1

EPA Technical Support Document in Review of Colorado Department of 

Public Health and Environment’s Demonstration Package for the 

March 18 and April 2, 2012 Lamar and Alamosa Exceptional Events

EXCEPTIONAL EVENT 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 

the 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. 

 

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 OF CONTENTS

Exceptional Event Rule Requirements ........................................................................................... 1

Summary......................................................................................................................................... 3

Overview ..................................................................................................................................... 3

March 18, 2012:...................................................................................................................... 4

April 2, 2012:.......................................................................................................................... 7

Not Reasonably Controllable or Preventable................................................................................ 10

Anthropogenic sources of dust have reasonable controls in place:........................................... 11

Lamar Specific Controls....................................................................................................... 11

Alamosa Specific Controls ................................................................................................... 14

Reasonable controls have been effectively implemented and enforced:................................... 15

Alamosa Disturbed Area Analysis........................................................................................ 19

Lamar Disturbed Area Analysis............................................................................................ 21

Wind speed was high enough to overwhelm the reasonable controls .................................. 30

Historical Fluctuations.................................................................................................................. 35

Clear Causal Relationship............................................................................................................. 37

March 18, 2012 ......................................................................................................................... 37

April 2, 2012 ............................................................................................................................. 38

Affects Air Quality (AAQ)........................................................................................................... 39

Natural Event ................................................................................................................................ 40

No Exceedance or Violation But For the Event............................................................................ 41

Schedule and Procedural Requirements........................................................................................ 42

Conclusion .................................................................................................................................... 43
3

SUMMARY

Overview

On March 10, 2015 the Colorado Department of Public Health and Environment (CDPHE)

submitted a demonstration (termed a Technical Support Document or TSD) for exceptional event

exceedances of the 24-hour PM10 standard that occurred at the monitoring stations in Lamar and 

Alamosa, Colorado, on March 18 and April 2, 2012. Table 1 summarizes the exceedance that 

CDPHE would like considered for exceptional event concurrence in the Air Quality System 

(AQS) database.

Table 1: EPA PM10 Exceedance Summary of the 150 ug/m3 24-hour NAAQS

Exceedance Date Monitor/Site Name AQS ID 24-hour Avg. 

(g/m3)

CDPHE Request 

to Consider for 

AQS Removal?

March 18, 2012 Alamosa-Adams 

State College

08-003-0001 324 Yes

March 18, 2012 Alamosa Municipal 

Building

08-003-0003 237 Yes

March 18, 2012 Lamar Power Plant 08-099-0001 220 Yes

March 18, 2012 Lamar Municipal 

Building

08-099-0002 242 Yes

April 2, 2012 Alamosa-Adams 

State College

08-003-0001 389 Yes

April 2, 2012 Lamar Municipal 

Building

08-99-0002 163 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.
4

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

Exceedance

March 18, 2012: 

On March 18, 2012 a powerful late winter storm system crossed the Rocky Mountain states. 

Strong southerly winds in advance of the storm’s cold front induced blowing dust in southern 

Colorado, as well as in central and southern New Mexico. An upper level trough extended south 

from the low, and the trough and associated cold fronts passed through eastern Colorado in the 

afternoon. Of March 18, 2012, CDPHE said:

The exceedances in Alamosa and Lamar were the result of intense surface winds in 

advance of an approaching cold front. These surface features were associated with a 

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

winds were predominantly out of a south to southwesterly direction and moved over 

erodible dry soils in New Mexico and southern Colorado producing significant blowing 

dust. This storm system transported PM10 dust into the southern and southeastern portions 

of Colorado.

2

 

2

“TSD for the March 18, 2012 Alamosa and Lamar Exceptional Events,” March 10, 2015, page 

7-8.
5

EPA Figure 2 (March 18, 2012 at 5:00 pm MST) from CDPHE’s demonstration is described 

with: 

Significant surface features during this period of time included a cold front that swept 

across Colorado. This front was associated with a strong area of surface low pressure that 

was slowly moving northward through northwestern Wyoming.

In addition, the upper level trough with this storm system aided in producing very strong 

winds at the surface.3

Figure 2: Surface Level Analysis at 5:00 pm MST on March 18, 2012 (CDPHE’s TSD Figure 6)

4

Figure 3 (Figure 9 from the CDPHE demonstration) shows the 700 mb level analysis for March 

18, 2012 at 5:00 pm MST. An upper level trough extends from two upper level lows in the 

northeast Pacific and western Canada southeast through the western U. S. and into northwestern 

Mexico.

 

3

Ibid., 11.

4

Ibid.
6

Figure 3: 700 mb Level Analysis at 5:00 pm MST on March 18, 2012 (CDPHE’s TSD Figure 9)

5

Figure 4 (Figure 26 from the CDPHE demonstration) shows National Oceanic and Atmospheric 

Administration (NOAA) reanalysis of 700 mb (approximately 3 km elevation) wind speeds at 

11:00 am on March 18, 2012. Only wind speeds greater than 30 knots (34.5 mph) are shown. 

Blue areas have winds of 30 to 45 knots (34.5 to 52 mph), green areas have winds 45 to 53 knots 

(52 to 61 mph), and yellow and orange areas have winds of 53 to 70 knots (61 to 81 mph). 

Alamosa is shown at the edge of the 30 knot zone, while winds in the area of Lamar are on the 

order of 60 knots (69 mph). EPA has overlayed PM10 data from AQS for New Mexico, Alamosa 

and Lamar, showing widespread PM10 dust impacts coinciding with the high wind region.

 

5

Ibid., 14.
7

Figure 4: 700 mb Modeled Wind Speed at 11:00 am MST on March 18, 2012 (CDPHE’s TSD 

Figure 26);

6 PM10 Data Added by EPA

Figures 4-13 and 23-38 from CDPHE’s demonstration (not all included here) use meteorology, 

radar imagery and monitoring analysis to support the evidence of wind direction and reach of the 

dust storm into Lamar and Alamosa.

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

and 5 of the demonstration. 

April 2, 2012: 

On April 2, 2012 a powerful spring storm system crossed the Rocky Mountain states. The PM10

monitors in both Alamosa and Lamar, Colorado were impacted by dust transported by strong 

surface winds in the wake of the passing cold front. In Alamosa, surface winds were from the 

 

6

Ibid., 45.
8

south and southeast, while in Lamar, post frontal winds were from the north. CDPHE described 

the April 2, 2012 event as:

The exceedance in Alamosa was the result of intense surface winds produced by a very 

tight pressure gradient in the wake of a passing cold front. The surface winds were 

predominantly out of an east to southeast direction and were likely enhanced by some of 

the mountain passes found in the Sangre De Cristo range that bounds the eastern side of 

the San Luis Valley. These winds moved over dry soils which resulted in significant 

blowing dust in Alamosa. Lamar was likewise impacted by post-frontal winds, but from a 

northerly direction. Lamar also received a brief period of strong outflow winds from 

evening thunderstorms located to the east in southwest Kansas. Blowing dust produced 

by those downburst winds also likely contributed to the PM10 exceedance recorded in 

Lamar. All of the surface features which aided in producing blowing dust in Alamosa and 

Lamar were associated with a strong upper-level trough that was moving across the 

western United States. This storm system transported PM10 dust into the southern and 

southeastern portions of Colorado.7

EPA Figure 5 (April 2, 2012 at 11:00 am MST, Figure 7 from CDPHE’s demonstration) is 

described with: 

Significant surface features at 5 AM MST . . . included an increasing amount of 

“bunching” of isobars in northeast Colorado and western Nebraska, indicating that a 

strong pressure gradient was developing. Wind speed is directly proportional to the 

pressure gradient, so a higher pressure gradient will produce stronger winds. . . . This 

tightening of the isobars spread southward as a cold front continued to move away from 

southeast Colorado. By 11 AM MST (18Z, Figure 7) the pressure gradient had become 

particularly strong between the plains of eastern Colorado and the San Luis Valley of 

south-central Colorado. This was in response to a building ridge of high pressure in 

eastern Colorado interacting with an intense low pressure trough extending from northcentral New Mexico northward into south-central Colorado.8

 

7

“TSD for the April 2, 2012 Alamosa and Lamar Exceptional Event,” March 10, 2015, page 1-2.

8

Ibid., 13.
9

Figure 5: Surface Level Analysis at 11:00 am MST on April 2, 2012 (CDPHE’s TSD Figure 7)

9

Figure 6 (Figure 4 from the CDPHE demonstration) shows the 700 mb level analysis for April 2, 

2012 at 5:00 am MST. An upper level trough extends from two upper level lows in northwestern 

and central Canada south through the U. S. Rocky Mountain states and into northwestern 

Mexico.

 

9

Ibid.
10

Figure 6: 700 mb Level Analysis at 5:00 am MST on April 2, 2012 (CDPHE’s TSD Figure 4)

10

Figures 4-7 and 8-18 from CDPHE’s demonstration (not all included here) use meteorology, 

radar imagery and monitoring analysis to support the evidence of wind direction and reach of the 

dust storm into Lamar and Alamosa. 

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

and 5 of the demonstration. 

NOT REASONABLY CONTROLLABLE OR PREVENTABLE

The 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:

 

10 Ibid., 12.
11

 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.11

The following nRCP analysis is broken down into three subsections that correspond to the three 

bullets above. 

Anthropogenic sources of dust have reasonable controls in place:

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

required and voluntary controls in the Lamar area, 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 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. ... This information shall confirm that no unusual 

anthropogenic actions occurred in the local areas of Lamar during this time.12

CDPHE’s demonstration 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.13

Lamar Specific Controls

Lamar has the following controls in place: 14

 

11 “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.

12 “TSD for the April 2, 2012 Lamar Exceptional Events,” March 10, 2015, page 53.

13 Ibid., 53-55.

14 Ibid., 67-71.
12

 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)15; 

 A PM10 Maintenance plan for the Lamar Attainment/Maintenance Area effective since 

November 25, 2005 with provisions for Prevention of Significant Deterioration (PSD) 

permitting requiring Best Available Control Technology (BACT)16;

 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 dripirrigation to control dust from the Lamar Transfer Station, establishing landfill controls 

such as opacity limits 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.17 Other BACM include installing 100,000 ft2of turf sod and irrigation at 

recreational open space Escondido Park, and fencing off and stabilizing lots that formerly 

contributed to fugitive dust;

 Other measures include: Art. XVII, Sec. 16-17-60 requiring off street parking lots to be 

swept. The Prowers County Land Use plan adopted in 2004 and amended in 2006-

through it the county has authority over “construction, siting, health, fire, environmental 

codes, and other social concerns with provisions to minimize airborne dust”18; 

 Non-enforceable measures include: 

o The Colorado State University CO-OP Extension Office efforts underway in the 

Lamar area to encourage no- or low-till practices, conduct outreach and education 

on soil management programs, and hold drought workshops to protect topsoil; 

o Voluntary and state-only measures including weekly street sweeping and a city 

policy requiring that new developments have paved streets;

o The Limestone-Graveyard Creeks Watershed Project, which reduces soil erosion 

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

of the 60,000 acres now have a conservation plan and are enacting improvements 

created by each farmer/owner with costs of conservation improvements split with 

the government; and

 

15 Ibid., 67 and at: 

http://www.colorado.gov/airquality/tech_doc_repository.aspx?action=open&file=LamarNaturalE

ventsActionPlan 2012.pdf.

16 “TSD for the April 2, 2012 Lamar Exceptional Events,” March 10, 2015, page 67-68.

17 Ibid., 69.

18 Ibid., 70.
13

o The 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.19

 The United States Department of Agriculture (USDA) NRCS Conservation Reserve 

Program (CRP) includes conservation provisions in the Farm Bill which encourages 

farmers to contract with USDA to “place erodible cropland and other environmentallysensitive land into long-term conservation practices for 10-15 years”20 in exchange for 

annual rental payments and cost-share assistance from the government. This mitigation 

strategy is a convincing argument for the existence of reasonable controls in place in the 

agricultural areas surrounding Lamar. Table 2 shows amounts of cropland under contract 

in surrounding counties in the years preceding the events. 

Table 2: Acres by County near Lamar Enrolled in the USDA NRCS CRP Program21

COUNTY 2008 2009 2010 2011 2012 2013 2014

Bent 25,649 25,700 24,056 24,412 33,886 23,566 33,567

Kiowa 216,307 217,881 187,394 192,222 177,100 181,169 177,788

Baca 260,040 258,469 161,147 274,281 277,508 264,071 267,732

Crowley 21,419 21,461 21,069 20,329 21,917 18,490 21,260

Otero 2,559 2,864 2,706 2,851 2,054 2,635 2,014

Las 

Animas 21,869 21,860 17,403 17,616 18,925 18,887 19,839

Cheyenne 142,075 140,071 94,852 113,753 122,862 99,074 122,218

Lincoln 155,505 155,425 137,099 145,248 118,948 116,289 114,581

Prowers 170,909 171,813 140,827 163,354 154,882 151,731 155,065

Total 1,016,333 1,015,544 786,554 954,066 928,082 875,912 914,064

 

19 Ibid., 90-91.

20 Ibid., 90.

21 Data for the USDA NRCS CRP program were provided as supplementary information per 

EPA request on April 17, 2014 by Ray Mohr of CDPHE. Data for 2014 was added by the EPA.
14

Alamosa Specific Controls

The following controls are in place in and around Alamosa: 22

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

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

implements BACM;

23

 Provisions for PSD permitting requiring BACT;

24

 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 Alamosa control measures include: requirements that all new streets and alleys be 

paved; requirements for underground automatic irrigation for landscaping at new large 

commercial and retail establishments;25

 Alamosa County control measures include: dust from feed lots, animal waste treatment or 

animal waste collection must be confined to the agricultural property; proposed oil and 

gas well installations must pave or otherwise abate dust from interior transportation 

networks; roads, driveways, parking lots and loading/unloading areas within 500 feet of 

any lot line must be graded and paved; off-street parking or vehicle use areas must be 

surfaced with asphalt, concrete or similar dustless material and maintained; dust control 

plans for selected construction or development projects;26 and

 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”27

in exchange for annual rental payments and cost-share assistance from the government.

CRP acreage in the San Luis Valley counties of Colorado is much smaller than in the area 

around Lamar in southeast Colorado. A new Conservation Reserve Enhancement 

Program aimed at water conservation was initiated in 2012,28 which is reflected in the 

larger acreages enrolled in 2014 as shown in Table 3.

 

22 “TSD for the April 2, 2012 Alamosa and Lamar Exceptional Event”, 57-59.

23 Ibid., 55 and at: 

http://www.colorado.gov/airquality/tech_doc_repository.aspx?action=open&file=AlamosaNatur

alEventsActionPlan2003.pdf.

24 “TSD for the April 2, 2012 Lamar Exceptional Events,” March 10, 2015, page 67-68.

25 Ibid., 56.

26 Ibid., 57-58.

27 Ibid., 90.

28 “USDA and Colorado Announce Rio Grande Basin Water Conservation Project Agreement”,

USDA Farm Service Agency, Office of Communications, September 20, 2012, 

http://www.fsa.usda.gov/FSA/printapp?fileName=nr_20120920_rel_0304.html&newsType=new

srel
15

Table 3: Acres by County in the San Luis Valley Enrolled in the USDA NRCS CRP Program29

COUNTY 2008 2009 2010 2011 2012 2013 2014

Alamosa 0 0 0 0 0 0 1,347

Conejos 32 32 32 32 32 70 51

Costilla 0 13 13 13 13 13 13

Mineral 0 0 0 0 0 0 0

Rio Grande 1 1 0 0 0 0 130

Saguache 0 0 0 0 0 0 672

Total 33 46 45 45 45 83 2,213

Reasonable controls have been effectively implemented and enforced:

Surface winds on March 18, 2012 were from the south in both Alamosa and Lamar. On April 2, 

2012, winds were from the east and southeast in Alamosa, and from the north in Lamar. The 

wind directions are shown in EPA figures 7-10. With these differing wind directions, CDPHE 

evaluated areas with disturbed soil upwind from the impacted monitors in the relevant directions 

on the two days.

 

29 United States Department of Agriculture, Farm Service Agency, Conservation Reserve 

Program Statistics, http://www.fsa.usda.gov/programs-and-services/conservationprograms/reports-and-statistics/conservation-reserve-program-statistics/index, accessed 

February 2, 2016.
16

Figure 7: Surface Wind Direction in Alamosa on March 18, 2012 (CDPHE Figure 67)30

 

30 “TSD for the March 18, 2012 Alamosa and Lamar Exceptional Event”, March 10, 2015, page 

89.
17

Figure 8: Surface Wind Direction in Lamar on March 18, 2012 (CDPHE Figure 73)31

 

31 Ibid., 99.
18

Figure 9: Surface Wind Direction in Alamosa on April 2, 2012 (CDPHE Figure 34)32

Figure 10: Surface Wind Direction in Lamar on April 2, 2012 (CDPHE Figure 45)33

 

32 “TSD for the April 2, 2012 Alamosa and Lamar Exceptional Event”, March 10, 2015, page 60.

33 Ibid., 72.
19

Alamosa Disturbed Area Analysis

Potential areas of disturbed soil south of the Adams State College monitoring site in Alamosa 

evaluated by the CDPHE are shown in Figure 11.

Figure 11: Potential Disturbed Soil Areas Upwind of the Adam’s State College Monitor on 

March 18, 2012 (CDPHE Figure 59)34

Site A in Figure 11 (approximately 85 acres) is zoned outside of the city’s limits by the city as a 

“Parcel.” The eastern portion of Area A is being considered for annexation into the city. Site A 

contains a combination of relatively dense grass and brush cover, periodic ponds and puddles, 

and dry soil in locations where ponds and puddles have dried. Sites D and C are similar. CDPHE 

notes that “Sites A, C and D are noted by Alamosa’s Public Works Director and County Health 

Director to be vacant land with natural vegetation (i.e. shrubland, mostly Chico bush) with no 

artificial irrigation and no access restriction. The city emphasizes that the areas are not suited for 

motorized travel. These lots are not considered to be anthropogenically disturbed soils and 

should be considered to be natural sources. If future high wind or other exceptional events occur, 

the APCD will re-assess these lots to determine if they are still natural sources.”35

 

34 “TSD for the March 18, 2012 Alamosa and Lamar Exceptional Event”, March 10, 2015, page 

89.

35 Ibid., 86.
20

Site B in Figure 11 (approximately 22 acres) is zoned outside of the city’s limits. Site E 

(approximately 30 acres) is zoned mostly as a “Commercial Business.” There is a small portion 

in the northeast corner that is zoned outside of the city’s limits. Site F (approximately 23 acres) is 

zoned as “Commercial business,” “Residential High” and a small portion as “Industrial.” Sites B, 

E, and F are naturally vegetated and partially irrigated. The sites are minimally (if at all) 

disturbed soil areas as of “this writing.”

36

Figure 7 showed additional potential disturbed soil areas upwind of the Alamosa Municipal 

Building monitor on March 18, 2012. Site G is zoned by the city as “Commercial Business” and 

is undisturbed gravel, dirt, and natural vegetation. The railroad runs through this narrow strip of 

land rendering it unlikely to be developed in the future.37 Site H is zoned by the city as 

“Commercial Business” and “Industrial.” It is private property with restricted access located just 

south of the rail yard. The land is naturally vegetated and undisturbed.38 Site I is zoned by the 

city as “Commercial Business”, but is now “Friends” Park. Friends Park has a well maintained 

gravel parking lot, a cement basketball court, an irrigated field, and a small hard packed clay 

BMX bike dirt track. The park is well maintained by the city, which implements reasonable dust 

control measures on a regular basis.39 Site J (approximately 9 acres) is zoned by the city as 

“Residential Medium.” It is a vacant lot behind a small apartment building. The land is natural 

and undisturbed. There is no irrigation but natural vegetation is present. The soil has a crust on 

the surface. When asked, residents of the adjacent apartment complex did not complain about 

blowing dust coming from Site J.40 Site K (approximately 26 acres) is zoned by the city as 

“Residential Medium”. It is vacant land that is naturally vegetated and undisturbed.41

Figure 12 shows areas of potentially disturbed soil upwind from the Adam’s State College 

monitor in Alamosa on April 2, 2012. Each of these sites were discussed above for the March 18, 

2012 event, with site A of Figure 12 corresponding to site H of Figure 7, site B of Figure 12 

corresponding to site G of Figure 7, site D of Figure 12 corresponding to site I of Figure 7 and 

site C of Figure 12 corresponding to site B of Figure 11.42

 

36 Ibid., 86.

37 Ibid., 90.

38 Ibid.

39 Ibid., 90-91

40 Ibid., 91.

41 Ibid.

42 “TSD for the April 2, 2012 Alamosa and Lamar Exceptional Event”, March 10, 2015, page 61.
21

Figure 12: Potential Disturbed Soil Areas Upwind of the Adam’s State College Monitor on 

April 2, 2012 (CDPHE Figure 36)43

Lamar Disturbed Area Analysis

Figure 13 shows areas of potential soil disturbance upwind of the Lamar PM10 monitors on 

March 18, 2012.44 Site A is the Lamar Power Plant where the Power Plant PM10 monitor resides. 

Particulate matter emissions are controlled in compliance with CDPHE permit No. 05PR0027, 

which includes the following provisions:

 Limestone and ash handling, processing, and storage are controlled by high efficiency 

baghouses.

 Water wash-down-systems are used for flushing down any accumulated dust on 

walkways, platforms, and other surfaces to prevent re-entrainment of the dust into the 

atmosphere.

 On-site haul roads are paved, and are inspected at least once each day during which 

hauling activities occur, and cleaned as needed. These activities emit less than 1 ton per 

year of PM10 and are APEN Exempt.

 All transport vehicles carrying substances that potentially generate fugitive particulate 

matter emissions (such as trucks containing limestone, inert material, or ash) are fully 

enclosed, or covered with a mechanical closing lid or a tight tarp-like cover at all times 

while on the facility grounds except during loading/unloading operations.

 

43 Ibid.

44 “TSD for the March 18, 2012 Alamosa and Lamar Exceptional Event”, March 1, 2015, page 

63.
22

 Emissions from emergency coal stockpile are effectively controlled with a water dust 

suppression system.

Access to the power plant is restricted by security fences. CDPHE considers the controls a 

combination of BACT for the limestone and ash handling, paving, wash-down systems and 

enclosures, and reasonable controls otherwise.45

Figure 13: Potential Disturbed Soil Areas Upwind of the Lamar PM10 monitors on March 18, 

2012 (CDPHE Figure 74)46

 

45 Ibid., 101.

46 Ibid., 63.
23

Other potentially disturbed soils in Figure 13 are characterized as follows:

 Site B is the Lamar Water Department and Lamar-Prowers County Volunteer Fire 

Department and is a restricted access site of grated (sic) and watered gravel on an asneeded basis; 

 Site C 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; 

 Site D 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 xeriscape; 

 Site E is Colorado Mills LLC sunflower oil and feed processing facility operating under 

CDPHE permit #95PR622. Permit conditions include 30% maximum opacity limit, PM 

limits and an Operation and Maintenance Plan. The last inspection on February 14, 2012 

found no visible emissions, and in-house monthly inspections and the use of cyclones for 

emission control demonstrate PM mitigation efforts; and

 Site F is partially owned by Century Link and is a fenced gravel lot with restricted access. 

The remainder of the site is a free chip-sealed crushed-gravel parking lot for Prowers 

County Jail and the Prowers County Municipal Court that is maintained by the county.

Figure 14 shows additional potential disturbed areas further south of the PM10 monitors relevant 

for the March 18, 2012 event.47 The areas identified are characterized as follows:48

 Site G is a paved parking lot;

 Site H is naturally vegetated undisturbed land with restricted access abutting the 

southeast edge of Lamar;

 Site I is the Lamar Ball Complex at approximately 100 Savage St., which has limited 

access through fencing. Recycled asphalt and gravel has been applied to reduce dust in 

the areas around the ball diamonds. Parking areas are periodically dragged and watered as 

needed to control dust; and

 Site J is the Lamar County Fairgrounds. The land is maintained by the county and is 

graded annually and watered frequently during most of the year.

 

47 Ibid., 63.

48 Ibid., 108.
24

Figure 14: Additional Potential Disturbed Soil Areas Upwind of the Lamar PM10 monitors on 

March 18, 2012 (CDPHE Figure 81)49

Winds were from the north for the April 2, 2012 event. 

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

parcels of land in Lamar. EPA Figures 15-16 (CDPHE Figures 46 and 55) below show 

that identified areas of soil disturbance have reasonable controls near the Lamar 

Municipal Building monitor. 50

 

49 Ibid., 107.

50 Ibid., p. 72.
25

o Site A is owned by Heath & Son & Turpin Trucking and HVH Transportation 

Inc., a large truck repair and freight service trucking company, respectively. It is a 

well-maintained gravel lot.

o Site B 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.

o Site C is owned by Heath & Son & Turpin Trucking and is a well-maintained 

gravel lot used for truck storage.

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

Department and is a restricted access site of grated (sic) and watered gravel on an 

as-needed basis.

o Site E is a power plant with a restricted access 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 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.

o Site F 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 xeriscape.

o Site G is Colorado Mills LLC sunflower oil and feed processing facility operating 

under CDPHE permit #95PR622. Permit conditions include 30% maximum 

opacity limit, PM limits, and an Operation and Maintenance Plan. The last 

inspection on February 14, 2012 found no visible emissions, and in-house 

monthly inspections and the use of cyclones for emission control demonstrate PM 

mitigation efforts.

o Site H is partially owned by Century Link and is a fenced gravel lot with 

restricted access. The remainder of the site is a free chip-sealed crushed-gravel 

parking lot for Prowers County Jail and the Prowers County Municipal Court that 

is maintained by the county.

o Site I is owned by Prowers County and leased to the Colorado State Highway

Patrol for office space. The lot is covered in gravel for dust suppression, drainage, 

and erosion control. The lot has restricted access and a 5 mph speed limit.

o Site J is owned by Ranco, a heavy duty construction trailer manufacturer. The 

property is covered in pavement, gravel, and natural vegetation, with no 

unnatural, disturbed areas that may have contributed to blowing dust.

o Site K is owned by Valley glass and the property has restricted access to a well 

maintained gravel lot.
26

Figure 15: Potential Disturbed Soil Areas Upwind of the Lamar PM10 monitors on April 2, 

2012 (CDPHE Figure 46)51

Figure 16 shows additional potential areas of disturbed soil north (upwind) of the Lamar 

Municipal Building monitor on April 2, 2012.

o Site L is 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.

52 Baghouse collection 

efficiency is 99%, there is a 20% opacity limit, and water sprays and magnesium 

 

51 “TSD for the April 2, 2012 Alamosa and Lamar Exceptional Event”, March 10, 2015, page 43.
27

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.

o Site M 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 needed.

o Site N is naturally vegetated and undisturbed.

o Site O 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. Partnering with the 

Division of Wildlife, the city of Lamar took 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).

o Site P is owned by the Ranchers Supply Co. Inc. and is a fenced 90% gravel lot 

for long-term oversize vehicle parking. It has a 10 mph policy, is watered asneeded, and meets Air Quality Control Commission (AQCC) Regulation 1 

requirements (Section III.D.1(a)).

o Site Q is owned by Ranco, a heavy duty construction trailer manufacturer. The 

property is covered in pavement, gravel, and natural vegetation, with no 

unnatural, disturbed areas that may have contributed to blowing dust.

o Site R 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.

o Site S is owned by Prowers County and leased to the Colorado State Highway 

Patrol for office space. The lot is covered in gravel for dust suppression, drainage, 

and erosion control. Lot has restricted access and a 5 mph speed limit.

o Site T is Lamar Feed and Grain – White Stone Farms, CDPHE permit 

#00PR0431. On the property is a grain receiving pit, shipping truck loadout 

station, grain storage, grain cleaning scalper, and grain handling and milling 

systems. The permit includes dust control measures for total PM, PM10 and PM 2.5

annual emissions limitations and visible emissions not to exceed 20%. All 

equipment is maintained consistent with good air pollution control practices, and 

the feed mill is equipped with a mineral oil spray system to control PM emissions.

o Site U was Dragon EPS beginning in 1993, but merged in 2011 with Ranco (site 

Q and J above). CPDHE permit #08PR0603 issued December 21, 2011 covers 

paint booths and abrasive blasting units with the following PM controls: permitted 

annual TSP, PM10 and PM2.5 emission limits, high volume low pressure paint 
28

spray guns, exhaust filters on paint spray booths, baghouse filters on blasting 

units, visible emissions not to exceed 20% and source must follow CPDHE 

operations and maintenance plan. It was last inspected on November 9, 2011 and 

found to be in compliance.

o Site V is a restricted access property that is naturally vegetated and appears to be 

undisturbed.

o Site W is a group of rotating crop fields, with a schedule to allow some fields to 

lay fallow between plantings; and

o Site X is the Robins Redi-Mix Concrete Batch Plant which opened in spring of 

2010 and consists of a dry truck mix plant using a cement and a dry ash silo 

operated with pneumatic conveyers and bag houses to control 98% of emissions. 

In April 2010 CDPHE issued a permit exempt letter (10PR1310.XP) which

includes PM point and fugitive dust control measures such as: uncontrolled PM 

cannot exceed 10 TPY and uncontrolled PM10 cannot exceed 5 TPY, and visible 

emissions cannot exceed 20%. The source waters the lot during processing and 

as-needed, uses CDPHE BACT for limestone and ash handling, paving, washdown systems and enclosures.
29

Figure 16: Additional Potential Disturbed Soil Areas Upwind of the Lamar PM10 monitors on 

April 2, 2012 (CDPHE Figure 55)

53

According to the CDPHE TSDs, 

The APCD conducted thorough assessments to determine if the potential soil 

disturbances . . .were present during the 2012 exceedance in Lamar. During the course of 

these assessments, the APCD discovered that these sites were reasonably controlled or 

considered to be natural sources during the April 2, 2012, high wind event. Therefore, 

these sites were not significant contributors to fugitive dust in the Lamar area during the 

April 2, 2012, high wind event.54

 

53 “TSD for the April 2, 2012 Alamosa and Lamar Exceptional Event”, March 10, 2015, page 81.

54 Ibid., 88.
30

Wind speed was high enough to overwhelm the reasonable controls

CDPHE provided the documentation summarized in EPA Table 4, and included in EPA Tables 

5-8 (CDPHE Tables 1 and 2 of each of the two demonstrations) showing that sustained wind 

speeds associated with these event were above 30 mph and gusts were above 40 mph. CDPHE 

previously established in its 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. The sustained winds and gusts in Lamar exceed this Colorado 

threshold. Transported dust from the upwind desert and arid plains regions appears to be a 

significant contribution to the exceedance, in addition to local winds overwhelming implemented 

local controls. EPA notes that the high local gust speeds in 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 each affected 

community” for Alamosa and Lamar during the March and April 2012 events.55

Table 4: Wind and Gust Highest Measured Speeds by Exceedance Date

Exceedance Date Wind Speed in mph Wind Gust in mph

March 18, 2012 

Alamosa 45 56

March 18, 2012 

Lamar 40 51

April 2, 2012 

Alamosa 41 54

April 2, 2012 

Lamar 35 54

 

55 “TSD for the March 18, 2012 Alamosa and Lamar Exceptional Event”, March 10, 2015, 

page 77; “TSD for the April 2, 2012 Alamosa and Lamar Exceptional Event”, March 10, 2015, 

page 53.
31

Table 5: Wind Speed Alamosa, CO on March 18, 2012 (CDPHE’s TSD Table 1)56

 

56 “TSD for the March 18, 2012 Alamosa and Lamar Exceptional Event”, March 10, 2015, 

page 20.
32

Table 6: Wind Speed Lamar, CO on March 18, 2012 (CDPHE’s TSD Table 2)

57

 

57 Ibid., 21.
33

Table 7: Wind Speed Alamosa, CO on April 2, 2012 (CDPHE’s TSD Table 1)

58

 

58 “TSD for the April 2, 2012 Alamosa and Lamar Exceptional Event”, March 10, 2015, page 16.
34

Table 8: Wind Speed Lamar, CO on April 2, 2012 (CDPHE’s TSD Table 2)

59

Section 2 of CDPHE’s demonstrations provides a complex meteorological analysis of the event, 

including: 

 Surface and upper air wind speed analysis from NOAA; 

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

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

NOAA, and the National Drought Mitigation Center; 

 Webcam imagery showing visibility impairment due to blowing dust;

 NOAA HYSPLIT Model backtrajectories;

 GOES Satellite imagery of surface dust plumes; and

 NEXRAD radar imagery of windblown dust fronts.

 

59 Ibid., 17.
35

These analyses demonstrate through the weight of evidence the existence of high wind blowing 

dust events originating upwind of the monitor in question. 

Sections 2 and 5 of CDPHE’s demonstrations show that the monitors in Alamosa and Lamar 

were affected by PM10 transport across a large region, with the main source areas located in 

agricultural areas in Colorado. In addition to transport, the wind speeds associated with the event 

factor into EPA’s evaluation of whether these events are nRCP in Alamosa and Lamar. 

Therefore, the EPA concludes that these events were nRCP pursuant to the Treatment of Data 

Influenced by the EER. Table 9 summarizes the EPA’s evaluation of CDPHE’s nRCP EE 

demonstration. 

Table 9: EPA’s Analysis of CDPHE’s TSD of nRCP

Exceedance 

Date

Reasonable 

Controls 

Demonstration 

Citation

Wind Speed 

Demonstration 

Citation

Sufficient 

Quality of 

Evidence?

EPA 

Criterion 

Met?

March 18, 2012 

Alamosa

Section 5: p. 45-94 Section 2: p. 9-55 Yes Yes

March 18, 2012 

Lamar

Section 5: p. 94-111 Section 2: p. 9-55 Yes Yes

April 2, 2012 

Alamosa

Section 5: p. 79-67 Section 2: p. 9-32 Yes Yes

April 2, 2012 

Lamar

Section 5: p. 67-91 Section 2: p. 9-32 Yes Yes

HISTORICAL FLUCTUATIONS 

The 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 

March 18 and April 2, 2012 data and a 6-year time series of 24-hour averages for the years of 

2007-2012. The 2007-2012 data set had between 1839 and 2181 samples for the four monitors 

found in Lamar and Alamosa, and each description below indicates the samples taken on these 

days exceed the typical samples for this site. Table 10 summarizes the statistical assessment of 

the March 18 and April 2, 2012 PM10 data.
36

Table 10: Statistical Analysis of March 18 and April 2, 2012 Samples Compared to 2007-2012 

Data

Sample Concentration, g/m3 Rank Percentile

March 18, 2012 

Alamosa Adams 

State

324 4

th of 1839 99.8th

March 18, 2012 

Alamosa Municipal 

Building

237 5

th of 2048 99.8th

March 18, 2012 

Lamar Power Plant

220 4

th of 2181 99.8th

March 18, 2012 

Lamar Municipal 

Building

242 1

st of 2114 99.95th

April 2, 2012 

Alamosa Adams 

State College

389 2

nd of 1839 99.9th

April 2, 2012 Lamar 

Municipal Building

163 4

th of 2114 99.8th

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

demonstrations also consider percentile ranks when dust impacted data is to be excluded.60

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

dust events, including those in 2012. This information indicates that values at the level seen on 

March 18 and April 2, 2012 are extremely rare in the absence of high wind dust exceptional 

events, and that it is unlikely that any sources of PM10 were involved in the 2012 exceedances 

other than wind-blown dust. Therefore, the EPA concludes that these events were in excess of 

HF pursuant to the Treatment of Data Influenced by the EER. Table 11 summarizes the EPA’s 

evaluation of CDPHE’s HF EE demonstration. 

 

60 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.
37

Table 11: EPA’s Analysis of CDPHE’s TSD of HF

Exceedance 

Date

Exceedance 

Location

Historical Fluctuations 

Demonstration Citation

Sufficient 

Quality of 

Evidence?

EPA 

Criterion 

Met?

March 18, 2012 Alamosa Section 3: p. 56-69 Yes Yes

March 18, 2012 Lamar Section 3: p. 56-69 Yes Yes

April 2, 2012 Alamosa Section 3: p. 33-43 Yes Yes

April 2, 2012 Lamar Section 3: p. 33-43 Yes Yes

CLEAR CAUSAL RELATIONSHIP 

The 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, pollutant species-specific 

information supporting a CCR between the event and the measured concentration.61

Section 2 of CDPHE’s demonstrations provides analyses that demonstrate the existence of high 

wind blowing dust events upwind of the monitors in question, but including southeastern 

Colorado contributions.

March 18, 2012: 

The CDPHE demonstration for March 18, 2012 states that:

Stations upwind from Alamosa and Lamar, predominantly in New Mexico, also reported 

numerous hours of blowing dust and/or haze along with significantly diminished 

visibility. It should be noted that many of the blowing dust conditions upwind from 

Alamosa and Lamar occurred several hours earlier in the day. This suggests the 

possibility that at least some portion of the dust that produced the exceedances in 

Alamosa and Lamar was transported from outside of Colorado.62

 

61 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. 

62 “TSD for the March 18, 2012 Alamosa and Lamar Exceptional Events,” March 10, 2015, page 

18.
38

April 2, 2012:

The CDPHE demonstration for April 2, 2012 states that: 

The Denver and Pueblo National Weather Service (NWS) forecast offices issue weather 

information and alerts for all of south-central and eastern Colorado, including Alamosa 

and Lamar. The NWS office in Cheyenne, Wyoming monitors the Nebraska Panhandle, a 

suspected source area that contributed to the blowing dust in eastern Colorado on April 2, 

2012. Appendix B provides several warnings, advisories and discussions from the 

Denver, Pueblo and Cheyenne NWS offices for April 1, 2012 to April 2, 2012. The text 

from these products, particularly those highlighted in yellow, clearly show that the NWS 

anticipated high winds and blowing dust. Additionally, the Colorado Department of 

Public Health and Environment (CDPHE) issued a Blowing Dust Advisory for portions 

of eastern Colorado and the San Luis Valley on April 2, 2012.63

In addition, the NOAA smoke and dust text products for April 2, 2012 state that:

Several areas of blowing dust continue to originate in Colorado. Southward moving dust 

was visible at sunrise in Cheyenne, Lincoln, Crowley and Pueblo Counties.64

Additionally:

A deep storm center over New Mexico was producing strong winds over the southwest 

Plains from northern Mexico into west Texas that was kicking up a broad area of blowing 

dust. The dust was mainly originating from several sources in northern Chihuahua and 

west Texas in the vicinity of Midland and Lubbock. The dust was curling 

counterclockwise across the region and extended to near Wichita Falls and the Texas 

Panhandle by sunset. Another smaller area of blowing dust was seen this afternoon north 

of the storm center in the Great Sand Dunes National Preserve of south central Colorado. 

This area was moving o [sic] the west.65

Included with this TSD is an enclosure which analyzes drought conditions in the Lamar area 

from 1897-2015, and associates the trends with high wind blowing dust events. It is titled 

Analysis of Lamar Drought Condition Severity and Blowing Dust: 1897-2015. The review finds 

some correlation between prolonged drought (as defined by a 7-year annual average) and 

blowing dust conditions in Lamar. The enclosure is at the end of this document.

The EPA concludes that there was a CCR for these events pursuant to the Treatment of Data 

Influenced by the EER. Table 12 summarizes the EPA’s evaluation of CDPHE’s CCR EE 

demonstration. 

 

63 “TSD for the April 2, 2012 Alamosa and Lamar Exceptional Events,” March 10, 2015, page 

32.

64 Satellite imagery analysis through 1530z April 2, 2012, NOAA Smoke and Dust text product, 

Ibid., p. B-10.

65 Ibid., p. B-10 & B-11.
39

Table 12: EPA’s Analysis of CDPHE’s TSD of CCR66

Exceedance Date Clear Causal Relationship 

Demonstration Citation 

Sufficient 

Quality of 

Evidence?

EPA 

Criterion 

Met?

March 18, 2012 Section 2: p. 9-55 Yes Yes

April 2, 2012

Section 2: p. 9-32 Yes Yes

AFFECTS AIR QUALITY (AAQ)

As stated in EPA’s Interim Guidance for High Wind Exceptional Events Section 3.4, the 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 13. Additionally, CDPHE states 

that: 

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.67

Therefore, the EPA concludes that these events Affected Air Quality pursuant to the Treatment 

of Data Influenced by the EER. Table 13 summarizes the EPA’s evaluation of CDPHE’s AAQ 

EE demonstration.

 

66 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.

67 “TSD for the March 18, 2012 Alamosa and Lamar Exceptional Events,” March 10, 2015, page 

92; “TSD for the April 2, 2012 Alamosa and Lamar Exceptional Events,” March 10, 2015, page 

111.
40

Table 13: EPA’s Analysis of CDPHE’s TSD of AAQ

Exceedance 

Date

HF 

and 

CCR

Affects Air Quality 

Demonstration Citation 

Sufficient 

Quality of 

Evidence

EPA 

Criterion 

Met?

March 18, 2012 HF Section 3: p. 56-69 Yes Yes

CCR Section 2: p. 9-55 Yes Yes

April 2, 2012 HF Section 3: p. 33-43 Yes Yes

CCR Section 2: p. 9-32 Yes Yes

NATURAL EVENT

As stated in the EPA’s Interim Guidance for High Wind Exceptional Events Section 6.3.6 the 

EPA will consider an event to be a natural event if both the nRCP and CCR requirements have 

been adequately demonstrated. CDPHE states that:

Due to the semi-arid nature of parts of the state, Colorado is highly susceptible to 

windblown dust events. These events are often captured by various air quality monitoring 

equipment throughout the state, sometimes resulting in exceedances or violations of the 

24-hour PM10 NAAQS. This document contains detailed information about the large 

regional windblown dust events that occurred on” March 18 and April 2, 2012. “The 

Colorado Department of Public Health and Environment (CDPHE) Air Pollution Control 

Division (APCD) has prepared this report for the U.S. Environmental Protection Agency 

(EPA) to demonstrate that the elevated PM10 concentrations were caused by a natural 

event.

68

CDPHE has sufficiently demonstrated the CCR and nRCP requirements for the March 18 and 

April 2, 2012 events. Therefore, the EPA concludes that these were natural events pursuant to the 

Treatment of Data Influenced by the EER. Table 14 summarizes the EPA’s evaluation of 

CDPHE’s Natural Event EE demonstration.

 

68 “TSD for the March 18, 2012 Alamosa and Lamar Exceptional Events,” March 10, 2015, page 

1; “TSD for the April 2, 2012 Alamosa and Lamar Exceptional Events,” March 10, 2015, page 1.
41

Table 14: EPA’s Analysis of CDPHE’s TSD of Natural Event

Exceedance 

Date

nRCP or CCR Natural Event 

Demonstration Citation 

Sufficient 

Quality of 

Evidence?

EPA 

Criterion 

Met?

March 18, 

2012

nRCP- Anthropogenic Section 5: p. 45-111 Yes Yes

nRCP-Wind Speed Section 2: p. 9-55 Yes Yes

CCR Section 2: p. 9-55 Yes Yes

April 2, 

2015

nRCP- Anthropogenic Section 5: p. 79-91 Yes Yes

nRCP-Wind Speed Section 2: p. 9-32 Yes Yes

CCR Section 2: p. 9-32 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 effects of the events. 

CDPHE provides a summary of the analysis and information presented in the demonstration that 

show both the nRCP and CCR requirements have been met for the March 18, 2012 exceedances, 

and states that: 

Elevated 24-hour PM10 concentrations were recorded in parts of Colorado on March 18, 

2012. All of the noted March 18, 2012, twenty-four-hour PM10 concentrations were 

above the 90th percentile concentrations for their locations (see Table 22). 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 this high wind blowing dust event, Alamosa and Lamar would not have exceeded 

the 24-hour NAAQS on March 18, 2012. 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.

69

Similarly for the April 2, 2012 exceedances, CDPHE states:

 

69 “TSD for the March 18, 2012 Alamosa and Lamar Exceptional Events,” March 10, 2015, page 

111.
42

Elevated 24-hour PM10 concentrations were recorded in parts of Colorado on April 2, 

2012. All of the noted April 2, 2012, twenty-four-hour PM10 concentrations were above 

the 90th percentile concentrations for their locations (see Table 9). This event exceeded 

the 99th percentile value for the entire dataset. 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 2, 2012. 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.70

Therefore, the EPA concludes that there would have been NEBF pursuant to the Treatment of 

Data Influenced by the EER. While not explicitly stated in the documentation, the EPA notes 

that PM10 concentrations before the periods of high winds on the event days were all well below 

the 24-hour PM10 NAAQS of 150 ug/m3, providing further support for CDPHE’s conclusion. 

Table 15 summarizes the EPA’s evaluation of CDPHE’s NEBF EE demonstration. 

Table 15: EPA’s Analysis of CDPHE’s TSD of NEBF

Exceedance Date No Exceedance But For the 

Event Demonstration Citation 

Sufficient 

Quality of 

Evidence?

EPA Criterion 

Met?

March 18, 2012 Section 6: p. 111 Yes Yes

April 2, 2012

Section 6: p. 92 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 16 outlines EPA’s evaluation of these 

requirements. 

 

70 “TSD for the April 2, 2012 Alamosa and Lamar Exceptional Events,” March 10, 2015, page 

92.
43

Table 16: EPA’s Analysis of Schedules and Procedural Criteria

Reference Demonstration 

Citation for 

Compliance

EPA 

Criterion 

Met?

Did the State provide prompt 

public notification of the event?

40 CFR 50.14(c)(1)(i) March 18, 2012 

Section 1: p. 7

Yes

April 2, 2012 

Section 1: p. 7.

Were flags and initial description 

placed on the data by July 1st of the 

following year?

40 CFR 

50.14(c)(2)(iii)

March 18, 2012: 

Flag April 18, 

2012; Initial 

Description May 

30, 2013

No

April 2, 2012: 

Flag April 27, 

2012; Initial 

Description May

30, 2012

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) March 10, 2015 Yes

Was the public comment process 

followed and documented?

40 CFR 

50.14(c)(3)(v)

March 18, 2012 

Section 1: p.8

Yes

April 2, 2012 

Section 1: p. 8.

CONCLUSION

The EPA has reviewed documentation provided by CDPHE to support claims that dust emissions 

generated by high winds resulted in PM10 transport from arid regions in Colorado and upwind 

states into the Lamar and Alamosa areas on March 18 and April 2, 2012. These high wind events 

caused exceedances of the 24-hour PM10 NAAQS at the Lamar and Alamosa PM10 monitor. EPA 

concurs that the flagged exceedances at the Lamar and Alamosa monitors on these days meet the 

definition of exceptional events: the events affected air quality, were nRCP, and met the 

definition as natural events. Specifically, the EPA has determined that the event was nRCP due 
44

to high wind conditions that transported PM10 from sources outside of the immediate Lamar and 

Alamosa areas and also subsequently may have overwhelmed some reasonable controls within 

Lamar and Alamosa. Also, regardless of transport into the area, information pertaining to the 

controls implemented within the affected area and the wind speeds associated with the high wind 

dust events provide sufficient evidence to conclude that these events were nRCP. Furthermore, 

the EPA has determined that there is a CCR between the event and the measured exceedance, 

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

The EPA finds that the weight of evidence is sufficient to concur on the flagging of the data for 

the 24-hour PM10 NAAQS exceedances at the Lamar and Alamosa monitors on March 18 and

April 2, 2012.

This concurrence does not constitute final EPA action regarding any matter on which the 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 the EPA completes notice and comment rulemaking on those determinations.
1

Enclosure

Analysis of Lamar Drought Condition Severity and Blowing Dust Events: 1897-2015

Due to the high number of exceedances in Lamar from 2008 to 2014 due to dust, the EPA 

conducted an historical analysis of the drought conditions in the surrounding area from 1897 to 

2015. The results of which confirm that these events, while recurrent, can be considered highly 

unusual and therefore truly exceptional events. The National Oceanic and Atmospheric 

Administration Climate Data Online service includes monthly and annual precipitation data for 

Lamar, Colorado beginning in 1897. When annual precipitation is plotted over time, two periods 

with seven consecutive years of below average precipitation are seen: 1931 through 1937 (The 

Dust Bowl years) and 2007 through 2013. Since both periods were seven years long, the running 

average of annual precipitation calculated over seven year intervals is a useful statistic for 

comparing multi-year drought severity. The two lowest periods for seven year running averages

in the 119 year data set are centered on 1934 and 2010. The 1934 minimum, at 9.39 inches 

(seven year average) is considerably lower than the 2010 level at 12.1 inches. These would be 

compared to the long term mean annual precipitation of 15.1 inches.

In the 7 years prior to 2007 (2000-2006), Lamar experienced dust storms leading to PM10

exceedances on 8 days. For the seven year period of 2007 through 2013, Lamar experienced 17 

dust storm days leading to exceedances, with an additional 8 exceedances in March and April 

2014, before above average rainfall began in May 2014. Dust storm activity was therefore more 

than twice as heavy during the dry 2007-2013 period as in the preceding seven years with a 

mixture of both above and below normal precipitation.

Since above normal rains began in May 2014, three dust storms leading to exceedances have 

been observed, in December 2014, on April 1-2, 2015, and in August 2015. The two storms in 

the spring and summer of 2015 compares to 7 in the spring and summer of 2013 and 8 in 2014, 

suggesting that normal or above normal rainfall will significantly decrease wind-blown dust 

events in the area. Therefore, the EPA can conclude that the increased amount of exceedances is 

due to an extreme fluctuation in precipitation that is highly unusual, and the events are not 

characteristic of normal PM10 conditions in and around Lamar. 
2

Figure 1: Annual Precipitation, Lamar, Colorado, 1897-July 20151

In the 7 years prior to 2007 (2000-2006), Lamar experienced dust storms leading to PM10

exceedances on 8 days. There were never more than two years in a row with PM10 exceedances 

before a year with no exceedances was observed. For the seven year period of 2007 through 

2013, Lamar experienced 17 dust storm days leading to exceedances, with an additional 8 

exceedances in March and April 2014, before above average rainfall began in May 2014. Five 

consecutive years (2011-2015) saw at least one PM10 exceedance day during a dust storm. Dust 

storm activity was therefore more than twice as heavy during the dry 2007-2013 period as in the 

preceding seven years with a mixture of both above and below normal precipitation. PM 

monitoring in Lamar began in 1975 with TSP monitoring. PM10 monitoring was added in 1985. 

Mean TSP expected exceedance counts2decreased from an initial level of 16 to 18 exceedances 

per year in 1976 and 1977 to a level of 5 to 6 exceedances per year in 1985-1986.3 Mean PM10

 

1 EPA Region 8 staff analysis conducted July 29, 2015.

2 Expected exceedances for PM10 correct the number of measured exceedances by correcting for 

unsampled days, in accordance with 40 CFR Part 50, Appendix K. TSP expected exceedances 

were calculated here in a similar manner to provide comparable data to PM10.

3 CDPHE data in the EPA AQS database, accessed by EPA Region 8 July 24, 2015.
3

expected exceedance counts were from zero to 3 expected exceedances per year from PM10

monitoring inception until 2013, when the three year mean jumped to seven at the end of the 

seven year dry spell.4 The Lamar exceedance on May 22, 2008, one of two exceedance dust 

storms observed that year, occurred in the second of the seven years of consecutive below 

average precipitation.

Figure 2: Lamar Precipitation and PM Exceedances, 1975-2015, EPA Region 8 Analysis5

 

4

Ibid.

5 EPA Region 8 staff analysis conducted July 29, 2015.