1



## EPA Technical Support Document i n Review of Colorado Department of Public Health and Environment’s Demonstration Package for the May 22 & 23 , 2010 Alamosa, Pagosa Springs, and Grand Junction

Exceptional Event s
EXCEPTIONAL EVENTS RULE REQUIREMENTS

The Environmental Protection Agency ( EPA ) promulgated the Exceptional Events Rule 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 R egulations (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 measureme nt 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 exceed ance 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, (Int erim Guidance for High Wind Exceptional Events) in addition to the applicable statutory and regulatory provisions.



## SUMMARY

Overview

On June 28, 2013, Colorado Department of Public Health and Environment ( CDPHE ) submitted a Technical Support Document (TSD) dated May 20, 2013, of exceptional events demonstrations for five exceedances of the 24

- hour PM 10 standard that occurred at several monitoring stations in southwestern

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

Colorado on May 22 and 23 , 2010. Table 1 summarizes t he exceedances that CDPHE would like considered for removal from the Air Quality System ( 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? May 22 , 2010 Alamosa

- Adams State College 08

- 003

- 0001 260 Yes

Alamosa Municipal Building 08

- 003

- 0003 194 Yes Pagosa Springs School 08

- 007

- 0001 187 Yes May 23 , 2010 Grand Junction

- Clifton

Sanitation Building 08

- 077

- 0019 189 Yes

Grand Junction

- Mesa County Powell Building 08

- 077

- 0017 155 Yes

Alamosa, Colorado lies in the broad, flat, high elevation San Luis Valley of the upper Rio Grande River. Alamosa is at an elevation of 7

, 600 feet, and is between the South San Juan and Sangre de Cristo Mountain ranges. Alamosa is generally surrounded by agricultural lands within the San Luis Valley. Pagosa Springs lies along the San Juan River, to the west and south of the San Juan Mounta ins. Grand Junction is located on the northeastern corner of the high desert Colorado Plateau. It is situated where the Gunnison River meets the Colorado River at an elevation of 4,579 feet , and at the midpoint of the 30 mile long and 5 mile wide Grand Val ley

. To the southwest of Pagosa Springs , Alamosa, and Grand Junction are the deserts of the New Mexico, Utah, and Arizona Four Corners region. The areas described are shown in Figure 1.3

Figure 1: Map of Desert, Four Corners, and Monitor Locations with PM 10 NAAQS Exceedances

In its exceptional event demonstration package CDPHE describes the May 22 and 23 , 2010 event as:

the consequence of strong southwesterly prefrontal winds beginning on May 22 and extending through May 23 in combination with dry conditions which caused significant blowing dust across much of Arizona, northwest New Mexico, southeast Utah and southwest Colorado. These winds were the result of a strong short wave in the upper atmosphere that was moving across the Great Basin and the associated surface cold front and low pressure system. This storm system transported PM 10 dust into the southwestern portions of Colorado. 2

CDPHE provides a comprehensive description and discussion of this overnight event in Sections 2, 3, 4, 5, and 6 of the demonstration. As noted below, the high wind event caus ed dust to blow and affected air quality in this area.

2 “ TSD for the May 22 and 23, 2010, Alamosa, Pagosa Springs, and Grand Junction Exceptional Event,” May 20, 2013, pages 2

- 3.4

EPA Figures 2 and 3 from CDPHE’s demonstration 3 visually demonstrates wind speed and direction of blowing dust a cross northeastern Arizona, southeastern Utah, and northwestern New Mexico into

sou theastern Colorado. Figures 1

- 36 from CDPHE’s demonstration use modeling, meteorology, and monitoring analysis to support the evidence of wind direction and reach of the dus t storm into Alamosa, Pagosa Springs, and Grand Junction.

Figure 2: Map of Wind Speed on May 22 , 2010 (CDPHE’s Figure 8 in the State’s Demonstration)

3 Ibid., 17 an d 21.5

Figure 3: Map of Wind Speed on May 23 , 2010 (CDPHE’s Figure 14 in the State’s Demonstration)

Not Reasonably Controllable or Preventable

EPA evaluates whether an event was n ot 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 h ave reasonable controls in place; The reasonable controls have been effectively implemented and enforced; and, The wind speed was high enough to overwhelm the reasonable controls. 4

In addressing reasonable controls, CDPHE provided detailed information on the current set of required and voluntary controls in the Alamosa, Pagosa Springs, and Grand Junction areas, including information on implementation of State Regulations 1, 3, 6, and 9, rule effectiveness, compliance, and public notification activities tha t occurred on the event day. As CDPHE states, they :

4 “Interim Guidance on the Preparation of Demonstrations in Support of Requests to Exclude Ambient Air Quality Data Affected by High Winds Under the Exceptional Events Rule,” May 2013, page 10.6

conducted thorough analyses and outreach with local governments to confirm that no unusual anthropogenic PM 10 - producing activities occurred in these towns and that despite reasonable control measures i n place, high wind conditions overwhelmed all reasonably available controls. 5

Section 5 of CDPHE’s documentation provides a thorough analysis of the s tate and local controls in place to control PM 10 emissions . 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 6

- Standards of Performance for New Stationary Sources ; and Regulat ion 9

- Open Burning, Prescribed Fire, and Permitting applied to both Pagosa Springs and Alamosa. 6

CDPHE provided the documentation listed in Figures 4 , 5, and 6 showing that sustained wind speeds associated with these events were above 25 mph (CDPHE tables 14, 15, and 21 ) 7 . For example, in Alamosa sus tained surface winds of up to 41 mph with gusts up to 56 mph were measured on May 22, 2010 , while Pagosa Springs saw gusts up to 44 mph. On May 23, 2010 Grand Junction experienced sustained winds up to 31 mph a nd gusts up to 43 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 (att ached as appendix A of CDPHE’s analysis). The wind speeds on May 22 and 23 , 2010 clearly exceed the established high

- wind threshold

. 8

5 “ TSD for the May 22 and 23, 2010, Alamosa, Pagosa Spr ings, and Grand Junction Exceptional Event,” May 20, 2013, page 103.
6 Ibid., 103

- 104.
7 Ibid., 42, 43, and 49.
8 Page 3 of EPA’s Interim Guidance for High Wind Events recommends air agencies establish wind thresholds based on local conditions above which reasonable dust controls might be overwhelmed and natural dust sources would be active. Had Colorado not been able to establish these thresholds at sustained winds of 30 mph and gusts of 40 mph, EPA would have accepted a threshold of 25 mph with evidence t hat it was an appropriate wind level. EPA has not established 25 mph as a bright line threshold for high wind events.7

Figure 4: Wind Speed in Alamosa

, CO on May 22 , 2010 (CDPHE’s Table 14 in the State’s Demonstration)8

Figure 5 : Wind Speed in Pagosa Springs

, CO on May 22 , 2010 (CDPHE’s Table 15 in the State’s Demonstration) 9

9 Local wind speeds were above the gust threshold of 40 mph defined for Colorado for only one hour in Pagosa Springs on May 22. Visibility degradation and reports of haze during other hours were highlighted by Colorado in the demonstration, and may be indicative of dust blowing into Pagosa Springs from desert areas upwind with higher wind speeds. MesoWest data show winds at Winslow, AZ first exceeding 30 mph, for example, between 10:56 and 11:56 am, MST.9

Figure 6 : Wind Speed in Grand Junction

, CO on May 23 , 2010 (CDPHE’s Table 21 in the State’s Demonstration) 10

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

S tatewide PM 10 monitoring maps ; S urface and upper air wind speed analysis from the National Oceanic and Atmospheric Administration (NOAA) ;

10 Colorado highlighted both hours where local winds were above the Colorado wind threshold of 30 mph sustained or 40 mph gusts, as well as periods with reported haze or limited visibility. The fact that poorest visibility is not coincident with peak local winds is supportive evidence for remote rather than local dust sources having significant impact. In evaluating nRCP, however, exceedance level PM at wind speeds lower than those expected to overwhelm implemented reasonable controls can be evidence of ineffective implementation or enforcement. The need for implementation evidence is discussed later in this TSD.10

M aps of real

- time weather data from the National Center for Atmospheric Research (NCAR) ; R egional wind and weather by hour through MesoWest ; NOAA HYSPLIT modeling of wind trajectories ; Naval Advanced Aerosol Prediction System (NAAPS) forecasted dust concentrations; MODIS Terra satellite image s demonstrating the blowing dust across the region ; GOES

- 11 L ongwave Infrared Difference images;
M aps establishing the lack of regional precipitation and drought status from U.S. Department of Agriculture (USDA)

, NOAA, and the National Drought Mitigation Center ; and
M aps of elevated friction velocities in the region from the NOAA National Centers for Environmental Prediction (NCEP) North American Model.

These analyses demonstrate persuasively through the weight of evidence the existence of a high wind b lowing dust event originating far southwest of the monitors in question.

Section 5 of CDPHE’s documentation provides a thorough analysis of the s tate and local controls in place to control PM 10 emissions . These controls include CDPHE’s Regulations 1, 3, 6 , and 9. 11

Alamosa has the following controls in place:

Natural Events Action Plan (NEAP) 12 for high wind events , completed in May 2003, which addresses public health programs, public notification, and implements Best Available Control Measures (BACM). CDPHE ensured in 2007 and 2013 that the NEAP was implemented satisfactorily ; 13 City Code of Ordinances Article VII of Section 21

- 140(5) which addresses dust control at homes ; Article V Sec. 17

- 87(3) requires pavement of new roads/alleys ; and
Article VI Sec. 21

- 119(3) requires new commercial establishments to install underground irrigation. 14

In addition, Alamosa conducts street sweeping, has irrigated and installed vegetative cover on all city parks, encourages low tilling and other soil conservation practic es outside of town through the Colorado State University Co

- Op Extension Office and the Natural Resources Conservation Service. Since 2008 t he
Mosca

- Hooper Conservation District has been working with the Natural Resources Conservation Service to implement the Colorado State Forest Service’s program to plant between 2,805 and 7,432 trees per year to prevent wind erosion in the area. 15

11 “ TSD for the May 22 and 23, 2010, Alamosa, Pagosa Springs, and Grand Juncti on Exceptional Event,” May 20, 2013, pages 103

- 104.
12 Ibid., Appendix C.
13 “EPA’s Natural Events Policy guidance requires the state to periodically reevaluate: 1) the conditions causing violations of the PM 10 NAAQS in the area, 2) the status of implementation of the NEAP, and 3) the adequacy of the actions being implemented. The State will reevaluate the NEAP for Alamosa at a minimum of every 5 years and make appropriate changes to the plan accordingly.” TSD f or the April 28 & 29, 2010, Alamosa, Pagosa Springs, and Durango Exceptional Event, May 17, 2013, Appendix C, page 18.
14 “ TSD for the May 22 and 23, 2010, Alamosa, Pagosa Springs, and Grand Junction Exceptional Event,” May 20, 2013, page 105.
15 Ibid., 107

.11

Maps are included of eight undeveloped parcels of land in town that were determined to be reasonably controlled or considered natural sources. All eight are covered with vegetation and five of those eight are confirmed to be irrigated. The three remaining sites in F igure 7 (Sites B, E, and H) are naturally vegetated and satellite images show minimal soil disturbance. 16

Figure 7 : Alamosa Site Assessment (CDPHE’s Figure 47 in the State’s Demonstration)

Pagosa Springs local controls include:

Land Use Development Code 6.6.3(h) and 6.6.3(m)(i) requiring paved streets, street sanding and sweeping/cleaning controls, encourages businesses to maintain cleanliness of private lots ; 17 EPA approved PM 10 Maintenance Plan for the Pagosa Springs Attainment/Maintenance Area, effective on August 14, 2001, requiring Prevention of Significant Deterioration (PSD) permitting requirements mandat ing Best Available Control Technology (BACT) at sources potentially emitting PM 10 ; and Vegetation, irrigation, fencing, and stabilized clay dust control measures are in place for undeveloped parcels of land in town. Figure 8 shows that identified areas o f soil disturbance have reasonable controls. For example, Site A was seeded in 2006 and has since been covered by vegetation. Site B was the recent construction of the Springs Resort and Spa and was completed in May 2009 and therefore couldn’t have impacte d the May 11, 2010 event. Site C was naturally vegetated and receives groundwater from a nearby stream; 18 it is also an area where off

- road

16 Ibid., 108

- 110.
17 Ibid., 113

- 117.
18 Colorado State Reg. 1 Section III.D.2.b considers natural vegetation with regular groundwater availability due to low lying terrain to be the appropriate available and practical method that is technologically feasibl e and economically reasonable in order to minimize fugitive particulate emissions for this lot at this time.12

recreational vehicles are prohibited by the parks department. Site D is an irrigated and maintained turf and stabiliz ed clay baseball field since April 2009. 19

Figure 8 : Pagosa Springs Site Assessment (CDPHE’s Figure 49 in the State’s Demonstration)

On March 16, 2000, CDPHE’s State Implementation Plan (SIP) was revised and amended to designate Pagosa Springs as a PM

- 1 0 attainment area with the effect of deleting road paving requirements, street sanding reporting requirements, and any other “unnecessary mandatory contingency measures in the [Telluride] 20 and Pagosa Springs areas. No additional control measures are needed in these areas to demonstrat e long

- term maintenance of the PM

- 10 NAAQS”. 21 The dust control strategies described in bullet three for Pagosa Springs local controls are voluntary measures and are not intended to be federally enforceable elements of the SIP or maintenance plan.

15 “ TSD for the May 22 and 23, 2010, Alamosa, Pagosa Springs, and Grand Junction Exceptional Event,” May 20, 2013, pages 115

- 117.
20 Telluride is not under consideration for this Exceptional Event documentation but was considered along with Pagosa Springs when removing the nonattainment designation on March 16, 2000

. 21 State Implementation Plan, Colorado Dept. of Public Health and Environment, Regulati on: Nonattainment

Attainment/Maintenance Areas, Rule #1, Rule Title: Pagosa Springs Attainment/Maintenance Area, Notice of Final Rule date 6/15/2001, 66 FR 32556.13

Grand Junction local controls include 22 :

County Dust Control rules and ordinances found in Figure 11 (CDPHE’s table 32) following 23 ; City Dust Control rules and ordinances found in Figure 12 (CDPHE’s table 33) following 24 ; Guidance from the Mesa County Air Quality Planning Committee made up of representatives from government, industry, education, medical, and legal sectors; Mesa County Solid Wast e Management’s composting project to provide an alternative to open burning; Controlling road dust through municipal street sweeping as well as de

- icing using a product composed of magnesium chloride, potassium chloride, and rust inhibitors as an alternati ve to spreading sand on roads; Vegetation, signage, and other dust control measures are in place for undeveloped parcels of land in Grand Junction Clifton

. F igure 9 shows that identified areas of soil disturbance have reasonable controls near t he Grand Ju nction Clifton monit o r . Site A is owned by the sanitation district and is vegetated. Site D is partially maintained for agriculture

, and the remainder is naturally vegetated private property. Site E is zoned for agriculture and is vegetated. Sites G, H, and I are irrigated and vegetated agricultur al land that is privately owned ; Vegetation and dust control measures are discussed for the following parcels in Figure 9: Site B is owned by Halliburton and is partially landscaped and irrigated, graded about o nce per year as needed, treated with magnesium chloride every 3

- 5 years, with the un

- vegetated area under contract to have the dust controlled by a third party with a watering truck that visits up to twice daily to water the lot depending on conditions. Si te C is a gravel pit with a comprehensive Particulate Emissions Control Plan

, is subject to Colorado’s Regulation 1 Section III.D , and has had a Conditional Use Permit “APCD Construction Permit #87ME343F”. 25 Site F is a gravel pit and with a comprehensive P articulate Emissions Control Plan

, is subject to Colorado’s Regulation 1 Section III.D

, and has had a Conditional Use Permit “APCD Construction Permit #86ME024F”. 26 The Interim Guidance for High Wind Exceptional Events, page 10, requires for demonstration o f nRCP a showing that reasonable controls were in place, effectively implemented and enforced, and that wind speeds were high enough to overwhelm the controls. Since winds were only moderately above the Colorado threshold in Grand Junction, and some identi fied controls are sporadic or “as needed,” additional demonstration material on effective implementation and enforcement at the time of the event is needed at sites B, C, and F ;

22 “ TSD for the May 22 and 23, 2010, Alamosa, Pagosa Springs, and Grand Junction Exceptional Event,” May 20, 2013, pages 119

- 122.
23 Ibid., 118

- 119.
24 Ibid., 120

- 121.
25 Ibid., 124.
26 Ibid., 125

- 126.14

Figure 9: Grand Junction Clifton Site Assessment (CDPHE’s Figure 67 in the State’s Demonstration)

Vegetation, signage, and other dust control measures are in place for undeveloped parcels of land in Grand Junction Powell. F igure 10 shows that identified areas of soil disturbance have reasonable controls near the Grand Junction Powell monitor. Site A is owned by Union Pacific Railroad Co. and controls dust through limiting vehicles to 5 mph, covering all dirt roads with

grave l in 2010, and is undergoing paving projects, the remainder being naturally vegetated or undisturbed compacted soil

. Site C is naturally vegetated park land. Sites E and F are the city’s municipal cemetery with fencing to control access and is maintained. No major disturbances occurred on this soil until 2012 (well after the EE) when it became a soil source for trail maintenance. The disturbance has since been re

- vegetated; and Vegetation and dust control measures are discussed for the following parcels in Figure 10: Site B is owned by IPE Holdings

, LLC and is fenced to prevent dust from off road vehicles, has been covered by a layer of crushed limestone over top soil to control dust, has been compacted, and treated with magnesium chloride . Site D is a c ombi nation of public open space for non

- motorized recreational use and a landsca ped and maintained subdivision. The Interim Guidance for High Wind Exceptional Events, page 10, requires for demonstration of nRCP a showing that reasonable controls were in place, effectively implemented and enforced, and that wind speeds were high enough to overwhelm the controls. Since winds were only moderately above the Colorado threshold in Grand Junction, and some identified controls are sporadic or “as needed,” additional de monstration material on effective implementation and enforcement at the time of the event is needed at sites B and D

.15

Figure 10: Grand Junction Powell Site Assessment (CDPHE’s Figure 75 in the State’s Demonstration)16

Figure 11 : Mesa County Dust Control Rules and Ordinances (CDPHE’s Table 32 in the State’s Demonstration)17

Figure 12: City of Grand Junction Dust Control Rules and Ordinances (CDPHE’s Table 33 in the State’s Demonstration)18

Sections 2 and 5 of CDPHE’s analysis demonstrate that monitors in Grand Junction , Pagosa Springs, and Alamosa were affected by PM 10 transport from outside the area, with the main source areas located to the southwest of the area in Arizona, southeastern Ut ah, and northwestern New Mexico. In addition to transport, the spatial extent of elevated PM 10 concentrations throughout the area and the wind speeds associated with the event contribute to EPA’s evaluation of whether these events are nRCP in Pagosa Spring s and Alam osa

. Based on the information provided in the demonstration, EPA cannot determine19

that s ites B, C, and F near the Grand Junction Clifton monitor and s ites B and D near the Grand Junction Powell monitor satisfy the expectation that, “reasonable co ntrols have been effectively implemented and enforced.” 27 CDPHE confirmed on August 20, 2013, that references to April 5, 2010 in Section 5 on pages 103, 110, 116, and 117 of the state’s demonstration were typos due to the inadvertent reuse of language from a previous demonstration, and were intended to read as May 22 and 23, 2010. Table 2 summarizes the EPA’s evaluation of CDPHE’s nRCP EE demonstration.

Table 2 : EPA’s Analysis of CDPHE’s Technical Support Documentation of nRCP
Excee dance Date Location Reasonable Controls Demonstration Citation Wind Speed

Demonstration Citation Sufficient

Quality of Evidence? EPA

Criterion Met?

May 22, 2010 Alamosa

Adams State College Section 5 .0:

p. 103

- 104 and Section 5 .1:
p. 105

- 112 Section 2: p.12

- 67

,

esp. p. 42 Yes Yes

Alamosa Municipal Building Section 5 .0:

p. 103

- 104 and Section 5 .1:
p. 105

- 112 Section 2: p.12

- 67

,

esp. p. 42 Yes Yes

Pagosa Springs School Section 5 .0:

p. 103

- 104 and Section 5.2 : p. 113

- 117 Section 2: p.12

- 67

,

esp. p. 43 Yes Yes

May 23, 2010 Grand

Junction

Clifton Sanitation Building Section 5 .0:

p. 103

- 104 and Section 5.3 : p. 118

- 130 Section 2: p.12

- 67

,

esp. p. 47 No No

Grand Junction

- Mesa County Powell Building Section 5 .0:

p. 103

- 104 and Section 5.3 : p. 118

- 130 Section 2: p.12

- 67

,

esp. p. 47 No No

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 7

- year time series plots of 2,214 samples (Alamosa

- Adams State College), 2, 168 samples (Alamosa

- Municipal Building), 2,287 samples (Pagosa Springs), 790 samples (Grand Junction Powell), and 507 samples (Grand Junction Clifton ) of 24

- hour

averages. CDPHE explains that concentrations measured on May 22 , 2010 were more rare than the 99.6 percentile level at the Alamosa Adams State College monitor and the Alamosa Municipal Building

27 “Interim Guidance on the Preparation of Demonstrations in Suppo rt of Requests to Exclude Ambient Air Quality Data Affected by High Winds Under the Exceptional Event Rule” of May 2012, page 10.20

monitor

, and were more rare than the 99.7 percentile at the Pagosa Springs School monitor. 28 The concentrations measured on May 23

, 2010 were more rare than the 99.8 percentile at the Grand Junction Powell monitor and were the maximum calculated value at the Grand J unction Clifton monitor. 29

The EPA “Interim Guidance on High Wind Exceptional Events” recommends that demonstrations also consider percentile ranks when dust impacted data is excluded. 30 The May 22 , 2010 Alamosa and Pagosa Springs

, and May 23 , 2010 Grand Junction values rank among the values exceeding the NAAQS that, since at least 2005, are only found during high wind dust events. This information indicates that values at the levels seen on May 22 and 23 , 2010 are extremely rare in the absence of high wi nd dust exceptional event impacts, and that it is unlikely that any sources of PM 10 were involved in the May 22 and 23 , 2010 exceedances other than wind

- blown dust. Table 3 summarizes the EPA’s evaluation of CDPHE’s HF EE demonstration.

Table 3 : EPA’s An alysis of CDPHE’s Technical Support Documentation of HF
Exceedance Date Exceedance

Location Historical Fluctuations

Demonstration Citation Sufficient Quality of Evidence? EPA Criterion

Met?

May 22 , 2010 Adams State

College Section 3: p. 68

- 73 Yes Yes

Alamosa Municipal Building Section 3: p.68

- 70

, 74

- 77 Yes Yes

Pagosa Springs School Section 3: p.68

- 70

, 77

- 80 Yes Yes

May 23 , 2010 Grand Junction

Powell Section 3: p.68

- 70

, 80

- 83 Yes Yes

Grand Junction Clifton Section 3: p.68

- 70

, 84

- 86 Yes Yes

Clear Causal Relationship

EPA considers a variety of evidence when evaluating whether there is a Clear and Causal Relationship (CCR) between the measurement under consideration and the event that is claimed to have affected the air quality in the area. D emonstrations 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 transporte d 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. 31

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

28 “ TSD for the May 22 and 23, 2010, Alamosa, Pagosa Springs, and Grand Junction Exceptional Event,” May 20, 2013, page 69, table 23.
29 Ibid., 69, table 24.
30 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.
31 Ibid., 21

- 22.21

S tatewide PM 10 monitoring maps ; S urface and upper air wind speed analysis from NOAA ; Wind speed maps from the North American Regional Analysis (NARR) ; M aps of real

- time weather data from NCAR ; R egional wind and weather by hour through MesoWest ; NOAA HYSPLIT modeling of wind trajectories ; Navy Aerosol Analysis and Prediction System (NAAPS) forecasted dust concentrations; MODIS Terra satellite images demonstrating the blowing dust across the region ; M aps establishing the lack of regional precipitation and drought status from the USDA

, NOAA, and the National Drought Mitigation Center ; and
M aps of elevated friction velocities in the region from the NOAA NCEP North A merican Model.

These analyses demonstrate persuasively through the weight of evidence the existence of a high wind blowing dust event originating far southwest of the monitors in question.

CDPHE’s documentation also provides dust

- on

- snow data from the Center for Snow and Avalanche Studies, an organization that studies the effects of wind

- blown desert dust from Arizona, New Mexico, and Utah on snowpack albedo and snowmelt in the San Juan Mountains of Colorado

. Figure 28 of CDPHE’s documentation show s that May 22 , 2010, was one of nine Dust

- on

- Snow events for the 2009/2010 water year. 32 This information helps to confirm that a regional blowing dust event with long

range transport caused the PM 10 exceedances measured across portions of Colorado beginning on May 22

, 2010.

The U.S. Geological Survey (USGS) Southwest Geographic Science Team’s dust monitoring web pages
list May 22 and 23 , 2010 as D ust E vent day s with the following characterization, “ The first of a two day long change in pressure sys tems brought consistently high winds to the Four Corners Region again this year. The resulting significant dust emissions from the Navajo Reservation reached well into southern Colorado and Utah each day

. ” 33

The Smoke Text Product from NOAA’s Satellite Serv ices Division characterized May 22, 2010 with the following characterization:

A large area of blowing dust has been kicked up due to strong winds associated with a potent storm system. The blowing dust is emanating from northeast Arizona, northwest New Mex ico and southwest/central Colorado. The dust is moving quickly to the northeast and extends from northeast Arizona, extreme southeast Utah and northwest New Mexico across Colorado and into the Nebraska panhandle. 34

32 “ TSD for the May 22 and 23, 2010, Alamosa, Pagosa Springs, and Grand Junction Exceptional Event,” May 20, 2013, page 59.
33 Ibid., 63.
34 Ibid., 63

.22

Also included are high

- wind blowing dust a ccounts from the Fox21 News, the Denver Post, Grand Junction NBC11 news, and the Community Collaborative Rain, Hail & S now Network

. 35

CDPHE generally summarizes that “the exceedances were the consequence of strong southwesterly prefrontal surface winds over dry soils which caused significant blowing dust across much of Arizona, northwest New Mexico, southeast Utah, and west

- central and southwest Colorado”. 36 CDPHE further states that “[w]hile it is likely that some dust was generated within the local communit ies as gusts from the regional dust storm passed through the area, the amount of dust generated locally was easily overwhelmed by, and largely unnoticeable as compared to the dust transported in from the sources regions of the dust storm”. 37 Table 4 summarizes the EPA’s evaluation of CDPHE’s CCR EE demonstration.

Table 4 : EPA’s Analysis of CDPHE’s Technical Support Documentation of CCR 38 Clear Causal Relationship Demonstration

Citation Sufficient Quality of Evidence ? EPA Criterion Met? Section 2: p.12

- 67, Figures 1

- 36 Yes Yes Section 2: p. 12, 28

- 49 , Tables 1

- 21 Yes Yes Section 2: p. 58

- 60, 63 Yes Yes Section 4: p. 91

- 102 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. CDPHE states that due to the information presented in the HF and CCR demonstrations on pages 1 9 and 20

- 21 of this (EPA’s) TSD, re spectively, and cited in Table 5 , “statistical and meteorological data clearly shows that but for this high wind blowing dust event, Alamosa, Pagosa Springs, and Grand Junction would not have exceeded the 24

- hour NAAQS on May 22 and 23 , 2010”. 39 Table 5 summarizes the EPA’ s evaluation of CDPHE’s AAQ EE demonstration.

35 Ibid., 91

- 102.
36 Ibid., 12.
37 Ibid., 103.
38 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.
39 “ TSD for the May 22 and 23, 2010, Alamosa, Pagosa Springs, and Grand Junction Exceptional Event,” May 20, 2013, page 131.23

Table 5 : EPA’s Analysis of CDPHE’s Technical Support Documentation of AAQ
HF and CCR Exceedance Location Affects Air Quality Demonstration Citation Sufficient Quality of Evidence EPA

Criterion Met? HF Adams State College Section 3: p. 68

- 73 Yes Yes

Alamosa Municipal Building Section 3: p.68

- 70

, 74

- 77 Yes Yes

Pagosa Springs School Section 3: p.68

- 70

, 77

- 80 Yes Yes

Grand Junction Powell Section 3: p.68

- 70

, 80

- 83 Yes Yes

Grand Junction Clifton Section 3: p.68

- 70

, 84

- 86 Yes Yes

CCR All Monitors Section 2: p.12

- 67, Figures 1

- 36 Yes Yes

Section 2: p. 12, 28

- 49 , Tables

1

- 21 Yes Yes

Section 2: p. 58

- 60, 63 Yes Yes Section 4: p. 91

- 102 Yes Yes

Natural Event

As stated in EPA’s Interim Guidance for High Wind Exceptional Events Section 6.3.6 EPA will consider an event to be a natural event if both the nRCP and CCR requirements have been adequately demonstrated. CDPHE generally states that, “There has never been an exceedance that was not associat ed with high winds carrying PM 10 dust from distant sources in these six areas since at least 2005” 40 , and that :

Multiple sources of data for the event in question and analyses of past dust storms in this area prove that this was a natural event and, more specifically, a significant natural dust storm originating in northeastern Arizona and northwestern New Mexico and spreading into southwestern and south

- central Colorado . B ut for the dust storm on May 22 and 23 , 2010, this exceedance would not have occurre d. 41

Although CDPHE has sufficiently demonstrated the CCR requirements for both May 22 and 23, 2010

events and the nRCP requirements for May 22, 2010 event , the state has not sufficiently demonstrated the nRCP requirements for May 23, 2010 event in Grand Junction. Table 6 summarizes the EPA’s evaluation of CDPHE’s Natural Event EE demonstration.

40 Ibid., 131.
41 Ibid., 132.24

Table 6 : EPA’s Analysis of CDPHE’s Technical Support Documentation of Natural Event
nRCP or CCR Exceedance Location Natural Event

Demonstration Cit ation Sufficient Quality of Evidence ? EPA

Criterion Met? nRCP

Anthropogenic Adams State College Section 5 .0: p. 103

- 104

and Section 5 .1: p. 105

- 112 Yes Yes

Alamosa Municipal Building Section 5 .0: p. 103

- 104

and Section 5 .1: p. 105

- 112 Yes Yes

Pagosa Springs School Section 5 .0: p. 103

- 104

and Section 5.2 : p. 113

- 117 Yes Yes

Grand Junction Powell Section 5 .0: p. 103

- 104

and Section 5.3 : p. 118

- 130 No No

Grand Junction Clifton Section 5 .0: p. 103

- 104

and Section 5.3 : p. 118

- 130 No No

nRCP

- Wind Speed Adams State College Section 2: p.12

- 67 , esp. p. 42 Yes Yes

Alamosa Municipal Building Section 2: p.12

- 67 , esp. p. 42 Yes Yes

Pagosa Springs School Section 2: p.12

- 67 , esp. p. 43 Yes Yes

Grand Junction Powell Section 2: p.12

- 67 , esp. p. 47 Yes Yes

Grand Junction Clifton Section 2: p.12

- 67 , esp. p. 47 Yes Yes

CCR All Monitors Section 2: p.12

- 67, Figures 1

- 36 Yes Yes

Section 2: p. 12, 28

- 49

, Tables 1

- 21 Yes Yes

Section 2: p. 58

- 60, 63 Yes Yes Section 4: p. 91

- 102 Yes Yes

No Exceedance or Violation But For the Event

Generally, the No Exceedance or Violation But for the Event (NEBF) demonstration is similar to the demonstration of the nRCP and CCR requirements, and should show that the measured concentration would have been below the applicable NAAQS without the affect of the event.

CDPHE provides a summary of the analysis and information presented in the documentation that demonstrate both the nRCP and CCR requirements have been met and states that:

The PM10 exceedances in Alamosa, Pagosa Springs, and Grand Junction on May 22 and 23, 2010, would not have occurred if not for the following: (a) dry soil conditions over northeast25

Arizona, northwest New Mexico, most of Utah, and parts of western Colorado with 30

- day precipita tion totals below the threshold identified as a precondition for blowing dust in northeastern Arizona; (b) a surface low pressure system and cold front that were associated with a strong upper

- level trough that caused strong prefrontal surface winds over t he area of concern; and (c) friction velocities over regions of northern Arizona, northwest New Mexico, and southeast Utah that were high enough to allow entrainment of dust from natural sources with subsequent transport of the dust to Colorado in strong w inds. 42

While not explicitly stated in the documentation, EPA notes that 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 Technical Support Documentation of NEBF
Exceedance Date No Exceedance But For the Event Demonstration Citation Sufficient Quality of Evidence ? EPA Criterion Met?

May 22

, 2010 Section 6: p.108

- 109 Yes Yes May 23, 2010 Section 6: p.108

- 109 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 some minor non

- substantive external comments during the 30 day comme nt period and appropriate corrections were made to the report. Table 8 outlines EPA’s evaluation of these requirements.

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

Cr iterion Met?

Did the State provide prompt public notification of the event? 40 CFR §50.14(c)(l)(i) Section 1:p. 10 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) Section 1:p. 10 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) June 28, 2013 Yes

Was the public comment process followed and documented? 40 CFR §50.14(c)(3)(v) Section 1:p.1 1 Yes

42 Ibid., 131.26



## CONCLUSION

EPA has reviewed documentation provided by CDPHE to support claims that dust emissions generated by high winds resulted in PM 10 transport from arid regions in Arizona, northwest New Mexico, and southeast Utah into the Pagosa Springs and Alamosa areas on May 22 , 2010. These high wind events caused exceedances of the 24

- hour PM 10 NAAQS at the locations identified in Table 1 of this document

on May 22, 2010, in Pagosa Springs and Alamosa. EPA concurs that the flag ged exceedances at the Pagosa Springs and Alamosa monitors on these days meet the definition of an exceptional event: the exceedances affected air quality, were nRCP, and meet the definition of a natural event. Specifically, EPA has determined that events were nRCP due to high wind conditions that transported PM 10 from sources outside of the Pagosa Springs and Alamosa areas and subsequently overwhelmed reasonable controls within Alamosa and Pagosa Springs . Also, regardless of transport into the area, information pertaining to the controls implemented within the affected areas, the spatial extent of elevated PM 10 concentrations measured in the area, and the wind speeds associated with the high wind dust event prov ide 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 flagging of the data for the NAAQS exceedances of 260 ug/m 3 at Alamosa Adams State College, 194 ug/m 3 at the Alamosa Municipal Building, and 187 ug/m 3 at the Pagosa Springs monitors on May 2 2, 2010.

In Grand Junction, CDPHE included a comprehensive description of the controls at each potential anthropogenic source and the wind speed in the area, but did not describe whether the controls were implemented on

, or immediately prior to May 23, 2010. Specifics describing the date of the last application of magnesium chloride, grading of the lots, or that the watering protocols were actually followed on the day in question are lacking. Section 3.1.3. of the guidanc e states that, “Cases where relevant control measures were not being fully implemented or properly enforced, but reasonably could and should have been, are unlikely to be eligible for data exclusion under the Exceptional Events Rule.” 43
EPA welcomes the sub mittal of further information on those controls employed on or immediately prior to May 23, 2010 at these sites that will allow the agency to concur on the flagged data.

Therefore, the flags on AQS data of 189 ug/m 3 at Grand Junction Clifton Sanitation Bu ilding and 155 ug/m 3 at the Grand Junction Mesa County Powell Building monitors on May 23 , 2010 will not receive

concurrence or non

- concurrence at this time

.

The Alamosa and Pagosa Springs concurrences do not constitute final EPA action regarding any matt er 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.

43 “Interim Guidance on the Preparation of Demonstrations in Support of Requests to Exclude Ambient A ir Quality Data Affected by High Winds Under the Exceptional Event Rule” of May 2012, Section 3.1.3.