas are equally protected against violations of the
air quality standard.
c. Comments on Source Threshold Options
    One public interest group and several states urged the EPA to adopt
the proposed Option 1 level of 1,000 tpy, but apply it uniformly,
regardless of population in order to ensure a basic level of health
protection to people who live around the sources. Some commenters
stated that because modeling has shown that sources with emissions
below 2,000 tpy have the potential to cause or contribute to modeled
NAAQS violations, an emissions threshold of 1,000 tpy is more
appropriate to ensure that air quality characterizations are accurately
capturing potential NAAQS violations.
    Several state and industry commenters supported Option 2 stating it
balances limited agency resources for the implementation of this rule
while still allowing important SO2 emission source areas to
be evaluated. Some industry commenters stated Option 2 appears to be
the best option because the difference between the number of sources
captured by Options 1 and 2 is substantial while the difference in
overall emissions covered by the two options is small.
    Numerous state and industry commenters supported Option 3, stating
it would apply reasonable thresholds without burdening states with
unnecessary modeling or monitoring. One industry commenter stated that
this option would allow states to focus their limited resources on the
areas with the largest 211 sources of SO2 emissions.
    One industry commenter stated that if the EPA decides that either
Option 1 or 2 is preferable, then the source

threshold needs to be revised to take into account the following
additional factors: The distance a source is located from population
centers in general and sensitive populations in particular; stack
heights; topography and meteorological factors unique to the source(s);
and economic conditions that will affect a source's expected
SO2 emissions. This commenter disagreed with the proposal's
statement explaining why the Agency does not believe it necessary for
air agencies to consider such factors, stating that the lack of a
nationwide database with respect to such factors is irrelevant since
the modeling is to characterize localized ambient air quality.
d. Comments on Discretion To Address Additional Areas
    Several state and tribal commenters requested clarification of
criteria the EPA would use to determine additional areas to be
characterized beyond those with sources emitting more than the
applicable threshold. A few commenters offered specific
recommendations, for example to characterize areas of 10 km or 25 km
diameters in which total emissions exceed the threshold but those of no
single source exceeding the threshold. A few commenters recommended
that the EPA should not have the discretion to subject additional areas
to characterization unless total emissions in the areas exceed the
applicable threshold. Some commenters recommended that the rule specify
criteria to be used to identify multi-source areas that would need to
be characterized. Conversely, some commenters recommended that the EPA
not codify any specific criteria, recommending instead that the EPA
provide guidance on how it envisions addressing areas with multiple
sources and rely on the professional judgment of air agency personnel
in consultation with the EPA to identify specific additional areas that
warrant being characterized. Also, one state commenter recommended that
any area ``that, based on the state's knowledge, has the potential to
exceed the NAAQS'' should become subject to requirements for air
quality characterization. Finally, a few industry commenters and a few
state commenters urged that the EPA not have the discretion to subject
additional areas to DRR requirements.
3. EPA Response
    The EPA considered the many and varied comments received on the
source threshold options presented in the proposal. After considering
the comments received and as explained below, the EPA has decided to
establish a requirement for air agencies to identify all sources with
annual SO2 emissions that exceed 2,000 tpy (using emissions
data from the most recent calendar year for which such data are
available) and characterize air quality around such sources according
to the timeline in section IV.C of this preamble. The following
subsections also address the other comments relating to applicability
of the requirements for air quality characterization described
previously.
a. Emissions Metric
    The EPA agrees with the many commenters who expressed support for
using an annual emissions metric because annual emissions data are most
readily available for all large SO2 sources, whereas 1-hour
emissions rate information is not readily available for all
SO2 sources. Since the tpy emissions metric is a common
denominator in the emissions inventory and reporting universe, the EPA
believes that the use of this metric is most appropriate to be required
under a rule that applies broadly to areas with sources that do not
already measure 1-hour emissions rates. Using tpy will provide air
agencies and the regulated community a common, easily verifiable,
straightforward approach for identifying sources around which air
agencies are required to characterize air quality. This approach will
rely on existing emission inventory collection systems that are already
in place. An approach based on tons of emissions per year also should
reduce unforeseen or otherwise uneven application of the requirements
for air quality characterization that could arise if different metrics
are used for different SO2 source sectors to identify areas
for which air agencies are required to characterize air quality.
    The EPA acknowledges that some state commenters suggested inclusion
of a 1-hour emissions rate-based criterion for identifying certain
sources with infrequent, episodic SO2 emissions at
atypically high rates that could impact nearby populations. The EPA
notes that the emissions threshold included in the final rule
establishes only minimum requirements for identifying sources. The EPA
agrees with state commenters who recommended that air agencies should
also characterize areas that, based on their knowledge of sources and
areas, may be at risk of violating the standard. Thus, under this rule
air agencies could also require characterization of air quality near
sources prone to episodic emissions with relatively high rates or
amounts, as appropriate. However, because short-term emissions data are
not available for all SO2 sources, the EPA did not include
in this rule a minimum requirement for identifying source areas needing
air quality characterization based on this metric.
b. Characterization Near Smaller Sources in Areas With Higher
Populations
    The EPA considered the comments received on the issue of whether a
lower emissions threshold should be included for areas with more dense
populations (e.g., CBSAs greater than 1 million population). A number
of commenters appeared to interpret the inclusion of a lower threshold
for areas with higher population as being less protective of the public
in less populated areas. The EPA wants to clarify that this was not the
intention behind the population-inclusive options included in the
proposed rule. The SO2 NAAQS, and all NAAQS, are intended to
provide equal protection for citizens throughout the country. The
proposed use of both population and emissions thresholds as a means to
require air quality characterization was simply one approach to focus
limited federal and state modeling and monitoring resources into
characterizing locations where a greater coincidence of people and
SO2 emissions occur, and thus a potentially greater
potential for exposure is presented. After reviewing the comments on
this issue, however, the EPA has decided not to move forward with the
proposed preferred approach, and instead to apply requirements for air
quality characterization based on emissions levels uniformly across the
country for both more urbanized and less urbanized populations so as to
focus primarily on the size of the sources.
    It should be noted here that any monitoring that occurs pursuant to
this rulemaking is potentially in addition to, or can possibly help to
satisfy, required SO2 monitoring stemming from 40 CFR part
58, appendix D, section 4.4. Those monitors required in 40 CFR part 58,
appendix D, section 4.4 are determined using a unique metric that
accounts for the coincidental occurrences of SO2 emissions
and population, namely the Population Weighted Emissions Index (PWEI).
This rulemaking does not supplant or otherwise modify those existing
requirements.
c. Emissions Threshold
    Regarding the comments EPA received expressing preferences on the
proposed emission threshold options, the EPA notes the wide range of
views. A few commenters recommended alternate thresholds in the range
from 1,000 tpy to 10,000 tpy, or

recommended pairs of thresholds within this range. Some commenters
provided modeling analyses as an indication that sources larger than
12,000 tpy did not cause a violation of the standard, while other
commenters recommended a single emissions threshold of 1,000 tpy and
provided modeling analyses of different sources as an indication that
sources less than 2,000 tpy caused modeled violations. These comments
demonstrate that ambient SO2 impacts can be variable, and
are dependent on many factors other than annual emissions (such as
meteorology, stack height, local topography and plant operations).
These factors can only be assessed through analytical approaches, such
as ambient monitoring or air quality modeling, which take many of these
related factors into account simultaneously. These comments demonstrate
why air quality characterization of the area around these sources is
needed to protect public health in the first place.
    The EPA believes that, for the purposes of establishing a minimum
threshold that prioritizes the resources that will be devoted to
characterizing air quality near SO2 sources nationally, the
2,000 tpy source emissions threshold strikes a reasonable balance
between the need to characterize air quality near sources that have a
higher likelihood of contributing to a NAAQS violation and the
analytical burden on air agencies. This threshold is on the lower end
of the range of thresholds recommended by commenters because sources on
the lower end of the range have the potential to cause or contribute to
violations of the NAAQS. As compared to the preferred option in the
proposal (i.e., 1,000 tpy sources in CBSAs over 1 million people; 2,000
tpy sources not in CBSAs over 1 million people), the 2,000 tpy
threshold would mean that, in the aggregate, air agencies would need to
address air quality near about 35 fewer sources (or 7 percent fewer).
Nevertheless, the total emissions addressed would still account for 89
percent of the SO2 emissions nationally (based on 2011
emissions), very close to the 90 percent level that has been considered
to be reasonable by many stakeholders in the past.\4\ National
SO2 emissions have declined by a significant amount from
2011 to 2013 (around 1.5 million tons, or more than 20 percent), for
various reasons. The EPA assessed the number of sources meeting a 2,000
tpy threshold based on 2013 emissions data now available for EGUs and
2011 emissions data for non-EGUs. Compared to the assessment in the
proposal, which assessed the number of sources meeting the proposed
threshold (1,000 tpy in urban areas/2,000 tpy elsewhere) based solely
on 2011 data, the EPA now estimates that approximately 70 fewer sources
(about 15 percent) will need nearby air quality to be characterized
than was estimated in the proposal. Based on the updated data, the EPA
estimates that already-designated sources plus sources currently
exceeding the final threshold in this rule still would account for 86
percent of national emissions. Under this rule, each air agency will be
required to identify all sources with annual SO2 emissions
that exceed 2,000 tpy (using emissions data from the most recent
calendar year for which such data are available) and characterize air
quality around such sources according to the timeline in section IV.C
of this preamble.
---------------------------------------------------------------------------

    \4\ The May 2012 White Paper and high-level summaries of
stakeholder meetings are available at: http://www.epa.gov/oaqps001/sulfurdioxide/implement.html. These documents and written comments
received from stakeholders are also included in the docket for this
rulemaking.
---------------------------------------------------------------------------

    Of course, if the trend in reduction of SO2 emissions
continues at individual sources, there will also be a corresponding
reduction in national emissions, and both kinds of reductions are
desirable for improving public health, even if that results in fewer
source areas becoming subject to the emissions characterization
requirements in the final rule. Conversely, if the trend reverses and
source emissions increase, more sources and areas will be required to
be characterized under the rule. Thus, the exact number of sources and
areas that will exceed the promulgated threshold when air agencies
begin characterizing areas under the rule cannot be precisely known at
this time, nor can their future percentage share of the national
inventory be precisely estimated. Nevertheless, the EPA believes that
the promulgated threshold strikes a reasonable balance based on the
information the Agency currently has regarding recent historical
SO2 emissions inventory levels. An analysis of potential
source threshold options and associated source coverage, emissions
coverage, and analytical costs is included in an EPA memorandum to the
docket for this rule.\5\
---------------------------------------------------------------------------

    \5\ See also: ``Analysis of Source Threshold Options for the
Final SO2 Data Requirements Rule,'' memorandum to docket
EPA-HQ-OAR-2013-0711, July 16, 2015.
---------------------------------------------------------------------------

d. Discretion To Address Additional Areas
    Section 114(a)(1) of the CAA already provides the EPA authority and
discretion to require emissions sources to install, use and maintain
monitoring equipment and provide other information as the Agency may
reasonably require, even in the absence of this DRR. In addition, the
EPA had several reasons for proposing as part of this rule to reinforce
state and the EPA discretion to also require air quality
characterization around sources with emissions below the proposed
thresholds. The purpose of proposing the use of emission levels as the
criterion for determining applicability of the air quality
characterization requirement is that emissions provide a simple means
of identifying the sources that are most likely to cause or contribute
to violations of the SO2 NAAQS. Nevertheless, the EPA
recognizes that a variety of factors other than emission levels can
influence the likelihood of NAAQS violations. As one example, source
characteristics such as stack height and plume buoyancy can
significantly affect source impacts. As another example, clusters of
multiple smaller sources that are in close proximity can cause as much
impact as a single larger source. Finally, the EPA recognizes that a
variety of other reasons may exist that may warrant further
characterizing air quality in particular areas, which supports
maintaining state and EPA Regional Administrator discretion to require
air quality characterization in the area. The EPA continues to believe
that states and the EPA should retain this authority and that it would
be unreasonable to restrict implicitly, via this rule, the inherent
authority that air agencies already have to require sources of air
pollution to measure their emissions and characterize their impacts.
    For these purposes, the EPA continues to believe that the rule
should make clear that states and the EPA retain the discretion to
subject additional areas to the requirements for air quality
characterization beyond areas with a single source exceeding the
emissions threshold. The use of a simple emission threshold in the rule
provides a convenient means of administering the application of the
requirements for air quality characterization for the majority of
cases. However, the impacts of a given level of emissions vary
substantially, such that many areas with a source or sources that do
not exceed the emission threshold might be known to have a high risk of
contributing to NAAQS violations, potentially resulting in a higher
risk of NAAQS violations than other areas exceeding the emission
threshold. As a result, a rule that sets forth minimum requirements
based on

an emissions threshold cannot reasonably be used to support an
assumption that no further characterization near smaller sources is
warranted, or to preclude authority that air agencies already have to
investigate the impacts of such sources. Therefore, while this rule
requires the air quality characterization near the above-threshold
sources, the EPA and air agencies will also need to consult regarding
the need for the characterization of air quality near sources below the
threshold as well.
    Among cases in which no single source meets the applicable emission
threshold, no simple indicator is available to indicate which of these
cases warrants air quality characterization. For areas with a single
source, the areas could warrant air quality characterization if the
stack height is low, if the plume rise is minimal, if terrain or
meteorology is conducive to high impacts, and/or if emissions are just
slightly below the threshold. For areas with multiple sources,
concentrations are influenced not only by these stack, terrain and
meteorological factors but also by the level of emissions at each
source, the distances between them and the wind directions in the
nearby area. The EPA appreciates the comments urging the establishment
of specific criteria in the rule for identifying additional areas that
warrant air quality characterization, but the EPA finds that these
areas are better identified on a case-by-case basis reflecting a
judgment considering the range of factors that influence the likelihood
of NAAQS violations. That is, the EPA agrees with the state commenter
urging that the rule provide for discretionary coverage of additional
areas, such that additional areas that in the air agency's (and the
EPA's) judgment have significant potential for violating the NAAQS can
be made subject to requirements for air quality characterization on
case-by-case bases.
    Consequently, the EPA is retaining the discretion for air agencies
and the EPA to require additional areas to be characterized beyond
those with a source exceeding the emission threshold. However, the EPA
is not revising the rule to establish specific criteria for identifying
such areas; the EPA is instead relying on case-by-case evaluation of
the various relevant factors to determine which additional areas
warrant air quality characterization.
    For areas with multiple sources, the EPA recognizes that a number
of such areas may have no single source that exceeds the threshold
discussed earlier and yet may have concentrations similar to other
areas with a single source exceeding the threshold. Commonly, such
areas would have multiple sources clustered in relatively close
proximity and would have total emissions at or above the threshold. The
EPA envisions the air agencies and the EPA evaluating multiple source
areas on a case-by-case basis to determine whether the areas warrant
the same priority as areas where a single source has emissions above
the threshold. Generally, the EPA strongly recommends that areas with
multiple sources, where the combined impact would be expected to be as
much as the impact of a typical single source emitting at least 2,000
tpy, should be carefully considered for air quality characterization,
and we expect the EPA Regional Administrators to focus on such areas in
exercising their discretion. As stated previously, a rule that sets
forth minimum requirements based on an emissions threshold cannot also
be reasonably used to support an assumption that no further
characterization near smaller sources may be required. Therefore, in
addition to requiring air quality characterization near sources above
the emission threshold, the rule also preserves the discretion of the
EPA and air agencies to require air quality characterization in
additional areas, which will necessitate consultation on a case-by-case
basis regarding the need for characterization of additional areas
beyond those containing a source exceeding the threshold in this rule.
    Regarding the comments recommending specific criteria for
subjecting multiple source areas to the requirements for air quality
characterization, the EPA believes that too many factors influence the
combined impact for the EPA to establish a single set of criteria for
determining whether each area warrants becoming subject to the
requirements for air quality characterization. Nevertheless, for the
EPA and state agencies considering using their discretion to require
characterization of additional areas, the EPA believes that the
recommendations of these commenters provide good suggestions for where
to begin making such decisions, to be followed by a case-by-case
judgment as to the expected degree of combined impacts.
    In numerous cases, areas include multiple operations that
previously were all part of a single source that now for business
reasons have subdivided their ownership, such that the operations that
previously were a single source must now be considered multiple
sources. For example, in many cases, where previously the area had a
single integrated iron and steel mill, the iron- and steel-making
operations now have separate ownership from the coke-making operations,
such that the former single source has now become two sources. In these
cases, an additional equity concern arises, that otherwise comparable
facilities should not be treated differently based on a business
decision that has no effect on air quality. If the combined emissions
of these now separately-owned operations exceed 2,000 tpy, the impact
would commonly be similar to the impacts of single facilities emitting
over 2,000 tpy, and such groups of separately owned operations would
thus warrant air quality characterization.
    Regarding the commenters who recommended that the EPA stipulate
that an area with multiple sources emitting less than the threshold
should not be required to characterize air quality under the rule
unless the combined emissions exceed the threshold, the EPA does not
agree with this approach. Even for single source areas, the EPA is
preserving the discretion air agencies and the EPA already have to
require air quality characterization where the source emits less than
the threshold but where concern about potential NAAQS violations
warrants further air quality characterization. By the same logic, the
combined impacts of multiple sources may warrant further
characterization even if the combined emissions are less than the
threshold.

C. Data Requirements and Program Implementation Timeline

1. Overall Timeline
a. Summary of Proposal
    In the proposed rule, the EPA proposed an implementation timeline
addressing feedback and concerns raised in previous stakeholder
meetings, which the EPA considered to provide air agencies with
sufficient flexibility and time to pursue either improved monitoring or
modeling to characterize air quality. The EPA designed the schedule to
allow air agencies to account for SO2 reductions that will
occur over the next several years as a result of implementation of
national and state level programs and facility decisions for complying
with such requirements (such as the Mercury and Air Toxics Standards
(MATS)).\6\ The

EPA solicited comments on the feasibility of the implementation of the
proposed timeline. See 79 FR 27456, May 13, 2014. The notice of
proposed rulemaking also included a discussion of when the EPA
envisioned the information could potentially be used in designation
actions.
---------------------------------------------------------------------------

    \6\ In 2012 the EPA promulgated the Mercury and Air Toxics
Standards under Section 112 of the CAA, 42 U.S.C. 7412, that set
emission limits for several hazardous air pollutants. See 77 FR 9304
(Feb. 16, 2012). Installing the technology necessary to reduce
emissions directly regulated by the MATS rule has already reduced
the emissions of SO2. Id. at 9305. On April 15, 2014, the
D.C. Circuit denied 26 consolidated petitions for review of the MATS
rule brought by state, industry, and environmental petitioners in
White Stallion Energy Ctr. v. EPA, No. 12-1100 (and consolidated
cases) (D.C. Cir.). The Supreme Court has reversed and remanded the
D.C. Circuit's decision for further proceedings. Michigan v. EPA,
Nos. 14-46, 14-47, 14-49, 2015 WL 2473453 (June 29, 2015). However,
the MATS rule remains in effect at this time.
---------------------------------------------------------------------------

b. Brief Summary of Comments
    Several state and industry commenters agreed that the EPA's
proposed timeline was reasonable for acquiring data by either modeling
or monitoring, and for evaluating the submitted data. Many also agreed
that it would be a reasonable schedule for supporting the issuance of
designations and submittal of any SIPs, provided future schedules for
those actions accommodate the schedule for implementing the rule.
However, a larger number of state and industry commenters asserted that
the time allotted for installation of monitors was not sufficient. One
state commenter stated that the feasibility of the schedule will depend
upon the threshold option selected by the EPA. Another state commenter
supported the timeline that the EPA proposed as long as the EPA
finalizes the rule by late 2014 and added that, if promulgation is
delayed, the timeline should be adjusted by as many weeks or months as
the delay in finalizing the rule. Some state and industry commenters
recommended an extension of at least 1 year on all the proposed actions
listed in the implementation timeline. Other commenters felt that the
proposed timeline was flawed for multiple reasons and is, therefore,
not achievable.
c. EPA Response
    The EPA recognizes the logistical and financial challenges that
were identified by commenters with respect to the timeline. In
response, the final rule contains changes to provide additional time
for air agencies to determine whether to use modeling or monitoring to
characterize air quality near their affected sources, discussed later
in this section. However, the final rule retains the proposed deadlines
for commencing monitoring or providing modeling. The Agency
acknowledges that these deadlines do not provide as much time as some
commenters would prefer; however, the EPA believes that these deadlines
can be achieved with the appropriate planning, coordination, and
program implementation by air agencies. The EPA notes that if air
agencies conclude that the timeline and resource burdens associated
with installing and conducting improved monitoring are not feasible for
particular areas, they may instead choose the modeling approach, which
is generally less expensive and can be performed more expeditiously
than monitoring, to characterize air quality. Alternatively, in some
cases the source owner and the air agency may be able to establish by
January 2017 a federally enforceable requirement limiting emissions to
less than 2,000 tpy, with the result that further modeling or
monitoring in that area would not be required under the rule unless air
agencies or EPA Regional Administrators conclude it is otherwise
warranted. Because the purpose of this rule is to obtain improved air
quality information in an efficient manner in order that these data may
be used in future actions (such as area designations, redesignations,
or other actions designed to ensure attainment of the 2010
SO2 NAAQS) to protect the public from the short-term health
effects associated with exposure to SO2 concentrations that
exceed the NAAQS, the EPA believes it would not be appropriate to
further extend the timelines for air quality characterization in the
rule.
    The EPA believes that any further delay in air quality
characterization around sources identified as a result of this
rulemaking would delay the implementation of the SO2 NAAQS
and, therefore, would impede public health protection in areas that in
the future show violations of the standard based on the data to be
gathered under the rule. The EPA also believes that any significant
delays in monitors becoming operational past the date of January 1,
2017, will certainly delay the potential for monitoring data to be used
to inform actions that depend upon ambient concentration assessments,
possibly past calendar year 2021. Finally, the EPA notes that under the
terms of the March 2015 consent decree, in order to avoid the EPA being
required to designate an area by December 31, 2017, an air agency will
need to have installed and begun operating the new SO2
monitoring system no later than January 1, 2017.
    The Agency believes that it is very important to maintain the
proposed timetable for conducting modeling and installing monitoring
sites because of the need for these new data to be available to support
future determinations concerning the attainment status of areas. The
EPA encourages each air agency to engage in early dialogue with the
appropriate EPA Regional Office and with the identified applicable
facilities in order to meet the requirements of the rule. In
particular, in light of the reality of the sometimes complex process of
identifying potential monitoring locations, securing funding, and
installing an appropriate number of new sites, if an air agency is
considering the monitoring approach for one or more areas, early
coordination should improve the air agency's potential for success in
meeting the timing and requirements of the rule.
    The final rule retains the January 15, 2016, date for submittal of
a list of sources, because the EPA expects that this information is
relatively straightforward to obtain, and it is beneficial for planning
purposes to have this list available as soon as possible. However, as
mentioned previously, in light of comments, the EPA is promulgating a
schedule that provides an additional six months for the air agency to
specify how it plans to address the area around each listed source. The
EPA is promulgating a schedule in which July 1, 2016, is the deadline
for selecting among the monitoring approach, the modeling approach, or
establishing source emission requirements. If the air agency selects
the monitoring approach for a source area, it must also include in the
annual monitoring plan (also due by July 1, 2016) information about any
new monitoring sites it will establish by January 1, 2017. If the air
agency selects the modeling approach for a source area, it must also
submit a modeling protocol at that time. If the air agency chooses the
option of establishing an enforceable source limit or limits as an
alternative to air quality characterization, it must also at that time
provide a description of the planned emission limitation, including
such information as emission rate, averaging time, and expected legal
mechanism for making the limitation federally enforceable. To suffice
as an alternative to the characterization requirement, the emission
requirements or limits would need to be adopted by the air agency, made
federally enforceable, and require compliance by January 13. 2017.
Further discussion of the rationale for these revisions to the
timetable is provided in the relevant subsections that follow. Table 1
shows

the final rule timetable, including this revision.

                Table 1--Timeline for DRR Implementation
------------------------------------------------------------------------
               Date                                Action
------------------------------------------------------------------------
From promulgation of this rule to   Air agency and the EPA Regional
 January 15, 2016.                   Office consult on list of SO2
                                     sources; air agency submits its
                                     list of sources to EPA by January
                                     15, 2016.
July 1, 2016......................  Air agency specifies for each source
                                     whether it will characterize air
                                     quality with modeling, characterize
                                     air quality with monitoring, or
                                     establish a federally enforceable
                                     requirement limiting annual
                                     emissions of the source to less
                                     than 2,000 tpy. For source areas to
                                     be modeled, the air agency submits
                                     a modeling protocol. For source
                                     areas to be monitored, the air
                                     agency submits information about
                                     any new monitoring sites it will
                                     establish by January 1, 2017. For
                                     areas where enforceable emission
                                     limits will be established as an
                                     alternative to air quality
                                     characterization, the air agency
                                     submits a description of the
                                     planned emission limit.
January 1, 2017...................  Air agency ensures that SO2 monitors
                                     to satisfy the Data Requirements
                                     Rule are installed and operational.
January 13, 2017..................  For any source identified for
                                     modeling pursuant to the July 1,
                                     2016, milestone, air agency submits
                                     modeling analyses. For any source
                                     identified for emission limit
                                     approach, air agency submits
                                     documentation showing that limits
                                     requiring annual emissions to be
                                     less than 2,000 tpy are effective
                                     and federally enforceable.
May 2020..........................  For any source area identified for
                                     monitoring approach, air agency
                                     certifies 2019 monitoring data,
                                     enabling official design values for
                                     the 2017-2019 time period to be
                                     calculated.
------------------------------------------------------------------------

    In addition, while the proposed rule discussed how the timing of
the implementation of this rule would fit with the anticipated schedule
for completing area designations, the proposed rule did not itself
purport to establish a binding schedule for completing designations.
Table 2 provides information concerning the schedule for taking action
to designate areas in the future in accordance with the March 2015
consent decree, but is intended for informational purposes only. In
this rulemaking, we are not addressing comments received on the
proposed rule concerning the designation process because those issues
would be beyond the intended scope of this rulemaking.

   Table 2--Anticipated Schedule for Future Rounds of SO2 Designations
------------------------------------------------------------------------

------------------------------------------------------------------------
July 2016.........................  Date by which the EPA must issue
                                     final designations for sources
                                     meeting specific criteria in the
                                     March 2015 consent decree.
August 2017.......................  Expected date by which the EPA would
                                     notify states of intended
                                     designations based on air quality
                                     data obtained pursuant to the first
                                     round of the data requirements
                                     rule.
December 2017.....................  Date by which the EPA must issue
                                     final designations for a majority
                                     of the country (pursuant to March
                                     2015 consent decree), except for
                                     areas with new monitoring networks
                                     commencing operation by January 1,
                                     2017.
August 2019.......................  Anticipated due date for state
                                     attainment plans for areas
                                     designated nonattainment in 2017.
May 2020..........................  Certification of 2019 monitoring
                                     data is required by this date.
August 2020.......................  Expected date by which the EPA would
                                     notify states of intended
                                     designations for the remainder of
                                     the country.
December 2020.....................  Date by which the EPA must issue
                                     final designations for the
                                     remainder of the country (pursuant
                                     to March 2015 consent decree).
August 2022.......................  Anticipated due date for state
                                     attainment plans for areas
                                     designated nonattainment in 2020.
------------------------------------------------------------------------

2. Issues Related to Submittal of List of SO2 Sources Where
Air Quality Is To Be Characterized, and Election of Modeling or
Monitoring
a. Submittal of List of Sources Where Air Quality Is To Be
Characterized
i Summary of Proposal
    In Sec.  51.1203(a), the EPA proposed to require each air agency to
submit to its respective EPA Regional Administrator by January 15,
2016, a list identifying the specific sources in the state around which
SO2 air quality is to be characterized. The EPA stated 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 Sec.  51.1203 of the
proposed rule, are appropriate steps necessary to characterize
SO2 air quality throughout the country, and are consistent
with sections 110(a)(2)(B), 110(a)(2)(K) and 301(a)(1) of the CAA. In
the docket, the EPA provided a preliminary list of sources that
appeared to meet the EPA's proposed thresholds (based on 2011 emissions
data), and the EPA solicited comments on this list. See 79 FR 27446,
27461, May 13, 2014.
ii. Brief Summary of Comments
    Some state and industry commenters opposed the requirement that, by
January 15, 2016, air agencies must submit a list of sources. Some
commenters also stated that submitting a list of sources is unnecessary
for various reasons such as data are already made publicly available on
an annual basis through the national emissions inventory; that it does
not make sense to establish a list that is expected to change; and that
air agencies and the EPA can work cooperatively without a binding
requirement. Commenters also recommended that any listing of sources,
and any identification of the selected air quality characterization
approach for specific source areas, should wait until the January 2017
analysis for individual sources or areas is to be completed. One state
commenter

indicated that they did not find merit in the citations that the EPA
provided in the proposal regarding the authority for requiring this
list submittal. This commenter stated that the CAA section 110(a)(2)
citations address the requirements for SIP submittals by states for
implementation, maintenance and enforcement of the standard. Several
state commenters also suggested updates or revisions to the EPA's
preliminary list of sources potentially subject to this rule.
iii. EPA Response
    The EPA does not agree with commenters who claim that submittal of
an initial list of sources near which air quality is to be
characterized is not needed in January 2016. The EPA believes that it
is important to receive the list of source areas to be characterized
under the rule by January 15, 2016, because it will provide timely
clarity for both EPA and the air agency about which sources and
associated areas are to be characterized for air quality under this
rule. In EPA's judgment, such timely clarity is essential to the
success of the characterization efforts that follow the source
identification step. The list will identify the sources in the state
that exceed the 2,000 tpy emissions threshold based on the most
recently available emissions data, as well as any other source or
sources identified by the air agency or the EPA Regional Administrator
as warranting air quality characterization. Development of this initial
list will be important for air agencies as they prepare to generate
timely air quality information that may be used to inform future
designation, redesignation, or other decisions concerning attainment of
the 2010 SO2 NAAQS.
    Retaining this deadline will provide the early opportunity for the
air agency and the EPA to discuss and resolve questions about whether
air quality characterization should be required for a particular area
if, for example, emissions are low in some years and high in others, if
an area has a cluster of smaller sources, or if source-specific or
other factors may warrant the need for air quality characterization. As
a further example, there may also be situations for which the state and
the EPA need to reach agreement on what constitutes the most recent
year of emissions data for specific EGU and non-EGU sources. The list
requirement and deadline will ensure resolution of such questions in
time to enable further characterization requirements to be met.
    Thus, the EPA is retaining the January 2016 deadline, as proposed,
for submittal of the list of sources in order to initiate an orderly
process to obtain additional information on ambient SO2
concentrations, and ensure these data are available to support actions
taken for the implementation of the 2010 SO2 NAAQS. While
the Agency has previously acknowledged that some of the deadlines in
this rule do not provide as much time as some commenters would prefer,
the EPA believes that the schedule for providing the list of sources is
a relatively straightforward exercise that can be accomplished within
the required time frame.
    The EPA strongly encourages each air agency to consult with its
respective EPA Regional Office to identify sources exceeding the
emission threshold in the final rule, and to identify any other areas
near sources that do not exceed the emission threshold but which would
be appropriate for further air quality characterization. It will be
important for air agencies and the EPA to carry out this consultation
process as early as possible and to reach agreement on the list of
sources to characterize under the rule as quickly and efficiently as
possible. It is also important to note that, due to the overlap between
the criteria for inclusion of sources in this final rule and those in
the March 2015 consent decree, all of the sources identified in the
March 2015 consent decree should also be included on the January 2016
list of sources required for characterization under this rule. The
consent decree requires the designation in July 2016 of areas
associated with an initial list of sources meeting specific criteria.
Depending on the specifics of those designation actions, information
developed to support those actions may serve to meet some or all of the
requirements of this data requirements rule. (See section IV.E, Other
Key Issues and Comments, for more discussion of these issues.)
    Regarding comments about EPA's authority to require submittal of a
source list, the EPA believes that the requirements of this rule for
air agencies to submit a list of source areas identified for further
air quality characterization, and the other data submittal requirements
found in Sec.  51.1203 of this rule are appropriate steps needed to
better understand SO2 air quality throughout the country,
and that including such requirements is consistent with sections
110(a)(2)(B), 110(a)(2)(K), and 301(a)(1) of the CAA.
    Section 110(a)(2)(B) of the CAA 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) of the CAA
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 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.'' Although both of these provisions
direct what air agencies are required to include in SIPs, they clearly
support the authority of the EPA to prescribe requirements that the
information that SIPs are to ensure can be provided is collected in the
first instance.
    In addition, CAA 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 that
additional information is collected and provided so that air agencies
and the EPA can ensure attainment and maintenance of the SO2
NAAQS throughout each state. Finally, the EPA notes that CAA section
114(a)(1) also provides broad authority for the EPA, for the purposes
of developing any implementation plan under section 110 or carrying out
any provision of the CAA, to require monitoring and provision of other
information the Agency may reasonably require (such as modeling
information).
    The EPA appreciates the comments on the preliminary list of sources
that appeared likely to be subject to this rule as proposed. The EPA
acknowledges that, for various reasons, such a list of sources could
change up until the time that the list is required to be submitted.
Accordingly, such a list is not being promulgated as part of this rule.
The EPA plans on continuing consultations with air agencies regarding
the source areas that the final rule will require to be characterized.
b. Choice Monitoring or Modeling
i. Summary of Proposal
    In Sec.  51.1203(b), the EPA proposed to require each air agency to
state whether it will characterize air quality through improved ambient
air quality monitoring or through air quality modeling techniques by
January 15, 2016. The EPA also proposed in Sec.  51.1203(b) that in an
area with multiple subject 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. For

situations where multiple sources are located in proximity across state
boundaries, the EPA recommended that the relevant air agencies work
together to determine a common analytical approach for assessing air
quality in that area. See 79 FR 27460, May 13, 2014.
ii. Brief Summary of Comments
    Several state and industry commenters stated that the EPA should
provide a more reasonable schedule for air agencies to elect the
monitoring option under the proposed rule. Some commenters suggested
that air agencies should have until January 1, 2017, to make this
determination because they could benefit from using initial modeling
results to inform this decision, such flexibility would reduce burdens
on state regulators, and it could lead to more accurate determinations,
while not impacting the EPA's expected attainment dates for such areas
should the areas become designated nonattainment.
iii. EPA Response
    In response to these comments, the EPA is providing additional time
for making the election of modeling or monitoring (or, as discussed
later, for making the election of an alternative approach that
enforceably limits an applicable source's emissions). Accordingly, the
deadline for this election will be July 1, 2016. The EPA recognizes
that evaluating the relative merits of modeling and monitoring for any
particular area, including identification of funding sources for any
new monitoring that might be under consideration, warrants more time
than was provided under the proposed rule. Consistent with this
revision, the EPA is also revising the deadline for air agencies using
modeling to submit modeling protocols for the applicable areas. Thus,
under the final rule, by July 1, 2016, the air agency must submit its
selection of whether each area will be characterized through modeling
or monitoring and, depending on that selection, either must submit a
modeling protocol or must include information in the Annual Monitoring
Network Plan that specifies the monitoring to be conducted to address
the requirements of this rule. The EPA believes that this revised
deadline still provides for timely planning for air quality
characterization to occur (through modeling) or begin (through
monitoring) at the beginning of 2017. Conversely, the EPA does not
agree that any later deadline for selecting the means of addressing air
quality characterization requirements would provide the time and
flexibility to address in a timely way any issues that arise after the
selection is made. The result would be that a later deadline for this
selection could jeopardize timely receipt of information characterizing
air quality.
    Notwithstanding this revision, the Agency encourages air agencies
to start their investigation of this issue as soon as practicable. The
EPA strongly encourages each air agency to consult with its respective
EPA Regional Office to identify sources exceeding the emission
threshold in the final rule and any other sources that do not exceed
the emission threshold but near which further air quality
characterization would be warranted. Similarly, the EPA strongly
encourages air agencies to hold early discussions regarding the manner
in which modeling or monitoring might be used. As one example, if the
air agency believes that the existing monitoring network suffices to
characterize air quality, early discussions with the EPA would be
essential for assuring that the intended selection of monitoring is
based on appropriate assumptions regarding the network's ability to
characterize air quality near the applicable source(s) without further
network adjustments.
c. Use of Most Recent Publicly Available Data
i. Summary of Proposal
    In Sec.  51.1202, the EPA proposed that the air agency should
identify applicable sources of SO2 based on the most recent
publicly available annual SO2 emissions data for such
sources. The EPA specified in proposed Sec.  51.1200, that ``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
requirements to report continuous emissions monitoring data for EGUs
subject to the acid rain program). The EPA stated that, by January 15,
2016, data for 2014 would be available for EGU sources and 2013 data
would be available for non-EGU sources. By considering the most recent
emissions data, the EPA noted that air agencies 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. The EPA included in the docket to the proposed rule a
preliminary list of sources that appeared to meet the criteria
described in the EPA's proposed source threshold approach and requested
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 from that preliminary list. See, 79 FR 27457, May 13, 2014.
ii. Brief Summary of Comments
    Several state and industry commenters generally supported the
approach that the basis for the emissions to be compared to the
threshold would be the latest available 1-year of SO2
emissions data. One industry commenter stated that using the most
recent year of data ensures that any recent emissions reductions that
have occurred will be properly taken into consideration.
    One public interest group commenter stated that using the most
recent year as a snapshot may fail to capture sources that simply have
a low year, but normally emit at higher levels, and recommended that
the EPA require that facilities only be excluded under the threshold
if, in prior years, the facilities had similar low total emissions
below the limit. A number of states provided information suggesting
specific modifications to the EPA's preliminary list of sources.
    One commenter stated that the rule should not take an ``all in'' or
``all out'' approach based on a simple analysis of 1 year's emissions
or even a 3-year average of emissions alone. The commenter stated that
the EPA seems to allow, or consider, the potential addition of non-
threshold-meeting sources but does not appear to recognize that there
may be instances where the air agencies knowledge and judgment warrants
exclusion of threshold triggering sources. They suggested that air
agencies should be able to take into consideration operational changes
during the 3-year period to determine if a different methodology is
appropriate for determining if a source should be a part of the
analysis.
iii. EPA Response
    The EPA continues to believe that the most appropriate generally
applicable basis for determining applicability of the air quality
characterization requirements is the most recent available year of
emissions data for a stationary source as reported to the EPA in
accordance with any existing regulatory requirement. As we have
previously explained, SO2 emissions are trending downward,
due to numerous national and regional requirements that have recently
been adopted and are taking effect. The Agency believes it is
reasonable to account for this trend by basing applicability for this
data requirements rule on the most recent available year of emissions.

    By January 15, 2016, the EPA would expect that 2014 data will be
available for all EGU sources, and 2015 data may be available for many
EGUs in accordance with the requirements of the Acid Rain program and
other emission trading programs that require data certification soon
after the end of the year. These sources report hourly emissions data
to the EPA on a quarterly basis. Emissions data for large
SO2 sources also would be available from annual reporting
required for the AERR. Every 3 years (i.e., 2011, 2014, 2017 and so
on), air agencies must submit to EPA emissions data for SO2
sources with the potential to emit more than 100 tpy. In other years,
the AERR requires states to report emissions data for SO2
sources with the potential to emit more than 2,500 tpy. These annual
reports under the AERR are due 12 months after the end of the emissions
year. Thus, the EPA would expect that in January 2016, states would
have emissions data for calendar year 2014 available for non-EGU
sources over 100 tpy potential to emit. Emissions reporting
requirements for the Acid Rain and AERR programs would be expected to
cover the vast majority, if not all, of the sources subject to the
SO2 DRR.
    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 rule or not. Although identifying sources based on
the most recent year of emissions is a reasonable basis for
prioritizing limited modeling and monitoring resources for
characterizing current air quality, the EPA recognizes the concern of
some commenters that there may be sources that in the most recent year
have emissions that are lower than normal and are not representative of
normal operations. In these cases, i.e., where recent emissions are
below 2,000 tpy but no controls have been installed and past
representative emission levels are typically above 2,000 tpy, the state
and the EPA should consider using their discretion to require
additional air quality characterization near such sources.
    The EPA also recognizes the concern about sources for which the
most recent year's emissions are unrepresentatively high, i.e., that
some sources may have recent year emissions above 2,000 tpy but
normally emit below that level. Given the trends in emissions, the EPA
believes that situation will be relatively rare. Moreover, the
existence of such sources does not negate the general conclusion that
recent emissions data are an appropriate means for targeting limited
modeling and monitoring resources for characterizing current air
quality.
    The EPA believes that a rule that prioritizes resources based on
the most recent year's data is more appropriate for a broader range of
circumstances. The EPA notes, however, that after a source is initially
identified, the air quality characterization requirements require air
agencies to provide at least 3 years of monitoring or modeling data.
The availability of such data will provide the opportunity to give
appropriate consideration to representative emissions when using such
data, as appropriate to the specific use.
d. Shutdowns and Limitations on Emissions Levels by January 13, 2017
i. Summary of Proposal
    The EPA noted in the proposed rule that 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 to a consent
decree or other legal requirement), or may choose to shut down, prior
to January 2017 (when the air agency should have ambient monitors
operational and air quality modeling completed). The EPA proposed 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 13, 2017, the air agency can provide the EPA with a legal
agreement confirming that the listed source has permanently and
enforceably shut down, then under the proposal the air agency would
have no further obligation regarding air quality characterization for
this source pursuant to this rulemaking. See 79 FR 27458, May 13, 2014.
ii. Brief Summary of Comments
    One state commenter recommended that the EPA revise the rule to
exempt from the list those sources that take an enforceable emission
limitation below the 2,000 tpy emissions threshold before January 13,
2017, even if reductions and applicability of the limitation are only
realized within a reasonable time after January 13, 2017. Several
commenters stated that there is no basis to distinguish between
situations in which a source may provide documentation it will shut
down, and cases where an enforceable limit is established, because in
each case the source would no longer meet the criteria for
characterization under the rule. Another commenter stated that sources
should be able to take federally enforceable limits on a tpy basis
prior to the January 13, 2017, date for air agencies to submit their
modeling analysis to avoid characterization under the rule. Another
state commenter stated that requiring sources to implement controls
prior to submittal of future required SIPs would encourage sources to
make emission reductions while allowing sufficient time to implement
these actions.
    Some state and industry commenters recommended that sources should
have until the applicable attainment date for a designated
nonattainment area to complete any enforceable actions that achieve
attainment, provided those actions are committed to by January 13,
2017. Commenters stated that there is insufficient time for sources to
take all the actions needed to implement these controls (including
conducting modeling, determining the required reductions and control
strategies, procuring capital funds, obtaining permits and installing
equipment) under the proposed rule. Commenters stated that allowing
sources to implement controls after January 13, 2017, but before future
attainment dates supports the EPA's desired outcome of achieving
emission reductions as quickly as possible; in contrast, under the
EPA's proposal, sources unable to have enforceable limits in place by
the January 13, 2017, deadline have little incentive to take any action
prior to the anticipated designation deadline of 2020.
iii. EPA Response
    The EPA is finalizing the proposed approach to allow a state with a
source that is in operation as of January 15, 2016, but that provides
documentation that the source will shut down permanently prior to
January 13, 2017 pursuant to a federally enforceable mechanism (e.g.,
source-specific SIP revision or minor NSR permit revision submitted to
the EPA by January 13, 2017), to avoid being subject to the requirement
to characterize air quality in the vicinity of the source.
    As a result of comments received on the proposed rule, the EPA is
clarifying how this exclusion would work relative to the requirement
for development and submittal in January 2016 of the list of sources
near which air quality is to be characterized. The EPA appreciates that
there might be a source whose most recent year of actual emissions
exceeds the threshold for inclusion on the list, but for which the
state has already adopted, or will soon adopt, enforceable requirements
to shut down by January 2017. Such a source may have significant
emissions during the most

recent available year, or may even still be in operation on January 15,
2016. The EPA has determined that the clearest way to implement the
exclusion from the air quality characterization requirement is to
require that the air agency initially identify such a source on its
list for SO2 air quality characterization because emissions
in the previous year, which serve as the basis for listing under this
rule, exceeded the emissions threshold. However, the final rule now
includes language in Sec.  51.1203(b) allowing the air agency to
indicate by July 1, 2016, that it will provide the EPA with a federally
enforceable requirement confirming that the source will be permanently
and enforceably shut down by January 13, 2017. For a source for which
the air agency provides documentation of a federally enforceable
requirement that the source will shut down, the air agency will have no
further obligation regarding air quality characterization pursuant to
this rulemaking. This approach accomplishes the intent of the proposal
by implementing the approach in a more clear and straightforward
manner.
    Commenters on the proposed rule also suggested that, in a similar
manner, an air agency should not be subject to the air quality
characterization obligation for any source that is initially on the
list of sources due in January 15, 2016 (based on most recent actual
emissions), but that becomes subject to a federally enforceable
requirement to limit annual SO2 emissions to below the 2,000
tpy emissions threshold. The EPA finds merit in those comments that
suggest that the rule allow for similar treatment for sources that
become subject to a federally enforceable emission limit as is allowed
for sources that provide documentation that they will shut down. The
EPA has revised the final rule accordingly, and provides further
discussion below. However, EPA does not agree with commenters who
suggest that sources should have until the applicable designation date,
or attainment date for an area that is designated nonattainment, to
implement controls that were committed to prior to January 13, 2017.
Relying on commitments for emission reductions to occur after 2017
would not be consistent with the main focus of this rule, which is to
provide current, updated information on priority SO2 sources
to the EPA beginning in early 2017 that will inform future area
designations (now required in December 2017 and December 2020 per the
March 2015 consent decree).
    As indicated above, a source would be listed for air quality
characterization if its most recent emissions were above the 2,000 tpy
threshold. However, the final rule also allows the air agency to meet
the requirements of this rule by submitting a federally enforceable
emissions limitation (e.g., source-specific SIP revision or minor NSR
permit revision) to the EPA by January 13, 2017, that requires the
affected source to reduce allowable emissions at the source to an
annual rate below the 2,000 tpy threshold level by January 13, 2017. By
July 1, 2016, the air agency would be required to identify the sources
on the list for which it would be using such an approach as an
alternative to modeling or monitoring. For such a source identified on
the list, if the affected air agency has adopted and the source has
become subject to federally enforceable control measures lowering
emissions below 2,000 tpy by January 13, 2017, the air agency will
generally not be required to further characterize the impacts from the
source's emissions solely due to its size as of January 15, 2016.
    Although air agencies may follow this option as an alternative to
characterizing areas with sources that limit their emissions to below
the 2,000 tpy size threshold, the EPA believes that air agencies and
the EPA must apply judgment as to whether there are still reasons to
characterize these areas due to other factors. As discussed above, some
areas where all sources emit less than 2,000 tpy may nevertheless
warrant air quality characterization, for example because the area has
a cluster of sources with intermediate emission levels or because the
characteristics of a source or the area warrant it. Thus, some areas
with all sources limited to below 2,000 tpy may still warrant air
quality characterization. Therefore, the EPA urges air agencies to
consult early with the EPA regarding areas that are under consideration
for being addressed in this manner, in order to develop a common
understanding as to whether emission limits under consideration would
suffice as an alternative to air quality characterization for the area.
    The EPA believes that allowance for this alternative emission limit
approach is not only consistent with the intent of this rule to
prioritize resources to focus on the largest sources of SO2,
but it also has the additional benefit of providing an incentive for
early emission reductions to occur which will improve air quality in
these areas in an expeditious manner. However, we do acknowledge the
distinction between a formerly large source with no future emissions
and a source with reduced but continuing emissions. The Agency does not
believe it would be appropriate to provide that the latter source can
be excluded from evaluation in all cases. It may be that a source with
emissions newly limited to below the applicability threshold--
particularly one with limits established just below the threshold--may
warrant further characterization, just as a source with actual
emissions below the threshold may warrant characterization in some
instances. For example, air quality characterization would continue to