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Federal Register / Vol. 86, No. 53 / Monday, March 22, 2021 / Rules and Regulations
visibility BART factor.74 The court in NPCA rejected that this flaw in the States analysis could be dismissed as harmless error.75
In this action, by contrast, both the State and EPA have evaluated the cumulative visibility impacts across all of the affected Class I areas. The State considered this with both of its methods of analysis, and EPA coupled those results with our own analysis of cumulative visibility improvement. DEQ
first included an analysis utilizing method 1 that shows that the BART
alternative controls achieve greater overall cumulative reductions in visibility impairment from the baseline cumulatively across the four Class I
areas when compared to BART 0.549
Ddv for the alternative versus 0.473 Ddv for BART. DEQ also determined using method 2 that the BART alternative controls reduce the overall cumulative visibility impairment from the baseline by 0.520 Ddv, which is greater than the overall visibility improvement modeled under BART, which is 0.516 Ddv. We complemented the States analysis by comparing the average visibility impact across the top ten highest impacted days at each Class I area average 8th to 17th highest. This analysis provided a broader look at those days with the highest impacts at each Class I area. The results were consistent with the States analysis based on the 98th percentile day, which was selected as representative of the highest impact i.e., the 8th highest day. The BART
alternative controls achieve greater overall visibility improvement from the baseline compared to BART for the ten highest impacted days 0.439 Ddv for the alternative versus 0.423 Ddv for BART. Thus, visibility benefits at each Class I area were considered and analyzed by multiple metrics that confirmed our proposed approval of the alternative.
The commenter argues that EPA fails to provide a basis for applying the 0.5
deciview threshold used by the State to determine if a source contributes to visibility impairment at a Class I area with the BART alternative analysis, noting that numerous BART
determinations relied on lower deciview thresholds that resulted in significant emission reducing outcomes. The meaning of this comment is not clear.
EPA did not apply a 0.5 deciview threshold to cut off its evaluation of other Class I areas. However, it is reasonable to provide additional analysis when one Class I area is much more heavily impacted by a source than 74 Id.
75 Id.

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others. In the case of Domtar, the baseline visibility impacts at Caney Creek are much larger than impacts at the other Class I areas, so it is reasonable to give greater weight to visibility benefits at Caney Creek resulting from the alternative as compared to BART. The level of visibility benefit from controls at the other three Class I areas are smaller than those at Caney Creek, and the baseline visibility impacts of the source at these areas was well below the 0.5 dv threshold used by the State to determine if a source contributes to visibility impairment at a Class I area. In making this observation, we do not categorically dismiss or ignore impacts to other Class I areas below 0.5 or any other threshold.
We simply note that the changes in visibility at these other Class I areas were individually very small and collectively smaller than the comparative gain in visibility achieved by the BART alternative at Caney Creek.
The commenter mentioned that Congress provided no authority for EPA
to treat one Class I area differently from others. As mentioned previously, we treated all Class I areas the same and measured the cumulative visibility impacts across all of them using multiple metrics. We specifically analyzed the effects at Caney Creek, since it is the Class I area impacted the most. But that analysis does not show favoritism and merely provides one metric for interpreting how impacts are correlated to overall emissions from the source at each Class I area.
B. Monitoring, Recordkeeping and Reporting Requirements Comment B.1: EPA lacks authority to approve the States SIP submission with respect to provisions pertaining to alternative test methods. EPA proposes to allow the State to authorize alternative sampling or monitoring methods equivalent to methods in the permit that EPA would concur on, outside the SIP process. Specifically, EPA proposes approving permit conditions 35 and 42 as a part of the SIP. Neither the States SIP nor EPAs proposal explains what criteria and process EPA would use to approve an alternative method. Arkansas alteration or elimination of SIP requirements can have no effect for purposes of federal law unless and until EPA ratifies that action with a SIP revision that is subject to the SIP requirements, including provisions for public notice and comment. Moreover, the monitoring, recordkeeping and reporting provisions in the States SIP are not approvable and therefore, those methods cannot be used a basis for assessing whether an
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alternative method is approvable. Based on Arkansas SIP provisions, there is no way for the public to assess whether an alternative method will comply with the Act. Therefore, EPA should not approve these provisions because they are inconsistent with the requirements of CAA section 110i, 110l and 110k3.
Response: We recognize that the commenter raises a concern that the States ability to authorize with EPA
concurrence alternative test methods in conditions 35 and 42 may be inconsistent with the Act insofar as neither the States SIP nor EPAs proposed approval explains what criteria and process EPA would use to approve an alternative method. In general, EPA agrees that SIP provisions cannot authorize a State to make changes in the EPA-approved and federally enforceable SIP requirements applicable to sources without going through the statutorily required SIPrevision process. EPA refers to SIP
provisions that purport to authorize States to make unilateral changes to existing SIP requirements as impermissible directors discretion provisions. However, EPA interprets the CAA to allow two types of such provisions: i Where the provision provides directors discretion for the State to make changes, but specifies that such changes have no effect for purposes of federal law or alter SIP
requirements unless and until the EPA
approves the changes through a SIP
revision pursuant to CAA requirements;
or ii where the provision provides directors discretion that is adequately bounded, such that at the time EPA
approves the SIP provision the agency can evaluate it for compliance with applicable CAA requirements and evaluate the potential impacts of the States exercise of that discretion. EPA
interprets CAA section 110i to allow SIP provisions with directors discretion of either type. In the case of an adequately bounded provision, EPA
considers such provisions consistent with section 110i because, at the time of initial approval into the SIP, the agency will already have evaluated the provision for compliance with applicable requirements and evaluated the potential impacts from exercise of the discretion. By their terms, conditions 35 and 42 do not specify that DEQ must seek a SIP revision to change the required monitoring at the source.
Thus, to be approvable, EPA would have to determine that the States discretion in these provisions is adequately bounded and assess the potential impacts from the exercise of that authority.

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