i 

Pinal County, Arizona 

Area Redesignation for the 1987 24-hour PM10 

National Ambient Air Quality Standard 

Technical Support Document 

9/21/2010 

US Environmental Protection Agency 

Region 9 

 
ii 

Table of Contents 

Introduction ...................................................................................................................................... 1

Factor 1: Air Quality Data ................................................................................................................... 5 

Factor 2: Emissions Data .................................................................................................................... 8

Factor 3: Population Density and Degree of Urbanization ................................................................. 15

Factor 4: Traffic and Commuting Patterns ........................................................................................ 17

Factor 5: Growth Rates and Patterns ............................................................................................... 22

Factor 6: Meteorology ..................................................................................................................... 23

Factor 7: Geography and Topography .............................................................................................. 25

Factor 8: Jurisdictional Boundaries .................................................................................................. 28

Factor 9: Level of Control of Emissions Sources ............................................................................... 31 

Conclusion...........................................................................................................................................................31 

Appendix A – Emissions in Pinal County: Primary PM10, NOx, NH3, SO2, VOCs ................................... A-1

Appendix B – ADEQ Maps of PM10 Sources ...................................................................................... B-1 
1 

TECHNICAL SUPPORT DOCUMENT

PINAL COUNTY, ARIZONA

AREA REDESIGNATION FOR THE 1987 24-HOUR PM10 NAAQS 

Introduction 

Pursuant to section 107(d)(3) of the Clean Air Act (CAA), EPA may notify the governor of any 

state that available information indicates that the designation of any area should be revised. 

Based on monitoring data that indicated persistent violations of the 1987 24-hour PM10 national 

ambient air quality standard (NAAQS), EPA notified the Governor of Arizona and tribal leaders 

for the Ak-Chin Indian Community (Ak-Chin), the Gila River Indian Community (GRIC), the 

San Carlos Apache Tribe, and the Tohono O’odham Nation (TON) that it was initiating the 

process to redesignate to nonattainment those violating areas within Pinal County, and any 

nearby areas that could be causing or contributing to those violations. EPA requested 

recommendations for the redesignation by February 11, 2010, consistent with the timelines set 

out in the CAA. 

Under section 107(d)(3)(A) of the CAA, EPA is directed by Congress to evaluate “air quality 

data, planning and control considerations, or any other air quality-related considerations the 

Administrator deems appropriate” in its redesignation actions. Because our redesignation 

involves a nonattainment area (NAA), we are also taking into account CAA section 

107(d)(1)(A), which provides that nonattainment areas are to include the geographic area that 

does not meet, or that contributes to ambient air quality in a nearby area that does not meet the 

NAAQS for a given pollutant. 

This technical analysis for Pinal County identifies the monitors that violate the 24-hour PM10

standard and evaluates surrounding areas for contributions to particulate concentrations in the 

area. EPA guidance1 provides for the use of “a qualitative analysis of the area of 

representativeness of the monitoring station, together with the consideration of terrain, 

meteorology, and sources of emissions...” in defining area boundaries. 

Consistent with that guidance, EPA has evaluated the area based on the weight of evidence of the 

following factors and other relevant information: 

- air quality data 

- pollutant emissions 

- population density and degree of urbanization 

- traffic and commuting patterns 

- growth 

- meteorology 

- geography and topography 

- jurisdictional boundaries 

- level of control of emissions sources 

 

1

 PM10 SIP Development Guideline, EPA-450/2-86-001, June 1987. 
2 

We also used analytical tools and data such as wind roses, particle composition monitoring data, 

and the correlation between meteorological data and particle composition data to evaluate the 

area. 

Figure 1 is a map of the area showing relevant information such as the locations of air quality 

monitors, boundaries for counties and Indian lands, and nearby PM10 nonattainment areas. 

Figure 1. Pinal County PM10 Monitors and Nearby Nonattainment Areas 

In response to EPA’s request for recommendations, on February 11, 2010, the Tohono O’odham 

Nation submitted a recommendation for designation as attainment/unclassifiable for TON’s 

lands. The Gila River Indian Community noted that certain exceedances have been flagged as 

caused by exceptional events, and declined to submit a recommendation until formal 

consultation has been conducted. GRIC reaffirmed this request in a letter dated May 27, 2010. 

The Ak-Chin Tribe made a verbal request for formal consultation and later, in a letter dated 

September 2, 2010, submitted a recommendation that EPA designate reservation lands as 

“attainment/unclassifiable.” The San Carlos Apache Tribe did not submit a recommendation. 

Arizona’s submittal, dated March 26, 2010, recommended that only a portion of central-western 

Pinal County be redesignated as nonattainment. EPA has taken these recommendations under 

consideration, and while EPA agrees that a partial county redesignation is appropriate, we find 

Florence

(Tohono O'Odham)

Village

San

(Tohono O'Odham)

Lucy Farm

Rillito planning

area

Phoenix planning area

Miami

planning

area

Hayden

planning

area

San

Carlos

Fort

McDowell

Salt River

Gila

River

Ak-Chin

Tohono

O'Odham

Cochise

County

Gila

County

Graham

County

Maricopa

County

Pima

County

Pinal

County

0 10 20 5 Miles

Violating PM-10 monitor

Attaining PM-10 monitor

Existing PM-10 nonattainment area

Tribal lands

County boundary

Sources: USEPA's Air Quality Systems (AQS) database (2010), TANA (2006).

AIR1000045_1 23 August 2010
3 

that the information provided to date does not adequately support the State’s recommended 

boundary. As discussed in more detail below EPA finds that the State’s recommended boundary 

does not include sources of emissions that are likely causing or contributing to violations of the 

24-hour PM10 standard. Accordingly, a larger portion of Pinal County is included within EPA’s 

intended nonatttainment area boundary. See Figure 2. EPA will consider any additional 

information that is provided by the State, tribal leaders, and the public in making its final 

decision on the designation. 

As shown in Figure 2, EPA is proposing that the main reservation of the TON, which lies to the 

south and west of EPA’s proposed NAA remain “unclassifiable.” EPA believes that the primary 

contributors to nonattainment in Pinal County, e.g., onroad emissions, agriculture, stationary 

industrial sources, and concentrated animal feedlot operations either are not present on the 

TON’s main reservation, or are present in relatively small amounts, and population density is 

very low. See Figures 4 and 7 and Table 5. EPA has concluded that activities occurring there are 

not contributing to nonattainment of the PM10 standard in Pinal County. 

EPA is also proposing to find that the San Carlos Apache lands, which lie to the east of the 

Hayden and Miami NAAs,2 remain “unclassifiable.” The population density of the reservation is 

very low. See Table 5. Additionally, the San Carlos Apache reservation is located about 40 miles 

east of the proposed nonattainment area and is separated from it by mountainous terrain and 

existing nonattainment areas. 

At this time, EPA is deferring its decision regarding redesignation of the Ak-Chin and GRIC, as 

well as the TON’s Florence Village and San Lucy Farm, pending consideration of issues unique 

to tribal lands, completion of formal consultation with the tribal governments, and consideration 

of certain exceptional events flags affecting the GRIC lands. 

Under EPA’s proposal, the Apache Junction area of Pinal County remains part of the Phoenix 

PM10 nonattainment area, and the existing Hayden and Miami PM10 nonattainment areas are 

unchanged. The remainder of the County retains its designation of “unclassifiable” for the 1987 

24-hour PM10 NAAQS. 

 

2

 A narrow strip of the San Carlos Apache Reservation is included within the eastern boundary of the Hayden PM10

nonattainment area, which lies to the east of the proposed nonattainment area. See Figure 12. Its status is not 

changed by this action. 
4 

Figure 2. EPA Proposed Nonattainment Area Boundary

101

101

79

77

88

60

60

8

10

Gila

County

Maricopa

County

Pima

County

Pinal

County

Tohono O'Odham

Gila Riverdeferred tribal area

Florence Villagedeferred tribal area

Ak-Chin deferred

tribal area

San Lucy Farmdeferred tribal area

0 20 10 Miles

Florence Village

deferred tribal area

Sources: USEPA's Air Quality Systems (AQS) database Commerce, U.S. Census Bureau, Geography Division (

Stationary PM-10 EmissViolating PM-10 monitorAttaining PM-10 monitoUnpaved RoadsIncorporated City BounWildernessExisting PM-10 nonattaiTribal LandsDeferred tribal areasCounty boundaryTownship and RangeArizona's recommended AgricultureEPA Proposed PM-10 no

AIR1000045_4 2 September 2010
5

EPA Technical Analysis for Pinal County

Factor 1: Air Quality Data 

This factor considers the 24-hour PM10 rate of expected exceedances for air quality monitors in 

Pinal County and nearby areas based on data for the years 2007-2009, which were certified on 

April 9, 2010, by Pinal County in accordance with 40 CFR 58.15. The rate of expected 

exceedances indicates whether a monitor attains the specified air quality standard. The 24-hour 

PM10 standard is met when the 3-year average of the expected exceedances is equal to or less 

than one. An “exceedance” of the 24-hour PM10 standard is a daily value that is above 150 

micrograms per cubic meter (μg/m3) after rounding to the nearest 10 μg/m3. 

The monitors listed in Table 1 are identified by their air quality system (AQS)3 ID number, 

which consists of state code, county code, site code, and poc (parameter occurrence code) 

number (state-county-site-poc). Monitors that have either a POC 1 or POC 2 designation are part 

of Pinal County’s state or local air monitoring stations (SLAMS) network or GRIC’s tribal 

monitoring network, which consist of filter-based federal reference method (FRM) monitors that 

operate on a 1-in-3 or 1-in-6 day sampling schedule. The SLAMS/POC 1 or POC 2 monitors are 

primarily used for NAAQS comparison. The monitors in Table 1 that have a POC 3 designation 

are considered special purpose monitors (SPMs). All SPMs in Pinal County are designated 

federal equivalent methods (FEMS).4

 Monitors eligible for providing design value data generally 

include SLAMS at population-oriented locations with a federal reference method (FRM) 

monitor. All data from SPMs using an FRM are eligible for comparison to the relevant NAAQS, 

subject to the requirements set out in the October 17, 2006 Revision to Ambient Air Monitoring 

Regulations (71 FR 61236).5

The 24-hour PM10 expected exceedances for Pinal County are summarized in Table 1. The third 

column shows the number of days that are expected to exceed the standard, based on monitored 

exceedances. Pinal County has flagged a number of exceedances for the years 2007-2009 as 

“high wind” exceptional events.6

 Without a more in-depth data analysis, it is difficult to 

determine which of the flagged days would be considered exceptional events under the 

Exceptional Events Rule (EER). However, given the overwhelming number of expected 

exceedances at multiple monitoring stations, even the exclusion of all flagged data would not 

bring Pinal County into attainment of the 24-hour PM10 standard. 

 

3

 AQS is an EPA database of ambient air quality data. 

4

 All PM10 SPMs in Pinal County are R & P TEOM 1400a (A/B) continuous analyzers, EPA designation number 

EQPM-1090-079, that produce hourly data. 

5

 Quality-assured SPMs are comparable to the NAAQS. 40 CFR 58.20 (c) states that “[a]ll data from a SPM using 

an FRM, FEM, or ARM which has operated more than 24 months is eligible for comparison to the relevant 

NAAQS...” subject to certain conditions. All SPM monitors in Pinal County have been operating for more than 24 

months, and are otherwise eligible. Thus, data from the monitors are comparable to the 24-hour PM10 NAAQS.

6

 On March 22, 2007, EPA adopted a final rule, Treatment of Data Influenced by Exceptional Events (EER) to 

govern the review and handling of certain air quality monitoring data for which the normal planning and regulatory 

processes are not appropriate. Under the rule, EPA may exclude data from use in determinations of National 

Ambient Air Quality Standard (NAAQS) exceedances and violations if a state demonstrates that an “exceptional 

event” caused the exceedances. See 72 FR 13560. 
6

Table 1. Pinal County - PM10 Air Quality Monitoring Data 

Site Name AQS ID 

PM10 

Expected Exceedances 

2007-2009 

Casa Grande 04-021-0001-1 

04-021-0001-3 

0 

4.7 

Apache Junction 04-021-3002-1 0 

Coolidge 04-021-3004-1 2 

Mammoth 04-021-3006-1 0 

Marana (Pinal Air Park) 04-021-3007-1 0 

Stanfield 04-021-3008-1 

04-021-3008-3 

16.4 

17.8 

Combs School 04-021-3009-3 17.6 

Maricopa 04-021-3010-3 12.6 

Pinal County Housing (PCH) 04-021-3011-1 

04-021-3011-2 

04-021-3011-3 

6.5 

5.9 

15.6 

Riverside 04-021-3012-1 0 

Cowtown 04-021-3013-1 

04-021-3013-3 

112.9 

139.8 

Eloy 04-021-3014-1 0 

Bapchule* 

(GRIC monitors) 

04-021-7004-1 

04-021-7004-2 

6.6 

7.9 

*EPA is deferring its decisions regarding redesignation of the Ak-Chin and Gila River Indian 

Community lands, as well as TON’s Florence Village and San Lucy Farm, pending 

consideration of issues unique to tribal lands, completion of formal consultation with the 

tribal governments, and consideration of exceptional events flags. 

Violating monitors are clustered in the central and western portion of Pinal County. See Figures 

1 and 3. Monitors located in the southern and eastern portions of the county show attainment 

with the 24-hour PM10 NAAQS, lending weight to a partial county redesignation. 

 
7

Figure 3. PM10 Monitors and Expected Exceedances 

A summary of the 24-hour PM10 expected exceedances for nearby counties is presented in Table 

2. 

Table 2. Nearby Counties – PM10 Air Quality Monitoring Data, 2007 – 2009 

County Name Total Number of 

PM10 Monitoring 

Sites 

Number of Sites 

in Violation of 

PM10 NAAQS 

Violating Monitor(s) Within 

Existing PM10 Non-Attainment 

Areas (NAAs) 

Cochise 2 1 1:Yes (Paul Spur NAA) 

Gila 4 1 1:Yes (Hayden NAA) 

Graham 1 0 N/A 

Maricopa 23* 14 13: Yes (Phoenix NAA) 

1: No (Buckeye) 

Pima 11 2 1:Yes (Rillito NAA) 

1:No (Santa Clara School, Tucson) 

*Includes sites located on both State and Tribal lands 

Almost all of the surrounding counties have monitors that violate the PM10 24-hour standard, 

with the exception of Graham County, which lies to the east of Pinal. For the most part, these 

Coolidge: 2

Cowtown: 139.8

Maricopa: 12.6

Stanfield: 17.8 Casa Grande: 4.7

Combs School: 17.6

Bapchule (GRIC): 7.9

Pinal County Housing (PCH): 15.6

Eloy: 0

Mammoth: 0

Riverside: 0

Apache Junction: 0

Marana - Pinal Air Park: 0

Pinal

County

Pima

County

Maricopa

County

Gila

County

Graham

County

Cochise

County

0 10 20 5 Miles

AIR1000045_7 17 August 2010

Sources: USEPA's Air Quality Systems (AQS) database (2010), TANA (2006)

Violating PM-10 monitor

Attaining PM-10 monitor

Existing PM-10 nonattainment area

Tribal lands

County boundary
8

monitors are included in nonattainment areas previously determined to be partial county 

designations to account for local conditions and air quality impacts. Given previous 

determinations regarding the more localized nature of the nonattainment problems in 

surrounding counties, they most likely do not contribute to exceedances of the PM10 standard 

within Pinal County and should not be included in the proposed nonattainment area. 

Nearby nonattainment areas are shown in Figure 1. A portion of Maricopa County and the 

Apache Junction area of Pinal County, which is contiguous with the Phoenix urban area, form 

the Phoenix planning area, a serious PM10 nonattainment area. The Rillito planning area, a 

moderate PM10 nonattainment area, is located in Pima County, just south of Pinal County. Each 

area has its own planning process in place to attain the standard. EPA determined in 2006 that 

the Rillito moderate nonattainment area had attained the PM10 standard.7 In 2007, the Rillito 

monitor measured the only exceedance of the NAAQS since 2000. The exceedance was flagged 

as caused by an exceptional event, and the State of Arizona submitted a limited maintenance plan 

and redesignation request to EPA for the Rillito PM10 nonattainment area in June of 2008. 

Eastern Pinal County and southern Gila County share portions of two other nonattainment areas: 

the Hayden moderate PM10 nonattainment area and the Miami moderate PM10 nonattainment 

area. EPA determined in 2007 that the Miami PM10 area in Gila and Pinal Counties had attained 

the PM10 standard.8 The State of Arizona submitted a limited maintenance plan and redesignation 

request for the Miami PM10 nonattainment area in July of 2008. Current data indicate the Miami 

area continues to attain the PM10 standard. 

Both Arizona’s recommended nonattainment area and EPA’s proposed nonattainment area 

encompass all violating monitors. However, section 107(d)(1)(A) of the Clean Air Act requires 

that areas that are contributing to ambient air quality must also be included within a 

nonatttainment area. As described in more detail below, EPA believes that Arizona’s 

recommended boundary excludes sources that are contributing to violations measured within the 

potential nonattainment area. In order to ensure contributing sources are included in the 

nonattainment area, EPA is proposing a nonattainment area boundary that encompasses more 

area to the east, south, and west. 

Factor 2: Emissions data 

For this factor, EPA evaluated emissions data for primary PM10 from the violating area within 

Pinal County and from potentially contributing nearby areas. “Primary PM10” represents direct 

emissions of PM10 and includes: “PM10 emissions carbon,” “PM10 emissions other,” primary 

sulfate (SO4), and primary nitrate (NO3). (Although primary sulfate and primary nitrate, which 

are emitted directly from stacks rather than forming in atmospheric reactions with SO2 and 

nitrogen oxides (NOx), are part of “PM10 emissions total,” they are not shown in Table 3 as

separate items). Emissions of SO2, NOx, VOCs (volatile organic compounds) and NH3

(ammonia), which are precursors of secondary PM10, are included for informational purposes in 

Appendix A but were not considered because the PM10 problem in Pinal County is primarily a 

fugitive dust problem. 

 

7

 See 71 FR 44920, August 8, 2006. 

8

 See 72 FR 14422, March 28, 2007. 
9

Table 3 shows total emissions of PM10 as well as individual source categories in Pinal County 

that emit direct (primary) PM10. The emissions data were derived from the most current version 

of the national emissions inventory - 2005 National Emissions Inventory, version 2 (NEIv2).9

Table 3. Pinal County Primary PM10 Emissions (2005 NEI version 2) 

Includes Filterables + Condensibles* 

Source Category 

Emissions (tons 

per year) 

% of Total Primary 

PM10 Emissions 

Nonpoint 

 Unpaved Roads 6,253 28% 

 Construction 5,439 25% 

 

Agriculture – Crop Tilling & Livestock 

Dust 5,008 23% 

 Paved Roads 2,171 10% 

 

Industrial Process – not elsewhere 

classified 955 4% 

 Waste Disposal - Open Burning 906 4% 

 Wildfires 466 2% 

 Other Nonpoint 149 1% 

Nonroad 

 Non-Road Equipment – Diesel 171 1% 

 Misc. Nonroad 106 0% 

Onroad 

 On-Road Vehicles – Diesel 135 1% 

 On-Road Vehicles – Gasoline 85 0% 

Point 

 Waste Disposal 205 1% 

 Misc. Point 39 0% 

TOTAL: 22,088 100%

* Filterable PM is particles that are directly emitted as a solid or liquid at stack or release conditions 

and captured on the filter of a stack test train. Condensable PM is material that is in the vapor phase at 

stack conditions but condenses and/or reacts upon cooling and dilution in the ambient air to form a 

solid or a liquid particulate immediately after discharge from the stack. 

The Arizona Department of Environmental Quality’s (ADEQ’s) boundary recommendation 

technical support document (TSD) provides a “preliminary” 2007 PM10 emissions inventory. 

Reproduced below, this emissions inventory identifies significant sources of PM10 emissions in 

the county as including paved and unpaved road dust, active and fallow agricultural fields, sand 

and gravel facilities, concentrated animal feeding operations, cattle feedlots, and construction.10 

 

 

9

http://www.epa.gov/ttn/chief/net/2005inventory.html#inventorydata . Retrieved February 3, 2010. 

10 Arizona Air Quality Designations Technical Support Document -Boundary Recommendation for the Pinal County 

24-hour PM10 Nonattainment Area; March 15, 2010. Submitted to EPA March 26, 2010. 
10

Table 4. Pinal County Preliminary 2007 PM10 Emissions Inventory 

Source Categories Emissions 

(tons per year)

% of Total 

Primary PM10 Emissions

Onroad 42,130 83% 

Tilling, 

Harvesting, and Agriculture 

2,538 5% 

Stationary Industrial Sources (including sand 

and gravel facilities)

2,342 5% 

Concentrated Animal Feeding Operations 2,045 4% 

Construction Emissions 1,757 3% 

Portable Industrial Sources 38 0% 

Off-highway Vehicles 23 0% 

Total 50,873 100%

While the NEI and ADEQ emissions inventories disagree in magnitude, there is general 

agreement in terms of significant sources of PM. These include generally: 

• Onroad (including paved and unpaved road) emissions; 

• Agriculture (including tilling and harvesting as well as concentrated animal feeding 

operations and livestock dust); 

• Stationary industrial sources, including waste disposal; and 

• Construction emissions. 

Figures 4 and 5 illustrate the concentration of significant sources of PM10 in the central-western 

portion of Pinal County, supporting a partial county nonattainment area. Appendix B contains 

additional maps showing individual source category emissions and locations. 
11

Figure 4. Pinal County Agriculture and Cattle Operations 

101

101

79

77

88

60

60

8

10

10

Gila

County

Maricopa

County

Pima

County

Pinal

County

0 10 

5 

A

Sources: USEPA's Air Quality Systems (AQS) 

Additional Cattle OFeedlotsDairiesViolating PM-10 moAttaining PM-10 mUnpaved RoadsExisting PM-10 noCounty boundaryTribal landsAgriculture
12

Figure 5. ADEQ Map of Preliminary 2007 Emissions Inventory for Pinal County 

Source: ADEQ Boundary Recommendation for the Pinal County 24-hour PM10 Nonattainment Area, Ma
13

Speciation analysis shows that the PM10 in Pinal County contains a significant crustal 

component. The 2003 Source Apportionment Study, conducted from October to November of 

2003, concluded that the dominant PM10 source in Pinal County was soil, with the exception of 

the Cowtown monitor which was significantly influenced by cattle feedlot emissions.11 For four 

of the five monitors studied, crustal emissions contributed between 62 and 73% of the total PM10

concentration, while feedlot or other manure sources contributed between 9 and 20%. At the 

fifth monitor, Cowtown, the feedlot contribution was 59%, with crustal components adding 

32%.12 These findings were reinforced by information gathered in 2009 during an EPA-funded 

RARE project.13

Figure 6 presents the PM10 source contributions for the Pinal County Housing (PCH) monitor. 

Figure 6. PM10 Source Contributions, Pinal County Housing (PCH) Monitor.14

Soil Geological soil ColPP Coal fired power plant 

Feedlot Feedlot soil AmSulf Ammonium sulfate 

MV Emi Motor vehicle 

combustion emissions 

 AmNitr Ammonium nitrate 

VgBr Vegetative burning Other Unclassified sources

These source signatures align with the sources identified in the emissions inventories. Crustal 

PM10 contributions may be associated with unpaved and paved roads, construction, and some 

stationary industrial sources (such as sand and gravel facilities). Agriculture (including tilling 

 

11 Pinal County Air Quality Control District Source Apportionment Study: July 29, 2005, page 43. 

12 Pinal County Air Quality Control District Source Apportionment Study: July 29, 2005 

13 "Chemical Analysis for Source Attribution of Fine and Coarse Particulate Matter in Pinal County, AZ" Andrea L. 

Clements, Yuling Jia, Matthew P. Fraser, Pierre Herckes, Michael Sundblom, and Paul A. Solomon, presentation to 

American Aerosol Research Association (AARA) 28th Annual Conference, Minneapolis, Minnesota, October 26 - 

30, 2009. 

14 Pinal County Air Quality Control District Source Apportionment Study: July 29, 2005, p. 37. 
14

and harvesting), concentrated animal feeding operations, livestock dust, and stationary industrial 

sources such as composting facilities may also emit both crustal PM10 and feedlot/manure PM10

emissions. Both emissions inventories and source apportionment studies indicate that these types 

of sources, which are concentrated in the western portion of the county, are responsible for the 

elevated PM10 levels in Pinal County. 

While EPA finds that the PM10 emissions inventory for Pinal County and ADEQ’s 

corresponding maps are helpful in defining the boundaries of the new nonattainment area, we do 

not believe that they justify ADEQ’s conclusions about its recommended boundaries. ADEQ 

claims that the emissions inventory and maps demonstrate that sources in the eastern and 

southern regions of the county do not “significantly contribute” to violations in the other regions 

of the county. See page ES-3 of ADEQ’s technical report. EPA notes, however, that CAA

section 107(d)(1)(A) defines a nonattainment area as one that does not meet, or that “contributes 

to” ambient air quality in a nearby area that does not meet the NAAQS. The definition of 

nonattainment areas is not limited to areas that, in ADEQ’s words, “significantly” contribute to a 

violating area. Moreover, ADEQ’s maps show that areas immediately to the east and south of the 

recommended area (but still within the western half of the county) include the same types of 

emissions sources, with similar emissions densities, as those that predominate within the 

recommended area. For example, figure 3-3 (page 8 of State’s technical report) shows emissions 

densities similar to those estimated within the State’s recommended boundaries to the east in 

Coolidge and Florence, as well as south to Eloy. In addition, figures 3-4, 3-7, and 3-10 (on pages 

11, 14, and 17, respectively, of the State’s technical report) illustrate the locations of unpaved 

roads (with average daily traffic volumes greater than 100) and show that higher relative 

concentrations of PM10 emissions from such sources as vehicle entrainment of dust over paved 

and unpaved roads, tilling and harvesting, and concentrated animal feeding operations (CAFOs) 

extend to central, and south central Pinal County. Thus, the emissions inventory data and related 

maps do not support the State’s recommended boundaries but rather argue for a larger 

nonattainment area consisting of the western half of the county. 

In contrast, EPA’s proposed boundaries include all of the areas for which emissions data show 

relatively higher PM10 emissions from the types of sources contributing the most to the overall 

PM10 emissions inventory. For instance, based on the information sources described above in the 

State’s technical report, EPA’s proposed boundaries include the areas of relatively higher 

emissions densities in and around Coolidge, Florence, and Eloy that reflect the same types of 

PM10-generating activities (vehicle entrainment of dust over paved and unpaved roads, tilling 

and harvesting, and CAFOs) as found within the smaller nonattainment area boundaries 

recommended by the State. 

 
15

Factor 3: Population density and degree of urbanization 

Table 5 shows the 2008 population density for municipalities and reservations within Pinal 

County. 

Table 5. Population Density within Pinal County 

Entity Area in 

Square 

Miles 

2008 

Population Density 

2008 

Population 

Pinal County 

Total 

5,369.6 65.3 350,558 

Apache 

Junction 

34.2 958.4 32,776 

Casa Grande 109* 377.5 41,152 

Coolidge 65* 157.9 10,261 

Eloy 110* 115.9 12,750 

Florence 50* 415.6 20,781 

Kearny 2.79 1,177.5 3,297 

Mammoth 1.08 2,339.1 2,573 

City of 

Maricopa* 

43* 1,059.8 45,571 

Queen Creek 26* 937 Pinal Co: 5,700 

Maricopa Co: 18,661 

Total: 24,361 

Superior 1.93 1,766.3 3,335 

Ak Chin 87.2 48.3 1,591 

GRIC** 581.1 37 21,665 

San Carlos 

Apache** 

2,896.6 3.6 10,416 

Tohono 

O’odham** 

4,453 3.1 13,635 

Source: U.S. Census Bureau and ADEQ’s PM10 boundary recommendation TSD dated March 15, 2010 

*Area in square miles was taken from Table 3-5 of ADEQ’s PM10 boundary recommendation 

**Population for entire reservation, including portions that lie outside of Pinal County. 

Figure 7 illustrates that, as a whole, Pinal County is sparsely populated. Within Pinal County, 

about 95% of the population resides in the more urbanized areas that lie in the western/central 

portion of the county where a number of relatively densely populated areas are located. Even 

within those more densely populated areas, the numbers of inhabitants are relatively low (see 

Table 5). 
16

Figure 7. Population density, PM10 monitors, and existing PM10 nonattainment area

BAPCHULE

Gila

County

Maricopa

County

Pima

County

Pinal

County

CASA

GRANDE

COOLIDGE

FLORENCE

APACHE

JUNCTION

SUPERIOR

QUEENCREEK

MARICOPA

KEARNY

MAMMOTH

ELOY

0 

Sources: USEPA's Air Quality 

Violating Attaining City BounExisting PTribal lanCounty b

People per squa

50 - 250251 - 500501 - 2,002,001 - 5,05,001 - 5050,001 - 2

ELOY
17

EPA believes that the size, density, and location of population can be indicative of emissions 

activity that contributes to violations of the 24-hour PM10 NAAQS in an area. For example, 

because on-road (paved and unpaved road) emissions contribute significantly to the PM10

emissions inventory in Pinal County, population data can give an indication of whether it is 

likely that an area is causing or contributing to violations of the 24-hour PM10 standard. Based 

solely on this factor, certain portions of Pinal County would not be considered for redesignation 

as nonattainment given their low population. Although areas with low population can 

nonetheless have activities that result in high emissions that contribute to violations of the 

NAAQS, EPA believes that, outside of the existing PM10 nonattainment areas, the majority of 

PM10-related emissions activities in Pinal County occur within the more densely populated 

central and western portion of the county, which is more urbanized and also includes the 

majority of agricultural lands, roads, and cattle operations, lending weight to a partial county 

redesignation. See Factor 2 discussion and Figures 4 and 5. 

In its technical report, ADEQ concludes that the eastern and southern portions of the county are 

largely undeveloped and have very low population densities, and finds that this information 

provides support for the State’s recommended boundaries. However, like the emissions data 

discussed above, we believe that the data do not justify the restricted nature of the State’s 

recommended boundaries, which exclude much of the western half of the County. Specifically, 

EPA believes that the State’s recommended exclusion of areas in the eastern and southern 

sections of the western half of the county is contradicted by evidence showing that land use 

development in Pinal County extends further east and south than the State’s recommended 

boundaries. For example, the State’s recommended boundaries fail to include the agricultural and 

more urbanized uses in and around Eloy and the future growth areas along the two Interstate 

corridors. See figures 3-13 and 3-14 from the State’s technical report. In contrast, EPA’s 

proposed boundaries would include all of the western half of Pinal County (excluding TON’s 

main reservation and the Apache Junction portion of the Phoenix PM10 nonattainment area) and 

thereby would include the areas with relatively higher population densities and most of the areas 

where significant levels of growth are expected. 

Factor 4: Traffic and commuting patterns 

This factor considers the number of commuters in each surrounding county who drive to Pinal 

County, the percent of total commuters in each county who commute to Pinal County, the 

percent of total commuters in each county who commute into the statistical area in which Pinal 

county is located, as well as the total vehicle miles traveled (VMT)15 for each county, in millions 

of miles per year (see Table 6). 

 

 

15The 2005 VMT data used for Tables 6 and 8 of this analysis has been derived using a methodology such as that 

described in “Documentation for the 2005 Mobile National Emissions Inventory, Version 2, December 2008, 

prepared for the Emission Inventory Group, U.S. EPA. This document can be found at: at 

ftp://ftp.epa.gov/EmisInventory/2005_nei/mobile_sector/documentation//2005_mobile_nei_version_2_report.pdf.
18

Table 6. Traffic and Commuting Patterns – 2005 

County 2005 VMT 

(millions 

of miles) 

Number 

Commuting 

to Pinal 

County 

Percent 

Commuting 

to Pinal 

County 

Number 

Commuting 

into 

Statistical 

Area* 

Percent 

Commuting 

into 

Statistical 

Area 

Pinal 3,126 35,960 60.1 55,880 93.4 

Maricopa 32,392 7,750 0.6 1,389,480 98.9 

Cochise 1,906 40 0.1 260 0.6 

Gila 536 330 1.9 1,390 7.9 

Graham 373 - 0.0 150 1.4 

Pima 8,759 1,970 0.5 3,810 1.0 

*Pinal and Maricopa Counties comprise the Phoenix-Mesa-Scottsdale CBSA 

Data on commuting illustrate that the majority of Pinal County’s working residents are employed 

within the county. Data from 200016 illustrate that a sizeable number (19,918) commute to 

Maricopa County to the north, with 7,750 commuters entering Pinal from Maricopa County. 

About 2,600 Pinal County residents commute to Pima County to the south, while 1,970 Pima 

County residents commute into Pinal County. The number of commuters to and from other 

surrounding counties is negligible. See Table 6 and Figure 8. 

According to the 2005 NEIv2, on-road emissions (from paved and unpaved roads) are the largest 

source of PM10 in Pinal County and account for 8,426 tpy, or 38% of the overall PM10 inventory. 

Traffic and VMT are therefore important considerations in the process of determining the 

nonattainment area boundary. ADEQ’s preliminary 2007 PM10 emissions inventory attributes 

83% (42,130 tpy) to on-road sources. See Factor 2 discussion. 

The principal route for traffic through Pinal County (serving in-county as well as out-of-county 

commuters) is Interstate 10, which bisects the western portion of the county and connects 

metropolitan Phoenix (largely in Maricopa County) to the north with metropolitan Tucson (in 

Pima County) to the south. Unpaved roads are also concentrated in the western side of the 

county. The eastern portion of the county has far fewer unpaved roads, and the main highways 

(AZ 77, 79, and 177) experience much lower traffic volumes. See Figure 8 and Appendix B, 

Figures 2 and 4. Figure 9, reproduced from Arizona’s boundary recommendation, illustrates the 

distribution of on-road emissions in Pinal County. 

ADEQ cites traffic and commuting patterns as a factor supporting the exclusion of the eastern 

half of the county from the new nonattainment area. While EPA agrees that it is reasonable to 

distinguish between the eastern and western sides of the county, EPA believes that the entire 

western half of the county, and not a small portion of it, as the State recommends, should be 

redesignated to nonattainment. EPA finds that traffic and commuting patterns do not make a case 

for the state’s recommendation, but rather lend support to the creation of a larger nonattainment 

area generally encompassing the western half of the County. See figure 3-17 from the State’s 

technical report, which shows much higher employment densities projections for year 2030 in 

the western half of the county than those in the eastern half but which also show higher 

 

16 Arizona Air Quality Designations Technical Support Document; Boundary Recommendation for the Pinal County 

24-hour PM10 Nonattainment Area, Table 3-6. March 15, 2010 
19

employment densities east and south of the State’s recommended boundaries (but still within the 

western half of the county). 
20

Figure 8. Traffic, commuting patterns, and PM10 monitors 

Tucson

Phoenix

19,918

2,601

35,961 

7,751

333

1,974

79

177

188

87

88

347

101

387

60

7

10

8

17

PinalCounty

PimaCounty

MaricopaCounty

GilaCounty

0 

AIR1000045_917 August 201

Sources: ADOT AQS (2010), FUSGS (2001), 

ViA

2002 Da

0 2,5,10

2002 Da

0 2,5,1025C

2,6
21

Figure 9. Preliminary PM10 Emissions Inventory for Pinal County (2007) – Paved and Unpaved 

year) 

Source: ADEQ Boundary Recommendation for the Pinal County 24-Hour PM10 Nonattainment Area 
22

Factor 5: Growth rates and patterns 

This factor considers population growth for 2000-2008 and growth in vehicle miles traveled for 

1996-2005 for Pinal County. 

Arizona has experienced rapid population growth in recent years (26.7% between 2000 and 

2008); however, vast areas remain sparsely inhabited. In Pinal County, the population increased 

82% between 2000 and 2008, with almost all the population growth occurring in the central and 

western portion of the county. See Factor 3, Figure 7. Table 7 shows the 2008 population growth 

and density for municipalities within Pinal County. Decreases in population density for some 

areas reflect the expansion of the boundaries of municipalities, rather than reductions in 

population. 

Table 7. Population Growth within Pinal County 

Entity Area in 

Square 

Miles 

2000/2009-10 

Population Density Population 

2000 2008 2000 2008 

Pinal County 

Total 

5,369.6 33.5 65.3 179,727 350,558 

Apache 

Junction 

34.23 929.3 958.4 31,814 32,776 

Casa Grande 48.17/109* 523.7 377.5 25,224 41,152 

Coolidge 5.03/65* 1,549.1 157.9 7,786 10,261 

Eloy 71.67/110* 144.8 115.9 10,375 12,750 

Florence 8.29/50* 2,056.2 415.6 17,054 20,781 

Kearny 2.79 805.4 1,177.5 2,249 3,297 

Mammoth 1.08 1,626.5 2,339.1 1,762 2,573 

City of 

Maricopa 

4.04/43* 257.6 1,059.8 1,040 45,571 

Queen 

Creek** 

25.7 167.3 944.2 Pinal Co: 119 

Maricopa Co: 

4,197 

Total: 4,316 

Pinal Co: 5,700 

Maricopa Co: 

18,661 

Total: 24,361 

 

Superior 1.93 1,684.6 1,766.3 3,254 3,335 

Source: U.S. Census Bureau and ADEQ’s PM10 boundary recommendation TSD, dated March 15, 2010.

*2009-2010 area in square miles is from Table 3.5 of ADEQ’s PM10 boundary recommendation TSD. 

** Queen Creek straddles the Pinal and Maricopa County border, with about 23.4% of the city’s area lying within 

Pinal County. The population figures in the table are pro-rated to reflect the proportion of the city that is within each 

county, but density is not pro-rated. 

Along with the growth in population, VMT has increased dramatically. 

Table 8. Population and VMT Values and Percent Change. 

Location Population 

(2005) 

Population

Density

(2005) 

Population 

% change 

(2000 - 

2005) 

2005 VMT 

(millions 

mi) 

VMT 

% change

(1996 to 

2005) 

Pinal 240,044 45 32 3,126 54 
23

ADEQ submitted maps showing population densities both under current conditions and 

projections for the year 2030 when the population of Pinal County is anticipated to exceed 

1,000,000. Under existing conditions, higher population densities are found in the west central 

portion of the county, but there are also population centers in the northern (Apache Junction and 

Queen Creek) and southern portions (Eloy) of the county. ADEQ’s maps show that future 

growth is expected to be concentrated in the Interstate 8 and 10 corridors which extend through 

the west central and southern portions of the county, although a certain amount of growth is also 

expected in the Falcon Valley area further to the east. See Figures 3-14 and 3-17 in ADEQ’s 

technical report. 

EPA finds that growth rates and patterns do not make a case for the state’s recommendation, but 

rather lend support to the creation of a larger nonattainment area generally encompassing the 

western half of the County. By redesignating the western portion of Pinal County as 

nonattainment for PM10, EPA would include most of the population and the rapidly growing 

areas along the I-10 and I-8 corridors. 

Factor 6: Meteorology 

Like most of Arizona, Pinal County is generally hot and dry. Average maximum temperatures at 

the Maricopa weather station (part of the National Weather Service Cooperative Network) range 

from 67 degrees Fahrenheit (o

F) in January to 107oF in July, and minimum temperatures from 

25oF in January to 75oF in August. The rainiest month is July, with just over an inch of rain; the 

yearly total averages 8 inches. Despite the dryness, there is substantial agriculture in Pinal 

County, supported by irrigation from groundwater and the Central Arizona Project. Weather 

systems typically arrive from the west, except during "monsoon" season, which occurs during 

June through August or September, when moisture from the south arrives and creates 

thunderstorms. 

EPA examined wind data collected at the Cowtown monitoring site and also at stations in the 

AZMET meteorological network. In the western portion of the County, at the Cowtown and 

Maricopa monitors, typically there is wind from the southeast during the cooler evening hours, 

corresponding to downhill drainage flow down the Gila River valley. Flow at other times is less 

consistent, though there can be steady winds from the west in late morning through the 

afternoon, and on occasion from the north or south. In the center of Pinal County, at Coolidge 

(near the Pinal County Housing monitor), flow can be from any direction, though it tends to 

range from the southwest to southeast in the second and third quarters of the year. In the north, 

at Queen Creek (near the Combs School monitor, where the Phoenix serious PM10 nonattainment 

area lies immediately to the west and to the north), flow is mainly from the southeast. There is 

some northwest flow in May through July; exceedances may occur then though they are more 

common in winter. Finally, in the south at Marana (near the Pinal Air Park monitor, which does 

not violate the NAAQS), flow is mainly from the east-southeast, with easterly flow predominant 

in the winter. With a few exceptions, flow is not from the north and northwest, making transport 

of PM10 from the metropolitan Phoenix area unlikely under most circumstances. See Figure 10. 
24

While there are periods of high wind and gusts, especially during “monsoon” season, wind 

speeds are most often 3 meters per second or less, with higher speeds usually from the west. 

High wind and gusts, especially over disturbed desert areas, can lead to substantial fugitive dust 

emissions. Sometimes there are “haboob” dust storms that have the appearance of an 

approaching “wall of dust,” in which visibility is very low and gusts very strong. It is possible 

that some PM10 exceedances are caused by wind-generated dust near the monitors, with some 

moderate-range transport. 

Figure 10. Pinal County Wind Roses for 2006 – 2008 
25

The State recommends including the agricultural basin region of the county where stagnation 

conditions are known to impact PM10 concentrations. While we agree that the new nonattainment 

area should include the agricultural basin region where stagnation conditions occur, we find that 

the State’s recommended boundaries do not in fact accomplish this. As shown on page 14 of 

ADEQ’s technical report, the agricultural basin region of the county, roughly defined based on 

tilling and harvesting emissions within the county, lies in the western half of the county, and also 

extends south of Interstate 10 towards the southern county line. Moreover, as discussed in the 

following paragraph, a review of available wind data supports the inclusion of areas to the south 

and east of the violating monitors (i.e., beyond the State’s recommended boundaries) based on 

the prevalence of winds from the southeast quadrant. 

EPA has considered the information provided by ADEQ but also reviewed available wind data 

for Pinal County and finds that winds are similar throughout central and western Pinal County in 

that the predominant wind directions are from the southeast quadrant. See Figure 10. The 

predominance of southeast winds support boundaries that extend south and east of the violating 

monitors because PM10 sources, including agricultural activities and unpaved roads, are found in 

those directions. EPA’s recommended boundaries encompass the types of sources that are 

believed to cause or contribute to the monitored violations and that are located east and south of 

the violating monitors, whereas the State’s recommended boundaries largely exclude these 

sources. See Figures 1, 4, and 5. 

Lastly, EPA recognizes that high wind events do occur in Pinal County, and that some of these 

events may result in monitored particulate matter exceedances that qualify as caused by 

exceptional events under EPA’s exceptional events rule.17 However, as ADEQ itself 

acknowledges, even if EPA were eventually to determine that all of the exceedances that ADEQ 

has flagged are caused by “exceptional events,” the area would still clearly be in violation of the 

PM10 NAAQS. 

Factor 7: Geography and topography 

The geography/topography analysis evaluates the physical features of the land that might have an 

effect on the airshed and, therefore, on the distribution of PM10 over the Pinal County area. 

Pinal County has topographical barriers significantly limiting air pollution transport within its 

airshed and from neighboring airsheds, though these barriers are not absolute. Therefore, this 

factor provides some support for EPA’s suggested boundary for the nonattainment area. 

As shown in Figure 11, Pinal County generally has fairly low relief and is at around 1,200 feet 

elevation, but it is punctuated by various mountains and ranges having peaks generally from 

 

17 On March 22, 2007, EPA adopted a final rule, Treatment of Data Influenced by Exceptional Events, to govern the 

review and handling of certain air quality monitoring data for which the normal planning and regulatory processes 

are not appropriate. Under the rule, EPA may exclude data from use in determinations of National Ambient Air 

Quality Standard (NAAQS) exceedances and violations if a state demonstrates that an “exceptional event” caused 

the exceedances, and satisfies other criteria set forth by the rule. See 72 FR 13560. 
26

3,000 to 5,000 feet. Some 50 miles east of the violating monitors, the eastern quarter of the 

county becomes more mountainous, ultimately rising to some 6,000 feet near the eastern borders 

with Gila and Graham Counties. The mountain ranges generally run southeast-northwest, and do 

not form closed basins. Rather, there are broad desert valleys. In the vicinity of the violating 

monitors, there are the Sacaton Mountains to the east, rising to 2,235 feet, the Maricopa 

Mountains to the west, with elevations up to 2,400 feet. Nearest is the southeastern tip of the 

Sierra Estrella Mountains, starting at about 10 miles northwest of the Cowtown monitor; they 

have peaks to 3,000 and 4,500 feet. To the north, between Pinal and Maricopa Counties, are the 

South Mountains rising to 2,500 feet; they run west-southwest to east-northeast, unlike most of 

the ranges. They are only 10 miles long, but along with the Sierra Estrella they do form a partial 

barrier between Pinal County and metropolitan Phoenix to the north. 

Overall, the mountains within the county can redirect winds, and form a partial barrier to 

transport from the eastern portions of Pinal County. 

ADEQ finds that topographic considerations support the State’s inclusion of the basin region of 

the county, which is characterized by open-ended valleys with few topographic barriers within 

the recommended boundaries. Conversely, ADEQ finds that topographic considerations support 

the State’s exclusion from the recommended boundaries of the eastern portion of the county, 

which is characterized by rough terrain and steep mountain ranges reaching over 7,000 feet in 

elevation. 

EPA generally agrees with ADEQ’s description of the topography of Pinal County. We believe 

that the various mountain ranges found on each side of the county inhibit transport of PM10

(which is largely crustal in composition – see Figure 6) from outside the county to the violating 

monitors within the county. Within the county itself, we believe that the mountains in the eastern 

quarter of the county, which rise to approximately 6,000 feet near the eastern borders with Gila 

and Graham counties, inhibit intra-county transport from sources located in the eastern quarter to 

the violating monitors. See figure 11 of EPA’s TSD. (The portion of the San Carlos Apache 

Reservation that lies within Pinal County is located in the eastern quarter of the county.) 

However, the existence of the steep mountain ranges in the eastern quarter of the County does 

not justify ADEQ’s recommendation to exclude from redesignation a much larger section of the 

western half of the County. EPA believes that, taking other factors into account, the western half 

of the County, located in the basin region that features few topographic barriers, should be 

redesignated to nonattainment. Indeed, it is arguable that topography alone would lend support to 

redesignating a far larger area than EPA is proposing, one that would encompass the entire 

county, excepting only the eastern quarter. However, EPA believes that topography when 

evaluated in the context of the various other factors, supports redesignation of the western half of 

the county, rather than the much more restricted boundaries that ADEQ suggests. 
27

Figure 11. Topography 

Florence(Tohono O'Odham)

Village

San(Tohono O'Odham)

Lucy Farm

Rillito planning

area

Phoenix planning area

Miami

planning

area

Hayden

planning

area

San

Carlo

Fort

McDowell

Salt River

Gila

River

Ak-Chin

Tohono

O'Odham

Gila

County

Maricopa

County

Pima

County

Pinal

County

Violating PM-10 monAttaining PM-10 monExisting PM-10 nonaCounty boundaryTribal lands12,000+ feet~100 feet

3,000 feet

Sources: USEPA's Air Quality Systems (AQS) data

AIR1000

0 10 

5 
28

Factor 8: Jurisdictional boundaries 

In evaluating the jurisdictional factor, EPA considered the planning and organizational structure 

of Pinal County and the State of Arizona to ensure that the implementation of controls within the 

prospective nonattainment area can be carried out in a cohesive manner. Figure 12 shows 

boundaries for Pinal and neighboring counties, nearby nonattainment areas, and Indian lands. 

The Arizona Department of Environmental Quality has overall jurisdiction over environmental 

programs in the state of Arizona, as well as jurisdiction over certain source types, including 

smelters, refineries, coal-fired power plants, and retains authority for regulating emissions from 

agricultural operations. Three Arizona counties, Maricopa, Pima, and Pinal, have their own air 

pollution control programs and operate pursuant to agreements with ADEQ. The lead air quality 

planning agencies responsible for state implementation plans (SIPs) for Maricopa County and 

Pima County are the metropolitan planning organizations (MPO), the Maricopa Association of 

Governments (MAG) and the Pima Association of Governments (PAG), respectively. There is 

no MPO and thus no lead air quality planning agency for SIP purposes in Pinal County. 

Therefore, ADEQ is responsible for developing SIPs for Pinal County. Pinal County has 

permitting authority, and can adopt control measures by rule, but is preempted from adopting 

rules regulating certain categories of sources that are regulated by the State. 

Four tribes are located in Pinal County. The Ak-Chin Indian Community tribal lands lie entirely 

within the County, and are encircled by the proposed nonattainment area. Approximately twothirds of the Gila River Indian Community tribal lands lie within the boundaries of Pinal County; 

the other third is in Maricopa County and is part of the Maricopa County serious PM10

nonattainment area.. A portion of the main reservation of the Tohono O’odham Nation lies in 

southeastern Pinal County, south of the proposed nonattainment area. Two additional areas (San 

Lucy Farm and Florence Village) lie to the east and northeast of the main TON reservation, 

within the proposed nonattainment area. A portion of the San Carlos Apache tribal lands lie 

within the eastern part of Pinal County, east of the proposed nonattainment area. See Figure 12. 

Of the four tribes, only the Gila River Indian Community has treatment as a state (TAS) status 

for Clean Air Act section 107 designations and an air quality monitoring network that reports 

quality-assured data to EPA’s Air Quality System (AQS). We recently proposed approval of 

GRIC’s submitted tribal implementation plan. See 75 FR 48880, August 12, 2010. None of the 

other tribes currently monitor for PM10, although the Ak-Chin Indian Community has been 

developing an air monitoring program. 

As noted above, EPA is deferring action on the Ak Chin and Gila River Inidan Community lands 

within Pinal County, and the San Lucy Farm and Florence Village portions of the TON, which 

like to the east and northeast of the main reservation in order to allow time for formal 

consultation to occur. Neither ADEQ nor Pinal County has jurisdiction over tribal lands. 

The Apache Junction area of Pinal County is part of the Phoenix PM10 nonattainment area. The 

Hayden and Miami PM10 nonattainment areas lie to the east. 
29

In its technical report, ADEQ notes that five cities and towns (Casa Grande, Coolidge, Eloy, 

Florence, and City of Maricopa), as well as a portion of a sixth (Queen Creek) are located in 

central and western Pinal County. ADEQ indicates that the incorporated boundaries of these 

municipalities have been taken into account in developing the nonattainment area boundaries. 

However, EPA’s review of the incorporated boundaries of these municipalities (see, e.g., Figure 

2) shows that the State’s recommended boundaries omit portions of the City of Maricopa and 

Coolidge, and most of Florence and Eloy. In contrast, EPA’s proposed nonattainment area 

boundaries encompass all of these cities and towns, where most of the county’s population 

resides. Inclusion of entire cities and towns within the nonattainment area boundaries would 

facilitate attainment planning to the extent that such local governments will ultimately be relied 

upon for development and/or implementation of specific PM10 control measures. 
30

Figure 12. Jurisdictional Boundaries 

Florence(Tohono O'Odham)

Village

San(Tohono O'Odham)

Lucy Farm

101

101

79

77

88

60

60

8

8

10

10

San

Carlo

Fort

McDowell

Salt

River

Gila

River

Ak-Chin

Tohono

O'Odham

Gila

County

Maricopa

County

Pima

County

Pinal

County

Rillito planning

area

Phoenix

planning area

Miami

planning

area

Hayden

planning

area

0 10 

5 

FreewaysViolating PM-10 monAttaining PM-10 monWildernessUS Forest Service ClNational Park ServicExisting PM-10 nonaTribal landsCounty boundaryAIR10

Sources: USEPA's Air Quality Systems (AQS) da
31

Factor 9: Level of control of emission sources 

Under this factor, we consider the existing level of control of emissions. The emissions 

data used by EPA in this technical analysis and provided in Table 3 (under Factor 2) 

represent emissions levels taking into account any control strategies implemented in Pinal 

and nearby counties before 2005 on stationary, mobile, and area sources. EPA is not 

aware of any additional information on emissions controls that is relevant to assessing 

sources contributing to the monitored violations. EPA is proposing to designate those 

portions of Pinal County that encompass the emissions sources and activities that 

contribute to the violations in this area. 

Pinal County AQCD has established rules for dust abatement purposes that apply within 

a subarea of Pinal County established under state law (Arizona Revised Statutes section 

49-541) and referred to as “Area A.” Within Pinal County, “Area A” generally refers to 

an area encompassing the Pinal County portions of Apache Junction and Queen Creek. 

Pinal County has also adopted a number of ordinances that are also intended to reduce 

dust generated within “Area A.” These include ordinances placing restrictions on 

residential fireplaces, leaf blowers, open burning, vehicle commute trips, and vehicle 

idling. For one township located within “Area A,” the township included in the Phoenix 

Area PM10 nonattainment area (i.e., Township 1 north, range 8 east; referred to as 

“Apache Junction”), Pinal County AQCD has adopted further dust abatement rules.18 The 

State’s recommended boundaries include a portion, but not all, of “Area A.” In contrast, 

EPA’s proposed boundaries for the new nonattainment area would encompass all of 

“Area A,” thereby facilitating review and modification of these existing PM10 emissions 

controls within the broader SIP attainment planning context. 

Conclusion

Based on the weight of evidence, and an evaluation of all the factors discussed above, 

EPA is proposing to redesignate the western portion of Pinal County, Arizona (excluding 

the main TON reservation), as nonattainment for the 1987 24-hour PM10 NAAQS, as set 

forth in Figure 2. Inventory and speciation data point to onroad emissions (paved and 

unpaved), agriculture (including feedlots), construction, and industrial processes as the 

primary contributors to nonattainment. The vast majority of these activities are occurring 

on the western side of Pinal County leading EPA to conclude that a nonattainment area 

(NAA) that incorporates the western portion of the County is appropriate. 

The expected exceedance values of monitors deployed throughout the area reinforce the 

partial county redesignation. EPA’s intended nonattainment area boundary encompasses 

all violating monitors that are not otherwise included in previously designated 

nonattainment areas. The intended nonattainment area also includes areas that are not 

 

18 The township referred as to Apache Junction would be unaffected by our proposed action and would 

remain part of the Phoenix planning area, which is designated as a “serious” PM10 nonattainment area. 
32

violating the standard, but by virtue of the source mix and meteorology, may be 

contributing to the violations recorded elsewhere. 

CAA section 107(d)(3)(C) provides that after notifying the Governor of State of its intent 

to redesignate an area, EPA shall promulgate the redesignation, if any, of the area or 

portion thereof, submitted by the Governor, “making such modifications as EPA may 

deem necessary....” Pursuant to CAA section 107(d)(3), we have reviewed the State’s 

recommendation (dated March 23, 2010) and related technical report (submitted on 

March 26, 2010). 

Both EPA and the State agree that sources outside of the county do not contribute to 

PM10 violations at the violating monitors within the county, and that sources in the 

eastern half of the county do not contribute to the violating monitors (which are 

concentrated in the central and western portions of the county). But while EPA and the 

State both use the nine-factor analysis for evaluation of the prospective nonattainment 

area boundaries, we reach quite different results. 

As explained above, EPA does not believe that the State’s recommended boundaries 

encompass the full geographic area from which emissions-generating activities contribute 

to the monitored PM10 violations. More specifically, we believe that the Governor’s 

recommended boundaries, which cut through municipalities and contiguous expanses of 

agricultural fields, exclude sources that have been identified as dominant sources of PM10

and that are contributing to elevated levels of PM10 at violating monitors. 

We believe that our proposed boundaries, which are defined as all land geographically 

located within Pinal County west of the north-south line defined by the boundary 

between Townships 10E and 11E, but excluding TON’s main reservation and excluding 

the existing Apache Junction portion of the existing Phoenix PM10 nonattainment area, 

encompass the areas in which PM10 violations are being monitored, as well as the areas 

that contribute to the monitored violations, and that they are thus consistent with the 

definition of nonattainment areas in CAA section 107(d)(1)(A). Our conclusion is based 

on EPA’s analysis of the factors as set forth in the body of this document. In sum, we 

base our proposed boundaries on the following considerations: (1) monitored violations 

occur in the west, central and northern portions of the western half of the county, not in 

the eastern half (i.e., outside of existing PM10 nonattainment areas); (2) the emissions 

from agricultural operations, feedlots, dairies, and other cattle operations, as well as 

roads, are concentrated in the western half of the county; (3) population densities are 

much greater in the western half of the county than in the eastern half and growth is 

expected to be concentrated primarily along the Interstate corridors that extend through 

the western half of the county; (4) Interstate 10, which connects Pinal County with the 

employment centers in metropolitan Phoenix and Tucson, bisects the western half of 

Pinal County; (5) predominant southeasterly winds support inclusion of PM10 sources in 

areas to the south and east of the violating monitors; (6) the western half of Pinal County 

encompasses the incorporated boundaries of all of the cities in Pinal County (Apache 

Junction, Casa Grande, Coolidge, Eloy, Maricopa), as well as the larger towns (Florence 

and Queen Creek) thereby potentially facilitating implementation of future control 
33

measures; and (7) dust abatement measures already in effect in “Area A” (within Pinal 

County) can readily be applied, as necessary and appropriate, throughout the other 

portions of the western half of Pinal County. Figure 2 compares the State’s recommended 

boundaries to EPA’s proposed boundaries. 

EPA therefore deems it necessary and appropriate to propose boundaries that differ from 

the State’s recommended boundaries and that we believe better satisfy air-quality data, 

planning, control and other air-quality related considerations. CAA Section 107(d)(3). 

Under CAA section 107(d)(3)(C), EPA must notify the State whenever EPA intends to 

modify State recommendations concerning boundaries for areas to be redesignated, at 

least 60 days prior to EPA promulgation of final redesignations. EPA will provide 

notification to Arizona shortly after the Federal Register notice proposing our action is 

signed. 

 
Appendix A 1

Appendix A 

Emissions in Pinal County: Primary PM10, NOx, NH3, SO2,, VOCs. 

 
Appendix A 2

Pinal County: Emission Totals Per County (tons per year). 2005 NEI version 2. 

County 

Primary PM10

Emissions NOx

 NH3 SO2 VOC 

Pinal 22,088 12,545 5,646 757 9,217

Pinal County: Primary PM10 (Includes Filterables + Condensibles) Sources. 2005 NEI 

version 2. 

Source Category 

Emissions 

(tpy) 

% of Total Primary 

PM10 Emissions 

Nonpoint

Unpaved Roads 6,253 28%

Construction 5,439 25%

Agric - Crop Tilling & Livestock Dust 5,008 23%

Paved Roads 2,171 10%

Indus Process - NEC 955 4%

Waste Disposal - Open Burning 906 4%

Wildfires 466 2%

Other Nonpoint 149 1%

Nonroad

Non-Road Equipment - Diesel 171 1%

Misc. Nonroad 106 0%

Onroad

On-Road Vehicles - Diesel 135 1%

On-Road Vehicles - Gasoline 85 0%

Point

Waste Disposal 205 1%

Misc. Point 39 0%

TOTAL: 22,088 100%

 
Appendix A 3

Pinal County: Nitrogen Oxides (NOx) Sources. 2005 NEIv2. 

Source Category 

Emissions 

(tpy) 

% of Total NOx Emissions, Pinal 

County 

Onroad 

 On-Road Vehicles - Diesel 3,889 31%

 On-Road Vehicles - Gasoline 3,715 30%

Nonroad 

 Planes, Trains, & Ships 2,275 18%

 Non-Road Equipment - Diesel 1,775 14%

 Non-Road Equipment - Gasoline 142 1%

Nonpoint 

 Waste Disposal - Open Burning 235 2%

 Wildfires 113 1%

 Fuel Comb - Industrial Boilers, ICEs 81 1%

 Fuel Comb - Residential Fossil 65 1%

 Other Nonpoint 35 0%

Point 

 Fuel Comb - Electric Utility 173 1%

 Misc. Point 47 0%

TOTAL: 12,545 100%

Pinal County: Ammonia (NH3) Sources. 2005 NEIv2. 

Source Category 

Emissions 

(tpy) 

% of Total 

NH3Emissions, Pinal 

County 

Nonpoint 

 Livestock Waste 4,344 77%

 Fertilizer Application 845 15%

 Other Nonpoint 75 1%

Onroad 

 On-Road Vehicles - Gasoline 305 5%

 On-Road Vehicles - Diesel 9 0%

Point 

 Fuel Comb - Electric Utility 65 1%

Nonroad 

 Misc. Nonroad 2 0%

TOTAL: 5,646 100%

 
Appendix A 4

Pinal County: Sulfur Dioxide (SO2) Sources. 2005 NEIv2. 

Source Category 

Emissions 

(tpy) 

% of Total SO2

Emissions, Pinal County 

Nonroad 

 Non-Road Equipment - Diesel 244 32%

 Planes, Trains, & Ships 163 22%

 Non-Road Equipment - Gasoline 1 0%

Nonpoint 

 Fuel Comb - Industrial Boilers, ICEs 130 17%

 Wildfires 48 6%

 Other Nonpoint 21 3%

Onroad 

 On-Road Vehicles - Diesel 105 14%

 On-Road Vehicles - Gasoline 38 5%

Point 

 Misc. Point 7 1%

TOTAL: 757 100%

Pinal County: Volatile Organic Compounds (VOC) Sources. 2005 NEIv2. 

Source Category 

Emissions 

(tpy) 

% of Total VOC 

Emissions, Pinal 

County 

Onroad 

 On-Road Vehicles - Gasoline 3,539 38%

 On-Road Vehicles - Diesel 200 2%

Nonroad 

 Non-Road Equipment - Gasoline 1,476 16%

 Non-Road Equipment - Diesel 195 2%

 Planes, Trains, & Ships 96 1%

Nonpoint 

 Wildfires 978 11%

 Gas Stations 687 7%

 Waste Disposal - Open Burning 642 7%

 Solvent - Non-industrial 518 6%

 Surface Coating - Industrial 206 2%

 Miscellaneous Sources 186 2%

 Surface Coating - Architectural 176 2%

 Other Nonpoint 239 3%

Point 

 Misc. Point 80 1%

TOTAL: 9,217 100%
Appendix B 1

Appendix B. 

ADEQ Maps of PM10 Sources. 

From Arizona Department of Environmental Quality, Boundary Recommendation for the 

Pinal County 24-hour PM10 Nonattainment Area: March 15, 2009. 

http://www.azdeq.gov/environ/air/plan/download/032910c.pdf
Appendix B 2

Figure 1. ADEQ Map of significant sources of PM10 in Pinal County (preliminary 2007 emissions in
Appendix B 3

Figure 2. ADEQ Map of Onroad Emissions - Unpaved Roads (preliminary 2007 Emiss
Appendix B 4

Figure 3. ADEQ Map of Construction Sources (preliminary 2007 Emissions Inventory)
Appendix B 5

Figure 4. ADEQ Map of Onroad Emissions – Paved Roads (preliminary 2007 Emissi
Appendix B 6

Figure 5. ADEQ Map of Tilling and Harvesing PM10 Emissions (preliminary 2007 Emi
Appendix B 7

Figure 6. ADEQ Map of Stationary Industrial Source PM10 Emissions (preliminary 2007 E
Appendix B 8

Figure 7. ADEQ Map of Concentrated Animal Feeding Operation (CAFO) PM10 Emissions. (pr

Inventory