1

EPA Technical Support Document in Review of Colorado Department of 

Public Health and Environment’s Demonstration Package for the 

April 3, 2011, Alamosa and Lamar Exceptional Event

EXCEPTIONAL EVENTS RULE REQUIREMENTS 

The Environmental Protection Agency (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 40 CFR 50.14(c)(3)(iv), the air agency demonstration to justify exclusion of data must provide 

evidence that:

 The event satisfies the criteria set forth in 40 CFR 50.1(j) for the definition of an exceptional 

event; 

 The event affects air quality;

 The event is not reasonably 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

 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; 

 The event is associated with a measured concentration in excess of normal historical fluctuations, 

including background; and

 There would have been no exceedance or violation but for the event.

This review applies the EPA’s “Interim Guidance of 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

Colorado Department of Public Health and Environment (CDPHE) submitted a demonstration (termed a 

Technical Support Document or TSD) dated November 20, 2013 for an exceptional event exceedance of 

the 24-hour PM10 standard that occurred at the monitoring stations in Alamosa and Lamar on 

April 3, 2011. Table 1 summarizes the exceedances that CDPHE would like considered for exceptional 

event concurrence in the Air Quality System (AQS) database.

 

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 PM10 Exceedance Summary of the 150 ug/m3 24-hour NAAQS

Exceedance 

Date

Monitor/Site Name AQS ID 24-hour Avg. 

(ug/m3)

CDPHE 

Request to 

Consider for 

AQS Removal?

April 3, 2011 Alamosa -Municipal Building 08-003-0003 372 Yes

Alamosa -Adams State College 08-003-0001 295 Yes

Lamar Power Plant 08-099-0001 169 Yes

Alamosa, Colorado lies in the broad, flat, high elevation San Luis Valley 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 Cristo 

Mountain ranges. Alamosa is generally surrounded by agricultural lands within the San Luis Valley. To 

the southwest of Alamosa are the deserts of the New Mexico, Utah, and Arizona Four Corners region. 

Lamar sits at 3,645 feet and is in southeastern Colorado on the Arkansas River. South and southwest of 

Lamar are the high, semi-arid plains of New Mexico, north Texas, and the Oklahoma panhandle. The 

areas described are shown in Figure 1.

Figure 1: Map of Desert, Four Corners, and Monitor Locations with the PM10 NAAQS Exceedance

In its exceptional event demonstration package, CDPHE describes the April 3, 2011 event as: 

the consequence of high winds from an intensifying surface low pressure system and vigorous 

cold front. These surface features were associated with a strong upper-level trough that was 

moving across the western United States. The prefrontal surface winds were out of a west to 

southwesterly direction and moved over dry soils in Arizona, northwest New Mexico, southeast 

Utah and southern Colorado producing significant blowing dust. Behind the cold front the winds 
3

were northerly which moved over dry soils in eastern Colorado, consequently also producing 

significant amounts of blowing dust.

2

CDPHE provides a comprehensive description and discussion of this overnight event in Sections 2, 3, 4, 

and 5 of their TSD. As noted in the figure below, the high wind event caused dust to blow and affected air 

quality in this area.

EPA Figure 2 from CDPHE’s TSD3 visually demonstrates wind speed and direction at an elevation of 

roughly 19,000 feet above sea level over northeastern Arizona, southeastern Utah, and northwestern New 

Mexico into south and southeastern Colorado at 11:00 AM mountain standard time on April 3. Figures 1-

39 from CDPHE’s TSD use modeling, meteorology, and monitoring analysis to support the evidence of 

wind direction into Alamosa and Lamar. 

EPA acknowledges that the winds originated from arid regions in Arizona, northwest New Mexico, 

southeast Utah and blew into the San Luis Valley of Colorado into the Alamosa area, and from northwest 

New Mexico and eastern Colorado blowing into the Lamar area. However, EPA analysis of the data 

indicates that significant amounts of dust was not transported across state lines, and that arid natural 

climate and surrounding agricultural lands were most likely a significant source of monitored dust.

Figure 2: Map of Wind Speed and Direction on April 3, 2011 (CDPHE’s TSD Figure 14)

 

2

“TSD for the April 3, 2011, Alamosa & Lamar Exceptional Event,” November 20, 2013, page 11.

3

Ibid., 19. 
4

Not Reasonably Controllable or Preventable

EPA evaluates whether an event was not 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 nRCP if:

 The anthropogenic sources of dust have reasonable controls in place;

 The reasonable controls have been effectively implemented and enforced; and,

 The wind speed was high enough to overwhelm the reasonable controls.4

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

and voluntary controls in the Alamosa and Lamar areas, including information on implementation of State 

Regulations 1, 3, 6, and 9, rule effectiveness, compliance, and public notification activities that occurred 

on the event day. As CDPHE states:

The [CDPHE Air Pollution Control Division] APCD conducted thorough analyses and outreach 

with local governments to confirm that no unusual anthropogenic PM10-producing activities 

occurred in these areas and that despite reasonable control measures in place, high wind 

conditions overwhelmed all reasonably available controls. The following subsections describe in 

detail Best Available Control Measures (BACM), other reasonable control measures, applicable 

federal, state, and local regulations, appropriate land use management, and an in depth analysis of 

potential areas of local soil disturbance for each affected community during the April 3, 2011 

event. This information shall confirm that no unusual anthropogenic actions occurred in the local 

areas of Alamosa and Lamar during this time.5

CDPHE’s TSD provides an analysis of the state and local controls in place to control PM10 emissions. 

Although specifically focusing on Regulations 1, 3 and 6, 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 4- New Wood Stoves and the Use of Certain Woodburning Appliances During High 

Pollution Days;

 Regulation 6- Standards of Performance for New Stationary Sources; and 

 Regulation 9- Open Burning, Prescribed Fire, and Permitting.6

CDPHE provided the documentation listed in Figures 3, 4, 5, and 6 showing that sustained wind speeds 

associated with these events were above 30 mph and gusts were above 40 mph (CDPHE tables 12, 13, 

and 14)

7

. For example, in Alamosa the sustained surface winds of up to 51 mph with gusts up to 70 mph 

 

4

“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.

5

“TSD for the April 3, 2011, Alamosa & Lamar Exceptional Event,” November 20, 2013, page 88.

6

Ibid., 88-90.

7

Ibid., 31-32, 43-44.
5

were measured on April 3, 2011, while Lamar saw sustained surface wind speeds of up to 44 mph and 

gusts up to 59 mph. CDPHE previously established in its exceptional events TSD 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 TSD). The sustained 

winds and gusts in both Alamosa and Lamar exceed this Colorado threshold. However, although wind 

speeds in Farmington and Gallup, NM exceeded the established thresholds and help indicate that the 

winds originated southwest of the monitors, wind speeds in Alamosa and Lamar are higher than upwind 

monitors. High resolution satellite imagery is available at the approximate time of the peak winds in 

Farmington and Gallup, and the large dust plumes in northwest New Mexico and northeast Arizona, 

visible in other, previous high wind dust events, are not visible on April 3, 2011. Given the wind direction 

evidence of Figure 2 above, the upwind desert and arid plains regions appears to be a less significant 

contribution to the exceedance than was local winds overwhelming implemented local controls. EPA 

notes that the high local gust speeds in Alamosa and Lamar would likely be capable of overwhelming 

some local controls. Section 5 of the TSD provided by CDPHE supports this conclusion by describing in 

detail “Best Available Control Measures (BACM), other reasonable control measures, applicable federal, 

state, and local regulations, appropriate land use management, and an in-depth analysis of potential areas 

of local soil disturbance for the affected community.”8

 

8

“TSD for the April 3, 2011, Alamosa & Lamar Exceptional Event,” November 20, 2013, page 88.
6

Figure 3: Wind Speed in Alamosa, CO on April 3, 2011 (CDPHE’s TSD Table 1)
7

Figure 4: Wind Speed Lamar, CO on April 3 2011 (CDPHE’s TSD Table 2)
8

Figure 5: Wind Speed in Farmington, NM on April 3, 2011 (CDPHE’s TSD Table 13)
9

Figure 6: Wind Speed in Gallup, NM on April 3, 2011 (CDPHE’s TSD Table 14)

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

 Statewide PM10 monitoring maps; 

 Surface and upper air wind speed analysis from the National Oceanic and Atmospheric 

Administration (NOAA); 

 North American Regional Reanalysis (NARR) jet stream maximum winds;

 Maps of real-time weather data from the National Center for Atmospheric Research (NCAR); 

 Regional wind and weather by hour, as well as wind direction, through MesoWest; 

 NOAA HYSPLIT modeling of wind trajectories; 

 Naval Advanced Aerosol Prediction System (NAAPS) forecasted dust concentrations;
10

 NOAA Geostationary Satellite Server (GOES) Aerosol Smoke Product (GASP) Optical Depth 

Images;

 Maps establishing the lack of regional precipitation and drought status from U.S. Department of 

Agriculture (USDA), NOAA, and the National Drought Mitigation Center; and 

 Maps 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 monitor in Lamar and south-southwest of the monitors 

in Alamosa. 

ALAMOSA:

Alamosa has the following controls in place:

 Natural Events Action Plan (NEAP)9for high wind events, completed in May 2003, 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 (see 

Colorado Regulation 1);

 City Code of Ordinances: Article VII of Section 21-140(5) addresses dust control at homes;

Article V Sec. 17-87(3) requires pavement of new roads/alleys (see Colorado Regulation 1); and

Article VI Sec. 21-119(3) requires new commercial establishments to install underground 

irrigation (see Colorado Regulation 3). 10

In addition, Alamosa conducts street sweeping, has irrigated and installed vegetative cover on all city 

parks, encourages 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 the 

Mosca-Hooper Conservation District has been working with the Natural Resources Conservation Service 

to implement the Colorado State Forest Service’s program to plant between 2,805 and 7,432 trees per year 

to prevent wind erosion in the area.11 Lastly, Alamosa and nearby counties participate in the United States 

Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) Conservation 

Reserve Program (CRP), but not at the scale that the counties near Lamar do. In 2014, more farmers 

began participating in the program, mostly due to concerns over depletion of the underground aquifer. By 

attempting to preserve the aquifer the farmers obtain a secondary benefit of controlling local dust sources. 

 

9

“TSD for the April 3, 2011, Alamosa & Lamar Exceptional Event,” November 20, 2013, Appendix D.

10 Ibid., 91 and 93. 

11 Ibid., 93-94.
11

Figure 12: Area Acres by County near Alamosa Enrolled in the USDA NRCS CRP Program12

2007 2008 2009 2010 2011 2012 2013 2014

Alamosa 0 0 0 0 0 0 0 1,346

Conejos 32 32 32 32 32 32 70 70

Costilla 0 0 13 13 13 13 13 13

Mineral 0 0 0 0 0 0 0 0

Rio

Grande 1 1 1 0 0 0 0 130

Saguache 0 0 0 0 0 0 0 558

Maps of eight undeveloped parcels of land in town are included that were determined to be reasonably 

controlled or considered natural sources. All eight parcels near the Adams State College monitor are 

covered with vegetation and five of those eight are confirmed to be irrigated. The three remaining sites in 

Figure 13 (Sites B, E, and H) are naturally vegetated and satellite images show minimal soil disturbance.13

Figure 13: Alamosa Site Assessment- Adams State College Monitor (CDPHE’s TSD Figure 63)

A map is also included of eight undeveloped parcels of land in town near the Alamosa Municipal 

Building monitor (Figure 14). The five sites of potential concern are covered with vegetation and two of 

 

12 Analysis for the six counties of the San Luis valley show very low participation in Conservation Reserve or 

Conservation Reserve Enhancement Programs. An January 12, 2012 article by Circle of Blue.org 

(http://www.circleofblue.org/waternews/2012/world/food-vs-water-high-commodity-prices-complicate-aquiferprotection-in-colorados-san-luis-valley/) describes how high agricultural product prices and relatively low costs of 

ground water make ongoing irrigation and agricultural production in the valley more economically viable than the 

reserve program set aside payments made available to date in farm legislation.

13 “TSD for the April 3, 2011, Alamosa & Lamar Exceptional Event,” November 20, 2013, pages 95-101.
12

those five include a maintained gravel rail yard (site J), a maintained gravel parking lot, irrigated field, 

cement basketball court, and a small hard-pack clay BMX track (site L). The three remaining sites in 

Figure 14 (Sites M, N, and K) are naturally vegetated and satellite images show minimal soil 

disturbance.14

The state has shown there are reasonable and preventable controls in place for the Alamosa area.

Figure 14: Alamosa Site Assessment- Alamosa Municipal Building Monitor (CDPHE’s TSD Figure 63)

LAMAR:

Lamar has the following controls in place15:

 A Natural Events Action Plan (NEAP) for High Wind Events completed in 2003, and updated in 

2012, which addresses public education, notification, and health advisory systems as well as 

implements Best Available Control Measures (BACM)16 (see Colorado Regulation 1); 

 A PM10 Maintenance plan for the Lamar Attainment/Maintenance Area effective since Nov. 25, 

2005 with provisions for Prevention of Significant Deterioration (PSD) permitting requiring Best 

Available Control Technology (BACT) 17 (see Colorado Regulation 3);

 State Implementation Plan (SIP) measures requiring owners/operators responsible for 

construction and/or maintenance of existing or new unpaved roadway with traffic of over 200 

vehicles per day to stabilize the road to prevent fugitive dust (see Colorado Regulation 1);

 City of Lamar BACM measures include: planting a wind-break of trees with drip-irrigation to 

control dust from the Lamar Transfer Station, establishing landfill controls such as opacity limits 

 

14

“TSD for the April 3, 2011, Alamosa & Lamar Exceptional Event,” November 20, 2013, pages 102-105.

15 Ibid., 107-111.

16 Ibid., Appendix E; the Natural Events Action Plan was updated in 2012, after the April 3, 2011 event.

17 Ibid., 107; the PM10 Maintenance Plan was updated in 2012, after the April 3, 2011 event.
13

at 20%, fugitive dust at no more than 5.77 tons per year, and immediately shutting down the 

landfill when winds exceed 35 mph (per the “Operations and Closure Plan for the East Lamar 

Landfill” section 3.5.1), among other listed landfill controls.18 Other BACM include installing 

100,000 ft2 of turf sod and irrigation at recreational open space Escondido Park, and fencing off 

and stabilizing lots that formerly contributed to fugitive dust (see Colorado Regulation 1);

 Other measures include: Lamar Charter and Code, Art. XVII, Sec. 16-17-60 requiring off street 

parking lots to be swept and the Prowers County Land Use Plan adopted in 2004 and amended in 

2006 whereby the county has authority over “construction, siting, health, fire, environmental 

codes, and other social concerns with provisions to minimize airborne dust”19 (see Colorado 

Regulation 1);

 Non-enforceable measures include: 

o The Colorado State University CO-OP Extension Office efforts underway to encourage 

no- or low-till practices, outreach and education on soil management programs, and 

drought workshops to protect topsoil. 

o Voluntary and State-Only measures including weekly street sweeping and a city policy 

requirement that new developments have paved streets;

o The Limestone-Graveyard Creeks Watershed Project reduces soil erosion from 60,000 

acres along the Arkansas River, 2,000 of which are near Lamar. Of the 60,000 acres, 99%

now have a conservation plan and are enacting improvements created by each 

farmer/owner with costs of conservation improvements split with the government. 

o The USDA Natural Resources Conservation Service (NRCS) is promoting: a rangeland 

management program, a tree planting program, a drip irrigation purchase program, a 

multi-party drought response effort through the State of Colorado Governor’s office, and 

a program to incentivize erosion mitigation.20

 The USDA NRCS CRP includes conservation provisions in the Farm Bill which encourages 

farmers to contract with USDA to “place erodible cropland and other environmentally-sensitive 

land into long-term conservation practices for 10-15 years”21 in exchange for annual rental 

payments and cost-share assistance from the government. This mitigation strategy further 

supports the existence of reasonable controls in the surrounding agricultural areas, especially due 

to the finding that the dust originated in the counties surrounding Lamar. The following amounts 

of cropland were under contract in surrounding counties. 

 

18 “TSD for the April 3, 2011, Alamosa & Lamar Exceptional Event,” November 20, 2013, page 108.

19 Ibid., 110.

20 Ibid., 119-122.

21 Ibid., 121.
14

Figure 7: Acres by County near Lamar Enrolled in the USDA NRCS CRP Program

2007 2008 2009 2010 2011

Bent 25,586 25,649 25,700 24,056 24,412

Kiowa 214,879 216,307 217,881 187,394 192,222

Baca 263,357 260,040 258,469 161,147 274,281

Crowley 22,032 21,419 21,461 21,069 20,329

Otero 2,624 2,559 2,864 2,706 2,851

Las Animas 21,983 21,869 21,860 17,403 17,616

Cheyenne 143,948 142,075 140,071 94,852 113,753

Lincoln 156,328 155,505 155,425 137,099 145,248

Prowers 173,030 170,909 171,813 140,827 163,354

Total 1,023,767 1,016,333 1,015,544 786,554 954,066

 Vegetation, signage, and/or other dust control measures are in place for undeveloped parcels of 

land in Lamar. Figure 8 below identifies the potential areas of soil disturbance. In Figure 8:

o Site A is owned by the Ranchers Supply Co. Inc. and is a fenced 90% gravel lot for longterm oversize vehicle parking. It has a 10 mph policy, is watered as-needed, and meets 

Air Quality Control Commission (AQCC) Regulation 1 requirements (Section 

III.D.1(a).22

o Site B is owned by Ranco Construction Trailer Manufacturing and consists of pavement, 

gravel, and naturally vegetated areas with restricted access.

23

o Site C is owned by Prowers County and rented to the Colorado State Patrol. It is a fenced, 

restricted access, gravel lot with a 5 mph limit, and drainage and erosion control 

measures per AQCC Regulation 1 requirements (Section III.D.1(a)).

24

o Site D is C.F. Mailer Composites Inc. and is a paved parking lot and surrounding natural 

vegetation with a short, maintained gravel road to a loading dock used once a day.25

o Site F was mined by All-Rite Paving and Redi-Mix Inc. and was a concrete batch plant 

permitted by CDPHE. Baghouse collection efficiency was 99%, there was a 20% opacity 

limit, and water sprays and magnesium chloride were used on storage piles and roads as 

needed. There was a 10 mph speed limit, transfer of materials occurred in enclosed areas, 

and the lot was fenced.26 Partnering with the Division of Wildlife, the City of Lamar took 

 

22, 23, 24, 25, 26 “The APCD considers restricted vehicle speeds, maintained gravel, natural vegetation, restricted access, 

pavement, compaction, revegetation, watering, and extraction limitation to be the appropriate available and practical 

method that is technologically feasible and economically reasonable in order to minimize fugitive particulate 

emissions for these sites. “TSD for the April 3, 2011, Alamosa & Lamar Exceptional Event,” November 20, 2013, 

pages 113 and 114.
15

over the lot in 2013 and has been reseeding it to create a fishing and wildlife park free of 

motorized vehicles. (It appears that All-Rite Paving and Redi-Mix Inc. moved to Site E, 

see below); 

Figure 8: Lamar Site Assessment (CDPHE’s TSD Figure 76)

 Vegetation and dust control measures are also in place for undeveloped parcels of land North of 

Lamar. Figure 9 below identifies the potential areas of soil disturbance. The state has shown there 

are reasonable and preventable controls. In Figure 9:

o Site E is also owned by All-Rite Paving and Redi-Mix Inc. and is a concrete batch plant 

permitted by CDPHE (#12PR1396). The facility is considered APEN exempt and emits 

less than 1 ton per year of PM10.”

27 As with Site F above, baghouse collection efficiency 

is 99%, there is a 20% opacity limit, and water sprays and magnesium chloride are used 

on storage piles and roads as needed. There is a 10 mph speed limit, transfer of materials 

occurs in enclosed areas, and the lot is fenced.28

o Site G is mined by Carder Inc. for sand and gravel and emits no more than 15 tons per 

year under CDPHE permit #99PR0180F. It is a wet mining operation to prevent fugitive 

dust, and uses the following preventative measures: watering as needed, re-vegetation 

within one year of disturbance, compacting piles, 10 mph speed limit, and temporary 

roads are graveled and watered as needed29, 30;

 

27, 28, 29, 30 “The APCD considers restricted vehicle speeds, maintained gravel, natural vegetation, restricted access, 

pavement, compaction, revegetation, watering, and extraction limitation to be the appropriate available and practical 

method that is technologically feasible and economically reasonable in order to minimize fugitive particulate 

emissions for these sites. “TSD for the April 3, 2011, Alamosa & Lamar Exceptional Event,” November 20, 2013, 

pages 114 and 115.
16

Figure 9: Lamar Site Assessment (CDPHE’s Figure 78 in the CDPHE’s TSD)

 Vegetation and dust control measures are also in place for undeveloped parcels of land northwest 

of Lamar. Figure 10 below identifies the potential areas of soil disturbance. The state has shown 

there are reasonable and preventable controls. In Figure 10:

o Site H is owned by Heath & Son & Turpin Trucking and HVH Transportation Inc., a 

large truck repair and freight service trucking company, respectively. It is a wellmaintained gravel lot.31

o Site I is a fenced, watered-as-needed gravel lot shared by Prowers Area Transit and the 

defunct Cowboy Corral Storage, feed supply, and grain storage companies. The transit 

company is on a concrete slab connecting to an asphalt road.32 Site J is owned by Heath 

& Son & Turpin Trucking and is a well-maintained gravel lot used for truck storage.33

o Site K is the Lamar Water Department and Lamar-Prowers County Volunteer Fire 

Department and is a restricted site of graded and watered gravel on an as-needed basis.34

o Site L is the power plant that hosts the monitor and is a restricted lot owned by Lamar 

Light and Power. It has been a gas fired boiler, natural gas power plant, and coal-fired 

boiler until being shut down in November 2011. It was permitted under CDPHE permit

#05PR0027 with the following dust control measures: high efficiency baghouses, water 

 

31, 32, 33, 34 “The APCD considers restricted vehicle speeds, maintained gravel, natural vegetation, restricted access, 

pavement, compaction, revegetation, watering, and extraction limitation to be the appropriate available and practical 

method that is technologically feasible and economically reasonable in order to minimize fugitive particulate 

emissions for these sites. “TSD for the April 3, 2011, Alamosa & Lamar Exceptional Event,” November 20, 2013, 

pages 115, 116, and 117.
17

wash-down systems for all surfaces to prevent dust re-entrainment, all roads were paved

and inspected daily and cleaned as needed while under the 1 ton per year APEN 

exemption, transfer locations were enclosed, and the emergency coal stockpile controlled 

through a water-dust suppression system.35

o Site M is the Burlington Northern Santa Fe railroad and is covered in gravel 50 feet on

either side of the tracks, surrounded by natural vegetation with xeriscape36; and

Figure 10: Lamar Site Assessment (CDPHE’s TSD Figure 79)

 Vegetation and dust control measures are also in place for undeveloped parcels of land west of 

Lamar. Figure 11 below identifies the potential areas of soil disturbance. Site N is owned and 

mined by Carder Inc for sand and gravel under CDPHE permit #99PR0179F. It emits 8 tons per 

year of PM10 and is a wet mining operation employing the following dust control measures:, revegetation within one year of disturbance, compacting piles, 10 mph speed limit, and temporary 

roads are graveled and watered as needed.37, 38

The state has shown there are reasonable and preventable controls in place for the Lamar area.

 

35, 36, 37, 38 “The APCD considers restricted vehicle speeds, maintained gravel, natural vegetation, restricted access, 

pavement, compaction, revegetation, watering, and extraction limitation to be the appropriate available and practical 

method that is technologically feasible and economically reasonable in order to minimize fugitive particulate 

emissions for these sites. “TSD for the April 3, 2011, Alamosa & Lamar Exceptional Event,” November 20, 2013, 

pages 118, 119, and Appendix D.
18

Figure 11: Lamar Site Assessment (CDPHE’s TSD Figure 84)

According to CDPHE’s TSD: 

The APCD conducted thorough analyses and outreach with local governments to confirm that no 

unusual anthropogenic PM10-producing activities occurred in these areas and that despite 

reasonable control measures in place, high wind conditions overwhelmed all reasonably available 

controls.

39

Sections 2 and 5 of CDPHE’s TSD assert that the monitors in Alamosa and Lamar were affected by PM10

transport from outside the immediate area of the monitor, with the main source areas from arid regions in 

Arizona, northwest New Mexico, southeast Utah and the San Luis Valley of Colorado into the Alamosa 

area, and from northwest New Mexico and eastern Colorado into the Lamar area. EPA analysis indicates 

that the wind was stronger locally, and that dust from surrounding areas within Colorado were the most

likely sources of the exceedances, especially in Lamar. In addition to transport, the spatial extent of 

elevated PM10 concentrations throughout southern Colorado and the wind speeds associated with the 

event contribute to EPA’s evaluation of whether this event is nRCP in Alamosa and Lamar. The EPA 

concludes that wind speeds on April 3, 2011 did exceed the blowing dust thresholds of 30 mph or greater 

and gusts of 40 mph or greater at which the CDPHE expects stable surfaces (i.e., controlled 

anthropogenic and undisturbed natural surfaces) to be overwhelmed, given that wind speeds were as high 

as 51 mph with wind gusts up to 70 mph. Therefore, the EPA concludes that this event was not 

reasonably controllable pursuant to the Treatment of Data Influenced by Exceptional Events rule. Table 2 

summarizes the EPA’s evaluation of CDPHE’s nRCP EE demonstration. 

 

39 “TSD for the April 3, 2011, Alamosa & Lamar Exceptional Event,” November 20, 2013, page 88.
19

Table 2: EPA’s Analysis of CDPHE’s TSD of nRCP

Exceedance 

Date

Location Reasonable 

Controls TSD

Citation

Wind Speed 

TSD Citation

Sufficient 

Quality of 

Evidence?

EPA 

Criterion 

Met?

April 3, 2011 Alamosa 

Adams State 

College

Section 5: p. 88-101 Section 2: p.11-

62, esp. p.31

Yes Yes

Alamosa 

Municipal 

Building 

Section 5: p. 88-94, 

102-106

Section 2: p.11-

62, esp. p.31

Yes Yes

Lamar Power 

Plant

Section 5: p. 107-122 Section 2: p.11-

62, esp. p.32

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, CDPHE provided a statistical analysis of the 2011 24-hour 

average data, 5-year time series of 24-hour averages for the years of 2006-2011, and monthly data 

showing that all readings greater than the NAAQS threshold of 150 g/m3 might be considered statistical 

outliers. CDPHE explains that for the concentration measured on April 3, 2011: 

Of those samples in excess of 150 g/m3all three are the maximum value for any sample taken in 

April. The samples at Alamosa ASC, Alamosa Muni and Lamar Power on April 3, 2011, 

exceeded the 99th% value of any evaluation criteria.40

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

percentile ranks when dust impacted data is excluded.41 CDPHE states that the percentile rank for these 

areas is 99.4% and above for the three monitors in question. See Figure 15 below.

 

40 “TSD for the April 3, 2011, Alamosa & Lamar Exceptional Event,” November 20, 2013, page 65.

41 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.
20

Figure 15: Percentile Analysis (CDPHE’s TSD Table 16)

42

Since at least 2005 in these areas, values exceeding the NAAQS are only found during high wind dust 

events, including April 3, 2011. This information indicates that values at the level seen on April 3, 2011

are extremely rare in the absence of high wind dust exceptional event impacts, and that it is unlikely that 

any sources of PM10 were involved in the April 3, 2011 exceedances other than wind-blown dust. 

Therefore, the EPA concludes that this event was in excess of historical fluctuations pursuant to the 

Treatment of Data Influenced by Exceptional Events rule. Table 3 summarizes the EPA’s evaluation of 

CDPHE’s HF EE demonstration. 

Table 3: EPA’s Analysis of CDPHE’s TSD of HF

Exceedance 

Date

Exceedance 

Location

Historical Fluctuations TSD

Citation

Sufficient 

Quality of 

Evidence?

EPA Criterion 

Met?

April 3, 2011 Alamosa Adams 

State College 

Section 3: p.63-68, 76-78 Yes Yes

Alamosa Municipal 

Building 

Section 3: p.63-65, 68-71, 76-

78

Yes Yes

Lamar Power Plant Section 3: p.63-65, 71-78 Yes Yes

Clear Causal Relationship 

EPA considers a variety of evidence when evaluating whether there is a Clear 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, 

 

42 “TSD for the April 3, 2011, Alamosa & Lamar Exceptional Event,” November 20, 2013, page 64.
21

pollutant species-specific information supporting a CCR between the event and the measured 

concentration.43

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

 Statewide PM10 monitoring maps; 

 Surface and upper air wind speed analysis from NOAA; 

 NARR jet stream maximum winds;

 Maps of real-time weather data from NCAR; 

 Regional wind and weather by hour, as well as wind direction, through MesoWest; 

 NOAA HYSPLIT modeling of wind trajectories; 

 NAAPS forecasted dust concentrations;

 NOAA GOES GASP Optical Depth Images;

 Maps establishing the lack of regional precipitation and drought status from USDA, NOAA, and 

the National Drought Mitigation Center; and 

 Maps of elevated friction velocities in the region from the NOAA NCEP North American Model. 

These analyses demonstrate the existence of a high wind blowing dust event originating far southwest of 

the monitors in question. 

NOAA’s Smoke Text Product Satellite Services Division described the April 3, 2011 event as follows, 

A few areas of blowing dust...could be seen moving southward through parts of far eastern 

Colorado and into western Kansas where high winds have picked up after the passage of a cold 

front this evening.

44

CDPHE generally summarizes that:

The exceedances were the consequence of high winds from an intensifying surface low

pressure system and vigorous cold front. These surface features were associated with a strong 

upper-level trough that was moving across the western United States. The prefrontal surface 

winds were out of a west to southwesterly direction and moved over dry soils in Arizona, 

northwest New Mexico, southeast Utah and southern Colorado producing significant blowing 

dust. Behind the cold front the winds were northerly which moved over dry soils in eastern 

Colorado, consequently also producing significant amounts of blowing dust.45

CDPHE further states that “The statistical and meteorological data clearly shows that but for this high 

wind blowing dust event, Alamosa and Lamar would not have exceeded the 24-hour NAAQS on April 3, 

2011”.46 EPA acknowledges the wind direction originating south and southwest of the monitors, but 

considers local sources of dust to be responsible for the exceedances, especially in Lamar. Therefore, the 

EPA concludes that there was a clear causal relationship for this event pursuant to the Treatment of Data 

 

43 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, pages 21-22. 

44 “TSD for the April 3, 2011, Alamosa & Lamar Exceptional Event,” November 20, 2013, page 58.

45 Ibid., 11.

46 Ibid., 123.
22

Influenced by Exceptional Events rule. Table 4 summarizes the EPA’s evaluation of CDPHE’s CCR EE 

demonstration. 

Table 4: EPA’s Analysis of CDPHE’s TSD of CCR47

Clear Causal Relationship TSD Citation Sufficient Quality of Evidence? EPA Criterion 

Met?

Section 2: p.11-62, Figures 1-39 Yes Yes

Section 2: p.11, 31-44, Tables 1-14 Yes Yes

Section 2: p.58 Yes Yes

Section 4: p.79-87 Yes Yes

Affects Air Quality (AAQ)

As stated in EPA’s 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. 

The information presented in the HF and CCR demonstrations on the preceding three pages of this 

(EPA’s) TSD are cited in Table 5. Additionally, CDPHE states that:

This event produced the maximum value for any sample taken in April and exceeded the 99th% 

value of any evaluation criteria... This is evidence that the event was associated with a measured 

concentration in excess of normal historical fluctuations including background.48

Therefore, the EPA concludes that this event affected air quality pursuant to the Treatment of Data 

Influenced by Exceptional Events rule. Table 5 summarizes the EPA’s evaluation of CDPHE’s AAQ EE 

demonstration.

 

47 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.

48 “TSD for the April 3, 2011, Alamosa & Lamar Exceptional Event,” November 20, 2013, page 123.
23

Table 5: EPA’s Analysis of CDPHE’s TSD of AAQ

HF and 

CCR

Exceedance Location Affects Air Quality TSD 

Citation 

Sufficient 

Quality of 

Evidence

EPA 

Criterion 

Met?

HF Alamosa Adams State 

College 

Section 3: p.63-68, 76-78 Yes Yes

Alamosa Municipal 

Building 

Section 3: p.63-65, 68-71, 76-

78

Yes Yes

Lamar Power Plant Section 3: p.63-65, 71-78 Yes Yes

CCR All Three Monitoring 

Sites

Section 2: p.11-62, Figures 1-

39

Yes Yes

Section 2: p.11, 31-44, Tables 

1-14

Yes Yes

Section 2: p.58 Yes Yes

Section 4: p.79-87 Yes Yes

Natural Event

As stated in EPA’s 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 states 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 

originating in northeastern Arizona, northwestern New Mexico, and southeastern Utah and 

spreading into southeastern Colorado. But for the dust storm on April 3, 2011, this exceedance 

would not have occurred. . . . GASP satellite imagery shows that the desert regions of northeast 

Arizona and northwest New Mexico along with the arid plains of eastern Colorado were source 

regions for the blowing dust on April 3. This is consistent with the climatology for many dust 

storms in Colorado as described in the Grand Junction, Colorado, Blowing Dust Climatology 

report contained in Appendix A and the Lamar, Colorado, Blowing Dust Climatology in 

Appendix B, both found at the end of this document. The observations of winds above blowing 

dust thresholds and restricted visibilities in the areas of concern demonstrate that this is a natural 

event that cannot be reasonably controlled or prevented. 49

EPA acknowledges that the winds originate from arid regions in Arizona, northwest New Mexico, 

southeast Utah and blew into the San Luis Valley of Colorado into the Alamosa area, and from northwest 

New Mexico and eastern Colorado blowing into the Lamar area. However, EPA analysis of the data 

indicates that significant amounts of dust do not appear to have been transported across state lines, and 

that in fact the arid natural climate and surrounding agricultural lands within Colorado were the more 

 

49 “TSD for the April 3, 2011, Alamosa & Lamar Exceptional Event,” November 20, 2013, page 124.
24

probable source of monitored dust. Regardless, sufficient local controls were in place and were likely

overwhelmed by the wind speed. CDPHE has sufficiently demonstrated the CCR and nRCP requirements 

for the April 3, 2011 event. Therefore, the EPA concludes that this was a natural event pursuant to the 

Treatment of Data Influenced by Exceptional Events rule. Table 6 summarizes the EPA’s evaluation of 

CDPHE’s Natural Event EE demonstration.

Table 6: EPA’s Analysis of CDPHE’s TSD of Natural Event

nRCP or CCR Exceedance 

Location

Natural Event TSD

Citation 

Sufficient Quality 

of Evidence?

EPA 

Criterion 

Met?

nRCPAnthropogenicAlamosa Adams 

State College 

Section 5: p. 88-101 Yes Yes

Alamosa 

Municipal 

Building 

Section 5: p. 88-94, 102-

106

Yes Yes

Lamar Power 

Plant

Section 5: p. 107-122 Yes Yes

nRCP-Wind Speed Alamosa Adams 

State College 

Section 2: p.11-62, esp. 

p.31

Yes Yes

Alamosa 

Municipal 

Building 

Section 2: p.11-62, esp. 

p.31

Yes Yes

Lamar Power 

Plant

Section 2: p.11-62, esp. 

p.32

Yes Yes

CCR All Three 

Monitoring Sites

Section 2: p.11-62, 

Figures 1-39

Yes Yes

Section 2: p.11, 31-44, 

Tables 1-14

Yes Yes

Section 2: p.58 Yes Yes

Section 4: p.79-87 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 TSD that show both the 

nRCP and CCR requirements have been met and states that: 

This event produced the maximum value for any sample taken in April and exceeded the 99th% 

value of any evaluation criteria. The statistical and meteorological data clearly shows that but for 
25

this high wind blowing dust event, Alamosa and Lamar would not have exceeded the 24-hour 

NAAQS on April 3, 2011. Since at least 2005, there has not been an exceedance that was not 

associated with high winds carrying PM10 dust from distant sources in these areas. This is 

evidence that the event was associated with a measured concentration in excess of normal 

historical fluctuations including background.

50

Therefore, the EPA concludes that there would have been no violation but for the event pursuant to the 

Treatment of Data Influenced by Exceptional Events rule. While not explicitly stated in the TSD, EPA 

notes that PM10 concentrations before the periods of high winds on the event days were below the 24-hour 

PM10 NAAQS, providing further support for CDPHE’s conclusion. Table 7 summarizes the EPA’s 

evaluation of CDPHE’s NEBF EE demonstration. 

Table 7: EPA’s Analysis of CDPHE’s TSD of NEBF

Exceedance Date No Exceedance But For the 

Event TSD Citation 

Sufficient Quality of 

Evidence?

EPA Criterion 

Met?

April 3, 2011 Section 6: p.124-125 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. CDPHE received no 

external comments during the 30 day comment period, but minor corrections were made to the report 

based on internal staff review. Table 8 outlines EPA’s evaluation of these requirements. 

Table 8: EPA’s Analysis of Schedules and Procedural Criteria

Reference Schedules and 

Procedural 

Criteria TSD

Citation

EPA 

Criterion 

Met?

Did the State provide prompt public 

notification of the event?

40 CFR 50.14(c)(1)(i) Section 1: p.9 Yes

Were flags and initial description placed 

on the data by July 1st 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) December 24, 2013 Yes

Was the public comment process 

followed and documented?

40 CFR 50.14(c)(3)(v) Section 1: p.10 Yes

 

50 “TSD for the April 3, 2011, Alamosa & Lamar Exceptional Event,” November 20, 2013, page 123.
26

CONCLUSION

EPA has reviewed the TSD provided by CDPHE to support claims that dust emissions generated by high 

winds resulted in PM10 transport from arid regions in Arizona, northwest New Mexico, southeast Utah 

and the San Luis Valley of Colorado into the Alamosa area, and from northwest New Mexico and eastern 

Colorado into the Lamar area on April 3, 2011. EPA acknowledges that the winds originated from arid 

regions in Arizona, northwest New Mexico, southeast Utah and blew into the San Luis Valley of 

Colorado into the Alamosa area, and from northwest New Mexico and eastern Colorado blowing into the

Lamar area. However, EPA analysis of the data indicates that significant amounts of dust do not appear to 

have been transported across state lines, and that in fact the arid natural climate and surrounding 

agricultural lands within Colorado were the more probable source of monitored dust, and that sufficient 

local controls in place were likely overwhelmed by the wind speed. This high wind event caused 

exceedances of the 24-hour PM10 NAAQS at the locations identified in Table 1 of this document on 

April 3, 2011, in Alamosa and Lamar. EPA concurs that the flagged exceedances at the Alamosa and 

Lamar monitors on this day meet the definition of an exceptional event: the exceedances affected air 

quality, were nRCP, and met the definition of a natural event. Specifically, EPA has determined that the 

event was nRCP due to high wind conditions that entrained PM10 from sources in the vicinity of the 

Alamosa and Lamar areas and overwhelmed reasonable controls within Alamosa and Lamar. Also, 

regardless of transport into the areas, information pertaining to the controls implemented within the 

affected areas, the spatial extent of elevated PM10 concentrations measured in the areas, 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 between the events and the measured 

exceedances, there would have been NEBF, and the measured exceedances are in excess of normal HFs. 

EPA finds that the weight of evidence is sufficient to concur on the flagged data for the NAAQS 

exceedance of 298 ug/m3at the Alamosa Adams State College monitor, 392 ug/m3at the Alamosa 

Municipal Building monitor, and 169 ug/m3 at the Lamar Power Plant monitor on April 3, 2011. 

This concurrence does 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 classification of the area. Final actions will take place only after EPA completes 

notice and comment rulemaking on those determinations.