Idaho Area Designation 

Recommendations for the 

2006 PM2.5 NAAQS 

State of Idaho 

Department of Environmental Quality 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS ii 

Idaho Area Designation Recommendations for the 

2006 PM2.5 NAAQS 

Contents 

Executive Summary........................................................................................................................ 1 

1. Purpose and Background ........................................................................................................... 2 

2. Applicable Guidance.................................................................................................................. 2 

3. Ambient Air Quality Data.......................................................................................................... 2 

4. Nonattainment Boundaries for the Areas Violating the 24-hour PM2.5 Standard – Nine-Factor 

Analysis..................................................................................................................................... 5 

4.1 Pinehurst – Shoshone County Nonattainment Area Boundaries ........................................ 6 

Proposed geographic boundaries for the Pinehurst NAA....................................................... 23 

4.2 Franklin County – Cache Valley Nonattainment Area Boundaries.................................. 24 

Proposed geographic boundaries for the Franklin County – Cache Valley Nonattainment 

Area......................................................................................................................................... 35 

5. Summary................................................................................................................................... 37 

6. References................................................................................................................................. 37 

Appendix A – All Designated and Non-Designated Area Descriptionss ..................................... 38 

Appendix B – Supporting Documentation Locations................................................................... 47 

Names of Contacts .................................................................................................................. 48 

List of Tables 

Table 1. Annual PM2.5 Design Valuesa.......................................................................................... 4 

Table 2. 24-hour PM2.5 Design Valuesa

......................................................................................... 4 

Table 3. Annual emissions after prescribed and wild fire emissions are deducteda...................... 7 

Table 4. 24-hour PM2.5 monitoring data from continuous monitors in counties adjacent to 

Shoshone County .......................................................................................................... 8 

Table 5. County populations and population densities .................................................................. 9 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS iii 

Table 6. Annual VMT (vehicle miles traveled) for Shoshone County and adjacent counties..... 12 

Table 7. Population numbers, density, and growth figures for Shoshone County and adjacent 

counties ....................................................................................................................... 14 

Table 8. Annual emissions after prescribed and wild fire emissions are deducted. .................... 26 

Table 9. 2006 population densities for Franklin County and adjacent counties.......................... 27 

Table 10. Annual VMT (vehicle miles traveled) for Franklin County and adjacent counties in 

both Idaho and Utah.................................................................................................... 30 

Table 11. Population growth in the Cache Valley from 2000 to 2006 ........................................ 32 

Table 12. Population growth in Franklin County, Idaho from 2000 through 2006..................... 32 

Table 13. Descriptions of all areas of the state and the designations .......................................... 39 

Table 14. Monitor locations and ID numbers for PM2.5 nonattainment areas ............................. 47 

List of Figures 

Figure 1. Idaho PM2.5 Ambient Air Monitoring Network. ............................................................. 3 

Figure 2. Relationship of Franklin, Idaho and Logan, Utah FRM data......................................... 5 

Figure 3. Location map showing Pinehurst and the main valley of the Coeur d'Alene River, 

known as the Silver Valley. .......................................................................................... 6 

Figure 4. Population densities for the area surrounding Pinehurst .............................................. 10 

Figure 5. Roadways and interstate highway in and around Pinehurst. ........................................ 13 

Figure 6. Temperature profiles measured at the Spokane, Washington airport on December 20, 

2006, at 5:00am (left) and 5:00pm (right). ................................................................. 17 

Figure 7. Windrose for Pinehurst, Idaho, December 18 - 22, 2006, the period of a PM2.5

stagnation episode....................................................................................................... 18 

Figure 8. Wind patterns during another winter PM2.5 stagnation episode in Pinehurst, Idaho, 

January 2 - 5, 2006...................................................................................................... 18 

Figure 9. Annual windrose for 2006, Pinehurst, Idaho................................................................ 19 

Figure 10. Windrose for Pinehurst, Idaho in the wintertime. Data from January, February, 

November, and December 2006. ................................................................................ 19 

Figure 11. Pollution rose for Pinehurst, Idaho for wintertime: November 2005 – March 2006. 20 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS iv 

Figure 12. Pollution rose for Pinehurst, Idaho for wintertime: November 2006 – March 2007. 20 

Figure 13. Modeling results of hypothetical sources, showing that sources located in the Silver 

Valley do not contribute to a violation of the PM2.5 standard in Pinehurst. ............... 21 

Figure 14. Pinehurst PM10 NAA (nonattainment area)................................................................ 22 

Figure 15. Proposed geographic boundary for the Pinehurst PM2.5 nonattainment area............. 24 

Figure 16. Location map showing the Cache Valley and the boundaries of Franklin County, 

Idaho and Cache County, Utah. .................................................................................. 25 

Figure 17. Population density for the Cache Valley.................................................................... 28 

Figure 18. Roadways in the Cache Valley................................................................................... 31 

Figure 19. January 2004 temperature contour map with PM2.5 concentration (yellow) and 1997 

PM2.5 National Ambient Air Quality Standard (green) (Martin, 2006)..................... 34 

Figure 20. Average temperature profiles in Cache Valley during January 1 - 17, 2004 (Martin, 

2006) ........................................................................................................................... 34 

Figure 21. Proposed geographic boundaries for the Idaho portion (Franklin County) of the 

proposed Cache Valley PM2.5 nonattainment area...................................................... 36 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 1 

Executive Summary 

In a July 20, 2007 letter, the Environmental Protection Agency (EPA) formally requested that 

Governor Otter submit a list of all areas of Idaho, including a recommendation for designation of 

each area, regarding attainment of the National Ambient Air Quality Standards (NAAQS) for 

fine particulate matter (PM2.5). 

Designation recommendations must adhere to EPA policy. For areas designated as 

nonattainment, EPA recommends determining the nonattainment area (NAA) boundary on a 

case-by-case basis using the nine-factor analysis suggested in EPA guidance. The nine-factor 

analysis includes the following: 

1. Emissions in areas potentially included vs. excluded from the NAA 

2. Air quality in areas potentially included vs. excluded from the NAA 

3. Population density and the degree of urbanization, including commercial development, 

in areas potentially included vs. excluded from the NAA 

4. Traffic and commuting patterns 

5. Expected growth (including extent, pattern, and rate of growth) 

6. Meteorology (weather/transport patterns) 

7. Geography/topography (mountain ranges or other air basin boundaries) 

8. Jurisdictional boundaries (e.g., counties, air districts, reservations, etc.) 

9. Level of control of emission sources. 

Based on monitoring data and the nine-factor analysis, DEQ recommends the following 

designations: 

• Attainment – the airsheds of Benewah County, the Treasure Valley (Ada and Canyon 

Counties), and Pocatello (Bannock County). 

• Nonattainment – the airsheds of Pinehurst (portion of Shoshone County) and the Idaho 

portion of the Cache Valley (a portion of Franklin County, Idaho). 

• Unclassifiable – all remaining airsheds not identified above. 

DEQ used the nine-factor analysis to determine the appropriate boundary for each of the areas 

designated as nonattainment. Figures 15 (page 24) and 21 (page 36) present the recommended 

NAA boundary for the Pinehurst area and the Idaho portion of the Cache Valley, respectively. 

The legal descriptions of recommended designated areas are included in Table 13 in 

Appendix A. 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 2 

1. Purpose and Background

The Environmental Protection Agency (EPA) revised the national ambient air quality standards 

(NAAQS) on October 17, 2006, to provide increased protection of public health and welfare 

from fine particle pollution. The 24-hour standard for PM2.5 (particles with an aerodynamic 

diameter of 2.5 micrometers or less) was revised from 65 micrograms per cubic meter (μg/m3) to 

35 μg/m3. The annual standard remained unchanged at 15 μg/m3. The effective date for the new 

standard was December 18, 2006. 

The state of Idaho is required to submit to EPA a list of all areas in the state and to recommend 

designations for each area as “attainment,” “nonattainment,” or “unclassifiable” with respect to 

the revised standard within one year of promulgation, in accordance with section 107(d)(1)(A) of 

the Clean Air Act. The recommendations are due to EPA by December 18, 2007. 

The Clean Air Act allows that areas may be designated as follows: 

(i) nonattainment, for any area that does not meet (or that contributes to ambient air 

quality in a nearby area that does not meet) the national primary or secondary 

ambient air quality standard for the pollutant; 

(ii) attainment, for any area (other than an area identified by clause (i)) that meets the 

national primary or secondary ambient air quality standard for the pollutant; and 

(iii) unclassifiable, for any area that cannot be classified on the basis of available 

information as meeting or not meeting the national primary or secondary ambient 

air quality standard for the pollutant. 

This document provides Idaho’s recommendations for PM2.5 designations of all areas within the 

state and fulfills Idaho’s requirements under section 107(d)(1)(A) of the Clean Air Act. 

2. Applicable Guidance

The following EPA guidance was used for developing the PM2.5 area designation 

recommendations: 

• Area Designations for the Revised 24-hour Fine Particle National Ambient Air 

Quality Standard; Memo from Robert Meyers, Acting Assistant Administrator to 

Regional Administrators, dated June 8, 2007. 

• Designations for the Fine Particle National Ambient Air Quality Standards; Memo 

from Jeffrey R. Holmstead, Assistant Administrator to Regional Administrators, 

dated April 1, 2003. 

3. Ambient Air Quality Data

EPA recommends that states identify violating areas using the most recent three years of air 

quality monitoring data (2004 – 2006). In general, violations are identified using data from 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 3 

federal reference method (FRM) and federal equivalent method (FEM) monitors that are sited 

and operated in accordance with 40 Code of Federal Regulations (CFR) Part 58, as revised on 

October 17, 2006. Idaho’s PM2.5 ambient monitoring network is shown in Figure 1. Currently 

operating monitors are indicated with a star; all others were operated previously but are no 

longer. 

Figure 1. Idaho PM2.5 Ambient Air Monitoring Network. 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 4 

Tables 1 and 2 present the annual and 24-hour PM2.5 design values, respectively, for those 

monitors that met the CFR requirements for determining PM2.5 violations. The precise design 

value for each standard is described in the appropriate table. 

Table 1. Annual PM2.5 Design Valuesa

Weighted Annual 

Arithmetic Mean 

3-Year Average of 

Annual Meansc 

City County MSAb 2004 2005 2006 2004 – 2006 

Pocatello Bannock Pocatello, ID 8.69 8.18 6.36 7.7 

St. Maries Benewah N/A 9.30 9.51 9.69 9.5 

Logan, Utahd Cache Logan, UT - ID 15.17 12.95 8.54 12.2 

Boise Ada Boise City – Nampa Idaho 8.98 8.59 7.99 8.5 

Nampa Canyon Boise City – Nampa Idaho 9.10 9.22 7.61 8.6 

Pinehurst Shoshone N/A 12.04 12.71 11.52 12.1 

a. Annual PM2.5 design value is the 3-year average of the annual means. 

b. MSA – metropolitan statistical area 

c. A value of 15.1 or greater indicates a violation. 

d. The Logan, Utah monitor is included because the city of Franklin in Franklin County, Idaho is part of the Logan, 

UT-ID Metropolitan Statistical Area. The Franklin County monitor does not meet the CFR requirements for 

determining PM2.5 violations. 

Table 2. 24-hour PM2.5 Design Valuesa

PM2.5 24-hour 98th

Percentile 

3-Year Average of 98th

Percentilesc 

City County MSAb 2004 2005 2006 2004 – 2006 

Pocatello Bannock Pocatello, ID 32.5 29.8 20.6 28 

St. Maries Benewah N/A 24.8 34.3 32.9 31 

Logan, Utahd Cache Logan, UT - ID 101.5 56.7 29.4 63

Boise Ada Boise City – Nampa Idaho 35.5 26.4 28.5 30 

Nampa Canyon Boise City – Nampa Idaho 43.8 36.3 22.4 34 

Pinehurst Shoshone N/A 35.7 45.7 33.5 38 

a. 24-hour PM2.5 design value is the 3-year average of the 98th percentile for each year. 

b. MSA – metropolitan statistical area. 

c. A value of 36 or greater indicates a violation, and is indicated in bold face. 

d. The Logan, Utah monitor is included because the city of Franklin in Franklin County, Idaho is part of the Logan, 

UT-ID MSA. The Franklin County monitor does not meet the CFR requirements for determining PM2.5 

violations. 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 5 

Based on the available monitoring data in Idaho that meets the 40 CFR Part 58 requirements for 

2004 – 2006, only Pinehurst in Shoshone County has a design value exceeding the 24-hour PM2.5

NAAQS. Therefore, DEQ recommends that portions of Shoshone County be designated as 

nonattainment. 

DEQ does not have three consecutive years of monitoring data on which to base an attainment 

decision for Franklin County. However, available monitoring data from Franklin County does show 

a significant relationship with data from the Logan monitor (Figure 2). Values from Franklin 

County data average about 90% of Logan values. This is consistent with the findings of a PM2.5

saturation study conducted by Utah’s DEQ. Based on the 2004-2006 data collected by the Logan 

monitor, the Cache County design value for the 24-hour NAAQS is 63 μg/m3 and it is appropriate 

to conclude that a portion of Franklin County should be included as part of the area that violates the 

24-hour NAAQS. Therefore, DEQ recommends a portion of Franklin County be designated as 

nonattainment. 

Logan v. Franklin, 2005 PM2.5 24-hour averages, all data

y = 0.9119x - 1.9131

R2

 = 0.8926

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60 70 80 90

Logan, ug/m3

Franklin, ug/m3

Figure 2. Relationship of Franklin, Idaho and Logan, Utah FRM data. 

4. Nonattainment Boundaries for the Areas Violating the 24-hour PM2.5

Standard – Nine-Factor Analysis 

According to EPA’s June 2007 Guidance Memorandum by Robert J. Meyers: 

“EPA believes that, in making their boundary recommendations for nonattainment areas, States 

and Tribes should evaluate each area on a case-by-case basis. The CAA requires that a

nonattainment area must include not only the area that is violating the standard, but also nearby 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 6 

areas that contribute to the violation. Thus, for each monitor or group of monitors that indicate 

violations of a standard, EPA will establish nonattainment boundaries that cover a sufficiently 

large area to include both the area that violates the standard and the areas that contribute to the 

violations. EPA recommends that States and Tribes base their boundary recommendations for 

violating areas on an evaluation of the nine factors used in the prior PM2.5 designations process, as 

well as on any other relevant factors or circumstances specific to a particular area.” 

Both of Idaho’s proposed nonattainment counties are rural; therefore, it would not be appropriate to 

identify the entire counties as nonattainment. Instead, Idaho evaluated Pinehurst in Shoshone 

County and Franklin County using the nine-factor analysis recommended in EPA guidance to 

determine the appropriate NAA boundary for each area. Both NAA boundaries must cover a 

sufficiently large area to include both the area that violates the standard and the areas that contribute 

to the violations. 

4.1 Pinehurst – Shoshone County Nonattainment Area Boundaries 

As can be seen in Figure 3, the town of Pinehurst is located in a small, enclosed, bowl-shaped valley 

in Shoshone County, Idaho. Based on air quality data for 2004-2006, the PM2.5 FRM located at the 

Pinehurst Elementary School recorded violations of the 24-hour PM2.5 standard, with a design value 

of 38 μg/m3

 (Table 2). 

Figure 3. Location map showing Pinehurst and the main valley of the Coeur d'Alene River, 

known as the Silver Valley. 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 7 

FACTOR 1: Emissions in areas potentially included vs. excluded from the NAA 

There are no major particulate-emitting industrial sources located in Shoshone County; wildfire and 

prescribed burning are large contributors to regional emissions totals during spring, summer, and 

fall. 

Shoshone County has emissions totals similar to those of adjacent counties in Idaho and Montana 

(Table 3). Shoshone and these bordering counties largely lack commercial and industrial 

development. The exceptions are Kootenai County's Coeur d'Alene area and the town of Sandpoint 

in Bonner County. Both of these areas have much higher population densities and are home to 

several industrial point sources, so the emissions totals are higher. Both Coeur d'Alene and 

Sandpoint are at least 45 kilometers to the west of the Pinehurst area. 

The Idaho 2005 emissions inventory indicates sources of pollutants in Shoshone County are 

residential wood heating, tailpipe emissions, paved road fugitive dust, and asphalt paving. With 

sparse roadway miles and low vehicles miles travelled, wood heating of homes is the predominant 

emissions source in Pinehurst. However, Pinehurst is surrounded by state owned and privately 

owned timber lands. Slash burning occurs on these lands and is a large emissions source in this 

area. Smoke generated from local slash burning activities has been directly linked to recent 

excursions of the PM2.5 24-hour standard. Open burning of yard debris is also considered a 

significant contributor to PM2.5 concentrations buildup in the Pinehurst airshed. 

Table 3. Annual emissions after prescribed and wild fire emissions are deducteda 

County 

SOx

(TPY) 

NOx

(TPY) 

NH3

(TPY) 

VOC 

(TPY) 

PM2.5

(TPY) 

Shoshone 68 998 52 2963 289 

Benewah 81 863 217 2029 208 

Bonner 331 4440 272 6019 944 

Clearwater 74 837 227 2043 128 

Kootenai 458 6339 1290 10628 2000 

Latah 191 2278 813 3770 579 

Mineral (MT) 87 933 133 609 195 

Sanders (MT) 75 525 229 617 298 

a. http://www.epa.gov/ttn/naaqs/pm/pm25_2006_techinfo.html (2005 NEI) 

SOx – oxides of sulphur; NOx – oxides of nitrogen; NH3 – ammonia; VOC – 

volatile organic compound; PM2.5 – particulate matter with an aerodynamic 

diameter of 2.5 micrometers or less; TPY – tons per year 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 8 

FACTOR 2: Air quality in areas potentially included vs. excluded from the NAA 

As seen in Table 2, the monitor located in Pinehurst has a 24-hour design value of 38 μg/m3

, which 

violates the 24-hour PM2.5 standard. Currently, no other PM2.5 air quality data, using either FRM or 

continuous monitors, have been collected at any other location within Shoshone County. 

DEQ operates real-time continuous PM2.5 particulate monitors in several counties adjacent to 

Shoshone County. The data gathered from these continuous monitors indicate that these adjacent 

counties do not violate the PM2.5 standard. Table 4 presents the data from continuous monitors 

from counties adjacent to Shoshone County, along with data from the monitor located in Pinehurst. 

Table 4. 24-hour PM2.5 monitoring data from continuous monitors in counties adjacent to 

Shoshone County 

PM2.5 24-hour 98th Percentile (μg/m3) 

3-Year Average of 

98th Percentiles 

County (City)a 2004 2005 2006 2004 – 2006 

Shoshone (Pinehurst)b 40.2 39.6 33.8 38 

Latah (Moscow) 14.6 11.3 26.9 18 

Kootenai (Coeur d’Alene) 26.7 24.1 27.5 26 

Bonner (Sandpoint) 21.7 19.7 24.2 22 

a. An FRM monitor is located in Benewah County (St. Maries). The data for this monitor is shown in 

Table 2. 

b. A real-time continuous PM2.5 monitor is co-located with the FRM monitor in Pinehurst. 

FACTOR 3: Population density and the degree of urbanization, including commercial 

development, in areas potentially included vs. excluded from the NAA 

As seen in Table 5, surrounding counties, with the exception of Kootenai, have low population 

densities. The town of Pinehurst has a higher population density than its immediately surrounding 

area (Figure 4). Shoshone County has just over 13,000 residents. There are several small towns 

along the Interstate 90 (I-90) corridor that bisects Idaho's panhandle along the Silver Valley. 

According to census data from the EPA technology transfer network (TTN), these towns range in 

size from the largest, Kellogg with 2,296 residents, to the second-largest, Pinehurst with 1,614, to 

Enaville, Gem, Kinston, and Silverton, which are small enough that they do not register in the 

census data. 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 9 

Table 5. County populations and population densities 

County 2006 Population County Size (km2) 

2006 Population Density 

(population per km2) 

Shoshone* 13,180 6822.1 2 

Benewah 9,347 2009.9 5 

Bonner 41,275 4500.4 9 

Clearwater 8,324 6375.4 1 

Kootenai 131,507 3225.1 41 

Latah 35,029 2788.7 13 

Mineral (MT) 4,057 3159.5 1 

Sanders (MT) 11,138 7154.3 2 

* Town of Pinehurst, Idaho population: 1,614; Pinehurst, Idaho population density: approximately 700 

population per km2

. (See population density map in Figure 3.) 

Sources: http://www.census.gov/popest/counties/CO-EST2006-03.html for 2006 populations; 

http://www.census.gov/population/censusdata/90den_stco.txt for size.
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 10 

Figure 4. Population densities for the area surrounding Pinehurst (http://sedac.ciesin.columbia.edu:9080/entri/index.jsp; accessed July 1, 2007). 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 11 

FACTOR 4: Traffic and commuting patterns 

Several counties surrounding Shoshone County have substantially higher annual vehicle miles 

traveled (VMT) than Shoshone County. The following commuter information indicates that this 

travel is not crossing county or state borders in substantial amounts, either into or out of 

Pinehurst or Shoshone County. 

Commuting information from the EPA TTN 2006 PM2.5 technical data: 

• Shoshone County, the county of interest, has a total of 5,275 commuters. 

- Commuters who remain in Shoshone County: 4,304 

• Benewah County, an adjacent county, has a total of 3,427 commuters. 

- Commuters from Benewah County to Shoshone County: 78 

- Commuters that remain in Benewah County: 2,875 

• Bonner County, an adjacent county, has a total of 15,570 commuters. 

- Commuters from Bonner County to Shoshone County: 16 

- Commuters that remain in Bonner County: 12,968 

• Clearwater County, an adjacent county, has a total of 3,207 commuters. 

- Commuters from Clearwater County to Shoshone County: 3 

- Commuters that remain in Clearwater County: 2,721 

• Kootenai County, an adjacent county, has a total of 49,351 commuters. 

- Commuters from Kootenai County to Shoshone County: 377 

- Commuters that remain in Kootenai County: 38,744 

• Latah County, an adjacent county, has a total of 16,837 commuters. 

- Commuters from Latah County to Shoshone County: 34 

- Commuters that remain in Latah County: 13,249 

• Mineral County (Montana), an adjacent county, has a total of 1,629 commuters. 

- Commuters from Mineral County to Shoshone County: 6 

- Commuters that remain in Mineral County: 1,220 

• Sanders County (Montana), an adjacent county, has a total of 3,902 commuters. 

- Commuters from Sanders County to Shoshone County: 0 

- Commuters that remain in Sanders County: 3,337 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 12 

Table 6 presents the VMT for Shoshone County and the bordering counties located in both Idaho 

and Montana. The roadways in and around Pinehurst are shown in Figure 5, along with I-90 just 

north of Pinehurst. The average annual VMT for the section of I-90 between Pinehurst and 

Smelterville is 8.18 million. The projected annual growth for the traffic on this section of I-90 is 

4.5%. 

Table 6. Annual VMT (vehicle miles traveled) for Shoshone County and adjacent counties 

County VMT (Millions) 

Shoshone 226.8688 

Benewah 153.2637 

Bonner 629.6788 

Clearwater 146.7322 

Kootenai 852.3298 

Latah 572.4237 

Mineral (MT) 202.5482 

Sanders (MT) 96.386 

Source: EPA TTN 2005_vmt_county_level-1.xls 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 13 

Figure 5. Roadways and interstate highway in and around Pinehurst. 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 14 

FACTOR 5: Expected growth (including extent, pattern, and rate of growth)

According to 2000 and 2006 census data (Table 7), the population of Shoshone County has 

decreased by 4.1%. However, data from the Idaho Department of Commerce indicates a slight 

increase (1.3%) in Pinehurst population from 2005 to 2006. 

(http://cl.idaho.gov/data/census/CityPops2000-2005.xls) 

Population growth is taking place in nearby Kootenai and Bonner counties. With its lakeside 

mountain setting, the Sandpoint area in Bonner County has become attractive to retirees, and it 

also provides employment; there are a few point sources located in the area. Coeur d'Alene is 

showing rapid growth in Kootenai County due to the same reasons. Furthermore, Coeur d'Alene 

is near Spokane, Washington, and it becomes even more attractive for relocating workers. These 

two population centers, Sandpoint and Coeur d'Alene, are more than 45 kilometers away from 

Pinehurst. 

Population and population growth figures for Shoshone County and the adjacent counties are 

presented in Table 7. 

Table 7. Population numbers, density, and growth figures for Shoshone County and 

adjacent counties 

County 

2000 

Population 

2006 

Population 

Growth 

2000 - 2006 % Change 

Shoshone* 13,747 13,180 -567 -4.1 

Benewah 9,196 9,347 151 1.6 

Bonner 37,031 41,275 4,244 11.5 

Clearwater 8,895 8,324 -571 -6.4 

Kootenai 109,550 131,507 21,957 20 

Latah 34,861 35,029 168 0.5 

Mineral (MT) 3,883 4,057 174 4.5 

Sanders (MT) 10,253 11,138 885 8.6 

* Town of Pinehurst, Idaho population: 1,614 (2006); Town of Pinehurst, Idaho population density 

(2006) approx. 700 pop. per sq. km (Figure3 

* Town of Pinehurst, Idaho population: 1,614 (2006); town of Pinehurst, Idaho population density 

(2006): approximately 700 population per km2

. (See population density map in Figure 3.); town of 

Pinehurst, Idaho population change: -2.8% (2000 to 2006). 

Sources: http://factfinder.census.gov/servlet for 2006 populations; 

http://www.census.gov/population/censusdata/90den_stco.txt for size; http://www.citydata.com/city/Pinehurst-Idaho.html for city data. 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 15 

FACTOR 6: Meteorology (weather/transport patterns) AND 

FACTOR 7: Geography/topography (mountain ranges or other air basin boundaries) 

Factors 6 and 7 are discussed together because they are thoroughly interrelated. 

Pinehurst is located in a valley near the western end of the Silver Valley, a historic mining area 

along the south fork of the Coeur d’Alene River. The Silver Valley is about 22 miles long and 

varies from only one-tenth of a mile to slightly more than three-fourths of a mile wide. Elevation 

in the western end of the valley is 2,200 feet rising to 3,300 feet at the eastern end. The city of 

Pinehurst sits in the Pine Creek Valley, which connects with the Silver Valley through a narrow 

gap. Figure 3 shows the relationship of Pinehurst and the Silver Valley. 

Although the climate in northern Idaho is often influenced by moist and relatively mild Pacific 

storms, occasional masses of arctic air can bring bitter cold weather during the winter months. 

When cold, stable air is advected into the region by arctic outbreaks or cold Pacific storms 

following the passage of a cold front, cold air becomes pooled in the narrow mountain valleys of 

the region. Such cold air masses can further stabilize when high pressure aloft overtakes the 

region. Under such a situation, a prolonged strong inversion layer (or layers) near the ground 

limits vertical mixing, trapping local pollutants close to the valley floor. Weak Pacific storms are 

prevalent; however, they often do not produce sufficient mixing to improve air quality in this 

valley. Figure 6 shows the upper air temperature profiles from the Spokane Airport during one 

such inversion episode. 

The pollutant concentrations may build from day to day when the inversion does not break up in 

the afternoon, as shown on the right hand side of Figure 6. During episodes such as this, 

emissions increase because more home heating is required due to the cold temperatures 

(Factor 1). The low sun angle at this latitude, short length of the days during winter months, light 

and variable winds, and strong likelihood of snow cover to reflect solar radiation all limit 

atmospheric heating and aggravate the situation. As a result, the inversion builds and may not 

break for many days. Under this kind of stagnation condition, pollutant concentrations may build 

quickly, especially in the areas like Pinehurst where airflow is greatly restricted by terrain. 

When local emissions are high, even short-lived overnight inversions can affect air quality 

sufficiently to produce high pollutant concentrations. The main Coeur d’Alene River valley (to 

the west) is more open and better aligned with synoptic westerly windflow and, as a result, 

appears to be better ventilated. 

The windrose graph in Figure 7 shows the frequency of wind speed and wind direction in the 

Pinehurst area for a PM2.5 stagnation episode from December 18 through December 22, 2006. 

The wind was light from the south for most of the time during this episode. The maximum 

24-hour PM2.5 concentration of 34.2 μg/m3 during this episode occurred on December 22, 2006. 

A similar wind pattern was observed for another PM2.5 stagnation episode (January 2-5, 2006, 

shown in Figure 8). The maximum 24-hour PM2.5 concentration of 21.1 μg/m3

 occurred on 

January 5, 2006. These wind patterns strongly suggest that under stagnation conditions, the 

exchange of air mass between Pinehurst and the other communities to the east in the Silver 

Valley is very limited. The wind data also show that wind speed is generally low in Pinehurst 

year-round (Figures 9 and 10). Pollution roses (Figures 11 and 12) also show that the highest 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 16 

PM2.5 concentrations occur when winds are south-southeast. A northeastern flow can actually 

infiltrate this valley and improve air quality. 

The airflow and dispersion patterns of the Pinehurst area were further analyzed by dispersion 

modeling. Modeling using the CALPUFF air quality dispersion model with 500-meter terrain 

resolution was conducted to simulate the episodes during January 3 – 4 and December 18 – 22, 

2006. A low level hypothetical “source” (similar to a woodstove chimney) was located first in 

Pinehurst, then in other communities in the Silver Valley, to observe the predicted relative flow 

patterns during inversion conditions. Figure 13 shows the modeling results. The results show 

insignificant air exchange between Pinehurst and other towns in the main Silver Valley. For a 

hypothetical source located in Smelterville, the predicted 24-hour relative concentration impact 

at the Pinehurst monitor is less than 0.1% of the impact in Smelterville itself and even lower 

when the source was located in the other towns in the Silver Valley more distant from Pinehurst. 

When the hypothetical source was located in Pinehurst, the predicted 24-hour relative 

concentration impact in Smelterville is less than 0.1% of the impact in Pinehurst itself. 

All the information presented for these two factors demonstrates that Pinehurst is largely cut off 

from the Silver Valley airshed. The minimal pollutant transfer behavior in the model runs is 

explained by the narrow gap in the terrain connecting Pinehurst with the Silver Valley. When 

stagnation occurs and cold air pools in Pinehurst, the cold air drains to the north, merging with 

the main Silver Valley drainage winds, thereby blocking the main valley flows from entering 

Pinehurst. 

The greatest contributing emissions source to PM2.5 concentrations above the 24-hour standard 

that occurs consistently is residential wood heating between the hours of 8 p.m. and 6 a.m. 

However, DEQ has recently gathered data, using a continuous monitor, which shows PM2.5

concentrations greater than the 24-hour standard that have been directly linked to slash burning 

events. Such impacts have been reported to occur from slash burns on the ridges surrounding 

Pinehurst and neighboring valley floors when smoke rises toward the ridge facing away from 

Pinehurst, then apparently downwashes on the lee side of the ridge in Pinehurst, resulting in 

short-term peak concentrations. These short-term peak concentrations (1 to 2 hours) can cause 

an excursion of the 24-hour standard because the background concentration, due to residential 

wood heating, is typically already elevated when the slash burning impacts Pinehurst. 

Although slash burning is infrequent and the location and time of year is rarely constant, the realtime monitoring data indicate that slash burning can contribute to a violation of the PM2.5

24-hour standard. These impacts suggest that the Pine Creek drainage, the nearest ridges 

immediately surrounding Pinehurst, and the nearest valley areas just beyond those ridges should 

be included in the NAA boundaries to address slash burning. 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 17 

Figure 6. Temperature profiles measured at the Spokane, Washington airport on December 20, 2006, at 5:00 

5:00 p.m. (right). A deep inversion layer persisted in the area, which did not break up during the daytime. When this occurs, ptrapped from day to day and the inversion builds. 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 18 

Figure 7. Windrose for Pinehurst, Idaho, December 18 – 22, 2006, the period of a PM2.5

stagnation episode. 

Very few north and northeasterly winds occurred throughout the period. This indicates 

that there was very little air mass exchange between Pinehurst and the nearby towns in the 

Silver Valley. 

Figure 8. Wind patterns during another winter PM2.5 stagnation episode in Pinehurst, 

Idaho, January 2 – 5, 2006. 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 19 

Figure 9. Annual windrose for 2006, Pinehurst, Idaho. 

This shows that the wind speed in Pinehurst is generally low throughout the entire year. 

Winds rarely reach Pinehurst from the Silver Valley to the north and northeast. 

Figure 10. Windrose for Pinehurst, Idaho in the wintertime. Data from January, 

February, November, and December 2006. 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 20 

Figure 11. Pollution rose for Pinehurst, Idaho for wintertime: November 2005 – March 

2006. 

Figure 12. Pollution rose for Pinehurst, Idaho for wintertime: November 2006 – March 

2007. 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 21 

Figure 13. Modeling results of hypothetical sources, showing that sources located in the 

Silver Valley do not contribute to a violation of the PM2.5 standard in Pinehurst. 

FACTOR 8: Jurisdictional boundaries (e.g., counties, air districts, reservations, etc.) 

The town of Pinehurst is currently designated nonattainment for PM10. Figure 14 illustrates that 

the PM10 NAA does not include locations within the Silver Valley or surrounding counties. 

Shoshone County lies entirely within DEQ’s Coeur d’Alene Region and EPA Region 10. The 

town of Pinehurst is also located in the Idaho/Montana Airshed Group, which implements the 

smoke management program for prescribed fire on both public and private lands. 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 22 

Figure 14. Pinehurst PM10 nonattainment area. 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 23 

FACTOR 9: Level of control of emission sources

As stated above, the town of Pinehurst is currently a PM10 NAA, and specific voluntary controls 

have been implemented that partially pertain to PM2.5 emissions. The major emissions sources 

of both PM10 and PM2.5 in Pinehurst are residential wood heating and open burning. DEQ 

implements a daily air quality advisory program for woodstove and open burning from 

November 1 through March 31 of each year. Open burning and slash burning in the fall is 

currently controlled by DEQ burn bans issued based upon ventilation predictive models. The 

Montana/Idaho Airshed Group also participates in burning restrictions during October and 

November.

Proposed geographic boundaries for the Pinehurst NAA 

Shoshone County is considered rural, and the main emissions sources that occur in the town of 

Pinehurst are residential wood heating and vehicles. However, open burning and slash burning is 

a large emissions source that can contribute to a violation of the 24-hour PM2.5 standard. The 

location and time of occurrence of slash burning and open burning vary from year to year. Slash 

burning can occur on all state and privately owned land that surrounds the town of Pinehurst. 

Analysis of the Pinehurst area shows that topographical features and wintertime meteorology 

limit transport of pollutants between the Silver Valley and Pinehurst. Pollutants emitted within 

Pinehurst remain trapped, and emissions from the Silver Valley do not contribute to PM2.5

pollutant concentrations. 

Due to topographical features, seasonal wintertime meteorology, and types of emission sources, 

DEQ determined that the appropriate boundary for the PM2.5 nonattainment area extends beyond 

the current PM10 NAA boundary. This expanded area includes those areas where, if slash 

burning occurs, it could contribute to a violation of the 24-hour PM2.5 standard. 

DEQ’s proposed geographic boundary for the Pinehurst PM2.5 NAA is shown in Figure 15.
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 24 

Figure 15. Proposed geographic boundary for the Pinehurst PM2.5 nonattainment area. 

4.2 Franklin County – Cache Valley Nonattainment Area Boundaries 

The Cache Valley straddles the Utah-Idaho border, extending into both Cache County, Utah and 

Franklin County, Idaho (Figure 16). The Cache Valley is a bowl-shaped valley measuring 

approximately 60 kilometers north to south and 20 kilometers east to west. The Wellsville 

Mountains lie to the west, and on the east lie the Bear River Mountains; both are northern 

branches of the Wasatch Range. The Idaho portion of the valley is relatively flat, traversed by 

the Bear River, and dotted with small farm towns in the west and the larger towns of Preston and 

Franklin in the east along the benches of the Bear River Mountains. 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 25 

Figure 16. Location map showing the Cache Valley and the boundaries of Franklin 

County, Idaho and Cache County, Utah. 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 26 

FACTOR 1: Emissions in areas potentially included vs. excluded from the NAA 

DEQ gathered emissions information for Franklin County and the bordering counties in Idaho. 

Utah will provide the information necessary for their adjacent counties and that portion of the 

proposed PM2.5 NAA when they submit their recommendations. 

The main sources of emissions during winter in Franklin County are vehicles (tailpipe emissions 

and fugitive road dust), residential wood heating, and agriculture (feedlot and dairy ammonia). 

With the exception of the ruminant animal emissions, emissions created in Franklin County 

during winter are population-based. All major industrial point sources located in Idaho are more 

than 60 to 90 kilometers from the Cache Valley. 

Table 8 presents direct PM2.5 emissions, as well as the pollutants that can act as PM2.5 precursors. 

Because elevated PM2.5 concentrations in the Cache Valley are a wintertime phenomenon that 

threaten only the 24-hour PM2.5 standard (Factors 6 and 7), prescribed and wild fire emissions 

occurring in the other seasons were not included in Table 8. 

Table 8. Annual emissions after prescribed and wild fire emissions are deducted. 

COUNTY 

SOx 

(TPY) 

NOx 

(TPY) 

NH3 

(TPY) 

VOC 

(TPY) 

PM2.5

(TPY) 

Franklin 57 851 1221 2290 447 

Bannock 177 4020 683 7178 1343 

Bear Lake 34 2103 361 2380 359 

Caribou 12623 2452 1221 2454 1536 

Oneida 40 509 325 1409 243 

Source: http://www.epa.gov/ttn/naaqs/pm/pm25_2006_techinfo.html (2005 

NEI) 

SOx – oxides of sulphur; NOx – oxides of nitrogen; NH3 – ammonia; VOC – 

volatile organic compound; PM2.5 – particulate matter with an aerodynamic 

diameter of 2.5 micrometers or less; TPY – tons per year

Factor 2: Air quality in areas potentially included vs. excluded from the NAA 

Air quality data have indicated that Cache Valley violates the 24-hour PM2.5 standard. In fact, 

the 24-hour design value for Logan, Utah is by far the highest of any station within Utah’s 

monitoring network. 

DEQ collected PM2.5 data in the Idaho portion of the Cache Valley. There is not yet a three-year 

data set to determine compliance with the PM2.5 standard, but indications are that once the data is 

available, it will also indicate a violation of the 24-hour standard in the Idaho portion (Figure 2). 

DEQ established monitors in both Franklin and Preston, Idaho in 2004. These monitors 

confirmed results of the Utah State University PM2.5 saturation study conducted by Dr. Randy 

Martin (2006), which indicated a fairly homogenous air mass throughout the Cache Valley 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 27 

during inversions. The monitor in Preston has been removed due to its high correlation with the 

Franklin monitor, but DEQ continues to operate the Franklin monitor. 

Factor 3: Population density and the degree of urbanization, including commercial 

development, in areas potentially included vs. excluded from the NAA 

Franklin County and the Cache Valley are part of the Logan core based statistical area (CBSA) 

according to EPA's 2005 national emissions inventory (NEI) data on their TTN Web site. The 

Idaho portion of the Cache Valley lies entirely within Franklin County. The majority of the 

population of this rural county is located in small towns. The two largest Idaho towns in the 

Cache Valley are Preston, with a 2006 population of 5,089, and Franklin, with 672 residents. 

The remainder of Franklin County and the surrounding counties have low populations and, 

therefore, low population densities. The one exception is Bannock County, home to the city of 

Pocatello (2006 population of 53,932). Pocatello is approximately 95 kilometers to the northnorthwest and also represents the commercial center for southeastern Idaho. There is little 

industrial or commercial development in Franklin County (Factor 1). 

Table 9 presents the population, county size, and population density for Franklin County and 

bordering counties within Idaho. Utah will provide the county information for their portion of the 

Cache Valley. A graphical representation of the population density in the Cache Valley is shown 

in Figure 17. 

Table 9. 2006 population densities for Franklin County and adjacent counties. 

County 

2006 

Population 

County Size 

(km2

) 2006 Population Density (residents per km2

) 

Franklin 12,494 1723.6 7 

Bannock 78,443 2883.2 27 

Bear Lake 6,167 2516 2 

Caribou 6,996 4574.2 2 

Oneida 4,176 3109.1 1 

Sources: http://www.census.gov/popest/counties/CO-EST2006-03.html for 2006 

populations; http://www.census.gov/population/censusdata/90den_stco.txt for size. 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 28 

Figure 17. Population density for the Cache Valley 

(http://sedac.ciesin.columbia.edu:9080/entri/index.jsp ; accessed July 1, 2007). 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 29 

Factor 4: Traffic and commuting patterns 

Commuting information from the EPA TTN 2006 PM2.5 technical data: 

• Franklin County, the county of interest, has a total of 4,838 commuters. 

- Commuters who remain in Franklin County: 2,852 

- Commuters from Franklin County to Cache County, Utah: 1,697 

- Commuters from Franklin County to Bannock County: 19 

- Commuters from Franklin County to Caribou County: 92 

- Commuters from Franklin County to Oneida County: 6 

- Commuters from Franklin County to Box Elder County, Utah: 82 

- Commuters from Franklin County to Rich County, Utah: 1 

• Bannock County, an adjacent county, has a total of 35,122 commuters. 

- Commuters who remain Bannock County: 30,566 

- Commuters from Bannock County to Franklin County: 70 

- Commuters from Bannock County to Cache County, Utah: 42 

• Bear Lake County, an adjacent county, has a total of 2,443commuters. 

- Commuters who remain in Bear Lake County: 1,823 

- Commuters from Bear Lake County to Franklin County: 2 

- Commuters Bear Lake County to Cache County, Utah: 26 

• Caribou County, an adjacent county, has a total of 2,944 commuters. 

- Commuters who remain in Caribou County: 2,622 

- Commuters from Caribou County to Franklin County: 34 

- Commuters from Caribou County to Cache County Utah: 38 

• Oneida County, an adjacent county, has a total of 1739 commuters. 

- Commuters who remain in Oneida County: 1,127 

- Commuters from Oneida County to Franklin County: 8 

- Commuters from Oneida County to Cache County, Utah: 34 

• Box Elder County, Utah, an adjacent county, has a total of 18,030 commuters. 

- Commuters who remain in Box Elder County: 13,570 

- Commuters from Box Elder County, Utah to Franklin County: 0 

- Commuters Box Elder County, Utah to Cache County, Utah: 631 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 30 

• Cache County, Utah, the county of interest, has a total of 43,731 commuters. 

- Commuters who remain in Cache County: 39,235 

- Commuters from Cache County, Utah to Franklin County: 179 

• Rich County, Utah, an adjacent county, has a total of 717 commuters. 

- Commuters who remain in Rich County: 512 

- Commuters from Rich County, Utah to Franklin County: 2 

- Commuters Rich County, Utah to Cache County, Utah: 41 

The commuter information above indicates that very few commuters enter Franklin County from 

counties other than Cache County, Utah. Several counties surrounding Franklin County have 

substantially higher annual VMT (Table 10). Franklin County accounts for approximately 17% 

of the total VMT in the Cache Valley (Franklin County and Cache County, Utah). The major 

roadways located in the Cache Valley are shown in Figure 18. 

Table 10. Annual VMT (vehicle miles traveled) for Franklin County and adjacent counties 

in both Idaho and Utah. 

County VMT (Millions) 

Franklin 189.8723 

Bannock 474.2377 

Bear Lake 104.2817 

Caribou 118.9588 

Oneida 68.1813 

Box Elder (Utah) 782.6866 

Cache (Utah) 935.9099 

Rich (Utah) 34.0305 

Source: EPA TTN 2005_vmt_county_level-1.xls 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 31 

Figure 18. Roadways in the Cache Valley. 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 32 

FACTOR 5: Expected growth (including extent, pattern, and rate of growth)

The Idaho portion of the Cache Valley is not a highly populated area (Factor 3). From 2000 to 

2006, the Idaho side of the Cache Valley experienced a 10.3% increase in population, to a total 

of 12,494 persons, while the Utah side of the Cache Valley, which is more urbanized, 

experienced an 8% increase in population, to a total of 98,661 (Table 11). 

Table 11. Population growth in the Cache Valley from 2000 to 2006 

State City April 2000 July 2006 Population change Percent Change 

Idaho Franklin County 11,329 12,494 1165 10.3% 

Utah Cache County 91,391 98,661 7271 8.0% 

Cache Valley NAA 

(nonattainment area) 

102,720 111,155 8435 8.2% 

The annual population estimates for Franklin County, including the annual percent change, from 

2000 through 2006, are presented in Table 12. 

Table 12. Population growth in Franklin County, Idaho from 2000 through 2006 

Year Population Estimates Population Difference Percent Change (%) 

2000 11,329 __ __ 

2001 11,500 171 1.5 

2002 11,802 302 2.6 

2003 11,846 44 0.37 

2004 12,160 314 2.7 

2005 12,410 250 2.1 

2006 12,494 84 0.68 

FACTOR 6: Meteorology (weather/transport patterns) AND

FACTOR 7: Geography/topography (mountain ranges or other air basin boundaries) 

Factors 6 and 7 are discussed together because they are thoroughly interrelated. 

The mountains surrounding the Cache Valley rise to 8,356 feet above sea level (asl) to the west 

and 9,900 feet (asl) to the east. The isolated valley floor ranges from 4,500 to 5,200 feet (asl). 

The mountains trap pollutants in the valley when dispersion conditions are poor. 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 33 

The Cache Valley experiences air stagnation events in the wintertime. During these periods, the 

stable layer above the ground is much deeper than a typical nocturnal inversion. Cold air is 

trapped in the basins, and the air mass stabilizes as high pressure aloft overtakes the region. 

Under such circumstances, a prolonged strong inversion layer (or layers) limits the vertical 

mixing, trapping local pollutants in a thin layer against the valley floor. During episodes such as 

this, emissions increase because more home heating occurs due to the cold temperatures 

(Factor 1). The low sun angle, short length of the days during winter months, and strong 

likelihood of snow cover to reflect the solar radiation are all factors that limit daytime surface 

heating and aggravate the situation. As a result, some inversions may not break for many days. 

A study of deep stable layers (DSLs) in western air basins (Wolyn and McKee, 1989) revealed 

that DSLs can cause the stagnation of cold air in basins. In other words, only light winds occur 

at the surface, even if moderately strong winds aloft are present, and restriction of the growth of 

daytime convective boundary layers occurs. DEQ analyzed DSLs in the Treasure Valley and 

found high correlation between DSLs and particulate levels in the area. Salt Lake City was found 

to have a high frequency of DSL occurrence, averaging about 12 days per year in the period from 

1959-1983 (Wolyn and McKee, 1989). The Cache Valley is most likely under the same 

stagnation conditions as the Salt Lake City area during most of these periods. Figure 19, which 

is from a Utah State University inversion study (Martin, 2006), provides an excellent example of 

correlation between the PM2.5 concentration levels and the evolution of the stable layer over the 

Cache Valley. In Figure 19, blue represents cold air and red indicates warmer air. The solid 

yellow line represents the ambient PM2.5 concentration as measured at the Logan monitoring site. 

The dotted green line represents the 1997 PM2.5 NAAQS. From January 9 through January 17, 

2004, the cold air pool strengthened and deepened each day, eventually reaching a depth of about 

5,500 feet (asl) on January 15 when the PM2.5 concentrations peaked. The PM2.5 concentration 

levels rose steadily as trapped pollutants accumulated from each day to the next. 

Under this type of stagnation condition, the pollutants may quickly build, especially in areas like 

the Cache Valley where airflow is greatly restricted by terrain. Figure 20, also taken from the 

Utah State University inversion study (Martin, 2006), provides an example of inverted 

temperature profiles in the Cache Valley during the January 2004 extended stagnation episode. 

During the period from January 1 to January 17, 2004, as shown in the figure, a strong inversion 

about 1,500 feet thick persistently occupied the area. The record high PM2.5 concentration of 

132.7μg/m3

 was observed at Logan on January 15, 2004. The strong, deep, stable layer persisted 

through the entire period, even in the afternoon hours (12 noon and 3 pm) when the base of the 

inversion rose to an average 5,500 feet (asl). The average 24-hour PM2.5 concentration observed 

at the Franklin monitor during this same period was 39.0 μg/m3, with the highest 24-hour 

concentration of 82.6 μg/m3 occurring on January 17, 2005. Thus, it appears that the afternoon 

mixing height during stagnation episodes (at approximately 5,500 feet asl) is the controlling 

factor in accumulating pollutants from day to day. 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 34 

Figure 19. January 2004 temperature contour map with PM2.5 concentration (yellow) and 

1997 PM2.5 National Ambient Air Quality Standard (green) (Martin, 2006) 

Figure 20. Average temperature profiles in Cache Valley during January 1 - 17, 2004 

(Martin, 2006) 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 35 

Factor 8: Jurisdictional boundaries (e.g., counties, air districts, reservations, etc.) 

Given the nature of PM2.5 as a regional rather than a localized pollutant, DEQ recommends the 

Cache Valley PM2.5 NAA extend from Cache County, Utah into Franklin County, Idaho. This 

NAA will span two states and two different EPA regions – Utah, EPA region 8 and Idaho, EPA 

Region 10. 

For transportation planning purposes, both Franklin County, Idaho and Cache County, Utah are 

part of the Logan MSA. The Logan MSA is complicated, since a metropolitan planning 

organization (MPO) exists on the more urban Utah side and not on the Idaho side. Idaho is 

committed to work with all stakeholders to determine the best approach to comply with 

transportation conformity. 

Maintaining separate nonattainment areas allows each state to develop strategies to reduce PM2.5

pollution that are most appropriate to each area and to implement processes that recognize the 

regulatory, political, and financial realities specific to the two counties and two states. Idaho 

DEQ and Utah DEQ are committed to working cooperatively to ensure their air quality 

improvement plans are integrated and mutually supportive. 

Factor 9: Level of control of emission sources 

As discussed in Factor 1, there are no major industrial sources in Franklin County; therefore, 

emissions in the Idaho portion of the Cache Valley are from vehicles (tailpipe and fugitive road 

dust), residential wood heating, and agriculture (feedlot and dairy ammonia). DEQ is beginning 

to evaluate emission reduction controls for woodstoves and vehicles. 

Proposed geographic boundaries for the Franklin County – Cache Valley Nonattainment Area 

Analysis of the Cache Valley, specifically the Idaho portion, shows that topographical features 

and wintertime meteorology limit the transport of pollutants into or out of the Cache Valley. 

Pollutants emitted within the Cache Valley (Utah and Idaho) remain trapped, and emissions from 

surrounding Idaho counties do not impact the PM2.5 monitor located in Franklin, Idaho. 

The Cache Valley experiences inversions that build from day to day when strong high-pressure 

systems are present in the region. The average afternoon mixing height during stagnation events 

is about 5,500 feet (asl). Therefore, any areas in Franklin County that are higher than 5,500 feet 

(asl) in elevation will not contribute to PM2.5 concentrations during wintertime inversions. 

However, not all areas below 5,500 feet (asl) are appropriate to be included in the nonattainment 

area. Only those areas with significant emissions and population should be included. The 

population in Franklin County is clustered in the towns, with the majority located in Preston and 

Franklin. The townships identified in Figure 21 are those that account for the higher population 

density and, therefore, emissions. These townships delineate those portions of Franklin County 

that are appropriate to include in the Franklin County – Cache Valley PM2.5 nonattainment area. 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 36 

Figure 21. Proposed geographic boundaries for the Idaho portion (Franklin County) of the 

proposed Cache Valley PM2.5 nonattainment area. 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 37 

5. Summary 

 The State of Idaho recommends only two areas in Idaho for nonattainment designation. Figures 

15 (page 24) and 21 (page 36) provide graphical representations of the townships Idaho is 

recommending to be included in the Pinehurst and Franklin County – Cache Valley NAAs, 

respectively. 

Table 13 (Appendix A) provides the legal description of all areas of the State and the 

designations Idaho is recommending for the PM2.5 standard. 

6. References 

Wolyn, P. G., and T. B. McKee, 1989: Deep Stable Layers in the Intermountain Western United 

States. Monthly Weather Review, 117, 461–472. 

Martin, Randy, 2006. Cache Valley Air Quality Studies; a Summary of Research Conducted 

(through 2006). Department of Civil & Environmental Engineering, Utah State University. 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 38 

Appendix A – All Designated and Non-Designated Area Descriptions
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 39 

Table 13. Descriptions of all areas of the state and the designations 

County Attainment Unclassifiable Nonattainment 

Nonattain

Area Na

Shoshone All portions of 

Shoshone County not otherwise designated nonattainment 

All portions of Shoshone County located in the following township/range/sections: 

T R S QQ 

49N 02E 31 

48N 02E 6 48N 02E 5 48N 01E 12 48N 02E 7 48N 02E 8 48N 02E 9 48N 01E 13 48N 02E 18 48N 02E 17 48N 02E 16 48N 01E 24 48M 02E 19 

Pinehurst 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 40 

County Attainment Unclassifiable Nonattainment 

Nonattain

Area Na

48N 01E 1 NENW NESW 

NWNE NWSE NENE NESE SWNW SWSWSENW SESW SWNE SWSE SENE SESE 

 NWSW 48N 01E 11 SESE SWSE 48N 01E 14 NENE NWSE  NWNE NESE  SWNE SWSE  SENE SESE 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 41 

County Attainment Unclassifiable Nonattainment 

Nonattain

Area Na

48N 01E 22 SENE NESE 48N 01E 23 NENW NWSW NWNE NESW  NENE NWSE  SWNW NESE  SENW SESW  SWNE SWSE  SENE SESE 48N 01E 25 NWNW SWNW NENW SENW  NWNE SWNE  NENE SENE 48N 01E 26 SWNE NWNE  SENE NENE 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 42 

County Attainment Unclassifiable Nonattainment 

Nonattain

Area Na

48N 02E 4 NWNW NWSW SENW SWSW NESW SESW  NWSE SWSE  SWNW SESE 48N 02E 10 SWSW 48N 02E 15 NWNW NWSW NENW NESW  SWNW SWSW SENW SESW 48N 02E 20 NWNW SENW  NENW SWNE  NWNE NWSW
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 43 

County Attainment Unclassifiable Nonattainment 

Nonattain

Area Na

 NENE NESW  SWNW SWSW48N 02E 21 NWNE NENE 48N 02E 22 NWNW NENW 48N 02E 29 NWNW SWNW48N 02E 30 NWNW SWNW NENW SENW  NWNE SWNE  NENE SENE 49N 01E 25 SESE 49N 01E 36 NENE NESE 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 44 

County Attainment Unclassifiable Nonattainment 

Nonattain

Area Na

 SWNE SESW  SENE SWSE  NWSE SESE 49N 02E 30 SWNW NWSW SENW NESE  NESW SWSW NWSE SESW  SWNE SWSE  SENE SESE 49N 02E 32 NWNW NWSE  SWNW NESE  SENW SWSW SWNE SESW  SENE SWSE  NWSW SESE 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 45 

County Attainment Unclassifiable Nonattainment 

Nonattain

Area Na

 NESW 49N 02E 33 SWSW 

Franklin All portions of 

Franklin County not otherwise designated nonattainment 

All portions of Franklin County located in the following townships: 15 south 39 east 16 south 38 east 16 south 39 east 16 south 40 east 

Franklin – Cache Val

Ada Canyon Bannock Benewah 

All portions of the respective county except for Tribal Lands 

Bear Lake Bingham Blaine 

Jefferson Jerome Kootenai 

 All portions of 

the respective County except for Tribal Lands 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 46 

County Attainment Unclassifiable Nonattainment 

Nonattain

Area Na

Boise Bonner Bonneville Boundary Butte Camas Caribou Cassia Clark Clearwater Custer Elmore Fremont Gem Gooding Idaho 

Latah Lemhi Lewis Lincoln Madison Minidoka Nez Perce Oneida Owyhee Payette Power Teton Twin Falls Valley Washington 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 47 

Appendix B – Supporting Documentation Locations 

Supporting Documentation (from the EPA Holmstead memo of 2003) 

The supporting information needed for nonattainment areas can be found in this document as 

follows: 

• PM2.5 design value(s) for the area: See Tables 1 and 2 

• The 3-yr period represented by the design value: See Section 3

• Site locations and ID numbers: See Table 14

Table 14. Monitor locations and ID numbers for PM2.5 nonattainment areas 

Site ID Location Address County 

16-079-0017 Pinehurst Elementary School S. 201 Third St. Shoshone 

16-041-0001 Franklin Water Treatment Facility East 4800 South Franklin 

The supporting information needed for attainment/unclassifiable AND nonattainment areas are 

as follows: 

• Names of counties and tribal lands included: See Table 13

• If partial counties or portions of tribal lands are included, the boundary 

definition/description 

o Legal definition: See Table 13

o hard copy map: See Figures 15 and 21

o digitized lat/long description: will be transmitted upon request

o Explanation of how the boundary is consistent with Sect. 107(d)(1) of the 

CAA: Paragraph A of Section 107(d)(1) of the Clean Air Act describes 

the three designations an area may carry. Idaho’s recommendations are 

consistent with the definitions provided therein.

The areas recommended for designation of “nonattainment” are areas 

represented by monitored ambient air data that does not meet the 

primary (or secondary) 24-hour standard for PM2.5. The surrounding 

areas were evaluated, using the EPA-recommended nine-factor analysis, 

to determine whether they were impacting the nonattainment areas. 
Idaho Area Designation Recommendations for the 2006 PM2.5 NAAQS 48 

The areas recommended for designation of “attainment” are represented 

by monitored ambient air data that does meet all the primary and 

secondary standards for PM2.5. 

The areas recommended for designation of “unclassifiable” are areas for 

which there is insufficient data to draw any conclusions. 

Names of Contacts 

Martin Bauer 

Administrator, Idaho Air Quality Division 

(208) 373-0552 

Robert Wilkosz 

Manager, Mobile and Area Source Program 

(208) 373-0302 

Bruce Louks 

Manager, Monitoring, Modeling, and Emission Inventory Program 

(208) 373-0294