January 26, 2011

MEMORANDUM

SUBJECT: Clean Air Act Section 110(k)(6) Error Corr ection for Ravalli County, Montana

FROM: Richard Payton, EPA Region 8 Air Permitting, Monitoring and Modeling Unit

TO: Docket EPA-HQ-OAR-2007-0562, Air Quality Design ations for the 2006 24-Hour

Fine Particle (PM 2.5 ) National Ambient Air Quality Standards

In the November 13, 2009 Federal Register Notice (7 4 FR 58688), EPA promulgated nationwide designations for most areas for the 2006 24-Hour PM 2.5 NAAQS. In that notice, EPA designated Ravalli County, Montana as “unclassifiab le.” The “unclassifiable” designation was assigned because at the time of promulgation, preli minary calculations of design values (DV) for the period from 2006 through 2008 indicated that Ravall i County had incomplete data and therefore EPA
could not make a determination whether or not the a rea attained the NAAQS. Subsequent review of the preliminary design value calculations showed th at a software error inappropriately labeled the Ravalli data as “incomplete” when acceptable data s ubstitution techniques were available to generate a complete data set for Ravalli County. After comp leting the data substitution routines and recalculating the design values, EPA has determined that Ravalli County was attaining the 2006 24-
hour PM 2.5 national ambient air quality standard using 2006-2 008 data and continues to meet these standards using the most current 2007 to 2009 data. See, for example, http://www.epa.gov/airtrends/pdfs/dv_pm25_2006_2008 rev102809.xls and http://www.epa.gov/airtrends/pdfs/PM2.5_DesignValue s_20072009_Final.xls.

EPA regulations provide for data substitution under appropriate circumstances. 40 CFR Part 50, Appendix N indicates in 4.2(b) provides that

(b) The use of less than complete data is subject t o the approval of EPA which may consider factors such as monitoring site closures/moves, mon itoring diligence, and nearby concentrations in determining whether to use such d ata for comparisons to the NAAQS.

The EPA document "Guideline on Data Handling Conven tions for the PM NAAQS" (EPA-454/R-99- 008, April 1999) contains guidance on substitution methods to allow incomplete data showing attainment to be considered complete for the purpos es of determining the attainment status of an area. Provided the data pass three qualifying tests, EPA may substitute either available data from collocated monitors at the same site, or may substi tute the highest monitored value from a given UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
REGION 8
1595 Wynkoop Street DENVER, CO 80202-1129

Phone 800-227-8917 http://www.epa.gov/region08

Printed on Recycled Papercalendar quarter considered over the three years ad dressed by the design value calculation. The three

qualifying tests for the data are:

1) the monitor must have collected at least 50% of the scheduled data for incomplete quarters 2) it must be shown that emissions and meteorology for the substituting data are comparable to the emissions and meteorology for the missing da ta 3) the incomplete data must be showing attainment

In the Ravalli monitor 2006-2008 data set, data for the 2 nd quarter 2006 and 3 rd quarter 2007 are incomplete. For 2 nd quarter 2006, 15 samples were scheduled (1 in 6 sa mpling schedule), but only 11 samples were collected. Thus 11/15 = 73% o f required samples were collected. This is less than the required 75%, but greater than 50%, so the 2006 data are incomplete, but they pass the 1 st qualifying test for substitution. For 3 rd quarter 2007, 31 samples were scheduled but only 1 9 scheduled samples (plus 2 creditable make-up sample s) were collected. (Note: the monitor was converted to a 1 in 3 sampling schedule on January 1, 2007). Thus 19/31 = 61% of scheduled samples were collected, which should be increased t o 21/31 = 68% by considering the 2 creditable make-up samples. Third quarter 2007 also passes th e 1 st qualifying test for data substitution.

Considering the 2 nd test, the quarterly mean for the incomplete data f rom 2 nd quarter 2006 equals 5.5 μ g/m 3 . The 2 nd quarter means for 2007 and 2008, with complete dat a, are each 4.5 μ g/m 3

. While emissions and meteorology were apparently sli ghtly higher in the incomplete 2 nd quarter of 2006, the difference of less than 1 μ g/m 3 in the three quarterly means, nearly complete data in 2006 (73%) and overall very low PM 2.5 (max 2 nd quarter value in 2006-2008 is 10.4 μ g/m 3 ), satisfy qualifying test 2 that emissions and meteorology fo r substituting data are comparable to emissions and meteorology for the missing data. For 3 rd quarter 2007, EPA concurred on 4 forest fire exceptional event data flags, resulting in a 3 rd quarter PM 2.5 mean of 11 μ g/m 3 . The 3 rd quarters for

2006 and 2008 had mean values of 20 and 8.6 μ g/m 3 , respectively. The 2007 quarterly mean with incomplete data falls between the quarterly means f or the other 2 years with complete quarterly data. Therefore, emissions and meteorology (with the exce ption of exceptional event wildfire emissions) are comparable, and the 2007 data also pass the 2 nd qualifying test.

The design value calculated using the incomplete da ta for Ravalli County is 30 μ g/m 3
compared to the 2006 PM 2.5 24-hour standard level of 35 μ g/m 3 , and the incomplete data show an attaining value, and thus pass the 3 rd qualifying test for substitution.

Given that the Ravalli County 2006-2008 data pass a ll the qualifying tests to allow data substitution, 2 substitution methods are provided b y EPA-454/R-99-008:

1) collocated data from other PM 2.5 monitors at the same site may be substituted for m issing data from the same day 2) the maximum value recorded in the same quarter as t hat which is incomplete, considered over the 3 year period under consideration may be s ubstituted for missing days, and the resulting 98 th percentile values can be averaged to a new design value.A continuous Federal Equivalent Method (FEM) monito r was first collocated with the Federal

Reference Method (FRM) monitor which had incomplete data on July 1, 2008; therefore, no
collocated data are available for the earlier incom plete quarters in 2006 and 2007. Substitution
method 1 is not available.

For substitution method 2, the highest 2 nd quarter value in 2006-2008 was the 10.4 μ g/m 3
recorded on May 18, 2007; the highest 3 rd quarter value in 2006-2008 (with the exception of EPA concurred exceptional events data) is the 34.8 μ g/m 3 recorded on August 19, 2008.

Prior to substitution, the 98 th percentile values and resulting design value for t he monitor are:

Raw, Incomplete Data: 2006 27.8 (2 nd max, 54 samples) 2007 27.8 (2 nd max, 96 samples) 2008 34.7 (3 rd max, 104 samples)

DV 30 μ g/m 3

After substituting 10.4 μ g/m 3 for missing 2 nd quarter 2006 samples and 34.8 μ g/m 3 for missing
3 rd quarter 2007 samples, these values are revised as follows:

With Substitution, Complete Data: 2006 27.8 (2 nd max, 58 samples) 2007 34.8 (3 rd max, 107 samples, counting 2 creditable samples an d the 2 substituted samples for the missing days preceding these two cr editable samples) 2008 34.7 (3 rd max, 104 samples)

DV 32 μ g/m 3

The substitutions above use the highest value recor ded in applicable quarters of 2006 through 2008 by the primary FRM monitor. The highest 24-ho ur value recorded by the secondary collocated
continuous FEM monitor in 2008 could instead be use d for the 3 rd quarter substitution. The continuous FEM was installed at the beginning of 3 rd quarter 2008. It had a high 3 rd quarter 2008

value of 36.8 μ g/m 3 . If the 36.8 μ g/m 3 from the collocated monitor is used for the data su bstitution for missing data in the 3 rd quarter of 2007, the resulting values are:

With Substitution of max POC 3 Continuous Data: 2006 27.8 (2nd max, 58 samples) 2007 36.8 (3rd max, 107 samples, counting 2 credita ble samples and the 2 substituted samples for the missing days preceding these two cr editable samples) 2008 34.7 (3rd max, 104 samples)

DV 33 μ g/m 3

Finally, because the continuous FEM has operated in Ravalli County since July of 2008, EPA has concluded that its data properly should be comb ined with the primary 1 in 3 day FRM at the same site. The resulting 2008 98 th percentile value (the 5 th maximum from 224 creditable days of data) isthereby reduced from the 34.7 μ g/m 3 shown above for the primary monitor to 32 μ g/m 3 . The

resulting decrease in design value for each of the 3 cases above is (34.7 - 32) / 3 = 0.9 μ g/m 3 . The ultimate result of combining the two collocated dat a sets from 2008 is a reduction in the attaining 2006-2008 design value shown for all the design val ue calculations considered. The actual final design value of 29 μ g/m 3 , reflecting the first substitution method above an d the combination of data from the primary FRM and secondary FEM in 2008 is s hown at http://www.epa.gov/airtrends/pdfs/dv_pm25_2006_2008 rev102809.xls

.

Given that the Ravalli monitor was eligible for dat a substitution using the 3 qualifying tests of EPA-454/R-99-008, and has an attaining design value both with the available incomplete data and with complete data as achieved through data substit ution in accordance with EPA guidance, EPA has determined that the draft 2006-2008 design value sp readsheet available when the designations rulemaking was signed was incorrect in showing Rava lli County as having attaining but incomplete (after substitution) data. The final spreadsheet a t http://www.epa.gov/airtrends/pdfs/dv_pm25_2006_2008 rev102809.xls was corrected to show Ravalli county as attainment and complete (with substitutio n) subsequent to the Administrator’s signature of the rulemaking. Accordingly, the initial designati on for the 2006 PM 2.5 NAAQS for the Ravalli area
should have been “unclassifiable/attainment” rather than “unclassifiable.” Rulemaking will be undertaken to correct Ravalli County, Montana’s des ignation to Unclassifiable/Attainment.