Ref: 8P-AR
MEMORANDUMUNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION 8 1595Wynkoop Street Denver, CO 80202-1129

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

SUBJECT: Element G, Emergency Powers, Adequate Contingency Plans.
FROM: Abby Fulton, Environmental Protection Specialist Air Program, Air Quality Planning Unit
TO: Docket File No. EPA-R08-0AR-2011-0725 

### NOV 2 52014

In the Emergency powers, Section 110(a)(2)(G) discussion ofEPA's Promulgation ofState Implementation Plan Revisions; Infrastructure Requirements for the 1997 and 2006 PM2.s, 2008 Lead, 2008 Ozone, and 2010 N02 National Ambient Air Quality Standards; South Dakota, proposed rule notice, we briefly discussed the events surrounding an elevated monitored level of 24-hour PM2.s on September4, 2009. Belowis a detailed description ofthe events ofthe date in question and ourreasoning for approval ofElement G.
For approval ofElement G, states must meet the requirements ofsubpart H of40 CFR Part 51 which requires states to classify regions and to develop contingency plans (also known as emergency episode plans) after ambient concentrations ofcertain criteriapollutants in an area have exceeded specified levels. For example, ifambient concentrations ofnitrogen dioxide in an area have exceeded 0.06 parts per million (annual arithmetic mean), then the area is classified as a Priority I region, and the state must develop a contingency planthat meets the requirements of sections 51.151 and 51.152. However, Subpart H does not currently address requirements for the 24-hour PM2.s standard.

In 2009, EPA issued a guidance memorandum that, among otherthings, recommended an approach for states to address the contingency plan requirements of 11O(a)(2)(G) with respect to the 2006 PM2.s NAAQS. 1The guidance, in Attachment A, suggested that states develop a contingency plan if, based on the most recent three calendaryears ofdata, an areawithin the state had monitored and recorded a 24-hour PM2.s level greaterthan 140.4 micrograms per cubic meter (!lglm\ For states that were to develop a contingency plan, the guidance recommended states set priority and emergency levels consistent with requirements of40 CFR 51.150 through 51.153. EPA notes that section 51.153 requires periodic reevaluation ofpriority classifications based onthe three most recent years ofair quality data.

1Memorandum from William T. Harnett, Director, Air Quality Policy Division, to Regional Air Division Directors, Guidance on SIP Elements Required under Sections 11O(a)(l) and (2) for the 2006 24-Hour Fine Particle (PM2 5) Standards (NAAQS), at 6-7 (Sep. 25, 2009).On September4, 2009, a continuous PM2.s air monitor operated by the State ofSouth Dakota in Wind Cave National Park registered a 24-hour level of303.6 Jlg/m3• Data for this monitor is contained within this docket. The monitor in question was a special purpose Federal Equivalent Method monitor collocated with a Federal Reference Method (FRM) State and Local Air Monitoring Stations (SLAMS) monitor. The SLAMS FRM was designated as the primary monitor at the site, and recorded 120.5 Jlg/m3 as the official regulatory value for the monitoring station that day. In order for EPAto determine if, as suggested by the guidance, it is appropriate to interpret section 110(a)(2)(G) as requiring South Dakotato develop a contingency plan, it is necessary to provide details surrounding the recorded value and air quality in South Dakota in general. On the day the secondary monitorrecorded a value of303.6 Jlg/m3

, the National Park Service conducted a prescribed burn in the Park.
The Park is adjacent to the Black Hills National Forest and lies entirely within rural Custer County (population 8,216, 2010 census). The closest majortown to the monitor is Hot Springs (population 3,711, 2010 census), 8 miles south ofthe monitor. The closest city is Rapid City (population 67,956,2010 census), 40 miles away. Onthe day oftheprescribed burn, PM2.s monitors elsewhere in the state recorded 24-hour levels from 4.3 Jlg/m3 to 20.8 Jlglm3

, well belowthe 24-hourprimary and secondary standard of35 Jlg/m3

.2The highest levels were in Sioux Falls and adjoining Union County, in the far southeastern part ofthe State. The two closest monitors to the Park, in Rapid City, recorded levels of9 and 10.5 Jlg/ m3• Generally, air quality in South Dakotawithrespect to PM2.s is good. No PM2.s monitor in South Dakotahas everrecorded a violation ofany PM2.s NAAQS, and the entire state, including Custer County, is designated unclassifiable/attainment for the 2006 PM2.s NAAQS. Formonitors with complete data for any given year, the highest ever 98th percentile 24-hr PM2.s value was 29.7 Jlg/m3 at the Union County site (30 miles NE ofSioux City, Iowa) in 2010. The highest ever annual mean3 PM2.s value (complete monitoring year) was 11.0 Jlg/m3at Watertown in 2012. Since 1999, PM2.s monitors in South Dakotarecord exceedances ofthe 24-hourPM2.s standard only once every four orfive years, on average. The top three exceedances, otherthan the one on September4, 2009, also occurred at the Wind Cave National Park monitor during prescribed burns; those recorded values ranged from 112.6 Jlg/m3 to 121.8 Jlg/m3

. After those, the next highest exceedance, 62 Jlg/m3

, was recorded in Rapid City. Furthermore, South Dakotahas recorded no levels ofambient air concentrations in the three most recent complete calendar years-2011, 2012, and 20134-thatexceed the 2009 guidance memorandum5 recommended levels for states to develop a contingencyplan for PM2.s.
Given this data, the unique circumstances oftheprescribed burn, and the fact that the official

2A table containingthe monitoring data is in the docket. 3 See 40 CFR Part 50, Appendix N, 4.3(a) for rounding requirements. 4A table containing the monitoring data is in the docket. 5 Memorandum from William T. Harnett, Director, Air Quality Policy Division, to Regional Air Division Directors, Guidance on SIP Elements Required under Sections llO(a)(l) and (2) for the 2006 24-Hour Fine Particle (PMzs) Standards (NAAQS), at p. 6-7 (Sep. 25, 2009).
2regulatory value from the SLAMS FRM on the day ofthe prescribed bum fell belowthe 140.4 ug/m3 threshold recommended inthe 2009 guidance memorandum, EPA finds it appropriate in these circumstances to interpret section 110(a)(2)(G) ofthe Act as not requiring the state to develop a contingency plan for PM2.s. However, this does not imply that other, future circumstances in the state cannottriggerthis requirement.

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