March 25, 2016

Ref: 8P-AR

MEMORANDUM

SUBJECT: Lamar 2011-2014 PM10 Design Value

FROM: Richard M. Payton

EPA Region 8 Air Quality Monitoring

TO: Lamar PM10 Maintenance Plan Approval Docket

In order to approve the Lamar 10-year PM10 Maintenance Plan Update, Lamar must be attaining the 

PM10 NAAQS. All PM10 exceedances in the past 10 years in Lamar have been flagged by the Colorado 

Department of Public Health and Environment (CDPHE) as high wind exceptional events. CDPHE has 

submitted sufficient demonstrations for these flagged exceedances, and EPA Region 8 has concurred or 

plans to concur on sufficient flags so that Lamar is currently in attainment of the NAAQS. EPA Region 

8 determined that, for the two PM10 exceedances at the Lamar municipal building and three at the Lamar 

Power Plant monitor in 2012, Lamar would attain the PM10 NAAQS even if Region 8 did not provide 

concurrence on those flags. Region 8 therefore deferred providing review and concurrence on the 2012 

demonstrations.

While Lamar attains the PM10 standard without EPA concurrence on the 2012 flags, calculations of 

PM10 design values for use in projecting forward future attainment with source growth in coming years 

are impacted by the flagged exceedances in 2012. Several methods of calculating the PM10 design value 

are provided in the PM10 SIP Development Guideline (EPA-4502-86-001, June 1987). The simplest is a 

table look up based on the number of samples collected. For 2012-2014, the Lamar Municipal monitor 

collected 1,083 samples; the SIP Development Guideline indicates that the PM10 design value may be 

approximated by the fourth highest value when more than 1,043 samples are collected over three years.

The EPA Exceptional Events Rule, 40 CFR Part 50.14, allows the EPA to concur on state exceptional 

event flags and omit concurred data from determinations of exceedances or violations of the NAAQS. 

The rule does not address non-exceedance exceptional event days which do not contribute to 

exceedances or violations of a NAAQS.

The top four flagged data values on which EPA is currently reviewing (or not reviewed because the 

flagged value did not contribute to and exceedance or violation of the NAAQS were those shown in 

Table 1. 

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

REGION 8

1595 Wynkoop Street

Denver, CO 80202-1129

Phone 800-227-8917

www.epa.gov/region08
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Table 1 First through Fourth Maximum PM10 in Lamar, 2012-2014 Without EPA Exceptional 

Event Concurrence

Date PM10 (g/m3

) Flag Concurrence?

March 18, 2012 242 rj No (Deferred)

April 2, 2012 163 rj No (Deferred)

Feb. 16, 2014 153 rj No (not an exceedance)

Nov. 10, 2012 152 rj No (not an exceedance)

While the third and fourth highest values in Table 1 are above the 150 g/m3level of the PM10 standard, 

they are not considered NAAQS exceedances because 40 CFR Part 50, Appendix K defines an 

exceedances as:

“a daily value that is above the level of the 24-hour standard after rounding to the nearest 10 

μg/m3(i.e., values ending in 5 or greater are to be rounded up).”

While not an exceedance, the 152 g/m3value given by the table look-up method of the PM10 SIP 

development guideline leaves essentially no room for growth in emissions over a future maintenance 

period.

Though EPA has not completed evaluation of the exceptional event demonstrations from CDPHE for 

March 18, 2012 and April 2, 2012, the EPA has no reason to believe that these exceedances will not 

receive concurrence when evaluated. Winds on March 18, 2012 in Lamar were from the south, with 

sustained winds as high as 40 mph and gusts as high as 51 mph. For April 2, 2012, sustained northerly 

winds were as high as 35 mph, with gusts to 54 mph. Based on the source control discussions in other 

Lamar demonstrations, these are conditions consistent with the dust storms which have received EPA 

concurrence.

Table 2 shows all Lamar PM10 data, whether flagged or with EPA concurrence or not, through the 4th

highest value lacking an exceptional event flag.
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Table 2 Highest Lamar PM10 Data, 2012-2014

Date PM10 (g/m3

) Flag Concurrence?

April 9, 2013 1220 rj Yes

May 24, 2013 406 rj Yes

March 11, 2014 387 rj Yes

April 23, 2014 350 rj Yes

April 29, 2014 321 rj Yes

March 18, 2014 299 rj Yes

Nov. 10, 2014 298 rj Yes

March 30, 2014 264 rj Yes

March 29, 2014 263 rj Yes

March 18, 2012 242 rj No (Deferred)

March 31, 2014 223 rj Yes

May 1, 2013 207 rj Yes

May 28, 2013 201 rj Yes

March 15, 2014 173 rj Yes

May 25, 2013 168 rj Yes

Dec. 24, 2013 168 rj Yes

April 2, 2012 163 rj No (Deferred)

Feb. 8, 2013 159 rj Yes

Feb. 16, 2014 153 rj No (not an exceedance)

Nov. 10, 2012 152 rj No (not an exceedance)

Apr. 25, 2013 147 rj No (not an exceedance)

Nov. 16, 2013 144 None

Jan. 11, 2013 141 None

June 3, 2013 140 None

June 21, 2013 135 None

As a first consideration, the theoretical design value using the table look-up method when the two 

NAAQS exceedances not yet reviewed by EPA are removed would be the fourth highest value of 144 

g/m3, recorded on Nov. 16, 2013. This data point is not flagged; winds on that day at the Lamar Airport 

peaked at 26.5 mph from the WSW, with gusts to 36.8 mph.

The PM10 SIP Development Guideline indicates that the table look-up method only provides an 

estimation of the PM10 design value, and that more accurate design values can be obtained through the 

upper tail data distribution curve fit method. In this method, data are ranked from smallest to largest 

concentration, an exponential or other function is fit to the top 5 or 10 percent of data, and the fit 

function is solved for a frequency of 1/365 (the value in the distribution that occurs once per year). 

Values with a 1 in 365 frequency lower than the NAAQS indicate that the area is attaining the standard. 

While the table look-up method is intended to be used only with three complete years of monitoring 

data, the upper tail curve fit method can potentially achieve more accurate results by using more than 

three years of data, provided emissions are relatively constant over the years evaluated. The guideline 

says that in general:
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“if more years of data with relatively unchanging emissions are available, they also may be 

considered in calculating design concentrations. The more years of data available, the more

stable the estimate of PM10 design concentrations.” 

Fitting more years of data under stable emission conditions can lead to a more accurate estimate of the 

design value.

Looking at the most recent five years of data which have been certified by CDPHE, from 2010 through 

2014, the design values corresponding to a 1/365 frequency after all flagged exceedances are removed is 

138 g/m3, as shown in Figure 1. Specifically, solving the least squares linear regression curve fit shown 

in the Figure for a frequency of 1/365 gives:

1/365 = 0.339e-0.035x

1/(365*0.339) = e-0.035x

Ln (1/(365*0.339)) = -0.035x

-1/0.035*Ln (1/(365*0.339)) = x = 137.7 g/m3

The design value for use in the roll forward analysis for the Lamar Maintenance Plan Update is therefore 

137.7 g/m3.

Figure 1 2010-2014 PM10 Data from Lamar, with Curve Fit of Top 10%, Exceedances Removed

y = 0.339e-0.035x

0.0001

0.001

0.01

0.1

1

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170

2010-2014 Lamar PM10, Flagged Exceedances 

Removed

All Data Top 10% 1/365 Expon. (Top 10%)