UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

REGION 10 

Larry Hartig, Commissioner 

1200 Sixth Avenue, Suite 900 

Seattle, Washington 98101-3140 

NOV 0 2 2012 

Alaska Department of Environmental Conservation 

P.O. Box 111800 

410 Willoughby Ave., Ste. 303 

Juneau, Alaska 99811-1800 

Dear Mr. Hartig: 

OFFICE OF THE 

REGIONAL ADMINISTRATOR 

This letter responds to Alaska Department of Environmental Conservation's June 7, 2012 submittal 

regarding the elevated 24-hour PMw National Ambient Air Quality Standard levels at the Eagle River 

Parkgate station site in the Municipality of Anchorage on October 30 and 31, 2009. The ADEC has 

requested that the EPA concur that these exceedances were due to a high wind exceptional event. The 

recorded 24-hour PM10 levels at the site were 163 J.Lg/m3 and 137 J.Lg/m3

, respectively. 

Our response to the ADEC's request is governed by the "Treatment of Data Influenced by Exceptional 

Events" rule (72 FR 13560, March 22, 2007). After careful consideration of the information provided, 

we concur with the ADEC's exceptional events flag for October 30, 2009. We have not acted on your 

request with regard to the event of October 31, 2009 given it does not have regulatory significance. The 

basis for our decision for the October 30, 2009 event is set forth in the enclosed document. The EPA's 

decisions on exceptional event exclusions are not considered final agency action until they are acted 

upon as part of a final regulatory action, which is subject to public notice and comment. 

Thank you for your timely submittal of this exceptional event documentation and for responding to our 

comments and questions about the documentation. If you have any questions or wish to discuss this 

matter further, please contact me or have your staff contact Justin Spenillo, of my staff at 

spenillo.justin@epa.gov or (206) 553-6125. 

Enclosure 

cc: Alice Edwards, ADEC 

Barbara Trost, ADEC 

Stephen Morris, Municipality of Anchorage 

Sincerely, 

~;:~c .. ~~' ~~_j} . 

Dennis 

··" 

J. McLerran 

f ; ... ~ 

Regional Administrator 
EPA Region 10 

Review of Exceptional Event Request 

Eagle River, AK 

24-hour PM10 NAAQS 

Date Analyzed: October 30, 2009 

Background 

On March 22, 2007, the EPA adopted a final rule, Treatment of Data brfluenced by 

Exceptional Events' (Exceptional Events Rule or EER) to govern the review and handling 

of certain air quality monitoring data for which the normal planning and regulatory 

processes are not appropriate. Under the EER, the EPA may exclude data from use in 

determinations of National Ambient Air Quality Standard (NAAQS) exceedances and 

violations if a state demonstrates that an "exceptional event'' caused the exceedances. 

Before the EPA can exclude data from these regulatory determinations, the state must flag 

the data in the EPA's Air Quality System (AQS) database and, after notice and opportunity 

for public comment, submit a demonstration to justify the exclusion. After con.sidering the 

weight of evidence provided in the demonstration, the EPA decides whether or not to 

concur with each flag. 2 

ADEC' s Request 

ADEC requested concurrence on flagged 24-hour PM 10 data for Eagle River, Alaska on 

October 30-31,2009, at the Parkgate station site (AQS site 02-020-1004). The recorded 

24-hour PM to level at the site was 163 !J,g/m~ on October 30111 and 137 !J,glnYl on October 

31st. During that time there were high winds coming from the direction of the glacial silt 

deposits along the Matanusk:.t River Valley. ADEC is requesting concurrence on these two 

days due to their regulatory significance and potential impact on air quality decisions for 

the Eagle River PM10 redesignation and maintenance plan. ADEC submitted exceptional 

event documentation to EPA Region 10 on June 12, 2012 for both the October 30 and 31, 

2009 values. 

The EPA's Exceptional Event Evaluation 

The EPA evaluated whether the documentation provided by ADEC for the tlagged value of 

the 24-hour PM10 NAAQS on October 30, 2009, in Eagle River, Alaska, demonstrated that 

the requirements of the Exceptional Events Rule were met. The October 31, 2009 flag was 

not acted upon because only the October 30, 2009 value was determined to have regulatory 

significance in terms of PM to limited maintenance plan eligibility for the area. 

I 72 FR 13560. 2 Note that the level of documentation may vary by the type of event and can be guided in part by the relative 

magnitude of the observed concentrations. To obtain concurrence. the EPA must determine that the 

demonstration is complete and provides a reasonable technical demonstration. 72 FR 13573 (March 22, 2007 ). 
The table below summarizes the requirements of the Exceptional Events Rule and describes 

how ADEC met each requirement. All references to page numbers, tables and figures relate 

to the June 7, 2012, documentation. · 

Procedural Requirements: EPA's Evaluation of Flagged Exceedances: 

• The data are flagged ADEC flagged and described the October 30, 2009, 24-

and include an initial hour PM10 value as a high wind exceptional event in 

event description in EPA's AQS database prior to the July 1, 2010 deadline. 

EPA's AQS database. 

40 CFR 50.14(c)(2)(i) 

and (iii) 

• The public had an ADEC provided a 30 day public comment period on the 

opportunity to review documentation for the October 30, 2009 claimed 

and comment on exceptional event. The public comment period closed 

demonstration on December 6, 2010. ADEC received no comments. 

justifying data 

exclusion. 40 CFR 

50.14(c)(3)(i) and (iv) 

• Demonstration EPA received demonstration documentation from 

justifying data ADEC on June, 2012, before the deadline of not later 

exclusion submitted than 3 years following the end of the calendar quarter in 

timely to EPA. 40 which the flagged concentration was recorded (in this 

CFR 50.14(c)(3)(i) case, December 31, 20 12). 

Technical Criteria: 

• The event satisfies ADEC provided PM 10 data (Table 1, page 3 ), satellite 

the criteria in 40 imagery (Figure 1, page 4), news reports (Appendix A) 

CFR 50.1 U) (i.e., and air quality alerts (Appendix A and B) as evidence 

affects air quality, is that the event affected air quality at the Eagle River 

not reasonably Parkgate station site on October 30, 2009. Textual 

controllable or support on page 3-8, Appendix A, Appendix C, and 

preventable, is an their associated images provide complete conceptual 

event caused by model showing the winds coming from the N-NE and 

human activity that primarily natural landscape. 

is unlikely to recur at 

a particular location ADEC describes the naturally occurring Matanuska 

or a natural event, winds and their direction and rare high speeds exceeding 

and is determined by 40 mph (paragraph 2, page 5, and Table 2, page 9) 

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EPA to be an 

exceptional event). 

40CFR 

50.14(c)(3 )(iii)(A) 

• There is a clear 

causal connection 

between the 

exceedance and the 

claimed exceptional 

event. 40 CFR 

50.14( c )(3 )(iii)(B) 

during the exceptional events. 

ADEC identified the large quantity of naturally 

occurring glacial silt deposits on its outwash plain 

(Figure 2, page 5, and Figure 3, page 6) that were 

susceptible to transport from these high winds. Given 

the lack of snow cover and vegetation (Table 2 page 9 

and Figure 4 page 8), the high winds described were 

able to transport the PM10 from the natural ecosystems 

from the N-NE. For areas with primarily natural land, 

no wind controls are expected according to the June 

2012 draft Guidance on High Wind Exceptional Events. 

This is evidence that the October 30, 2009, event was 

not reasonably controllable or preventable. 

ADEC also identified a small portion of land used for 

agricultural and recreational biking. A separate EPA 

R 10 March 21, 2012 analysis showed that within the 50 

mile area surrounding the Parkgate station monitor, less 

than 1% of the area was agricultural. Most of the 

developed or controllable area was downwind of the 

event. Given that the exceedance was primarily caused 

by emissions from natural sources, this served as 

supporting evidence that the October 30, 2009, event 

was not reasonably controllable or preventable. 

ADEC described through text and wind data (Table 2, 

page 9) how the wind came from the N-NE and created 

a dust storm that in satellite imagery (Figure 1, page 4) 

visibly shows the dust hitting the downwind areas 

including the monitoring station. The magnitude of the 

event is made visible by multiple large dust storms on 

the image coming out of the large glacially-influenced 

valleys. 

ADEC also provided a detailed analysis of wind 

direction, speed, and PM 10 data that showed the 

progression of particulate matter from the N-NE in 

Palmer and proceeding southwest through the Eagle 

River site and down to Anchorage (Figure 6, page 11-

12). 

Based on the suite of evidence provided, including 

satellite images, maps, PM10 data, wind-speed- PM1o 

compared data, and the absence of evidence of significant 

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sources of anthropogenic PM10, EPA concludes that there 

is a clear causal connection between the Parkgate monitor 

values and the exceptional event caused by the Matanuska 

high winds on October 30, 2009. 

• The event is To show PM 10 concentrations during the 2009 high wind 

associated with event were in excess of normal historical fluctuations, 

measured including background, ADEC cited data (Table 3, page 

concentrations in 13) that showed that PM10 levels had only exceeded the 

excess of normal NAAQS three times in 17 years. These exceedences 

historical only occurred in conjunction with high winds and no 

fluctuations snow cover (Figure 5 ). ADEC prepared a frequency of 

including distribution chart (Figure 7, page 13) showing that over 

background. 40 CFR the 17 year period, 95% of the observed PM 1o values 

50.14 (c)(3)(iii)(C) were Jess than 50[.!glm3 and 99.7% were below 

3 lOO[.!g/m . Based on the presented data, EPA concludes 

that the October 30, 2009 value of 163[.!g/m3 is in excess 

of normal historical fluctuations including background. 

• There would have To show there would have been no exceedances "but 

been no exceedances for'' the event, ADEC plotted all 24-hour PM 10 averages 

"but for" the event. over the past 12 years as compared to the maximum 

40CFR wind speed as measured at the Eagle River Parkgate 

50.14(c )(3 )(iii)(D) station site (Figure 9). Values were distinguished by 

snow depth and wind direction. It was shown that 

values exceeded lOO[.!g/m3 only when winds exceeded 

40 mph and there was no snow cover. There was only 

one exception and it was shown that the high winds 

were short-lived and thus there was minimal PM 10 

transport. 

Based on historic information, provided there is snow 

cover, values at the Eagle River Parkgate station are 

normally well below the 24-hour PM10 NAAQS. EPA 

concludes that but for the high wind and Jack of snow 

cover at the time of the October 30, 2009 event, there 

would have been no exceedances of the 24-hour PM10 

NAAQS at the Eagle River Parkgate Station site. 

Conclusion 

Based on the documentation submitted by ADEC on June 1 2, 2012, EPA concurs on the 

October 30, 2009 PM 10 level of 163 [.!g/m3 flagged as an exceptional event. The 

4 
information and analyses presented in the ADEC's exceptional event demonstration 

package provided weight of evidence sufficient for concurrence on the flagged data from 

the Eagle River Parkgate station monitor on October 30, 2012. Accordingly, we are placing 

a concurrence indicator in the EPA's AQS database for October 30, 2009. 

Note that the EPA's decisions on exceptional event exclusions are not considered final 

agency action until they are acted upon as part of a final regulatory action, such as in an 

action concluding that the affected data may be excluded from use in a designation or 

determination of attainment, which is subject to public notice and comment. 

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