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Federal Register / Vol. 86, No. 5 / Friday, January 8, 2021 / Proposed Rules
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conditions, and several monitors under high wind conditions, were chosen with inconsistent criteria and/or have data inaccuracies. In turn, these inconsistencies and inaccuracies led to design day concentration values that were likely too low to address adequately the range of exceedances experienced in the nonattainment area.
For example, in selecting the stagnation scenario design day for Cowtown, ADEQ limited selection to fall 2008
September to November exceedance days despite the higher PM10
concentrations and a comparable number of exceedance days in the spring season March to May.
Ultimately, the selected 2008 design day was the 68th highest out of the 137 total low wind/stagnation exceedance days identified by the State i.e., approximately 49% of the low wind/
stagnation exceedance days had higher concentrations than the design day selected.60 This middle range day was insufficiently conservative and was inadequate to represent the attainment issues during stagnation conditions and to address the range and severity of exceedances experienced at CWT.61
Second, we conclude that several data inputs and assumptions associated with modeling the control strategy were unsupported, overstated, or insufficiently conservative leading to an overestimate of the overall efficacy of the control strategy within the attainment demonstration. Specifically, in calculating the control effectiveness of the rules in the control strategy, two component assumptions or estimates were the primary cause of this overestimate: 1 Rule effectiveness, i.e., the percentage of compliant facilities;
and, 2 aggregate or net best management practices BMP control efficiencies. For example, we found that despite limited or no compliance data, the lack of compliance assistance program efficacy figures, the lack of automatic reporting requirements, and little to no farm experience implementing BMPs, ADEQ assumed high compliance rates with the AgBMP
rule; in turn, this unjustifiably inflated the overall control effectiveness calculations. In addition, we found that the domain modeling micro-emissions inventory estimates that ADEQ derived 60 Low wind/stagnation exceedance days for purposes of this document are the exceedance days that remain once days identified by ADEQ as high wind day exceedances in IPP, Appendix C, Table C1 are removed. See Cowtown 2008
Exceedances.xlxs in the docket for this action.
61 See Section III.B.1. of the TSD for our complete review of design day selection for stagnation scenario at the Cowtown monitor. Also, see Section III.B.2 of the TSD for our complete review of design day selection for the high wind scenario.

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from this limited BMP implementation data were not appropriately documented or supported and were insufficiently conservative due to overly optimistic or simplifying assumptions used to aggregate BMP control efficiency estimates, such as assuming that farms will either choose not to operate or will routinely implement higher cost and higher control efficiency BMPs on high risk days. Consequently, ADEQ assumed farms reduced emissions from cropland operations and unpaved roads to a greater extent than what could be supported by the documentation in the Plan.62
Based on our evaluation of the design days and modeling and control effectiveness assumptions in the Plan, we find that these several deficiencies in the analyses preclude approval of the attainment demonstration. In addition, after reviewing past and recent PM10
data against the West Pinal County PM10
Plans attainment demonstration predictions, we conclude that:
There is no clear evidence of a sustained decrease in the number of exceedances in recent years as control measures have been implemented 20152018;
PM10 concentrations well above the level of the 24-hour PM10 NAAQS 150
mg/m3 continue to be a major air quality problem in the West Pinal County nonattainment area despite the implementation of control measures designed to reduce PM10 levels thus far;
and The Plans control strategy, whether considered as adopted RACM/RACT or as the entire suite of rules submitted with the Plan, was inadequate to attain the PM10 NAAQS by December 31, 2018, as evidenced by the ambient PM10
data.
Consequently, we propose to disapprove the modeled attainment demonstration in the West Pinal County PM10 Plan because it does not meet the requirements of CAA section 189a1B and section 188c1.
E. Reasonable Further Progress Demonstration 1. Statutory and Regulatory Requirements The requirement for RFP in PM10
nonattainment areas is specified in CAA
section 172c2 and is described in the General Preamble.63 Under CAA section 1711, RFP is defined as meaning such annual incremental reductions in emissions of the relevant air pollutant as are required under part D Plan 62 See Section III.C. of the TSD for our complete review of control effectiveness estimates.
63 57 FR at 13539.

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Requirements for Nonattainment Areas of the CAA or as may reasonably be required by the EPA for the purpose of ensuring attainment of the applicable NAAQS by the applicable date. In addition, CAA section 189c1
requires quantitative milestones that demonstrate RFP and must be achieved every 3 years until the nonattainment area is redesignated to attainment, beginning 4.5 years after a Moderate areas designation to nonattainment of the PM10 NAAQS.64 Therefore, Moderate area plans should contain quantitative milestones for 4.5 and 7.5
years after designation. These quantitative milestones should be constructed so that they can be tracked, quantified and/or measured adequately, and provide for an objective evaluation of RFP toward attainment of the NAAQS, particularly as part of milestone reporting.65
2. Summary of the States Submission The West Pinal County PM10 Plan discusses how the Plan provides for RFP
in Section 7.2 and Appendix D and provides visual representation in Figure 71 and Figure D 51.66 For the purposes of calculating annual increments of emission reductions for RFP, ADEQ assumed a linear glidepath with equal annual emissions reductions over the 2016
2018 implementation timeframe. This annual increment representing RFP is 7,475 tons per year.67 The implementation of the Plans control strategy is projected to produce almost all the needed emissions reductions in the first year, 2016, with slight and incremental emission reductions to follow in 2017 and 2018. Because ADEQ
projected that most of the emissions reductions would come in the first year, the projected emissions were below the glidepath and ADEQ concluded that RFP was demonstrated.
3. The EPAs Review of the States Submission Based in part on our review of the 20162018 ambient data and in part on the flaws identified in the West Pinal County PM10 Plan attainment demonstration, we find that ADEQ did not adequately provide for annual increments of emissions reductions needed to attain the PM10 NAAQS by 2018. Because the West Pinal County 64 Ibid.
65 81

FR 5806364.
Pinal County PM10 Plan, 99 and Figure 7
1, 101; Appendix D, 45.
67 West Pinal County PM
10 Plan, 100. Expected emission reductions from 2015 to 2018, 22,426 tons per year, are divided into 3 annual increments of 7,475 tons per year.
66 West
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