Vol. 80 Friday, 

No. 162 August 21, 2015 

Part V 

Environmental Protection Agency 

40 CFR Part 51 

Data Requirements Rule for the 2010 1-Hour Sulfur Dioxide (SO2) Primary 

National Ambient Air Quality Standard (NAAQS); Final Rule 


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51052 Federal Register / Vol. 80, No. 162 / Friday, August 21, 2015 / Rules and Regulations 

1The 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. 

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. 

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 nonbinding draft technical assistance 

documents recommending how air 

agencies should conduct such 

monitoring or modeling. The air quality 

data developed by air agencies pursuant 

to this rule may be used by the EPA in 

future actions to evaluate areas’ air 

quality under the 2010 1-hour SO2

National Ambient Air Quality Standard 

(NAAQS), including area designations 

and redesignations, as appropriate. 

DATES: This final rule is effective on 

September 21, 2015. 

ADDRESSES: The EPA has established a 

docket for this action under Docket ID 

No. EPA–HQ–OAR–2013–0711. All 

documents in the docket are listed on 

the http://www.regulations.gov Web 

site. Although listed in the index, some 

information is not publicly available, 

i.e., confidential business information or 

other information whose disclosure is 

restricted by statute. Certain other 

material, such as copyrighted material, 

will be publicly available only in hard 

copy. Publicly available docket 

materials are available either 

electronically in http://

www.regulations.gov or in hard copy at 

the Docket ID No. EPA–HQ–OAR–2013– 

0711, EPA/DC, William Jefferson 

Clinton West Building, Room 3334, 

1301 Constitution Avenue NW., 

Washington, DC. The Public Reading 

Room is open from 8:30 a.m. to 4:30 

p.m., Monday through Friday, excluding 

legal holidays. The telephone number 

for the Public Reading Room is (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: http://

www.epa.gov/epahome/dockets.htm. 

FOR FURTHER INFORMATION CONTACT: For 

further general information on this 

rulemaking, contact Dr. Larry D. 

Wallace, Office of Air Quality Planning 

and Standards, U.S. Environmental 

Protection Agency, by phone at (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: http://

www.epa.gov/air/sulfurdioxide/

implement.html. Upon its publication in 

the Federal Register, only the published 

version may be considered the final 

official version of the notice, and will 

govern in the case of any discrepancies 

between the Federal Register published 

version and any other version. 

C. How is this document organized? 

The information presented in this 

document is organized as follows: 

I. General Information 

A. Does this action apply to me? 

B. Where can I get a copy of this document 

and other related information? 

C. How is this document organized? 

II. Background for Final Rulemaking 

III. Summary of the Final Rule Requirements 

IV. Responses to Significant Comments on 

the Proposed Rule 

A. The Use of Monitoring and/or Modeling 

Data 

B. Source Coverage and Emission 

Threshold Options 

C. Data Requirements and Program 

Implementation Timeline 

D. Technical Issues Relating to Modeling 

and Monitoring 

E. Other Key Issues and Comments 

V. Environmental Justice Considerations 

VI. Statutory and Executive Order Reviews 

A. Executive Order 12866: Regulatory 

Planning and Review and Executive 

Order 13563: Improving Regulation and 

Regulatory Review 

B. Paperwork Reduction Act (PRA) 

C. Regulatory Flexibility Act (RFA) 

D. Unfunded Mandates Reform Act 

(UMRA) 

E. Executive Order 13132: Federalism 

F. Executive Order 13175: Consultation 

and Coordination With Indian Tribal 

Governments 

G. Executive Order 13045: Protection of 

Children From Environmental Health 

and Safety Risks 

H. Executive Order 13211: Actions 

Concerning Regulations That 

Significantly Affect Energy Supply, 

Distribution, or Use 

I. National Technology Transfer and 

Advancement Act 

J. Executive Order 12898: Federal Actions 

To Address Environmental Justice in 

Minority Populations and Low-Income 

Populations 

K. Congressional Review Act (CRA) 

L. Judicial Review 

Statutory Authority 

II. Background for Final Rulemaking 

On May 13, 2014, the EPA proposed 

the Data Requirements Rule (DRR) for 

the 2010 1-hour SO2 Primary NAAQS. 

The preamble to the proposal provided 

a discussion of the events that led to the 

EPA’s proposal of a new regulation to 

direct state, tribal and local agencies 1 to 

better characterize ambient air SO2

concentrations near large polluting 

sources. See 79 FR 27447, May 13, 2014. 

This discussion addressed the adoption 

of the 2010 SO2 NAAQS and the 

suggested implementation approach 

described in the preamble of that 

rulemaking; the area designations 

process under section 107 of the Clean 

Air Act (CAA); the history of 


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2The May 2012 White Paper and high-level 

summaries of stakeholder meetings are available at: 

http://www.epa.gov/oaqps001/sulfurdioxide/

implement.html. These documents and written 

comments received from stakeholders are also 

included in the docket for this rulemaking. 

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. 

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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3The 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. 

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. 

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 § 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 

§ 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 coalfired 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 § 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 


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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 

§ 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 


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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 § 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 ‘‘twopronged’’ 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 


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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 


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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 multisource 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 shortterm 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 populationinclusive 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 


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Federal Register / Vol. 80, No. 162 / Friday, August 21, 2015 / Rules and Regulations 51061 

4The May 2012 White Paper and high-level 

summaries of stakeholder meetings are available at: 

http://www.epa.gov/oaqps001/sulfurdioxide/

implement.html. These documents and written 

comments received from stakeholders are also 

included in the docket for this rulemaking. 

5See also: ‘‘Analysis of Source Threshold Options 

for the Final SO2 Data Requirements Rule,’’ 

memorandum to docket EPA–HQ–OAR–2013–0711, 

July 16, 2015. 

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. 

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

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 


asabaliauskas on DSK5VPTVN1PROD with RULES
51062 Federal Register / Vol. 80, No. 162 / Friday, August 21, 2015 / Rules and Regulations 

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. 

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 abovethreshold 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-bycase 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 cokemaking 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 


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Federal Register / Vol. 80, No. 162 / Friday, August 21, 2015 / Rules and Regulations 51063 

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. 

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. 

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 


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the final rule timetable, including this 

revision. 

TABLE 1—TIMELINE FOR DRR IMPLEMENTATION

Date Action 

From promulgation of this rule to 

January 15, 2016.

Air agency and the EPA Regional 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 § 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 § 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 


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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 § 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 § 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 

§ 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 


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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 § 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 

§ 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. 


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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 nonEGU 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 


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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 § 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., sourcespecific 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 

§ 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 


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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 reconduct 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-fitsall 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 § 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 


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51070 Federal Register / Vol. 80, No. 162 / Friday, August 21, 2015 / Rules and Regulations 

7The SO2 NAAQS Designations Source-Oriented 

Monitoring Technical Assistance Document can be 

found at http://www.epa.gov/airquality/

sulfurdioxide/pdfs/SO2MonitoringTAD.pdf. 

in the draft Monitoring TAD.7 See 79 FR 

27458, May 13, 2014. 

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 § 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 


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Federal Register / Vol. 80, No. 162 / Friday, August 21, 2015 / Rules and Regulations 51071 

8The Draft SO2 NAAQS Designations Modeling 

Technical Assistance Document can be found at 

http://www.epa.gov/airquality/sulfurdioxide/pdfs/

SO2ModelingTAD.pdf. 

9The EPA issued initial guidance on the SO2 area 

designations process on March 24, 2011. See http:// 

www.epa.gov/air/sulfurdioxide/pdfs/20110411SO2

designationsguidance.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: 

http://www.epa.gov/airquality/sulfurdioxide/pdfs/

20150320SO2designations.pdf. 

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 resourcedemanding 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 § 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. 

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. 

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 


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51072 Federal Register / Vol. 80, No. 162 / Friday, August 21, 2015 / Rules and Regulations 

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-sizefits-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 


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


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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 § 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 § 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 


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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 

§ 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 § 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 § 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 qualityassured 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 


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10Revision 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 http://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. 

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 sitespecific 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 overprediction of the SO2 concentrations in 

the context of the 1-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. 

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 overestimates, 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 


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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 


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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 sitespecific 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 


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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 § 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 

§ 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 multisource 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 emissionsbased 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 areaspecific 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 


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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 ongoing 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. 


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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 qualityassured 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-bycase 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 emissionsair 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 § 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 § 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, § 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 PostAttainment 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 


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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-cv3953–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 repropose 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. 


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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 qualityassured 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 


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12While 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 http://www.epa.gov/

airquality/sulfurdioxide/pdfs/

20150320SO2designations.pdf. 

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 

§ 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). 

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 § 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, 

§ 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 


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13The Draft SO2 NAAQS Designations Modeling 

Technical Assistance Document can be found at: 

http://www.epa.gov/airquality/sulfurdioxide/pdfs/

SO2ModelingTAD.pdf. 

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 multijurisdiction 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, lowincome, 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. 

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 


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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. 


asabaliauskas on DSK5VPTVN1PROD with RULES
Federal Register / Vol. 80, No. 162 / Friday, August 21, 2015 / Rules and Regulations 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 

■ 1. The authority citation for part 51 

continues to read as follows: 

Authority: 23 U.S.C. 101; 42 U.S.C. 7401– 

7671q. 

■ 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 

§ 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 § 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 qualityassured 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. 

§ 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 shortterm health effects associated with 

exposure to SO2 concentrations that 

exceed the NAAQS. 

§ 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. 

§ 51.1203 Air agency requirements. 

(a) The air agency shall submit a list 

of applicable SO2 sources identified 

pursuant to § 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 


asabaliauskas on DSK5VPTVN1PROD with RULES
51088 Federal Register / Vol. 80, No. 162 / Friday, August 21, 2015 / Rules and Regulations 

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 § 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. 

§ 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 § 51.1205 for such area 

if the air quality modeling and other 

analyses demonstrate that the area will 

not violate the 2010 SO2 NAAQS. 

§ 51.1205 Ongoing data requirements. 

(a) Monitored areas. For any area 

where SO2 monitoring was conducted to 

characterize air quality pursuant to 

§ 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 

§ 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 


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