\O ST 41

.

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY X\ifL REGION IX 17 :“

L PRO1 75 Hawthorne Street

San Francisco, CA 94105-3901

OFFICE OF THE 

### JUL u i 

### 2013
REGIONAL ADMINISTRATOR Mr. Eric Massey

Director, Air Division

Arizona Department of Environmental Quality

1110 W. Washington St.

Phoenix. Arizona 85(07

Dear Mr. Massey:

This letter responds to Arizona Department of Environmental Quality’s (ADEQ) February 13. 2013

submittal regarding 37 exceeedanccs of the 24—hour PIV1 10 standard that occurred at several monitoring

stations within the Phoenix PM 10 nonattainment area on the following days: September ii and 12, 2011.

June 16, June 27. July 11. August 11, August 14. and September 6, 2012.

ADEQ’s submittal included documentation that these exceedances were caused by high wind
exceptional events. EPA has reviewed the documentation provided by ADEQ to demonstrate that the

exceedances on these days meet the criteria for an exceptional event in the Exceptional Events Rule
(EER). EPA concurs based on the weight of the evidence that the exceedances were caused by high

wind exceptional events and finds that ADEQ has successfully made the demonstrations referred to in

40 CPR 50. 14 to EPA’s satisfaction. In addition, ADEQ has met the schedule and procedural requirements in section 50.14(c) with respect to the same data. A more detailed assessment of ADEQ’s

demonstration is enclosed. My staff has or shortly will enter “concurrence flags” for these data into

EPA’s AQS data system.

Based on these determinations. EPA will exclude these data from the following types of calculations and

activities:

• EPA’s Air Quality Data system (AQS) will not count these days as exceedanees when generating user reports, or include them in design values estimates, unless the AQS user specifically indicates that they should be included.

• EPA will accept the exclusion of these data for the purposes of selecting appropriate background concentrations for New Source Review air quality analyses.’

• EPA will accept the exclusion of these data for the purposes of selecting appropriate background concentrations for transportation conformity hot spot analyses. 2

o The data will continue to be publicly available, but EPA’s publications and public
information statements on the status of air quality in the affected area will not reflect these

data in any summary statistic of potential regulatory application, unless such inclusion is specifically noted.

liwe are the pernlitting authority, we will propose permits on this basis. If we are commenting on another permitting authority’s proposed action, our comments will be consistent with the determinations in this letter.

2 Applicable only to PM 10 and PM 2

These data may be included in statistics intended to describe trends in actual air quality in the area.

Printed on Recycled PaperIn addition. EPA will rely on calculated values that exclude these data in proposed regulatory actions. such as a proposed designation. classification, attainment demonstration, or finding as to whether the Phoenix PM 10 nonattainment area has met the PM 10 NAAQS. These regulatory actions require EPA to provide an opportunity for public comment prior to taking a final Agency action. If EPA is pursuing one of these actions for the Phoenix PM 10 nonattainment area. EPA will open a new comment period during which EPA may receive comments on the exceptional event submission you have made and the determinations conveyed in this letter. If so, we must consider and respond to those comments before taking final regulatory action. Accordingly, the determinations conveyed in this letter do not constitute

final EPA action regarding any matter on which EPA is required to provide an opportunity for public comment. In particular. this point applies to determinations regarding the attainment status or classification of the area. Final actions will take place only after EPA completes notice and comment

rulemaking on those determinations. As an additional clarification, the determinations conveyed in this letter are applicable only to determinations incorporating the submitted data relative to the PM in NAAQS. If you have any questions or wish to discuss this matter further, please contact Deborah Jordan, Director of the Air Division at (415) 947-8715. Sincerely, / /4 1 ’kiared Blumenfeld Enclosure cc: Ms. Theresa Rigney. ADEQ1 

### EXCEPTIONAL EVENTS RULE REQUIREMENTS

EPA promulgated the Exceptional Events Rule (EER) in 2007, pursuant to the 2005 amendment of Clean Air Act (CAA) Section 319. The EER added 40 CFR §50.1(j), (k) and (l); §50.14; and §51.930 to

the Code of Federal Regulations (CFR). These sections contain definitions, criteria for EPA approval, procedural requirements, and requirements for air agency demonstrations, all of which must be met before EPA can concur under the EER on the exclusion of air quality data fro m regulatory decisions.

Under 40 CFR §50.14(c)(3)(iv), the air agency demonstration to justify exclusion of data must provide

evidence that:

A. “The event satisfies the criteria set forth in 40 CFR §50.1(j)” for the definition of an exceptional event;

 Th e event “affects air quality.”

 The event “is not reasonably controllable or preventable.”

 The event is “caused by human activity that is unlikely to recur at a particular location or [is] a natural event.” 1

B. “There is a clear causal relationship between the measurement under consideration and the

event that is claimed to have affect ed the air quality in the area;”

C. “The event is associated with a measured concentration in excess of normal historical

fluct uations, including background;” and

D. “There would have been no exceedance or violation but for the event.”

Not Reasonably Controllable or Preventable (nRCP)

EPA evaluates whether an event was not reasonably controllable or preventable at the time of the event by taking into account controls in place and wind speed, along with other factors. 2 For natural sources of dust, a high wind dust event can generally be considered to be not reasonably controllable or preventable if winds are high enough to cause emissions from natural undisturbed areas . For anthropogenic sources of dust, a high wind dust event is also eligible to be considered to be not reasonably controllable or preventable if:

1. The anthropogenic sources of dust have reasonable controls in place,

2. The reasonable controls have bee n effectively implemented and enforced, and 3. The wind speed was high enough to overwhelm the reasonable controls.

Historical Fluctuations (HF)

EPA evaluates whether a measured exceedance is in excess of historical fluctuation by taking into

a ccount th e level of the exceedance in relation to historical data, which is typically 3 to 5 years.

1 A natural event is further described in 40 CFR 50.1(k) as “an event in which human activity plays little or no direct causal role.”

2 See e.g., Affirmation of Attainment of PM

- 10 NAAQS for the San Joaquin Valley Nonattainment Area, 73 FR 14691 (March 19, 2008).2

Clear Causal Relationship (CCR)

EPA considers a variety of evidence when evaluating whether there is a clear causal relationship

between the measurement under cons ideration and the event that is claimed to have affected the air quality in the area. Demonstrations typically include documentation showing that the event in fact occurred and that emissions related to the event were transported in the direction of the mo nitor(s) where

elevated concentrations measurements were recorded; the size of the area affected by the transported emissions; the relationship in time between the event, transport of emissions, and recorded concentrations; and, as appropriate, pollutant s pecies

- specific information supporting a causal relationship between the event and the measured concentration.

Affects Air Quality (AAQ)

EPA will generally consider events to have affected air quality if the CCR and HF requirements have been adequately demonstrated.

Natural Event

EPA will generally consider a high wind dust event to be a natural event in cases where windblown dust is entirely from natural sources or where contributing anthropogenic sources of windblown dust are reasonably controlled. 3 This generally involves adequately demonstrating both the nRCP and CCR requirements.

No Exceedance or Violation But For the Event (NEBF)

Generally, for high wind dust events, the NEBF demonstration is similar to and informed by the

demonstration of the nRCP and CCR requirements, and is expected to show that the measured concentration would have been below the applicable NAAQS without the effect of the event.



### OVERVIEW OF EVENTS

On February 13 , 2013

, Arizona Department of Environmental Quality ( ADEQ ) submitted seven exceptional events demonstration s for 37 exceedances of the 24

- hour PM 10 standard that occurred at several monitoring stations within the Phoenix PM 10 nonattainment area on the following days: September 11 & 12, 2011, June 16, June 27, Jul y 11, August 11, August 14, and September 6, 2012

. Table 1 summarized these exceedances

.

3 EPA will generally consider human activity to have played little or no direct role in causing emissions of the dust generated

b y high wind for purposes of the regulatory definition of “natural event” if contributing anthropogenic sources of the dust are reasonably controlled, regardless of the amount of dust coming from these reasonably controlled anthropogenic sources,

and thus t he event could be considered a natural event. In such cases, EPA believes that it would generally be a reasonable interpretation of its regulations to find that the anthropogenic source had “little” direct causal role. If anthropogenic sou rces of windblown dust that are reasonably controllable but that did not have those reasonable controls applied at the time of the high wind event have contributed significantly to a measured concentration, the event would not be considered a natural event. See preamble to the EER at 72 FR 13566, f.n. 11.3

Generally, ADEQ explains that the exceedances measured on September 11 & 12, 2011, June 16, June 27, July 11, August 11, August 14, and September 6, 2012

, were associated with “monsoonal thunderstorm activity” and “thunderstorm

- driven high winds

. ” ADEQ provided a comprehensive description and discussion of each of these events in the respective demonstrations. ADEQ's narrative is summarized in the following secti ons.

Table 1: EPA PM 10 Exceedance Summary

Exceedance Date Monitor /Site Name AQS ID 24

- hour Avg. ( μ g/m 3 )

September 11, 2011 JLG Supersite 04

- 013

- 9997

- 3 185 JLG Supersite 04

- 013

- 9997

- 4 178

North Phoenix 04

- 013

- 1004

- 1 184

North Phoenix 04

- 013

- 1004

- 2 183

West Phoenix 04

- 013

- 0019

- 1 168
September 12, 2011 Durango Complex 04

- 013

- 9812

- 1 229

West 43 rd 04

- 013

- 4009

- 1 161

West Phoenix 04

- 013

- 0019

- 1 200

June 16, 2012 Buckeye 04

- 013

- 4011

- 1 202 Durango Complex 04

- 013

- 9812

- 1 186 Dysart 04

- 013

- 4010

- 1 167 Higley 04

- 013

- 4006

- 1 194

South Phoenix 04

- 013

- 4003

- 1 165

West 43 rd 04

- 013

- 4009

- 1 211

West Phoenix 04

- 013

- 0019

- 1 189

June 27, 2012 Central Phoenix 04

- 013

- 3002

- 4 340 Durango Complex 04

- 013

- 9812

- 1 221

Glendale 04

- 013

- 2001

- 1 337

Greenwood 04

- 013

- 3010

- 1 323 Higley 04

- 013

- 4006

- 1 224 JLG Supersite 04

- 013

- 9997

- 3 344 JLG Supersite 04

- 013

- 9997

- 4 329

North Phoenix 04

- 013

- 1004

- 1 178

South Phoenix 04

- 013

- 4003

- 1 342 Tempe 04

- 013

- 4005

- 1 169

West 43 rd 04

- 013

- 4009

- 1 221

West Chandler 04

- 013

- 4004

- 1 220

Zuni Hills 04

- 013

- 4016

- 1 285
July 11, 2012 Durango Complex 04

- 013

- 9812

- 1 217

Greenwood 04

- 013

- 3010

- 1 212

South Phoenix 04

- 013

- 4003

- 1 285

West 43 rd 04

- 013

- 4009

- 1 172
August 11, 2012 Higley 04

- 013

- 4006

- 1 159

West Chandler 04

- 013

- 4004

- 1 219
August 14, 201 2 Durango Complex 04

- 013

- 9812

- 1 179

West 43 rd 04

- 013

- 4009

- 1 254
September 6, 2012 West Chandler 04

- 013

- 4004

- 1 1644 

### Event Days: September 11 & 12, 2011

Table 2 : EPA PM 10 Exceedance Summary

Exceedance Date Monitor /Site Name AQS ID 24

- hour Avg. ( μ g/m 3 )

September 11, 2011 JLG Supersite 04

- 013

- 9997

- 3 185 JLG Supersite 04

- 013

- 9997

- 4 178

North Phoenix 04

- 013

- 1004

- 1 184

North Phoenix 04

- 013

- 1004

- 2 183

West Phoenix 04

- 013

- 0019

- 1 168
September 12, 2011 Durango Complex 04

- 013

- 9812

- 1 229

West 43 rd 04

- 013

- 4009

- 1 161

West Phoenix 04

- 013

- 0019

- 1 200

Not Reasonably Controllable or Preventable (nRCP)

In addressing reasonable controls, ADEQ provided detailed information on the current set of required

controls in the Phoenix PM 10 nonattainment area, including information on rule implementation, rule effectiveness, compliance and enforcement, real

- time monitoring alert systems and public notification activities that occurred on the event days. ADEQ stated, “BACM

- approved control me asures on significant anthropogenic sources were in place and enforced during the events, and pro

- active tracking and response to the events by regulatory agencies and local governments confirmed the uncontrollable nature of the dust emissions; therefore, these pre

- existing/prior approved required controls are adequate for meeting the requirements of an exceptional event and should be considered ‘reasonable’ for these purposes.”

ADEQ provided documentation showing that sustained wind speeds associated with these events were above 20 mph on September 11, 2011

, and above 25 mph on September 12, 2011. For example, maximum sustained wind speeds of 20 mph with gusts of 25 mph were measured at Phoenix Sky Harbor Airport on September 11, 2011, and maximum sustaine d wind speeds of 25 mph with gusts of 32 mph, 25 mph with gusts of 36, and 26 mph with gusts of 33 mph were measured at Phoenix Sky Harbor, Casa Grande Municipal Airport, and Williams Gateway Airport on Sep tember 12, 2011, respectively. Also,

while not inc luded in the demonstration, it is important to note that the National Oceanic and Atmospheric Administration’s ( NOAA ) National Climatic Data Center Storm events database included

reports of strong thunderstorm winds in upwind areas of the exceeding monitor ing stations in the area north of the city of Maricopa in Pinal County that were observed to be in excess of 46 mph. Also, 50 mph winds were observed in conjunction with a NOAA report of a dust storm in the greater Phoenix

Area on September 11, 2011

.

ADE Q further explained that “ despite the deployment of comprehensive control measures and sophisticated response programs and one localized, low

- impact violation of the dust control rules, high

wind conditions associated with thunderstorms and thunderstorm ou tflows brought high concentrations

of PM 10 emissions into, and also overwhelmed controls within, the Phoenix PM 10 nonattainment area. Strong thunderstorm outflows with sustained winds ranging from 20

- 30 mph, and even greater speeds nearest the source regio ns... were enough to overwhelm all available efforts to limit PM 10 concentrations from the events. The fact that these were natural events involving strong thunderstorm outflow winds that transported PM 10 emissions into the Phoenix PM 10 nonattainment area, w ith a majority of the PM 10 emissions recorded by Maricopa County area monitors coming from sources to the south and southeast of the nonattainment area, provides strong evidence that the events and exceedances5

of September 11 & 12, 2011, recorded within th e Phoenix PM 10 nonattainment area, were not reasonably controllable or preventable .”

Section V of ADEQ’s documentation included a complex Geographic Information System ( GIS ) analysis of the event that supports the PM 10 transport described above. This analysis indicates that

monitors in the Phoenix PM 10 nonattainment area were affected by PM 10 transport from outside the nonattainment area, with the main source areas located south and southeast of the nonattainment area

. Some of these source areas are located in Pinal County

, portions of which were recently designated as a moderate nonattainment area (West Pinal) for the 1987 24

- hour PM 10 NAAQS (77 FR 32024, May 31, 2012). Currently, the state is undergoing the appropriate process of developing a state implementation plan (SIP), due January 2, 2014, that provides for attainment of the PM 10 standard as expeditiously as practicable but no later than the end of the sixth calendar year after redesignation. The SIP development

p rocess includes the requirement to identify and implement reasonably available control measures for

the area. In addition to transport, information pertaining to the controls implemented within the nonattainment area, the spatial extent of elevated PM 10 c oncentrations throughout the area, and the wind speeds associated with the event sufficiently establishes that the event was not reasonably controllable or preventable.

Table 3 : Documentation of nRCP

Exceedance Date Demonstration Citation Quality of Evid ence Criterion Met?
September 11, 2011 Section IV: p. 20

- 26, Section V: p. 27

- 42 , App. E Sufficient Yes September 12, 2011 Section IV: p. 20

- 26, Section V: p. 43

- 63, App. E Sufficient Yes

Historical Fluctuations (HF)

To demonstrate that this requirement was met, ADEQ provided 5

- year time series plots of both PM 10 daily maximum hourly averages and PM 10 24

- hour averages and stated that these figures show that “events that occurred on September 11 & 12, 2011, resulted in one of the top ten highes t 24

- hour average PM 10 concentrations seen in the last five years .” ADEQ's analysis sufficiently establishes that

the 24

- hour PM 10 concentrations measured on September 11 & 12, 2011

, were in excess of normal

historical fluctuations.

Table 4 : Documentation of HF

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
September 11, 2011 Section III: p. 16

- 19, App. A Sufficient Yes September 12, 2011 Section III: p. 16

- 19, App. A Sufficient Yes

Clear Causal Relationship (CCR)

Section II of ADEQ’s demonstration included a comprehensive conceptual model of the events, including a general overview of the geo graphic setting of the monitors and climate information

. The conceptual model also included a very detailed discussion of the event s that occurred on September 11 &12, 2011

, and a time series graph for the four day period from September 10, 2011

, to September 13,

2011

, that included hourly PM 10 concentrations for monitors in the Phoenix PM 10 nonattainment area.

Section V of the demonstration included time

- lapse video evidence, satellite imagery, metrological data

from various National Weather Service ( NWS ) stations within the Phoenix PM 10 nonattainment area and Pinal County, time series graphs for the events that include d hourly PM 10 concentrations from monitors6

within the Phoenix PM 10 nonattainment area, visibility and sustained with speed from Phoenix Sky Harbor Airport. ADEQ also included an additional times series graph s for the September 11 & 12, 2011

, event s that in cluded 5

- minute PM 10 concentrations from various PM 10 monitors within the Phoenix

PM 10 nonattainment area compared to 5

- min ute wind speed from the Central Phoenix monitor ing station, and PM 10 concentrations from monitors located in Pinal County compared to wind speed and visibility at Casa Grande Municipal Airport, respectively. Finally, ADEQ included a detailed and extensive GIS analysis that included PM 10 concentrations, sustained wind speed s, wind gusts, wind direction, base velocity radar, and visibility to track the transport of PM 10 throughout the region. Accompanying the analysis, ADEQ provided a discussion for every map that described the conditions at

that time. These data show the spa tial and temporal representation of the event as it moves throughout Maricopa and Pinal Counties. The time

- lapse videos of the event can be found at the following

locations :

 September 11, 2011: http://www.phoenixvis.net/videos/mpeg4/SOMT_09112011.mp4

 September 12, 2011: http://www.phoenixvis.net/videos/mpeg4/ SOMT_09122011.mp4

While not included in the demonstration, it is important to note that NOAA’s National Climatic Data Center Storm events database included dust storm observations on September 11, 2011

, at 6:15 PM (greater Phoenix area). The timing of the se dust storm reports for this event is consistent with the issuance of a NWS Dust Storm Warning for the period of 6:00 PM to 7:00 PM, NWS Significant Weather Advisory for the period of 5:19 PM to 7:00 PM

, the observed increased PM 10 concentrations in

the area, increased wind speed, reduced visibility, and NWS station reports of blowing dust (BLDU), haze (HZ), and dust (DU). Also, as previously mentioned in the nRCP section of this document, the wind speeds associated with this event reached the 20 mph rang e at meteorological stations in the area, but the NOAA’s National Climatic Data Center Storm events database included observations of strong thunderstorm winds in excess of 46 mph just north of the City of Maricopa in Pinal County at 5:30 PM.

These observa tions are consistent with the base velocity radar data included in the GIS analysis in Figure 5

- 4 in ADEQ’s demonstration, as well as the location of the collapsing thunderstorm and the area of formation of the outflow boundary as described by ADEQ in Sect ion V on p. 27 and p. 32 and of the September 11, 2012

, event demonstration. The timing of the September 12, 2011

, event is consistent

with the observed increased PM 10 concentrations in the area, increased wind speed, reduced visibility, and NWS station reports of thunderstorms (TS) and blowing dust.

ADEQ stated that the evidence presented has “demonstrated a clear causal relationship between the emissions generated by uncontrollable natural events and the exceedances measured at the monitors

. ” ADEQ further stated that “ t he satellite images, time series graphs, and meteorological data tables provided in this section for September 11 & 12, 2011, show the temporal progres sion of the dust events from the development of the thunderstorms, to the increase in wind speeds, and to the rise in PM 10 concentrations. The GIS maps for September 11 th also showed how soon after the main outflow boundary passed through the Phoenix area, that stagnation allowed PM 10 concentrations to remain high at a few sites. The GIS maps for September 12 th showed how strong winds and high PM 10 concentrations in Pinal County traveled northward into Maricopa County, leading to a subsequent increase in wi nd speeds and PM 10 concentrations at the Phoenix area PM 10 monitors. The combination of the PM 10 concentrations and wind data from Maricopa County on September 11 th , and from Maricopa and Pinal Counties on September 12 th , supports the conclusion that the events were primarily caused by windblown dust from emission sources outside of Maricopa County and the transport of PM 10 into the

Phoenix PM 10 nonattainment area .”7

The analysis in Sections II and V, specifically, the PM 10 time series graph, winds speed and direction measurements, the complex GIS maps, time

- lapse video evidence, NOAA dust storm and thund er storm wind observations, NWS advisories, and NWS station reports of reduced visibility, blowing dust, haze, and dust, sufficiently establishes that ther e was a clear causal relationship between uncontrollable emissions generated from thunderstorm outflow winds and the exceedance s measured at monitors

identified in Table 2 of this document.

Table 5 : Documentation of CCR

Exceedance Date Demonstration Cita tion Quality of Evidence Criterion Met?
September 11, 2011 Section II: p. 4

- 15, Section V: p. 27

- 42, App. D, App. E Sufficient Yes September 12, 2011 Section II: p. 4

- 15, Section V: p. 43

- 63, App. D, App. E Sufficient Yes

Affects Air Quality (AAQ)

ADEQ stated that based on the information presented in the demonstrations for both the CCR and HF requirements, “we can reasonably conclude that the event[s] in question affected air quality.” ADEQ's summary regarding the CCR and HF requirements sufficient ly establishes that the event affected air quality.

Table 6 : Documentation of AAQ

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
September 11, 2011 Section VII: p. 66 Sufficient Yes September 12, 2011 Section VII: p. 66 Sufficient Yes

Natural Event

ADEQ stated that based on the documentation for both the nRCP and CCR requirements, “ events shown

to cause these exceedances were emissions of PM 10 driven by high winds caused by thunderstorm activity and related outflow boundaries on September 11 & 12, 2011 ” and that “the events therefore qualify as a natural events.” ADEQ's summary regarding the CCR and HF requirements sufficiently

establishes that the event was a natural event.

Table 7 : Documentation of Natural Event

E xceedance Date Demonstration Citation Quality of Evidence Criterion Met?
September 11, 2011 Section VII: p. 66

- 67 Sufficient Yes September 12, 2011 Section VII: p. 66

- 67 Sufficient Yes

No Exceedance or Violation But For the Event (NEBF)

ADEQ provided a summary of the analysis and information regarding the nRCP and CCR requirements

and stated that “ t he body of evidence presented in this submittal provides no alternative that could tie the exceedances to any other causal source but transpor ted and re

- entrained PM 10 generated from thunderstorm outflows, confirming that there would have been no exceedances but for the presence of

these uncontrollable natural events .” ADEQ’s summary regarding the nRCP and CCR requirements sufficiently establish es that the NEBF criterion has been met.8

Table 8 : Documentation of NEBF

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
September 11, 2011 Section VI: p. 65 Sufficient Yes September 12, 2011 Section VI: p. 65 Sufficient Yes

Schedule and Procedural Requirements

In addition to technical demonstration requirements, 40 CFR § 50.14 (c) specifies the schedule and procedural requirements an air agency must follow to request data exclusion. Table 9 outlines EPA’s

evaluation of these requirements.

Table 9 : Schedules and Procedural Criteria

Reference Demonstration

Citation Criterion Met? Did the State provide prompt public

notification of the event? 40 CFR § 50.14 (c)(1)(i) Section I: p.1 App. B Yes

Were flags and initial description placed on the data by July 1 st of the following year? 40 CFR § 50.14 (c)(2)(iii) Section I: p. 1

- 2 Yes

Was the demonstration submitted within 3 years of the end of the quarter in which the event occurred and 12 months prior to the date that any regulatory decision must be made by EPA? 40 CFR § 50.14 (c)(3)(i) February 13

, 2013 letter 4 Yes

Was the public comment process followed

and documented? 40 CFR § 50.14 (c)(3)(v) Section I: p. 2 App. D 5 Yes

Conclusion

EPA has reviewed documentation provided by ADEQ to support claims that dust emissions generated by monsoonal thunderstorm high winds were transported into the Phoenix PM 10 nonattainment area from areas in Pinal County and caused exceedances of the 24

- hour PM 10 NAAQS at the locations

out lined in Table 2 on September 11 & 12, 2011 . EPA has determined that the flagged exceedances at

these locations on th ese day s meet the defin ition of an exceptional event: the exceedances affected air quality, were not reasonably controllable or preventable , and meet the definition of a natural event

. In

addition to transport into the area, information pertaining to the controls implemented within the nonattainment area, the spatial extent of elevated PM 10 concentrations measured in the area, and the wind sp eeds associated with the events provide sufficient evidence to conclude that the events were not reasonably controllable or preventable. Furthermore, EPA has determined that there was a clear causal relationship between the events and the measured exceedan ces, there would have been no exceedances but for the events, and the measured exceedances were in excess of normal historical fluctuations.

4 See letter from Eric Massey, Director, Air Quality Division, ADEQ

, to Deborah Jordan, Director, U.S. EPA Region IX Air Division, dated February 13, 2013.

5 A copy of the affidavit was not included in App. D, as stated in Section I of the final demonstration, but was submitted to EPA as part of the February 13, 2013 submission.9 

### Event Day: June 16, 2012

Table 10 : EPA PM 10 Exceedance Summary

Exceedance Date Monitor /Site Name AQS ID 24

- hour Avg. ( μ g/m 3 )

June 16, 2012 Buckeye 04

- 013

- 4011

- 1 202 Durango Complex 04

- 013

- 9812

- 1 186 Dysart 04

- 013

- 4010

- 1 167 Higley 04

- 013

- 4006

- 1 194

South Phoenix 04

- 013

- 4003

- 1 165

West 43 rd 04

- 013

- 4009

- 1 211

West Phoenix 04

- 013

- 0019

- 1 189

Not Reasonably Controllable or Preventable (nRCP)

In addressing reasonable controls, ADEQ provided detailed information on the current set of required

controls in the Phoenix PM 10 nonattainment area, including information on rule implementation, rule

effectiv eness, compliance and enforcement, real

- time monitoring alert systems and public notification activities that occurred on the event days. ADEQ stated, “BACM

- approved control measures on significant anthropogenic sources were in place and enforced during th e events, and pro

- active tracking and response to the events by regulatory agencies and local governments confirmed the uncontrollable nature of the dust emissions; therefore, these pre

- existing/prior approved required controls are adequate for meeting the requirements of an exceptional event and should be considered ‘reasonable’ for these purposes.”

ADEQ provided documentation showing that sustained wind speeds associated with these events were above 25 mph in multiple locations throughout the Phoenix PM 10 nonattainment area and Pinal County. For example, maximum sustained wind speeds of 29 mph with gusts of 39 mph , and 3 2 mph with gusts

of 4 6 mph , and 30 mph with gusts of 37 were measured at Williams Gateway Airport, Casa Grande Municipal Airport, and Falcon Field Airport, respectively.

ADEQ further explained that “ despite the deployment of comprehensive control measures and sophisticated response programs and a few localized, low

- impact violations of the dust control rules, high wind conditions a ssociated with thunderstorms and thunderstorm outflows brought high

concentrations of PM 10 emissions into, and also overwhelmed controls within, the Phoenix PM 10 nonattainment area. Strong thunderstorm outflows with sustained winds ranging from 20

- 30 mph, and even greater speeds nearest the source regions, described in Section V, were enough to overwhelm all

available efforts to limit PM 10 concentrations from the event. The fact that these were natural events involving strong thunderstorm outflow winds that transported PM 10 emissions into Maricopa County, with a majority of the PM 10 emissions recorded by Maricopa County area monitors coming from sources

outside of the Phoenix PM 10 nonattainment area, provides strong evidence that the events and

exceedances o f June 16, 2012, recorded within the Phoenix PM 10 nonattainment area, were not reasonably controllable or preventable .”

Section V of ADEQ’s documentation included further analysis of the event that supports the PM 10 transport described above. This analysis indicates that monitors in the Phoenix PM 10 nonattainment area were affected by PM 10 transport from outside the nonattainment area, with the main source areas located

to the south and southeast of the nonattainment area. Some of these source areas are located in Pinal County

, portions of which were recently designated as a moderate nonattainment area (West Pinal) for10

the 1987 24

- hour PM 10 NAAQS (77 FR 32024, May 31, 2012). Currently, the state is undergoing the

appr opriate process of developing a state implementation plan (SIP), due January 2, 2014, that provides

for attainment of the PM 10 standard as expeditiously as practicable but no later than the end of the sixth calendar year after redesignation. The SIP develo pment process includes the requirement to identify and implement reasonably available control measures for the area. In addition to transport, information pertaining to the controls implemented within the nonattainment area, the spatial extent of elevated PM 10 concentrations throughout the area and the wind speeds associated with the event sufficiently establishes

that the event was not reasonably controllable or preventable.

Table 11 : Documentation of nRCP

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?

June 16, 2012 Section IV: p.18

- 24, Section V: p. 25

- 34, App. E Sufficient Yes

Historical Fluctuations (HF)

To demonstrate that this requirement was met, ADEQ provided 5

- year time series plots of both PM 10 daily maximum hourly averages and PM 10 24

- hour averages and stated that these figures show that “event that occurred on June 16, 2012, resulted in one of the top 12 highest 24

- hour average PM 10 concentrations seen in the last five

- plus years.” ADEQ's analysis sufficient ly establishes that the 24

- hour

PM 10 concentrations measured on June 16, 2012

, were in excess of normal historical fluctuations.

Table 12 : Documentation of HF

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?

June 16, 2012 Section III: p. 14

- 17, App. A Sufficient Yes

Clear Causal Relationship (CCR)

Section II of ADEQ’s demonstration included a comprehensive conceptual model of the events, including a general overview of the geographic setting of the monitors, and climate information. The conceptual model also included a very detailed discussion of the event that occurred on June 16, 2012

, and a time series graph for the event that included hourly PM 10 concentrations for monitors in the

Phoenix PM 10 nonattainment area.

Se ction V of the demonstration included satellite imagery, time

- lapse video evidence, a time series graph for the event that contained hourly PM 10 concentrations from monitors in the Phoenix PM 10 nonattainment area, visibility and sustained wind speed from P hoenix Sky Harbor International Airport, and sustained wind speed from Williams Gateway Airport. The CCR analysis also included a time series graph that contained PM 10 concentrations from monitors in Pinal County, visibility, and sustained wind speed from Casa Grande Municipal Airport , and the raw data tables for numerous NWS stations in Maricopa and Pinal Counties . These data show the spatial and temporal representation of the event as it moves throughout Maricopa and Pinal Counties. T ime

- lapse video of th e event was included and can be found at the following location:

 South Mountain: http://www.phoenixvis.net/videos/mpeg4/SOMT_06162012.mp4

While not included in the demonstration, it is important to note that NOAA’s National Climatic Data
Center Storm events database included dust storm observations on June 16, 2012

, at 4:30 PM (central deserts) and 5:09 PM (greater Phoenix area). The timing of these dust storm reports for this event i s11

consistent with the issuance of a NWS Significant Weather Advisory for the period of 4:24 PM to 6:00 PM, NWS Dust Storm Warning for the period of 4:30 PM to 7:00 PM, the observed increased PM 10 concentrations in the area, increased wind speed, reduced vi sibility, and NWS station reports of blowing dust (BLDU), haze (HZ), and dust storms (DS).

ADEQ stated that the evidence presented shows a clear causal relationship “ between the emissions generated by uncontrollable natural events and the exceedances meas ured at the monitors. ” ADEQ

further stated that “ the satellite images, time series graphs, and meteorological data tables provided in this section show the temporal progression of the dust events from the development of the thunderstorms, to the increase i n wind speeds, and to the rise in PM 10 concentrations. The combination

of the PM 10 and wind data from Maricopa and Pinal counties shows the transport of particulate matter from the south through Pinal County and into the Phoenix PM 10 nonattainment area. Th is information supports the conclusion that the events were primarily caused by windblown dust from emission sources outside of Maricopa County and the transport of PM 10 into the Phoenix PM 10 nonattainment area .”

The analysis in Sections II and V, specif ically, the PM 10 time series graph, winds speed and direction measurements, time

- lapse video evidence, NOAA dust storm observations, NWS advisories, and NWS station reports of reduced visibility, blowing dust, haze, and dust storms, sufficiently establishe s that there was a clear causal relationship between uncontrollable emissions generated from thunderstorm

outflow winds and the exceedance s measured at the monitors identified in Table 10 of this document

.

Table 13 : Documentation of CCR

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?

June 16, 2012 Section V: p. 25

- 34, App. D, App. E Sufficient Yes

Affects Air Quality (AAQ)

ADEQ stated that based on the information presented in the demonstrations, “we can reasonably

conclude that the event in question affected air quality

. ” ADEQ's summary regarding the CCR and HF requirements sufficiently establishes that the event affected air quality.

Table 14 : Documentation of AAQ

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?

June 16, 2012 Section VII: p. 36 Sufficient Yes

Natural Event

ADEQ stated that based on the documentation for both the nRCP and CCR requirements, “events shown

to cause these exceedances were emissions of PM 10 driven by high winds caused by thunderstorm activity and related outflow boundary on June 16, 2012” and that “the events therefore qualify as natural events.” ADEQ's summary regarding the CCR and HF requirements sufficiently establishes that the

event was a natural event.

Tab le 15 : Documentation of Natural Event

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?

June 16, 2012 Section VII: p. 36 Sufficient Yes

No Exceedance or Violation But For the Event (NEBF)12

ADEQ provided a summary of the analysis and information regarding the nRCP and CCR requirements and stated that “the body of evidence presented in this submittal provides no alternative that could tie the exceedances of June 16, 2012, to any other causal s ource but transported and re

- entrained PM 10 generated from thunderstorm outflows, confirming that there would have been no exceedances but for the presence of these uncontrollable natural events.” ADEQ’s summary regarding the nRCP and CCR requirements suff

iciently establishes that the NEBF criterion has been met.

Table 16 : Documentation of NEBF

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?

June 16, 2012 Section VI: p.35 Sufficient Yes

Schedule and Procedural Requirements

In addition to technical demonstration requirements, 40 CFR §50.14 (c) specifies the schedule and procedural requirements an air agency must follow to request data exclusion. Table 17 outlines EPA’s evaluation of these requirements.

Table 17: Schedules an d Procedural Criteria

Reference Demonstration

Citation Criterion Met? Did the State provide prompt public

notification of the event? 40 CFR § 50.14 (c)(1)(i) Section I: p.1, App. B Yes

Were flags and initial description placed on the data by July 1 st of the following year? 40 CFR § 50.14 (c)(2)(iii) Section I: p.1

- 2 Yes

Was the demonstration submitted within 3 years of the end of the quarter in which the event occurred and 12 months prior to the date that any regulatory decision must be made by EPA? 40 CFR § 50.14 (c)(3)(i) February 13,

2013 letter 6 Yes

Was the public comment process followed

and documented? 40 CFR § 50.14 (c)(3)(v) Section I: p.2, App. C 7 Yes

6 See letter from Eric Massey, Director, Air Quality Division, ADEQ

, to Deborah Jordan, Director, U.S. EPA Region IX Air Division, dated February 13, 2013.

7 A copy of the affidavit was not included in App. C, as stated in Section I of the final demonstration, but was submitted to E PA as part of the February 13, 2013 submission.13

Conclusion

EPA has reviewed documentation provided by ADEQ to support claims that dust emissions generated by monsoonal thunderstorm high winds were transported into the Phoenix PM 10 nonattainment area from areas in Pinal County and caused exceedances of the 24

- hour PM 10 NAAQS at the locations

outlined in Table 10 on June 16, 2012. EPA has determined that the flagged exceedances at these locations on this day meet the definition of an exceptional event : the exceedances affected air quality, were not reasonably controllable or preventable, and meet the definition of a natural event. In addition to transport into the area, information pertaining to the controls implemented within the nonattainment area, the spatial extent of elevated PM 10 concentrations measured in the area, and the wind speeds associated with the event provide s suffic ient evidence to conclude that the event was not reasonably controllable or preventable. Furthermore, EPA has determined that there was a clear causal relationship between the event and the measured exceedances, there would have been no exceedance s but for the event, and the measured exceedances were in excess of normal historical fluctuations.14 

### Event Day: Ju ne 27, 2012

Table 18 : EPA PM 10 Exceedance Summary

Exceedance Date Monitor /Site Name AQS ID 24

- hour Avg. ( μ g/m 3 )

June 27, 2012 Central Phoenix 04

- 013

- 3002

- 4 340 Durango Complex 04

- 013

- 9812

- 1 221

Glendale 04

- 013

- 2001

- 1 337

Greenwood 04

- 013

- 3010

- 1 323 Higley 04

- 013

- 4006

- 1 224 JLG Supersite 04

- 013

- 9997

- 3 344 JLG Supersite 04

- 013

- 9997

- 4 329

North Phoenix 04

- 013

- 1004

- 1 178

South Phoenix 04

- 013

- 4003

- 1 342 Tempe 04

- 013

- 4005

- 1 169

West 43 rd 04

- 013

- 4009

- 1 221

West Chandler 04

- 013

- 4004

- 1 220

Zuni Hills 04

- 013

- 4016

- 1 285

Not Reasonably Controllable or Preventable (nRCP)

In addressing reasonable controls, ADEQ provided detailed information on the current set of required

controls in the Phoenix PM 10 nonattainment area, including information on rule implementation, rule effectiveness, compliance and enforcement, real

- time monitoring alert systems an d public notification

activities that oc curred on the event days. ADEQ stated, “BACM

- approved control measures on significant anthropogenic sources were in place and enforced during the events, and pro

- active tracking and response to the events by regulato ry agencies and local governments confirmed the uncontrollable nature of the dust emissions; therefore, these pre

- existing/prior approved required controls are adequate for meeting the requirements of an exceptional event and should be considered ‘reasonab le’ for these purposes.”

ADEQ provided documentation showing that sustained wind speeds associated with these events were above 25 mph in multiple locations throughout the Phoenix PM 10 nonattainment area and Pinal County. For example, maximum sustained wi nd speeds of 38 mph with gusts of 45 mph, 34 mph with gusts of 47 mph, 31 mph with gusts of 39 mph , and 31 mph with gusts of 44 mph were measured at Chandler Municipal Airport, Williams Gateway Airport, Casa Grande Municipal Airport, and Phoenix Sky

Harbor

, respectively.

Section V of ADEQ’s documentation included further analysis of the event that supports the PM 10 transport described above. This analysis indicates that monitors in the Phoenix PM 10 nonattainment area were affected by PM 10 transport from o utside the nonattainment area, with the main source areas located

to the southeast of the nonattainment area. Some of these source areas are located in Pinal County

, portions of which were recently designated as a moderate nonattainment area (West Pinal) f or the 1987

24

- hour PM 10 NAAQS (77 FR 32024, May 31, 2012). Currently, the state is undergoing the appropriate process of developing a state implementation plan (SIP), due January 2, 2014, that provides for

attainment of the PM 10 standard as expeditiously as practicable but no later than the end of the sixth calendar year after redesignation. The SIP development process includes the requirement to identify and implement reasonably available control measures for the area. In addition to transport, informatio n pertaining to the controls implemented within the nonattainment area, the spatial extent of elevated PM 1015

concentrations throughout the area and the wind speeds associated with the event sufficiently establishes

that the event was not reasonably controll able or preventable.

Table 19 : Documentation of nRCP

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?

June 27, 2012 Section IV: p. 18

- 25, Section V: p. 26

- 35, App. E Sufficient Yes

Historical Fluctuations (HF)

To demonstrate that this requirement was met, ADEQ provided 5

- year time series plots of both PM 10 daily maximum hourly averages and PM 10 24

- hour averages and stated that these figures show that the “event that occurred on June 27, 2012, resulted in one of the top 10 high est 24

- hour average PM 10 concentrations seen in the last five

- plus year s .” ADEQ's analysis sufficiently establishes that the 24

- hour

PM 10 concentrations measured on July 18, 2011

, were in excess of normal historical fluctuations.

Table 20 : Documentation of HF

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?

June 27, 2012 Section III: p. 14

- 17. App. A Sufficient Yes

Clear Causal Relationship (CCR)

Section II of ADEQ’s demonstration included a comprehensive conceptual model of the events, including a general overview of the geographic setting of the monitors, and climate information. The conceptual model also included a very detailed discussion of the event that occurred on June 27, 2012

, and a time series graph for the event that included hourly PM 10 concentrations for monitors in the

Phoenix PM 10 nonattainment area.

Section V of the demonstration included satellite imagery, time

- lapse video evidence, a time series graph for the event t hat contained hourly PM 10 concentrations from monitors in the Phoenix PM 10 nonattainment area, visibility and sustained wind speed from Phoenix Sky Harbor International Airport, and sustained wind speed from Williams Gateway Airport. The CCR analysis also included a time series graph that contained PM 10 concentrations from monitors in Pinal County, visibility, and sustained wind speed from Casa Grande Municipal Airport, and the raw data tables for numerous NWS stations in Maricopa and Pinal Counties. These data show the spatial and temporal representation of the event as it moves throughout Maricopa and Pinal Counties. T ime

- lapse video of the event was included and can be found at the following location:

 South Mountain: http://www.phoenixvis.net/videos/mpeg4/SOMT_06272012.mp4

 Superstition Mountains: http://www.phoenixvis.net/videos/mpeg4/SUPM_06272012.mp4

While not in cluded in the demonstration, it is important to note that NOAA’s National Climatic Data
Center Storm events database included dust storm observations on June 17, 2012

, at 6:00 PM (central deserts) and 6:40 PM (greater Phoenix area)

. The timing of these dus t storm reports for this event is consistent with the issuance of a NWS Blowing Dust Advisory for the period of 5:30 PM to 6:00 PM, NWS Severe Thunderstorm Warning for the period of 6:09 PM to 7:30 PM, NWS Significant Weather Advisory for the period of 6:5 8 PM to 8:15 PM, NWS Dust Storm Warning for the period of 6:02 PM to 9:00 PM, NWS preliminary local storm reports of dust storms, the observed increased PM 1016

concentrations in the area, increased wind speed, reduced visibility, and NWS station reports of b lowing dust , haze , dust , and dust storms (DS).

ADEQ stated that the evidence presented shows a clear causal relationship “between the emissions generated by uncontrollable natural events and the exceedances measured at the monitors .” ADEQ

further stated that “the satellite images, time series graphs, and meteorological data tables provided in this section show the temporal progression of the dust events from the development of the thunderstorms, to the increase in wind speeds, and to the rise in PM 10 concentrations. The combination

of the PM 10 and wind data from Maricopa and Pinal counties shows the transport of particulate matter from the south through Pinal County and into the Phoenix PM 10 nonattainment area. This information supports the conclusi on that the PM 10 exceedances observed on June 27, 2012, were the result of emissions entrained into the atmosphere by strong thunderstorm outflow boundary winds from source areas to the southeast, outside of the Phoenix PM 10 nonattainment area, and transpo rted into the Phoenix

PM 10 nonattainment area .”

The analysis in Sections II and V, specifically, the PM 10 time series graph, winds speed and direction measurements, time

- lapse video evidence, NOAA dust storm observations, NWS local storm reports,

NWS advi sories, and NWS station reports of reduced visibility, blowing dust, haze, dust, and dust storms, sufficiently establishes that there was a clear causal relationship between uncontrollable emissions generated from thunderstorm outflow winds and the exceeda nce s measured at monitors

identified in Table 18 of this document.

Table 21 : Documentation of CCR

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?

June 27, 2012 Section V: p. 26

- 35, App. D, App. E Sufficient Yes

Affects Air Quality (AAQ)

ADEQ stated that based on the information presented in the demonstrations for both the CCR and HF requirements, “ we can reasonably conclude that the event in question affected air quality

. ” ADEQ's summary regarding the CCR and HF requirement s sufficiently establishes that the event affected air quality.

Table 22 : Documentation of AAQ

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?

June 27, 2012 Section VII: p. 37 Sufficient Yes

Natural Event

ADEQ stated that based on the documentation for both the nRCP and CCR requirements, “the events

shown to cause these exceedances were emissions of PM 10 driven by high winds caused by thunderstorm activity and related outflow boundary on June 27, 2012” and that “the events therefore qualify as natural events.” ADEQ's summary regarding the CCR and HF requirements sufficiently

establishes that the event was a natural event.

Table 23 : Documentation of Natural Event

Exceedance Date Demonstration Citation Qualit y of Evidence Criterion Met?

June 27, 2012 Section VII: p. 37 Sufficient Yes17

No Exceedance or Violation But For the Event (NEBF)

ADEQ provided a summary of the analysis and information regarding the nRCP and CCR requirements

and stated that “ the body of evidence presented in this submittal provides no alternative that could tie the exceedances of June 27, 2012, to any other causal source but transported and re

- entrained PM 10 generated from thunderstorm outflows, confirming that there would hav e been no exceedances but for the presence of these uncontrollable natural events.” ADEQ’s summary regarding the nRCP and CCR requirements sufficiently establishes that the NEBF criterion has been met.

Table 24 : Documentation of NEBF

Exceedance Date Demo nstration Citation Quality of Evidence Criterion Met?

June 27, 2012 Section VI: p. 36 Sufficient Yes

Schedule and Procedural Requirements

In addition to technical demonstration requirements, 40 CFR §50.14 (c) specifies the schedule and procedural requirements an air agency must follow to request data exclusion. Table 25 outlines EPA’s evaluation of these requirements.

Table 25: Schedules and Procedural Criteria

Reference Demonstration

Citation Criterion Met? Did the State provide prompt public

notification of the event? 40 CFR § 50.14 (c)(1)(i) Section I: p. 1 App. B Yes

Were flags and initial description placed on the data by July 1 st of the following year? 40 CFR § 50.14 (c)(2)(iii) Section I: p 1

- 2 Yes

Was the demonstration submitted within 3 years of the end of the quarter in which the event occurred and 12 months prior to the date that any regulatory decision must be made by EPA? 40 CFR § 50.14 (c)(3)(i) February 13,

2013 letter 8 Yes

Was the public comment process followed

and documented? 40 CFR § 50.14 (c)(3)(v) Section I: p. 2 App. C Yes

8 See letter from Eric Massey, Director, Air Quality Division, ADEQ

, to Deborah Jordan, Director, U.S. EPA Region IX Air Division, dated February 13, 2013.18

Conclusion

EPA has reviewed documentation provided by ADEQ to support claims that dust emissions generated by monsoonal thunderstorm high winds were transported into the Phoenix PM 10 nonattainment area from areas in Pinal County and caused exceedances of the 24

- hour PM 10 NAAQS at the locations outlined in Table 18 on June 27, 2012. EPA has determined that the flagged exceedances at these locations on this day meet the definition of an exceptional event : the exceedances affected air quality, were not reasonably controllable or preventable, and meet the definition of a natural event

. In addition to transport into the area, information pertaining to the controls implemented within the nonattainment area, the spatial extent of elevated PM 10 concentrations measured in the area, and the wind speeds associated with the event provides suffic ient evidence to conclude that the event was not reasonably controllable or preventable. Furthermore, EPA has determined that there was a clear causal relationship between the event and the measured exceedances, there would have been no exceedance s but for the event, and the measured exceedances were in excess of normal historical fluctuations.19 

### Event Day: July 11 , 2012

Table 26 : EPA PM 10 Exceedance Summary

Exceedance Date Monitor /Site Name AQS ID 24

- hour Avg. ( μ g/m 3 )

July 11, 2012 Durango Complex 04

- 013

- 9812

- 1 217

Greenwood 04

- 013

- 3010

- 1 212

South Phoenix 04

- 013

- 4003

- 1 285

West 43 rd 04

- 013

- 4009

- 1 172

Not Reasonably Controllable or Preventable (nRCP)

In addressing reasonable controls, ADEQ provided detailed information on the current set of required

controls in the Phoenix PM 10 nonattainment area, including information on rule implementation, rule effectiveness, compliance and enforcement, real

- time monitoring alert systems and public notification

activities that occurre d on the event days. ADEQ stated, “BACM on significant anthropogenic sources were in place and enforced during the events, and pro

- active tracking and response to the events by regulatory agencies and local governments confirmed the uncontrollable nature o f the dust emissions; therefore, these pre

- existing/prior approved required controls are adequate for meeting the requirements of an exceptional event and should be considered ‘reasonable’ for these purposes .”

ADEQ provided documentation showing that sust ained wind speeds associated with these events were above 20 mph in multiple locations nearby and upwind of the exceeding monitoring stations throughout

the Phoenix PM 10 nonattainment area and above 25 mph in Pinal County. For example, maximum

sustained wi nd speeds of 23 mph with gusts of 33 mph, and 25 mph with gusts of 33 mph were measured at Phoenix Sky Harbor Airport and Casa Grande Municipal Airport, respectively.

ADEQ further explained that “ despite the deployment of comprehensive control measures a nd sophisticated response programs, high

- wind conditions associated with thunderstorms and thunderstorm outflows brought high concentrations of PM 10 emissions into, and also overwhelmed controls within, the

Phoenix PM 10 Nonattainment Area. Widespread thund erstorm outflows with sustained winds in excess of 20 mph with gusts over 30 mph were enough to overwhelm all available efforts to limit PM 10 concentrations during the event. The fact that these were natural events involving strong thunderstorm

outflow win ds that transported PM 10 emissions into and across the Phoenix area, with a majority of the

PM 10 emissions recorded by Phoenix area monitors coming from sources outside of the Phoenix PM 10 Nonattainment Area, provides strong evidence that the exceedances o f July 11, 2012

, recorded within

the Phoenix PM 10 Nonattainment Area were not reasonably controllable or preventable. ”

While ADEQ states that the majority of the PM 10 emissions were generated outside of the Phoenix PM 10 Nonattainment Area, ADEQ’s documentation included information on the event that indicates that

monitors in the Phoenix PM 10 nonattainment area may have been affected by PM 10 transport primarily

from within the nonattainment area , specifically, the areas in the southeastern po rtion of the

nonattainment area

. I nformation pertaining to the controls implemented within the nonattainment area, the spatial extent of elevated PM 10 concentrations throughout the area and the wind speeds associated with the event sufficiently establishes that the event was not reasonably controllable or preventable.

Table 27 : Documentation of nRCP

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
July 11, 2012 Section V: p 1

- 7, Section III: p. 1

- 7, App. A Sufficient Yes20

Historical Fluctuations (HF)

To demonstrate that this requirement was met, ADEQ provided 5

- year time series plots of both PM 10 daily maximum hourly averages and PM 10 24

- hour averages and stated that these figures show that “ the

PM 10 concentrations measured...on July 11, 2012, were among the highest 24

- hr averages...measured

over the five

- year period. ” ADEQ's analysis sufficiently establishes that the 24

- hour PM 10 concentrations measured on July 1 1 , 201 2

, were in excess of normal historic al fluctuations

.

Table 2 8 : Documentation of HF

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
July 11, 2012 Section IV: p. 1

- 2, App. C Sufficient Yes

Clear Causal Relationship (CCR)

Section II of ADEQ’s demonstration included a conceptual model of the events, including a general overview of the geographic setting of the monitors, and climate information. The conceptual model also

included a discussion of the event that occurred on Jul y 11, 2012

, and general map of the region of the thunderstorm development in relation to the Phoenix PM 10 nonattainment area.

Section III, Appendix A, and Appendix B of the demonstration included satellite imagery visibility photos, time

- lapse video evidence, a map of the Phoenix area that displays wind speed and direction at the peak hour of PM 10 concentrations during the event, a map with radar base velocity data that identifies thunderstorm outflow boundaries, a time series of ho urly PM 10 concentrations from PM 10 monitors in Pinal County, a time series graph that shows hourly PM 10 concentrations from monitors in

the Phoenix PM 10 nonattainment area and visibility from Phoenix Sky Harbor Airport, and the raw data

tables for numerous NWS stations in Maricopa and Pinal Counties. These data show the spatial and temporal representation of the event as it moves throughout Maricopa and Pinal Counties. ADEQ also provided a discussion for every map that described the conditions at that time. T ime

- lapse videos of the

event can be found at the following location :

 South Mountain: http://www.phoenixvis.net/videos/mpeg4/SOMT_07112012.mp4

The timing of the event is consist ent with the issuance of a NWS Blowing Dust Advisory for the period

of 8 : 3 0 PM to 12 :00 A M, NWS Significant Weather Advisory for the period of 10:35 PM to 11:15 PM,

the observed increased PM 10 concentrations in the area, increased wind speed, reduced visib ility, and NWS station reports of thunderstorms, haze, and dust

.

ADEQ stated that the evidence presented shows a clear causal relationship “ between the windblown dust

and the PM 10 exceedances measured at four Phoenix

- area monitors on July 11, 2012. The r adar and wind data shown in this section illustrate the spatial and temporal extent of the dust storm as it moved through the Phoenix area. In addition, the time

- series plots of air quality and meteorological data found in this section and in Appendix A sh ow that the sharp increase in PM 10 concentrations coincided with the strong wind speeds and wind gusts .” The analysis in Sections II, III, Appendix A , and Appendix B, specifically, the PM 10 time series graphs, winds speed and direction measurements, maps, time

- lapse video evidence, NWS advisories, and NWS station reports of reduced visibility, thunderstorms, haze

, and dust, s ufficiently establishes that there was a clear causal relationship between uncontrollable emissions generated from thunderstorm outflow

winds and the exceedance measured at the monitors identified in Table 26 of this document.21

Table 2 9 : Documentation of CCR

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
July 11, 2012 Section II: p. 1

- 9 Section IV: p. 1

- 2, App. C, B, & D Sufficient Yes

Affects Air Quality (AAQ)

ADEQ stated that based on the information presented in the demonstrations for both the CCR and HF requirements, “we can reasonably conclude that the event in question affected air quality.” ADEQ's summary regarding the CCR and HF requirements sufficiently establishes that the event affected air quality.

Table 30 : Documentation of AAQ

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
July 11, 2012 Section VII: p. 1 Sufficient Yes

Natural Event

ADEQ stated that based on the documentation for both the nRCP and CCR requirements, “ PM 10 exceedances on July 11, 2012, were shown to be caused by PM 10 transported into the Phoenix area by

thunderstorm outflow ” and that “the event therefore qualifies as a natural event.” ADEQ's summary regarding the CCR and HF requirements sufficiently establishes that the event was a natural event.

Table 31 : Documentation of Natural Event

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
July 11, 2012 Section VII: p. 1 Sufficient Yes

No Exceedance or Violation But For the Event (NEBF)

Table 32 : Documentation of NEBF

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
July 11, 2012 Section VI : p. 1 Sufficient Yes

ADEQ provided a summary of the analysis and information regarding the nRCP and CCR requirements

and stated that “ t he weight of evidence presented in this submittal provides no alternative that could tie

the exceedance of July 11, 2012, to any causal source other than PM 10 transported by thunderstorm outflow, confirming that there would have been no exceedance but for the presence of th is

uncontrollable natural event .” ADEQ’s summary regarding the nRCP and CCR requirements

suff iciently establishes that the NEBF criterion has been met.

Schedule and Procedural Requirements

In addition to technical demonstration requirements, 40 CFR §50.14 (c) specifies the schedule and procedural requirements an air agency must follow to request data exclusion. Table 33 outlines EPA’s evaluation of these requirements.22

Table 33 : Schedules and Procedural Criteria

Reference Demonstration

Citation Criterion Met? Did the State provide prompt public

notification of the event? 40 CFR § 50.14 (c)(1)(i) Section I, p. 1 App. D Yes

Were flags and initial description placed on the data by July 1 st of the following year? 40 CFR § 50.14 (c)(2)(iii) Section I, p. 1 Yes

Was the demonstration submitted within 3 years of the end of the quarter in which the event occurred and 12 months prior to the date that any regulatory decision must be made by EPA? 40 CFR § 50.14 (c)(3)(i) February 13,

2013 letter 9 Yes

Was the public comment process followed

and documented? 40 CFR § 50.14 (c)(3)(v) Section I, p. 1

- 2 App. E 10 Yes

Conclusion

EPA has reviewed documentation provided by ADEQ to support claims that dust emissions generated by monsoonal thunderstorm high winds were transported into the Phoenix PM 10 nonattainment area from areas in Pinal County and caused exceedances of the 24

- hour PM 10 NAAQS at the locations outlined in Table 26 on July 11, 2012. EPA has determined that the flagged exceedances at these locations on this day meet the definition of an exceptional event: the exceedances affected air quality, were not reasonably controllable or preventable, and meet the definition of a natural event. Specifically,

EPA has determined that the event was not reasonably controllable and preventable due to high wind

conditions that overwhelmed reasonable controls within the Phoenix PM 10 nonattainment area.

I nformation pertaining to the controls implemented within the nonattainment area, the spatia l extent of

elevated PM 10 concentrations measured in the area, and the wind speeds associated with the event provide sufficient evidence to conclude that the event was not reasonably controllable or preventable. Furthermore, EPA has determined that there w as a clear causal relationship between the event and the measured exceedances, there would have been no exceedance but for the event, and the measured

exceedances were in excess of normal historical fluctuations.

9 See letter from Eric Massey, Director, Air Quality Division, ADEQ

, to Deborah Jordan, Director, U.S. EPA Region IX Air Division, dated February 13, 2013.

10 A copy of the af

fidavit was not included in App. E, as stated in Section I of the final demonstration, but was submitted to EPA as part of the February 13, 2013 submission.23 

### Event Day: August 11, 2012

Table 34 : EPA PM 10 Exceedance Summary

Exceedance Date Monitor /Site Name AQS ID 24

- hour Avg. ( μ g/m 3 )

August 11, 2012 Higley 04

- 013

- 4006

- 1 159

West Chandler 04

- 013

- 4004

- 1 219

Not Reasonably Controllable or Preventable (nRCP)

In addressing reasonable controls, ADEQ provided detailed information on the current set of required

controls in the Phoenix PM 10 nonattainment area, including information on rule implementation, rule effectiveness, compliance and enforcement, real

- time monitoring alert systems an d public notification activities that occurred on the event days. ADEQ stated, “BACM on significant anthropogen ic sources were in place and enforced during the events, and proactive tracking and response to the events by regulatory agencies and local gover nments confirmed the uncontrollable nature of the dust emissions; therefore, these pre

- existing prior

- approved required controls are adequate for meeting the requirements of an exceptional event and s hould be considered ‘reasonable’ for these purposes

. ”

ADEQ provided documentation showing that sustained wind speeds associated with these events were above 25 mph in multiple locations throughout the Phoenix PM 10 nonattainment area and Pinal County. For example, maximum sustained wind speeds of 32 mph with gusts of 41 mph, and 25 mph with gusts of 36 mph were measured at Chandler Municipal Airport, and Casa Grande Municipal Airport, respectively.

ADEQ further ex plained that “despite the deployment of comprehensive control measures and sophisticated response programs, high wind conditions associated with the thunderstorm outflow transported high concentrations of PM 10 into, and also overwhelmed controls within, th e Phoenix PM 10 nonattainment area. Widespread sustained winds in excess of 20 mph with gusts over 30 mph were strong enough to overwhelm available efforts to limit PM 10 concentrations during the event. The fact that these were natural events involving stro ng winds that transported PM 10 emissions into and across Maricopa County, with a majority of the PM 10 emissions recorded by Maricopa County area monitors coming from sources outside of the Phoenix PM 10 nonattainment area, provides strong evidence that the exceedances of August 11, 2012, recorded within the Phoenix PM 10 nonattainment area were not reasonably controllable or preventable.”

Section III of ADEQ’s documentation included a complex GIS analysis of the event that supports the

PM 10 transport describ ed above. This analysis indicates that monitors in the Phoenix PM 10 nonattainment area were affected by PM 10 transport from outside the nonattainment area, with the main

source areas located to the south of the nonattainment area. Some of these source area s are located in Pinal County

, portions of which were recently designated as a moderate nonattainment area (West Pinal)

for the 1987 24

- hour PM 10 NAAQS (77 FR 32024, May 31, 2012). Currently, the state is undergoing the appropriate process of developing a state implementation plan (SIP), due January 2, 2014, that provides

for attainment of the PM 10 standard as expeditiously as practicable but no later than the end of the sixth calendar year after redesignation. The SIP development process includes the requi rement to identify and implement reasonably available control measures for the area. In addition to transport, information pertaining to the controls implemented within the nonattainment area, the spatial extent of elevated PM 10 concentrations throughout t he area, and the wind speeds associated with the event sufficiently establishes that the event was not reasonably controllable or preventable.24

Table 35 : Documentation of nRCP

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
August 11, 2012 Section V: p. 1

- 8, Section III: p. 1

- 10, App. A Sufficient Yes

Historical Fluctuations (HF)

To demonstrate that this requirement was met, ADEQ provided 5

- year time series plots of both PM 10 daily maximum hourly averages and PM 10 24

- hour averages and stated that these figures show that “the

PM 10 concentrations measured...on August 11, 2012, resulted in some of the highest 24

- hr

averages... measured over the five

- year period .” ADEQ's analysis sufficiently establishes that the

24

- hour PM 10 concentrations measured on August 11, 2012

, were in excess of normal historical

fluctuations.

Table 36 : Documentation of HF

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
August 11, 2012 Section IV: p. 1

- 2, App. C Sufficient Yes

Clear Causal Relationship (CCR)

Section II of ADEQ’s demonstration included a conceptual model of the events, including a general overview of the geographic setting of the monitors, and climate information. The conceptual model also included a discussion of the event that occurred on August 11, 2012

, and general map of the region of the thunderstorm development in relation to the Phoenix PM 10 nonattainment area.

Section III and Appendix A of the demonstration included satellite imag ery visibility photos

, time

- lapse video evidence, the raw data tables for numerous NWS stations in Maricopa and Pinal Counties, and a number of time series graphs that include hourly PM 10 data from Pinal and Maricopa Counties, wind speed, and visibility fr om Chandler Airport. ADEQ also included a detailed GIS analysis with PM 10 concentrations, sustained wind speeds, wind gusts, wind direction, base velocity radar, and visibility to track the transport of PM 10 throughout the region. These data show the spati al and temporal representation of the event as it moves throughout Maricopa and Pinal Counties. ADEQ also provided a discussion for every map that described the conditions at that time. T ime

- lapse videos of the event can be found at the following locations :

 South Mountain: http://www.phoenixvis.net/videos/mpeg4/SOMT_08112012.mp4

 Superstition Mountains: http://www.pho enixvis.net/videos/mpeg4/SUPM_08112012.mp4

While not included in the demonstration, it is important to note that NOAA’s National Climatic Data

Center Storm events database included dust storm observations on August 11 , 201 2

, at 4 : 30 PM (central deserts) a nd 5 :00 PM (greater Phoenix area). The timing of these dust storm reports for this event is consistent with the issuance of a NWS Dust Storm Warning for the period of 4 : 00 PM to 6 :00 PM, NWS preliminary local storm reports of dust storms, the observed increased PM 10 concentrations in the area, increased wind speed, reduced visibility, and NWS station reports of blowing dust and dust storms.

ADEQ stated that the evidence presented shows a clear causal relationship “ between the windblown dust

and the PM 10 exceedances measured in the Phoenix PM 10 nonattainment area on August 11, 2012.” ADEQ further stated that “ t he wind, visibility, PM 10 , and radar data shown in this section illustrate the spatial and temporal extent of the dust storm as it moved through Maricopa County. In addition,25

meteorological data tables found in Appendix A show that the sharp increase in PM 10 concentrations coincided with gusty winds, low visibilities, and airport observer reports of blowing dust. The fact that

PM 10 concentrations i n Pinal County peaked prior to PM 10 concentrations peaking in Maricopa County illustrates that a vast majority of the dust that impacted the nonattainment area monitors originated outside of Maricopa County and was transported into the Phoenix PM 10 nonatta inment area .”

The analysis in Sections II, III, and Appendix A specifically, the PM 10 time series graph s , winds speed and direction measurements, GIS maps, time

- lapse video evidence, NOAA dust storm observations, NWS advisories, NWS preliminary local sto rm reports , and NWS station reports of reduced visibility, blowing dust and dust storms

, s ufficiently establishes that there was a clear causal relationship between uncontrollable emissions generated from thunderstorm outflow winds and the exceedance s mea sured at

the West Chandler and Higley monitors

. Furthermore, while exceedances occurring at only a few monitors in the network are inherently more complex,the GIS analysis (Figures 3

- 7 through 3

- 10 in ADEQ’s demonstration) indicates higher wind speeds were measured in the eastern portion of the nonattainment area influenced the spatial extent of PM 10 throughout the Phoenix PM 10 nonattainment area and was likely responsible for the exceedances at the West Chandler and Higley monitors.

Table 37 : Documentation of CCR

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
August 11, 2012 Section III: p. 1

- 10, App. A, App. B, App. D Sufficient Yes

Affects Air Quality (AAQ)

ADEQ stated that based on the information presented in the demonstrations for both the CCR and HF requirements, “we can reasonably conclude that the event in question affected air quality.” ADEQ's summary regarding the CCR and HF requirements sufficiently establishes that the event affected air quality.

Table 38 : Documentation of AAQ

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
August 11, 2012 Section VII: p. 1 Sufficient Yes

Natural Event

ADEQ stated that based on the documentation for both the nRCP and CCR requirements, “ PM 10 exceedances in the Phoenix area on August 11, 2012, were shown to be caused by transport of PM 10 into the Phoenix area from gusty winds associated with thunderstorm outflow ” and that “the event therefore qualifies as a natural event.” ADEQ's summary regarding the CCR and HF requirements sufficiently

establishes that the event was a natural event.

Table 39 : Documentation of Natural Event

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
August 11, 2012 Section VII: p. 1 Section VII: p. 1 Yes26

No Exceedance or Violation But For the Event (NEBF)

ADEQ provided a summary of the analysis and information regarding the nRCP and CCR requirements

and stated that “ t he weight of evidence presented in this submittal provides no alternative that could tie the exceedance of August 11, 2012, to any causal source other than PM 10 transported by gusty winds due to thunderstorm outflow, confirming that there would have been no exceedance but for the presence

of th is uncontrollable natural event .” ADEQ’s summary regarding the nRCP and CCR requirements sufficiently establishes that th e NEBF criterion has been met.

Table 40 : Documentation of NEBF

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
August 11, 2012 Section VI: p.1 Sufficient Yes

Schedule and Procedural Requirements

In addition to technical demonstration requirements, 40 CFR §50.14 (c) specifies the schedule and procedural requirements an air agency must follow to request data exclusion. Table 41 outlines EPA’s evaluation of these requirements.

Table 41: Schedules an d Procedural Criteria

Reference Demonstration

Citation Criterion Met? Did the State provide prompt public

notification of the event? 40 CFR § 50.14 (c)(1)(i) Section I: p.2 App. D Yes

Were flags and initial description placed on the data by July 1 st of the following year? 40 CFR § 50.14 (c)(2)(iii) Section I: p.2 Yes

Was the demonstration submitted within 3 years of the end of the quarter in which the event occurred and 12 months prior to the date that any regulatory decision must be made by EPA? 40 CFR § 50.14 (c)(3)(i) February 13,

2013 letter 11 Yes

Was the public comment process followed

and documented? 40 CFR § 50.14 (c)(3)(v) Section I: p.2

- 3 App. E 12 Yes

11 See letter from Eric Massey, Director, Air Quality Division, ADEQ

, to Deborah Jordan, Director, U .S. EPA Region IX Air Division,

dated February 13, 2013.

12 A copy of the affidavit was not included in App. E, as stated in Section I of the final demonstration, but was submitted to E PA as part of the February 13, 2013 submission.27

Conclusion

EPA has reviewed documentation provided by ADEQ to support claims that dust emissions generated by monsoonal thunderstorm high winds were transported into the Phoenix PM 10 nonattainment area from areas in Pinal County and caused exceedances of the 24

- hour PM 10 NAAQS at the locations outlined in Table 34 on August 11, 201 2. EPA has determined that the flagged exceedances at these locations on this day meet the definition of an exceptional event : the exceedances affected air quality, were not reasonably controllable or preventable, and meet the definition of a natural event In addition to transport into the area, information pertaining to the controls implemented within the nonattainment area, the spatial extent of elevated PM 10 concentrations measured in the area, and the wind speeds

associated with the event provide suffici ent evidence to conclude that the event was not reasonably controllable or preventable. Furthermore, EPA has determined that there was a clear causal relationship between the event and the measured exceedances, there would have been no exceedance s but for the event, and the measured exceedances were in excess of normal historical fluctuations.28 

### Event Day: August 14, 2012

Table 42 : EPA PM 10 Exceedance Summary

Exceedance Date Monitor /Site Name AQS ID 24

- hour Avg. ( μ g/m 3 )

August 14, 2012 Durango Complex 04

- 013

- 9812

- 1 179

West 43 rd 04

- 013

- 4009

- 1 254

Not Reasonably Controllable or Preventable (nRCP)

In addressing reasonable controls, ADEQ provided detailed information on the current set of required

controls in the Phoenix PM 10 nonattainment area, including information on rule implementation, rule effectiveness, compliance and enforcement, real

- time monitoring alert systems and public notification activities that occurred on the event days. ADEQ stated, “BACM on significant anth ropogenic sources were in place and enforced during the events, and proactive tracking and response to the events by regulatory agencies and local governments confirmed the uncontrollable nature of the dust emissions; therefore, these pre

- existing prior

- ap proved required controls are adequate for meeting the requirements of an exceptional event and should be considered ‘reasonable’ for these purposes.”

ADEQ provided documentation showing that sustained wind speeds associated with these events were

abov e 25 mph in multiple locations throughout the Phoenix PM 10 nonattainment area and Pinal County. For example, maximum sustained wind speeds of 34 mph with gusts of 41 mph, and 31 mph with gusts of 40 mph were measured at Luke Air Force Base, and Casa Grande Municipal Airport, respectively. Sustained wind speeds of 23 mph with gusts of 33 mph were also measured at Phoenix Sky Harbor Airport.

ADEQ further explained that “despite the deployment of comprehensive control measures and sophisticated response prog rams, high wind conditions associated with the thunderstorm outflow transported high concentrations of PM 10 into, and also overwhelmed controls within, the Phoenix PM 10 nonattainment area. Widespread sustained winds in excess of 20 mph with gusts over 40 m ph were strong enough to overwhelm available efforts to limit PM 10 concentrations during the event. The fact that these were natural events involving strong winds that transported PM 10 emissions into and across Maricopa County, with a majority of the PM 10 emissions recorded by Maricopa County area monitors coming from sources outside of the Phoenix PM 10 nonattainment area, provides strong evidence that the exceedances of August 1 4 , 2012, recorded within the Phoenix PM 10 nonattainment area were not

reasonabl y controllable or preventable.”

Section III of ADEQ’s documentation included a complex GIS analysis of the event that supports the

PM 10 transport described above. This analysis indicates that monitors in the Phoenix PM 10 nonattainment area were affected by PM 10 transport from outside the nonattainment area, with the main

source areas located to the south of the nonattainment area. Some of these source areas are located in Pinal County

, portions of which were recently desi gnated as a moderate nonattainment area (West Pinal)

for the 1987 24

- hour PM 10 NAAQS (77 FR 32024, May 31, 2012). Currently, the state is undergoing the appropriate process of developing a state implementation plan (SIP), due January 2, 2014, that provides

for attainment of the PM 10 standard as expeditiously as practicable but no later than the end of the sixth calendar year after redesignation. The SIP development process includes the requirement to identify and implement reasonably available control measu res for the area. In addition to transport, information pertaining to the controls implemented within the nonattainment area, the spatial extent of elevated PM 1029

concentrations throughout the area, and the wind speeds associated with the event sufficiently establishes that the event was not reasonably controllable or preventable.

Table 43 : Documentation of nRCP

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
August 14, 2012 Section V: p. 1

- 7, Section III: p. 1

- 12, App A Sufficient Yes

Historical Fluctuations (HF)

To demonstrate that this requirement was met, ADEQ provided 5

- year time series plots of both PM 10 daily maximum hourly averages and PM 10 24

- hour averages and stated that these figures show that “the

PM 10 concentrations measured...on August 1 4 , 2012, resulted in one of the highest 24

- hr averages...measured over the five

- year period.” ADEQ's analysis sufficiently establishes that the

24

- hour PM 10 concentrations measured on August 14 , 201 2

, were in excess of no rmal historical

fluctuations.

Table 44 : Documentation of HF

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
August 14, 2012 Section IV: p. 1

- 2, App. C Sufficient Yes

Clear Causal Relationship (CCR)

Section II of ADEQ’s demonstration included a conceptual model of the events, including a general overview of the geographic setting of the monitors, and climate information. The conceptual model also included a discussion of the event that occurred on Aug ust 14 , 2012

, and a general map of the region of the thunderstorm development in relation to the Phoenix PM 10 nonattainment area.

Section III of the demonstration included satellite imagery visibility photos, time

- lapse video evidence,

the raw data table s for numerous NWS stations in Maricopa and Pinal Counties, and a number of time series graphs that include hourly PM 10 data from Pinal and Maricopa Counties, wind speed, and visibility from Phoenix Sky Harbor Airport. ADEQ also included a detailed GIS ana lysis with PM 10 concentrations, sustained wind speeds, wind gusts, wind direction, base velocity radar, and visibility to track the transport of PM 10 throughout the region. These data show the spatial and temporal representation of the event as it moves th roughout Maricopa and Pinal Counties. ADEQ also provided a discussion for every map that described the conditions at that time. T ime

- lapse videos of the event can be found at the following locations:

 South Mountain: http://www.phoenixvis.net/videos/mpeg4/SOMT_08142012.mp4

The timing of the August 14, 2012

, event is consistent with the issuance of a NWS Blowing Dust Advisory for the period of 8:00 PM to 11:00 PM, the observed increased PM 10 concentrations in the area, increased wind speed, reduced visibility, and NWS station reports of thunderstorms, blowing dust, haze, and dust storms

.

ADEQ stated that the evidence presented shows a clear causal relationship “ between the windblown dust

and the PM 10 exceedances measured in the Phoenix PM 10 nonattainment area on August 1 4 , 2012.” ADEQ further stated that “ Th e wind, visibility, PM 10 , and radar data shown in this section illustrate the spatial and temporal extent of the dust storm as it moved through Maricopa County. In addition,30

meteorological data tables found in Appendix A show that the sharp increase in PM 1 0 concentrations coincided with the gusty winds, low visibilities, and airport reports of blowing dust. The fact that PM 10 concentrations in Pinal County spiked before PM 10 concentrations increased in Maricopa County shows that a vast majority of the dust that impacted the nonattainment area monitors originated outside of Maricopa County and was transported into the Phoenix PM 10 nonattainment area .”

The analysis in Sections II, III, and Appendix A specifically, the PM 10 time series graphs, winds speed

and direction measurements, GIS maps, time

- lapse video evidence, NWS advisories, and NWS station reports of reduced visibility, blowing dust and dust storms, sufficiently establishes that there was a clear causal relationship between uncontrollable emissions generated from thunderstorm outflow winds and

the exceedance s measured at the West 43 rd Avenue and Durango Complex monitors. Furthermore, while exceedances occurring at only a few monitors in the network are inherently more complex, the GIS analysis (Figures 3

- 7 through 3

- 10 in ADEQ’s demonstration) indicates higher wind speeds were measured in the western portion of the nonattainment area and variation in wind direction at nearby

monitors influenced the spatial extent of PM 10 throughout the Phoenix P M 10 nonattainment area and was likely responsible for the exceedance s at the West 43 rd Avenue and Durango Complex monitor s

.

Table 45 : Documentation of CCR

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
August 14, 2012 Section III: p. 1

- 12, App. A, App. B, App. D Sufficient Yes

Affects Air Quality (AAQ)

ADEQ stated that based on the information presented in the demonstrations for both the CCR and HF requirements, “we can reasonably conclude that the event in question affected air quality.” ADEQ's summary regarding the CCR and HF requirements sufficiently establishes that the event affected air quality.

Table 46 : Documentation of AAQ

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
August 14, 2012 Section VII: p. 1 Sufficient Yes

Natural Event

ADEQ stated that based on the documentation for both the nRCP and CCR requirements, “ PM 10 exceedances in the Phoenix area on August 1 4 , 2012, were shown to be caused by transport of PM 10 into the Phoenix area from gusty winds associated with thunderstorm outflow ” and that “the event therefore qualifies as a natural event.” ADEQ's summary regarding the CCR and HF requirements sufficiently

establishes that the event was a natural event.

T able 47 : Documentation of Natural Event

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
August 14, 2012 Section VII: p. 1 Sufficient Yes31

No Exceedance or Violation But For the Event (NEBF)

ADEQ provided a summary of the analysis and information regarding the nRCP and CCR requirements

and stated that “ t he weight of evidence presented in this submittal provides no alternative that could tie the exceedance of August 1 4 , 2012, to any causal sour ce other than PM 10 transported by gusty winds due to thunderstorm outflow, confirming that there would have been no exceedance but for the presence

of th is uncontrollable natural event .” ADEQ’s summary regarding the nRCP and CCR requirements sufficiently e stablishes that the NEBF criterion has been met.

Table 48 : Documentation of NEBF

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
August 14, 2012 Section VI: p. 1 Sufficient Yes

Schedule and Procedural Requirements

In addition to technical demonstration requirements, 40 CFR §50.14 (c) specifies the schedule and procedural requirements an air agency must follow to request data exclusion. Table 49 outlines EPA’s evaluation of these requirements.

Table 49: Schedules and Procedural Criteria

Reference Demonstration

Citation Criterion Met? Did the State provide prompt public

notification of the event? 40 CFR § 50.14 (c)(1)(i) Section I: p. 1 App. D Yes

Were flags and initial description placed on the data by July 1 st of the following year? 40 CFR § 50.14 (c)(2)(iii) Section I: p. 2 Yes

Was the demonstration submitted within 3 years of the end of the quarter in which the event occurred and 12 months prior to the date that any regulatory decision must be made by EPA? 40 CFR § 50.14 (c)(3)(i) February 13,

2013 letter 13 Yes

Was the public comment process followed

and documented? 40 CFR § 50.14 (c)(3)(v) Section I: p. 2

- 3 App. E 14 Yes

13 See letter from Eric Ma ssey, Director, Air Quality Division, ADEQ

, to Deborah Jordan, Director, U.S. EPA Region IX Air Division,

dated February 13, 2013.

14 A copy of the affidavit was not included in App. E, as stated in Section I of the final demonstration, but was submitted to EPA as part of the February 13, 2013 submission.32

Conclusion

EPA has reviewed documentation provided by ADEQ to support claims that dust emissions generated by monsoonal thunderstorm high winds were transported into the Phoenix PM 10 nonattainment area from areas in Pinal County and caused exceedances of the 24

- hour PM 10 NAAQS at the locations outlined in Table 42 on August 14, 201 2. EPA has determined that the flagged exceedances at these locations on this day meet the definition of an exceptional event : the exceedances affected air quality, were not reasonably controllable or preventable, and meet the definition of a natural event In addition to transport into the area, information pertaining to the controls implemented within the nonattainment area, the spatial extent of elevated PM 10 concentrations measured in the area, and the wind speeds associated with the event provide suffici ent evidence to conclude that the event was not reasonably controllable or preventable. Furthermore, EPA has determined that there was a clear causal relationship between the event and the measured exceedances, there would have been no exceedance s but for the event, and the measured exceedances were in excess of normal historical fluctuations.33 

### E vent Day: September 6, 2012

Table 50 : EPA PM 10 Exceedance Summary

Exceedance Date Monitor /Site Name AQS ID 24

- hour Avg. ( μ g/m 3 )

September 6, 2012 West Chandler 04

- 013

- 4004

- 1 164

Not Reasonably Controllable or Preventable (nRCP)

In addressing reasonable controls, ADEQ provided detailed information on the current set of required

controls in the Phoenix PM 10 nonattainment area, including information on rule implementation, rule effectiveness, compliance and enforcement, real

- time monitoring alert systems and public notification activities that occurred on the event days. ADEQ stated, “BACM on significant anth ropogenic sources were in place and enforced during the events, and proactive tracking and response to the events by regulatory agencies and local governments confirmed the uncontrollable nature of the dust emissions ; therefore, these pre

- existing prior

- ap proved required controls are adequate for meeting the requirements of an exceptional event and should be considered ‘reasonable’ for these purposes.”

ADEQ provided documentation showing that sustained wind speeds associated with these events were

abov e 20 mph in multiple locations nearby and upwind of the exceeding monitoring stations throughout

the Phoenix PM 10 nonattainment area and Pinal County. For example, maximum sustained wind speeds of 23 mph with gusts of 40 mph, 24 mph with gusts of 29, and 2 4 mph with gusts of 33 mph were measured at Chandler Municipal Airport, Phoenix Sky Harbor Airport, and Casa Grande Municipal Airport, respectively.

ADEQ further explained that “despite the deployment of comprehensive control measures and sophisticated r esponse programs, high wind conditions associated with the thunderstorm outflow transported high concentrations of PM 10 into, and also overwhelmed controls within, the Phoenix PM 10 nonattainment area. Widespread wind gusts over 30 mph were strong enough to overwhelm available

efforts to limit PM 10 concentrations during the event. The fact that these were natural events involving strong winds that transported PM 10 emissions into and across Maricopa County, with a majority of the

PM 10 emissions recorded by Ma ricopa County area monitors coming from sources outside of the

Phoenix PM 10 nonattainment area, provides strong evidence that the exceedances of September 6, 2012,

recorded within the Phoenix PM 10 nonattainment area were not reasonably controllable or prev entable.”

Section III of ADEQ’s documentation included a complex GIS analysis of the event that supports the

PM 10 transport described above. This analysis indicates that monitors in the Phoenix PM 10 nonattainment area were affected by PM 10 transport from outside the nonattainment area, with the main

source areas located to the south of the nonattainment area. Some of these source areas are located in Pinal County

, portions of which were recently designated as a moderate nonattainment area (West Pinal)

for the 1987 24

- hour PM 10 NAAQS (77 FR 32024, May 31, 2012). Currently, the state is undergoing the appropriate process of developing a state implementation plan (SIP ), due January 2, 2014, that provides

for attainment of the PM 10 standard as expeditiously as practicable but no later than the end of the sixth calendar year after redesignation. The SIP development process includes the requirement to identify and impleme nt reasonably available control measures for the area. In addition to transport, information pertaining to the controls implemented within the nonattainment area, the spatial extent of elevated PM 10 concentrations throughout the area, and the wind speeds a ssociated with the event sufficiently establishes that the event was not reasonably controllable or preventable.34

Table 51 : Documentation of nRCP

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
September 6, 2012 Section V: p. 1

- 8, Section III: p. 1

- 10, App. A Sufficient Yes

Historical Fluctuations (HF)

To demonstrate that this requirement was met, ADEQ provided 5

- year time series plots of both PM 10 daily maximum hourly averages and PM 10 24

- hour averages and stated that these figures show that “the

PM 10 concentrations measured at the West Chandler monitor on September 6 , 2012, resulted in some of the highest 24

- hr averages...measured over the five

- year period.” ADEQ's analysis sufficiently

establishes that the 24

- hour PM 10 concentrations measured on September 6 , 2012

, were in excess of

normal historical fluctuations.

Table 52 : Documentation of HF

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
September 6, 2012 Se ction IV: p. 1

- 2 Sufficient Yes

Clear Causal Relationship (CCR)

Section II of ADEQ’s demonstration included a conceptual model of the events, including a general overview of the geographic setting of the monitors, and climate information. The conceptual model also

included a discussion of the event that occurred on Sep tember 6 , 2012.

Section III and Appendix A of the demonstration included satellite imagery visibility photos, time

- lapse video evidence, the raw data tables for numerous NWS stations in Maricopa County, and a number of time series graphs that include hour ly PM 10 data from Pinal and Maricopa Counties, wind speed, and visibility from Chandler Airport. ADEQ also included a detailed GIS analysis with PM 10 concentrations, sustained wind speeds, wind gusts, wind direction, base velocity radar, and visibility to track the transport of PM 10 throughout the region. These data show the spatial and temporal representation of the event as it moves throughout Maricopa and Pinal Counties. ADEQ also provided a discussion for every map that described the conditions at that time. T ime

- lapse videos of the event can be found at the following locations:

 South Mountain: http://www.phoenixvis.net/videos/mpeg4/SOMT_09062012.mp4

 Superstition Mountains: www.phoenixvis.net/videos/mpeg4/SUPM_09062012.mp4

While not included in the demonstration, it is important to note that NOAA’s National Climatic Data

Center Storm events database included dust storm observations on September 6, 2012

, at 4:15 PM (central deserts) and 4:50 PM (greater Phoenix area). The timing of these dust storm reports for this event is consistent with the issuance of a NWS Dust Storm Warning for the period of 4:16 PM to 7:00

PM , NWS Blowing Dust Advisory for the period of 4:41 PM to 5:00 PM, NWS Severe Thunderstorm Warning for the period of 4:19 PM to 5:00 PM, NWS preliminary local storm reports of dust storms, the

observed increased PM 10 concentrations in the area, increased wi nd speed, reduced visibility, and NWS station reports of thunderstorms, blowing dust , haze

, and dust storms.

ADEQ stated that the evidence presented shows a clear causal relationship “between the windblown dust

and the PM 10 exceedances measured in the Phoenix PM 10 nonattainment area on September 6, 2012 .” ADEQ further stated that “ The wind, visibility, PM 10 , and radar data shown in this section illustrate the35

spatial and temporal extent of the dust storm as it moved through Maricopa County

. In addition, meteorological data tables found in Appendix A show that the sharp increase in PM 10 concentrations coincided with the gusty winds, low visibilities, and airport observer reports of blowing dust. The fact

that PM 10 concentratio ns in Pinal County spiked prior to PM 10 concentrations increasing in Maricopa County illustrate that a vast majority of the dust that impacted the nonattainment area monitors originated outside of Maricopa County and was transported into the Phoenix PM 10 n onattainment area

. ”

The analysis in Sections II, III, and Appendix A specifically, the PM 10 time series graphs, winds speed and direction measurements, GIS maps, time

- lapse video evidence, NOAA dust storm observations, NWS advisories, NWS preliminary loc al storm reports , and NWS station reports of reduced visibility,

blowin g dust and dust storms, sufficiently establishes that there was a clear causal relationship between uncontrollable emissions generated from thunderstorm outflow winds and the exceedance measured at

the West Chandler monitor

. Furthermore, while exceedances occurring at only one monitor in the network are inherently more complex, the GIS analysis (Figures 3

- 6 through 3

- 9 in ADEQ’s

demonstration ) indicates that a shift in wind direction fro m the southwest to west i nfluenced the spatial

extent of PM 10 throughout the Phoenix PM 10 nonattainment area and was likely responsible for the

isolated exceedance at the West Chandler monitor.

Table 53 : Documentation of CCR

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
September 6, 2012 Section III: p. 1

- 10, App. A, App. B, App. C Sufficient Yes

Affects Air Quality (AAQ)

ADEQ stated that based on the information presented in the demonstrations for both the CCR and HF requirements, “we can reasonably conclude that the event in question affected air quality.” ADEQ's summary regarding the CCR and HF requirements sufficiently establishes that the event affected air quality.

Table 54 : Documentation of AAQ

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
September 6, 2012 Section VII: p. 1 Sufficient Yes

Natural Event

ADEQ stated that based on the documentation for both the nRCP and CCR requirements, “ PM 10 exceedances in the Phoenix area on September 6, 2012 , were shown to be caused by transport of PM 10 into the Phoenix area from gusty winds assoc iated with thunderstorm outflow ” and that “the event therefore qualifies as a natural event.” ADEQ's summary regarding the CCR and HF requirements sufficiently establishes that the event was a natural event.

Table 55 : Documentation of Natural Event

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
September 6, 2012 Section VII: p. 1 Sufficient Yes36

No Exceedance or Violation But For the Event (NEBF)

ADEQ provided a summary of the analysis and information regarding the nRCP and CCR requirements

and stated that “ t he weight of evidence presented in this submittal provides no alternative that could tie

the exceedance of September 6, 2012 , to any causal source other than PM 10 transported by gusty winds due to thunderstorm outflow, confirming that there would have been no exceedance but for the presence

of th is uncontrollable natural event .” ADEQ’s summary reg arding the nRCP and CCR requirements sufficiently establishes that the NEBF criterion has been met.

Table 56 : Documentation of NEBF

Exceedance Date Demonstration Citation Quality of Evidence Criterion Met?
September 6, 2012 Section VI: p. 1 Sufficient Yes

Schedule and Procedural Requirements

In addition to technical demonstration requirements, 40 CFR §50.14 (c) specifies the schedule and procedural requirements an air agency must follow to request data exclusion. Table 49 outlines EPA’s

evaluation of these requirements.

Table 57: Schedules and Procedural Criteria

Reference Demonstration

Citation Criterion Met? Did the State provide prompt public

notification of the event? 40 CFR § 50.14 (c)(1)(i) Section I: p. 1 App. C Yes

Were flags and initial description placed on the data by July 1 st of the following year? 40 CFR § 50.14 (c)(2)(iii) Section I: p. 1 Yes

Was the demonstration submitted within 3 years of the end of the quarter in which the event occurred and 12 months prior to the date that any regulatory decision must be made by EPA? 40 CFR § 50.14 (c)(3)(i) February 13,

2013 letter 15 Yes

Was the public comment process followed

and documented? 40 CFR § 50.14 (c)(3)(v) Section I: p. 1 App. D 16 Yes

15 See letter from Eric Massey, Director, Air Quality Division, ADEQ

, to Deborah Jordan, Director, U.S. EPA Region IX Air Division,

dated February 13, 2013.

16 A copy of the affidavit was not included in App. D , as stated in Section I of the final demonstration, but was submitted to EPA as part of the February 13, 2013 submission.37

Conclusion

EPA has reviewed documentation provided by ADEQ to support claims that dust emissions generated by monsoonal thunderstorm high winds were transported into the Phoenix PM 10 nonattainment area from areas in Pinal County and caused an exceedance of the 24

- hour PM 10 NAAQS at t he location outlined in Table 50 on September 6, 2012. EPA has determi ned that the flagged exceedance at th is

location on this day meets the defin ition of an exceptional event: the exceedances affected air quality,

was not reasonably con trollable or preven table, and m et the definition of a natural event. In addition to transport into the area, information pertaining to the controls implemented within the nonattainment area, the spatial extent of elevated PM 10 concentrations measured in the area, and the win d speeds associated with the low pressure system provide sufficient evidence to conclude that the event was not reasonably controllable or preventable. Furthermore, EPA has determined that there was a clear causal relationship between the ev ent and the mea sured exceedance , there would have been no exceedance but for the event, and the meas ured exceedance was in excess of normal historical fluctuations.38 

### CONCLUSION

EPA finds that the weight of evidence is sufficient for concurrence on the flagging of the data for the

monitors identified in Table 1 on Sep tember 11 & 12, 2011, June 16, June 27, July 11, August 11, August 14, and September 6, 2012 . These concurrences do not constitute final EPA action to exclude these data from consideration for purposes of determining the attainment status of the area. Final actions will come only after EPA completes notice and comment rulemaking on any such determinations.