Treasure State Resource Industry Association

EPA Additional Information Requests

Petition for Reconsideration of EPA’s SO2

Nonattainment Designation for a Portion 

of Yellowstone County, Montana 

2/18/2014

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2/18/2014

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Air quality data from 2013 (“New Data”) that only became available after the close of 

the comment period provide convincing evidence that Coburn Road 2010 Data 

(“Coburn 2010”) are flawed, unreliable, and unrepresentative, and thus EPA should 

not rely upon Coburn 2010 to make a nonattainment designation for a portion of 

Yellowstone County (“Designation”). 

The New Data show that unlike all other surrounding years:

1. Coburn 2010 does not track upwind peak hourly emissions;

2. Coburn 2010 has disproportionately high peak readings, even when controlled 

for meteorology and emissions;

3. Coburn 2010 diverges markedly from all other nearby, downwind monitors;

4. Coburn 2010 produced numerous, high, outlier readings in contrast to all other 

surrounding years;

5. Coburn 2010 does not reflect emission controls and limits that have gone into 

effect since 2008; and

6. Coburn 2010 had an exceptionally high number of quality assurance failures 

associated with the very readings EPA relies on to make the nonattainment 

designation.

Because Coburn 2010 does not meet EPA’s rigorous quality assurance requirements or 

satisfy stakeholder expectations of accuracy and reliability, the Designation was in 

error and should be repealed.
• All monitoring data from the Billings area support attainment – except for Coburn 2010.

• Past and present data for other Billings-area monitors are included with this submission.

• MSCC comments provide analysis of data from the other monitors. (Docket EPA-HQ-OAR-2012-0233-0286).

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Map 1: SO2 Monitors and Major Sources in Yellowstone County

Lockwood Park Monitor

Phillips 66 Billings Refinery

PPL Montana – JE Corette

Western Sugar Cooperative

MT Sulphur & Chemical

Yelp

ExxonMobil Billings Refinery

CHS Inc. Refinery

Lockwood Park Monitor

Wind Rose

(Coburn Road: 2009 - 2012)
Chart 1 Series: 

Only Coburn 2010 Departs Markedly from the Upwind 

Hourly Emission Correspondence of Surrounding Years.

• Peak ambient concentrations generally track peak 

hourly emissions from sources upwind of Coburn Road 

– except Coburn 2010. 

• Lower Coburn peak ambient readings in 2013 align 

with lower and less frequent peak hourly emissions, 

unlike Coburn 2010.

• PPL hourly emissions of approximately 800 lb/hour 

roughly correspond with emission limits of the new 

Regional Haze requirements effective since April 13, 

2013. PPL 2013 emissions reflect these new limits.

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Chart 1a: Coburn 2010 departs markedly from the trend of 

surrounding years that track peak hourly PPL emissions.

• Coburn 99th% ambient readings generally track 99th% PPL hourly emissions - except Coburn 2010.

• Coburn 2013 lower 99th% is explained by lower peak PPL hourly emissions.

• Coburn 2010 is inexplicably inverse to lower PPL 99th% hourly emissions.

• Using wind analysis, EPA concluded that Coburn 2010 high readings resulted from emissions at PPL and not 

from prevailingly downwind sources (see EPA TSD at 8 and 11-12).

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Chart 1b: 

Results from all upwind sources show similar discrepancies 

between Coburn 2010 and peak hourly emissions.

• Upwind (southwest) sources include: PPL, Western Sugar, Phillips 66 and CHS.

• Prevailing winds in the Billings area are from the southwest (see Wind Rose on Map 1, Slide 3).

• Peak upwind hourly emissions generally track with peak Coburn readings - except Coburn 2010.

• Lower 2013 99th% ambient is again explained by lower peak hourly emission rate from all upwind sources.

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Chart 1c: 

Coburn 2010 99th% departs markedly from the trend of 

surrounding years, rising almost 20 ppb from 2009 while PPL

hourly emission peaks visibly decline.

• Coburn 99th% annual readings generally reflect the frequency and magnitude of PPL hourly emission peaks –

except Coburn 2010.

• Coburn 2010 has higher ambient readings despite peak emissions decline from 2008 and 2009.

• Coburn 2010 anomalies are not explained by wind direction or emissions (see Charts 2a and 2b and EPA TSD).

• 2013 PPL peak hourly emissions rarely exceed 800 lb/hour and track with lower ambient readings.

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Chart 1d: 

Coburn 2010 99th% ambient similarly departs markedly from PPL

daily and rolling 30-day emission peaks.

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• The black line shows the PPL emissions decline from 2008-2013.

• 2013 PPL peak daily emissions remain under 800 lb/hour (meeting the Regional Haze limit) and 

track with lower ambient readings of 2013.

• Even though PPL hours of operation increased from 2012 to 2013, peak emissions decreased.
Chart 2a:

Coburn 2010 has a disproportionately high number of peak 

readings during “conducive” meteorology and emissions.

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• “Conducive” meteorology and emissions = (1) winds of 5 to 25 mph; (2) from direction 230-250o, and (3) PPL is 

operating (meaning PPL emissions >100 lb/hr).

• Over 90% of all SO2readings ≥ 60 ppb at Coburn (“peak” readings) occur during conducive conditions from 

2008-2013.

• Coburn 2010 peak readings occur ≈ 3 times more frequently when controlled for conducive conditions than 

any other year. 
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Chart 2b:

Coburn 2010 inexplicably has highest number of peak readings 

while experiencing lowest number of conducive conditions.

• Coburn 2010 shows the highest frequency of readings ≥ 60 ppb despite having the 

lowest amount of conducive conditions in the six year period.

• Coburn 2010 has the second fewest daily emissions ≥ 800 lb/hr and yet shows the 

highest 99th% compared to all other years.

• These anomalies makes Coburn 2010 suspect.

• Coburn 2013 has the lowest number of peak readings as well as the lowest hours of 

conducive conditions other than 2010.
Chart 3: 

Coburn 2010 departs markedly from other downwind monitors.

• All four downwind monitoring sites generally track each other – except Coburn 2010.

• Coburn resumes general tracking in 2011.

• The four monitors are all downwind of PPL and within 3 miles of each other (see Map 1 on Slide 3).

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Chart 4a:

Coburn 2010 produces an exceptional number of high outlier 

readings.

• Yellow line represents a visual outlier boundary for ambient readings.

• Coburn 2010 produces five of the seven outlier readings for the six-year period.

• PPL hourly emission rate is less than 800 lb/hour for all but one (non-2010) outlier case. 

• All outlier points/red diamonds are associated with known QA/QC failures (see Chart 5).

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Chart 4b:

Removing Coburn 2010 greatly reduces outlier readings.

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• The remaining 5 years show a more regular relationship between peak hourly emissions 

and peak ambient concentrations.

• Coburn 2010 departs markedly from the trends of the other 5 years and is thus suspect.
Chart 5: Coburn 2010 has the highest number of QA/QC failures.

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 The most frequent QA/QC failures occurred in 2010 during 

2 of the 3 highest readings (5 failures/reading).

 Every reading above 75 ppb during 2009-2011 had at least 

one QA/QC failure.

 Data in 2012 show markedly fewer QA/QC failures.

 Data in 2013 show no QA/QC failures.

 Average QA/QC failure rate per high-end reading: 

 2009 – 2011 = 2.0

 2012 = 0.4

 2013 = 0.0

 Improved data quality leads to better correlation with peak 

emissions and fewer apparent outliers.

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Chart 5 notes: 

QA/QC has improved considerably since 2010.
Chart 6: 

Continuous program of emission reductions in Billings area has 

resulted in reductions of ambient SO2.

• Reductions are real, permanent, and enforceable but were not all manifest in 2010.

• PPL is scheduled to be mothballed in April 2015; any re-start will be subject to MATS emission controls, 

which will include the co-benefit of SO2 emission reductions.

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Chart 7: 

Yellowstone County demonstrates continuous SO2 NAAQS

attainment since July 10, 2010.

• The daily rolling 3-year design value has continually been ≤ 75 ppb since July 10, 2010. The data enabling this 

analysis occurred in 2013, after the close of the comment period but before the deadline for judicial review.

• Most recent calendar-year design value is 64 ppb (2011 – 2013).

• If the faulty Coburn 2010 is removed, EPA has no basis for the 2010 SO2 NAAQS nonattainment designation.

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Analyses using the New Data more fully expose the 

faults of Coburn 2010 and the associated QA/QC 

failures. Because Coburn 2010 does not meet the high 

standards required for a NAAQS designation and does 

not accurately represent the air quality in Yellowstone 

County, the 2010 SO2 Designation was in error. 

TSRIA requests that EPA reconsider and repeal the SO2

Nonattainment Designation for a portion of 

Yellowstone County and accurately designate 

Yellowstone County through its on-going designation 

process for all other non-designated areas of the U.S.

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