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## EPA Technical Support Document in Review of Colorad o Department of Public Health and Environment’s Demonstration Packa ge for the

January 19, 2009, Lamar Exceptional Event
EXCEPTIONAL EVENTS RULE REQUIREMENTS

The Environmental Protection Agency (EPA) promulgat ed the Exceptional Events Rule (EER) in 2007, pursuant to the 2005 amendment of Clean Air Act (CA A) Section 319. 42 U.S.C. §7619. The EER added 40 CFR 50.1(j), (k) and (l); 50.14; and 51.930 to t he Code of Federal Regulations (CFR). These section s contain definitions, criteria for EPA approval, pro cedural requirements, and requirements for air agen cy 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 demons tration to justify exclusion of data must provide evidence that:

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

• The event affects air quality;

• The event is not reasonably controllable or prevent able; and

• The event is caused by human activity that is unlik ely to recur at a particular location or [is] a natural event. 1

• There is a clear causal relationship between the me asurement under consideration and the event that is claimed to have affected the air quality in the area;

• The event is associated with a measured concentrati on in excess of normal historical fluctuations, including background; and

• There would have been no exceedance or violation bu t 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 Affect ed 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 Publ ic 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 PM 10 standard that occurred at two monitoring stations i n Lamar on

1 A natural event is further described in 40 CFR 50. 1(k) as “an event in which human activity plays lit tle or no direct causal role”.2

January 19, 2009. Table 1 summarizes the exceedance s that CDPHE would like considered for exceptional event concurrence in the Air Quality Sy stem (AQS) database.

Table 1: EPA PM 10 Exceedance Summary of the 150 ug/m 3 24-hour NAAQS Exceedance Date Monitor/Site Name AQS ID 24-hour Avg. (ug/m 3 ) CDPHE

Request to Consider for AQS Removal?
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 Col orado 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 Col orado, southeastern Wyoming, and southwestern Nebraska. The areas described are shown in Figure 1

. Figure 1: Map of High Plains and Monitor Location w ith the PM 10 NAAQS Exceedances3

In its exceptional event demonstration package, CDP HE describes the January 19, 2009 event as:
the consequence of strong northerly winds in combin ation with dry soil conditions which caused significant blowing dust across the plains of easte rn Colorado, western Kansas, and western Nebraska. The winds were partly the result of a str ong pressure gradient between a 1048 millibar high pressure system over the western U.S. and a co mplex 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. W inds this strength will cause blowing dust if soils are dry. Sustained wind speeds of 30 mph or g reater and gusts of 40 mph or higher have been shown to cause blowing dust in eastern Colorad o. 3
EPA considers the event to originate from arid regi ons in Wyoming, southwest Nebraska, and northeast Colorado into the Lamar area. CDPHE provides a comp rehensive 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 affecte d air quality in this area.
EPA Figure 2 from CDPHE’s TSD 4 visually demonstrates dust plumes and their direct ion originating in southeastern Wyoming, southwestern Nebraska, and no rtheastern Colorado at 12:27 PM mountain standard time on January 19, 2009. Figures 1-18 fro m 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 Ev ent,” 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 C ontrollable 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 general ly be considered to be nRCP if winds are high enoug h5

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 c ontrols in place;

• The reasonable controls have been effectively imple mented and enforced; and,

• The wind speed was high enough to overwhelm the rea sonable controls. 5
In addressing reasonable controls, CDPHE provided d etailed 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 notifica tion activities that occurred on the event day. As CDPHE states:
The City of Lamar and Prowers County have identifie d a number of contributing dust sources that have either implemented BACM [Best Available Contro l Measures] controls or have phased-in BACM controls as economically and technically feasi ble. 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, C O, the sustained surface winds of up to 48 mph with gusts up to 56 mph were measured on Januar y 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 thres hold. And wind speeds upwind of Lamar in Akron, Burlington, and Limon, CO exceeded the established thresholds to a greater extent, helping indicate th at the winds and blowing dust originated north of the monitors. Given the wind direction evidence of Fig ure 2 above, transported dust from the upwind arid plai ns region appears to be a more significant contribu tion to the exceedances than was local winds overwhelmin g implemented local controls. EPA notes that the high local gust speeds in Lamar would likely be cap able of overwhelming some local controls. Section 5 of the TSD provided by CDPHE supports this conclusi on by describing in detail local control measures.

5 “Interim Guidance on the Preparation of Demonstrat ions in Support of Requests to Exclude Ambient Air Quality Data Affected by High Winds Under the Exceptional E vents Rule,” May 2013, page 10. 6 “TSD for the January 19, 2009, Lamar Exceptional E vent,” 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, 20 09 (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, 20 09 (CDPHE’s TSD Table 3)9

Figure 6: Wind Speed in Lamar, CO on January 19, 20 09 (CDPHE’s TSD Table 4)

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

• Statewide PM 10 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) fo recasted dust concentrations; and10

• Maps establishing the lack of regional precipitatio n 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 place 9 :

• A Natural Events Action Plan (NEAP) for High Wind E vents completed in 2003, and updated in 2012, which addresses public education, notificatio n, and health advisory systems as well as implements Best Available Control Measures (BACM) ( see Colorado Regulation 1); 10

• A PM 10 Maintenance plan for the Lamar Attainment/Maintena nce Area effective since Nov. 25, 2005 with provisions for Prevention of Significant Deterioration (PSD) permitting requiring Best Available Control Technology (BACT) (see Colorado R egulation 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 f ugitive dust (see Colorado Regulation 1);

• City of Lamar BACM measures include: planting a win d-break of trees with drip-irrigation to control dust from the Lamar Transfer Station, estab lishing 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 “Operati ons and Closure Plan for the East Lamar Landfill” section 3.5.1), among other listed landfi ll controls. 11 Other BACM include installing 100,000 square feet of turf sod and irrigation at r ecreational open space Escondido Park, and fencing off and stabilizing lots that formerly cont ributed 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 Lan d 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 Offic e efforts underway to encourage no- or low-till practices, outreach and education o n 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 street s;

o The Burlington Northern Santa Fe railroad is covere d in gravel 50 feet on either side of the tracks, surrounded by natural vegetation with x eriscape; 12

o The Limestone-Graveyard Creeks Watershed Project re duces 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 impro vements created by each farmer/owner with costs of conservation improvement s split with the government.

9 “TSD for the January 19, 2009, Lamar Exceptional E vent,” November 22, 2011, pages 27-31.
10 Available online: https://www.colorado.gov/pacific/ sites/default/files/AP_PO_Lamar-Natural-Events-Acti onPlan-NEAP_1.pdf.
11 “TSD for the January 19, 2009, Lamar Exceptional E vent,” November 22, 2011, page 27.
12 Ibid., 2811 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 mult i-party drought response effort through the State of Colorado Governor’s office; an d a program to incentivize erosion mitigation. 13

• The USDA NRCS Conservation Reserve Program (CRP) in cludes 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 conse rvation 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 t hat the dust originated in the counties surrounding Lamar. The following amounts of croplan d 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 th e USDA NRCS CRP Program 15

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 PM 10 State Implementation Plan (SIP) and Maintenance Plan for the area. 16

Sections 2 and 5 of CDPHE’s TSD show that the monit ors in Lamar were affected by PM 10 transport from outside the area, with the main source areas f rom arid regions in Wyoming, southwest Nebraska, and northeast Colorado into the Lamar area. In addi tion to transport, the wind speeds associated with the event contribute to EPA’s evaluation of whether thi s event is nRCP in Lamar. The EPA concludes that wind speeds on January 19, 2009 did exceed the blow ing dust thresholds of 30 mph or greater and gusts of 40 mph or greater at which the CDPHE expects sta ble surfaces (i.e., controlled anthropogenic and

13 Ibid., 29-31.
14 “TSD for the January 19, 2009, Lamar Exceptional Ev ent,” 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, gi ven that wind speeds were as high as 38 mph with wind gusts up to 56 mph. Subsequent to the submissi on of the demonstration for the January 19, 2009 high wind event, CDPHE submitted an evaluation of t he permitted operations north of Lamar with disturbed soils which might be subject to high wind dust generation with the demonstration for the Apr il 3, 2011 high wind exceptional event. That informati on demonstrated that reasonable controls were in place for those sources. 17 EPA considers the 2011 evaluation to be accurate f or this analysis due to the limited development in the area between 2009 and 20 11. Therefore, the EPA concludes that this event was nRCP pursuant to the Exceptional Events Rule. T able 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 e xcess 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 exclude d. 18 CDPHE states that the percentile rank for these areas is 99% and above for the two monitors in ques tion. To demonstrate that this requirement was met, CDPHE provided a statistical analysis of the 24-hou r 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 t he

17 “TSD for the April 3, 2011 Alamosa and Lamar Except ional Event,” November 20, 2013, pages 107-119.
18 See “Interim Guidance on the Preparation of Demons trations in Support of Requests to Exclude Ambient Air Quality Data Affected by High Winds Under the Excep tional Events Rule” of May 2013, page 20.13

NAAQS of 150 μ g/m 3 might be considered statistical outliers as they a re so rare as to be above the 99 th percentile. CDPHE explains that for the concentrati on 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 bet ween 30 and 33 (sic) μ g/m3 and 24 and 31
μ g/m3 (corresponding to the 75th and 84th Percentile values) for Lamar Power and Lamar Municipal Building, respectively. Using these conse rvative values as “typical” would indicate that the event provided an additional 135 – 141 μ g/m3 and 142 – 149 μ g/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 exceedin g the NAAQS are only found during high wind dust events, including January 19, 2009. This informatio n indicates that values at the level seen on Januar y 19, 2009 are extremely rare in the absence of high wind dust exceptional event impacts, and that it is unl ikely that any sources of PM 10 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 CD PHE’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 E vent,” November 22, 2011, page 22.
20 “TSD for the January 19, 2009, Lamar Exceptional Ev ent,” 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 occurr ed and that emissions related to the event were transp orted in the direction of the monitor(s) where measurements were recorded; the size of the area af fected by the transported emissions; the relationsh ip 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 meteoro logical analysis of the event, including:

• Statewide PM 10 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 precipitatio n and drought status from USDA, NOAA, and the National Drought Mitigation Center.

NAAPS forecasted dust storm concentrations contribu te to the analysis. Figure 9 shows the forecast its elf. Specifically, the
NAAPS forecast products provide an independent calc ulation of the potential for blowing dust and the spatial extent of blowing dust for this eve nt. All of the products discussed here point to a widespread, regional-scale dust storm that originat ed in areas extending far beyond the PM 10 nonattainment area boundaries for Lamar. 22

21 See “Interim Guidance on the Preparation of Demons trations in Support of Requests to Exclude Ambient Air Quality Data Affected by High Winds Under the Excep tional Events Rule” of May 2013, pages 21-22.
22 “TSD for the January 19, 2009, Lamar Exceptional Ev ent,” November 22, 2011, page 18.15

Figure 9: NAAPS Forecasted Dust Storm January 19, 2 009 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 o f 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 Col orado, southeastern Wyoming, and southwestern Nebraska; and (b) the tight surface pr essure gradient and strong upper level winds mixing to the surface that lead to strong gusty sur face winds over eastern Colorado, western Kansas, and western Nebraska. Clearly the PM10 exce edances at Lamar are due to an exceptional event associated with regional windstorm-caused emi ssions 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 windstor m under abnormally dry or moderate drought conditions. 23
CDPHE further states that “the meteorological and m onitoring data sections demonstrate that the exceptional event affected the air quality on Janua ry 19, 2009, and “but for” this regional blowing du st 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 Even ts Rule. Table 4 summarizes the EPA’s evaluation of CDPHE’s CCR EE demonstration.

23 “TSD for the January 19, 2009, Lamar Exceptional Ev ent,” November 22, 2011, page 18.
24 Ibid., 34.16

Table 4: EPA’s Analysis of CDPHE’s TSD of CCR 25 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 E xceptional 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 demonst rations on the preceding pages of this (EPA’s) TSD are cited in Table 5. Additionally, CDPHE state s that:

...the concentrations measured at both monitors excee ded the historical 99 th percentile level for these sites, and conservative estimates of the cont ribution of the dust storm to measured PM 10 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 Affect s Air Quality pursuant to the Exceptional Events Ru le. 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 Demons trations in Support of Requests to Exclude Ambient Air Quality Data Affected by High Winds Under the Excep tional Events Rule” of May 2013 page 21.
26 “TSD for the January 19, 2009, Lamar Exceptional Ev ent,” November 22, 2011, page 2.17

Natural Event
As stated in EPA’s Interim Guidance for High Wind E xceptional 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 Colo rado, western Kansas and western Nebraska. A clear causal relationship was established in Sect ion 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 o ther weather data clearly substantiate the direction of transport high wind speeds, and precon ditions 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 Eve nts Rule. Table 6 summarizes the EPA’s evaluation of CD PHE’s Natural Event EE demonstration.
Table 6: EPA’s Analysis of CDPHE’s TSD of Natural E vent 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 Ev ent,” November 22, 2011, page 34.18

No Exceedance or Violation But For the Event
Generally, the No Exceedance or Violation But for t he 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 inform ation presented in the TSD that show both the nRCP and CCR requirements have been met and states that:

The meteorological and monitoring data sections dem onstrate 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 t hat PM 10 concentrations before the periods of high winds on the event days were below the 24-hour PM 10 NAAQS, providing further support for CDPHE’s conclusion. Table 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 t o 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 EP A’s evaluation of these requirements.

28 “TSD for the January 19, 2009, Lamar Exceptional E vent,” 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 event 29 Yes

Were flags and initial description placed on the data by July 1 st of the following year? 40 CFR 50.14(c)(2)(iii) CDPHE Letter to EPA dated January 10, 2012 30 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, 2012 31 Yes



## CONCLUSION

EPA has reviewed the TSD provided by CDPHE to suppo rt claims that dust emissions generated by high winds resulted in PM 10 transport from arid regions north of Lamar in east ern Colorado, western Kansas and western Nebraska, including Wyoming, into the L amar area on January 19, 2009. This high wind event caused exceedances of the 24-hour PM 10 NAAQS at the locations identified in Table 1 of thi s 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: th e exceedances affected air quality, were nRCP, and met the definition of a natural event. Specifically, EP A has determined that the event was nRCP due to hig h wind conditions that transported PM 10 from sources outside of the Lamar areas and subsequ ently

29 According to 40 CFR 50.14(c)(1)(i): “All States and, where appli cable, their political subdivisions must notify the public promptly whenever an event occurs or is reas onably anticipated to occur which may result in the exceedance of an applicable air quality standard.” CDPHE’s Add endum to the Technical Support Document explains th at the event was not captured by real time samplers but ra ther from filter-based samplers analyzed weeks afte rward.
30 CDPHE letter accompanying TSD from Gordon E. Pierc e, Program Manager, Technical Services Program, Air Pollution Control Division to Adam Eisele of EPA da ted January 10, 2012.
31 Ibid.20

overwhelmed reasonable controls within Lamar. Also, regardless of transport into the areas, informatio n pertaining to the controls implemented within the a ffected areas, the spatial extent of elevated PM 10 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 meas ured exceedances, there would have been NEBF, and the measured exceedances are in excess of normal HF s. EPA finds that the weight of evidence is sufficient to concur on the flagged data for the 24-hour PM 10 NAAQS exceedances of 173 ug/m 3 at the Lamar Municipal Building monitor, and 174 u g/m 3 at the Lamar Power Plant monitor on January 19, 2009.

This concurrence does not constitute final EPA acti on regarding any matter on which EPA is required to provide an opportunity for public comment. In parti cular, this applies to determinations regarding the attainment status or classification of the area. Fi nal actions will take place only after EPA complete s notice and comment rulemaking on those determinatio ns.