1 

EPA Technical Support Document in Review of Colorado Department of 

Public Health and Environment’s Demonstration Package for the 

January 19, 2009, Lamar Exceptional Event 

EXCEPTIONAL EVENTS RULE REQUIREMENTS 

The Environmental Protection Agency (EPA) promulgated the Exceptional Events Rule (EER) in 2007, 

pursuant to the 2005 amendment of Clean Air Act (CAA) Section 319. 42 U.S.C. §7619. The EER added 

40 CFR 50.1(j), (k) and (l); 50.14; and 51.930 to the Code of Federal Regulations (CFR). These sections 

contain definitions, criteria for EPA approval, procedural requirements, and requirements for air agency 

demonstrations, all of which must be met before EPA can concur under the EER on the exclusion of air 

quality data from regulatory decisions. 

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

evidence that: 

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

event; 

• The event affects air quality; 

• The event is not reasonably controllable or preventable; and 

• The event is caused by human activity that is unlikely to recur at a particular location or 

[is] a natural event.1

• There is a clear causal relationship between the measurement under consideration and the event 

that is claimed to have affected the air quality in the area; 

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

including background; and 

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

This review applies the EPA’s “Interim Guidance 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, (Interim Guidance for High Wind Exceptional Events) in addition to the applicable 

statutory and regulatory provisions. 

SUMMARY 

Overview 

On January 10, 2012 the Colorado Department of Public Health and Environment (CDPHE) submitted a 

demonstration (termed a Technical Support Document or TSD) dated November 22, 2011 for exceptional 

event exceedances of the 24-hour PM10 standard that occurred at two monitoring stations in Lamar on 

 

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 

January 19, 2009. Table 1 summarizes the exceedances 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?

January 19, 

2009 

Lamar Municipal Building 08-099-0002 173 Yes 

Lamar Power Plant 08-099-0001 174 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. North of 

Lamar is the arid high plains region of eastern Colorado, southeastern Wyoming, and southwestern 

Nebraska. The areas described are shown in Figure 1. 

Figure 1: Map of High Plains and Monitor Location with the PM10 NAAQS Exceedances 
3 

In its exceptional event demonstration package, CDPHE describes the January 19, 2009 event as: 

the consequence of strong northerly winds in combination with dry soil conditions which caused 

significant blowing dust across the plains of eastern Colorado, western Kansas, and western 

Nebraska. The winds were partly the result of a strong pressure gradient between a 1048 millibar 

high pressure system over the western U.S. and a complex series of low pressure systems over the 

eastern U.S.2 

The combination of the mixing and the tight surface pressure gradient caused sustained surface 

winds of 30 to 40 mph with gusts of 35 to 60 mph. Winds this strength will cause blowing dust if 

soils are dry. Sustained wind speeds of 30 mph or greater and gusts of 40 mph or higher have 

been shown to cause blowing dust in eastern Colorado.3

 

EPA considers the event to originate from arid regions in Wyoming, southwest Nebraska, and northeast 

Colorado into the Lamar area. CDPHE provides a comprehensive description and discussion of this event 

in Sections 2, 3, 4, and 5 of the TSD. As visually demonstrated by the image of dust plumes in Figure 2, 

the high wind event caused dust to blow and affected air quality in this area. 

EPA Figure 2 from CDPHE’s TSD4

 visually demonstrates dust plumes and their direction originating in 

southeastern Wyoming, southwestern Nebraska, and northeastern Colorado at 12:27 PM mountain 

standard time on January 19, 2009. Figures 1-18 from CDPHE’s TSD use modeling, meteorology, and 

monitoring analysis to support the evidence of wind direction and reach of the dust storm into Lamar. 

 

2

“TSD for the January 19, 2009, Lamar Exceptional Event,” November 22, 2011, page 3.

3

 Ibid., 3. 

4

 Ibid., 16. 
4 

Figure 2: Satellite image of Dust Plumes on January 19, 2009 (CDPHE’s TSD Figure 16 a & b) 

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 
5 

to cause emissions from natural undisturbed areas. For anthropogenic sources of dust, a high wind dust 

event can be nRCP if: 

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

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

• The wind speed was high enough to overwhelm the reasonable controls.5

 

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 local ordinances,

rule effectiveness, compliance, and public notification activities that occurred on the event day. As

CDPHE states: 

The City of Lamar and Prowers County have identified a number of contributing dust sources that 

have either implemented BACM [Best Available Control Measures] controls or have phased-in 

BACM controls as economically and technically feasible.6

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

associated with these events were above 30 mph and gusts were above 40 mph (CDPHE tables 1, 2, 3, 

and 4)7

. For example, 175 miles north of Lamar in Akron, CO, the sustained surface winds of up to 48 

mph with gusts up to 56 mph were measured on January 19, 2009, while Lamar saw sustained surface 

wind speeds of up to 36 mph and gusts up to 45 mph. CDPHE established that wind speeds of 30 mph 

and/or gusts of 40 mph or higher have been shown to cause blowing dust in Colorado in a climatological

study of blowing dust in eastern Colorado (attached as appendix A of CDPHE’s TSD).8

 The sustained 

winds and gusts in Lamar exceed this Colorado threshold. And wind speeds upwind of Lamar in Akron, 

Burlington, and Limon, CO exceeded the established thresholds to a greater extent, helping indicate that 

the winds and blowing dust originated north of the monitors. Given the wind direction evidence of Figure 

2 above, transported dust from the upwind arid plains region appears to be a more significant contribution 

to the exceedances than was 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 local control measures. 

 

5

 “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. 

6

 “TSD for the January 19, 2009, Lamar Exceptional Event,” November 22, 2011, page 27. 

7

 Ibid., 12-15. 

8

Ibid., Attachment A, “Lamar, Colorado Blowing Dust Climatology,” March 10, 2010, pages 37-82. 
6 

Figure 3: Wind Speed in Akron, CO on January 19, 2009 (CDPHE’s TSD Table 1) 
7 

Figure 4: Wind Speed Burlington, CO on January 19, 2009 (CDPHE’s TSD Table 2) 
8 

Figure 5: Wind Speed in Limon, CO on January 19, 2009 (CDPHE’s TSD Table 3) 
9 

Figure 6: Wind Speed in Lamar, CO on January 19, 2009 (CDPHE’s TSD Table 4) 

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

• Statewide PM10 monitoring maps; 

• Surface and upper air wind speed analysis National Weather Service; 

• Sounding analysis from the National Weather Service; 

• MODIS satellite images of blowing dust; 

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

• NOAA HYSPLIT modeling of wind trajectories; 

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

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

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

These analyses demonstrate persuasively through the weight of evidence the existence of a high wind 

blowing dust event originating far northwest of the monitor in Lamar. 

Lamar has the following controls in place9: 

• 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) (see Colorado Regulation 1);10

 

• 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) (see Colorado Regulation 3); 

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

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

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

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

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

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.11 Other BACM include installing 

100,000 square feet of turf sod and irrigation at recreational open space Escondido Park, and 

fencing off and stabilizing lots that formerly contributed to fugitive dust (see Colorado 

Regulation 1); 

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

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

2006 (see Colorado Regulation 1); 

• Non-enforceable measures include: 

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

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

drought workshops to protect topsoil. 

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

requirement that new developments have paved streets; 

o The Burlington Northern Santa Fe railroad is covered in gravel 50 feet on either side of 

the tracks, surrounded by natural vegetation with xeriscape;12

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

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

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

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

 

9

 “TSD for the January 19, 2009, Lamar Exceptional Event,” November 22, 2011, pages 27-31. 

10 Available online: https://www.colorado.gov/pacific/sites/default/files/AP_PO_Lamar-Natural-Events-ActionPlan-NEAP_1.pdf. 

11 “TSD for the January 19, 2009, Lamar Exceptional Event,” November 22, 2011, page 27. 

12 Ibid., 28
11 

o The United States Department of Agriculture (USDA) Natural Resources Conservation 

Service (NRCS) is promoting: a rangeland management program; a tree planting 

program, a drip irrigation purchase program; a multi-party drought response effort 

through the State of Colorado Governor’s office; and a program to incentivize erosion 

mitigation.13

• The 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 

environmentally-sensitive land into long-term conservation practices for 10-15 years”14 in 

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

mitigation strategy further supports the existence of reasonable controls in the surrounding 

agricultural areas, especially due to the finding that the dust originated in the counties 

surrounding Lamar. The following amounts of cropland were under contract in surrounding 

counties. Kiowa, Cheyenne and Lincoln counties were upwind of Lamar on January 19, 2009. 

Figure 7: Acres by County near Lamar Enrolled in the USDA NRCS CRP Program15 

2007 2008 2009 2010 2011 

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

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

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

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

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

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

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

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

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

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

According to CDPHE’s TSD: 

Blowing dust sources within the NAA [Non-Attainment Area] and Prowers County have been 

reasonably controlled, as demonstrated by the PM10 State Implementation Plan (SIP) and 

Maintenance Plan for the area.16

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

from outside the area, with the main source areas from arid regions in Wyoming, southwest Nebraska, 

and northeast Colorado into the Lamar area. In addition to transport, the wind speeds associated with the 

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

wind speeds on January 19, 2009 did exceed the blowing dust thresholds of 30 mph or greater and gusts 

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

 

13 Ibid., 29-31.

14 “TSD for the January 19, 2009, Lamar Exceptional Event,” November 22, 2011, page 29. 

15 Data for the USDA NRCS CRP program were provided as supplementary information per EPA request on April

17, 2014 by Ray Mohr of CDPHE. 

16 Ibid., 34.
12 

undisturbed natural surfaces) to be overwhelmed, given that wind speeds were as high as 38 mph with 

wind gusts up to 56 mph. Subsequent to the submission of the demonstration for the January 19, 2009 

high wind event, CDPHE submitted an evaluation of the permitted operations north of Lamar with 

disturbed soils which might be subject to high wind dust generation with the demonstration for the April 

3, 2011 high wind exceptional event. That information demonstrated that reasonable controls were in 

place for those sources.17 EPA considers the 2011 evaluation to be accurate for this analysis due to the 

limited development in the area between 2009 and 2011. Therefore, the EPA concludes that this event 

was nRCP pursuant to the Exceptional Events Rule. Table 2 summarizes the EPA’s evaluation of 

CDPHE’s nRCP EE demonstration. 

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

Exceedance 

Date 

Location Reasonable 

Controls TSD 

Citation

Wind Speed 

TSD Citation

Sufficient 

Quality of 

Evidence?

EPA 

Criterion 

Met?

January 19, 

2009 

Lamar 

Municipal 

Building 

Section 5: p. 27-31 

& 

“TSD for the April 

3, 2011 Alamosa 

and Lamar 

Exceptional Event,” 

November 20, 2013, 

pages 107-119. 

Section 2: p.3-

18, esp. p.15 

Yes Yes 

Lamar Power 

Plant 

Section 5: p. 27-31 

& 

“TSD for the April 

3, 2011 Alamosa 

and Lamar 

Exceptional Event,” 

November 20, 2013, 

pages 107-119. 

Section 2: p.3-

18, esp. p.15 

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. 

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

percentile ranks when dust impacted data is excluded.18 CDPHE states that the percentile rank for these 

areas is 99% and above for the two monitors in question. To demonstrate that this requirement was met,

CDPHE provided a statistical analysis of the 24-hour average data, 18-year monthly percentile and box 

plots of 24-hour and monthly averages for the years of 1992-2010 showing that all readings exceeding the 

 

17 “TSD for the April 3, 2011 Alamosa and Lamar Exceptional Event,” November 20, 2013, pages 107-119. 

18 See “Interim Guidance on the Preparation of Demonstrations in Support of Requests to Exclude Ambient Air 

Quality Data Affected by High Winds Under the Exceptional Events Rule” of May 2013, page 20. 
13 

NAAQS of 150 μg/m3 might be considered statistical outliers as they are so rare as to be above the 99th

percentile. CDPHE explains that for the concentration measured on January 19, 2009: 

An estimation of PM10 due to the event is presented here and in Table 7. Based on the entirety of 

data in the Historical Summary (including multiple high wind events), a conservative estimate of 

the “typical” values in January would have been between 30 and 33(sic) μg/m3 and 24 and 31 

μg/m3 (corresponding to the 75th and 84th Percentile values) for Lamar Power and Lamar 

Municipal Building, respectively. Using these conservative values as “typical” would indicate 

that the event provided an additional 135 – 141 μg/m3 and 142 – 149 μg/m3 for Lamar Power 

Plant and Lamar Municipal Building, respectively.19 

See Figure 8 below for descriptive statistics. 

Figure 8: Statistical Analysis (CDPHE’s TSD Table 6)

20

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

events, including January 19, 2009. This information indicates that values at the level seen on January 19, 

2009 are extremely rare in the absence of high wind dust exceptional event impacts, and that it is unlikely 

that any sources of PM10 were involved in the January 19, 2009 exceedances other than wind-blown dust. 

Therefore, the EPA concludes that this event was in excess of HF pursuant to the Exceptional Events 

Rule. Table 3 summarizes the EPA’s evaluation of CDPHE’s HF EE demonstration. 

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

Exceedance 

Date 

Exceedance 

Location 

Historical Fluctuations 

TSD Citation 

Sufficient 

Quality of 

Evidence? 

EPA Criterion 

Met? 

January 19, 

2009 

Lamar Municipal 

Building 

Section 3: p.19-23 Yes Yes 

Lamar Power Plant Section 3: p.19-23 Yes Yes 

 

19 “TSD for the January 19, 2009, Lamar Exceptional Event,” November 22, 2011, page 22. 

20 “TSD for the January 19, 2009, Lamar Exceptional Event,” November 22, 2011, page 20.
14 

Clear Causal Relationship 

EPA considers a variety of evidence when evaluating whether there is a Clear Causal Relationship (CCR)

between the measurement under consideration and the event that is claimed to have affected the air 

quality in the area. Demonstrations should include documentation showing that the event in fact occurred 

and that emissions related to the event were transported in the direction of the monitor(s) where 

measurements were recorded; the size of the area affected by the transported emissions; the relationship 

in time between the event, transport of emissions, and recorded concentrations; and, as appropriate, 

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

concentration.21

 

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

• Statewide PM10 monitoring maps; 

• Surface and upper air wind speed analysis National Weather Service; 

• Sounding analysis from the National Weather Service; 

• MODIS satellite images of blowing dust; 

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

• NOAA HYSPLIT modeling of wind trajectories; 

• NAAPS forecasted dust concentrations; and 

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

the National Drought Mitigation Center. 

NAAPS forecasted dust storm concentrations contribute to the analysis. Figure 9 shows the forecast itself. 

Specifically, the 

NAAPS forecast products provide an independent calculation of the potential for blowing dust 

and the spatial extent of blowing dust for this event. All of the products discussed here point to a 

widespread, regional-scale dust storm that originated in areas extending far beyond the PM10 

nonattainment area boundaries for Lamar.22

 

21 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. 

22 “TSD for the January 19, 2009, Lamar Exceptional Event,” November 22, 2011, page 18.
15 

Figure 9: NAAPS Forecasted Dust Storm January 19, 2009 11 am to 6 pm (CDPHE’s TSD Figure 18) 

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

the monitors in question. 

CDPHE generally summarizes that: 

The PM10 exceedances at Lamar on January 19, 2009, would not have occurred if not for the 

following: (a) dry soil conditions over eastern Colorado, southeastern Wyoming, and 

southwestern Nebraska; and (b) the tight surface pressure gradient and strong upper level winds 

mixing to the surface that lead to strong gusty surface winds over eastern Colorado, western 

Kansas, and western Nebraska. Clearly the PM10 exceedances at Lamar are due to an exceptional 

event associated with regional windstorm-caused emissions from erodible soil sources over a 

large area of eastern Colorado and western Nebraska, and these sources are not reasonably 

controllable during a significant regional windstorm under abnormally dry or moderate drought 

conditions.23

CDPHE further states that “the meteorological and monitoring data sections demonstrate that the 

exceptional event affected the air quality on January 19, 2009, and “but for” this regional blowing dust 

storm Lamar would not have exceeded the NAAQS”.24 Therefore, the EPA concludes that there was a 

CCR for this event pursuant to the Exceptional Events Rule. Table 4 summarizes the EPA’s evaluation of

CDPHE’s CCR EE demonstration. 

 

23 “TSD for the January 19, 2009, Lamar Exceptional Event,” November 22, 2011, page 18.

24 Ibid., 34. 
16 

Table 4: EPA’s Analysis of CDPHE’s TSD of CCR25

Clear Causal Relationship TSD Citation Sufficient Quality of 

Evidence? 

EPA Criterion 

Met? 

Section 2: p.3-18, Figures 1-18 Yes Yes 

Section 2: p.3, 12-15, Tables 1-4 Yes Yes 

Section 4: p.79-87 Yes Yes 

Affects Air Quality (AAQ) 

As stated in EPA’s Interim Guidance for High Wind Exceptional Events Section 3.4, EPA will consider 

events to have affected air quality if the CCR and HF requirements have been adequately demonstrated. 

The information presented in the HF and CCR demonstrations on the preceding pages of this (EPA’s) 

TSD are cited in Table 5. Additionally, CDPHE states that: 

...the concentrations measured at both monitors exceeded the historical 99th percentile level for 

these sites, and conservative estimates of the contribution of the dust storm to measured PM10 

generally exceed 80% of the total. But for the high winds over dry soils, these measured 

exceedances would not have occurred.26

Therefore, the EPA concludes that this event Affects Air Quality pursuant to the Exceptional Events Rule. 

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

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

HF and 

CCR 

Exceedance Location Affects Air Quality TSD 

Citation 

Sufficient 

Quality of 

Evidence 

EPA 

Criterion 

Met? 

HF Lamar Municipal 

Building 

Section 3: p.19-23 Yes Yes

Lamar Power Plant Section 3: p.19-23 Yes Yes 

CCR Both Monitoring Sites 

Section 2: p.3-18, Figures 1-

18 

Yes Yes 

Section 2: p.3, 12-15, Tables 

1-4 

Yes Yes 

Section 4: p.79-87 Yes Yes 

 

25 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. 

26 “TSD for the January 19, 2009, Lamar Exceptional Event,” November 22, 2011, page 2.
17 

Natural Event 

As stated in EPA’s Interim Guidance for High Wind Exceptional Events Section 6.3.6, EPA will consider 

an event to be a natural event if both the nRCP and CCR requirements have been adequately 

demonstrated. CDPHE states that, 

The [CDPHE] APCD has clearly shown in this analysis that the exceedance concentrations in 

Lamar on January 19, 2009 were caused by a regional dust storm that brought dust in from the 

source areas located north of Lamar in eastern Colorado, western Kansas and western Nebraska. 

A clear causal relationship was established in Section 2, Meteorological Analysis of the January 

19, 2009, Blowing Dust Event. Satellite images show the blowing dust from the source areas, soil 

moisture analyses, a back trajectory analysis and other weather data clearly substantiate the 

direction of transport high wind speeds, and preconditions necessary for a regional dust storm.27

While generally agreeing with CDPHE’s analysis, EPA considers the event to originate from arid regions

north of Lamar in eastern Colorado, western Kansas and western Nebraska, including Wyoming, into the 

Lamar area. CDPHE has sufficiently demonstrated the CCR and nRCP requirements for the January 19, 

2009 event. Therefore, the EPA concludes that this was a natural event pursuant to the Exceptional Events 

Rule. Table 6 summarizes the EPA’s evaluation of CDPHE’s Natural Event EE demonstration. 

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

nRCP or CCR Exceedance 

Location 

Natural Event TSD 

Citation 

Sufficient 

Quality of 

Evidence? 

EPA 

Criterion 

Met? 

nRCPAnthropogenic Lamar Municipal 

Building 

Section 5: p. 27-31 Yes Yes 

Lamar Power 

Plant 

Section 5: p. 27-31 Yes Yes 

nRCP-Wind Speed LamarMunicipal 

Building 

Section 2: p.3-18, esp. 

p.15 

Yes Yes 

Lamar Power 

Plant 

Section 2: p.3-18, esp. 

p.15 

Yes Yes 

CCR Both Monitoring 

Sites 

Section 2: p.3-18, 

Figures 1-18 

Yes Yes 

Section 2: p.3, 12-15, 

Tables 1-4 

Yes Yes 

Section 4: p.79-87 Yes Yes 

 

27 “TSD for the January 19, 2009, Lamar Exceptional Event,” November 22, 2011, page 34.
18 

No Exceedance or Violation But For the Event 

Generally, the No Exceedance or Violation But for the Event (NEBF) demonstration is similar to the 

demonstration of the nRCP and CCR requirements, and should show that the measured concentration 

would have been below the applicable NAAQS without the affect of the event. 

CDPHE provides a summary of the analysis and information presented in the TSD that show both the 

nRCP and CCR requirements have been met and states that: 

The meteorological and monitoring data sections demonstrate that the exceptional event affected 

the air quality on January 19, 2009, and “but for” this regional blowing dust storm Lamar would 

not have exceeded the NAAQS.28 

Therefore, the EPA concludes that there would have been NEBF pursuant to the Exceptional Events Rule. 

While not explicitly stated in the TSD, EPA notes that PM10 concentrations before the periods of high 

winds on the event days were below the 24-hour PM10 NAAQS, providing further support for CDPHE’s 

conclusion. Table 7 summarizes the EPA’s evaluation of CDPHE’s NEBF EE demonstration. 

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

Exceedance Date No Exceedance But For the 

Event TSD Citation 

Sufficient Quality 

of Evidence? 

EPA Criterion 

Met? 

January 19, 2009 Section 7: p.34-35 Yes Yes 

Schedule and Procedural Requirements 

In addition to technical demonstration requirements, 40 CFR 50.14(c) specifies the schedule and 

procedural requirements an air agency must follow to request data exclusion. CDPHE received no 

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

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

 

28 “TSD for the January 19, 2009, Lamar Exceptional Event,” November 22, 2011, page 34. 
19 

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

Reference Schedules and 

Procedural 

Criteria 

Demonstration 

Citation

EPA 

Criterion 

Met?

Did the State provide prompt public 

notification of the event?

40 CFR 50.14(c)(1)(i) No real-time 

samplers were in 

use at the time of 

this event29

Yes

Were flags and initial description 

placed on the data by July 1st of the 

following year?

40 CFR 50.14(c)(2)(iii) CDPHE Letter to 

EPA dated January 

10, 201230

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) January 10, 2012 Yes

Was the public comment process 

followed and documented?

40 CFR 50.14(c)(3)(v) CDPHE Letter to 

EPA dated January 

10, 201231

Yes

CONCLUSION 

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

winds resulted in PM10 transport from arid regions north of Lamar in eastern Colorado, western Kansas 

and western Nebraska, including Wyoming, into the Lamar area on January 19, 2009. This high wind 

event caused exceedances of the 24-hour PM10 NAAQS at the locations identified in Table 1 of this 

document on January 19, 2009. EPA concurs that the flagged exceedances at the Lamar monitors on this 

day meet the definition of an exceptional event: the exceedances affected air quality, were nRCP, and met 

the definition of a natural event. Specifically, EPA has determined that the event was nRCP due to high 

wind conditions that transported PM10 from sources outside of the Lamar areas and subsequently 

 

29 According to 40 CFR 50.14(c)(1)(i): “All States and, where applicable, their political subdivisions must notify the

public promptly whenever an event occurs or is reasonably anticipated to occur which may result in the exceedance 

of an applicable air quality standard.” CDPHE’s Addendum to the Technical Support Document explains that the 

event was not captured by real time samplers but rather from filter-based samplers analyzed weeks afterward. 

30 CDPHE letter accompanying TSD from Gordon E. Pierce, Program Manager, Technical Services Program, Air

Pollution Control Division to Adam Eisele of EPA dated January 10, 2012. 

31 Ibid. 
20 

overwhelmed reasonable controls within Lamar. Also, regardless of transport into the areas, information 

pertaining to the controls implemented within the affected areas, the spatial extent of elevated PM10 

concentrations measured in the areas, and the wind speeds associated with the high wind dust event 

provide sufficient evidence to conclude that these events were nRCP. Furthermore, EPA has determined 

that there is a CCR between the events and the measured exceedances, there would have been NEBF, and 

the measured exceedances are in excess of normal HFs. 

EPA finds that the weight of evidence is sufficient to concur on the flagged data for the 24-hour PM10

NAAQS exceedances of 173 ug/m3 at the Lamar Municipal Building monitor, and 174 ug/m3 at the Lamar 

Power Plant monitor on January 19, 2009. 

This concurrence does not constitute final EPA action regarding any matter on which EPA is required to

provide an opportunity for public comment. In particular, this applies to determinations regarding the

attainment status or classification of the area. Final actions will take place only after EPA completes 

notice and comment rulemaking on those determinations.