1

EPA Technical Support Document in Review of Colorado Department of 

Public Health and Environment’s Demonstration Package for the 

April 1 and 2, 2015 Lamar 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

April 1 & 2, 2015 ........................................................................................................................ 4

Not Reasonably Controllable or Preventable.................................................................................. 9

Anthropogenic sources of dust have reasonable controls in place:........................................... 10

Reasonable controls have been effectively implemented and enforced:................................... 12

Wind speed was high enough to overwhelm the reasonable controls:...................................... 19

Historical Fluctuations.................................................................................................................. 22

Clear Causal Relationship............................................................................................................. 23

April 1, 2015 ............................................................................................................................. 24

April 2, 2015 ............................................................................................................................. 24

Affects Air Quality (AAQ)........................................................................................................... 26

Natural Event ................................................................................................................................ 27

No Exceedance or Violation But For the Event............................................................................ 28

Schedule and Procedural Requirements........................................................................................ 28

Conclusion .................................................................................................................................... 29
3

SUMMARY

Overview

On December 4, 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 station in Lamar on 

April 1 and 2, 2015. 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. 

(ug/m3)

CDPHE Request 

to Consider for 

AQS Removal?

April 1, 2015 Lamar Municipal 

Building

08-99-0002 253 Yes

April 2, 2015 Lamar Municipal 

Building

08-99-0002 419 Yes

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. Further west and southwest of Lamar are the deserts of the New Mexico, 

Utah, and Arizona Four Corners region. The areas described are shown in Figures 1 and 2.

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

Exceedances
4

Figure 2: Map of High Plains and Monitor Location with the PM10 NAAQS Exceedances

April 1 & 2, 2015: 

On April 1 and 2, 2015 a strong upper level low pressure system transited southern Canada from 

west to east. An upper level trough extended south from the low, and the trough and associated 

cold fronts passed through eastern Colorado. The cold front remained in southeast Colorado from 

late April 1 through April 2, and the front passed over Lamar, Colorado the evening of April 1 

and again twice on April 2. Strong surface winds associated with the trough and frontal passages 

occurred in the evening of both April 1 and April 2. Of April 1, 2015, CDPHE said:

The exceedance in Lamar was the result of intense surface winds in the wake of a passing 

cold front. The surface winds in southeast Colorado were also likely enhanced by postfrontal thunderstorms moving to the north of Lamar. 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 northerly direction which moved 

over dry soils in eastern Colorado, producing significant blowing dust.

2

 

2

“TSD for the April 1 and 2, 2015 Lamar Exceptional Events,” December 4, 2015, page 7.
5

Of the April 2, 2015 winds, CDPHE said:

In advance of the cold front the wind in southeast Colorado was predominantly out of a 

south to southeasterly direction and was quite gusty at times. However, the wind 

increased significantly once the cold front passed. ... By 8:00 PM MST, a significant 

amount of “bunching” of isobars was occurring in southeast Colorado behind the cold 

front. ... This indicates that a strong pressure gradient was in place. Wind speed is 

directly proportional to the pressure gradient, so a higher pressure gradient will produce 

stronger winds ...3

EPA Figure 3 (April 1 at 5:00 pm MST) from CDPHE’s demonstration is described with: 

The 700 mb level is located roughly 3 kilometers above mean sea level (MSL). This chart 

shows that a deep trough of low pressure was present at the 700 mb level at the onset of 

the blowing dust event of April 1, 2015, and that it was moving over eastern Colorado.4

 

3

Ibid., 22.

4

Ibid., 8.
6

Figure 3: 700 mb Upper Level Analysis at 5:00 pm MST on April 1, 2015 (CDPHE’s TSD 

Figure 2)5

Figure 4, also from the CDPHE demonstration, shows a similar view for April 2 at 5:00 pm 

MST. The low pressure system has progressed eastward, but the upper level trough continues to 

extend to the southwest into eastern Colorado.

 

5

Ibid., 9.
7

Figure 4: 700 mb Upper Level Analysis at 5:00 pm MST on April 2, 2015 (CDPHE’s TSD 

Figure 12)6

Figure 5 from the CDPHE demonstration shows the surface level analysis for April 1 at 8:00 pm 

MST. A cold front extends south and west of the low pressure system in southern Canada, and 

lies just south of Lamar, having passed over Lamar earlier that evening. A similar view in Figure 

6, from 5:00 pm MST on April 2 shows the same front still in southern Colorado and again lying 

over Lamar.

 

6

Ibid., 21.
8

Figure 5: Surface Level Analysis at 8:00 pm MST on April 2 (CDPHE’s TSD Figure 4)7

 

7

Ibid., 10.
9

Figure 6: 700 mb Upper Level Analysis at 5 PM MST on April 2, 2015 at 5:00 pm MST 

(CDPHE’s TSD Figure 14)8

Figures 2-10 and 12-23 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. 

CDPHE provides a comprehensive description and discussion of these events in Sections 2, 3, 4, 

and 5 of the demonstration. 

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;

 

8

Ibid., 23.
10

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

 The wind speed was high enough to overwhelm the reasonable controls.9

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.10

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.11

Lamar has the following controls in place:12

 

9

“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.

10 “TSD for the April 1 and 2, 2015 Lamar Exceptional Events,” December 4, 2015, page 45.

11 Ibid., 45-47.

12 Ibid., 47-51.
11

 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)13; 

 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) 14;

 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.15 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 have 

a dust free surface,16 and 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”17; 

 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, outreach and education on soil 

management programs, and drought workshops to protect topsoil;18

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

policy requiring that new developments have paved streets;19

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. 99% of 

 

13 Ibid., 47-48 and at: 

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

ventsActionPlan2012.pdf.

14 “TSD for the April 1 and 2 2015 Lamar Exceptional Events,” December 4, 2015, page 48.

15 Ibid., 49.

16 Ibid., 50.

17 Ibid., 51.

18 Ibid., 66.

19 Ibid., 48.
12

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;20 and

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.

21

 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”22 in exchange for 

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

strategy is 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 Program23

COUNTY 2008 2009 2010 2011 2012 2013

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

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

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

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

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

Las Animas 21,869 21,860 17,403 17,616 18,925 18,887

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

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

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

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

Reasonable controls have been effectively implemented and enforced: 

The following analysis corresponds to aerial maps provided by CDPHE identifying lots that 

could possibly contribute to anthropogenic blowing dust, and effectively explains the 

 

20 Ibid., 68.

21 Ibid.

22 Ibid., 67.

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

EPA request on April 17, 2014 by Ray Mohr of CDPHE.
13

implementation of dust control in place for each lot, or explains the permit and monitoring 

history of the site, as applicable.

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

parcels of land in Lamar. Figures 7 and 8 below show that identified areas of soil 

disturbance north of the monitor have reasonable controls near the Lamar monitor. 24

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 the power plant that hosts the monitor and is 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 2/14/12 found no visible emissions, and in-house monthly 

inspections and the use of cyclones for emission control demonstrate PM 

mitigation efforts.

 

24

“The APCD considers the enforceable conditions of the permit, including identified 

continuous controls such as gravel roads with miles per hour restrictions, compaction, revegetation, watering, and extraction limitation, to be technologically feasible and economically 

reasonable for a facility of this size in order to minimize fugitive particulate emissions for this 

site.” “TSD for the April 1 and 2 2015 Lamar Exceptional Events,” December 4, 2015, page 62.
14

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. 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;

Figure 7: Lamar Site Assessment (CDPHE’s TSD Figure 35)25

 

25 “TSD for the April 1 and 2 2015 Lamar Exceptional Events,” December 4, 2015, page 54.
15

Figure 8 shows areas of disturbed soil further north from the Lamar monitor than those shown in 

Figure 7.

 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.

26 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.

 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.

 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.27 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).

 Site P 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).

 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.

 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.

 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. 

 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: total PM, PM10 and PM 2.5 annual emissions limitations, visible emissions not 

to exceed 20%, all equipment maintained consistent with good air pollution control 

 

26 Ibid., p. 61.

27 Ibid., p. 63
16

practices and the feed mill equipped with a mineral oil spray system to control PM 

emissions.

 Site U was Dragon EPS beginning in 1993, but merged in 2011 with Ranco (site Q and J 

above). CPDHE permit #08PR0603 issued 12/21/11 covers paint booths and abrasive 

blasting units with the following PM controls: permitted annual TSP, PM10 and PM 2.5

emission limits, High Volume Low Pressure paint spray guns, exhaust filters on paint 

spray booths, baghouse filters on blasting units, visible emissions not to exceed 20%, 

source must follow CPDHE operations and maintenance plan. It was last inspected on 

11/9/11 and found to be in compliance.

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

undisturbed.
17

Figure 8: Lamar Site Assessment (CDPHE’s TSD Figure 44)28

Site W, shown in Figure 9 (Figure 49 in the CDPHE demonstration) is the Robins Redi-Mix 

Concrete Batch Plant approximately 4.5 miles north of the Lamar monitor. It 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 

 

28 Ibid., 61.
18

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 Best Available 

Technology (BACT) for limestone and ash handling, paving, wash-down systems and 

enclosures.

Figure 9: Site W, Robins Redi-Mix Concrete Batch Plant (CDPHE’s TSD Figure 49)29

According to CDPHE’s demonstration: 

The APCD conducted thorough assessments to determine if the potential soil 

disturbances shown in Figure 34 through Figure 49 were present during the 2015 

exceedances in Lamar. During the course of these assessments, the APCD discovered that 

these sites were either reasonably controlled or considered to be natural sources during 

the 2015, high wind events. Therefore, these sites were not significant contributors to 

fugitive dust in the Lamar area during the April 2015, high wind events.

30

 

29 Ibid., 66.

30 Ibid.
19

Wind speed was high enough to overwhelm the reasonable controls:

CDPHE provided EPA Tables 3 and 4 (CDPHE Tables 1 and 4) showing that sustained wind 

speeds associated with these events 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 Lamar 

during the April 2015 events.”31

 

31 Ibid., 45.
20

Table 3: Wind Speed Lamar, CO on April 1, 2015 (CDPHE’s TSD Table 1)

32

 

32 Ibid., 17.
21

Table 4: Wind Speed Lamar, CO on April 2, 2015 (CDPHE’s TSD Table 4)33

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

including: 

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

Administration (NOAA); 

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

 

33 Ibid., 17.
22

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

NOAA and the National Drought Mitigation Center.

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 demonstration show that the monitor in Lamar was affected by 

PM10 transport across a large region, with the main source areas located in agricultural areas in 

Colorado and Kansas. In addition to transport, the wind speeds associated with the event factor 

into EPA’s evaluation of whether these events are nRCP in Lamar. Therefore, the EPA 

concludes that these events were nRCP pursuant to the Treatment of Data Influenced by the 

EER. Table 5 summarizes the EPA’s evaluation of CDPHE’s nRCP EE demonstration. 

Table 5: 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?

April 1, 2015

Section 5: p. 45-69 Section 2: p. 7-19 Yes Yes

April 2, 2015

Section 5: p. 45-69 Section 2: p. 20-32 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 

April 1 and 2, 2015 data and a 5-year time series of 24-hour averages for the years of 2010-June 

2015. The 2010-2015 data set had 1,875 samples, and each description below indicates the 

samples taken on these days exceed the typical samples for this site. CDPHE explains that for the 

concentration measured on April 1, 2015: 

The PM10 sample on April 1, 2015, at Lamar Municipal of 253 g/m3exceeds the 99th 

percentile value for all evaluation criteria and is the 11th largest sample of the dataset. 

The ten samples greater than the event sample are all associated with high wind events.

34

 

34 Ibid., 33.
23

CDPHE explains that for the concentration measured on April 2, 2015:

The PM10 sample on April 2, 2015, at Lamar Municipal of 419 g/m3exceeds the 99th 

percentile value for all evaluation criteria and is the 2nd largest sample of the dataset. The 

only sample greater than the event sample is associated with a high wind event.

35

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

demonstrations also consider percentile ranks when dust impacted data is to be excluded.36

CDPHE states that the percentile rank for these data are both at the 99.5 percentile level.

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

dust events, including those in 2013. This information indicates that values at the level seen on 

April 1 and 2, 2015 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 2013 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 6 summarizes the EPA’s evaluation of 

CDPHE’s HF EE demonstration. 

Table 6: EPA’s Analysis of CDPHE’s TSD of HF

Exceedance 

Date

Exceedance 

Location

Historical Fluctuations 

Demonstration Citation

Sufficient 

Quality of 

Evidence?

EPA 

Criterion 

Met?

April 1, 2015 Lamar Municipal 

Building

Section 3: p. 33-38 Yes Yes

April 2, 2015 Lamar Municipal 

Building

Section 3: p. 38-43 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 

 

35 Ibid., 38.

36 See “Interim Guidance on the Preparation of Demonstrations in Support of Requests to 

Exclude Ambient Air Quality Data Affected by High Winds Under the Exceptional Events Rule” 

of May 2013, page 20.
24

emissions, and recorded concentrations; and, as appropriate, pollutant species-specific 

information supporting a CCR between the event and the measured concentration.37

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

wind blowing dust events originating north of the monitors in question, but including 

southeastern Colorado contributions.

April 1, 2015: 

The National Weather Service Pueblo, Colorado forecast discussion webpage issued at 

4:12 am on April 1, 2015 stated that: 

“Models are showing potential for isol[ate]d to sc[a]t[tered] high-based 

convection developing this afternoon over the SE plains. Given surface dewpoints 

in the 20s...there is a potential for isol[ate]d dry lighting (sic)...and erratic gusty 

winds from virga and convective downdrafts.”38

The 3:08 pm forecast discussion from the Goodland, Kansas office of the National 

Weather Service stated: 

“North winds will rapidly increase as the low level jet and rapid surface pressure 

rises move through the area. Gusts approaching 40 mph are certainty (sic) likely 

during the evening as a result. Due to the very dry conditions...there could be 

some blowing dust for locations that have not yet received rainfall.”39

April 2, 2015:

The NOAA Satellite Services Division was in agreement with the conclusion that 

blowing dust was occurring in the wake of the cold front which passed over Lamar late 

on April 1 and then impacted Lamar again on April 2, 2015. The Smoke Text Product 

from NOAA at 11:45 am MST on April 2, 2015 stated: 

“Further southwest and west, the aerosol is more likely to be blowing dust behind 

the cold front that is dropping south through the Texas Panhandle.”40

CDPHE issued a blowing dust advisory for southeast Colorado, including Lamar, at 

12:00 pm MST: 

 

37 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. 

38 TSD for the April 1 and 2, 2015 Lamar Exceptional Events,” December 4, 2015, page 13, 

citing http://mesonet.agron.iastate.edu/wx/afos/ as the source for the quote.

39 Ibid.

40 TSD for the April 1 and 2, 2015 Lamar Exceptional Events, December 4, 2015, page 18, citing 

http://www.ssd.noaa.gov/PS/FIRE/DATA/SMOKE/2015D021754.html as the source.
25

“Strong gusty winds will create areas of blowing dust through Thursday evening. 

Winds and the threat for blowing dust will decrease after about 10 PM.”41

The Pueblo National Weather Service office forecast discussion at 7:57 pm MST stated:

This front has produced very gusty north winds...much stronger than originally 

anticipated...and these strong winds have kicked up an (sic) rather large area of 

dust and reduced visibilities. Therefore...dust advisory has been issued for 

portions of the SE plains through this evening until midnight.42 (Source: 

http://mesonet.agron.iastate.edu/wx/afos/)

CDPHE generally summarizes that:

The PM10 exceedances in Lamar would not have occurred if not for the following: (a) dry 

soil conditions over source regions with 30-day precipitation totals below the threshold 

identified as a precondition for blowing dust; and (b) meteorological conditions that 

caused strong surface winds over the area of concern.

43

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 7-year annual average) and blowing 

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

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

Influenced by the EER. Table 7 summarizes the EPA’s evaluation of CDPHE’s CCR EE 

demonstration. 

 

41 Ibid., page 26, citing 

http://www.colorado.gov/airquality/forecast_archive.aspx?seeddate=04%2f02%2f2015 as the 

source.

42 Ibid., citing http://mesonet.agron.iastate.edu/wx/afos/ as the source.

43 Ibid., 70.
26

Table 7: EPA’s Analysis of CDPHE’s TSD of CCR44

Exceedance Date Clear Causal Relationship 

Demonstration Citation 

Sufficient 

Quality of 

Evidence?

EPA 

Criterion 

Met?

April 1, 2015 Section 2: p. 7-19 Yes Yes

April 2, 2015

Section 2: p. 20-32 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 8. 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 

events were associated with a measured concentration in excess of normal historical 

fluctuations including background.45

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

of Data Influenced by the EER. Table 8 summarizes the EPA’s evaluation of CDPHE’s AAQ EE 

demonstration.

Table 8: 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?

April 1, 2015 HF Section 3: p. 33-38 Yes Yes

CCR Section 2: p. 7-19 Yes Yes

April 2, 2015 HF Section 3: p. 38-43 Yes Yes

CCR Section 2: p. 20-32 Yes Yes

 

44 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.

45 TSD for the April 1 and 2, 2015 Lamar Exceptional Events, December 4, 2015, page 70.
27

NATURAL EVENT

As stated in 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 April 1st and 2nd, 2015. 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.

46

CDPHE has sufficiently demonstrated the CCR and nRCP requirements for the April 1 and 2, 

2015 events. Therefore, the EPA concludes that these were natural events pursuant to the 

Treatment of Data Influenced by the EER. Table 9 summarizes the EPA’s evaluation of 

CDPHE’s Natural Event EE demonstration.

Table 9: 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?

April 1, 

2015

nRCP- Anthropogenic Section 5: p. 45-69 Yes Yes

nRCP-Wind Speed Section 2: p. 33-38 Yes Yes

CCR Section 2: p. 33-38 Yes Yes

April 2, 

2015

nRCP- Anthropogenic Section 5: p. 45-69 Yes Yes

nRCP-Wind Speed Section 2: p. 38-43 Yes Yes

CCR Section 2: p. 38-43 Yes Yes

 

46 Ibid., 1.
28

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 and states that: 

Elevated 24-hour PM10 concentrations were recorded at the Lamar Municipal Building 

monitor on April 1st and 2nd, 2015. Both of the noted twenty-four-hour PM10

concentrations were above the 90th percentile concentrations for their locations (see 

Section 3) and exceeded the 99th percentile value of any evaluation criteria. The 

statistical and meteorological data clearly show that but for these high wind blowing dust 

events, Lamar would not have exceeded the 24-hour NAAQS on April 1st and 2nd, 2015. 

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 measured concentrations in excess of normal historical 

fluctuations including background.

47

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, 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 

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

Table 10: 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?

April 1, 2015 Section 6: p. 70 Yes Yes

April 2, 2015

Section 6: p. 70 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 

 

47 Ibid., 70.
29

the report based on internal staff review. Table 11 outlines EPA’s evaluation of these 

requirements. 

Table 11: 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) Section 1: p.5 Yes

Were flags and initial description 

placed on the data by July 1st of the 

following year?

40 CFR 

50.14(c)(2)(iii)

Flag May 22, 

2015; Initial 

Description April 

29, 2016

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 4,

2015

Yes

Was the public comment process 

followed and documented?

40 CFR 

50.14(c)(3)(v)

Section 1: p.6 Yes

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 western 

Kansas into the Lamar area on April 1 and 2, 2015. These high wind events caused exceedances

of the 24-hour PM10 NAAQS at the Lamar PM10 monitor. The EPA concurs that the flagged 

exceedances at the Lamar monitor on these days meet the definition of exceptional events: the 

events affected air quality; the events were nRCP; and the events met the definition as natural 

events. Specifically, the EPA has determined that the event was nRCP due to high wind 

conditions that transported PM10 from sources outside of the immediate Lamar area and also 

subsequently may have overwhelmed some reasonable controls within Lamar. 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 
30

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 exceedance of 253 ug/m3at the Lamar monitor on April 1, 2015 and 

419 ug/m3on April 2, 2015.

This concurrence does not constitute the EPA’s final 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 multiyear 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 

 

1 EPA Region 8 staff analysis conducted July 29, 2015; 2015 rainfall updated April 29, 

2016.

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.

y = -0.0025x + 20.23

0

5

10

15

20

25

30

1897 1917 1937 1957 1977 1997 2017 2037 Annual Precipitation, in.

Lamar Annual Precip, 1897-2015

Precip Mean Prc. Running 7 year mean Linear (Precip)

Below Average Precip,

2007-2013

1930s Dust Bowl

7 years below average

8 of 9 years below average
3

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

 

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

4

Ibid.

5 EPA Region 8 staff analysis conducted July 29, 2015; 2015 rainfall updated April 29, 

2016.

0

4

8

12

16

20

24

0

5

10

15

20

25

30

1975 1980 1985 1990 1995 2000 2005 2010 2015 Annual Precipitation, in.

Lamar Annual Precip and PM, 1975-2015

Precip Mean Prc. Running 7 year mean TSP Exceedances PM10 Exceedances 3-yr mean TSP 3-yr mean PM10

Below Average Precip,

2007-2013