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Page 1 of 145 6560 - 50 - P **ENVIRONMENTAL PROTECTION AGENCY 40 CFR Part 5**  **1 [EPA**  **- HQ**  **- OAR** **- 2013**  **- 0711**  **; FRL**  **- 9928**  **- 18**  **- OAR** **] RIN 2060**  **- AR19**  **Data Requirements Rule**  **for the 2010**  **1 -**  **Hour Sulfur Dioxide (SO 2**  **) Primary National Am**  **bient Air Quality Standard (NAAQS) AGENCY:**  Environmental Protecti on 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 (SO 2 ) emissions to identify maximum 1 - hour SO 2 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 SO 2 air quality . Air agencies remain free to also characterize air quality in additional areas beyond those required to be characterized under the rule. The final rule also sets forth a process and timetables by which air agencies must characterize air quality through ambient monitoring and/or air quality modeling techniques and submit such data to the EPA . The EPA has issued separate non - binding draft technical assistance documents recommending how air agencies should conduct such monitoring or modeling. The air quality data developed by air agencies pursuant to this rule may be used b y the EPA in future actions to evaluate area s’ air quality under the 2010 1 - hour SO 2 Natio nal Ambient Air Quality Standard (NAAQS ) , including area designations and redesignations, as appropriate .*** E.O. 1286 6 Review

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Page 2 of 145 **DATE S**  **:** This final rule is effective on **[INSERT DATE 3**  **0 DAYS AFTER**  **DATE OF PUBLICATION IN THE FEDERAL REGISTER]**  . **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 w ebsite. Although listed in the index, some information is not publicly available, i.e., confidential business inform ation or other information whose disclosure is restricted b y statute. Certain other material, such as cop yri ghted material, will be publicly available onl y in hard copy . Publicly available docket materials are available either electronicall y in http:// www. regulations.gov or in hard cop y at the Docket ID No. EPA - HQ - OAR - 2013 - 0711, EPA/DC, William Jefferson Clinton West Building, Room 3334, 1301 Constitution Avenue , NW , Washington, D . C. The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday , excluding legal holiday s. 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 D r. Larry D. Wallace , Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency , by phone at (919) 54l - 0906 , or b y 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) 54l - 5592, or b y email at damberg. rich@epa.gov
. **SUPPLEMENTARY INFORMATION:***** E.O. 1286 6 Review

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Page 3 of 145 **I. General Information**  A. Does this action apply to me? Entities potentially

affected directl y b y 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 SO 2 emissions (such as coal - fired power plants, refineries, smelters, pulp and paper related fac ilities, waste incinerators, chemical manufactur ers and facilities with industrial boilers for power generation) that contribute to ambient SO 2 concentrations, as well as people whose air quality

is affected by

these facilities. B. Wh ere can I get a copy of this document and other related information? In addition to being available in the docket, an electronic cop y of this notice will be posted at : http://www.ep a.gov/air/sulfurdioxide/implement.html . Upon its publication in the Federal Register , onl y 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 appl y to me? B. Where can I get a cop y of this document and other related information? C . How is this document organized? II. Background for Final R ulemaking 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*** E.O. 1286 6 Review

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Page 4 of 145 D. Technical Is sues Relating to Modeling and Monitoring E. Other Key

I ssues and Comments V. Environmental Justice Considerations V I . 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

Suppl y, Distribution, or Use I. National Technology Transfer and Advancement Act J. Executive Order 12898: Federal Actions to Address Environmental Justice in Minority Populations and Lo w - Income Populations K. Congressional Review Act (CRA) L. Judicial Review Statutory Authority **II. Background for**  **Final R ulemaking**  On May 13, 2014, the EPA proposed the Data Requirements Rule (DRR) for the 2010 1 - h our SO 2 Primary NAAQS , 79 FR 2744 6 , May 1 3, 2014 . 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 SO 2 concentrations near large polluting sources. See 79 FR 27446, 27447 , May 13, 2014 . Th is discussion addressed the adoption of the 2010 SO 2 NAAQS, and the suggested implementation approach described in the preamble of that

1 The final rule applies to air agencies in all states. The definition of “state” in section 302(d) of the Clean Air Act (CAA or Act) means a s tate, 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.*** E.O. 1286 6 Review

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Page 5 of 145 rulemaking ; the area designations process under section 107 of the C lean Air Act (C AA) ; the history of designations for prior SO 2 NAAQS, including the use of air quality modeling information ; the Agency ’s 2 subsequent issuance of an implementation white paper in May 2012 and input received from stakeholder groups; and the EPA’s February 2013 SO 2 NAAQS implementation and designations strategy paper , developed in response to feedback received through this outreach process . 3 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 SO 2 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 SO 2 concentration impacts from emissions s ources. To more effectivel y assess potential public health impacts from exposure to high SO 2 concentrations, the proposed rule presented options for requiring air agencies to characterize air quality in the vicinity

of large sources of SO 2 emissions that e xceed 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 SO 2 per year and are located in more highl y 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 SO 2 per year and are located outside

2 The term Agency

is intended to refer to the EPA. 3 The May

2012 White Paper and high - level summaries of stakeholder meetings are available at: http://www.epa.gov/oaqps001/sulfurdioxide/implement.html . These documents and written comments received from stakeholders are also included in the docket for this rulemaking.*** E.O. 1286 6 Review

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Page 6 of 145 metropolitan areas of at least 1 million population. (The EPA also identified two other emission threshold options and requested public comment on the se potential emission thresholds values, a CBSA population threshold of 1 million , the combination of emis sions and population thresholds as a means of determining how SO 2 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 27446, 27453 , May 13, 2014 . Under the proposed rule, the air agencies would determine for each emissions s ource e xceeding the threshold whether air quality characterization for that source would be done either through air quality modeling analy sis or b y conducting ambient monitoring. Apart from the proposed rule, the EPA issued two draft technical assistance documents (TAD s ) on modeling and monitoring to assist air agencies with this anal ytical work. The proposed rule also describ ed a process and timetable b y which air agencies would be required to identify sources to be characterized, conduct the relevant anal ys es and submit such data to the EPA . See 79 FR 27446, 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 27446, 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 p roposed r ule for the technical, policy and legal rationale that were presented in support of the proposal ,*** E.O. 1286 6 Review

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Page 7 of 145 and for a complete discus sion of the issues for which the EPA requested public comment . Several supporting memoranda, anal ys es and data were included in the docket for the proposed action . The 60 - day public comment period for the p roposed r ule closed on July

14, 2014. In section IV of this preamble , we summarize each key issue from the proposal, briefl y summarize major comments received and provide a response , and describe the final policy in the rule, including any changes made to the approach es presented in the proposal. A more detailed response to comment s document can be found in the docket for this rulemaking, presenting a comprehensive descriptio n of comments received and response s to those comments. **III. Summary of the Final Rule**  **Requirements** Th is 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 r ule directing air agencies to gather additional data to characterize ambient air in the vicinity of larger SO 2 sources is uniquel y suited for implementation of the 1 - hour SO 2 NAAQS, and the Agency does not anticipate it to be used for other NAAQS pollutant s. The final rule establishes minimum requirements for air agencies to characterize 1 - hour SO 2 air quality concentrations across the country , with an emphasis on doing so in the vicinity of sources that have the largest annual SO 2 emissions. Note that there are already minimum SO 2 ambient monitoring requirements in place that were established when the 1 - hour SO 2 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*** E.O. 1286 6 Review

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Page 8 of 145 to establish a flexible yet effective program for characterizing SO 2 air quality in priority areas across the country , given existing funding and resource constraints , and given the particular characteristics of SO 2 air pollution in the affected areas . This final rule also reflects the fact that numerous larger sources of SO 2 across the country have in recent ye ars installed , and are expected to install in the near future , additional control measures that may substantially

reduce SO 2 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 SO 2 emissions that exceeded the 2,000 t ons per year (t

py) annual threshold during the most recent ye ar for which emissions data for that source are available, plus any additional sources and their associated areas identified b y the air agency

or b y the EPA as also warranting air quality characterization. (The list does not need to include sources located in areas already designated as nonattainment for the 2010 SO 2 NAAQS.) 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, w ould result in that source and its associated area not being subject to requirements for air quality characterization. The EPA anticipates discussions with air agencies earl y in 2016 to resolve any questions as to what areas warrant air quality characterization . These discussions are intended to address whether any additional areas (e.g. , areas with clusters of sources) warrant air quality characterization , whether existing monitoring networks might serve to address air quality characterization requirements,*** E.O. 1286 6 Review

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Page 9 of 145 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 agenc y choose s 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 b y J anuary 1, 2017. The required monitors shall be sited and operated either as State and L ocal Air Monitoring Stations 4 ( 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., quarterl y reporting of monitoring data to the Air Quality System, and the annual certification of data by May 1 of the following ye ar) , and must satisfy applicable criteria in 40 CFR part 58 , a ppendices 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

4 The SLAMS network is an air quality surveillance system that consists of a network of monitoring stations designated as SLAMS which measure ambient concentrations of those pollutants for which standards have been established in 40 CFR part 50.*** E.O. 1286 6 Review

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Page 10 of 145 consultation with the EPA Regional Office. The modeling analyses must then be submitted to the EPA by January 13, 2017. If the air agenc y choose s the third option, to provide federall y enforceable emissions limitations that limit emissions of an applicable source to less than 2,000 tpy , or to provide document ation that the applicable source has permanently shut down , th e air agency must notify the EPA of its decision by Jul y 1, 2016 , and provide a description of the planned emission limitation , including identification of the level of the limitation being planned . Especiall y 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 con currence 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 SO 2 emissions under the rule. If EPA approval is required to make a limit federally

enforceable, the submittal must be s ent to the EPA earl y enough such that the EPA has enough time to complete a rulemaking to make the limit federally enforceable by the January

13, 2017 , date. S ection 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 SO 2 source is to be designed, or how air quality modeling must be specificall y 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*** E.O. 1286 6 Review

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Page 11 of 145 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 pot ential options and recommendations on different anal ys es and approaches that could be considered to help the air agency site source - oriented SO 2 monitors in locations of expecte d maximum 1 - hour concentrations. The TAD for air quality modeling explains that refined dispersion models are able to characterize SO 2 air quality impacts from the modeled sources across the domain of interest on an hourl y basis with a high degree of spatial resolution . It suggests that in order to characterize recent air quality lev els around a source, it w ould 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 an d 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 anal ytical approaches, and air agencie s are expected to use their best professional judgment , consulting as appropriate with the EPA, in conducting these anal ys es. A ir agencies should also contact their respective EPA Regional Office s 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*** E.O. 1286 6 Review

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Page 12 of 145 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 comm encement 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 - ye ar period or second 3 - ye ar period is no greater than 50 percent of the 1 - hour SO 2 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 recomm ending to the EPA whether further modeling is warranted to assess any expected changes in recent air quality . For example, it may be appropriate for the air agency to conduct updated modeling for an area if there have been increases in short term emissions rates, an increase in annual emissions, or changes in facility operations. Where warranted, the air agency shall conduct updated modeling to characterize air quality in light of the identified emissions changes and present the results in its annual report to the EPA. Analogous to the monitor shutdown provisions noted earlier , the requirement for the annual emissions assessments for an area originall y characterized by modeling may be terminated i f the air agency provide s a modeling anal ys is demonstrating that actual emissions in the previous year for SO 2 sources in the area*** E.O. 1286 6 Review

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Page 13 of 145 result s 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 s ource emissions threshold approach wa s changed to a single 2 , 000 ton annual SO 2 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 SO 2 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 r

ule also includes a set of monitor shutdown provisions that is a hy brid 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 SO 2*** E.O. 1286 6 Review

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Page 14 of 145 standard during one of the first two 3 - ye ar 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 annuall y 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 t py . The final rule now includes such a provision. This ty pe of limit would need to be adopted and in effect by January 2017. **I V**  **. Responses to Significant Comments on the Proposed Rule**  A. The Use ofMonitoring and /or Modeling Data 1 . L egal Authority to Require States to Submit D ata Pursuant to This Rule a . Summary of Proposal In the p roposed r

ule , the EPA explained that th e requirement s for the air agency to submit the SO 2 monitoring and modeling data described in § 51.1203 of the p roposed r ule are appropriate steps needed to understand SO 2 air quality throughout the country , and are consistent*** E.O. 1286 6 Review

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Page 15 of 145 with section 110(a)(2)(B), section 110(a)(2)(K) and section 301(a)(1) of the CAA. See 7 9 FR 27446, 27457 , May

13, 2014 . b
. Brief S

ummary 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 modifie s 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 s tate and industry commenters stated that the proposed requirements and schedules conflict with requirements that appl y 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 SO 2 standard no later than June 3, 2013, and that the EPA failed to comply

with that mandatory

obligation. Therefore, the commenters claim ed , 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 propos ed because it fails to follow the mandatory timelines for promulgating area designations, and, therefore, exceeds the EPA's statutory authority . c . EPA Response*** E.O. 1286 6 Review

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Page 16 of 145 The comments that assert that the EPA has not designated areas under the 2010 SO 2 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 SO 2 . Through this r ulemaking, the EPA is not establishing or modifying any area designation requirements provided for in section 107 of the CAA , n or does any aspect of this final rule conflict with any provision of section 107 that directs states and the EPA to take timely a ction 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 adequatel y characterizing peak 1 - hour SO 2 ambient air concentrations . The air quality data obtained as a result of this rulemaking then may be used in future anal ytical actions by the EPA, including designations of any undesignated areas or redesignations of already designated areas . It is true th at in the p roposed r ule 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 de signations. 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 co mplete area designations for the 2010 1 - hour SO 2 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 EP A’s schedule for completing designations*** E.O. 1286 6 Review

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Page 17 of 145 have been placed in the docket for this this rulemaking. Under the schedule ordered b y the court, the EPA is required to complete the designations in no more than three future rounds. First, by July 2, 2016 ( 16 mo nths 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 b y M arch 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 o f SO 2 in 2012, or (2) emitted more than 2,600 tons of SO 2 and had an annual average emission rate of 0.45 lbs. SO 2 /Mmbtu or higher in 2012. ( The March 2015 consent decree defines “announced for retirement” as meaning “any stationary

source in the United St ates with a coal - fired unit that as of January

1, 2010, had a capacity

of over five (5) megawatts (MW) and that has announced it will cease burning coal at that unit through a company public announcement, public utilities commission filing, consent decree, public legal settlement, final state or federal permit filing, or other similar means of communication.”) Second, by

December 31, 2017, the EPA must sign such a notice promulgating designations for remaining undesignated areas in which, by January 1, 2017 , states have not installed and begun operating a new SO 2 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 area s. The EPA notes that the schedule imposed b y the court will allow at least the latter two stages of designations to be informed and benefited by the additional information that is timely*** E.O. 1286 6 Review

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Page 18 of 145 obtained pursuant to this final rule, as appropriate . However, we also note that the round of designations that is required to be completed b y 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 separatel y developed or obtained during the designations process. Nevertheless, as explained later in this notice, depending on how those areas become designated in 2016, the rule may still result in additional information that could inform future asses sments 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 source s 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 SO 2 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 SIPs are to “provide for establishment and operation of appropriate devices, methods, sy stems, and procedures necessary to (i) monitor, compile and anal yz e data on ambient air quality and (ii) upon request, make such data available to the Administrator.” Section 110(a)(2)(K) states that State Implementation Plans ( SIPs ) shall “provide for (i) the performance of such air quality modeling as the Administrator may presc ribe 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.” S ection 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 SO 2 NAAQS*** E.O. 1286 6 Review

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Page 19 of 145 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 chap ter.” The EPA often establishes and revises monitoring requirements for implementing NAAQS . Those requirements will not necessarily alway s 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 ne ar larger sources of SO 2 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 “unclassifiabl e ” ( and then us es 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 SO 2 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 reasonabl y required to improve characterization of ambient air quality near larger sources of SO 2 . 2 . Legal Authority to Base Air Quality Evaluations on Modeling Data*** E.O. 1286 6 Review

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Page 20 of 145 a . Summary of Proposal In the proposal, the EPA stated that existing air quality modeling tools are technicall y sound and historically

have been used to characterize SO 2 air quality when monitoring data were not available; therefore, the EPA considers these modeling tools appropriate for assessing air quality impacts from SO 2 emissions. The EPA stated that historical use of modeling to characterize SO 2 air quality concentrations has been affirmed as technically valid and lawful under the CAA b y reviewing courts. See 7 9 FR 27446, 27448 , May 13, 20 14 . b
. Brief Summary of Comments Some industry

group commenters stated that the DRR provisions allowing for modeling to characterize ambient SO 2 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 onl y basis for determining if the SO 2 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 SO 2 . (b) The 1 - hour primary

standard is met at an ambient air quality monitoring site when the 3 - ye ar average of the annual (99th percentile) of the daily maximum 1 - hour average concentrations is less than or equal to 75 ppb, as determined in accordance with appendix T of this part.*** E.O. 1286 6 Review

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Page 21 of 145 (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 th e 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 SO 2 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 SO 2 NAAQS, several state and industry commenters stated that monitoring , not modeling, has historically been used for designatio n 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*** E.O. 1286 6 Review

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Page 22 of 145 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 SO 2 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 were addressed to potential final implementatio n 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 , 6 86 F.3d 803 (D.C. Cir. 2012). Li kewise 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 clearl y 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

SO 2 sources,*** E.O. 1286 6 Review

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Page 23 of 145 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 SO 2 , which may not be captured b y the current limited monitoring network. It is true that p ast 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 SO 2 NAAQS preamble, that there is a long history of also using dispersion modeling information to inform area designations for the SO 2 NAAQS. See , e.g., 75 FR 35520, 35551 , June 22, 2010 . The EPA and the air quality management community have recognized over many years that peak concentrations of SO 2 are commonly caused by

one or a few major point sources in an area , and that peak concentrations are typicall y observed relativel y close to the source. Many factors influence the observed SO 2 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 SO 2 emissions per hour, stack height, topography , meteorology , monitor location and source operating schedule. But because ambient SO 2 concentrations are not the result of complex atmospheric chemical reactions (unlike ozone or PM 2.5 ), they can be modeled accuratel y using well - understood air quality modeling tools, especially in areas where one or onl y a few sources exist. Inthe 1970’s, when the original SO 2 NAAQS were established, there were significantly

more SO 2 monitors in operation nationall y than today. Even then, the*** E.O. 1286 6 Review

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Page 24 of 145 EPA and air agencies acknowledged the utility of modeling in order to inform area designations under the SO 2 NAAQS. See e.g., 43 FR 45993 , Oct ober 5, 1978 . 3 . The Use of Monitoring and/or M odeling for Making Decisions a bout Air Quality a . Summary of Proposal In the p roposed r

ule , the EPA explained that the current ambient SO 2 monitoring network, on the whole, is not appropriatel y positioned , or of adequate size , for purposes of the 2010 SO 2 standard to characterize the air quality around many of the nation’s larger SO 2 sources in operation today . The EPA stated that, because ambient SO 2 concentrations are not the result of complex chemical reactions (unlike ozone or PM 2.5 ), they can be modeled accuratel y 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 27446, 27448 , May 13, 2014 . b
. Brief Summary of Comments Several state and industry commenters supported the provision in the proposed rule allow ing air agencies to have the option to use modeling and/or monitoring to characterize SO 2 ambient air concentrations , as it provides appropriate flexibility for both the states and affected sources. Several c ommenters supported the EPA’s observation that modeling may not be appropriate for all SO 2 evaluation scenarios , and supported the ability of states to choose to evaluate NAAQS attainment through either dispersion modeling or ambient monitoring. However, several state and industry commenters cautioned that monitoring data should be the primary basis for such decisions, e speciall y designating nonattainment areas. Several*** E.O. 1286 6 Review

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Page 25 of 145 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 ye ar monit oring. Other comment ers 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 analy tical approach under the rule. c . EPA Response The EPA agrees with commenters who stressed the need to give air agencies the option to characterize SO 2 ambient air quality through either enhanced monitoring or modeling, and the EPA is maintaining that approach in th is final rule. The EPA believes that the comment er s have not present ed any persuasive reasons for changing the basic position s previously discussed in the preamble to the final rule of the 2010 SO 2 NAAQS rulemaking, the February 2013 Strategy Paper, or in the p roposed r ule for why both air quality modeling and ambient monito ring are appropriate tools for characterizing ambient air quality for purposes of informing future decisions to implement the SO 2 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 subse quent 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 .*** E.O. 1286 6 Review

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Page 26 of 145 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 SO 2 sources nationally would not be feasible. The proposal stated that the key objective to be achieved by using SO 2 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 SO 2 emitting sources due to the fact that larger sources can be expec ted to be the most likely potential contributors to violations of the SO 2 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 likel y to occur , the SO 2 annual emission threshold options in th e rule are designed to meet a similar objective. See 79 FR 27446, 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 appro priate 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*** E.O. 1286 6 Review

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Page 27 of 145 additional proposed features, summariz es 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, also all presented together, 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 th e 1 - hour SO 2 NAAQS, the ideal metric for identifying sources near which air quality is to be characteriz ed would be a 1 - hour SO 2 emissions rate. However, the EPA observed that while 1 - hour SO 2 emissi on 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 propos al stated that the emissions threshold options presented in this rulemaking should be expressed in terms of annual emissions of SO 2 because annual emissions information is readil y available for all large SO 2 sources. The EPA requested comment on the use of annual emissions (i.e., tons of SO 2 per year) as the metric to be used for an emissions and population - based threshold approach, or, alternativel y, for a solel y emissions - based threshold approach, to identify SO 2 sources around which further ambient air quality characterization with respect to the 1 - hour SO 2 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 availabi lity of data related to any alter native factor for all SO 2 sources nationall y, the time and resources*** E.O. 1286 6 Review

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Page 28 of 145 needed to develop a database for this alternative factor, any associated technical anal ys is and rationale for using these other factors in defining source thresholds. See 79 FR 27446, 2745 4 , May 13, 2014 . b
. Should the threshold options require air quality characterization near smaller sources in areas with higher populations? In the proposed rule, the proposed emissions threshold option and the other two options on which the EPA requested comment each had a “two - pronged” form. Each potential option was expressed with a higher emissions threshold for identifying sources located outside of CBSA s 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 c ould help increase public health pro tection because there are more people in an area that could be impacted by relativel y smaller sources. The EPA requested comment on its proposed use of the 1 million person CBSA population threshold for representing the population exposure component of the source threshold options in this rule. The EPA also requested comment on whether to include a population exposure - based threshold at all ; and on whether alternative , or additional , criteria would be appropriate to further focus resources on characterizing air quality in areas with a higher likelihood of population exposure. See 79 FR 27446, 2745 5 , 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 propos ed one preferred option and took comments on two additional options. Option 1 (proposed preferred option) would require ambient air quality characterization around*** E.O. 1286 6 Review

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Page 29 of 145 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 tp y 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 sourc es 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 request ed comment on the preferred option and the other two option s 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 i dentified by

these options but that have confirmed documentation to show that they will shut down in the next several ye ars. The EPA noted in the propos ed rule th at, 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 , where the air agency , or the EPA Regional Administrator , determines that they may have the potential to violate the NAAQS. See 79 FR 27446, 27455 , May 13, 2014 . d. Discretion for air agencies and the EPA to address additional sources*** E.O. 1286 6 Review

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Page 30 of 145 The EPA proposed to authorize the states and EPA Regional A dministrator s to apply the DRR requirements to additional areas in addition to those with sources emitting above the applicable threshold. Application of air quality characterization requirements w as noted to be possibly warranted where sources emitting below the threshold have the potential to cause or contribute to violations of the NAAQS , for example where multiple smaller sources located in close proximity

may collectivel y exceed the emissions thresholds and/or cause or contribute to NAAQS exceedances . 2. Summary

of Comments This section provides a brief summary of comments received on each of the 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 th e emission s metric issue supported using annual SO 2 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 widel y reported to the EPA and are readil y 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 local, state , tribal and federal resources. Several other c ommenters stated that the use of additional factors such as stack height, 1 - hour SO 2 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*** E.O. 1286 6 Review

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Page 31 of 145 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 o f a lower emission threshold in urban areas. Some c ommenters stated that p opulation 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 SO 2 exposure risk. Several state and industry commenters stated that a threshold approach based purel y on emissions could inappropriatel y focus limited resources on areas with limited to no public exposure. Some state commenters noted that, a s a precedent, a population threshold has been used to establish the minimum monitoring requirements for the SO 2 NAAQS as well as the NAAQS for nitrogen dioxide, carbon monoxide, and particulate matter. Some commenters stated that many sources located within an existin g 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 effected facilities out to a radius of 10 km and, if average population density from the 2010 census in this area exceeds a certain threshold (e.g. 100 persons/sq

uare 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.*** E.O. 1286 6 Review

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Page 32 of 145 c . Comments on s ource threshold o ptions One public interest group and several states urged the EPA to adopt the proposed Option 1 level of 1,000 tpy , but apply it uniforml y, regardless of population in order to ensure a basic level of health protection to people who live around the sources. Some c ommenters 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 accuratel y 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 SO 2 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 b y the two options is small. Numerous state and industry commenters supported Option 3, stating it would apply reasonabl e 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 SO 2 emissions . One industry

commenter stated that if the EPA decides that either Option 1 or 2 is preferable, then the s ource 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 S O 2 emissions.*** E.O. 1286 6 Review

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Page 33 of 145 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 quali ty . d. Comments on discretion to apply data requirements to 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 kilometer or 25 kilometer diameter s in which total emissions exceed the threshold but those of no single source exceed the thresh old . A few commenters recommended that the EPA should not have the discretion to subject additional areas to characterization unless total emissions in the areas exceed the applicable threshold. Some commenters recommended that the rule specify

criteria to be used to identify multi - source areas that would need to be characterized . Conversely , some commenters recommended that the EPA not codify any specific criteria, recommending instead that the EPA provide guidance on how it envisions addressing areas with multiple sources and rel y 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. Finall y, 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*** E.O. 1286 6 Review

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Page 34 of 145 The EPA consider ed 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 SO 2 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 ac cording to the timeline in section 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 readil y available for all large SO 2 sources, whereas 1 - hour emissions rate information is not readily available for all SO 2 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 sy stems 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 SO 2 source sectors to identify areas for which air agencies are required to characterize air quality .*** E.O. 1286 6 Review

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Page 35 of 145 The EPA acknowledges that some state commenters suggested inclusion of a 1 - hour emissions rate - based criterion for identifying certain sources with infrequent , episodic SO 2 emissions at aty

picall y high rates that c ould impact nearb y populations. The EPA notes that the emissions threshold included in the final rule establishes only minimum requirements for identifying sources . The EPA agrees with state commenters who recommended that air agencies should also characterize areas that, based on their knowledge of sources and areas, may be at risk of violating the standard. Thus, under this rule air agencies could also require characterization of air quality

near sources prone to episodic emissions with relatively high rates or amounts, as appropriate . However, because short - term emissions data are not available for all SO 2 sources, the EPA did no t include in this rule a minimum requirement for identifying source areas needing air quality characterization based on this metric. b . No separate threshold for areas with higher population The EPA considered the comments received on the issue of whether a lower emissions threshold should be included for areas with more dense populations (e.g., CBSAs greater than 1 million population). A number of commenters appeared to interpret the inclusion of a lower threshold for areas with higher population as being less protective of the public in less populated areas . The EPA wants to clarify that this was not the intention behind the population - inclusive options included in the proposed rule. The SO 2 NAAQS , and all NAAQS, provide equal protection for citizens thr oughout 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 SO 2 emissions occur, and thus a potentially*** E.O. 1286 6 Review

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Page 36 of 145 greater potential for exposure is presented . A fter reviewing the comments on this issue, however, the EPA has decided not to mov e 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 primaril y 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 possibl y help to satisfy , required SO 2 monitoring stemming from 40 CFR p art 58 , a

ppendix D, s ection 4.4. Those monitors required in 40 CFR p art 58 , a ppendix D, s ection 4.4 are determined using a unique metric that accounts for the coincident al occur r ences of SO 2 emissions and population, namely the Population Weighted Emissions Index (PWEI). This rulemaking does not supplant or otherwise modify those existing requirements. c . Emissions threshold of 2,000 tpy Regarding the comments EPA received expressing preferences on the proposed emission threshold options , the EPA notes the wide range of views. A few c ommenters recommended alternate thresholds in the rang e from 1 , 000 tpy to 10,000 tpy , or recommended pairs of thresholds within this range. Some commenters provided modeling anal ys es 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 anal ys es of different sources as an indication that sources less than 2,000 tpy ca used modeled violations. These comments demonstrate th at ambient SO 2 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 anal ytical approaches , such as*** E.O. 1286 6 Review

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Page 37 of 145 ambient monitoring or air quality modeling, which take many of these relate d factors into account simultaneousl y. These comments demonstrate why air quality characterization of the area around these source s is needed to protect public health in the first place. The EPA believes that , for the purposes of esta blishing a minimum threshold that prioritizes the resources that will be devoted to characterizing air quality near SO 2 sources nationally , th e 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 anal ytical burden on air agencies . This threshold is on the low er end of the range of thresholds recommended b y 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 SO 2 emissions nationally (based on 2011 emissions) , very close to the 90 percent level that has been c onsidered to be reasonable by many stakeholders in the past . 5 National SO 2 emissions have declined b y 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 bas ed o n 2013 emissions data now available for EGUs and 2011 emissions data for

5 The May

2012 White Paper and high - level summaries of stakeholder meetings are availabl e 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.*** E.O. 1286 6 Review

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Page 38 of 145 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 solel y on 2011 data, the EPA now estimates that approximately 70 fewer sources ( about 15 percent) will need nearb y air quality to be characteriz ed than was estimated in the proposal . Based on the updated data, the EPA estimates that already- designated sources plus sources currentl y exceeding the final threshold in this rule still would account for 86 percent of national emission s. Under this rule, each air agency will be required to identify all sources with annual SO 2 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 SO 2 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 emiss ions characterization requirements in the final rule. Conversel y, 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 precisel y known at this time, nor can their future percentage share of the national inventory be precisel y estimated. Nevertheless, the EPA believes that the promulgated threshold strikes a reasonable balance based on the information the Agency currentl y has regarding recent historical SO 2 emissions inventory

levels. An anal ys is of potential source threshold options and associated*** E.O. 1286 6 Review

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Page 39 of 145 source coverage, emissions coverage, and anal ytical costs is included in an EPA memorandum to the docket for this rule. 6 d
. Discretion to require air quality characterization in 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 data requirements r ule. In addition, the EPA had several reasons for proposing as part of this rule to reinforce state and the EPA discretion to require air quality characterization around additional sources beyond those with emissions above the proposed thresholds. The purp ose 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 vi olations of the SO 2 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 significantl y affect source impacts. As another exampl e, 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 re strict
6 See also: Solomon and Damberg, “ Anal ys is of Source Threshold Options for the Final SO 2 Data Requirements Rule , ” memorandum to docket EPA - HQ - OAR - 2013 - 0711 , July 16, 2015.*** E.O. 1286 6 Review

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Page 40 of 145 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 p rovides a convenient means of administering the application of the requirements for air quality characterization for the majority of cases . However , the impacts of a given level of emissions vary substantially , such that many areas with a source or sources that do not exceed the emission threshold might be known to have a high risk of contributing to NAAQS violations, potentially resulting in a higher risk of NAAQS violations than other areas exceeding the emission threshold. As a result, a rule that sets forth minimum requirements based on an emissions threshold cannot reasonabl y be used to support an assumption that no further characterization near smaller sources is warranted , or to preclude authority that air agencies already

have to investigate the impacts of such sources . Therefore , while this rule requires the air quality characterization near the above - threshold sources, the EPA and air agencies will also need to consult regarding the need for the characterization of air quality near sources below the threshold as well . Among cases in which no single source meets the applicable emission threshold, no simple indicator is available to indicate which of these cases warrants air quality characterization. For areas with a single source, the areas could warrant air quality characterization if the stack height is low, if the plume rise is minimal, if terrain or meteorology is conducive to high impacts, and /or if emissions are just slightl y below the threshold. For areas*** E.O. 1286 6 Review

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Page 41 of 145 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 and the distances and wind directions between the sources. 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 rang e of factors that influence the likelihood of NAAQS violations. That is, the EPA agrees with the state commenter urging that the rul e provide for discretionary

coverage of additional areas, such that additional areas that in the air agenc y ’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 rel ying on cas e - 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 thresh old 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 relativel y 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 ,*** E.O. 1286 6 Review

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Page 42 of 145 the EPA strongl y recommends that area s with multiple sources , where the combined impact would be expected to be as much as the impact of a ty pical single source emitting at least 2,000 tpy , should be carefully

considered for air quality characterization , and we expect EPA Regional Administrators to focus on such areas in exercising their discretion . As stated previousl y , 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 requir e air quality

characterization in additional areas, which will necessitate consultation on a case - bycase 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 criteri a 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 EPA and state agencies considering using their discretion to require characterization of additional areas, the EPA believes that the recommendations of these commenters provide good suggestions for where to begin making such decisions , to be followed by a case - by- case judgment as to the expected degree of combined impacts. In numerous cases, areas include multiple operations that previously were all part of a single source that now for business reasons have subdivided their ownership, such that the operations that previously were a single source must now be considered multiple sources. For*** E.O. 1286 6 Review

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Page 43 of 145 example, in many

cases, where previousl y the area had a single integrated iron and steel mill, the iron - and steel - making operations now have separate ownership from the coke - making operations, such that the former single source has now become two sources. In these cases, an additional equity

concer n arises, that otherwise comparable facilities should not be treated differentl y 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 separatel y owned operations would thus warrant air quality characterization . Regarding the commenters who recommended that the EPA stipulate that an area with multiple source s 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 pres erving 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 c haracterization 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 propos ed rule , the EPA proposed an implementation timeline addressing feedback and concerns raised in previous stakeholder meetings , which the EPA considered to provid e air agencies with sufficient flexibility and time to pursue either improved monitoring or modeling to*** E.O. 1286 6 Review

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Page 44 of 145 characterize air quality . The EPA designed the schedule to allow air agencies to account for SO 2 reductions that will occur over the next several ye ars as a result of implementation of national and state level programs and facility decision s for complying with such requirements (such as the Mercury and Air Toxics Standards (MATS)). 7 The EPA solicited comments on the feasibility of the i mplementation of the proposed timeline. See 79 FR 27446, 27456 , May 13, 2014 . The notice of proposed rulemaking also includ e d a discussion o f when the EPA envisioned the information could potentially

be used in designation actions. b
. Brief Summary of C o mments Several state and industry commenters agre ed that the EPA’s proposed timeline was rea sonable for acquiring data b y either modeling or monitoring, and for evaluating the submitted data . Many also agree d that it would be a reasonable schedule for supporting the issu ance of designations and submitt al of any S IP s , provided future schedules for those actions accommo date the schedule for implementing the rule . However, a larger number of state and industry commenters asserted that the time allotted for install ation of monitors was not sufficient. O ne state commenter stated that the feasibility of the schedule will dep end upon the threshold option selected b y the EPA. Another state commenter supported the timeline that the EPA

7 I n 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 Fed. Reg. 9304 (Feb. 16, 2012). Installing the technology necessary

to reduce emissions directly regulated b y the MATS rule has already reduced the emissions of SO 2 . Id. at 9305. On April 15, 201 4, 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 reverse d and remanded the D.C. Circuit’s decision for further proceedings. Michigan v. EPA, Nos. 14 - 46, 14 - 47, 14 - 49, 2015 WL2473453 (June 29, 2015). However, the MATS rule remains in effect at this time.*** E.O. 1286 6 Review

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Page 45 of 145 p roposed as long as the EPA finalizes th e 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 ye ar 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 comment er s 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 the se deadlines do not provide as much time as some commenters would prefer ; however, the EPA believes that the se deadlines can be achieved with th e 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 less 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 b y J anuary 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*** E.O. 1286 6 Review

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Page 46 of 145 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 SO 2 NAAQS ) to protect the public from the short - term health effects associated with exposure to SO 2 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 SO 2 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 delay s in monitors becoming operational past the date of January 1, 2017, will certainl y 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 b y December 31, 2017, an air agency will need to have installed and begun operating the new SO 2 monitoring s ys tem 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 encoura ges each air agency to engage in earl y 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*** E.O. 1286 6 Review

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Page 47 of 145 monitoring location s , securing funding, and installing an appropriate number of ne w site s , i f 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 th e timing and requirements of the r ule . 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, a s 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 app roach, 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 limit s 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 limitati on federall y enforceable. To suffice as an alternative to the characterization requirement, the emission requirements or limit s would need to be adopted by the air agency , made federall y enforceable , and require compliance by January 13. 2017. Further*** E.O. 1286 6 Review

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Page 48 of 145 discussion of the rationale for these revisions to the timetable is provided in the relevant subsections that follow. Table 1 shows the final rule timetable, including this revision.

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 preliminary

information concerning a possible schedule for taking action to designate areas in the future, but is intended for informational purposes onl y. In this rulemaking we are not **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 SO 2 sources; air agency

submits its list of sources to EPA by January 15, 2016 . July 1, 2016 Air agency specif ies for each source whether it will characterize air quality with modeling, characterize air quality with monitoring, or establish a federall y 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 ch aracterization , the air agency submits a description of the planned emission limit. January 1, 2017 Air agenc y ensure s that SO 2 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 agenc y submit s modeling anal ys es . For any source identified for emission limit approach, air agency submits documentation showing that l imits requiring annual emissions to be less than 2,000 t

py are effective and federally enforceable . May 2020 For any source area identified for monitoring approach, air agency

certifies 2019 monitoring data , enabling official d esign values for the 2017 - 2019 time period to be calculated .*** E.O. 1286 6 Review

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Page 49 of 145 addressing comments received on the proposed rule concerning the designation process because those issues would be beyond the intended scope of this rulemaking.
2 . Issu es Rela ted to Sub mitt al of L ist of SO 2 S ources Where Air Quality is to Be Characterized , and Election of Modeling or Monitoring
a . A ir agency submit s its 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 SO 2 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 **Table 2: Anticipated Schedule for Future Rounds of SO 2**  **Designations** July 2016 Date b y 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 D ate b y 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 C ertification 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 D ate b y 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

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Page 50 of 145 rule, are appropriate steps necessary to un derstand SO 2 air quality throughout the country , and are consistent with section s 110(a)(2)(B), 110(a)(2)(K) and 301(a)(1) of the CAA. Inthe docket, the EPA provided a preliminary list of sources that appear ed 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, b y J anuary 15, 2016, air agencies must submit a list of sources . Some c ommenters also stated that submitting a list of sources is unnecessary for various reasons such as data is already made publicly

available on an annual basis through the national emissions inventory ; that it does not make sense to es tablish a list that is expected to change ; and that air agencies and the EPA can work cooperativel y 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 anal ys is for individual sources or areas is to be complete d . One state commenter indicated that they did not find merit in the citations that the EPA provided in the proposal regarding the authority for requiring this list submittal. This commenter stated that the section 110(a)(2) citations address the requirements for SIP submittals by s tates 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*** E.O. 1286 6 Review

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Page 51 of 145 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 chara cterized 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 . See section 51.1203(a). 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 ton emissions threshold based on the most recentl y available emissions data , as well as any other sources or groups of 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 agen cies as they prepare to generate timely air quality information that may be used to inform future designation, redesignation, or other decisions concerning whether sources are affecting the attainment of areas. 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 factors may warrant 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 ye ar 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.*** E.O. 1286 6 Review

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Page 52 of 145 Thus, the EPA is retaining the January 2016 deadline, as proposed , for submittal of the list of sources in order to initiate an orderl y process to obtain additional information on ambient SO 2 concentrations, and ensure these data are available to support actions taken for the implementation of the 2010 SO 2 NAAQS. While t he Agency has previously acknowledge d 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 relativel y straightforward exercise that can be accomplished within the required time frame. The EPA strongl y 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 agenc ies and the EPA to carry

out this consultation process as earl y as possible and to reach agreement on the list of sources to characterize under the rule as quickl y and efficiently as possible . Itis also important to n ote 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 I ssues and Comments, for more discussion of these issues.)*** E.O. 1286 6 Review

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Page 53 of 145 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 rul e are appropriate steps needed to better understand SO 2 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) indicates that state SIPs are to “provide for establishment and operation of appropriate devices, methods, s ys tems, and procedures necessary to (i) monitor, compile and anal yz e data on ambient air quality and (ii) upon request, make such data available to the Administrator.” Sec tion 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.” Although both of these provisions direct what air agencies are required to include in SIPs, they clearl y 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. Inaddition, s ection 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 SO 2 NAAQS throughout each state. Finally , the EPA notes that CAA section 114(a)(1) also provides broad a uthority for the EPA , for the purposes of*** E.O. 1286 6 Review

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Page 54 of 145 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 likel y 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. Accordingl y, such a list is not being promulgated as part of this rule . The E PA plans on continuing consultations with air agencies regarding the source areas that the final rule will require to be characterized. b. C hoose 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 situations where multiple so urces are located in proximity across state boundaries, the EPA recommended that the relevant air agencies work together to determine a common analy tical approach for assessing air quality in that area. See 79 FR 27446, 27460 , May 13, 2014 . ii. Brief Su mmary of Comments Several state and industry c ommenters stated that the EPA should provide a more reasonable schedule for air agencies to elect the monitoring option under the p roposed r ule.*** E.O. 1286 6 Review

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Page 55 of 145 Some c ommenters 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 determinati ons, 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 enforceabl y limits an applicable source’s emissions) . Accordingl y, 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 rev ision, 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. Conversel y, 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*** E.O. 1286 6 Review

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Page 56 of 145 address in a timel y way any issues that arise after the selection is made. The result would be that a later deadline for this se lection 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 strongl y encourages each air ag ency 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 warr anted . Similarly , the EPA strongl y encourages air agencies to hold earl y 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 , earl y discussions with the EPA would be essential for assuring that the intended selection of monitoring is based on appropriate assumptio ns regarding the network’s ability to characterize air quality near the applicable source(s) without further network adjustments. c . Use most recent publicly available data i. Summary of Proposal In § 51.1202, the EPA proposed that the air agency should identify applicable sources of SO 2 based on the most recent publicly available annual SO 2 emissions data for such sources. The EPA specified in proposed § 51.1200, that “annual SO 2 emissions data” means the qualityassured annual SO 2 emissions data f or 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, b y J anuary 15,*** E.O. 1286 6 Review

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Page 57 of 145 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 agenc ies 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 th e proposed rule a preliminary list of sources that appeared to meet the criteria described in the EPA’s proposed so urce 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 th at preliminary list. See , 79 FR 27446, 27457 , May

13, 201 4 . ii. Brief Summary of Comments Several state and industry commenters generall y supported the approach that the basis for the emissions to be compared to the threshold would be the latest available 1 - ye ar of SO 2 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 properl y taken into consideration. One public interest group commenter stated that using the mos t recent ye ar as a snapshot may fail to capture sources that simply have a low year, but normall y emit at higher levels, and recommended that the EPA require that facilities only be excluded under the threshold if, in prior ye ars, 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 anal ys is of 1 ye ar ’ 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 -*** E.O. 1286 6 Review

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Page 58 of 145 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 - ye ar period to determine if a different methodology is appropriate for determining if a source should be a part of the anal ys is. iii. EPA Response The EPA continues to believe that the most appropriate generall y applicable basis for determining applicability of the air quality characterization requirements is the most recent available ye ar of emissions data for a stationary source as reported to the EPA in accordance with any existing regulatory

requirement . As we have previousl y explained, SO 2 emissions are trending downward, due to numerous national and regional requirements that have recentl y 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 avail able ye ar of emissions. By January 15, 2016, the EPA would expect that 2014 data w ill 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 ye ar. These sources report hourly emissions data to the EPA on a quarterly basis. Emissions data for large SO 2 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 SO 2 sources with the potential to emit more than 100 tpy . In other years, the AERR requires states to report emissions data for SO 2 sources with the potential*** E.O. 1286 6 Review

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Page 59 of 145 to emit more than 2,500 tpy . These annual reports under the AERR are due 12 months after the end of the emissions year. Thus, the EPA would expect that in January 2016, states would have emissions data for calendar year 2014 available for non - EGU sour ces over 100 tons 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 SO 2 data requirements rule. 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 so urces based on the most recent ye ar 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 th e most recent ye ar 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 t py , 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 t

py but normally

emit below that level. G iven the trends in emissions, the EPA believes that situation will be relativel y 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 .*** E.O. 1286 6 Review

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Page 60 of 145 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 mo nitoring 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
. S hutdowns and limitations on emissions levels b y January 1 3 , 2017 i. Summary of Proposal The EPA noted in the propos ed 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 s hut down but is still in operation on January 15, 2016, should be included on the air agency ’s list for SO 2 air quality

characterization . H owever, if b y J anuary 1 3 , 2017, the air agency can provide the EPA with a legal agreement confirming that the listed source has permanently and enforc ea bl y shut down, then under the proposal the air agency w ould have no further obligation regarding air quality characterization for this source pursuant to this rulemaking. See 79 FR 27446, 2745 8 , May 13, 2014 . ii. Brief Summary of Comments One state c ommenter 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*** E.O. 1286 6 Review

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Page 61 of 145 threshold before January

13, 2017, even if reductions and applicability of the limitation are only realized within a reasonable time after January 1 3 , 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 cas es 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 federall y enforceable limits on a tpy basis prior to the January 13, 2017 date for air agencies to submit their modeling anal ys is 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 s tate and industry c ommenter s 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 1 3 , 2017. Commenters stated that there is insufficient time for sources to take all the actions needed to implement these controls (including c onducting modeling, determining the required reductions and control strategies, procuring capital funds, obtaining permits and installing equipment) under the p roposed r

ule. C ommenter s stated that allowing sources to implement controls after January 1 3 , 2017 , but before future attainment date s 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

1 3 , 2017 , deadline have little incentive to take any action prior to the anticipated designation deadline of 2020. iii. EPA Response*** E.O. 1286 6 Review

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Page 62 of 145 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 permanentl y prior to January 1 3 , 2017 pursuant to a federall y enforceabl e mechanism (e.g., source - specific SIP revision or minor NSR permit revision submitted to the EPA by January 1 3 , 2017 ) , to avoid b e ing 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 rec ent ye ar of actual emissions exceed s 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 emission s during the mo st 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 SO 2 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 § 51.120 3(b) allowing the air agency to indicate by July 1, 2016 that it will provide the EPA with a federall y enforceable requirement confirming that the source will be permanentl y and enforceably shut down by January 1 3 , 2017. For a source for which the air agency p rovides documentation of a federall y enforceable requirement that the source will shut down , the air agency

will have no further obligation regarding air quality characterization*** E.O. 1286 6 Review

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Page 63 of 145 pursuant to this rulemaking. This approach accomplishes the intent of the proposal b y 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 federall y enforceable requirement to limit annual SO 2 emissions to below the 2 , 000 t

py 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 accordingl y, 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 non attainment, to implement controls that were committed to prior to January 1 3 , 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 informatio n on priority SO 2 sources to the EPA beginning in earl y 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 s ource would be listed for air quality characterization if its most recent emissions were above the 2,000 tpy threshold . However, the final rule also allow s the air agenc y to meet the requirement s of this rule by submitting a federall y enforceable emissions limitation (e.g., source - specific SIP revision or minor NSR permit revision) to the EPA prior to January 1 3 , 2017 that requires th e affected source to reduce allowable emissions at the source to*** E.O. 1286 6 Review

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Page 64 of 145 an annual rate below the 2 , 000 t py threshold level prior to January 1 3 , 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, i f the affected air agency

has adopted and the source ha s become subject to effective federally enforceable control measures lowering emissions below 2,000 tpy by January 1 3 , 2017 , the air agency will generall y no t be required to further characterize the impacts from the source’s emissions solely

due to its size as of January 1 5 , 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 mu st apply j udgment 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 ha s 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 urge s air agencies to consult earl y 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 prioritiz e resources to focus on the largest sources of SO 2 , but it also has the additional benefit of providing an incentive for early emission reductions*** E.O. 1286 6 Review

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Page 65 of 145 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 applic ability threshold

– particularl y 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 area s with other sources over the applicability threshold , and in area s where no single source has emissions over the threshold but the combined emissions of multiple sources warrant air quality ch aracterization . 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 applicabi lity 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 s hould continue to be required to characterize air quality notwithstanding the new emission limits. Air agencies are thus advised to consult with their EPA Regional O ffice before pursuing this alternative to air quality characterization for a particular source area . 3 . Issues Related to Submittal of M odeling P rotocols. a. Summary ofProposal For source areas that an air agency identifies are to be evaluated through air quality modeling, the EPA propose d in § 51.1203(d) that an air agency must also provide a modeling*** E.O. 1286 6 Review

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Page 66 of 145 protocol to the EPA Regional Administrator for review by January 15, 2016. Inthe 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 27 446, 27458 , May 13, 2014 . b
. Brief Summary of Comments Several commenters stated that 1 ye ar 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 ye ars to complete the 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 p rotocols . 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*** E.O. 1286 6 Review

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Page 67 of 145 be left up to the respective state agency , consistent with past practices in PSD SIP approved states as well as past practi ces 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 norm al 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). Itis reasonable for the EPA to establish a process that provides an opportunity

for preliminary

EPA assistance to air agencie s to ensure that their subsequent modeling is conducted in a manner that result s in information that can reliably inform subsequent EPA actions determining air quality status under the SO 2 NAAQS. As explained below, the submission of modeling protocols will reduce the likelihood that subsequent air*** E.O. 1286 6 Review

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Page 68 of 145 agency modeling is insufficient 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 approx imately 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 b y which information for characterizing air quality becomes available. Consistent with this revision, the EPA is delayingthe deadline for states to submit modeling protocols for sources for which they choos e to characterize air quality through modeling , to match the July 1, 2016 , deadline fo r 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 accuratel y characteriz es air quality

near sources. Requiring modeling protocols w ill 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 wi th the EPA and, if it occurred, could result in the air agency needing to re - conduct modeling after submission to the EPA . The EPA does not intend to formally approve these protocols, nor does the EPA believe that a one - size fits - all timeline, process, or presumption regarding approval or disapproval of these protocols is warranted. Nevertheless, the EPA believes that submittal of protocols will facilitate identification, and resolution of modeling issues, and will thereb y help to avoid a later situation in which the EPA would not be able to rel y upon the air agency ’s modeling in subsequent actions determining air quality

status . Review of modeling protocols b y the EPA will help ensure that the air agency ’s modeling will be appropriate for use in making future determinations regarding*** E.O. 1286 6 Review

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Page 69 of 145 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 model ing protocol s 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 dat a 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 expedi tious. 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

o f the air quality

information. The EPA Regional Office staff will be available to consult with air agency officials to refine the modeling protocol s 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 SO 2 M o nitoring N etwork M odifications to S atisfy the DRR . a . Summary ofProposal In area s where air quality will be characterized through ambient monitoring to satisfy this rulemaking , the EPA proposed monitoring requirements in § 51.1203(c), including the*** E.O. 1286 6 Review

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Page 70 of 145 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. Inthe 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 in the draft M onitoring TAD. 8 See 79 FR 27446, 2 7458 , May 13, 2014 and proposed § 51.1203(c) . 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 b y the proposed July 1, 2016 , deadline. Some c ommenter s 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 l ocated, obtaining access to sites, identifying funding, and procuring and installing equipment. Furthermore, one co mmenter 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 adequatel y maintained and that data are reported in a timel y and complete manner , and (2) to put in place a

8 The SO 2 NAAQS Designations Source - Oriented Monitoring Technical Assistance Document can be found at http://www.epa.gov/airquality/sulfurdioxide/pdfs/SO2MonitoringTAD.pdf .*** E.O. 1286 6 Review

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Page 71 of 145 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 appropriatel y put in place by the January

1, 2017 , deadline to satisfy this rule, particularl y if air agencies begin planning as soon as possible. The EPA has encouraged air agencies to begin the monitor planning process earl y, particularl y 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 agenc ies . The EPA strongl y 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 characterizati on of nearb y air quality . In addition, as stated previously , the EPA believes that it is necessary to establish expeditious timelines to ensure timel y 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 Region al Office s well in advance of the time by which the Annual Monitoring Network Plan is due. Notabl y, there is nothing preventing a state*** E.O. 1286 6 Review

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Page 72 of 145 from sharing their draft SO 2 network design plan for SO 2 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 earl y interaction between air agencies and the EPA Region al Office s and indus try will likely improve the potential for success in installing an appropriate amount of monitors in appropriate locations around SO 2 emitting facilities identified for characterization in this rulemaking. 5 . Issues Related to Deadline for Operation o f SO 2 M onitors a . Summary ofProposal The EPA propose d 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 b y May 2020 . This would allow thes e 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 designation s and redesignations . See 79 FR 27458 , May

13, 2014 , and proposed § 51.1203(c). 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 SO 2 NAAQS is being met.*** E.O. 1286 6 Review

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Page 73 of 145 One state commenter also asserted that the feasibility of this time period will be dependent upon the threshold option selected b y the EPA and thus the number of affected sources . However, m ore 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 technicall y infeasib le to implement the p roposed r ule 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 ye ars of the new monitoring data are obtained and certified . This commenter also not ed that, if the EPA ’s approval of an SO 2 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 b y J anuary 1, 2017. Another state c ommenter noted that other recent rules establishing new monitoring requirements ( such as NAAQS revisions for NO 2 , SO 2 and PM 2.5 ) h ave not required such rapid deploy ment 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 burden s of install ing an ambient air monitoring station can v ary in difficulty and the resources required . However, as noted earlier*** E.O. 1286 6 Review

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Page 74 of 145 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 b y 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 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 relativel y timely manner for use in making attainment status decisions concerning SO 2 areas in the country . Therefore, the EPA is finalizing the date b y which monitors being used to satisfy this rulemaking must be operational to be Janu ary 1, 2017. As noted previousl y, if a state has chosen 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 their respective EPA Regions well in advance of the time by which the Annual Monitoring Network Plan and network operations are due. T he EPA is encouraging air agencies to engage their respective EPA Regional Office s , and possibly the industrial sources needing nearb y ai r quality characterization, to plan an adequate network design as earl y 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*** E.O. 1286 6 Review

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Page 75 of 145 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 SO 2 emitting facilities identified in this rulemaking as needing nearb y ai r 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 monitor s are less feasible for particular areas, they may instead choose the less resource - demanding and more expeditious method of modeling to characterize SO 2 emissions impacts in such areas . 6 . Issues Related to Submittal of M odeling Anal ys es to the EPA a . Summary ofProposal The EPA proposed in § 51.1203(d) (3) that air agencies that cho o se modeling to characterize ambient air quality be required to submit modeling anal ys es to the EPA Regional Office b y J anuary

1 3 , 2017 . Inthe proposal , the EPA recommended that these modeling anal ys es should be conducted in accordance with the recommendations in the EPA’s M odeling TAD 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 activel y in consultation to understand the inputs, assumptions and findings associated with each air quality modeling anal ys is ; the air agency

should submit thorough documentation of its modeling anal ys is ; and the air agency should pro vide the EPA with supplemental information about the anal ys is upon request. The proposal also indicated that where areas have not already been designated under the 2010 NAAQS, air agencies could submit updated designation recommendations , if appropriate , as informed b y their modeling anal ys es. The proposal noted that in developing any updated*** E.O. 1286 6 Review

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Page 76 of 145 designation recommendations, the air agency should follow the EPA’s most recent SO 2 designation guidance. 9 See 79 FR 27446, 27458 , May 13, 2014 and proposed § 51.1203(d). b
. Brief Summary of Comments One state commenter disagreed with the requirement that comprehensive modeling anal ys es and related supporting information need to be submitted to the EPA. This commenter asserted that the modeling anal ys es will be conducted by the facility

owners and reviewed b y the state air agency , and the air agency should be able to forward just a summary of the analy ses 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 anal ys es to the EPA Regional Office . Irrespective of whether the state or a third party conducts the model ing, 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 applica ble requirements . Moreover, the EPA anticipates that the submittal would provide adequate information for the EPA to review the adequacy of the anal ys is as well.

9 The EPA issued a first round of guidance on the SO 2 area designations process on March 24, 2011. See http://www.epa.gov/air/sulfurdioxide/pdfs/20110411SO2designationsguidance.pdf
. Note: The EPA issued an updated SO 2 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
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Page 77 of 145 D . Technical Issues Relating to Modeling and Monitoring 1 . Technical A ssistance D ocuments (TADs) This section of the preamble presents a discussion of the threshold - based air quality characterization approach to implement the SO 2 NAAQS in areas that contain sources with larger SO 2 emissions, in order to address areas where there may be higher potential for NAAQS violations that adversel y 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 propos ed rulemaking , the EPA noted that the Agency has produced draft, non - binding M onitoring and M odeling TADs that discuss options , suggested approaches and methods on how monitoring or modeling efforts to ch aracterize air quality around an identified source might be conducted. The EPA stated that these documents c an be used to assist air agencies in the implementation of this rulemaking. 10 See 79 FR 27446, 2746 0 , M ay 13, 2014 . b
. Brief Summary of Comments One industry

commenter stated that the proposed rule references and relies upon guidance provided in the M odeling and M onitoring TADs and in Appendix W ; therefore, the commenter asserted that the documents are subject to review and comment for th e p roposed r ule.

10 The EPA considered the TADs as being living documents that may be update d on a recurring basis as necessary .*** E.O. 1286 6 Review

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Page 78 of 145 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

c ommenters urged the EPA to be clearer in the final preamble that the TADs are guidance and therefore are not binding. One state c ommenter 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 c ommenter stated th at the EPA's reliance on technical guidance documents that have not been subject to public notice and comment undermines protections guaranteed by the Administrative Procedure Act. One state c ommenter 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 . A lthough 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 SO 2 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 updat e as necessary over time. The Agency believes that a modeling protocol*** E.O. 1286 6 Review

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Page 79 of 145 or monitoring network design that follows or references the recommended approaches in the TADs is likel y 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 ref erence 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. Inresponse 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 b y stakeholders, and revised versions of the TADs were developed in response to those comments. 2 . Monitoring and N etwork D esign I ssues 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*** E.O. 1286 6 Review

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Page 80 of 145 network; they

do not, however, have to be designated as SLAMS monitors . Inthe proposal , the EPA stated that the moni tors should use Federal Reference Methods (FRMs) or Federal Equivalent Methods (FEMs) and meet the requirements of 40 CFR part 58 , a ppendices A, C , and E. Further, the EPA stated that the resulting data should be reported to the Air Quality S ys tem (AQS) an d 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 27446, 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 SO 2 source - oriented monitoring network puts air agencies in the unreasonable position of designing a monitoring network without knowing whether it will be approved b y 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*** E.O. 1286 6 Review

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Page 81 of 145 for SO 2 are likel y 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 , possibl y 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 latt er 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 p art 58 , a ppendices A , C , and E, and adhere to data reporting requirements also contained in 40 CFR part 58. This do es 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 submi tted data that satisfies the intent of this rulemaking. With respect to concerns over a lack of clear criteria for designing an SO 2 source - oriented monitoring network , the likelihood to appropriately place one or more monitors, and the issue of what number of monitors might be required around a source, there is no one - size - fits - all answer to this question . The EPA indicated in the preamble to the proposal , and in the draft M onitoring 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 SO 2 concentration maxima are expected to occur. Site selection for any monitoring network is subject to logistical hurdles*** E.O. 1286 6 Review

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Page 82 of 145 including site access, identification or installation of appropriate infrastructure, telecommunications access, and safety, and s tate, 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 ambi ent air monitoring, responsible air agencies are expected to establish a clear rationale for the number and placement of any one or more monitors it is using to satisfy the requirements of th e rule. Inthis process, there is flexibility

for the state to us e 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, th e air agency’s recommended number o f monitors and preliminary rationale should be discussed with the EPA Region al Offices well in advance of the development of an Annual Monitoring Network Plan. As discussed in the M onitoring TAD, the development of a network design and its rationale can be informed b y a number of ty pes of anal ys es which can include the use of air quality modeling, exploratory

monitoring, or anal ys is of existing data. In any scenario, the state would need to have a technically

credible rationale that supports the monit oring network design approach that has been chosen to satisfy

requirements in this rulemaking. As stated previousl y, the TADs provide recommendations for air agencies, but are not binding or enforceable , and they create no obligations on any entity . Altho ugh 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*** E.O. 1286 6 Review

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Page 83 of 145 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 F ailing to H aving N ew M onitors Operational by January 1, 2017 a. Summary of Proposal Where an air agency has chosen the monitoring approach and submitted a list identifying th e source s near which air quality is to be monitored, the proposed rule addressed the situation where it becomes evident that sufficient and appropriate monitoring wil l not be operational in a timely manner . The EPA propose d 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 request ed comment on th is approach , and on any alternative approaches that could most effective ly address a situation where an air agen c y 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 27446, 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 miss ed 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 s uperior accuracy of actual monitored data; and that they believe the lower costs of modeling do not offset the regulatory*** E.O. 1286 6 Review

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Page 84 of 145 costs and other burdens on sources and communities that could result from nonattainment designations based on modeling. One public int erest group commenter stated that because the monitoring approach already could lead to designations occurring a full decade after the NAAQS was promulgated, it should be regarded as an absolute edge - of - the - envelope approach , meaning that f ailure 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 properl y incentivize actors to transmit information to the EPA in a timely manner. A number of state and industry commenters did not agree that a would - be monitored area should be automatically designated at the same time as areas for which the modeling option was chosen in the event of any delay in monitoring. Commenters also stated that the proposed penalty for unanticipated monitoring site delay s 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 monito rs 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 timel y 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.*** E.O. 1286 6 Review

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Page 85 of 145 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 b y the court, in order for the EPA to no t be required to designate an area b y 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 rul e 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 b y J anuary 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 onl y if the monitor is timely

installed and operate d. 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 cho o se s to characterize air quality with new*** E.O. 1286 6 Review

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Page 86 of 145 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 anticipat es promulgating designations for areas characterizing air quality through a new monitoring network . The EPA must n ow comply with a court ordered designation schedule, in which the court expressly requires that areas that have not b egun operation of a new monitoring network b y J anuary 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 , an d comm i ts 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 SO 2 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 accordingl y. 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 . M onitor S hut D own a. Summary of Proposal*** E.O. 1286 6 Review

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Page 87 of 145 In the preamble, the EPA proposed that a monitor that has been deplo ye d 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 SO 2 monitor identified in an approved state annual monitoring network plan to satisfy the rule requirements may be eligible for shut down if the f ollowing criteria are met: (1) the monitor is not also satisfying other m inimum SO 2 monitoring requirements listed in 40 CFR part 58 , a ppendix D; (2) the monitor is not otherwise required to meet requirements in a SIP or permit; and (3) the monitor has recorded a 3 - ye ar design value (DV) that is no greater than 50 percent of the 1 - hour SO 2 NAAQS. The EPA also propose d that any SO 2 monitor eligible for shutting down would need to be approved b y the EPA Regional Administrator before monitoring operations could cease. As an alternative, the EPA also propos ed an option in which th e same criteria noted earlier would need to be met, except that the monitor would be eligible to cease operations if it recorded a DV in the three - year period that is no greater than 80 percent of the 1 - hour SO 2 NAAQS. The EPA request ed comment on the two proposed options for DV criteria for SO 2 monitor shutdown , as well as other potential values within the 50 - 80 percent range. The EPA request ed that commenters provide specific technical rationale supporting any approach they recommend. See 79 FR 27446, 274 62 , 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*** E.O. 1286 6 Review

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Page 88 of 145 more appropriatel y. One industry commenter stated that, if the sources are properl y 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 o ne 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 SO 2 emission to cause an exceedance of the 1 - hour SO 2 NAAQS . S ome s tate commenters recommended that the threshold of 50 percent be dropped in the fin al 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 p art 58 and, if the EPA wishes to change th ose 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 SO 2 emissions with the possibility that further monitoring could be required, argues against the more stringent 50 percent option. O ver 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 a SO 2 mo nitor and the 80 percent criteri on is consistent with criteria for shutting down most regulatory monitors. One public interest group c ommenter 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 SO 2 monitor network needs to be rebuilt. In addition, this c ommenter recommended that monitors not be removed if the concentrations they are recording are trending upward, indicative of potential future problems.*** E.O. 1286 6 Review

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Page 89 of 145 c. EPA Response The EPA is finalizing the rule to allow any SO 2 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 SO 2 nonattainment area, and is not also being used to satisfy other ambient SO 2 minimum monitoring requirements listed in 40 CFR part 58 , a ppendix 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 SO 2 NAAQS in the first or second 3 - ye ar period s of its operation . See § 51.1203(c)(3). The EPA has chosen to adopt this shut down allowance so that those monitors that record ambient concentrations that are well below the NAAQS after 3 or 4 ye ars 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 reliev e 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 estimat es of future concentration s as do existing shutdown provis ions in 40 CFR 58.14. More specificall y, this monitor shutdown provision works by assessing how two design values ( i.e, , one calculated from monitor data collected in ye ars 1 through 3 , and one from ye ars 2 through 4 ) would compare to the 50 percent of the NAAQS shutdown criterion . I f a moni t or produces a design value from data collected in years 1 through 3 that is no gr e ater than 50 percent of the NAAQS, it is eligible for shutdown if it is not otherwise required to operate . If the design value is above the 50 percent threshold, the monitor must continue operation. If that monitor produces a design value no greater than 50 percent of the NAAQS f rom data in ye ars 2*** E.O. 1286 6 Review

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Page 90 of 145 through 4, it is eligible for shutdown if not otherwise required to operate . If , inste ad, the design value is again above the 50 percent threshold, the air agency must continue to operate the monitor . F rom 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 probab i listic estimation s 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 p art 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 Regional Administrator approval for : “Any PM 2.5 , O 3 , CO, PM 10 , SO 2 , Pb, or NO 2 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 ye ars based on the levels, trends, and variability

observed in the pa st, and which is not specificall y required by an attainment plan or maintenance plan. In a nonattainment or maintenance area, if the most recent attainment or maintenance plan adopted b y the state , and approved b y the EPA , contains a contingency

measure to be triggered b y 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 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*** E.O. 1286 6 Review

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Page 91 of 14 5 are two sequential routes for possibly shutting down a monitor. I f a monitor shows concentration readings greater than 50 percent of the NAAQS after the first two sets of 3 - ye ar periods of its operation and cannot be approved for shut down under the first sequential route , the monitoring will continue. However , after 5 ye ars 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) app ly , 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 F ollowing M onitor S hutdown a. Summary of Proposal For any area for which the EPA has approved an air agency ’s request for an SO 2 monitor to cease operations, the EPA propose d that the air agency be required to assess SO 2 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 SO 2 emissions increase over the emissions for the previous ye ar, 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 agen cy

to the EPA pursuant to § 51.1205 indicates that an area is not attaining the 2010 SO 2 NAAQS, the EPA may take appropriate action, including but not limited to disapproving the monitoring plan,*** E.O. 1286 6 Review

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Page 92 of 145 requiring adoption of enforceable emission limits to ensure c ontinued attainment of the 2010 SO 2 NAAQS, redesignation of the area to nonattainment, or issuance of a SIP Call. The EPA propose d 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 propose d 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 subm itted to the EPA Regional Administrator by July 1 st 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 co mment s 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 nearb y 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

1 st 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 27446, 27462 , May 13, 2014 , and proposed § 51.1205(d) . 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*** E.O. 1286 6 Review

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Page 93 of 145 reporting requirement, stating that SO 2 emissions from sources are already available to the EPA and the need for ongoing data requirement s 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 anal yses since an increase in emissions that would result in such a drastic increase in monitored design values would surel y 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 1 st submittal date is unrealistic because states will not have the required quality- assured emissions monit oring data processed b y July

1 st . Some state and industry commenters recommended a less burdensome process in which this verification would take place every 3 to 5 ye ars instead of annuall y, 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 sh ould be based on an increase greater than the 3 ye ar average of emissions during the initial monitoring analysis, an increase above the highest single year of emissions during the initial monitoring anal ys is, or some other metric. Some commenters recommend ed 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 SO 2 may have resulted in total*** E.O. 1286 6 Review

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Page 94 of 145 SO 2 emissions levels well below the annual emission rates during the ye ars when monitoring data showed compliance. One tribal and several state commenters supported the option of including the annual emissions analy sis with the annual monitoring plan. One commenter stated that the anal y sis of emissions is closely

related to network planning, and this procedure would provide a single document for public 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 finaliz e the proposed requirement that any state with an area for which the EPA has approved the air agency ’s request for an SO 2 monitor to cease operations must still assess SO 2 emissions changes annuall y, beg inning in the year after the monitor ceases operation . The EPA made this decision based upon comments on the p roposed r ule , and in recognition that a cessation of monitoring will not occur unless a monitor has measured SO 2 concentrations well below the NAAQS for a given time period and an EPA Regional Administrator has allowed the shut - down . The Agency is persuaded b y commenters that monitor shutdown provisions , along with generall y applicable emissions reporting requirements, are of sufficient strength that subsequent additional annual observation and reporting of SO 2 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 unlikel y s cenario occurs where*** E.O. 1286 6 Review

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Page 95 of 145 SO 2 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 p art 58 , a ppendix D, s ection 4.4.3. 6 . Modeling I ssues a . AERMOD i. Summary of Proposal In the proposal, the EPA stated that the Agency anticipates that in implementing the rule air agencies would likel y 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 SO 2 air quality

given appropriate input data. The EPA explained in the propos ed rule that, as part of its development, AERMOD was evaluated using 17 field studies, several of which involved short - term measurements of SO 2 , robust site - specific meteorology and accurate measurements of emissions. The EPA stated in the proposal that the Agency is confident that AERMOD can provide accurate predictions of ac tual SO 2 concentrations g iven representative meteorology and accurate emissions inputs. See 79 FR 27446, 2746 3 , M ay 13, 2014 . ii. Brief Su mmary of Comments One industry

commenter stated that, for certain conventional SO 2 emission scenarios, such as tall stacks at coal fired EGUs, AERMOD can be at least reasonabl y predictive. One public interest group commenter stated that AERMOD modeling performs particularl y well in evaluating emission sources with one or a handful of la rge 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 SO 2 NAAQS in which he stated that AERMOD is capable of accuratel y*** E.O. 1286 6 Review

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Page 96 of 145 predicting whether the revised primary SO 2 NAAQS is attained and whether individual sources cause or contribute to a violation of the SO 2 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 SO 2 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 ove r - predicting SO 2 concentrations, including buo yantline sources, building downwash, conservative assumptions in terms of model input , modeling of multiple sources, periods of low wind speed, steep terrain and lack of representative meteorological data. Commenters stated that the individual aspects of AERMOD and the EPA’s guidance that contribute to over- prediction of the SO 2 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 M odeling 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*** E.O. 1286 6 Review

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Page 97 of 145 as the Buo yant Line and Point Source Dispersion Mod el (BLP). Models recommended for particular applications are listed in a ppendix A of a

ppendix W. Section 3.2 of a ppendix W 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 SO 2 source identified in this rulemaking. The TADs have been provided in order to pot entiall y aid air agencies seeking advice in the air quality characterization process required b y this rulemaking. With regards to concerns regarding model conservatism, EPA is working on updates to AERMOD to address concerns regarding buo yant line sources , building downwash, and low wind speed issues. With regards to comments about model inputs that lead to over- estimates, as part of its development, AERMOD has been shown to perform well against observed concentrations when actual emissions have been used. The modeling of actual emissions for

11 Itis the EPA’s intention to update the M odeling and M onitoring 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.*** E.O. 1286 6 Review

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Page 98 of 145 multiple sources is not anticipated to cause over- predictions. The modeling TAD also discusses that the number of sources explicitly modeled in an application is expected to be low and that in many cases, a number of s ources 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 SO 2 emissions from the most recent 3 ye ars or federally enforceable allowable emissions. The EPA referred readers to the M odeling 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 in formation and recommendations on this approach are discussed in the M odeling 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 effectivel y serve as a surrogate for comprehensive ambient monitoring results. Several c ommenters suggested that the use of allowable emissions as an input to air quality modelin g anal ys es would result in modeled air quality values that were higher than air quality levels that would be expected to be observed b y a properl y sited ambient monitor . Commenters stated that*** E.O. 1286 6 Review

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Page 99 of 145 using actual emissions is even more important when conducting a cumulative impact anal ys is (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 industr

y commenters supported the EPA’s proposal to base the modeling analy ses on actual emissions over a 3 - ye ar period. One commenter noted that, in situations where multiple sources are being modeled, the most recent 3 ye ars 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 ye ars 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 avai lable. iii. EPA Response When using actual emissions, the EPA believes the most recent 3 ye ars of time varying emissions (e.g . , emissions that vary hourl y, seasonal ly , monthly , dail y, etc.) should be modeled since the air quality

modeling is being used as a surrogate for monitoring. The M odeling TAD gives recommendations on inputting hourly emissions into AERMOD for those sources with hourly continuous emissions monitoring (CEM) data and als o gives recommendations on inputting time varying emissions (e.g. seasonal ly , monthly, etc.) when no hourly emissions are available and onl y annual emissions and data such as production logs or fuel usage are available. However, the final rule does not res trict the ability of air agencies to use more conservative*** E.O. 1286 6 Review

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Page 100 of 145 allowable emissions in conducting their modeling. Inthe event that a particular source does not have the most recent 3 ye ars of emissions, it may be possible to use the most recentl y available emissions or develop the most recent 3 ye ars of emissions using recommendations in the TAD . The reviewing authority

should work with the appropriate EPA Regional Office on the use o f 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 TAD. Once a modeling protocol or modeling an aly ses 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 change s do not warrant a revision to the protocol or modeling analy ses . c . Accounting for recent emission reductions in modeling anal ys es 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 SO 2 standard and, t o address such situations, the air agency may wish to consult with the source (s) and take action to adopt enforceable emissi ons limitations as necessary prior to January

2017 to potentially

avoid a nonattainment designation . The EPA proposed that, a s long as these controls are implemented and enforceable as of January 2017, i t would be appropriate for the new lower allowable em ission s to be used in the modeling anal ys is 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 modif y its designation*** E.O. 1286 6 Review

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Page 101 of 145 recommendation accordingl y , if that designation has not yet been issued . See 79 FR 27446, 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 timel y 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 SO 2 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 ye ars. 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*** E.O. 1286 6 Review

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Page 102 of 145 and enfor ceable by

January 2017, the new allowable emission limit may be input into the model instead of the actual emissions of the most recent 3 ye ars. The EPA expects that a number of emissions sources may be candidates for this optional approach. Many EGUs will need to meet compliance deadlines for the MATS in April 2015 (or in some cases , April 2016 ) , and the EPA expects that many will become subject to Title V permits that require compliance with MATS SO 2 emission limits as the means of demonstrating complianc e 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 SO 2 as well as mercury . Similarl y, industrial boiler operators will have the incentive to adopt SO 2 emission limits as part of their strategy for compl ying with the Industrial Boiler Maximum Achievable Control Technology

Standard. Therefore, the EPA believes that as long as these emissions reductions are implemented and enforceable prior to January 2017, it would be appropriate for the new lower allowable emission s to be used in a modeling analysis in place of the high er actual emissions . The air quality impacts from such a source would be characterized by the new enforceable allowable limit (at worst) 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, i f an air agency chooses to use allowable*** E.O. 1286 6 Review

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Page 103 of 145 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 M odeling TAD. See 79 FR 27446, 2746 4 , 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, s everal 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 accuratel y 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 c ommenter stated that the concern a bout giving inappropriate credit for dispersion techniques is irrelevant in the context of this designation modeling as 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*** E.O. 1286 6 Review

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Page 104 of 145 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 c onsistent 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 b y an ambient monitor, th e EPA recommended the use of 3 ye ars of meteorological data . The EPA stated that, i deally , air agencies would use the most recent 3 years of meteorological data and the same 3 ye ars of actual emissions data when modeling f or designations. The EPA noted that the M odeling TAD has additional suggestions on these meteorological inputs. See 79 FR 27446, 2746 5 , May 13, 2014 . ii. Brief S

ummary of Comments Some commenters recommended the use of 1 ye ar of meteorological data rather than 3 ye ars and provided several reasons : use of 1 year of on - site meteorological data would yi eld a very robust data set ; 3 ye ars does not provide a si gnificant benefit over 1 ye ar; 1 ye ar of meteorological data is sufficient for PSD purposes ; collection of 3 ye ars of data would delay the running of AERMOD ; and collection of 3 years of data would be unnecessarily expensive.*** E.O. 1286 6 Review

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Page 105 of 145 Commenters stated that, while relativel y few meteorological databases with 3 ye ars 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 - ye ar period may not provide adequate confidence in the anal ys is, 5 ye ars will provide more 3 - ye ar 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.

 G iven th e lack of 3 ye ars 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 ye ars of representative site specific data or when site - specific data are not readily available , or it is not feasible or cost effective to collect site - specific data, the most recent 3 years of representative National Weather S ervice 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 M odeling TAD offers recommendations on sy nching the older meteorological data with the more recent emissions, especiall y for those sources utilizing hourly

emissions. The TAD provides an explanation of the need for 3 ye ars of*** E.O. 1286 6 Review

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Page 106 of 145 meteorological data , even if only 1 ye ar 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, a

ppendix W should be consulted on the latest acceptable forms 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 timel y 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. Specificall y, 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 appro ach 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 SO 2 concentrations. The EPA stated th at d etails on the suggested protocol elements and the recommended standard format of this protocol can be found in the M odeling TAD . See 79 FR 27446, 274 65 , May

13, 2014 . ii. Brief Summary of Comments*** E.O. 1286 6 Review

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Page 107 of 145 Some state and industry

commenters requested that the EPA provide more specific guidance on conducting multi - source modeling analy ses. 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 b y 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 anal ys e s, and who would be responsib le for conducting anal ys e s when sources are located in multi - state area s . One state commenter requested that guidance on modeling facilities across state lines should be addressed. iii. EPA Response The determination of whether to includ e nearb y s ources 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 nearb y sources. The EPA has offered technical recommendations in the M odeling TAD. The identification of nearb y 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 M odeling TAD and s ection 8.2 of a ppendix W. As stated previousl y, 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*** E.O. 1286 6 Review

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Page 108 of 145 required to be adhere d to by any air agency who is required to characterize air quality around an SO 2 source identified in this rulemaking. The TADs have been provided in order to potentiall y 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 l iving documents which the EPA may updat e as necessary . g. Ongoing air agency data requirements for areas that were initially modeled i. Summary of Proposal The EPA propos ed 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 propos ed 3 options for how air agencies that rely on modeling of actual emissions would need to conduct additional emissions and/or modeling anal ys es. In the propos ed rule , the EPA believed that such additional anal ys es w ould onl y be needed for areas that had been designated as “unclassifiable/attainment” based on actual emissions - based modeling . The EPA further note d in the propos ed rule that modeled source areas would not be subject to these ongoing data requirements if ( 1) modeling for the source was cond

ucted 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.*** E.O. 1286 6 Review

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Page 109 of 145 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 SO 2 emissions data annually , beginning in the year after the area is designated unclassifiab le/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 . A ir 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 design value 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 SO 2 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 determine s 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 continu es 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 previousl y 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 generall y simulates air quality levels that are more “conservative” than levels that would be estimated using area - specific parameters. In the proposal, the EPA stated that a complete, full -*** E.O. 1286 6 Review

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Page 110 of 145 scale modeling anal ys is with updated emissions and meteorological inputs would only be required if the state performs screening modeling that indicates a potential violation. Under all three options, if the modeling performed indicates that air quality levels in an area exceed the SO 2 NAAQS, the EPA may take any appropriate action, including, but not limited to, requiring adoption of enf

orceable emission limits to ensure th at future air quality levels in the area do not exceed the SO 2 NAAQS ; redesignation of the area to nonattainment ; or issuance of a SIP c all requiring action b y the state to bring the area into attainment . The EPA reque sted comment on the se 3 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 27446, 2746 5 , May 13, 2014 . ii. Brief Summary of Comments Several state , environmental, and tribal commenters supported Option 1. These c ommenters stated that an approach that simply assess es SO 2 emissions changes at large sources would not account for variations in meteorological conditions, increased SO 2 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 o f protecting the public health, and suggested that modeling once every 3 ye ar s is an extremel y 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.*** E.O. 1286 6 Review

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Page 111 of 145 S everal state and industry commenters opposed Option 1 and stated that modeling assessments should not be conducted on a 3 - ye ar or any other regular basis. S ome believe d 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 anal ys is 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 O ption 1 on the grounds that no other ambient standard requires such a detailed on - going anal ys is . Consistent with their concerns about resources, commenters supported the aspect of O ption 1 that would enable the air agency to terminate certain ongoing data requirements if air quality modeling indicated a design value equal to or less than 50 percent of the 1 - hour SO 2 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’ alreadylimited 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 c ommenters noted that with SO 2 emissions declining on a national level, remodeling would not be expected to be required and a simple anal ys is of the c hange 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*** E.O. 1286 6 Review

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Page 112 of 145 further evaluation of sources, rather than having the air agency provid e an assessment for each source with increased emissions. The c ommenter suggested ( 1) i f 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 b y 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, ideall y, under Option 2, agencies would have a 2.5 ye ar tim eframe 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 ye ar; 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, s everal state and industry commenters disagreed with having any default modeling require ment , even for screening modeling, and opposed this option. Several commenters objected to the required use of a screening model for the following reasons: m ost 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 s creening modeling is almost as complex and time consuming as full - scale modeling and thus this option w ould not be a good use of state and the EPA resources.*** E.O. 1286 6 Review

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Page 113 of 145 Lastl y, 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 3 options, where the air agency would evaluate emissions changes each ye ar, and then conduct screening modeling or full - scale modeling if the magnitude of emission changes warrant. iii. EPA Response The EPA rec ognizes 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 b y this rule is important to meeting the public health objectives of this NAAQS while balancing resource constraints of air agencies in a manageabl e 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 effectivel y s erving 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 monit oring, and areas where air quality was initially characterized by modeling.*** E.O. 1286 6 Review

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Page 1 14 of 145 After considering the comments received on the p roposed r ule , the EPA is finalizing a combination of elements from Option 1 and O ption 2 . As outlined in proposed O ption 2 , the final approach require s the air agency to conduct an assessment of emissions changes annuall y 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 ag ency must provide this assessment to the EPA in the form of a report , to be submitted by July 1 of the following ye ar . This assessment should reflect the most recent quality- assured emissions data available for the relevant sources in the area. The report must also describ e 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 b y 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 i s best judged on a case - by- case basis reflecting case specific information on emissions changes and prior modeling results. For example, if the emissions increase was substantial and the p revious modeling had indicated that air quality in the area was just under the standard, then air quality modeling would be warranted. In other cases*** E.O. 1286 6 Review

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Page 115 of 145 where air quality has been modeled to be well below the standard and annual emissions increase only slightl y in the following ye ar, the air agency would be able to exercise j udgment regarding whether additional modeling would be needed. The use of case - specific judgment will be especiall y important in cases involving multiple sources or multiple emission units that may have different emissions - air quality relationships. The mo deling anal ys is 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). See § 51.1205(b)(1) of the final rule. Inthis way , if new modeling is recommended, the whole process ideall y would take 18 months from the end of the “ongoing data requirement” ye ar to when new modeling would be due (not 30 months as suggested by a state commenter). The EPA finds that the relative ly straightforward approach described in pro posed O ption 2 requiring the examin ation 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 prov ides 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 O ptions 1 and 3, this approach also would be e xpected to involve less overall worklo ad 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 allow s for the air agency

to obtain EPA approval to cease operation of a new ambient monitor if the most recent design value is low enough to meet certain criteria (e.g. less than or equal to 50 percent of*** E.O. 1286 6 Review

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Page 116 of 145 the level of th e NAAQS , or meeting the criteria of 40 CFR 58.14 ) . Thus, f or areas that were originall y 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 submit s an air quality modeling analy sis , using updated actual emissions data from the most recent 3 ye ars, that demonstrat es that air quality design values at all receptors in the anal ys is are less than or equal to 50 percent of the 1 - hour SO 2 NAAQS, and such demon stration is approved by the EPA Regional Administrator. Li kewise, if the initial modeling of a source area demonstrates that air quality design values at all receptors in the anal ys is are less than or equal to 50 percent of the 1 - hour SO 2 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 ty pe of provision in the final rule structure s th e rule in a balanced way for both modeled and monitored areas in order to meet the objective s of ensuring that such areas continue to not exceed the standard and continue to protect public health, while recognizing the resource constraints of air agencies. h
. Procedural approach for p ost- attainment annual reporting i. Summary of Proposal The EPA also propose d two options regarding the procedure s by which air agencies would submit ongoing d ata reports to the EPA for source areas characterized through modeling , and by which the EPA would review and act on them. Under procedural Option 1 , the EPA propose d 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 Jul y 1 each ye ar . The inclusion of this report as an appendix to the*** E.O. 1286 6 Review

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Page 117 of 145 annual monitoring plan would ensure that the report would be subject to the same opportunities for public review and comment that are to be provide d 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 comment on its proposed action. 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 approv ing or disapproving the plan. Under procedural Option 2 , the ongoing report would not be submitted to the EPA as an appendix to the annual monitoring network plan, but i t would take the form of a separate, independent submittal from the state to the EPA Regional Administrator. The EPA propose d that this report would be due by the same July

1 st 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 describ ed in procedural Option 1, but the report would onl y include the annual assessments associated with sources in areas that were designated unclassifiable/attainment based on modeling of actual emissions. In the p roposed rule, the EPA requested comment on the two procedural options presented earlier as well as any alternative ideas suggested b y commenters. For any such*** E.O. 1286 6 Review

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Page 118 of 145 recommendations, the EPA request ed that the commenter provide a detailed rationale and estimate of any associate d costs. See 79 FR 27446, 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. On e commenter stated that, since both options have a deadline of July 1 st each ye ar, a separate document would only

add more time and resource use. Several state commenters recommended that the assessment be submitted separatel y 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 m odeling, 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 timel ines, it would be better to deliver the products separatel y rather than delay one or the other to deliver them together. iii. EPA Response After considering the comments received related to b oth of the proposed options , the EPA believe s 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 ag enc y will have the flexibility under the final rule to select the approach that best meets the agency ’s workload , schedule , and particular need s. The EPA believe s that either of the procedural approach es will be sufficient to implement the ongoing data requirement s . Regardless of which*** E.O. 1286 6 Review

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Page 119 of 145 approach is chosen by

the air agency , the report must be submitted to the respective EPA Region al Office by

July 1 st annually and made available for public review and comment. The first report is due on July 1 st of the year after the effective date of the area’ s initial designation and additional reports are due July 1 st 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 C onsent D ecree The proposed rule did not contain any regulatory deadlines for the EPA to complete area designations under the 2010 SO 2 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 gro ups 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 f or 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 b y which the EPA would complete its duties. This resulted in a settlement between the EPA and the public interest group plaintiffs, which the plaintiff - interven ers did not join. On June 2, 2014, the EPA published notice of a proposed consent decree (CD) reflecting th is settlement (

Sierra Club et al v. McCarthy, Civil Action No. 3:13 - cv - 3953 - SI(N.D. Cal.)). 79 F R 31325. This proposed CD 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*** E.O. 1286 6 Review

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Page 120 of 145 designations dates in the preamble to the proposed DRR. The EPA received several comments on the notice informing the public of the proposed CD 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 CD itself are outside the scope of this rulemaking, and we will not respond to them here. Instead, as di scussed earlier in this notice , on March 2, 2015, the court issued an order entering the CD 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 b y the CD 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 b y 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 b y the court’s order to be completed by July 2, 2016 . 2 . Recommendations for the EPA to D esignat e 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 c ommenter s asserted that the EPA cannot use the rule to supersede the statutory schedule under which the EPA is require d to make area designations, including statutoril y- 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*** E.O. 1286 6 Review

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Page 121 of 145 redesignating unclassifiable areas as either attainment or nonattainment later. Simi larly , a state commenter expressed the view that further data are not necessary to meet the CAA. Several c ommenters also stated that the p roposed r ule effectively

nullifies the “unclassifiable ” designation, use of which would have allowed the EPA to meet i ts statutory deadline. One c ommenter also stated that the EPA should continue to use the "unclassifiable" designation where appropriate, and should not seek to designate all areas attainment or nonattainment. Several commenters also addressed the interrel ationship 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 conflict s with the proposed schedule and compromises a commenter ’ s ab ility to comment on the impact of that consent decree on the rule . An industrial commenter found the consent decree to undermine the proposed rule . These commenters urged that the EPA re - propose the relationship between the consent decree and the rule . An industry group stated that the issuance of the proposed consent decree undermines the rule because it would require an early round of designations that would be based on modeling, in contravention of the process under the proposed rule that offers the opti on of basing designations on monitoring data. As stated previousl y, 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 adequatel y characterizing peak 1 - hour SO 2*** E.O. 1286 6 Review

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Page 122 of 145 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 high ly 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 201 7 or in 202 0 , 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 r ulemaking , or whether areas are first designated unclassifiable and subsequentl y redesignated to attainment or nonattainment, the same timetable , and substance of requirements for data to support more properly informed future judgments regarding areas’ att ainment 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.*** E.O. 1286 6 Review

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Page 123 of 145 The proposed consent decree referenced b y the comments concerns separate legal proceedings that are addressing the EPA’s obligations to designate area s under CAA section 107. The commenters have not identified why any potential out come 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 process es , 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 C ost of M onitoring or M odeling Under this R ule . 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 likel y need to be done b y 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*** E.O. 1286 6 Review

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Page 124 of 145 submit the data to the EPA’s Air Quality S ys tem (AQS) datab ase 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 the fact that there will be costs and resources required to satisfy the requirements of this rulemaking. As suggested b y both state and industry stakeholders who attended the 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. Earl y 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 operat e 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 th is rul e , provided that the state provides oversight to assure that (1) any monitoring is conducted in a manner that is equivalent to SLAMs and quality- assured in accordance with applicable requirements , and (2) any modeling analy sis that the state submits , even if it was initially*** E.O. 1286 6 Review

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Page 125 of 145 provided to the state b y a third party, is done in a reasonable manner and follows the recommendations in the Modeling TAD . 4 . How Should the DRR A ddress SO 2 S ources in Areas that Are A lready D esignated ? The intent of this SO 2 data requirements rulemaking is to direct state and tribal air agencies to characterize air quality in areas around the largest sources of SO 2 emissions, through the use of either air quality modeling or ambient monitoring, and to provide such data to the EPA. The additional information required b y this rule will be able to inform future action by the EP A or the state (e.g., future designation decision s ). The proposed rule did not specificall y address whether the requirement to characterize a sources’ SO 2 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 appl y onl y to areas that remained undesignated at the time of the rule’s implementation. The EPA b elieves 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 subsequent round s of designations pursuant to the March 2015 consent dec ree or this rule . 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, w e have*** E.O. 1286 6 Review

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Page 126 of 145 concluded that an air agency will not be required under this rule to characterize air quality around SO 2 sources located in a nonattainment area . Specificall y, we have clarified the definition of “applicable source” in § 51.1200 of the rule to be “ a stationary source that is (1) not located in a designated nonattainment area, and (2) has annual actual SO 2 emissions of 2,000 tons or more , or has been identified b y an air agency or b y 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 nonattainment. However, i t may

be possible that in some cases an SO 2 source or group of source s within the boundary of an e xisting 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 f or such cases , the air agency and the Regional Administrator retain the authority under th is 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 ar e below the emissions threshold identified in th is rule. Related questions also arise for source s in areas that will be subject to evaluation and designation b y July

2016 under the March 2015 consent decree regarding SO 2 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 data requirements rule, 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*** E.O. 1286 6 Review

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Page 127 of 145 permanent list of prioritized sources that excludes sources in areas designated nonattainment before January

2016 but 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 i f 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 th is 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 appl y these designations to some areas in the designations required to be completed b y 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 previousl y 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 th is rule will be used to inform possible future action s by the

12 While states have and may continue to submit designations recommendations identifying areas as “ attainment, ” the EPA expects to continue its traditional approach, where appropriate, of using a designation category

of "unclassifiable/attainment” for areas that the EPA determines meet the NAAQS. The EPA expect s 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 nearb y area. See SO 2 designations guidance issued by Stephen D. Page on March 20, 2015, available at http://www.epa.gov/airquality/sulfurdioxide/pdfs/20150320SO2designations.pdf .*** E.O. 1286 6 Review

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Page 128 of 145 EPA or the state (e.g., to determine whether th e 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 designation s 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 b y the EPA as “unclassifiable/attainment” by July 2016 pursuant to the consent decree, then the EPA expects that, as was the case for areas 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 b y July*** E.O. 1286 6 Review

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Page 129 of 145 2016 or conducted onl y for satisfying the requirements of this rule. Accordingl y, § 51.1205(b) has been modified to apply to any unclassifiable/attainment area “where modeling of actual emissions was conducted to characterize air quality pursuant to § 51.1203 of this subpart or pursuant to the March 2015 consent decree .” 5. How A ir A gencies S hould A ddress M odeling and M onitoring in Multi - state Areas to M eet the Requirements of the R ule . 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 h as an impact on SO 2 concentrations in one or more other jurisdictions. While the final rule preserve s the option of the air agenc y of the jurisdiction in which the source is located to choose how to sati sfy 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 or monitoring would be the most effective method to characterize the peak 1 - hour SO 2 concentrations in the ambient air affected by such sources . If the jurisdiction in which the source is located prefers to employ ambient monitoring to charac terize 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 jurisdictio n (in which peak 1 - hour SO 2 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*** E.O. 1286 6 Review

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Page 130 of 145 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 anal ys es 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 earl y and active coordination among all involved parties can lead t o beneficial agreements for characterizing air quality in multi - jurisdiction areas , and the EPA will work with air agencies to help facilitate such agreements. **V. Environmental Justice Considerations**  The EPA believes the human health or environmental risk addressed b y this action will not have disproportionately high and adverse human health or environmental effects on minority , low - income, or indigenous populations because it does not affect the level of protection provided to human health or the environment under the SO 2 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 redu ce 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 SO 2 . Inaddition, this rule will help c ommunities by informing residents about ambient air quality around the largest sources of SO 2 . **V I**  **. Statutory and Executive Order Reviews** *** E.O. 1286 6 Review

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Page 131 of 145 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 re commendations 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 (I CR) document that the EPA prepared has been assigned EPA ICR number 2495.01 . A cop y of the I CR 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 SO 2 air quality concentrations, pursuant to section s 110(a)(2)(B) , 110(a)(2)(K) , 301(a) and 114 of the CAA. For purposes of analy sis of the estimated paperwork burden, the EPA assumed that 4 3 states and tribes would take actions to characterize air quality through either air quality modeling or ambient monitoring in 4 12 areas around SO 2 sources emitting 2,000 tpy of more across the country , and such states would submit the results of these analy ses to the EPA. Under this rule, the air agency

will have the ability

to choose, on an area - by- area basis, the anal ytical 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*** E.O. 1286 6 Review

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Page 132 of 145 costs, one that assumes all source area s would be characterized through ambient monitoring, and the other that assumes that all source area s 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 4 12 SO 2 sources exceeding the 2,000 ton per year 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 n ecessary to properl y characterize peak 1 - hour SO 2 concentrations in certain areas , which would increase costs proportionally .) Estimates are provided for a 3 - ye ar period and include a calculation for equipment amortization over 7 years (as is typically don e in monitoring - related ICRs). For the period of 2016, 2017 , and 2 018 (monitoring related expenditures would begin in 201 6 ), 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 . In cluded 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 SO 2 monitoring station is $ 92,614 (does not include equipment amortization). In addition to the costs that would be incurred b y 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 assumptio n that air quality for each of the 412 SO 2 sources exceeding the 2,000 ton per year threshold would be characterized through air quality modeling anal ys es. Based on market research, stakeholder*** E.O. 1286 6 Review

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Page 133 of 145 feedback and assumptions about the procedures to follow when c onducting 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 anal ys es around all 4 12 sources expected to be identified as exceeding the source threshold, then total national costs for modeling analy ses would be estimated at $ 12,360,000 . If these costs were incurred over the course of 3 ye ars, then the approximate annual cost for each ye ar 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 control numb er. The OMB control numbers for the EPA's regulations in 40 CFR are listed in 40 CFR p art 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 co ntrol 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

13 The Draft SO 2 NAAQS Designations Modeling Technical Assistance Document can be f ound at : http://www.epa.gov/airquality/sulfurdioxide/pdfs/SO2 ModelingTAD.pdf.*** E.O. 1286 6 Review

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Page 134 of 145 entities. Entities potentially affected directly

by this final rule include state, local and tribal governments and none of these governments are small entities . Other ty pes 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 uniquel y 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 SO 2 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 do es not affect the relationship or distributi on 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 do es nothing to modify that relationship. Thus, Executive Order 13175 does not apply to this action.*** E.O. 1286 6 Review

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Page 135 of 14 5 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 SO 2 implementation White Paper. The EPA provide d 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 conducte d 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, Distrib ution, 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 SO 2 DRR to require air agencies to more extensively charac terize ambient SO 2 air quality concentrations, pursuant to section s 110(a)(2)(B) , 110(a)(2)(K) , 301(a) and 114 of the CAA. The*** E.O. 1286 6 Review

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Page 136 of 145 rule does not prescribe specific control strategies by which the SO 2 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, thereb y 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 Te chnology 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 th e 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 b y 5 U.S.C. 804(2).*** E.O. 1286 6 Review

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Page 137 of 145 **Page 136**  **of 1 45**  **- Data Requirements Rule for the**  **2010 1**  **- Hour Sulfur Dioxide (SO**  **2 )**  **Primary National Ambient Air Quality Standard (NAAQS)** 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 **[ INSERT DATE 60 DAYS**  **AFTER DATE OF PUBLICATION IN THE**  **FEDERAL REGISTER** **]** . 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 sh all not postpone the effectiveness of this action. **Statutory Authority** The statutory

authority for this action is provided by 42 U.S.C. sections 7401 et seq., and particularl y sections 7403, 7407, 7410 , 7414 and 7601. **List of Subjects in**  **40 CFR Part 51** Environmental protection, Air pollution control, Intergovernmental relations, Sulfur oxides.

______________________________________ Dated:

**______________________________________** Gina McCarthy , Administrator .*** E.O. 1286 6 Review

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Page 138 of 145 For the reasons stated in the preamble, title 40, chapter I, part 51 of the Code of Federal Regulations is amended as follows: **P ART**  **51**
**– REQUIREMENTS FOR PREPARATION, ADOPTION, AND SUBMITTAL**  **OF IMPLEMENTATION PLANS** 1. The authority citation for p art 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 SO 2**  **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 SO 2**  **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 of this part or in the CAA. Air agency means the agency or organization responsible for air quality management within a state, local governmental jurisdiction, territory or area subject to tribal government. Annual SO2 emissions data means the quality- assured annual SO 2 emissions data for a stationary source . Such data may

have been required to be reported to the EPA in accordance with an*** E.O. 1286 6 Review

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Page 139 of 145 existing regulatory

requirement (such as the Air Emissions Reporting Rule or the Acid Rain Program) ; however, annual SO 2 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 SO 2 emissions data of 2,000 tons or more , or has been identified by an air agency

or b y the EPA Regional Administrator as requiring further air quality characterization. 2010 SO2 NAAQS means the primary N ational Ambient A ir Q uality S tandard 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 SO 2 across the United States through either ambient air quality monitoring or air quality modeling analys i s at the air agency ’s election. These monitoring and modeling data may be used in future determinations by the EPA regarding areas’ SO 2 NAAQS attainment status , or for other actions designed to ensure attainment of the 2010 SO 2 NAAQS and provide protection of the public from the short - term health effects associated with exposure to SO 2 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 SO 2 emissions that have annual actual SO 2 emissions of 2,000 tons or more; or in whose jurisdiction is located one or more sources of SO 2 emissions that ha ve been identified b y the air agency

or b y the EPA Regional Administrator as requiring further air quality*** E.O. 1286 6 Review

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Page 140 of 145 characterization. For the purposes of this subpart, the subject air agency shall identify

applicable sources of SO 2 based on the most recently available annual SO 2 emissions data for such sources. **§51.1203 Air**  **a gency**  **r equirements.**  (a) The air agency

sh all submit a list of applicable SO 2 sources located in its jurisdiction to the EPA by

January 15, 2016. This list may

be revised by

the Regional Administrator after review based on available SO 2 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 ( 1) characterize peak 1 - hour SO 2 concentrations in such area through ambient air quality monitoring ; ( 2) characterize peak 1 - hour S O 2 concentrations in such area through air quality modeling techniques ; or ( 3) provide federall y enforceable emission limitations by January 13, 2017 that limit emissions of applicable sources to less than 2,000 tpy , in accordance with §51.1203(e) , or provide documentation that the applicable source has permanently shut down . Emission limits in accordance with §51.1203(e) may be established in lieu of conducting monitoring or modeling unless, in the judgment of the air agency or the EPA Regional Adminis trator, 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 a pplicable sources in an area , the notification from the air agency shall describe the requirements and emission limit s 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*** E.O. 1286 6 Review

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Page 141 of 145 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 § 51.1203(b) of this subpart as an area for which SO 2 concentrations will be characterized through ambient monitoring, the required monitors shall be sited and operated either as SLAMS or in a manner equivalent to SLAM S. In either case, monitors shall meet applicable criteria in 40 CFR part 58 , a ppendices 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 S ys tem , 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 paragraph (c) in th e air agency ’s Annual M onitoring N etwork P lan required b y 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 SO 2 monito ring network pursuant to the requirements of 40 CFR part 58 and of this subpart . ( 2 ) A ll existing, new , or relocated ambient monitors intended to meet the requirements of paragraph (c) must be operational by January 1, 2017 and must be operated continually until approved for shut down by EPA. ( 3 ) Any SO 2 monitor identified by an air agency

in its approved Annual Monitoring Network Plan as having the purpose of meeting the requirements of paragraph (c) that: is not located in an SO 2 nonattainment area ; is not also being used to satisfy other ambient SO 2 minimum monitoring requirements listed in 40 CFR part 58 , a ppendix D, section 4.4 ; and is not*** E.O. 1286 6 Review

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Page 142 of 145 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 SO 2 NAAQS from data collected in either its first or second 3 - ye ar 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 . (d) Modeling . For each area identified in the notificati on submitted pursuant to § 51.1203(b) of this subpart as an area for which SO 2 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 limit ed to the model to be used, modeling domain, receptor grid, emissions dataset, meteorological dataset and how the air agency will account for background SO 2 concentrations. (2) M odeling anal ys es shall characterize air quality based on either actual SO 2 em issions from the most recent 3 years, or on any federall y 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 of this subpart, the air agency shall conduct the modeling analy sis for any applicable source identified by the air agency

pursuant to § 51.1203(a)*** E.O. 1286 6 Review

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Page 143 of 145 of this subpart , and for its associated area and any nearb y area, as applicable, and submit the modeling analy sis to the EPA Regional Office b y January 13, 2017. (e) Federall y enforceable requirement to limit SO 2 emissions to under 2,000 tons per ye ar. For each area identified in the notification submitted pursuant to §51.1203(b) of this subpart as an area for which th e 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 and been made federall y enforceable b y J anuary 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 SO 2 per year for calendar ye ar 2017 and thereafter; or ( 2 ) document that the applicable sources in the area have permanently shut down by

January 13, 2017. **§51.1204 Enforceable**  **e mission**  **l imits**  **p roviding for**  **a ttainment.**  At any time prior to January

13, 2017, the air agency

may submit to the EPA effective federally enforceable SO 2 emissions limit s for one or more applicable sources that provide for attainment of the 2010 SO 2 NAAQS in the area affected by such emissions. The submittal shall include associated air quality

modeling and other analy ses that dem onstrate that all modeling receptors in the area will not violate the 2010 SO 2 NAAQS, taking into account the updated allowable emission limits on applicable sources as well as emissions limits that apply to any other sources in the area. The air agency sh all not be subject to the ongoing data requirements of §51.1205 for such area if the air quality modeling and other analy ses demonstrate that the area will not violate the 2010 SO 2 NAAQS . **§51.1205 Ongoing**  **d ata**  **r equirements**  **.***** E.O. 1286 6 Review

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Page 144 of 145 (a) Monitored areas . For any area where SO 2 monitoring was conducted to characterize air quality

pursuant to §51.1203 of this subpart, 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) of this subpart or pursuant to 40 CFR 58.14. (b) Modeled areas . For any area where modeling of actual emissions was conducted to characterize air quality pursuant to § 51.1203 of this subpart or pursuant to the March 2015 consent decree and such area was designated as attaining the 2010 SO 2 NAAQS , the air agency shall submit an annual report to the E PA Regional Administrator by July 1 of each ye ar , either as a stand - alone document made available for public inspection, or as an appendix to its Annual M onitoring Network P lan ( also due on July 1 each year under 40 CFR 58.10) , that document s the annual SO 2 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 SO 2 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.*** E.O. 1286 6 Review

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Page 145 of 145 ( 2 ) An air agency

will no longer be subject to the requirements of § 51.1205(b) for a particular area if it provides air quality modeling demonstrating that air quality values at all receptors in the anal ys is are no greater than 50 p ercent of the 1 - hour SO 2 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 pursuant to § 51.1205(b) 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 SO 2 NAAQS, the EPA may tak e appropriate action, including but not limited to requiring adoption of enforceable emission limits to ensure continued attainment of the 2010 SO 2 NAAQS, designation or redesignation of the area to nonattainment, or issuance of a SIP Call.