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## EPA Technical Support Document on Review of Colorado Department of Public Health and Environment ’ s Demonstration Package for the May 11,

2010 Alamosa and Pagosa Springs Exceptional Event

EXCEPTIONAL EVENTS RULE REQUIREMENTS

EPA promulgated the Exceptional Events Rule (EER) in 2007, pursuant to the 2005 amendment of Clean Air Act (CAA) Section 319. 42 U.S.C. §7619. The EER added 40 CFR 50. 1 (j), (k) and (l); 50.14; and 51.930 to the Code of Federal Regulations (CFR). These sections contain definit ions, criteria for EPA approval, procedural requirements, and requirements for air agency demonstrations, all of which must be met before EPA can concur under the EER on the exclusion of air quality data from regulatory decisions.

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

A. The event satisfies the criteria set forth in 40 CFR 50.l(j) for the definition of an exceptional
event; The event affects air quality ; The event is not reasonably controllable or preventable ; and/or The event is caused by human activity that is unlikely to recur at a particular location or [is] a natural event. 1

B. There is a clear causal relationship between the measurement under consideration and the event that is claimed to have affected the air quality 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.

This review applies the EPA’s “ Interim Guidance o n the Preparation of Demonstrations in Support of Requests to Exclude Ambient Air Quality Data Affected by High Winds Under the Exceptional Events Rule of May 2013 ” (Interim Guidance for High Wind Exceptional Events) in addition to the applicable statutory and regulatory provisions.



## SUMMARY

Overview

On July 1 , 2013, the Colorado Department of Public Health and Environment ( CDPHE ) submitted

ex ceptional events demonstrations for 3 exceedances (one in Pagosa Springs and two in Alamosa) of the
24 hour PM 10 standard that occurred at the Pagosa Springs School (08

- 007

- 0001) monitor, the Alamosa Municipal Building (08

- 0 03

- 0003) monitor, and the Adams State College (08

- 003

- 0001) monitor. Table 1
summarize s these exceedances.

1 A natural event is further described in 40 CFR 50.1(k) as “an event in which human activity plays little or no direct causal role”.2

Table 1: EPA PM 10 Exceedance Summary of the 150 ug/m 3 24

- hour NAAQS
Exceedance Date Monitor/Site Name AQS ID Measured Exceedance (ug/m 3 ) May 11, 2010 Pagosa Springs School 08

- 007

- 0001 200

Alamosa Municipal Building 08

- 003

- 0003 161 Adams State College 08

- 003

- 0001 160

Alamosa, Colorado lies in the broad, flat, high elevation San Luis V alley of the upper Rio Grande River

. Alamosa is at an elevation of 7

, 600 feet, and is between the South San Juan and Sangre de Chris t o M ountain ranges. Alamosa is generally surrounded by agricultural lands within the San Luis Valley. Pagosa Springs lies along the San Juan R iver, to the west and south of the San Juan M ountains. To the southwest of Pagosa Springs are the deserts of the New Mexico and Arizona Four Corners region.

Figure 1: EPA Map of Monitor Locations3

In its exceptional events demonstration package CDPHE describes the May 11, 2010 event as a high wind blowing dust event and explains that “[s]ince at least 2005, there has not been an exceedance that was not associated with high winds carrying PM 10 dust from distant sources in these areas. 2 ” CDPHE asserts that
the exceedances would n ot have occurred but for :

(a) dry soil conditions over southeastern Utah, northeastern Arizona, and portions of extreme northwestern New Mexico; (b) a combination of strong surface low pressure and a cold front associated with an intense upper

- level troug h that was moving across the western United States that created conditions necessary for widespread strong gusty winds over the area of concern; (c) elevated friction velocities and the deep mixing of the blowing dust from desert regions o f Arizona, northw est New Mexico, and southeast Utah

. . . These sources are not reasonably controllable during a significant windstorm under abnormally dry or moderate drought
conditions. 3

CDPHE provides a comprehensive description and discussion of the event in Sections 2 , 3, 4, 5, and 6 of
the demonstration. As noted below, the high wind event caus ed dust to blow and affected air quality in
this area.

EPA Figure 2 from page 40 of the state’s demonstration ( CDPHE’s Figure 20) visually demonstrates plumes of dust blowing across northeastern Arizona and northwestern New Mexico into southeastern Colorado. Figures 1

- 29 from CDPHE’s demonstration use modeling, meteorology, and monitoring analysis to support the wind direction and th e reach of the dust storm into Alamosa and Pagosa Springs.

2 “Technical Support Document for the May 11, 2010, Alamosa and Pagosa Springs Exceptional Event” May 20, 2013, page 1.
3 “Technical Support Document for the May 11, 2010, Alamosa and Pagosa Springs Exceptional Event” May 20, 2013, page 82.4

Figure 2: Satellite Image of Dust Storm (CDPHE’s Figure 20 in the state’s demonstration )

The following material documents our review of CDPHE’s June 30, 2013 exceptional event
demonstration package for the May 11, 2010 exceptional event

.

Not Reasonably Controllable or Preventable

EPA evaluates whether an event was n ot R easonably C ontrollable or P reventable (nRCP) at the time of the event by taking into account controls in place and wind speed, along with other factors. For natural sources of dust, a high wind dust event can generally be considered to be nRCP if winds are high enough
to cause emissions from natural undisturbed areas. For anthropogenic sources of dust, a high wind dust

event can be not reasonably controllable or preventable if:

1. The anthropogenic sources of dust have reasonable controls in place ; 2. The reasonable controls have been effectively implemente d and enforced ; and

, 3. The wind speed was high enough to overwhelm the reasonable controls.

In addressing reasonable controls, CDPHE provided detailed information on the current set of required and voluntary co ntrols in the Pagosa Springs PM 10 maintenance area and in Alamosa, including information on implementation of State Regulations 1, 3, 6, and 9, implementation effectiveness, compliance, and public notification activities that occurred on the event day. As CDPHE states, they5

“ conducted th orough analyses and outreach with local governments to confirm that no unusual anthropogenic PM10

- producing activities occurred in these town s and that despite reasonable control measures in place, high wind conditions overwhelmed all reasonably available controls ”

. 4

CDPHE provided the documentation listed in figures 3 & 4 (CDPHE tables 9 & 10 ) showing that sustained wind speeds associated with these events were above 25 mph

. For example, in Alamosa sustained surface winds of up to 43 mph with gusts up to 58 mph were measured on May 11, 2010 , while Pagosa Springs saw sustained wind speeds up to 30 mph and gusts up to 48 mph

. CDPHE previously
established in its exceptional events demonstration for the January 19, 2009 event in Lamar , Colorado that wind spee ds of 30 mph and/or gusts of 40 mph or higher have been shown to cause blowing dust in Colorado (attached as appendix A of CDPHE’s analysis). The wind speeds on May 11, 2010 clearly
exceed the established high

- wind threshold

. 5

4 “Technical Support Document for the May 11, 2010, Alamosa and Pagosa Springs Exceptional Event” May 20, 2013, page 67.
5 The EPA’s minimum high wind threshold for wind speed in the West (although not intended to draw a bright line) is 25 mph sustained wind speeds, according to page 3 of the “Interim Guidance on the Preparation of Demonstrations in Support of Requests to Exc lude Ambient Air Quality Data Affected by High Winds Under the Exceptional Events Rule” of May 2013 . CDPHE has establishe d that 30 mph sustained winds and 40 mph gusts are an appropriate threshold in Colorado

.6

Figure 3 : Wind Speed in Alamosa, Colo. On May 11, 20107

Figure 4 : Wind Speed in Pagosa Springs, Colo. On May 11, 20108

Section 2 of CDPHE’s documentation provides a complex meteorological analysis of the event, including :

S tatewide PM 10 monitoring maps ; S urface and upper air wind speed analysis from the National Oceanic and Atmospheric Administration ( NOAA ) ; M aps of real

- time weather data from the National Center for Atmospheric Research ( NCAR ) ; R egional wind and weather by hour through MesoWest ; NOAA HY S PLIT modeling of wind trajectories from NOAA HYSPLIT modeling runs ; MODIS Terra satellite images demonstrating the blowing dust across the region ; GOES

- 11 longwave spl i t window time

- lapse images showing dust originating in Arizona ; M aps establishing the lack of regional precipitation and drought status from U.S. Department of Agriculture ( USDA ) ; NOAA, and the National Drought Mitigation Center ; and
M aps of elevated friction velocities in the region from the NOAA National Centers for
En vironmental Prediction ( NCEP ) North American Model.

These analyses demonstrate persuasively through the weight of evidence the existence of a high wind blowing dust event originating far southwest of the monitors in question.

Section 5 of CDPHE’s documen tation provides a thorough analysis of the State and local controls in place to control PM 10 emissions

. These controls include CDPHE’s:

Regulation 1

- Emission Control for Particulate Matter, Smoke, Carbon Monoxide, and Sulfur
Oxides ; Regulation 3

- Stationary Source Permitting and Air Pollutant Emission Notice Requirements ; Regulation 6

- Standards of Performance for New Stationary Sources ; and Regulation 9

- Open Burning, Prescribed Fire, and Permitting applied to both Pagosa Springs and
Alamosa.

A lamosa has the following controls in place:

Natural Events Action Plan (NEAP)

, completed in May 2003

, which addresses public health programs, public notification, and implements Best Available Control Measures (BACM). CDPHE ensured in 2007 and 2013 that th e NEAP was implemented satisfactorily ; City Code of Ordinances Article VII of Section 21

- 140(5) which addresses dust control at homes ; Article V Sec. 17

- 87(3) requires pavement of new roads/alleys ; and
Article VI Sec. 21

- 119(3) requires new commercial esta blishments to install underground irrigation.

In addition, Alamosa conducts street sweeping, has irrigated and installed vegetative cover on all city parks, enco urages low tilling and other soi l conserva tion practices outside of town through the Colorado State University Co

- Op Extension Office and the Natural Resources Conservation Service.

Maps are included of eight undeveloped parcels of land in town that were determined to be reasonably
controlled or considered natural sources

. All eight are covered with vegetation and five of those eight are9

confirmed to be irrigated. The three remaining sites in the following figure (Sites B, E, and H)

, are naturally vegetated, and satellite images show minimal soil disturbance. 6

Figure 5 : Alamosa Site Assessment

Pagosa Springs local controls include :

Land Use Development Code 6.6.3(h) and 6.6.3(m)(i) requiring paved streets, street sanding and sweeping/cleaning controls, encourages businesses to maintain cleanliness of private lots ; EPA approved PM 10 Maintenance Plan, effective on August 14, 2001

, requir ing Prevention of Significant Deterioration (PSD) permitting requirements mandating Best Available Control Technology (BACT) at sources potentially emitti ng PM 10 ; and Vegetation, irrigation, fencing, and stabilized clay dust control measures are in place for undeveloped parcels of land in town. The map following shows that identified areas of soil disturbance have reasonable controls. For example, Site A was seeded in 2006 and has since been covered by vegetation. Site B was the recent construction of the Springs Resort and Spa was completed in May 2009 and therefore couldn’t have impacted the May 11, 2010 event. Site C was naturally vegetated and receives groundwater from a nearby stream; 7 it is also an area where
off

- road recreational vehicles are prohibited by the parks department. Site D is an irrigated and maintained turf and stabilized clay baseball field since April 2009. 8

6 “Technical Support Document for the May 11, 2010, Alamosa and Pagosa Springs Exceptional Event” May 20, 2013, pages 75

- 78.

7 Colorado State Reg. 1 Section III.D.2.b considers natural vegetation with regular groundwater availability due to low lying terrain to be the appropriate available and practi cal method that is technologically feasible and economically reasonable in order to minimize fugitive particulate emissions for this lot at this time.
8 “Technical Support Document for the May 11, 2010, Alamosa and Pagosa Springs Exceptional Event” May 20, 2013, pages 79

- 84.10

Figure 6 : Pagosa Springs S ite Assessment

On March 16 th , 2000, Colorado’s State Implementation Plan (SIP) was revised and amended to designate Pagosa Springs as a PM 10 attainment area with the effect of deleting road paving requirements, street sanding reporting requirements, and any other “unnecessary mandatory contingency measures in the [Telluride] 9 and Pagosa Springs areas. No additional control measures are needed in these areas to demonstration long

- term maintenance of the PM

- 10 NAAQS.” 10 The dust control strategies described in previous bullet 3 for Pagosa Springs local controls are voluntary measures and are not intended to be federally enforceable elements of the SIP or maintenance plan.

9 Telluride is not under consideration for this Exceptional Event documentation but was considered along with Pagosa Springs when removing the nonattainment designation on 3/16/2000.
10 State Implementation Plan, Colorado Dept. of Public Health and Environment, Regulation: Nonattainment

Attainment/Maintenance Areas, Rule #1, Rule Title: Pagosa Springs Attainment/Maintenance Area, Notice of Final Rule date 6/15/2001, 66FR 32556.11

Sections 2 and 5 of CDPHE’s analysis clearly demonstrate that monitors in Pagosa Sprin gs and Alamosa were affected by PM 10 transport from outside the area, with the main source areas located to the southwest of the area in Arizona, southeastern Utah, and northwestern New Mexico. In addition to transport, the spatial extent of elevated PM 10 concentrations throughout the area and the wind speeds associated with the event contribute to EPA’s evaluation of whether these events are not reasonably
controllable or preventable. Potential anthropogenic sources nearer the monitors were shown to have reasonable dust control in place.

Table 2: Evaluation of CDPHE’s Technical Support Documentation of nRCP
Location Reasonable Controls

Demonstration Citation Wind Speed Demonstration Citation Sufficient Quality of Evidence ? EPA

Criterion Met? Pagosa Springs Section 5.2: p. 67

- 68, 77

- 81 Section 2: p. 10

- 45 , esp. p. 17 & 31 Yes Yes

Alamosa Municipal Building Section 5.1: p. 67

- 68

- , 69

- 76 Section 2: p. 10

- 45 , esp. p. 17 & 31 Yes Yes

Adams State College Section 5.1: p. 67

- 68, 69

- 76 Section 2: p. 10

- 45 , esp. p. 17 & 31 Yes Yes

Historical Fluctuations

EPA evaluates whether a measured exceedance is in excess of H istorical F luctuation (HF) by taking into account the level of the exceedance in relation to historical data, which is typically at least 3 to 5 years.

To demonstrate that this requirement was met, CDPHE provided 7

- year time series plots of 2,214 samples (Alamosa) and 2,287 samples (Pagosa Springs) of daily 24

- hour averages. CDPHE explains that concentrations measured on May 11 , 2010 were more rare than t he 99 .5 percentile level in both Pagosa Springs 11 and Alamosa

, 12 indicating that on average PM10 this high recurs no more often than 2 times each year. The EPA “ Interim Guidance on High Wind Exceptional E v ents ” 13 recommends that demonstrations also consider p ercentile ranks when dust impacted data is excluded. The May 11, 2010 Pagosa Springs value of 200 ug/ m 3 ranks among the values exceeding the NAAQ S that, since at least 2005, are only found during high wind dust events. This information indicates that values at the levels seen on May 11, 2010 are extremely rare in the absence of high wind dust exceptional event impacts, and that it is extremely unlikely that any sources of PM 10 were involved in the May 11 , 2010 exceedances
other than wind

- blown dust.

11 “Technical Support Document for the May 11, 2010, Alamosa and Pagosa Springs Exceptional Event” May 20, 2013, page 57.
12 Ibid pages 51 & 54.
13 See “Interim Guidance on the Preparation of Demonstrations in Support of Requests to Exclude Ambient Air Quality Data Affected by High Winds Under the Exceptional Events R ule” of May 2013 p. 20.12

Table 3: Evaluation of CDPHE’s Technical Support Documentation of HF
Exceedance Location Historical Fluctuations Demonstration Citation Sufficient Quality of Evidence ? EPA Criterion

Met? Pagosa Springs School Section 3: p. 54

- 55 , Figure 38 Yes Yes Alamosa Municipal Building Section 3: p.51

- 52, Figure 3 4 Yes Yes Adams State College Section 3: p. 48

- 49 , Figure 30 Yes Yes

Clear Causal Relationship

EPA considers a variety of evidence when evaluating whether there is a C lear and C ausal R elationship (CCR) between the measurement under consideration and the event that is claimed to have affected the air quality in the area. Demonstrations should include documentation showing that the event in fact occurred and that emissions related to the event were t ransported in the direction of the monitor(s) where measurements were recorded; the size of the area affected by the transported emissions; the relationship in time between the event, transport of emissions, and recorded concentrations; and, as appropriate

, pollutant species

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

Section 2 of CDPHE’s demonstration included a comprehensive conceptual model of the events, including a complete overview of the meteorology, climate, and drought conditions for the Four C orners region. The analysis also included a detailed discussion of the even t that occurred on May 11, 2010, including 29 geospatial figures and 10 tables with statewide PM 10 monitoring maps, surface and upper air wind speed analysis from NOAA, maps of real

- time weather data from NCAR, regional wind and weather by hour through Mes oWest, HYSPLIT modeling of wind trajectories from NOAA, MODIS Terra satellite images demonstrating the blowing dust across the region, GOES

- 11 longwave spilt window time

lapse images showing dust originating in Arizona, maps establishing the lack of region al precipitation and drought status from USDA, NOAA, and the National Drought Mitigation Center, and lastly maps of elevated friction velocities in the region from the NOAA NCEP North American Model. Taken together

, this analysis demonstrates a high wind b lowing dust event originating far southwest of the monitors in question.

CDPHE’s analysis, Section 2 Figure 20

, shows a MODIS Terra satellite image of the blowing dust originating in Arizona. Figures 21

- 23 include a GOES

- 11 longwave split window modeled ti me

- lapse that, using color enhancement to highlight the negative temperature differences for select wavelengths associated with blowing dust, demonstrate the dust originating from outside of Colorado’s borders, approaching from the south and southwest.

CDPHE’s demonstration includes the following information from NOAA and the U.S. Geological Survey (USGS) which helps to confirm that a regional blowing dust event with long

- range transport caused the
PM 10 exceedances measured across portions of Colorado on May 11, 2010 :13

NOAA

- An area of moderately dense to locally dense blowing dust originating from point sources in northeastern Arizona and northwestern New Mexico moved northeastward across far southeastern Utah and southwestern Colorado toward central Col orado. 14

USGS

- A strong pacific storm front moved through the southwest today [May 11, 2010], bringing very strong winds but no precipitation. The dominant wind direction was out of the south

- west. Severe dust was viewable from satellite by both visible ban d and thermal imaging in the Four
Corners area. Activity was apparent from early morning on to well after sunset. Interstate 40 in Arizona was closed from Winona to Winslow for most of the day. Peak gusts in the Winslow area at the heart of the western dus t sources reached 77 mph. 15 USGS categorized May 11, 2010 as a
D ust E vent day.

Also included are eyewitness accounts from the Community Collaborative Rain, Hail, & Snow Network that describe low visibility, high winds, wind damage, and dust; as well as a t ravel log from tourists in the region noting high wind and dust conditions in this area

. CDPHE generally summarizes that “these exceedances were the consequence of strong southwesterly prefrontal surface winds over dry soils which caused significant blowing dust across much of Arizona, northwest New Mexico, southeast Utah, and southwest Colorado ”

. 16 CDPHE further states that “[w]hile it is likely that some dust was generated within the local communities as gusts from the regional dust storm passed thro ugh the area, the amount of dust generated locally was easily overwhelmed by, and largely unnoticeable as compared to the dust transported in from the sources regions of the dust storm ”

. 17

Table 4: Evaluation of CDPHE’s Technical Support Documentation of CC R 18 Clear Causal Relationship Demonstration

Citation Sufficient Quality of Evidence ? EPA Criterion Met? Section 2: p. 10

- 45 , Figures 1

- 29 Yes Yes Section 2: p. 10, 21

- 30 , Tables 1

- 10 Yes Yes Section 2: p.43

- 44 Yes Yes

Section 4: p. 65

- 69 Yes Yes

Affects Air Quality

As stated in the Interim Guidance for High Wind Exceptional Events Section 3.4

, EPA will consider
events to have A ffected A ir Q uality (AAQ) if the CCR and HF requirements have been adequately

14 “Technical Support Document for the May 11, 2010, Alamosa and Pagosa Springs Exceptional Event” May 20, 2013, page 43.
15 “Technical Support Document for the May 11, 2010, Alamosa and Pagosa Springs Exceptional Event” May 20, 2013, page 43

- 44.
16 “Technical Support Document for the May 11, 2010, Alamosa and Pagosa Springs Exceptional Event” May 20, 2013, page 10.
17 “Technical Support Document for the May 11, 2010, Alamosa and Pagosa Springs Exceptional Event” May 20, 2013, page 67.
18 See “Interim 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” of May 2013 page 21.14

demonstrated. CDPHE states that due to the informat ion presented in the HF and CCR demonstrations on pages 8

- 9 and 9

- 11 of this TSD , respectively, and cited in Table 5 below , “data clearly shows that but for this high wind blowing dust event, Alamosa and Pagosa Springs would not have exceeded the 24

- hour
N AAQS on May 11, 2010. 19 ”

Table 5: Evaluation of CDPHE’s Technical Support Documentation of AAQ
HF or CCR Affects Air Quality Demonstration Citation Sufficient Quality of Evidence ? EPA Criterion Met? HF Section 3: p.54

- 55, Figure 38 Yes Yes HF Section 3: p.51

- 52, Figure 34 Yes Yes HF Section 3: p.48

- 49, Figure 30 Yes Yes CCR Section 2: p.10

- 45, Figures 1

- 29 Yes Yes CCR Section 2: p.10, 21

- 30, Tables 1

- 10 Yes Yes CCR Section 2: p.41 Yes Yes CCR Section 4: p.62

- 66 Yes Yes

Natural Event

As stated in the Interim Guidance for High Wind Exceptional Events Section 6.3.6 EPA will consider an event to be a natural event if both the nRCP and CCR requirements have been adequately demonstrated. CDPHE generally states that, “[s]ince at lea s t 2005, there has not been an exceedance that was not associated with high winds carrying PM 10 dus t from distant sources in these areas” and that “multiple sources of data for the event in question and analyses of past dust storms in this area prove that this was a natural event ”

. 20

Table 6: Evaluation of CDPHE’s Technical Support Documentation of Natural Event
nRCP or CCR Natural Event Demonstration Citation Sufficient Quality of Evidence ? EPA Criterion

Met? nRCP Section 5.2: p.67

- 68, 77

- 81 Yes Yes nRCP Section 5.1: p.67

- 68

- , 69

- 76 Yes Yes nRCP Section 5.1: p.67

- 68, 69

- 76 Yes Yes CCR Section 2: p.10

- 45, Figures 1

- 29 Yes Yes CCR Section 2: p.10, 21

- 30, Tables 1

- 10 Yes Yes CCR Section 2: p.41 Yes Yes CCR Section 4: p.62

- 66 Yes Yes Conclusion Section 6: p.8 2

- 83 Yes Yes

19 CDPHE’s “Technical Support Document for the April 28 & 29, 2010, Alamosa, Pagosa Springs, and Durango Exceptional Event,” page 85.
20 “Technical Support Document for the May 11, 2010, Alamosa and Pagosa Springs Exceptional Event” May 20, 2013, page 85.15

No Exceedance or Violation But For the Event

Generally, the No Exceedance But For the event ( NEBF ) demonstration is similar to the demonstration of the nRCP and CCR requirements, and should show that the measured concentration would have been below the applicable NAAQS without the affect of the event.

CDPHE provides a summary of the analysis and inform ation presented in the documentation that demonstrate both the nRCP and CCR requirements have been met and states that :

[t]he PM 10 exceedances in Alamosa and Pagosa Springs on May 11, 2010, would not have occurred if not for the following: (a) dry soil c onditions over southeastern Utah, northeastern Arizona, and portions of extreme northwestern New Mexico; (b) a combination of strong surface low pressure and a cold front associated with an intense upper

- level trough that was moving across the western Unit ed States that created conditions necessary for widespread strong gusty winds over the area of concern; and (c) elevated friction velocities and the deep mixing of the blowing dust from desert regions of Arizona, northwest New Mexico, and southeast Utah. 21

While not explicitly stated in the documentation, EPA acknowledges that PM 10 concentrations before the periods of high winds on the event days were below the 24

- hour PM 10 NAAQS, providing further support for CDPHE’s conclusion.

Table 7: Evaluation of CDPHE’s Technical Support Documentation of NEBF
Exceedance Date No Exceedance But For the Event Demonstration Citation Sufficient Quality of Evidence ? EPA Criterion Met?

May 1 1, 2010 Section 6: p. 85

- 86 Yes Yes

Schedule and Procedural Requirements

In addition to technical demonstration requirements, 40 CFR 50.14(c) specifies the schedule and procedural requirements an air agency must follow to request data exclusion. Table 8 outlines EPA’s evaluation of these requirements.

21 “Technical Support Document for the May 11, 2010, Alamosa and Pagosa Springs Exceptional Event” May 20, 2013, page 85.16

Table 8: Schedules and Procedural Criteria
Reference Schedules and Procedural Criteria Demonstration Citation Criterion

Met?

Did the State provide prompt public notification of the event? 40 CFR §50.14(c)(l)(i) Section 1:p. 8 Yes

Were flags and initial description placed on the data by July 1 st of the following year? 40 CFR §50.14(c)(2)(iii) Section 1:p. 8

- 9 Yes

Was the demonstration submitted within 3 years of the end of the quarter in which the event occurred and 12 months prior to the date that any regulatory decision must be made by EPA? 40 CFR §50.14(c)(3)(i) June 28 , 2013 Yes

Was the public comment process followed and documented? 40 CFR §50.14(c)(3)(v) Section 1:p. 9 Yes



## CONCLUSION

EPA has reviewed documentation provided by CDPHE to support claims that dust emissions generated by high winds resulted in PM 10 transport from arid regions in Arizona, northwest New Mexico, and southeast Utah into the Pagosa Springs and Alamosa areas on Ma y 11, 2010 . These high wind events
caused exceedances of the 24

- hour PM 10 NAAQS at the location s identified in Table 1 of this document on May 11, 2010. EPA has determined that the flagged exceedances at these locations on this day meet the definition of an exceptional event: the exceedances affected air quality, were nRCP , and meet the definition of a natural event. Specifically, EPA has determined that events were nRCP due to high wind conditions that transported PM 10 from sources outs ide of the Pagosa Springs and Alamosa areas and subsequently overwhelmed reasonable controls within Alamosa and Pagosa Springs. Also, regardless of transport into the area, information pertaining to the controls implemented within the affected areas, the

s patial extent of elevated PM 10 concentrations measured in the area, and the wind speeds associated with the high wind dust event provide sufficient evidence to conclude that these events were nRCP

. Furthermore, EPA has determined that there is a CCR betwee n the events and the measured exceedances, there would have been no exceedance but for the events, and the measured exceedances are in excess of
normal HF

. EPA finds that the weight of evidence is sufficient to concur on the flagging of the data for these monitors on May 11, 2010. These concurrences do not constitute final EPA action regarding any matter on which EPA is required to provide an opportunity for public comment. In particular, this applies to determinations regarding the attainment status or cl assification of the area. Final actions will take place only after EPA completes notice and comment rulemaking on those determinations.