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Proposed Rule

Approval and Promulgation of State Implementation Plans; Idaho; Regional Haze Progress Report

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Start Preamble

AGENCY:

Environmental Protection Agency.

ACTION:

Proposed rule.

SUMMARY:

The Environmental Protection Agency (EPA) is proposing to approve Idaho's Regional Haze Progress Report (“progress report” or “report”), submitted by the State of Idaho on June 28, 2016, as a revision to the Idaho Regional Haze State Implementation Plan (SIP). Idaho submitted its progress report and a negative declaration stating that further revision of the existing Regional Haze SIP is not needed at this time. The progress report addresses requirements of the Clean Air Act (CAA) and the federal Regional Haze Rule that require states to submit periodic reports describing progress made toward achieving reasonable progress goals (RPGs) established for regional haze and a determination of the adequacy of the state's existing plan addressing regional haze.

DATES:

Comments are due no later than May 6, 2019.

ADDRESSES:

Submit your comments, identified by Docket ID No. EPA-R10-OAR-2017-0571 at http://www.regulations.gov. Follow the online instructions for submitting comments. Once submitted, comments cannot be edited or removed from 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 the disclosure of which 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://www.epa.gov/​dockets/​commenting-epa-dockets.

Start Further Info

FOR FURTHER INFORMATION CONTACT:

John Chi, Air Planning Unit, Office of Air and Waste (OAW-150), EPA, Region 10, 1200 Sixth Avenue, Suite 900, Seattle, Washington 98101; (206) 553-1185; chi.john@epa.gov.

End Further Info End Preamble Start Supplemental Information

SUPPLEMENTARY INFORMATION:

Throughout this document whenever “we,” “us,” or “our” is used, it is intended to refer to the EPA.

Table of Contents

I. Background

II. Context for Understanding Idaho's Progress Report

A. Framework for Measuring Progress

B. Data Sources for Idaho's Progress Report

III. The EPA's Evaluation of Idaho's Progress Report

A. Status of Implementation of All Measures Included in the Regional Haze SIP

1. BART-Level Controls

2. Prevention of Significant Deterioration (PSD)/Major New Source Review (NSR)

3. Smoke Management

B. Summary of Visibility Conditions

C. Visibility Monitoring Strategy

D. Summary of Emissions Reductions

E. Determination of Adequacy (40 CFR 51.308 (h))

F. Consultation With Federal Land Managers (40 CFR 51.308 (i))

IV. The EPA's Proposed Action

V. Statutory and Executive Order Reviews

I. Background

Idaho submitted its initial Regional Haze SIP to the EPA on October 25, 2010, for the first regional haze planning period ending in 2018, which the EPA approved on June 22, 2011, and November 8, 2012.[1] Five years after submittal of the initial regional haze plan, states were required to submit progress reports that evaluate progress towards the RPGs for each mandatory Class I Federal area [2] (Class I area) within the state and in each Class I area outside the state which may be affected by emissions from within the state. 40 CFR 51.308(g). States were also required to submit, at the same time as the progress report, a determination of the adequacy of the state's existing regional haze plan. 40 CFR 51.308(h). On June 28, 2016, the Idaho Department of Environmental Quality (IDEQ) submitted, as a SIP revision, a report on the progress made in the first implementation period towards the RPGs for Class I areas. EPA is proposing to approve Idaho's progress report on the basis that it satisfies the requirements of 40 CFR 51.308. We also propose to find that Idaho's progress report demonstrates that the state's long-term strategy and emission control measures in the existing Regional Haze SIP are sufficient to enable Idaho to meet all established RPGs for 2018.

II. Context for Understanding Idaho's Progress Report

To facilitate a better understanding of Idaho's progress report as well as the EPA's evaluation of it, this section provides background on the regional haze program in Idaho.

A. Framework for Measuring Progress

The EPA has established a metric for determining visibility conditions at Class I areas referred to as the “deciview index,” which is measured in deciviews, as defined in 40 CFR 51.301. The deciview index is calculated using monitoring data collected from the Interagency Monitoring of Protected Visual Environments (“IMPROVE”) network monitors. Idaho has five Class I areas: Hells Canyon Wilderness, Sawtooth Wilderness, Craters of the Moon National Monument, Yellowstone National Park, and Selway-Bitterroot Wilderness. Both Hells Canyon Wilderness and Yellowstone National Park have portions within Idaho, but the majority of the land masses for both of these Class I areas are in other states. For this reason, Idaho set the RPGs for Hells Canyon Wilderness, Sawtooth Start Printed Page 13583Wilderness, and Craters of the Moon National Monument and the 5-year Progress Report analyzes progress towards the RPGs at these three Class I areas.

In developing its initial Regional Haze SIP as part of the Western Regional Air Partnership (“WRAP”), Idaho determined, and the EPA in its approval agreed, that implementation of best available retrofit technology (“BART”) and other existing measures in the State's regional haze plan was sufficient to address the visibility impact of sources in Idaho on Class I areas in other states. See 77 FR 66929, 66933. Therefore, Idaho's progress report does not address the visibility impact of Idaho sources on Class I areas in other states.

Under the Regional Haze Rule, a state's initial Regional Haze SIP must establish two RPGs for each of its Class I areas: One for the 20-percent least impaired days and one for the 20-percent most impaired days. The RPGs must provide for an improvement in visibility on the 20-percent most impaired days and ensure no degradation in visibility on the 20-percent least impaired days, as compared to visibility conditions during the baseline period. In establishing the RPGs, a state must consider the uniform rate of visibility improvement from the baseline to natural conditions in 2064 and the emission reductions measures needed to achieve it. Idaho set the RPGs for the Hells Canyon Wilderness, Sawtooth Wilderness, and the Craters of the Moon National Monument Class I areas. In setting the RPGs for these three Class I areas, Idaho used atmospheric air quality modeling based on projected emission reductions from control strategies in Idaho's Regional Haze SIP, as well as emission reductions expected to result from other federal, state, and local air quality programs.

B. Data Sources for Idaho's Progress Report

Idaho relied on the WRAP technical data and analyses in a report titled “Western Regional Air Partnership Regional Haze Rule Reasonable Progress Summary Report” (“WRAP Report”), dated June 28, 2013, included as an appendix to the progress report. The WRAP Report analyzes monitoring data collected in Idaho during the 2005-2009 period, and it relies on emission data reported to the EPA's National Emissions Inventory (NEI) up until 2011. Idaho then supplemented the information in the WRAP report with more current 2007-2011 visibility data for its Class I areas as part of the progress report adopted by the state in 2015.

III. The EPA's Evaluation of Idaho's Progress Report

This section describes the contents of Idaho's progress report and the EPA's evaluation of the report, as well as the EPA's evaluation of the determination of adequacy required by 40 CFR 51.308(h) and the requirement for state and Federal Land Manager (FLM) coordination in 40 CFR 51.308(i).

A. Status of Implementation of All Measures Included in the Regional Haze SIP

In its progress report, Idaho provided a description of the control measures in the state's Regional Haze SIP that the state relied on to implement the regional haze program. Idaho relied in its Regional Haze SIP upon, among other things, BART controls, its Prevention of Significant Deterioration/New Source Review permitting program, and its smoke management programs for agricultural and forestry burning to achieve the RPGs it established for its Class I areas. Idaho included a description of these programs in the progress report, which is summarized below.

1. BART-Level Controls

Idaho's original Regional Haze SIP imposed BART-level controls on two sources, the #5 Rotary Kiln at the P4 Production (formerly Monsanto) Soda Springs facility and the Riley Boiler at The Amalgamated Sugar Company (TASCO), Nampa facility. In 2005, P4 Production underwent a Best Available Control Technology (BACT) review and installed a lime-concentrated dual-alkali (LCDA) scrubber on the #5 Rotary Kiln to control sulfur dioxide (SO2) emissions. Idaho determined, and EPA in its approval agreed, that BART for the #5 Rotary Kiln was an emission limit of 143 pounds per hour of SO2 achieved through application of the LCDA scrubber. See 76 FR 36329, 36339 (Jun. 22, 2011).[3] Idaho also concluded that existing controls were BART for the nitrogen oxide (NOX) and particulate matter (PM) emissions from the #5 Rotary Kiln. EPA also approved this determination. See 76 FR 36329, 36339 (Jun. 22, 2011). The emission limits are embodied in federally enforceable permits that Idaho continues to administer.

For TASCO, Idaho determined that flue gas desulfurization and low NOX burners with over-fire air were the appropriate control technologies for the BART-eligible Riley Boiler. EPA approved BART for the Riley Boiler on May 22, 2012 (77 FR 66929). Subsequently, Idaho submitted revisions to its Regional Haze SIP that included a revised BART determination for the TASCO Nampa facility. Specifically, Idaho's revised BART determination included a more stringent NOX emission limit, a more stringent PM emission limit, and a BART alternative to replace the SO2 BART determination. In addition to the more stringent NOX and PM emission limits for the Riley Boiler, the BART alternative relied on control of NOX emissions from two non-BART eligible boilers at the TASCO Nampa facility, as well as taking into account the emission reductions resulting from the permanent shutdown of three coal-fired pulp dryers. EPA approved Idaho's revised BART determination for the TASCO Nampa facility on April 28, 2014. See 79 FR 23273, 23277. The BART emissions limits are embodied in a federally enforceable permit that went into effect on December 23, 2011. Idaho continues to administer this permit.

2. Prevention of Significant Deterioration (PSD)/Major New Source Review (NSR)

Idaho's progress report states that a key regulatory program for addressing visibility impairment from new or modified industrial stationary sources is the state's PSD/NSR program. This program protects visibility in Class I areas from impacts from new major or modified major stationary sources. According to the progress report, Idaho's PSD program requires new or major modifications to model the emissions impacts on Class I areas within 300 kilometers to determine if the change in visibility above natural levels is significant. According to the progress report, Idaho continues to implement the PSD/NSR program.

3. Smoke Management

In addition, Idaho continues to implement its crop residue and burning program. EPA published its approval of Idaho's SIP revisions relating to open burning and crop residue disposal requirements on August 1, 2008 (73 FR 44915, 44919), March 19, 2013 (78 FR 16760, 16791), and most recently on June 19, 2018 (83 FR 28382, 28385). The compliance rate has improved through education and outreach, and Idaho DEQ has hired a meteorologist to guide burn decisions. There have also been improvements in the prescribed burning (forestry) program. Specifically, Idaho Start Printed Page 13584DEQ is working closely with the Idaho and Montana Airshed group, and Idaho DEQ's smoke manager and meteorologist are involved in the day to day burn decisions. Both the crop residue and burning and the prescribed burning programs have improved through cooperative agreements with the Idaho Department of Lands and the burn permits now have specific language requiring burners to comply with Idaho open burning rules.

B. Summary of Visibility Conditions

In addition to the evaluation of control measures, Idaho documented the differences between the visibility conditions during the baseline period (2000-2004), the first progress period (2005-2009), and the most current five-year averaging period (2010-2014). Idaho used data available at the time Idaho developed the progress report in 2015. As part of our review, the EPA supplemented this information with current 2012-2016 data, as shown in Table 1.[4]

Table 1—Idaho Class I Area Visibility Conditions on the 20-Percent Most and Least Impaired Day

IMPROVE monitorClass I areaBaseline (2001-2004) (dv) 5First progress period (2005-2009) (dv)Progress report update (2010-2014) (dv)Most recent data (2012-2016) (dv)2018 reasonable progress goal (dv)
20-percent Most Impaired Days
CRMO1Craters of the Moon NM14.013.614.114.113.06
SWAT1Sawtooth Wilderness13.814.815.715.213.22
SULA1Selway-Bitterroot Wilderness13.417.015.011.312.94
20-percent Least Impaired Days
CRMO1Craters of the Moon NM4.33.43.02.83.9
SWAT1Sawtooth Wilderness43.83.02.53.8
SULA1Selway-Bitterroot Wilderness2.62.51.71.52.5

As shown in Table 1, all Class I areas experienced improvements in visibility for the 20-percent least impaired days between the baseline (2000-2004) and the most recent (2012-2016) visibility periods. According to Idaho's progress report, all Class I areas are meeting the RPGs for the 20-percent least impaired days. Idaho's progress report included an analysis of progress and impediments to progress. Regarding the 20-percent most impaired days, according to the most recent monitoring data (2012-2016), the Selway-Bitterroot Wilderness (SULA1 monitor) is meeting the RPG for the 20-percent most impaired days. However, according to the 2012-2016 data, visibility in the Sawtooth Wilderness (SWAT1 monitor) and the Craters of the Moon NM (CRMO1 monitor) is not meeting the 2018 RPGs for the 20-percent most impaired days.

According to the progress report, visibility has not improved in the Sawtooth Wilderness and Craters of the Moon NM due to smoke from episodic wildfires in the area. Figures 6, 7, and 8 in the progress report show that SO2 and NOX emissions have decreased since 2000. In contrast, coarse PM emissions have increased during the same period. Figure 14, Figure 15, and Appendix D of the progress report show that, even though there has been a steady reduction in ammonium sulfate formation since 2000, indicative of a reduction in anthropogenic contributions to visibility impairment, particulate organic mass has consistently remained the dominant contributor to light extinction. The Sawtooth Wilderness and Craters of the Moon NM experienced a notable spike in light extinction caused by particulate organic mass emissions in 2012, which likely contributed to the areas not meeting their RPGs. The 2012 fires potentially impacting the Sawtooth Wilderness and Craters of the Moon NM include the Halstead Fire (181,000 acres), Mustang Complex (340,600 acres), and the Trinity Ridge Fire (146,800 acres).[6]

C. Visibility Monitoring Strategy

The progress report also contained a review of Idaho's visibility monitoring strategy. Idaho concluded that the IMPROVE network continues to comply with the monitoring requirements in the Regional Haze Rule and that no modifications to Idaho's visibility monitoring strategy are necessary at this time.

D. Summary of Emissions Reductions

The Idaho progress report also included a summary of the emissions reductions achieved throughout the state from the control measures discussed above. Specifically, Idaho identified emissions reductions achieved through emissions controls on Idaho BART-eligible sources, including the P4 Production and the TASCO Nampa facilities. According to Idaho, implementation of BART caused significant reductions in emissions at both facilities. Installation of the LCDA scrubber on the P4 Production facility reduced SOX emissions by 11,000 tons per year. NOX emissions at the TASCO Nampa facility have also declined due to compliance with the BART requirements, namely implementation of low NOX burners, switching to natural gas, and the permanent shutdown of pulp dryers. Specifically, the BART alternative for the TASCO Nampa Facility achieved NOX emissions reductions of 221 tons per year, SO2 emissions reductions of 20.6 tons per year, and PM emissions reductions of 113 tons per year (78 FR 38872).

The progress report also discussed improvements in Idaho's smoke management programs made during the first planning period, as noted above. The progress report summarized changes in emission inventories for all major visibility impairing pollutants from point, area, on-road mobile, off-road mobile, oil and gas, fugitive and road dust, and anthropogenic fire source categories in the state. For these summaries, emissions during the baseline years are represented using a Start Printed Page 135852002 inventory, which was developed with support from the WRAP for use in the original Regional Haze SIP development. Differences between inventories are represented as the differences between the 2002 inventory, the 2008 inventory, and the 2011 inventory which leverages recent inventory development work performed by the WRAP for the West-wide Jump Start Air Quality Modeling Study (WestJumpAQMS) and Deterministic & Empirical Assessment of Smoke's Contribution to Ozone Project (DEASCO3) modeling projects.

The progress report also included an analysis tracking the change in emissions since the first progress period and the most recent progress period. Specifically, Idaho states that there has been a substantial reduction in anthropogenic sources of both SO2 and NOX. Estimated emissions reductions for SO2 and NOX are summarized in Table 2 and Table 3, below. These reductions are primarily attributed to the BART controls and the Tier II reductions in sulfur content of fuels and NOX vehicle emission standards. We note that the other visibility impairing pollutants (primary organic aerosols, elemental carbon) also generally declined as detailed in Chapter 2.3 of the progress report. As shown in Table 4 below, emissions increased for fine and coarse particulate matter because of a major change to the fugitive road dust calculations between 2008 and 2011.[7]

Table 2—Sulfur Dioxide Emissions by Category

Sulfur dioxide emissions (tons/year)
200220082011
Anthropogenic Sources
Point17,6137,4906,954
Area3,2809,0682,070
On-Road Mobile1,662339198
Off-Road Mobile3,702281122
Fugitive and Road Dust42595
Anthropogenic Fire8952,4992,460
Total Anthropogenic27,15619,70211,899
Natural Sources
Natural Fire12,0088523,005
Biogenic000
Wind Blown Dust000
Total Natural12,0088523,005
All Sources
Total Emissions39,16420,55414,904

Table 3—Nitrogen Oxides Emissions by Category

Nitrogen oxides emissions (tons/year)
200220082011
Anthropogenic Sources
Point11,48712,67111,591
Area30,31819,8926,205
On-Road Mobile44,61144,55645,575
Off-Road Mobile27,92214,13220,900
Fugitive and Road Dust51350
Anthropogenic Fire3,46111,3686,122
Total Anthropogenic117,804102,63290,443
Natural Sources
Natural Fire39,4013,8157,878
Biogenic16,9824,8064,459
Wind Blown Dust000
Total Natural56,3838,62112,337
Start Printed Page 13586
All Sources
Total Emissions174,187111,253102,780

Table 4—Fine Particulate Emissions by Category

Fine particulate emissions (tons/year)
200220082011
Anthropogenic Sources
Point3050246
Area4,7492,364408
On-Road Mobile0175185
Off-Road Mobile0460
Fugitive and Road Dust4,83912,56444,037
Anthropogenic Fire1,5368,35818
Total Anthropogenic11,42923,50744,894
Natural Sources
Natural Fire3,0132,78018
Biogenic000
Wind Blown Dust5,0505,28611,068
Total Natural8,0638,06611,086
All Sources
Total Emissions19,49231,57355,980

In its progress report, Idaho concluded that the state is making adequate progress in improving visibility as a result of actions identified in the Regional Haze SIP, as well as actions taken by adjoining states, the federal government, the WRAP, and the Western States Air Resources Council.

E. Determination of Adequacy (40 CFR 51.308(h))

In accordance with 40 CFR 51.308(h)(1), if the state determines that the existing implementation plan requires no further substantive revision in order to achieve established goals for visibility improvement and emissions reductions, the state must provide to the Administrator a negative declaration that further revision of the existing implementation plan is not needed at this time. Within the progress report, Idaho provided a negative declaration stating that further revision of the existing implementation plan is not needed. The basis for the state's negative declaration is the finding that visibility on the 20-percent least impaired days has improved from the baseline period, and the Selway-Bitterroot Wilderness Class I area attained its 2018 RPGs at the IMPROVE monitor. The Sawtooth Wilderness and the Craters of the Moon NM did not meet the 2018 RPGs for the 20-percent most impaired days at their respective monitors, which Idaho demonstrated was due to smoke from wildfires in 2012.[8]

Accordingly, the EPA proposes to find that Idaho adequately addressed the requirements in 40 CFR 51.308(h) in its determination that the existing Idaho Regional Haze SIP requires no substantive revisions at this time.

F. Consultation With Federal Land Managers (40 CFR 51.308(i))

In accordance with 40 CFR 51.308(i), the state must provide the FLMs with an opportunity for consultation, in person and at least 60 days prior to holding any public hearings on an implementation plan (or plan revision). The state must also include a description of how it addressed any comments provided by the FLMs. The State of Idaho invited the FLMs to comment on its draft progress report on January 28, 2016, for a 60-day comment period ending March 28, 2016, prior to releasing the report for public comment. Idaho included the FLM comment and a description of how it addressed the comment in Appendix E of the progress report.

The EPA proposes to find that Idaho has addressed the requirements in 40 CFR 51.308(i). Idaho provided a 60-day period for the FLMs to comment on the progress report, which was at least 60 days before seeking public comments, and provided a summary of these comments and responses to these comments in the progress report.

IV. The EPA's Proposed Action

The EPA is proposing to approve the Idaho Regional Haze Progress Report submitted to the EPA on June 28, 2016, as meeting the applicable requirements of the CAA and Regional Haze Rule, as set forth in 40 CFR 51.308(g). The EPA proposes to find that the existing Start Printed Page 13587Regional Haze SIP is adequate to meet the state's visibility goals and requires no substantive revision at this time, as set forth in 40 CFR 51.308(h). We propose to find that Idaho fulfilled the requirements in 40 CFR 51.308(i) regarding state coordination with FLMs.

V. Statutory and Executive Order Reviews

Under the Clean Air Act, 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 choices, provided that they meet the criteria of the Clean Air Act. Accordingly, this proposed action merely approves state law as meeting Federal requirements and does not impose additional requirements beyond those imposed by state law. For that reason, this proposed 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);
  • Is not an Executive Order 13771 (82 FR 9339, February 2, 2017) regulatory action because SIP approvals are exempted under Executive Order 12866;
  • 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 in Executive Order 13132 (64 FR 43255, August 10, 1999);
  • Is not an economically significant regulatory action based on health or safety risks subject to Executive Order 13045 (62 FR 19885, April 23, 1997);
  • Is not a significant regulatory action subject to Executive 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 it does not involve technical standards; 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, under Executive Order 12898 (59 FR 7629, February 16, 1994).

The proposed SIP would not be approved to 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 proposed 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). Therefore, Executive Order 13175 does not apply to this action.

Start List of Subjects

List of Subjects in 40 CFR Part 52

  • Environmental protection
  • Air pollution control
  • Incorporation by reference
  • Intergovernmental relations
  • Nitrogen dioxide
  • Particulate matter
  • Reporting and recordkeeping requirements
  • Sulfur oxides
  • Visibility, and Volatile organic compounds
End List of Subjects Start Authority

Authority: 42 U.S.C. 7401 et seq.

End Authority Start Signature

Dated: March 27, 2019.

Chris Hladick,

Regional Administrator, Region 10.

End Signature End Supplemental Information

Footnotes

1.  See 76 FR 36329 (Jun. 22, 2011) and 77 FR 66929 (Nov. 8, 2012).

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2.  Areas designated as mandatory Class I Federal areas consist of national parks exceeding 6,000 acres, wilderness areas and national memorial parks exceeding 5,000 acres, and all international parks that were in existence on August 7, 1977 (42 U.S.C. 7472(a)). See 40 CFR part 81, subpart D for a list of Class I areas.

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3.  The SO2 emissions limit is embodied in Idaho Permit T2-2009.0109, which is included in the Docket for this action.

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4.  See document entitled “visibility data trends” included in the Docket for this action.

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5.  For all Idaho Class I monitoring sites, monitoring began in late 2000; therefore, only three complete years of monitoring data, 2002-2004, define their baselines.

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7.  Fine soil and coarse mass decreased for the windblown dust inventory comparisons and increased for the combined fugitive/road dust inventories. Idaho noted that large variability in changes in windblown dust was observed for the contiguous WRAP states, which was likely due in large part to enhancements in dust inventory methodology, rather than changes in actual emissions. For most parameters, especially primary organic aerosols, volatile organic compounds, and elemental carbon, natural fire emission inventory estimates decreased, and anthropogenic fire estimates increased.

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8.  EPA acknowledged in its approval of Idaho's Regional Haze SIP that the overwhelming amount of visibility impairment due to fire on the 20-percent most impaired days at Idaho's Class I areas is due to natural fire. See 77 FR 66929, 66933. In our approval of Idaho's Regional Haze SIP, we agreed with Idaho's conclusion that no additional controls on non-BART stationary sources in Idaho were reasonable for the first planning period because any visibility improvement expected from additional controls would likely be minimal due to the outsized influence of wildfires on visibility impairment. Id. at 66931.

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[FR Doc. 2019-06739 Filed 4-4-19; 8:45 am]

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