Data Requirements Rule for the 2010 1-Hour Sulfur Dioxide (SO2, 51051-51088 [2015-20367]

Agencies

• ENVIRONMENTAL PROTECTION AGENCY

[Federal Register Volume 80, Number 162 (Friday, August 21, 2015)]
[Rules and Regulations]
[Pages 51051-51088]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2015-20367]



[[Page 51051]]

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

[[Page 51052]]


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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 https://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 
https://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 (202) 566-1744 and the telephone number for the Air and 
Radiation Docket Information Center is (202) 566-1742. For additional 
information about the EPA's public docket, visit the EPA Docket Center 
homepage at: https://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 (919) 541-0906, or by email at wallace.larry@epa.gov; or Mr. Rich 
Damberg, Office of Air Quality Planning and Standards, U.S. 
Environmental Protection Agency, by phone at (919) 541-5592, or by 
email at damberg.rich@epa.gov.

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: https://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

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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: https://www.epa.gov/oaqps001/sulfurdioxide/implement.html. These documents and written comments 
received from stakeholders are also included in the docket for this 
rulemaking.
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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

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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

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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

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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

[[Page 51057]]

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

[[Page 51058]]

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

[[Page 51059]]

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

[[Page 51060]]

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

[[Page 51061]]

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: https://www.epa.gov/oaqps001/sulfurdioxide/implement.html. These documents and written comments 
received from stakeholders are also included in the docket for this 
rulemaking.
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    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

[[Page 51062]]

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

[[Page 51063]]

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

[[Page 51064]]

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

[[Page 51065]]

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

[[Page 51066]]

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.

[[Page 51067]]

    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

[[Page 51068]]

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 
be warranted in areas with other sources over the applicability 
threshold, and in areas where no single source has emissions over the 
threshold but the combined emissions of multiple sources warrant air 
quality characterization. In evaluating such cases, the air agency 
should account for all source emissions contributing to ambient 
concentrations in the area, including those remaining emissions from 
the source that has just reduced its levels to below the applicability 
threshold. For this reason, the rule does not automatically exempt 
sources with emissions limited to less than 2,000 tpy from air quality 
characterization requirements; the rule instead provides that the air 
agency or the EPA may judge that the area should continue to be 
required to characterize air quality notwithstanding the new emission 
limits. Air agencies are thus advised to consult with their EPA 
Regional Office before pursuing this alternative to air quality 
characterization for a particular source area.
3. Issues Related to Submittal of Modeling Protocols
a. Summary of Proposal
    For source areas that an air agency identifies are to be evaluated 
through air quality modeling, the EPA proposed in Sec.  51.1203(d) that 
an air agency must also provide a modeling protocol to the EPA Regional 
Administrator for review by January 15, 2016. In the proposal, the EPA 
stated that the EPA Regional Offices would review the submitted 
information and consult with the air agency as expeditiously as 
practicable, either approving the submitted information in a similar 
manner to approval of annual monitoring plan updates, or having further 
discussion with the air agency if adjustments to modeling protocols are 
warranted. See 79 FR 27458, May 13, 2014.
b. Brief Summary of Comments
    Several commenters stated that 1 year is not enough time to 
complete modeling demonstrations. These commenters stated that 
depending on the scope of the modeling required, it would take 2 to 4 
years to complete the

[[Page 51069]]

entire process. The modeling time estimate will increase if refined 
modeling is required to site monitors and if the EPA expects the states 
to submit modeling protocols and not conduct any refined modeling to 
support monitor placement decisions until the EPA approves the 
protocols.
    Several state and industry commenters objected to the EPA oversight 
of the modeling protocols. Commenters were concerned that the EPA could 
not review the plans in a timely manner and could cause delays in the 
process. One state commenter stated that, if this oversight and 
approval is finalized in this rule, they have serious concerns about 
whether 2 years from promulgation of the final rule is a reasonable 
amount of time for air agencies to prepare the necessary data inputs 
and conduct such modeling for all subject sources. One state commenter 
suggested that the EPA should clarify that air agencies could provide 
to the EPA a modeling protocol framework for review and approval, and 
that source-specific review of protocols should be left up to the 
respective state agency, consistent with past practices in PSD SIP 
approved states as well as past practices supporting Best Available 
Retrofit Technology (BART).
    Some state and industry commenters recommended that the EPA 
oversight/approval of model protocols should be eliminated and air 
agencies should be able to determine the best approach, using the 
normal course of discussion and cooperation with their respective EPA 
Regional modeling contacts, and document that approach with the final 
submittal to the EPA. One industry commenter stated that it is 
arbitrary and capricious to require EPA approval of state monitoring 
and modeling plans when the EPA's technical resources are too stretched 
to provide this oversight in a timely manner.
c. EPA Response
    The EPA recognizes the concerns of the commenters about the time 
and resources needed to develop effective modeling protocols. To 
clarify, the final rule does not require EPA approval of modeling 
protocols before air agencies may begin conducting modeling, but does 
direct air agencies to submit to the EPA modeling protocols by July 1, 
2016. As with the modeling itself, directing submission of protocols is 
within the EPA's authority to prescribe modeling for the purpose of 
predicting the effect on ambient air quality of emissions under CAA 
section 110(a)(2)(K), and to prescribe such regulations as are 
necessary for the EPA to carry out its functions under CAA section 
301(a)(1). It is reasonable for the EPA to establish a process that 
provides an opportunity for preliminary EPA assistance to air agencies 
to ensure that their subsequent modeling is conducted in a manner that 
results in information that can reliably inform subsequent EPA actions 
determining air quality status under the SO2 NAAQS. As 
explained below, the submission of modeling protocols will increase the 
likelihood that subsequent air agency modeling is sufficient for this 
purpose, and thus will clearly assist the EPA in carrying out its 
functions of determining air quality status.
    As noted above, the EPA is allowing air agencies approximately six 
additional months to determine whether to characterize air quality 
through modeling or monitoring in order to accommodate the concerns 
about time needed to make this determination, without delaying the date 
by which information for characterizing air quality becomes available. 
Consistent with this revision, the EPA is delaying the deadline for 
states to submit modeling protocols for sources for which they choose 
to characterize air quality through modeling, to match the July 1, 
2016, deadline for selecting an air quality characterization approach. 
The EPA believes that it is important and valuable for the EPA Regional 
Offices to work closely with air agencies to ensure that modeling 
protocols are adequate to ensure that the modeling for sources 
accurately characterizes air quality near sources. Requiring modeling 
protocols will help to keep air agencies from getting too far into the 
modeling process in a manner that may not be appropriate, which could 
occur absent such preliminary consultation with the EPA and, if it 
occurred, could result in the air agency needing to re-conduct modeling 
after submission to the EPA. The EPA does not intend to formally 
approve these protocols, nor does the EPA believe that a one-size-fits-
all timeline, process, or presumption regarding approval or disapproval 
of these protocols is warranted. Nevertheless, the EPA believes that 
submittal of protocols will facilitate identification, and resolution 
of modeling issues, and will thereby help to avoid a later situation in 
which the EPA would not be able to rely upon the air agency's modeling 
in subsequent actions determining air quality status. Review of 
modeling protocols by the EPA will help ensure that the air agency's 
modeling will be appropriate for use in making future determinations 
regarding areas' attainment status, such as designations or 
redesignations. If an air agency's modeling protocol is not submitted 
in advance of the subsequent modeling, the chances are greater that the 
EPA may not have critical air quality information when it is needed 
(for example, when the EPA intends to make area designations). 
Therefore, the EPA believes that a requirement for the air agency to 
provide modeling protocols for relevant sources to the EPA Regional 
Administrator by July 1, 2016 is a reasonable requirement. The modeling 
protocol should include information about issues such as emissions 
input data, modeling domain, receptor grid, meteorological data and how 
to account for background concentrations.
    As was the case for the development of the list of sources and 
characterization approaches, the Agency acknowledges that the schedule 
for state submittal and the EPA review of modeling protocols is 
expeditious. The EPA nevertheless believes that the schedule can be 
achieved with appropriate planning, coordination, and program 
implementation by air agencies, and believes that it is necessary to 
establish expeditious timelines to ensure timely availability of the 
air quality information. The EPA Regional Office staff will be 
available to consult with air agency officials to refine the modeling 
protocols for relevant sources. The EPA Regional Offices will review 
the submitted information and consult with the air agency expeditiously 
to discuss any recommended adjustments to the protocol.
4. Issues Related To Submittal of Annual Monitoring Network Plans That 
Include SO2 Monitoring Network Modifications To Satisfy the 
DRR
a. Summary of Proposal
    In areas where air quality will be characterized through ambient 
monitoring to satisfy this rulemaking, the EPA proposed monitoring 
requirements in Sec.  51.1203(c), including the requirement that air 
agencies submit relevant information about these monitoring sites to 
the EPA Regional Administrator by July 1, 2016, as part of their annual 
monitoring network plan, in accordance with the EPA's monitoring 
requirements specified in 40 CFR part 58. In the proposal, the EPA 
encouraged air agencies to work with the EPA Regional Offices in the 
development of an appropriate network plan which would include the 
rationale for why the proposed number of sites and their individual 
locations are appropriate. The EPA stated in the proposal that optional 
considerations for siting these monitors are discussed

[[Page 51070]]

in the draft Monitoring TAD.\7\ See 79 FR 27458, May 13, 2014.
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    \7\ The SO2 NAAQS Designations Source-Oriented 
Monitoring Technical Assistance Document can be found at https://www.epa.gov/airquality/sulfurdioxide/pdfs/SO2MonitoringTAD.pdf.
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b. Brief Summary of Comments
    Several state and industry commenters asserted that it is 
unreasonable for the EPA to assume monitoring plans can be submitted by 
the proposed July 1, 2016, deadline. Some commenters stated that it may 
not be determined that monitoring would be appropriate in certain areas 
until after a lengthy round of initial modeling is complete. Other 
commenters stated that siting monitors is a lengthy process which 
involves, among other steps, working with the sources and the EPA to 
determine where monitors should be located, obtaining access to sites, 
identifying funding, and procuring and installing equipment. 
Furthermore, one commenter stated that, for sources that choose to 
operate monitoring equipment, additional time will be needed to (1) 
develop documentation between air agencies and sources to ensure that 
sites are adequately maintained and that data are reported in a timely 
and complete manner, and (2) to put in place a quality assurance 
program consistent with the EPA requirements for the entire monitoring 
network.
c. EPA Response
    The EPA is finalizing the requirement that any plans to conduct 
monitoring to satisfy requirements of this rule (by air agencies, 
industry, or other parties) shall be reflected in the state's Annual 
Monitoring Network Plan due by July 1, 2016. The Agency believes that 
monitoring resources can be appropriately put in place by the January 
1, 2017, deadline to satisfy this rule, particularly if air agencies 
begin planning as soon as possible. The EPA has encouraged air agencies 
to begin the monitor planning process early, particularly for the 
largest sources. As stated previously, the EPA believes that while the 
schedule for meeting the requirements of this rule is expeditious, the 
schedule can be achieved with the appropriate planning, coordination, 
and program implementation by affected air agencies. The EPA strongly 
encourages air agencies to start their investigation of this issue as 
soon as practicable. The EPA also 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 which would warrant the 
characterization of nearby air quality. In addition, as stated 
previously, the EPA believes that it is necessary to establish 
expeditious timelines to ensure timely availability of air quality 
information. With this in mind, and in light of the many logistical 
concerns raised by commenters and recognized by the EPA, the Agency is 
encouraging air agencies to engage with their respective EPA Regional 
Offices well in advance of the time by which the Annual Monitoring 
Network Plan is due. To this end, states should share their draft 
SO2 network design plan for SO2 monitoring 
intended to satisfy this rule with the EPA and the public in advance of 
the complete Annual Monitoring Network Plan.
    The reality of the sometimes complex process of identifying a 
location, securing funding and installing a new monitoring site, 
necessitates such an approach. The Agency believes that early 
interaction between air agencies and the EPA Regional Offices and 
industry will likely improve the potential for success in installing an 
appropriate number of monitors in appropriate locations around 
SO2 emitting facilities identified for characterization in 
this rulemaking.
5. Issues Related to Deadline for Operation of SO2 Monitors
a. Summary of Proposal
    The EPA proposed in Sec.  51.1203(c)(1) that air agencies that have 
chosen to characterize air quality through ambient monitoring must have 
any relocated and/or new monitors operational by January 1, 2017. In 
the preamble, the EPA explained that, under this approach, it is 
anticipated that the first 3 calendar years of data would be collected 
from 2017 through 2019, allowing the first design value for each 
monitor to be calculated by May 2020. This would allow these new 
monitoring data to be used to inform air agency and the EPA 
determinations of areas' attainment status in actions that occur in 
2020, which could include designations and redesignations. See 79 FR 
27458, May 13, 2014.
b. Brief Summary of Comments
    One industry commenter stated that the proposed rule reflected a 
reasonable timeframe for air agencies to collect the data, either 
through monitoring or modeling, that are needed to characterize air 
quality in areas and determine whether the 1-hour SO2 NAAQS 
is being met. One state commenter also asserted that the feasibility of 
this time period will be dependent upon the threshold option selected 
by the EPA and, thus, the number of affected sources.
    However, more than 10 state and industry commenters asserted that 
the short time period between the dates when the monitoring plans need 
to be submitted and the monitors are required to be operational is 
inadequate. One industry commenter stated that it is technically 
infeasible to implement the proposed rule by 2017 and, thus, the EPA's 
proposal is arbitrary and capricious.
    Several state and industry commenters recommended an extension of 
at least 1 year for air agencies to begin actual monitoring. One state 
commenter suggested that the EPA should allow monitoring to begin 
operation between May 1, 2017, and July 1, 2017, which would be 
consistent with its suggested approach allowing air agencies to notify 
the EPA of selection of the monitoring option up to January 1, 2017. 
This commenter recognized that this approach would likely require 
delaying the attainment date, if designations are not made until after 
3 calendar years of the new monitoring data are obtained and certified. 
This commenter also noted that, if the EPA's approval of an 
SO2 monitoring plan under this proposal does not occur until 
late 2016, air agencies with winter weather concerns would simply not 
have sufficient time to set up a monitoring network by January 1, 2017. 
Another state commenter noted that other recent rules establishing new 
monitoring requirements (such as NAAQS revisions for NO2, 
SO2 and PM2.5) have not required such rapid 
deployment of monitors, but have each allowed at least 1.5 years from 
submittal of the network plan to operation of the monitor.
c. EPA Response
    The EPA recognizes that the logistical and financial burdens of 
installing an ambient air monitoring station can vary in difficulty and 
the resources required. However, as noted earlier with regard to the 
overarching timetables effected by this rule, the Agency believes that, 
as with other parts of the implementation schedule, while the schedule 
for operating monitors is expeditious, it can be achieved with 
appropriate planning, coordination, and program implementation by the 
air agency which will allow monitoring resources to be in place by the 
deadline. The EPA believes that any further delay in air quality 
characterization around sources identified as a result of this 
rulemaking will delay implementation of the standard and public health 
protection in areas where there may be a violation of

[[Page 51071]]

the standard. The Agency believes that it is most prudent to maintain 
the proposed timetable for monitoring network installation because of 
the need for use of these new data in a relatively timely manner for 
use in making attainment status decisions concerning SO2 
areas in the country. Therefore, the EPA is finalizing the date by 
which monitors being used to satisfy this rulemaking must be 
operational to be January 1, 2017.
    As noted previously, if a state chooses to monitor to satisfy the 
requirements of this rule, planning for the installation of new 
monitors must occur early on, soon after this rule is promulgated. With 
this in mind, and in light of the many logistical concerns raised by 
commenters and recognized by the EPA, the Agency is encouraging air 
agencies to engage with their respective EPA Regions well in advance of 
the time by which the Annual Monitoring Network Plan and network 
operations are due. The EPA is encouraging air agencies to engage with 
their respective EPA Regional Offices, and possibly the industrial 
sources needing nearby air quality characterization, to plan an 
adequate network design as early as possible after this rule is 
promulgated. The reality of the sometimes complex process of 
identifying a location, securing funding and installing a new 
monitoring site, necessitates such an approach. The Agency believes 
that early interaction between air agencies and the EPA Regional Office 
and industry will likely improve the potential for success in 
installing an appropriate number of monitors in appropriate locations 
around SO2 emitting facilities identified in this rulemaking 
as needing nearby air quality to be characterized. The EPA also notes 
that if air agencies conclude that the timeline and resource burdens 
associated with installing and conducting improved monitors are not 
feasible for particular areas, they may instead choose the less 
resource-demanding and more expeditious method of modeling to 
characterize SO2 emissions impacts in such areas.
6. Issues Related To Submittal of Modeling Analyses to the EPA
a. Summary of Proposal
    The EPA proposed in Sec.  51.1203(d)(3) that air agencies that 
choose modeling to characterize ambient air quality be required to 
submit modeling analyses to the EPA Regional Office by January 13, 
2017. In the proposal, the EPA recommended that these modeling analyses 
should be conducted in accordance with the recommendations in the EPA's 
Modeling TAD \8\ or as otherwise agreed upon with the EPA Regional 
Office on a case-by-case basis. The EPA stated that the EPA Regional 
Office and the air agency should engage actively in consultation to 
understand the inputs, assumptions and findings associated with each 
air quality modeling analysis; the air agency should submit thorough 
documentation of its modeling analysis; and the air agency should 
provide the EPA with supplemental information about the analysis upon 
request.
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    \8\ The Draft SO2 NAAQS Designations Modeling 
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    The proposal also indicated that where areas have not already been 
designated under the 2010 SO2 NAAQS, air agencies could 
submit updated designation recommendations, if appropriate, as informed 
by their modeling analyses. The proposal noted that in developing any 
updated designation recommendations, the air agency should follow the 
EPA's most recent SO2 designation guidance.\9\ See 79 FR 
27458, May 13, 2014.
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    \9\ The EPA issued initial guidance on the SO2 area 
designations process on March 24, 2011. See https://www.epa.gov/air/sulfurdioxide/pdfs/20110411SO2designationsguidance.pdf. Note: The 
EPA issued updated SO2 designations guidance. See 
``Updated Guidance for Area Designations for the 2010 Primary Sulfur 
Dioxide National Ambient Air Quality Standard'', March 20, 2015. 
Available at: https://www.epa.gov/airquality/sulfurdioxide/pdfs/20150320SO2designations.pdf.
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b. Brief Summary of Comments
    One state commenter disagreed with the requirement that 
comprehensive modeling analyses and related supporting information need 
to be submitted to the EPA. This commenter asserted that the modeling 
analyses will be conducted by the facility owners and reviewed by the 
state air agency, and the air agency should be able to forward just a 
summary of the analyses to the EPA with sufficient information for the 
EPA to evaluate.
c. EPA Response
    The EPA is finalizing its proposed approach of requiring that air 
agencies choosing modeling to characterize ambient air quality be 
required to submit modeling analyses to the EPA Regional Office. 
Irrespective of whether the state or a third party conducts the 
modeling, it is the state's responsibility under the CAA to submit the 
information that this rule requires. The EPA anticipates that any state 
submittal of third-party modeling would reflect a review as to whether 
it believes that the modeling satisfies applicable requirements. 
Moreover, the EPA anticipates that the submittal would provide adequate 
information for the EPA to review the adequacy of the analysis as well.

D. Technical Issues Relating to Modeling and Monitoring

1. Technical Assistance Documents (TADs)
    This section of the preamble presents a discussion of the 
threshold-based air quality characterization approach to implement the 
SO2 NAAQS in areas that contain sources with larger 
SO2 emissions, in order to address areas where there may be 
higher potential for NAAQS violations that adversely affect public 
health. This section discusses the different recommended approaches air 
agencies may use to provide the necessary air quality information to 
the EPA for areas around those identified sources.
a. Summary of Proposal
    In the preamble of the proposed rulemaking, the EPA noted that the 
Agency has produced draft, non-binding Monitoring and Modeling TADs 
that discuss options, suggested approaches and methods on how 
monitoring or modeling efforts to characterize air quality around an 
identified source might be conducted. The EPA stated that these 
documents can be used to assist air agencies in the implementation of 
this rulemaking. See 79 FR 27460, May 13, 2014.
b. Brief Summary of Comments
    One industry commenter stated that the proposed rule references and 
relies upon guidance provided in the Modeling and Monitoring TADs and 
in EPA's Guideline on Air Quality Models; therefore, the commenter 
asserted that the documents are subject to review and comment for the 
proposed rule. One state commenter asserted that it is challenging to 
prepare meaningful comments on the proposal since much of it is 
contingent upon the use of the TADs.
    Some state and industry commenters urged the EPA to be clearer in 
the final preamble that the TADs are guidance and, therefore, are not 
binding. One state commenter urged the EPA to explicitly state in the 
final rule that air agencies retain the ability to use alternative 
methods to those outlined in the TADs. One industry commenter stated 
that the EPA's reliance on technical guidance documents that have not 
been subject to public notice and comment undermines protections 
guaranteed by the Administrative

[[Page 51072]]

Procedure Act. One state commenter stated that because the rule 
``requires'' the use of ``. . . separate non-binding draft technical 
assistance documents . . .'' and creates significant regulatory 
uncertainty for air agencies, they oppose the proposal.
c. EPA Response
    The EPA reiterates that the TADs provide recommendations but are 
not binding or enforceable and create no obligations on any person. 
Although the draft TADs are referenced as recommended approaches in the 
preamble to the proposal and in this final rulemaking, they are not 
required to be adhered to by any air agency required to characterize 
air quality around an SO2 source identified in this 
rulemaking. The EPA developed the TADs to aid air agencies seeking 
advice in the air quality characterization process required by this 
rulemaking. The Agency has indicated that the TADs are meant to be used 
as possible tools to aid air agencies. This rulemaking does not codify 
the TADs, and none of the comments on the proposed rule regarding the 
TADs resulted in changes to the rule itself. The TADs are considered to 
be living documents that the EPA may update as necessary over time. The 
Agency believes that a modeling protocol or monitoring network design 
that follows or references the recommended approaches in the TADs is 
likely to be adequate, and will better ensure the success and a timely 
fulfilment of the requirements of this rulemaking. However, air 
agencies remain free under the final rule to suggest alternative 
approaches to those suggested in the TADs. Whether an agency chooses to 
follow a TAD or suggest an alternative approach does not affect the 
fact that for every approach chosen, the air agency will need to submit 
their rationale and approach to the EPA for review on a case-by-case 
basis.
    The EPA disagrees with the commenters who claimed that the 
proposal's reference to the TADs violates the rulemaking requirements 
of the Administrative Procedure Act. The Agency did not propose, and is 
not promulgating language that the TADs are required to be followed, 
and is not changing their status as non-binding technical assistance 
documents. In response to the request that the TADs be subjected to 
notice and comment, in fact the first drafts of the TADs were 
circulated for review and comment by stakeholders, and revised versions 
of the TADs were developed in response to those comments.
2. Monitoring and Network Design Issues
a. Summary of Proposal
    The EPA proposed that air agencies that select the monitoring 
approach to characterize air quality in an area would have the option 
to identify appropriate existing monitoring sites, relocate monitors as 
appropriate or install new monitors, and have them operational by 
January 1, 2017, in order to provide data for use in the anticipated 
designations process in calendar year 2020. The EPA proposed to require 
that any relocated or new monitors be operated either as SLAMS, or in a 
manner equivalent to those monitors operated elsewhere in the SLAMS 
network; they do not, however, have to be designated as SLAMS monitors. 
In the proposal, the EPA stated that the monitors should use Federal 
Reference Methods (FRMs) or FEMs and meet the requirements of 40 CFR 
part 58, appendices A, C, and E. Further, the EPA stated that the 
resulting data should be reported to the Air Quality System (AQS) and 
would be subject to the same annual data reporting and certification 
requirements listed in 40 CFR 58.15 and 58.16 as required for SLAMS 
data. See 79 FR 27461, May 13, 2014.
b. Brief Summary of Comments
    Some commenters suggested that the rule should allow a third party, 
such as a facility owner, to cover the expenses of siting and operating 
new monitors in coordination with the air agency. One public interest 
group commenter stated that there are numerous considerations that make 
it unlikely that monitors could be sited at ideal modeled locations, 
including access to the location, power hookups, local pollutant 
effects and safety from vandalism. Several commenters expressed concern 
that the lack of clear criteria for designing an SO2 source-
oriented monitoring network puts air agencies in the unreasonable 
position of designing a monitoring network without knowing whether it 
will be approved by the EPA.
    Some commenters stated that guidance is needed on the number of 
monitors required. Commenters stated this issue should not be left up 
to negotiations with the EPA Regional Office; rather, a procedure 
should be outlined that will provide consistency for all regional 
offices and air agencies. Some state and industry commenters suggested 
that one monitor may be sufficient and recommended the final rule 
include a discussion of the adequacy of one monitor in certain 
situations. One industry commenter stated that, because large gradients 
in design concentrations for SO2 are likely not present to 
the extent that the EPA may expect, the use of a single monitor to 
demonstrate NAAQS attainment is sufficient in many cases.
c. EPA Response
    The EPA believes that there are no limitations as to who might 
operate a monitor or monitors being used to satisfy the requirements of 
this rulemaking. It can be a state, local or tribal government, 
industry, other third parties or a mix thereof. Whatever the case, the 
monitor or monitors should be included as a part of the state's 
monitoring plan. The critical issue is that the monitor or monitors 
must be either a SLAMS monitor or SLAMS-like monitor, where the latter 
might be an industrial or other third party-operated monitor. In either 
case, the monitor or monitors must be an FRM or an FEM monitor, and 
must adhere to requirements in 40 CFR part 58, appendices A, C, and E, 
and adhere to data reporting requirements also contained in 40 CFR part 
58. This does require states to provide oversight to any non-SLAMS 
sites for which they are claiming to satisfy this rulemaking, as the 
states have the final responsibility to ensure the quality of submitted 
data that satisfies the intent of this rulemaking.
    With respect to concerns over a lack of clear criteria for 
designing an SO2 source-oriented monitoring network, the 
likelihood to appropriately place one or more monitors, and the issue 
of what number of monitors might be required around a source, there is 
no one-size-fits-all answer to this question. The EPA indicated in the 
preamble to the proposal, and in the draft Monitoring TAD, that the 
relative location and number of monitors that might be sufficient to 
characterize the air quality around a source is a case-by-case 
determination. In general, the main objective is to monitor at, or as 
near as possible to, the location(s) where ambient SO2 
concentration maxima are expected to occur. Site selection for any 
monitoring network is subject to logistical hurdles including site 
access, identification or installation of appropriate infrastructure, 
telecommunications access, and safety, and state, local, and tribal air 
agencies are well versed in the variety of logistics that can be 
involved in the installation of an ambient air monitoring station. 
These issues undoubtedly can play into what any ambient air monitoring 
network ultimately looks like. However, as is the case with all 
required ambient air monitoring, responsible air agencies are expected 
to establish a clear rationale for the number and placement

[[Page 51073]]

of the monitors it is using to satisfy the requirements of the rule. In 
this process, there is flexibility for the state to use professional 
judgment in determining what is appropriate for their individual 
situations, but they are expected to perform due diligence in 
attempting to locate monitors in the most ideal locations possible. 
Further, the air agency's recommended number of monitors and 
preliminary rationale should be discussed with the EPA Regional Offices 
well in advance of the development of an Annual Monitoring Network 
Plan. As discussed in the Monitoring TAD, the development of a network 
design and its rationale can be informed by a number of types of 
analyses which can include the use of air quality modeling, exploratory 
monitoring, or analysis of existing data. In any scenario, the state 
would need to have a technically credible rationale that supports the 
monitoring network design approach that has been chosen to satisfy 
requirements in this rulemaking.
    As stated previously, the TADs provide recommendations for air 
agencies, but are not binding or enforceable, and they create no 
obligations on any entity. Although the draft TADs are referenced as 
providing recommended approaches in the preamble to the proposal and in 
this final rulemaking, there is no specific provision in this rule that 
requires the air agency to adhere to the TADs. The TADs have been 
provided in order to potentially aid air agencies seeking advice in the 
air quality characterization process required by this rulemaking.
3. Areas Failing to Having New Monitors Operational by January 1, 2017
a. Summary of Proposal
    Where an air agency has chosen the monitoring approach and 
submitted a list identifying the sources near which air quality is to 
be monitored, the proposed rule addressed the situation where it 
becomes evident that sufficient and appropriate monitoring will not be 
operational in a timely manner. The EPA proposed that the area around 
the source in question would be functionally ``moved'' to the modeling 
pathway, where air quality data characterized by the state under this 
rule could inform potential future designations that would be intended 
to occur by December 2017. The EPA requested comment on this approach, 
and on any alternative approaches that could most effectively address a 
situation where an air agency is acting in good faith to deploy 
monitors on time but experiences a delay which may be outside of its 
control, as well as a situation where an air agency does not act in 
good faith to deploy monitors on time. See 79 FR 27461, May 13, 2014.
b. Brief Summary of Comments
    One public interest group commenter stated that the 2017 modeling 
pathway discussed in the proposal offers a swifter, cheaper, and more 
accurate way of assessing air quality, and so did not believe that 
states that missed deadlines along the monitoring pathway should be 
allowed to further delay designations. Other commenters stated that the 
fact that modeling is less expensive than monitoring is not a 
substitute for what they believe is the superior accuracy of actual 
monitored data; and that they believe the lower costs of modeling do 
not offset the regulatory costs and other burdens on sources and 
communities that could result from nonattainment designations based on 
modeling.
    One public interest group commenter stated that because the 
monitoring approach already could lead to designations occurring a full 
decade after the NAAQS was promulgated, it should be regarded as an 
absolute edge-of-the-envelope approach, meaning that failure to meet 
monitoring deadlines should result in areas being treated under the 
modeling pathway as a default. This commenter stated that setting such 
a policy in any final rule would properly incentivize actors to 
transmit information to the EPA in a timely manner.
    A number of state and industry commenters did not agree that a 
would-be monitored area should be automatically designated at the same 
time as areas for which the modeling option was chosen in the event of 
any delay in monitoring. Commenters also stated that the proposed 
penalty for unanticipated monitoring site delays is excessive and there 
are too many uncertainties which argue against such automatic actions; 
especially in cases where the air agency has exercised all due 
diligence to ensure that the monitors are operational by the deadline 
in the rule.
c. EPA Response
    The EPA is clarifying the relationship between this rule and the 
schedule for promulgating designations under CAA section 107. This rule 
does not establish any deadlines for designations or prescribe the 
manner in which future designations would occur. Therefore, it has 
never been the role of this rule, even as proposed, to promulgate 
schedules for designations of areas based on whether air agencies 
timely implement the rule. However, the proposed milestones for 
implementation of the rule were devised in consideration of the 
Agency's preferred and anticipated schedule for completing area 
designations.
    While this rule does not promulgate designation schedules, separate 
litigation activities have affected the schedule. On March 2, 2015, the 
U.S. District Court for the Northern District of California issued an 
order directing the EPA to complete designations pursuant to the 
schedule discussed earlier in this document. Affected air agencies 
considering the monitoring option under this rule should be aware of 
this schedule. Under the terms of the consent decree entered by the 
court, in order for the EPA to not be required to designate an area by 
December 31, 2017, air agencies choosing the monitoring option under 
this rule will need to install and begin operating those monitors by 
January 1, 2017. This is the date that the rule requires. However, 
while the rule does not provide designations schedules, and thus does 
not address how designation schedules would be affected by an air 
agency missing this deadline, the March 2015 consent decree does. If 
the monitor is not operational by January 1, 2017, the EPA will not be 
able to use the future monitoring information to be generated by those 
monitors in the initial designation for the area, because the court's 
order allows those designations to occur as late as 2020 only if the 
monitor is timely installed and operated. Where the January 1, 2017, 
deadline is not met, the designations must occur by December 31, 2017, 
and will have to depend upon other information available at that time.
    The EPA's proposal addresses circumstances in which an air agency 
chooses to characterize through monitoring but fails to have monitors 
become operational on time. The proposal suggests that in these 
circumstances, the agency (or, for that matter, the EPA) would be 
required to conduct modeling under this rule and be relieved of further 
obligations to conduct monitoring, albeit late. The EPA's intent in its 
notice of proposed rulemaking was to explain that in these 
circumstances, where an air agency chooses to characterize air quality 
with new monitors but failed to have the new monitors operational by 
the January 1, 2017, deadline, the EPA envisioned designating such 
areas in conjunction with areas being characterized by modeling. That 
is, the EPA did not envision delaying the designation for such areas to 
the envisioned 2020 date when the Agency anticipates promulgating 
designations for areas characterizing air quality through a new

[[Page 51074]]

monitoring network. The EPA must now comply with a court-ordered 
designation schedule, in which the court expressly requires that areas 
that have not begun operation of a new monitoring network by January 1, 
2017, must be designated by December 2017.
    Nevertheless, the EPA wishes to clarify that an air agency that 
chooses monitoring as its means to meet the air quality 
characterization requirements, and commits in its July 2016 Annual 
Monitoring Network Plan to conduct such monitoring, remains obligated 
to fulfill the original requirement to monitor and to provide the 
resulting air quality characterization around a given SO2 
source, even if operation of new monitors commences after the January 
1, 2017, deadline. If a state fails to meet the January 1, 2017, 
deadline, the state must still meet the monitoring requirements for the 
area pursuant to 40 CFR part 58, or the EPA may disapprove the state's 
monitoring plan for the following year, unless, of course, the 
monitoring plan is revised accordingly. Although, as discussed 
previously, the EPA will not be able to rely upon the future monitoring 
data to issue the designation on the court-ordered schedule, the future 
monitoring data may be useful for other purposes such as tracking 
progress and making later attainment status determinations needed for 
redesignations.
4. Monitor Shut Down
a. Summary of Proposal
    In the preamble, the EPA proposed that a monitor that has been 
deployed under the monitoring option pursuant to this rule, and is 
located in an area that is subsequently designated attainment, may be 
eligible for shut down provided that the monitor meets certain 
criteria. The EPA proposed in Sec.  51.1203(c)(3) that any 
SO2 monitor identified in an approved state annual 
monitoring network plan to satisfy the rule requirements may be 
eligible for shut down if the following criteria are met: (1) The 
monitor is not also satisfying other minimum SO2 monitoring 
requirements listed in 40 CFR part 58, appendix D; (2) the monitor is 
not otherwise required to meet requirements in a SIP or permit; and (3) 
the monitor has recorded a 3-year design value (DV) that is no greater 
than 50 percent of the 1-hour SO2 NAAQS. The EPA also 
proposed that any SO2 monitor eligible for shutting down 
would need to be approved by the EPA Regional Administrator before 
monitoring operations could cease. As an alternative, the EPA also 
proposed an option in which the same criteria noted earlier would need 
to be met, except that the monitor would be eligible to cease 
operations if it recorded a design value (DV) in the 3-year period that 
is no greater than 80 percent of the 1-hour SO2 NAAQS. The 
EPA requested comment on the two proposed options for DV criteria for 
SO2 monitor shutdown, as well as other potential values 
within the 50-80 percent range. The EPA requested that commenters 
provide specific technical rationale supporting any approach they 
recommend. See 79 FR 27462, May 13, 2014.
b. Brief Summary of Comments
    Some state and industry commenters agreed with the proposal that 
monitors placed pursuant to the monitoring option and located in areas 
that are designated as attainment should be eligible for shut down. 
Commenters also stated that providing state agencies with the 
flexibility to shut down unneeded monitors allows agencies to allocate 
their limited resources more appropriately. One industry commenter 
stated that, if the sources are properly controlled and/or limited by 
permit, the risk of significant increases in DVs over time is 
relatively low absent new sources entering the affected area. Several 
state and industry commenters supported the proposal, with one state 
commenter indicating that the use of the 50 percent threshold would be 
safe to use because the area would require a significant increase in 
future SO2 emission to cause an exceedance of the 1-hour 
SO2 NAAQS.
    Some state commenters recommended that the threshold of 50 percent 
be dropped in the final rule since 40 CFR 58.14 already contains 
provisions for shutting down a monitor at 80 percent of the NAAQS. 
Commenters stated that there does not seem to be a reason to make the 
criteria more stringent than the existing criteria in 40 CFR part 58 
and, if the EPA wishes to change those criteria, a revision to 40 CFR 
58.14(c)(1) should be considered and made available for comment. 
Industry commenters stated that the requirement for annual reporting of 
changes in SO2 emissions with the possibility that further 
monitoring could be required, argues against the more stringent 50 
percent option.
    Over 25 commenters supported the use of the 80 percent threshold. 
Commenters stated that 80 percent of the NAAQS is a strong enough 
criterion for shut down of an SO2 monitor and the 80 percent 
criterion is consistent with criteria for shutting down most regulatory 
monitors. One public interest group commenter stated that new monitors 
should not be shut down since (1) short-term monitor readings may not 
be consistent with long-term attainment and (2) the SO2 
monitor network needs to be rebuilt. In addition, this commenter 
recommended that monitors not be removed if the concentrations they are 
recording are trending upward, indicative of potential future problems.
c. EPA Response
    The EPA is finalizing the rule to allow any SO2 monitor 
identified by an air agency in its approved Annual Monitoring Network 
Plan as having the purpose of satisfying Sec.  51.1203 which is not in 
an SO2 nonattainment area, and is not also being used to 
satisfy other ambient SO2 minimum monitoring requirements 
listed in 40 CFR part 58, appendix D, section 4.4, and is not otherwise 
required as part of a SIP, permit, attainment plan or maintenance plan, 
to be eligible for shut down if it produces a DV of no greater than 50 
percent of the 1-hour SO2 NAAQS in the first or second 3-
year periods of its operation. The EPA has chosen to adopt this 
shutdown allowance so that those monitors that record DVs that are well 
below the NAAQS after 3 or 4 years of operation would no longer be 
required to operate under the unique provisions of this rule, if they 
are otherwise not required under other requirements. This potential 
ability to shut down monitors would relieve any resource burden under 
this rule on air agencies where NAAQS violations have not and likely 
will not occur. This particular provision will not require estimates of 
future concentrations as do existing shutdown provisions in 40 CFR 
58.14.
    More specifically, this monitor shutdown provision works by 
assessing how two DVs (i.e, one calculated from monitor data collected 
in years 1 through 3, and one from years 2 through 4) would compare to 
the 50 percent of the NAAQS shutdown criterion. If a monitor produces a 
DV from data collected in years 1 through 3 that is no greater than 50 
percent of the NAAQS, it is eligible for shutdown if it is not 
otherwise required to operate. If the DV is above the 50 percent 
threshold, the monitor must continue operation. If that monitor 
produces a DV no greater than 50 percent of the NAAQS from data in 
years 2 through 4, it is eligible for shutdown if not otherwise 
required to operate. If, instead, the DV is again above the 50 percent 
threshold, the air agency must continue to operate the monitor. From 
that point forward (i.e., for data collection year 2021 and beyond), 
the applicable monitor shutdown provisions are those that exist in 40 
CFR 58.14, which include

[[Page 51075]]

probabilistic estimations of future concentrations and other 
circumstantial situations that might allow for monitor shutdown.
    The Agency would like to note language of particular relevance from 
40 CFR part 58 regarding eligibility for shutdown based on recorded 
data and calculated design values that exists in Sec.  58.14(c)(1). 
This particular provision allows monitoring discontinuation with the 
Regional Administrator approval for: ``Any PM2.5, 
O3, CO, PM10, SO2, Pb, or 
NO2 SLAMS monitor which has shown attainment during the 
previous 5 years, that has a probability of less than 10 percent of 
exceeding 80 percent of the applicable NAAQS during the next 3 years 
based on the levels, trends, and variability observed in the past, and 
which is not specifically required by an attainment plan or maintenance 
plan. In a nonattainment or maintenance area, if the most recent 
attainment or maintenance plan adopted by the state, and approved by 
the EPA, contains a contingency measure to be triggered by an air 
quality concentration and the monitor to be discontinued is the only 
SLAMS monitor operating in the nonattainment or maintenance area, the 
monitor may not be discontinued.''
    In any circumstance regarding monitor shutdown, whether pursuant to 
this final rule or 40 CFR part 58, the air agency must receive the EPA 
Regional Administrator approval of a request to cease operation of the 
monitor as part of its action on the annual monitoring plan under 40 
CFR 58.10 prior to the shutdown of any qualifying monitor. Therefore, 
under the final rule, there are two sequential routes for possibly 
shutting down a monitor. If a monitor shows DVs greater than 50 percent 
of the NAAQS after the first two 3-year periods of its operation and 
cannot be approved for shut down under the first sequential route, the 
monitoring will continue. However, after 5 years of operation it can be 
considered for shutdown if it meets the criteria that the EPA's rules 
at 40 CFR 58.14(c)(1) apply, with the EPA Regional Administrator's 
approval. These monitors might also be subject to shut down eligibility 
as set forth in Sec.  58.14(c)(2), (3), (5), and (6).
5. Annual Reporting Following Monitor Shutdown
a. Summary of Proposal
    For any area for which the EPA has approved an air agency's request 
for an SO2 monitor to cease operations, the EPA proposed 
that the air agency be required to assess SO2 emissions 
changes annually, beginning in the year after the monitor ceases 
operation. (The proposal contained a similar requirement for modeled 
areas, discussed later in this section.) For areas around these sources 
in which total SO2 emissions increase over the emissions for 
the previous year, the EPA proposed that the air agency would be 
required to submit to the EPA an assessment of the cause of the 
increase and provide an initial determination of whether the air 
quality around that source should be further re-assessed. The EPA 
proposed that the air agency could choose to reinstate the operation of 
the air monitor or complete air quality modeling for the source area to 
verify that the area continues to attain the standard. In the proposal, 
the EPA stated that, if modeling or monitoring information required to 
be submitted by the air agency to the EPA pursuant to Sec.  51.1205 
indicates that an area is not attaining the 2010 SO2 NAAQS, 
the EPA may take appropriate action, including but not limited to 
disapproving the monitoring plan, requiring adoption of enforceable 
emission limits to ensure continued attainment of the 2010 
SO2 NAAQS, redesignation of the area to nonattainment, or 
issuance of a SIP Call.
    The EPA proposed two options for how the air agency would submit 
this report and how the EPA would review and act on it. Under the first 
option, the EPA proposed that the air agency would submit a report to 
the EPA annually as an appendix to the air agency's annual monitoring 
plan; the annual monitoring plan is required to be submitted to the EPA 
Regional Administrator by July 1st each year. In the proposal, the EPA 
stated that the inclusion of this verification report as an appendix to 
the annual monitoring plan would ensure that the report would be 
subject to public review and comments that are to be provided for the 
monitoring plan pursuant to regulations at 40 CFR 58.10.
    Under the second option, the annual report of emissions data for 
sources for which the state ceased the operation of nearby monitors 
would be submitted to the EPA in the form of a separate, independent 
annual submittal from the state to the EPA Regional Administrator due 
by the same July 1st date each year. This independent submittal would 
follow the general guidelines set forth in 40 CFR 58.10 regarding 
opportunities for public review and comment as described in Option 1, 
but the report would only include the annual assessments associated 
with sources in areas that were designated unclassifiable/attainment 
and for which the EPA granted approval to cease monitoring. The EPA 
invited comment on any suggested alternatives to these procedural 
options. See 79 FR 27462, May 13, 2014.
b. Brief Summary of Comments
    Several state and industry commenters stated that the proposed 
annual reporting requirement appears to be unduly burdensome. Some 
industry commenters opposed the annual reporting requirement, stating 
that SO2 emissions from sources are already available to the 
EPA and the need for ongoing data requirements has not been 
demonstrated. One state commenter suggested that, if the monitors that 
were removed were providing data under 50 percent of the standard, 
there is no reason to perform such analyses since an increase in 
emissions that would result in such a drastic increase in monitored 
design values would surely be associated with changes to operations 
that would necessitate air permitting, which evaluates projects for 
NAAQS compliance.
    One group of state commenters stated that the EPA's proposed July 
1st submittal date is unrealistic because states will not have the 
required quality-assured emissions monitoring data processed by July 
1st. Some state and industry commenters recommended a less burdensome 
process in which this verification would take place every 3 to 5 years 
instead of annually, pointing out that the EPA publishes the NEI data 
every 3 years, the EPA reviews the NAAQS every 5 years, and there is a 
5-year ambient monitoring assessment plan required by 40 CFR 58.10.
    Commenters requested clarification regarding the determination of 
an emissions increase. One state commenter stated that it is unclear 
whether an emission increase should be based on an increase greater 
than the 3 year average of emissions during the initial monitoring 
analysis, an increase above the highest single year of emissions during 
the initial monitoring analysis, or some other metric. Some commenters 
recommended the comparison be based on some compliant level of 
emissions from the year(s) where the monitor demonstrated attainment 
with the standard, since the ``increase'' or ``decrease'' in emissions 
of SO2 may have resulted in total SO2 emissions 
levels well below the annual emission rates during the years when 
monitoring data showed compliance.
    One tribal and several state commenters supported the option of 
including the annual emissions analysis with the annual monitoring 
plan. One commenter stated that the analysis of emissions is closely 
related to network planning, and this procedure would provide a single 
document for public

[[Page 51076]]

inspection and EPA review and approval. Another commenter stated that 
the annual monitoring plan may not be the best tool or location to 
place modeled data, emission reports, ongoing data requirements, and 
requests to cease modeling. Other state commenters recommended that the 
monitoring plan verification report be considered a separate element 
for ease of processing and for public review.
c. EPA Response
    The EPA has decided not to finalize the proposed requirement that 
any state with an area for which the EPA has approved the air agency's 
request for an SO2 monitor to cease operations must still 
assess SO2 emissions changes annually, beginning in the year 
after the monitor ceases operation. The EPA made this decision based 
upon comments on the proposed rule, and in recognition that a cessation 
of monitoring will not occur unless a monitor has measured 
SO2 concentrations well below the NAAQS for a given time 
period and an EPA Regional Administrator has allowed the shut-down. The 
Agency is persuaded by commenters that monitor shutdown provisions, 
along with generally applicable emissions reporting requirements, are 
of sufficient strength that subsequent additional annual observation 
and reporting of SO2 source emissions profiles by states 
specifically due to this rulemaking is unnecessary. Further, there are 
means by which monitoring can be reinitiated in the future if the 
unlikely scenario occurs where SO2 emissions rise 
significantly in an area, or other data indicate possible NAAQS 
violations in an area after a monitor has been shut-down, mainly 
through the EPA Regional Administrator authority granted in 40 CFR part 
58, appendix D, section 4.4.3.
6. Modeling Issues
a. AERMOD
i. Summary of Proposal
    In the proposal, the EPA stated that the Agency anticipates that in 
implementing the rule air agencies would likely use AERMOD to conduct 
modeling, as AERMOD is the EPA's preferred near-field dispersion model 
and has been demonstrated to be a reliable predictor of SO2 
air quality given appropriate input data. The EPA explained in the 
proposed rule that, as part of its development, AERMOD was evaluated 
using 17 field studies, several of which involved short-term 
measurements of SO2, robust site-specific meteorology and 
accurate measurements of emissions. The EPA stated in the proposal that 
the Agency is confident that AERMOD can provide accurate predictions of 
actual SO2 concentrations given representative meteorology 
and accurate emissions inputs. See 79 FR 27463, May 13, 2014.
ii. Brief Summary of Comments
    One industry commenter stated that, for certain conventional 
SO2 emission scenarios, such as tall stacks at coal fired 
EGUs, AERMOD can be at least reasonably predictive. One public interest 
group commenter stated that AERMOD modeling performs particularly well 
in evaluating emission sources with one or a handful of large emission 
points. This public interest group commenter cited a declaration of 
Roger W. Brode (EPA) filed in the EPA's successful defense of the 2010 
SO2 NAAQS in which he stated that AERMOD is capable of 
accurately predicting whether the revised primary SO2 NAAQS 
is attained and whether individual sources cause or contribute to a 
violation of the SO2 NAAQS. This commenter also stated that 
AERMOD has been tested and performs very well during conditions of low 
wind speeds, citing comments of Camille Sears.
    A number of commenters expressed concern with the use of AERMOD. 
Some commenters stated that AERMOD was intentionally designed to over-
predict SO2 concentrations. Several commenters referenced 
studies that indicate AERMOD over-predicts, including studies by the 
Electric Power Research Institute (EPRI), AECOM and some air agencies. 
Commenters identified a number of issues that they believe need to be 
addressed because they lead to over-predicting SO2 
concentrations, including buoyant line sources, building downwash, 
conservative assumptions in terms of model input, modeling of multiple 
sources, periods of low wind speed, steep terrain and lack of 
representative meteorological data. Commenters stated that the 
individual aspects of AERMOD and the EPA's guidance that contribute to 
over-prediction of the SO2 concentrations in the context of 
the 1[hyphen]hour NAAQS are multiplicative.
iii. EPA Response
    In this final rule, the EPA is not promulgating a requirement that 
air agencies use AERMOD in all cases, but is retaining the existing 
flexibility otherwise provided by the EPA's rules for agencies to 
support the use of the best model for a particular case. The EPA's 
latest recommendations for making this assessment are contained in the 
Modeling TAD. In most cases, the EPA believes that AERMOD will likely 
be the model of choice by air agencies to address the requirements of 
this rule, unless the application involves a different recommended 
model, such as the Buoyant Line and Point Source Dispersion Model 
(BLP). Models recommended for particular applications are listed in 
appendix A of the EPA's Guideline on Air Quality Models.\10\ Section 
3.2 of the EPA's Guideline on Air Quality Models outlines the 
procedures for use of alternative models for those cases where an 
alternative model may be more appropriate than a preferred model. In 
addition, the Modeling TAD also discusses past use of alternative 
models for particular applications.\11\ The EPA recommends consultation 
with the appropriate reviewing authority or EPA Regional Office to 
determine if the use of an alternative model is valid for that 
application.
---------------------------------------------------------------------------

    \10\ Revision to the Guideline on Air Quality Models: 
Enhancements to the AERMOD Dispersion Modeling System and 
Incorporation of Approaches to Address Ozone and Fine Particulate 
Matter'' can be found at https://www.epa.gov/ttn/scram/11thmodconf.htm.
    \11\ It is the EPA's intention to update the Modeling and 
Monitoring TADs as necessary to reflect any change in policy or to 
make clarifications that are necessary. Therefore, any comments on 
the TADs themselves that have been submitted in response to the 
proposed rule will be addressed as a part of any updates made to the 
TADs in the future, rather than in this final rule.
---------------------------------------------------------------------------

    In addition, as stated previously, the TADs are documents that 
provide recommendations but are not binding or enforceable and create 
no obligations on any person. Although the draft TADs are referenced as 
recommended approaches in the preamble to the proposal and in this 
rulemaking, they are not required to be adhered to by any state who is 
required to characterize air quality around an SO2 source 
identified in this rulemaking. The TADs have been provided in order to 
potentially aid air agencies seeking advice in the air quality 
characterization process required by this rulemaking.
    With regards to concerns regarding model conservatism, EPA recently 
proposed updates to AERMOD to address concerns regarding buoyant line 
sources, building downwash, and low wind speed issues. See 80 FR 45340 
July 29, 2015. With regards to comments about model inputs that lead to 
over-estimates, as part of its development, AERMOD has been shown to 
perform well against observed concentrations when actual emissions have 
been used. The modeling of actual emissions for multiple sources is not 
anticipated to cause over-predictions. The modeling TAD also discusses 
that the number of sources explicitly modeled in an

[[Page 51077]]

application is expected to be low and that in many cases, a number of 
sources in a modeling domain can be represented by background 
concentrations instead of being explicitly modeled, thus reducing 
potential overestimates in modeling.
b. Emissions Data
i. Summary of Proposal
    The EPA proposed that modeling analyses be based on either actual 
1-hour SO2 emissions from the most recent 3 years or 
federally enforceable allowable emissions. The EPA referred readers to 
the Modeling TAD for a more detailed discussion of a range of 
recommended options for determining actual emissions. While actual 
emissions would be the preferred choice to use for emissions inputs, 
air agencies have the option of using a more conservative approach by 
inputting a source's most recent 3 years of allowable, or ``potential 
to emit,'' emissions. Additional information and recommendations on 
this approach are discussed in the Modeling TAD. See 79 FR 27446, 
27464, May 13, 2014.
ii. Brief Summary of Comments
    More than 30 state and industry commenters supported statements in 
the EPA's proposal that allow the use of actual emissions as an input 
in the air quality modeling in order to most effectively serve as a 
surrogate for comprehensive ambient monitoring results. Several 
commenters suggested that the use of allowable emissions as an input to 
air quality modeling analyses would result in modeled air quality 
values that were higher than air quality levels that would be expected 
to be observed by a properly sited ambient monitor. Commenters stated 
that using actual emissions is even more important when conducting a 
cumulative impact analysis (assessing potential impacts from two or 
more sources) since the model's tendency to overestimate ambient air 
impacts is compounded when numerous sources are all modeled at peak 
emissions at all times.
    Several state and industry commenters supported the EPA's proposal 
to base the modeling analyses on actual emissions over a 3-year period. 
One commenter noted that, in situations where multiple sources are 
being modeled, the most recent 3 years of actual emissions data may not 
be the same for all sources, particularly if there is a mix of EGUs and 
non-EGUs. One state commenter suggested that, if justification can be 
provided for an alternative dataset, it too may be considered for 
modeling. One state commenter recommended the rule clarify that states 
must use the most recent 3 years of emissions data that are available 
at the time that a modeling protocol for that area is submitted to the 
EPA, and that revised modeling should not be required if more recent 
emissions data become available.
iii. EPA Response
    When using actual emissions, the EPA believes the most recent 3 
years of time varying emissions (e.g., emissions that vary hourly, 
seasonally, monthly, daily, etc.) should be modeled since the air 
quality modeling is being used as a surrogate for monitoring. The 
Modeling TAD gives recommendations on inputting hourly emissions into 
AERMOD for those sources with hourly continuous emissions monitoring 
(CEM) data and also gives recommendations on inputting time varying 
emissions (e.g. seasonally, monthly, etc.) when no hourly emissions are 
available and only annual emissions and data such as production logs or 
fuel usage are available. However, the final rule does not restrict the 
ability of air agencies to use more conservative allowable emissions in 
conducting their modeling. In the event that a particular source does 
not have the most recent 3 years actual of emissions, it may be 
possible to use the most recently available emissions or develop the 
most recent 3 years of emissions using recommendations in the Modeling 
TAD. The reviewing authority should work with the appropriate EPA 
Regional Office on the use of such emissions. For an application that 
contains a mix of sources whose emissions data are not concurrent with 
each other, it is possible to model all of these sources together 
following recommendations in the Modeling TAD. Once a modeling protocol 
or modeling analyses have been submitted, there is no requirement to 
revise the protocol or modeling respectively if more recent emissions 
have become available since the submission, and in the best 
professional judgment of the reviewing authority, those emission 
changes do not warrant a revision to the protocol or modeling analyses.
c. Accounting for Recent Emission Reductions in Modeling Analyses
i. Summary of Proposal
    In the proposal, the EPA noted that, in some cases, air quality 
modeling conducted in advance of January 2017 may indicate a violation 
of the 1-hour SO2 standard and, to address such situations, 
the air agency may wish to consult with the source(s) and take action 
to adopt enforceable emissions limitations as necessary prior to 
January 2017 to potentially avoid a nonattainment designation. The EPA 
proposed that, as long as these controls are implemented and 
enforceable as of January 2017, it would be appropriate for the new 
lower allowable emissions to be used in the modeling analysis in place 
of the higher actual emissions. The EPA proposed that, if the air 
agency is able to demonstrate attainment with the new controls or 
emission limits, the governor of the state has the opportunity to 
modify its designation recommendation accordingly, if that designation 
has not yet been issued. See 79 FR 27464, May 13, 2014.
ii. Brief Summary of Comments
    A number of commenters supported the inclusion of language 
providing the option for states to model more recent emission rates 
based on enforceable limits implemented in advance of the January 2017 
modeling deadline. Commenters stated that this approach is a reasonable 
option which would provide industry with an incentive to achieve timely 
emission reductions to meet the regulatory requirements while 
potentially relieving air agencies from the requirements that a 
nonattainment designation entails, if such a designation has not yet 
been issued. One industry commenter requested that the method for 
reducing emissions not be limited to installing controls.
    Some state commenters requested that the EPA develop methodologies 
for air agencies to work with sources whose 2015 emissions are above 
the threshold to establish permanent and enforceable emission 
limitations that show attainment with the SO2 standards 
prior to a designation of such sources' areas. One state commenter 
stated that there must be a process that allows for the air agencies' 
discretion under extenuating circumstances in order to account for 
significant changes at a facility that occurred during the most recent 
3 years.
iii. EPA Response
    After review of the comments, the EPA continues to believe that it 
is appropriate for the air agency to consult with the affected 
source(s) and take action to adopt enforceable emissions limitations as 
necessary prior to January 2017. As long as the emissions limitations 
are in place and enforceable by January 2017, the new allowable 
emission limit may be input into the model instead of the actual 
emissions of the most recent 3 years.
    The EPA expects that a number of emissions sources may be 
candidates for this optional approach. Many EGUs

[[Page 51078]]

were subject to compliance deadlines for the MATS in April 2015 (or in 
some cases are subject to April 2016 deadlines), and the EPA expects 
that many will become subject to title V permits that require 
compliance with MATS SO2 emission limits as the means of 
demonstrating compliance with the MATS requirements related to acid gas 
emissions. These EGUs may be able to adopt control technologies and 
enforceable emission limits to reduce emissions of SO2, as 
well as mercury. Similarly, industrial boiler operators will have the 
incentive to adopt SO2 emission limits as part of their 
strategy for complying with the Industrial Boiler Maximum Achievable 
Control Technology Standard. 78 FR 7162, January 31, 2013.
    Therefore, the EPA believes that as long as these emissions 
reductions are implemented and enforceable by to January 2017, it would 
be appropriate for the new lower allowable emissions to be used in a 
modeling analysis in place of the higher actual emissions. The air 
quality impacts from such a source would be characterized by the new 
enforceable allowable limit and could be used as a basis for future 
determinations regarding areas' attainment status.
d. Stack Height
i. Summary of Proposal
    The EPA described its view in the proposed rule that actual stack 
height is appropriate to use in conjunction with actual emissions in a 
modeling approach to characterize current air quality. The EPA also 
described its view that, if an air agency chooses to use allowable 
emissions, then it should use good engineering practice (GEP) stack 
height when the actual stack height exceeds the GEP height because the 
GEP height is used when calculating the allowable emission rates. The 
EPA noted that additional recommendations on the use of actual stack 
height can be found in the Modeling TAD. See 79 FR 27464, May 13, 2014.
ii. Brief Summary of Comments
    A number of state and industry commenters supported the EPA's views 
on the use of actual stack height in conjunction with actual emissions. 
However, several state and industry commenters did not agree that GEP 
stack height should be used if a state chooses to use allowable 
emissions. Commenters stated the EPA should allow sources to model 
using actual stack height regardless of whether they are modeling 
actual emissions or allowable emissions since the purpose of the rule 
is to estimate, as accurately as possible, conditions that would be 
measured at a monitor. Commenters also stated that GEP stack height is 
not always a factor in establishing the emissions limit, where such 
limits are not established under an implementation plan subject to the 
restrictions of CAA section 123; for example, in the context of 
emission limits that are established based on emission standards under 
CAA section 112, such as the MATS rule. One commenter stated that the 
concern about giving inappropriate credit for dispersion techniques is 
irrelevant in the context of this designation modeling as CAA section 
123 applies only to emission limitation controls.
iii. EPA Response
    After consideration of comments, the EPA continues to recommend the 
use of actual stack heights when using actual emissions and the use of 
GEP height when modeling with allowable emissions where such emissions 
limits are or would be subject to CAA section 123 and to the EPA's 
corresponding regulations implementing GEP requirements. This would 
include limits established under any CAA provision that are intended to 
be credited in an implementation plan for attaining and maintaining the 
NAAQS. The use of GEP for allowable emissions modeling in such 
situations is based on the fact that the modeling conducted to 
determine the emissions limits was or would be based on GEP stack 
heights. Therefore, if actual stack heights (when above GEP) were used 
in such situations, the behavior of the modeled sources would not be 
consistent with the modeling results used to determine the emissions 
limits relied upon to demonstrate attainment of the NAAQS.
e. Meteorological Data
i. Summary of Proposal
    For purposes of conducting modeling that simulates what might be 
expected to be measured by an ambient monitor, the EPA recommended the 
use of 3 years of meteorological data. The EPA stated that, ideally, 
air agencies would use the most recent 3 years of meteorological data 
and the same 3 years of actual emissions data when modeling for 
designations. The EPA noted that the Modeling TAD has additional 
suggestions on these meteorological inputs. See 79 FR 27465, May 13, 
2014.
ii. Brief Summary of Comments
    Some commenters recommended the use of 1 year of meteorological 
data rather than 3 years and provided several reasons: Use of 1 year of 
on-site meteorological data would yield a very robust data set; 3 years 
does not provide a significant benefit over 1 year; 1 year of 
meteorological data is sufficient for PSD purposes; collection of 3 
years of data would delay the running of AERMOD; and collection of 3 
years of data would be unnecessarily expensive. Commenters stated that, 
while relatively few meteorological databases with 3 years of on-site 
meteorological data exist, many sources may have previously collected a 
full year of data and should be able to use that data without starting 
all over again on an expensive 3-year effort. One state commenter asked 
the EPA to clarify what is meant by ``the most recent 3 years.''
    One state commenter recommended that up to 5 years of 
meteorological data be used and stated that, while a single 3-year 
period may not provide adequate confidence in the analysis, 5 years 
will provide more 3-year combinations that can be compared to the 
NAAQS, and more meteorological data improves confidence in the result. 
Some commenters requested that the EPA clarify:
     That air agencies need not use concurrent meteorological 
data, given that some sites simply do not have concurrent 
meteorological data.
     Given the lack of 3 years of on-site data in many areas, 
the EPA should approve the use of prognostic meteorological data.
iii. EPA Response
    The EPA's recommendation is to use the most recent 3 years of 
representative site-specific data or when site-specific data are not 
readily available, or it is not feasible or cost-effective to collect 
site-specific data, the most recent 3 years of representative National 
Weather Service meteorological data or other representative data. When 
the most recent 3 years of representative meteorological data are not 
available, the use of older representative meteorological data can be 
used. For such cases, the Modeling TAD offers recommendations on 
synching the older meteorological data with the more recent emissions, 
especially for those sources utilizing hourly emissions. The Modeling 
TAD provides an explanation of the need for 3 years of meteorological 
data, even if only 1 year of on-site meteorological data are available. 
With regards to the type of meteorological data that are available, 
i.e. site-specific, NWS data, or prognostic data, the EPA's Modeling 
Guideline should be consulted on the latest acceptable forms

[[Page 51079]]

of meteorological data at the time of the modeling analyses.
f. Modeling Protocol, Including Multiple Sources
i. Summary of Proposal
    This rulemaking proposed that each state list the sources that are 
to be addressed under this rule and the approach to be used to meet 
this rule's requirements (air quality characterization through 
monitoring, air quality characterization through modeling, or 
establishment of a requirement for a timely source shutdown) for each 
source. In preparation for conducting modeling, the EPA proposed that 
the state would need to develop a modeling protocol for all the sources 
the state plans to model. Specifically, in Sec.  51.1203(d), the EPA 
proposed that the air agency consult with the appropriate EPA Regional 
Office in developing modeling protocols and submit the protocol to the 
Regional Administrator for review. In Sec.  51.1203(d)(1), the EPA 
proposed that the modeling protocol shall include information about the 
modeling approach to be followed, including but not limited to the 
model to be used, modeling domain, receptor grid, emissions dataset, 
meteorological dataset and how the state will account for background 
SO2 concentrations. The EPA stated that details on the 
suggested protocol elements and the recommended standard format of this 
protocol can be found in the Modeling TAD. See 79 FR 27465, May 13, 
2014.
ii. Brief Summary of Comments
    Some state and industry commenters requested that the EPA provide 
more specific guidance on conducting multi-source modeling analyses. 
Commenters stated that leaving these topics for negotiation with the 
EPA Regional Office will lead to inconsistent application of guidance 
among states. Commenters requested guidance on when a source should be 
modeled by itself, when a source should be modeled with other sources 
in the surrounding area, more detail on the size and location of 
sources that should be included in a multi-source analyses, and who 
would be responsible for conducting analyses when sources are located 
in multi-state areas. One state commenter requested that guidance on 
modeling facilities across state lines should be addressed.
iii. EPA Response
    The determination of whether to include nearby sources in a 
modeling exercise around a source that exceeds the emissions threshold 
is case specific, and a standardized methodology cannot be developed to 
fit all scenarios. Therefore, the final rule does not promulgate 
requirements addressing nearby sources. The EPA has offered technical 
recommendations in the Modeling TAD. The identification of nearby 
sources for modeling should rely on sound technical reasoning and best 
professional judgment. The EPA emphasizes that not all emissions 
sources near the source of interest need to be explicitly modeled, as 
in some cases the impacts of those sources can be sufficiently 
represented by a background monitor as discussed in the Modeling TAD 
and section 8.2 of the EPA's Modeling Guideline.
    As stated previously, the TADs provide recommendations but are not 
binding or enforceable and create no obligations on any person. 
Although the draft TADs are referenced as recommended approaches in the 
preamble to the proposal and in this rulemaking, they are not required 
to be adhered to by any air agency who is required to characterize air 
quality around an SO2 source identified in this rulemaking. 
The TADs have been provided in order to potentially aid air agencies 
seeking advice in the air quality characterization process required by 
this rulemaking. The Agency has indicated that the TADs are meant to be 
used as possible tools to aid air agencies. The EPA is not codifying 
changes to the TADs in this rulemaking in response to any comments 
received on the proposed rule. The TADs are living documents which the 
EPA may update as necessary.
g. Ongoing Air Agency Data Requirements for Areas That Were Initially 
Modeled
i. Summary of Proposal
    The EPA proposed that, for areas with modeled air quality data 
based on actual emissions that did not exceed the standard, air 
agencies would be required to continue to submit information to the EPA 
in subsequent years that provide a reasonable assurance that the area 
continues to have air quality that does not exceed the standard. The 
EPA proposed three options for how air agencies that rely on modeling 
of actual emissions would need to conduct additional emissions and/or 
modeling analyses. In the proposed rule, the EPA believed that such 
additional analyses would only be needed for areas that had been 
designated as ``unclassifiable/attainment'' based on actual emissions-
based modeling. The EPA further noted in the proposed rule that modeled 
source areas would not be subject to these ongoing data requirements if 
(1) modeling for the source was conducted using allowable emissions, or 
(2) the modeling for the source was conducted using actual emissions 
and the relevant sources then adopted enforceable emission limits 
consistent with the actual emissions rates used in the modeling.
    In Option 1, the EPA proposed that any air agency that will be 
subject to an ongoing data requirement for modeled areas would be 
required to assess the most recent SO2 emissions data 
annually, beginning in the year after the area is designated as 
unclassifiable/attainment, and to conduct updated air quality modeling 
every 3 years, and in additional years when the air agency or the EPA 
determines that such modeling is warranted. Air agencies would be able 
to request that the EPA Regional Administrator approve a suspension of 
the triennial modeling requirement for an area if their most recent 
modeling DV was less than 50 percent of the NAAQS.
    In Option 2, the EPA proposed to require the air agency to provide 
the EPA with an assessment of SO2 emissions changes for each 
source annually, as in Option 1, but to not have a requirement to 
conduct updated air quality modeling every 3 years. For sources for 
which the air agency determines that emissions have increased, the air 
agency would be required to submit to the EPA an assessment of the 
cause of the increase, and provide the EPA with an initial 
determination of whether air quality modeling would be needed to verify 
that the area around the source continues to have air quality levels 
that do not exceed the standard. If the air agency or the EPA 
determines that additional air quality modeling is necessary, the air 
agency would be required to submit the results of that assessment in a 
timely fashion--within 12 months.
    In Option 3, the EPA proposed to require the state to perform 
periodic screening modeling every 3 years for all source areas that had 
been previously modeled and determined to be attaining the standard, 
and submit such modeling for review to the EPA. Screening modeling is 
commonly performed using a set of default parameters rather than area-
specific parameters, and it generally simulates air quality levels that 
are more ``conservative'' than levels that would be estimated using 
area-specific parameters. In the proposal, the EPA stated that a 
complete, full-scale modeling analysis with updated emissions and 
meteorological inputs would only be required if the state performs 
screening modeling that indicates a potential violation. Under all

[[Page 51080]]

three options, if the modeling performed indicates that air quality 
levels in an area exceed the SO2 NAAQS, the EPA may take any 
appropriate action, including, but not limited to, requiring adoption 
of enforceable emission limits to ensure that future air quality levels 
in the area do not exceed the SO2 NAAQS; redesignation of 
the area to nonattainment; or issuance of a SIP call requiring action 
by the state to bring the area into attainment.
    The EPA requested comment on these three options for ongoing data 
requirements for air agencies with sources modeled based on actual 
emissions, and requested that each commenter provide a clear rationale 
for their position. The EPA also invited comments on any alternative 
ideas and asked that the commenter provide a detailed rationale and 
estimate of any associated costs for any such recommendations. See 79 
FR 27465, May 13, 2014.
ii. Brief Summary of Comments
    Several state, environmental, and tribal commenters supported 
Option 1. These commenters stated that an approach that simply assesses 
SO2 emissions changes at large sources would not account for 
variations in meteorological conditions, increased SO2 
emissions from interactive sources, or improvements to the actual 
modeling computer program. One commenter stated that annual modeling 
makes far more sense from the perspective of protecting the public 
health, and suggested that modeling once every 3 years is an extremely 
periodic and slow way of assessing air quality, such that people living 
in the impacted area could be unaware for years, and thus unable to 
take action to protect themselves or place pressure on their government 
to correct the problem.
    Several state and industry commenters opposed Option 1 and stated 
that modeling assessments should not be conducted on a 3-year or any 
other regular basis. Some believed the requirement to model every 3 
years would be an inefficient use of resources and arbitrary since it 
would not take into account information which might show that 
undergoing a revised modeling analysis would be unnecessary. They 
claimed that as long as conditions have remained the same or possibly 
improved in the intervening timeframe, additional modeling will provide 
no additional useful information. Others opposed Option 1 on the 
grounds that no other ambient standard requires such a detailed on-
going analysis. Consistent with their concerns about resources, 
commenters supported the aspect of Option 1 that would enable the air 
agency to terminate certain ongoing data requirements if air quality 
modeling indicated a DV equal to or less than 50 percent of the 1-hour 
SO2 NAAQS.
    A number of state and tribal commenters objected to Option 2. One 
tribal commenter stated that the proposed emissions assessments 
required in Option 2, which lack a regular air quality modeling 
requirement, are not stringent enough. Some state commenters expressed 
concern that this option could lead to an indeterminate number of 
future analyses required, and that such open-ended requirements have 
cost implications that could strain states' already-limited resources. 
On the other hand, more than 20 state and industry commenters supported 
Option 2 because it balances providing air quality protection with 
level of effort from state regulatory authorities. Several commenters 
noted that with SO2 emissions declining on a national level, 
remodeling would not be expected to be required and a simple analysis 
of the change in emissions would be sufficient to determine the need 
for additional modeling. A state commenter suggested providing clearer 
guidance regarding what level of emissions increase would trigger 
further evaluation of sources, rather than having the air agency 
provide an assessment for each source with increased emissions. The 
commenter suggested (1) if the original modeling level was equal to or 
greater than 90 percent of the standard, then new modeling would be 
required for the area in the event there is any increase in emissions 
in the area; (2) if the original modeling level was between 50 percent 
and 75 percent of the standard, then new modeling would be required for 
the area if area emissions increased by 15 percent or more; and (3) if 
the original modeling level was less than 50 percent of the standard, 
then the ongoing modeling requirement should not apply (similar to the 
provision in Option 1).
    Another state commenter stated that, ideally, under Option 2, 
agencies would have a 2.5-year timeframe to complete the entire ongoing 
data requirement process: The first year would consist of preparing and 
submitting data for the national emissions inventory for the previous 
year; 6 months thereafter agencies would submit a report to the EPA 
stating whether air quality modeling is needed; and 12 more months 
would then be permitted to perform any additional modeling deemed 
necessary.
    Regarding Option 3, several state and industry commenters disagreed 
with having any default modeling requirement, even for screening 
modeling, and opposed this option. Several commenters objected to the 
required use of a screening model for the following reasons: Most of 
the facilities will have multiple emission points and the screening 
tools were not designed to evaluate such complex situations; the 
mandatory use of screening models will result in an overly cautious, 
ineffective approach to verification; and screening modeling is almost 
as complex and time consuming as full-scale modeling and thus this 
option would not be a good use of state and the EPA resources.
    Lastly, some commenters suggested that the air agency should be 
able to choose which ongoing data requirement approach it intends to 
follow for a particular area. Another commenter suggested an approach 
that would be a combination of all three options, where the air agency 
would evaluate emissions changes each year, and then conduct screening 
modeling or full-scale modeling if the magnitude of emission changes 
warrant.
iii. EPA Response
    The EPA recognizes the concerns of commenters about the resource 
considerations associated with Options 1 and 3, which for areas with 
modeling based on actual emissions and designated as attaining would 
require full-scale modeling or screening modeling every 3 years, even 
if annual emissions in the area were not increasing. We disagree with 
those commenters who oppose any requirement for ongoing data assessment 
at all; and with those commenters who suggest a requirement for annual 
modeling for all areas. The EPA believes that a reasonable requirement 
for ongoing evaluation of priority areas identified by this rule is 
important to meeting the public health objectives of this NAAQS while 
balancing resource constraints of air agencies in a manageable way. The 
EPA agrees with commenters that suggest it would be reasonable to check 
emissions changes first, and based on that information, then make a 
determination about whether to conduct additional modeling. The EPA is 
also mindful of the fact that in this rule, modeling is effectively 
serving as a surrogate for monitoring, and so the EPA believes it is 
reasonable to have similar approaches for terminating the ongoing data 
requirements for both areas where air quality was initially 
characterized by monitoring, and areas where air quality was initially 
characterized by modeling.

[[Page 51081]]

    After considering the comments received on the proposed rule, the 
EPA is finalizing a combination of elements from Option 1 and Option 2. 
As outlined in proposed Option 2, the final approach requires the air 
agency to conduct an assessment of emissions changes annually for all 
source areas for which the initial air quality modeling was based on 
actual emissions and the area was designated as attaining the standard. 
The air agency must provide this assessment to the EPA in the form of a 
report, to be submitted by July 1 of the following year. This 
assessment should reflect the most recent quality-assured emissions 
data available for the relevant sources in the area. The report must 
also describe the reason for emissions increases in the previous year 
at any listed sources, and must include a recommendation indicating for 
which sources and areas the emissions increase was substantial enough 
to warrant updated air quality modeling that would help determine air 
quality levels relative to the standard.
    Adapting suggested criteria from a state commenter (with some 
modification), the EPA recommends as a general guideline that the air 
agency should conduct additional modeling (using the most recent actual 
emissions as inputs) for an area if (1) the original modeling level was 
equal to or greater than 90 percent of the standard, and there is any 
increase in emissions in the area; or (2) if the original modeling 
level was between 50 percent and 90 percent of the standard, and 
emissions in the area increased by 15 percent or more. However, the EPA 
is not promulgating specific criteria for when additional modeling is 
required because the EPA believes that the need for additional modeling 
is best judged on a case-by-case basis reflecting case-specific 
information on emissions changes and prior modeling results. For 
example, if the emissions increase was substantial and the previous 
modeling had indicated that air quality in the area was just under the 
standard, then air quality modeling would be warranted. In other cases 
where air quality has been modeled to be well below the standard and 
annual emissions increase only slightly in the following year, the air 
agency would be able to exercise judgment regarding whether additional 
modeling would be needed. The use of case-specific judgment will be 
especially important in cases involving multiple sources or multiple 
emission units that may have different emissions-air quality 
relationships.
    The modeling analysis for the area would then be due within 12 
months of the air agency recommendation that such modeling is warranted 
(i.e. by July 1 of the following year). In this way, if new modeling is 
recommended, the whole process ideally would take 18 months from the 
end of the ``ongoing data requirement'' year to when new modeling would 
be due (not 30 months as suggested by a state commenter).
    The EPA finds that the relatively straightforward approach 
described in proposed Option 2 requiring the examination of emissions 
data annually (rather than conducting updated air quality modeling 
every 3 years for every area) is consistent with the frequency with 
which ambient monitoring data is evaluated. This approach also provides 
some flexibility to the air agency in recommending whether the 
magnitude of emissions changes in an area would be large enough to 
warrant new modeling. As compared to Options 1 and 3, this approach 
also would be expected to involve less overall workload for air 
agencies over time.
    In addition, as provided in Option 1, the final rule also includes 
a provision in Sec.  51.1205(b) enabling the air agency to terminate 
the ongoing data requirement for a modeled area if it meets certain 
criteria. The provision is analogous to Sec.  51.1205(a), which allows 
for the air agency to obtain EPA approval to cease operation of a new 
ambient monitor if the most recent DV is low enough to meet certain 
criteria (e.g. less than or equal to 50 percent of the level of the 
NAAQS, or meeting the criteria of 40 CFR 58.14). Thus, for areas that 
were originally modeled based on actual emissions, Sec.  51.1205(b) of 
the rule allows termination of the air agency's annual emission 
reporting requirement if the air agency submits an air quality modeling 
analysis, using updated actual emissions data from the most recent 3 
years, that demonstrates that air quality DVs at all receptors in the 
analysis are less than or equal to 50 percent of the 1-hour 
SO2 NAAQS, and such demonstration is approved by the EPA 
Regional Administrator. Likewise, if the initial modeling of a source 
area demonstrates that air quality DVs at all receptors in the analysis 
are less than or equal to 50 percent of the 1-hour SO2 
NAAQS, and such demonstration is approved by the EPA Regional 
Administrator, the area would not be subject to ongoing data 
requirements as well. The EPA believes that including this type of 
provision in the final rule structures the rule in a balanced way for 
both modeled and monitored areas in order to meet the objectives of 
ensuring that such areas continue to meet the standard and continue to 
protect public health, while recognizing the resource constraints of 
air agencies.
h. Procedural Approach for Post-Attainment Annual Reporting
i. Summary of Proposal
    The EPA proposed two options regarding the procedures by which air 
agencies would submit ongoing data reports to the EPA for source areas 
characterized through modeling, and by which the EPA would review and 
act on them. Under Option 1, the EPA proposed that the air agency would 
submit a report to the EPA annually as an appendix to its annual 
monitoring plan. The annual monitoring plan is required to be submitted 
to the EPA Regional Administrator by July 1 each year. The inclusion of 
this report as an appendix to the annual monitoring plan would ensure 
that the report would be subject to the same opportunities for public 
review and comment that are to be provided for the monitoring plan 
pursuant to regulations at 40 CFR 58.10. Those regulations specify that 
if the air agency modifies the monitoring plan from the previous year, 
then prior to taking final action to approve or disapprove the plan, 
the EPA would be required to provide an opportunity for public review 
and comment on the modified plan. The regulations also indicate that if 
the air agency has already provided a public comment opportunity in 
developing its revised monitoring plan and has made no further changes 
to the plan after reviewing the public comments that were received, 
then it could submit the public comments along with the revised plan to 
the EPA, and the EPA Regional Administrator would not need to provide a 
separate opportunity for comment before approving or disapproving the 
plan.
    Under Option 2, the ongoing report would not be submitted to the 
EPA as an appendix to the annual monitoring network plan, but it would 
take the form of a separate, independent submittal from the state to 
the EPA Regional Administrator. The EPA proposed that this report would 
be due by the same July 1st date each year and that this independent 
submittal would follow the general guidelines set forth in 40 CFR 58.10 
regarding opportunities for public review as described in Option 1, but 
the report would only include the annual assessments associated with 
sources in areas that were designated unclassifiable/attainment based 
on modeling of actual emissions.
    In the proposed rule, the EPA requested comment on the two 
procedural options as well as any alternative ideas suggested by 
commenters. For any such recommendations, the EPA requested

[[Page 51082]]

that the commenter provide a detailed rationale and estimate of any 
associated costs. See 79 FR 27467, May 13, 2014.
ii. Brief Summary of Comments
    Some state, tribal and industry commenters recommended that this 
information be included as an appendix to the annual monitoring plan, 
rather than as a stand-alone document. One commenter stated that, since 
both options have a deadline of July 1st each year, a separate document 
would only add more time and resource use. Several state commenters 
recommended that the assessment be submitted separately from the annual 
monitoring plan. These commenters provided the following rationale: 
Since these documents are not related, they should be kept separate; 
since the annual report refers to modeling, it will cause less 
confusion for the general public if it is a separate document from the 
annual monitoring plan; and because the annual monitoring plan and the 
emissions inventory submittals are performed by separate work units on 
different timelines, it would be better to deliver the products 
separately rather than delay one or the other to deliver them together.
iii. EPA Response
    After considering the comments received related to both of the 
proposed options, the EPA believes that the best approach for the final 
rule is to allow the affected air agencies the discretion to either 
include the required annual data requirements report for modeled areas 
either as an appendix to the state's monitoring plan, or as a stand-
alone document. The air agency will have the flexibility under the 
final rule to select the approach that best meets the Agency's 
workload, schedule, and particular needs. The EPA believes that either 
of the procedural approaches will be sufficient to implement the 
ongoing data requirements. Regardless of which approach is chosen by 
the air agency, the report must be submitted to the respective EPA 
Regional Office by July 1st annually and made available for public 
review and comment. The first report is due on July 1st of the year 
after the effective date of the area's initial designation and 
additional reports are due July 1st of each subsequent year.

E. Other Key Issues and Comments

    Comments on the proposed rule also raised several other issues not 
already addressed in this document. This section identifies and 
addresses the key issues raised by those comments.
1. March 2015 Consent Decree
    The proposed rule did not contain any regulatory deadlines for the 
EPA to complete area designations under the 2010 SO2 NAAQS. 
However, at the same time that the EPA was developing the proposed rule 
and the final rule, the agency was also engaged in district court 
litigation from public interest groups and some states and state 
agencies seeking to have the EPA placed on a binding schedule to 
complete the designations. The parties in these cases filed complete 
briefs in one of these cases, resulting first in the court finding that 
the EPA was liable for having failed to meet the statutory deadline to 
complete all area designations. Subsequently, the EPA and the other 
parties conducted extensive settlement discussions over the remedy, 
i.e., the schedule by which the EPA would complete its duties. This 
resulted in a settlement between the EPA and the public interest group 
plaintiffs, which the plaintiff-interveners did not join.
    On June 2, 2014, the EPA published notice of a proposed consent 
decree reflecting this settlement (Sierra Club et al v. McCarthy, Civil 
Action No. 3:13-cv-3953-SI (N.D. Cal.)). 79 FR 31325. This proposed 
consent decree included deadlines for the EPA to complete designations 
in three phases, the latter two of which were due on the same dates 
that the EPA discussed as its intended designations dates in the 
preamble to the proposed DRR. The EPA received several comments on the 
notice informing the public of the proposed consent decree itself, and 
in response to this proposed rule.
    The EPA is not promulgating deadlines for its completion of area 
designations in this final rule. Therefore, any comments directed to 
the merits of the consent decree itself are outside the scope of this 
rulemaking, and we will not respond to them here. Instead, as discussed 
earlier in this document, on March 2, 2015, the court issued an order 
entering the consent decree and establishing its deadlines as binding 
on the EPA. As also explained earlier, the 2017 and 2020 deadlines for 
the latter two stages of designations established by the consent decree 
will allow the EPA and states to use the new data and information that 
is timely generated by the implementation of this rule to inform the 
designations required to be completed by those dates, but it is not 
likely that full implementation of the rule can occur quickly enough to 
support the next round of designations required by the court's order to 
be completed by July 2, 2016.
2. Recommendations for the EPA To Designate Areas as Unclassifiable
    Several commenters recommended that the EPA take prompt action to 
designate areas with inadequate data for air quality characterization 
as unclassifiable. A number of commenters asserted that the EPA cannot 
use the rule to supersede the statutory schedule under which the EPA is 
required to make area designations, including statutorily-appropriate 
``unclassifiable'' designations. One industry group commented that the 
CAA does not authorize the EPA to conduct designations according to the 
schedule anticipated by the proposed rule preamble, commenting that the 
EPA must instead complete designations in accordance with the schedule 
under CAA section 107(d)(1) (designating areas unclassifiable where 
appropriate), and then redesignating unclassifiable areas as either 
attainment or nonattainment later. Similarly, a state commenter 
expressed the view that further data are not necessary to meet the CAA. 
Several commenters also stated that the proposed rule effectively 
nullifies the ``unclassifiable'' designation, use of which would have 
allowed the EPA to meet its statutory deadline. One commenter also 
stated that the EPA should continue to use the ``unclassifiable'' 
designation where appropriate, and should not seek to designate all 
areas as attainment or nonattainment.
    Several commenters also addressed the interrelationship between the 
proposed rule and the proposed consent decree for settling the lawsuit 
regarding the EPA's failure to promulgate designations for areas 
without monitored violations. One state commenter urged that the EPA 
codify the proposed consent decree into the rule. Another state 
commenter objected to this suggestion, stating that the proposed 
consent decree specifies a designations schedule that conflicts with 
the proposed schedule and compromises a commenter's ability to comment 
on the impact of that consent decree on the rule. An industrial 
commenter found the consent decree to undermine the proposed rule. 
These commenters urged that the EPA re-propose the relationship between 
the consent decree and the rule. An industry group stated that the 
issuance of the proposed consent decree undermines the rule because it 
would require an early round of designations that would be based on 
modeling, in contravention of the process under the proposed rule that 
offers the option of basing designations on monitoring data.

[[Page 51083]]

    As stated previously, the EPA is not establishing or modifying any 
area designation requirements provided for in section 107 of the CAA 
through this rulemaking. The purpose of this rulemaking is to require 
states to characterize air quality in priority areas throughout the 
country where existing ambient monitors may not be adequately 
characterizing peak 1-hour SO2 concentrations. The air 
quality data obtained as a result of this rulemaking then may be used 
in future designations or redesignations, as appropriate. While the 
notice of proposed rulemaking described the EPA's anticipated 
designations schedule, for purposes of explaining the timeline by which 
the EPA anticipates that the data the EPA was proposing to require will 
be used, the timeline for possible future use of these data does not 
dictate the schedule or the substantive features of the requirements 
for obtaining data for air quality characterization purposes, and the 
Agency believes it will be highly valuable to obtain these data even if 
that occurs after initial designations occur.
    While the notice of proposed rulemaking described the EPA's 
expectations that designations for areas not already completed in 
August 2013 would be completed either in 2017 or in 2020, the 
timetables for obtaining additional data are as prompt as the EPA 
considers reasonable whether or not such data can be used to inform the 
remaining designations, and thus alternate approaches and timetables 
for designations would not result in a different timetable for 
implementation of the rule's requirements. In particular, whether 
designations proceed according to the approach described in the EPA's 
notice of proposed rulemaking, or whether areas are first designated 
unclassifiable and subsequently redesignated to attainment or 
nonattainment, the same timetable, and substance of requirements for 
data to support more properly informed future judgments regarding 
areas' attainment status is warranted. Because this rulemaking is not 
intended to define the designations process and did not propose 
regulatory deadlines for issuing designations, it would be 
inappropriate in this final rulemaking to codify any particular 
schedule for designations action.
    The proposed consent decree referenced by the comments concerns 
separate legal proceedings that are addressing the EPA's obligations to 
designate areas under CAA section 107. The commenters have not 
identified why any potential outcome of those proceedings warrants any 
particular revision to the rule, nor have they explained why the 
validity of the DRR is contingent on use of any particular designations 
approach. While the court's decision establishing timing requirements 
for the EPA's designations obligations will of course affect the EPA's 
approach to designations, including affecting the extent to which the 
EPA will be able to use the data required under the rule at various 
times in the designations or redesignations processes, these effects do 
not determine the validity of the data collection requirements of the 
rule. For these reasons, the EPA believes that the ability of 
commenters to address issues relevant to the rule was not compromised 
by the proposed consent decree and other actions or statements in the 
proceedings regarding the EPA's timetable for designations, and the EPA 
finds that re-proposal of the rule is not justified.
3. The Cost of Monitoring or Modeling Under this Rule
    Several state and industry commenters stated that, because of 
funding limitations at the state level, any monitoring or modeling done 
to meet the requirements of the rule would likely need to be done by 
the affected sources. Commenters also stated that the rule will present 
yet another burden on the regulated community when facilities are 
already spending resources on emissions reductions projects that are 
required as the result of other EPA air quality rules.
    Commenters also stated that even if sources voluntarily set up and 
operate their own monitors, state and local agencies will nevertheless 
still need to dedicate resources to administer the program, provide 
technical assistance, conduct performance audits, ensure data quality 
and submit the data to the EPA's AQS database each year. Commenters 
also stated that the initial state funding should be provided by the 
EPA through CAA section 103 or 105 grant funds in order to establish 
the monitoring sites required to meet the requirements of the rule.
    The EPA recognizes that there will be costs and resources required 
to satisfy the requirements of this rulemaking. As suggested by both 
state and industry stakeholders who attended the EPA's May-June 2012 
stakeholder meetings, in the absence of increased grant funding it may 
be necessary for air agencies to rebalance their existing grant funds 
for this purpose, or to consider alternative funding approaches such as 
working closely with affected sources to assist in funding either the 
modeling or monitoring required to meet the requirements of the rule. 
Early planning may be helpful to address these funding needs.
    Because the CAA assigns to states much of the responsibility for 
developing air quality characterization data, the EPA describes the 
requirements of this rule in a consistent manner: Air agencies are the 
entities with principal responsibility to establish and operate 
monitors, and conduct modeling, and to provide air quality data to the 
EPA. However, the EPA recognizes that other parties (such as facility 
owners) also may perform significant portions of the work that this 
rule requires. The EPA would consider monitoring or modeling conducted 
by a third party to be an appropriate means for air agencies to obtain 
the data necessary to meet the requirements of this rule, provided that 
the state provides oversight to assure that (1) any monitoring is 
conducted in a manner that is equivalent to SLAMs and quality-assured 
in accordance with applicable requirements, and (2) any modeling 
analysis that the state submits, even if it was initially provided to 
the state by a third party, is done in a reasonable manner and follows 
the recommendations in the Modeling TAD or as otherwise agree upon with 
the EPA Regional Office on a case-by-case basis.
4. How the DRR Addresses SO2 Sources in Areas That Are 
Already Designated
    The intent of this DRR is to direct state and tribal air agencies 
to characterize air quality in areas around the largest sources of 
SO2 emissions, through the use of either air quality 
modeling or ambient monitoring, and to provide such data to the EPA. 
The additional information required by this rule will be able to inform 
future action by the EPA or the state (e.g., future designation 
decisions).
    The proposed rule did not specifically address whether the 
requirement to characterize a sources' SO2 emission impacts 
would apply differently based on whether areas containing sources were 
still undesignated, or whether they had already been designated as 
nonattainment, attainment, or unclassifiable. However, much of the 
discussion in the proposed rule preamble concerned how implementation 
of the rule might inform future area designations, thus implying that 
the air quality characterization requirement might apply only to areas 
that remained undesignated at the time of the rule's implementation. 
The EPA believes it is necessary to clarify how the rule applies to 
areas that have already been designated in some manner, either during 
the initial round of designations in August 2013 or in

[[Page 51084]]

subsequent rounds of designations pursuant to the March 2015 consent 
decree.
    The first question is whether air agencies are required under this 
rule to characterize air quality near sources in areas that were 
designated as nonattainment in August 2013. See 78 FR 47191, August 5, 
2013. In general, we expect nonattainment plans to provide adequate 
characterization of the impacts of sources within those nonattainment 
areas. Therefore, we have concluded that an air agency will not be 
required under this rule to characterize air quality around 
SO2 sources located in a designated nonattainment area. 
Specifically, we have clarified the definition of ``applicable source'' 
in Sec.  51.1200 of the final rule to be ``a stationary source that is 
(1) not located in a designated nonattainment area, and (2) has annual 
actual SO2 emissions of 2,000 tons or more, or has been 
identified by an air agency or by the EPA Regional Administrator as 
requiring further air quality characterization.'' Thus, as a general 
matter, this rule does not require the state's January 2016 list of 
sources triggering the requirements of this rule to include sources 
located within areas already designated as nonattainment.
    However, it may be possible that in some cases an SO2 
source or group of sources within the boundary of an existing 
nonattainment area can have significant impacts outside the 
nonattainment area, potentially raising concerns that these impacts 
might not be adequately evaluated in a nonattainment plan. The EPA 
notes that for such cases, the air agency and the EPA Regional 
Administrator retain the authority under this rule to require 
additional characterization of air quality around specific sources 
located in an existing nonattainment area, in the same manner that they 
retain the authority, as warranted, to require characterization of air 
quality around sources that are below the emissions threshold 
identified in this rule.
    Related questions also arise for sources in areas that will be 
subject to evaluation and designation by July 2016 under the March 2015 
consent decree regarding SO2 designations. Because all 
sources that meet the March 2015 consent decree criteria for 
designation by July 2016 will also exceed the 2,000 ton threshold under 
this DRR, these sources will need to be included on the January 2016 
list of sources subject to requirements for air quality 
characterization under this rule. Subsequent designations do not alter 
this list. 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 promulgated after January 2016. 
In particular, the list of sources would not be altered by promulgation 
of nonattainment designations in July 2016. Nevertheless, the EPA 
expects that if the area around a ``consent decree'' source is 
designated as nonattainment by July 2016, pursuant to the consent 
decree, then the information that was adequate to inform this 
designation would also satisfy the air agency's obligation under this 
rule to submit modeling information in January 2017 characterizing air 
quality around that source.
    The next question is how this rule applies to sources in areas that 
have been designated as ``unclassifiable'' or as ``unclassifiable/
attainment.'' \12\ The EPA did not apply these designations to any 
areas in August 2013, but the EPA may apply these designations to some 
areas in the designations required to be completed by July 2016. This 
rule requires air quality characterization for areas previously 
designated as unclassifiable, just as it requires air quality 
characterization for undesignated areas. If the EPA has previously 
determined through a designation action that sufficient information has 
not yet been identified to support an attainment or nonattainment 
designation (i.e., the area was initially designated as 
unclassifiable), then the additional information required by this rule 
will be used to inform possible future actions by the EPA or the state 
(e.g., to determine whether the area is attaining or not attaining the 
standard, and change designation status).
---------------------------------------------------------------------------

    \12\ While states have and may continue to submit designations 
recommendations identifying areas as ``attainment,'' the EPA expects 
to continue its traditional approach, where appropriate, of using a 
designation category of ``unclassifiable/attainment'' for areas that 
the EPA determines meet the NAAQS. The EPA expects to reserve the 
category ``unclassifiable'' for areas where the EPA cannot determine 
based on available information whether the area is meeting or not 
meeting the NAAQS or where the EPA cannot determine whether the area 
contributes to a violation in a nearby area. See SO2 
designations guidance issued by Stephen D. Page on March 20, 2015, 
available at https://www.epa.gov/airquality/sulfurdioxide/pdfs/20150320SO2designations.pdf.
---------------------------------------------------------------------------

    With regard to ``unclassifiable/attainment'' areas, no areas were 
given this designation in the August 2013 designations. However, it is 
possible that some areas may be given this designation in the July 2016 
designations based on relevant air quality characterization information 
(such as air quality modeling) that has been provided by the air agency 
or other parties in the designations process. The applicable sources in 
any such areas designated pursuant to the March 2015 consent decree 
would have also been included in the list of sources that air agencies 
would be required to submit to the EPA in January 2016 according to 
this rule. If an area has already been designated by the EPA as 
``unclassifiable/attainment'' by July 2016 pursuant to the consent 
decree, then the EPA expects that, as was the case for areas as 
designated nonattainment, the information that was adequate to inform 
an unclassifiable/attainment designation would also satisfy the air 
agency's obligation under this rule to submit modeling information in 
January 2017 characterizing air quality around that source. As a 
result, under this rule, the air agency would not be required to 
provide additional air quality characterization information to the EPA 
by January 2017.
    However, these already-designated ``unclassifiable/attainment'' 
areas would nevertheless be subject to the ongoing data requirements 
included in Sec.  51.1205 of this rule. While modeling for purposes of 
informing designations promulgated by July 2016 would also be 
considered modeling to address the requirements of this rule, the EPA 
is promulgating revised rule language that clarifies that the ongoing 
data requirements apply to areas modeled based on actual emissions 
whether that modeling was conducted for purposes of informing 
designations by July 2016 or conducted only for satisfying the 
requirements of this rule. Accordingly, Sec.  51.1205(b) has been 
modified to apply to any attainment area designated based on modeling 
of actual emissions to characterize air quality.
5. How Air Agencies Should Address Modeling and Monitoring in Multi-
State Areas To Meet the Requirements of the Rule
    As with the previous issue, a review of the comments and questions 
received from states has made the EPA aware of the need to clarify how 
the rule applies to situations where an applicable source that is 
located in one state or tribal jurisdiction has an impact on 
SO2 concentrations in one or more other jurisdictions. While 
the final rule preserves the option of the air agency of the 
jurisdiction in which the source is located to choose how to satisfy 
the air quality characterization requirements of the rule (i.e., 
through either monitoring or modeling), the EPA urges all air agencies 
involved to consult and coordinate in order to make appropriate 
decisions concerning whether modeling

[[Page 51085]]

or monitoring would be the most effective method to characterize the 
peak 1-hour SO2 concentrations in the ambient air affected 
by such sources.
    If the jurisdiction in which the source is located prefers to 
employ ambient monitoring to characterize air quality, the EPA believes 
it would be appropriate to use ambient monitoring only if: (1) The air 
agency coordinates with the other jurisdiction in identifying 
appropriate ambient monitoring sites; and (2) there is an agreement 
established with the other jurisdiction (in which peak 1-hour 
SO2 impacts are being experienced), and possibly with the 
facility owner, regarding logistical, financial and operational 
responsibilities associated with the purchase, installation and 
operation of the monitor or monitors that is acceptable to all parties. 
However, if one or both jurisdictions do not wish to employ ambient 
monitoring, and a monitoring agreement cannot be reached, the EPA 
believes that the obligation to characterize air quality rests with the 
jurisdiction in which the source is located. Without an adequate multi-
jurisdiction monitoring plan, the air agency would need to use modeling 
analyses to characterize air quality in the multi-jurisdiction area. 
Consultation among all involved jurisdictions will be important for 
planning and conducting technically appropriate modeling. The EPA 
expects that early and active coordination among all involved parties 
can lead to beneficial agreements for characterizing air quality in 
multi-jurisdiction areas, and the EPA will work with air agencies to 
help facilitate such agreements.

V. Environmental Justice Considerations

    The EPA believes the human health or environmental risk addressed 
by this action will not have disproportionately high and adverse human 
health or environmental effects on minority, low-income, or indigenous 
populations because it does not affect the level of protection provided 
to human health or the environment under the SO2 NAAQS. When 
promulgated, these regulations will require that air agencies 
characterize air quality around certain large emissions sources, or 
secure emission limits on sources to reduce annual emissions below 
2,000 tpy. It is intended that the actions resulting from this rule 
would lead to greater protection for U.S. citizens, including minority, 
low-income, or indigenous populations, by reducing exposure to high 
ambient concentrations of SO2. In addition, this rule will 
help communities by informing residents about ambient air quality 
around the largest sources of SO2.

VI. Statutory and Executive Order Reviews

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

    This action is not an economically significant action, but raises 
novel policy issues and was submitted to the Office of Management and 
Budget (OMB) for review. Any changes made in response to OMB 
recommendations have been documented in the docket.

B. Paperwork Reduction Act (PRA)

    The information collection activities in this rule have been 
submitted for approval to the Office of Management and Budget (OMB) 
under the PRA. The Information Collection Request (ICR) document that 
the EPA prepared has been assigned EPA ICR number 2495.01. A copy of 
the ICR is available in the docket for this rule, and is briefly 
summarized here. The information collection requirements are not 
enforceable until OMB approves them.
    The EPA is requiring air agencies to more extensively characterize 
ambient SO2 air quality concentrations, pursuant to sections 
110(a)(2)(B), 110(a)(2)(K), 301(a) and 114 of the CAA. For purposes of 
analysis of the estimated paperwork burden, the EPA assumed that 43 
states and tribes would take actions to characterize air quality 
through either air quality modeling or ambient monitoring in 412 areas 
around SO2 sources emitting 2,000 tpy of more across the 
country, and such states would submit the results of these analyses to 
the EPA. Under this rule, the air agency will have the ability to 
choose, on an area-by-area basis, the analytical approach to follow for 
characterizing air quality around each qualifying source. For this 
reason, there is no way of determining exactly how many areas may be 
characterized through ambient monitoring versus air quality modeling 
approaches. Therefore, this section presents two sets of estimated 
costs, one that assumes all source areas would be characterized through 
ambient monitoring, and the other that assumes that all source areas 
would be characterized through air quality modeling.
    Potential ambient air monitoring costs are estimated based on the 
assumption that air quality for each of the 412 SO2 sources 
exceeding the 2,000 tpy threshold would be characterized through a 
single newly deployed air monitor. (Note, however, that the Monitoring 
TAD discusses situations where more than one monitor may be appropriate 
or necessary to properly characterize peak 1-hour SO2 
concentrations in certain areas, which would increase costs 
proportionally.) Estimates are provided for a 3-year period and include 
a calculation for equipment amortization over 7 years (as is typically 
done in monitoring-related ICRs). For the period of 2016, 2017, and 
2018 (monitoring related expenditures would begin in 2016), the total 
approximate average annual monitoring cost, including a calculation for 
equipment amortization, is $8,662,110 (total capital, and labor and 
non-labor operation and maintenance) with a total burden of 102,869 
hours. The annual labor costs associated with these hours is 
$7,080,572. Included in the $8,662,110 total are other annual costs of 
non-labor operations and maintenance of $706,827 and equipment and 
contract costs of $874,711. For reference purposes, an estimate for 
initial establishment of a new SO2 monitoring station is 
$92,614 (does not include equipment amortization). In addition to the 
costs that would be incurred by the state and local air agencies, there 
would be an estimated burden to the EPA related to salary cost and 
equipment cost, etc., of a total of 52,717 hours and $776,005.
    Potential air quality modeling costs are estimated based on the 
assumption that air quality for each of the 412 SO2 sources 
exceeding the 2,000 tpy threshold would be characterized through air 
quality modeling analyses. Based on market research, stakeholder 
feedback and assumptions about the procedures to follow when conducting 
modeling for designations purposes,\13\ an estimate of modeling costs 
for a single modeling run centered on an identified source would be 
approximately $30,000. If air agencies choose to characterize air 
quality through modeling analyses around all 412 sources expected to be 
identified as exceeding the source threshold, then total national costs 
for modeling analyses would be estimated at $12,360,000. If these costs 
were incurred over the course of 3 years, then the approximate annual 
cost for each year over that period would be $4,120,000.
---------------------------------------------------------------------------

    \13\ The Draft SO2 NAAQS Designations Modeling 
Technical Assistance Document can be found at: https://www.epa.gov/airquality/sulfurdioxide/pdfs/SO2ModelingTAD.pdf.
---------------------------------------------------------------------------

    An agency may not conduct or sponsor, and a person is not required 
to respond to, a collection of information unless it displays a 
currently valid OMB

[[Page 51086]]

control number. The OMB control numbers for the EPA's regulations in 40 
CFR are listed in 40 CFR part 9. When OMB approves this ICR, the agency 
will announce that approval in the Federal Register and publish a 
technical amendment to 40 CFR part 9 to display the OMB control number 
for the approved information collection activities contained in this 
final rule.

C. Regulatory Flexibility Act (RFA)

    I certify that this action will not have a significant economic 
impact on a substantial number of small entities under the RFA. In 
making this determination, the impact of concern is any significant 
adverse economic impact on small entities. An agency may certify that a 
rule will not have a significant economic impact on a substantial 
number of small entities if a rule relieves regulatory burden, has no 
net burden or otherwise has a positive economic effect on the small 
entities subject to the rule. This final rule will not impose any 
requirements directly on small entities. Entities potentially affected 
directly by this final rule include state, local and tribal governments 
and none of these governments are small entities. Other types of small 
entities are also not directly subject to the requirements of this 
rule.

D. Unfunded Mandates Reform Act (UMRA)

    This action does not contain any unfunded mandate of $100 million 
or more as described in UMRA, 2 U.S.C. 1531, and does not significantly 
or uniquely affect small governments.

E. Executive Order 13132: Federalism

    This action does not have federalism implications. It will not have 
substantial direct effects on the states, on the relationship between 
the national government and the states, or on the distribution of power 
and responsibilities among the various levels of government. The 
requirement to characterize air quality to inform the area designation 
process for the revised NAAQS is imposed by the CAA. This rule is 
intended to interpret those requirements as they apply to the 2010 1 
hour SO2 NAAQS.

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

    This action does not have tribal implications, as specified in 
Executive Order 13175. It would not have a substantial direct effect on 
one or more Indian tribes. Furthermore, this regulation does not affect 
the relationship or distribution of power and responsibilities between 
the federal government and Indian tribes. The CAA and the Tribal Air 
Rule establish the relationship of the federal government and tribes in 
characterizing air quality and developing plans to attain the NAAQS, 
and this regulation does nothing to modify that relationship. Thus, 
Executive Order 13175 does not apply to this action.
    Consistent with the EPA Policy on Consultation and Coordination 
with Indian tribes, the EPA held several meetings with tribal 
environmental professionals to discuss issues associated with this 
rule, including discussions at the National Tribal Forum on May 1, 
2013, and on National Tribal Air Association policy calls. These 
meetings discussed the SO2 implementation White Paper. The 
EPA provided an opportunity for tribes and stakeholders to provide 
written comments on the concepts discussed in the White Paper. 
Summaries of these meetings are included in the docket for this rule. 
The EPA also provided information on the proposed rule and conducted 
consultation with the National Tribal Air Association in the form of a 
briefing on April 24, 2014, and a webinar on May 21, 2014.

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

    The EPA interprets Executive Order 13045 as applying only to those 
regulatory actions that concern environmental health or safety risks 
that the EPA has reason to believe may disproportionately affect 
children, per the definition of ``covered regulatory action'' in 
section 2-202 of the Executive Order. This action is not subject to 
Executive Order 13045 because it does not directly involve an 
environmental health risk or safety risk.

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

    This action is not a ``significant energy action'' because it is 
not likely to have a significant adverse effect on the supply, 
distribution or use of energy. The EPA is finalizing this 
SO2 DRR to require air agencies to more extensively 
characterize ambient SO2 air quality concentrations, 
pursuant to sections 110(a)(2)(B), 110(a)(2)(K), 301(a) and 114 of the 
CAA. The rule does not prescribe specific control strategies by which 
the SO2 NAAQS will be met. Such strategies will be developed 
by states on a case-by-case basis only if the information generated by 
this rule results in an area being designated nonattainment, thereby 
triggering the need for the state to develop an attainment plan for the 
area. The EPA cannot predict whether the attainment plan prepared by 
the state will include regulations on energy suppliers, distributors, 
or users. Thus, the EPA concludes that this rule is not likely to have 
any adverse energy effects.

I. National Technology Transfer and Advancement Act

    This action does not involve technical standards.

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

    The EPA believes the human health or environmental risk addressed 
by this action will not have potential disproportionately high and 
adverse human health or environmental effects on any population, 
including any minority, low-income or indigenous populations, because 
it does not affect the level of protection provided to human health or 
the environment. That level of protection is established by the NAAQS 
itself. The results of the evaluation of environmental justice 
considerations is contained in section V of this preamble titled, 
``Environmental Justice Considerations.''

K. Congressional Review Act (CRA)

    This action is subject to the CRA, and the EPA will submit a rule 
report to each House of the Congress and to the Comptroller General of 
the United States. This action is not a ``major rule'' as defined by 5 
U.S.C. 804(2).

L. Judicial Review

    Under section 307(b)(1) of the CAA, petitions for judicial review 
of this final action must be filed in the United States Court of 
Appeals for the District of Columbia Circuit by October 20, 2015. 
Filing a petition for reconsideration by the Administrator of this 
final action does not affect the finality of this action for the 
purposes of judicial review nor does it extend the time within which a 
petition for judicial review must be filed, and shall not postpone the 
effectiveness of this action.

Statutory Authority

    The statutory authority for this action is provided by 42 U.S.C. 
7401 et seq., and particularly sections 7403, 7407, 7410, 7414 and 
7601.

[[Page 51087]]

List of Subjects in 40 CFR Part 51

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

    Dated: August 10, 2015.
Gina McCarthy,
Administrator.

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

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

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

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


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

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


Sec.  51.1200  Definitions.

    The following definitions apply for the purposes of this subpart. 
All terms not defined herein will have the meaning given them in Sec.  
51.100 or in the Clean Air Act (CAA). Air agency means the agency or 
organization responsible for air quality management within a state, 
local governmental jurisdiction, territory or area subject to tribal 
government. Annual SO2 emissions data means the quality-
assured annual SO2 emissions data for a stationary source. 
Such data may have been required to be reported to the EPA in 
accordance with an existing regulatory requirement (such as the Air 
Emissions Reporting Rule or the Acid Rain Program); however, annual 
SO2 emissions data may be obtained or determined through 
other reliable means as well.
    Applicable source means a stationary source that is:
    (1) Not located in a designated nonattainment area, and
    (2) Has actual annual SO2 emissions data of 2,000 tons 
or more, or has been identified by an air agency or by the EPA Regional 
Administrator as requiring further air quality characterization. 2010 
SO2 NAAQS means the primary National Ambient Air Quality 
Standard for sulfur oxides (sulfur dioxide) as codified at 40 CFR 
50.17, as effective August 23, 2010.


Sec.  51.1201  Purpose.

    The purpose of this subpart is to require air agencies to develop 
and submit air quality data characterizing maximum 1-hour ambient 
concentrations of SO2 across the United States through 
either ambient air quality monitoring or air quality modeling analysis 
at the air agency's election. These monitoring and modeling data may be 
used in future determinations by the EPA regarding areas' 
SO2 NAAQS attainment status, or for other actions designed 
to ensure attainment of the 2010 SO2 NAAQS and provide 
protection to the public from the short-term health effects associated 
with exposure to SO2 concentrations that exceed the NAAQS.


Sec.  51.1202  Applicability.

    This subpart applies to any air agency in whose jurisdiction is 
located one or more applicable sources of SO2 emissions that 
have annual actual SO2 emissions of 2,000 tons or more; or 
in whose jurisdiction is located one or more sources of SO2 
emissions that have been identified by the air agency or by the EPA 
Regional Administrator as requiring further air quality 
characterization. For the purposes of this subpart, the subject air 
agency shall identify applicable sources of SO2 based on the 
most recently available annual SO2 emissions data for such 
sources.


Sec.  51.1203  Air agency requirements.

    (a) The air agency shall submit a list of applicable SO2 
sources identified pursuant to Sec.  51.1202 located in its 
jurisdiction to the EPA by January 15, 2016. This list may be revised 
by the Regional Administrator after review based on available 
SO2 emissions data.
    (b) For each source area subject to requirements for air quality 
characterization, the air agency shall notify the EPA by July 1, 2016, 
whether it has chosen to characterize peak 1-hour SO2 
concentrations in such area through ambient air quality monitoring; 
characterize peak 1-hour SO2 concentrations in such area 
through air quality modeling techniques; or provide federally 
enforceable emission limitations by January 13, 2017 that limit 
emissions of applicable sources to less than 2,000 tpy, in accordance 
with paragraph (e) of this section, or provide documentation that the 
applicable source has permanently shut down. Emission limits in 
accordance with paragraph (e) of this section may be established in 
lieu of conducting monitoring or modeling unless, in the judgment of 
the air agency or the EPA Regional Administrator, the area warrants 
further air quality characterization even with the establishment of any 
new emission limit(s). If the air agency has chosen to establish 
requirements to limit emissions for applicable sources in an area, the 
notification from the air agency shall describe the requirements and 
emission limits the air agency intends to apply. For any area with 
multiple applicable sources, the air agency (or air agencies if a 
multi-state area) shall use the same technique (monitoring, modeling, 
or emissions limitation) for all applicable sources in the area. If 
multiple air agencies have applicable sources in an area, the air 
agencies must consult with each other to employ a common technique for 
the area.
    (c) Monitoring. For each area identified in the notification 
submitted pursuant to paragraph (b) of this section as an area for 
which SO2 concentrations will be characterized through 
ambient monitoring, the required monitors shall be sited and operated 
either as SLAMS or in a manner equivalent to SLAMS. In either case, 
monitors shall meet applicable criteria in 40 CFR part 58, appendices 
A, C, and E and their data shall be subject to data certification and 
reporting requirements as prescribed in 40 CFR 58.15 and 58.16. These 
requirements include quarterly reporting of monitoring data to the Air 
Quality System, and the annual certification of data by May 1 of the 
following year.
    (1) The air agency shall include relevant information about 
monitors used to meet the requirements of this paragraph (c) in the air 
agency's Annual Monitoring Network Plan required by 40 CFR 58.10 due 
July 1, 2016. The air agency shall consult with the appropriate EPA 
Regional Office in the development of plans to install, supplement, or 
maintain an appropriate ambient SO2 monitoring network 
pursuant to the requirements of 40 CFR part 58 and of this subpart.
    (2) All existing, new, or relocated ambient monitors intended to 
meet the requirements of this paragraph (c) must be operational by 
January 1, 2017 and must be operated continually until approved for 
shut down by EPA.
    (3) Any SO2 monitor identified by an air agency in its 
approved Annual Monitoring Network Plan as having the purpose of 
meeting the requirements of this paragraph (c) that: Is not located in

[[Page 51088]]

an area designated as nonattainment as the 2010 SO2 NAAQS is 
not also being used to satisfy other ambient SO2 minimum 
monitoring requirements listed in 40 CFR part 58, appendix D, section 
4.4; and is not otherwise required as part of a SIP, permit, attainment 
plan or maintenance plan, may be eligible for shut down upon EPA 
approval if it produces a design value no greater than 50 percent of 
the 2010 SO2 NAAQS from data collected in either its first 
or second 3-year period of operation. The air agency must receive EPA 
Regional Administrator approval of a request to cease operation of the 
monitor as part of the EPA's action on the Annual Monitoring Network 
Plan under 40 CFR 58.10 prior to shutting down any qualifying monitor 
under this paragraph (c).
    (d) Modeling. For each area identified in the notification 
submitted pursuant to paragraph (b) of this section as an area for 
which SO2 concentrations will be characterized through air 
quality modeling, the air agency shall submit by July 1, 2016, a 
technical protocol for conducting such modeling to the Regional 
Administrator for review. The air agency shall consult with the 
appropriate EPA Regional Office in developing these modeling protocols.
    (1) The modeling protocol shall include information about the 
modeling approach to be followed, including but not limited to the 
model to be used, modeling domain, receptor grid, emissions dataset, 
meteorological dataset and how the air agency will account for 
background SO2 concentrations.
    (2) Modeling analyses shall characterize air quality based on 
either actual SO2 emissions from the most recent 3 years, or 
on any federally enforceable allowable emission limit or limits 
established by the air agency or the EPA and that are effective and 
require compliance by January 13, 2017.
    (3) Except as provided by Sec.  51.1204, the air agency shall 
conduct the modeling analysis for any applicable source identified by 
the air agency pursuant to paragraph (a) of this section, and for its 
associated area and any nearby area, as applicable, and submit the 
modeling analysis to the EPA Regional Office by January 13, 2017.
    (e) Federally enforceable requirement to limit SO2 
emissions to under 2,000 tons per year. For each area identified in the 
notification submitted pursuant to paragraph (b) of this sectionas an 
area for which the air agency will adopt federally enforceable 
requirements in lieu of characterizing air quality through monitoring 
or modeling, the air agency shall submit documentation to the EPA by 
January 13, 2017, showing that such requirements have been adopted, are 
in effect, and been made federally enforceable by January 13, 2017, 
through an appropriate legal mechanism, and the provisions either:
    (1) Require the applicable sources in the area to emit less than 
2,000 tons of SO2 per year for calendar year 2017 and 
thereafter; or
    (2) Document that the applicable sources in the area have 
permanently shut down by January 13, 2017.


Sec.  51.1204  Enforceable emission limits providing for attainment.

    At any time prior to January 13, 2017, the air agency may submit to 
the EPA federally enforceable SO2 emissions limits 
(effective no later than January 13, 2017) for one or more applicable 
sources that provide for attainment of the 2010 SO2 NAAQS in 
the area affected by such emissions. The submittal shall include 
associated air quality modeling and other analyses that demonstrate 
that all modeling receptors in the area will not violate the 2010 
SO2 NAAQS, taking into account the updated allowable 
emission limits on applicable sources as well as emissions limits that 
may apply to any other sources in the area. The air agency shall not be 
subject to the ongoing data requirements of Sec.  51.1205 for such area 
if the air quality modeling and other analyses demonstrate that the 
area will not violate the 2010 SO2 NAAQS.


Sec.  51.1205  Ongoing data requirements.

    (a) Monitored areas. For any area where SO2 monitoring 
was conducted to characterize air quality pursuant to Sec.  51.1203, 
the air agency shall continue to operate the monitor(s) used to meet 
those requirements and shall continue to report ambient data pursuant 
to existing ambient monitoring regulations, unless the monitor(s) have 
been approved for shut down by the EPA Regional Administrator pursuant 
to Sec.  51.1203(c)(3) or pursuant to 40 CFR 58.14.
    (b) Modeled areas. For any area where modeling of actual 
SO2 emissions serve as the basis for designating such area 
as attainment for the 2010 SO2 NAAQS, the air agency shall 
submit an annual report to the EPA Regional Administrator by July 1 of 
each year, either as a stand-alone document made available for public 
inspection, or as an appendix to its Annual Monitoring Network Plan 
(also due on July 1 each year under 40 CFR 58.10), that documents the 
annual SO2 emissions of each applicable source in each such 
area and provides an assessment of the cause of any emissions increase 
from the previous year. The first report for each such area is due by 
July 1 of the calendar year after the effective date of the area's 
initial designation.
    (1) The air agency shall include in such report a recommendation 
regarding whether additional modeling is needed to characterize air 
quality in any area to determine whether the area meets or does not 
meet the 2010 SO2 NAAQS. The EPA Regional Administrator will 
consider the emissions report and air agency recommendation, and may 
require that the air agency conduct updated air quality modeling for 
the area and submit it to the EPA within 12 months.
    (2) An air agency will no longer be subject to the requirements of 
this paragraph (b) for a particular area if it provides air quality 
modeling demonstrating that air quality values at all receptors in the 
analysis are no greater than 50 percent of the 1-hour SO2 
NAAQS, and such demonstration is approved by the EPA Regional 
Administrator.
    (c) Any air agency that demonstrates that an area would meet the 
2010 SO2 NAAQS with allowable emissions is not required 
pursuant to paragraph (b) of this section to submit future annual 
reports for the area.
    (d) If modeling or monitoring information required to be submitted 
by the air agency to the EPA pursuant to this subpart indicates that an 
area is not attaining the 2010 SO2 NAAQS, the EPA may take 
appropriate action, including but not limited to requiring adoption of 
enforceable emission limits to ensure continued attainment of the 2010 
SO2 NAAQS, designation or redesignation of the area to 
nonattainment, or issuance of a SIP Call.

[FR Doc. 2015-20367 Filed 8-20-15; 8:45 am]
 BILLING CODE 6560-50-P