# Technical Support Document for the EPA’s Action on the 2012 Five Percent Plan

Air Division

U.S. EPA Region 9 January 14 , 2014ii For information on this technical support document, please contact:

Scott Bohning Office of Air Quality Analysis U.S. Environmental Protection Agency

– Region 9

75 Hawthorne Street San Francisco, California 94105 (415) 947

- 4127 bohning.scott@epa.gov

Michael Flagg Office of Air Quality Analysis U.S. Environmental Protection Agency

– Region 9

75 Hawthorne Street San Francisco, California 94105 (415) 972

- 3372 flagg.michaela@epa.gov

Greg Nudd Office of Air Planning U.S. Environmental Protection Agency

– Region 9

75 Hawthorne Street San Francisco, California 94105 (415) 947

- 4107 nudd.gregory@epa.goviii



### Table of Contents I. Purpose of this Document

................................ ................................ ................................ ............ 1
II. Emissions Inventories

................................ ................................ ................................ ................ 1
II.A. Evaluation of the 2008 PM

- 10 Inventory

................................ ................................ ........... 1
II.A.1. O verview

................................ ................................ ................................ ..................... 1 II.A.1. Area Sources (Other than Windblown Dust)

................................ .............................. 2
II.A.2. Windblown Dust

................................ ................................ ................................ .......... 3
II.A.2. Nonroad Sources

................................ ................................ ................................ ......... 3
II.A.3. Onroad Mobile Sources

................................ ................................ ............................... 4 II.B. Annual Inventories Derived from the 2008 Periodic Inventory

................................ ......... 5
II.B.1. Base Case Inventories

................................ ................................ ................................ .. 5
II.C.2. Controlled Inventories

................................ ................................ ................................ . 5 III. Air Quality Data

................................ ................................ ................................ ........................ 6 III.A. Requirements for Demonstrating Attainment by December 31, 2012

.............................. 6 III.B. Exceptional Events

................................ ................................ ................................ ............ 8
III.C. Tribal Data

................................ ................................ ................................ ......................... 9
III.D. EPA Conclusion

................................ ................................ ................................ .............. 10
IV. Attainment Demonstration

................................ ................................ ................................ ...... 10
IV.A. Overview

................................ ................................ ................................ ......................... 10 IV.B. Technical Approach

................................ ................................ ................................ ........ 11 IV.C. Selection of Design Days

................................ ................................ ................................ 14 IV.D. Modeling Domain

................................ ................................ ................................ ........... 15 IV.E. Estimating the Impact of Control Measures

................................ ................................ .... 15
IV.F. Results of Attainment Demonstration and EPA Assessment

................................ .......... 161 

## Technical Support Document for the EPA’s Action on the Maricopa County (Phoenix) PM

- 10 Nonattainment Area

Five Percent Plan

I. Purpose of this Document

This Technical Support Document (TSD) is intended to support EPA’s action on the submitted SIP revision “ Maricopa Association of Governments Five Percent Plan for PM

- 10 for the Maricopa County Nonattainment Area ” submit ted on May 25, 2011. (2012 Five Percent Plan). This TSD provides more technical detail on the topics discussed in the Federal Register notices for this action (see docket number EPA

- R09

- OAR

- 2013

- 0762). Readers should consult those Federal Register notices for more background and context on the topics covered in this TSD.



### II

. Emissions Inventor ies

The 2012 Five Percent Plan included annual inventories for 2007

- 2012 in order to demonstrate compliance with the Clean Air Act 189(d) requirement for a five percent emissions reduction annually until the standard is attained. The annual inventories were also needed for the reasonable further progress and contingency measure demonstrations. These demonstrations are all discussed in our Federal Register notice proposing action on the plan.

The inventories are based on the “ 2008 PM10 Periodic Emissions Inventory for the Maricopa County, Arizona Nonattainment Area, Revised June 2011” (2008 PM

- 10 Inventory) that was developed by the Maricopa Co unty Air Quality De partment (MCAQD) with assistance from the Maricopa Association of Governments (MAG). See Appendix A, Exhibit 1 of the 201 2 Five Percent Plan. This document only assesses the annual inventory for PM 10 for the Maricopa County PM 10 Nonattainment Area. While t he 2008 PM

- 10 Inventory includes typical daily data and data for other pollutants, these pollutants are not relevant to our action on the plan. 1

II. A

. Evaluation of the 2008 PM

- 10 Inventory

II. A .1. Overview

Table 1

, below summarizes the annual PM 10 emis sions in the Maricopa County PM 10 Nonattainment area for 2008, as provided in the 2008 PM

- 10 Inventory, Section 1.6 . The table also highlights any source subcategories contributing more than 1,000 tons per year (tpy) of PM 10 emissions

.

1 See footnote 6 in the proposed action regarding PM 10 precursors.2 Table 1 : Overview of the 2008 PM

- 10 Inventory Source Category Significant Sub

- Categories > 1,000 tpy Annual PM 10 Emissions [tpy] Point Sources 150 Area Sources 24,521

Windblown Dust 4,815 tpy Commercial Construction 4,057 tpy Travel on unpaved parking lots 2,365 tpy Offroad recreational vehicles 2,014 tpy Road Construction 2,051 tpy Residential Construction 1,692 tpy Nonroad sources 1,92 8

Construction and mining equipment 1,249 tpy Onroad sources 21,549

Unpaved road and alley fugitive dust 11,710 tpy Paved road fugitive dust 6,694 tpy Exhaust, tire and brake wear 3,144 tpy Total Emissions 48,148

Point sources are larger industrial sources such as power plants and large manufacturing facilities. These sources self

- report their emissions to the MCAQD. The self

- reported emissions are quality assured and validated by MCAQD. However, as Table 1 shows, these sources are not si gnificant contributors to PM 10 emissions in the nonattainment area. This document will focus on the other, more significant source categories.

II. A .1

. Area So urces (Other than Windblown Dust)

Area sources are stationary sources which are too small and numerous to be treated as point sources. EPA has reviewed the list of area sources estimated by MCAQD and agrees that their list inc ludes all of the significant PM 10 area sources. The methodology for calculating PM 10 emissions from area sources depends on the source, but generally one uses a combination of emission factor s and activity data. For example, the Western Regional Air Partnership ( WRAP ) Fugitive Dust Handbook 2 recommends using 0.42 ton PM 10 /acre

- month for road construction. So, for every acre of land impacted by road construction for a month, one could expect 0.42 tons of PM 10 emissions. These emission factors are combined with activity data to estimate emissions. For example, Maricopa County issues permits for large construction projects

, and tha t data can be used to estimate how many acres were impacted by construction and for how long. Both the emission factors and the activity data can vary significantly in uncertainty. EPA has reviewed the area source emissions calculations and found that appr opriate emission factors were used and that the most accurate possible activity data was also used.

The key area source categories in Table 1 above were carefully analyzed in the 2008 PM

- 10 Inventory. MCAQD took particular care in getting the best data an d emission factors for construction sources (see Section 3.3.9 of the 2008 PM

- 10 Inventory) using their databases of construction permits and inspections . Offroad vehicle emissions are difficult to calculate because

2 WRAP Fugitive Dust Handbook, prepared by Countess Environmental for the Western Governors’ Association, Sept. 7, 2006.3

the emission factors are not well establ ished and the activity data is not easy to develop. See Section 3.5.8 of the 2008 PM

- 10 Inventory. Nevertheless, MCAQD’s estimate of offroad vehicle emissions appears to be sufficiently accurate. Travel on unpaved parking lots is similarly difficult to calculate because “unpaved parking lots” are not necessarily registered or indicated as such on maps. Still, the MCAQD used the best and most current emission calculation methods and developed suffic iently accurate activity data for the purposes of the 2012 Five Percent Plan (see Section 3.5.9 of the 2008 PM

- 10 Inventory).

II. A .2. Windblown Dust

Windblown dust is the largest component of the a rea source inventory and is a key source category relatin g to PM 10 violations in the Maricopa County PM 10 Nonattainment Area. Since 2007, nearly all of the exceedances of the PM 10 standard have been measured on days with elevated or high winds. 3 Windblown dust is only about 10 percent of the annual inventory

, bu t it is a greater concern on windy days.

MCAQD in cooperation with MAG developed a detailed method for calculating windblown dust emissions (see Appendix 4 of the Inventory). Levels of w indblown dust emissions are particularly difficult to quantify. 4 MCA QD and MAG developed initial inventory measurements using methods developed in the scientific literature , taking into account the best available data on land use and on the degree to which soil is disturbed

. S ince this method only accounts for the generati on of the dust and not how it behaves once it is generated , it tends to overestimate the emissions of windblown dust that impact the area because it does not account for the precipitation of dust from the atmosphere and deposition on the ground. T o address this issue

, MCAQD and MAG analyzed ambient monitoring data to determine the percentage of PM 10 mass that was measured at the monitors at various wind speeds. S ee Table A4

- 9 of Appendix 4 of the 2008 PM

- 10 Inventory. This analysis showed that on an annual basis, the percentage of PM 10 measured at wind speeds greater than 12 miles per hour ranged from 3.37% to 14.07% with an average of 7.58%. Using this data , MCAQD and MAG scaled down the windblown dust emissions to account for no more than 10% of the annual inventory. EPA has considered this method and finds it to be technically justifiable and sufficiently accurate for the purposes of this plan. This method would not be appropriate for an attainment demonstration, however, and it was not used in the attainment demonstration.

II. A .2

. Nonroad Sources

Nonroad sources are mobile sources that are not licensed or certified as highway vehicles. The development of this inventory is covered in Section 4 of the 2008 PM

- 10 Inventory. MCAQD used EPA’s NONROAD model (version 2008.1.0) (the current version of the model) to develop emissions estimates for most nonroad sources in the 2008 PM

- 10 Inventory. MCAQD used a Federal Aviation Administration model for aircraft and airport ground support equip ment and they used surveys of railroad companies operating in the area to develop estimates of emissions from locomotives and support equipment. The methods and input data are

3 See pages 3.8

- 3.12 of the 2012 Five Percent Plan
4 Appendix 4 of the 2008 PM

- 10 Inventory references studies regarding how the dust is generated by the wind on various soil types with various degrees of disturbance. EPA is not aware of any studies that a ttempt to quantify transported dust or the extent to which it is re

- deposited to the ground.4

reasonable and current for these two sources and EPA considers the resulting emi ssions estimates to be sufficiently accurate for the purposes of the 2008 Five Percent Plan.

The most significant nonroad source is construction and mining equipment. MCAQD used construction employment as a measure of construction activity in order to ca lculate the construction emissions , rather than the recommended factor of the total dollar value of construction. Data for the preferred parameter was not available and the use of construction employment is an acceptable substitute, Therefore, EPA finds th at this is an acceptable method to estimate these emissions with the NONROAD model.

II. A .3

. Onroad Mobile Sources

The process for calculating the emissions from onroad sources is documented in the 2008 PM

- 10 Inventory Section 5 and in the MAG TSD, Section II . Emissions from exhaust, brake and tire wear were estimated using EPA’s Motor Vehicle Emissions Simulator (MOVES) model. Other emissions were estimated using calculation methods specified in EPA’s AP

- 42.

EPA’s MOVES model was used to develop emissions estimates for vehicle exhaust, tire wear and brake wear. MAG used MOVES2010a, which was the recommended model at the time the inventory was developed. These emissions were originally estimated for the 2008 P eriodic Emissions Inventory using the relevant data available at that time for input parameters such as fuel usage, vehicle population, vehicle miles traveled and others. Later, when MAG developed the Technical Support Document, newer data was available. S ignificantly, the latest vehicle registration data from the Arizona Department of Transportation indicated a greater proportion of older vehicles than expected. MAG used the same version of MOVES, which was appropriate but with updated data on fleet mix an d the distribution of traffic. The resulting emissions estimate was 22.4 percent higher than was estimated in the 2008 Periodic Emissions Inventory. 5 EPA finds that it was appropriate for MAG to make this change and to incorporate these higher estimates in to the 2008 emissions estimate.

Emissions of fugitive dust from paved and unpaved roads were estimated using the January 2011 updated versions of Sections 13.2.1 and 13.2.2 of the EPA Compilation of Air Pollutant Emission Factors, AP

- 42 (EPA, 2006). These are the current and best available methods for estimating emissions from these sources.

The paved road dust emissions depend on the level of silt on the road (silt loading), the weight of the vehicles traveling on the road, the number of wet days in a y ear and the miles driven on the road. Fugitive dust emissions can be reduced by sweeping silt off the streets with PM 10 - certified street sweepers. The 2008 PM

- 10 Inventory details these calculations in Section 5.3.1. MAG updated the calculations to reflect the most current available data on vehicle weight and updated assumptions about the extent of street sweeping beginning on page II

- 11 of the MAG TSD. EPA finds that the methods were appropriate and the data used was the best available at the time the emis sions were estimated.

5 MAG TSD, page II

- 10.5

Fugitive dust emissions from unpaved roads depend on the surface material silt content, the average vehicle speed, the surface material moisture content and the annual number of wet days per year. Emissions can be reduced by paving roads and limiting speeds on unpaved roads. Section 5.3.2 of the 2008 PM

- 10 Inventory provides information on the assumptions used. MAG updated these assumptions with more recent and reliable data in the MAG TSD, starting on page II

- 16. EPA finds that the methods were appropriate and the data used was the best available at the time the emissions were estimated.

II. B

. Annual Inventories Derived from the 2008 Periodic Inventory

II. B .1. Base Case Inventories

The 2008 PM

- 10 Inventory (with some improvements b y MAG for onroad sources) served as the basis for the base case and controlled inventories for 2007, 2009, 2010, 2011 and 2012. The methodology used to estimate these base case inventories is described in Section II of the MAG TSD. The first step in this process is adjusting the inventory for population and economic changes to convert a 2008 inventory into an inventory for a different year. The second step is to account for the benefits of the control measures in the plan to produce emissions inventories tha t reflect what the emissions would have been if the measures were not in place.

MAG used population and economic data from Marshall Vest of the Economic and Business Research Center at the University of Arizona

. The economic data included population, manufacturing employment

, and construction employment. This is a reasonable source for these data

. MAG also used data from the Arizona Agricultural Statistics Bulletins to quantify changes in agricultural activity in the nonattainment area. This is also a reasonable source for this information. MAG used the data to modify the 2008 inventory to estimate the emissions in other
years. These calculations are shown in detail in Section II of the MAG TSD

. For the nonroad sources whose emissio ns were estimated with the EPA NONROAD model, MAG used the NONROAD model to develop estimates for the other years. This is the appropriate approach for those source types. For exhaust, tire wear and brake wear

, MAG updated the vehicle and vehicle activity and used the projection methods internal to the MOVES model to develop emissions estimates for the other years. This is EPA’s recommended method for this part of the emissions inventory. For the paved road and unpaved road fugitive dust , MAG adjusted the v ehicle miles traveled according to their data as the local transportation agency. EPA finds that the appropriate methods and data were used to project the 2008 inventory and develop baseline inventories for 2007, 2009, 2010, 2011 and 2012.

II.C.2. Controlled Inventories

The majority of the emission reductions claimed in the 2012 Five Percent Plan are from improvements in rule effectiveness. Some additional reductions are claimed from the 2012 implementation of the Dust Action General Permit. But th e majority of reductions during this period arise from improved compliance with Maricopa County Rules 310, 310.01 and 316. The controlled inventories reflect the benefits of these reductions.6

Rule effectiveness is the estimate of the extent to which a sta te rule in the SIP is achieving the intended reductions. A rule is only 100 percent effective if every impacted source is in compliance at all times. Often, rules are not 100 percent effective, and this aspect must be considered when calculating the emissions reductions from the rule . EPA provides guidance on rule effectiveness calculations in the document “ Emissions Inventory Guidance for Implementation of Ozone and Particulate Matter National Ambient Air Quality Standards (NAAQS) and Regional Haze R egulations ”, EPA, August 2005 (2005 EI Guidance).

Appendix 3 of the 2008 P M

- 10 Inventory describes the methods MCAQD used to calculate rule effectiveness for rules 310, 310.01 and 316. Rule 310 most often applies to construction sites. Rule 310.01 typical ly applies to vacant lots. Rule 316 applies to sources such as sand, gravel and the production of con crete

. MCAQD conducts thousands of inspections of Rule 310 and 301.01 sources and hundreds of inspections of 316 sources annually . T hey analyze all of that data to determine the compliance rate. This is a robust and valid method to determine compliance rates

an d therefore rule effectiveness. This new method was developed in cooperation with EPA and is an improvement over previous methods of rule effectivenes s calculation in Maricopa County which depended upon a few targeted inspections.

The resulting rule effectiveness rates are shown in Table 5

- 1 of the 201 2 Five Percent Plan. The rule effectiveness rate for construction was improved from 76% in 2007 to 94% in 2012. The rule effectiveness rate for mining and quarrying improved from 40% in 2007 to 73% in 2012.

As explained i n Section III of the MAG TSD, MAG uses the rule effectiveness results from MCAQD’s analysis of their inspection data to calculate the be nefits of improved compliance with these rules. These controlled inventories were then used to demonstrate that the 5% annual reduction requirement had been met and that Reasonable Further Progress was being demonstrated. The improved compliance rates for these sources were also included in the inventories used in the attainment demonstration.



### III. Air Quality Data

III.A. Requirements for Demonstrating Attainment by December 31, 2012

The 2012 Five Percent Plan predicts attainment of the PM 10 NAAQS by December 31, 2012

. Generally, EPA determines whether an area’s air quality is meeting the PM 10 NAAQS based on complete, quality assured, and certified data collected at state and local air monitoring stations (SLAMS) in the nonattainment area. Ac cordingly, EPA relies primarily on data in AQS when determining whether an area has attained a particular NAAQS. EPA will also consider air quality data from other air monitoring stations meeting the monitoring requirements in 40 CFR part 58, including the criteria in 40 CFR part 58, appendices A, D, and E, if appropriate.

Attainment of the 24

- hour PM 10 standard is determined by calculating the average number of expected exceedances of the standard over a three

- year period

. Specifically, t he 24

- hour PM 10
s tandard is attained when the expected number of exceedances averaged over a three

- year period7

is less than or equal to one at each monitoring site within the nonattainment area. Generally, three consecutive years of complete air quality data are required t o show attainment of the 24

- hour PM 10 standard. Furthermore, the monitor must provide sufficient data to perform the required calculations in 40 CFR part 50, appendix K

. To be considered complete, valid measurements must be made for 75 percent of all the scheduled sampling dates in each quarter of the year, and generally, three years of representative monitoring data that meet the 75 percent criterion should be utilized, where available. Data not meeting these criteria may also suffice to show attainment; however, such exceptions must be approved by the appropriate Regional Administrator in accordance with EPA guidance

. For this action, EPA is primarily relying on 2010

- 2012 design values for monitoring stations located within the nonattainment area. During the 2010

- 2012 time period the Maricopa County Air Quality Division (MCAQD) operated fifteen PM 10 SLAMS , while the Arizona Department of Environmental Quality (ADEQ) and Pinal County Air Quality Control District (PCAQCD) operated an additional three PM 10 m onitoring stations in the area. In addition to the State and local monitoring agency PM 10 networks, there are a number of Tribal PM 10 monitors operated by the Salt River Pima

- Maricopa Indian Community (SRPMIC) and the Fort McDowell Yavapai Nation (Fort McD owell) within the nonattainment area. Table 2 summarizes the SLAMS PM 10 data collected over the past three years

.

Tabl e 2 : Summary of 2010

- 2012 SLAMS PM 10 Data f or the Phoenix Nonattainment Area

Monitoring Site AQS Site Identification Number Highest 24

- hour

PM 10 Concentration (μg/m 3 ) 3

- Year

Average of Expected Exceedances a 2010 2011 2012 2010

- 2012 West Phoenix 04

- 013

- 0019

- 1 86 139 189 0.3 Mesa b 04

- 013

- 1003

- 1 86 127 64 0.0 * North Phoenix b 04

- 013

- 1004

- 1 44 132 140 0.0 Glendale 04

- 013

- 2001

- 1 92 141 136 0.0 Central Phoenix 04

- 013

- 3002

- 4 106 144 137 0.0 South Scottsdale b 04

- 013

- 3003

- 1 37 119 102 0.0 * Greenwood 04

- 013

- 3010

- 1 158 148 145 0.3 South Phoenix 04

- 013

- 4003

- 1 120 168 144 0.3 West Chandler 04

- 013

- 4004

- 1 76 126 402 0.7 Tempe c 04

- 013

- 4005

- 1 NA NA 145 0.0 * Higley 04

- 013

- 4006

- 1 83 152 162 0.3 West 43 rd Avenue 04

- 013

- 4009

- 1 112 150 209 0.7 Dysart 04

- 013

- 4010

- 1 81 136 127 0.0 Zuni Hills 04

- 013

- 4016

- 1 70 411 147 0.3 Bethune d 04

- 013

- 8006

- 1 71 30 NA 0.0 * Durango Complex 04

- 013

- 9812

- 1 111 151 144 0.0
JLG Supersite e 04

- 013

- 9997

- 3 74 150 120 0.0 04

- 013

- 9997

- 4 NA 151 120 0.0 *
Apache Junction e 04

- 021

- 3002

- 1 66 125 89 0.0 04

- 021

- 3002

- 3 NA 173 130 0.8 * * Completeness criterion not met for all quarters during the 2010

- 2012 time period.

a Excludes Exceptional Events concurred upon by EPA.8 b Hourly data was also submitted under POC 2 for limited periods of time during monitor changes. See AQS Raw Data Repor t, August 2, 2013.

c Monitor began operating on March 1, 2012.
d SPM shutdown June 30, 2011. See ANP approval letter dated December 1, 2011, from Matthew Lakin, Manager, Air Quality Analysis Office, EPA Region IX, to Eric Massey, Air Division, ADEQ.

e Both the JLG Supersite POC 4 and Apache Junction POC 3 monitors began operating in January and August of 2011, respectively

During the 2010

- 2012 time period, only six monitors within the Maricopa County N onattainment A rea do not meet the completeness criterion for all quarters. Both the Mesa and South Scottsdale monitors have incomplete data for the 2010

- 2012 time period. Specifically, the Mesa monitor has complete data for 8 of the required 12 quarters, and the South Scottsdale m onitor has complete data for 11 o f the required 12 quarters. While complete data should be used whenever possible, data not meeting these criteria may also suffice to show attainment. In the case of the Mesa monitor, the incomplete data was primarily due t o a temporary shutdown and relocation due to construction at the monitoring site, while the incomplete data at the South Scottsdale monitor was due to a small number of samples that were not collected during August and September of 2011. 6 These monitoring sites are not the high concentration sites in the nonattainment area, and the number of currently operating monitors in the area far exceeds EPA’s regulatory requirements, and therefore, the incomplete data does not inhibit EPA’s ability to determine area has attained the 24

- hour PM 10 NAAQS. Based on data from these monitoring stations, EPA has determined that the area has attained the 24

- hour PM 10 NAAQS for the 2010

- 2012 time

- period, as the 3

- year average of expected exceedances for all the monitoring sta tions are less than one.

III.B. Exceptional Events

On March 14, 2012, February 13, 2013, and January 28, 2013 ADEQ submitted eighteen high wind PM 10 exceptional events demonstrations for a total of one hundred thirty

- three exceedances occurring over twent y seven

- days in the years 2011 and 2012 at monitors within the Phoenix nonattainment area. EPA has reviewed the documentation provided by ADEQ to demonstrate that the exceedances on these days meet the criteria for an exceptional event under the Exceptiona l Events Rule (EER). EPA has concurred, based on the weight of evidence, that one hundred thirty

- one of the exceedances were caused by high wind exceptional events and found that ADEQ has successfully made seventeen of the eighteen of the demonstrations re ferred to in 40 CFR 58.14 to EPA’s satisfaction

. 7

ADEQ has also recently submitted, in accordance with EPA guidance, a letter of intent for a number of PM 10 exceedances that occurred in 2013. 8 The letter outlines that ADEQ will be preparing exceptional events demonstrations for three event days (April 8, 2013, June 30, 2013, and July2, 2013) that will cover twenty

- four exceedances of the 24

- hour PM 10 NAAQS. ADEQ subsequently submitted a notice of intent for an additional three days (August 17, 2013, August

6 See AQS Raw Data Report, August 2, 2013 and letter from Ben Davis, Air Monitoring Manager, MCAQCD to Michael Flagg, Air Quality Analysis O ffice, EPA Region IX, dated January 13, 2012.
7 See concurrence letters dated September 6, 2012, May 6, 2013,and July 1, 2013 from Jared Blumenfeld, Regional Administrator, EPA Region IX, to Eric Massey, Air Division, ADEQ
8 See letter dated September 11

, 20 1 3 from Eric Massey, Air Division, ADEQ , to, Deborah Jordan, Air Division Director, EPA Region IX.9

26, 2013, and October 9, 2013) that will cover six more exceedances of the 24

- hour PM 10 NAAQS. 9 While EPA has determined that the area has attained the NAA QS by December 31, 2012 with data from 2010

- 2012, ADEQ submission and EPA approval of the 2013 exceptional events identified in the letter of intent will be critical to ensuring the area continues to attain the 24

- hour PM 10 NAAQS with data from 2011

- 2013.

III.C. Tribal Data

As mentioned above, there are a number of Tribal monitoring stations located within the Maricopa County N onattainment A rea. Specifically, the SRPMIC operates three PM 10 monitoring stations and Fort McDowell operates one station in the northeastern portion of the nonattainment area. Table 3 summarizes the Tribal PM 10 design values and Table 4 summarizes the individual exceedance data collected over the past three years

.

Tabl e 3 : Summary of 2010

- 2012 Tribal PM 10 Data f or the Maricopa County Nonattainment Area

Monitoring Site AQS Site Identification Number Highest 24

- hour

PM 10 Concentration (μg/m 3 ) 3

- Year

Average of Expected Exceedances 2010 2011 2012 2010

- 2012

Fort McDowell

– Yuma Frank 04

- 013

- 5100

- 1 62 34 NA 0.0 * 04

- 013

- 5100

- 3 NA 559 125 2.3 * SRPMIC

– Senior Center 04

- 013

- 7020

- 1 59 163 126 1.9 SRPMIC

– Lehi 04

- 013

- 7022

- 1 55 167 150 2.0 SRPMIC

– High School 04

- 013

- 7024

- 1 75 216 90 2.2
* Non

- regulatory monitor, for information al purposes only.

Tabl e 4 : Summary of 2010

- 2012 Tribal PM 10 Exceedances

Exceedance Date AQS Site

Identification Number Monitoring Site 24

- hour PM 10 Concentration (μg/m 3 ) s 7/2/11 04

- 013

- 7024

- 1 SRPMIC

– High School 216 7/5/11 04

- 013

- 5100

- 3 Fort McDowell

– Yuma Frank 559 * 7/6/11 04

- 013

- 5100

- 3 Fort McDowell

– Yuma Frank 401 * 7/8/11 04

- 013

- 7020

- 1 SRPMIC

– Senior Center 163 7/8/11 04

- 013

- 7022

- 1 SRPMIC

– Lehi 167 7/8/11 04

- 013

- 5100

- 3 Fort McDowell

– Yuma Frank 329 * 8/28/11 04

- 013

- 5100

- 3 Fort McDowell

– Yuma Frank 305 * 9/2/11 04

- 013

- 5100

- 3 Fort McDowell

– Yuma Frank 195 * 11/4/11 04

- 013

- 5100

- 3 Fort McDowell

– Yuma Frank 237 *
* Non

- regulatory monitor, for information al purposes only.

9 See email dated December 2, 2013 from Bradley Busby, Evaluation Unit Manager, ADEQ, to Michael Flagg, Air Quality Analysis Office, Air Division, EPA Region IX.10

As shown in Table 3 , the PM 10 data from Tribal monitors within the nonattainment area continue to violate the 24

- hour PM 10 NAAQS. T he PM 10 data from SRPMIC has met the monitoring requirements in 40 CFR part 58, including the criteria in 40 CFR part 58, appendices A, D, and E, and may be used in determining whether the area attains the PM 10 NAAQS. T wo of the three exceedance dates in 2011 measured on SRPMIC monitors were coincident with an EPA approved high wind exceptional event on July 8, 2011 that affected monitors located in the eastern portion of the nonattainment area

. The remaining exceedance date of July 2, 201 1 was not associated with an EPA approved excepti onal event. Nearby monitors on tribal land operated by SRPMIC (Senior Center) and SLAMS operated by MCAQD did not measure exceedances of the PM 10 NAAQS. P reliminary analysis of nearby monitoring data and information obtained from SRPMIC monitoring staff su ggest that the contribution from the storm was small and that local sources are likely responsible for the exceedance at the High School station on July 2, 2011

. Pursuant to 40 CFR 49.10, however, EPA cannot disapprove a state SIP submittal because of the “ failure to address air resources within the exterior boundaries of an Indian Reservation or other areas within the jurisdiction of an Indian tribe .” Therefore, we did not further consider these exceedances as part of this proposed action to approve the 20 12 Five Percent Plan.

The PM 10 data from Fort McDowell is considered “informational” and does not fully meet the monitoring requirements of 40 CFR part 58. Thus it is not appropriate for use in determining if an area has attained the PM 10 NAAQS . However

, it is important to note that five of the six exceedance dates in 2011 correspond to dates where EPA has concurred with ADEQ’s exceptional events demonstrations ( July 5, 2011, July 8, 2011, August 28, 2011, September 2, 2011, and November 4, 2011 ) and the remaining exceedance date of July 6, 2011 at Fort McDowell is likely associated with the large dust storm event on July 5, 2011. Thus, the monitoring data from Fort McDowell is consistent with the other SLAMS information considered for EPA’s proposed actio n.

III.D. EPA Conclusion Considering SLAMS and tribal data collected from 2010

- 2012, EPA believes that the Phoenix PM 10 nonattainment area has attained the 24

- hour PM 10 NAAQS by the December 31, 2012 deadline in the 2012 Five Percent Plan. EPA also acknow ledges that future concurrence on 2013 exceptional events demonstrations is critical to ensuring the area continues to attain the 24

- hour PM 10 NAAQS with data from 2011

- 2013.



### IV. Attainment Demonstration

IV.A. Overview

Although m onitoring data shows that the Phoenix area already attains the 24

- hour PM 10 NAAQS, an attainment demonstration based on modeling provides assurance that the NAAQS will continue to be attained based on the control measures that are in place. MAG and ADEQ developed an attainment dem onstration using a proportional rollback approach that takes into account the timing and geographic location of emissions contributing to NAAQS exceedances.11

The State’s analysis adequately demonstrates that controls implemented during 2007

- 2012 brought the area into attainment, and will continue to assure NAAQS compliance.

IV.B. Technical Approach

EPA guidance allows considerable latitude in the choice of attainment demonstration approach for fugitive dust

- dominated PM 10 nonattainment areas. The approach used by the State is a form of proportional rollback and a microinventory method. It w as concurred upon in advance by EPA, and satisfies the available guidance.

EPA has issued several guidance documents and me moranda that describe PM 10 modeling procedures . However, some of this available guidance is rather dated, it is not comprehensive

, and is sometimes aimed only at Moderate Area , rather than Serious Area PM 10 plans. Sometimes, too, it assumes that the emissions to be modeled are predominantly from well

quantified point sources, such as industrial stacks, rather than from the more poorly characterized fugitive dust emissions. Interpretation and judgment is therefore needed in applying the guidance; also, the guidance explicitly recognizes that case

- by

- cas e evaluations of SIP modeling may be needed at times.

The term “rollback” refers to the assumption that the PM 10 concentration is directly proportional to emissions. To predict the ambient effect of an emissions change, the concentration can be scaled, or “rolled back”, by the same percentage that emissions reduce. In “ proportional rollback ” , each source or each source category is rolled back separately, since emissions from each will have a different level of control, and in general a different degree of dispersion. As in simple rollback, the ambient contribution of each individual source category scales with its emissions. However, the proportion that each category contributes to the total concentration may be different than its proportion of the total em issions. Thus, a source with only small emissions may nevertheless have a large contribution to the concentration, for example if it is nearby . A change in a source’s emissions causes a change in total concentration in proportion to that source’s particula r contribution

.

The PM

10 SIP Development Guidelin e (EPA

- 450/2

- 86

- 001, June 1987) ( “ PSDG ” ), chapter 4 states that, in order of preference, the modeling used in the demonstration can be 1) a combination of receptor and dispersion models, 2) dispersion model s alone, or 3) two receptor models alone if dispersion modeling is inappropriate. Section 6.4.2 put forward alternatives such as the Chemical Mass Balance (CMB) receptor model and the microinventory method. 10 However, generally receptor models such as CMB cannot distinguish between the many source categories that create fugitive dust, like roadways, vacant lots, construction activities, etc. Thus for fugitive dust

- dominated areas, a CMB analysis does little but confirm conclusions from the emission inventor y, and the recommendation of a combination of receptor and dispersion model

10 The microinventory method is the intensive inventorying and modeling of emissions in a small area that contributes to exceedances, and is a reasonable one for assessing pollutants like PM 10 , which has relatively sharp spatial gradients as dust settles out with distance from the source. It is also cited in the Receptor Model Technical Series, Volume I, Overview of Receptor Model Application to Particulate Source Apportionment , EPA

- 450

- 4

- 81

- 016a, July 1981, p. 27.12

does not seem appropriate. And in any case, previous work 11 has already showed the preponderance of fugitive dust in PM 10 concentrations in the Phoenix area. Thus, the three

option typology of approaches cited in the PSDG is not directly applicable.

The Guideline On Air Quality Models (Revised), 2005, 40 CFR §51 Appendix W (“GAQM”) deals with model use in general, including recommendations for input preparation. It also addresses PM 10 specifically in §5.2.2.2(d): “Under certain conditions, recommended dispersion models may not be reliable. In such circumstances, the modeling approach should be approved by the Regional Office on a case

- by

- case basis.”

Earlier versions of GAQM (in th en

- numbered section §7.2.2(d)) followed this with: “For example, where there is no recommended air quality model and area sources are a predominant component of PM

- 10, an attainment demonstration may be based on rollback of the apportionment derived from two reconciled receptor models, if the strategy provides a conservative demonstration of attainment.”

In addition, GAQM §5.2.2.2(e) states: “In some unique cases a model developed specifically for the situation may be needed. Due to the difficult nature of characterizing and modeling fugitive dust and fugitive emissions, it is recommended that the proposed procedure be cleared by the Regional Office for each specific situation before the modeling exercise is begun.”

Finally, the EPA memorandum

, “PM10 SI P Demonstrations for Small Isolated Areas with Spatially Uniform Emissions” ( Robert Bauman & Joseph Tikvart, July 5, 1990)

, is relevant. While Phoenix is not a “small isolated area”, the reasoning in this memorandum applies because of the predominance of a rea sources in the Salt River area and in Phoenix generally, for which the memorandum allowed the use of proportional rollback as a form of attainment demonstration modeling.

All of these help justify the acceptability of the State approach.

The latitude for judgment allowed in EPA guidance is especially important for fugitive dust PM 10 areas. It is widely recognized that fugitive dust emissions are markedly uncertain, and can have large temporal and spatial variability. The uncertainty of these crucial i nputs can make dispersion modeling problematic, since the model output is only as good as the model input. Previous modeling experience in the Phoenix area has amply demonstrated this. Accurately estimating emissions for dispersion modeling of widespread a rea sources of fugitive dust is much more difficult than for industrial point sources of gaseous pollutants, which were the archetypes for much of the modeling guidance. Point sources are relatively few in number, and their emissions are relatively constan t in time and can be directly measured. By contrast, fugitive dust

11 MAG, 2008. PM

- 10 Source Attrib ution and Deposition Study . March, 2008. Available on web page http://www.azmag.gov/Projects/Project.asp?CMSID2=1120&MID=Environmental%20Programs . Also Wat son, Chow, Lurman, and Stefan. “ Ammonium Nitrate, Nitric Acid, and Ammonia Equilibrium in Wintertime Phoenix, Arizona ”

, Journal of the Air and Waste Management Association , 44:405

- 412, April 199413

sources are numerous and vary in space and time, with indirectly measured emissions stemming from human activity and location

- specific winds that are known with poor temporal and spatial

re solution. In addition, fugitive dust sources are generally ground

- based, whereas dispersion model algorithms are generally based on studies of elevated sources (i.e., emitting from a point above the ground, such as the exit of a smoke stack). For all of th ese technical reasons, case by case judgment is needed in assessing PM 10 attainment demonstrations for fugitive

- dust dominated areas.

The State’s attainment demonstration approach is described in the 2012 Five Percent Plan Chapter 6, “ Attainment Demonstr ation ”, and the Plan’s own TSD ( Appendix B, Exhibit 1: Technical Document in Support of the MAG 2012 Five Percent Plan for PM

- 10 for the Maricopa County Nonattainment Area , Maricopa Association of Governments, especially chapter V, Attainment Modeling ). Th e general approach used by the State was to 1) determine the source areas contributing to PM 10 NAAQS exceedances using meteorological and dispersion modeling analyses, 2) develop hourly PM 10 emissions inventories for those source areas, and then 3) “roll b ack” or scale the monitored PM 10 concentration in proportion to the declining source emissions, taking into account their distance from the exceeding monitor. (This is a “modeling” approach in the general sense of a scientific model of concentrations, rath er than in the narrow sense of a dispersion model.) The concentration scaling was done hour

- by

- hour, since emissions vary hourly, in proportion to changes due to control measures during 2007

- 2012, including increased rule effectiveness improvements. The re sults were averaged to get a 24

- hour concentration. A background concentration was held constant during the scaling, reflecting the effect of distant sources not affected by local control measures.

The source

- to

- monitor distance was taken into account via an inverse distance factor (1/d). Analyses of data from temporary monitors and the relationships between their concentrations showed that it was crucial to include some kind of distance dependence to reflect the actual effect of source emissions at the mo nitors (Plan TSD, V

- 7 ). The 1/d factor was determined from AERMOD dispersion model runs showing how concentrations fall off with distance from a source, reflecting increased dispersion and dilution as the pollutant plume travels. The power function that fi ts the concentration curve, i.e. the best exponent for distance d, varied depending on which set of distances was used, but appeared to center on 1/d ( Source Weighting Analysis

, Plan TSD, V

- 21 ). While there is some danger of “over

- fitting” the exponent to the AERMOD curve, this was a rational approach, and the data probably do not justify a more complex function than 1/d. (Also, the 1/d was used even for the low

- wind day inventories, though it was derived using modeling for high wind speeds.) The rollback o f emissions with 1/d distance dependence served as a substitute for actually modeling the emissions with AERMOD. As noted in the Plan TSD (“Conceptual Model”, Plant TSD V

- 5), rollback has the advantage of mathematical simplicity in calculation time and in arriving at a set of source emission reductions needed for attainment. It also has the advantage of relying on actual measured concentrations, instead of on estimates from a steady state model that does not incorporate deposition, which would be important for PM 10
. As mentioned above, rollback incorporates a background concentration that is held constant during the overall concentration scaling, since it is due to sources outside the area not affected by local controls. Hourly background concentrations wer e developed by State using monitors on the14

upwind (west) edge of the area, the Buckeye monitor and the temporary Arlington monitor. Hourly concentration data and wind speed and direction data help the State choose a concentration that was indeed arriving f rom outside the area, reflected high wind conditions (defined as above 12 mph), and excluded values for which Arlington measured higher than Buckeye. (Buckeye is downwind of Arlington, and so should register the effects of any local emissions between the t wo when background pollution is transported into the area (Plan TSD, V

33).) Using 400 concentration pairs at the sites, the median of 21.9 μg/m 3 was chosen as a representative background; using the median avoided overemphasizing the lower concentrations from relatively low

- wind hours, were more frequent. The State followed a reasonable and thorough procedure in choosing a background concentration.

EPA believes that the modified rollback attainment demonstration approach used by the State meets the relevant guidance, and is technically sound based on extensive analysis of the sources and meteorological conditions that lead to NAAQS exceedances in t he Maricopa County PM 10 Nonattainment Area.

IV. C . Selection of Design Days

The goal of an attainment demonstration is to show that the NAAQS will be met at all times and places in the nonattainment area . Depending on the form of the NAAQS, a particular me asured concentration may exceed the numerical value of the standard one or more times per year (for PM 10 , 150 μg/m 3 may be exceeded once per year, on an average basis). But because it is often impractical to model every day of the year ( for example for hig hly variable fugitive dust PM 10 emissions that would have to be estimated for 8760 separate hours ) , attainment demonstrations instead focus on a smaller set of days that have experienced, or are conducive to, the highest concentrations. Designing a plan’s control strategy around these “design days”, to ensur e that controlled concentrations are below the numerical value of the NAAQS, is an economical, but still conservative, approach to attainment demonstrations. Note that other considerations beside high co ncentration must be considered in choosing design days, such as the availability of data needed to analyze the day, how widespread NAAQS exceedances were, the feasibility of analyzing the day given limitations of models, and other regulatory considerations

. Starting from the full set of PM 10 exceedances in the base year of 2007, the year just before new control measures were implemented, the State eliminated days that would be likely to qualify as having exceedances due to Exceptional Events. Such days cou ld be either caused by human activity unlikely to recur at a given location, or by natural events, such as high wind, sufficient to overcome reasonable control measures in place on emissions. The State has had extensive experience in classifying such candi date Exceptional Event days and has found they are typically caused by high wind during a frontal passage or during thunderstorm outflow. These conditions

are identifiable by specific patterns of using meteorological and concentration data, with frontal
pa ssages having long periods of high wind over a large areas, and thunderstorm outflows being of shorter duration and more localized, but also gustier (Plan TSD, V

- 42). It is reasonable to exclude such days from consideration as design days, since by definit ion they are not within the power of the State to ameliorate via emission controls.15

The design days chosen were May 4, 2007 for the Salt River area

, with 197 μg/m 3 monitored at the West 43rd Street monitor, and J une 6, 2007 for the nonattainment area as a whole, with 181.0 μg/m 3 at Higley and 225.7 μg/m 3 at West 43rd Street. These days satisfied the criteria of having among the highest concentrations and being high

- wind days

, but not candidate Exceptional Events. EPA agrees that these days are a good choic e for design day analysis.

IV. D . Modeling Domain

A modeling domain is a geographic area chosen for analysis. In the State’s approach, this was the area covering emission sources contributing to PM 10 exceedances for a design day. The contributing source a rea was determined by analyzing back trajectories using wind data to showing transport paths from upwind source locations to the West 43rd Street monitor; the timing of changes in PM 10 concentration and in wind speed and direction; the alignment of monitor s with each other, with wind direction, and with possible source areas; and AERMOD dispersion model runs for different wind speeds that showed the distances over which sources were likely to have a significant effect on concentration (Plan TSD, p.V

- 7 on in sights from temporary monitors, and V

- 53, domain discussion).

Back trajectories were generally from the west

- southwest, the predominant wind direction, following the valley of the Salt River, and formed the central segmented axis of the domain for a give n modeled day. So, the axis of the domain ran from the West 43d Street monitor upwind some 20 miles toward the west

- southwest, terminating beyond developed areas, whether urban or agricultural. The domain width was set at 2 miles, 1 mile on either side of the trajectory axis, reflecting the plume width determined using the AERMOD dispersion model. An example area source was modeled with AERMOD, to find that distance that the plume concentration falls to 1% of its value just downwind of the source; the plume width at that distance was about 1 mile (Plan TSD, p.V

- 57). (The “plume width” was defined somewhat unconventionally, as the angle subtended by the plume when it first had an off

- axis non

- zero concentration.)

Separate domains were developed for the Salt River area, and for the Phoenix nonattainment area as whole. In addition, additional “domains” were needed to provide emissions locations for low

wind hours, since the trajectory

- based domains are geared to high

- wind hours. These domains were larger areas encompassing either the Salt River area (36 mi 2 ), the Higley monitor (16 mi 2 ), or the Central City (40 mi 2 ), encompassing the Central Phoenix, Greenwood, Super Site

, and West Phoenix monitors and the surrounding urban area.

These various domains include all the violating monitors, the emission sources leading to PM 10 exceedances, and mixes of source types that are typical of the full nonattainment area. As in previous plans, the State applies control measures to the full nonattainment area. By focusing

an alysis on the subareas causing the high concentrations, yet having attainment area

- wide controls, the State addresses the PM 10 problem adequately.

IV. E . Estimating the Impact of Control Measures16

As discussed above, the State used a rollback approach, in which a change in PM 10 emissions causes a proportional change in the monitor PM 10 concentrations. The proportion is determined partly by the emissions, and partly by a 1/ d distance factor. There was a 2007 emission rate and a distance associated with each 10 acre parcel in the high

- wind model domain. The inverse distance

- weighted sum over all the parcels gives the total (weighted) emissions contributing to the monitored concentration. Changing the emissions to 2012 levels for the various activities and land uses in each parcel gives a new total emissions value ; the percent change in that total yields the percent change to apply to the original monitored concentration, giving the projected 2012 concentration. This approach is done for each hour, and the 24

- ho ur average taken for the final 24

- hour PM 10 concentration.

Emissions were based on industrial and agricultural activity present, and also on wind speed for a given hour, since that drives fugitive emissions from bare soil areas. For each 5 mph increment

o f wind speed, a different emission factor was used, one for stabilized land and one for disturbed land. ( 2012 Five Percent Plan TSD, V

- 62) Since the proportion of stabilized and disturbed land is difficult to know for the many, many individual parcels in t he domain, rule effectiveness for the relevant fugitive dust control measures was used as a surrogate for disturbance level. These

measures were Rule 310, earthmoving activities, Rule 310.01, open and vacant areas, and Rule 316, sand and gravel sites . The increasing rule effectiveness over the years 2007

- 2012 ( 2012 Five Percent Plan TSD, V

- 65) provided much of the overall emission reductions that lead to decreased PM10 concentrations for 2012.

This method for estimating the impact of control measures is in herent in the modified rollback approach, which EPA believes is a reasonable one, as stated earlier.

IV. F . Results of Attainment Demonstration and EPA Assessment

The attainment demonstration itself consists of carrying out the emissions change and totalin g calculation just described to arrive at a projected 2012 PM 10 concentration. The individual hourly concentration changes for the various monitor and design days are shown in a series of tables in the Plan ( 2012 Five Percent Plan TSD, V

- 80

– 88). In each case , the resulting 2012 PM 10 concentration meets the NAAQS. In one case, the West 43rd Street monitor for the June 6, 2007 design day, the end concentration is 153.8 μg/m 3 , just barely below the 154 μg/m 3 that is considered to in compliance with the NAAQS , using regulatory rounding conventions for PM 10 data ( 2012 Five Percent Plan TSD, Table V

- 44, p.V

- 88). For other days and monitors, the end concentration is well below the NAAQS. This demonstrates attainment for the Phoenix PM 10 nonattainment area.

Its e xtensive reliance on real

- world meteorological and monitoring data in deriving the approach lends confidence to the Plan’s conclusions. EPA believes that the attainment demonstration in the 2012 Five Percent P lan is technically sound, and meets the availab le guidance for PM 10
.