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Federal Register / Vol. 86, No. 53 / Monday, March 22, 2021 / Rules and Regulations revision,54 the Arkansas Regional Haze SO2 and PM SIP revision,55 and the Arkansas Regional Haze Phase III SIP
revision together fully address the deficiencies of the 2008 Arkansas Regional Haze SIP that were identified in the March 12, 2012, partial approval/
partial disapproval action. As an alternative basis for approval of the States CAA section 110a2DiII
prong 4 submittals for these NAAQS, we are finalizing our determination that Arkansas has provided an adequate demonstration in the October 4, 2019
submittal that emissions within its jurisdiction do not interfere with other air agencies plans to protect visibility.
The public comment period for the NPRM closed on April 15, 2020. We received two sets of public comments concerning our proposed action. The comments are included in the publicly posted docket associated with this action at https www.regulations.gov.
We received a comment letter with adverse comments dated April 15, 2020, submitted on behalf of the National Parks Conservation Association, the Sierra Club, and Earthjustice regarding our proposed approval. We also received another comment letter dated April 15, 2020, from Domtar that was largely in support of our proposed approval. Below we provide a summary of the comments with our detailed responses. The complete comments can be found in the docket associated with this final rulemaking. After careful consideration of the public comments received, we have decided to finalize our action with no changes from the proposed action. For our complete, comprehensive evaluation of the Arkansas Regional Haze Phase III SIP
revision, please refer to the proposed approval See 85 FR 14847. Our final actions regarding the NPRM are summarized in section IV of this notice.

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III. Public Comments and EPA
Responses A. Demonstration That the BART
Alternative Is Better-Than-BART
Comment A.1: The BART alternative measure submitted by the State fails to demonstrate that the BART alternative achieves greater reasonable progress than BART. Rather than submit a revised BART analysis determination, DEQs Arkansas Regional Haze Phase III
SIP includes what it asserts are approvable SIP measures in a BART
alternative for two subject-to-BART
54 Final
action approved on February 12, 2018 83

FR 5927.
55 See 83 FR 62204 November 30, 2018 for proposed approval and 84 FR 51033 September 27, 2019 for final approval.

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sources Power Boilers No. 1 and 2 at the Domtar Ashdown paper mill located in Ashdown, Arkansas. Compared to BART, the BART alternative results in an overall Power Boilers No. 1 and 2
increase in sulfur dioxide SO2
emissions and decrease in NOX
emissions. While DEQ claims that the NOX decrease mitigates the SO2
increase, the SIP fails to demonstrate the BART alternative achieves greater reasonable progress than BART.
Response: We disagree with the commenters assertion that the BART
alternative measure submitted by the State fails to demonstrate that the BART
alternative achieves greater reasonable progress than BART.
As explained in the proposed action, the BART alternative would result in an overall decrease in SO2, NOX, and particulate matter PM10 emissions from the baseline for both power boilers at Domtar Ashdown paper mill. The BART alternative results in greater emission reductions of NOX and PM10
than the BART controls in the FIP. The BART alternative controls would reduce NOX and PM10 emissions by 1,096 and 111 tons per year tpy, respectively, from the baseline. The BART alternative results in a smaller reduction in SO2
emissions compared to the BART
controls BART achieves 3,051 tpy SO2
reduction but still achieves a decrease of 1,637 tpy SO2 from the baseline.
Despite a smaller reduction in SO2
emissions than BART a 1,414 tpy SO2
difference, the BART alternative results in 300 tpy fewer NOX emissions and 157
tpy fewer PM10 emissions compared to BART. Model results show that the additional reduction in NOX emissions under the BART alternative controls results in more overall modeled visibility improvement across the impacted Class I areas than BART even with the smaller reduction in SO2
emissions.
We explained in our proposed action that greater visibility improvement occurs because Domtars baseline NOX
emissions are the primary driver of visibility impacts from the source and contribute more to visibility impairment across the four-affected Class I areas in Arkansas and Missouri for Power Boiler No. 1, and also contribute more at Caney Creek for Power Boiler No. 2 than other pollutants emitted by the source. DEQ
first included an analysis utilizing method 1 56 that shows that the BART
alternative controls achieve greater 56 Method 1 assessed visibility impairment on a per source per pollutant basis and Method 2
allowed for interaction of the pollutants from both boilers. See descriptions of method 1 and 2
modeling evaluations in the March 16, 2020
proposed approval 85 FR 14847, 1485714858.

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overall cumulative reductions in visibility impairment as expressed by the change in deciviews or Ddv from the baseline across the four Class I areas when compared to BART 0.549 Ddv for the alternative versus 0.473 Ddv for BART. DEQ then determined that the BART alternative controls reduce the overall visibility impairment from the baseline by 0.520 Ddv under its method 2 evaluation and is greater than the overall visibility improvement modeled under BART, which is 0.516 Ddv. The DEQ noted that the most impacted Class I area, Caney Creek 1.137 dv baseline impairment, improved the greatest 0.384 Ddv with the BART alternative under method 2, and would experience greater visibility improvement under the BART alternative scenario than under the BART scenario, which improves by 0.361 Ddv.
The States weight of evidence analysis of visibility improvement in the SIP was supported by our analysis of various metrics, which reinforced that the BART alternative achieves greater reasonable progress. We analyzed the pollutant species contribution to visibility impacts at the Class I areas from each power boiler. Specifically, for Power Boiler No. 1, baseline modeled nitrate NO3 and nitrogen dioxide NO2 impacts had the highest contribution to visibility impairment at all Class I areas. For Power Boiler No.
2, baseline modeled NO3 and NO2
impacts are the primary driver for visibility impacts at Caney Creek, which is the Class I area impacted the most by the Domtar units. For Power Boiler No.
2, the visibility impacts resulting from NOX at Caney Creek outweigh SO42
species contributions from SO2
precursors to impacts at the other three Class I areas combined. In addition to pollutant species contributions to impacts, we also considered the ten highest impacted days.57 This analysis provided a broader look at those days with the highest impacts at each Class I area. The results were consistent with 57 The ten highest impacted days means the 8th to 17th highest days at each Class I area. The 98th percentile means that for a given distribution, it is equal to or higher than 98 percent of the rest of the distribution. The 98th percentile impact day means that only two percent of the 365 days in a calendar year, or 7.3 days rounded up to 8 days have higher impacts. The simplified chemistry in the CALPUFF
model tends to magnify the actual visibility effects of that source so it is appropriate to use the 98th percentile, or 8th highest day, to not give undue weight to the extreme tail of the distribution. This approach will effectively capture the sources that contribute to visibility impairment in a Class I area, while minimizing the likelihood that the highest modeled visibility impacts might be caused by unusual meteorology or conservative assumptions in the model. See 70 FR 39104, 39121 July 6, 2005, Regional Haze Regulations and Guidelines for BART Determinations.

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