UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION 10



### LarryHartig, Commissioner 1200 Sixth Avenue, Suite 900 Seattle, Washington 98101-3140


## NOV 0 22012

AlaskaDepartment ofEnvironmental Conservation P.O. Box 111800 410 WilloughbyAve., Ste. 303 Juneau, Alaska 99811-1800
DearMr. Hartig: OFFICE OF THE REGIONAL ADMINISTRATOR



### This letterresponds to AlaskaDepartment ofEnvironmental Conservation's June 7, 2012 submittal regarding the elevated 24-hour

### PMw National Ambient AirQuality Standardlevels atthe Eagle River Parkgate station site in the MunicipalityofAnchorage on October30 and 31, 2009. TheADEC has requested that the EPA concurthat these exceedances were due to ahigh wind exceptional event. The recorded 24-hourPM 10 

### levels at the site were 163 J.Lg/m3 

### and 137 J.Lg/m3

, 

### respectively.
Ourresponse to the ADEC'srequest is governedbythe "TreatmentofDataInfluenced byExceptional Events"rule (72 FR 13560, March 22, 2007). After careful consideration ofthe informationprovided, we concurwith the ADEC's exceptional events flag for October30, 2009. Wehavenot acted onyour request withregard to the event ofOctober 31, 2009 given it does nothaveregulatory significance. The basis for ourdecision for the October 30, 2009 event is set forth in the enclosed document. TheEPA's decisions on exceptional event exclusions are not considered final agency action until theyare acted upon as part ofa final regulatory action, which is subject to publicnotice and comment. Thank you for your timely submittal ofthis exceptional event documentation and for responding to our comments and questions about the documentation. Ifyou have anyquestions orwishto discuss this matter further, please contactme orhave your staffcontactJustin Spenillo, ofmy staffat spenillo.justin@epa.gov or(206) 553-6125.

Enclosure

cc: Alice Edwards, ADEC BarbaraTrost, ADEC Stephen Morris, MunicipalityofAnchorage Sincerely,

# ~;:~c

# ..**~~' ~~_j}**  . ··" f**~** ; ... 

### Dennis J. McLerran Regional Administrator

### EPA Region 10 Review ofExceptional Event Request Eagle River, AK 24-hour PM10

### NAAQS Date Analyzed: October30, 2009
Background
On March 22, 2007, the EPA adopted a final rule, 

### Treatment of Data brfluencedby Exceptional Events' (Exceptional Events Rule orEER) to govern the review and handling ofcertain airqualitymonitoring data for which the normal planning and regulatory processes are not appropriate. Under the EER, the EPA may exclude data from use in determinations ofNational Ambient Air Quality Standard (NAAQS) exceedances and violations ifa 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 tojustifythe exclusion. After con.sidering the weight ofevidence provided in the demonstration, the EPA decides whether ornot to concur with each flag.2

ADEC's Request
ADEC requested concurrence on flagged 24-hour PM 10data for Eagle River, Alaska on October 30-31,2009, at the Parkgate station site (AQS site 02-020-1004). The recorded 24-hour PMtolevel 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 ofthe 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 airquality decisions for the Eagle RiverPM 10redesignation 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 byADEC for the tlagged value of the 24-hourPM 10NAAQS on October 30, 2009, in Eagle River, Alaska, demonstrated that the requirements ofthe 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 ofPMto limited maintenance plan eligibility for the area.

I 72 FR 13560. 2 Note that the level ofdocumentation may vary by the type ofevent and can be guided in part by the relative magnitude ofthe 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 ofthe 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 ofFlagged 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 priorto the July 1, 2010 deadline. EPA's AQS database. 40CFR 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 ofnot later exclusion submitted than 3 years following the end ofthe calendarquarter in timely to EPA. 40 which the flagged concentration was recorded (in this CFR 50.14(c)(3)(i) case, December 31, 2012).



### Technical Criteria:


# • The event satisfies ADEC provided PM 10data (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 unlikelyto recur at a particular location ADEC describes the naturallyoccurring 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)

2EPA 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 ofnaturally 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 ofsnow cover and vegetation (Table 2 page 9 and Figure 4 page 8), the high winds described were able to transport the PM 10 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 orpreventable.
ADEC also identified a small portion ofland used for agricultural and recreational biking. A separate EPA R10 March 21, 2012 analysis showed that within the 50 mile area surrounding the Parkgate station monitor, less than 1% ofthe area was agricultural. Most ofthe developed orcontrollable area was downwind ofthe event. Given that the exceedance was primarilycaused by emissions from natural sources, this served as supporting evidence that the October 30, 2009, event was not reasonably controllable orpreventable.

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 ofthe event is made visible by multiple large dust storms on the image coming out ofthe large glacially-influenced valleys.
ADEC also provided a detailed analysis ofwind direction, speed, and PM 10 data that showed the progression ofparticulate 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 ofevidence provided, including satellite images, maps, PM10 data, wind-speed- PM1o compared data, and the absence ofevidence ofsignificant



### 3sources ofanthropogenic PM 10, EPA concludes that there is a clearcausal 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 10concentrations during the 2009 high wind associated with event were in excess ofnormal historical fluctuations, measured includingbackground, ADEC cited data (Table 3, page concentrations in 13) that showed that PM 10 levels had onlyexceeded the excess ofnormal 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% ofthe 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 ofnormal historical fluctuations includingbackground.


# • There would have To show there would have been no exceedances "but been no exceedances for'' the event, ADEC plotted all 24-hourPM 10 averages "but for" the event. overthe 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-hourPM 10 NAAQS. EPA concludes that but for the high wind and Jack ofsnow cover at the time ofthe October 30, 2009 event, there would have been no exceedances ofthe 24-hourPM 10 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 PM10level of 163 [.!g/m3 flagged as an exceptional event. The



### 4information and analyses presented in the ADEC's exceptional event demonstration package provided weight ofevidence 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 ofa final regulatory action, such as in an action concluding that the affected data maybe excluded from use in a designation or determination ofattainment, which is subject to public notice and comment.

5