1



## EPA Technical Support Document i n Review of Colorado Department of Public Health and Environment’s Demonstration Package for the April 5, 2010 Alamosa, Pagosa Springs, Durango , and Telluride 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 definitions, criteria for EPA approval, procedural requirements, and requirements for air agency demonstrations, all of which must be met before EPA can concur under the EER on the exclusion of air quality data from regulatory decisions.

Under 4 0 CFR 50.14(c)(3)(iv), the air agency demonstration to justify exclusion of data must provide evidence that:

A. The event satisfies th e criteria set forth in 40 CFR 50.1 (j) for the definition of an exceptional

event : The event affects air quality ; The event i s not reasona bly controllable or preventable; and 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 ev ent 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 eve nt.
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 Exceptio nal Events Rule” of May 2013, ( Interim Guidance for High Wind Excep tional Events ) in addition to the applicable statutory and regulatory provisions.



## SUMMARY

Overview

On June 28, 2013, the Colorado Department of Public Health and Environment ( CDPHE ) submitted excepti onal event demonstrations for six exceedances and four high readings of the 24

- hour PM 10 standard that occurred at several monitoring stations in southwestern Colorado on April 5 , 2010. Table 1 summarizes these exceedances, T able 2 summarizes the high sample readings that CDPHE would like

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

considered in suppor t of the existence of the high wind blowing dust event but not for removal from the Air Quality System ( AQS ) database

.

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

- hour NAAQS
Exceedance Date Monitor/Site Name AQS ID 24

- hour Avg. (ug/m 3 ) CDPHE

Request to Consider for AQS Removal? 2 April 5, 2010 Telluride 08

- 113

- 0004 354 Yes

Pagosa Springs School 08

- 007

- 0001 349 Yes Durango River City Hall 08

- 067

- 0004 320 Yes Alamosa Adams State College 08

- 003

- 0001 185 Yes Crested Butte 08

- 051

- 0004 174 Yes Mt. Crested Butte 08

- 051

- 0007 168 Yes

Table 2: EPA PM 10 High Samples Included in CDPHE’s TSD for Demonstration Purposes Only High Sample Date Monitor/Site Name 24

- hour Avg. (ug/m 3 ) CDPHE

Request to Consider for AQS Removal? April 5, 2010 Delta 115 No 3

Clifton 75 No 4
Aspen 70 No 5

Grand Junction Powell 51 No 6

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 Christo
M ountain ranges. Alamosa is generally surrounded by agricultural lands within the San Luis Valley. Pagosa Springs lies along the San Juan River, to the west and south of the San Juan M ountains. Durango lies along the Animas River at an elevation of 6,512 feet in a valley running north to south. Telluride sits at 8,750 feet at the top of a valley that runs downhill to the west. The east end of the valley is similar to a box canyon. Crested Butte and Mt. Crested Butte sit at 8,885 feet at the top of a valley that descends south ward and widens into the relatively flat mountain park through which the westward flowing Delta

2 “Technical Support Document for the April 5, 2010, Alamosa, Pagosa Springs, and Durango Exceptional Event,” May 17, 20 13, page 1

. 3 CDPHE included these values in their report to demonstrate the regional nature of the event but did not specifically request their removal.
4 CDPHE included these values in their report to demonstrate the regional nature of the event but did not specifically request their removal.

5 CDPHE included these values in their report to demonstrate the regional nature of the event but did not specifically request their removal.
6 CDPHE included these values in their report to demonstrate the regional nature of the event but did not specifically request their removal.3

River runs. To the southwest of all of these sites are the deserts of the New Mexico, Utah, and Arizona Four Corners reg ion.

Figure 1: Map of Desert, Four Corners, and Monitor Locations with PM 10 NAAQS Exceedances

In its exceptional event demonstration package CDPHE describes the April 5, 2010 event as:

the consequence of strong southwesterly prefrontal surface winds in combination with dry conditions which caused significant blowing dust across much of Arizona, northwest New Mexico, southeast Utah and southwest Colorado. These winds were the result of a strong short wave in the upper atmosphere that was moving across the Great Basin and the associated surface cold front and low pressure system . This dust storm originated in the desert regions of northern central Arizona and northwestern New Mexico. It transported PM 10 dust into the southern and central portions of Colo rado

. 7

7 “Technical Support Document for the April 5, 2010, Alamosa, Pagosa Springs, and Durango Exceptional Event,” May 17, 2013, pages 1

- 2.4

CDPHE provides a comprehensive description and discussion of this overnight 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.

CDPHE’s inclusion o f Figure 2 from pages 46 of the state’s d emonstration 8 visually demonstrates wind speed and direction of blowing dust across northeastern Arizona, southeastern Utah, and northwestern New Mexico into southeastern Colorado. Figure 3 is a close

- up of the plume in Arizona

. 9 Furthermore, f igures 1

- 35 from CDPHE’s demonstration use modeling, meteorology, and monitoring analysis to support the evidence of wind direction and reach of the dust storm into Durango, Alamosa

, Pagosa Springs , Telluride, and Crested B utte

. This EPA evaluation of the state’s demonstration find s that Durango, Alamosa, Pagosa Springs, and Telluride all have complete demonstrations that warrant concurrence on the flagged AQS data, while Crested Butte and Mt. Crested Butte are lacking suffi cient analysis, as explained below.

Figure 2: Satellite Image of Dust Storm (CDPHE’s Figure 30 in the s tate’s d emonstration)

8 “Technical Support Document for the April 5, 2010, Alamosa, Pagosa Springs, and Durango Exceptional Event,” May 17, 2013, page 46.
9 “Technical Support Document for the April 5, 2010, Alamosa, Pagosa Springs, and Durango Exceptional Event,” May 17, 2013, page 48.5

F igure 3: Satellite Image of Dust Storm in Arizona (Figure 32 in CDPHE’s d emonstration)

Not Reasonably Controllable or Preventable

EPA evaluates whether an event was n ot Reasonably Controllable or Preventable (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:6

1. The anthropogenic sources of dust have reasonable controls in place; 2. The reasonable controls have been effectively implemented and enforced; and, 3. The wind speed was high enough to overwhelm the reasonable controls. 10

In addressing reasonable controls, CDPHE provided detailed informat ion on the current set of required and voluntary controls in the Alamosa, Pagosa Springs, and Durango areas , including information on implementation of State Regulations 1, 3, 6, and 9, rule effectiveness, compliance, and public notification activities tha t occurred on the event day. As CDPHE states, they :

conducted thorough analyses and outreach with local governments to confirm that no unusual anthropogenic PM 10 - producing activities occurred in these towns and that despite reasonable control measures i n place, high wind conditions overwhelmed all reasonably available controls. 11

CDPHE provided the documentation listed in F igures 4 & 5 (CDPHE tables 7 & 9 ) 12

, which EPA supplemented with Figure 6, showing that sustained wind speeds associated with these events were above 25 mph. For example, in Alamosa sus tained surface winds of up to 44 mph with gusts up to 60 mph were measured on April 5 , 2010, while Durango saw sustained wind speeds up to 30 mph and gusts up to 43 mph. CDPHE previously established in i ts exceptional events demonstration for the January 19, 2009 event in Lamar, Colorado that wind speeds 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 speed s on April 5 , 2010 clearly exceed the established high

- wind threshold

. 13

10 “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,” May 2013, page 10.
11 “Technical Support Document for the April 5, 2010, Alamosa, Pagosa Springs, and Durango Exceptional Ev ent” May 17, 2013, page 87.
12 “Technical Support Document for the April 5, 2010, Alamosa, Pagosa Springs, and Durango Exceptional Event” May 17, 2013, pages 28 and 30.
13 The EPA’s minimum high wind threshold for wind speed in the West (although not intende d 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 Exclude Ambient Air Quality Data Affected by High Winds Under the Exceptional Events Rule” of May 2013 . CDPHE has established that 30 mph sustained winds and 40 mph gusts are an appropriate threshold in Colorado

.7

Figure 4 : Wind Speed in Durango, Colo. on April 5, 20108

Figure 5 : Wind Speed in Alamosa, Colo. on April 5, 20109

Figure 6: Wind Speed in Pagosa Springs ( left ) and Telluride (right) on April 5, 2010

Pagosa Springs Monitor

- MesoWest Telluride Monitor

- MesoWest

ID = KPSO Wind mph GUST mph ID = KTEX Wind mph GUST mph
4

- 5

- 2010 0:15 MDT 3.5 4

- 5

- 2010 0:15 MDT 10.4 41.4
4

- 5

- 2010 0:35 MDT 0 4

- 5

- 2010 0:33 MDT 15 32.2
4

- 5

- 2010 0:55 MDT 3.5 4

- 5

- 2010 0:53 MDT 10.4 20.7
4

- 5

- 2010 1:15 MDT 0 4

- 5

- 2010 1:13 MDT 13.8 19.6
4

- 5

- 2010 1:35 MDT 0 4

- 5

- 2010 1:35 MDT 18.4 29.9
4

- 5

- 2010 1:55 MDT 0 4

- 5

- 2010 1:53 MDT 13.8 21.9
4

- 5

- 2010 2:15 MDT 0 4

- 5

- 2010 2:13 MDT 15 29.9
4

- 5

- 2010 2:35 MDT 0 4

- 5

- 2010 2:33 MDT 19.6 32.2
4

- 5

- 2010 2:55 MDT 0 4

- 5

- 2010 2:55 MDT 19.6 34.5
4

- 5

- 2010 3:15 MDT 0 4

- 5

- 2010 3:13 MDT 6.9 27.6
4

- 5

- 2010 3:35 MDT 0 4

- 5

- 2010 3:35 MDT 17.3 25.3
4

- 5

- 2010 3:55 MDT 0 4

- 5

- 2010 3:53 MDT 12.7 32.2
4

- 5

- 2010 4:15 MDT 0 4

- 5

- 2010 4:15 MDT 8.1 18.4
4

- 5

- 2010 4:35 MDT 0 4

- 5

- 2010 4:33 MDT 6.9
4

- 5

- 2010 4:55 MDT 0 4

- 5

- 2010 4:52 MDT 10.4 18.4
4

- 5

- 2010 5:15 MDT 0 4

- 5

- 2010 5:13 MDT 16.1 24.2
4

- 5

- 2010 5:35 MDT 0 4

- 5

- 2010 5:35 MDT 18.4 24.2
4

- 5

- 2010 5:55 MDT 0 4

- 5

- 2010 6:16 MDT 8.1 25.3
4

- 5

- 2010 6:15 MDT 0 4

- 5

- 2010 6:33 MDT 17.3 31.1
4

- 5

- 2010 6:35 MDT 0 4

- 5

- 2010 6:53 MDT 3.5 9.2
4

- 5

- 2010 6:55 MDT 0 4

- 5

- 2010 7:13 MDT 9.2 40.3
4

- 5

- 2010 7:15 MDT 0 4

- 5

- 2010 7:33 MDT 8.1
4

- 5

- 2010 7:35 MDT 0 4

- 5

- 2010 7:53 MDT 17.3 31.1
4

- 5

- 2010 7:55 MDT 0 4

- 5

- 2010 8:13 MDT 18.4 29.9
4

- 5

- 2010 8:15 MDT 0 4

- 5

- 2010 8:35 MDT 19.6 35.7
4

- 5

- 2010 8:35 MDT 0 4

- 5

- 2010 8:53 MDT 13.8 28.8
4

- 5

- 2010 8:55 MDT 0 4

- 5

- 2010 9:15 MDT 15 33.4
4

- 5

- 2010 9:15 MDT 0 4

- 5

- 2010 9:33 MDT 18.4 32.2
4

- 5

- 2010 9:35 MDT 11.5 17.3 4

- 5

- 2010 9:55 MDT 19.6 34.5
4

- 5

- 2010 9:55 MDT 8.1 4

- 5

- 2010 10:13 MDT 28.8 39.1
4

- 5

- 2010 10:15 MDT 10.4 4

- 5

- 2010 10:36 MDT 15 50.6
4

- 5

- 2010 10:35 MDT 13.8 24.2 4

- 5

- 2010 10:54 MDT 21.9 43.7
4

- 5

- 2010 10:55 MDT 18.4 25.3 4

- 5

- 2010 11:13 MDT 17.3 35.7
4

- 5

- 2010 11:15 MDT 10.4 20.7 4

- 5

- 2010 11:33 MDT 23 51.8
4

- 5

- 2010 11:35 MDT 11.5 17.3 4

- 5

- 2010 11:53 MDT 17.3 35.710

4

- 5

- 2010 11:55 MDT 16.1 20.7 4

- 5

- 2010 12:13 MDT 29.9 44.9
4

- 5

- 2010 12:15 MDT 13.8 23 4

- 5

- 2010 12:34 MDT 16.1 35.7
4

- 5

- 2010 12:35 MDT 17.3 24.2 4

- 5

- 2010 12:53 MDT 11.5 27.6
4

- 5

- 2010 12:55 MDT 11.5 24.2 4

- 5

- 2010 13:33 MDT 28.8 49.5
4

- 5

- 2010 13:15 MDT 12.7 21.9 4

- 5

- 2010 13:53 MDT 24.2 49.5
4

- 5

- 2010 13:35 MDT 8.1 4

- 5

- 2010 14:13 MDT 27.6 50.6
4

- 5

- 2010 13:55 MDT 13.8 18.4 4

- 5

- 2010 14:33 MDT 25.3 61
4

- 5

- 2010 14:15 MDT 11.5 21.9 4

- 5

- 2010 14:53 MDT 24.2 59.8
4

- 5

- 2010 14:35 MDT 16.1 24.2 4

- 5

- 2010 15:13 MDT 33.4 58.7
4

- 5

- 2010 14:55 MDT 17.3 25.3 4

- 5

- 2010 15:33 MDT 24.2 59.8
4

- 5

- 2010 15:15 MDT 26.5 35.7 4

- 5

- 2010 15:53 MDT 18.4 46
4

- 5

- 2010 15:35 MDT 19.6 31.1 4

- 5

- 2010 16:13 MDT 24.2 50.6
4

- 5

- 2010 15:55 MDT 28.8 35.7 4

- 5

- 2010 16:33 MDT 23 52.9
4

- 5

- 2010 16:15 MDT 24.2 31.1 4

- 5

- 2010 16:55 MDT 12.7 25.3
4

- 5

- 2010 16:35 MDT 24.2 38 4

- 5

- 2010 17:13 MDT 20.7 35.7
4

- 5

- 2010 16:55 MDT 23 35.7 4

- 5

- 2010 17:33 MDT 12.7 25.3
4

- 5

- 2010 17:15 MDT 20.7 33.4 4

- 5

- 2010 17:53 MDT 15 29.9
4

- 5

- 2010 17:35 MDT 24.2 33.4 4

- 5

- 2010 18:15 MDT 16.1 39.1
4

- 5

- 2010 17:55 MDT 19.6 34.5 4

- 5

- 2010 18:33 MDT 16.1 38
4

- 5

- 2010 18:15 MDT 19.6 32.2 4

- 5

- 2010 18:53 MDT 15 28.8
4

- 5

- 2010 18:35 MDT 16.1 31.1 4

- 5

- 2010 19:12 MDT 17.3 32.2
4

- 5

- 2010 18:55 MDT 20.7 29.9 4

- 5

- 2010 19:35 MDT 15 31.1
4

- 5

- 2010 19:15 MDT 18.4 25.3 4

- 5

- 2010 19:53 MDT 20.7 31.1
4

- 5

- 2010 19:35 MDT 15 23 4

- 5

- 2010 20:13 MDT 17.3 40.3
4

- 5

- 2010 19:55 MDT 16.1 32.2 4

- 5

- 2010 20:54 MDT 24.2 31.1
4

- 5

- 2010 20:15 MDT 19.6 29.9 4

- 5

- 2010 21:13 MDT 16.1 34.5
4

- 5

- 2010 20:35 MDT 19.6 32.2 4

- 5

- 2010 21:33 MDT 18.4 28.8
4

- 5

- 2010 20:55 MDT 26.5 34.5 4

- 5

- 2010 21:53 MDT 18.4 39.1
4

- 5

- 2010 21:15 MDT 19.6 35.7 4

- 5

- 2010 22:13 MDT 24.2 38
4

- 5

- 2010 21:35 MDT 19.6 40.3 4

- 5

- 2010 22:34 MDT 11.5 24.2
4

- 5

- 2010 21:55 MDT 20.7 29.9 4

- 5

- 2010 22:53 MDT 20.7 41.4
4

- 5

- 2010 22:15 MDT 26.5 36.8 4

- 5

- 2010 23:13 MDT 20.7 35.7
4

- 5

- 2010 22:35 MDT 19.6 36.8 4

- 5

- 2010 23:36 MDT 25.3 40.3
4

- 5

- 2010 22:55 MDT 12.7 28.8 4

- 5

- 2010 23:54 MDT 15 32.2
4

- 5

- 2010 23:15 MDT 24.2 38
4

- 5

- 2010 23:35 MDT 21.9 34.5
4

- 5

- 2010 23:55 MDT 19.6 28.811

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) ; Upper air sounding analysis from the University of Wyoming ; 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 HYSPLIT modeling of wind trajectories from NOAA HYSPLIT modeling runs ; MODIS Terra satellite images demonstrating the blowing dust across the region ; 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 Environmental 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.

Rather than catalogue the anthropogenic controls in place in Telluride, Crested Butte, and Mt. Crested Butte, CDPHE provided a comprehensive analysis of snow depth at elevation in early April. The analysis demonstrates that any potential anthropogenic sources were covered by 70 inches of snow in Telluride and 20 or more inches of snow in Crested Butte and Mt. Crested Butte. 14 The following NOAA figure indicates the depth of snow at the time of th e event, an image supported by NOAA Snow Water Equivalent, Snow Depth, Snow Cover, and Snow Melt analysis charts and narrative. 15 Based on the snowpack at the time of the event it is reasonable to conclude expected seasonal anthropogenic controls such as ve getation, irrigation, fencing, or clay stabilization of undeveloped lots were neither appropriate

nor applicable

. Additionally, s atellite imagery of the valley in the spring of 2010 shows no potential undeveloped parcels of land of concern.

14 “Technical Support Document for the April 5, 2010, Alamosa, Pagosa Springs, and Durango Exceptional Event,” May 17, 2013, pages 40

- 41.
15 “Technical Support Document for the April 5, 2010, Alamosa, Pagosa Springs, and Durango Exceptional Event,” May 17, 2013, pages 40

- 44.12

Figure 7 : NOAA Snow Depth in Southern Colo. on April 5, 2010

Section 5 of CDPHE’s documentation provides a thorough analysis of the s tate and local controls in place to control PM 10 emissions . These controls include CDPHE’s:

Regulation 1

- Emission Contr ol of Particulate s , Smoke, Carbon Monoxide, and Sulfu r 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. 16

16 “Technical Support Document for the April 5, 2010, Alamosa, Pagosa Springs, and Durango Exceptional Event,” May 1 7, 2013, pages 87

- 88.13

Alamosa has the following controls in place:

Natural Events Action Plan (NEAP) 17 , 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 the 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 establishments to install underground irrigation. 18

In addition, Alamosa conducts street sweeping, has irrigated and installed vegetative cover on all city parks, encourag es low tilling and other soil conservation practices outside of town through the Colorado State University Co

- Op Extension Office and the Natural Resources Conservation Service. Since 2008 t he
Mosca

- Hooper Conservation District has been working with the Na tural Resources Conservation Service to implement the Colorado State Forest Service’s program to plant between 2,805 and 7,432 trees per year since 2008 to prevent wind erosion in the area. 19

Maps are included of eight undeveloped parcels of land in town t hat were determined to be reasonably controlled or considered natural sources. All eight are covered with vegetation and five of those eight are confirmed to be irrigated. The three remaining sites in the following figure 8 (Sites B, E, and H) are naturall y vegetated and satellite images show minimal soil disturbance. 20

Figure 8 : Alamosa Site Assessment 21

17 “Technical Support Document for the April 5 , 2010, Alamosa, Pagosa Springs, and Durango Exceptional Event,” May 17, 2013, Appendix C.
18 “Technical Support Document for the April 5 , 2010, Alamosa, Pagosa Springs, and Durango Exceptio nal Event,” May 17, 2013, page 89.
19 “Technical Support Document for the April 5 , 2010, Alamosa, Pagosa Springs, and Durango Exceptional Event,” May 17, 2013, page 91.
20 “Technical Support Document for the April 5, 2010, Alamosa, Pagosa Springs, and Durang o Exceptional Event” May 17, 2013, pages 92

- 94.
21 This image is from 2007, EPA review of Google Earth satellite images as recent as 2011 show that there is still adequate vegetation.14

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 ; 22 EPA approved PM 10 Maintenance Plan for the Pagosa Springs Attainment/Maintenance Area

, effective on August 14, 2001 , requiring Prevention of Significant Deterioration (PSD) permitti ng requirements mandating Best Available Control Technology (BACT) at sources potentially emitting PM 10 ; and
V egetation, irrigation, fencing, and stabilized clay dust control measures are in place for undeveloped parcels of land in town. The map below 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 theref ore couldn’t have impacted the May 11, 2010 event. Site C was naturally vegetated and receives groundwater from a nearby stream; 23 it is also an area where off

- road recreational vehicles are prohibited by the parks department. Site D is an irrigated and mai ntained turf and stabilized clay baseball field since April 2009. 24

22 “Technical Support Document for the April 5, 2010, Alamosa, Pagosa Spr ings, and Durango Exceptional Event,” May 17, 2013, pages 96

- 100.
23 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 practical method tha t is technologically feasible and economically reasonable in order to minimize fugitive particulate emissions for this lot at this time.
24 “Technical Support Document for the April 5, 2010, Alamosa, Pagosa Springs, and Durango Exceptional Event,” May 17, 2 013, pages 98

- 100.15

Figure 9 : Pagosa Springs Site Assessment

On March 16, 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 and Pago sa Springs areas. No additional control measures are needed in these areas to demonstrat e long

- term maintenance of the PM

- 10 NAAQS ”

. 25 The dust control strategies described in 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.

Durango local controls include:

Dust Control rules and ordinances found in Figure 1 1 (CDPHE’s table 30 ) following ; 26 The City or Durango, La P lata County, and the S outhern Ute Indian Tribe work together to implement the following programs: street sweeping and sanding cont rols, dust suppressant for gravel roa ds, landfill dust control, and s moke mitigation for locomotives ; 27

25 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, 6 6FR 32556.
26 “Technical Support Document for the April 5 , 2010, Alamosa, Pagosa Springs, and Durango Exceptional Event,” May 17, 2013, pages 101

- 102.
27 “Technical Support Document for the April 5, 2010, Alamosa, Pagosa Springs, and Durango Exceptional Event,” May 17, 2013, pages 102

- 103.16

La Plata County and th e Southern Ute Indian Tribe have surface operating standards to control dust from oil & gas development in the area. This includes maintaining roads to well pads, establishing speed limits, and designating gradient to minimize dust. Guidelines are found in the Bureau of Land Management’s (BLM) “Surface Operating Standards and Guidelines for Oil and Gas Exploration and Development, The Gold Book” 4 th edition, 2007 ; 28 and Vegetation, signage, and other 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. Site A is a former industrial site that was leveled and then compacted and allowed to

r eturn to a natural state. CDPHE confirmed that the soil remains compacted and vegetated and should not be considered an anthropogenic source. Site B is naturally vegetated and has not been developed. Site C is an off

- leash dog park with signage to indicate that it is an area where off

road recreational vehicles are prohibited by the parks department

. 29

Figure 10 : Durango Site Assessment

28 Online version: http://www.blm.gov/pgdata/etc/medialib/blm/wo/MINERALS__REALTY__AND_RESOURCE_PROTECTION_/e nergy/oil_and_gas.Par.18714.File.dat/OILgas.pdf
29 “Technical Support Document for the April 5 , 2010, Alamosa, Pago sa Springs, and Durango Exceptional Event,” May 17, 2013, pages 104

- 107.17

Figure 1 1 : Durango and La Plata County Dust Control Rules and Ordinances1819

Telluride local controls include:

Woodburning 30 controls which t he Town of Telluride and San Miguel County have adopted as wood and coal burning emission reduction measures. These wood and coal burning controls were adopted and implemented throughout the 1980s and early 1990s, were approved by EPA in 1994, and are defined in detail in Section II. A. of the “State Implementation Plan

- Specific Regulations for Nonattainment

– Attainment/Maintenance Areas (Local Elements). ” All of these requirements remain effective, until th ey are removed or revised by a future SIP revision ; Emissions from stationary sources of pollution are regulated by several Air Quality Control Commission Regulations 31 ; Street Sanding Controls requir ing that any user that applies street sanding material in the Telluride attainment/maintenance area must use materials containing less than two percent fines. This strategy was adopted in 1994 and approved by EPA in 1996, and it is defined in detail in Sectio n II.B. of the “State Implementation Plan

- Specific Regulations for Nonattainment

– Attainment/Maintenance Areas (Local Elements) ; and Control Measures Included in the Attainment/Maintenance Plan , including federal fuels and tailpipe standards and regulatio ns 32

.

30 Air Quality Control Commission Regulation No. 4 covers wood stoves, conventional fireplaces and woodburning on high pollution days, as approved by EPA as part of the federal SIP in 1997. This maintenance plan makes no changes to Regulation No. 4.

31 1) Reg ulation No. 1 regulates emissions of particulates, smoke, sulfur dioxide, and nitrogen oxides and establishes limits on these pollutants from covered sources. Sections I

- IV, Sections VI

- IX, and Appendices A and B are already included in the approved SIP. T his maintenance plan incorporates the regulatory limits in calculations of maximum allowable emissions for stationary sources. No additional revisions are made to Regulation No. 1 as part of the maintenance plan revision. 2) Regulation No. 3 lays out provi sions of the State of Colorado’s stationary source permitting program. Parts A and B of Regulation No. 3 are already included in the approved SIP. Part C implements the federal operating permit program and this reference to Part C of Regulation No. 3 shall not be construed to mean that these regulations are included in the SIP. 3) Regulation No. 6 implements the federal standards of performance for new stationary sources. This maintenance plan makes no changes to this regulation. This reference to Regulatio n No. 6 shall not be construed to mean that these regulations are included in the SIP. 4) The Common Provisions Regulation contains general provisions applicable to all emissions sources in Colorado. This maintenance plan makes no changes to this regulatio n. The emission inventories for stationary sources supporting the maintenance demonstration have followed all relevant EPA rules and guidance documents for calculating such emissions. As an attainment/maintenance area since August 14, 2001, the State and f ederal attainment PSD permitting requirements remain in effect in the Telluride area. This program requires the application of Best Available Control Technology when constructing new or modified major stationary sources.

32 The Telluride area will rely on t he control programs listed below to demonstrate maintenance of the 24

- hour PM10 standard through 2021. No emission reduction credit has been taken in the attainment/maintenance demonstration for any other current State or local control programs and no othe r such programs, strategies, or regulations shall be incorporated or deemed as enforceable measures for the purposes of this maintenance demonstration.20

Examination of available satellite imagery in Telluride has shown very limited construction and soil disturbance within the village since 2003, particularly south of the PM10 monitor. The monitor is only 2 blocks north from the base of the ski mount ain, and available land south of the monitor is essentially built out. One 1.4 acre project was constructed approximately 1⁄2 mile WSW of the monitor sometime between June 2005 and August 2011. Construction to the south of the monitor is unlikely to have p layed a significant role in the April 2013 exceedance.

Credit is taken in this attainment/maintenance plan for current federal regulations concerning motor veh icles, fuels, small engines, diesels, and non

- road mobile sources. While credit is taken for these federal requirements, they are not part of the Colorado SIP.21

Figure 12: June 2005 and August 2011 GoogleEarth views of Telluride, with one 1.4 acre project

Sections 2 and 5 of CDPHE’s analysis demonstrate that monitors in Telluride, Pagosa Springs, Alamosa, Durango, Crested Butte, and Mt. Crested Butte 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 whethe r these events are not reasonably controllable or preventable. Table 3 summarizes the EPA’s evaluation of CDPHE’s nRCP EE demonstration.22

Table 3: Evaluation of CDPHE’s Technical Support Documentation of nRCP
Exceedance Date Location Reasonable Controls D emonstration Citation Wind Speed

Demonstration Citation Sufficient

Quality of Evidence? EPA

Criterion Met?

April 5, 2010 Alamosa

Adams State College Section 4.0:

p.87

- 88 and Section 4 .1:
p. 89

- 95 Section 2: p.11

- 55,

esp. p. 22

- 31 Yes Yes

Pagosa Springs School Section 4.0:

p.87

- 88 and Section 4.2: p.96

- 100 Section 2: p.11

- 55,

esp. p.22

- 31 Yes Yes

Durango River City Hall Section 4.0:

p.87

- 88and Section 4.3: p.101

- 107 Section 2: p.11

- 55,

esp. p.22

- 31 Yes Yes

Telluride Section 2.0:

p.40

- 44 Section 2: p.11

- 55,

esp. p.22

- 31 Yes Yes

Crested Butte Section 2.0:

p.40

- 44 Section 2: p.11

- 55,

esp. p.22

- 31 Yes Yes

Mt. Crested Butte Section 2.0:

p.40

- 44 Section 2: p.11

- 55,

esp. p.22

- 31 Yes Yes

Historical Fluctuations

EPA evaluates whether a measured exceedance is in excess of Historical Fluctuation (HF) by taking into account the level of the exceedance in relation to historical data, which is typically 3 to 5 years. To demonstrate that this requirement was met, CPDHE provided 7

- year time series plots of 2,214 samples (Alamosa Adams State College), 2,232 samples (Pagosa Springs), 811 samples (Durango) of daily 2 4 hour averages. CDPHE did not provid e extensive analysis of the Telluride, Crested Butte, and Mt. Crested Butte monitors because the state believes that the attainment status of the sites will not be affected by the April 5, 2010 exceedances 33

. The EPA is interested in the historical fluctuatio ns of the Telluride monitor since Telluride’s 10

- year maintenance plan is currently under review by EPA

. T herefore , EPA is including a brief analysis here of the historical fluctuations at the monitor.

The Interim Guidance for High Wind Exceptional Events asks for a times series concentration for the event and percentile rank of the concentration relative to annual and seasonal data. Figure 1 2 following is a time series concentration of the Telluride monitor from 2000 to 2012. There was a sing l e exceedance of the NAAQS, and it occurred on April 5, 2010. With 1

, 380 samples collected in 2000 to 2012, the highest value is the equivalent of the 99.93 percentile, but more directly, one exceedance was recorded in this 13 year period, showing that any exceedance o f the 150 ug/m 3 NAAQs in Telluride is well outside normal historical fluctuations.

33 “Technical Support Document for the April 5, 2010, Alamosa, Pagosa Springs, and Durango Exce ption al Event,” May 17, 2013, page 56

.23

Figure 1 3 : EPA Time Series Concentration for Telluride from 2000 to 2012

CDPHE explains that concentrations measured on April 5, 2010 were more rare than the 99.6 percentile level at the Alamosa Adams State College monitor and were the highest values ever recorded at the Pagosa Springs , Telluride, and Durango monitors. 34

The EPA “Interim Guidance on High Wind Exceptional Events” recommends that demonstrations also

c onsider percentile ranks when dust impacted data is excluded. 35 EPA calculates this p ercentile as more rare than 99.68 percentile for the Alamosa monitors. The April 5 , 2010 Pagosa Springs

, Durango , and Alamosa values rank among the values exceeding the N AAQS that, since at least 2005, are only found during high wind dust events. This information indicates that values at the levels seen on April 5 , 2010 are extremely rare in the absence of high wind dust exceptional event impacts, and that it is unlikely t hat any sources of PM 10 were involved in the April 5 , 2010 exceedances other than wind

- blown dust. Table 4 summarizes the EPA’s evaluation of CDPHE’s HF EE demonstration.

34 “Technical Support Document for the April 5, 2010, Alamosa, Pagosa Springs, and Durango Exceptional Event,” May 17, 2013, page 58.
35 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 20.24

Table 4: Evaluation of CDPHE’s Technical Support Documentation of HF
Exceedance Date Exceedance

Location Historical Fluctuations

Demonstration Citation Sufficient Quality

of Evidence? EPA Criterion

Met?

April 5, 2010 Alamosa Adams

State College Section 3: p.56

- 59, 59

- 62 Yes Yes

Pagosa Springs Section 3: p.56

- 59, 62

- 65 Yes Yes

Durango Section 3: p.56

- 59, 65

- 66 Yes Yes

Telluride Section 3: p.56

- 59 Yes 36 Yes

Crested Butte Section 3: p.56

- 59 No 37 No

Mt. Crested Butte Section 3: p.56

- 59 No 38 No

Clear Causal Relationship

EPA considers a variety of evidence when evaluating whether there is a Clear and Causal Relationship (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 transported 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. 39

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 NOAA ; Upper air sounding analysis from the University of Wyoming ;

36 As supplemented by EPA’s analysis.
37 According to the “ 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, pages 48

- 49, the state needed to include (but did not) the following ana lysis for sufficient HF quality of evidence: 1) A time series for concentration for the event area for the previous three years; 2) Percentile rank of concentration relative to annual data; and 3) Percentile rank of concentration relative to seasonal data.
38 See f ootnote above

. 39 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 s 21

- 22.25

M aps of real

- time weather data from NCAR ; R egional wind and weather by hour through MesoW est ; NOAA HYSPLIT modeling of wind trajectories from NOAA HYSPLIT modeling runs ; MODIS Terra satellite images demonstrating the blowing dust across the region ; M aps establishing the lack of regional precipitation and drought status from the USDA

, NOAA, and the National Drought Mitigation Center ; and
M aps of elevated friction velocities in the region from the NOAA NCEP North American Model.

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

CDPHE’s documentation also provides dust

- on

- snow data from the Center for Snow and Avalanche Studies, an organization that studies the effects of wind

- blown desert dust from Arizona, New Mexico, and Utah on snowpack albedo and snowmelt in the San Juan Mountains of Colorado

. Figure 29 of CDPHE’s documentation shows that April 5 , 2010, was one of nine Dust

- on

- Snow events for the 2009/2 010 water year. 40 This information helps to confirm that a regional blowing dust event with long

range transport caused the PM 10 exceedances measured across portions of Colorado on April 5, 2010.

The U.S. Geological Survey (USGS) Southwest Geographic Scien ce Team’s dust monitoring web pages list April 5 , 2010 as a D ust E vent day with the following characterization:

A nother frontal system advanced into the interior from the Pacific on Monday April 5 th , 2010 bringing strong winds and gusts in excess of 50 mph . The dominant wind direction was out of the south

- west. There was no apparent dust activity visible from satellite until mid

- afternoon and only then in the 4 corners region of the southwest. From the images... it is apparent that yet again the regions just north of the Little Colorado River on the Navajo Nation were the predominant dust sources for this event. We noted an ancillary dust source in New Mexico on the eastern edge of the Navajo Nation. Both Thermal Differencing and Visible images show atmospheri c dust moving well into southern Colorado

. 41

Also included are high

- wind blowing dust accounts from the Crestone Weather Center, the Durango Herald, the Arizona Daily Sun, The Denver Post, and the local NBC news affiliate in Grand Junction that describe low visibility, high winds, wind damage, and dust. 42

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”. 43 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

40 “Technical Support Document for the April 5, 2010, Alamosa, Pagosa Springs, and Durango Exceptional Event,” May 17, 2013, pages 44

- 45.
41 “Technical Support Document for the April 5, 2010, Alamosa, Pagosa Springs, and Durango Exceptional Event,” May 17, 2013, pages 45

- 46.
42 “Technical Support Document for the April 5, 2010, Alamosa, Pagosa Springs, and Durango Exceptional Event,” May 17, 2013, pages 74

- 86.
43 “Technical Support Document for the April 5, 2010, Alamosa, Pagosa Springs, and Durango Exceptional Event,” May 17, 2013, page 12.26

passed through 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”. 44 Table 5 summarizes the EPA’s evaluation of CDPHE’s CCR EE demonstration.

Table 5: Evaluation o f CDPHE’s Technical Support Documentation of CCR 45 Clear Causal Relationship Demonstration

Citation Sufficient Quality of Evidence ? EPA Criterion Met? Sec tion 2: p.11

- 55 , Figures 1

- 40 Yes Yes Section 2: p.11

- 12

, 22

- 31, Tables 1

- 1 0 Yes Yes

Section 2: p.44

- 4 6 Yes Yes Section 4: p. 74

- 86 Yes Yes

Affects Air Quality (AAQ)

As stated in the Interim Guidance for High Wind Exceptional Events Section 3.4, EPA will consider events to have affected air quality if the CCR and HF requirements have been adequately demonstrated. CDPHE states that due to the information presented in the HF and CCR demonstrations on pages 17 and 18

- 19 of this TSD, respectively, and cited in Table 6 below, “ statistical and meteorological data clearly shows that but for this h igh wind blowing dust event, Alamosa, Pagosa Springs, and Durango would not have exceeded the 24

- hour NAAQS on April 5 , 2010”. 46 EPA concludes this was also true for Telluride. Table 6 summarizes the EPA’s evaluation of CDPHE’s AAQ EE demonstration.

44 “Tec hnical Support Document for the April 5, 2010, Alamosa, Pagosa Springs, and Durango Exceptional Event,” May 17, 2013, page 87.
45 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.
46 “Technical Support Document for the April 5, 2010, Alamo sa, Pagosa Springs, and Durango Exceptional Event,” May 17, 2013, page 108.27

Table 6: Evaluation of CDPHE’s Technical Support Documentation of AAQ HF or CCR Exceedance Location Affects Air Quality Demonstration Citation Sufficient Quality of Evidence ? EPA

Criterion Met? HF Alamosa Adams State

College Section 3: p.56

- 59, 59

- 62 Yes Yes

Pagosa Springs Section 3: p.56

- 59, 62

- 65 Yes Yes

Durango Section 3: p.56

- 59, 65

- 66 Yes Yes

Telluride Section 3: p.56

- 59 Yes Yes

Crested Butte Section 3: p.56

- 59 No 47 No

Mt. Crested Butte Section 3: p.56

- 59 No 48 No

CCR All Monitors Section 2: p.11

- 55, Figures 1

- 40 Yes Yes

Section 2: p.11

- 12, 22

- 31, Tables 1

- 10 Yes Yes

Section 2: p.44

- 46 Yes Yes Section 4: p.74

- 86 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, “There has never been an exceedance that was not associated with high winds carrying PM 10 dust from dist ant sources in these six areas since at least 2005” 49 , 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 and, more specifically, a significant natural dust storm

o riginating in northeastern Arizona and northwestern New Mexico and spreading into southwestern and south

- central Colorado but for the dust storm on April 5, 2010, this exceedance would not have occurred. 50

Table 7 summarizes the EPA’s evaluation of CDPHE’s Natural Event EE demonstration.

47 See HF section in this document, especially footnotes to Table 4.

48 See HF section in this document, especially footnotes to Table 4.
49 “Technical Support Document for the April 5, 2010, Alamosa, Pagosa Springs, and Durango Exceptional Event,” May 17, 2013, page 108.
50 “Technical Support Document for the April 5, 2010, Alamosa, Pagosa Springs, and Durango Exceptional Event,” May 17, 2013, page 109.28

Table 7: Evaluation of CDPHE’s Technical Support Documentation of Natural Event nRCP or CCR Exceedance Location Natural Event

Demonstration Citation Sufficient Quality of Evidence ? EPA

Criterion Met? nRCP

Anthropogenic Alamosa Adams

State College Section 4.0: p.87

- 88 and

Section 4.1: p.89

- 95 Yes Yes

Pagosa Springs School Section 4.0: p.87

- 88 and

Section 4.2: p.96

- 100 Yes Yes

Durango River City Hall Section 4.0: p.87

- 88and

Section 4.3: p.101

- 107 Yes Yes

Telluride Section 2.0: p.40

- 44 Yes Yes Crested Butte Section 2.0: p.40

- 44 Yes Yes Mt. Crested Butte Section 2.0: p.40

- 44 Yes Yes nRCP

- Wind Speed Alamosa Adams State College Section 2: p.11

- 55, esp. p.22

- 31 Yes Yes

Pagosa Springs School Section 2: p.11

- 55, esp.

p.22

- 31 Yes Yes

Durango River City Hall Section 2: p.11

- 55, esp. p.22

- 31 Yes Yes

Telluride Section 2: p.11

- 55, esp. p.22

- 31 Yes Yes

Crested Butte Section 2: p.11

- 55, esp. p.22

- 31 Yes Yes

Mt. Crested Butte Section 2: p.11

- 55, esp. p.22

- 31 Yes Yes

CCR All Monitors Section 2: p.11

- 55, Figures 1

- 40 Yes Yes

Section 2: p.11

- 12, 22

- 31, Tables 1

- 10 Yes Yes

Section 2: p.44

- 46 Yes Yes Section 4: p.74

- 86 Yes Yes

No Exceedance or Violation But For the Event

Generally, the No Exceedance or Violation 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 information presented in the documentation that demonstrate both the nRCP and CCR requirements have been met and states that:

The PM10 exceedances in Durango, Telluride, Pagosa Springs, Crested Butte, Mount Crested Butte and Alamosa on April 5, 2010, would not have occurred if not for the following: (a) dry soil conditions over northeastern Arizona, most of Utah, and parts of western Colorado with 30

- day precipitation totals below the threshold identified as a precondition for blowing dust in northeastern Arizona; (b) a strong surface and upper

- level low pressure system that caused widespread strong gusty winds through a deep layer of the atmosphere over the area of concern;29

and (c) friction velo cities over the desert regions of northwest New Mexico, Utah, and Arizona that were high enough to allow entrainment of dust from natural sources with subsequent transport of the dust to Colorado in strong, southwesterly winds. These winds were the result of a strong short wave in the upper atmosphere that was moving across the Great Basin and the associated surface cold front and low pressure system. 51

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 8 summarizes the EPA’s evaluation of CDPHE’s NEBF EE demonstration.

Table 8: 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?

April 5 , 2010 Section 6: p. 108

- 109 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 9 outlines EPA’s evaluation of these requirements.

Table 9 : Schedules and Pr ocedural Criteria Reference Schedules and Procedural Criteria Demonstration Citation EPA

Criterion Met?

Did the State provide prompt public notification of the event? 40 CFR §50.14(c)(l)(i) Section 1:p.9 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.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.10 Yes

51 “Technical Support Document f or the April 5, 2010, Alamosa, Pagosa Springs, and Durango Exceptional Event,” May 17, 2013, page 108.30



## 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 Telluride, Crested Butte, Mt. Crested Butte, Pagosa Springs, Alamosa, and Durango areas on April 5, 2010. These high wind events caused exceedances of the 24

- hour PM 10 NAAQS at the locations identified in Table 1 of this document on April 5 , 2010. EPA concurs that the flagged exceedances at the Alamosa, Pagosa Springs, Telluride, and Durango locations on these days meet the d efinition 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 outside of the Pagosa Springs, Alamosa, Telluride, and Durango areas and subsequently overwhelmed reasonable controls within Alamosa, Pagosa Springs, Telluride, and Durango. Also, regardless of transport into the area, information pertaining to the controls implemen ted within the affected areas, the spatial 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 d etermined that there is a CCR between the events and the measured exceedances, there would have been NEBF, and the measured exceedances are in excess of normal HFs.

EPA will not take action at this time on the flagged exceedances at the Crested Butte and Mt. Crested Butte locations d ue to CDPHE’s decision not to submit an analysis of HF at the locations and at present the data for these monitors are not expected to influence any anticipated EPA rules

. T he exceedances are nRCP, and meet the definition of a natural event, but the AAQ is dependent upon sufficient evidence to determine HF and CCR. The EPA is interested in the historical fluctuations of the Telluride monitor since Telluride’s 10

- year maintena nce plan is currently under review by EPA. Due to the large number of EE demonstration packages that EPA Region 8 receives only those that occur at monitors which have a potential bearing on regulatory activities are being reviewed at this time.

40 CFR 50.14(a)(1) states:

A State may request EPA to exclude data showing exceedances or violations of the national ambient air quality standard that are directly due to an exceptional event from use in determinations by demonstrating to EPA’s satisfaction that such event caused a specific air pollution concentration at a particular air quality monitoring location. 52

The monitoring values of 115 ug/m 3 at Delta

, of 75 ug/m 3 at Clifton

, of 70 ug/m 3 at Aspen, and 51 ug/m 3

at the Grand Junction Powell monitors on A pril 5 , 2010 are not exceedances or violations of the NAAQS and therefore not able to be considered under the EER . CDPHE included these values in their report to demonstrate the regional nature of the event but did not specifically request their removal.

EPA finds that the weight of evidence is sufficient to concur on the flagging of the data for the NAAQS exceedances of 185 ug/m 3 at Alamosa Adams State College, 349 ug/m 3 at Pagosa Springs, 354 ug/m 3 at Telluride, and 320 ug/m 3 at the Durango monitors on April 5, 2010. These concurrences do not constitute

52 40 CFR 50.14(a)(1).31

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 attainm ent status or classification of the area. Final actions will take place only after EPA completes notice and comment rulemaking on those determinations.