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 Environmental Protection Agency 40 CFR Part 52
[EPA-R08-OAR-2017-0339; FRL-9967-66-Region 8]
 AGENCY: Environmental Protection Agency (EPA).
 ACTION: Direct final rule.
 SUMMARY: The Environmental Protection Agency (EPA) is taking direct final action approving a State Implementation Plan (SIP) revision submitted by the State of Montana. On September 19, 2016, the Governor of Montana submitted to the EPA a Clean Air Act (CAA) section 175A(b) second 10-year maintenance plan for the Missoula, Montana area for the carbon monoxide (CO) National Ambient Air Quality Standard (NAAQS). This limited maintenance plan (LMP) addresses maintenance of the CO NAAQS for a second 10-year period beyond the original redesignation. This action is being taken under sections 110 and 175A of the CAA.
 DATES: This rule is effective on November 13, 2017 without further notice, unless the EPA receives adverse comment by October 16, 2017. If adverse comment is received, the EPA will publish a timely withdrawal of the direct final rule in the 
                        **Federal Register**
                         informing the public that the rule will not take effect.
 ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R08-OAR-2017-0339 at 
                        *https://www.regulations.gov.*
                         Follow the online instructions for submitting comments. Once submitted, comments cannot be edited or removed from 
                        *www.regulations.gov.*
                         The EPA may publish any comment received to its public docket. Do not submit electronically any information you consider to be Confidential Business Information (CBI) or other information whose disclosure is restricted by statute. Multimedia submissions (audio, video, etc.,) must be accompanied by a written comment. The written comment is considered the official comment and should include discussion of all points you wish to make. The EPA will generally not consider comments or comment contents located outside of the primary submission (
                        *i.e.,*
                         on the web, cloud, or other file sharing system). For additional submission methods, the full EPA public comment policy, information about CBI or multimedia submissions, and general guidance on making effective comments, please visit 
                        *https://www2.epa.gov/​dockets/​commenting-epa-dockets.*
 FOR FURTHER INFORMATION CONTACT: Adam Clark, Air Program, U.S. Environmental Protection Agency (EPA), Region 8, Mail Code 8P-AR, 1595 Wynkoop Street, Denver, Colorado 80202-1129. (303) 312-7104, 
                        *clark.adam@epa.gov.*


SUPPLEMENTARY INFORMATION:  I. General Information What should I consider as I prepare my comments for EPA? 1. 
                    *Submitting Confidential Business Information (CBI).*
                     Do not submit CBI to the EPA through 
                    *https://www.regulations.gov*
                     or email. Clearly mark the part or all of the information that you claim to be CBI. For CBI information on a disk or CD ROM that you mail to the EPA, mark the outside 
                    ( print page 43181)
                    of the disk or CD ROM as CBI and then identify electronically within the disk or CD ROM the specific information that is claimed as CBI. In addition to one complete version of the comment that includes information claimed as CBI, a copy of the comment that does not contain the information claimed as CBI must be submitted for inclusion in the public docket. Information so marked will not be disclosed except in accordance with procedures set forth in 40 CFR part 2. 2. 
                    *Tips for preparing your comments.*
                     When submitting comments, remember to: Identify the rulemaking by docket number and other identifying information (subject heading,**Federal Register**
                     volume, date, and page number);
                Follow directions and organize your comments;
                Explain why you agree or disagree;
                Suggest alternatives and substitute language for your requested changes;
                Describe any assumptions and provide any technical information and/or data that you used;
                If you estimate potential costs or burdens, explain how you arrived at your estimate in sufficient detail to allow for it to be reproduced;
                Provide specific examples to illustrate your concerns, and suggest alternatives;
                Explain your views as clearly as possible, avoiding the use of profanity or personal threats; and
                Make sure to submit your comments by the comment period deadline identified. II. Background Under the CAA Amendments of 1990, the Missoula area was designated as nonattainment and classified as a “moderate” CO area, with a design value of less than or equal to 12.7 parts per million (ppm) (56 FR 56694, November 6, 1991). On May 27, 2005, the Governor of Montana submitted to the EPA a request to redesignate the Missoula CO nonattainment area to attainment for the 8-hour CO NAAQS. Along with this request, the Governor submitted a CAA section 175A(a) maintenance plan which established an attainment year of 2000, and demonstrated that the area would maintain the 8-hour CO NAAQS through 2020. The EPA approved the State's redesignation request, CAA section 175A(a) maintenance plan and base year emissions inventory on August 17, 2007 (72 FR 46158). Eight years after an area is redesignated to attainment, CAA Section 175A(b) requires the state to submit a subsequent maintenance plan to the EPA, covering a second 10-year period.[1]
                    
                     This second 10-year maintenance plan must demonstrate continued maintenance of the applicable NAAQS during this second 10-year period. To fulfill this requirement of the Act, the Governor of Montana submitted the second 10-year Missoula CO maintenance plan (hereafter, “revised Missoula Maintenance Plan”) to the EPA on September 19, 2016. With this action, we are approving the revised Missoula Maintenance Plan. The 8-hour CO NAAQS—9.0 ppm—is attained when such value is not exceeded more than once a year. 40 CFR 50.8(a)(1). The Missoula area has attained the 8-hour CO NAAQS from 1992 to the present.[2]
                    
                     In October 1995, the EPA issued guidance that provided nonclassifiable CO nonattainment areas the option of using a less rigorous “limited maintenance plan” (LMP) option to demonstrate continued attainment and maintenance of the 8-hour CO NAAQS.[3]
                    
                     According to this guidance, areas that can demonstrate design values at or below 7.65 ppm (85% of exceedance levels of the 8-hour CO NAAQS) for eight consecutive quarters qualify to use a LMP. For the revised Missoula Maintenance Plan, on which we are finalizing action, the State used the LMP option to demonstrate continued maintenance of the 8-hour CO NAAQS in the Missoula area through 2027. We have determined that the Missoula area qualifies for the LMP option for this plan revision, since the area's maximum design value for the most recent eight consecutive quarters with certified data (years 2009 and 2010) was 2.4 ppm.[4] III. The EPA's Evaluation of the Revised Missoula Maintenance Plan The following are the key elements of an LMP for CO: Emission Inventory, Maintenance Demonstration, Monitoring Network/Verification of Continued Attainment, Contingency Plan, and Conformity Determinations. Below, the EPA describes our evaluation of each of these elements as it pertains to the revised Missoula Maintenance Plan. A. Emission Inventory The revised Missoula Maintenance Plan contains an emissions inventory for the base year 2010. The emission inventory is a list, by source category, of the air contaminants directly emitted into the Missoula CO maintenance area on a typical winter day in 2010.[5]
                    
                     The data in the emission inventory were developed using EPA-approved emissions modeling methods. A more detailed description of the 2010 inventory is documented in the Missoula CO maintenance plan. 
                    *See*
                     Revised Missoula Maintenance Plan, p. 4-6. Included in this inventory are residential wood burning, natural gas combustion, commercial equipment, construction equipment, industrial equipment, residential lawn and garden equipment, commercial lawn and garden equipment, railway maintenance equipment, railway locomotives, motor vehicle exhaust, and point sources. Notably, motor vehicle exhaust from onroad mobile sources accounted for 71% of total CO emissions in the Missoula Maintenance Area during the inventory period. The revised maintenance plan contains detailed emission inventory information that was prepared in accordance with EPA guidance, and is acceptable to the EPA.[6] B. Maintenance Demonstration The EPA considers the maintenance demonstration requirement to be satisfied for areas that qualify for and are using the LMP option. As mentioned above, a maintenance area is qualified to use the LMP option if that area's maximum 8-hour CO design value for eight consecutive quarters does not exceed 7.65 ppm (85% of the CO NAAQS). The EPA maintains that if an 
                    ( print page 43182)
                    area begins the maintenance period with a design value no greater than 7.65 ppm, the air quality along with the continued applicability of prevention of significant deterioration requirements, the control measures already in the SIP, and federal measures should provide adequate assurance of maintenance over the 10-year maintenance period and the EPA would not require such areas to project emissions over the maintenance period. Because the last recorded CO design values in the Missoula area were consistently well below the LMP threshold (See Table 1 below) and no changes are proposed to the area's permanent and enforceable control measures, the State has adequately demonstrated that the Missoula area will maintain the 8-hour CO NAAQS into the future. Table 1—8-Hour CO Design Values for Missoula, Montana
Design value 
                             
                                (ppm) 7
Year3.6
20032.9
20043.6
20052.4
20062.4
20072.7
20082.5
20092.2
20102.1 8
2011
 C. Monitoring Network/Verification of Continued Attainment In the revised Missoula Maintenance Plan, the State adopted an alternative monitoring strategy for Missoula that was previously approved by the EPA to satisfy this requirement for both the Billings CO Maintenance Area (80 FR 16571, March 30, 2015) and Great Falls CO Maintenance Area (80 FR 17331, April 1, 2015). The State adopted the alternative monitoring strategy to conserve resources by discontinuing the gaseous CO ambient monitor in the Missoula CO maintenance area. In place of the gaseous ambient monitor, the State's alternative method relies on rolling 3-year Average Daily Traffic (ADT) vehicle counts collected from permanent automatic traffic recorders (devices installed into a street's pavement to continuously collect data) in each maintenance area. Since 2006, no Missoula monitor has registered a design value greater than 2.7 ppm, roughly 30% of the NAAQS.[9]
                    
                     Citing these consistently low monitor values, and expressing a desire to conserve monitoring resources, the State requested to discontinue CO monitoring in Missoula and instead use an alternative strategy for monitoring maintenance of the 8-hour CO NAAQS. The alternative monitoring strategy utilizes ADT vehicle counts collected from permanent automatic traffic recorders in the Missoula CO maintenance area to determine average monthly traffic during the traditional high CO concentration season of November through February (the winter season). The State will compare the latest rolling 3-year ADT volumes during the winter season to the 2008-2011 baseline ADT volumes (see Table 2) that correlate to the low CO monitored values during that period (see Table 1).[10]
                    
                     Because mobile sources are the biggest driver of CO pollution, the Montana Department of Environmental Quality (MDEQ) reasoned that any significant increase in CO emissions would have to be accompanied by a significant increase in ADT.[11]
                    
                     The EPA agrees with the State's reasoning. Table 2—Traffic Volumes for Missoula, Montana
Winter season
Average daily traffic for site A-037Winter 
                             monthly 
                             average
Rolling three-
                             year average
% Difference 
                             from 
                             2008-2011  
                             baselineNovember 2008-January 2009 *
19,134November 2009-February 2010
20,320November 2010-February 2011
20,221
(Baseline) 19,892November 2011-February 2012
20,120
20,220
1.65November 2012-February 2013
20,004
20,115
1.12November 2013-February 2014
19,943
20,022
0.66November 2014-February 2015
21,037
20,328
2.19November 2015-February 2016
21,763
20,914
5.14* There is no ADT information available for February 2009.
 If the rolling 3-year ADT value is 25% higher than the monthly average value from the November 2008-February 2011 baseline period of 19,892, the State, in cooperation with the Missoula City-County Health Department (MCCHD), will reestablish CO ambient monitoring in Missoula the following high season (November-February). If the CO design value in the following high season has not increased from the baseline mean by an equal or greater rate at which the ADT has increased, and the monitor values remain at or below 50% of the 8-hour CO NAAQS (2nd max concentration ≤4.5 ppm), the monitor may be removed and the ADT counts will continue to be relied upon to determine compliance with the NAAQS. This process will be repeated each time the rolling 3-year ADT increases by a factor of 25% (
                    *e.g.,*
                     50%, 75%) above the baseline 2008-2011 period, and the same analysis will be conducted to determine if the monitors can be removed. 40 CFR 58.14(c) allows approval of requests to discontinue ambient monitors “on a case-by-case basis if discontinuance does not compromise 
                    ( print page 43183)
                    data collection needed for implementation of a NAAQS and if the requirements of appendix D to 40 CFR part 58, if any, continue to be met.” The EPA finds that the alternative monitoring strategy in the revised Missoula Maintenance Plan meets the criteria of 40 CFR 58.14(c) for the Missoula CO maintenance area. Given the long history of low CO concentrations in the Missoula area and the adequacy of the alternative monitoring strategy at ensuring continued attainment of the CO NAAQS in the area, the EPA finds it appropriate to approve the State's request to not operate a gaseous CO monitor in Missoula and use the alternative monitoring strategy in its place. D. Contingency Plan The revised Missoula Maintenance Plan stated that a trend of increasing CO concentrations or a single 8-hour average of 9.5 ppm or greater would trigger a voluntary, local process by the Missoula Air Pollution Control Board to identify and evaluate potential contingency measures. The plan also indicated that a violation of the 8-hour CO NAAQS (two or more values of 9.5 ppm or greater during a calendar year) would trigger mandatory implementation of contingency measures. As noted in the previous section, the alternative monitoring strategy in the revised Missoula Maintenance Plan requires reestablishment of a CO monitor in Missoula if traffic levels (responsible for 71% of CO emissions in Missoula) increase from the 2008-2011 baseline by a factor of 25% and provides that any reestablished monitors showing values above 50% of the NAAQS cannot be removed. Therefore, the EPA finds that CO emissions in Missoula are very unlikely to increase to the point of an 8-hour NAAQS exceedance (the trigger for voluntary contingency measures) without that exceedance being observed by a gaseous monitor, as such an increase would most likely coincide with a significant increase in traffic volume. The revised Missoula Maintenance Plan retains two contingency measures adopted as part of the area's fully approved SIP. The first expands the oxygenated fuel program to other months besides November, December, January and February, as described in Rule 10.110 of the Missoula City-County Air Pollution Control Program. The second further restricts woodstove burning as described in Rule 9.601 of the Missoula City-County Air Pollution Control Program. The revised Missoula Maintenance Plan indicates that contingency measures will be implemented within 60 days of notification by MDEQ and the EPA that the Missoula area has violated the 8-hour CO NAAQS. Upon notification of a CO NAAQS violation, MCCHD will review relevant information and implement one or both of the contingency measures to correct the violation. In the event that violations continue to occur after contingency measures have been implemented, additional contingency measures will be implemented until the violations are corrected. 
                    *See*
                     Revised Missoula Maintenance Plan, p. 11. We find that the contingency measures provided in the revised Missoula Maintenance Plan are sufficient and meet the requirements of section 175A(d) of the CAA. E. Transportation Conformity Transportation conformity is required by section 176(c) of the CAA. Conformity to a SIP means that transportation activities will not produce new air quality violations, worsen existing violations, or delay timely attainment of the NAAQS (CAA 176(c)(1)(B)). The EPA's conformity rule at 40 CFR part 93, subpart A requires that transportation plans, programs and projects conform to SIPs and establish the criteria and procedures for determining whether or not they conform. To effectuate its purpose, the conformity rule requires a demonstration that emissions from the Regional Transportation Plan (RTP) and the Transportation Improvement Program (TIP) are consistent with the motor vehicle emission budget (MVEB) contained in the control strategy SIP revision or maintenance plan (40 CFR 93.101, 93.118, and 93.124). A MVEB is defined as the level of mobile source emissions of a pollutant relied upon in the attainment or maintenance demonstration to attain or maintain compliance with the NAAQS in the nonattainment or maintenance area.[12] Under the LMP guidance, MVEBs generally are treated as not constraining for the length of the maintenance period. While the EPA's LMP guidance does not exempt an area from the need to affirm conformity, it explains that the area may demonstrate conformity without submitting a MVEB. According to the LMP guidance, it is unreasonable to expect that a LMP area will experience so much growth in that period that a violation of the CO NAAQS would result.[13]
                    
                     We note that the CO maintenance plan for Missoula that we approved in 2007 (72 FR 46158, August 17, 2007) contains a MVEB for 2020 of 42.67 tons per day of CO. However, the State did not revise or remove this 2020 MVEB from the SIP with the revised Missoula Maintenance Plan. Therefore, under our conformity regulation, consistency with the 2020 MVEB must continue to be demonstrated by the Missoula Metropolitan Planning Organization (MPO) as long as that year is within the timeframe of the RTP (
                    *i.e.,*
                     through 2020). 
                    *See*40 CFR 93.118(b)(2)(i) and (d)(2). When the year 2020 is no longer within the timeframe of the transportation plan (
                    *i.e.,*
                     2021 and beyond), there will no longer be a need to demonstrate conformity with any MVEB for the Missoula CO maintenance area, for the reasons described in the EPA's LMP guidance. From that point forward, all actions that require conformity determinations for the Missoula CO maintenance area under our conformity rule provisions will be considered to have already satisfied the regional emissions analysis and “budget test” requirements in 40 CFR 93.118, because of our approval of the revised Missoula Maintenance Plan. However, since LMP areas are still maintenance areas, certain aspects of transportation conformity determinations will be required for transportation plans, programs and projects. Specifically, for such determinations, RTPs, TIPs and projects will have to demonstrate that they are fiscally constrained (40 CFR 93.108) and meet the criteria for consultation and timely implementation of Transportation Control Measures (40 CFR 93.112 and 40 CFR 93.113, respectively). In addition, projects in LMP areas will be required to meet the applicable criteria for localized CO hot spot analyses to satisfy “project level” conformity determinations (40 CFR 93.116 and 40 CFR 93.123), which must also incorporate the latest planning assumptions and models available (40 CFR 93.110 and 40 CFR 93.111, respectively). Our approval of the revised Missoula Maintenance Plan affects future CO RTP and TIP transportation conformity determinations as prepared by the Missoula MPO, the Montana Department of Transportation, the Federal Highway Administration and the Federal Transit Administration. 
                    *See*40 CFR 93.100.
                    ( print page 43184) IV. Final Action We are approving the revised Missoula Maintenance Plan submitted on September 19, 2016. This maintenance plan meets the applicable CAA requirements, and we have determined it is sufficient to provide for maintenance of the 8-hour CO NAAQS over the course of the second 10-year maintenance period out to 2027. We are publishing this rule without prior proposal because we view this as a noncontroversial amendment and anticipate no adverse comments. However, in the Proposed Rules section of today's 
                    **Federal Register**
                     publication, we are publishing a separate document that will serve as the proposal to approve the SIP revision if adverse comments are filed. This rule will be effective November 13, 2017 without further notice unless we receive adverse comments by October 16, 2017. If we receive adverse comments, we will publish a timely withdrawal in the 
                    **Federal Register**
                     informing the public that the rule will not take effect. We will address all public comments in a subsequent final rule based on the proposed rule. We will not institute a second comment period on this action. Any parties interested in commenting must do so at this time. Please note that if we receive adverse comment on an amendment, paragraph, or section of this rule and if that provision may be severed from the remainder of the rule, we may adopt as final those provisions of the rule that are not the subject of an adverse comment. V. Statutory and Executive Order Reviews Under the CAA, the Administrator is required to approve a SIP submission that complies with the provisions of the Act and applicable federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). Thus, in reviewing SIP submissions, the EPA's role is to approve state actions, provided that they meet the criteria of the CAA. Accordingly, this action merely approves some state law provisions as meeting federal requirements; this action does not impose additional requirements beyond those imposed by state law. For that reason, this action: Is not a significant regulatory action subject to review by the Office of Management and Budget under Executive Orders 12866 (58 FR 51735, October 4, 1993) and 13563 (76 FR 3821, January 21, 2011);
                Does not impose an information collection burden under the provisions of the Paperwork Reduction Act (44 U.S.C. 3501 
                    *et seq.*);
                Is certified as not having a significant economic impact on a substantial number of small entities under the Regulatory Flexibility Act (5 U.S.C. 601 
                    *et seq.*);
                Does not contain any unfunded mandate or significantly or uniquely affect small governments, as described in the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-4);
                Does not have federalism implications as specified inExecutive Order 13132 (64 FR 43255, August 10, 1999);
                Is not an economically significant regulatory action based on health or safety risks subject toExecutive Order 13045 (62 FR 19885, April 23, 1997);
                Is not a significant regulatory action subject toExecutive Order 13211 (66 FR 28355, May 22, 2001);
                Is not subject to requirements of Section 12(d) of the National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 note) because application of those requirements would be inconsistent with the Clean Air Act; and
                Does not provide the EPA with the discretionary authority to address, as appropriate, disproportionate human health or environmental effects, using practicable and legally permissible methods, underExecutive Order 12898 (59 FR 7629, February 16, 1994). In addition, the SIP does not apply on any Indian reservation land or in any other area where the EPA or an Indian tribe has demonstrated that a tribe has jurisdiction. In those areas of Indian country, the rule does not have tribal implications and will not impose substantial direct costs on tribal governments or preempt tribal law as specified by Executive Order 13175 (65 FR 67249, November 9, 2000). The Congressional Review Act, 5 U.S.C. 801 
                    *et seq.,*
                     as added by the Small Business Regulatory Enforcement Fairness Act of 1996, generally provides that before a rule may take effect, the agency promulgating the rule must submit a rule report, which includes a copy of the rule, to each House of the Congress and to the Comptroller General of the United States. The EPA will submit a report containing this action and other required information to the U.S. Senate, the U.S. House of Representatives, and the Comptroller General of the United States prior to publication of the rule in the 
                    **Federal Register**
                    . A major rule cannot take effect until 60 days after it is published in the 
                    **Federal Register**
                    . This action is not a “major rule” as defined by 5 U.S.C. 804(2). Under section 307(b)(1) of the Clean Air Act, petitions for judicial review of this action must be filed in the United States Court of Appeals for the appropriate circuit by November 13, 2017. Filing a petition for reconsideration by the Administrator of this final rule 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 may be filed, and shall not postpone the effectiveness of such rule or action. Parties with objections to this direct final rule are encouraged to file a comment in response to the parallel notice of proposed rulemaking for this action published in the proposed rules section of today's 
                    **Federal Register**
                    , rather than file an immediate petition for judicial review of this direct final rule, so that the EPA can withdraw this direct final rule and address the comment in the proposed rulemaking. This action may not be challenged later in proceedings to enforce its requirements. (See CAA section 307(b)(2).) List of Subjects in 40 CFR Part 52 Environmental protection
Air pollution control
Carbon monoxide
Incorporation by reference
Intergovernmental relations
Reporting and recordkeeping requirements
 Authority:
                    42 U.S.C. 7401 
                        *et seq.* Dated: August 31, 2017. Debra H. Thomas, Acting Regional Administrator, Region 8.
 40 CFR part 52 is amended to read as follows: PART 52—APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS
 1.The authority citation for part 52 continues to read as follows: Authority:
                        42 U.S.C. 7401 
                            *et seq.* Subpart BB—Montana
 2.Section 52.1373 is amended by revising paragraph (d) to read as follows: § 52.1373
  
 (d) Revisions to the Montana State Implementation Plan, revised Carbon Monoxide Maintenance Plan for Missoula, as submitted by the Governor on September 19, 2016.


# Footnotes

1.
    
                         In this case, the initial maintenance period described in CAA section 175A(a) was required to extend for at least 10 years after the redesignation to attainment, which was effective on September 17, 2007. See 72 FR 46158. The first maintenance plan showed maintenance through 2020. CAA section 175A(b) requires that the second 10-year maintenance plan maintain the NAAQS for “10 years after the expiration of the 10-year period referred to in [section 175A(a)].” Thus, for the Missoula area, the second 10-year period ends in 2027. Back to Citation
 2.
    
                         
                        *http://www.epa.gov/​airdata/​.* Back to Citation
 3.
    
                         Memorandum “Limited Maintenance Plan Option for Nonclassifiable CO Nonattainment Areas” from Joseph W. Paisie, Group Leader, EPA Integrated Policy and Strategies Group, to Air Branch Chiefs, October 6, 1995 (hereafter referred to as “LMP Guidance”). Back to Citation
 4.
    
                         See Table 1 below. Additionally, according to the LMP guidance, an area using the LMP option must continue to have a design value “at or below 7.65 ppm until the time of final EPA action on the redesignation.” Table 1, below, demonstrates that the area meets this requirement. Back to Citation
 5.
    
                         Violations of the 8-hour CO NAAQS are most likely to occur on winter weekdays, as weekdays see more consistent workweek traffic and the Missoula area is prone to temperature inversions in the winter which lead to stagnant air conditions. The typical winter day from 2010 was used because monitoring in Missoula ceased in 2011. Back to Citation
 6.
    
                         See “Procedures for Processing Requests to Redesignate Areas to Attainment,” from John Calcagni, Director, Air Quality Management Division, EPA, September 4, 1992. Back to Citation
 7.
    
                         Design values were derived from the EPA AirData Web site (
                        *https://www.epa.gov/​airdata/​*). 8.
    
                         The monitor only operated for 47 days in 2011, and ceased operation on March 31, 2011. The 2.1 ppm value in Table 1 indicates the highest value recorded at the CO monitor in 2011. Back to Citation
 9.
    
                         See Table 1 above. Design values were derived from the EPA AirData (
                        *https://www.epa.gov/​airdata/​*) Web site. Back to Citation
 10.
    
                         In the revised Missoula Maintenance Plan, the State refers to this period 2008-2010 baseline. Back to Citation
 11.
    
                         See “Review of National Ambient Air Quality Standards for Carbon Monoxide,” 76 FR 54294, August 31, 2011. Back to Citation
 12.
    
                         Further information concerning the EPA's interpretations regarding MVEBs can be found in the preamble to EPA's November 24, 1993 transportation conformity rule (see 58 FR 62193-62196). Back to Citation
 13.
    
                         LMP Guidance at 4. Back to Citation


[FR Doc. 2017-19460 Filed 9-13-17; 8:45 am] BILLING CODE 6560-50-P