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Federal Register / Vol. 86, No. 53 / Monday, March 22, 2021 / Rules and Regulations unreasonable for EPA to provide weight to the information.
Response: We disagree with the commenters assertion that the information on which our approval of the States SIP is based fails to provide an adequate clear weight of evidence analysis to meet the requirements in 40
CFR 51.308e. The commenter is apparently alleging that the analysis provided by the State instead falls under 40 CFR 51.308e3 rather than under 40 CFR 51.308e2iE because it is based on an emission reduction comparison and modeling. The argument that the kind of data and analysis to be used under the clear weight of evidence test must somehow be sufficiently different from what would be required under 40 CFR
51.308e3 is not a reasonable interpretation of these regulations. EPA
interprets 40 CFR 51.308e2iE as permitting data and analysis that may be relevant under 40 CFR 51.308e3
analysis to be used in supporting a clear weight of evidence demonstration.
Pursuant to 40 CFR 51.308e2iE, the state must provide a determination under 40 CFR 51.308e3 or otherwise based on clear weight of evidence that the alternative measure achieves greater reasonable progress than BART. The State relied on a modeling analysis to determine if the BART alternative could be shown to make greater reasonable progress than BART, but that modeling was different than the modeling described under 40 CFR 51.308e3.
The State used an air quality modeling methodology approach using the maximum 98th percentile visibility impact of three modeled years using the CALPUFF model instead of modeled overall visibility conditions for the twenty percent best and worst days, as would be required under 40 CFR
51.308e3. The States approach could be considered a modified version of the two-part modeling test under 40 CFR
51.308e3 and is more appropriate to classify under the weight of evidence analysis approach instead allowed under 40 CFR 51.308e2iE.
The States methodology and analysis under the clear weight of evidence test is reasonable. The States CALPUFF
modeling approach utilizing the 98th percentile visibility impacts is consistent with the approach recommended by the BART
guidelines 59 for comparing different control options at a single source when developing BART determinations relying on the 98th percentile visibility 59 See 40 CFR 51 Appendix Y section III.A.3 and IV.D.5, Guidelines for BART Determinations Under the Regional Haze Rule.

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impact as the key metric. It is also consistent with the methodology followed in EPAs 2016 FIP BART
determination 60 61 for Domtar.
CALPUFF is a single source air quality model that is recommended in the BART Guidelines. Since CALPUFF
was used for this BART alternative analysis, the modeling results were post-processed in a manner consistent with the BART guidelines. This approach is, therefore, acceptable and reasonable for the comparison of the proposed BART alternative to the FIP
BART determination for Domtar since it is the same modeling used to determine BART in the FIP, and the BART
alternative is focused on only the BART
sources at Domtar. The State also considered two methods of modeling evaluation provided by Domtar for this approach of using the maximum 98th percentile visibility impact. Method 1
assessed visibility impairment on a per source per pollutant basis and method 2 allowed for interaction of the pollutants from both boilers. The State followed the same general CALPUFF
modeling protocol and used the same meteorological data inputs for the BART
alternative assessment as discussed in Appendix B to the FIP TSD. Only the modeled emission rates changed to represent the modeled scenarios for each method.
DEQ determined that the visibility benefits as measured under method 2
and the previous FIP BART
determination formed an appropriate BART benchmark for the purposes of the evaluation of Domtars BART
alternative. We continue to agree with DEQ that because method 2 provides for the full chemical interaction of emissions from both power boilers, method 2 analysis results are a reliable assessment of the anticipated overall visibility improvement of controls utilizing the 98th percentile impact.
Under the weight of evidence approach, we made use of all available information and data which could inform our decision while recognizing the relative strengths and weaknesses of that information in arriving at the soundest decision possible.62 This array of 60 See proposed FIP on April 8, 2015 80 FR
18979.
61 See final FIP action on September 27, 2016 81
FR 66332 as corrected on October 4, 2016 81 FR
68319 and the associated TSD, AR020.000200
TSD for EPAs Proposed Action on the Arkansas Regional Haze FIP in Docket No. EPAR06OAR
20150189 for the FIP BART analysis for SO2 and NOX for Power Boiler No. 1; and SO2, NOX, and PM10 for Power Boiler No. 2. This was included as part of the Phase III submittal and included in the docket of this action.
62 See 71 FR 60612, 60622 October 13, 2006.
Factors which can be used in a weight of evidence
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information and other relevant data was of sufficient quality to inform our comparison of visibility impacts between BART and the BART
alternative. We carefully considered this evidence in evaluating the Arkansas Phase III SIP revision submitted by the State. Overall, the difference in visibility impacts between the BART
and the BART alternative scenarios was large enough to show that the BART
alternative achieves greater reasonable progress than BART based on the clear weight of the evidence.
As explained in response to comment A.1 in section III.A of this final action, we evaluated DEQs analysis and additional model results relying primarily on the analysis of the 98th percentile impacts,63 the analysis of emission reductions,64 and the analysis of Domtars visibility impacts due to NO3 compared to SO4.65 In addition, we also considered our analysis of the ten highest impacted days 8th to 17th highest 66 and our analysis of the number of days impacted over 0.5 dv and 1.0 dv.67 All of these metrics, except the number of days impacted over 0.5 dv which only very slightly favored BART, provided substantial evidence and collectively supported the conclusion that the BART
alternative provides for greater reasonable progress than BART. For these reasons, we are finalizing our approval of the States weight of evidence analysis approach and the conclusions reached by the State. In the course of evaluating the SIP submittal, EPA developed some additional analysis that complements and supports determination in this context may include, but not be limited to, future projected emissions levels under the alternative as compared to under BART;
future projected visibility conditions under the two scenarios; the geographic distribution of sources likely to reduce or increase emissions under the alternative as compared to BART sources;
monitoring data and emissions inventories; and sensitivity analyses of any models used.
63 See Tables 7 and 8 of the proposed approval, 85 FR 14847, 14858.
64 See Tables 5 and 6 of the proposed approval, 85 FR 14847, 1485614857.
65 See Appendix C Supplemental BART
Determination Information Domtar A.W. LLC, Ashdown Mill AFIN 4100002, originally dated June 28, 2013 and revised on May 16, 2014, prepared by Trinity Consultants Inc. in conjunction with Domtar A.W. LLC.
66 See 85 FR 14847, 14859. This data is based on the CALPUFF modeling provided by Domtar and relied on by the State in the Phase III SIP. See EPACALPUFF summary for Method 2.xlsx for the EPAs summary of the modeling data, available in the docket for this action.
67 See 85 FR 14847, 14860. This data is based on the CALPUFF modeling provided by Domtar and relied on by the State in the Phase III SIP revision.
See EPACALPUFF summary for Method 2.xlsx for the EPAs summary of the modeling data, available in the docket for this action.

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