# Draft Guidance on the Preparation of Demonstrations in Support of Requests to Exclude Ambient Air Quality Data Affected by High Winds under the Exceptional Events

Rule

United States Environmental Protection Agency

June 2012Draft for Public Notice and Comment

Revision Date: June 2012 ii


### Table of Contents
Acronyms ...................................................................................................................... ................. iii 1. Highlights ................................................................................................................. ................... 1 2. Overview of Exceptional Events Rule ........................................................................................ 5

2.1 Definition of the “Event” for High Wind Dust Events .................................................... 5

2.2 Evidence Necessary to Support Exceptional Events Requests ........................................ 5

2.3 Mitigation Requirement ................................................................................................... 7

2.4 Process Requirements per EER ........................................................................................ 7 3. Evidence to be Included in a High Wind Dust Event Demonstration Package ......................... 8

3.1 Not Reasonably Controllable or Preventable (nRCP) .................................................... 10

3.1.1 Controls on Natural versus Anthropogenic Sources 10

3.1.2 Factors Considered in Determining the Reasonableness of Controls 12

3.1.3 Implementation and Enforcement of High Wind Dust Control Measures 15 3.1.4 Consideration of Wind Speed 16

3.1.5 Controls Analysis fo r Individual Events 17

3.1.6 Consideration of Controls on Tribal Lands 19

3.2 Historical Fluctuations (HF) ........................................................................................... 19

3.3 Clear Causal Relationship (CCR) .................................................................................. 20

3.4 Affects Air Quality (AAQ) .......................................................................................... 21

3.5 Caused by Human Activity Unlikely to Recur at a Particular Location (HAURL) or a Natural Event (Natural Event) ................................................................................................. . 22

3.6 No Exceedance or Violation But For the Event (NEBF) ............................................... 23

3.7 Optional Analyses for nRCP Requirement .................................................................... 24

3.7.1 Prospective Controls Analysis 24

3.7.2 High Wind Action Plan 25 4. Mitigation ................................................................................................................. ................. 30 5. Process Issues for Exceptional Events Including High Wind Dust Events .............................. 31

5.1 Demonstrations Package Submittal and Review ............................................................ 31

5.2 Timeframes .................................................................................................................... . 31

5.3 Public Comment ............................................................................................................. 33 6. Recommendations for Preparing High Wind Dust Exceptional Event Demonstrations .......... 34

6.1 Framework for Preparing Evidence to Suppor t a High Wind Dust Exceptional Event . 34

6.2 Preparing a Prospective Contro ls Analysis (Optional) .................................................. 36

6.3 Recommended Methods for the Technical El ements of a High Wind Dust Exceptional Events Package ................................................................................................................ ......... 37 6.3.1 Step 1: Develop a Conceptual Model 38 6.3.2 Step 2: Address not Reasonably Controllable or Preventable (nRCP) 39 6.3.3 Step 3: Present Historical Fluctuations (HF) Analyses 47 6.3.4 Step 4: Address Clear Causal Relationship (CCR) 49 6.3.5 Address Affects Air Quality (AAQ) 63 6.3.6 Address [HAURL] / Natural Event 63 6.3.7 Step 5: Address No Exceedance But For the Event (NEBF) 63

6.4 Prepare High Wind Action Plan (optional) .................................................................... 64 Appendix A1. Summary of Studies on Windblown Dust Emissions ........................................... 66 Appendix A2. Summary of Available Relevant Lite rature Related to Establishing Area-Specific High Wind Thresholds .......................................................................................................... ........ 70 Appendix A3. Methods for Establishing Ar ea-Specific High Wind Thresholds .......................... 73 Appendix B1. Checklist for High Wind Exceptiona l Events Demonstration Submission ........... 75 Appendix B2. Flowchart of Potential Review Process ................................................................. 78 Appendix C. Sample Letter of Intent ........................................................................................... . 79Draft for Public Notice and Comment

Revision Date: June 2012 iii 

### Acronyms
AAQ Affects Air Quality

ADEQ Arizona Department of Environmental Quality

AQS Air Quality System

BACM Best Availabl e Control Measures

BMP Best Management Practice

CAA Clean Air Act

CCR Clear Causal Relationship

CFR Code of Federal Regulation

CLASS Clean Air Support System

DAQEM Department of Air Quality and Environmental Management (Clark County, NV)

DRI Desert Research Institute

EER Exceptional Events Rule

EPA Environmental Protection Agency

FEM Federal Equivalent Method

FRM Federal Reference Method

GIS Geographic Information System

HAURL Human Activity Unlikely to Recur at a particular Location

HF Historical Fluctuations

MAG Maricopa Association of Governments (Arizona)

MODIS Moderate Resolution Imaging Spectroradiometer

MSM Most Stringent Measure

nRCP not Reasonably Cont rollable or Preventable

NAAQS National Ambient Air Quality Standards

NEBF No Exceedance But For the event

NSR New Source Review

NWS National Weather Service

RACM Reasonably Availa ble Control Measures

PM Particulate Matter

SCAQMD South Coast Air Quality Mana gement District (California)

SIL Significant Impact Level

SJV San Joaquin Valley

SIP State Implementation Plan

TOEM Tapered Element Oscillating Microbalance

UNLV University of Nevada, Las Vegas

WEG Wind Erodibility Group

WGA Western Governors’ Association

WRAP Western Regiona l Air PartnershipDraft for Public Notice and Comment

Revision Date: June 2012 1



### 1. Highlights

The EPA developed this document to assist air agencies 1 in meeting the requirements of the Exceptional Events Rule 2 (EER) for high wind dust (i.e., particulate matter) events 3 and to provide example recommended elements for excep tional event demonstrations. High winds can entrain and transport particulate matter (PM) to a monitoring site. These pa rticles can consist of

both PM 10 (i.e., particles less than 10 micr ometers (μm) in diameter) and PM 2.5 (i.e., particles less than 2.5 μm in diameter). Hi gh wind dust events can include both PM 10 and PM 2.5.

Purpose of this Document The purpose of this document is to provide assistance and illustration to air agencies implementing the EER for high wind dust events. 4

The EPA recognizes the limited resources of the ai r agencies that prepare and submit exceptional event demonstration packages and of the EPA re gional offices that review these demonstration packages. One of the EPA’s goals in developing this document and the other exceptional event implementation guidance 5 is to establish clear expectations to enable affected agencies to better manage resources as they prepare the docum entation required under the EER. The EPA expects submitters to prepare and submit the appropriate level of supporting documentation, which will vary on a case-by-case basis using the wei ght-of-evidence approach. The EPA expects the resources required to prepare (and review) high wind dust exceptional event packages, and demonstrations for other event types, to decrease as we continue to identify ways to streamline the process and continue to build our database of example demonstrations and analyses. In addition, the EPA acknowledges that certain extr eme exceptional event cases may require more limited demonstration packages.

To Whom does this Document Apply? High wind dust events are typically a phenomenon experienced in the western United States where rainfall is seasonal, creati ng dry and dusty landscapes. Theref ore, this document may be of

most use to the states from the Great Plains (North Dakota, South Da kota, Nebraska, Kansas, Oklahoma, and Texas) and west. Generally, this includes the states that comprise the Western Regional Air Partnership, which is mo st of EPA Regions 6, 7, 8, 9, and 10.

1 References to “air agencies” are meant to include state, local, and tribal air agencies responsible for implementing

the EER.

2 “Treatment of Data Influenced by Exceptional Events; Final Rule”, 72 FR 13560, March 22, 2007.

3 The term “high wind dust event” is used in this document to refer to the same type of event that was discussed as a “high wind event” in the EER. The EPA believes the term “high wind dust event” more clearly describes the

referred-to event.

4 This draft guidance document presents examples to illust rate specific points. These examples are not necessarily required for all demonstrations.

5 Other draft exceptional event guidance documents include the following: “Draft Guidance to Implement Requirements for the Treatment of Air Quality Monitoring Data Influenced by Exceptional Events,” the “Draft Exceptional Events Rule Frequently Asked Questions,” and “Request for Comments on the Draft Guidance Documents on the Implementation of the Exceptional Events Rule.” Additional information and examples of exceptional event submissions and best practice components can be found at the EPA’s Exceptional Events website located at http://www.epa.gov/ttn/analysis/exevents.htm.Draft for Public Notice and Comment

Revision Date: June 2012 2

Guiding Principles for the Development of this Document

1. Air agencies should not be held accountable for exceedances due to events that were beyond their control at th e time of the event.

2. It is desirable to implement reasonabl e controls to prot ect public health. 6

3. Clear expectations will enable the EPA and othe r air agencies to bett er manage resources related to the exceptional events process.

Definition of a High Wind Dust Event A high wind dust event includes both the high wi nd and the dust that the wind entrains and transports to a monitoring site. The event is not merely the occurr ence of the high wind.

Elements for the Technical Demons tration of High Wind Dust Events

 Air agencies’ demonstrations must address the following six techni cal elements under the

EER before the EPA can concur on a high wind dust event demonstration:

1. whether the event was not reasonably controllable or preventable (nRCP),

2. whether there was a clear causal relationship (CCR),

3. whether there would have been no exceedance or violation but for the event (NEBF),

4. whether the event affect s air quality (AAQ),

5. whether the event was caused by human activity unlikely to recur or was a natural event (HAURL / Natural Event), and

6. whether the event was in excess of nor mal historical fluctuations (HF).

If a demonstration fails to sufficiently address an y one of the above, the EPA will not be able to concur with the request to exclude data under the EER.

 During the EPA’s review of several high wi nd dust events flagged by air agencies as exceptional events, the EPA has found that th e following EER elements play a significant role in air agencies’ supporting docu mentation: nRCP, CCR, and NEBF.

 The EPA has also found for a high wind dust ev ent that satisfying the requirements for nRCP, CCR, and HF criteria also generally satisfies the requirements for two elements identified by statute, AAQ and Natural Event.

 The EPA has not set pass/fail statistical criteria for the HF element, but will use a weight-ofevidence approach to assess each demonstrati on on a case-by-case basis. The air agency’s role in satisfying this element is to provide analyses and statistics as recommended by the EPA in this document and conclude that the prov ided data show that the event was in excess

of normal historical fluctuations. The EPA w ill review the information provided by the air agency. Events do not necessarily have to be rare to satisfy this element.

6 With respect to exceptional events, Section 319 of the Clean Air Act states the following guiding principles (among others); (i) the principle that protection of public health is the highest priority

*** (iv) the principle that each State must take necessary measures to safegua rd public health regardless of the source of the air pollutionDraft for Public Notice and Comment

Revision Date: June 2012 3

 While not listed as a technical element requir ed by the EER, wind data (e.g., wind speed and direction) will generally play a vital role in informing the EPA’s decision on elements such as whether the event was not reasonably contro llable or preventable and establishing a clear causal relationship.

Not Reasonably Controllable or Preventable

 Exceedances caused in whole or in part by anthropogenic dust sources within the air agency’s control are unlikely to be eligible for treatment as exceptional events under the EER, even under conditions of elevated winds, unl ess the air agency s hows that the event, including the emissions from the anthropogenic dust sources, was not reasonably controllable or preventable. The EPA intends to eval uate whether an event was not reasonably controllable or preventable at the time of the event by taking into account the wind speed; the controls in place; the controls required in the State Implementation Plan (SIP), which depends on an area’s attainment status; th e frequency and severity of exceedances; contributing sources; benefits of the controls; co sts of controls; a nd other factors.

 The EPA also judges the reasonableness of cont rols based on the technical information that was available to the air agency at the time the event occurre d. The EPA generally expects air agencies to already have the technical information needed to reasonably control sources

within nonattainment areas.

 The degree of event-specific information a nd data necessary for demonstrating “not reasonably controllable or preventable” will gene rally be less for sustained wind speeds at or above the high wind threshold and greater for sp eeds below that the threshold. The high wind threshold is the minimum threshold wind speed capable of overwhelming reasonable controls on anthropogenic sources (i.e., significant emi ssions from controlled sources) or causing

emissions from natural undisturbed areas. The EPA recommends that ai r agencies establish area-specific high wind thresholds based on local or applicable conditions and information. If an agency is unable to develop an area-specific high wind threshold, the EPA will accept a threshold of a sustained wind of 25 mph for ar eas in the West provided the agencies submit

evidence of this as the level at which they expect stable surfaces (i.e., controlled anthropogenic and undisturbed natural surfaces) to be overwhelmed. In identifying a high wind threshold, the EPA does NOT intend to set a br ight line as to whatspeed constitutes a high wind dust event or to categorically concur with all events with sustained winds above a given threshold.

 An air agency has the option of submitting a prosp ective controls analysis in advance or with a demonstration package. Described in more detail in Section 3.7.1, a prospective controls analysis is a generic 7 review of an area’s existing windblown dust controls and high wind threshold. In the prospective c ontrols analysis, the air agency would provide information on attainment status, identify natural and anthropogenic windbl own dust sources and emissions, provide the status of SIP submittals (if applicab le), and identify the high wind threshold up to

which the collective windblown dust controls are expected to be effective. Once the EPA approves the prospective controls analysis, an air agency’s subsequent high wind exceptional event packages could reference the approved se t of controls in the prospective controls

7 “Generic” means a general review rather than a review specific to an identified event.Draft for Public Notice and Comment

Revision Date: June 2012 4

analysis and show that the wind speed for the ev ent in question is at or above the high wind threshold established in the prospective controls analysis. Air agencies would also include in their demonstration some posit ive showing that control requi rements were being met on the day in question. An EPA-approved prospective cont rols analysis would ge nerally be effective for a minimum of three years.

 The EPA and the submitting air agency may also consider developing a voluntary High Wind Action Plan. Air agencies can develop High Wi nd Action Plans to document their plans to implement needed controls on newly-iden tified sources that could emit dust during subsequent high wind events. A High Wind Ac tion Plan is an optional mechanism to implement necessary controls more expeditious ly than with the nor mal regulatory planning process. Preparation of such a plan and its approval by the EPA could promote a common understanding between the air agency and the EPA about whether subsequent high wind dust events are not reasonably controllable or preventable.

Clear Causal Relationship As described in Section 3.3, air ag encies can use the following ex ample analyses to establish a clear causal relationship:

 analyses showing that the event in fact occurred and that emi ssions were transported in the

direction of the monitors wher e measurements were recorded

 the size of the area affected by the emissions

 comparison to non-event days

 the spatial and temporal relationship between th e event, transport of emissions, and recorded

concentrations

No Exceedance But For the Event The NEBF demonstration may be relatively straight forward for areas with typical concentrations on non-event days well below the applicable Na tional Ambient Air Quality Standards (NAAQS). However, demonstrating NEBF becomes increasi ngly difficult if concentrations on non-event days during the same season exceed the standard and/or if the contribution of non-event pollution sources produce concentrations near the applicable NAAQS.

Disclaimer The Exceptional Events Rule is the source of th e regulatory requirements for exceptional events and exceptional event demonstrations. This doc ument provides guidance and illustrations of events for the Exceptional Events Rule rather than imposing any new requirements. Further, any determination that an event is exceptional made on the basis of this guidance will need the facts

in the documentation to support the decision.Draft for Public Notice and Comment

Revision Date: June 2012 5



### 2. Overview of Exceptional Events Rule

The EER and the preamble describe specific cr iteria for an event to be considered an “exceptional event” for purposes of exclusion of air quality data from regulatory decisions and acknowledge that “natural events” can be recurring.

2.1 Definition of the “Event” for High Wind Dust Events

In high wind dust events, the meteorological pheno menon (i.e., wind) is purely natural but the pollution from the event may be a mixture of natural sources (e.g., undisturbed soil) and anthropogenic sources (e.g., soil disturbed by hu man activity, emissions from sand and gravel facilities, etc.). The EPA classifies high wind dus t events as “natural events” in cases where windblown dust is entirely from natural sources or where all significant anthropogenic sources of windblown dust have been reasonably controlled. 8 This long-standing policy of considering both the wind and the dust as part of the event was established in the Natural Events Policy where high winds were defined as:

“Ambient PM-10 concentrations due to dust raised by unusually high winds will be

treated as due to uncontrollable natural even ts under the following conditions: (1) the dust originated from nonanthropogenic sour ces, or (2) the dus t originated from anthropogenic sources controlled with be st available control measures (BACM).” 9

A high wind dust event is defined as the co mbination of high wind and uncontrollable dust

emissions. Uncontrollable windblown dust emissi ons only occur in the presence of high wind. Therefore, for exceptional events purposes, it is n ecessary to consider both the emissions and the corresponding high wind as the “event.”

2.2 Evidence Necessary to Support Exceptional Events Requests

The EPA promulgated the Exceptional Events Rule in 2007, pursuant to the 2005 amendment 10
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. These sections contain defin itions, criteria for EPA approval, procedural requirements, and requirement s for air agency demonstrations, all of which

8 Human activity would be considered to have played little or no direct causal role in causing emissions of the dust by high wind 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 the event would be considered a natural event. If anthropogenic sources 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.

9 “Areas Affected by PM10 Natural Events” (the PM10 Natural Events Policy), memorandum from Mary D. Nichols, Assistant Administrator for Air and Radiation, to EPA Regional Offices, May 30, 1996. The EPA intended to uphold the principle that windblown emissions from controlled sources would be considered natural, however, due to a technical drafting error, the language in the section of the EER preamble titled “ B. High Wind Events ” beginning on 72 FR at 13576 was ruled legally null in NRDC v. EPA, No. 07-1151 (D.C. Cir. 3/20/09).

10 Safe, Accountable, Flexible, Effici ent Transportation Equity Act: a Lega cy for Users (SAFETEA-LU), section6013 amending CAA §319, became law August 10, 2005; available at http://thomas.loc.gov/cgibin/query/z?c109:H.R.3:Draft for Public Notice and Comment

Revision Date: June 2012 6

must be met before the EPA can concur under the EER on the exclusion of air quality data from regulatory decisions.

The definition of an exceptional event given in 40 CFR §50.1(j) parallels the statutory definition

of Section 319 of the CAA and itself contai ns certain criteria for approval by the EPA:

 The event “affects air quality.”

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

 The event is “caused by human activity that is un likely to recur at a particular location or [is] a natural event.” 11

Additional criteria for the EPA approval to excl ude data affected by a high wind dust event are given (with some repetition of key phr ases) in 40 CFR §50.14(a) and (b)(1). 12 Under these provisions the air agency must:

 “demonstrat[e] to EPA’s satisfaction that such event caused a specific air pollution concentration at a particular ai r quality monitoring location.”

 “demonstrate a clear causal relationship between the measured exceedance or violation of

such standard and the event ...”

 “demonstrat[e] to EPA’s satisfaction that an exceptional event cau sed a specific air pollution concentration in excess of one or more national ambient air quality standards at a particular air quality mon itoring location and otherwise sa tisfies the requirements of this section [regarding schedules, procedur es and submission of demonstrations].”

Under 40 CFR §50.14(c)(3)(iv), 13 the air agency demonstration to justify exclusion of data must provide evidence that:

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

B. “There is a clear causal relationship betw een the measurement unde r consideration and

the event that is claimed to have a ffected the air quali ty in the area”;

C. “The event is associated with a measured concentration in excess of normal historical fluctuations, including background”; and

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

The definition of an exceptional event provide d in 40 CFR § 50.1(j) explicitly excludes “stagnation of air masses or meteorological inve rsions, a meteorological event involving high temperatures or lack of precipitation, or pollution relating to source noncompliance.” 14
Exceedances due to these events would not be eligible for exclusion under the EER. For

11 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.”

12 §50.14 (b)(2) and (b)(3) contain criteria relevant only to firework events and prescribed fire events.

13 Prior to the publishing of the 2010 CFR the citation was §50.14(c)(3)(iii)

14 For further explanation see “Treatment of Data Influenced by Exceptional Events; Final Rule,” 72 FR at 13577, (March 22, 2007).Draft for Public Notice and Comment

Revision Date: June 2012 7

example, if sources out of comp liance with fugitive dust or othe r rules contributed significantly to an exceedance, then the exceedance would not be excluded as due to an exceptional event.

2.3 Mitigation Requirement

40 CFR §51 Subpart Y includes mitigation re quirements at 51.930. While the EER does not require that mitigation measures be submitted to the EPA as part of the demonstration package (or otherwise), it is nonetheless a requirement of Subpart Y that “[a] State requesting to exclude air quality data due to exceptional events must ta ke appropriate and reasonable actions to protect public health from exceedances or violations of the national ambient air quality standards.” The mitigation requirement is addressed in Section 4 of this document.

2.4 Process Requirements per EER

In addition to technical demonstration requirement s, the EER specifies the process an air agency must follow to request data exclusion:

 "A State shall notify EPA of its intent to exclude one or more measured exceedances of an applicable ambient air quality standard as being due to an exceptional event by placing a flag in the appropriate field for the data record of concern which has been submitted to the AQS database.” 40 CFR § 50.14(c)(2)(i).

 “The placement of the flags and the submittal of an initial event desc ription must be done not later than July 1st of the calendar y ear following the year in which the flagged

measurement occurred.” 40 CFR § 50.14(c)(2)(iii).

 “A State that has flagged data as being due to an exceptional event and is requesting

exclusion of the affected m easurement data shall, after notice and opportunity for public comment, submit a demonstration to justify data exclusion to EPA not later than the lesser of, 3 years following the end of the calendar qua rter in which the fla gged concentration was recorded or, 12 months prior to the date that a regulatory de cision must be made by EPA. A State must submit the public comments it rece ived along with its demonstration to EPA.” 40 CFR § (50.14(c)(3)(i)).

 With the submission of the demonstration, th e air agency “must document that the public comment process was followed.” 40 CFR § (50.14(c)(3)(iv)).Draft for Public Notice and Comment

Revision Date: June 2012 8



### 3. Evidence to be Included in a High Wind Dust Event Demonstration Package

As discussed in Section 2.2, the EER identifies tec hnical elements (i.e., crit eria or evidence) that an air agency must address and demonstrate befo re the EPA can concur that an exceedance is due to an exceptional event. Table 1 shows the comp lete list of technical elements air agencies must submit and satisfy as part of a demons tration for high wind dust events. The EPA cannot concur on an air agency’s request to exclude data unde r the EER if the air agency has failed to satisfy any of the criteria.

Table 1. EER Technical Demonstration Elem ents Required by the EER for High Wind

Dust Events

Element Abbreviation Section of this Document Containing Additional Explanation affects air quality* AAQ 3.4 not reasonably c ontrollable or preventable nRCP 3.1 caused by human activity unlikely to recur at a particular location OR a natural event 15 * HAURL /

Natural Event 3.5

clear causal relationship between the measurement

and the event CCR 3.3

no exceedance or violation but for the event NEBF 3.6

the event is associated with a measured

concentration in excess of normal historical fluctuations, including background HF 3.2

*These elements are typically met when the other elements have been satisfied.

The EPA uses a “weight-of-evidence” approach in reviewing air agency requests for data

exclusion under the EER. Evidence and narrative that co nstitute a strong demonstration for one element can also be part of the demonstration for another element, but cannot make up for the absence or failure to satisfy another elemen t. Although a strong demonstration on one element should not compensate for a failure of another, the strength of the demonstration for one requirement could influence the persuasive ness of evidence used for another.

In reviewing the supporting documentation in se veral high wind dust event demonstrations, the EPA has found the following EER elements play a significant role: nRCP, CCR, and NEBF.

The criterion that the event be in excess of norma l historical fluctuations (HF) is a technical element that the EPA expects to be satisfied by th e submittal of data as outlined in Section 3.2. In addition to satisfying the HF criterion, these da ta are expected to inform the CCR and NEBF

demonstrations.

15 High wind dust events are considered natural events if sources are entir ely natural or if contributing anthropogenic sources are reasonably controlled and therefore it is not re levant to consider whether the event was caused by human activity unlikely to recur.Draft for Public Notice and Comment

Revision Date: June 2012 9

The EPA has generally found that two elements identified by statute, AAQ 16 and Natural Event, are necessarily also satisfied for a high wind dust event if the other elements are satisfied. Air agencies can typically meet these criteria by satisfying the requirements for nRCP, CCR, and

HF. While not identified as a se parate demonstration element in Table 1, wind data (e.g., wind speed and direction) is vital in informing the EPA’s decisi on regarding “not reasonably controllable or preventable” a nd “clear causal relationship.”

Finally, the EPA recommends that air agencies begin their tec hnical demonstration for a high wind dust event with a conceptual model of how the event occurre d. An air agency’s conceptual

model can use text and/or schematics to identif y and describe the relationship between various phenomena (e.g., weather and dust emissions) that caused an exceedance. In its simplest form, the conceptual model could be a narrative descrip tion of how the event unfolded and resulted in the exceedance(s). The conceptual model will be si milar to a report abstract and should help tie the various rule criteria together into a cohesive explanation of the event.

Sections 3.1-3.6 of this document describe and clarify each element identified in Table 1. Section 6 provides example analyses and a recommended st ructure for the preparation of demonstration packages for high wind dust events.

In summary, the technical demonstration for a high wind dust event pack age should include the following technical elements:

 Not Reasonably Controllable or Preventable
- Analyses and descriptions should show that the event was not reasonably controlla ble or preventable. Required by EER.

 Clear Causal Relationship - Analyses and descriptions s hould show that there was a clear causal relationship between the ambient con centration measurement under consideration

and the event that is claimed to have affected the air quality in the area. Required by EER.

 No Exceedance But For the Event - Analyses and descriptio ns should show that there

would have been no exceedance or viola tion but for the event. Required by EER.

 Affects Air Quality - Statutory technical element that is generally satisfied once the submitter provides historical fluctuations analyses (HF), establishes a clear causal relationship (CCR), and provides explicit inform ation indicating satisf action of requirement through clear causal and historical fluc tuations showings. Required by EER.

 Natural Event - Statutory technical element that is generally satisfied once the submitter shows the event to be not reasonably contro llable or preventable (nRCP), establishes a clear causal relationship (CCR), and provi des information demonstrating these requirements have been met. Required by EER.

16 The preamble to the EER clarifies the AAQ criteria in section V.B. (p. 13569) by stating that the following criteria establish that the event affected air quality: “there is a clear causal relationship between the measurement under

consideration and the event that is claimed to have affected the air quality in the area” and “the event is associated with an unusual measured concentration beyond typical fl uctuations including background.” On this basis AAQ is satisfied once CCR has been demonstrated and evidence for HF has been provided.Draft for Public Notice and Comment

Revision Date: June 2012 10

 Historical Fluctuations – Air agencies should provide an alyses and descriptions in the format suggested in this document. The EPA will review this information in a weight-ofevidence showing. Required by EER.

 Wind Data - Data on wind speed and direction suppor t the technical elem ents required by

the EER such as CCR and nRCP.

 Conceptual Model
- Narrative summary at the beginni ng of a demonstration package describing how the event unfolded to produce elevated PM at the monitor(s) that recorded the exceedance(s) and providing cont ext for the supporting elements.

3.1 Not Reasonably Controllable or Preventable (nRCP)

Exceedances caused in whole or in part by anthr opogenic dust sources within the air agency’s control are unlikely to be elig ible for treatment as exceptiona l events under the EER, even under conditions of high winds, unless th e air agency shows th at the event (i.e., dust entrained by high winds) was not reasonably controll able or preventable. The EPA evaluates whether an event was not reasonably contro llable or preventable at th e time of the event by taking into account controls in place and wind speed, along with other factors. 17 The factors and approach identified in this section should assist air agencies in devel oping adequate high wind dust exceptional event demonstration packages and promote consistency. The EPA will consider each package on a case-by-case basis per the EER.

3.1.1 Controls on Natural versus Anthropogenic Sources

According to the definition of an exceptional event, the event must be “not reasonably controllable or preventabl e” (40 CFR § 50.1(j)). For natural sources of dust, a high wind dust event can generally be considered to be not reasonably controllable or preventable 18 , 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 been ef fectively implemented and enforced.

3. The wind speed was high enough to ove rwhelm the reasonable controls.

Reasonable controls on anthropoge nic sources (item 1 on the list above) are fundamental to the event being not reasonably cont rollable or preventable. An event with both anthropogenic and natural components can be considered a “natur al” event if the anthropogenic component is reasonably controlled. Air agencies must also de monstrate that natural events are reasonably controlled by showing that no additional controls are reasonable for the event. Additionally,

“reasonable controls” refers to a collection of reasonably controlled sources. The term “not

17 See SJV Attainment Affirmation, 73 FR73 14691, for a prior high wind dust event in which the EPA considered controls and wind speed, along with other factors.

18 The EPA expects that in most cases it would not be reasonab le to have controls on natural sources but this will be

evaluated for each event.Draft for Public Notice and Comment

Revision Date: June 2012 11

reasonably controllable or preventable” refers to the event (i.e., dust entrained by high winds), rather than to any particular so urce. Further, in determining wh ether the event is not reasonably controllable or preventable, the EPA will consider whether the collection of anthropogenic sources has been reasonably controlled. For anthropogenic sources, it is the high wind overwhelming the collection of reasonable controls , that have been effectively implemented and enforced, that make the event not reas onably controllable or preventable.

For purposes of evaluating high wind dust exceptional events in the West, the EPA will generally use the definitions of natural and anthropoge nic windblown dust emissions that have been developed in the Western Regional Air Partners hip (WRAP) Fugitive Dust Handbook

. 19
According to the WRAP Fugitive Dust Handbook , all mechanically suspended dust from human

activities should be considered anthropogenic emissions, while windblown dust from lands not disturbed or altered by human ac tivity should be considered natural emissions. Furthermore, windblown dust from surfaces that have been sign ificantly disturbed or altered by humans should be categorized as anthropogenic emissions. Such surfaces may include: undeveloped lands 20

, construction and mining sites, material storage piles, landfills, vacant lots, agricultural lands, roadways, parking lots, artificially exposed beds of natural lakes and ri vers, exposed beds of artificial water bodies, areas subj ect to off-road vehicle activit y, and areas burned by prescribed or other human-ignited fires. Natural sources may include: naturally-dry river and lake beds; barren lands; sand dunes; exposed rock; sea spray from natural water bodies; non -agricultural grass, range, and forest lands; areas burned by wildfires; and glacial silt.

The EPA generally considers dust entraine d by high wind from undisturbed land (e.g., undisturbed desert) to be not reas onably controllable or preven table, because of the likely disturbance to natural ecosystems and the cost of treating large land areas. The EPA also generally considers that windblown dust from previ ously disturbed land that is being allowed to fully return to natural conditions by effective prevention of any new di sturbance is also not reasonably controllable or preventable, provide d that there are no reasonable active measures

that could be taken to cont rol dust during the transition back to natural conditions. 21 While

emissions from most other natu ral sources of windblown dust coul d be similarly not reasonably controllable, the EPA will consider those on a case -by-case basis. In areas where events recur, the EPA may request increased ch aracterization of the natural s ources (e.g., historical surface disturbance, water diversions , vegetation changes, etc.).

While the EPA generally does not expect cont rols on emissions from natural sources (e.g., undisturbed land) for an event to be not reasonably c ontrollable or preventable, the EPA does expect reasonable controls to be in place on the windblown anthropogenic contribution to the concentration measured during the event. Expe rience in several areas in the western United States has shown that it is practical and r easonable to apply dust-suppression controls to disturbed lands and other anthropogenic dust sour ces, and that these cont rols help limit ambient concentrations of PM during high wind dust even ts, up to certain wind speeds. For example, many areas in the west have successfully cont rolled dust with measures such as water or

chemical stabilization of disturbed areas such as construction zones, or limiting disturbance

19 WRAP Fugitive Dust Handbook , Prepared for Western Governors’ Association, Countess Environmental (WGA Contract No. 30204-111), September 7, 2006. Available at http://www.wrapair.org/forums/dejf/fdh/index.html

20 Undeveloped lands refer to those that are disturbed for purposes of development but not yet developed.

21 An example of such a measure might be the restora tion of all or part of natural surface water flows.Draft for Public Notice and Comment

Revision Date: June 2012 12

activities on windy days. If reas onable controls on windblown an thropogenic sources were in place, then the event would be considered “not reasonably controllable or preventable” and would satisfy the nRCP element of the definition of an exceptional event. That is, an air agency can generally meet the nRCP element for high wind events by identifying the contributing anthropogenic sources of windblown dust for a part icular event and show ing that reasonable controls were in place, eff ectively implemented, and enforced (as appropriate). The prior preparation of and EPA approval of a prospective controls analysis or high wind action plan (see Sections 3.7.1 and 3.7.2) addressi ng all the anthropogenic sources that might contribute during

wind events can alleviate the need for this s howing in each event case. For each event with windblown anthropogenic contributions, it will be impor tant for an air agency to explicitly show that the exceedance occurred desp ite the implementation of those reasonable controls (i.e., to show that wind speeds were high enough to ove rwhelm the reasonable controls). The prior establishment of a high wind threshold (see Se ction 3.1.4 below) can make this showing less resource intensive per event. The EPA will evaluate the reasonableness of controls based on the controls that should have been in place given th e information the air agency had when the event occurred (see Section 3.1.2 for factors that the EPA will consider in determining the reasonableness of the controls). The level of rigor required to demonstrate that reasonable controls were in place, implemented/enfor ced, and overwhelmed by high winds, will depend upon the wind speed of the event re lative to the high wind threshold if one has been established (see Section 3.1.4 and 3.1.5).

Typically, measured ambient air concentrations during an event will include some contribution from natural or anthropogenic sources whose emissions are not affected by high wind, for example transportation and indus trial point sources: these ar e considered non-event sources.

Non-event sources are not subject to the nRCP requirement of the EER, but an air agency may apply full-time or event-dependent controls on such sources as part of its attainment/maintenance SIP or as part of meeting the mitigation requirement under 40 CFR §51.930.

3.1.2 Factors Considered in Determin ing the Reasonableness of Controls

This section describes an appro ach for determining the reasonable ness of the controls in place. Among other factors to consider, reasonableness needs to be judge d in light of the technical information available to the air agency at th e time the event occurred. The EPA would consider air agencies experiencing the following scen arios and/or with the following technical

information to have had technical information indicating the need for high wind dust controls:

 More than one expected exceedan ce per year from high wind dust

 Exceedances due to windblown dust when the sustained wind speed is less than the high wind threshold (or default) for the area

 Requirement for high wind dust BACM resultin g from either nonattainment status or previous Natural Events Action Plan (NEAP) 22

22 On May 30, 1996, Mary D. Nichols, Assistant Administ rator for Air and Radiation issued a memorandum to EPA regional offices entitled, “Areas Affected by PM 10 Natural Events.” The policy, known as the PM 10 Natural Events Policy, or simply the Natural Events Policy, set fort h procedures for protecting public health through the development of a Natural Events Action Plan, which impl ements Best Available Cont rol Measures (BACM) for human-generated particulate emissions in areas that could violate the PM 10 NAAQS due to natural events. Promulgation of the Exceptional Events Rule superseded the Natural Events Policy.Draft for Public Notice and Comment

Revision Date: June 2012 13

 Formal communication from the EPA indicat ing the need for high wind dust controls

 Promulgation of new/revised Federal rules that would require controls on particular sources

The EPA does not expect high wind dust controls in areas wi th no history of high wind dust

exceedances.

The set of control requirements ma ndated by the area’s designation status is the primary factor used in evaluating reasonableness (see Secti on 3.1.2.2 for additional detail). Table 2 shows example factors that the submitter and the EPA ma y consider when assessing the reasonableness of controls as part of the nRCP criterion. Ta ble 2 is not intended to be all-inclusive or quantitative.

Table 2. Example Factors Considered In Determining the Reasonableness of Controls. “Reasonableness” Factor Descriptio n of “Reasonableness” Factor 1. Control requirements based on area

attainment status The reasonableness of th e controls depends upon

historical concentrations and designation status. 2. Frequency and severity of past

exceedances More stringent controls ma y be reasonable if an area experiences frequent 23 and/or severe 24 exceptional event exceedances due to high winds than if the area has experienced only non-recurring 25 and/or mild isolated

exceedances. 26

3. Ease and effectiveness of control implementation The EPA may consider cost-effective and readily deployable controls more reasonable.

4. Use of measures that are in widespread use Controls that are considered “standard practices” and/or measures in widespread use for dust control in other

areas would be considered more reasonable. 5. Jurisdiction The EPA expects air agency demonstration submittals to

address the status of control measures for interstate and international transport. However, the EPA also expects that air agency demonstrati ons can generally satisfy the “not reasonably controllable or preventable” criterion

with less detailed characterization of sources in the upwind state or country than of sources in the same state

as the affected monitor. 27

23 Frequent is enough exceedances from high wind dust events to cause of violation of the NAAQS.

24 A severe exceedance could be a 24-hou r average PM10 con centration > 250 μg/m 3

. 25 Non-recurring is fewer than one high wind dust event per year

26 A mild isolated exceedance could be, for example, an exceedance at one site close to the standard.

27 Considering the sovereignty issues associated with inte rstate and international transport, the EPA believes that “reasonable control” showings can rely on the concept that it is not reasonable to expect the downwind state (i.e., the state submitting the demonstration) to have convinced the upwind country or state to have implemented controls on

sources sufficient to limit event-related air concentratio ns in the downwind state. As with any demonstration submittal, the submitting (downwind) st ate should sufficiently identify all natural and anthropogenic contributing sources of emissions (both in-state and out-of-state) to sh ow the causal connection betwee n an event and the affected air concentration values. A submitting state may provide a less detailed characterization of sources in the upwind state or country than of sources within its jurisdiction. After completing the source characterization, the submitting

state should assess whether emissions from sources within its jurisdiction (i.e., in-state sources) were not reasonably controllable or preventable. Although the submitting state sh ould also provide available in formation on the status ofDraft for Public Notice and Comment

Revision Date: June 2012 14

Table 2. Example Factors Considered In Determining the Reasonableness of Controls. “Reasonableness” Factor Descriptio n of “Reasonableness” Factor 6. Controls on primary sources expected to have contributed to the

event Were primary sources of anthropogenic windblown dust controlled during the event?

7. Significant contribution of sources

to the exceedance There is no defined de minimis emission rate or ambient

contribution that limits which sources should be considered for control, and the EPA will review this on a case-by-case basis. However, as a starting point, we believe it is generally reasonable to consider source categories that may contribute 5 μg/m 3 or more to an exceedance of the 150 μg 24-hour PM 10 standard. 28 In some cases (i.e., wind speeds above the high wind threshold) it may not be nece ssary to consider sources down to 5 μg, while in other situations it may be appropriate to consider sour ces below 5 μg. This starting point may be revisited should the PM 10 NAAQS be

revised. De minimis levels for PM 2.5 have not been clearly established.

8. Overall benefit of controls There ma y be benefits to c ontrolling even small anthropogenic sources. Reducing ambient concentrations may have a public health benefit.

3.1.2.2 Consideration of attainment st atus in judging reasonableness

In order for the anthropogenic s ources to be considered to be reasonably controlled, the EPA expects, at a minimum, that it is reasonable for an air agency to have the controls required for an area’s attainment status. Generally, the EPA doe s not expect areas clas sified as attainment, unclassifiable, or maintenance for a NAAQS to have the same level of cont rols as areas that are nonattainment for the same NAAQS. Also, if an area has been recently designated to nonattainment but has not yet been required to imp lement controls, the EPA will expect the level of controls that is appropri ate for the planning stage.

3.1.2.3 Consideration of BACM/RACM

control measures for emissions from out-of-state sources, the submitting state may determine based on available information that the implemented controls on out-of state sources constitute reasonable controls and that the “not reasonably controllable or preventable” cr iterion is satisfied. When assessing em issions transported from other states or countries, the submitting state can sa y that it characterized the out of state sources, determined that these sources contributed to the noted exceedance or violation, and determined, based on jurisdictional boundaries and other available information, that contributing emissions from the upwind state or country were not reasonably controllable or preventable. Submitting states are further required to submit evidence/statements su pporting the other exceptional event criteria (i.e., clear causal relationship, but for, human activity unlikely to recur or a natural event, affects air quality, and historical fluctuations). The EPA refers the read er to Question 23 in the “Draft Exceptional Events Rule Frequently Asked Questions” for additional information on this topic.

28 5μg is the “significant impact level” (SIL) used in NSR permitting to decide whether an individual source has a significant contribution to a 24-hr PM 10 NAAQS violation, based on 40 CFR 51.165(b)(2), and so is used here for a

similar use.Draft for Public Notice and Comment

Revision Date: June 2012 15

Although Reasonably Available Control Measur es (RACM) and Best Available Control Measures (BACM) for windblown dust are not necessar ily required to have been in place at the time of the event for all areas, they are measur es that the EPA and affected agencies have identified as being reasonable. Th e CAA requires BACM for serious PM 10 nonattainment areas

and RACM in moderate PM 10 nonattainment areas; therefore, for such areas, the EPA, at a minimum, will use the local list of BACM or RACM measures (as applicable) as a reference point to review the reasonableness of controls. Th e control measures evaluated must be related to windblown dust. Having BACM/RACM in place duri ng the time of the event is an important consideration, but may not be sufficient on it s own (e.g., the BACM/RACM measures may not be related to windblown dust, they may not be suffi cient by themselves particularly if the SIP has not been recently reviewed or revised), or if it focuses on air quality issues during specific periods without high winds (such as winter stagnation events). Generally, the EPA will consider

windblown dust BACM to constitu te reasonably controls if th ey have been reviewed and approved in the context of a SIP revision for the emission source area within the past three years. In some cases, a lower level of control could be reasonable, while in ot her cases it could be reasonable to require controls mo re stringent than current BACM or RACM, for example, if a new significant source is identi fied. Other areas (i.e., attainment , maintenance, or unclassified areas) are not required to have put BACM in place and also may not have implemented RACM. In these cases, the EPA may use local RACM measures, where available, along with other RACM measures that may be appropriate for the location and source categories, as the reference point. RACM/BACM lists may be a reference point, but not the sole means, by which the

EPA assesses the reasonableness of controls. If an air agency believes that RACM/BACM should not be used by the EPA as the reference poi nt to judge the reasonab leness of controls, the air agency should include this justification in th e demonstration package.

In addition to BACM/RACM, the U.S. Depart ment of Agriculture’s Natural Resources Conservation Service develops best management practices (under various program titles), some of which are designed to effec tively reduce fugitive dust air em issions and prevent loss of soil during high winds, which may also be informative a nd useful controls in particular situations. These best management practices are not intend ed to be a surrogate for BACM/RACM but could

be included in the collec tion of control measures.

3.1.3 Implementation and Enforcement of High Wind Dust Control Measures

As stated in Section 3.1.1, the second condition the EPA will consider in its determination of

whether the event meets the nRCP criterion is implementation and enforcement (where appropriate) of control measures on contributin g sources of dust. In their demonstration submittals, air agencies should submit available in spection reports and/or notices of violations (NOVs) in upwind areas as evid ence that all reasonable cont rols were implemented and functioning properly at the time of the event. 29 The EPA recognizes that records may not be

29 The EPA recognizes that agencies have varied methods of permitting and enforcement and does not expect all agencies to have these records for all events. The EPA does, however, expect agencies to make a general showing that controls are being enforc ed to a reasonable degree (not necessarily on the particular day of the event); if several categories of anthropogenic sources are identified as significan t or likely contributors to an event, the means used to determine compliance with re asonable control requirem ents for each category should be described in the

demonstration.Draft for Public Notice and Comment

Revision Date: June 2012 16

available for all events. Cases where relevant co ntrol measures were not being fully implemented or properly enforced, but reasonab ly could and should have been, ar e unlikely be eligible for data exclusion under the Excep tional Events Rule.

3.1.4 Consideration of Wind Speed

The third condition stated in Section 3.1.1 for the EPA to consider for the nRCP criteria for an event with anthropogenic sources is whethe r the wind speed was high enough to overcome

reasonable controls. In all cases (i.e., those includi ng natural and/or anth ropogenic sources) wind speed informs the rigor of the nRCP analysis. It is important to note that the EPA is not setting a bright line as to what speed cons titutes a high wind dust event or to categorically concur with all events with sustained winds above a given leve l. This section describes how the EPA will use wind speed in its evaluati on of the nRCP criterion.

Typically, undisturbed dese rt landscapes in the west have a natu ral crust that protects the surface and tends to prevent windblown dust emissi ons. Similarly, many reasonably-controlled anthropogenic sources (e.g., disturbed surfaces) em ploy techniques that stabilize surfaces to reduce or prevent emissions since disturbed surf aces are a primary source of anthropogenic dust.

Numerous studies have been conducted to de termine the minimum wind speed capable of overwhelming reasonable controls on anthropogen ic sources or causing emissions from natural undisturbed areas. The speed at which this occurs varies by location, depending on characteristics of the local landscape (e.g., soil type) and controls (See Appendix A). The EPA recommends that agencies develop a high wind threshold for each area experiencing high wind dust events (see Appendix A3 for additional information on the development of a high wind threshold). Appropriate area-s pecific thresholds would cons ider local conditions and the variation in control strategies and specify a minimum wind speed above which these controls would be overwhelmed. If nonanthropogenic sources are a significant source of emissions for a particular area, a high wind threshold may also be based on the level of wind speed capable of causing emissions from those specific natural undist urbed areas. This approach is consistent with the Natural Events Policy where the EPA required the air agencies to define the conditions in

which BACM level controls were overwhelmed. The area-specific high wi nd threshold should be representative of conditions (i.e., sustained wind speeds 30 ) that are capable of overwhelming reasonable controls (whether BACM, RACM, or other) on anthropogenic sources and/or causing

emissions from natural undisturbed areas. The threshold is not inte nded to represent the minimum wind speed at which any level of emissions could occur (e.g., aerodynamic entrainment), but rather when significant emission s begin due to reasonable controls or natural undisturbed areas becoming overwhelmed. The high wind threshold can be submitted in advance of submittal of the demonstration package, with a letter of intent, with a demonstration package, as part of a prospective controls analysis, or as part of a High Wind Action Plan. If an agency is unable to develop an area-specific high wind threshold, the EPA will accept a threshold of a sustained wind of 25 mph for areas in the west provi ded the agencies support this as the level at which they expect stable surfaces (i.e., controlled anthropogenic and undisturbed natural surfaces) to be overwhelmed. 31 If the EPA has specific informati on based on relevant studies to choose an alternative high wind threshold, the EPA will notify the air agency once this

30 See Section 6.2.2.2 for details on the calculation of sustained wind speed.

31 The 25 mph threshold is based on studies conducted on natural surfaces.Draft for Public Notice and Comment

Revision Date: June 2012 17

information has been submitted. Throughout this doc ument, the term “high wind threshold” will

be used to define the minimum threshold wind speed capable of overwhelming reasonable controls on anthropogenic sources (i.e., significant emissions from controlled sources) or causing

emissions from natural undisturbed areas.

If a demonstration can show that the sustaine d wind speed was at or above the high wind threshold at or proximately upwind of the lo cation of the exceedance, then two streamlined approaches are available to meet the nRCP criterion:

1. Rely on an already-approved prospective contro ls analysis. A set of controls for an area could be approved with the high wind threshold in advance of submittal of a package for a specific event (see Section 3.7.1). Once the pr ospective controls an alysis was approved, additional information on controls for specifi c packages would typically be limited to information on enforcement and implementation.

2. Conduct a basic controls analysis. Minima l amounts of information on sources and controls would be required for each event (see Section 3.1.5 and 3.1.5.1).

If the sustained wind speed for an event was below the high wind threshold, the EPA can still review the package and possibly concur provide d the air agency submits additional controls information as described in the comprehensiv e controls analysis (S ee section 3.1.5 and 3.1.5.2).

The EPA believes that streamlined information (i.e ., a pre-approved prospective controls analysis or a basic controls analysis) is sufficient when wind speeds are at or above the high wind threshold because, in this situation, controls to prevent windblown dust are likely to become overwhelmed. Thus, the event is more likely to be not reasonably controllabl e or preventable. If

most controls on wind-blown dust become overwhe lmed at or above the high wind threshold, air agencies would likely find it difficult to identify additional reasonable contro ls that could be put into place to reduce windblown dust.

In contrast, if the wind speeds associated with the event are below the threshold levels required

to initiate dust emissions from natural or stable (i.e., r easonably-controlled) sources, the EPA is likely to require that air agencies submit mo re detailed information (i.e., a comprehensive controls analysis) to satisfy th e nRCP requirement. The EPA believes air agencies should submit a comprehensive controls analysis when wind speeds are below the high wind threshold because events with wind speeds below this threshold should entrain very little dust from natural and reasonably-controlled disturbed surfaces. Furthe r, the EPA expects that windblown emissions would include significant contributions from s ources that are neither natural nor reasonablycontrolled. Thus, the event is less likely to be not reasonably controllable or preventable. In these cases it is important for air agencies to identif y the various land areas co ntributing to the event, evaluate the controls in place on those land areas , and determine whether those controls were

reasonable based on those factor s identified in Section 3.1.2.

3.1.5 Controls Analysis for Individual Events

Air agency demonstration submittals need a co ntrols analysis for each specific high wind dust event. The extent of the controls analysis should primarily depend upon the level of the wind speed relative to that of the high wind threshol d for the area. A basic controls analysis may beDraft for Public Notice and Comment

Revision Date: June 2012 18

sufficient for cases when the sust ained wind speed at the source area 32 is greater than or equal to the high wind threshold, while a comprehensive controls analysis may be necessary when sustained wind speeds are below the high wind thre shold (Table 3). If an air agency has not prospectively determined the high wind threshold for the area, then this determination, or establishing that the default thre shold of 25 mph applies, is th e first step in the controls analysis. 33 Next, the EPA recommends that air agencies develop their nRCP an alysis to evaluate the sustained wind speed during th e event. This process may indi cate that only the streamlined basic controls analysis is needed. See Secti on 6.3.2.2 for wind speed considerations for nRCP.

Table 3. Summary of Recommended Controls Analysis Elements for not Reasonably

Controllable or Preventable Demonstration

Control Analysis Elements Basic Controls Analysis Comprehensive Controls Analysis
Description of anthropogenic sources within the area and existing controls X X

Description of natural sources within the area and existing controls X X

Statement regarding reasonableness of

controls X X

Explanation that emissions occurred despite controls X X

Identification and implementation status of controls previously recommended by the EPA as reasonable, if applicable X X

Evidence of effective implementation and enforcement of reasonable controls, if applicable X X

Back trajectories of source area X Source apportionment X Source-specific emissions inventories X

3.1.5.1 Basic controls analysis

The most basic controls analysis would include a brief description of local/upwind sources that were suspected to significantly contribute to the event and a description of the controls on the anthropogenic sources in place at the time of th e event (e.g., local BACM measures). The EPA also expects evidence that the controls determined to be reasonable, if any, were effectively implemented and appropriately enforced. For the sources identified, the an alysis should explain how significant dust emissions occu rred despite having reasonable controls in place (e.g., that controls were overwhelmed by high wind). In addition to identifying co ntrols on anthropogenic sources, it is important that the analysis indica te whether the natural s ources could have been

32 Cases where dust was entrained by sustained winds at or above the high wind threshold upwind of the monitor and subsequently transported at lower wind speeds to the monitor could still qualify for the basic controls analysis category as long as the state shows that sustained winds we re at or above the high wind threshold in the expected source area. Cases of long-ran ge transport (e.g., >50 miles) could still qu alify for a basic controls analysis but a robust trajectory analysis (and/or satellite plume imagery) would need to be included as part of the nRCP or CCR

demonstration.

33 See Appendix A3 for additional methods for esta blishing area-specific hi gh wind thresholds.Draft for Public Notice and Comment

Revision Date: June 2012 19

reasonably-controlled. If the EP A recommended controls improveme nts as part of a previous high wind dust exceptional event review then the controls analysis should address the reasonableness and potential impact of these control improvements. See Section 6.3.2.3 for examples of a basic control analysis. Even if a prospective controls analysis has b een approved and included as part of the basic controls analysis, the air agency should specifically identify li kely sources in the upwind source area and discuss specific controls if these we re not discussed in the prospective analysis.

3.1.5.2 Comprehensive controls analysis

When events occur under conditions with sustai ned wind speeds below the high wind threshold, the EPA and the air agency must further consid er the appropriateness, implementation, and enforcement of controls. For example, exceedances can occur when reasonable controls are in place but not properly enforced. Or, new or addi tional uncontrolled sources may be contributing to the exceedance. In these cases, the demons tration would need to be more complex and compelling for the EPA to concur. Examples of mo re complex analysis include: back-trajectories of source area, source apportionment, day specific emissions inventories of specific sources in source area, and evidence of effective implemen tation and enforcement, where appropriate, of controls. In addition to identifying controls on anthropogenic sources, it is important that a submitting agency indicate whether any natural sources could have been reasonably-controlled. As with the basic controls analysis, if the EP A recommended controls improvements as part of a previous high wind dust exceptiona l event review, then the contro ls analysis should address how these controls improvements have been addr essed. See Section 6.3.2.4 for an example of a comprehensive controls analysis.

3.1.6 Consideration of Controls on Tribal Lands

When reviewing the “reasonableness of contro ls” element within tribal exceptional event demonstration submittals, the EPA will consider both controls on tribal sources and cultural factors for tribal lands. For example, the EPA could consider tribal cultural factors and subsequently identify “reasonable” controls. It might have been reasonable for the tribal government to encourage the use of certain practices, but not to ha ve required them as a matter

of tribal law.

3.2 Historical Fluctuations (HF)

Air agencies should include data showing historical fluctuations of concen tration in the area in their demonstration package and make a conclusion as to whether the agency considers the data

to be outside the normal historical fluctuations. This information satisfies the HF criterion and serves as an important basis for the CCR, NEBF, and AAQ criteria (see Table 2). The more a

concentration stands out from hist orical concentrations, the more plausible it is that the event

was the cause of the exceedance. The objective of the HF analysis is to give a full and accurate portrayal of the historical context for the clai med event day. The EPA expects, at a minimum:

1. comparison of concentrations on the claimed ev ent day with past historical data (3-5 years), with previous high wind dust events identified;Draft for Public Notice and Comment

Revision Date: June 2012 20

2. percentile of concentration relative to annual data with and without high wind dust events; and

3. percentile of concentration re lative to seasonal data withand without high wind dust

events.

4. comparison of concentrations on the claimed event day with a narrower set of similar days

Because the methods of analyses influence the conclusions that can properly be drawn from the

historical fluctuation statistics (e.g., percentile calculations are dependent on the number of data points included), the EPA recommends specific anal yses, statistics, and calc ulations as described

in Section 6.3.3 of this document.

It is important to note, however, that there is no outcome of the “historical fluctuation” statistical comparison that, by itself, can guarantee that the CCR and NEBF elements will also be successfully demonstrated. The EPA will use a weight-of-evidence approach to assess each demonstration and comparison of the concentrations during event(s) in qu estion with historical concentration data on a case-by-case basis. The EPA acknowledges that natural events, such as high wind dust events, can recur and still be e ligible for exclusion under the EER. Therefore, events do not necessarily have to be rare to satisfy this element.

3.3 Clear Causal Relationship (CCR)

40 CFR §50.14(c)(3)(iv) requires de monstration of a clear caus al relationship between the

ambient concentration measurement under considerat ion and the event that is claimed to have affected the air quality in the area. The CCR demonstration must show that dust from high wind caused an exceedance of the NAAQS. The CCR demonstr ation is expected to establish causality between the event and a portion of the ambient concentration. Simply showing that high wind was coincident with high concentrations is un likely to establish causality. A correlation between high wind and high concentrations is important, but does not independently demonstrate that

windblown dust from the natural un disturbed and/or reasonably cont rolled anthropogenic sources caused the high concentrations. CCR demonstrations should include analyses showing that the

event in fact occurred and that emissions were transported in the direction of the monitors recording the elevated concentr ation measurements. CCR analyses should support the conceptual model and address the concepts identified in Tabl e 4. Examples of the quantitative analyses that could be performed are included in Section 6.3.4.

Table 4. Example Evidence and An alyses for CCR Demonstration Example CCR Evidence Types of An alyses/Information to Support

Evidence 1. Occurrence and geogra phic extent of the

event Special weather statements, advisories, news reports, nearby visibility readings, measurements from monitoring stations, satellite imagery 2. Transport of emissions related to the event in the direction of the monitor(s) where

measurements were recorded Wind direction data showing that emissions from sources identified as part of the nRCP demonstration were upwind of the monitor(s) in question, satellite imageryDraft for Public Notice and Comment

Revision Date: June 2012 21

Example CCR Evidence Types of An alyses/Information to Support

Evidence 3. Spatial relationship between the event, sources, transport of emissions, and recorded

concentrations Map showing likely source area, wind speeds, wind direction, and PM concentrations for affected area during the time of the event, trajectory analyses 4. Temporal relationship between the high

wind and elevated PM concentrations at the monitor in question 24-hour time series showing PM

concentrations at the monitor in question in

combination with sustained and maximum wind speed data at area where dust was

entrained 5. Chemical composition and/or size distribution of measured pollution that links the pollution at the monitor(s) with particular sources or phenomenon Chemical speciation data from the monitored exceedance(s) and sources; size distribution

data

6. Comparison of event-affected day(s) to specific non-event days Comparison of concentration and wind speed to days preceding and following the event;; comparison to high concentration days in the same season (if any) without high wind; comparison to other high wind days without elevated concentrations (if any); comparison of chemical speciation data 7. Historical comparison of PM concentration and wind speed (e.g., 3-5 years) data Identification of historical trends or relationships between wind speed and PM

concentrations.

A demonstration will be less compelling if there is evidence that is inconsistent with the conceptual model of how the event caused the ex ceedance. For example, if the agency describes

the event as a regional dust storm, then the EPA would expect monitors within the same regional scale to be similarly affected by the dust st orm. Comparison of concentrations and conditions at other monitors could thus be very important for the demonstration of a clear causal relationship. Alternatively, elim inating plausible non-event ca uses may also support a causal relationship to the high wind dust event. (See Section 6.3.4.7 for an example of eliminating alternative hypotheses.)

3.4 Affects Air Quality (AAQ)

The AAQ element is generally supported by historic al fluctuations in concentration data (HF) and demonstrated as part of th e clear causal relationship (CCR). 34 Submitting agencies that

34 In the definition of “exceptional event”, 40 CFR §50.1(j) begins: “Exceptional event means an event that affects air quality...” The preamble clarifies this in section V.B. What Does It Mean for an Event To “Affect Air Quality”? (p. 13569) :Draft for Public Notice and Comment

Revision Date: June 2012 22

provide HF analyses and conclu sions and that demonstrate the CCR element will generally, have also satisfied the “affects air qua lity” (AAQ) part of the definiti on of an exceptional event. The

demonstration should neverthele ss explicitly recognize this elem ent, and describe how this requirement is met through meeting the HF and the CCR criteria.

3.5 Caused by Human Activity Unlikely to Recur at a Particular Location (HAURL) or a Natural Event (Natural Event)

According to both the regulatory and statutory definition, an exceptional event must be “an event caused by human activity that is unlikel y to recur at a particular location or a natural event.” High wind dust events that meet the criteria es tablished in this guidance document would be considered natural events, thus the HAURL does not apply and would not need to be considered for a high wind dust event.

A natural event is defined as “an event in which human activity plays little or no direct causal role” (40 CFR §50.1(k)). An event involving win dblown dust solely from undisturbed natural sources is clearly a natural event. However, many high wind dust events affecting the ambient monitoring network include signifi cant contributions from anth ropogenic sources of dust, and

their treatment under the EER is more complicated. In these case s, a high wind dust event can be considered a natural event, even when a portion of the wind-driven emissions are anthropogenic, as long as those emissions were determined to be not reasonably controllable or preventable. Exceedances that include a significant contri bution by anthropogenic sources of windblown dust that were not reasonably-controlled will not be considered as due to a natural high wind dust event. In addition, high dust concentrations outsi de the period of high wind (e.g., dust from rockcrushing or tilling that precedes the period of high wind) cannot be considered as due to a natural

event and therefore could not be considered as part of a high wind dust ev ent. In both of the above cases, it would be assumed that human activ ity played a large and direct causal role and therefore these exceptional events claims could only be consider ed under the crite rion of “human activity unlikely to recur.” 35

Under the Final Rule, the demonstration to justify data exclusion must provide a justification that: (a) The event qualifies in acco rdance with section IV.D. an d if applicable, with the EP A policies and guidance for certain events as described in section IV.E, (b) there is a clear causal relationship between the measurement under consideration and the event that is claimed to have affected the air quality in the area, (c) the event is

associated with an unusua l measured concentration beyond typical fluctuations including background, and (d) there would have been no exceedance or violation but for the event (discussed in section V.C). The second and third criteria establish that the event affected air quality. [emphasis added] In this passage, the second criterion is (b) “clear causal relationship”, and the third is (c) “concentration beyond typical fluctuations”. These are the same as the EER requi rements for CCR (“clear causal relationship”) and HF (“in

excess of normal historical fluctuations”) at 40 CFR §50.14(c)(3)(iii)(B) and (C).

35 In theory, a high wind dust event for which anthropogenic sources were not reasonably-controlled could be considered an anthropogenic ev ent if the event satisfies certain criteria, including being unlikely to recur. However, if the event (which includes the dust from both natural and anthropogenic sources) was not “not reasonably controllable or preventable” then the event does not meet the definition of an exceptional event. For this reason, the EPA does not believe it is useful to pursue a line of reasoning that would consider a high wind dust event to be an anthropogenic event. If the very unlikelihood of recurrence of similarly high winds means that controls in addition to those that were in place would not have been reasonable, the event can be treated as a natural event and must then

meet the criteria laid forth in the EER and explained in this document.Draft for Public Notice and Comment

Revision Date: June 2012 23

Since anthropogenic sources of windblown dust must be reasonably-controlled for the event to be considered a natural event under the EER, the ai r agency must demonstr ate that the criterion for nRCP is met (see Section 3.1). Further, to satisfy the EER, air agencies must also demonstrate that the windblown dust generated by high wind has a clear causal relationship (CCR) to the measured exceedance. In summary, the EPA will generally consider a high wind dust event to be a natural event if the air agency demonstrates both the nRCP and CCR elements

to the EPA’s satisfaction.

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

40 CFR 50.14(b)(1) directs the EPA to exclude data only where an air agency demonstrates that

an event caused a concentration in excess of a NAAQS. This means that there was a concentration in excess of the NAAQS when the event occurred that would have been below the NAAQS if the event had not occurred. §50.14(c) (3)(iv)(D) requires the air agency to submit evidence that “[t]here would have been no exceedance or violation but for the event.” 36 Figure 1 depicts the NEBF concept.

Figure 1. Depiction of the Concept of No Exceedance But For the Exceptional Event.

This analysis generally does not need a singl e or precise approximation of the estimated air quality impact from the event. The EPA is not pres cribing the type of analysis that air agencies need to perform to satisfy this regulatory requ irement, but air agencies should show that the

measured concentration would have been belo w the applicable NAAQS without the impact of the high wind dust event. For most cases, the EPA expects a quantitative NEBF analysis. For

36 In addition, Section 319 of the Clean Air Act requires that a clear causal relationship must exist between the measured exceedances and the exceptiona l event, meaning that exceptional events dealt with in the EER must be

exceedancesDraft for Public Notice and Comment

Revision Date: June 2012 24

events where the typical concentrations on non-event days are well below the applicable NAAQS, the NEBF demonstration may be relati vely straightforward and a qualitative NEBF demonstration may be acceptable. However, dem onstrating NEBF becomes increasingly difficult if concentrations on non-event days during the sa me season exceed the standard and/or if the contribution of non-event pollution sources produ ce concentrations near the applicable NAAQS. For example, if days without high winds that neighbor the claimed event day were near the standard (e.g., 150 μg/m 3 for PM 10 ), the NEBF analysis would need to be very rigorous to show that the exceedance would not have happened but for the high wind dust event. Examples of how to conduct the NEBF analysis are provided in Section 6.3.7.

The NEBF demonstration builds upon and will be informed by the rigor of the nRCP and CCR analyses and further supported by information provided for HF. To illustrate the NEBF and CCR relationship, if there is no CCR, then NEBF becomes moot since there is no portion of the exceedance that can clearly be attributed to th e event. For these reasons, the EPA recommends that the air agency complete the NEBF anal yses after it complete s all other analyses.

3.7 Optional Analyses for nRCP Requirement

3.7.1 Prospective Controls Analysis

As stated in Section 3.1.1, a hi gh wind dust event that includes anthropogenic sources can meet

the nRCP criterion if:

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

2. The reasonable controls have been ef fectively implemented and enforced.

3. The wind speed was high enough to ove rwhelm the reasonable controls.

A prospective controls analys is is an optional, generic 37 review of the current windblown dust controls (item 1 above) and the hi gh wind threshold (item 3 above) fo r an area. This optional step

would occur in advance of the EPA’s review of a ny particular event. In the prospective controls analysis, the air agency would provide informa tion on attainment status , identify natural and anthropogenic windblown dust sources and emissions , provide the status of SIP submittals (if applicable), and identify the wind speed up to which the collective windblown dust controls are expected to be effective (see Section 6.2 for de tails on how to prepare a prospective controls analysis). Air agencies could subm it their prospective controls anal ysis in advance of an agency submittal and the EPA review of any specific dem onstration submittal, with the letter of intent, or with their demonstration package submittal. Once the EPA approves a prospective controls analysis, air agencies could reference this pre- approved analysis in subsequent packages for

events with winds above the es tablished/approved high wind thre shold to satisfy items 1 and 3 above and provide information on implementation and enforcement of controls (item 2 above).

The EPA review and approval of co ntrols identified in the prosp ective controls analysis would typically be effective for a minimum of three ye ars. After the three-year time period, the EPA will notify the agency if the EPA intends to re-r eview the controls. In some limited cases, the EPA may re-review the controls within the three-year timeframe if information on sources or

37 “Generic” means a general review rather than a review specific to an identified event.Draft for Public Notice and Comment

Revision Date: June 2012 25

enforcement suggests that controls may be in adequate or not implemented/enforced. The EPA may also re-evaluate the controls identified in the prospective controls analysis when an area that does not typically have recurring high wind dust events experiences unexpected recurrent events.

If the EPA has approved a SIP revi sion to windblown dust controls w ithin the past three years of the event, then the submitting agency can use the SIP-approved controls to satisfy item 1 of a prospective controls analysis.

3.7.2 High Wind Action Plan

3.7.2.1 Purpose

Air agencies can develop High Wind Action Plans to document their plans to implement needed controls on newly-identified s ources that could emit dust during subsequent high wind events (similar to the process used in a Natural Even ts Action Plan). A High Wind Action Plan is an optional mechanism to implement necessary contro ls more expeditiously than with the normal regulatory planning process. Prep aration of such a plan and its approval by the EPA could promote a common understanding between the air agency and the EPA about whether subsequent high wind dust events ar e not reasonably controllable or preventable. In addition, the High Wind Action Plan could document current windblown dust controls and current and/or planned mitigation measures as part of §51.930.

3.7.2.2 How Does the High Wind Action Plan Option Work?

The EPA will judge the reasonablene ss of controls based on information that was available to the air agency at the time of the ev ent (see Section 3.1.2). However, in the course of preparing or reviewing a high wind dust exceptional event demons tration submittal, the air agency or the EPA may identify previously unknown sour ces that should be subject to reasonable controls. The EPA and/or the air agency may determine that additi onal controls could mini mize the likelihood or the health impact of future events. The EPA does not want to penalize air agencies for lack of

controls on sources unknown to the air agency at the time of the event, but air agencies must recognize that EPA cannot consider the collection of sources and asso ciated controls to meet the nRCP criterion for subsequent events once eith er party identifies a significant uncontrolled source. The High Wind Action Plan provides an optional mechanism that allows the EPA to concur on an air agency’s request to exclude data associated w ith the current and subsequent events while the air agency implements controls on previously unidentif ied sources. Preparation of a High Wind Action Plan and its appr oval by the EPA could promote a common understanding between the air agency and the EPA about whether subsequent high wind dust events are not reasonably controllable or prev entable. Note that a High Wind Action Plan does not replace planning actions required under the Cl ean Air Act based on an area’s attainment status. For example, a PM 10 serious nonattainment area is still required to implement BACM. In this type of case the High Wind Action Plan can address sources identified after BACM has been implemented.Draft for Public Notice and Comment

Revision Date: June 2012 26

An air agency can submit a High Wind Action Plan with the exceptional events demonstration package or as a separate submittal. 38 Establishing a High Wind Action Plan to address additional

reasonable controls consists of the following steps:

1. Air agency development and submittal of th e High Wind Action Plan after an opportunity for public comment

2. The EPA approval of th e High Wind Action Plan

3. Air agency implementation of the iden tified and approved control measures

Assuming all other exceptional event criteria are met, once the EPA approves the High Wind Action Plan, the EPA could then concur upon the event under current consideration. If an air agency chooses to develop a High Wind Action Pla n, it will have six months from the time the EPA provides notification that ne wly-identified sources require r easonable controls to submit an adequate (i.e., approvable) plan. If the air ag ency meets this timeframe, then the EPA will consider anthropogenic sources co ntributing to high wind dust events that occur within the sixmonth timeframe to be reasonably-controll ed, assuming the air agency appropriately implemented and enforced required controls and wind speeds are high enough to overwhelm

those reasonable controls.

If an agency does not meet the six-month timef rame and/or the High Wind Action Plan is not approvable, the EPA would treat any high wind exceptional events that occur within and beyond the six months as not meeting the nRCP crite rion. Therefore, under most conditions, the EPA

would not be able to concur on high wind exceptional events. Unde r this scenario, the EPA and the air agency would include associated event data in planning deci sions. The High Wind Action Plan is unlikely to be an opti on for an area in the midst of a planning action since the planning timeframes are unlikely to accommodate a mu lti-month development of a High Wind Action

Plan.

Once approved, an air agency’s High Wind Action Plan is effective for three years and would

establish that sources have reasonable contro ls for events where wind speeds exceed the high

wind threshold. For future events that occur und er an approved High Wind Action Plan, the EPA would consider whether controls were implem ented effectively according to the High Wind Action Plan as part of the nRCP evaluation. Wh ile the High Wind Action Plan is not in itself enforceable, the EPA’s concurrence of exceptional events relies upon the implemented plan (i.e., the newly-identified sources woul d not be considered to meet the nRCP criterion if the High Wind Action Plan is violated). Th erefore, if an air agency doe s not effectively implement its plan, the EPA may be unable to concur on future exceptional events.

An approved High Wind Action Plan does not auto matically mean that the EPA will find all subsequent events to meet the not reasonably controllable or pr eventable criterion. For example,

38 If an air agency submits the High Wind Action Plan se parately from the exceptional event demonstration package, the air agency should provide an opportunity for public comment as the High Wind Action Plan would be part of the basis for the EPA’s decision on subsequent events.Draft for Public Notice and Comment

Revision Date: June 2012 27

the EPA may not concur if the EPA finds that an air agency did not effectively implemented or enforced the controls in place. 39

3.7.2.3 Content of a High Wind Action Plan

At a minimum, a High Wind Action Plan to addr ess new sources should include the following:

 identification of sources and proposed controls

 an assessment of reasonableness

 timeframes for implementation

 a plan for enforcement, if appropriate.

The High Wind Action Plan should also identify the current high wind threshold and whether

this threshold should be revise d as a result of the newly id entified controls. As mentioned previously, a High Wind Action Plan could also document current c ontrols, especially if these were not included in a previous demonstration package, and mitigation measures.

3.7.2.4 Comparison of a Natural Events Action Plan and High Wind Action Plan

The concept of a High Wind Action Plan originat ed from the Natural Events Action Plan (NEAP). Table 5 presents a co mparison of the two plans.

Table 5. Comparison of Natural Events Action Plan and High Wind Action Plan.

Element Natural Events Action Plan High Wind Action Plan Establish public notification and education programs Required component of plan. Op tional component of plan to address mitigation requirement for EER (40 CFR 51.930). Minimize public exposure to high levels of windblown dust Required component of plan. Op tional component of plan to address mitigation requirement for EER (40 CFR 51.930).

Current reasonable controls on contributing controllable

sources Required component of plan (BACM). Required component of plan (but not necessarily BACM).

Plan for putting reasonable controls in place on contributing controllable

sources Required component of plan. Re quired component of plan if

additional controls are needed

as condition for concurrence on current event(s).

Re-evaluate the controls Every five years. ≥ 3 years or if high wind dust patterns change and suggest

new sources. Timeframe for submittal Within 18 months of violation. Within 6 months from the

39 Note that if and when the EPA takes a regulatory actio n that hinges on a decision to exclude data under the Exceptional Events Rule, the EPA may be required to consider and appropriately respond to public comments on whether the event was “not reasonably controllable or preventable.”Draft for Public Notice and Comment

Revision Date: June 2012 28

Element Natural Events Action Plan High Wind Action PlanEPA’s notification of newlyidentified uncontrolled source(s). Timing of EE concurrence Prior to NEAP submittal. 40 After the EPA’s approval of High Wind Action Plan. High wind threshold Required part of Natural Events Policy 41 but not specifically required to be

included in NEAP. Required component of plan.

3.7.2.5 Attainment status and the role of High Wind Action Plan

The High Wind Action Plan can be a useful tool for any area that has newly identified sources requiring reasonable controls. However, depending on an area’s attainment status, air agencies may have other options as identified below.

Attainment/unclassifiable/maintenance: As mentioned previously, the EPA agrees that controls are not expected for the first high wind dust exceptional event in a PM attainment area. However, the EPA is unlikely to consider a first high wind dust event, because th e first event is unlikely to result in a violation of the NAAQS. If an area is violating the standard because of more than one high wind dust event in a three-year period, then the EPA will consider the area to “have a history” of high wind dust events. If wind speeds exceed a predetermined wind threshold, then the EPA may not consider the implementation of controls at the time of the event to be a

condition for a determination that the event wa s not reasonably controllable. The EPA will determine this during the demonstration review process. The EPA does not expect to simply

concur on events where sources that were not controlled caused a violation just because the area was previously in attainment. The EPA expects to look closely exceedances that occurred with wind speeds below the wind threshold to overwhe lm reasonable controls or cause emissions

from natural undisturbed areas. If an attainme nt area has violations below the high wind

threshold and the EPA determines that the concentra tions are attributable to sources that could be reasonably controlled going forward, the EPA will do one of the following:

1. Request that the submitting agency develop and implement an adequate High Wind Action Plan and concur upon a pproval of the HWAP going forward if all other EER

criteria have been met.

2. Nonconcur. If the nonconcurrence results in an area’s designation as non-attainment, then

this nonconcurrence would also trigger preparation of a SI P incorporating appropriate

PM controls.

40 Unless the NEAP was not adhered to (e.g., BACM never implemented for previous events).

41 “Areas Affected by PM10 Natural Events” (the PM10 Natural Events Policy), memorandum from Mary D. Nichols, Assistant Administrator for Air and Radiation, to EPA Regional Offices, May 30, 1996, page 7, “The conditions that create high wind events vary from area to area with soil type, precipitation and the speed of wind gusts. Therefore, the State must determine the unusually high wind conditions that will overcome BACM in each region or subregion of the State.”Draft for Public Notice and Comment

Revision Date: June 2012 29

The EPA intends to work with the air agency to determine which approach listed above, or other approach, will get reasonable controls in place most effectively and efficiently.

Nonattainment: A PM nonattainment area is expected to have reasonable controls in place, but there may be new sources or improved controls that are identified after the original implementation of the reasonable controls. A dditionally, during high wi nd conditions, sources outside the designated nonattainment area may contri bute to violations in the nonattainment area. The EPA will consider the wind speeds in the ev ent(s) in question relative to the high wind threshold in determining if additional contro ls are reasonable. In cases where additional reasonable controls are needed, the EPA may be compelled to do one of the following:

1. Request that the submitting agency devel op and implement an adequate High Wind Action Plan, and concur on exceptional events upon approval of the HWAP if all other EER criteria have been met. Subsequent events with wind speeds above the high wind threshold could similarly be concurred upon.

2. Nonconcur in the absence of additional acti ons beyond what is required by the SIP and its associated deadlines. In these cases, th e EPA would not remove the events from regulatory decisions. As a result, the event-re lated concentrations may play a role in regulatory actions such as a cl ean data finding or a failure to attain decision. For example, this option may be most sensible to all parties early in a plan ning cycle when an agency is working on implementing controls that are e xpected to result in significant improvements

in an area’s dust control.

3. Nonconcur and conduct a SIP call. If the EPA identifies a major deficiency in the SIP controls, then the EPA may choose to nonc oncur and issue a SIP call to expedite implementation of reasonable cont rols on particular sources.

The EPA intends to work with the air agency to determine which approach listed above, or other approach, will get reasonable controls in place most effectively and efficiently.Draft for Public Notice and Comment

Revision Date: June 2012 30



### 4. Mitigation

The EER was promulgated pursuant to Section 319 of the Clean Air Act which contains a provision that each air agency “must take nece ssary measures to safeguard public health regardless of the source of the air pollution...” This provision was the basis for the mitigation requirements in 40 CFR §51.930 and the requiremen t in the EER at 40 CFR §50.14(c)(1)(i) that all air agencies must “notify the public promptly whenever an event occurs or is reasonably anticipated to occur which may result in the exce edance of an applicable air quality standard.” The language at 40 CFR §51.930 requires that:

“(a) A State requesting to exclude air quality data due to exceptional events must take appropriate and reasonable actions to protect public health from exceedances or violations of the national ambient air quality standards. At a minimum, the State must:

(1) Provide for prompt public notifi cation whenever air quality c oncentrations exceed or are expected to exceed an applicable ambient air quality standard;

(2) Provide for public education concerning acti ons that individuals may take to reduce exposures to unhealthy levels of air quality during and fo llowing an exceptional event;

and

(3) Provide for the implementation of appropria te measures to protect public health from

exceedances or violations of ambient ai r quality standards caused by exceptional

events.”

Although the language at 40 CFR §51.930 does not re quire the preparation or submittal of a mitigation plan, it does require that the air agency develop and implement processes and measures that could easily become the elements of a formal, written plan. The mitigation criteria focus on specific measures and actions to protect public health, rather than on measures that control or prevent emissions associated with a specific event. So, a mitigation plan may include measures that apply to emissions sources in general (e.g., dust suppression or covering techniques for mineral processing) rather than thos e measures or controls that might be discussed in the “not reasonably controllable or prev entable” portion of an ev ent demonstration (e.g., controls/measures X, Y, and Z were in place on sources A, B, and C during the time of the event). A mitigation plan may also include proce dures and responsibilities for public alerts and sheltering advisories. Because having a mitigation pl an in place will help air agencies meet the EER requirements at 40 CFR §50.14(c)(1)(i) related to public notification more systematically, the EPA encourages the development and submittal of a mitigation plan with the demonstration package if one has not already been adopted.Draft for Public Notice and Comment

Revision Date: June 2012 31



### 5. Process Issues for Exceptional Eve nts Including High Wind Dust Events

5.1 Demonstrations Package Submittal and Review

The EPA encourages air agencies to engage in regular communication wi th the EPA to prepare complete demonstration packages that meet the requirements of the EER as interpreted by this document, but that also avoid unnecessary detail and the associated preparation effort. The EPA

will make its decision based on information presented by the air agency, along with any information that the EPA may have or ge nerate. Determinations on Exceptional Event demonstrations do not constitute final agency action until they are reli ed upon in a regulatory decision such as a finding of attainment ornonattainment which will be made through noticeand-comment rulemaking process.

5.2 Timeframes

The EPA recommends the following timeframes for exceptional events processes as outlined in

Table 6 below.

Table 6. Timeframe for Exceptional Event Processes. Exceptional Event

Demonstration

Action Timing Timing Specified by

EER? Air agency submits a prospective controls analysis Any time in advance of the EPA’s review of a particular event or set of events. No

1. Air agency places flags in AQS Flags and an initial even t description should be placed in AQS in accordance with the schedules for submission of data to the AQS database (i.e., within 90 days of the end of the previous quarter) but not later than July 1 st of the calendar year following the event in which the flagged measurement occurred. Yes

2. Air agency submits

letter of intent to submit a package (optional) To promote early communi cation, the EPA suggests that air agencies provide a letter of intent to submit a demonstration package for flagged data in AQS as soon as possible after th e agency identifies the significance of the event, if possible within 12

months from the event occurrence. 42
This is an optional step that would alert the EPA of an air agency state’s inten tion to submit a package for a flag. See Appendix C fo r an example letter of

intent. No

42 The Letter of Intent is an optional step and the EPA reco gnizes that states may need additional time to prepare and submit demonstration packages particularly where the basis of the exclusion is violating an annual standard or a 3- year design value. Similarly, a state could consider submitting an annual letter of intent if annual submittal makes sense for resource planning or for histor ically seasonal events. If a state deci des to submit a letter of intent, the EPA recommends that it be submitted as expeditiously as possible following the state identifying the event or events as having significance.Draft for Public Notice and Comment

Revision Date: June 2012 32

Exceptional Event

Demonstration

Action Timing Timing Specified by

EER? 3. The EPA responds to an air agency’s

notice of intent and informs the air agency

of EPA’s review plans. Anticipated to be within 60 da ys of receipt of letter of intent to submit a package from air agency. The EPA response will provide th e regional office’s best assessment of the priority that can be given to the submission once received and any case-specific advice the EPA may have to offer for the preparation

of the demonstration.

The EPA will generally give priority to exceptional

event decisions that aff ect near-term regulatory

decisions. No

4. Air agency submits exceptional event package to the EPA The EER allows air agencies to submit packages up to 3 years following the end of the calendar quarter in which the event occurred, or 12 months prior to the date that a regulatory deci sion must be made by the EPA, whichever is sooner . Schedules are generally

tailored in 40 CFR Part 50 when NAAQS revisions

result in initial desi gnations for new NAAQS. Yes

5. Air agency submits High Wind Action Plan (optional) Submit with EE package or w ithin 6 months from the

EPA’s notification of newl y-identified uncontrolled source(s). No

6. The EPA completes

initial review of exceptional event package & sends letter to air agency outlining preliminary

assessment of completeness of package/need for

additional

information 43 Anticipated within 120 days of receipt by the EPA. No

7. Air agency provides supplemental information requested by the EPA, if needed Requested within timeframe identified by the EPA in the initial review letter (step 4). This will typically be 60 days from receipt of th e letter from the EPA. The EPA recognizes that air agencies may need more than 60 days to prepare and submit some types of supplemental information. The EPA is willing to work with agencies on supplemental timeframes; however, the mandatory timing of EPA actions may limit the response time the EPA allows. No

43 The EPA may also request additional information during late r steps (e.g., as part of the final review (step 8)).Draft for Public Notice and Comment

Revision Date: June 2012 33

Exceptional Event

Demonstration

Action Timing Timing Specified by

EER?

8. The EPA final review of EE package For EE packages that impact a regulatory decision the EPA intends to make a decision regarding

concurrence within 18 months of submittal of the complete package, or sooner if required by a regulatory action. No

5.3 Public Comment

If an air agency submits substa ntial supplemental information to the EPA after the air agency’s initial opportunity for public comment, the ai r agency may need to provide an additional opportunity for public comment. The EPA will make a case-by-case decision regarding supplemental opportunities for public comment duri ng the demonstration pr eparation, submittal, and review process and will inform the air agency of this decision. As part of this decision, the EPA may consider potentia l impact and/or expressed public inte rest in the claimed event, data uncertainty, historical applic ation of demonstration appro ach, etc. Additionally, certain regulatory actions that may rely on exceptional event data exclus ions (e.g., proposed designation or redesignation classifi cations and attainment determinati ons) require the EPA to provide an opportunity for public comment prior to the EPA’s taking final Agency action.

If an additional opportunity for public commen t is needed, the air ag ency should submit the

additional information to the EPA within the timef rame outlined in step 7 above and then make the information available for public comment. Once the opportunity for public comment has closed, the air agency should s ubmit the public comments, if a ny, along with the air agency’s responses, to the EPA within 30 days of the clos e of the public comment period. If air agencies do not submit High Wind Action Plans as part of the exceptional event de monstration package, air agencies should also provide opportunity for public comment for the Plan.Draft for Public Notice and Comment

Revision Date: June 2012 34



### 6. Recommendations for Preparing High Wind Dust Exceptional Event

Demonstrations

Section 6 provides practical information on pr eparing and evaluating exceptional events demonstrations for high wind dust events based on the guidance in this document and the EPA’s experience from demonstrations that the EPA ha s reviewed since the promulgation of the EER. Section 6.1 provides the general, suggested framework to prepare a high wind dust event demonstration. Section 6.2 outlines the suggested steps to creating a prospective controls analysis. Section 6.3 provides details and ex amples for the technical elements. The EPA encourages air agencies to include a descrip tion of mitigation strategies as part of the demonstration although submission of a mitigati on plan is not a regulatory requirement.

6.1 Framework for Preparing Evidence to Support a High Wind Dust Exceptional

Event

While the technical elements outlined in the EER suggest that each element can be demonstrated independently, many of the elements are linked. The EPA suggests the following approach to a demonstration, as depicted in Figure 2.

Optional Pre-Step. Provide a prospective controls anal ysis to EPA for approval, which can subsequently be used to supplem ent the evidence in step 2.

Step 1. Develop a conceptual model of how the event unfolded and resulted in the exceedance(s).

Step 2. Address not Reasonably Controll able or Preventable (nRCP).

 Identify high wind threshold (see Appendix A)

 Calculate sustained wind speed: wind speed wi ll inform whether a basic or comprehensive controls analysis is needed.

 Assess general wind direction a nd identify poten tial sources

 Develop controls analysis

Step 3. Present Historical Fluctuations analyses and a conclusion for EPA’s review of whether

the event was in excess of normal historical fluctuations (HF).

Step 4. Address Clear Causal Relationship (CCR).

 Conduct CCR analyses
 Consider whether CCR identified so urces not addressed in nRCP.

Step 5. Once sufficient HF analyses have been co mpleted and CCR has been demonstrated, then Affects Air Quality (AAQ) will ge nerally have also been satisfied. Provide information that AAQ has been met by providing HF an alyses and demonstrating CCR.

Step 6. Once nRCP and CCR have been satisfied, then the element for Natural Event will generally have also been satisfi ed. Provide information that Natu ral Event has been satisfied by demonstrating nRCP and CCR.Draft for Public Notice and Comment

Revision Date: June 2012 35

Step 7. Address No Exceedance But For the event (NEB F) only after all previous criteria have

been satisfied.

The EPA recommends reviewing an d revising if necessary the c onceptual model after the air agency completes each identified step.

Figure 2. Suggested order for preparing techni cal elements for demonstration packages for high wind dust events.

Step 1 Develop a Conceptual

Model Step 2

nRCP

Basic Controls Analysis

 wspd ≥ high wind

threshold Comprehensive Controls Analysis

 wspd < high wind

threshold

Step 4

CCR Step 3

HF

Step 5

NEBF Natural Event (derived from nRCP and CCR)

AAQ

(derived from HF

and CCR ) Optional Pre-step Prospective Controls AnalysisDraft for Public Notice and Comment

Revision Date: June 2012 36

6.2 Preparing a Prospective Controls Analysis (Optional)

An air agency's request for a prospective determ ination of reasonable controls, independent of a specific exceptional event request, shoul d include the following elements:



### 1. Statement of which NAAQS (i.e., pollutant, date of relevant NAAQS, averaging time), area (e.g., Ventura County, California) and time period (e.g., January 1, 2012 – December 31, 2015) are to be covered by the prospective determination.



### 2. Statement of the area's attainment status for the pollutants (e.g., seri ous nonattainment with

an extended attainment date for the 2006 24-hour PM 2.5 standard) and resultant required CAA control level (e.g., nothing, RACT, RACM , BACT, BACM and/or Most Stringent Measures (MSM)).



### 3. Current emissions inventory quantifying natural (if available) and anthropogenic sources of the pollutants and identifying all those the air agency considers significant.



### 4. Information on whether natural sour ces are reasonably controlled.



### 5. Chronology of agency SIP (and NEAP) submittals to address the required CAA control level

and EPA actions on these submittals. This shoul d identify whether the submittals relied on any commitment for subsequent action and whether the EPA actions were less than full approval. The air agency’s request for a prospecti ve determination shou ld summarize the status of SIP submittals and EPA action for each significant source category. The EPA will

consider this in its review.



### 6. Summary of all exceptional event requests a nd other exceedances for the pollutants in the area over the last 10 years. This should incl ude the number, location, cause (sources) and EPA action for all requests.



### 7. Discussion of any and changes to presence/unde rstanding/requirements for controls and/or

emission sources since EPA’s approval in #5 including:

a. Significant evolution in unde rstanding of control leve ls in #2 (e.g., while 15 ppm was approved as BACM in 2001, 4 ppm is now widely accepted as BACM).

b. Significant changes in the emissions inventory since #5 suggests possible additional significant sources (e.g., past planning efforts focused on wood-smoke, but recent information suggests significan t wind-blown dust so urces as well).

c. Exceptional event requests and other ex ceedances discussed in #6 (e.g., newly recurring exceptional event requests might suggest a new source that lacks reasonable controls despite previous EPA approval of c ontrols and an attainment demonstration).



### 8. A wind speed threshold up to which controls ar e expected to be e ffective (i.e., high wind threshold (See Section 3.1.4 and Appendix A)). Should address controlled anthropogenic

sources as well as undisturbed natural surfaces.Draft for Public Notice and Comment

Revision Date: June 2012 37

Upon review of the prospective controls anal ysis EPA will approve, disapprove, or request

additional information. The EPA e xpects to approve prospective c ontrols determinations when all of the following occur:

 The air agency provide s all the above items.

 EPA has fully approved the requi red CAA control level in #5.

 EPA has confirmed fulfillment of all underlying commitments in #5.

 The air agency certifies there are no additi onal considerations in #7 and EPA agrees.

 EPA agrees with the wind threshold (#8).

EPA does not expect to approve prospective de terminations if any of the following occur:

 The air agency's request does not include all the items listed above.

 The air agency has not demonstrated th e required CAA cont rol level in #5.

 The air agency has not confirmed fulfillment of commitments in #5.

 Considerations in #7 indicat e that some significant sources are lacking reasonable controls and/or implementation of controls.

 EPA disagrees with th e wind threshold (#8).

The EPA may subsequently approve an initially unapprovable prospective c ontrols analysis, if the submitting air agency revises the demonstration to address EPA concerns (e.g., missing elements are provided, the high wind threshold is altered, or new information on existing controls is provided). If the EPA’ s inability to approve the prospect ive controls analysis is based

on the need for reasonable controls on additional sources, then EPA may not be able to approve the prospective controls analysis until the subm itting agency develops, submits, and establishes a plan (e.g., High Wind Action Plan) to implement the needed controls.

6.3 Recommended Methods for the Tec hnical Elements of a High Wind Dust Exceptional Events Package

This section contains recomme ndations for preparing and demons trating the technical elements for high wind dust events. These recommendations and examples do not represent the full suite of analyses that could be conducted as part of a high wind dust exceptional events package, but are intended to show the kinds of analyses and descriptions that EPA expects. The examples were taken from EPA Region 9 analyses and th e following high wind dust event demonstration packages that were submitted to EPA Region 9: 44

44 Full exceptional event demonstration packages are available as follows:

 Anaheim (SCAQMD, event date: October 13, 2008) at

http://www.aqmd.gov/pub_edu/notice_ exceptional_events_2009.html

 Assessment of Qualification for Treatment under the Fede ral Exceptional Events Rule: High Particulate (PM10)

Concentration Event in the Phoenix Area on April 30, 2008. Technical report prepared by the Arizona Department of Environmental Quality, Air Quality Division. August 16, 2010.

 State of Arizona Exceptional Event Documentation for the Events of July 2 nd through July 8 th 2011, for the Phoenix PM10 Nonattainment Area. Report prepared by Arizona Department of Environmental Quality (ADEQ), March 8. 2012.Draft for Public Notice and Comment

Revision Date: June 2012 38

 Anaheim: South Coast Air Qualit y Management District (SCAQMD)

 Phoenix: Arizona Department of Environmental Quality (ADEQ)

6.3.1 Step 1: Develop a Conceptual Model

A demonstration package for a high wind dust even t should include a conceptual model of how the event occurred. A conceptual model is generally used to describe various concepts and their relationships. For exceptional events, the conceptual mode l should identify the various phenomena (e.g., high wind conditions and emissions ) that occurred that resulted in the exceedance. In its simplest form, this could be a narrative description of how the event unfolded and resulted in the exceedance(s). The conceptual model will be similar to an abstract and should help tie the various rule criteria together into a cohesive explanation of the event. The following information is suggested to be in cluded in the conceptual model:

 Description of weather phenomen a that resulted in high wind

 Description of sources (la nd areas, industrial sources, other anthropogenic sources, natural sources, types of PM/dust) likely entrained by the high wind

 Explanation of the path by which the dust reached the monitor(s)

 Description of and map showing relevant monitors, topography, and other relevant geographic features that assist in understanding how the event developed and resulted in

the exceedance.

 Description of how the event da y differs from non-event days

 Description of concentration and wind pa tterns for the exceeding monitor(s) and for surrounding area

The following is an example of the type of na rrative EPA suggests for the conceptual model. 45

Southern California’s South Coast Air Basin (Basin) consists of 10,743 square miles and consists of Orange County and the non-desert portions of Los Angeles, Riverside and San Bernardino Counties. The population of the Ba sin is approximately 16 million people, with approximately 11 milli on gasoline powered vehicles and 300,000 diesel vehicles. The coastal plain contains most of the popul ation of the Basin, which is surrounded by tall mountains, including the San Gabriel M ountains to the north, the San Bernardino Mountains to the northeast, a nd the San Jacinto Mountains to the east. The coastal range of the Santa Ana Mountains separates the in land part of Orange County from Riverside County. The proximity of the Pacific Ocean to the west has a strong influence on the climate, weather patterns and air quality of the Basin. The mountains also have a significant impact on the wind patterns of the Basin. Offshore winds flow down slope and are warmed and dried by compressional heating, gaining momentum through the passes and canyons. Northeasterly winds, known as Sa nta Ana winds, typically account for the highest wind events in the Basin, occurri ng several times each year. Onshore high-wind

45 Letter dated November 22, 2010 to Matthew Lakin, Mana ger Air Quality Analysis Office USEPA Region 9, from Karen Magliano, Chief Air Quality Data Branch Californi a Air Resources Board, tran smitting final report dated August 5, 2010 entitled, “Analysis of Exceptional Events Contributing to High PM10 Concentrations in the South Coast Air Basin on October 13, 2008.”Draft for Public Notice and Comment

Revision Date: June 2012 39

events also occur with the strongest winds typically occurring in the mountains and

deserts.

Violations of the PM 10 NAAQS were recorded at the South Coast Air Basin Anaheim monitoring station on October 13, 2008, due to high winds. The 24-hour mass

concentration at Anaheim was measured with a federal equivalent method (FEM) Tapered Element Oscillating Microbalance (TEOM) continuous monitor, with a midnight-to-midnight 24-hour av erage concentration of 199  g/m 3 . This was not a sampling day for the Federal Reference Met hod (FRM) filter measurements in the Basin.

While no other PM 10 measurements exceeded the federal standard level (150  g/m 3 ),

other stations in the Basin had elevated concentrations during the same period.

A strong Santa Ana wind event developed on October 13 th , causing very high northerly through easterly winds in the mountains and deserts, especially through and below the wind-favored passes and canyons in the Basi n. National Weather Service (NWS) weather stations measured extremely high peak wind gusts throughout the da y in areas upwind of the high SCAQMD PM 10 stations, including : 87 mph by in [ sic ] the Santa Ana Mountains of Orange County (Freemont Canyon RAWS); 87 mph in the San Gabriel Mountains of Los Angeles County (Chilao RA WS); 79 mph in the Malibu Hills of Los Angeles County; 61 mph at Ontario Internat ional Airport in San Bernardino County; 55 mph at Corona Airport in Ri verside County; 51 mph at Chi no Airport in San Bernardino County and 41 mph at the Santa Ana – John Wayne Airport in Orange County. Due to the widespread winds, sources of the windblown dust were both natural areas, particularly from the mountains and de serts, and BACM-cont rolled anthropogenic sources. The timing of this event is verified with the high wind observations and reports of reduced visibility and blowing sand and dust, in conjunction with the hourly TEOM

and BAM PM 10 measurement data from nearby monitors in the Basin, when available.

The following maps support the conceptual model:

 Map of the South Coast Air Basin Showi ng Air Monitoring Sta tions and Forecast

Areas

 Map of South Coast Air Basin with Selected Cities and Topography

 Map of South Coast Air Basin PM 10 Monitors

6.3.2 Step 2: Address not Reasonably Controllable or Preventable (nRCP)

The nRCP demonstration should identify the emissions that were expected to have contributed to the event, both natural and anthropogenic, and indicate how they were not reasonably controllable or preventable. Generally, the nRCP will include identification of natural sources and whether they are reasonably controllable, an d identification of anthropogenic sources and the

associated reasonable controls.

6.3.2.1 Identify source areas and source categories expected to have contributed to the event

EPA recommends that the first step of the nRCP demonstration is to identify the likely source area and source categories expected to have co ntributed to the event. The source areas and categories can be general, such as, “The area upwind of the monitor in cludes portions of theDraft for Public Notice and Comment

Revision Date: June 2012 40

Santa Ana Mountains to the NE of the station a nd extending down into the Basin. Sources of the windblown dust were both natural areas, particul arly from the mountains and deserts, and BACM-controlled anthropogenic sources.” 46 It is important to identi fy the geographic references

on a map.

6.3.2.2 Consideration of wind speed

The demonstration should indicate what the expe cted high wind threshold is for the local area and whether the sustained wind speed exceeded this level (See Appendix A2 and A3 for information on developing a high wind threshold). The wind speed data do not necessarily have to be at the location of the exceedance, but they should represent the s ource area generating the emissions. Generally, the EPA will accept that hi gh winds could be the cause of a high 24-hour average PM 10 or PM 2.5 concentration if there was at leas t one full hour in which the hourly average wind speed was above the area-specific high wind threshold. Potential issues arise when determining the hourly average wind speed if wind speeds are not recorded at specified intervals throughout each hour. While some sources of wind speed data use hourly averages, other data sources employ 1 - 5 minute (“short-period”) av erages. When the available wind speed data consist of only the wind speed dur ing a fixed short period of each hour (e.g., the first or last five minutes of each hour) or the wind speed during th e variable short period when wind speed was at its maximum during the hour, the EPA will genera lly accept that the hourly average wind speed was above the threshold if the reported short- period wind speed was above the threshold. Where wind speed is recorded at specified interval s throughout each hour, agencies should use all

recorded data to calculate the hourly average wind speed. 47 EPA may, however, consider multiple occurrences of high wind measured at th ese shorter averaging times as part of the weight-of-evidence demonstration. At a minimum, demonstrations should include the maximum sustained wind speed for each hour of the event a nd also the number of periods above the high

wind threshold.

The EPA notes that The National Climate Center has started archiving the 2-minute winds for every 2-minute period of each hour for all ASOS st ations in the country. Almost all sites have data since March 2005, with most archiving da ta since 2000. The EPA has further developed a preprocessor to AERMOD, called AERMINUTE, that takes short-period wind speed observations and calculates an hourly average wind that can be fed into AERMET, the AERMOD meteorological proce ssor. The AERMINUTE output is user friendly. AERMET can also accept, process, and calculate hourly av erage wind speeds from sub-hourly data with a resolution equal or greater than 5-minutes from sources other than AERMINUTE.

The EPA will consider shorter-te rm “snapshots” of wind data such as National Weather Service hourly summaries as part of the weight-of-evidence demonstration.

46 Letter dated November 22, 2010 to Matthew Lakin, Mana ger Air Quality Analysis Office USEPA Region 9, from Karen Magliano, Chief Air Quality Data Branch Californi a Air Resources Board, tran smitting final report dated August 5, 2010 entitled, “Analysis of Exceptional Events Contributing to High PM10 Concentrations in the South Coast Air Basin on October 13, 2008.”

47 While the National Weather Service defines a “sustained wind” as the wind speed determined by averaging observed values over a two-minute period, the EPA believes that it would take a longer period of high wind speeds to raise enough dust to significantly influence measured 24-hour average values of PM10 or PM2.5Draft for Public Notice and Comment

Revision Date: June 2012 41

Generally, the EPA recommends using NWS data or the National Climate Data Center. Where meteorological data are not availa ble for a particular area and su ch data are critical for the demonstration, agencies may substitute modeled surface wind speeds for actual measured data. Models that agencies can use to develop estimates for actual measured wind speed surface measurements include MM5, WRF, and, possibly, NAM. Wind speed data from a multitude of sources and with different averaging times, incl uding model outputs may be included in a high

wind dust event demonstration.

6.3.2.3 Basic controls analysis

Generally, if the wind speed data is at or above the area-specific high wind threshold, the air agency can provide a basic controls analysis to show that the event was not reasonably controllable or preventable (see Section 3.1.5.1). A basic controls analysis should identify all contributing emission sources in upwind areas an d provide evidence that those sources were reasonably controlled, whether anthropogenic or natural.

A basic controls analysis would include a brief description of local/upwind sources contributing to the event and a descrip tion of the controls on the anthropogeni c sources in place at the time of the event (e.g., local BACM measures). In gene ral, EPA expects all upwind areas of disturbed soil to be considered potential contributing sources. For the sources identified, the submitter should explain that dust emissions occurred de spite having reasonable co ntrols in place (e.g., controls that overwhelmed by high wind). Th e EPA may request additional information on specific sources once the information has been reviewed.

An example of a basic controls analysis for the anthropogenic sources in a nonattainment area

is: 48

This requirement is met by demonstrating that despite reasonable and appropriate measures in place, the October 13, 2008 wi nd event caused the NAAQS violation. During this event, there were no other unusual PM 10 -producing activities o ccurring in the Basin and anthropogenic emissions were approximate ly constant before, during and after the event. SCAQMD has implemented regulatory measures to control emissions from fugitive dust sources and open burning in the South Coast Air Basin. Implementation of Best Available Control Measures (BACM) in the Basin has been carried out through SCAQMD Rule 403 (Fugitive Dust), as well as s ource-specific rules. With its approvals

of the South Coast PM 10 Attainment Plans in the State Implementation Plan (SIP), EPA has concluded that this control strategy repr esents BACM and Most Stringent Measures (MSM) for each significant s ource category, and that the im plementation schedule was as expeditious as practicable.

 SCAQMD Rule 403 establishes best availa ble fugitive dust control measures to reduce fugitive dust emissions associat ed with agricultural operations, construction/demolition activities (including grading, excavation, loading, crushing, cutting, planning, shaping or gr ound breaking), earth-moving activities,

48 Letter dated November 22, 2010 to Matthew Lakin, Mana ger Air Quality Analysis Office USEPA Region 9, from Karen Magliano, Chief Air Quality Data Branch Californi a Air Resources Board, tran smitting final report dated August 5, 2010 entitled, “Analysis of Exceptional Events Contributing to High PM10 Concentrations in the South Coast Air Basin on October 13, 2008.”Draft for Public Notice and Comment

Revision Date: June 2012 42

track-out of bulk material onto public pa ved roadways, and open storage piles or

disturbed surface areas.

 SCAQMD Rule 1156, Further Reductions of Particulate Emissions from Cement Manufacturing Facilities, is a source-specific rule that applies to all operations, including material handling, storage a nd transport at cement manufacturing

facilities. It restricts vi sible emissions from facility operations, open piles, roadways and unpaved areas and requires enclosed systems for loading, unloading and transfer of materials. Other opera tions must employ wind fencing and wet suppression systems or be enclosed with permitted control equipment.

 SCAQMD Rule 1157, PM 10 Emissions Reductions from Aggregate and Related Operations, is a source-specific rule app licable to all permanent and temporary aggregate and related oper ations that produce sand, gravel, crushed stone or quarried rocks. Like Rule 1156, this rule restricts the discharge of fugitive dust emissions into the atmosphere through plume opacity tests and limiting visible plume travel to within 100 feet of th e operation. This rule requires: prompt removal of material spillage; stabilizati on of piles with dust suppressants; the control of loading, unloadi ng, transferring, conveyors, and crushing or screening activities with dust suppressants or ot her control methods; stabilization of unpaved roads, parking and staging areas; sweeping of paved roads; and the use of track-out control systems.

 SCAQMD Rule 1158, Storage, Handling, a nd Transport of Coke, Coal and Sulfur, is a source-specific ru le that applies to any fac ility that produces, stores, handles, transports or uses these material s. This rule restricts visible emissions and requires that piles be maintained in enclosed storage and that unloading operations be conducted in enclosed stru ctures with water spray systems or venting to permitted air pollution contro l equipment. It also has specific requirements to control emissions from roadways, other facility areas, and conveyors and the load ing of materials.

 SCAQMD Rule 1186, PM 10 Emissions from Paved and Unpaved Roads and Livestock Operations, requires rapid rem oval of paved road dust accumulations

and establishes a treatment schedule for unpaved roads, street sweeper procurement standards, and design st andards for new road construction. SCAQMD Rule 1186.1, Less-Polluting Sweep ers, requires procurement of alternative-fueled equipment when gove rnmental agencies replace street

sweepers.

 SCAQMD Rule 444, Open Burning, ensures that open burning is conducted in a manner that minimizes emissions and impacts, and that smoke is managed to protect public health and safety. This rule requires authorization for agricultural and prescribed fire, limited to days th at are predicted to be meteorologically conducive to smoke dispersion and that will not contribute to air quality that is unhealthy for sensitive groups or worse. It also restricts re sidential and waste burning.

 SCAQMD Rule 445, Wood Burning Devi ces, reduces pollution from woodburning fireplaces and other devices thr ough requirements for new construction, curtailment of wintertime wood burning in sp ecified areas when poor air quality is

forecast and restriction of the sa le of unseasoned firewood. The SCAQMD Healthy Hearths program provides pub lic education on how to reduce airDraft for Public Notice and Comment

Revision Date: June 2012 43

pollution from wood burning and encourag es the conversion to natural gas burning fireplaces through an incentive program.

October 13, 2008 was designated an agricultural and prescribed wildland “no-burn” day, in accordance with SCAQMD rule 444. The PM 2.5 24-hour averages at all stations in the Basin, including Anaheim, were well below the 24-hour PM 2.5 NAAQS and the PM 10 was estimated to be composed of 87% PM-Coarse particles (PM 10-2.5 ) and only 13 percent PM 2.5 . This shows that mostly crustal material comprised the PM 10 mass and not transported or locally generated ur ban pollution or combustion sources.

A survey of the SCAQMD complaint records and inspection reports for Anaheim and all

other areas of the Basin indicated no evid ence of unusual particulate emissions on October 13, 2008 other than related to the st rong winds. The complaints are summarized in Table 2-7 from the SCAQMD Clean Air Support System (CLASS) database for complaints and compliance actions. Due to the windy conditions, SCAQMD compliance staff responded to 17 compla ints related to windblown dus t on October 13. Most were in Riverside and San Bernardino County, but two were in Orange County with no further compliance action taken. No Notices of Violation or Notices to Comply were issued in the Basin for fugitive dust on this day. Several complaints were directly related to the strong winds and windblown dust that overwhelmed the strict fugitive dust controls that

are enforced in the Basin. The control met hods were generally effective throughout the Basin, but were apparently overwhelmed in se veral instances by the strong, gusty winds, causing windblown dust and sand to be entrained in the atmosphere.

In addition to the information provided in the ex ample above, the basic co ntrols analysis should also include an explanation of w hy the control measures should be considered as reasonable. For example, an explanation could include statements similar to: “the source area is within the

boundaries of a serious nonattainme nt area and therefore control measures required to reduce windblown dust as part of the ar ea’s approved SIP should suffice as reasonable controls, as additional controls, beyond what is currently required, are economically and technically

infeasible.” The basic controls analysis should also ensure that the controls discussed include controls for disturbed areas and materials open storage areas susceptible to winds, as well as controls on production sources such as materials loading and unloading.

While the above example provided a basic controls analysis for anthropogenic sources in a nonattainment area, an area attaining the NAAQS can similarly present the current rules, if any, and

how the identified rules are reasonable given the attainment status.

In addition to identifying controls on anthropogen ic sources, it is important to indicate whether the natural sources could have been reasonably-c ontrolled. For example, the following statement could fulfill this need: “Wind speeds were high enough to entrain dust from natural areas including undisturbed mountain a nd desert areas upwind of the m onitor. Emissions from these sources were not reasonably controllable due to the cost of applying controls over such a large land area and because of the detrimental effect on the natural ecosystem that could result.” Finally, if EPA recommended controls improvement s (e.g., as part of a previous high wind dust exceptional event review) then the controls an alysis should address how these controls improvements have been addressed.Draft for Public Notice and Comment

Revision Date: June 2012 44

6.3.2.4 Comprehensive controls analysis

Generally, if the wind speed data is below the area-specific high wind threshold, the air agency will be expected to provide a comprehensive cont rols analysis to show that the event was not reasonably controllable or preventable (s ee Section 3.1.5.2). Significant emissions from reasonably-controlled anthropogeni c or natural sources are not expected below the high wind threshold, and therefore the analys is should further consider whet her all contributing sources are reasonably-controlled. Comprehensive controls anal ysis should include detailed analyses such as: back-trajectories indicating specific sources in the upwind ar ea, a day specific inventory of the contribution for significant sources, detailed descriptions of contro ls and their effective implementation and enforcement (where appropriate), and also include a de tailed explanation of why the control measures should be considered as reasonable.

For comprehensive controls analysis, EPA will place significantly more weight on the wind speed data associated with high particulate matte r concentrations. The dem onstration is likely to be increasingly difficult as sustained wind sp eeds decrease below the applicable high wind threshold and many of these cases may not be concurrable.

One type of analysis that an air agency coul d use when developing a comprehensive controls analysis is a source contribution analysis, simila r to the analysis presented below, for multiple hours of the day. For most events, a single back trajectory may not account for wind direction fluctuations during the event and may not accura tely capture all the sources that may be contributing to the exceedance, and where c ontinuous PM measurements are available, trajectories for hours with the greatest PM concentr ations are most critical. Also, when moderate winds are responsible for high leve ls of measured particulate matte r, considerably more attention should also be placed on the hours of the day pr eceding the event to adequately assess the sources contributing to the exceedance that may have influenced particulate matter

concentrations before the arrival of the claimed event.

Following is an example of a methodology of a back-trajectories and inventory for a comprehensive controls analysis 49 :

Back-trajectories were plotted in 5-minut e links based on 5-minute average wind speed

and wind direction data recorded at the West 43 rd Avenue station. The back-trajectory plot for April 30, 2008 is shown in the followi ng figure. These back-trajectories revealed that winds accompanying peak PM 10 concentrations typically blew from the westsouthwest to the West 43 rd Avenue station, crossing a mosaic of agricultural, residential, industrial, and riverbed lands. GIS files were used to determine the zoned uses of all lands within 1⁄2 mile of each back-traject ory track over which wind parcels travelled during the two hours prior to delivering the peak PM 10 concentration to the West 43 rd
Avenue monitor. Lands under active construction on each exceedance day were identified from earthmoving permit records. Parcel area s were aggregated within seven general

49 Assessment of Qualification for Treatment under the Federal Exceptional Events Rule: High Particulate (PM10) Concentration Event in the Phoenix Area on April 30, 2008. Technical report prepared by the Arizona Department of Environmental Quality, Air Quality Division. August 16, 2010.Draft for Public Notice and Comment

Revision Date: June 2012 45

categories for which limited emission factor data were available: vacant, agriculture, construction, open/restricted access, riverbed , sand and gravel/landfill, and other lands. The uses of these land categories ar e generally defined as follows:

Vacant – represents undeveloped land to wh ich public access is not restricted; Agriculture – represents lands under agricultural cu ltivation;

Construction – represents lands being developed for long term use that will include ground coverage elements such as pavement, structures, or landscaping that will prevent the generation of windblown dust; Passive/restricted open space – represents undeveloped or partially developed lands to which public vehicular access is restricted (these lands include public parks, national forests, military posts, and Indian reservations);

Riverbed – represents riverbed channels of the Salt and Gila River branches; Landfill/sand and gravel – represents lands being us ed for mineral extraction or waste deposit;

Other – represents developed lands that are protected from windblown dust generation by elements such as paving, structures, and landscaping.

PM 10 emissions were calculated for each b ack-trajectory hour using emission factors derived from the Nickling and Gillies data, 5- minute wind speed averages recorded at the

West 43 rd Avenue monitoring station, and the landuse acreage along each back-trajectory computed by MAG staff. The emission factor equations were used to compute PM 10Draft for Public Notice and Comment

Revision Date: June 2012 46

emissions for each 5-minute portion of each back-trajectory hour. For each 5-minute period, the measured average wind speed was co mpared to the threshold friction velocity calculated at a 10-meter height to determin e whether the threshold wind speed necessary to the generation of windblown PM 10 on each land use, undisturbed and disturbed, had been exceeded. If the threshold velocity was exceeded, the appropriate Nickling and Gillies emission factor equation was used to compute PM 10 emissions in units of gm/cm 2

- sec. Emissions for each 5-minute period within each hour and within each land use category were converted to units of lb/ acre-hr and then summed to produce hourly average PM 10 emission rates per land use category. Th e emission rates for the other land use categories and the 2nd hour were calculated using a similar methodology. The land use category emission rates were then multiplied by the acreages within each appropriate land use category to derive PM 10 emissions for each back-t rajectory hour by land use category. The PM 10 emissions for each of the back-t rajectory hours on each exceedance day were summed together to calculate to tal emissions over each exceedance day backtrajectory by land use category. These land us e category emissions were then grouped by anthropogenic and nonanthropogeni c categories to assess the relative contribution of nonanthropogenic sources to exceed ances recorded at the West 43 rd Avenue monitoring station during 2008. A summary of the results of these calculations for the April 30, 2008 exceedance day is presented in the following table.

The analysis should also include informati on on controls on anthropogenic sources were appropriately implemented and enforced during th e time of the event. In addition to identifyingDraft for Public Notice and Comment

Revision Date: June 2012 47

controls on anthropogenic sources, it is important to indicate whether th e natural sources could have been reasonably-controlle d. Available inspection reports and/or notic es of violations (NOVs) in upwind areas should be submitted, if av ailable. The EPA recognizes that agencies have varied methods of permitting and enforcement and does not expect all agencies to have

these records for all events. The EPA does, however, expect agencies to make a general showing that the agency has a program in place to ensure controls are being enforced as appropriate (even if no specific evidence exists for the particular day of the event). The EPA will also consider the overall compliance rates for specific source ca tegories in determining whether reasonable controls were in place.

The controls analyses when wind speeds ar e below the high wind threshold should address whether control improvements were recommended by EPA (e.g., as part of a previous high wind dust exceptional event review). If controls improvement had been previously recommended then the controls analysis should a ddress how these controls improve ments have been implemented.

6.3.3 Step 3: Present Histori cal Fluctuations (HF) Analyses

As described in Section 3.2, the historical fluc tuations (HF) analyses and an air agency

conclusion will aid EPA’s review and will also inform CCR, NEBF, and AAQ. Specific analyses expected to provide the historical context for the event include:

1. A time series for concentration for the event area for the previous three years, or longer if available, with hi gh wind dust events identified: Concentration data should be 24-hour concentrations for each day. De pending on the quantity of data, it may be appropriate to present monthl y maximums (note that it is not appropriate to present monthly-averaged daily data or any other average of the daily data as this masks other high values). It is appropriat e to identify information su ch as: seasonal or monthly 24-hour means, other event days, and re levant standards. The following figure 50 is an appropriate example of th is type of analysis.

50 State of Arizona Exceptional Event Documentation for the Events of July 2 nd through July 8 th 2011, for the Phoenix PM10 Nonattainment Area. Report prepared by Ar izona Department of Envi ronmental Quality (ADEQ),

March 8. 2012.Draft for Public Notice and Comment

Revision Date: June 2012 48

2. Percentile of concentration relative to a nnual data with and without all high wind dust events: The percentile of the 24-hour aver age PM concentration should be provided for the event day relative to all measurement days over the previous three years or longer. The EPA expects a minimum of 300 data points to be included in this calculation. If the sampling schedule is 1- in-6 day sampling then this percentile should include five years of data (60 samp le days/year for five years provides 300 data points). Higher frequency sampling can ut ilize fewer years of data but not fewer than three years. If three years is not available, consult with EPA.

3. Percentile of concentration relative to s easonal data with and without all high wind dust events: The percentile of the 24-hour average PM concentration should be provided for the event day re lative to all measurement days for the season (or appropriate alternative 3-month period) of the event over the previous three years or longer. It is appropr iate to use the same time horizon as used for the percentile

calculated relative to annual data.Draft for Public Notice and Comment

Revision Date: June 2012 49

6.3.4 Step 4: Address Clear Causal Relationship (CCR)

As described in Section 3.3, the following types of evidence can support the CCR demonstration:

 Occurrence and geographic extent of the event

 Transport of emissions related to the event in the direction of the monitor(s) where

measurements were recorded

 Spatial relationship between th e event, sources, transport of emissions, and recorded

concentrations

 Temporal relationship between the high wind and elevated PM concentrations at the monitor in question

 Chemical composition and/or size distribution of measured pollution that links the pollution at the monitor(s) with particular sources or phenomena

 Comparison of event-affected day( s) to specific non-event days

Each of these types of evidence is treated in detail below. Note that information generated in this portion of the demonstration submittal may result in revisions to the conceptual model and controls analysis. As the flow diagram (Figur e 2) suggests, preparation of a high wind dust exceptional event package is not necessarily a step-wise process.

6.3.4.1 Occurrence and geographic extent of the event

Air agencies can provide the following inform ation to help establish the occurrence and geographic extent of the event: special weathe r statements, advisories , news reports; nearby visibility readings; measurements from monito ring stations; MODIS and other satellite maps; and description of weather condi tions that created the high wind.

 Special weather statements, advisories, news reports on both predic tions and occurrence

of the event: SCAQMD provided the following information for an exceptional event showing for

Anaheim (Note that Appendices from the SC AQMD demonstration submittal are referenced in the excerpt below, but they are not provided as part of this document or the example).

The National Weather Service had predicted this first strong Santa Ana event of the season well in advance and Governor Schwarzenegge r issued a press rele ase on October 10 to prepare the state for Santa Ana winds and the associated wildfire potential (see Appendix A.7).

The Appendix to this document (Sections A.2 through A.6) contains the forecast discussions, short-term forecasts (nowcasts), fire weathe r forecasts, warnings and significant wind reports, as available from the NWS Los Ange les/Oxnard and San Diego Forecast Offices, whose areas of responsibility c over the Basin and much of sout hern California. These show that the strong Santa Ana wind event was well pr edicted in advance, warning the public of potentially damaging winds and windblown dust and sand, along with reduced visibilities.

NWS advisories and warnings for high winds (Appendix, Section A.5) were already in place on October 12, extending through Tuesday, Oct ober 14, or longer. A Wind Advisory isDraft for Public Notice and Comment

Revision Date: June 2012 50

issued by NWS when sustained winds of 30 to 39 mph are expected for 1 hour or longer. A High Wind Warning is issued when sustained wi nds of 40 mph or more are expected for 1 hour or longer, or for wind gusts of 58 mph or more with no time limit. NWS Oxnard issued High Wind Warnings on October 12, extending through the period for the Los Angeles and Ventura County Mountains and Wind Advisori es for the Santa Monica Mountains, the Ventura County coastal and in terior valleys, the Santa Cl arita Valley, the Los Angeles County San Fernando Valley, and the Ventura and Los Angeles County coasts, including Downtown Los Angeles. NWS San Diego issued High Wind Warnings for the San Bernardino and Riverside County valleys (Inland Empire) and the Santa Ana mountains and

foothills and Wind Advisories for the San Bernardino County mountains, Orange County coastal areas, the Riverside County mountains, the San Diego County mountains, and the San Diego County valleys, In short, High Wind Advi sories and Warnings were in place for most

of the South Coast Air Basin and much of southe rn California to warn the public of this high wind event. Northeasterly winds with sustai ned speeds in the 35 to 45 mph range were predicted throughout the region, along with damaging gusts to 70 mph, especially in the mountains and below passes and canyons in th e Inland Empire. Hazardous driving conditions were predicted, especially through and below canyons and passes, as well as blowing dust and sand with reduced visibility, brok en tree limbs and downed power lines.

The AQMD Meteorology Section predicted high winds for Oc tober 13 in the Coachella Valley for AQMD Rule 403.1, which requires specific actions in this area when wind gusts exceed 25 mph. While there are no other AQMD ru le requirements to forecast winds in the Basin, the daily forecast discussion by AQMD issued on October 12 for Monday, October 13 predicted the strong winds. A smoke advisory was already in effect in the morning of October 12 and the strong winds were prominent in the forecast discussion, as follows:

 SMOKE ADVISORY for Sunday: Concentra tions of fine particulates may reach Unhealthy for Sensitive Groups or higher in areas of Los Angeles County directly impacted by smoke from a wild fire in the Angeles National Forest north of Pacoima.

 Monday will be mostly clear, windy and warmer as the offshore Santa Ana winds strengthen. Gusty winds through and below canyons and passes will cause elevated particulate concentrations due to windbl own dust and possibly continued wildfire activity.

PM10 predictions were increased throughout th e Basin for October 13 and agricultural and prescribed burning was prohibited with a No -Burn declaration for the entire Basin. AQMD issued a Smoke and Windblown Dust Advisory in the morning of October 13, reproduced in the Appendix, Section A.10, that warned of th e likelihood of strong Sa nta Ana winds causing high PM10 concentrations in several areas of the Basin, including Central Orange County (Forecast Area 17, including Anaheim), as follows: In addition, strong Santa Ana winds will likely cause PM10 concentrations to reach Unhealthy for Sensitive Groups concentrations or higher in areas throughout the Basin downwind of the winds areas. This includes any areas where windblown dust is visible, especially through and below passes and canyons, until the winds subside. Wind prone areasDraft for Public Notice and Comment

Revision Date: June 2012 51

are likely to include: the San Bernardino Va lley (Areas 32, 33, 34, 35), Riverside County Valleys (Areas 22, 23, 24, 25, 26), Orange County (Areas 16, 17, 18, 19, 20) and the Los Angeles County northern and southern coastal areas (Areas 2 and 4).

 Nearby visibility readings: SCAQMD supplied the visibility readings and ADEQ submitted the visibility pictures for nearby airports during Arizona events.

 MODIS satellite maps: SCAQMD provided the following maps showi ng the spatial distribution of windblown

dust.

 Description of weather conditions that created the high wind: SCAQMD provided the following description of weather conditions around the time of

the event:Draft for Public Notice and Comment

Revision Date: June 2012 52

An upper level trough of low pressure moved through California, between October 9 and 11. The low pressure system did not create mu ch rain in California during this period, but temperatures were cool thr oughout the state. By Sunday, October 12, the backside of the trough was over California, prov iding upper level support for a developing strong Santa Ana wind event. The strong pressure gradient s that developed between the high and low pressure aloft created strong winds. The National Weather Service (NWS) 500 millibar (MB) analyses every 12 hours betwee n 0400 PST on October 12 and 0400 PST on October 14 are shown in the Appendix, Sect ion A.11. The winds ove r California at the 500 MB pressure level started out northwes terly in the morning of October 12 with speeds to 81 mph (70 knots), then became more northerly by the morning of Monday, October 13 with speeds to 57 mph (50 knots). The strong northerly flows aloft, coupled with strong northeasterl y surface pressure gradients, enhanced the offshore flows at the

surface.

The passage of the low pressure trough aloft brought the first str ong cold front of the

season at the surface. Section A.12 in the Appendix shows the NWS sea-level pressure analyses, every three hour s between 1600 PST on October 12 and 0100 PST on October 14. By 1600 PST October 12, the surface low and cold front was over the northeastern border of New Mexico and high pressure wa s building over northern Nevada, increasing the northerly gradients. By 0100 PST on Octobe r 13, the high pressure over Nevada had increased to 1033 MB, strengthening the gradie nt flows across Calif ornia. By 0700 PST, the area of high pressure had expanded and p eaked at 1037 MB. The strength of the high pressure remained nearly the same through th e rest of the day, while the broad area of high pressure slowly moved to the east, cau sing the winds to shift from northerly to northeasterly, then eas terly throughout the day. The strong pressure gradients caused strong winds, especially in s outhern California as the flow of cold air from the area of high pressure further enhanced the winds as it flowed across the mountains. Some gusty winds had already been observed on October 12, but they increased considerably in the early morning of October 13.

This is the classic Santa Ana wind pattern that brings strong winds to southern California. High pressure builds over the Great Basin desert region of the western United States in

the cold air behind the front w ith lower pressure off the sout hern California coast. This pressure gradient creates strong north th rough northeasterly winds, enhanced by thermal gradients due to denser cold air over the Gr eat Basin. The relatively cool air from the

Great Basin deserts flows over the southern California mountains, gaining momentum on the lee side. The downslope flow causes comp ressional warming and drying of the air in

the South Coast Air Basin. This combinati on of strong wind, high te mperatures and low

relative humidities make these Santa Ana c onditions highly conducive to wildfires in

southern California.

The AQMD Meteorology Section routinely anal yzes sea-level pressure gradients in

southern California to assess winds and ai r pollution potential. Th e Summation Pressure Gradient (SPG) is a good indica tor of the strength of the flow and whether it is onshore (positive) or offshore (negative), whereDraft for Public Notice and Comment

Revision Date: June 2012 53

SPG = (SAN-LAS) 51 + (LGB-DAG) 52 + (RIV-DAG) 53

In the morning of October 12, the 0700 PST SPG was

 5.5 MB, indicating moderate

offshore flow. At the same time in the morn ing of October 13, the SPG strengthened to

 14.7 MB, indicating a stronger offshore gradie nt. The gradient was enhanced by the upper level pattern and thermal gradient as described above, to create a strong wind event, especially for several hours through the morning of October 13.

 Measurements from monitoring stations: The following figures show the kind of an alyses based on measurements from air monitoring and meteorological stations that could be used to s how the occurrence and geographic extent of the event. 54 The figures also show that only when the wind speeds

became elevated did PM 10 concentrations also become elevated, supporting the causal relationship.

51 Sea Level Pressure difference between San Diego and Las Vegas

52 Sea Level Pressure difference between Long Beach and Daggett

53 Sea Level Pressure difference between Riverside and Daggett

54 EPA Region 9. ArcGIS analysis using PM10, wind speed, and wind direction data from AQS.Draft for Public Notice and Comment

Revision Date: June 2012 54Draft for Public Notice and Comment

Revision Date: June 2012 55

Further analysis may include more refined GIS da ta combined with surface measurements from various sources. The EPA acknowledges that there are few areas, except large metropolitan areas

that have the number of monitors to document th e sequential nature of an event. The following is an example 55 of the type of analysis that can occur with these types of resources.

55 ADEQDraft for Public Notice and Comment

Revision Date: June 2012 56Draft for Public Notice and Comment

Revision Date: June 2012 57

6.3.4.2 Transport of emissions related to the e vent in the direction of the monitor(s) where

measurements were recorded

Example information to support transport of event -related emissions in th e direction of monitor

includes wind direction data show ing that emissions from sources identified as part of the nRCP demonstration were upwind of the monitor(s) in question.

 Map showing local sources and wind direction 56
Note that the topography gives an indication of sources in this map. Ideally, the likely significant sources such as ag riculture fields, desert ar eas, mountains, and industrial sources would be identified (see next example).

56 EPA Region 9Draft for Public Notice and Comment

Revision Date: June 2012 58

 Back Trajectories: Even if extensive comprehensive controls analysis is not needed, a back-trajectory analysis as shown in Section 6.2.2.5 would be appropriate as part of the CCR demonstration. Note that HYSPLIT trajector ies that cover hundred s of miles are of limited use if the sources of dust are local. The example 57 below uses 1-hour back trajectories based on local surface wind m easurements during periods of high PM 10 and GIS data to identify contributing source categor ies as well as the geogr aphic extent of the event. The total area between the green lin es represents the range of hourly back trajectories during periods of high PM 10 , while the hatched green area represents the portion of the total area that is located with the Gila Ri ver Indian Community boundaries (signified by the solid red line).

57 GRIC Expected Source AreaDraft for Public Notice and Comment

Revision Date: June 2012 59

 Wind roses: A wind rose for periods of the event day show ing wind speed and direction at or near the concentration monitor, coupled with a descript ion of the area suggested by the wind rose, could provide evidence of where the dust wa s transported from. This approach may not

suffice for situations where the sources of dust are not proximate to the monitor.

6.3.4.3 Spatial relationship between the event, so urces, transport of emissions, and recorded

concentrations

The type of information that would support this evidence could be a map showing likely source area, wind speeds, wind direction, and particulate matter concentra tions for the affected area during the time of the event: see the example figure below. 58

58 EPA Region 9Draft for Public Notice and Comment

Revision Date: June 2012 60

6.3.4.4 Temporal relationship between the high wi nd and elevated PM concentrations at the monitor in question

Evidence for establishing the temporal relations hip can include 24-hour time series showing PM

concentrations at the monitor in question in combination w ith sustained and maximum wind speed data at the area where emissions originate d. As shown below, it is most informative to include the sustained wind speed data and the concentration data on the same figure.Draft for Public Notice and Comment

Revision Date: June 2012 61

6.3.4.5 Similarity of chemical composition of measured pollution with that expected from sources identified as upwind

Information such as chemical speciation data fr om the monitored exceedance(s) and sources, or size distribution data, could be part of this type of evidence. These data are not always available, but should be included wherever possible. An example of this type of analysis will be incorporated in this document as one becomes available.

6.3.4.6 Comparison of event-affected day(s) to specific non-event days:

The following types of analyses could be part of this piece of evidence:

 comparison of concentrations and wind speed in the area to days preceding and following

the event

 comparison of concentration data to specific da ys that are similar to the event day with respect to emissions and meteorology

 comparison to other high wind days without elevated concentrations

 comparison of chemical composition (if available) 0 100 200 300 400 500 600 700 800 900

0 10 20 30 40 50 60 70 80 90

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23AnaheimTEOMPM10(μg/m3)WindSpeed(mph)

Time (PST)

Anaheim Hourly TEOM PM10 Anaheim Hourly Wind Speed

Anaheim 1

‐ Minute Wind Speed Freemont Canyon RAWS Wind Speed

Freemont Canyon RAWS GustDraft for Public Notice and Comment

Revision Date: June 2012 62

The following figure is an example of a compar ison of concentrations in the area to days preceding and following the event. 59

6.3.4.7 Alternative Hypotheses

Eliminating other possible non-event causes suppor ts the claimed causal relationship to the high wind event, although conclusively proving the absen ce of all possible or pl ausible other causes is not required or expected. For exam ple, SCAQMD provided the following:

Three wildfires were reported in southern California on October 13, fanned by the strong, dry Santa Ana winds, two in the San Gabriel Mountains north of the San Fernando Valley and one at Camp Pendleton in the north coas tal part of San Diego County. Only one of these, the Marek Fire, was active during the early morning hours when the hourly PM 10 concentrations spiked at Anaheim. Als o, the northeasterly wind flows throughout the period, make it unlikely the smoke or ash from the fires contributed significantly to the

PM 10 measured at Anaheim. Crustal materi al from windblown dust was the primary

59 Letter dated November 22, 2010 to Matthew Lakin, Manage r Air Quality Analysis Office USEPA Region 9, from Karen Magliano, Chief Air Quality Data Branch Californi a Air Resources Board, tran smitting final report dated August 5, 2010 entitled “Analysis of Exceptional Events Contributing to High PM10 Concentrations in the South Coast Air Basin on October 13, 2008.” 0 20 40 60 80 100 120 140 160 180 200

10/6 10/7 10/8 10/9 10/10 10/11 10/12 10/13 10/14 10/15 10/16 10/17 10/18 10/19 10/2024-Hour Average Conc., μg/m3

Date

Anaheim Long Beach Los Angeles Glendora

Rubidoux Lake Elsinore Fontana San Bernardino October 13Draft for Public Notice and Comment

Revision Date: June 2012 63

component of the measured PM 10 , as confirmed by comparing with the PM 2.5 measured on this day. Prescribed, agricultural or resi dential burning did not a ppear to have added any significant amount of PM 10 to the concentrations measured in the Basin; these activities were not permitted on this day. The PM 2.5 portion of PM 10 , which would indicate combustion sources, was very small throughout the Basin. PM 10 was emitted from some BACM-controlled sources (mainly agricultural and constr uction activities) as BACM controls were locally overwhelmed by the high winds. Natural particulate sources

areas also contributed to the measured PM 10 , particularly the upwi nd mountain and desert

areas.

6.3.5 Address Affects Air Quality (AAQ)

Once sufficient HF analyses have been provided and CCR has been demonstrated the event will generally have been considered to have affected air quality at the exceeding monitor, and thus the AAQ element will have been met. The demonstration should include a statement that AAQ has been met by providing HF analyses and demonstrating CCR.

6.3.6 Address [HAURL] / Natural Event

Once both CCR and nRCP have been demonstrate d, the event will generally be considered a natural event, thus satisfying the [HAURL]/Natural Event elem ent. The demonstration should

include a statement that the Natural Event crite rion has been met by demonstrating nRCP and

CCR.

6.3.7 Step 5: Address No Exceedance But For the Event (NEBF)

The NEBF demonstration generally builds on information gathered to support other elements of an exceptional event demonstra tion. Further, if the exceptional events demonstration fails on a different element then the NEBF analysis be comes moot since there is no portion of the

concentration than can be attributed to an exceptional event. For th ese reasons, EPA suggests that air agencies complete the NEBF demonstrati on last after addressing all other EER elements.

6.3.7.1 Qualitative NEBF If non-event pollution levels are typically signi ficantly below the NAAQS during the season of the event then a qualitative NEBF may be adequa te. The following is provided as an example 60 :

Activities that generate anthropogenic PM 10 were approximately constant in the Basin immediately preceding, during and after the ev ent. Activity levels in the Basin were typical for the time of year and PM 10 emissions control programs were being implemented, not only for fugitive dust-generat ing activities, but also for agricultural burning in the Basin. Furthermore, due to the forecasts for high winds on October 13, the SCAQMD compliance teams were ready to act quickly to fugitive dust complaints to

60 Letter dated November 22, 2010 to Matthew Lakin, Manage r Air Quality Analysis Office USEPA Region 9, from Karen Magliano, Chief Air Quality Data Branch Californi a Air Resources Board, tran smitting final report dated August 5, 2010 entitled “Analysis of Exceptional Events Contributing to High PM10 Concentrations in the South Coast Air Basin on October 13, 2008.”Draft for Public Notice and Comment

Revision Date: June 2012 64

minimize emissions and to enforce mitigation methods like watering and soil

stabilization.

Vehicular traffic, cooking and residen tial fires do not directly cause PM 10 24-hour NAAQS violations in the Basin. Activity levels in the Basin were typical for the time of year and PM 10 emissions control programs were being implemented, for fugitive dustgenerating activities, as well as open burning. With the unsettled conditions on October 13, such emissions would not cont ribute significantly to the PM 10 measured. There were reasonable and appropriate meas ures in place to control PM 10 in the Basin on October 13, 2008, including SCAQMD Rules 403, 444, 445, 1156, 1157, 1158 and 1186.

Examining the make-up of the PM 10 in the Basin on this day using PM 2.5 data, the coarse particles (PM 10-2.5 ), which are associated with wi ndblown dust, represent well over 75%

of the total PM 10 mass collected in the Basin. The thre e wildfires that were burning in the Basin, one of which started on October 12 and two other after the high hourly PM 10 concentrations started, were not the primary cause of the high PM 10 . PM 2.5 remained relatively low throughout the Basin on this day with no exceedance of the 24-hour NAAQS. While there were no PM 10 filters collected on this day for laboratory analyses for soluble potassium, an indicator of wood smok e, the predominance of coarse particles, the timing of the fires and the lack of s upporting wind directions to bring smoke to Anaheim provide support the conclusion that while there could have been a minor contribution from the wildfires, it was relatively small portion of the PM 10 measured.

Based on the data provided in this report, SCAQMD concludes that there would not have

been exceedances of the PM 10 NAAQS in the Basin on October 13, 2008 if high winds were not present. Even if the extreme 99.5 percentile concentra tion for the Basin, 139.5

 g/m 3 , were used as the background concentr ation to compare to the measured PM 10 concentrations, the particulate contribution fr om the high wind event clearly caused these

exceedances. The causal connection of the measured PM 10 and the strong winds in the Basin, and throughout southern California, along with the high contribution of fugitive

dust to the PM 10 mass indicate that but for the high wind event this NAAQS violation

would not have occurred.

6.3.7.2 Quantitative NEBF

A quantitative NEBF will generally be expected if concentrations on days without events during

the same season exceed the standard or are near the standard and/or if the contribution of nonevent pollution produces concentrations near the applicable NAAQS. An example of a quantitative NEBF analysis will be incorporated in this document as one becomes available.

6.4 Prepare High Wind Action Plan (optional)

A High Wind Action Plan is primarily used to do cument controls on additional sources that need

reasonable controls for future events to be cons idered not reasonably cont rollable or preventable. If an air agency discovers (an) uncontrolled source(s) of dust during the course of the event demonstration, the air agency may choose to su bmit a High Wind Action Plan, either separately or along with the demonstration package. Alte rnatively, EPA may identify a source previouslyDraft for Public Notice and Comment

Revision Date: June 2012 65

unidentified by the air agency that EPA considers to be reasonably controllable. In this case, an air agency could submit a High Wind Action Plan following the submission of the demonstration package. A High Wind Action Plan is developed to address sources that could reasonably be

controlled to minimize the occurrence of futu re events. As such, the following information

would be included:

 Source(s) targeted for controls

 Description of controls

 Oversight/enforcement plan, in cluding on/before event days

 Implementation timeline

 Documentation of effective implementation and enforcement

 The high wind threshold for the collective set of high wind dust source s, including those previously subject to reasonable controls and those that are being proposed for reasonable controls in the High Wind Action Pl an (refer to Appendix A3 for determining this threshold).

EPA has not established a particular format for the High Wind Action Plan but notes that most of the information needed for an approvable Hi gh Wind Action Plan was required in a Natural Events Action Plan (see Section 3.7.2); therefore, a NEAP may pr ovide a useful template. When the High Wind Action Plan is submitted with a demonstration package, EPA recommends including it as an appendix and referencing it in the nRCP section. As mentioned in Section 3.7.2, the High Wind Action Plan can be submitte d before, with, or after submittal of a demonstration package.Draft for Public Notice and Comment

Revision Date: June 2012 66



### Appendix A1. Summary of Studies on Windblown Dust Emissions

Windblown dust is often but not always a c ontrollable and preventable form of PM 10 pollution. To ensure effective implementation of the EER, it is useful to determine the wind speed at which windblown dust no longer becomes reasonably cont rollable. Agencies may develop a high wind threshold for each area experiencing high wind dust events. Appropriate area-specific thresholds would consider local conditions, sources, and co ntrols and specify a speed above which these controls would be overwhelmed. This approach is consistent with the Natural Events Policy where the EPA required the states /local agencies to define the conditions in which BACM level controls were overwhelmed. If an agency is una ble to develop an area-specific wind threshold, the EPA will accept a default threshold of 25 mph. Areas with local data supporting of an areaspecific high wind threshold should submit this information to EPA for review and approval.

The default 25 mph high wind threshold is mainly based on extensive windblown dust emissions research performed by the University of Ne vada, Las Vegas (UNLV). The Clark County Department of Air Quality and Environmenta l Management (DAQEM) contracted with the Department of Civil and Environmental Engineer ing, University of Nevada, Las Vegas (UNLV) to conduct field studies to ge nerate refined wind-blown PM 10 emissions factors for stable natural, and unstabilized, disturbed surfaces. 61 The latest study was performed in 2004 using a portable wind tunnel at 31 locations in the Las Vegas valley that represented nine different soil groups. 62

All of the test sites were dete rmined to be stable through th e same methods as outlined in DAQEM’s fugitive dust rules for ope n areas and vacant lots and thus provide a consistent

measure of “stable” conditions. 63 The sites chosen for the wind tunnel tests were determined to be stable “as-is” (i.e. no physical stabilization was performed to alter the site conditions).These same test sites were then intentionally destab ilized and subsequently re tested using the same wind tunnel approach that had been used on the pr eviously stabilized surfaces. A summary of the 2004 field study results can be seen in Figure ES -1. The 2004 data show that non-linear increases

in PM 10 flux generally begin to occur at sustai ned 10 meter velocities exceeding 25 mph. Note that the Clark County study found small amount s of entrainment below 25 mph. The small PM 10 fluxes observed at lower winds speeds could be attributed to aerodynamic entrainment, which occurs primarily when fine particles are lifted directly off the ground and remain elevated. While it is expected that small amounts of aerodynamic entrainment could occur when wind speeds are below 25 mph, these are not expected to result in exceedances in most western areas, particularly the desert areas such as in Clark County.

61 Refined PM 10 Aeolian Emission Factors for Na tive Desert and Disturbed Vacant Land Areas. Final Report, June 30, 2006, http://www.clarkcountynv.gov/Depts /daqem/Documents/Planning/SIP/PM10/App_E_- Refined%20Emission%20Factors.pdf.

62 Sites were characterized in terms of Wind Erodibility Groups (WEGs).

63 Clark County Department of Air Quality and Environmen tal Management Air Quality Regulations, Section 90 –

Fugitive Dust from Open Areas and Vacant lots, Su bsection 90.4. Test Methods, revised 12/17/2002.Draft for Public Notice and Comment

Revision Date: June 2012 67

The EPA believes that for Clark County and areas si milar to it, these results clearly differentiate

emissions from stable and distur bed conditions and provide a reas onable baseline for establishing a high wind threshold for ex ceptional events purposes.

Furthermore, studies conducted by the Desert Research Institute (D RI) in Clark County, NV

have concluded that windblown desert dust contributes to appr oximately 20% of measured PM 10 in urban areas and that only desert soils that have been disturbed by an thropogenic activities are large emitters under common high wind conditions. 64 These studies also conclude that

windblown PM 10 from urban/disturbed surfaces are not seen until 10 meter hourly average wind speeds are greater than 7 m/s (16 mph), while no nurban desert show a si gnificant increase in

PM 10 emissions only when hourly average wind speed s are greater than 11 m/s (25 mph). See Figure 3-1 for a graphical representation of these data. The authors note that these results refute the argument that most urban dust derives from natural surfaces.

64 Watson, J.G. and Chow, J.C. 2000. Reconciling Urban Fugitive Dust Emissions Inventory and Ambient Source Contribution Estimates: Summary of Current Knowledge and Needed Research. DRI Document No. 6110.4F

.Draft for Public Notice and Comment

Revision Date: June 2012 68

These results are also consiste nt with results obtained from wind tunnel studies performed throughout the state of Arizona. 65 These studies suggest that windblown dust emissions from

scrub desert and dune fl at areas occur when wind speeds ar e greater than 11.3 m/s (25 mph) and 18.31 (41 mph), respectively. The same study revealed that surfaces that had been disturbed by anthropogenic activities began to produce emissi ons when wind speeds ranged from 5.11 m/s (11 mph) to 8.11 m/s (18 mph). The effect of surf ace disturbance on threshold wind speeds was

further examined for a number of natural desert soils by a number of researchers. 66 The main conclusion was that disturbance of soils profoun dly lowers the threshold friction velocity of

desert soils.

65 Nickling, W.G. and Gillies, J.A. 1989. Emission of Fine Grained Particulates From Desert Soils. In Paleoclimatology and Paleometeorology: Maodern and Past Patterns of Global Atmospheric Transport . Leinen, M. and Sarnthein, M., (Eds.) Kluwer Academic Publishers. 133-165.

66 Gillette, D.A. 1980. Threshold Velocities for Input of Soil Particles into the Air by Desert Soils. Journal of Geophysical Research . 85: 5621-5630; Gillette, D.A. 1982. Threshol d Friction Velocities and Rupture Moduli for Crusted Desert Soils for the Input of Soil Particles into the Air. Journal of Geophysical Research . 87: 9003-9015; Belnap, J. 2007. Wind Erodibility of Soils at Fort Irwi n, California (Mojave Desert), USA, Before and After Trampling Disturbance: Implications for Land Management. Earth Surface Processes and Landforms. 32: 74-84; Belnap, J. 1998. Vulnerability of Desert Biological Soil Crusts to Wind Erosion: The Influences of Crust Development, Soil Texture, and Disturbance. Journal of Arid Environments. 39: 133-142.Draft for Public Notice and Comment

Revision Date: June 2012 69

In EPA’s weight-of-evidence analysis of high wind dust events, the EPA will assumed that sustained wind speeds above the applicable high wi nd threshold (area specif ic or 25 mph default) are capable of overwhelming reasonable controls on anthropogenic sources or causing emissions

from natural undisturbed areas in arid, semi-arid, or seasonally dr y regions, such as in Clark County, NV. The EPA will further assume that wi nd speeds below this threshold will entrain more dust emissions per acre or square mile from disturbed anthropogenic sources that have not been reasonably-controlled than from natural surfaces and stabilized disturbed surfaces.

.Draft for Public Notice and Comment

Revision Date: June 2012 70



### Appendix A2. Summary of Availabl e Relevant Literature Related to Establishing Area-Specifi c High Wind Thresholds

Alfaro, S. 2004. Estimation of PM20 Emissions by Wind Erosion: Main Sources of

Uncertainties. Geomorphology , 59: 63-74.

Alfaro, S. 2001 Modeling Mineral Aerosol Pro duction by Wind Erosion: Emission Intensities

and Aerosol Size Distributions in Source Areas. Journal of Geophysical Research , 106: NO. D16, 18075-18084.

Benlap, J. and Gillette, D. 1998. Vu lnerability of Desert Biological Soil Crusts to Wind Erosion: the Influences of Crust Developmen t, Soil Texture, and Disturbance. Journal of Arid

Environments. 39: 133-142.

Brazel, A.J. and Nickling, W.G. 1986. The Rela tionship of Weather Types to Dust Storm Generation in Arizona (1965-1980). Journal of Climatology . 6: 255-275

Brazel, A.J. and Nickling, W.G. 1984. Temporal a nd Spatial Characteristics of Arizona Dust Storms (1965-1980). Journal of Climatology. 4: 645-660.

Breed, C.S., and Reheis, M.C. (Eds.) 1999. De sert Winds: Monitoring Wind-Related Surface Processes in Arizona, New Mexico, and California. U.S. Geological Survey Professional Paper 1598.

Chow, J.C., Pace, T.G., and Watson, J. G. 2000. Fugitive Dust Emissions. In Air Pollution Engineering Manual , Davis, W.T., (Ed.) Van Nostrand Reinhold, New York, NY.

Countess Environmental. 2006. WRAP Fug itive Dust Handbook. Prepared for Western Governors’ Association by Countess Envir onmental, Westlake Village, California. September 7.

Cowherd, C. 1995. Wind Tunnel Studies of BACM E ffectiveness. Final Test Report. Prepared for South Coast Air Quality Management District by Midwest Research Institute (MRI). Contract No. 95017. MRI Project No. 3826.

Cowherd, C. 2000. Wind Erodibility Assessment of th e Stabilized Soils in the Antelope Valley. Test Report. Prepared for Southern Calif ornia Edison and the City of Los Angeles Department of Airports by Midwest Resear ch Institute (MRI). Contract No. U1109008. MRI Project No. 110028

ENVIRON. 2004. Determining Fugitive Dust Em issions from Wind Erosion. Final Report. Prepared for Western Governors’ Associat ion by ENVIRON Interna tional Corporation, Novato, California; ERG, Inc., Sacramento, California; Desert Research Institute, Reno, Nevada, MACTEC Engineering & Consulting, Gainsville, Florida and University of California Riverside, Rivers ide, California. March 12.Draft for Public Notice and Comment

Revision Date: June 2012 71

ENVIRON. 2006. Fugitive Windblown Dust Emi ssions and Model Performance Evaluation Phase II Final Report. Prepared for West ern Governors’ Asso ciation by ENVIRON International Corporation, Novato, Californi a and University of California Riverside, Riverside, California. May 5.

Environmental Quality Management and MRI. 2 006. An Inventory of Vacant Land Soil Stability and Private Unpaved Roads in the Las Ve gas Valley Using Remote Sensing Imagery. Prepared for Clark County Department of Finance Purchasing and Contracts by Environmental Quality Management, Inc. and Midwest Research Institute. PN

70204.001.

Gillette, D.A. 1978. Tests with a Portable Wind Tunnel for Determining Wind Erosion

Threshold Velocities. Atmospheric Environment . 12: 2309-2313.

Gillette, D.A., Adams, J., Endo, A., and Smith, D. 1980. Threshold Velocities for Input of Soil Particles into the Air by Desert Soils. Journal of Geophysical Research . 85: 5621-5630

Gillete, D.A., Adams, J., Muhs, D., and Kihl, R. 1982 Threshold Friction Velocities and Rupture

Moduli for Crusted Desert Soils for the Input of Soil Particles into the Air. Journal of Geophysical Research. 87: 9003-9015.

Gillette, D.A and Stockton, P.H. 1989. The Effect of Nonerodible Particles On Wind Erosion of

Erodible Surfaces. Journal of Geophysical Research. 94: 12855-12893.

Gillette, D.A. 1999. A Qualitative Geophysical Explan ation for “Hot Spot’ Dust Emitting Source Regions. Contr. Atomos. Phys . 72: 67-77.

Gillies, J.A. and Berkofsky, L. 2004. Eolian Suspension Above the Saltation Layer, the

Concentration Profile. Journal of Sedimentary Research. 72: 176-183.

Goudie, A.S. and Middleton, N.J. 1992. The Changi ng Frequency of Dust Storms Through Time. Climatic Change . 20: 197-225

Houser, C.A. and Nickling, W.G. 2007. The Emissi on and Vertical Flux of Particulate Matter

<10 μ g from a Disturbed Clay Crusted Surface. Sedimentology . 48: 255-267.

Fitz, D.R. 1996. Field Study to Determine Limits of Best Available Control Methods for Fugitive Dust Under High Wind Conditions. Final Report. Prepared for South Coast Air Quality Management District by Univ ersity of California Rivers ide, CA. Contract R-C94159.

Kjelgaard, J. 2004. PM10 Emission from Agricu ltural Soils on the Columbia Plateau: Comparision of Dynamic and Time-Integr ated Field-Scale Measurements and

Entrainment Mechanisms. Agriculture and Forest Meteorology . 125: 259-277.

Mansell, G.E., Lau, S., Russell, J. and Omar y, M. 2006. Fugitive Wind Blown Dust Emissions

and Model Performance Evaluation Phase II. Prepared for Western Governors’Draft for Public Notice and Comment

Revision Date: June 2012 72

Association by ENVIRON International Corporat ion and the University of California at Riverside College of Engineering.

Macpherson, T., Nickling, W.G., Gillies, J.A., and Etyemezian, V. 2008. Dust Emissions from Undisturbed and Disturbed Supply-Limited Desert Surfaces. Journal of Geophysical

Research . doi: 10.1029/2007JF000800.

Neuman, C.M., Boulton, J.W., and Sa nderson, S. 2009. Wind Tunnel Simulation of Environmental Controls on Fugitive Du st Emissions from Mine Tailings. Atmospheric

Environmen t. 43: 520-529.

Nickling, W.G. and Gillies, J.A. 1989. Emission of Fi ne Grained Particulates From Desert Soils.

In Paleoclimatology and Paleometeorology : Maodern and Past Patterns of Global Atmospheric Transport . Leinen, M. and Sarnthein, M., (Eds.) Kluwer Academic

Publishers. 133-165.

Ono, D. 2006 Application of th e Gillette Model for Windblown Dust at Owens Lake, CA. Atmospheric Environment . 40: 3011-3021.

Roney, R.A. and White, B.R. 2004. Definition and Measurement of Dust Aeolian Thresholds. Journal of Geophysical Research . doi: 10.1029/2003JF000061.

Shao, Y., 2000a. Physics and Modelling of Wind Erosion. Kluwer Academic Publishers, Dordrecht, 393 pp.

Sharratt, B., Feng, G, and Wending, L. 2007. Loss of Soil and PM10 From Agricultural Fields Associated with High Winds on the Columbia Plateau. Earth Surface Processes and Landforms . 32: 621-630.

Sierra Research. 2003. Final BACM Technological a nd Economic Feasibility Analysis. Prepared for San Joaquin Valley Unified Air Pollution C ontrol District by Sierra Research, Inc, Sacramento, California. March 21.

U.S. EPA 1992. Fugitive Dust Background Document and Technical Information Document for

Best Available Control Measures. EPA-450/2-92-004.

Wancaser, R., James D., Jeong, H., and Pulur gurtha, S. 2006. Refined PM10 Aeolian Emission

Factors for Native Desert and Disturbed Vacant Land Area. Final Report, June 30,2006.

Watson, J.G. and Chow, J.C. 2000. Reconciling Ur ban Fugitive Dust Em issions Inventory and

Ambient Source Contribution Estimates: Su mmary of Current Knowledge and Needed

Research. DRI Document No. 6110.4F.Draft for Public Notice and Comment

Revision Date: June 2012 73



### Appendix A3. Methods for Establishing Area-Specific High Wind Thresholds

As explained in Appendix A1, the EPA primar ily based the 25 mph threshold on extensive windblown dust emissions research performed by the University of Nevada, Las Vegas (UNLV). During UNLV’s studies, researchers used a wind tunnel to quantify emissi ons from undisturbed areas meeting the definition of “stable” surfaces within Clark County’s (Nevada) BACM level fugitive dust regulations and mechanically disturbed open areas. The research performed by

UNLV is one of the few field st udies that clearly relate BACM level control of windblown dust from open areas and PM 10 emissions. The EPA believes that the study results clearly differentiate emissions from these two types of conditions and provide a reasonable baseline for establishing a high wind threshold for excepti onal events purposes for such areas.

While the UNLV study stands out as the most de finitive source of in formation concerning wind speeds capable of overwhelming BACM for ope n area windblown dust sources and/or causing emissions from natural undisturbed areas, EPA belie ves that other sources of information can be used to develop an area-specific high wind threshold.

First, the EPA encourages state, local, and trib al agencies to evaluate the existing windblown dust literature identified in Appendix A2 wh en developing an area-s pecific threshold and determine if any of the preexisting inform ation is applicable to their area.

Secondly, while full-scale windblown dust emissi ons field studies are not always feasible, agencies may deploy temporary monitoring stations or use existing monitoring data to evaluate the effects of wind speed on different source cate gories. For example, as explained in Appendix A1, DRI used existing monitoring sites in Clar k County to evaluate th e relationship between

urban/construction and non- urban/desert conditions. 67 While this data was independent of the detailed wind tunnel emissions studies performe d by UNLV in the same area, the results were

similar: nonurban desert show a significant increase in PM 10 emissions only when wind speeds are greater than 11 m/s (25 mph). The EPA believes that this is valid method for determining an area-specific threshold, but the use of existing mon itoring sites (or temporary sites) to establish a wind speed/PM relationship for different source categories should be carefully evaluated for representativeness. For example, sites used to ev aluate emissions from natural undisturbed desert areas should not be located downwind of any potential anthropogenic sour ces, as the influence from such sources would lower the expected high wind threshold. Also, simply correlating PM to wind speed without assessing repr esentativeness of the monitoring site locations does not provide useful information for exceptional events purposes.

Finally, area and/or source specif ic research may be performed, if needed. Specific information on the techniques used to assess windblown dust emissions can be found within the literature listed in Appendix A2.

Regardless of the method used, an area-specific high wind threshold must consistent with the requirements of the EER, specifically nRCP, a nd representative of wind speeds capable of

67 Watson, J.G. and Chow, J.C. 2000. Reconciling Urban Fugitive Dust Emissions Inventory and Ambient Source Contribution Estimates: Summary of Current Knowledge and Needed Research. DRI Document No. 6110.4F

.Draft for Public Notice and Comment

Revision Date: June 2012 74

overwhelming reasonable controls or causing em issions from natural undisturbed areas. The EPA will not approve the use of an area-specific threshold if these basic principles are not upheld. The EPA encourages the state, local, and tribal agencies respons ible for developing an area-specific threshold to consult with their respective regional offi ce during the development

process.Draft for Public Notice and Comment

Revision Date: June 2012 75



### Appendix B1. Checklist for High Wind Exceptional Events Demonstration

Submission

Completeness Checklist for High Wind Dust Exceptional Events.

Instructions: This checklist is provided as a guideline to help submitting agencies identify the types of information and analyses to include in an exceptional events demonstration package. In some cases (e.g., wind speeds above the identified high wind threshold), agencies will not need to include all parameters under each criterion. The EPA encourages agencies to include a completed checklist with their submitted excepti onal events demonstration package. Note that completion of this checklist does not indicate that the event in question is concurrable nor does it guarantee a “complete” package. The EPA may ask fo r clarification or additional information to support a specific criterion.

Site Name/AQS ID: ____________________________________________________________

Pollutant: ____________________________________________________________________

Date(s): ______________________________________________________________________

Procedural Criteria EPA Use
Did an exceedance of the NAAQS occur? [Y/N] Were data flagged by July 1 s t of following year? [Y/N] Was there a 30-day public comment period? Is documentation for the comment period included? [Y/N] [Y/N] If public comments were received, ar e the public comments and responses

included? [Y/N]

Was the package submitted within 3 years of the end of the quarter in

which the event occurred and 12 mont hs prior to the date that any regulatory decision must be made by EPA? [Y/N]

(over)Draft for Public Notice and Comment

Revision Date: June 2012 76

Evidence Information Included Page(s) EPA Use
Conceptual Model
-description of weather phenomena resulting in high wind [Y/N] [page #]

-description of what sources were likely entrained by the high wind [Y/N] [page #]

-explanation of the path by which the dust reached the monitor(s) [Y/N] [page #]

-map showing relevant monitors, topography, other relevant geographic features [Y/N] [page #]

-description of how the event day differs from non-event days [Y/N] [page #]

-description of concentration and wind patterns for the exceeding monitor(s) and surrounding

area [Y/N] [page #]

Wind Statistics -max sustained wind (Hourly avg) [X mph] [page #] - max sustained wind (1-5 min avg) [X mph] [page #] -max gust (1 min avg) [X mph] [page #] -wind trajectories included? [Y/N] [page #]

-other: [list other wind analyses] [page #]

nRCP -Area-specific high wind threshold (default = 25mph) [25 mph] [page #]

-sources contributing to event identified, including anthropogenic vs. natural? [Y/N] [page #]

-controls identified for anthropogenic sources? (note: level of contro l analysis depends on wind speed) [Y/N] [page #]

-are natural sources not reasonabl y controllable? [Y/N] [page #] -was a High Wind Action Plan included? [Y/N] [page #]

HF -were time-series analyses for concentration and

wind data included? [Y/N] [page #]

-annual comparison to hist orical data (wind and concentrations) [%ile] [page #]

-seasonal comparison to hi storical data (wind and concentrations) [%ile] [page #]

CCR (=> AAQ & / Natural Event)Draft for Public Notice and Comment

Revision Date: June 2012 77

-were spatial analyses included, establishing a spatial relationship between the event, sources, transport of emissions, and recorded

concentrations? [Y/N] [page #]

-were temporal analyses included, establishing a temporal relationship between the high wind and

elevated PM concentrations at the monitor? [Y/N] [page #]

-comparison of event-affected day(s) to specific non-event days? [Y/N] [page #]

-was the dust shown to be from the sources

discussed in the nRCP section? [Y/N] [page #]

-were alternative hypo theses discussed? [Y/N] [page #] -was a causal (not just correlational) relationship

established? [Y/N] [page #]

NEBF -was a but-for analysis included? [Y/N] [page #]Draft for Public Notice and Comment

Revision Date: June 2012 79



### Appendix C. Sample Letter of Intent

September 16, 2011

Matthew Lakin U. S. Environmental Protection Agency, Region 9

75 Hawthorne Street

Mail Code: AIR-7 San Francisco, CA 94105

SUBJECT: Exceptional Event Documentation District: San Luis Obispo APCD Event Type: PM2.5 - Wildfire/Smoke Impact

Event Date: August 14, 2009

Site AQS No POC Pollutant /Monitor Concentration

Atascadero 060798001 3 PM2.5 FEM BAM 51.6  g/m 3

Dear Mr. Lakin:

The San Luis Obispo County Air Pollution Control Distri ct (APCD) submitted Exceptional Event Documentation on July 22, 2010 to the U. S. Environmental Protection Agen cy and the California Air Resources Board (CARB) that addresses wildfire emission impacts on PM2.5 concentrations at the Atascadero monitoring station on August 14, 2009. This data has been appropriately flagged in the AQS data base. The EPA was notified of the intent to submit this documentation via a CARB email on June 21, 2010. CARB provided comments to the APCD and the APCD revised and resubmitted the report to CARB on May 25 , 2011. On June 15, 2011, CARB provided additional comments to the APCD illustrating how the documentation shoul d be specifically modified to ensure acceptance by

EPA.

Before the APCD proceeds with furthe r modifications to the documentati on based on CARB comments, the APCD respectfully requests that EPA provide feedback as to whether EPA will act on this Exceptional Event Documentation package. In addition, please indicate whether the 2009 data year will be used for future San Luis Obispo County PM2.5 attainment demonstrations.

The Exceptional Event Documentation dated July 22, 2010 is located on the APCD website:

http://www.slocleanair.org/air/pdf/2010/ExceptionalEventAug_14_2009_AtascaderoPM2.pdf

The revised working draft dated May 25, 2011 that was submitted to CARB for comment is located on a not-public

location on the APCD website:

http://www.slocleanair.org/air/epa.php

If you have need for additional materials, please contact me at (805) 781 5743 or garcemont@co.clo.ca.us.

Sincerely,

Gary Arcemont Air Quality Specialist

GJA/arr

cc: Karen Magliano, ARB